WO1999036677A1

WO1999036677A1 - Cam and cam followers for engines

Info

Publication number: WO1999036677A1
Application number: PCT/AU1999/000034
Authority: WO
Inventors: Barry Wallace Coombs
Original assignee: Darut Pty. Ltd.
Priority date: 1998-01-19
Filing date: 1999-01-19
Publication date: 1999-07-22
Also published as: JP2002537508A; EP1157192A1; CN1357079A; EP1157192A4; AU2143099A; AUPP139598A0

Abstract

A cam shaft assembly (50), which engages a plurality of cam followers (51) which operate valves (52) of an internal combustion engine. The cam shaft assembly (50) has a rotatably driven central shaft (56) to which a first cam lobe (57) is attached. An outer tubular shaft (58) has attached to it a further lobe (59). The shafts (56 and 58) are angularly displaceable to angularly displace the lobes (57 and 59) to alter valve timing and dwell angle.

Description

Cam and Cam Followers for Engines

Technical Field

The present invention relates to cam shafts and cam followers for engines.

Background of the Invention Typically, cam followers are provided with a generally planar surface which is engaged by the cam profile.

The angle through which the cam maintains the valve in the fully opened position is limited by the inter-reaction between the cam profile and the above mentioned cam follower surface. In addition to the above, conventional cam and cam follower constructions have generally not permitted altering the timing of the cam shaft relative to the engine crankshaft to meet various operating conditions to which the engine is subjected, nor the period during which the valves are manufactured in the open position.

USA Patent 4794893 discloses an engine valve driving apparatus in which the cam shaft is provided with a number of lobes which drive a single cam follower. Axial movement of the cam followers in response to engine operating conditions can change the speed of operation and timing of the valves. This arrangement has the disadvantage that only preselected cam configurations can be employed.

USA Patent 5505168 discloses a cam having a cam lobe of variable height. The extremity of the cam lobe includes a movable cam portion which is moved in accordance with operating conditions.

USA Patent 5129407 describes an interacting cam shaft and cam follower. The shaft is provided with a pair of lobes for each follower. Again, this arrangement only provides for discrete operating conditions. USA Patent 5253622 describes a mechanism for controlling the valves of an internal combustion engine. The cam shaft has cooperating pairs of lobes which are angularly displaceable.

USA Patent 4388897 discloses a cam shaft with cooperating pairs of cam lobes. The lobes are angularly displaceable so as to enable alteration of the associated valve timing.

USA Patent 5161429 shows a cam shaft in which the cam lobe is angularly displaceable about the shaft to alter valve timing.

USA Patent 1757046 again shows a cam shaft consisting of lobe elements which are angularly displaceable to vary valve timing. USA Patent 4522085 is similar to a number of the above discussed cam shafts in that there is again provided a cam shaft having cooperating pairs of lobes. The lobes are relatively angularly displaceable to alter valve timing. USA Patent 4794893 shows a cam shaft and cooperating cam followers.

USA Patent 4498352 discloses a cam shaft having cam lobes consisting of lobe portions which are angularly displaceable to alter valve timing.

USA Patent 4869215 discloses a cam shaft and cam follower arrangement. The cam follower has a shaped upper surface which is rotated to vary valve timing. The upper surface of the cam follower may be convex or concave.

Less relevant valve, cam shaft and cam followers are disclosed in USA Patents 3608862, 5577420, 5165303, 4895045 and 3687010.

Object of the Invention It is the object of the present invention to overcome or substantially ameliorate the above disadvantages.

Summary of the Invention

There is firstly disclosed herein in combination, an engine cam shaft having at least one cam lobe and an associated cam lobe engagement member, wherein: said lobe has a valve opening portion extending through an opening arc, a valve closing portion extending through a closing arc, and an extended dwell portion extending through a dwell arc; said engagement member having cam lobe engaging surfaces which are inclined so as to extend to an apex. Preferably the surfaces are inclined to a plane normal to the direction of movement of the engagement member by acute angles, with the dwell angle being at least the sum of the acute angles.

There is further disclosed herein a cam shaft assembly having: a central shaft; an outer tubular shaft within which the central shaft is located, the outer shaft having at least one aperture, a first lobe mounted on the outer shaft for angular movement relative thereto and being located adjacent said aperture; a drive member coupling the first lobe with the inner shaft; a second lobe mounted on and fixed to the outer shaft, and located adjacent the first lobe so as to cooperate therewith to provide a valve opening portion, a valve closing portion and a dwell portion; a first epicyclic gear train drivingly coupled to said central shaft, said gear train including a ring gear; a second epicyclic gear train drivingly coupled to said outer shaft, said second gear train including a ring gear; a common drive gear drivingly coupled to both epicyclic gear trains; and drive means drivingly engaged with each ring gear to cause angular displacement between the central shaft and the outer shaft to cause angular displacement between the two lobes to alter the dwell portion.

There is further disclosed herein a cam shaft assembly having: a central shaft; an outer tubular shaft within which the central shaft is located, the outer shaft having at least one aperture; a first lobe mounted on the outer shaft for angular movement about the outer shaft and being located adjacent said aperture; a drive member extending through the aperture and coupling the central shaft with the first lobe so that the first lobe moves with the central shaft; a second lobe mounted on and fixed to the outer shaft; an epicyclic gear train, including a ring gear, drivingly coupled to the central shaft or outer shaft to cause angular displacement therebetween so as to also cause angular displacement between the first and second lobes; a common drive gear drivingly coupled to the central shaft and outer shaft to cause rotation thereof; and a worm gear meshingly engaged with the ring gear to cause angular movement thereof to thereby cause the angular displacement between the first and second shafts. There is further disclosed herein in combination, a cam shaft assembly having at least one pair of cooperating cam lobes and a cam lobe engaging member engaged by the lobes, said assembly including: means to cause angular displacement between the two lobes to alter a dwell angle provided by the two lobes; and wherein said cam follower has a pair of converging lobe engaging surfaces extending to an apex.

Brief Description of the Drawings

A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Figure 1 is a schematic illustration of a conventional cam and cam follower;

Figure 2 is a schematic illustration of a cam and cam follower embodying a preferred construction of the present invention;

Figure 3 is a schematic side elevation of a cam shaft and associated cam followers and valves; Figure 4 is a schematic part section end elevation of the cam, cam follower and valve of Figure 3;

Figure 5 is a schematic illustration of a pair of cam elements employed in the cam shaft of Figure 3; Figure 6 is a schematic side elevation of a cam shaft assembly and associated cam followers and valves;

Figure 7 is a schematic section side elevation of a drive assembly employed in the cam shaft assembly of Figure 6; Figure 8 is a schematic end elevation of a gear assembly employed in the drive assembly of Figure 7;

Figure 9 is a schematic perspective view of a portion of the cam shaft assembly of Figure 6;

Figure 10 is a schematic perspective view of a further portion of the cam shaft assembly of Figure 6;

Figure 11 is a schematic sectioned end elevation of a portion of the cam shaft assembly of Figure 6; and

Figure 12 is a schematic end elevation of a portion of a cam shaft assembly of Figure 6.

Detailed Description of the Preferred Embodiments

In Figure 1 of the accompanying drawings there is schematically depicted a conventional cam element 10 which engages a generally planar surface 12 of a cam follower 11. The cam element 10 has a peripheral surface 13 providing the cam element 10 with a cam profile. The cam profile provides a leading or opening portion 15 extending through an opening arc C, a closing portion 14 extending through a closing arc B, and a dwell portion 16 extending through a dwell arc D. The cam element 10 therefore provides an operating arc A, with the lift of the cam element 10 being the difference between the length L and the length M. The cam lobe includes the portions 14, 15 and 16. In the preferred embodiment of Figure 2, the cam element 10 is provided with a dwell portion 16 which extends through a greater arc relative to the portion 16 of Figure 1. The cam follower 11 of this embodiment has a pair of inclined cam engaging surfaces 17 and 18 which are inclined to the general direction of movement of the cam follower 11 and converge to an apex 19. The surfaces 17 and 18 need not be symmetrical nor need they be planar. However, in this embodiment the surfaces 17 and 18 are planar and are complimentary to the angle of the cam portions 14 and 15. However, they could be convex or concave. The cam followers 11 are restrained to linearly oscillate only and cannot rotate about their longitudinal axes.

In the above described preferred embodiment of Figure 2, the portions 14 and 15 cooperate with the surfaces 17 and 18 to more rapidly move the associated valve between its open and closed positions. In addition to this, the increase in dwell angle maintains the valve in the open position for a greater period relative to the rotational speed of the cam element 10 about the longitudinal axis of the cam shaft. This occurs while maintaining the valve timing, that is valve opening and closing.

The cam follower 11 would need to co-act with its surrounding supporting surface to prevent rotation of the cam follower 11 about its longitudinal axis while permitting sliding movement of the cam follower 11 in the direction of its longitudinal axis.

As can be noted from Figure 2, the opening arc C and closing arc B are reduced relative to the cam element 10 of Figure 1. The increase in dwell angle is equal to the sum of the angles G and H, as seen in Figure 2. The cam shaft therefor has a dwell angle D (Figure 2) which is the sum of the dwell angle D (Figure 1) plus the increase in the dwell angle provided by the cam element of Figure 2.

The angles G and H are preferable 2° to 45°, more preferable 10° to 25°, with the most preferred angle being about 20°. Therefor the dwell angle is greater than 10° but less than 90°. In Figure 3 there is schematically depicted a cam assembly 20. The cam assembly 20 engages a plurality of cam followers 21 which engage valves 22 slidably mounted in valve guides 23 secured within the engine head 24 or cylinder block. Valve springs 25 urge the valves 22 to the closed position and maintain the cam followers 21 in engagement with the cam shaft assembly 20. The cam shaft assembly 20 is mounted so that it may be rotatably driven about its longitudinal axis 26.

The cam shaft assembly 20 includes a central shaft 27 upon which there is mounted a plurality of cam elements 28 and 29, arranged in pairs 41. Each pair 41 is associated with a particular one of the cam followers 21. Each adjacent pair of cam elements 28 is joined by a bridge portion 31 so that they rotate in unison, while each pair of adjacent cam portions 29 is joined by a bridge portion 32 so that they also rotate in unison.

Each bridge portion 31 and 32 acts as a bearing element and engages within a support 33, while the end elements 29 are secured to bearing portions 30 engaged in axial restraint supports 34.

The shaft 27 is also mounted for movement longitudinally of the axis 26 and would be coupled to a means which would cause such movement. The cam elements

28 and 29 as well as bearing portions 34 are slidably mounted on the shaft 27 but are effectively coupled thereto so as to rotate with the shaft 27 while permitting longitudinal relative movement therebetween. It should be appreciated that the cam elements 28 and 29 of each pair 41 have abutting sliding surfaces to permit relative angular movement between adjacent cam elements 28 and 29.

The central shaft 27 is provided with a plurality of inclined slots 35 and a plurality of oppositely inclined slots 36. Each bridge portion 31 is provided with a socket 37 which receives a coupling element 38, which elements 38 extend between the sockets 37 and the associated slot 36. The slots 36 are configured so as to permit movement of the coupling elements 38 along the slots 36 when the shaft 27 is moved longitudinally of its axis 26. In this embodiment the elements 38 are spherical with the slots 36 and sockets 38 having a complimentary profile. The elements 38 cause the cam elements 28 to rotate with the shaft 27.

Each bridge portion 32 and bearing portion 30 is provided with a socket 39 which receives a coupling element 40 which extends between the socket 39 and an associated slot 35. The slot 35 is configured so that the coupling element 40 may move along the slot 35 as the shaft 27 is moved longitudinally of its axis 26. In this embodiment the coupling elements 40 are of a spherical configuration, with the slots 35 and sockets 39 being of a complimentary profile. Again the elements 40 cause the cam elements 29 to rotate with the shaft 27.

In the above described preferred embodiment of Figure 3, the cam followers 21 are of a configuration such as that described with reference to Figure 2, that is they have inclined cam engaging surfaces converging to an apex.

In operation of the above described cam shaft assembly 20, longitudinal movement of the shaft 27 causes angular displacement of the cam elements 29 with respect to the cam elements 28. The elements 29 are displaced due to the inclination of the slots 35 relative to the longitudinal axis 26. The elements 28 are counter-displaced angularly about the shaft 27 as the slots 36 are counter-inclined to the longitudinal axis 26. However, it should be appreciated that the slots 35 or 36 could also be parallel to the axis 26 if so required should no angular displacement of the segments 28 or 29 be found advantageous. As best seen in Figure 5, when the elements 28 and 29 are aligned, a dwell angle Dl is provided. When the segment 28 and 29 are displaced angularly, the dwell angle D2 is provided. As can be seen from Figure 5 the dwell angle D2 is considerably larger than the dwell Dl.

It should further be appreciated that the timing of the cam element 29 is altered in that the opening portion 15 has been advanced in the general direction of rotation of the shaft 27 and the closing portion 14 retarded in the general direction of rotation of the shaft 27.

In operation of the above described assembly 20, the position of the shaft 27 along its longitudinal axis 26 would be determined by the operating conditions of the motor.

By increasing the dwell angle, the valve is maintained opened over a greater angle during rotation of the cam shaft assembly 20.

In Figures 6 to 12 there is schematically depicted a cam shaft assembly 50 which engages a plurality of cam followers 51. Each cam follower 51 is associated with a valve 52 of an internal combustion engine. The cam shaft assembly 50 is mounted to be rotatably driven about its longitudinal axis 53 to cause actuation of the valves 52. The cam shaft assembly 50 includes a drive assembly 54 which drives the cam shaft 55. The cam shaft 55 includes a rotatably driven central shaft 56 which drives lobes 57. The shaft 56 is slidably mounted within outer shaft 58 which drives lobes 59. The outer shaft 58 is of tubular form and is provided with regular apertures 60. Projecting through each aperture 60 is a drive key 61 that engages within a cooperating recess 62 in the shaft 56 so as to drive the associated cam lobe 57. Each cam lobe 57 includes a recess 62 which receives a portion of the drive key 61 so as to drivingly link each lobe 57 with its associated drive key 61. Each aperture 60 is angularly elongated to permit angular displacement between the shafts 56 and 58 about the longitudinal axis 53. Attached to the outer shaft 58 are lobes 59. Spacers 63 are located between adjacent pairs of lobes 57 and 59.

Angular displacement between the lobes 57 and 59 about the longitudinal axis 53 alters the valve timing and dwell angle.

The shafts 56 and 58 are angularly displaced by means of operation of the drive assembly 54 including an epicycle gear assembly 80. The assembly 80 includes two epicyclic gear trains 82 and 83. The gear trains 82 and 83 include the following:

The shaft 56 is driven by a flange 64 upon which there is mounted a series of planetary gears 65. The planetary gears 65 are rotatably mounted on shafts 66 for rotation about the individual axes 67. The gears 65 are meshingly engaged with a "sun" gear 68 fixed to a sleeve 69. The planetary gears 65 are meshingly engaged with the internal teeth of a ring gear 70. The ring gear 70 has external gears 71 which are of an arcuate configuration and meshingly engaged with worm gears 72. The shaft 58 is driven by a flange 73 which rotatably supports a plurality of planetary gears 74. The planetary gears 74 are meshingly engaged with a "sun" gear 75 attached to the sleeve 69. The gears 74 are also meshingly engaged with the internal teeth of a ring gear 76, with the ring gear having radial outer teeth of an arcuate formation meshingly engaged with a worm gear 77. The sleeve 69 is attached to a drive gear 78 driven by a timing belt 79.

The worm gears 72 and 77 are fixed and are generally stationary if the relative positions of lobes 57 and 59 are not to be changed. However, upon rotation of either or both of the worm gears 72 or 77, by means of a drive (not illustrated) one or both of the ring gears 70 or 76 is rotated to alter the position of the cam lobes 57 and/or the cam lobes 59. The shafts 56 and 58 are driven at the same angular velocity by the timing belt 79 and gear 78 when the worm gears 72 and 73 are stationary. The gear 78 merely causes rotation of both flanges 64 and 73 and the associated planetary gears 65 and 74, as the ring gears 70 and 76 are essentially stationary. Rotation of either or both of the worm gears 72 and 77 displaces the associated lobes 57 and/or 59 about the longitudinal axis 53 to alter timing of the valves 52 (that is the opening and closing of the valves 52) as well as the dwell angle.

The worm gears 72 and 77 may be driven by independent gear trains, or may be hydraulically or electrically driven. Typically, this would enable the drive mechanisms for the gears 72 and 77 to be computer controlled so that the cam shaft assembly 50 can be varied in configuration to meet engine requirements.

Each lobe 57 is slidable mounted on the shaft 58 by including a ring part 81 located around the shaft 58. When the worm gear 72 and 77 are stationary, the valve configuration provided by the cam lobes 57 and 59 is not altered. In that regard it should be appreciated that the worm gears 72 and 77 operate to maintain the desired position of the ring gears 70 and 76.

Further to the above, it should be appreciated that the worm gears 72 and 77 may be operated to move the lobes 57 and 59 in unison to retard or advance valve timing.

In another preferred embodiment the primary driving means for the planetary gear trains 82 and 83 is the worm gears 72 and 77. The gear 78 is then operated to advance or retard the lobes 57 and 59 in unison. Alteration of the dwell angle is achieved by moving the worm gears 72 and 77 out of the phase. This causes angular relative movement between the lobes 57 and 59.

A still further embodiment would have the shafts 56 and 58 attached to the ring gears 70 and 76, with the primary drive being the flanges 64 and 73. The sum gears 68 and 75 would then be separated so as not to have a common drive. A further modification would be to drive the sum gears 68 and 75 and retard and advance the lobes 57 and 59 by operation of the flanges 64 and 73.

The above embodiments include, one, two or more planetary gear trains, the number being determined by the number of relatively movable cam lobes.

Claims

1. In combination, an engine cam shaft having at least one cam lobe and an associated cam lobe engagement member restrained to move linearly, wherein: said lobe has a valve opening portion extending through an opening arc, a valve closing portion extending through a closing arc, and a dwell portion extending through an extended dwell arc; said engagement member having cam lobe engaging surfaces which are inclined so as to extend to an apex.

2. The combination of claim 1 wherein the surfaces are inclined to a plane normal to the direction of movement of the engagement member by acute angles, with the dwell angle being at least the sum of the acute angles.

3. The combination of claim 2, wherein the acute angles are each 2┬░ to

45┬░.

4. The combination of claim 3 wherein said acute angles are each 10┬░ to 25┬░.

5. The combination of claim 4 wherein said acute angles are each about

20┬░.

6. The combination of any one of claims 1 to 5, wherein the inclined surfaces are generally planar.

7. A cam shaft assembly having: a central shaft; an outer tubular shaft within which the central shaft is located, the outer shaft having at least one aperture, a first lobe mounted on the outer shaft for angular movement relative thereto and being located adjacent said aperture; a drive member coupling the first lobe with the inner shaft; a second lobe mounted on and fixed to the outer shaft, and located adjacent the first lobe so as to cooperate therewith to provide a valve opening portion, a valve closing portion and a dwell portion; a first epicyclic gear train drivingly coupled to said central shaft, said gear train including a ring gear; a second epicyclic gear train drivingly coupled to said outer shaft, said second gear train including a ring gear; a common drive gear drivingly coupled to both epicyclic gear trains; and drive means drivingly engaged with each ring gear and selectively operable to cause angular displacement of one or both ring gears so as to cause angular displacement of the central shaft and/or the outer shaft to cause angular displacement of one or both lobes.

8. The cam shaft of claim 7, wherein each epicyclic gear train includes a sun gear, with the sun gears being driven by said common drive gear, a flange attached to each shaft, each flange rotatably supporting a plurality of planetary gears meshingly engaged with the associated, each set of planetary gears being meshingly engaged with an associated one of the ring gears.

9. A cam shaft assembly having:

5 a central shaft; an outer tubular shaft within which the central shaft is located, the outer shaft having at least one aperture; a first lobe mounted on the outer shaft for angular movement about the outer shaft and being located adjacent said aperture; a drive member extending through the aperture and coupling the central shaft with the first lobe so that the first lobe moves with the central shaft; a second lobe mounted on and fixed to the outer shaft; an epicyclic gear train, including a ring gear, drivingly coupled to the central shaft or outer shaft to cause angular displacement therebetween so as to also cause 5 angular displacement between the first and second lobes; a common drive gear drivingly coupled to the central shaft and outer shaft to cause rotation thereof; and drive means engaged with the ring gear to cause angular movement thereof to thereby cause the angular displacement between the first and second shafts. 0 10. In combination, a cam shaft assembly having at least one pair of cooperating cam lobes and a cam lobe engaging member engaged by the lobes and restrained to move linearly, said assembly including: means to cause angular displacement either together or between the two lobes; and wherein 5 said cam follower has a pair of converging lobe engaging surfaces extending to an apex.

11. The combination of claim 10, wherein the surfaces are inclined to a plane normal to the direction of movement of the engagement member by acute angles, with the dwell angle being at least the sum of the acute angles. o 12. The combination of claim 11 , wherein the acute angles are each 2┬░ to

45┬░.

13. The combination of claim 12 wherein said acute angle are each 10┬░ to

25┬░.

14. The combination of claim 13 wherein said acute angles are each about 5 20┬░.

15. The combination of any one of claims 10 to 14, wherein the inclined surfaces are generally planar.

16. A cam shaft assembly having: a central shaft; an outer tubular shaft within which the central shaft is located, the outer shaft having at least one aperture; a first lobe mounted on the outer shaft for angular movement about the outer shaft and being located adjacent said aperture; a drive member extending through the aperture and coupling the central shaft with the first lobe so that the first lobe moves with the central shaft; a second lobe mounted on and fixed to the outer shaft; an epicyclic gear train, including a ring gear, drivingly coupled to the central shaft or outer shaft to cause angular displacement therebetween so as to also cause angular displacement between the first and second lobes; and drive means to cause operation of the gear train to cause rotation of the shafts and relative angular displacement of the lobes.

17. A cam shaft assembly having: a central shaft; an outer tubular shaft within which the central shaft is located, the outer shaft having at least one aperture, a first lobe mounted on the outer shaft for angular movement relative thereto and being located adjacent said aperture; a drive member coupling the first lobe with the inner shaft; a second lobe mounted on and fixed to the outer shaft, and located adjacent the first lobe so as to cooperate therewith to provide a valve opening portion, a valve closing portion and a dwell portion; a first epicyclic gear train drivingly coupled to said central shaft, said gear train including a ring gear; a second epicyclic gear train drivingly coupled to said outer shaft, said second gear train including a ring gear; and drive means to cause operation of the gear trains to cause rotation of the shafts and relative angular displacement of the lobes.

18. A cam shaft assembly substantially as hereinbefore described with reference to Figures 3 to 5 or 6 to 12.

19. In combination, a cam shaft and cam follower substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.