Honing Method and Honing Tool

Abstract

In a honing method for machining the internal surface of a bore in a workpiece with the aid of at least one honing operation, during a honing operation, an expandable honing tool is moved up and down within the bore in order to produce a reciprocating movement in the axial direction of the bore and at the same time is rotated in order to produce a rotational movement combined with the reciprocating movement. In the process, a bottle-shaped bore is produced, said bore having, following a bore inlet, a first bore section with a first diameter, a second bore section with a second diameter, which is larger than the first diameter, away from the bore inlet, and a transition section with a continuous transition from the first to the second diameter between the first and the second bore section. During at least one honing operation, use is made here of an annular tool (200) which has at least one annular cutting group (220) having a plurality of radially infeedable cutting material bodies which are distributed around the circumference of a tool body and are designed as honing segments which are wide in the circumferential direction and are narrow in the axial direction, wherein an axial length of the honing segments, as measured in the axial direction, is smaller than the width measured in the circumferential direction, and the axial length of the cutting region equipped with cutting material bodies is smaller than the effective outside diameter of the honing tool. The method is particularly suitable for honing cylinder faces during the production of cylinder blocks or cylinder liners for reciprocating piston engines.

Description

BACKGROUND

The invention relates to a honing method for machining the internal surface of a bore in a workpiece with the aid of at least one honing operation according to the preamble of claim 1, and to a honing tool, which is usable for carrying out the honing method, according to the preamble of claim 6. A preferred field of use is the honing of cylinder faces during the production of cylinder blocks or cylinder liners for reciprocating piston engines.

The cylinder faces in cylinder blocks (cylinder crank cases) or cylinder liners of internal combustion engines or other reciprocating piston engines are exposed to a severe tribological stress during operation. During the production of cylinder blocks or cylinder liners, said cylinder faces therefore have to be machined in such a manner that sufficient lubrication by means of a lubricant film is subsequently ensured under all operating conditions and the frictional resistance between parts moving relative to one another is kept as low as possible.

The quality-determining finish-machining of such tribologically stressable internal surfaces generally takes place with suitable honing methods which typically comprise a plurality of successive honing operations. Honing is a cutting process using geometrically undefined cutting edges. During a honing operation, an expandable honing tool is moved up and down or to and fro within the bore to be machined in order to produce a reciprocating movement in the axial direction of the bore at a reciprocating frequency and at the same time is rotated in order to produce a rotational movement, which is combined with the reciprocating movement, with a rotational frequency. The cutting material bodies attached to the honing tool are pressed against the internal surface to be machined by an infeed system having an infeed force acting radially with respect to the tool axis. During the honing, a cross-grinding pattern which is typical of the honing machining and has intersecting finishing marks, which are also referred to as “honing grooves” is produced on the internal surface.

With increasing requirements for economy and environmental friendliness of engines, the optimization of the tribological system of piston/piston rings, cylinder face is of particular importance in order to achieve a low level of friction, low level of wear and low oil consumption. The friction portion of the piston group can be up to 35%, and therefore reduction of friction in this region is desirable.

Different approaches for reducing the mechanical losses of an engine are pursued. These include, inter alia, the use of thermally sprayed cylinder faces, the use of coated piston rings, the development of particularly optimized honing surfaces, etc.

A technology which is gaining increasing importance for reducing the friction and the wear is the avoidance or reduction of cylinder distortions or deformations of the engine block (cylinder crank case) during assembly and/or during operation. After conventional honing machining, a cylinder bore is intended typically to have a bore shape which deviates as little as possible, for example at maximum a few micrometers, from an ideal circular-cylinder shape. However, during the assembly or the operation of the engine, it is possible for significant shape errors to occur which amount to up to several hundredth of a millimeter and may reduce the performance of the engine. The causes of distortions or deformations differ. They may involve static or virtually static thermal and/or mechanical loads or dynamic loads. The construction and the design of cylinder blocks also have an effect on the deformation tendency. The sealing function of the piston ring package is typically made worse by such deformations which can be difficult to control, as a result of which the blow-by, the oil consumption and also the friction may increase.

In order to reduce problems due to distortions during assembly or in certain operating states, it has been proposed, for example, in DE 28 10 322 C2 to use a tensioning device to deform the engine block for the honing machining in such a manner that the subsequent deformation is simulated by the cylinder head. In the braced state which corresponds to the state subsequently present after assembly, honing machining takes place in order to produce a circular-cylindrical bore shape which is then also intended to be set again after the assembly.

Another technology which, by inverting the cylinder distortions (production of a negative shape of the error) during the machining, is intended to ensure or approximate the production of an ideal shape after the assembly or in the operating state of the engine is what is referred to as shape honing. A bore shape deviating in a defined manner from the circular-cylinder shape, for example a clover leaf shape, is produced here on the unbraced workpiece by means of honing. Such bore shapes are generally asymmetrical because the deformations of the cylinder block are generally also not symmetrical. In the operating state, an ideal a circular-cylinder shape as possible is intended to be produced such that the piston ring package can provide a good seal over the entire circumference of the bore. Various variants of shape honing are described, for example, in EP 1 790 435 B1 and in the prior art mentioned therein.

Problem and Solution

It is a problem of the present invention to provide a honing method of the type in question and a honing tool usable for carrying out said honing method, said honing method and honing tool making it possible to produce reciprocating piston engines which have improved properties in respect of friction losses, oil consumption and blow-by.

In order to solve this problem, the invention provides a honing method with the features of claim 1. Furthermore, a honing tool with the features of claim 6, which can be used within the scope of the honing method, is provided.

Advantageous developments are specified in the dependent claims. The wording of all of the claims is provided by reference to the contents of the description.

In the honing method, a bottle-shaped bore, i.e. a bore having a bottle shape, is produced. A “bottle-shaped bore” has, directly following a bore inlet, a first bore section with a first diameter, a second bore section with a second diameter, which is larger than the first diameter, away from the bore inlet, and a transition section with a continuous transition from the first diameter to the second diameter between the first and the second bore section. The first bore section and the second bore section generally have a circular-cylindrical basic shape and lie coaxially with respect to each other. The transition section can be partially conically formed and can merge at the ends thereof which face the outer bore sections into the adjacent bore sections, in each case with suitable radii.

Given a suitable configuration of the bottle-shaped macro shape, substantial advantages can be obtained with respect to reduction of friction, reduced blow-by and reduced oil consumption. Furthermore, improvements in the wear resistance of the piston ring package and positive influences on the production of noise during the operation can be produced. A substantial part of the combustion in an internal combustion engine takes place in the relatively narrow first bore section in the vicinity of the bore inlet, i.e. in the “bottle neck”. A possible high provision of oil in this section could lead to emission and oil consumption problems. In this narrower first bore section, the annular package of the piston rings can readily carry out the conventional functions thereof (in particular the sealing against combustion gases and the scraping off of the oil film in the return movement) because of a relatively high edge stress. By means of the pressure waves of the combustion, the piston is accelerated in the first bore section and reaches the transition section with a gradually increasing diameter. In the transition section, the piston ring tension is reduced by increasing the diameter. Since, however, a considerable piston speed is already present here and the internal pressure in the cylinder space is diminished, blow-by, oil consumption value and engine noise emission are not adversely affected. By means of suitable radii between the transition section and the adjacent first and second bore sections, a gentle entry and exit of the piston rings can be achieved at the transition section, and therefore ring wear or engine seizures can be avoided. In the downward movement, the annular package, after passing through the transition section, reaches its lowest tension on entry into the second bore section, and therefore the friction loss is automatically reduced at the point at which the piston reaches its maximum speed.

Within the context of the honing method, which leads to a bottle-shaped bore with a surface structure optimum for use, during at least one honing operation use is made of a honing tool which is particularly suitable for this purpose and which is also referred to here because of the construction thereof as an “annular tool”. An “annular tool” within the context of this application has at least one annular cutting group having three or more radially infeedable cutting material bodies which are distributed around the circumference of the tool body of the honing tool and are configured as honing segments which are relatively wide in the circumferential direction of the honing tool and are relatively narrow in the axial direction of the honing tool. The axial length of the honing segments, as measured in the axial direction of the honing tool, is smaller here than the width measured in the circumferential direction, and the axial length of the cutting region equipped with cutting material bodies is smaller than the effective outside diameter of the honing tool.

If at least three honing segments are provided, the machining forces can be distributed readily over the entire effective outside diameter region, which is available because of radial infeeding, of the honing tool and relatively uniformly over the circumference. For example, precisely three, precisely four, precisely five or precisely six honing segments of identical or different circumferential width can be provided in a cutting group. Although more than six honing segments within a cutting group are possible, these make the construction more complicated and are generally not required. In some cases, it may optionally suffice if the honing tool has only two honing segments.

The effect which can be achieved by the radial infeedability (displacement of the honing segments in the radial direction during the infeeding) is that the engagement conditions between cutting material body and bore internal surface remain virtually constant irrespective of the diameter set. Nonuniform wear can be avoided by avoiding tilting of the cutting material bodies during the radial infeeding.

The measures can have a positive effect individually and in combination on the surface quality which can be achieved, in particular with regard to the uniformity of the surface quality over different bore sections.

The axial length of the honing segments can be, for example, less than 30% of the effective outside diameter of the honing tool, in particular can be between 10% and 20% of said outside diameter. In the case of annular tools for machining typical cylinder bores in engine blocks for passenger vehicles or trucks, the axial length can be, for example, within the range of 5 mm to 20 mm. Based on the bore length of a bore to be machined, the axial length is typically less than 10% of said bore length. If the upper limits are significantly exceeded, the possibility for axial following of the contours or production of the contours generally suffers. In addition, small axial lengths are advantageous in order to produce a sufficient surface pressure for the machining. On the other hand, a minimum length in the axial direction is advantageous in order to permit a honing overrun for machining the bore ends and in order to limit a tendency of the honing tool to tilt.

An annular tool of this type constitutes a reversal of conventional concepts of the configuration of a honing tool that are based on the fact that, in order to obtain small shape errors in a honed bore, honing tools having honing sticks which are relatively long in the axial direction, but are relatively narrow in the circumferential direction should be used. An annular tool is particularly readily adapted to the machining of bottle-shaped bore shapes or in general of bore shapes having a bore diameter which significantly varies in the axial direction. In an annular cutting group, the cutting material (bonded cutting grains of suitable grain size, density and hardness) is concentrated in an axially relatively narrow ring, wherein typically more than half of the circumference of an annular cutting group is occupied with cutting means and accordingly effectively contributes to the removal of material.

In comparison to the effective outside diameter of the honing tool, the cutting region in which one or more annular cutting groups lie is short or narrow in the axial direction, as a result of which the production and/or following of a contour running in the axial direction is possible.

In comparison to conventional honing sticks, an annular cutting group is distinguished in that there is substantially more contact surface between cutting material bodies and bore internal surface in the axial section covered by the annular cutting group than in a comparatively narrow axial section of a conventional honing tool. In some embodiments, with an annular cutting group, more than 60% of the circumference, possibly even more than 70% or more than 80% of the circumference of the honing tool is occupied with cutting means.

A cutting group is preferably arranged in the vicinity of a spindle-remote end of the tool body in such a manner that the cutting group is exclusively located in the spindle-remote half of the tool body. If a plurality of annular cutting groups are provided, this condition can apply to all cutting groups. An arrangement in the vicinity of the spindle-remote end permits, inter alia, machining operations with a very small honing overrun.

During honing machining, the stroke position of the honing tool within the bore can be used as a command variable in order, with high local resolution, to predetermine the press-on pressure or the infeed force as a function of the stroke position of the annular cutting group. As a result, it is possible, with the aid of an infeedable annular cutting group, to produce a bore with an axially variable contour or else to follow an already previously produced, axially varying contour without undesired contact pressure force peaks. When an annular tool is used, the operation can be carried out in all axial regions of the bore with substantially identical overlap such that, when the need arises, highly uniform roughness images or surface structures can be produced. When an annular tool is used, the operation can optionally also be carried out with a very small honing overrun at the axial ends of a bore without problems with nonuniform wear of the cutting bodies occurring.

The operation is preferably carried out with an electromechanical cutting-group infeed system. In contrast to a hydraulic expansion, a precise predetermination of the infeed travel (travel control) is thereby possible, as a result of which an axial contour can be produced in a specific manner and/or a predetermined axial contour can be precisely followed.

One or more sensors of a diameter measuring system can be arranged on the honing tool, and therefore an in-process diameter measurement is possible. For example, measuring nozzles of a pneumatic diameter measuring system can be attached in each case to the tool body between adjacent honing segments. By this means, the precision of the bore contours which can be achieved can be improved.

By means of the use of an annular tool, uniform wear of the cutting material bodies and very good shape values and uniform surface roughnesses of the bore are ensured over the entire surface life of the annular cutting group.

Different configurations of annular tools are possible, between which a user can choose depending on the machining task to be carried out.

In some embodiments, the annular tool has a single annular cutting group, the honing segments of which can be fed in radially or pulled back via a single common infeed system. The annular cutting group typically has three or more, generally no more than six, honing segments distributed uniformly or nonuniformly over the circumference of the honing tool. The single annular cutting group is preferably arranged in the vicinity of the spindle-remote free end of the tool body, for example flush with the spindle-remote end side. Constructions of this type are particularly readily suitable for machining cylinder bores with a reduced honing overrun. Restrictions of this type in the machining arise, for example, in the case of blind hole bores or in the case of cylinder bores in engine blocks for monoblock engines or V engines.

It is also possible for an annular cutting group to have two groups of honing segments which are infeedable independently of each other, wherein the honing segments of the groups are arranged in an alternating manner in the circumferential direction. By this means, it is possible to combine the advantages of a single annular cutting group (for example with respect to the machining of bores with a short honing overrun) with the advantages of a double infeeding of two groups of honing segments which are independent of each other. With a tool of this type, two consecutive honing operations can be carried out with different cutting materials without an intermediate changing of the tool. The honing segments of one group of honing segments normally have the same cutting layer while the groups have cutting layers which differ from one another, for example diamond layers of different grain size.

It is also possible for an annular tool to have a first annular cutting group and at least one second annular cutting group which is arranged in a manner offset axially with respect to the first annular cutting group and can be infed independently of the first annular cutting group. By this means, two consecutive honing operations are also possible with different cutting materials without an intermediate changing of the tool. Since the different cutting materials are distributed to the at least two annular cutting groups which are offset axially in relation to each other and can each cover a large part of the circumference of the honing tool, particularly high removal capacities or relatively short honing times are possible here in both honing operations. Annular tools of this type can be used for all bores which permit a sufficient honing overrun. With two or more annular cutting groups, bridging of pulsation windows or transverse bores or bore interruptions of any type is also possible in a particularly simple manner. Such an annular tool preferably has precisely two annular cutting groups, as a result of which flexible use is possible despite a simple construction.

In preferred embodiments, an integrated, multiaxially movable joint, for example a ball and socket joint or a cardanic joint, is provided on the tool body. Position errors of the machine and/or a core offset of the bore can thereby be compensated for without changing the bore position. Exemplary embodiments without a joint are also possible. Annular tools of this type can be coupled rigidly to a honing spindle or to a drive rod coupled rigidly to the honing spindle.

The bottle shape of the bore can be produced by any suitable chip-removing machining method, for example by precision turning (precision spindles), i.e. with the aid of a machining method with a geometrically determined cutting edge, or by means of honing. This can be followed by one or more honing operations in order to arrive at the finally desired bore geometry with a suitable surface structure.

A bore with a circular-cylindrical bore shape is preferably initially produced by precision turning or honing and then, in a bottle honing operation, a bottle-shaped bore shape is produced by honing with axially varying honing removal. In comparison to precision turning, surfaces can be produced with a particularly uniform surface quality without peripheral marks by means of honing. The self-sharpening effect of the cutting material bodies also contributes to the uniformity of the surface quality. In the case of honing, continuous process monitoring is possible.

In a method variant, during the bottle honing operation, use is made of an expandable honing tool having at least one annular cutting group, i.e. an annular tool. Honing segments of the cutting group are infed radially outward here in a travel- and/or force-controlled manner in a downward stroke in accordance with the bottle shape depending on the stroke position and, during an upward stroke, are retracted radially in accordance with the bottle shape depending on the stroke position. By means of this machining variant, a relatively smooth contour profile is produced from the outset in the transition section which is particularly difficult to machine.

Alternatively, it is also possible that, during the bottle honing operation, use is made of an expandable honing tool with honing sticks, the length of which is more than 50% of the length of the bore. The length of the honing sticks can be, for example, between 50% and 80% of the length of the bore. During the bottle honing operation, in a first phase, the honing tool is then moved up and down or to and fro between an upper and a lower reversing point in a first stroke position, in order to bring the bore initially over the entire length thereof into a circular-cylindrical shape. Then, in a second phase, the upper reversing point is changed incrementally, i.e. by a plurality of strokes, in the direction of the lower reversing point, and therefore the stroke length is gradually reduced. As a result, the stroke position is shifted in the direction of a second stroke position which lies in the region of the second bore section. In a third phase, the honing tool is then moved to and fro in the second stroke position. In this method variant, the basic shape of the transition section is substantially produced during the second phase of the gradual shifting of the stroke position and reduction in the stroke height, wherein the increase in diameter in the second bore section is also produced both at the same time and in the third phase.

If the bottle honing operation is carried out by means of a honing tool having relatively long honing sticks, a relatively rough surface structure with a profile similar to a saw profile can be produced in the transition section. In order also to obtain the desired uniform surface structure in the transition section, a smoothing honing operation for smoothing the bore profile in the transition region is therefore carried out preferably after the bottle honing operation, wherein an annular tool is used in the smoothing honing operation, i.e. an expandable honing tool with at least one annular cutting group. With the aid of the annular tool, grooves or burrs in the transition section can be eliminated and the radii of the transition section can be rounded.

It has proven advantageous if, during the smoothing honing operation, the cutting material bodies of the annular cutting group are pressed with a constant infeed force onto the internal surface of the bore. This is achieved in some method variants in that use is made of a honing machine having a hydraulic infeed system for the annular tool. The following of the contour of the bottle-shaped bore by the honing segments of the annular tool can already be produced here from the design-induced flexibility of the hydraulic expansion.

The invention also relates to a honing tool which is suitable particularly for carrying out the honing method, but can also be used in other honing methods which are not according to the invention.

The invention also relates to a workpiece with at least one bore which has a honed internal surface, wherein the bore is a bottle-shaped bore which, following a bore inlet, has a first bore section with a first diameter, a second bore section with a second diameter, which is larger than the first diameter, away from the bore inlet, and a transition section with a continuous transition from the first to the second diameter between the first and the second bore section, wherein the workpiece has been machined using a honing tool according to the invention.

In particular, the workpiece can be a cylinder block or a cylinder liner for a reciprocating piston machine. The reciprocating piston machine can be, for example, an internal combustion engine (combustion engine) or a compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic longitudinal section through a bottle-shaped cylinder bore in an engine block;

FIG. 2 shows, in 2A, a longitudinal section through an embodiment of an annular tool with single expansion of a single annular cutting group and, in 2B, a cross section through the cutting group;

FIG. 3 shows, in 3A, a longitudinal section through an embodiment of an annular tool with double expansion of a single annular cutting group and, in 3B, a cross section through the cutting group;

FIG. 4 shows, in 4A, a longitudinal section through an embodiment of an annular tool with double expansion with two annular cutting groups arranged one above the other and, in 4B, a cross section through one of the cutting groups;

FIG. 5 shows schematically a longitudinal section through a bore which is machined by means of a honing tool having relatively long honing sticks;

FIG. 6 shows schematically the stroke position of a honing tool having long honing sticks as a function of the honing time t during the bottle honing operation;

FIG. 7 shows a measuring diagram of a rounded profile of a bottle-shaped cylinder after the use of an annular tool;

FIG. 8 shows a schematic diagram which shows the dependency of the stroke position HP (solid line) and the expansion position AP (dashed line) as a function of the honing time t in a second exemplary embodiment.

DETAILED DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS

The following is a description of exemplary embodiments of honing methods and honing tools which can be used within the context of embodiments of the invention during the material-removing machining of workpieces which have one or more bores which, in the end-machined state, are intended to have the macroshape of a bottle.

FIG. 1 shows a schematic longitudinal section through one such bottle-shaped bore 110 in a workpiece 100 in the form of an engine block (cylinder crank case) for an internal combustion engine. The bore is rotationally symmetrical with respect to the bore axis 112 thereof and extends over a bore length L from a bore inlet 114, which faces the cylinder head in the installed state, as far as the bore outlet 116 at the opposite end. The bore can be divided into three mutually adjacent sections of differing function which merge in a sliding manner in one another, i.e. without the formation of steps or edges.

A first bore section 120 at the inlet-side end has a first diameter D1 and a first length L1. At the opposite, outlet-side end, a second bore section 130, the inside diameter (second diameter) D2 of which is larger than the first diameter D1, extends over a second length L2. A partially conical transition section 140, in which a continuous transition from the first diameter to the second diameter takes place, is located between the first bore section 120 and the second bore section 130. A first radius R1 is formed between the central, substantially conical part of the transition section and the first bore section, while a second radius R2 is formed between the transition section and the second bore section. The radii R1 and R2 can be substantially identical, but it is also possible for the first radius to be smaller or larger than the second radius.

In the case of typical bore geometries, the first length L1 can be, for example, between 15% and 40% of the bore length L. The second length L2 is typically larger than the first length and frequently is between 40% and 60% of the bore length L. The transition section is normally relatively short in relation to the adjoining bore sections. Typical third lengths L3 can be within the range of 5% to 20% of the bore length L. Deviations from said geometrical ratios are also possible.

The diameter difference between the first diameter D1 and the second diameter D2 lies significantly outside the tolerances which are typical for the honing machining and, for a cylinder shape, lie within the order of magnitude of at maximum 10 μm (based on the diameter). In the case of an absolute value of the inside diameter in the order of magnitude of between 70 mm and 150 mm, the diameter difference can lie, for example, between 20 μm and 90 μm.

The radii R1, R2, the lengths of the outer bore sections and of the transition section and the tangent angle T between the bore axis and a tangent to the transition section can be optimized in such a manner that low blow-by, low oil consumption and low wear of the piston rings are produced in typical operating states of the engine.

The bottle shape of the bore results in the bore being comparatively narrow in the region in the vicinity of the inlet, and therefore the piston rings of the piston moving in the bore are pressed against the bore internal surface 118 under high edge stress. As a result, reliable sealing is achieved at the location where the combustion primarily takes place and high pressures occur, and the oil film is scraped off in the downward stroke. The piston which is accelerated by the combustion then moves in the direction of the bore outlet, with the piston rings first of all running (partially) through the transition section with the continuously widened inside diameter and subsequently through the second bore section. The piston rings can gradually relax in the transition section, with the sealing remaining to a sufficient extent because the pressure difference drops at the piston rings. At the beginning of the second bore section, the ring package reaches the lowest stress thereof, and therefore friction losses are reduced precisely in the region of maximum piston speed because of reduced edge stress. During the upward stroke, the edge stress then increases again as soon as the piston rings reach the outlet-side radius of the transition section and run through the latter in the direction of the first bore section.

A precision machining process which can economically produce such a bore both with respect to the macroshape (bottle shape) and with respect to the surface structure of the tribologically stressed bore internal surface in high quality comprises, in the embodiments of the invention, at least one honing operation, in which use is made of a honing tool of particular construction which is also referred to in this application as an “annular tool”. An annular tool has at least one cutting group which is attached annularly to the tool body and has cutting material bodies which are distributed around the circumference of the tool body and can be infed in the radial direction by means of an associated infeed system or retracted. The cutting material bodies are designed as honing segments, the width of which is significantly larger in the circumferential direction than the length thereof in the axial direction. The cutting material bodies responsible for removing material from the workpiece are concentrated in an axially relatively narrow zone (a ring of the cutting group) and take up a relatively large portion of the circumference of the honing tool. As a result, bore shapes in which bore sections of differing diameter are adjacent to one another in the axial direction can be produced with a relatively high material removal capacity.

FIG. 2 shows, in 2A, a longitudinal section through an embodiment of an annular tool 200 with a single annular cutting group 220 and single expansion. FIG. 2B shows a cross section through the cutting group. The annular tool 200 has a tool body 210 which defines a tool axis 212 which is at the same time the axis of rotation of the ring tool during the honing machining. A coupling structure (not illustrated specifically) for coupling the annular tool to a drive rod of a honing machine or of another machining machine which has a working spindle, which is both rotatable about the spindle axis and also movable in an oscillating manner to and fro parallel to the spindle axis, is located at the spindle-side end of the annular tool (at the top in FIG. 2A).

The annular cutting group 220 which has a plurality (three in the case of the example) of cutting material bodies 220-1, 220-2, 220-3, which are distributed uniformly over the circumference of the tool body and can be infed outward radially with respect to the tool axis 212 with the aid of a cutting material body infeed system, in order to press the abrasively acting outer sides of the cutting material body with a defined contact pressure or press-on force against the internal surface of a bore to be machined, is located at the spindle-remote end of the tool body (at the bottom in FIG. 2A). Each of the three cutting material bodies, which are curved arcuately, is designed as a honing segment which is very wide in the circumferential direction but is narrow in the axial direction and which covers a circumferential angle region of between 115° and 120°. The honing segments are decoupled from the tool body and are displaceable relative to the latter radially with respect to the tool axis 212. The ring formed by the honing segments ends at the spindle-remote side flush with the tool body such that the ring sits completely within the spindle-remote half of the tool body at the spindle-remote end of the annular tool.

The axial length LHS of the honing segments is less than 15%, in particular less than 10% of the bore length L. The height of the honing segments is approx. 4 mm to 35 mm, in particular approx. 10 mm (in the axial direction), which, in the case of the example, corresponds to between 5% and 30%, in particular between 10% and 20%, of the effective outside diameter of the cutting group. The axial length LHS corresponds here at the same time to the axial length of the entire cutting region of the honing tool.

Each cutting material body is fastened by soldering to an outer side of an associated steel support strip 224-1, 224-2. Alternatively, the cutting material body can also be fastened by adhesive bonding or by means of screws, as a result of which easier replacement is possible. The inner side of each support strip has an oblique surface which interacts with a conical outer surface of an axially displaceable infeed cone 232 in such a manner that the support strips with the cutting material bodies carried by them are infed radially outward when the infeed cone is pressed in the direction of the spindle-remote end of the annular tool counter to the force of restoring springs 234, 226, 228 by means of a machine-side infeed device. In the case of an opposed infeed movement, the support strips are retrieved radially inwardly with the honing segments with the aid of peripheral retrieving springs 226, 228. As a result, the radial position of the cutting material bodies is controlled in a manner free from play via the axial position of the infeed cone 232.

This tool concept is particularly suitable for machining cylinder bores with a reduced honing overrun, for example with a honing overrun of at maximum 5 mm. Geometries of this type typically occur in the case of blind hole bores or in monoblock engines or V engines.

FIG. 3 shows an exemplary embodiment of an annular tool 300 which likewise has a single annular cutting group 320 which is arranged at the spindle-remote, end-side end of the tool body 310. FIG. 3A shows a longitudinal section through the annular tool, FIG. 3B shows a cross section through the cutting group. However, in contrast to the exemplary embodiment of FIG. 2, a honing tool with double expansion is involved. The annular cutting group 320 has two groups of honing segments which are infeedable independently of each other, wherein the honing segments of the groups are each arranged in an alternating manner with respect to one another in the circumferential direction. A first group of honing segments has three first honing segments 320-1 arranged offset circumferentially with respect to one another by 120° in each case. Three second honing segments 320-2 of a second group of honing segments are in each case arranged therebetween. The first group has cutting material bodies with a relatively coarse cutting layer while the second group has cutting material bodies with a cutting layer which is relatively finer with respect thereto. Axial guide strips 326 are in each case arranged between directly adjacent honing segments. A ball and socket joint 350 is provided between the tool body 310 and the coupling structure 340, which is provided for coupling the honing tool to a working spindle or the like, and therefore the honing tool is movable to a limited extent in a plurality of axes in relation to the honing spindle.

The first honing segments can be infed radially with the aid of a first infeed system. The latter includes a first infeed rod 332-I which runs centrally on the tool body and, at the spindle-remote end, has a conical section which interacts with the oblique surfaces of support strips of the first group of honing segments. A second infeed system serves for infeeding the second group of honing segments and has a tubular infeed element 332-A, which encloses the infeed rod 332-I and, at the spindle-remote end thereof, has a conical outer surface which interacts with oblique surfaces on the support strips of the second honing segments.

The three honing segments of the first group of honing segments can be expanded with the aid of the first infeed system in order to carry out a certain honing operation, for example a smoothing honing operation or a structure honing operation. If, instead, the other group of honing segments which have a different type of cutting layer is infed, a different honing operation, for example a deburring honing operation or a plateau honing operation, can be carried out. With the aid of the annular tool with double expansion, two different honing operations can be carried out successively without in the meantime undertaking a change of tool or using a different honing spindle for the machining.

FIG. 4 shows, in 4A, a schematic longitudinal section through an embodiment of an annular tool 400 with double expansion, which, in contrast to the exemplary embodiment of FIG. 3, has two annular cutting groups 420-1 and 420-2 which are attached in a manner offset axially with respect to each other in the spindle-remote part of the tool body 410. Each of the annular cutting groups (cross section in FIG. 4B) has three common infeedable honing segments which each cover between approx. 110° and 115° of the circumference. By contrast, the axial length of the honing segments is small and is typically less than 10% of the bore length and/or between 10% and 20% of the effective outside diameter of the honing tool in the region of the cutting material bodies. Measuring nozzles 440 of a pneumatic diameter measuring system are in each case attached to the tool body between adjacent honing segments. The cutting groups are located axially close to one another such that the cutting region of the honing tool, in which the two annular cutting groups are located, is substantially shorter in the axial direction than the effective outside diameter of the honing tool.

In some embodiments, the cutting material bodies are mounted in an elastically flexible manner with respect to the tool body. As a result, the capability of following the contours during the axial movement can optionally be improved. For example, spring elements (for example, leaf springs, spiral compression springs or the like) can be connected between the carrier elements and the cutting material bodies. It is also possible to design the carrier elements to be elastically flexible per se, for example by weakenings of the carrier material cross section in the form of slots or the like being structurally provided at suitable points.

There are various possibilities for producing bottle-shaped bores with a desired surface structure of the bore internal surface with the use of one or more annular tools of the type described in this application. A first exemplary embodiment is described in conjunction with FIGS. 5 and 6.

In the case of this method variant, first of all use has been made of a conventional honing tool having axially relatively long, narrow honing sticks in order, starting from a bore premachined, for example, by precision drilling, to produce a honed bore with a circular-cylinder shape. The axial stick length I was approx. ½ to ⅔ of the entire bore length L here. In a first honing operation (preliminary honing), the operation was carried out using diamond sticks of type D107, and a subsequent intermediate honing operation was carried out with a fine grain size (grain size D54). As a result, a substantially circular-cylindrical bore shape with little deviation from the ideal shape and with a relatively smooth surface (R_z<8 μm) was produced. The inlet-side and outlet-side honing overrun S here was approx. ⅓ of the stick length, similarly as in conventional methods. The honing overrun can be reduced during the machining of V- or monoblock engines.

A subsequent third honing operation was designed as a bottle honing operation. With the aid of a bottle honing operation, a bottle-shaped bore shape is produced by axially varying removal of material using geometrically undefined cutting edges. In the third honing operation (bottle honing operation), the operation was likewise carried out with relatively long honing sticks with a stick length I=⅔ L and a special stroke control which is explained with reference to FIG. 6. FIG. 6 schematically shows the stroke position HP of the honing tool as a function of the honing time t during the bottle honing operation. After insertion of the honing tool, the machining of the cylinder face initially proceeds from a first time t₁ to a second time t₂ with the same stroke length in a first stroke position precisely as in the case of the machining of a circular-cylindrical bore. The term “stroke position” refers here to the region between the upper reversing point UO and the lower reversing point UU of a reciprocating movement. Each shifting of a reversing point therefore also changes the stroke position.

From a defined second time t₂, the honing machine automatically switches over to an incremental change in the stroke position and, after each stroke, the upper reversing point UO is changed incrementally in the direction of the lower reversing point UU. The temporal position of the second time t₂ can be defined, for example, via a certain number of strokes or via a predetermined honing time or via a predetermined removal of material or another triggering parameter. The extent of the increment IN about which the upper reversing point changes between two consecutive strokes can likewise be adjusted as required. After the stroke shifting phase has ended at a third time t₃, the bore is honed with the new third stroke position reached until the second bore section reaches the desired diameter and the bottle shape (cf. FIG. 1) is produced.

Depending on how the incremental variation in the stroke shifting and the temporal sequence of the stroke shifting are predetermined, different radii and tangent angles are produced in the transition section. These parameters can therefore be predetermined via the parameters of the stroke shifting. The bottle honing operation is expediently carried out with honing sticks, the cutting material grains of which are finer than those for the preliminary honing or intermediate honing. For example, the operation can be carried out with diamond grains within the range of D35 in order to obtain a bottle shape having a surface structure which is already relatively fine.

During the production of the bottle shape with the aid of relatively long honing strips and incremental stroke shifting, a relatively rough surface structure having small steps similar to a saw profile may be produced in the transition region. Structures of this type are generally undesired. In order to obtain the desired surface structure uniformly over the entire internal surface of the bore including the transition section and the adjoining radii, in the method described here, after the bottle honing operation a rounding of the radii and smoothing of the surface are therefore carried out with the aid of an annular tool. The operation here can be carried out with even finer cutting means, for example within the range of D10 to D15, in particular D12. The selection of a suitable annular tool (for example single expansion, double expansion with two cutting groups, arranged in a common ring, or double expansion with two cutting groups, arranged in two axially offset annular cutting groups), depends, inter alia, on the design of the cylinder block. The tool selection can be oriented, for example, to the extent of the possible honing overruns and/or to the position and size of transverse bores. If, for example, a cylinder crank case has a large transverse bore, it is generally expedient to carry out the operation using an annular tool with single expansion (cf., for example, FIG. 2). In an exemplary process, use has been made of such an annular tool with an annular cutting group in order to smooth grooves or burrs which have arisen in the transition section during the machining of the bottle honing operation. With the aid of the annular tool, the radii of the transition region can also be rounded and the surface values changed in such a manner that they are substantially identical to the surface values in the adjacent first and third bore sections.

To this end, FIG. 7 shows a measuring diagram of a rounded profile of a bottle-shaped cylinder after use of an annular tool with single expansion in the process illustrated here. The scale on the x axis of the diagram (parallel to the bore axis) is 5 mm per unit of measurement shown, and on the y axis (in the radial direction of the bore) is a unit of measurement of 10 μm.

The use of an annular tool not only affords advantages here in respect of the smooth, edge-free profile of the bore contour in the axial direction. Since, in the case of annular tools of the type described here, the cutting material bodies of an annular cutting group occupy a large part of the circumference of the honing tool (for example between 70% and 80%), a very uniform overlapping of the machined bore internal surface is also produced in all axial positions during the honing. The term “overlapping” refers here qualitatively to the uniformity of the distribution of honing grooves over the entire bore length and the circumference. If use is made of conventional honing tools having axially relatively long honing sticks, under some circumstances a nonuniform roughness or waviness can be generated in the bore. Depending on the design of the block, this problem may occur even more acutely if, for example, engine blocks have to be machined with shorter honing tool outlets. In the case of a honing tool outlet of just a few millimeters in length, a nonuniform wear of the long honing sticks may occur, and therefore the bore may obtain a smaller diameter in the lower reversing point than in the upper reversing point. Although such problems should be substantially avoided by selection of suitable honing parameters when conventional honing tools (with long honing sticks) are used, the configuration of the corresponding honing processes is relatively time- and cost-intensive. A plurality of tests frequently have to be carried out until a honing process configuration is optimized such that nonuniform machining with long sticks is avoided. When an annular tool is used, a multiplicity of the conventionally occurring problems can be avoided. The advantages of annular tools include, inter alia:

• 1. Because a large portion of the circumference of the honing tool in the region of an annular cutting group is occupied with cutting material bodies, a bore internal surface can be structured much more rapidly with the aid of an annular tool than with the aid of a stick tool. As a result, cycle times can optionally be reduced.
• 2. If the stroke length is adjusted in order, for example, to correct the shape, no annoying nonuniformities in the distribution of roughness arise when annular tools are used since the overlapping is retained even when the stroke length is changed.
• 3. Annular cutting groups wear substantially uniformly, and therefore undesired conicities can be avoided particularly in the region of the lower reversing point when annular tools are used.
• 4. The installation of a honing machine for a new honing process can proceed much more simply and rapidly when annular tools are used than when conventional stick honing tools are used. The overlapping will be sufficiently uniform within the scope of the requirements because of the tool construction.

If, instead of an annular tool having single expansion, use is made of an annular tool having a single cutting group ring and double expansion (cf., for example, FIG. 3) for the structuring, it will generally be required to increase the stroke number in comparison to the use of an annular tool with single expansion, in order to ensure a uniform overlapping. However, the advantages of annular tools are maintained and the required number of strokes for a uniform structuring of the bore internal surface is still always lower than the corresponding number of strokes during use of a conventional honing tool with long honing sticks.

When an annular tool is used, the infeed force can expediently be exerted by means of a hydraulic expansion, and therefore the surface can be substantially machined with a constant force. The following of the contour which varies in the axial direction can then be brought about solely by means of the design because of the flexibility of the hydraulic expansion.

After the smoothing of the bore internal surface and rounding of the radii with the aid of an annular tool, one or more further honing operations can subsequently be carried out in order to produce the finally desired surface structure on the bottle-shaped bore.

The process described here by way of example is first of all adjoined by a fifth honing operation which is referred to here as “spiral structure honing with an annular tool”. In this honing operation, the axial speeds and the speed of rotation of the honing tool are coordinated with each other in such a manner that relatively large honing angles, for example of the order of magnitude of 140°, are produced. Of course, in other method variants, other honing angles and/or roughness profiles can also be produced. In the case of the example, the spiral structure honing is configured in such a manner that virtually no more global removal of material is obtained, but rather grooves of suitable depth and distribution are produced merely in the surface, which is very smooth after the rounding operation, with the aid of a relatively rough-grained cutting material body having a low cutting grain density. For example, cutting material bodies having a cutting agent grain density of 1.25 to 15% by vol. and/or a grain size of 35 to 200 μm can be used (cf., for example, DE 10 2005 018 277 A1).

Subsequently, in a sixth and final honing operation, the previously structured surface is also deburred (deburring honing). For this purpose, use is preferably likewise made of an annular tool with fine cutting agents, for example the same annular tool which was also used for the fourth honing operation (rounding of the radii and smooth honing). The operation here can be carried out with different expansion types. The expansion type can be configured hydraulically/hydraulically, hydraulically/mechanically or mechanically/mechanically. In the case of a mechanical expansion, the movement can be carried out, for example, in a force-controlled manner via a servomechanical expansion (hydraulic-like) or in a position- and force-controlled manner.

In an alternative method variant, use is made of an expandable annular tool in the bottle honing operation, i.e. when producing a bottle-shaped bore shape from a previously still circular-cylindrical bore shape. For this purpose, it is provided that the control of the expansion system for the radial infeeding of the honing segments is coupled to the control for the stroke position so that the annular tool can precisely generate the transition section with the changing diameter and also operates with a suitable contact pressure force in the cylindrical first and second bore section (cf. FIG. 8). The bottle honing operation can be provided as a second honing operation immediately after the preliminary honing and in this respect can replace the second to fourth honing operations of the first exemplary embodiment. The stroke-dependent control of the expansion then takes place in such a manner that the honing segments of the cutting group are infed radially outward in a travel- and force-controlled manner during a downward stroke in accordance with the bottle shape depending on the stroke position and are retracted radially again in the region of the transition section during an upward stroke in accordance with the bottle shape depending on the stroke position. A smooth contour profile can thus be achieved in the transition section from the outset.

This can be achieved at the honing machine by the fact that certain stroke ranges corresponding to the first to third bore sections are input in the control program, and therefore the cutting group expands from the end of the first bore section during the downward stroke by means of travel- and force-controlled expansion. During the upward stroke, the expansion of the cutting group then retracts from the end of the third bore section such that the desired, programmed, bottle-shaped cylinder is generated. For this purpose, FIG. 8 shows, by way of example, a schematic diagram which shows the dependency of the axial stroke position HP (solid line) and of the radial expansion position AP (dashed line) as a function of the honing time t during the bottle honing using an annular tool.

Annular tools of the type described here can not only be used for producing or machining bottle-shaped bores, but can afford considerable advantages, even without modification, during the machining of bores having a different geometry. For example, it is possible to use an annular tool with double expansion and a single cutting group ring in an identical or similar manner to the exemplary embodiment of FIG. 3 for producing a free shape with a noncircular bore cross section on a bore. This is customarily referred to as shape honing. For example, a bore section with a clover leaf shape or elliptical shape of the cross section can be produced with the aid of the annular tool. For this purpose, the honing machine has to have the possibility of simultaneously controlling the first infeed system and the second infeed system, wherein, depending in each case on the stroke position and angular position of the cutting group with respect to the bore, the expansions have to be controlled with a differing force/position such that the free shape can arise.

It is also possible to use an annular tool to produce and/or to machine a bore shape which has a frustoconical bore section (conical section) which merges relatively abruptly or with a transition radius into an adjacent cylindrical bore section without the connection of a further bore section. As a result, for example, a bore can be produced with a funnel shape which has an input-side, cylindrical first bore section with a first diameter, which increases conically in an adjacent, second bore section toward the bore base as far as a maximum diameter. The diameter difference between the cylindrical first bore section and the maximum diameter in the conical second bore section can be, for example, between approx. 20 μm and approx. 90 μm. The axial length of the cylindrical first bore section can be, for example, between 20% and 80% of the entire bore length.

Furthermore, it is possible to produce a barrel-shaped bore section in a bore, i.e. a bulge in an otherwise substantially cylindrical bore, with the aid of an annular tool. The bulge can lie approximately centrally or else in the vicinity of one of the bore ends.

When an annular tool is used, it is also possible relatively cost-effectively to machine a cylinder face in such a manner that in the region of the upper dead center and/or in the region of the lower dead center there are narrow strips having different surface structures than in the central region of highest piston speed. This variant is referred to here as “strip honing”. A conventional method suitable for this purpose and a correspondingly adapted honing tool are described, for example, in DE 195 42 892 C2. In addition to honing machining, which machines the entire axial length of the honing tool with long honing sticks, short-stroke honing machining is carried out here with the aid of short honing sticks, wherein this honing machining covers only the region of the upper dead center and/or of the lower dead center.

When an annular tool with double expansion and two axially offset cutting groups is used (cf., for example, FIG. 4), corresponding surface machinings are likewise possible. For example, with the first annular cutting group, long-stroke machining of the entire bore length can be carried out before then, for example, with the second cutting group, short-stroke machining is carried out in the region of the upper dead center in order to produce a specific structure in the region of the upper dead center.

In the event of corresponding variable control of the ratio between stroke frequency and rotational frequency of the working spindle, it is also possible in a simple manner to achieve the effect that such strip honing can be carried out with different honing angles in different axial bore sections (cf., for example, FIG. 4 from DE 10 2007 032 370 A1).

Claims

1. A honing method for machining the internal surface of a bore in a workpiece with the aid of at least one honing operation, in particular for honing cylinder faces during the production of cylinder blocks or cylinder liners for reciprocating piston engines,

wherein, during a honing operation, an expandable honing tool is moved up and down within the bore in order to produce a reciprocating movement in the axial direction of the bore and at the same time is rotated in order to produce a rotational movement combined with the reciprocating movement,

wherein a bottle-shaped bore is produced, said bore having, following a bore inlet, a first bore section with a first diameter, a second bore section with a second diameter, which is larger than the first diameter, away from the bore inlet, and a transition section with a continuous transition from the first to the second diameter between the first and the second bore section,

wherein, during at least one honing operation, use is made of an annular tool which has at least one annular cutting group having a plurality of radially infeedable cutting material bodies which are distributed about the circumference of a tool body and are designed as honing segments which are wide in the circumferential direction and are narrow in the axial direction,

wherein an axial length of the honing segments, as measured in the axial direction, is smaller than the width measured in the circumferential direction, and the axial length of the cutting region equipped with cutting material bodies is smaller than the effective outside diameter of the honing tool.

2. The honing method as claimed in claim 1, wherein first of all a bore having a circular-cylindrical bore shape is produced and then, in a bottle honing operation, a bottle-shaped bore shape is produced by honing with axially varying honing removal.

3. The honing method as claimed in claim 2, wherein, during the bottle honing operation, use is made of an expandable honing tool having at least one annular cutting group, wherein honing segments of the cutting group are infed radially during a downward stroke in accordance with the bottle shape depending on the stroke position and are radially retracted during an upward stroke in accordance with the bottle shape depending on the stroke position.

4. The honing method as claimed in claim 2, wherein, during the bottle honing operation, use is made of an expandable honing tool with honing sticks, the length of which is more than 50% of the length of the bore, wherein, in a first phase, the honing tool is moved up and down between an upper and a lower reversing point in a first stroke position, then, in a second phase, the upper reversing point is changed incrementally in the direction of the lower reversing point, and therefore the stroke position is shifted in the direction of a second stroke position in the region of the second bore section, and then, in a third phase, the honing tool is moved up and down in the second stroke position.

5. The honing method as claimed in claim 4, wherein, after the bottle honing operation, a smoothing honing operation for smoothing the bore profile in the transition region is carried out, wherein, during the smoothing honing operation, use is made of an expandable honing tool having at least one annular cutting group.

6. A honing tool, in particular for carrying out the honing method as claimed in claim 1, with a tool body which defines a tool axis, at least one cutting group which is attached to the tool body and has cutting material bodies for the material-removing machining of the internal surface of a bore, and a cutting-group infeed system, assigned to the cutting group, for exerting an infeed force, acting radially with respect to the tool axis, on the cutting material bodies of the cutting group,

wherein the honing tool is designed as an annular tool and has at least one annular cutting group having three or more radially infeedable cutting material bodies which are distributed around the circumference of the tool body and are designed as honing segments which are wide in the circumferential direction and are narrow in the axial direction, wherein an axial length (LHS) of the honing segments, as measured in the axial direction, is smaller than the width measured in the circumferential direction, and the axial length of the cutting region equipped with cutting material bodies is smaller than the effective outside diameter of the honing tool.

7. The honing tool as claimed in claim 6, wherein the axial length of the honing segments is less than 30% of the effective outside diameter of the honing tool, and/or the axial length of the honing segments lies within the range of 5 mm to 20 mm, and/or the axial length of the honing segments is less than 10% of the bore length of the bore to be honed.

8. The honing tool as claimed in claim 6, wherein more than half of the circumference of an annular cutting group is occupied with cutting material bodies.

9. The honing tool as claimed in claim 6, wherein a cutting group is composed of three, four, five or six honing segments.

10. The honing tool as claimed in claim 6, wherein the cutting group is arranged in the vicinity of a spindle-remote end of the tool body in such a manner that the cutting group is located exclusively in the spindle-remote half of the tool body.

11. The honing tool as claimed in claim 6, wherein the annular tool has a single annular cutting group which is arranged at a free end of the tool body.

12. The honing tool as claimed in claim 6, wherein an annular cutting group has two groups of honing segments which are infeedable independently of each other, wherein honing segments of the groups are arranged in an alternating manner in the circumferential direction.

13. The honing tool as claimed in claim 6, wherein the annular tool has a first annular cutting group and at least one second annular cutting group which is arranged axially offset with respect to the first annular cutting group and is infeedable independently of the first annular cutting group.

14. The honing tool as claimed in claim 6, wherein one or more sensors of a diameter measuring system are arranged on the honing tool, wherein measuring nozzles of a pneumatic diameter measuring system are in each case attached to the tool body.

15. The honing tool as claimed in claim 6, wherein an integrated, multiaxially movable joint is provided on the tool body.

16. The honing method as claimed in claim 5, wherein, during the smoothing honing operation, the cutting material bodies are pressed at a constant infeed force on to the internal surface of the bore.

17. The honing tool as claimed in claim 7, wherein the axial length of the honing segments is between 10% and 20% of said outside diameter.

18. The honing tool as claimed in claim 8, wherein more than 70% of the circumference of an annular cutting group is occupied with cutting material bodies.

19. The honing tool as claimed in claim 13, wherein the annular tool has precisely two annular cutting groups.

20. The honing tool as claimed in claim 14, wherein the measuring nozzles of a pneumatic diameter measuring system are in each case attached to the tool body between adjacent honing segments.

21. The honing tool as claimed in claim 15, wherein the integrated, multiaxially moveable joint is a ball and socket joint.