GB2307669A

GB2307669A - A parking brake in a four-wheel-drive vehicle transmission

Info

Publication number: GB2307669A
Application number: GB9524695A
Authority: GB
Inventors: Philip John Guest; Keith Gary Reginald Parsons; David John Tickle
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1995-12-02
Filing date: 1995-12-02
Publication date: 1997-06-04
Anticipated expiration: 2015-12-02
Also published as: GB9524695D0; GB2307669B

Abstract

The parking brake (32) of a four wheel drive vehicle is arranged in a transfer transmission (14) which comprises a centre differential (16) through which drive is transmitted to outputs (43, 45) for driving respective front and rear wheels of the vehicle. The parking brake comprises a first disc brake (53) arranged to brake output shaft (45) to the transmission casing (84) and a second disc brake (65) arranged to brake the pinion carrier (38) of the centre differential to the casing. The operating arrangement (74) comprises two annular actuating plates (76, 78) which can be moved apart axially by balls (98) to apply the disc brakes.

Description

A VEHICLE DRIVE TRANSMISSION AND A PARKING BRAKE THEREIN The invention relates to a parking brake in a vehicle drive transmission which includes a differential transmission through which drive is transmitted by first and second output members to respective front and rear wheels of the vehicle. In such vehicles, which may be four wheel drive or with a greater number of wheels, such a differential transmission is usually referred to as a centre differential.

Hitherto, it has been common to provide a brake on an output member of the centre differential directly connected to the rear propeller shaft of a four wheel drive vehicle to provide a parking brake for the vehicle. Typically, a drum brake has been used for that purpose. However, when parking the vehicle facing down very steep hills, it has been found that wheel adhesion on the rear wheels may be insufficient to hold the vehicle and adequate adhesion can be obtained only when a locking device is also provided to lock the centre differential. This may be difficult to provide if the centre differential is of a limited slip type which does not positively lock the propeller shafts together.

An object of the present invention is to provide an improved parking brake in a vehicle drive transmission.

According to the invention there is provided a vehicle drive transmission which includes a differential transmission comprising a casing, a rotatable input member for receiving drive from an engine of the vehicle and first and second rotatable output members for transmitting drive to respective front and rear wheels of the vehicle and a parking brake comprising a first brake arranged to brake one of said rotatable members to the casing and a second brake arranged to brake another of said rotatable members to the casing.

Conveniently, the first brake is arranged to brake one of the output members and the second brake is arranged to brake the input member.

Common operating means is provided for actuating the first and second brakes, preferably simultaneously.

In a preferred arrangement, each of the first and second brakes comprises a respective disc rotationally fast with the respective rotatable member, a respective reaction member rotationally fast with the housing and a pair of actuating members operable by the operating means to clamp the respective disc between braking surfaces on the respective reaction member and the respective actuating member.

Conveniently, the actuating members are moveable away from each other to apply the first and second brakes, in which case the actuating members may be mounted for relative rotary movement,- at least one of the actuating members having one or more ramp surfaces thereon for cooperation with a corresponding separating element arranged between the ramp surface and an opposing surface of the other actuating member such that such relative rotary movement between the actuating members will cause the ramp and separating element to move the actuating members apart and actuate the first and second brakes.

Each actuating member may have an abutment for reacting against a stop on the casing, rotational movement of the respective actuating member away from the stop being in the direction to actuate the brakes.

Conveniently, both the actuating members have ramp surfaces thereon, preferably with the or each of the separating elements, which may be balls, arranged between both ramp surfaces.

The invention will now be described by way of example with reference to the accompanying drawings in which: Fig.l is a diagrammatic plan view of a four wheel drive transmission incorporating a parking brake in accordance with the invention, Fig.2 is a cross section through part of the transmission shown in Fig.l illustrating details of the parking brake, Fig.3 is a cross section to the parking brake shown in Fig.2 on the line III-III in Fig.2 shown partly broken away and showing an operating arrangement for the parking brake, Fig.4 is a cross section of the brake operating arrangement shown in Fig.3 on line IV-IV in Fig.3; and Figs.5 and 5A are cross-sections of the brake operating arrangement shown in Fig.3 on line V-V in Fig.3 and showing brake "off" and brake "on" positions respectively.

As shown in Fig.l, a vehicle has an engine 10, a change speed transmission 12 and a transfer transmission 14 which receives drive from the change speed transmission 12. The transfer transmission 14 includes a centre differential 16 controlled by a viscous coupling 20. The centre differential 16 drives a front propeller shaft 18 which drives front road wheels 22 via a differential 24. The centre differential 16 also drives a rear propeller shaft 26 which drives rear road wheels 28 via a differential 30.

The transfer transmission 14 incorporates a transmission parking brake 32 and this and other parts of the transfer transmission will now be described in detail with reference to the remaining drawings.

As shown in Figs.2 to 4, the transfer transmission 14 receives drive from the change speed transmission 12 through a gear wheel 33 and a syncromesh clutch 35 which either selects a gear wheel 34 to transmit low ratio drive to a gear wheel 36 fastened to a pinion carrier 38 of the centre differential 16 or a gear wheel 37 to transmit high ratio drive to another gear wheel 39 splined to the pinion carrier 38. The centre differential 16 is a conventional bevel type, one of the input bevel pinions being indicated diagrammatically at 40 in Fig.2. However, any other type of differential gearing may be used, e.g. a Torsen (Trade Mark type).The bevel pinions 40 mesh with output bevel pinions (not shown) which are connected to the splined ends 42, 44 of front and rear output shafts 43, 45 directly coupled to the front and rear propeller shafts 18, 26. The pinion carrier 38 of the centre differential 16 is drivably connected to a first member 46 of the viscous coupling 20 and the front output shaft 43 is drivably connected to a second member 48 of the viscous coupling which thus controls relative rotation of the pinion carrier 38 with the front output shaft 18 in known manner.

The rear output shaft 45 is formed with a splined section 50 which is rotationally fast with the splined hub 52 of a disc 56 forming part of a first brake indicated generally at 53. The disc 56 carries two friction facings 58, 60. An annular reaction member or plate 54 has a braking surface 55. The bevel pinion carrier 38 has a splined section 62 rotationally fast with the splined hub 64 of another disc 68 forming part of a second brake indicated generally at 65. The disc 68 carries two friction facings 70, 72. Another annular reaction plate 66 has a braking surface 67. The brake discs 56, 58 are axially slidable on their associated splined sections 50, 62.

A brake operating arrangement indicated generally at 74 is provided between the brake discs 56, 68 and comprises two annular actuating members or plates 76, 78 which are mounted for limited rotary movement on two guide pins 80, 82 and a stop pin 88 carried by a casing 84 of the transfer transmission 14. The actuating plates 76, 78 have respective braking surfaces 77, 79. Actuating plate 76 has an abutment 86 which makes contact with an upper surface of the stop pin 88 as viewed in Fig.3 and the other actuating plate 78 has an abutment 90 which makes contact with the underside of the stop pin. The stop pin 88 and the two guide pins 80 maintain the actuating plates 76, 78 coaxial with the output shaft 45.

The stop pin 88 and the guide pins 80, 82 also serve to locate the reaction plates 54, 66.

The two actuating plates 76, 78 are biased axially towards each other by a series of circumferentially spaced tension springs 92 which pass around fingers 94 and are formed with circumferentially spaced elongate pear-shaped recesses 96 which locate separating elements in the form of balls 98. Each of the balls 98 is located partly in a recess 96 in one actuating plate 76 and partly in a recess 96 of the other displaceable section 78. The springs 92 urge the actuating plates 76, 78 into firm contact with the balls 98. As shown in Figs.5 and 5a, the recesses 96 taper circumferentially and form ramp surfaces 97 for the balls 98 such that when the actuating plates 76, 78 are urged axially towards each other the actuating plates are also rotationally biased such that the abutments 86, 90 are urged towards the stop pin 88.

Actuating plate 76 is formed with a lobe 100 connected to one end of a link 102 and actuating plate 78 is formed with a similar lobe 104 which is connected to one end of another link 106. The two links 102, 106 are connected together by means of a pivot pin 108 and the pin is connected to an operating member 110. The operating member 110 may comprise one end of a mechanical brake linkage which can be manually operated, e.g. by means of a convention park brake lever or pedal.

When it is desired to operate the parking brake, the actuator member 110 is moved in the direction of arrow A in Fig.3 thereby causing the links 102, 106 to draw the lobes 100, 104 in the respective directions indicated by arrows B and C in Fig.3. Such action causes the abutments 86, 90 to move out of contact with the stop pin 88 and causes the balls 98 to ride up the ramp surfaces 97 of the recesses 96 as shown in Fig.5a thereby act as separating elements urging the actuating plates 76, 78 apart so that they press the brake discs 56, 68 against the reaction plates 54, 66.

The reaction plates 54, 66 abut surfaces 84a and 84b respectively on the casing 84 so that the brake discs 56, 68 are clamped between respective brake surfaces 55, 77 and 67, 79 on the reaction plates 54, 66 and the actuating plates 76, 78. By braking an input member of the centre differential 16, i.e. the pinion carrier 38, and one of the output members, i.e. output shaft 26, the torque reaction through the centre differential is effective to brake both the rear propeller shaft 26 and the front propeller shaft 18. Hence braking is simultaneously effective on all four wheels 22, 28 by a common operating means which includes the actuator member 110, links 102, 104 and balls 98.

Although the initial effort of applying the parking brake through the co-operating member 110 and the links 102, 106 tends to rotate the actuating members 76, 78 such that both abutments 86, 90 move away from the stop pin 88, the torque reacted when the braking surfaces 77, 79 press on the discs 56, 68 is such that one of the actuating members is rotated to bring its abutment back into contact with the stop pin whilst the other is rotationally biased so that its abutment tends to move away from the stop pin and provides a self-servo torque which supplements the actuating torque applied by the associated link.

In order to release the parking brake 32, the operating member 110 relieves the load on the links 102, 106 and allows the springs 92 to draw the displaceable sections 76, 78 axially together. In that way, the sockets 96 and balls 98 take up the Fig.S position again and the links 102, 106 to move back to the positions shown in Fig.3 with the abutments 86, 90 contacting the stop pin 88.

The parking brake device 32 is immersed in oil within the casing 84, thus protecting the brake from dirt and water. The arrangement of reaction plates 54, 66, discs 56, 68, actuating plates 76, 78, recesses 96, balls 98 and operating levers 102, 106 is similar to that commonly employed in disc brakes used in agricultural tractors and similar machinery and it will be appreciated that variants common to such brakes can be used in the present invention.

In particular, additional rotating discs and non-rotating reaction plates can be used in one or both of the brakes 53, 65 to increase the braking torque capacity as required.

Similarly, whilst the brakes 53, 65 have a self-servo action as described, an alternative operating mechanism may be used - - urge the actuating plates apart to operate the brake 32.

Claims

1. A vehicle drive tra7nsmission which includes a differential transmission comprising a casing, a rotatable input member for receiving drive from an engine of the vehicle and first and second rotatable output members for transmitting drive to respective front and rear wheels of the vehicle and a parking brake comprising a first brake arranged to brake one of said rotatable members to the casing and a second brake arranged to brake another of said rotatable members to the casing.

2. A transmission according to Claim 1 in which the first brake is arranged to brake one of the output members and the second brake is arranged to brake the input member.

3. A transmission according to Claim 1 or 2 and comprising common operating means for actuating the first and second brakes.

4. A transmission according to Claim 3 in which the first and second brakes are arranged to be braked simultaneously by the operating means.

5. A transmission according to Claim 3 or 4 in which each of the first and second brakes comprises a respective disc rotationally fast with the respective rotatable member, a respective reaction member rotationally fast with the housing and a pair of actuating members operable by the operating means to clamp the respective disc between braking surfaces on the respective reaction member and the respective actuating member.

6. A parking brake according to Claim 5 in which the actuating members are moveable away from each other to apply the first and second brakes.

7. A parking brake according to Claim 6 in which the actuating members are mounted for relative rotary movement, at least one of the actuating members having one or more ramp surfaces thereon for co-operation with a corresponding separating element arranged between the ramp surface and an opposing surface of the other actuating member such that such relative rotary movement between the actuating members will cause the ramp and separating element to move the actuating members apart and actuate the first and second brakes.

8. A parking brake according to Claim 7 in which each actuating member has an abutment for reacting against a stop on the casing, rotational movement of the respective actuating member away from the stop being in the direction to actuate the brakes.

9. A parking brake according to Claims 7 or Claim 8 in which both the actuating members have ramp surfaces thereon.

10. A parking brake according to Claim 9 in which the or each separating element is arranged between both ramp surfaces.

11. A parking brake according to any of Claims 7 to 10 in which the separating element comprises a ball.

12. A vehicle drive transmission substantially as described herein with reference to the accompanying drawings.

13. A parking brake in a vehicle drive transmission, the parking brake being constructed and arranged substantially as described herein with reference to the accompanying drawings.