DE3687661T2 - VALVE DRIVE MECHANISM FOR INTERNAL COMBUSTION ENGINE. - Google Patents

Description

The invention relates to a valve actuating mechanism for an internal combustion engine, which comprises a camshaft rotatable in synchronism with the rotation of the internal combustion engine with integral cams for actuating a pair of intake or exhaust valves and further rocker arms held angularly movable on a rocker arm shaft for opening and closing the intake and exhaust valves in response to rotation of the cams.

Valve actuation mechanisms used in internal combustion engines are generally designed to meet the requirements for high speed operation of the engines. In particular, valve diameter and valve lift are selected to provide substantially no resistance to the flow of a fuel-air mixture introduced through a valve into a combustion chamber at a rate for maximum engine power.

When an intake valve is operated over an entire engine speed range from low to high speeds with constant valve timing and constant valve lift, the flow rate of a fuel-air mixture into the combustion chamber changes from engine speed to engine speed because the amount of fuel-air mixture changes from engine speed to engine speed. At low engine speeds, the flow rate of the fuel-air mixture is reduced and the fuel-air mixture is subjected to less turbulence in the combustion chamber, resulting in slow combustion therein. Therefore, the combustion efficiency and also the fuel economy are reduced and due to the slow combustion, the knock limit is lowered.

From DE-A-3 119 133 it is known to provide a mechanism for actuating a valve which has low- and high-speed rocker arms which engage low- and high-speed cams, respectively, the valve being connected to the low-speed rocker arm and the rocker arms being connected in such a way that the valve is driven by the high-speed rocker arm during high-speed operation of the engine. During low-speed operation of the engine, the pivot axis of the high-speed rocker arm is shifted to an upper position so that the rocker arm is not engaged with its high-speed cam, whereby the valve can be actuated by the low-speed rocker arm and cam. Thus, the rocker arms remain connected at all times and it is necessary to bring the high-speed rocker arm into and out of engagement with the high-speed cam in order to change the valve operating mode.

According to the arrangement known from Japanese Patent Laid-Open No. 59(1984)-226216, some of the intake or exhaust valves remain closed when the engine is operating at low speed, whereas when the engine is operating at high speed, all of the intake or exhaust valves are operated, i.e. opened and closed alternately. Therefore, the valves are controlled differently in the low and high speed ranges. From GB-A-2 162 245 (on which the preamble of claim 1 is based) and from GB-A-2 141 172 it is also known to provide a mechanism in which one of a pair of intake or exhaust valves is continuously closed during low speed operation of the engine.

In the prior art valve actuation mechanisms described above, those intake valves which are not actuated in the low speed range remain at rest for a long period of time under certain operating conditions. When an intake valve remains at rest for a long period of time, soot or carbon generated by fuel combustion tends to accumulate between the intake valve and its valve seat, causing the intake valve to stick to the valve seat. When the engine starts operating in the high speed range, the intake valve which has remained at rest is forcibly separated from the valve seat. This brings about the problem of reduced sealing ability between the intake valve and the valve seat. Furthermore, fuel tends to accumulate on the intake valve while it is kept at rest, with the result that when the intake valve is opened, the accumulated fuel excessively enriches the fuel-air mixture introduced through it.

From EP-A-0 213 758 (Figs. 14 and 15) and EP-A-0 213 759 (Figs. 1 to 6) (state of the art according to Art. 54(3) EPC) it is known to provide a pair of valves, both of which are operated at low engine speeds. In both cases there are two low-speed cams, each of which actuates a corresponding valve in low-speed operation.

With regard to DE-A-3 613 945, the applicant has voluntarily restricted the scope of protection of the present application and filed separate claims for the Federal Republic of Germany.

According to a first aspect of the invention, there is provided a valve actuating mechanism for actuating a pair of valves of an internal combustion engine, comprising

a camshaft that can be rotated synchronously with the rotation of the internal combustion engine and has a pair of low- and high-speed cams with different cam profiles, whereby only two such cams are present,

a pair of first and second rocker arms selectively operable by the low and high speed cams to actuate the valves according to the cam profiles of the cams, and

a clutch device operatively arranged between the first and second rocker arms and adapted to is provided to interconnect the first and second rocker arms in high speed operation of the engine to effect actuation of the valves by the high speed cam, wherein the coupling device is further provided to separate the first and second rocker arms for independent movement in low speed operation of the engine so that the first rocker arm is actuated by the low speed cam to effect actuation of one of the valves in accordance with the cam profile of the low speed cam,

which valve actuating mechanism is characterized in that only two such rocker arms are provided and that during low speed operation of the engine the second rocker arm is actuated by the high speed cam to cause actuation of the other valve in accordance with the cam profile of the high speed cam, whereby neither valve is continuously closed.

In a preferred embodiment, the first and second rocker arms are held in sliding contact with the low and high speed cams, respectively, for actuating the pair of valves.

According to a second aspect of the invention, there is provided a valve actuating mechanism for actuating a pair of valves of an internal combustion engine, comprising

a camshaft that can be rotated synchronously with the rotation of the internal combustion engine and has a pair of low- and high-speed cams with different cam profiles, whereby only two such cams are provided,

a pair of first and second rocker arms selectively operable by the low and high speed cams to actuate the valves according to the cam profiles of the cams, and

a clutch device operatively arranged between the first and second rocker arms and arranged to interconnect the first and second rocker arms during high speed operation of the engine in order to to cause actuation of the valves by the high speed cam, the clutch device being further arranged to separate the first and second rocker arms from each other for independent movement during low speed operation of the engine,

which valve actuating mechanism is characterized in that only two such rocker arms are provided and that during low speed operation of the engine the first rocker arm is actuated by the low speed cam to cause actuation of the pair of valves in accordance with the cam profile of the low speed cam whereby none of the valves is continuously closed.

In a preferred embodiment, the first and second rocker arms are held in sliding contact with the low and high speed cams, respectively, with the first rocker arm having a pair of arms for respectively actuating the pair of valves.

In the following, some embodiments of the invention will be explained by way of example and with reference to the accompanying drawing. It shows:

Fig. 1 is a vertical cross-section of a valve actuating mechanism according to an embodiment of the invention taken along the line I-I in Fig. 2;

Fig. 2 is a plan view of the valve actuation mechanism shown in Fig. 1;

Fig. 3 is a cross-section along the line III-III in Fig. 1, showing the first and second rocker arms connected to each other;

Fig. 4 is a cross-section analogous to Fig. 3, showing the first and second rocker arms separated from each other;

Fig. 5 is a vertical cross-section of a valve actuating mechanism according to another embodiment of the invention taken along the line V-V in Fig. 6;

Fig. 6 is a plan view of the valve actuation mechanism shown in Fig. 5;

Fig. 7 is a cross-sectional view taken along line VII-VII in Fig. 5, showing the first and second rocker arms connected to each other;

Fig. 8 is a cross-section similar to Fig. 7, showing the first and second rocker arms separated from each other.

In the figures, identical or corresponding parts are provided with identical or corresponding reference symbols.

Figs. 1 and 2 show a valve operating mechanism according to an embodiment of the invention. The valve operating mechanism is installed in an internal combustion engine which includes a pair of intake valves 1a, 1b in each engine cylinder for introducing a fuel-air mixture into a combustion chamber formed in an engine body.

The valve operating mechanism comprises a camshaft 2 which is rotatable in synchronism with the rotation of the engine at a speed ratio of 1/2 with respect to the rotation speed of the crankshaft of the engine. The camshaft 2 has a low-speed cam 3 and a high-speed cam 5 which are arranged integrally on the circumference of the camshaft 2. The valve operating mechanism further comprises on the camshaft 2 a rocker arm shaft 6 which runs parallel to the camshaft 2 and first and second rocker arms 7, 8 which are held angularly movable on the rocker arm shaft. and are held against the low-speed cam 3 and the high-speed cam 5, respectively. The intake valves 1a, 1b are operated by the first and second rocker arms 7, 8, which are actuated by the low- and high-speed cams 3, 5.

The camshaft 2 is rotatably mounted above the engine body. As can be seen from Fig. 2, the high-speed cam 5 is arranged in a position corresponding to an intermediate position between the intake valves 1a, 1b. The low-speed cam 2 is arranged in alignment with the intake valve 1a. The low-speed cam 3 has a cam lobe 3a which projects radially outward to a small extent in order to accommodate the low-speed operation of the engine. The high-speed cam 5 has a cam lobe 5a which projects radially outward further than the cam lobe 3a in order to accommodate the high-speed operation of the engine, the cam lobe 5a extending over a larger angle than the cam lobe 3a.

The rocker arm shaft 6 is fixed below the camshaft 2. The first rocker arm 7 is pivotally supported on the rocker arm shaft 6 and aligned with the low-speed cam 3. The second rocker arm 8 is pivotally supported on the rocker arm shaft 6 and aligned with the high-speed cam 5. The rocker arms 7, 8 have cam sliders 10 and 11 on their upper surfaces, respectively, which are held in sliding contact with the cams 3 and 5, respectively. The first and second rocker arms 7, 8 have arms 7a, 8a, respectively, which extend above the intake valves 1a and 1b. Adjusting screws 12, 13 are adjustably screwed through the distal ends of the arms 7a, 8a and have tips that can be engaged with the upper ends of the valve stems of the intake valves 1a, 1b, respectively.

Flanges 14, 15 are attached to the upper end of the valve stems of the intake valves 1a, 1b. The intake valves 1a, 1b are normally preloaded by helical compression springs 16, 17 which are arranged between the flanges 14, 15 and the machine body under compression around the valve stems.

As shown in Fig. 4, the first and second rocker arms 7, 8 have opposing side walls held in sliding contact with each other. A selective clutch 21 is operatively disposed in and between the first and second rocker arms 7, 8 to selectively separate the rocker arms 7, 8 from each other for relative displacement and further to connect the rocker arms 7, 8 for their co-directional movement.

The selective clutch 21 includes a piston 23 that is movable between a position in which it connects the first and second rocker arms 7, 8 and a position in which it separates the first and second rocker arms 7, 8. The selective clutch 21 further includes a circular stopper 24 for limiting the movement of the piston 23 and a coil spring 25 for biasing the stopper 24 to move the piston 23 toward the position of separation of the first and second rocker arms 7, 8.

The first rocker arm 7 has a first guide hole 26 opening toward the second rocker arm 8 and extending parallel to the rocker arm shaft 6. The first rocker arm 7 further has a smaller diameter hole 28 near the closed end of the first guide hole 26 with a step or shoulder 27 formed between the smaller diameter hole 28 and the first guide hole 26. The piston 23 is slidably fitted into the first guide hole 26. The piston 23 and the closed end of the smaller diameter hole 28 define a hydraulic pressure chamber 29 therebetween.

The first rocker arm 7 has a hydraulic line 30 formed therein, which is connected to the hydraulic pressure chamber 29 in The rocker arm shaft 6 has a hydraulic line 31 formed axially therein which is coupled to a hydraulic pressure source (not shown) through a suitable hydraulic pressure control mechanism. The hydraulic lines 30, 31 are kept in communication with each other regardless of the angular movement of the first rocker arm 7 about the rocker arm shaft 6 through a hole 32 formed in a side wall of the rocker arm shaft 6.

The second rocker arm 8 has a second guide hole 35 in match with the first guide hole 26 in the first rocker arm 7, which opens towards the first rocker arm 7. The circular stopper 24 is slidably fitted in the second guide hole 35. The second rocker arm 8 further has, near the closed end of the second guide hole 35, a smaller diameter hole 37 with a step or shoulder 36 formed to limit movement of the circular stopper 24 between the second guide hole 35 and the smaller diameter hole 37. The second rocker arm 8 further has a through hole 38 formed coaxially with the smaller diameter hole 37. A guide rod 39 coaxially connected to the circular stopper 24 extends through the hole 38. The coil spring 25 is arranged around the guide rod 39 between the stopper 24 and the closed end of the smaller diameter hole 37.

The piston 23 has an axial length which is selected such that when one end of the piston 23 abuts against the step 27, the other end of the piston 23 is located just between the side walls of the first and second rocker arms 7, 8 and thus lies flush therewith, and that when the piston 23 is moved into the second guide hole 35 until it brings the stopper 24 into abutment against the step 36, the one end of the piston 23 remains in the first guide hole 26 and the piston 23 thus extends between the first and second rocker arms 7, 8. The piston 23 is normally under the elastic force a coil spring 33 in the direction of the second rocker arm 8, which coil spring 33 is arranged in the hydraulic pressure chamber 29 and acts between the piston 23 and the closed bottom of the hole 28 of smaller diameter. The elastic force of the spring 33 placed under compression in the hydraulic pressure chamber 29 is selected to be smaller than that of the spring 25 placed under compression.

The operation of the valve actuation mechanism will be explained below using Figs. 3 and 4.

When the engine is to operate in the low speed range, the selective clutch 21 is operated to separate the first and second rocker arms 7, 8 from each other as shown in Fig. 4. Specifically, the hydraulic pressure is released from the hydraulic pressure chamber 29 by the hydraulic pressure control mechanism and thus the stopper 24 can move toward the first rocker arm 7 under the elastic force of the spring 25 until the piston 23 abuts against the step 27. When the piston 23 is engaged with the step 27, the mutually contacting ends of the piston 23 and the stopper 24 are flush with the sliding side walls of the first and second rocker arms 7, 8. Therefore, the first and second rocker arms 7, 8 are held in mutual sliding contact for relative angular movement.

When the first and second rocker arms 7, 8 are thus separated, the first rocker arm 7 is angularly moved in sliding contact with the low-speed cam 3, whereas the second rocker arm 8 is angularly moved in sliding contact with the high-speed cam 5. Therefore, the intake valve 1a opens and closes the intake port alternately with the valve timing and the valve lift according to the profile of the low-speed cam 3, and the intake valve 1b opens and closes the intake port alternately with the valve timing and the valve lift according to the profile of the high-speed cam 5.

Since the intake valves 1a, 1b are operated with different valve timing and different valve lift, the turbulence of the fuel-air mixture in the combustion chamber is increased for a higher resistance to a reduction in the density of the fuel-air mixture. This also helps to improve fuel economy.

As shown in Fig. 3, the first and second rocker arms 7, 8 are connected to each other through the selective clutch 21 for high-speed operation of the engine. Specifically, hydraulic pressure is supplied to the hydraulic pressure chamber 29 of the selective clutch 21 to cause the piston 23 to push the stopper 24 into the second guide hole 35 against the elastic force of the spring 25 until the stopper 24 is engaged with the step 36. The first and second rocker arms 7, 8 are now connected to each other for co-directional angular movement.

Since the second rocker arm 8 held in sliding contact with the high-speed cam 5 swings by a larger amount than the first rocker arm 7, the first rocker arm 7 is caused to swing together with the second rocker arm. Therefore, the intake valves 1a, 1b open and close the respective intake ports alternately with the valve timing and the valve lift according to the profile of the high-speed cam 5. The intake efficiency is now increased for higher engine output and higher engine output torque.

In the low and high speed ranges of the engine operation, the intake valves 1a, 1b are actuated at all times. Therefore, no soot will be deposited between the intake valves 1a, 1b and their valve seats and no fuel will accumulate on the intake valves 1a, 1b.

5 and 6 illustrate a valve operating mechanism according to another embodiment of the invention. The valve operating mechanism shown in Figs. 5 and 6 differs from the valve operating mechanism shown in Figs. 1 and 2 in that the first rocker arm 7 has a pair of arms 7a, 7b which together form a V, and that the adjusting screws 12, 13 for engaging the upper ends of the valve stems of the intake valves 1a, 1b are adjustably screwed through the distal ends of the arms 7a, 7b. The second rocker arm 8 has no arm for directly acting on the intake valves 1a, 1b. As shown in Fig. 5, a bottomed cylindrical lifting member 19 is arranged in supporting engagement against a lower surface of the second rocker arm 8. The lifting element 19 is normally biased upward by a compression spring 20 of relatively weak elastic force, wherein the compression spring 20 is interposed between the lifting element 19 and the machine body in order to bias the cam slider 11 of the second rocker arm 8 slidably against the high-speed cam.

The valve actuating mechanism shown in Figs. 5 and 6 has a selective clutch 21 which, as shown in Fig. 7, has an identical structure to the selective clutch 21 shown in Fig. 3.

The operation of the valve actuating mechanism shown in Figs. 5 and 6 will be explained with reference to Figs. 7 and 8. When the engine is to operate in the low speed range, the selective clutch 21 is actuated as shown in Fig. 8 to separate the first and second rocker arms 7, 8 from each other. The first and second rocker arms 7, 8 are now held in mutual sliding contact for relative angular movement.

When the first and second rocker arms 7, 8 are thus separated, the first rocker arm 7 is angularly moved in sliding contact with the low-speed cam 3, whereas the second rocker arm 8 is angularly moved in sliding contact with the high-speed cam 5. Therefore, the intake valves 1a, 1b are operated by the corresponding arms 7a, 7b of the first rocker arm 7 to alternately open and close the respective intake ports with the valve timing and valve lift according to the profile of the low-speed cam 3. Since the second rocker arm 8 is separated from the first rocker arm 7, the angular movement of the second rocker arm 8 has no influence on the operation of the intake valves 1a, 1b. The valve operating mechanism has relatively small friction losses since the second rocker arm 8 is held in sliding contact with the high-speed cam by the relatively small elastic force of the spring 20.

Therefore, during low-speed operation of the engine, the intake valves 1a, 1b open and close the corresponding intake ports alternately with the valve timing and the valve lift according to the profile of the low-speed cam 3. Accordingly, the fuel-air mixture flows into the combustion chamber at a rate suitable for the low-speed operation of the engine, resulting in improved fuel economy and prevention of knocking.

For high-speed operation of the engine, the first and second rocker arms 7, 8 are connected to one another by the selective clutch 21 as shown in Fig. 7. The first rocker arm 8 is now caused to pivot in the same direction as the second rocker arm 8 held in sliding contact with the high-speed cam 5.

The intake valves 1a, 1b are operated by the arms 7a, 7b of the first rocker arm 7 to alternately open and close the respective intake ports with the valve timing and the valve lift according to the profile of the high-speed cam 5. The intake efficiency is now increased for higher engine output and higher engine output torque.

Although the intake valves 1a, 1b are actuated by each of the valve actuating mechanisms in the illustration, exhaust valves can also be actuated by the valve actuating mechanisms of the invention. In this case, in the low-speed operation of the engine, unburned portions can be reduced due to exhaust gas turbulence, whereas in the high-speed operation of the engine, high engine output power and high engine output torque can be generated by reducing the resistance to the flow of exhaust gas from the combustion chamber.

It will thus be seen that the invention, at least in its preferred embodiments, provides a valve actuating mechanism for an internal combustion engine which increases the turbulence of a fuel-air mixture in the combustion chamber during low speed operation of the engine to improve fuel economy, increases the resistance to a reduction in the density of the fuel-air mixture, and is designed to solve the problems which would otherwise arise due to a continuously closed intake valve.

Claims (6)

1. Valve actuation mechanism for actuating a pair of valves (1a, 1b) of an internal combustion engine, comprising: a camshaft (2) that can be rotated synchronously with the rotation of the internal combustion engine and has a pair of low- and high-speed cams (3, 5) with different cam profiles, with only two such cams being present; a pair of first and second rocker arms (7, 8) selectively operable by the low and high speed cams to actuate the valves in accordance with the cam profiles of the cams; and a clutch device (21) arranged in and between the first and second rocker arms and arranged to connect the first and second rocker arms together in high speed operation of the engine to cause actuation of the valves by the high speed cam, the clutch device further arranged to separate the first and second rocker arms from each other for independent movement in low speed operation of the engine so that the first rocker arm (7) is actuated by the low speed cam (3) to cause actuation of one of the valves (1a) in accordance with the cam profile of the low speed cam (3); characterized in that only two such rocker arms (7, 8) are provided and that during low speed operation of the engine, the second rocker arm (8) is actuated by the high speed cam (5) to cause actuation of the other valve (1b) according to the cam profile of the high speed cam (5), whereby none of the valves is continuously closed. 2. A valve operating mechanism according to claim 1, wherein the first and second rocker arms (7, 8) for respectively operating the pair of valves (1a, 1b) are held in sliding contact with the low and high speed cams (3, 5). 3. Valve actuation mechanism for actuating a pair of valves (1a, 1b) of an internal combustion engine, comprising: a camshaft (2) that can be rotated synchronously with the rotation of the internal combustion engine and has a pair of low- and high-speed cams (3, 5) with different cam profiles, only two such cams being provided; a pair of first and second rocker arms (7, 8) selectively operable by the low and high speed cams to actuate the valves in accordance with the cam profiles of the cams; and a clutch device (21) arranged in and between the first and second rocker arms and arranged to interconnect the first and second rocker arms during high speed operation of the engine to effect actuation of the valves by the high speed cam, the clutch device further arranged to separate the first and second rocker arms from each other for independent movement during low speed operation of the engine, characterized in that that only two such rocker arms (7, 8) are provided and that during low speed operation of the engine, the first rocker arm (7) is actuated by the low speed cam (3) to cause actuation of the pair of valves (1a, 1b) according to the cam profile of the low speed cam (3), whereby none of the valves is continuously closed. 4. A valve operating mechanism according to claim 3, wherein the first and second rocker arms (7, 8) are held in sliding contact with the low and high speed cams (3, 5), respectively, the first rocker arm (7) having a pair of arms (7a, 7b) for respectively operating the pair of valves (1a, 1b). 5. A valve operating mechanism according to claim 4, comprising lift means (19) for urging the second rocker arm (8) normally elastically into sliding contact with the high speed cam (5). 6. Valve operating mechanism according to one of the preceding claims, wherein the clutch means comprises a selective clutch (21) consisting of a first guide hole (26) formed in the first rocker arm (7), a second guide hole (35) formed in the second rocker arm (8) in alignment with the first guide hole, a piston (23) slidably fitted in the first guide hole (26), a spring (25) arranged in the second guide hole (35) to normally urge the piston (23) into the first guide hole (26), and means (29, 30, 31, 32) for applying hydraulic pressure to the piston (23) to move it against the elastic force of the spring (25) into a position between the first and second guide holes (26, 35).