VALVE OPERATING APPARATUS FOR INTERNAL COMBUSTION ENGINE

Abstract

A valve operating apparatus includes: a first intermediate arm and a first rocker arm that are interposed between a first cam unit and a first valve; a second intermediate arm and a second rocker arm that are interposed between a second cam unit and a second valve; and hydraulic lash adjusters that rockably support the rocker arms. The intermediate arms are rockably supported by a rocker shaft. In the axial direction of the rocker shaft, the distance between the first transmission part and a bearing nearest thereto is shorter than the distance between the first pressure receiving part and a bearing nearest thereto, and likewise, the distance between the second transmission part and a bearing nearest thereto is shorter than the distance between the second pressure receiving part and a bearing nearest thereto.

Description

BACKGROUND

Technical Field

Embodiments of the present disclosure relate to a valve operating apparatus for an internal combustion engine.

Background Art

For example, JP 2001-263015 A discloses a variable valve operating apparatus for an internal combustion engine. The variable valve operating apparatus is an apparatus that can continuously change the lift amount and the operating angle of a valve (an intake valve or an exhaust valve).

More specifically, the variable valve operating apparatus includes an intermediate drive mechanism in a transmission path for the pressing force which is transmitted from a cam to valves. The intermediate drive mechanism includes an input part and rocking cams which are rockably supported by a support pipe that is disposed in parallel with a camshaft. The rocking cams are provided for the respective two valves included in the same cylinder. The input part and the rocking cams are configured to rock integrally. The input part receives a pressing force from the cam, and the rocking cams transmit the pressing force from the cam to the valves via rocker arms.

Further, the above described variable valve operating apparatus includes an actuator that displaces, in an axial direction of a control shaft, the control shaft which is disposed in the support pipe. The intermediate drive mechanism is configured to be able to change a relative phase difference of the input part and the rocking cams in accordance with a position in the axial direction of the control shaft. According to the variable valve operating apparatus having the above configuration, the relative phase difference of the input part and the rocking cams is changed by adjusting the position in the axial direction of the control shaft, and as a result, the lift amount and the operating angle of each of the valves can be changed.

JP 2010-019126 A and JP 2003-201814 A also show the state of the art at the date of filing of this application.

Technical Problem

The variable valve operating apparatus disclosed in JP 2001-263015 A is configured to transmit the pressing force of a single cam to two valves via the input part and the two rocking cams of the intermediate drive mechanism. Meanwhile, a valve operating apparatus for an internal combustion engine is known, in which a cam unit, an intermediate arm (a member interposed between the cam unit and a valve) that is rockably supported by a rocker shaft, a rocker arm that is interposed between the intermediate arm and the valve, and a hydraulic lash adjuster that operates to eliminate a gap between the valve and the rocker arm and a gap between the rocker arm and the intermediate arm are included independently for each valve. Here, in the intermediate arm, a part which is pressed by the cam unit is referred to as a “pressure receiving part”, and a part which transmits the pressing force of the cam unit to a valve side (that is, the rocker arm) is referred to as a “transmission part”.

In the valve operating apparatus, it sometimes becomes necessary to offset the position of the transmission part in the axial direction of the locker shaft with respect to the position of the pressure receiving part in the same direction, for a reason, such as a constraint on the layout of the cam unit. When such an offset is provided, the position where the locker shaft receives a load from the cam side, and the position where the rocker shaft receives a load from the valve side differ in the axial direction. When these loads become large, a deflection occurs to the rocker shaft at a time of valve opening. When the offset is provided, if the positional relation of the pressure receiving part and the transmission part in the axial direction of the rocker shaft is not proper, the displacement amount of the transmission part (more specifically, a contact position with the rocker arm in the transmission part) becomes large when a deflection occurs to the rocker shaft.

When a deflection of the rocker shaft which supports the intermediate arm occurs at a time of valve opening, a very small gap sometimes is produced between the intermediate arm and the rocker arm. The hydraulic lash adjuster acts to eliminate the gap instantly. At a time of valve closing, the load to the intermediate arm from the rocker arm becomes small, and therefore, the deflection of the rocker shaft is eliminated or becomes small. However, even when the deflection of the rocker shaft becomes small, it takes time until oil drains out of the hydraulic lash adjuster. Consequently, if the positional relation between the pressure receiving part and the transmission part in the axial direction of the rocker shaft is not appropriate, a closing failure of the valve may occur.

SUMMARY OF THE INVENTION

Embodiments of the present disclosure address the above-described problem and have an object to provide a valve operating apparatus for an internal combustion engine that can improve a closing failure of a valve due to the displacement of a transmission part accompanying the deflection of a rocker shaft, in the internal combustion engine that includes a cam unit and an intermediate arm for each valve, and adopts a configuration in which the position of the transmission part in the axial direction of the rocker shaft is offset to the position of a pressure receiving part in the same direction.

A valve operating apparatus for an internal combustion engine according to the present disclosure includes: a first cam unit and a second cam unit configured to respectively drive a first valve and a second valve that are installed in a cylinder; a first intermediate arm interposed between the first cam unit and the first valve, and including a first pressure receiving part that is pressed by the first cam unit and a first transmission part that transmits a pressing force of the first cam unit to a side of the first valve; a second intermediate arm interposed between the second cam unit and the second valve, and including a second pressure receiving part that is pressed by the second cam unit and a second transmission part that transmits a pressing force of the second cam unit to a side of the second valve; a rocker shaft configured to support the first intermediate arm and the second intermediate arm to be rockable between bearings that are respectively installed at both sides of the cylinder; a first rocker arm interposed between the first intermediate arm and the first valve, and configured to transmit a pressing force from the first transmission part to the first valve; a second rocker arm interposed between the second intermediate arm and the second valve, and configured to transmit a pressing force from the second transmission part to the second valve; a first hydraulic lash adjuster configured to rockably support the first rocker arm, and act to eliminate a gap between the first valve and the first rocker arm, and a gap between the first rocker arm and the first intermediate arm; and a second hydraulic lash adjuster configured to rockably support the second rocker arm, and act to eliminate a gap between the second valve and the second rocker arm, and a gap between the second rocker arm and the second intermediate arm. In an axial direction of the rocker shaft, a distance between the first transmission part and the bearing that is nearest to the first transmission part is shorter than a distance between the first pressure receiving part and the bearing that is nearest to the first pressure receiving part, and a distance between the second transmission part and the bearing that is nearest to the second transmission part is shorter than a distance between the second pressure receiving part and the bearing that is nearest to the second pressure receiving part.

The first pressure receiving part and the second pressure receiving part, and the first transmission part and the second transmission part may be disposed on a same side with respect to the rocker shaft, seen from an axial direction of the cylinder.

The first cam unit may be configured by a first cam group including a plurality of cams having different profiles. The valve operating apparatus may further include a device that switches a cam that gives a pressing force to the first intermediate arm among the cams of the first cam group.

The second cam unit may be configured by a second cam group further includes a plurality of cams having different profiles. The valve operating apparatus may further include a device that switches a cam that gives a pressing force to the second intermediate arm among the cams of the second cam group.

According to the valve operating apparatus for an internal combustion engine of the present disclosure, in the configuration including a cam unit and an intermediate arm for each of valves, the positions of the respective transmission parts in the axial direction of the rocker shaft are offset with respect to the positions of the respective pressure receiving parts in the same direction, in the following form. That is, in the axial direction of the rocker shaft, the distance between the first transmission part and the bearing that is the nearest to the first transmission part is configured to be shorter than the distance between the first pressure receiving part and the bearing that is the nearest to the first pressure receiving part. Similarly, in the axial direction of the rocker shaft, the distance between the second transmission part and the bearing that is the nearest to the second transmission part is configured to be shorter than the distance between the second pressure receiving part and the bearing that is the nearest to the second pressure receiving part. According to the offsets in the form like this, the transmission parts are nearer to the bearings which are the fixed ends as compared with the pressure receiving parts, and therefore, the displacement amounts of the transmission parts at the time of the pressing forces of the cams acting on the intermediate arms can be restrained to be small. The gaps which should be adjusted by the hydraulic lash adjusters thereby become small, and therefore, a closing failure of the valves can be improved, which is caused by the hydraulic lash adjusters pushing the rocker arms excessively when the pressing forces of the cams do not act on the intermediate arms (that is, at the time of valve closing).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of the outline of a valve operating apparatus for an internal combustion engine according to a first embodiment of the present disclosure, seen from the axial direction of a cylinder;

FIG. 2A and FIG. 2B are sectional views of the valve operating apparatus cut along a line A-A in FIG. 1;

FIG. 3 is a perspective view of a pair of intermediate arms;

FIG. 4A and FIG. 4B are views for explaining an example of a specific configuration of a cam switching device included by the valve operating apparatus shown in FIG. 1;

FIG. 5A to FIG. 5C are views for explaining switch operations of a cam unit which are performed by the cam switching device;

FIG. 6A and FIG. 6B are views which relate to the first embodiment of the present disclosure, and are for explaining a difference of influence of deflection of a rocker shaft due to a difference in the form of offsets;

FIG. 7 is a view of a main part of a valve operating apparatus for an internal combustion engine according to a second embodiment of the present disclosure, seen from the axial direction of a cylinder, and shows a configuration included by each of the cylinders in the valve operating apparatus;

FIG. 8 is a view of cam units, intermediate arms, rocker arms, hydraulic lash adjusters and valves seen from the axial direction of a rocker shaft; and

FIG. 9A and FIG. 9B are views that relate to the second embodiment of the present disclosure, and are for explaining a difference in influence of deflection of the rocker shaft due to difference in the manner of offsets.

DETAILED DESCRIPTION

First Embodiment

Configuration of Valve Operating Apparatus According to First Embodiment

(Entire Configuration)

FIG. 1 is a view of the outline of a valve operating apparatus 10 for an internal combustion engine according to a first embodiment of the present disclosure, seen from the axial direction of a cylinder. FIG. 2A and FIG. 2B are sectional views of the valve operating apparatus 10 cut along a line A-A in FIG. 1. More specifically, FIG. 2A is a view at a time of a first valve 12a being in a valve closed state. FIG. 2B is a view at a time of the first valve 12a being in a valve open state. FIG. 3 is a perspective view of a pair of intermediate arms 20 (20a, 20b).

Each cylinder of the internal combustion engine is equipped with two intake valves and two exhaust valves. The valve operating apparatus 10 is an apparatus for driving two valves (the two intake valves or the two exhaust valves) 12 which are disposed in each cylinder of the internal combustion engine. When the two valves 12 need to be distinguished from each other, the two valves are referred to as a first valve 12a and a second valve 12b (this similarly applies to the components other than the valves 12). For the valve operating apparatus 10, FIG. 1 shows a configuration which is equipped for each of the cylinders.

The valve operating apparatus 10 includes a camshaft 14. The camshaft 14 is connected to a crankshaft (not illustrated) via a timing pulley and a timing chain (or a timing belt) which are not illustrated, and is configured to rotate at a half of the speed of the crankshaft by the rotational force of the crankshaft.

As shown in FIG. 1, a first cam unit 16a and a second cam unit 16b for each cylinder are attached to the camshaft 14. The first cam unit 16a drives the first valve 12a via a first intermediate arm 20a and a first rocker arm 22a which will be described later. The second cam unit 16b drives the second valve 12b via a second intermediate arm 20b and a second rocker arm 22b which will be described later. In the present embodiment, as an example, the first cam unit 16a is configured by a first cam group including three cams 16a1, 16a2 and 16a3, and the second cam unit 16b is configured by a second cam group including three cams 16b1, 16b2 and 16b3. A configuration around the camshaft 14 will be described later with reference to FIGS. 4A and 4B and FIGS. 5A to 5C. Furthermore, as described below, the valve operating apparatus 10 includes a rocker shaft 18, an intermediate arm 20, a rocker arm 22 and a cam switching device 24 (see FIG. 4A) as main components.

As shown in FIG. 1, the rocker shaft 18 is disposed in parallel with the camshaft 14. The rocker shaft 18 is supported by a plurality of bearings 26. More specifically, each of the bearings 26 is configured by a bearing part which is formed at a cylinder head (or a cam carrier which is attached to the cylinder head), and a cam cap (a camshaft support member) which is combined with the bearing part, and only the cam caps are illustrated in FIG. 1. A journal of the rocker shaft 18 is supported by the bearing part and the cam cap. In order to allow the intermediate arm 20 to rock freely, a clearance for forming an oil film is provided between the journal, and the bearing part and the cam cap.

As shown in FIG. 1, the bearings 26 are respectively installed at both sides of the cylinder. The first intermediate arm 20a and the second intermediate arm 20b for the same cylinder are rockably supported by the rocker shaft 18 between a pair of bearings 26 which are installed in this way. As long as the intermediate arms 20a and 20b for the same cylinder are disposed between the pair of bearings 26, the two bearings 26 do not have to be always included on a cylinder to cylinder basis. That is, one or both of the pair of bearings 26 may be shared by adjacent cylinders.

The first intermediate arm 20a is interposed between the first cam unit 16a and the first valve 12a. More specifically, since the first rocker arm 22a is interposed between the first intermediate arm 20a and the first valve 12a, the first intermediate arm 20a is interposed between the first cam unit 16a and the first rocker arm 22a. In the first intermediate arm 20a, a first cam roller 28a is rotatably attached to a position facing the first cam unit 16a (more specifically, at a position facing the first cam 16a2 in an operation state shown in FIG. 1 and FIGS. 2A and 2B). The first cam roller 28a corresponds to a “first pressure receiving part” which is pressed by the first cam unit 16a (to be more specific, 16a1 or 16a2).

Further, in the first intermediate arm 20a, a first transmission part 32a is provided at a position facing a rocker roller 30 of the first rocker arm 22a. The first transmission part 32a is a part that transmits the pressing force of the first cam unit 16a to the first valve 12a via the first rocker arm 22a. The first transmission part 32a is formed as a non-working surface 32a1 and a working surface 32a2. The non-working surface 32a1 is a surface (a base circle part) in a circular-arc shape which is formed so that the distance from the center of rocking (that is, the axial center of the rocker shaft 18) of the first intermediate arm 20a is constant. The working surface 32a2 is a surface which is provided so as to continue from the non-working surface 32a1, and is formed so that the distance from the center of rocking (the axis of the rocker shaft 18) of the first intermediate arm 20a becomes gradually longer as the working surface 32a2 is away from the non-working surface 32a1.

The second intermediate arm 20b which is interposed between the second cam unit 16b and the second valve 12b is configured similarly to the aforementioned first intermediate arm 20a, except that a point which will be described in detail later (that is, a positional relation between the pressure receiving part and the transmission part) is different. That is, the second intermediate arm 20b includes a second cam roller 28b corresponding to the “second pressure receiving part” which is pressed by the second cam unit 16b. Further, the second intermediate arm 20b is provided with a second transmission part 32b which transmits a pressing force of the second cam unit 16b to the second valve 12b via the second rocker arm 22b. The second transmission part 32b is formed as a non-working surface 32b1 and a working surface 32b2, similarly to the first transmission part 32a.

As above, the valve operating apparatus 10 of the present embodiment includes the cam unit 16 and the intermediate arm 20 independently for each valve 12. Further, in order to be able to keep contact of the cam unit 16 and the cam roller 28 at all times during rotational operation of the cam unit 16, the intermediate arm 20 is urged to the cam unit 16 by a spring 34 (see FIG. 2A and FIG. 2B). An end part which is located at an opposite side of an end part at the intermediate arm 20 side in the spring 34 is provided at the cylinder head or the cam carrier not illustrated.

Further, one end of the rocker arm 22 is supported by a valve shaft end of the valve 12, and the other end is supported by a hydraulic lash adjuster 36 (see FIG. 2A and FIG. 2B). More specifically, the valve operating apparatus 10 includes a first hydraulic lash adjuster 36a for the first valve 12a, and a second hydraulic lash adjuster 36b for the second valve 12b. The first hydraulic lash adjuster 36a rockably supports the first rocker arm 22a, and acts to eliminate a gap between the first valve 12a and the first rocker arm 22a and a gap between the first rocker arm 22a and the first intermediate arm 20a. The second hydraulic lash adjuster 36b rockably supports the second rocker arm 22b, and acts to eliminate a gap between the second valve 12b and the second rocker arm 22b and a gap between the second rocker arm 22b and the second intermediate arm 20b. Further, the valve 12 is urged, by a valve spring 38 (see FIG. 2A and FIG. 2B), in a closing direction, that is, a direction to push up the rocker arm 22.

Next, an opening and closing action of the valve 12 will be described with the second valve 12b taken as an example. As shown in FIG. 2A, in a state where a pressing force of the second cam 16b2 is not given to the second intermediate arm 20b, the non-working surface 32b1 of the second transmission part 32b abuts on the rocker roller 30 of the second rocker arm 22b. In this state, the second rocker arm 22b is not pressed down by the second intermediate arm 20b, and therefore, the second valve 12b keeps a valve closed state.

Meanwhile, when a pressing force of the second cam 16b2 is given to the second intermediate arm 20b, the second intermediate arm 20b rocks with the rocker shaft 18 as a center as shown in FIG. 2B, and the part of the second transmission part 32b which contacts the rocker roller 30 is switched from the non-working surface 32b1 to the working surface 32b2. As a result, the second rocker arm 22b is pressed down by the second intermediate arm 20b, and the second valve 12b lifts. In this way, the second cam 16b2 rotates, the second intermediate arm 20b thereby rocks, and with this, the second rocker arm 22b rocks, whereby the second valve 12b opens and closes.

(Cam Switching Device)

FIG. 4A and FIG. 4B are views for explaining an example of a specific configuration of the cam switching device 24 included by the valve operating apparatus 10 shown in FIG. 1. More specifically, FIG. 4A is a view showing a configuration around the cam switching device 24 provided for each of the cylinders of the internal combustion engine. FIG. 4B is a view of a cam unit 40 seen from the direction of an arrow B (the axial direction of the camshaft 14) shown in FIG. 4A.

The first cam unit 16a and the second cam unit 16b described above are provided as components of the cam unit 40. The cam unit 40 is supported by the camshaft 14 in a form in which the cam unit 40 is movable in the axial direction of the camshaft 14 and movement in the rotational direction thereof is restricted.

The cam switching device 24 switches the cam which is to be mechanically connected to each of the valves 12 (that is, gives the pressing force to the cam roller 28 of the intermediate arm 20) among the three cams (16a1 to 16a3, or 16b1 to 16b3) having different profiles. The cam switching device 24 may include a configuration other than the configuration which will be described below as long as the cam switching device is a device that can switch a plurality of cams which the cam unit 16 has.

Here, an example of profiles of the three cams 16a1, 16a2 and 16a3 of the first cam group will be described. The following explanation similarly applies to profiles of the three cams 16b1, 16b2 and 16b3 of the second cam group. The profile of the cam 16a2 which is disposed in the center of the first cam group (16a1, 16a2 and 16a3) is set as a large cam for obtaining a relatively large lift amount and operating angle as a lift amount and an operating angle of the first valve 12a. The cam 16a1 is disposed adjacently (the right side of the cam 16a2 in FIG. 4A) to the cam 16a2. The profile of the cam 16a1 is set as a small cam which obtains a smaller lift amount and operating angle than the lift amount and the operating angle obtained by the cam 16a2. The cam 16a3 is disposed adjacently to the cam 16a2 (the left side of the cam 16a2 in FIG. 4A) at an opposite side of the cam 16a1. The profile of the cam 16a3 is set as a cam that only includes a base circle part in which the distance from the axis of the camshaft 14 is equal, that is, a zero lift cam which does not give a pressing force to the first valve 12a.

Further, the cam unit 40 includes a guide groove 42. Although a location of the guide groove 42 on the cam unit 40 is not specially limited, and in the present embodiment the guide groove 42 is formed on an outer peripheral surface of the cam unit 40, next to (at the left side of the second cam 16b3 in FIG. 4A) the second cam 16b3. The guide groove 42 is formed to extend in a Y-shape in the circumferential direction. More specifically, the guide groove 42 has a pair of branch parts 42a and 42b which is branched into a Y-shape, and a junction part 42c which is a location where the pair of branch parts 42a and 42b join each other.

At a position facing the guide groove 42, an electromagnetic solenoid type actuator 44 having three cylindrical movable elements 44a, 44b and 44c capable of engaging with and disengaging from the guide groove 42 is disposed. The actuator 44 is electrically connected to an electronic control unit (ECU) 46 for controlling the internal combustion engine including the valve operating apparatus 10. Energization of the actuator 44 is controlled on the basis of an instruction from the ECU 46. The actuator 44 is configured to be able to push out a movable element of the three movable elements 44a, 44b and 44c toward the guide groove 42 in a state where electric power is turned on.

More specifically, each of the movable elements 44a, 44b and 44c is urged, by a spring not illustrated, in a direction to separate from the guide groove 42. The actuator 44 is configured so that the thrust force of a solenoid which is generated as a result of energization surpasses the force of the spring, and thereby the movable element 44a, 44b or 44c can protrude (advance) to the guide groove 42. Further, the actuator 44 is attached to the cylinder head or the cam carrier not illustrated. The cam switching device 24 is equipped with a stopper device (not illustrated) between the cam unit 40 and the camshaft 14, in order to keep an axial position of the cam unit 40 on the camshaft 14, in a state where none of the movable elements 44a, 44b and 44c is engaged with the guide groove 42.

Further, as shown in FIG. 4A, the distance between groove center lines of the first branch part 42a and the junction part 42c in the guide groove 42, and the distance between groove center lines of the second branch part 42b and the junction part 42c are configured to be equal to the distance between cam center lines in the width direction of the adjacent cams in the cam unit 16. Further, each of distances between center lines of the respective movable elements 44a, 44b and 44c of the actuator 44 is configured to be equal to the above described distance between the groove center lines.

FIG. 5A to FIG. 5C are views for explaining switch operations of the cam unit 16 which are performed by the cam switching device 24. FIG. 5A shows an operation state (state using the large cams) where the cam 16a2 of the first cam group and the cam 16b2 of the second cam group respectively contact the first cam roller 28a and the second cam roller 28b, similarly to FIG. 4A. The cam switching device 24 is configured so that in this operation state, the groove center line of the first branch part 42a coincides with the center line of the first movable element 44a, and the groove center line of the second branch part 42b coincides with the center line of the third movable element 44c.

When the actuator 44 is operated so that the first movable element 44a is inserted into the first branch part 42a during use of a common base circle part concerning the first cam unit 16a and the second cam unit 16b in the operation state shown in FIG. 5A, the guide groove 42 slides the cam unit 40 in a direction shown in FIG. 5B by using a rotational force of the camshaft 14. As a result, the cams respectively contacting the cam rollers 28a and 28b are switched to the cams 16a3 and 16b3 from the cams 16a2 and 16b2 as a result of rotation of the camshaft 14. In this way, with the operation of the actuator 44, the operation state of the cam switching device 24 is switched to an operation state shown in FIG. 5B (a valve stopped state). When a state where the position of the first movable element 44a coincides with the position of the junction part 42c in the axial direction of the camshaft 14 is brought about as a result of the aforementioned slide operation, energization of the actuator 44 is stopped quickly. As a result, the first movable element 44a is removed from the guide groove 42. In addition, the axial position of the cam unit 40 is kept by the aforementioned stopper device. This similarly applies to switch of other operation states which will be described below.

In the operation state shown in FIG. 5B, the groove center line of the second branch part 42b of the guide groove 42 coincides with the center line of the second movable element 44b. When the actuator 44 operates in this operation state so that the second movable element 44b is inserted into the second branch part 42b during use of the common base circle part concerning the first cam unit 16a and the second cam unit 16b, the guide groove 42 switches, by using the rotational force of the camshaft 14, the cams which respectively contact the cam rollers 28a and 28b to the cams 16a2 and 16b2 from the cams 16a3 and 16b3 as a result of rotation of the camshaft 14. The operation state of the cam switching device 24 is thereby switched (is returned) to the operation state shown in FIG. 5A again as a result of the operation of the actuator 44.

Meanwhile, when the actuator 44 operates in the operation state shown in FIG. 5A so that the third movable element 44c is inserted into the second branch part 42b during use of the common base circle part concerning the first cam unit 16a and the second cam unit 16b, the guide groove 42 slides the cam unit 40 in a direction shown in FIG. 5C by using the rotational force of the camshaft 14. As a result, the cams which respectively contact the cam rollers 28a and 28b are switched to the cams 16a1 and 16b1 from the cams 16a2 and 16b2 as a result of rotation of the camshaft 14. The operation state of the cam switching device 24 is thereby switched to the operation state (a state using small cams) shown in FIG. 5C as a result of the operation of the actuator 44.

In the operation state shown in FIG. 5C, the groove center line of the first branch part 42a of the guide groove 42 coincides with the center line of the second movable element 44b. When the actuator 44 operates in this operation state so that the second movable element 44b is inserted into the first branch part 42a during use of the common base circle part concerning the first cam unit 16a and the second cam unit 16b, the guide groove 42 switches, by using the rotational force of the camshaft 14, the cams which respectively contact the cam rollers 28a and 28b to the cams 16a2 and 16b2 from the cams 16a1 and 16b1 as a result of rotation of the camshaft 14. The operation state of the cam switching device 24 is thereby switched (is returned) to the operation state shown in FIG. 5A again as a result of the operation of the actuator 44.

The above described cam switching device 24 is configured by the aforementioned components (that is, the cam unit 40 which is attached to the camshaft 14 in a form that the cam unit 40 is movable in the axial direction of the camshaft 14 and the movement thereof is restricted in the rotational direction, the guide groove 42 and the actuator 44).

As described above, according to the valve operating apparatus 10 of the present embodiment, the lift amounts and the operating angles of the valves 12 can be changed stepwise, which includes realization of the valve stopped state where the valves 12 are kept in a closed state, by switching, with the cam switching device 24, the cams which give the pressing forces to the cam rollers 28 of the intermediate arms 20 among the plurality of cams which the cam units 16 have. In this way, the valve operating apparatus 10 of the present embodiment is configured as a variable valve operating apparatus capable of changing the valve opening characteristics of the valves 12. In the configuration so far, the cams 16a3 and 16b3 are both zero lift cams, but the present disclosure is not limited to this. If only either one of the cam 16a3 and the cam 16b3 is, for example, a zero lift cam, an operation of stopping only one of the valves 12 can be implemented.

Characteristic Configuration of Valve Operating Apparatus According to First Embodiment and Effect by the Configuration

The valve operating apparatus which is mounted in an internal combustion engine is requested to be established in a limited mounting space in the cylinder head. For the configuration of the intermediate arms 20, the valve operating apparatus 10 of the present embodiment has a feature that will be described as follows. As a result, in the configuration in which each of the valves 12 includes the cam unit 16 and the intermediate arm 20 which is rockably supported by the rocker shaft 18, occurrence of a negative effect which is caused by displacement of the transmission part accompanying deflection of the rocker shaft 18 can be restrained while a space necessary to mount the valve operating apparatus 10 is reduced to be small, as described in detail below.

(Saving Space in Height Direction of Cylinder Head)

According to the valve operating apparatus 10 of the present embodiment described above, the intermediate arms 20 are configured so that the first cam roller 28a (the first pressure receiving part) and the second cam roller 28b (the second pressure receiving part), and the first transmission part 32a and the second transmission part 32b are located on the same side with respect to the rocker shaft 18, seen from the axial direction of the cylinder (see FIG. 1). Hereinafter, the disposition like this will be referred to as a “disposition A” for convenience. To add to that, in the intermediate arms 20, the position of the first transmission part 32a in the axial direction of the rocker shaft 18 is offset with respect to the position of the first cam roller 28a (the first pressure receiving part), and the position of the second transmission part 32b in the axial direction of the rocker shaft 18 is similarly offset with respect to the position of the second cam roller 28b (the second pressure receiving part). If the above described offsets are adopted in an example where the above described disposition A is adopted, the mounting position of the camshaft can be restrained to be low as compared with an example without offsets. As a result, the height of the cylinder head can be restrained to be low. In other words, a space in the height direction of the cylinder head (that is, the axial direction of the cylinder) shown in FIG. 3 can be saved.

(Restraint on Displacement of Transmission Part Due to Deflection of Rocker Shaft)

In addition, the above described offsets in the intermediate arms 20 are set with the following form (hereinafter, referred to as a “form A” for convenience of explanation). That is, according to the form A mentioned here, in the axial direction of the rocker shaft 18, the distance between the first transmission part 32a and the bearing 26 (the bearing 26 at the right side in FIG. 1) which is the nearest to the first transmission part 32a is set to be shorter than the distance between the first cam roller 28a (the first pressure receiving part) and the bearing 26 (the same bearing 26 at the right side in FIG. 1) which is the nearest to the first cam roller 28a. Further, according to the form A, in the axial direction of the rocker shaft 18, the distance between the second transmission part 32b and the bearing 26 (the bearing 26 at the left side in FIG. 1) which is the nearest to the second transmission part 32b is set to be shorter than the distance between the second cam roller 28b and the bearing 26 (the same bearing 26 at the left side in FIG. 1) which is the nearest to the second cam roller 28b (the second pressure receiving part). An effect obtained by providing the offsets in the form A like this will be described below with reference to FIG. 6A and FIG. 6B.

FIG. 6A and FIG. 6B are views which relate to the first embodiment of the present disclosure, and are for explaining a difference of influence of deflection of the rocker shaft due to a difference in the form of offsets. More specifically, FIG. 6A is a view of an example where offsets in the form A which is adopted in the present embodiment are provided. FIG. 6B is a view showing a comparative example which is referred to for the purpose of being compared with the configuration of the present embodiment. As a form that can be adopted as the above described offsets, there is a form that is adopted in the comparative example shown in FIG. 6B, other than the form A. That is, the offsets can also be provided in this form in which the positions where loads from the cams are received are nearer to the bearings as compared with the positions where loads from the rocker arms (valve side) are received, contrary to the form A.

First, as shown in the respective views in FIG. 6A and FIG. 6B, if the pressing force of each cam is given to the intermediate arm, the load from the cam acts on the pressure receiving part of the intermediate arm. In addition, if the pressing force is given, a load which is caused by a valve spring reaction force that is produced by receiving the aforementioned pressing force and the magnitude of which is equivalent to the load from the cam, acts on the transmission part of the intermediate arm from the valve side (acts via the rocker arm 22 in the example of the valve operating apparatus 10). If the offsets are provided, in the axial direction the position where the rocker shaft receives the load from the cam side differs from the position where the rocker shaft receives the load from the valve side, even though either form of the forms in FIG. 6A and FIG. 6B is adopted. As a result, a deflection occurs to the rocker shaft.

In the comparative example shown in FIG. 6B, at the position where the load from each rocker arm (each valve side) is received, the distance from the bearing which is nearer to the intermediate arm out of the pair of bearings is longer than that at the position where the load from the cam is received. Consequently, the moment which is produced with the bearing as the center and which is of the load from each rocker arm (each valve side) becomes larger than the moment of the load from each cam. FIG. 6B shows a state where the rocker shaft deflects in a manner where the rocker shaft is pushed toward the cam side (in the upward direction in FIG. 6B).

Meanwhile, the configuration of the present embodiment shown in FIG. 6A adopts offsets in the opposite form (that is, form A) to the comparative example shown in FIG. 6B as described above. Consequently, concerning the moment with, as the center, the bearing 26 nearer to the intermediate arm 20 to which attention is paid, the moment of the load from each rocker arm 22 (each valve 12 side) is smaller than the moment of the load from each cam unit 16. FIG. 6A shows a state where the rocker shaft deflects in a manner where the rocker shaft is pushed toward the valve side (in the downward direction in FIG. 6A).

In the example where the form A is used, the position of each transmission part becomes nearer to the bearing (the bearing nearer to the intermediate arm to which attention is paid) which is a fixed end, as compared with the example where the form in which the positional relation of the pressure receiving part and the transmission part are opposite to the form A is used. Consequently, as is understandable when FIG. 6A and FIG. 6B are compared, when attention is paid to the position of each transmission part in the axial direction of the rocker shaft, the deflection amount δ of the rocker shaft in the position of each transmission part becomes smaller in the configuration shown in FIG. 6A, as compared with the configuration shown in FIG. 6B. Accordingly, the displacement amount of each transmission part (more specifically, the displacement amount of each contact position with a mating member (in the valve operating apparatus 10, the rocker roller 30 corresponds to this) in each transmission part) at the time of the pressing force of each cam acting on the intermediate arm becomes smaller in the configuration shown in FIG. 6A, as compared with the configuration shown in FIG. 6B. A straight line L1 in each of FIG. 6A and FIG. 6B represents the center axis of the rocker shaft at a time of no deflection occurring to the rocker shaft, and straight lines L2 and L2′ in FIG. 6A and FIG. 6B represent center axes of the rocker shafts at a time of deflection occurring. This similarly applies to FIG. 9A and FIG. 9B which will be described later.

When the rocker shaft which supports the intermediate arms deflects in the upward direction in FIG. 6A at a time of opening of the valves, very small gaps are generated between the intermediate arms and the rocker arms. More specifically, gaps are generated between the rocker rollers of the rocker arms and the non-working surfaces (the base circle parts) of the intermediate arms. The hydraulic lash adjusters act to eliminate the gaps instantly. Meanwhile, the loads to the intermediate arms from the rocker arms become small at a time of valve closing, and therefore, the deflection of the rocker shaft is eliminated or decreases. However, even though the deflection of the rocker shaft becomes small, it takes time until oil drains from the hydraulic lash adjusters. Consequently, when deflection decreases in the state where the positions of support points of the rocker arms at the hydraulic lash adjuster side become high as a result of the hydraulic lash adjusters acting to eliminate the gaps, there is a possibility that the valves may be pressed by the rocker arms due to the fact that the positions of the support points have become high (that is, the fact that the gaps have been eliminated), even during a time period in which the pressing forces from the cams do not act on the intermediate arms. Consequently, if the displacement amounts of the transmission parts of the intermediate arms due to deflection of the rocker shaft are large, a closing failure of the valves may occur.

However, according to the configuration of the intermediate arms 20 of the present embodiment, the displacement amounts of the transmission parts 32 can be reduced when deflection occurs to the rocker shaft 18 due to adoption of offsets. As a result, the closing failure of the valves 12 due to the influence of the action of the aforementioned hydraulic lash adjusters 36 can be improved.

(Saving of Space in Axial Direction in Example of Having Configuration of Making Opening Characteristics of Valves Variable by Using Slide Operations of Cams)

The offsets in the form A of the present embodiment also provides the following effect when the offsets in the form A are applied to a valve operating apparatus having the configuration in which the opening characteristics of the valves are made variable by switching the cams which press the valves by sliding a plurality of cams in the axial direction of the camshaft as in the valve operating apparatus 10. That is, in the example of having the configuration in which a plurality of cams are slid in the axial direction of the camshaft, a large space is required in the axial direction of the camshaft in order to establish the slide operation. The issue becomes more remarkable as the number of cams to be slid is larger.

For the above described issue, according to the offsets in the form A, in other words, the form in which the pressure receiving parts (that is, the cam rollers 28) are disposed at inner sides of the first valve 12a and the second valve 12b in the axial direction of the rocker shaft 18, a space between the first valve 12a and the second valve 12b in the axial direction of the rocker shaft 18 can be more effectively used for the slide operations of the cam units 16, as compared with the form in which the positional relation of the pressure receiving parts and the transmission parts is opposite to that in the form A. The reason is that the first and second cam units 16a and 16b are disposed near to the center side of the cylinders, so that the variable device for changing the opening characteristics of the valves 12 is easily disposed at outer sides of the cylinder relative to the first and second cam units 16a and 16b. As a result, the space in the axial direction (the axial direction shown in FIG. 3) of the camshaft 14 can be saved, and therefore, the configuration which makes the opening characteristics of the valves variable can be easily established by using the slide operation of the cams.

(Saving Space in Width Direction of Cylinder Head)

In the intermediate arms 20, the first cam roller 28a (the first pressure receiving part) and the second cam roller 28b (the second pressure receiving part), and the first transmission part 32a and the second transmission part 32b are disposed on the same side with respect to the rocker shaft 18 seen from the axial direction of the cylinder (see FIG. 1). According to the disposition A, even where the space ensured to mount the valve operating apparatus is small for the reason that bore diameters of the cylinders are small, for example, the valve operating apparatus can be easily established in the limited space. More specifically, the space can be saved in the width direction of the cylinder head shown in FIG. 3 (that is, a direction that is orthogonal to each of the axial direction of the cylinders and the axial direction of the camshaft 14).

Modified Example of First Embodiment

In the first embodiment described above, explanation is made by taking, as an example, the valve operating apparatus (that is, the variable valve operating apparatus) 10 including, as the first cam unit 16a which drives the first valve 12a, the first cam unit 16a configured by the first cam group formed of a plurality (three as an example) of the cams 16a1 to 16a3 having different profiles, and also including the similar configuration concerning the second cam unit 16b. However, the first cam unit and the second cam unit included by the valve operating apparatus of the internal combustion engine which is the object of the present disclosure may be each configured by a single cam. More specifically, the valve operating apparatus to be the object of the present disclosure may be, for example, configured as a valve operating apparatus which does not have the function of making variable the opening characteristics of the valves by adopting, for each intermediate arm 20, the configuration which drives, via the intermediate arm 20 and the rocker arm 22, a valve by a single fixed cam. Alternatively, the valve operating apparatus to be the object of the present disclosure may be configured as a variable valve operating apparatus having the function of making variable the opening characteristics of the valves by adopting, for each intermediate arm, a configuration that includes a known variable device which makes the operation of the intermediate arms variable while including, for each of the intermediate arms, the configuration that drives a valve by a single cam via the inter mediate arm and the rocker arm.

Further, in the first embodiment described above, explanation is made by taking, as an example, the valve operating apparatus 10 including the first cam roller 28a and the second cam roller 28b respectively as the first pressure receiving part and the second pressure receiving part. However, the parts corresponding to the first pressure receiving part and the second pressure receiving part in the present disclosure are not limited to the parts that contact the cams with rolling contact as in the example of using the cam rollers 28, but may be parts using slide contact similarly to a valve operating apparatus 50 which will be described later. That is, the above described parts may be formed at the intermediate arms as pads having curved surfaces or flat surfaces which contact the cams. Further, the pressure receiving part in the present disclosure is not necessarily limited to the part that directly contacts the cam itself as long as the part is pressed by the cam, and may be configured to be pressed by the cam via a member, for example.

Further, in the first embodiment described above, explanation is made by taking, as an example, the valve operating apparatus 10 including the single cam-switching device 24 for each of the cylinders. However, the single cam-switching device in the present disclosure may be included for each of the valves. If the single cam-switching device is included for each of the valves, single valve control (for example, single valve stop control of bringing only one of the valves into a stopping state, for example) that causes the opening characteristic of one of the first valve and the second valve to differ from the opening characteristic of the other one can be performed. Alternatively, the device which switches the cam in the present disclosure may be shared among a plurality of cylinders which share the base circle part of the cams.

Second Embodiment

Next, a second embodiment of the present disclosure will be described with reference to FIG. 7 to FIG. 9B.

Configuration of Valve Operating Apparatus According to Second Embodiment

In the first embodiment described above, explanation is made by taking, as an example, the valve operating apparatus 10, which adopts the disposition A (that is, the disposition in which the first cam roller 28a (the first pressure receiving part) and the second cam roller 28b (the second pressure receiving part), and the first transmission part 32a and the second transmission part 32b are included on the same side with respect to the rocker shaft 18 seen from the axial direction of the cylinder). Here, in the valve operating apparatus for an internal combustion engine, disposition as follows, that is, a disposition (hereinafter, referred to as a “disposition B” for convenience of explanation) is sometimes used in which a pressure receiving part is provided at an opposite side of a transmission part with respect to a rocker shaft, seen from the axial direction of a cylinder, other than the aforementioned disposition A. Even in the valve operating apparatus adopting the disposition B like this, it is sometimes necessary to offset the positions of the transmission parts in the axial direction of the rocker shaft with respect to the positions of the pressure receiving parts in the same direction, for the reason, such as a constraint on the layout of the cam units. The valve operating apparatus 50 of the present embodiment which will be described below is preferable in restraining occurrence of the harmful effect due to displacement of the transmission parts accompanying a deflection of the rocker shaft when the disposition B is adopted.

FIG. 7 is a view of a main part of the valve operating apparatus 50 for an internal combustion engine according to the second embodiment of the present disclosure, seen from the axial direction of a cylinder, and shows a configuration included by each of the cylinders in the valve operating apparatus 50. FIG. 8 is a view of cam units 56, intermediate arms 54, the rocker arms 22, the hydraulic lash adjusters 36 and the valves 12 seen from the axial direction of a rocker shaft 58. In FIG. 7 and FIG. 8, the same components as the components shown in FIG. 1 described above will be assigned with the same reference signs and explanation thereof will be omitted or simplified.

As shown in FIG. 7, for each cylinder, a first cam unit 56a which drives the first valve 12 via a first intermediate arm 54a and the first rocker arm 22a, and a second cam unit 56b which drives the second valve 12b via a second intermediate arm 54b and the second rocker arm 22b are attached to a camshaft 52. In the example of the valve operating apparatus 50 of the present embodiment, the first cam unit 56a and the second cam unit 56b are each configured by a single cam. The first intermediate arm 54a and the second intermediate arm 54b are rockably supported by the rocker shaft 58.

The first intermediate arm 54a includes a first pressure receiving part 60a which is pressed by the first cam unit 56a, and a first transmission part 62a which transmits the pressing force of the first cam unit 56a to the first valve 12a side (the first rocker arm 22a). Similarly, the second intermediate arm 54b includes a second pressure receiving part 60b which is pressed by the second cam unit 56b, and a second transmission part 62b which transmits the pressing force of the second cam unit 56b to the second valve 12b side (the second rocker arm 22b).

As shown in FIG. 7, the valve operating apparatus 50 adopts the disposition B in which the pressure receiving parts 60a and 60b are provided at the opposite side of the transmission parts 62a and 62b with respect to the rocker shaft 58, seen from the axial direction of the cylinder. In addition to that, in the intermediate arms 54 of the present embodiment, offsets concerning the pressure receiving parts 60 and the transmission parts 62 are set in a manner as follows (hereinafter, referred to as a “manner A′” for convenience of explanation). That is, in the manner A′ mentioned here, in the axial direction of the rocker shaft 58, the distance between the first transmission part 62a and the bearing 26 (the bearing 26 at the right side in FIG. 7) which is the nearest to the first transmission part 62a is set to be shorter than the distance between the first pressure receiving part 60a and the bearing 26 (the same bearing 26 at the right side in FIG. 7) which is the nearest to the first pressure receiving part 60a. Further, in the manner A′, the distance between the second transmission part 62b and the bearing 26 (the bearing 26 at a left side in FIG. 7) which is the nearest to the second transmission part 62b the second transmission part 62b is set to be shorter than the distance between the second pressure receiving part 60b and the bearing 26 (the same bearing 26 at the left side in FIG. 7) which is the nearest to the second pressure receiving part 60b. An effect by providing offsets in the manner A′ like this will be described below with reference to FIG. 9A and FIG. 9B.

FIG. 9A and FIG. 9B are views that relate to the second embodiment of the present disclosure, and are for explaining a difference in influence of deflection of the rocker shaft due to difference in the manner of offsets. More specifically, FIG. 9A is a view of a configuration where offsets in the mariner A′ which is adopted in the present embodiment are provided. FIG. 9B is a view showing a comparative example which is referred to for the purpose of being compared with the configuration of the present embodiment.

First, when the disposition B is adopted, loads from the cams and loads from the valves are both act onto the rocker shaft 58 in substantially the same direction as shown in FIG. 8, unlike the disposition A described in the first embodiment. As a result, the rocker shaft deflects in such a manner as to be pressed to the upward direction in FIG. 9A and FIG. 9B, in both configurations in FIG. 9A and FIG. 9B.

As described above, in the manner A′ of the present embodiment, the distances between the transmission parts 62a and 62b and the bearings 26 which are the nearest to them are set to be shorter than the distances between the pressure receiving parts (cam rollers) 60a and 60b and the bearings 26 which are the nearest to them. According to the configuration like this, the deflection amount δ of the rocker shaft in each of the positions of the transmission parts becomes smaller as shown in FIG. 9A, as compared with the comparative example (FIG. 9B) which adopts the configuration opposite from this. Accordingly, by the valve operating apparatus 50 of the present embodiment which adopts the offsets in the manner A′, the harmful effect (more specifically, a closing failure of the valves 12) due to displacements of the transmission parts 62a and 62b accompanying the deflection of the rocker shaft 58 can also be restrained, similarly to the valve operating apparatus 10 of the first embodiment.

Claims

1. A valve operating apparatus for an internal combustion engine, comprising:

a first cam unit and a second cam unit configured to respectively drive a first valve and a second valve that are installed in a cylinder;

a first intermediate arm interposed between the first cam unit and the first valve, and including a first pressure receiving part that is pressed by the first cam unit and a first transmission part that transmits a pressing force of the first cam unit to a side of the first valve;

a second intermediate arm interposed between the second cam unit and the second valve, and including a second pressure receiving part that is pressed by the second cam unit and a second transmission part that transmits a pressing force of the second cam unit to a side of the second valve;

a rocker shaft configured to support the first intermediate arm and the second intermediate arm to be rockable between bearings that are respectively installed at both sides of the cylinder;

a first rocker arm interposed between the first intermediate arm and the first valve, and configured to transmit a pressing force from the first transmission part to the first valve;

a second rocker arm interposed between the second intermediate arm and the second valve, and configured to transmit a pressing force from the second transmission part to the second valve;

a first hydraulic lash adjuster configured to rockably support the first rocker arm, and act to eliminate a gap between the first valve and the first rocker arm, and a gap between the first rocker arm and the first intermediate arm; and

a second hydraulic lash adjuster configured to rockably support the second rocker arm, and act to eliminate a gap between the second valve and the second rocker arm, and a gap between the second rocker arm and the second intermediate arm,

wherein, in an axial direction of the rocker shaft, a distance between the first transmission part and the bearing that is nearest to the first transmission part is shorter than a distance between the first pressure receiving part and the bearing that is nearest to the first pressure receiving part, and a distance between the second transmission part and the bearing that is nearest to the second transmission part is shorter than a distance between the second pressure receiving part and the bearing that is nearest to the second pressure receiving part.

2. The valve operating apparatus according to claim 1,

wherein the first pressure receiving part and the second pressure receiving part, and the first transmission part and the second transmission part are disposed on a same side with respect to the rocker shaft, seen from an axial direction of the cylinder.

3. The valve operating apparatus according to claim 1,

wherein the first cam unit is configured by a first cam group including a plurality of cams having different profiles, and

wherein the valve operating apparatus further comprises a device that switches a cam that gives a pressing force to the first intermediate arm among the cams of the first cam group.

4. The valve operating apparatus according to claim 1,

wherein the second cam unit is configured by a second cam group further includes a plurality of cams having different profiles, and

wherein the valve operating apparatus further comprises a device that switches a cam that gives a pressing force to the second intermediate arm among the cams of the second cam group.