EP0471451A1

EP0471451A1 - Reciprocating piston device

Info

Publication number: EP0471451A1
Application number: EP91306482A
Authority: EP
Inventors: Bryan Nigel Victor Parsons
Original assignee: Jaguar Cars Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 1990-08-11
Filing date: 1991-07-17
Publication date: 1992-02-19
Also published as: JPH04255501A; GB9017642D0

Abstract

A wobble plate engine has a cylinder block (10) defining a series of cylinders (11) disposed in circular relationship, a shaft (15) having a wobble crank (16) intermediate of its extremities is mounted coaxially of the cylinders (11), a wobble plate (20) is rotatably mounted on the wobble crank (16), a piston (27) is slidably sealed in each of the cylinders (11), each piston (27) being universally pivoted with respect to the wobble plate (20), the wobble plate (20) is interconnected to the cylinder block (10) via a tubular cage (37), a first spider (32) being pivotally connected to the wobble plate (20) and to one end of the cage (37) and a second spider (32) being pivotally connected to the cylinder block (10) and the other end of the cage (37), the first and second spiders (32) having an annular central portion (33) with trunnions (34, 35) extending radially outwardly therefrom at 90 intervals, the first and second spiders (32) and cage (37) defining an annular envelope through which the shaft (15) and a portion of the wobble crank (16) extend and are able to rotate.

Description

The present invention relates to a reciprocating piston device and in particular to a wobble plate engine or pump.
In wobble plate engines or pumps, a series of pistons are connected to a plate which is mounted on a wobble crank, so that rotation of the crank will cause the plate to wobble and the pistons to reciprocate in associated cylinders. The cylinders are disposed about a circle in a cylinder block. In order to convert rotary motion of the wobble crank into linear reciprocal motion of the pistons or vice versa, it is necessary to react the torque applied to the wobble plate so that there is no relative rotation between the wobble plate and cylinder block.
It is also desirable in such devices that the drive or driven shaft should extend on both sides of the wobble plate coaxially of the cylinder block, so that drive may be taken off or applied at the end remote from the cylinder block, while the other end of the shaft may be used to drive the valve gear of the engine or pump.
In British Patent Application No GB 2239304A, the torque applied to the wobble plate is reacted by means of bearing surfaces associated with each of the pistons, said bearing surfaces engaging the walls of the cylinder associated with the piston. This arrangement has the disadvantage that axial loads must be taken by the wobble crank and also wear occurs between the walls of the cylinders and the bearing surfaces associated with the piston.
The present invention provides a means of reacting the torque applied to the wobble plate while permitting a drive or driven shaft to extend coaxially of the wobble plate in both directions.
According to one aspect of the present invention a reciprocating piston device comprises a cylinder block defining a series of cylinders disposed in circular relationship, a shaft having a wobble crank intermediate of its extremities, a wobble plate rotatably mounted on the wobble crank, a piston slidably sealed in each of the cylinders, each piston being universally pivoted with respect to the wobble plate, characterised in that the shaft is mounted coaxially of the cylinder, the wobble plate being interconnected to the cylinder block via a tubular cage, a first spider being pivotally connected to the wobble plate and to one end of the cage and a second spider being pivotally connected to the cylinder block and to the other end of the cage, the first and second spiders having an annular central portion with trunnions extending radially outwardly therefrom at 90° intervals,the first and second spiders and cage defining an annular envelope through which the shaft and a portion of the wobble crank extend and are able to rotate.
With the above arrangement, a torque is transmitted from the wobble plate to the cylinder block via the first and second spiders and cage which provide a double universal joint. The annular form of the cage and spiders permits the shaft to extend on either side of the wobble crank so that it may pass concentrically of the cylinders to drive suitable valve means.
Furthermore, the cage may be connected to a member which is non-rotatably mounted with respect to the cylinder block but slidable axially thereof so that the relative axial position of the cylinder block and wobble plate may be varied to vary compression ratio of the engine or pump.
An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings in which:-

Figure 1 shows a part sectional elevation of a wobble plate engine formed in accordance with the present invention;
Figure 2 is a plan view of a spider used in the engine illustrated in Figure 1;
Figure 3 illustrates an alternative method of universally pivoting the piston with respect to the wobble plate; and
Figure 4 is a view in the direction of arrow IV of the modification illustrated in Figure 3.

As illustrated in Figures 1 and 2, a wobble plate engine has a cylinder block 10 defining a series of cylinders 11 arranged in a circle at equiangular spaced locations. A shaft 15 is mounted coaxially of the cylinder block 10, the shaft 15 having a wobble crank 16, the shaft extending in opposite directions from each end of the wobble crank 16.
A wobble plate 20 is rotatably mounted on the wobble crank 16 by means of bearing 21. The wobble plate 20 has a series of legs 22 extending radially from a hub 23, in the same angularly spaced relationship as the cylinders 11. A ball formation 25 is provided at the end of each leg 22, the ball 25 engaging in a socket 26 on a piston 27 which is slidably sealed in one of the cylinders 11. Each piston 27 has a piston ring 28 which sealingly engages the wall of the cylinder 11. The piston head 29 is tapered away from the ring 28 converging upwardly and the skirt 30 is tapered away from ring 28 converging downwardly; to permit tilting of the piston 27 as it moves up and down the cylinder 11, in order to accommodate movement of the ball formation 25 transverse to the axis of the cylinder 11. Alternatively, a parallel skirted piston 27 may be provided, the ball formation 25 engaging in a socket 26 which is eccentric of the piston 27, so that transverse movement of the ball formation 25 may be accommodated by rotation of the piston 27. In a further alternative, the socket may be provided in a slide on the piston 27, said slide being movable relative to the piston transverse to the axis of the shaft 15.
The hub 23 of wobble plate 20 has a pair of diametrically opposed axially extending lug formations 30 which define a pair of trunnion bearings 31. A spider 32, as illustrated in Figure 2, has an annular body portion 33 with a first pair of diametrically opposed radially outwardly extending journals 34 which engage in trunnion bearings 31. A second pair of diametrically opposed radially outwardly extending journals 35 disposed at 90° to the journals 34, engage bearings 36 at one end of a tubular cage member 37. The other end of the cage member 37 is connected in like manner to a sleeve member 40 which is slidably mounted on interengaging splines 42 in an axial bore 41 in the cylinder block 10. The annular spiders 32 and cage member 37 thereby provide a double universal joint preventing relative rotation between the wobble plate 20 and cylinder block 10.
Opposed ends of the hub 23 and sleeve member 40 are contoured to provide a clearance for cage member 37 and the inner circumferences of the annular spiders 32 and cage member 37 provide an envelope which accommodates the end of the wobble crank 16 and portion of the shaft 15 extending therefrom through the cylinder block 10 and permits rotation thereof. The part of the shaft 15 extending through the cylinder block 10 may be adapted to drive suitable valve means (not shown) to control inlet and exhaust ports of each of the cylinders 11.
In operation, detonation of an air/fuel mixture in the cylinders 11 will cause the pistons 27 to move down the cylinder 11. This downweard movement will be transmitted through the ball and socket joint 25, 26 to the associated arm 22 of wobble plate 20 and will cause that arm 22 to move downwardly. The cylinders 11 will fire in a circular sequence producing a swashing motion of the wobble plate 20 which will cause the wobble crank 16 and hence shaft 15 to rotate.
Axial movement of the sleeve member 40 relative to the cylinder block 10 and the wobble plate 20 on wobble crank 16, will permit relative axial motion between the wobble plate 20 and cylinder block 10, thereby moving the pistons 27 axially relative to the cylinders 11 and varying the compression ratio of the engine.
While a wobble plate engine is described above, the invention is equally applicable to pumps, where rotation of the wobble crank 16 will cause the pistons 27 to move up and down cylinders 11 so that upon downward movement of the pistons fluid can be drawn into the cylinders and upon upward movement expelled from the cylinders.
In the modification illustrated in Figures 3 and 4, the ball and socket joints 25, 26 between the wobble plate 20 and piston 27 are replaced by universal joints 45. The universal joints 45 comprise an intermediate member 46 which is pivotally mounted on a journal 47 extending radially from the end of the leg 22 of the wobble plate 20. The intermediate member 46 has a pair of axially extending journals 48 disposed at right angles to the journal 47, these journals 48 engaging in trunnion bearings 49 on the piston 27. As with the ball and socket joints 25, 26 provision must be made to accommodate transverse movement of the end of the leg 22 as the piston 27 moves up and down the cylinder 11. This may be achieved by tapering the head 29 and skirt 30 of the piston 27 as in the embodiment described with reference to Figure 1.
Various modifications may be made without departing from the invention. For example, in the above embodiments the pistons 27 have an integral connecting rod so that provision must be made for tilting of the piston. Alternatively, the connecting rod may be universally connected to the piston to accommodate transverse movement of the connection to the wobble plate and permit the piston to remain coaxial with the cylinder at all times.

Claims

1. A reciprocating piston device comprising a cylinder block (10) defining a series of cylinders (11) disposed in circular relationship, a shaft (15) having a wobble crank (16) intermediate of its extremities, a wobble plate (20) rotatably mounted on the wobble crank (16), a piston (27) slidably sealed in each of the cylinders (11), each piston (27) being universally pivoted with respect to the wobble plate (20), characterised in that the shaft (15) is mounted coaxially of the cylinders (11), the wobble plate 20 being interconnected to the cylinder block (10) via a tubular cage (37), a first spider (32) being pivotably connected to the wobble plate (20) and to one end of the cage (37) and a second spider (32) being pivotally connected to the cylinder block (10) and to the other end of the cage (37), the first and second spiders (32) having an annular central portion (33) with trunnions (34, 35) extending radially outwardly therefrom at 90° intervals, the first and second spiders (32) and cage (37) defining an annular envelope through which the shaft (15) and a portion of the wobble crank (16) extend and are able to rotate.

2. A reciprocating piston device according to Claim 1 characterised in that the tubular cage (37) is pivotally connected to the cylinder block (10) via a sleeve (40) which is non-rotatably located in an axial bore (41) through the cylinder head (10), the shaft (15) passing axially through the sleeve (40) and the axial bore (41).

3. A reciprocating piston device according to Claim 2 characterised in that the sleeve (40) is mounted for axial movement within the axial bore (41) to permit axial movement of the cylinder block (10) relative to the wobble plate (20), so that the compression ratio of the reciprocating piston device can be varied.

4. A reciprocating piston device according to Claim 3 characterized in that the wobble plate (20) is movable axially of the wobble crank (16) so that it may be moved relative to the cylinder block (10).

5. A reciprocating piston device according to any one of the preceding claims characterised in that each piston (27) is connected to the wobble plate (20) by means of a ball and socket joint (25, 26).

6. A reciprocating piston device according to any one of Claims 2 to 4 characterised in that each piston (27) is connected to the wobble plate (20) by means of a universal joint (45).

7. A reciprocating piston device according to Claim 6 characterised in that an intermediate member (46) defining a pair of diametrically opposed trunnions (48) is pivotally mounted about a radial axis on the wobble plate (20), the trunnions (48) engaging a pair of trunnion bearings (49) on the piston (27).

8. A reciprocating piston device according to any one of the preceding claims characterised in that provision is made for transverse movement of the connection between the piston (27) and wobble plate (20) relative to the axis of the cylinder (11).

9. A reciprocating piston device according to Claim 8 characterised in that the piston (27) has a connecting rod formed integrally therewith, the piston head (29) and piston skirt (30) being contoured to permit tilting of the piston (27) within the cylinder (11) as the piston (27) moves up and down the cylinder (11).