GB2373545A

GB2373545A - Camshaft assembly with selectively engageable and disengageable cam lobes

Info

Publication number: GB2373545A
Application number: GB0106891A
Authority: GB
Inventors: William John Hurr
Original assignee: Powertrain Technology Ltd
Current assignee: Powertrain Technology Ltd
Priority date: 2001-03-20
Filing date: 2001-03-20
Publication date: 2002-09-25
Also published as: GB0106891D0

Abstract

A camshaft assembly comprising a cam lobe which can be selectively engaged to and disengaged from the cam shaft and means to ensure that there is no relative motion between the cam shaft and the cam lobe during operation of the zero lift portion. This enables engagement and disengagement at any rotational speed of the camshaft assembly. In the illustrated embodiment, a switchable cam lobe 1 having a zero lift portion 16 is provided with a slot 13 within which a flat sided cam shaft segment 2 is located. A compression spring 6 is located in the slot and urges the zero lift portion of the cam lobe into contact with the cam shaft segment. Latching pins 8 are slidably located within passages 15 in the cam shaft segment and, when the zero lift portion of the cam lobe is in contact with the cam shaft segment, return pins 9 are located opposite the latching pins. The return pins we located in passages 14 in the cam lobe and are biased towards the cam shaft segment by return springs 11. Outward movement of the latching pins into the passages 14, against the action of the return pins, engages the cam shaft segment with the cam lobe. Movement of the latching pins is effected by oil pressure from a gallery 7 in the cam shaft segment. Inward movement of the latching pins to disengage the cam shaft from the cam lobe is effected by the return springs.

Description

SWITCHABLE CAM-LOBE ARRANGEMENT FOR VALVE MOTION CONTROL Conventionally, I. C. engine valves have fixed opening durations throughout the entire operating range. In order to more closely match the valve opening to the speed and load requirements, a means to vary the opening duration is required. Most examples of the prior art in this respect employ a variable cam follower mechanism. This has the disadvantage that the variable follower tends to be heavier and less rigid than its conventional counterpart, which impairs engine performance. The described invention uses a special camshaft assembly with switchable cam lobes that can be selectively engaged or disengaged, so that different valve timings can be achieved or the valve left closed for cylinder deactivation strategies.

The broadest aspect of the invention is as set out in Claim 1 and comprises a camshaft assembly comprising a cam shaft, a cam lobe mounted on the cam shaft, switching means to selectively engage and disengage the cam lobe from the cam shaft, and means to ensure that there is no relative motion between the cam lobe and the cam shaft during operation of the zero lift portion of the cam lobe. This lack of relative motion enables the switching means to operate to engage the cam lobe to or disengage it from

the camshaft when the zero lift portion of the cam lobe is operative and at any rotational speed of the camshaft.

Figure la shows the cross section through one switchable cam lobe disengaged from the cam shaft at its zero lift position.

Figure lb shows the cross-section through one switchable cam lobe engaged to the cam shaft at its zero lift position.

Figure 1 c shows the part longitudinal section through the camshaft assembly Figures 2a and 3a show comparative operation at the part lift position of the switchable cam lobe with the cam lobe engaged and disengaged respectively.

Figures 2b and 3b show comparative operation at the full lift position of the switchable cam lobe with the cam-lobe engaged and disengaged respectively.

With reference to Figure la, a switchable cam lobe 1, having a zero lift portion 16 and a lift portion 17, is provided with a slot 13 within which a flat sided cam shaft segment 2 is located. A return spring 6 is located within the slot and biases the cam lobe in such a way that the zero lift portion 16 of the cam lobe is urged into contact with one end of the cam shaft segment. The cam shaft segment is provided with latching passages 15 within which are slidably located latching pins 8. The cam lobe is provided with return passages 14 within which are slidably located return pins 9 biased towards the cam shaft segment by return springs 11. Outward movement of the pins 9 away from the cam shaft segment is limited by stops 10. Inward movement of each pin 9 towards the cam shaft segment is limited by engagement of a shoulder 19 on the pin with a shoulder 18 in the passage.

The cam shaft is provided with an oil gallery 7 connected with the latching passages 15. When oil pressure is applied to or increased in the gallery an outward force is applied to the latching pins 8. When the pressure in the gallery is reduced or withdrawn, then the latching pins 8 are free to slide inwardly. At a position in which the zero lift portion 16 of the cam lobe is in contact with the cam shaft segment, as is shown in Figure 1 a, the return passages in the cam lobe are aligned with the latching passages 15 in the camshaft segment.

There may be one cam lobe or a plurality of cam lobes mounted upon a single cam shaft. The or each cam lobe may be used in conjunction with one or more supplementary cam lobes 5 mounted adjacent to it (see Figure lc). Alternatively, no supplementary cam lobes need be used.

Operation of the cam lobe mechanism when the cam lobe 1 is in the unlatched condition is illustrated by Figures la, 3a, and 3b. With reference to Figure la, the cam lobe is shown in the position in which its zero lift portion 16 is urged by the force of the spring 6 into contact with the end of the cam shaft segment 2. The zero lift portion 16 of the cam lobe contacts or is closely spaced from the cam follower 3 which operates the valve 4. In this position, the latching and return passages are in alignment.

When oil pressure is withdrawn from or reduced in the oil gallery 7, the return pins 10 are urged inwards by springs 11 to force the return pins 9 inwardly to the position shown in Figure la. In this position, the cam lobe 1 is free to slide relative to the cams shaft segment but is still constrained to rotate with it. As the cam shaft rotates and the cam lobe rotates with it, the cam lobe is forced to slide relative to the cam shaft segment against the action of the spring 6 by contact with the cam follower. However, it has no action upon the follower. Thus when a supplementary cam lobe with a lift profile is used, the lift profile of the supplementary cam lobe alone is operative upon the cam follower. When a supplementary cam lobe with zero lift is used or there is no supplementary cam lobe, then the valve is cfectively fully deactivated since the cam lobe 1 has no effect. Figures 3a and 3b illustrate this situation. As the cam lobe 1 nears

and then reaches the full lift position, the cam lobe slides relative to the cam shaft segment and the lift portion of the cam lobe 1 has no effect on the cam follower.

Operation of the cam lobe mechanism when the cam lobe is in the latched condition is illustrated by Figure Ib, 2a and 2b. With reference to Figure Ib, the cam lobe is once again shown in the position in which the zero lift portion 16 is in contact with or is closely spaced from the cam follower 3 and is urged into contact with the end of the cam shaft segment by spring 6.

In this position, the passages in the cam lobe and the cam shaft segment are aligned.

Oil pressure is applied to or increased in the oil gallery 7 to push the latching pins 8 outwardly against the action of spring biased return pins 9 to the position shown in Figure lb. This effectively locks the cam lobe to the cam shaft segment. When the cam shaft rotates, the cam lobe rotates with it but no relative sliding movement is possible.

Thus the cam lobe 1 acts as a conventional cam lobe as can be seen by Figures 2a and 2b in which the lift portion 17 of the cam lobe 1 is clearly operative upon the cam follower. Thus the action of the cam lobe 1 takes over from the action of any supplementary cam lobe, and it acts upon the cam follower in the manner of a conventional cam lobe.

Various embodiments of the cam lobe return spring are possible, such as torsion springs or compression springs operating through profiled ramps or linkages.

In another embodiment, the latching pin mechanism could be reversed so that oil pressure causes the latching pins to withdraw from the cam lobe against a spring force, and relieving the oil pressure causes the springs to push the latching pins into the cam lobe.

In another embodiment, the flat sided cross-section of the camshaft segment could be replaced by a circular, elliptic or profiled cross-section

Claims

CLAIMS 1) A camshaft assembly comprising a cam shaft, a cam lobe mounted on the cam shaft, switching means to selectively engage and disengage the cam lobe from the cam shaft, and means to ensure that there is no relative motion between the cam lobe and the cam shaft during operation of the zero lift portion of the cam lobe.

2) A camshaft assembly as claimed in Claim 1 in which the cam lobe has a slotted hole or recess which allows the cam lobe to slide relative to the cam shaft along a path perpendicular to the rotational axis of the cam shaft and means are provided to bias the zero lift portion of the cam lobe towards the rotational axis of the cam shaft.

3) A camshaft assembly as claimed in Claim 2 in which a section of the cam shaft has a flattened area which locates in the slotted hole or recess of the cam lobe.

4) A camshaft assembly as claimed in claim 2 in which a section of the cam shaft has an elliptical cross section which locates in the slotted hole or recess of the cam lobe.

5) A camshaft assembly as claimed in claim 2 in which one section of the cam shaft has a circular cross section which locates in the slotted hole or recess of the cam lobe.

6) A camshaft assembly as claimed in claim 2 in which a section of the cam shaft has a profiled cross section which locates in the slotted hole or recess of the cam lobe.

7) A camshaft assembly as claimed in any of claims 2 to 6 in which the biasing means comprises a spring.

8) A camshaft assembly as claimed in claim 7 in which the spring is a compression spring acting directly between one end of the slotted hole or recess and the zero lift portion of the cam lobe.

9) A camshaft assembly as claimed in claim 7 in which the spring is a torsion spring acting through a ramp or linkage.

10) A camshaft assembly as claimed in claim 7 in which the spring is a compression spring acting through a ramp or linkage.

11) A camshaft assembly as claimed in any preceding claim in which the switching means comprises one or more latching pins provided in one or more passages in the camshaft.

12 A camshaft assembly as claimed in claim 11 in which the or each latching pin is moved by oil pressure.

13) A camshaft assembly as claimed in Claim 12 in which the oil pressure is provided by an internal gallery within the cam shaft. 14) A camshaft assembly as claimed in claim 13 in which the or each latching pin is opposed by a spring loaded return pin located in a passage in the cam lobe during operation of the zero lift portion of the cam lobe.

15) A camshaft assembly substantially as hereinbefore described with reference to the Figures.

16) A camshaft assembly substantially as hereinbefore described.