The present invention relates to a brake operating system for the remote actuation of a brake assembly, and in particular to a control device for use in the brake operating system. The invention has particular application for use in the operating system of a motor vehicle park brake incorporating drum brakes and is herein described in this context. However, it should be appreciated that the invention has broader application and is not limited to this use. In particular the system may be used in conjunction with disc brakes or other brake arrangements.

A brake operating system employing drive cables is commonly used to actuate the park brake in a motor vehicle. In a typical arrangement, an actuator in the form of a cabin lever is located in the vehicle cabin and is connected to the two drum brakes assemblies via the cables. Actuation of the hand brake lever imparts a force to the cables causing them to move in a predetermined direction to actuate a park brake actuating mechanism located in each of the brakes. Typically, each of the drive cables is subjected to a return load from the respective park brake actuating mechanism to ensure that the shoe is disengaged from the drum when the actuator is moved from an operative to a rest position. This return load may vary with the extent of lining wear in the brake and also with other factors such as the lost travel, stiffness and ratio change in the brake actuating mechanism.

A cable equaliser is provided in the operating system to ensure that similar actuating forces are applied to each brake drum. Typically, the equaliser comprises a pivotal plate with each of the cables being connected to the plate.

When the loading is uneven in the cables, the plate is caused to move until such time as the loading in the cables becomes equal.

A problem with this arrangement is that the return loads in the drive cables are not normally equal and when the actuator is in a rest position, the return loads transferred to the equaliser cause the plate to move with the result that the cable with the higher return load may apply an actuating force to the cable with the

lower return load resulting in the actuating mechanism in that brake being inadvertently applied.

In normal, or service use, of the brake, the brake lining is prone to wear and this causes the running clearance between the lining and the drum in each brake to increase. To limit the distance required to actuate the drum brakes on wearing of the lining, each brake shoe may be adjusted such that the running clearance between the lining and the drum is reduced.

This adjustment may be made either manually or as is common in modern brake assemblies, through an automatic adjustment mechanism. In one form of automatic adjusting mechanism, the effective length of the cables in the brake operating system is shortened, to cause the brake assembly to move towards its actuated position when the brake operating system is in its rest position. This arrangement is preferred in some instances to automatic adjustment mechanisms which are located within the brakes, as it minimises the component parts which are required to be located within the brake housing. This arrangement is also preferred when a manual adjustment is made to the brake operating system as this is conveniently made external to the brakes.

A problem with this type of adjusting mechanism is that the brake with the lower return load will respond to cable slack adjustment first. When the clearance in this brake is at a minimum, the lost travel in the brake operating system could still be excessive because the brake with the higher return load is not yet at its minimum clearance. Further, when the brake system is adjusted to enable the brake with the higher return load to be at its minimum clearance, the other brake may be caused to be partially engaged. To limit the effect of the return load in the respective drive cables, in a previous arrangement, each drive cable incorporates a stop, if there is an in-built lining wear adjuster, or an adjustable stop, if there is no in-built adjuster. In either case, the stop is arranged to abut the respective drum brake housing on return of the drive cables to its rest position such that any return load which is imparted to

the drive cable is transferred to the drum brake housing through this mount and therefore not transferred to the equaliser via the drive cable.

However, in adjusting the cable length to adjust the running clearance, it is necessary to make adjustments to the cable as well as to each of the stops and this arrangement has been found time consuming and inconvenient.

An aim of the present invention is to provide a brake operating system which in a preferred form, ameliorates the problems associated with unequal return loading. In a further aim, the present invention provides a control device for use in the brake operation system. In a first aspect, the present invention provides a brake operating system including two force transmitting means each of which is connected to a respective one of two brake assemblies and both being connected to an actuation means enabling the actuation means to impart an actuating force in the force transmitting means to actuate the respective brake assemblies, and a control device, the control device being responsive to the load condition in the two force transmitting means and being operable to limit the differential between the loads only once the difference between the loads reaches a predetermined level.

By allowing a certain amount of difference between the loads in each of the force transmitting means before the control device becomes operative, the brake operating system may accommodate different return loading in the force transmitting means without causing inadvertent actuation of one of the brake actuating mechanisms.

In a preferred arrangement the control device is operative to influence the loads in each of the force transmitting means to prevent the load differential increasing beyond the predetermined level. Preferably, the control device includes control means operable to inhibit operation of the control device to limit the differential between the loads until the predetermined level is reached. Once the difference between the loading in the respective force transmitting means

drops below the predetermined level, the control device will become passive or inoperative and not further influence the forces in the force transmitting means.

Preferably the control device includes connecting means connected to each of the force transmitting means. Preferably the connecting means interconnects the force transmitting means and the control device is operable to limit the differential by enabling loading to be transferred from one force transmitting means to the other force transmitting means by movement of the connecting means to cause relative movement of the force transmitting means. Preferably the control means is operable to restrict the control device by preventing this transfer of loading from one force transmitting means to the other by restricting movement of the connecting means.

The particular movement of the connecting means to cause transfer of loading from one force transmitting means to the other may vary depending on the type of force transmitting means and the configuration of the brake operating system and may include a linear or rotational displacement of the connecting means or a combination thereof.

Preferably the force transmitting means includes pull cables or the like which are operable in tension, or push rods or other arrangements which are also operable in compression, or a combination of pull cables and push rods. Preferably the actuation means is connected to the control device enabling the actuation means to impart an actuating force to the force transmitting means through the control device. Preferably the actuating force is imparted by movement of at least part of the control device.

Accordingly, in a preferred arrangement, the control device is operable through movement of the connecting means to undergo a first movement to cause transfer of loading from one force transmitting means to the other to limit the differential between the loads and this first movement is controlled to some extent by the control means. The control device is also operable under a second

movement to impart an actuating force to both the force transmitting means and preferably the second movement is independent of the control means.

In one arrangement, the control device is connected in line to the force transmitting means. The control device includes a two part assembly; one part comprising connecting means which is connected to the two force transmitting means, and the other part being a hub portion which is connected to an actuating cable or rod which forms part of the actuation means. In this arrangement, the actuation cable extends substantially along the same line as each of the force transmitting means. The connecting means is rotatable relative to the hub portion to enable the control device to undergo the first movement to cause transfer of the loading between force transmitting means and the control device further includes control means in the form of a clutch operable between the connecting means and the hub portion to inhibit the rotation therebetween.

To enable the control device to effect the second movement to impart an actuating force to the force transmitting means, the connecting means and the hub portion are caused to move together under operation of the actuation means. This movement imparts a corresponding movement to both the force transmitting means causing the actuating force to be imparted therein. As there is no relative movement of the connecting means and the hub portion the second movement is independent of the clutch.

Another form of control device is particularly applicable to a "cross-pull" routing configuration where the force transmitting means extends substantially orthogonally to the actuation rod or cable. In this arrangement, the control device includes a base portion which is securable to a support structure, and connecting means which is movable relative to the base portion via an intermediate lever arm. A first pivot axis is formed between the base portion and the lever arm and a second pivot axis is formed between the connecting means and the lever arm. In this arrangement the control means comprises a clutch which is operable at the first pivot axis between the base portion and the lever arm.

Each of the force transmitting means is connected to and extends outwardly from a respective opposite side of the connecting means. Further the actuation rod or cable is connected to the connecting means. In this arrangement, the control device is operable to undergo the first movement to transfer the loading between the force transmitting means by rotation of the lever arm about the base portion around the first pivot axis. This movement causes a displacement of the connecting means which imparts a relative movement to the force transmitting means to cause transfer of loading therebetween. The second movement to impart an actuating force to the drive cables is caused by rotation of the connecting means relative to the lever arm about the second pivot axis. Again the second movement is independent of the clutch and therefore independent of the control means.

In a variation of this latter arrangement, the first movement is effected by a translation of the connecting means relative to the base portion. In this latter arrangement, the intermediate lever arm is replaced by a guide arm which is slidably mounted to the base portion via a slip joint. A linear clutch is operable between the guide arm and the base portion. The connecting means is pivotally connected to the guide arm and with this arrangement, the first movement of the control device is effected by sliding of the guide arm relative to the base portion and the second movement is effected by pivoting of the connecting means relative to the guide arm.

In a further aspect, the present invention provides a control device for a brake operating system having two force transmitting means each of which is connected to a respective one of two brake assemblies and each being operable to transfer an actuating force to actuate a respective one of said brake assemblies, the control device being arranged to be connected to the respective force transmitting means and being responsive to the load condition in the force transmitting means and being operable to limit the differential between the two loads, the control device including connecting means and control means, the

connecting means being arranged in use to interconnect the force transmitting means and the control means being responsive to the operating loading in each of the force transmitting means and being operable to restrict the control device in limiting the differential between the two loads until said differential reaches a predetermined level.

An advantage of the control device is that it enables the braking system to tolerate different return loading without causing inadvertent actuation of one of the brake assemblies. Consequently when the actuator is in a rest position, the difference between the running clearance between the brake assemblies will not be increased by inadvertent actuation of one of the assemblies due to unequal return loads. In this way, the difference between the running clearances is minimised enabling a single adjustment to be made to the effective length of the brake operating system to adjust the running clearance in each of the brake assemblies without the total lost travel in the operating system being excessive as would be the case if this difference was large. Further as it no longer required to include stops at the brake drum housings, the cable slack can be taken up through a single adjustment to the cable length without needing to make corresponding adjustments to the position of each of the stops.

It will be convenient to hereinafter describe a brake operating system according to embodiments of the invention in greater detail by reference to the accompanying drawings. The particularity of these drawings in the related description is not to be understood as superseding the generality of the preceding broad description of the invention. In the drawings: Figure 1 is a schematic illustration of a brake operating system including a control device according to a first embodiment of the present invention;

Figure 2 is a schematic partially cut-away illustration of the control device of Figure 1 ;

Figure 3 is a schematic view of the control device according to a second embodiment of the present invention;

Figure 4 is a schematic view of the brake operating system including the control device of Figure 3 mounted to a motor vehicle; and Figure 5 is a schematic view of a control device according to a third embodiment of the present invention.

Figures 1 and 2 illustrate a first embodiment of a motor vehicle brake operating system 10. The system includes an actuator 11 in the form of a cabin lever, two brake assemblies 12, 13, and a force transmitting link 14 interconnecting the cabin lever 11 and the respective brake assemblies.

Each drum brake assembly includes a shoe 15 incorporating a friction lining (not shown) on an outer surface 16 which is movable into engagement with an inner surface 17 of a drum 18 of that brake assembly. The shoe 15 is engagable with the drum 18 on operation of an actuating mechanism 19 associated with each of the brake assemblies. Each assembly also includes a return spring 20 to bias the shoe 15 out of engagement with the drum 18.

The force transmitting link 14 of the system 10 includes two drive cables

21 , 22 each of which is connected to the actuating mechanism 19 of a respective one of the brake assemblies 12,13. The cabin lever 11 includes an actuating rod 23 and the drive cables 21 , 22 are connected to the actuating rod through a control device 24.

In the illustrated arrangement, the drive cables 21 , 22 are in the form of pull cables which are operable only in tension. However it should be appreciated that the operating systems could include push rods or the like which are also operable under compressive loading.

As best illustrated in Figure 2, the control device 24 includes a connecting plate 29 and a hub plate 30. The connecting plate 29 is pivotally mounted relative to the hub plate 30 about a pivot 31 which is illustrated as a stepped rivet.

A clutch 32 is operable between the connecting plate 29 and the hub plate 30 and comprises opposing faces 33, 34 each of which is formed on a respective one of the connecting plate 29 and the hub plate 30. In the illustrated arrangement, each of the contacting surface of opposing faces includes a friction element 35, 36. A biasing spring 37 is also provided to bias the friction elements into engagement. With this arrangement, the clutch 32 restricts movement of the connecting plate 29 relative to the hub plate 30 about the pivot 31 until there is a sufficient torque force applied at the clutch 32 to overcome the friction resistance provided by the friction elements 35, 36 of the clutch. Each of the cables 21 , 22 is connected to the connecting plate 29. In the embodiment illustrated in Figure 2, each cable includes a cylindrical ferrule 38 which is secured to an end 39 of the respective cables 21 , 22 which is captured within a respective socket formed on the connecting plate 29 on opposing sides of the pivot 31. The resistance in the clutch 32 is arranged to off set the expected differences in the return loading which may occur in the respective brake assemblies during operation of the brake system 10. The return loading is dependent on various factors including the shoe stiffness, the extent of lining wear, the strength of the return spring, the drum and shoe lining diameter and the cable routing. By estimating the expected highest design return load and the lowest design return load which may occur in the cables and assuming the situation where one drive cable transfers this highest return load to the connecting plate and the other cable transfer the lowest return load, the resultant level of torque generated at the clutch 32 under these conditions can be determined. In practice, the resistance in the clutch is designed to be equal to or slightly greater than this level of torque.

A control rod 41 is mounted to the hub plate 30. In the illustrated arrangement the control rod includes a thread formed on a first end 42 of the rod

and an eyelet 43 formed on the other end. The eyelet 43 provides a connection to the actuation rod 23.

The control rod 41 is mounted to the hub plate 30 in a manner that permits limited movement of the rod relative to the plate in the axial direction of the rod 41. In the illustrated arrangement, the plate includes a pair of guide brackets 44 in which the rod is arranged to be received. A nut 45 is secured on the threaded end 42 of the control rod and is arranged to provide an abutment surface 46 which abuts an outer surface 47 of one of the guide brackets 43.

The brake operating system 10 is arranged to operate as follows. The cabin lever 11 is movable from a rest position to an operative position and on operation of the cabin lever, an actuating force is imparted to the actuating rod 23 which in illustrated arrangement places the rod 23 in tension. This actuating force is imparted to each of the drive cables 22, 23 through the control device 24 by movement of both the connecting plate 29 and hub plate 30 of the control device. As the control device 24 is not fixed to any supporting structure such as the vehicle chassis, the device is floating and there is no impediment to this movement. This actuating force is then imparted to the respective actuating mechanism causing the brake assemblies to actuate the respective brakes.

If there is unequal loading in the cables 21 , 22 such as would occur if one brake assembly engages before the other brake assembly, then a moment is applied at the connecting plate 29 about the pivot 31. If the resultant torque from this moment is sufficient to overcome the resistance in the clutch 32, then the connecting plate will move about the pivot 31 relative to the hub plate 30 causing the loading in the cables to be redistributed until such time as the moment being applied is less than the resistance in the clutch. As the actuating loading in the cables is significantly greater than the return loading, in practice the resultant discrepancy between the load in the actuating cables due to the resistance in the clutch does not affect operation of the brake operating system.

To reduce the excessive running clearance between the brake shoe and the drum in each of the brake assemblies, the effective length of the brake operating system is reduced to further apply each of the actuating mechanisms when the cabin lever is at rest. In the illustrated arrangement, this adjustment is provided at the control rod 41 by movement of the nut 45 on the threaded end 42. This changes the position of the abutment surface 46 thereby altering the overall length of the system.

A second embodiment of the control device is illustrated in Figure 3 and 4 which has particular application for operating systems for cables which are orthogonal such as in a "cross-pull" cable routing configuration.

As in the earlier embodiment, the control device is connected to a brake operating system having a force transmitting link including drive cables 20, 21 and actuation cable 23. However, in this arrangement, the respective drive cables 21 , 22 extend outwardly from the control device 24 in opposite directions and both drive cables extend transversely to the actuation cable 23. Further, the drive cables 21 , 22 are interconnected such that they form part of a single cable 48. As illustrated in Figure 4, each of the cables 21 , 22 are slidably mounted in respective conduits 25, 26 which are secured to the vehicle through mounting blocks 27 and 28. The control device 24 includes a connecting plate 50, base plate 51 , and an intermediate lever arm 52 interconnecting the connecting plate and the base plate.

A first pivot 53 is formed between the base plate 51 and the lever arm 52 and a second pivot 54 is formed between the connecting plate 50 and the lever arm 52. A clutch 55 of the same or similar construction as the clutch 32 illustrated in Figure 2 is formed between the lever arm 52 and the base plate 51 and is operable to inhibit rotation of the lever arm about the first pivot 53 until the friction resistance in the clutch is overcome.

As distinct from the first embodiment, the drive cables 21 , 22 as well as the actuation cable 23 are connected to the connecting plate 50. The cable 48 is located in a channel 56 incorporated in the connecting plate which is doglegged such that there is a lateral displacement between the drive cables 21 and 22. Further to enable each of the cables to accommodate individual loads, the channel 56 is crimped at opposite ends 57, 58 to prevent sliding of the cable 56 relative to the channel 56. In this way, the drive cables 21 , 22 are effectively separate and consequently it should be appreciated that they could be formed separately as in the first embodiment. Further for ease of reference, future reference shall be made to the cables 21 and 22 as if they were separately formed.

To connect the actuation cable 23 to the connecting plate 50, in the illustrated arrangement, the cable 23 incorporates a cylindrical ferrule 59 which is captured within a socket 60 formed on the connecting plate. As in the first embodiment, the control device 24 is operable to undergo two separate movements. A first movement is provided to limit the differential in the loading in the two drive cables and the second movement is provided to impart an actuating force from the actuating means to the drive cables. In this embodiment, this first movement is provided by rotation of the lever arm relative to the base plate 51 about the first pivot 53 whereas the second movement is provided by rotation of the connecting plate 50 about the lever arm 52 about the second pivot 54. Further as in the earlier embodiment, the clutch 55 is provided to inhibit this first movement until the differential in the loading in the drive cable reaches a predetermined level which is sufficient to overcome the friction resistance in the clutch.

As mentioned above, to impart the actuating force to the drive cables, the connecting plate 50 is pivotable about the second pivot 54 under operation of the actuator 11. As this pivot 54 is located between the cables 21 , 22 and because the cables extend in opposite directions, pivoting of the connecting plate 50 does

not transfer loading from one drive cable to the other drive cable but only applies an equal loading to each of the cables. In this way on operation of the actuator, the actuating force is imparted to the actuation cable 23 which causes the connecting plate to rotate about second pivot 54 thereby imparting an actuating force to each of the drive cables 21 ,22.

If there is an unequal loading in the drive cables 21 , 22 then a resultant force is imparted at the second pivot 54. This resultant force is transferred to the lever arm 52 and causes it to be biased to move about the first pivot 53. Movement of the lever arm 52 about the first pivot 53 results in a displacement of the connecting plate 50 which causes the actuating force to be applied to one cable and released from the other. In this way, loading is transferred from one cable to the other.

The clutch 55 resists movement of the lever arm 52 about the base plate 51 until a predetermined level torque is applied to the clutch 55 to overcome the friction resistance therein. As in the earlier arrangement, if the resultant torque at the first pivot 53 is sufficient to overcome the resistance in the clutch 55, then the lever arm will move about the first pivot 53 relative to the base plate 51 causing the loading in the cables to be redistributed until such time as the moment being applied is less than the resistance in the clutch. An advantage of this arrangement is that the base plate 51 remains stationary and accordingly, may be fixed to the vehicle body. Further as the actuating cable imparts loading to the drive cables through rotation of the connecting plate around second pivot 54, the spacings between the second pivot 54 and the actuating cable 23 and the second pivot 54 and the drive cables 21 , 22 can be chosen to match the stiffness of the actuator to achieve a desired feel for the brake operating system.

To adjust the brake operating system to take up any cable slack, adjustment is typically made at either the ferrule 59 or through an appropriate adjustment mechanism (not shown) incorporated at the actuator.

A further embodiment is disclosed in Figure 5, which is similar to the embodiment in Figure 3 except that the first movement of the control device 24 to limit the differential between the loading in the cables 21 and 22 is by a translation of the connecting plate 29 relative to the base plate 51 rather then by a pivoting action.

In this embodiment, the lever arm 52 is replaced by a guide arm 61 which is slidably mounted to the base plate 51 and at slip joint 62.

The connecting plate 50 is pivotably mounted to the guide plate 61 through the second pivot 54 and as in the earlier arrangement, an actuating force is imparted to the drive cables by rotation of the connecting plate 50 about the second pivot 54.

A linear clutch 63 is formed at the slip joint 62 between the guide arm 61 and base plate 51 and inhibits movement of the guide arm, and as such, the connecting plate 50, relative to the base plate 30 until a predetermined difference in the loading between the drive cables 21 and 22 is reached to cause a resultant force which will overcome the friction resistance in the linear clutch 63. While not shown typically the linear clutch includes a slotted arrangement and a biasing spring which is operable to bias the guide arm 61 into contact with the base plate 51. Preferaby friction elements are located on the guide arm and the base plate and form the engagement faces for the clutch.

Accordingly, in this embodiment, the first movement to limit the differential between the loading in the drive cables is provided by translation of the guide arm relative to the base plate 51 with the linear clutch 63 operable to control this movement and the second movement of the control device to impart an actuating force to the drive cables is provided by pivoting of the connecting plate 50 about the second pivot 54.

It will appreciated from the foregoing description that the brake operating system in accordance with the invention overcomes many of the problems associated with unequal return loading. Further the system enables easy

adjustment to compensate for increased running clearance in the brake assemblies and existing brake systems may be modified to incorporate the invention with only a minimal change to existing components.

Finally, it is understood that various alterations, modifications and/or additions may be introduced into the construction and arrangement of the parts previously described without departing from the spirit or ambit of the invention.