This invention relates to a locking device for transmission systems of vehicles such as commercial vehicles.

It is well known that commercial vehicles, when fully loaded and being driven are susceptible on occasions to roll backwards on steep inclines and of course, this becomes an even greater problem should the braking system of the commercial vehicle fail.

This problem has to some extent been solved by the provision of a drum which is fixed to the drive shaft of the vehicle to rotate therewith. A strap is located around the drum and is connected in such a manner that upon reverse motion of the vehicle, the strap automatically tightens around the drum and prevents further rotation of the drum and hence movement of the vehicle.

However, the main disadvantage of such construction is that in spite of the braking effect of the belt or the drum and the continual tightening of the strap on the drum, the more the vehicle rolls backwards the more the strap has a tendency to slip about the drum and stopping of the reverse motion of the vehicle is not always guaranteed.

It is therefore desirable to provide a locking device for transmission systems of vehicles in which the above disadvantages are substantially alleviated.

According to the present invention there is provided a locking device for locking the transmission system of the vehicle to prevent reverse rotation of the transmission system, the locking device comprising rotatable means adapted to be rotatable with a drive shaft of the vehicle in a direction corresponding to reverse motion of the vehicle, ratchet means fixed relative to the drive shaft for rotation therewith in either direction of rotation of the drive shaft, and coupling means interconnected with the rotatable means so that upon reverse motion of the said rotatable means the coupling means engages the ratchet means and

locks the ratchet means and the drive shaft against the said reverse motion of the vehicle.

In one embodiment of a locking device in accordance with the present invention, the rotatable means comprises a gear wheel ^" arranged to be mounted for rotational movement with a drive shaft of a vehicle and being fixedly rotatable with the drive shaft for rotation in a reverse direction of the vehicle but to freewheel in forward motion of the vehicle. The ratchet means preferably comprises a wheel having ratchet teeth around the outer circumferential surface thereof and is fixedly mounted on the drive shaft for rotation therewith. Conveniently, the gear wheel and the ratchet wheel are interconnectable by the coupling means in the form of a quadrant gear directly engagable with teeth about the outer circumferential surface of the said gear wheel and coupled with a roller support pivotal with the quadrant gear to engage the roller with the teeth of the ratchet wheel and prevent further rotation of the drive shaft in a direction corresponding to the reverse direction of the motion of the vehicle.

Conveniently, release means are provided for disengaging the inter engagement between the gear wheel and quadrant gear to allow the vehicle to be movable in a reverse direction when required. The release means can be a lever mechanism operable manually by cable from the ^" driver's cab of the vehicle and/or an electro-mechanical device for displacing the quadrant gear axially from engagement with the freewheel gear for instance when the reverse gear in the gear box is engaged.

In an alternative embodiment of the locking device according to the present invention, the rotatable means comprises a pulley wheel located remotely from the drive shaft of a vehicle and is rotatable with the drive shaft when it rotates in a direction corresponding to the reverse motion of the vehicle by a belt drive. Conveniently, the ratchet means is again a gear wheel having ratchet teeth about its outer circumferential surface and is fixedly mounted on the drive shaft for rotation therewith. Preferably, the coupling means comprises an arm drivable by the free wheel pulley whereupon a free end of the arm carrying a roller engages the teeth on the

ratchet gear wheel to prevent rotation of the drive shaft in a direction corresponding to reverse motion of the vehicle.

In another convenient arrangement the coupling means comprises a plurality ^" of centrifugally operated ratchets which upon cessation of rotation provide engagement of the ratchet means to lock the drive shaft against reverse motion of the vehicle.

Conveniently, release means can also be provided for disengaging the inter-engagement between the locking arm and ratchet gear so that the vehicle can be driven backwards if required. As previously described a lever mechanism can be operated from the driving cab of the vehicle or by an electromagnetic device for disengaging a clutch mechanism interconnecting the arm of the pulley which freewheels in one direction.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which;

Fig. 1 is a side elevational view of a locking device according to the present invention;

Fig. 2 is a cross sectional view along the line X-X in Fig. 1;

Fig. 3 is a partial sectional view along the line Y-Y of Fig. 2;

Fig. 4 is a side elevational view along the line Z-Z of Fig. 3;

Fig. 5 is a side elevational view similar to that in Fig. 1 but the second embodiment of a locking device according to the present invention;

Fig. 6 is a diagrammatic representation of the device of Fig. 5 as viewed from the direction of the arrow A in Fig. 5;

Fig. 7 is a diagrammatic view along the line W-W in Fig. 6;

Fig. 8 is a side elevational ^' view similar to Fig. 5 but illustrating a third embodiment of a locking device according to the present invention; and

Fig. 9 is a side elevation of a fourth embodiment of the present invention.

Referring to the drawings in more detail Figs. 1 to 4 illustrate a preferred embodiment of a locking device according to the present invention. The locking device comprises a frame having an enlarged plate 1 and sidewalls 2 extending outwardly orthogonally from one side of the plate 1 and together enclose a ratchet wheel 3 and a free wheel toothed gear 4 which freewheels in one direction but rotates with a drive shaft 5 in the opposite direction. The ratchet wheel 3 is fixed against rotation relative to the drive shaft 5 by splines 6 at the end of the drive shaft. Simultaneously, the ratchet wheel is bolted to an output shaft 7 which can take the form of the input shaft to a differential drive unit for example.

The freewheel gear 4 has a plurality of castellated teeth about its external circumferential surface and these teeth are engagable with similarly shaped teeth of a quadrant gear 8 which is mounted on an elongate spindle 9. A support 10 having two outstanding plates 11, 12 extends radially outwardly from the spindle 9 and is mounted thereon for pivotal movement about the rotational axis of the elongate spindle 9. A roller 13 is located between the plates 11, 12 on a spindle 14 so that upon rotational or pivotal movement of the support 10 about the spindle 9 the roller 13 engages in curved recessed areas 14 of the ratchet teeth about the outer circumferential surface of the ratchet wheel 3.

The quadrant gear 8 is pivotally mounted on a shaft 15 supported at one end by support 10. The shaft 15 is fixed against rotation thereof but movable longitudinally of its elongate axis as indicated by arrow B in Fig. 2. The shaft also supports in addition to the quadrant gear 8 a coil spring 16 which is fixed relative to the quadrant gear at one end and at the other end is located against an arm 17 fixed to support 10 in the region of plate 12. The arm 17

extends in a direction parallel to the shaft 15. As the quadrant gear rotates the spring 16 tensions and after a small delay caused by the tensioning of the spring the arm 17 moves transversely causing support 10 to pivot as will be described herein below in more detail.

The end of the shaft 15 remote from the support 10 is connected to a lever 20 pivotally mounted on a fulcrum 21. The lever 20 is connected on the other side of the fulcrum to an actuating shaft 22 of an electromagnet 23 which operates to pivot lever 20 and thus move the shaft 15 longitudinally until the quadrant gear 8 has disengaged from the teeth of the freewheel gear 4. The electromagnet is mounted on one side wall 2 of the locking device.

The frame of the locking device is conveniently attached to the body of the vehicle on the underside thereof by the side walls 2 so that an aperture 24 in the frame plate 1 is of a size sufficient to receive therethrough drive shaft 5 of a commercial traction unit for example. A splined end of the drive shaft is received within an internally splined flange 25

extending outwardly from, and axially about the central axis of the ratchet wheel 3. Splines 6 on the drive shaft 5 interlock with the internal splines of the flange 25 to lock the ratchet wheel 3 relative to the drive shaft 5 in either direction of rotation thereof.

Conveniently, the freewheel gear 4 is mounted on the external surface of the flange 25 via a freewheeling bearing for example ball race 26.

The ratchet wheel 3 has a flange 27 on the opposite side to that side from which the flange 25 extends. The flange 27 has an internal diameter which is substantially identical to the external diameter of shaft 7 which fits snugly in and abuts end face 28 having four equally spaced holes 29, Fig. 1, through which bolts 30 extend through and into the end of the shaft 7 to fix the shaft 7 relative to the ratchet wheel 3.

The support 10 is pivotally mounted on the spindle 9 which is itself supported at its ends in supports 31. The plates 11, 12 pivot inwardly with support 10

towards the ratchet wheel 3 so that the roller 13 rolls down the face 32 of the tooth and into recess 14 whereupon the ratchet wheel is prevented from further rotation.

The support 10 has, towards its base in the region of spindle 9, outwardly extending flanges 33. Two springs 34 extend between flanges 33 and a respective small recess 35 in the support 31. The springs 34 bias the flanges 33 upwardly in Fig. 1 so that the support 10 pivots in an anti-clockwise direction about spindle 9 and ensures the roller 13 remains disengaged from the teeth of the ratchet wheel 3.

As will be seen more clearly in Figure 2, one of the plates 12, that is the plate adjacent to the quadrant gear 8, has attached to its elongate arm 17 which is engaged by one end of the coil spring 16. The latter is mounted on the longitudinally movable shaft 15 and is fixed at its opposite end to the quadrant gear 8 so that when the quadrant gear begins to rotate by the drive of the freewheel 4 it rotates in the reverse direction movement. The spring 16 begins to tension leaving the arm 17 and hence the support 10

stationary. When the spring 16 is completely tensioned the end of the spring forces the arm 17 to move the support 10 to pivot the support until the roller 13 engages within a recess 14 of the ratchet wheel 3. When the motion of the vehicle to which the locking device is attached is in the forward direction, the freewheel gear 4 begins to rotate in the forward direction under the influence of the spring 16 until the quadrant gear is returned to its stationary position. Simultaneously, the spring 16 forces the support 10 to pivot anti-clockwise in Fig. 1 disengaging roller 13 from the teeth of the ratchet 3 whilst the rod 17 returns to the position shown in Fig. 2. The operation of the locking device will now be described in more detail.

When a vehicle to which the drive shaft 5 is attached to the engine (not shown) , moves in a forward direction of motion of the vehicle the drive shaft rotates in one direction which will hereinafter be referred to as the forward direction to rotate the ratchet wheel 3 and hence, the shaft 7 attached therto. The freewheel gear 4 remains in a substantially stationary condition through the

freewheel bearing 24 and the ^' roller 13 is in the disengaged position shown in Fig. 2. When the vehicle comes to a halt the locking device will be in the same configuration as shown in Fig. 2.

Should the vehicle begin to roll backwards, the drive shaft 5 begins to rotate in a reverse direction whereupon the bearing 26 locks the drive shaft to the freewheel gear 4 for reverse motion thereof. Such motion causes the quadrant gear 8 to rotate tensioning the spring 16. As the quadrant gear 8 continues to rotate the spring 16 begins to pull the arm 17 in the same direction thereby pivoting the support 10 and the roller 13 until such time as the roller engages in the recess 14 of the ratchet wheel 3 and locks the ratchet wheel against further rotation in the reverse direction.

When the vehicle begins to move in a forward direction the drive shaft 5 begins to rotate in a forward direction and the freewheel gear 4 no longer rotates with the drive shaft 5. However, the spring 16 begins to unwind initially causing the quadrant gear to rotate in its opposite direction to the direction

of reverse motion. Simultaneously, the spring 34 force the support 10 and roller 13 to disengage from the ratchet wheel 3. The arm 17 forces the spring 16 in the same direction which imparts further rotational movement to the quadrant gear 8 until the support 10 is totally disengaged from the ratchet wheel and the tension in the spring 16 is substantially released.

An electrical switch (not shown) is conveniently located on the selector gear lever used to select gears for driving the vehicle so that when reverse gear is selected the solenoid 23 is energised to actuate its actuator shaft 22 into the solenoid thus causing lever 20 to pivot about fulcrum 21 whereupon shaft 15 moves outwardly in the direction of the arrow

B thereby moving in the quadrant gear axially in the same direction until the quadrant gear disengages from the teeth of the freewheel gear 4. The disengagement of the quadrant and freewheel gears allows reverse rotation of the shaft 5 to drive the freewheel gear 4 in its reverse direction without effecting movement of the support 10. Therefore the vehicle can be driven normally in the reverse direction thereof.

In one alternative in embodiment of the locking device according to the present invention the lever 20 is provided with an aperture at its end opposite to that connected to the shaft for connection by cable to an operating lever 15 in the driver's cab of the vehicle so that upon the failure or the solenoid the driver's operating lever can be actuated. The lever 20 will pivot about the fulcrum 21 to disengage the quadrant gear 8 from freewheel 4 to obtain the normal reverse motion of the vehicle.

A further alternative embodiment of a locking device in accordance with the present invention is disclosed in Figs. 5 to 7 where like parts carry the same referenced numerals as corresponding parts in Figs. 1 to 4.

In Fig. 5 there is disclosed a locking device comprising frame having a plate 1 and side walls 2 which together enclose a ratchet wheel 3 having a pulley fixedly mounted relative thereto for rotation with the ratchet wheel. A drive belt 51 extends about the pulley and also about a freewheel pulley 52 mounted on an outer shaft 53 via a freewheel ball race

54. The outer shaft 53 is supported between the frame plate 1 and a support bracket 55 (Fig. 6). The support bracket 55 further supports an inner shaft 56 on which is mounted a radially outwardly extending arm 57 having directly connected towards its end remote from the inner shaft an overriding unit 58 which is also connected at its opposite end to another arm 59 mounted on spindle 9 as shown in Fug. 5. The arm 59 extends radially outwardly from the spindle 9 and at its free end 60 supports a roller 61 on a spindle 62. Whilst in Fig. 5 only one arm 59 is seen there are in fact two such arms and the spindle 62 extends between the free ends 60 of each of the arms.

The ratchet wheel 3 has, as in the previously described embodiment, a plurality of recesses defining teeth about its outer circumferential surface so that during its operation the roller 61 can enter a recess in the surface of the ratchet wheel to prevent movement of the ratchet wheel in one direction corresponding to the reverse direction of movement of vehicle for example.

As shown in Fig. 7, a solenoid ^' 62 is mounted on the side wall 2 externally thereof. An actuator shaft 22 of the solenoid is connected to lever 20, pivotly mounted about fulcrum 21. The lever 20, at the opposite side of the fulcrum to that to which the actuator shaft of the solenoid is connected, is provided with a ball joint 63 connected to the exposed end of the inner shaft 56. The inner shaft 56 is coupled with the outer shaft 53 via a clutch mechanism 64.

During operation of the locking device of Figs. 5 to 7 ratchet wheel 3 is again similarly interconnected to a drive shaft (not shown) in the same manner as described with reference to Figs. 1 to 4. However, instead of a freewheel gear being mounted on a flange of the ratchet wheel 3, the present embodiment has a pulley 50 fixedly mounted relative to the ratchet wheel with the belt 51 driving the pulley wheel 52 in both directions as necessary. One direction of rotation will hereinafter be referred to as the forward direction corresponding to forward motion of the vehicle to which the locking device is attached. The opposite direction of rotation will be referred to

as the reverse direction corresponding to reverse motion of the vehicle. Conveniently, a belt tensioner 65 in the form of a small pulley wheel is mounted on the plate 1 to ensure the tension in the belt remains correct.

As the vehicle and hence the ratchet wheel moves in a forward direction, the freewheel rotates without operating the operating arm 57 and the operating arm is held in a position in which arm 60 and roller 61 are disengaged from the ratchet wheel 3.

When the vehicle stops and begins to move in a reverse direction, the ratchet wheel 3 and pulley 50 rotate in the reverse direction causing the idling or freewheel pulley 52 to rotate in its reverse direction with the pulley 52 and arm 57 locked together via outer and inner shafts 53, 56 to rotate together forcing the overriding unit 58 to compress and subsequently rotate arm 60 to pivot the arm about spindle 9 so that the roller 61 engages in a recess 14 of one of the teeth on the outer circumferential surface of the ratchet wheel 3.

When the drive shaft of the vehicle again rotates in a forward direction the ratchet wheel rotates in a forward direction and roller 61 rolls along surface 32 of the engaged recess thereof pivoting arm 60 in an anti-clockwise direction in Fig. 5. As roller 61 and arm 60 are released from ^" the recess 14 the arm 57 is pushed upwardly in Fig. 5 by the overriding unit 58 which then pulls the arm 60 completely out of disengagement with the ratchet wheel 3.

As described in the previous embodiment the solenoid 62 can be operated to pivot the lever 20 to disengage the idling pulley 52 from the arm 57 so that the vehicle can be driven in a reverse direction if necessary. This is achieved in the present embodiment by having the lever 20 disengage a mechanical clutch device 64 interlinked between the outer and inner shafts 53, 56 of the pulley 52. The lever 20 may be provided with, at its end opposite to that having the ball joint 63, an aperture into which a cable is connected for mechnically operating the lever 20 from the driver's cab when the solenoid is inoperative.

Whilst two mechanically operated embodiments have been described above, the disengagement and engagement of the freewheel device can be operated electrically by electronically controlling the actuation of appropriate actuating devices. Moreover, the locking devices described above - are manufactrued from metal but particularly in the second described embodiment the pulley wheels can be made of plastic material greatly reducing the weight of the locking device.

In Fig. 8 there is shown a locking device similar to that shown in Fig. 5 and like parts carry the same reference numerals.

In the embodiment of Fig. 8 the arm 57 and overriding unit 58 are replaced by a solenoid 70 which is actuable by a switch device represented by numeral 71 which is responsive to the forward and reverse motions of the free wheel pulley 52. The switch 71 in fact replaces the clutch 64 described in Fig. 7.

The solenoid 70 has an axially extending operating rod 72 which is pivotally interconnected to an arm 73

which is in turn fixedly • connected to arm 59 supporting a roller 6 (not shown) at its free end.

Upon reverse rotation of the free wheel pulley 52 the switch is switched to its "ON" condition thereby energising the solenoid ^" which forces the arm 72 inwardly rotating arms 73 and 59 in a clockwise direction in Fig. 8 so that the roller enters a recess of the ratchet wheel 3 in a similar manner to that described in the previous embodiments to prevent further reverse movement of the vehicle on which the locking device is mounted. As the pawl 59 engages the recess of the ratchet wheel 3 the pawl operates a switch 74 which de-energises solenoid 70. However, because the ratchet wheel 3 hold pawl arm 59 during applied forces in the reverse direction arms 72 and 73 remain stationary. When the ratchet wheel 3 moves in the forward direction solenoid arm 72 moves outwardly of the solenoid to rotate arm 73 in an anti-clockwise direction thereby pulleying the roller out of engagement with the recess in the ratchet wheel 3.

Referring to Figure 9 a fourth embodiment of the invention will now be described using the same reference numerals where the same features arise.

A frame having an enlarged plate 1 and side walls 2 carries a ratchet wheel 3 "and a control ring 84.

The ratchet wheel is splined to a drive shaft (not shown) and carries a peripherally recessed flange 85. The ratchet wheel and flange arrangement carries a series, generally 6, of spring loaded ratchets 86. Each ratchet 86 is pivoted about a pivot attaching it to the ratchet wheel assembly and enabling it to pivot between two positions.

The ratchet includes a tooth member 87 and a counter weight 88, whose dispositions change in these two positions.

The ratchet is spring loaded so that in the rest position the ratchet tooth 87 is extending outwards while the counter weight 88 is depressed inwards into one of the recesses in the flange 85; whereas in the rotation position the counter weight is forced

outwards by centrifugal force so as to depress the ratchet 87.

The control ring 84 includes a segment of internal teeth 89 which are engagable by the ratchet teeth 87 when these teeth are urged outwards and carries attached thereto, a collar 90.

Running within the collar 90 is a guide rod 91 which carries a spring 92 whereby when the collar 90 is forced to rotate counter clockwise under the action of the ratchets 86, this acts on a linkage 93.

The linkage 93 is arranged to transmit the motion of the spring 92 via linked arms to a pair of pivoted carrier plates 11 pivoted on a spindle 19 and carrying a roller 13. The carrier plates 11 are spring biased against spring 94 and are moveable into engagement with a recess 14 within the ratchet wheel 3.

Thus, action of the spring 92 by the linkage 93 forces the roller 13 against the action of the spring 94 into engagement with a recess 14 of the ratchet wheel 3.

In summary therefore, the ratchet 14 and drive shaft will be rotating in a clockwise direction during forward movement of the vehicle, and at that stage, the ratchets 86 will be disengaged owing to the centrifugal force on the counter weights 88.

When motion of the vehicle ceases the ratchets 87 will fly outwards to engage the inward teeth 89 and rearward motion of the vehicle causes the control ring 84 to move in a counter clockwise direction to force the spring 91 to the left (as shown in the figure) and thereby via the linkage 93 to force the wheel 13 resiliently into engagement with the ratchet wheel 3 so as to stop the backward motion of the vehicle, such as might happen when on a hill.

In the event that the safety device is to be overriden (e.g. when engaging reverse gear), a linkage 20 operated by a solenoid 23 and its actuating shaft 22 causes a lever 20 to pivot about a fulcrum 21 and thereby to draw the actuating ring 84 out of engagement with the ratchet 87.

As a further safety feature in. the event that the solenoid does not act correctly, a manual cable operated lever in the cab can act on the lever 20 via a cable 95 for disengagement of the actuating ring 84.

In addition the locking device in any of its forms can be provided with a plurality of switches which are actuated to check the operation of the locking device and can energise lights in the driver's cab so that the driver can determine the stage or state of operation of the locking device. An audible alarm or flashing lights may be provided when the locking device becomes faulty or otherwise non-operative.

Therefore there is disclosed an embodiment of the locking device according to the present invention which is operable electronically. The switch may be a direction responsive electronic circuit operated by reading bar codes or by an electronic eye or may simply be a toggle type switch operated by an extension on the free wheel pulley.

This invention has been described with particular reference to commercial vehicles but it is applicable to transmission systems of motor cars, motor bikes, trains, buses, bicycles, the driving mechanism for elevators, or moving staircases, lifting gear such as hoists or cranes, and the i.ike.