WO1987003056A1

WO1987003056A1 - A variable drive mechanism

Info

Publication number: WO1987003056A1
Application number: PCT/GB1986/000688
Authority: WO
Inventors: Frederick Michael Stidworthy
Original assignee: Stidworthy Frederick M
Priority date: 1985-11-07
Filing date: 1986-11-06
Publication date: 1987-05-21
Also published as: EP0245345A1; AU6549286A; GB8527526D0; GB2183780A; GB8626537D0; GB2183780B; CN86107594A

Abstract

A variable drive mechanism comprises an input shaft (9) which is rotated by suitable means (not shown). The shaft (9) has a square section portion (4) on which is received a first helical gear (1) disposed between the end plates (3b and 3c) of a carrier (3) also having a cross-piece (3a) formed with a rack (5) engaged with a pinion (6) to an adjustment shaft (7). A second helical gear (2) on a second shaft (8) is engaged with the first helical gear (1) which has a greater axial extent than gear (2) and thereby transmits rotation of the shaft (9) to the shaft (8). The phase of the rotation of the second shaft (8) relative to the rotation of the first shaft (9) is adjusted by rotating adjustment shaft (7) to displace carrier (3) and thus the first helical gear (1) to vary the axial region of the gear (1) engaged with the gear (2).

Description

Description of Invention

"A variable drive mechanism"

THIS INVENTION relates to a variable drive mechanism in which first and second rotatable members are coupled together for rotation at a phase relative to one another which is variable.

According to the invention, there is provided a variable drive mechanism in which first and second rotatable members are coupled together for rotation at a phase relative to one another which is variable, which mechanism comprises a first helical gear rotatable with the first member, a second helical gear which is rotatable with the second member and is coupled to the first helical gear to transmit rotation of the first member to the second member, and adjusting means for varying the axial regions of the helical gears which are coupled together to vary the relative phase of the rotations of the first and second members.

According to the invention in another aspect thereof, there is provided a variable drive mechanism in which first and second rotatable members are coupled together for rotation at a phase relative to one another which is variable, which mechanism comprises a first helical gear rotatable with one of the first and second members, a second gear which is rotatable with the other member and is coupled to the first helical gear to transmit rotation of one member to the other, and adjusting means for varying the axial region of the first helical gear coupled to the second gear to vary the relative phase of the rotations of the first and second members.

A mechanism embodying the invention enables one shaft or component to have the timing of its rotation advanced and/or retarded in relation to another shaft or component.

The abil ity to vary the relative timing of the rotation of components is extremely useful, especially in relation to camshaft drives as provided in internal combustion engines, for example. In such engines a direct drive is usually provided from the crankshaft to the camshaft by way of a chain or belt arrangement driving a fixed sprocket wheel mounted on the nose of the camshaft. The required 2:1 reduction in rotational speed between the camshaft and the camshaft is provided by making the camshaft sprocket wheel larger than the driving sprocket wheel on the crankshaft.

A camshaft which can be advanced and retarded offers a means of providing considerable improvement in engine performance, both as regards power and emission control and various devices have been suggested to enable the rotation of a camshaft to be advanced or retarded. However, the known devices only provide an all or nothing adjustment in a limited range. In contrast, a mechanism embodying the invention enables the phase of rotation of a camshaft to be fully and steplessly varied.

In order that the invention may be readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which:

Figures 1 A and 1 C are respectively a partly sectioned side elevation, a setion on line A-A and a section on line B-B illustrating a variable drive mechanism for a camshaft in accordance with a first embodiment of the invention;

Figure 2 is an axial cross-sectional view of a variable drive mechanism in accordance with a second embodiment of the invention;

Figure 3 is an axial cross-sectional view of a variable drive mechanism in accordance with a third embodiment of the invention; and

Figure is an axial cross-sectional view of a variable drive mechanism in accordance with a fourth embodiment of the invention.

Throughout the drawings, bearing surfaces are indicated by thick lines and like parts in the different embodiments are identified by the same reference numerals. Figure I of the drawings shows in side elevation and partly sectioned a simple embodiment using two helical gears I and 2, the gear I being driven by a square section portion 4 of an input shaft 9. Gear I is, therefore in constant driven communication with shaft 9, with the shaft portion 4 providing drive at all times, but gear I can slide along the shaft portions 4 in a lateral fashion while still maintaining drive contact. Input shaft 9 and camshaft 8 are journal led in supports 10 and 12 of an engine. As gear I is a wide gear, as compared with gear 2, it will be seen that lateral sliding (in either direction) of gear I will still retain the engaged situation between the two gears, i.e. gears I and 2 remain constantly engaged at a ratio of 2 : I . Gear I has, for example, 20 teeth and gear 2 has, for example, 40 teeth, although any required ratio can be envisaged. By including a 2 : I reduction between the two gears, the size of a drive sprocket (not shown) mounted on the left hand or front end of the shaft 9 can be reduced, thereby allowing overall engine height, at the most important point (i.e. the extreme front end) to be reduced and allowing for considerable flexibility in the body styling of a vehicle incorporating a camshaft with the proposed drive mechanism.

The helical engagement between gears I and 2 is sufficient to create the required advance/retard characteristics, and left, or right hand helices may be chosen for gear I with the appropriate opposite hand provided for gear 2.

Sliding the gear I along shaft 9 parallel to the axis of rotation Y-Y of the shaft presents the problem of allowing gear 1 to retain rotation, while being relocated and, when once relocated, to be retained in that new location. This is solved by providing a sliding carrier 3.

Carrier 3 is a saddle type device which is bearing located upon shaft 9 and a parallel control shaft 7. The carrier has two end plates 3b and 3c which each have two circular apertures (See Figure 2c). These apertures are of similar diameter to the two shafts 9 and 7, thereby allowing free sliding movement of the carrier along the two parallel shafts. The plates 3b and 3c are interconnected by a cross-tie 3a.

Figure l c indicates, however, that while end plates 3b and 3c can -4-

slide along shafts 7 and 9, the flanged shape of these items will not allow clearance in respect of gear I . Therefore, any movement of carrier 3 will cause gear I to move in unison with it. However, as shaft 9 can pass through end-plates 3b and 3c in an unobstructed fashion, the rotational characteristics of shaft 9 and gear I are unimpaired.

Carrier 3 is also provided with a section of rack gearing 5, located in this particular design on the underside of the cross-tie 3a which also serves to fix together into a single unit the two end plates 3b and 3c. The items 3a, 3b, 3c and 5 can be manufactured in one or more pieces to form either an assembly or a single component.

Rack 5 is engaged with a worm pinion 6 which is fixed to, or part of, shaft 7. A standard pinion could be used with shaft 7 at right angles to the rack 5 - this is not shown on the drawing of Figure I .

The lead angle of the worm pinion 6 is a so-called "locking" angle, e.g. around 10 , with the result that the rack can be driven by the worm pinion but the worm pinion cannot be rotated by the rack 5. Therefore, any rotation of shaft 7 will drive the rack 5 in either direction according to the direction of shaft rotation, and that movement is only restricted by the distance between the two end plates 3b and 3c and the worm pinion 6.

Depending upon whether the helix is a left-hand or right-hand helix, the result of sliding gear I along shaft 9 will be to advance or retard the established rotational characteristics of gear 2. As gear 2 is fixed to, or part of, camshaft 8, it will be appreciated that any advance/retard of gear 2 will result in advance/retard of the camshaft.

This type of device can be provided for a complete camshaft (outlet or inlet) or any single cam, or groups of cams.

The shaft portion 4 can be replaced by a straight spline, a groove or the like, or may be of any cross-section able to provide drive of a rotational nature between shaft 9 and gear 1.

A further variation which can be anticipated is that gear 2 might also be given sliding abilities, with control being supplied in a similar fashion to that described for gear I , so that either or both of gears I and 2 can be relocated upon their respective shafts.

Drive for the or each control shaft (7 as an example) is supplied by any suitable drive means, e.g. an electric or hydraulic motor, the commands for such drive means coming from an overall engine management system, or some other dedicated control source. Manual control could also be used if required.

If the basic advance/retard characteristics are supplied, as shown by Figure I , via gear I , and gear 2 is aiso capable of sliding upon shaft 8 while still retaining the ability to drive shaft 8^" via a square section portion of the shaft, then another possibility can be envisaged. Thus, by providing a compression spring between gear 2 and journal 1 1 , for example, and fixing to gear 2 a face cam on the side opposite to the spring contact and then providing a fixed roller or other follower against the face cam it will be seen that the gear 2 can be made to reciprocate in an axial fashion upon shaft 8, thereby creating an oscillatory motion for shaft 8. The number of oscillatory pulses is determined by the number of undulations or lobes present upon the face cam, or by the number of followers.

This oscillatory motion can also be variable, In that, the follower or roller can be mounted upon a carrier capable of concentric (or other) advance/retard, thereby allowing an advance and/or retard of the pulse sequence.

This coupled with overall advance/retard of the original drive, allows for complete management of the opening and closing of the engine valves controlled by the camshaft 8.

If oscillatory characteristics are included in the Figure I mechanism, they can be generated via either gear I and/or gear 2, and the basic sliding advance/retard ability can be given to either gear. Furthermore, the oscillatory ability can be included without the basic advance/retard characteristic being included, i.e. gear I , for example, could be fixed to shaft 9. Figure 2 shows α device capable of providing advance/retard characteristics, but does not include the 2 : I (or any other ratio) reduction as demonstrated by Figure I . However, it offers a very simple mechanism for camshaft management.

In the Figure 2 arrangement, gear I is fixed to, or part of, input shaft 9 and gear 2 is fixed to, or part of, shaft 8. In this case, shaft 8 is indicated as the camshaft, and shaft 9 as the shaft fixed to sprocket 14. Shaft 15 is a location shaft for centring the sprocket 14.

The basic construction of the mechanism shown in Figure 2 is derived from a piston and cylinder combination, in which a cylinder 21 .provides the support and bearing location for a piston 22. The piston 22 is able to slide within the cylinder 21 but is not able to rotate.

The positioning and movement of the piston 22 is provided by way of a screwed section 28 of control shaft 27 engaged within a threaded aperture 15, in much the same way as in a lathe, for example, thereby ensuring that any rotation of shaft 7 will cause piston 22 to move along the inside of cylinder 21. This movement along the cylinder (in either direction) is similar to that described in Figure I in respect of the carrier 3, and it is noted that the screw and thread arrangement herein described, can be used in the Figure I embodiment in place of the rack and worm pinion as previously described. Likewise, the rack and worm pinion could be used in the Figure 2 embodiment in place of the screw and thread arrangement. Ail carrier drive mechanisms are interchangeable throughout this specification.

It will be seen that internally of the piston 22 there is a free-running, bearing located carrier 23 which is, in this embodiment, indicated as circular in section, with a circular aperture passing through its centre. The external surface of the carrier 23 is not, however, constant, in that there is about the centre an enlarged section 24. This radial spline 24 is located in a bearing location of similar section in the piston 22, thereby allowing carrier 23 to rotate but not move axϊally of the cylinder in either direction without similar movement being present in the piston 22. Therefore, any axial movement in either direction, by piston 22 along the length of cylinder 21 will cause carrier 23 to move in a similar fashion. However, such movement will in no way impair the rotational abilities of carrier 23.

Carrier 23 is also engaged with gears I and 2 via four engaement lugs 25a - 25d. Lugs 25a and 25b are engaged with gear I and lugs 25c and 25d are engaged with gear 2.

The number of lugs employed will be determined by the number of teeth present upon the two helical gears.

Gears I and 2 are of opposite hands (i.e. have opposite helical spirals). As the two helics are of opposite hands, the side loadings are balanced and the carrier 23 is held in an unbiased state.

The mechanism has outer casing or journal housings 10 and 1 2.

The piston and cylinder arrangement illustrated in Figure 2 can be replaced by any suitable sliding carrier arrangement, e.g. the piston could be a saddle type of device, running upon one or more flat surfaces or upon a roller bed.

Figure 3 shows a mechanism which is similar in principle to that of Figure 2 but the method of moving the piston 22 is different.

It is assumed that the two helical gears I and 2 are left and right- hand helixes, or, as in Figure 2, either of the gears is a helical component, while the other is a straight cut spur-gear. The internal splines 25a - 25d can be of any suitable number, i.e. one or more, and the fact that they are of such short length precludes the need for these items to be helical. They are, in fact, merely location pins.

The carrier 23 is in Figure 3 caused to slide backwards and forwards by virtue of the fact that the cylinder or barrel 3 1 is screw threaded, and the carrier is correspondingly threaded so that it constitutes a threaded insert. It will be seen that the piston 22 has an extension 38 having an external gear face 38a which is engaged with a drive gear 37 mounted upon control shaft 7. By applying a driving force to shaft 7, the drive gear 37 is caused to rotate, thereby rotating assembly 22, 38, 38a. The rotation of this assembly causes piston 22 to be screwed into, or out from, barrel 31. The angle of the lead (or leads) of the screw-thread is sufficient to prevent any lateral 5. movement other than that instigated by gears 37 and 38a. Therefore, this is a totally locked carrier assembly, capable of repositioning to cause shaft 8 to be advanced and/or retarded in relation to shaft 9.

The control of shaft 7, which is driven by any suitable means (e.g. 10 electric motor, or manual lever coupling) is again decided by the engine management system or other timing control.

The mechanism shown in Figure 3 does not therefore require a worm and worm-wheel combination to adjust and lock it. The length of the gear- 15 cut section 38 of the piston 22 remains in contact with gear 37 throughout the entire range of movement.

Figure 4 shows a drive mechanism embodying the invention and having an oscillatory pulse generator section coupled with an 20 advance/retard section. The two sections can be advanced, and/or retarded independently of one another or in conjunction with each other.

Carrier 43 is bearing located concentrically of the main centre axis 'x' - 'x' of the mechanism and is driven axϊaily (in either direction) by a novel 25 radial rack arrangement. The teeth, resembling radial fins as seen as cooling elements on air-cool engines, are engaged with a normal type spur- gear 47. This is fixed to shaft 46 and is controlled and driven by a worm and worm-wheel arrangement (not shown).

30 The fins pass through the teeth of gear 47 and as gear 47 can be rotated, the rack can be driven in either direction.

Carrier 43 is provided with internal pins 45a - 45d and these are engaged with two gears I and 2, one of which must be helical.

35

Gear 2 is not fixed to shaft 8 but is straight spline coupled, thereby allowing gear 2 to slide along shaft 8 but remain in rotational driving coπtαct.

A spring 42 Is provided between gears I and 2 and their respective end plates 51 and 52. Any axial repositioning of carrier 43 will cause shaft 8 to be advanced and/or retarded relative to shaft 9. However, gear 2 is also provided with two radial arms 48 and 49 which are provided with follower contact fingers, one of which is indicated at 50.

These contact fingers are forced into firm contact with face cam 53 by spring 42, and therefore, as cam 53 has one or more undulations lobes upon its active surface engaged by fingers 50, gear 2 is caused to reciprocate as the follower 50 or followers are rotated across its face. The number of pulses is determined by design requirements and the shape of the lobe or lobes determines the pulse shape. Oscillatory motion can thus be applied to gear 2 regardless of the already established advance/retard characteristics via carrier 43 and gear I .

In order to provide ability to advance/retard the pulse sequence, face cam 53 is fixed to sleeve-shaft 54 and this in turn is fixed to, or part of, worm-wheel 55. This is engaged via a locking angle with worm 56 which is mounted upon its own control shaft 7. This allows rotation of cam 53 relative to the follower 50 and thereby advance/retard the oscillatory motions created.

In Figure 4 inadvertent axial movement is controlled by the radial rack assembly but in Figures 2 and 3 the radial flange 24 prevents the pin carrier 23 from moving without the piston 22.

The above described mechanisms can be used to provide gradual advancing and retarding of the phase of rotation of a shaft and will not add to the noise difficulties associated with gearing when it is used in a normal way.

An inverse of each device can be contemplated, in that the carrier could be provided with two helical gears (or one helical and one straight cut spur) and the two shafts could be provided with the contact pins. The resultant function and performance envelope would remain the same as for the devices as described.

Claims

CLAIMS:

1. A variable drive mechanism in which first and second rotatable members are coupled together for rotation at a phase relative to one another which is variable, which mechanism comprises a first helical gear rotatable with the first member, a second helical gear which is rotatable with the second member and is coupled to the first helical gear to transmit rotation of the first member to the second member, and adjusting means for varying the axial regions of the helical gears which are coupled together to vary, the relative phase of the rotations of the first and second members.

0 2. A drive mechanism according to claim I , in which the first and second rotatable members are rotatable about parallel axes with the first and second helical gears engaged with one another, one of the helical gears is dϊsplaceable axially of the respective rotatable member and the adjusting means comprise means for shifting the dϊsplaceable helical gear axially of 5 the respective rotatable member by a selectable amount.

3. A drive mechanism according to claim 2, in which the means to shift the displaceable helical gear comprise a carrier movable with the displaceable helical gear along the respective rotatable member and means 0 for driving the carrier.

4. A drive mechanism according to claim 3, in which the carrier comprises a pair of end plates between which the displaceable helical gear is disposed and a cross-piece connecting the end plates and carrying a driven 5 element engaged with a driving element of the adjusting means.

5. A drive mechanism according to claim 4, in which the driven element comprises a rack and the driving element comprises a pinion rotatable with an adjustment shaft to displace the rack and thus the carrier and Q displaceable helical gear.

6. A drive mechanism according to claim I , in which the first and second rotatable members are rotatable about a common axis, the first and second helical gears are helical gears of opposite hand, the first and second 5 helical gears are coupled by a coupling gear which is rotatable about and displaceable along the common axis and has respective ax^'rally spaced portions engaging the first and second helical gears, and the adjusting means comprises means for shifting the coupling gear along the common axis.

7. A drive mechanism according to claim 6, in which the means for shifting the coupling gear comprise a piston which is coupled to the coupling gear and is axially movably but non-rotatably received in a cylinder and means for displacing the piston in the cylinder.

10

8. A drive mechanism according to claim 7, in which the means for displacing the piston in the cylinder comprise a rotatable lead screw engaged in a threaded bore of the piston which extends parallel to the_ common axis of rotation.

15

9. A drive mechanism according to claim 7, in which the means for displacing the piston in the cylinder comprise a gear wheel rotatable about an adjustment axis parallel to the common axis of rotation and engaged with a toothed surface on the piston.

20

10. A drive mechanism according to claim 7, in which the means for displacing the piston in the cylinder comprise a rack on the piston and a pinion rotatable about an axis normal to the common axis of rotation.

^5 I I . A drive mechanism according to any preceding claim, including oscillating means for superimposing an oscillatory angular motion on the rotational motion of the second rotatable member.

12. A drive mechanism according to claim I I , in which the oscillating '^ means comprise resilient means for biasing a follower surface on one of the helical gears against a cam surface adapted to improve the desired oscillatory motion on the rotation of the helical gear.

13. A drive mechanism according to claim 12, in which the oscillating 5 means comprise means for setting the angular position of the cam to vary the phase of the oscillations improved by the cam surface.

14. A drive mechanism according to claim 13, in which the setting means comprise a shaft with which the cam is rotatable, a worm-wheel rotatable with the shaft and a worm engaged with the worm-wheel for rotating the worm-wheel to set the angular position of the cam.

15. A drive mechanism in which first and second rotatable members are coupled together for rotation at a phase relative to one another which is variable, which mechanism comprises a first helical gear rotatable with one of the first and second members, a second gear which is rotatable with the other member and Is coupled to the first helical gear to transmit rotation of one member to the other, and adjusting means for varying the axial region of the first helical gear coupled to the second gear to vary the relative phase of the rotations of the first and second members.

16. A drive mechanism substantially as hereinbefore described with reference to the accompanying drawings.

17. A camshaft drive mechanism according to any preceding claim, in which the camshaft constitutes the second rotatable member and the first rotatable member comprises a layshaft carrying a driven element for driving the camshaft.

18. Any novel feature or combination of features disclosed herein.