Variable valve control system for internal combustion engine

Abstract

An improved valve operating system for a multi-cylinder engine wherein the valve lift and timing of individual cylinders can be adjusted relative to each other so as to promote smoother running to compensate for cylinder-to-cylinder variation and improve output.

Description

BACKGROUND OF INVENTION

[0001] This invention relates to a variable valve control system for internal combustion engine and more particularly to such a system for an engine having a plurality of combustion chambers.

[0002] As is well known, many forms of internal combustion engines employ not only multiple cylinders but also variable valve timing and/or lift mechanism for adjusting the valve timing and/or lift in response to specific engine running conditions. That is, the optimum valve timing and valve lift for an engine depends upon both the running speed and load. The optimum valve timing and lift varies as the engine speed varies. Therefore, it has been proposed to employ any of a number of such type mechanisms in order to improve the engine performance throughout the entire engine load and speed operating ranges.

[0003] It is also known, however, that multiple cylinder engines also operate in such a manner that the cylinders do not necessarily all have the same volumetric efficiency. This can be caused by a variety of factors. For example, if the engine is of the V-type and has its cylinders at 90° angle with a two-plane type crank, the ignition intervals for the left and right banks are different and the burning conditions in those cylinders vary significantly because of interfering waves in the exhaust and intake systems. Although variable valve lift and timing arrangements are employed, the adjustments are made simultaneously for all cylinders. As a result, the optimum performance cannot be obtained.

[0004] It is therefore; a principal object to this invention to provide a valve actuating mechanism for an engine wherein the valve actuation for one cylinder can be adjusted relative to another cylinder so as to improve and compensate for variations in volumetric efficiency.

[0005] It is also a further object to this invention to provide an improved but simplified arrangement that permits such independent valve control without unduly complicating the system.

SUMMARY OF INVENTION

[0006] This invention is adapted to be embodied in an internal combustion engine that has at least two combustion chambers, which are defined by relatively moveable components that are driven in synchronism with each other. At least one intake valve and at least one exhaust valve is associated with each of the combustion chambers for controlling the emission of a charge thereto and the discharge of a burnt charge therefrom. A valve operating mechanism controls the degree of opening and timing of operation for at least one valve associated with each combustion chamber. The valve operating mechanism is operative to adjust at least one of the degree of opening and the timing of operation of the one valve of one of the combustion chambers relative to at least one of the degree of opening and timing operation of the one valve of one of the other combustion chambers to promote even running.

BRIEF DESCRIPTION OF DRAWINGS

[0007] FIG. 1 is a partial cross sectional view taken through one bank of a V-type engine constructed in accordance with an embodiment of the invention.

[0008] FIG. 2 is an exploded perspective view, with certain components shown schematically, of the valve operating mechanism associated with one of the valve sets of one of the cylinders of the engine.

[0009] FIG. 3 is a top plan view showing the actuating rocker arm assembly associated with the valve mechanism.

[0010] FIG. 4 is a cross sectional view showing the rocker arm construction when operating in accordance with the low lift condition.

[0011] FIG. 5 is a cross sectional view, looking at the same direction as FIG. 4, and shows the associated cam mechanism and how the high left cam has no effect on the valve lift in this operating condition.

[0012] FIG. 6 is a view, in part similar to FIG. 5, but shows the condition when the high lift valve actuation occurs.

[0013] FIG. 7 is a valve timing diagram showing the operating conditions of both the intake and exhaust valves with a single cylinder and shows the lift curves when the valve timing is not adjusted.

[0014] FIG. 8 is a diagrammatic view, in part similar to FIG. 7, and shows how the valve timing can also be changed in connection with the lift characteristics and shows the various overlap conditions.

[0015] FIGS. 9, 10 and 11 are additional timing curves showing how the lift and timing can be changed to accommodate for different volumetric efficiencies from cylinder to cylinder.

[0016] FIGS. 12 and 13 are views showing how the cylinder-to-cylinder fluctuations and volumetric efficiency affect the output in relation to varying engine speeds and loads.

DETAILED DESCRIPTION

[0017] Referring now in details to the drawings and initially primarily to FIG. 1, a four cycle multi-cylinder internal combustion engine constructed and operated in accordance with an embodiment of the invention as shown partially and in cross section and is indicated generally by the reference numeral 21. In the illustrated embodiment, the engine 21 is of the V8 type and is comprised of a pair of cylinder banks, each of which has four cylinder bores. Because the description of the entire engine is not necessary to understand the invention, the engine is only shown partially and an illustration of only the upper portion of one cylinder of one bank is believed to be all that is necessary to permit those skilled in the art to understand and practice the invention.

[0018] The engine 21 includes a cylinder block having a pair of angularly disposed cylinder banks 22 each of which is formed with four cylinder bores 23. Pistons 24 reciprocate in these cylinder bores 23 and are connected by means of piston pins 25 to the upper or small end of connecting rods 26. The lower or big ends of the connecting rods 26 are journalled on the throws of a crankshaft, which is not shown, but which is rotatably journalled at the lower end of the cylinder block in a known manner.

[0019] As is typical with V-type engine constructions, the cylinder bores 23 of the respective banks 22 are staggered relative to each other so that the connecting rod big ends can be journalled in side-by-side relationship on the same throws of the crankshaft.

[0020] A cylinder head member 27 is connected in a suitable manner to each cylinder bank 22 and has a lower surface which is held in sealing relationship with the cylinder bank 22 around the cylinder bore 23. This lower surface of the cylinder head member 27 is provided with recesses 28 which cooperate with the heads of the pistons 24 and the cylinder bores 23 to define the combustion chambers of the engine 21. Because of the fact that the cylinder head recess 28 forms substantially the entire clearance volume of the engine at top dead center position, as seen in FIG. 1, at times the reference numeral 28 will also be referred to as the combustion chamber.

[0021] One side of the cylinder head member 27 comprises the intake side and normally this is the side that faces the valley between the cylinder banks 22. Intake passages are formed in this side of the cylinder head member 27 and these are served by an induction system that is shown only partially and includes intake manifold runners 31.

[0022] In the illustrated embodiment, the engine 21 is provided with a fuel injection system of the manifold type. To this end, therefore, fuel injectors 32 are mounted in the cylinder head member 27 and spray into the intake passages 29. The fuel injectors 32 are supplied with fuel under pressure and are operated periodically to inject: this fuel in the desired amounts in any suitable manner.

[0023] Each of the intake passages 29 terminates in an intake valve seat 31, which is valved by a respective intake valve 32. The intake valves 32 are each operated by a variable valve lift mechanism, indicated generally by the reference numeral 33 and which will be described later by reference to FIGS. 2 through 6. Basically this valve actuating mechanism 33 is operated by an intake camshaft 34 in a manner, which will also be described in detail later. The intake camshaft 34 is driven by a variable valve timing mechanism (VVT) 35, which is driven from the crankshaft in timed relationship by a suitable mechanism such as a timing chain or belt 36. The variable valve timing mechanism 35 may be of any known type and preferably is hydraulically operated so as to vary the phase angle between the intake camshaft 34 and the crankshaft.

[0024] The fuel/air charge that has been delivered to the combustion chambers 28 by the intake passages 29 and fuel injectors 32 is fired by centrally positioned spark plugs 37 mounted in the cylinder head member 27 generally on the axis of the cylinder bore 23. Each of these spark plugs 37 is fired by a suitable ignition system in accordance with any desired timing strategy.

[0025] The burnt charge is discharged from the combustion chambers 28 through exhaust passages 38 formed in the cylinder head member 27 on the side opposite the intake passages 29. There are preferably provided two exhaust passages 38 for each combustion chamber 28. These exhaust passages 38 communicate with the combustion chamber 28 through exhaust valve seats 39 which are valved by a pair of exhaust valves 41 mounted in the cylinder head member 27 in a known manner. The exhaust valves 41 are operated by a variable valve lift mechanism, indicated generally by the reference numeral 42, and which has a construction of the type which will be described later and which is basically similar to that of the intake valve lift mechanism 33.

[0026] This exhaust valve lift mechanism 42 is operated by an exhaust camshaft 43, which is journalled for rotation in the cylinder head member 27 about an axis parallel to the intake camshaft 34. Like the intake camshaft 34, the exhaust camshaft 43 is driven by a variable valve timing mechanism 44, which is effective to change the phase angle of the exhaust camshaft 43 relative to both the intake camshaft, 34 and the crankshaft. This variable valve timing mechanism 44 may be of any known type and is also driven by the timing chain or belt 36.

[0027] The valve operating mechanism as thus far described is contained within a cam chamber closed by a cam cover 45 that is detachably affixed to the cylinder head member 27 in a known manner.

[0028] The exhaust passages 38 of the cylinder head member 27 communicate with the individual runners 46 of an exhaust manifold, which cooperates with a suitable, exhaust system (not shown) for discharging the exhaust gases to the atmosphere.

[0029] The variable valve lift mechanisms 33 and 42 will now be described by particular references to FIGS. 2 through 6 wherein the intake variable valve lift mechanism 33 is depicted in detail. it is to be understood, however, that the variable valve lift mechanism 42 associated with the exhaust valves 41 can have substantially the same construction.

[0030] As may be seen in this figure, the paired intake valves 32 are associated with three cam lobes formed on the intake camshaft 34. These include a common high speed, high load cam lobe 47 and a pair of singularly configured low speed, low load cam lobes 48 disposed on opposite sides of the high speed cam lobe 47.

[0031] The shapes of the cam lobes 47 and 48 may be varied but, in accordance with conventional practice, the points of maximum lift of both the low speed lobes 48 and the high speed lobe 47 are at the same circumferential position as shown best in FIGS. 5 and 6. However, because of the incorporation of the variable valve timing mechanism 35, it is possible to change the timing of the maximum lift of one cam relative to the other by changing the phase angle during engine running.

[0032] The variable valve timing mechanism is shown schematically at 35 in FIG. 2 and is controlled by an ECU 49 in accordance with a suitable control strategy, which will be described later in more detail.

[0033] These cam lobes 47 and 48 operate the valves 32 through a rocker arm assembly indicated generally by the reference numeral 51 and which is comprised of a rocker arm shaft 52 on which low speed, low load followers 53 and a single high speed follower 54 are positioned. These rocker arm followers 53 and 54 have respective bearing surfaces 55 and 56, which are engaged with the cam lobes 48 and 47, respectively. The low speed followers 53 have end portions 57 which are engaged with the stems of the intake valves 32 so that under all circumstances the movement of the low speed followers 53 operates the intake valves 32. However, when operating at the high speed, high load condition, the high speed follower 54 is coupled to the low speed followers 53 so that the latter will be actuated by the high speed cam lobe 47 rather than the low speed cam lobes 48.

[0034] This mechanism may be best understood by reference to FIGS. 4 through 6. As may be seen in these figures, the low speed rocker followers 53 are directly journalled on the rocker arm shaft 52. The high speed follower 54, on the other hand, is journalled on a pivot pin 58, which is, in turn, fixed to an upstanding lug 59 of each the low speed rocker followers 53.

[0035] A lost motion mechanism, indicated generally by the reference numeral 61 is interposed between the high speed follower 54 and the low speed follower 53. This lost motion mechanism includes a pair of plungers 62, each of which bears against a respective shoulder 63 formed on the low speed rocker followers 53. A coil compression spring 64 is received in a bore 65 of the high speed rocker follower 54 and urges the plunger 62 into engagement with the low speed follower surface 63.

[0036] A locking lever 66 is pivotally supported on the low speed rocker followers 53 by means of a pivot shaft 67 and is normally biased to a disengaged position as shown in FIGS. 4 and 5 by means of a biasing plunger 68. The locking lever 66 has an actuating tab 69 that is engaged by hydraulically actuated pistons 71 slidably supported in the low speed followers 53.

[0037] The rocker shaft 52 is provided with a hollow bore 72, which receive hydraulic fluid from a lift control mechanism, indicated schematically at 73 in FIG. 2. The rocker shafts 52 is formed with cross drillings 74 that communicate the bore 72 with the plungers 71 so as to cause them to pivot from the position shown in FIGS. 4 and 5 to the position shown in FIG. 6 where the locking lever 66 engages a surface 75 of the high speed follower 54 so as to cause its motion to be transmitted to the low speed followers 53 so as to increase the lift of the intake valves 32 when in the position shown in FIG. 6 wherein the high speed cam 47 will actually operate the intake valves 32.

[0038] Thus, by controlling the hydraulic pressure asserted from the lift control 73 it is possible to shift the operation of the valves 32 from the low speed cam lobes 43 to the high speed cam lobe 47.

[0039] Although the system as thus far described includes two low speed cams and followers and single high speed cam and follower, the invention may also be used where one of the low speed cams is replaced by an intermediate speed and load cam and a further coupling mechanism between that and the rocker followers 53 to provide a wider range of adjustment. Those skilled in the art will readily understand how this can be accomplished from the foregoing description.

[0040] FIG. 7 shows the valve timing events when the variable valve timing control 35 is not actuated and only the lift of the valve is changed by the lift actuating mechanism 73. It will be seen that the maximum opening point of the intake valves and exhaust valves occur at the same crank angle regardless of whether they are operated by the high speed cam or the low speed cam. In accordance with the invention, however, since it is possible to vary the valve timing of both the intake camshaft 34 and the exhaust camshaft 43 of each cylinder bank from the other, it is possible to change the timing when maximum valve lift occurs.

[0041] This may be best understood by reference to FIG. 8 where it is shown that the maximum lift of the intake and exhaust valves can be adjusted and in addition, the timing adjusted so that the maximum lifts occur at different phase angles from each other. Thus, it is possible to alter the valve timing for one cylinder of one bank relative to a cylinder of another bank and compensate for differences in volumetric efficiency so as to have more uniform running because the cylinders are producing substantially the same output.

[0042] For example, as seen in FIG. 9, it is possible to have a relative small overlap when operating under low speed conditions. However, by shifting the intake side timing relative to that of the exhaust side, it is possible to increase the overlap time. This effect can be seen in FIG. 10. Also, the overlap time can be adjusted when operating under high speed cams as seen in FIG. 11.

[0043] The affect of this control can be seen in the volumetric efficiency curves shown in FIGS. 12 and 13 respectively where FIG. 12 shows the cylinder-to-cylinder variations when the timing is not adjusted in FIG. 12 but the cylinder-to-cylinder variations can be substantially reduced when the valve timing is changed as shown in FIG. 13. This is particularly important in the critical engine speed range of 1500 rpm to 2500 rpm for an eight cylinder V type engine in spite of varying the valve lift as seen in FIG. 12.

[0044] However, if opening/closing timings of the intake valves are advanced, for example, by 20° with respect to the ordinary valve timings only for low speed cams 25 in cylinders of poor volumetric efficiency, irregularities in volumetric efficiency can be decreased, as seen in FIG. 13.

[0045] As also seen in this latter figure, although irregularities between cylinders are large in the intermediate and high speed range, if in this range, the valve lift varying means A actuates the valve lift switching control valve 41 for the switching to the high speed cam 26 mode and the valve timing varying means B actuates the valve timing drive means 43 to adjust valve timings to be optimum, irregularities between cylinders can be kept in a smallest level.

[0046] In addition, as shown in FIG. 13, irregularities between cylinders are separated into an irregularity group of cylinders #1-#4 and an irregularity group of cylinders #5-#8. In order to decrease the difference in irregularities between these groups to a minimum, shapes of cams are set respectively for the two groups. For example, if the cylinders #1-#4 have the same first valve timing and the cylinders #5-#8 have the same second valve timing, the difference in irregularities in volumetric efficiency between two cylinder groups can be corrected. Hence, it is actually possible to obtain an improvement of engine output by improving or reducing the cylinder to cylinder variations caused by the changes in volumetric efficiency and thus, better running performance is obtained.

[0047] Thus, from the foregoing description it should be readily apparent that the described construction provides an improved smoothness in running and accordingly an increase in output torque to compensate for cylinder-to-cylinder variations in volumetric efficiency by changing not only the valve lift but also the valve timing from one cylinder to others. Of course, the foregoing description is that of a preferred embodiment of the invention and various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.

Claims

1. A four cycle, internal combustion engine having at least two combustion chambers defined by relatively moveable components driven in synchronism with each other, at least one intake valve associated with each of said combustion chambers for controlling the induction of a charge thereto, at least one exhaust valve associated with each of said combustion chambers for controlling the discharge of a charge therefrom, a valve operating mechanism for controlling the degree of opening and timing of operation for at least one valve associated with each of said combustion chambers, said valve operating mechanism being operative to adjust at least one of the degree of opening and the timing of operation of the one valve of one of said combustion chambers relative to at least one of the degree of opening and the timing of operation of the one valve of one of the other of said combustion chambers to promote even running.

2.A four cycle, internal combustion engine as set forth in claim 1, wherein both the degree of opening and the timing of operation of the one valve of ore of the combustion chambers is adjusted relative to both the degree of opening and the timing of operation of the one valve of one of the other of said combustion chambers to promote even running.

3. A four cycle, internal combustion engine as set forth in claim 1, wherein at least one of the valve operating mechanisms is comprised of a rotating cam mechanism comprised of a pair of cams comprised of a low speed and a high speed cam each providing a different degree of lift.

4. A four cycle, internal combustion engine as set forth in claim 3, wherein the location of maximum lift of the low speed cam and the high speed cam is at the same angular position on the cam shaft, the timing of maximum lift for each cam is varied by the valve operating mechanism.

5. A four cycle, internal combustion engine as set forth in claim 1, wherein the cylinders are disposed at an angle to each other.

6. A four cycle, internal combustion engine as set forth in claim 5, wherein both the degree of opening and the timing of operation of the one valve of one of the combustion chambers is adjusted relative to both the degree of opening and the timing of operation of the one valve of one of the other of said combustion chambers to promote even running.

7. A four cycle, internal combustion engine as set forth in claim 5, wherein at least one of the valve operating mechanisms is comprised of a rotating cam mechanism comprised of a pair of cams comprised of a low speed and a high speed cam each providing a different degree of lift.

8. A four cycle, internal combustion engine as set forth in claim 7, wherein the location of maximum lift of the low speed cam and the high speed cam is at the same angular position on the cam shaft, the timing of maximum lift for each cam is varied by the valve operating mechanism.