Multi cylinder internal combustion engine and control method therefor

Abstract

 The present invention relates to a multi-cylinder internal combustion engine and a control method therefor, wherein maximum-lift timings of a low speed and high speed cams in at least one cylinder of the multi-cylinder internal combustion engine are varied so as to correct irregularities in volumetric efficiency between cylinders.

Description

[0001] The present invention relates to a multi-cylinder internal combustion engine and a control method therefor.

[0002] In some internal combustion engines, valve drive mechanisms are disposed two for each cylinder to opening/closing intake and exhaust valves disposed in a plurality of cylinders, so as to vary valve lifts of the intake and exhaust valves by the switching of high speed cams having large valve lifts and low speed cams having low valve lifts in the valve drive mechanisms in response to the operating condition of the engine.

[0003] In a variable valve drive system for an internal combustion engine with such variable valve lift means, the switching of high speed and low speed cams in response to an operating condition such as a given engine speed, allows coexistence of engine performance during high speed running and that during low speed running.

[0004] Conventional valve lift varying means are arranged such that a low speed and a high speed cam are disposed in each cylinder and they are switched in response to the operating condition so as to change the valve lift, but maximum-lift timings of the low speed and the high speed cam are the same. Further, this valve lift varying means is provided additionally with a mechanism for changing phases of camshafts continuously with respect to the crank angle to change the phase difference between intake and exhaust timings in response to the operating condition, so as to optimize volumetric efficiency.

[0005] However, with such a construction, in multi-cylinder engines having Vtype eight cylinders of 90° crank (two plane), for example, ignition intervals in the left and the right bank are irregular, and volumetric efficiency and the burning condition of the engine differ greatly between cylinders because of interfering waves in the intake and exhaust systems, preventing elimination of irregularities in performance between cylinders.

[0006] In view of the foregoing, it is an objective of the present invention to provide a multi-cylinder internal combustion engine capable of varying maximum-lift timings of a low speed and a high speed cam in at least one cylinder of the multi-cylinder engine so as to correct irregularities of volumetric efficiency between cylinders.

[0007] This objective is solved in an inventive manner by a multi-cylinder internal combustion engine comprising a plurality of intake and exhaust valves per cylinder and a variable valve drive system having valve drive mechanisms disposed on the intake and exhaust sides of the cylinders to open and close the intake or exhaust valves, respectively, a valve lift varying means adapted to vary valve lifts of the intake and/or exhaust valves separately between the cylinders, and a valve timing varying means adapted to vary opening/closing timings of the intake and/or exhaust valves for the respective cylinders, wherein the variable valve drive system is adapted to vary opening/closing timings of the intake and/or exhaust valves in at least one of the cylinders in response to the operating condition of the engine.

[0008] According to this multi-cylinder internal combustion engine, as a result of varying opening/closing timings of the intake and/or exhaust valves at least in one cylinder in response to the operating condition of the engine, intake and exhaust pulsating waves are effectively utilized for each cylinder and irregularities in volumetric efficiency between cylinders are corrected, so that an intended engine performance can be achieved over the operating range from a low engine speed to a high engine speed.

[0009] Preferably, the variable valve drive system comprises a plurality of camshafts, in particular two for each cylinder, with cams having different valve lifts, wherein said cams having different valve lifts comprise either two cams for a low speed and a high speed, or three cams for a low speed, an intermediate speed and a high speed.

[0010] According to this preferable arrangement, if two cams of a low speed and a high speed cam are provided, or even if three cams of a low, an intermediate and a high speed cam are provided, irregularities in volumetric efficiency between cylinders can be corrected.

[0011] Beneficially, the opening/closing timings of the intake and/or exhaust valves correspond to maximum-lift timings of the respective cams having different valve lifts operating same.

[0012] It is further preferable if the valve lift varying means is adapted for the intake side and/or the exhaust side of the cylinders to switch between the cams having different valve lifts operating the valves on the respective side of the cylinder.

[0013] According to a preferred embodiment of the multi-cylinder internal combustion engine the valve drive mechanisms comprise a rocker shaft, a rocker arm fixed to the rocker shaft, a high speed follower member pivotally supported by the rocker shaft, a camshaft, a lost motion mechanism adapted to bias the high speed follower member towards the high speed cam and a lever pivotally supported by the rocker arm and adapted to control movement of the high speed follower member.

[0014] According to a further preferred embodiment of the multi-cylinder internal combustion engine the valve lift varying means comprises at least one valve lift switching control valve, wherein a controller is adapted to control the valve lift switching control valve in response to the operating condition such as an engine speed and/or the valve timing varying means comprises at least one valve timing drive means, in particular a hydraulic actuator, wherein the controller is adapted to control the valve timing drive means in response to the operating condition such as an engine speed.

[0015] Beneficially, the cylinders are divided into at least two groups of cylinders, and shapes of cams having different valve lifts are set for each of said groups of cylinders.

[0016] As a plurality of cylinders are divided into a plurality of cylinder groups and shapes of cams are set for each cylinder group within this preferable arrangement, irregularities in volumetric efficiency can be corrected for each cylinder group.

[0017] It is further preferable if a maximum-lift timing of a low speed cam in at least one cylinder differs from the maximum-lift timings of the low speed cams in the respective further cylinders.

[0018] Accordingly, as the maximum-lift timing of a low speed cam in at least one cylinder differs from maximum-lift timings of low speed cams in the other cylinders, intake and exhaust waves can be effectively utilized for each cylinder at least in a low speed range, so that irregularities in volumetric efficiency between cylinders can be corrected.

[0019] It is also preferable if the maximum-lift timings of the low speed cams and/or the high speed cams in at least one cylinder differ from those of low speed cams and/or high speed cams in the respective further cylinders.

[0020] In particular, if the maximum-lift timings of both low speed and high speed cams in at least one cylinder differ from those of low speed and high speed cams in the other cylinders, intake and exhaust pulsating waves can be effectively utilized for each cylinder at least in a low and a high speed range, so that irregularities in volumetric efficiency between cylinders can be corrected.

[0021] According to yet another preferred embodiment, the opening/closing timings of the low speed cams are within ranges of those of the high speed cams.

[0022] If, opening/closing timings of intake and exhaust valves produced by the low speed cams are within ranges of those produced by the high speed cams, the engine performance in a lower speed range can be satisfied.

[0023] According to still another embodiment, the internal combustion engine is a four-valve or five-valve engine.

[0024] It is a further objective of the present invention to provide a control method for a multi-cylinder internal combustion engine having a plurality of intake and exhaust valves effectively correcting irregularities in volumetric efficiency.

[0025] This objective is solved in an inventive manner by a control method for a multi-cylinder internal combustion engine having a plurality of intake and exhaust valves per cylinder and a variable valve drive system having valve drive mechanisms respectively disposed on the intake and exhaust sides of the cylinders to open and close the intake or exhaust valves, wherein valve lifts of the intake and/or exhaust valves are varied separately between the cylinders and opening/closing timings of the intake and/or exhaust valves are varied for the respective cylinders, and wherein opening/closing timings of the intake and/or exhaust valves in at least one cylinder are varied in response to the operating condition of the engine.

[0026] It is preferable if, the intake and/or exhaust valves are operated by means of cams having different valve lifts being provided on camshafts.

[0027] It is further preferable, if valve timings of the cams having different valve lifts for an intake and/or an exhaust side of at least one of the cylinders, in particular a low speed cam and a high speed cam, are set separately from each other.

[0028] According to a preferred embodiment of the control method an overlapping time between opening and closing of the intake and/or the exhaust valves is increased or decreased in response to the operating conditions such as an engine speed with the cams having different valve lifts provided for respective cylinders.

[0029] In the following the present invention is explained in greater detail with respect to the multi-cylinder internal combustion engine and the control method therefor with reference to several embodiments thereof in conjunction with the accompanying drawings, wherein:

Fig. 1

is a sectional view of an internal combustion engine with a variable valve drive system;

Fig. 2

is an exploded perspective view of the variable valve drive system;

Fig. 3

is a plan view of the follower of the variable valve drive system;

Fig. 4

is a sectional view of a portion of the variable valve drive system;

Fig. 5

is a sectional view of the variable valve drive system in operation at a low engine speed;

Fig. 6

is a sectional view of the variable valve drive system in operation at a high engine speed;

Fig. 7

are graphs showing the lift characteristics;

Fig. 8

are graphs showing the operating characteristics of intake and exhaust valves; and

Fig. 9

are graphs showing the relation between engine speed and engine volmetric efficiency for each cylinder of an V type 8-cylinder internal combustion engine.

[0030] An embodiment of a variable valve drive system for an internal combustion engine will be described below in detail.

[0031] Fig. 1 is a sectional view of an internal combustion engine with a variable valve drive system; Fig. 2 is an exploded perspective view of the variable valve drive system; Fig. 3 is a plan view of the follower of the variable valve drive system; Fig. 4 is a sectional view of a portion of the variable valve drive system; Fig. 5 is a sectional view of the variable valve drive system in operation at a low engine speed; and Fig. 6 is a sectional view of the variable valve drive system in operation at a high engine speed.

[0032] The teaching of the present embodiments may be applied to multi-cylinder engines, and in this particular embodiment, description will be made on a four-stroke V type 8-cylinder engine, in which one cylinder bank of the V type 8-cylinder engine is referred to because of the other cylinder bank having the same construction.

[0033] In a cylinder block 2 of the V type 8-cylinder engine 1 are provided pistons 3 for reciprocal movement. The reciprocal movement of the pistons 3 causes a crankshaft disposed in a crankcase (not shown) to be rotated through connecting rods.

[0034] On the cylinder block 2 is mounted a cylinder head 5 and on the cylinder head 5 is mounted a head cover 6. Combustion chambers 7 are defined by the cylinder block 2, tops of the pistons 3 and the cylinder head 5. In the cylinder head 5 are fitted ignition plugs 8 facing the combustion chambers 7.

[0035] In the cylinder head 5 are formed intake passages 9 and exhaust passages 10, and intake pipes 11 are connected to the intake passages 9. To the exhaust passages 10 are connected exhaust pipes 12.

[0036] An opening of the intake passage 9 facing the combustion chamber 7 is adapted to be opened/closed by an intake valve 13, and an opening to the exhaust passage 12 facing the combustion chamber 7 by an exhaust valve 14. In the cylinder head 5 are provided fuel injectors 15 for injecting fuel into the intake passages 9.

[0037] In this V type 8-cylinder engine 1 are provided, in each cylinder, two valves drive mechanisms 20 for opening/closing two intake valves 13 and two exhaust valves 14 in the cylinder. The valve drive mechanisms 20 disposed on either of the intake and exhaust sides have the same construction, and the valve drive mechanism 20 disposed on the intake side is shown in Figs. 2- 6 for description.

[0038] This valve drive mechanism 20 has a rocker shaft 21, a rocker arm 22, a high speed follower member 23 and a camshaft 24. The rocker arm 22 is mounted on the rocker shaft 21 for rocking movement, and on the rocker arm 22 is mounted pivotally the high speed follower member 23 through a follower shaft 90. The rocker arm 22 has a pair of low speed followers 22a, and the high speed follower member 23 has a high speed follower 23a, the high speed follower 23a being located between the pair of low speed followers 22a.

[0039] On the cam shaft 24 are provided a pair of low speed cams 25 having small lifts for lower speed, and a high speed cam 26 having a large lift for higher speed. Rotation of the camshaft 24 causes the pair of low speed cams 25 to push down the pair of low speed followers 22a, and rotation of the high speed cam 26 causes the high speed follower 23a to be pushed down. The construction of the low speed followers 22a and the high speed follower 23a is not limited to this embodiment, but may be varied widely.

[0040] Although two cams of a low speed and a high speed cam are used in this embodiment, three cams of a low speed, an intermediate speed and a high speed cam may be used.

[0041] On the rocker arm 22 is provided a lost motion mechanism 29 consisting of a lost motion plunger 29a and a lost motion spring 29b, and the high speed follower member 23 is biased by the lost motion mechanism 29 toward the high speed cam 26.

[0042] In the rocker arm 22 is also provided an oil plunger 30, which is actuated by oil supplied through an oil passage 40 formed in the rocker shaft 21, to push a lever 31. The lever 31 is pivotally mounted on the rocker arm 22 through a lever shaft 32 and is biased by a return plunger 33 in the direction of its disengagement from an engaging section 23b of the high speed follower member 23.

[0043] Oil supply to the oil passage 40 is performed by switching action of a valve lift switching control valve 41, and a controller 42 controls the valve lift switching control valve 41 in response to the operating condition such as an engine speed, whereby the function of the valve lift varying means A is effected.

[0044] At the end of the cam shaft 24 is provided a drive gear 27 as shown in Fig. 1, which is adapted to rotate in association with the crankshaft through a cam chain 28.

[0045] Between the drive gear 27 and the cam shaft 24 is disposed a valve timing drive means (hydraulic actuator) 43 for displacing the angular position of the cam shaft 24 relative to the drive gear 27; oil pressure is supplied by the controller 42 in response to the operating condition; and the angular displacement of the cam shaft 24 drives the low speed and high speed cams 25, 26 simultaneously so as to change the phase of the cam shaft 24 relative to the crank angle.

[0046] The valve timing drive means 43 is disposed at the end of the cam shaft, and the angular position of the cam shaft 24 is displaced to drive the low speed and high speed cams 25, 26 simultaneously, so that the low speed and high speed cams 25, 26 change their valve timings simultaneously, whereby the function of the valve timing varying means B is effected. Besides, since the variable valve lift drive mechanism allows the switching of cams used in response to the operating condition, it is possible that the low speed and high speed cams 25, 26 set their valve timings separately.

[0047] With the controller 42, the variable valve lift means A is driven to vary the valve lifts of the intake and exhaust valves separately between cylinders by the switching of cams having different valve lifts of the intake and exhaust valves; and the valve timing varying means B is driven to vary the opening/closing timings of the intake and exhaust valves with cams having different valve lifts for the respective cylinders, so as to vary the maximum-lift timings of cams having different valve lifts in at least one cylinder in response to the operating condition of the engine.

[0048] For example, regarding the valve lift varying means A, during low speed engine running, oil supply from the valve lift switching control valve 41 is shut off (OFF) as shown in Fig. 5 to thereby disable the oil plunger 30, so that the return plunger 33 causes the lever 31 to be disengaged from the engaging section 23b of the high speed follower member 23.

[0049] As a result, even if the high speed follower 23a of the high speed follower member 23 is pushed down by the high speed cam 26, the lost motion mechanism 29 allows free movement of the high speed follower member 23, causing the low speed cam 25 to push down the pair of low speed followers 22a, so that the low speed cam 25 causes the rocker arm 22 to open/close the intake valves 23, and the intake passages 9 are opened/closed as shown in Fig. 7 by a dash line.

[0050] During high speed engine running, oil pressure is supplied (ON) from the valve lift switching control valve 41 to actuate the oil plunger 30, so that the lever 31 is pushed down for rocking movement to be engaged with the engaging section 23b of the high speed follower member 23, limiting the rocking movement of the high follower member 23.

[0051] As a result, when the high speed follower 23a of the high speed follower member 23 is pushed down by the high speed cam 26, the rocking arm 22 is actuated to open/close the intake valves 23, and the intake passages 9 are opened/closed as shown in Fig. 7(a) by a solid line.

[0052] A valve drive mechanism 20 disposed on the exhaust side is arranged similarly, and the exhaust passages 10 are opened/closed with the lift characteristic shown in Fig. 7(a).

[0053] Thus, the valve lifts of the intake and exhaust valves are varied separately between cylinders by the switching of cams having different valve lifts of the intake and exhaust valves.

[0054] In addition, the valve timing varying means actuates the valve timing drive means 43 to displace the angular position of the cam shaft 24, so that the low speed and high speed cams 25, 26 are driven simultaneously and change their valve timings simultaneously.

[0055] Thus, opening/closing timings of the intake and exhaust valves 13, 14 are varied in response to the operating condition such as an engine speed with high speed and low speed cams 25, 26 provided for respective cylinders.

[0056] For example, during idle running, the intake and exhaust valves 13,14 are actuated by the low speed cams 25, and regarding opening/closing timings of the intake and exhaust valves, the overlapping time a can be decreased, as shown in Fig. 8(a), to improve idling stability.

[0057] Further, during low and intermediate speed running, the intake and exhaust valves 13, 14 are actuated by the low speed cam 25, and regarding opening/closing timings of the intake and exhaust valves 13, 14, the opening/closing timing of the intake valves 13 is advanced by θ₁ to increase the overlapping time a to some extent, so that the torque during low and intermediate speed running can be improved.

[0058] Furthermore, during high speed running, oil pressure is supplied (ON) from the valve lift switching control valve 41 to actuate the oil plunger 30, so that the mechanism is switched to the high speed cam 26 mode. Regarding intake and exhaust opening timings, the opening/closing timing of the intake valves 13 is advanced by θ₂ and the opening/closing timing of the exhaust valves 14 is delayed by θ₃ as shown in Fig. 8(c), so that the overlapping time a can be increased, improving the maximum output.

[0059] As a result of lifts and/or opening/closing timings of the intake and exhaust valves 13, 14 being varied in response to the operating condition of the engine, intake and exhaust pulsating waves can be effectively utilized for each cylinder and irregularities in volumetric efficiency between cylinders can be corrected, thus achieving an intended engine performance over the operating range of a low engine speed to a high engine speed.

[0060] In addition, opening/closing timings of the intake and exhaust valves 13, 14 produced by the low speed cam 25 are within those produced by the high speed cam 26, thus satisfying engine performance in a lower speed range.

[0061] Fig. 9 are graphs showing the relation between engine speed and engine volumetric efficiency for each cylinder of a V type 8-cylinder internal combustion engine. In Fig. 9, irregularities in volumetric efficiency can be seen in the operating range of 1500-2500 rpm in spite of the valve lifts being varied. 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.

[0062] In Fig. 9(b), 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.

[0063] In addition, as shown in Fig. 9(b), irregularities between cylinders are separated into an irregularity group of cylinders # I - # 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 # I - # 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.

[0064] Although in the above, the opening/closing of the intake valves 13 and the exhaust valves 14 has been performed by valve drive mechanisms 20 operating with cams provided on camshafts, it is noted that the intake and the exhaust valves 13, 14 may also be operated without using cams. In particular, the intake and/or exhaust valves 13, 14 may be operated by valve drive mechanisms like hydraulic actuators. Within this embodiment a camshaft with cams would not be required, and an individual hydraulic actuator could be provided for each of the intake and/or exhaust valves 13, 14.

[0065] The embodiments described above disclose variable valve drive system for an internal combustion engine having valve drive mechanisms disposed two for each cylinder to opening/closing intake and exhaust valves disposed in a plurality of cylinders, said system comprising valve lift varying means for varying valve lifts of the intake and exhaust valves separately between cylinders by the switching of cams having different valve lifts of the intake and exhaust valves, and valve timing varying means for varying opening/closing timings of the intake and exhaust valves with cams having different valve lifts for respective cylinders, whereby maximum-lift timings of cams having different valve lifts in at least one cylinder, are varied in response to the operating condition of the engine.

[0066] As maximum-lift timings of cams having different valve lifts in at least one cylinder, are varied in response to the operating condition of the engine, intake and exhaust pulsating waves can be effectively utilized for each cylinder and irregularities in volumetric efficiency between cylinders can be corrected, thus achieving an intended engine performance over the operating range from a low engine speed to a high engine speed.

[0067] Within the embodiments described above it is preferable if, said cams having different valve lifts are two cams of a low speed and an intermediate speed cam, or three cams of a low speed, an intermediate speed and a high speed cam.

[0068] Accordingly, if two cams of a low speed and an intermediate speed cam are provided, or even if three cams of a low speed, an intermediate speed and a high speed cam are provided, irregularities in volumetric efficiency between cylinders can be corrected.

[0069] Beneficially, said plurality of cylinders are divided into a plurality of cylinder groups, and shapes of cams are set for each of said cylinder groups.

[0070] Accordingly, if a plurality of cylinders is divided into a plurality of cylinder groups, and shapes of cams are set for the respective cylinder groups, irregularities in volumetric efficiency between cylinder groups can be corrected.

[0071] It is further preferable, if the maximum-lift timing of a low speed cam in at least one cylinder differs from maximum-lift timings of low speed cams in the other cylinders.

[0072] Accordingly, if the maximum-lift timing of the low speed cam in at least one cylinder differs from maximum-lift timings in the other cylinders. Therefore, intake and exhaust pulsating waves can be effectively utilized for each cylinder at least in a low speed range, irregularities in volumetric efficiency between cylinders can be corrected.

[0073] It is also preferable, if maximum-lift timings of both low speed and high speed cams in at least one cylinder differ from those of low speed and high speed cams in the other cylinders.

[0074] Accordingly, maximum-lift timings of both low speed and high speed cams in at least one cylinder differ from those in the other cylinders, therefore intake and exhaust pulsating waves can be effectively utilized for each cylinder at least in a low speed and a high speed range, so that irregularities in volumetric efficiency between cylinders can be corrected.

[0075] Additionally, opening/closing timings of the low speed cams are preferably ranges of those of high speed cams.

[0076] Accordingly, opening/closing timings of the intake and exhaust valves produced by the low speed cams, are within the ranges of those produced by the high speed cams, thus satisfying engine performance in a lower speed range.

[0077] Thus, based on the teaching of the embodiments described above maximum-lift timings of a low speed and a high speed cam in at least one cylinder in a multi-cylinder engine, are varied so as to correct irregularities in volumetric efficiency between cylinders by a variable valve drive system for an internal combustion engine having valve drive mechanisms disposed two for each cylinder to opening/closing intake and exhaust valves disposed in a plurality of cylinders, comprising valve lift varying means A for varying valve lifts of the intake and exhaust valves separately between cylinders by the switching of cams having different valve lifts of the intake and exhaust valves, and valve timing varying means B for varying opening/closing timing of the intake and exhaust valves with cams having different valve lifts for respective cylinders, whereby maximum-lifts in at least one cylinder are varied in response to the operating condition of the engine.

Claims

1. Multi-cylinder internal combustion engine comprising a plurality of intake and exhaust valves per cylinder and a variable valve drive system having valve drive mechanisms (20) disposed on the intake and exhaust sides of the cylinders to open and close the intake or exhaust valves (13,14), respectively, a valve lift varying means (A) adapted to vary valve lifts of the intake and/or exhaust valves (13,14) separately between the cylinders, and a valve timing varying means (B) adapted to vary opening/closing timings of the intake and/or exhaust valves (13,14) for the respective cylinders, wherein the variable valve drive system is adapted to vary opening/closing timings of the intake and/or exhaust valves (13,14) in at least one of the cylinders in response to the operating condition of the engine (1).

2. Multi-cylinder internal combustion engine according to claim 1, characterized in that the variable valve drive system comprises a plurality of camshafts (24), in particular two for each cylinder, with cams (25,26) having different valve lifts, wherein said cams (25,26) having different valve lifts comprise either two cams (25) for a low speed and a high speed (26), or three cams for a low speed, an intermediate speed and a high speed.

3. Multi-cylinder internal combustion engine according to claim 1 or 2, characterized in that the opening/closing timings of the intake and/or exhaust valves (13,14) correspond to maximum-lift timings of the respective cams (25,26) having different valve lifts operating same.

4. Multi-cylinder internal combustion engine according to claim 2 or 3, characterized in that the valve lift varying means (A) is adapted for the intake side and/or the exhaust side of the cylinders to switch between the cams having different valve lifts operating the valves on the respective side of the cylinder.

5. Multi-cylinder internal combustion engine according to at least one of the preceding claims 1 to 4, characterized in that the valve drive mechanisms (20) comprise a rocker shaft (21), a rocker arm (22) fixed to the rocker shaft (21), a high speed follower member (23) pivotally supported by the rocker shaft (21), a camshaft (24), a lost motion mechanism (25) adapted to bias the high speed follower member (23) towards the high speed cam (26) and a lever (31) pivotally supported by the rocker arm (22) and adapted to control movement of the high speed follower member (23).

6. Multi-cylinder internal combustion engine according to at least one of the preceding claims 1 to 5, characterized in that the valve lift varying means (A) comprises at least one valve lift switching control valve (41), wherein a controller (42) is adapted to control the valve lift switching control valve (41) in response to the operating condition such as an engine speed and/or the valve timing varying means (B) comprises at least one valve timing drive means (43), in particular a hydraulic actuator, wherein the controller (42) is adapted to control the valve timing drive means (43) in response to the operating condition such as an engine speed.

7. Multi-cylinder internal combustion engine according to at least one of the preceding claims 2 to 6, characterized in that the cylinders are divided into at least two groups of cylinders, and shapes of cams (25,26) having different valve lifts are set for each of said groups of cylinders.

8. Multi-cylinder internal combustion engine according to at least one of the preceding claims 2 to 7, characterized in that a maximum-lift timing of a low speed cam (25) in at least one cylinder differs from the maximum-lift timings of the low speed cams (25) in the respective further cylinders.

9. Multi-cylinder internal combustion engine according to at least one of the preceding claims 2 to 7, characterized in that the maximum-lift timings of the low speed cams (25) and/or the high speed cams (26) in at least one cylinder differ from those of low speed cams (25) and/or high speed cams (26) in the respective further cylinders.

10. Multi-cylinder internal combustion engine according to at least one of the preceding claims 2 to 9, characterized in that the opening/closing timings of the low speed cams (25) are within ranges of those of the high speed cams (26).

11. Multi-cylinder internal combustion engine according to at least one of the preceding claims 1 to 10, characterized in that the internal combustion engine is a four-valve or five-valve engine.

12. Control method for a multi-cylinder internal combustion engine having a plurality of intake and exhaust valves per cylinder and a variable valve drive system having valve drive mechanisms (20) respectively disposed on the intake and exhaust sides of the cylinders to open and close the intake or exhaust valves (13,14), wherein valve lifts of the intake and/or exhaust valves (13,14) are varied separately between the cylinders and opening/closing timings of the intake and/or exhaust valves (13,14) are varied for the respective cylinders, and wherein opening/closing timings of the intake and/or exhaust valves (13,14) in at least one cylinder are varied in response to the operating condition of the engine (1).

13. Control method according to claim 12, characterized in that the intake and/or exhaust valves are operated by means of cams (25,26) having different valve lifts being provided on camshafts (24).

14. Control method according to claim 13, characterized in that valve timings of the cams (25,26) having different valve lifts for an intake and/or an exhaust side of at least one of the cylinders, in particular a low speed cam (25) and a high speed cam (26), are set separately from each other.

15. Control method according to claim 14, characterized in that an overlapping time (a) between opening and closing of the intake and/or the exhaust valves (13,14) is increased or decreased in response to the operating conditions such as an engine speed with the cams having different valve lifts (25,26) provided for respective cylinders.

Drawing