GB2327711A - Variable timing i.c. engine valve actuating arrangement eg for internal EGR - Google Patents

Abstract

At least one cam 4 of a camshaft 3 is engaged by a face 5b of a tappet 5 which is mounted slidably and rotatably in a tappet holder 8. The tappet holder 8 is mounted in a bore 22 in the engine structure so as to be rotatable about an axis of rotation which is inclined to a normal to the cam-engaging face 5b of the tappet 5. Tappet holder 8 carries a pinion or gear segment 11 which is engaged eg by a linear rack 12 driven by a hydraulic or solenoid actuator in response to sensed engine speed and throttle position. To enable EGR, the tappet holder 8 is rotated through about 180 degrees from a neutral position A to an operating position B (broken lines in fig.2). The point of contact of the tappet 5 thus moves around the cam 4. For, example, a rotation of 7.5 degrees of the tappet holder 8 can produce a timing retard of 30 degrees of the exhaust valve to induce sufficient internal EGR. With internal EGR, the expansion stroke is increased, and HC and NOx emissions are reduced compared to external EGR.

Description

DEVICE FOR ACTUATING OF AT LEAST ONE VALVE OF AN INTERNAL COMBUSTION ENGINE The present invention relates to a device for actuating of at least one valve of an internal combustion engine, comprising a camshaft with at least one cam and a tappet being mounted slideably in a tappet holder transmitting lifting of said cam to said valve, wherein a face of said tappet is touching said cam.

It is well known to use EGR (exhaust gas recirculation) in order to reduce exhaust emissions of internal combustion engines. In particular EGR will be required to meet strict emission regulation in order to reduce or avoid catalyst aftertreatment.

But there are major issues with application of conventional EGR systems, especially to single cylinder utility engines, namely achievement of adequate EGR at higher loads, EGR valve durability and intake system fouling. Apart from this the exhaust emission reduction shall be realized at slight costs.

Conventional EGR concepts cannot settle all of said issues.

External EGR devices have the disadvantage of intake system fouling. To avoid this disadvantage expensive additional features, e. g. catalysts are necessary.

According to the invention said tappet holder is mounted rotatably in a bore of the engine structure, having its axis of rotation inclined to a normal to the face of the tappet, wherein the rotation of the tappet holder is effected by a rotary device. The face of the tappet may be flat or convex.

By this simple arrangement an internal EGR retarded exhaust cam phasing can be realized, wherein shifting of the period happens by moving the point of contact of the tappet around the cam.

Internal EGR by suction of exhaust gas into the cylinder on the induction stroke enables following associated benefits: - hydrocarbon emissions are reduced mostly between 15% and 25% versus external EGR. At the exhaust valve during the exhaust process of internal combustion engines there are two spikes in hydrocarbon mass flow and concentration. The first spike happens after exhaust valve opening, the second larger spike occurs before conventional exhaust valve closing, e. g. in a range between 300" and 3600 crank angle. With the internal EGR according the invention the second hydrocarbon spike is pulled back from the exhaust part into the cylinder; - there is a fuel economy benefit, partly because of the extended expansion due to the later exhaust valve opening, the hydrocarbon pullback and the reduced throttling during induction; - inlet fouling can be reduced, without additional and expensive devices; - no EGR valve is required.

Preferably the rotation angle range of said tappet holder is about 180 . Rotation of the tappet holder will enable or disable EGR. The tappet can be mounted rotatably in a bore of said tappet holder, having its axis of rotation offset from the axis of the tappet holder.

More in detail the axis of said bore is inclined to the rotation axis of said tappet holder. When the holder is rotated 180 whilst on the cam base circle (i. e. no lift point), the point of contact of the tappet with the cam will move two times the inclination angle, and the effective phase shift relative to crank timing will be four times the tappet inclination. By inclining the tappet holder instead of the tappet so that the tappet has no imposed side thrust in one of its two positions increase of friction losses due to the tappet inclination can be avoided. The inclination of said axis of said bore to the rotation axis of said tappet holder is in a range from 1" to 100. More preferably the inclination is in a range from 7" to 80. For example only about 7,5 inclination is required for a 30 crank angle shift which is what is expected to be the exhaust valve retard to induce sufficient internal EGR in most cases.

Rotation of the tappet holder can be realized in several ways.

In one preferred variant of the invention said rotary device includes one of a pinion and a gear rim segment being attached to the tappet holder. More in detail said rotary device further includes a linear rack being engaged with said pinion or gear rim segment, said rack being joined with a linear propulsion device. In a first preferred embodiment said linear propulsion device may include a hydraulic piston, wherein the hydraulic pressure may be controlled by an electrical solenoid actuator.

For controlling of the shift of the valve opening the device for actuating comprises control means. Said control means include a control circuit combining a throttle quadrant contact and a speed sensitive or centrifugal actuated contact, both of which being engaged at a predefined load and speed respectively.

To avoid unacceptable edge contact between the tappet and the cam during the transition period of tappet rotation the axial profile of the base circle of said cam is shaped convexly.

Thereby the base circle axial profile can be reduced to a cylindrical bull nose with minimal machining/finishing. A further palliative of edge contact will be use of a crowned tappet face.

In a second preferred embodiment said linear propulsion device may include a mechanical drive unit.

More in detail said mechanical drive unit may include a shifting device to shift said rack, wherein said shifting device is mounted rotatably and comprises a cylindrical cam having a shifting profile consisting of at least one guide groove comprising a displacement section and a return section, which sections are configured as oppositely oriented helixes and which join via at least partly annular dwell sections, each of said dwell sections defining different rotation positions of the tappet holder, and wherein an engaging element being attached to the rack is running in said guide groove.

The advantage of the mechanical drive unit is, that no external power source such as a hydraulic system is required. Preferably the device further comprises a clutch to engage or disengage the shifting device with the camshaft. This enables a controlled movement of the rack. Further the clutch may include a key being mounted slideably or pivotably on said shifting device, wherein said key is engageable with a keyway of the camshaft. In this manner the shifting device is being phased to the engine exhaust cam. The keyway may be formed on the inside lateral area of an tubular section of said camshaft.

More preferably said clutch may be activated by said electric solenoid activator, which may have a slower response time than that required for the drive unit. As the synchronisation of rack movement to camshaft rotation is achieved mechanically the electric operating pulse phase is not critical. Therefore only relatively simple electronic control means may be required.

In a preferred variant of the second embodiment of the invention the device further comprises a release lever being contact able to said key and being mounted on the engine structure, and a latch mechanism being operated by the solenoid activator, wherein the clutch mechanism engages and disengages the release lever.

Following is a more detailed description of the invention as illustrated by the attached drawings, in which Figure 1 is a sectional view of the device for actuating of at least one valve, Figure 2 a detail of the sectional view shown in Fig. 1, Figure 2a a detail of a device for actuating in a second embodiment, Figure2b a detail of a device for actuating in a further embodiment, Figure 3 a sectional view of the device according to the line 111-111 in Fig. 2, Figure 4 a perspective view of the device, Figure 5 control and activation means for the inventive device in a first embodiment, Figure 6 control and activation means for the inventive device in a second embodiment, Figure 7 a front view of a mechanical shifting device, Figure 8 a back view of the mechanical shifting device, Figure 9 a timing diagram of the mechanical shifting device, Figure 10 a longitudinal section of the mechanical shifting device, Figure 11 a longitudinal section of another variant of the mechanical shifting device, Figure 12 a cross section of the mechanical shifting device along line XII-XII in Fig. 10, Figure 13 a detail of the activating mechanism of the shifting device shown in Fig. 12, Figure 14 a further detail of the activating mechanism, and Figure 15 a detail of the shifting device shown in Fig. 12.

Similar parts are referenced with same numbers.

sig. 1 shows the device 1 for actuating the exhaust valve 2 of a cylinder of an internal combustion engine. The device 1 comprises a camshaft 3 including at least one cam 4 per cylinder. Said cam 4 actuates via a tappet 5, pushrod 6 and a rocker 7 said exhaust valve 2. The tappet 5 is mounted slideably and rotatably in a bore 20 of a tappet holder 8, which in its turn is mounted rotatably in a bore 22 of the engine structure 9.

The rotation of the tappet holder 8 is affected by a rotary device 10. Said rotary device 10 includes a pinion or a gear rim segment 11, e. g. a quadrant, which is attached to it or integral with it. Said pinion or gear rim segment 11 is engaged with either a linear rack 12 being joined to a linear propulsion device 13, which is shown in Fig. 4 or a rotary propulsion device (not shown). The linear propulsion device 13 for example is an hydraulic drive including a hydraulic piston 14 using oil from the lubrication circuit of the engine. Just as well the rack 12 can be moved by a direct acting high power electrical solenoid. In the variant shown in Fig. 5, the propulsion device 13 includes an electrical switching solenoid actuator 15 to control the oil pressure supply 13a to the hydraulic piston 14 which then pushes the rack 12. Further the device 1 comprises control means 16, which include an electromechanical control circuit 17 combining a throttle quadrant contact 18 and a speed sensitive (e. g. pulse generator 19a) or centrifugal actuated contact 19 (e. g. an air vane or centrifugal contact). Both of which are made for the circuit to trigger the linear propulsion device 13.

The rotary device 10 comprises a neutral position A disabling EGR, and an operating position B enabling EGR. To enable internal EGR the tappet holder 8 is rotated by the rotary device 10 from position A to position B, which is indicated in Fig. 2 by broken lines. The rotation angle range of the tappet holder 8 is about 1800. In this way the point of contact of the tappet 5 moves around the cam 4, as the axis 8a of rotation of the tappet holder 8 is configured offset from the rotation axis 5a of the tappet 5. To realize different valve timing between position A and position B of the rotary device 10 a normal line to the face Sb, Sc of the tappet 5 is inclined to the axis 8a of rotation of the tappet holder 8, in at least one point of contact between tappet 5 and cam 3. In other words the flat face 5b of the tappet 5 is inclined to a normal plane 21 to the rotation axis 8a of the tappet holder 8. When the tappet holder 8 is rotated whilst on the cam base circle 4a (i. e. no lift point), the point of contact of the tappet 5 with the cam 4 will move two times the inclination angle a, and the effective phase shift relative to crank timing will be four times the tappet inclination a. Therefore only about 7,5 inclination is required for a 30 crank angle shift which is expected to be the exhaust valve retard to induce sufficient internal EGR. It should be noted that Fig. 2 shows the inclination angle a exaggerated for illustrative reasons.

Fig. 2a and 2b show alternative variants of the invention, wherein the axis 5a of the tappets 5 are arranged parallel relative to the axis 8a of rotation of the tappet holder 8. The axis 5a of the tappet 5 shown in Fig. 2a is arranged concentrically relative to the axis 8a of rotation of the tappet holder 8. In contrast to this the axis 5a of the tappet 5 shown in Fig. 2b is arranged offset to the axis 8a of rotation of the tappet holder 8.

When the tappet holder 8 is rotated, the point of contact of the tappet 5 with the cam 4 will move two times the inclination angle a. In this way a phase shaft relative to crank timing happens, too.

To avoid an increase of friction losses due to the side thrust of the tappet 5 it is proposed to incline the tappet holder 8 instead of the tappet 5 so that the tappet 5 has no side thrust in one of its two positions.

During the transition period of tappet rotation in some cases unacceptable edge between the tappet 5 and the cam 4 may occur.

This can be avoided by reducing the axial profile of the base circle 4a of the cam 4 to a cylindrical bull nose 4b, as illustrated in Fig. 3 by broken lines, with minimal machining/finishing. A further palliative can be use of a convex or crowned tappet face Sc instead of a flat tappet face 5b, again illustrated in Fig. 3 by broken lines.

In the embodiments shown in Fig. 6 to 16 the linear propulsion device 13 includes a mechanical drive unit 23.

The general arrangement of the control and actuation system 17 is shown in Fig. 6.

The essential input signals to the control system 17 are engine speed and throttle position (engine load).

A pulse generator 19a, comprising speed sensor 19b and excitor 19, uses the variable reluctance magnetic principle which generates an alternating voltage whose frequency is proportional to the speed of the engine. The high NOx generation in a 6-Mode test is primarily at one speed (c.3000r/min) and between 50-75%1Oad. These operating conditions can be characterised by a specific frequency bandwidth of the alternating voltage generated by the speed sensor 19b and excitor 19c and an OFF-ON-OFF throttle sector contact switch 18a, as shown in Fig. 6. Reference 18b indicates the air flow of the intake pipe. The series connection / logic between the pulse generator 19a and throttle sector switch 18a and diode arrangement 17a provides a pulse to energise the fast response solenoid actuator 15a, which operates the release lever 24 of the drive unit 23. When the release lever 24 is operated, the drive unit 23 engages with the camshaft 3, and is rotated one complete revolution. As the solenoid actuator 15a approaches its full travel, a latch mechanism 25 disengages and the release lever 24 is returned by a spring 43. The release lever 24 then disengages the drive unit 23. The solenoid ctuator 15a is returned by its spring.

Rotation of the drive unit 23 causes displacement of the rack 12 by means of a cylindrical cam 33 of a shifting device 26.

The shifting device 26 is phased so that displacement of the rack 12 occurs when the tappet 5 is on the base circle 4a.

Displacement of the rack 12 is used to cause the gear rim segment 11 of the tappet-holder 8 of the rotary device 10 to rotate. Depending on the circumferential distance moved by the tappet holder 8, it may be advantageous to introduce a compound pinion gear 27 so that the maximum displacement of the shifting device 26 of the drive unit 23 in relation to the forces in the mechanism may be optimised.

Phasing of the rotation of the tappet holder 8 to the camshaft angular position is essentially achieved mechanically. However, it may also be found necessary to energise the solenoid activator 15a within an ' approximate pre-determined range of camshaft angular position and this may require an additional input from the speed sensor or from the ignition system.

In order to return the tappet holder 8 (and hence the exhaust valve timing to its original setting) the circuit is broken as the throttle switch 18a is closed, the solenoid 15a retracts and the process is repeated with the rack 12 returned by the shifting device 26.

The rack movement is controlled by the cylindrical ca-n 33 of the shifting device 26, which is shown in detail in Fig. 7 and 8. Two complete rotations of the shifting device 26 moves the rack 12 and returns it by means of a guide groove 28 comprising a displacement section 29 and a return section 30, which are configured as oppositely oriented helixes and which join via partly annular dwell sections 31. The dwell sections 31 representing zero and full displacements of the rack 12 are phased to the active part of the profile of the exhaust cam 4.

Thereby an engaging element 12a, which is attached to the rack 12, runs in the guide grooves 28. The phase of the shifting device 26 in relation to the exhaust cam profile is shown in Fig. 9. Therein reference Ao indicates a region of key disengagement and arrest of drive unit, reference Bo indicates key engagement and acceleration of drive unit, and reference Co indicates the movement of the rack (either direction). Further reference A1 indicates the rest position of the drive unit.

The construction of the drive unit 23 is shown in Fig. 10. The camshaft, runs freely over a shaft 32 of the shifting device 26, wherein said cylindrical cam 33 comprising the shifting profile is pinned to the shaft 32. There is a keyway 34 in the shaft 32, which is deep enough to fully accommodate a clutch 44 including a key 35, which is spring loaded outwards by the spring 36. Fig. 10 illustrates engagement of the shaft 32 (position C). A release lever 25 has been retracted and the spring 36 has pressed the key 35 outwards by means of shaft 37 to engage with a keyway 38 in a tubular section 3a of the camshaft 3. The drive unit 23 is then free to rotate through one revolution and the rack 12 moved from one position to the other. The release lever 24 is returned so that its cam profiled surface 24a presses against the protruding follower surface on the shaft 37, forcing it to the inner position D, which is indicated by broken lines, and locating it by means of a limit stop 24b. In this position the key 35 does not engage with the camshaft 3. The camshaft 3 continues to rotate freely until the release lever 24 is operated again and the timing is returned to its initial setting.

An alternative arrangement, in which the key 35a is pivoted is also shown in Fig.ll.

Fig. 12 shows the key 35 in the inner position D with the release lever 24 in its return position allowing the camshaft 3 to run freely with the drive unit 23 located in the rest position. The release lever 24 provides an arrest cam surface profile 24a and limit stop 24b.

The release lever 24 is operated via a latch mechanism 25 by the actuator rod 39, which has a spring loaded latch 40, which causes the release lever 24 to rotate in a clockwise direction when the actuator 1Sa is energised.

The initial part of the actuator rod movement causes the location pin 41 to be retracted from a slot 41a on the release lever 24. As the velocity of the actuator rod 39 increases, the latch 40 makes contact with a lug 42 on the release lever 24 resulting in a rapid rotation of the release lever 24. Rotation of the release lever 24 is completed when the latch 40 is clear of the lug 42, the release 24 then being returned by a spring 43 to a stop 24b. The spring loaded location pin 41 re-locates the release lever 24 whilst the drive unit 23 rotates through its revolution. The actuator 15a as well as the rod 39 is returned by its own spring (Fig. 13, 14).

The shifting device 26 needs to be accelerated and arrested with controlled shock. As no load is being transmitted under acceleration and deceleration (the cylindrical cam 33 is on dwell), only its inertia needs to be overcome. The drive unit 23 would therefore be designed for low inertia. The drive unit 23 would only need to operate at primarily one speed and the key 35 and keyway 38 surface materials together with spring force may be selected to employ an appropriate friction drive effect at this speed. As shown in Fig. 15 the profiling / surface finish of the keyway 38 in the camshaft 3 would be designed to assist traction (position "a") and reduce shock, the latter by doing work on recompression of the spring 36 and overcoming side friction of the key 35 (position "b") as the drive load comes on (position "c").

Arrest of the drive unit would be controlled by design of the cam surface 24a and limit stop 24b of the release lever 23.

Internal EGR via exhaust cam retarding will extend the expansion stroke, increasing work and reducing hydrocarbon emissions, and extend the overlap into the induction stroke, thus inducing more internal EGR and pulling back the second reak of hydrocarbon concentration at the exhaust valve during the exhaust process. Apart from HC advantages internal EGR via retarding outlet has also NOx advantages over external EGR.

It should be understood that the invention is not limited to actuating devices for exhaust valves. In the same way inlet phase change may be carried out, preferably in addition to outlet retard.

Claims (22)

I CLAIM

1. A device (1) for actuating at least one valve (2) of an internal combustion engine, said device comprising: - a camshaft (3) with at least one cam (4), and - a tappet (5) being mounted slideably in a tappet holder (8), transmitting lifting of said cam (4) to said valve (2), wherein a face of said tappet (5) is touching said cam (4), characterized in that said tappet holder (8) is mounted rotatably in a bore (22) of the engine structure (9), having its axis (8a) of rotation inclined to a normal to the face (5b) of the tappet (5), wherein the rotation of the tappet holder (8) is effected by a rotary device (10).

2. The device as defined in claim 1, wherein the rotation angle range of said tappet holder (8) is at least 1800.

3. The device as defined in claim 1 or 2, wherein said tappet (5) is mounted rotatably in a bore (20) of said tappet holder (8), having its axis (20a) of rotation offset from the axis (8a) of the tappet holder (8).

4. The device as defined in claim 3, wherein the axis (20a) of said bore (20) is inclined to the rotation axis (8a) of -said tappet holder (8).

5. The device as defined in claim 4, wherein the inclination angle (a) of said axis (20a) of said bore (20) to the rotation axis (8a) of said tappet holder (8) is in a range from 10 to 100.

6. The device as defined in claim 5, wherein the inclination is in a range from 7" to 80.

7. The device as defined in one of the claims 1 to 6, wherein said rotary device (10) includes one of a pinion and a gear rim segment (11) being attached to the tappet holder (8).

8. The device as defined in claim 7, wherein said rotary device (10) further includes a linear rack (12) being engaged with said pinion or gear rim segment (11), said rack (12) being joined with a linear propulsion device (12).

9. The device as defined in claim 8, wherein said linear propulsion device (13) includes a hydraulic piston (14).

10. The device as defined in claim 8 or 9, wherein said linear propulsion device (13) includes an electrical solenoid actuator (15, 15a).

11. The device as defined in one of the claims 1 to 10, further including control means (16) to actuate the rotary device (10) as a function of speed and throttle position.

12. The device as defined in claim 11, wherein said control means (16) include a control circuit (17) combining a throttle quadrant contact (18) and a speed sensitive (19a) or centrifugal actuated contact (19), both of which being engaged at a predefined load and speed respectively.

13. The device as defined in one of the claim 1 to 12, wherein the axial profile of the base circle (4a) of said cam (4) is shaped convexly.

14. The device as defined in one of the claims 1 to 13, wherein the face (5b) of said tappet (5) is crowned.

15. The device as defined in one of the claims 1 to 14, wherein said linear propulsion device (15) includes a mechanical drive unit (23).

16. The device as defined in claim 15, wherein said mechanical drive unit (23) includes a shifting device (26) to shift said rack (12), wherein said shifting device (26) is mounted rotatably and comprises a cylindrical cam (33) having a shifting profile consisting of at least one guide groove (28) comprising a displacement section (29) and a return section (30), which sections (29, 30) are configured as oppositely oriented helixes and which join via at least partly annular dwell sections (31), each of said dwell sections (31) defining different rotation positions (A, B) of the tappet holder (8), and wherein an engaging element (12a) being attached to the rack (12) is running in said guide groove (28).

17. The device as defined in claim 16, further comprising a clutch (44) to engage or disengage the shifting device (26) with the camshaft (3).

18. The device as defined in claim 17, wherein the clutch (44) includes a key (35) being mounted slightably or pivotably on said shifting device (26), wherein said key (35) is engageable with a keyway (38) of the camshaft (3).

19. The device as defined in claim 18, wherein said keyway (38) is formed on the inside lateral area of an tubular section (3a) of said camshaft (3).

20. The device as defined in claim 18 or 19, wherein said clutch (44) is activated by said electric solenoid activator (15a), which preferrably has a slower response time than that required for the drive unit (23).

21. The device as defined in claim 20, further comprising a release lever (24) being contactable to said key (35) and being mounted on the engine structure, and a latch mechanism (25) being operated by the solenoid activator, wherein the clutch mechanism (25) engages and disengages the release lever (24).

22. A device for actuating at least one valve of an internal combustion engine, substantially as hereinbefore described with reference to the accompanying drawings.