DIFFERENTIAL CAMSHAFT

Abstract: A camshaft arrangement including a pair of cams (7, 8) mounted on the same camshaft (1) with at least one of the cams rotatable relative to the camshaft (17) and with the cams (7, 8) maintained at a given axial spacing on the camshaft (1), a differential mechanism (a, b, c, d) coupling the two cams (7, 8) together for rotation about the camshaft axis with a selected relative angular phase, and phase adjusting means (14, 15) for acting on the differential mechanism (a, b, c, d) to effect a relative rotation of the cams (7, 8) to adjust the selected angular phase of the cams (7, 8) and thereafter to retain the cams in the adjusted position.

Description: Description of Invention "Differential Camshaft" THIS INVENTION is directly, but not exclusively, concerned with the ability to vary the phase, or relative timing, of the Inlet and exhaust valves of an internal combustion engine, and, more particularly, with providing means for realising timing variations in respect of single camshaft engines. The benefits of being able to effect such a variation when instigated according to engine speed and load etc., are torque increase, and emission reduction. Furthermore, fuel economy can be drammatically improved over the whole revolution range without power output penalties. Variable valve timing has been proposed for some considerable time. However, the majority of the solutions proposed are quite complicated and usually require a twin-camshaft engine in order to be effective. The variable abilities rely upon the availability of separate camshafts for the inlet and exhaust valves. This means that by varying one (or both) shaft(s) relative to the other, an advance/retard situation can be realised thereby changing the overlap between the valve cycles and offering a wider "optimum" timing regime. The present invention offers these abilities to twin camshaft layouts, but also, and more importantly, provides a means of realising timing variations in respect of singie camshaft engines. The present invention can be applied to single cylinder engines and those employing two or more cylinders. Furthermore, the invention can be used in conjunction with pumping and compressor devices or the like. The present invention can also be used (as herein described) with standard types of cam devices, or in conjunction with annular cams, shafts and followers, wherein the annular cams and/or the followers can be differentiated in the same way as intended for the standard external cams etc. In order that the invention may be more readily understood, embodiments thereof will now be described with reference to the accompanying drawings in which: Figure I shows an arrangement embodying the principles of the invention; Figure 2 shows a second embodiment of the invention; Figure 3 is a section on the line 1II-1I1 of Figure 2; Figure is an end elevation of Figure 3; Figure 5 is a further application of the principles embodying the invention; Figure 6 shows the principles of the inention applied to a differential camshaft having 3 cams per cylinder; Figure 7 shows the principles of the invention applied to an eight valve camshaft unit; Figure 8 shows an embodiment of the invention using cam action to replace a differential carrier; Figure 9 is a plan view of Figure 8; Figure 10 is a view on the line Y/Y of Figure 9; Figure I I is a view on the line W/W of Figure 10. Referring now to the Figures, Figure 1 shows two cams 9, 10, bearing located upon a camshaft 1 in free-running communication. It is assumed that the cams 9, 10 are able to rotate upon camshaft I but are restricted from ail lateral movement. A set of bevelled differential gearing a/b/c/d is provided between the two cams 9, 10 with the idler-bevels c, d mounted in free-running bearing location upon stub-axles 3, and retained thereon by end-plates 7, 8. C and d are engaged with bevel ied-g ears a and b with gear a being fixed to, or part of cam sleeve-shaft 5 and bevel led-gear b being fixed to, or part of cam sleeve-shaft 6. Cam 9 is fixed to, or part of, sleeve-shaft 5 and cam 10 is fixed to, or part of, sleeve-shaft 6. It is assumed that shaft I is driven by way of a sprocket for example, in the usual way. However, any other suitable drive means could be used. The differential hub 2, being fixed to, or part of, camshaft I , will, therefore, also be driven. If the cam assembly 9/5/a were "locked" to shaft I , then the whole assembly 1 /2/3/4/5/6/7/8/9/ 10/a/b/c/d wouid rotate en masse. Therefore, if means were provided, whereby the assembly 9/5/a could be rotated relative to shaft I , preferably in a controlled fashion, then the resultant differential action created between assembly 9/5/a and assembly b/6/ 10 wouid be equal, and opposite in effect. That is, if cam 9 were advanced relative to shaft I , then cam 10 would be retarded relative to shaft I by a similar rotational amount. Therefore, if it is assumed that cam 9 is an 'inlet' cam and cam 10 is an 'exhaust' cam, then it will be seen that the relative timings can be changed with the overlap being extended, or reduced by any required amount. Furthermore, if (as in a four-valve per cylinder arrangement etc) the two cams 9, 10 were, for example, inlet cams, then it will be appreciated that the overall inlet event could be altered. That is to say, that by causing one inlet cam to advance, and the second to retard, relative to the camshaft I the whole event could be extended (or reduced). The ability to extend or reduce the event is very desirable. In order to change phase between, for example, cam 9 and shaft I , a typical type of mechanism can be found in British Patent Application No. 8527525. If, as described, the two cams 9, 10 are assumed to be inlet and exhaust cams respectively, then it will be understood that by providing differential capabilities between cam 10 and a further inlet cam (not shown), or by fixing a second exhaust cam (not shown) to cam 10, and then providing differential capabilities between this second cam and a further inlet cam (or cams); for example, infet cam/exhaust cam-exhaust cam/inlet cam-ϊnfet cam etc. (to any combination), with differential capabilities between pairs or single units etc., it is only necessary to provide relative phase changing capabilities between the first cam and the camshaft as all other coupled items will advance and/or retard in unison and by similar amounts. This ability to provide phase changing capability to a single camshaft is particularly significant. Any type of gear coupfing, capable of differentiation can be used. In Figures 2, 3 and 4, the two cams 6, 7 are differentially coupled by way of two levers 4/5 and 4a/5a. These levers are bearing iocated upon a cross-axle 2 which is fixed to, or part of, camshaft I . Lever arm 4 is in contact with cam 6 and lever arm 5 in contact with cam 7. Lever 4a/5a is included in order to balance the mechanism but is not functional ly necessary. It is assumed that cams 6, 7 are laterally restricted, and that the camshaft I is bearing supported. Furthermore, the valve-spring loadings applied to the cams 6, 7 would be sufficient to ensure continuous contact between the levers 4/5 and 4a/5a and the cams 6, 7. If some phase changing mechanism is interposed between either cam and the main shaft I , then by changing the relative phase of the said cam in relation to the shaft 1 , an equal and opposite reaction will be described by the other cam. If the lever arm lengths were not equal, however, arm 4 being longer than arm 5 for example, then the relative rotary motion of cam 6 in relation to shaft I would be greater than that of cam 7. Lever 4/3/5 and lever /4a/3a/5a would be responsible for driving the two free-running cams 6, 7 together with the "locked" phase changing mechanism (not shown). A typical eight valve camshaft layout coυid be as follows: Inlet-Cam = !C; Exhaust-Cam = EC; Lever = L; Phase Changing Mechanism = PCM PCM-IC/L/EC-EC/L/IC-IC/L/EC-EC//L/IC. ; The compound cams enabling the use of only four levers between the eight valves. In Figure 5, the use of concentric shafts al lows for a very compact layout for this type of differential camshaft embodiment. Sleeve-shaft 6 is provided with the main drive sprocket 13, cam 7 and bevelled-gear a. Sleeve-shaft 5 is provided with cam 8 and bevel led-gear b. These two assemblies are located in free-running bearing communication upon the 'fixed' concentric centre shaft I . The whole device being bearing located ' within the main journals I I and 1 2. Centre-shaft I is provided with end-plate I a, differential hub 2, stub- axles 3, 4, end-plates 9, 10 and worm-wheel 15. This assembly being capable of rotary movement. i Worm-wheel 15 is engaged with worm 14. The iead angle being around 10°, thereby providing a "locking" angie. If sprocket 13 is rotated, cam 7 wil l rotate in a similar direction and at a similar speed. If, however, the centre-shaft is prevented from movement by the worm/worm-wheel combination 14/ 15, the engaged differential-idler gears c and d wi l l cause gear b to rotate in a direction opposite to that of gear a. This wil l, in turn, cause cam 8 to rotate in a direction opposite to that of cam 7 but at the same speed. If worm 14 is provided with rotational capabil ity in either direction, the centre-shaft I wili be caused to rotate. This wili cause a change of phase of any degree in either direction between 7 " and 8. The αdvαnce/retαrd capability is adjustable through 360 . All "solid" black areas represent bearing surfaces and/or devices etc. Throughout Figures I to 5, the centre rotational datum is indicated Figure 6 is a representation of a differential camshaft which features three cams 3, 4 and 5 per cyfinder. In some situations, particularly large diesel engines, it is not unusual to find three cams in use: one to operate the inlet valve, one to operate the exhaust valve and a third to provide the introduction of the fuel. If all three cams are mounted upon a single camshaft, then the ability to provide a simple variable valve timing capability is, of course, made more difficult. However, this invention offers that prospect and Figure 6 provides one solution to the problem. It is assumed, as with Figures 1 and 2, that camshaft I is mounted, in some kind of bearing location. If carrier-gear 2 is ocked', and drive is applied to gear 1 I , then the cams 3, 4 will rotate in the same direction as gear I I. As bevelled-gear a is fixed to, or part of the main camshaft assembly, this wil l also rotate in a similar direction as cams 3 and 4. The differential action across idlers c and d will, however, cause gear b to rotate at the same speed as gear a but in the opposite rotational direction. As cam 5 is fixed to, or part of, concentric sleeve-shaft 7, which is itself fixed to, or part of, gear b, this too wil l rotate in the opposite rotational direction to that of the assembly I l / l /3/4/a/6. If carrier-gear 2 is to remain 'locked' (by any suitable means; i.e. a worm/worm-wheel combination etc), then this situation of two cams driving forward with one reversed wil l remain constant. However, if carrier-gear 2 is caused to rotate by any degree, no matter how small, assembly b/7/5 will be caused to change phase and, depending upon which direction carrier-gear 2 is rotated, cam ~ is advanced or retarded. If the rotational drive applied to gear 2 is continuous, then a totally different, but constant, timing will result. However, if gear 2 is simply rotated through a few degrees and then relocked, then cam 5 wili only have changed phase. If gear 2 is rotated through, for example, 5 it should be remembered that cam 5 wili in fact rotate, relative to gear 2, 10 owing to differential action. It will be seen, therefore, that in the case of the single camshaft diesel engine, a means for changing the timing of the exhaust (or other) cam can be effected without a major alteration to the basic design. 5 • The inclusion of a carrier-gear 2 enables the 'ganging' of several differentials or, if required, (as in any of the examples herein described), a lay-shaft (not shown) coupling of the assembly b/7/5 with other sleeve-shaft mounted exhaust-cams can be accomplished. Only one differential per 10. camshaft would be required, with the lay-shaft coupling 'ganging' the remaining exhaust valves. Figure 7 is a layout for a simple eight valve camshaft unit in which the inlet valves are fixed to the camshaft and the exhaust valves are carried 15 upon concentric sleeve-shafts. This camshaft arrangement, suitable for the four cylinder in-line engine, allows timing changes to be effected within the area of a single camshaft. However, if a iay-shaft were introduced, the second differential . 0 unit could be eliminated. Cams 7, 8 could be drived off sleeve-shaft 14, or the two differentials couid be driven and controlled by a single worm/worm- wheel combination. The two assemblies b/3/ 14/4 and g/8/ 17/7 can change phase relative 5 to assembly I /2/c/5/6/h/9 through 360 if required and can be locked in position according to requirement. The differential camshafts described through Figures I to 7 achieve differential action by way of gears and/or levers of the pivoted type. 0 Figure 8 shows a device which uses a cam action in piace of the differential unit of Figures I to 6. Follower 5 is fixed to, or part of follower-arm 7, which is, itself, 5 fixed to, or part of cam 3. Cam 3 is mounted, in free-running bearing location, concentrically upon camshaft I . Similarly, follower 6 is fixed to, or part of follower-arm 8 which is fixed to, or part of cam 4. This is also concentrically mounted upon camshaft I in free-running bearing location. Followers 5, 6 are shown to be in constant communication with the two sloping faces of the double-cam 2 which is fixed to, or part of camshaft I . It should be emphasised that Figure 8 is purely diagrammatic and that the double-cam 2 would require to be radially curved in such a way as to allow for maximum contact between its driving faces and the two followers 5 and 6. Assuming that the vafve-spring loadings and component inertia is of usual proportions, then the resistance felt by the cams 3 and 4 will be more than sufficient to keep followers 5 and 6 in constant contact with the driving faces of the double-cam 2 (the rotational direction r as indicated can be reversed by repositioning the double-cam, or by providing a second double-cam for example). As assemblies 3/7/5 and 6/8/4 are laterally restricted by the bearings indicated at the Main Journals 9 and 10, (or other means), any rotation of camshaft I as 'indicated will cause cams 3, 4 to rotate in a similar direction and at a similar speed. If, however, while rotating as indicated, (r), camshaft I is moved laterally (in either direction) by any suitable amount, the cam action created by the double cam 2 will, in respect of one assembly, cause it to accelerate relative to the camshaft I , and in the case of the other, allow it to decelerate. The lateral movement of the double-cam will, if moved from left to right as shown, cause assembly 6/8/4 to accelerate, and assembly 3/7/5 to decelerate relative to the camshaft I . Therefore, by providing a double-cam 2 between each pair of inlet and. exhaust cams and by providing a means of rotating the camshaft I and providing a controlled lateral movement in either direction to the said camshaft, full differential phase control can be added to any present single camshaft engine in a very effective and simple way. The drive-sprocket (not shown) could be splined so as to allow lateral movement of the camshaft and, if this type of arrangement was used in the three cam (Diesel) situation, wherein it might be required that the fuel cam be kept constant, then the double-cam could be divided with the fuel cam situated between the two sections. This wouid require the fuel cam to be wider than normal in order to allow for the lateral movement or, as in the case of the sprocket (or drive gear), this too couid be splined. A further variation would be to fix, for example, the inlet cam to the camshaft and only provide differential drive to the exhaust cam assembly. If, instead, of a double-faced driving cam 2 a slot or spline were used, then the assemblies can be driven in either direction. Figure 9 together with Figures 10 and I I is a camshaft assembly which uses both lateral movement and rotational movement to effect timing variation. A phase changing device as suggested in respect of Figure 1 for example, wil l be interposed between cam 3 and camshaft I . If, therefore, cam 3 is rotated relative to camshaft I in, for example, a direction opposite to that of the camshaft rotation, then the face-cam 5 wili cause follower 7 to respond by causing saddle 2 to move laterally away from cam 3, and in doing so, cause follower 8 to engage face cam 6 with a driving pressure sufficient to cause rotation of cam 4 relative to camshaft I . The square- section 9 will ensure that the saddle 2 cannot rotate other than in unison with camshaft I . If, in a diesei application (three cam layout etc), the fuel cam were mounted upon the saddle 2, it could remain constant with the camshaft although a wider cam wouid again be required. Lateral movement of cams 3 and 4 would, of course, be restricted. Throughout this specification the various methods of achieving differential cam action have been described in terms of 'inlet' and 'exhaust' cams etc. However, these are terms of identification only and any type of descriptive term in respect of functional intention can be included. While the single camshaft capability is very important, most engines built throughout the world being single camshaft units, it should be understood that if these arrangements are used in twin or multi camshaft engines, then the ability to alter the events and periods of any valve combination can be enjoyed ^ The use of bevelled gears in the various differential mechanisms is included for simplicity. However, any type of differential gearing can be substituted and ratio changes between the various elements can be contemplated. Throughout the specification, it is envisaged that the followers mentioned can, if required, be replaced by rollers.

Claims: CLAIMS: I . A camshaft arrangement including a pair of earns mounted on the same camshaft with at least one of the cams rotatable relative to the camshaft and with the cams maintained at a given axial spacing on the camshaft, a differential mechanism coupling the two cams together for rotation about the camshaft axis with a selected relative angular phase, and phase adjusting means for acting on the differential mechanism to effect a relative rotation of the cams to adjust the selected angular phase of the cams and thereafter to retain the cams in the adjusted position. 2. A camshaft arrangement according to claim I , wherein both of the cams are rotatable relative to the camshaft. 3. A camshaft arrangement according to claim 2, wherein the phase adjusting means comprises means to rotate one of the cams relative to the camshaft in one rotational direction and thereby rotate the other cam relative to the camshaft in the other rotational direction. 4. A camshaft arrangement according to claim 3, wherein the differential mechanism comprises a set of differential gears having an input gear rotatable with the one cam and an output gear rotatable with the other cam. 5. A camshaft arrangement according to claim 4, wherein the set of differential gears comprises an input bevel gear rotatable with the one cam, an output bevel gear rotatable with the other cam, and an idler bevel gear engaged with the input and output bevel gears and rotatable about a radially extending stub shaft on the camshaft. 6. A camshaft arrangement according to claim 3, wherein the differential mechanism comprises a iever pivotable about a radially extending stub shaft on the camshaft, the Iever comprising a pair of respective Iever arms operatively engaged with the cams so that the Iever is rolaled by rotation of the one cam relative to the camshaft to effect ro . a1 io~ι of tru- o. 'ic-r ram. 7. A camshaft arrangement according to claim 2, wherein the differential mechanism comprises a driving projection on the camshaft which is rotatable with the camshaft and located between the two cams and a pair of respective followers attached to the cams for abutment by respective inverse cam faces on the driving projection so that the cams are driven in rotation with the camshaft, and the phase-adjusting means comprises means to displace the driving projection axially relative to the cams:- whereby to adjust the regions of the cam faces of the driving projection abutting the followers on the cams and thereby effect a relative - rotation of " the cams about the camshaft to adjust their reltive angular phase.- 8. A camshaft arrangement according to claim 7, wherein the driving projection is axially immovable on the camshaft and the phase adjusting means comprises means to displace the camshaft axially relative to the cams. 9. A camshaft arrangement according to claim 2, wherein the differential mechanism comprises a saddle on the camshaft which, is rotatable with the camshaft and located between the two cams and a pair of driving followers carried by the saddle for abutting respective phase- determinfng cam faces on respective drive projections on the cams so that the cams are driven in rotation with the camshaft, and the phase-adjusting means comprises means to displace the saddle axially relative to the cams whereby to adjust the regions of the cam faces of the drive projections abutted by the driving followers of the saddle and thereby effect a relative rotation of the cams about the camshaft to adjust their relative angular phase. 10. A camshaft arrangement according to claim 9, wherein the saddle is axially movable on the camshaft and the phase adjusting means comprises means for moving the saddle axially relative to the camshaft. 1 1. A camshaft arrangement according to claim 10, wherein the phase adjusting means comprises means for rotating one of the cams relative to the camshaft, thereby to displace the saddle axially of the camshaft and effect rc'iction of the other cam. 12. A camshaft arrangement according to claim 5, wherein the two ca rotate about the camshaft with a selected relative angular phase and t phase adjusting means comprises drive means for rotating the camshaft t adjust the relative angular phase of the cams. 5 13. A camshaft arrangement according to claim 12, wherein the phas adjusting means comprises a worm wheel fixed to the camshaft for rotatio therewith artd a worm engaged with the worm wheel to rotate the wor wheel and thus the camshaft.- 10.. 14. A camshaft arrangement according to claim I , wherein one of cam is non-rotatable relative to the camshaft. 15. A camshaft arrangement according to claim 14, wherein th 15 differential mechanism comprises a set of differential gears having an inpu gear rotatable with the one cam and an output gear rotatable with the othe cam. i 16. A camshaft arrangement according to claim 15, wherein the set o 20 ' differential gears comprises an input bevel gear rotatable with the one cam, an output bevel gear rotatable with the other cam, and an idler bevel gear engaged with the input and output bevel gears and rotatable about a stub shaft which extends radially of the camshaft and is carried by a differential carrier rotatable about the camshaft, and the phase adjusting means 25 comprises drive means for rotating the differential carrier relative to the camshaft. 17. A camshaft arrangement according to claim 16, wherein the phase- adjusting means comprises a worm wheel fixed to the carrier for rotation 30 therewith and a worm engaged with the worm wheel to rotate the worm wheel and thus the differential carrier. 18. Camshaft arrangements substantially as hereinbefore described with „ reference to the accompanying drawings. I ° Any novel feature or combination of features described herein.

Inventors: STIDWORTHY FREDERICK MICHAEL, STIDWORTHY, FREDERICK, MICHAEL
Applicants: LONRHO PLC
Application year: 1987
Main classification: F01L1
IPC codes: F01L1