GB2048184A

GB2048184A - Steering brake device for a hydraulically brakable vehicle

Info

Publication number: GB2048184A
Application number: GB8005939A
Authority: GB
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co OHG
Priority date: 1979-03-09
Filing date: 1980-02-21
Publication date: 1980-12-10
Also published as: GB2048184B; IT1130933B; FR2450726A1; DE2909279C2; DE2909279A1; IT8020441A0; FR2450726B1

Abstract

A steering brake device for a hydraulically brakable vehicle of the type provided with two brake pedals for selectively braking opposite wheels so that a small turning circle may be achieved, includes a housing (10) in which a pair of control valves (35, 36) are mounted in abutment with a spring loaded balance beam (47). The valves (35, 36) are separately operable by brake pedals (15, 16) to control communication of a master cylinder (20) with ports (51, 52) leading to one or other of the wheel brake cylinders (not shown). A locking plate (50) carried on the balance beam (47) isolates the unoperated cylinder by blocking compensating bores 43, 44 which are open in the unactuated condition to accommodate changes in the volume of fluid, e.g. due to temperature changes. In a modification the device includes further valve means for applying front wheel brakes in addition to both rear wheel brakes when both pedals are actuated. <IMAGE>

Description

SPECIFICATION Steering brake device for a hydraulically brakable vehicle This invention relates to steering brake devices for hydraulically brakable vehicles.

Generally steering brake devices are provided in agricultural vehicles such as e.g. tractors in order to enable as small a turning circle as possible in cross-country driving. A typical steering brake device is described in German Printed Patent Application (DE-AS) No. 16 80 246. This known device provides that but one of the rear wheels of a vehicle is braked for the purpose of assisting the steering action. As, however, during normal road driving it is necessary to brake both rear wheels together the two pedals will be coupled or locked together when driving on a road. This join actuation also provides for a joint opening of the two valves.

In the steering brake device disclosed in the German Printed Patent Application (DE-AS) No 16 80 246 the master brake cylinder is arranged together with one control valve each and one compensating valve each in a valve unit. Each control valve is connected both with the master brake cylinder and the appertaining wheel brake cylinder, via the compensating valve. Master cylinder, control valve, and compensating valve are actuated by the respective brake pedals which have to have a specific curved path for each valve.

Further, an additional lever is provided for the actuation of the master brake cylinder, said lever being caught by the brake pedal by a catch. In the released position of a brake pedal the appertaining control valve is closed while the appertaining compensating valve is open and the line to the master brake cylinder is connected with a fluid storage tank. In the braking position, however, the chamber of the compensating valve is closed in respect of the storage tank while the control valve is open in consequence whereof the master brake cylinder, which is actuated by the lever, is connected to the wheel brake cylinder via the control valve and the compensating valve. Upon the actuation of both brake pedals the master brake cylinder will be connected with both wheel brake cylinders.If the brake pedals are not actuated the lines and cylinders appertaining to each brake pedal are connected with the fluid storage tank so that any changes in volume caused by temperature variations in the fluid may be compensated. This steering brake device, however, suffers from the disadvantage that the master brake cylinder must be integrated with the valves in a common valve unit and in that the control and compensating valve each must be actuated via specific curved paths which implies a price increase for the steering brake device.

Further, the compensating valves must be connected with the storage tank.

According to the present invention there is provided a steering brake device for a hydraulically brakable vehicle of the type provided with two brake pedals which act on a common master brake cylinder, the brake device including two control valves each connectible to a respective brake pedal, said control valves being closed in the released position of the brake; and at least one compensating valve which is open in the released position of the brake, wherein, upon actuation of the respective brake pedal, the master brake cylinder is connectible to the right brake cylinder of the vehicular brake system via the one control valve and to the left brake cylinder via the other control valve, wherein the master cylinder is connected to a chamber which serves as a common inlet chamber of the control valves and wherein the compensating valve(s) is (are) so arrangd that, upon actuation of a said control valve at least that compensating valve being closed thereby closing the hydraulic path to the non-actuated wheel cylinder.

The master cylinder is connected to a chamber which serves as common inlet chamber of the control valves and wherein the compensating valve(s) is (are} arranged, upon actuation of one control valve at least that compensating valve being closed by means of which the compensating line can be locked which leads to the nonactuated wheel cylinder.

The device is not restricted to the brakes of the rear wheels but may also apply to the brakes of the front wheels which, however, are not operated for steering assistance in cross-country driving but are only used when driving on the road.

Nonetheless, a volume compensation is also possible in the hydraulic system for the brakes of the front wheels if the steering brakes are not actuated while, upon the actuation of a steering brake pedal for the purpose of steering assistance in cross-country driving, the braking pressure generated by the master brake cylinder may not act on the brakes of the front wheels.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a cross-sectional view of a steering brake valve for the wheels of the rear axle; and Fig. 2 shows a similar view of a steering brake valve for the brakes of the front and rear axles, the part for the rear axle being a modification of Fig. 1.

Referring to Fig. 1, the brake valve includes a housing 10 in which valve transmission bolts 11 and 12 are arranged in an axially displaceable manner. Transmisison elements 13 and 14 connect these bolts with the brake pedals 1 5 and 16. The brake pedals 1 5 and 16 are movable supported in the centres of motion 1 7 and 18, respectively, at the body 1 9 of the vehicle which is but schematically represented. Springs 21 and 22 keep the brake pedals 1 5 and 16 in the illustrated position.

The transmission rods 23 and 24 enable the actuation of respectively the master brake cylinder 20 and of a brake booster integrated with the master brake cylinder. Upon steering-brakeassisted driving, each brake pedal 15 or 16, may actuate the master cylinder and the brake booster, respectively, independently of the position of the other pedal. When driving on the road, the two pedals are interlocked, thus the master brake cylinder 20 now also being actuated.

The axial travel of the valve transmission bolts is limited by the collars 25, 27 and 26, 28, respectively. In the illustrated position of nonactuated brake pedals 1 5 and 16, the collars 25 and 26 are resting against the housing 1 0. Upon actuation of the brake pedals the valve transmission bolts 11 and 12 are moved to the left and will then abut the housing 10 by means of the collars 27 and 28, respectively. The steering transmission bolts also have extensions 29 and 30 the ends of which have end plates 31 and 22, respectively. The valve transmission bolts 11 and 12, respectively, project into the valve chambers 33 and 34, respectively, by means of their collars 27 and 28, respectively, and of the extensions 29 and 30. Furthermore, the valves 35 and 36 are arranged in these valve chambers.In the illustrated rest position the valves 35 and 36 are closing the openings 37 and 38 provided between an inlet chamber 39 and the valve chambers 33 and 34. The valves 35 and 36, respectively, are hollow, the extensions 29 and 30, respectively, of the valve transmission bolts 11 and 12, respectively, projecting into these cavities. The end plates 31 and 32, respectively, are also in the cavities of the valves. Springs 41 and 42 abut end plates 31 and 32, respectively, and urge the valves into their closed position. Besides the openings 37 and 38, there also are compensating bores 43 and 44 provided between the valve chambers 33, 39 and 34, 39, respectively. These compensating bores provide for possible changes in the volume of the fluid, e.g. in case of temperature differences.

The valves 35 and 36 have pin-like extensions 45 and 46 at their closing sides, these extensions projecting into the inlet chamber 39. In said inlet chamber they abut a balance beam 47. The balance beam 47 is supported on a pivot in the part 49 which features a displaceable and parallel arrangement in respect of the valve bodies and which is loaded by the spring 48 such as to ensure that the balance beam will rest with a slight force against the pin-like extensions 45 and 46.

Besides, a locking plate 50 of a compensating valve is arranged at the part 49, said locking plate closing the two compensating bores 43 and 44 if at least one valve 35 or 36 is opened. The steering brake valve or rather the inlet chamber 39 is connected with the pressure chamber of the master cylinder by means of the connection opening 40. The valve chambers 33 and 34 are communicating with the wheel cylinders of respectively the right and left sides of the vehicle by means of the openings 51 and 52.

The mode of operation of the steering brake valve illustrated in Fig. 1 is as follows.

Upon the actuation of the brake pedal 1 5 for the right-hand side of the vehicle, the valve transmission bolt 11 is axially displaced to the left, the collar 27 coming into abutment within the housing. The valve 35 opens the passage 37 and the pressure generated by the master brake cylinder 20 reaches the wheel brake cylinder of the right wheel via the connection 40, the inlet chamber 39, the open passage 37, the valve chamber 34, and the connection 51. The wheel brake cylinder and the wheel themselves are not represented in this drawing.

Upon the movement of the valve 35 to the left the contact between the balance team 47 and the pin-like extension 45 is maintained. The balance beam thus swings around the point of contact between the pin-like extension 46 and the balance beam 47 (reference numeral corrected by translator). After the opening of the valve 35, the compensating bores 43 and 44 will be locked by the locking plate 50. This measure prevents the pressure prevailing in the inlet chamber 39 reaching the other wheel brake cylinder and cause a braking effect at that point upon a prolonged actuation of the steering brake pedal.

While Fig. 1 discloses a steering brake valve for the brakes of the rear wheels only, Fig. 2 represents a steering brake valve for the brakes of the front and rear wheels. The arrangement of the steering brake pedals and their functions is the same as in Fig. 1. Therefore, the same reference numerals have been used. The master brake cylinder 113 here is a schematically indicated tandem piston brake cylinder wheren the hydraulic volume for the actuation of the rear wheel brake cylinders is separated from that for the actuation of the front wheel brake cylinders.

The housing 110 of the steering brake valve contains the valves for the front and rear wheels.

The transmission elements 13 and 14 connect the steering brake pedals 1 5 and 1 6 with the valve transmission bolts 111 and 112. The valve transmission bolts in Fig. 2 show another design which, however, remains without any influence on the invention. It only serves to illustrate that components of different design may be used in the invention.

The openings 118 and 119 are closed by the balls 114 and 115 arranged in the valve transmission bolts and loaded by the springs 11 6 and 11 7. The locking plates 121 and 122 arranged at the balance beam 120 are touching the balls 114 and 11 5 by means of their pin-like extensions 123 and 124. The design of the locking plates 121 and 1 22 is such as to ensure that upon actuation of one valve, e.g. of the valve 125, the locking plate 121 will close the opening 126 for the compensating bore 129 of the other valve. The pressurized fluid in the inlet chamber 1 31 may reach the connection 134 and hence the right wheel brake cylinder via the line 132 and the open vlave 1 25. The master brake cylinder 113 communicates with the inlet chamber 131 via the connection 1 36. The balance beam 1 20 is pivoted on the pin 137 which is displaceable in the longitudinal direction. The springs 1 38 and 142 which act on the pin 137 via the valve body 139 are loading the pin 137 and hence the balance beam 120.

The spring 138 acts on the valve body 1 39 via the locking plate 140. The locking plate 140 closes the opening 141 for the volume compensation of the brake system of the front wheels if the valve body 1 39 is axially moved for the distance sl. If, however, the valve body 139 is axially moved for the distance s2 the valve cone 143 opens the opening 144. The connection 145 at which the master brake cylinder 113 is connected communicates with the outlet 146 via the open bore 144. The outlet 146 leads to the brake cylinders of the front wheels.

The embodiment of Fig. 2 works as follows: Upon actuation of one brake pedal, e.g. of brake pedal 15, during cross-country driving, the rod 23 actuates the master brake cylinder 113. At the same time, the rod 13 moves the valve transmission bolt 111 to the left, the ball 114 releasing the communication between the inlet chamber 131 and the connection 134, which is connected with the brake cylinder of the right rear wheel. Simultaneously with the axial displacement of the valve 125, the locking plate 121 follows this valve or the ball 114, respectively and closes the opening 127 which is connected with the brake cylinder of the left rear wheel and by means of which a volume compensation is possible in case of changes of volume of the brake fluid.The opening 127 and hence the compensating line has to be closed upon the actuation of one brake pedal in order to prevent the pressure prevailing in the inlet chamber 131 acting on the brake cylinder of the left rear wheel via the compensating line. By having the locking plate 121 follow the valve, the pin 137 also moves axially. Hence the valve body 139 is axially displaced. The valve 139 will be moved for the distance sl, only, if one steering brake pedal is actuated. The locking plate 140 closes the compensating opening 141, thus preventing the pressure generated in the inlet chamber 147 by the master brake cylinder 11 3 acting on the brake cylinders of the front wheels.

However, if during normal driving on a road the two brake pedals 1 5 and 1 6 are interlocked both valve 125 and 126 will axially be moved to the left upon actuation, the balance beam 120 following the balls 114 and 11 5. The axial stroke of the pin 137 and hence of the valve body 139 will correspond to the distance s2. The valve cone 143 will be lifted off the opening 144, hence the connection 145 being connected to the outlet 146 that leads to the brake cylinders of the front wheels. The driver thus need not additionally switch on the front wheel brake system.

Claims

1. A steering brake device for a hydraulically brakable vehicle of the type provided with two brake pedals which act on a common master brake cylinder, the brake device including two control valves each connectible to a respective brake pedal, said control valves being closed in the released position of the brake, and at least one compensating valve which is open in the released position of the brake, wherein, upon actuation of the respective brake pedal, the master brake cylinder is connectible to the right brake cylinder of the vehicular brake system via the one control valve and to the left brake cylinder via the other control valve, wherein the master cylinder is connected to a chamber which serves as a common inlet chamber of the control valves and wherein the compensating valve(s) is (are) so arranged that, upon actuation of a said control valve at least that compensating valve being closed thereby closing the hydraulic path to the nonactuated wheel cylinder.

2. A steering brake device as claimed in claim 1 , wherein the common inlet chamber one or a plurality of closure members of the compensating valves may be pressed against the valve bodies of the two control valves by spring means acting in the direction of the valve bodies of the control valves and may follow the valve body upon the opening of a control valve.

3. A steering brake device as claimed in claim 2, wherein each control valve is coordinated with a spring-loaded closure member of the compensating valve which follows the control valve when the latter is opened and which closes the compensating line of the nonopened control valve.

4. A steering brake device as claimed in claim 2, wherein a closure member of a compensating valve is arranged each on an end of a springloaded balance beam and wherein the balance beam follows the movements of the valve bodies of the control valves.

5. A steering brake device as claimed in claim 2, wherein both control valves are jointly coordinated with a spring-loaded closure member of a compensating valve which is moved by mechanical means such that upon the opening of at least one control valve the compensating lines leading to the two control valves are closed.

6. A steering brake device as claimed in claim 5, wherein a spring-loaded balance beam abuts the valve bodies of the control valves via its two beam ends, and wherein its central area carries the closure member of the compensating valve.

7. A steering brake device as claimed in claim 4, 5 or 6, wherein the axis of rotation of the balance beam is vertical in respect of the plane determined by the longitudinal axis of the two valve bodies of the control valves.

8. A steering brake device as claimed in claim 2, and having a third control valve for the supply of the braking pressure of the master cylinder to the brake cylinders of the vehicle front wheels upon the actuation of both brake pedals of the vehicular brake system, wherein means are provided for closing the compensating bore for the brake cylinders of the front wheels if one brake pedal is applied and for opening the connection between the master brake cylinder and the wheel brake cylinders of the front wheels upon the actuation of both brake pedals.

9. A steering brake device as claimed in claim 8, wherein a valve body of the third control valve moves a first distance upon the actuation of one brake pedal whereby the compensating bore for the brake circuit of the front wheels is closed; and wherein the valve body is moved a second distance, larger than the first distance, upon the actuation of both brake pedals, the hydraulic path between the master brake cylinder and the wheel brake cylinders being enabled.

10. A steering brake device as claimed in claim 9, wherein the ends of a spring-loaded balance beam are connected to the brake pedals and wherein the centre of oscillation of the beam moves a first distance upon the actuation of one brake pedal and a second distance upon the actuation of both brake pedals, this movement being transmitted to the valve body of the third control valve.

11. A steering brake device as claimed in claim 8 or 9, wherein the centre of oscillation of the spring-loaded balance beam which carries the closure members of the compenating valves and whose ends follow the valve bodies of the control valves, move a first distance upon the opening of one control valve and move a certain second distance upon the opening of both control valves, this movement being transmitted to the valve body of the third control valve.

12. A steering brake device as claimed in claim 11, wherein the balance beam abuts a pin or bolt which is axially and in parallel displaceable in respect of the longitudinal axis of the valve bodies of the two control valves against one or more springs and which acts on a resiliently supported and likewise axially displaceable valve body of the third control valve, said valve body being so designed that a compensating opening is closed after a first predetermined valve stroke travelled by the transmission pin upon the actuation of one steering brake pedal, and wherein the master brake cylinder and the brake cylinders of the front wheels are connected with one another after a second predetermined valve stroke travelled by the transmission pin upon the actuation of both steering brake pedals.

13. A steering brake device substantially as described herein with reference to Fig. 1 or Fig.2 of the accompanying drawings.

14. A vehicle provided with a steering brake device as claimed in any one of the preceding claims.