GB2153937A

GB2153937A - Hydraulic brake apparatus

Info

Publication number: GB2153937A
Application number: GB08500211A
Authority: GB
Inventors: Wilhelm Zirps
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1984-02-06
Filing date: 1985-01-04
Publication date: 1985-08-29
Also published as: GB8500211D0; FR2559113A1; DE3404016A1

Abstract

A hydraulic brake apparatus has two individually operable brake pedals (10, 15), which serve to modulate two traction vehicle brakes (14, 19) of a driven rear axle of a traction vehicle. A controlled check valve (23) is arranged between the brake master cylinder (12) operated by the first brake pedal (10), and a trailer brake valve (40). The second brake pedal (15) is operatively associated with the valve opening piston (32) of the valve (23). If the first brake pedal (10) alone is operated, then pressurised medium can flow only to the traction vehicle brake (19), because the valve (23) is closed. If the second brake pedal (15) alone is operated, then the valve (23) is opened. However, because the brake pedal (10) is not operated, no pressurised medium flows through the valve (23). If both brake pedals (10, 15) are operated simultaneously, then the trailer brake valve (40) is operated and the trailer brakes (48) come into operation. The brake apparatus is of simple and compact construction. <IMAGE>

Description

SPECIFICATION Hydraulic brake apparatus Prior art The invention starts from a hydraulic brake apparatus according to the pre-characterising clause of the main Claim. A known brake apparatus of this type has the disadvantage that both the brake cylinders are connected via valves to the trailer brake valve, and the brake pedals are constructed correspondingly.

This makes this construction complicated and its serviceability extremely restricted.

Advantages of the invention In contrast to the above, the brake apparatus according to the invention having the characterising features of the main Claim possesses the advantage that only one commutating valve is necessary, which is connected to both the brake cylinders. The brake apparatus is of simple and compact construction and also suitable for special fields of application.

The rear wheels of the traction vehicle can be operated individually in order to steer the traction vehicle, without the trailer brakes being switched on.

Advantageous further developments and improvements of the features stated in the main claim are possible by the measures enumerated in the subordinate Claims.

Drawing An exemplary embodiment of the invention is illustrated in the drawing and described more fully in the following description. This shows a hydraulic brake apparatus in a diagrammatic view and a detail in section.

Description of the exemplary embodiment On a traction vehicle, not illustrated in greater detail, a first brake pedal 10 is arranged, which operates a brake cylinder 1 2 by means of a linkage 11. A pipe 1 3 leads from the brake cylinder 1 2 to a traction vehicle brake 1 4 of the driven rear axle of the traction vehicle. A second brake pedal 1 5 operates, by means of a linkage 16, a second brake cylinder 17, which is connected via a pipe 1 8 to a second traction vehicle brake 1 9 of the rear axle. The brake pedals 10, 1 5 are operable individually or in common. The traction vehicle brakes 14, 1 9 each influence one wheel of the rear axle of the traction vehicle.

From each of the pipes 1 3 and 18, a pipe 21 or 22 respectively leads to a commutating valve 23, which is constructed as an unblockable non-return valve. It has a housing 24 which exhibits a shouldered central blind bore 25 with a conically convergent bore bottom 26. This bore has two sections 27, 28 of approximately equal diameter, a section 29 of medium diameter located between the latter, and an orifice 30 of minimum diameter, into which the pipe 22 leads. An unblocking piston 32, which is guided to slide with a close fit in the section 28, can influence by its tappet 33 a spherical closing element 34. The shoulder 35 formed between section 29 and section 27 then serves as a valve seat. A duct 36, into which the pipe 21 leads, is constructed in the housing 24 oriented transversely to the blind bore 25 and starting from the section 27.Just behind the section 29, a duct 37 connects the section 28 to a pipe 38, which leads to a modulating head 39 of a trailer brake valve 40.

A pipe 42 leads from the trailer brake valve 40 to a trailer coupling 43 of the traction vehicle. This coupling is coupled to a counterpart 44, arranged on the trailer, which is connected via a pipe 45 to a brake cylinder 46. The brake cylinder 46 is operatively associated via a linkage 47 with both trailer brakes 48 of one trailer axle.

If the brake pedal 10 alone is operated, then pressurised medium flows from the brake cylinder 1 2 via the pipe 1 3 to the traction vehicle brake 14, and via the pipe 21 and the duct 36 into the section 27 of the commutating valve 23. The liquid pressure forces the closing element 34 against the valve seat 35, whereby only the traction vehicle brake 14 is now operated, and any flow of the pressurised medium to the trailer brake valve 40 is prevented. Only one wheel of the driven rear axle of the traction vehicle is braked, so that the traction vehicle turns about this braked wheel and can therefore be steered in the minimum space.

If the brake pedal 1 5 alone is operated, then pressurised medium flows from the brake cylinder 1 7 via the pipe 1 8 to the traction vehicle brake 19, and via the pipe 22 and the orifice 30 into the section 28 of the commutating valve 23. The pressure influences the traction vehicle brake 1 9 and also slides the unblocking piston 32, so that its tappet 33 lifts the closing element 34 from the valve seat 35. However, since the brake pedal 10 is not operated, no pressurised medium flows through the opened commutating valve 23, so that when the brake pedal 1 5 is operated individually, the trailer brake valve 40 is again unmodulated and the trailer brakes 48 are not operated.On the contrary, only the second wheel of the rear axle of the traction vehicle is braked, so that the traction vehicle turns about the second wheel, that is to say, can be steered counter to the direction produced by the traction vehicle brake 1 4.

If both brake pedals 10, 1 5 are operated simultaneously, then the closing element 34 is lifted from its valve seat 35. The pressurised medium flowing from the brake cylinder 12 via the pipe 21 and the duct 36 flows through the opened valve seat 35, through the duct 37 and the pipe 38 to the modulating head 39 of the trailer brake valve 40. The latter is now modulated, so that pressurised medium flows via the pipe 42, the coupling 43 and the pipe 45 to the brake cylinder 46 of the trailer brakes 48, whereby the trailer brakes 48 are operated. This causes the traction vehicle to be braked by means of both traction vehicle brakes 14, 1 9, and the trailer by means of the trailer brakes 48.

Because a pressurised medium exchange in the commutating valve 23 cannot be totally avoided, a common pressurised medium tank 10, not shown, is present for both the brake cylinders 1 2, 1 7. However, in the case of two individual tanks, these may also be connected by a pipe.

Claims

1. Hydraulic brake apparatus for traction vehicle brakes (14, 1 9) operable by brake pedals (10, 15) and for a trailer brake (48) of at least one trailer hitched to a traction vehicle, having a trailer brake valve (40) arranged on the traction vehicle, which can be modulated by at least one brake cylinder (12, 17) operable from one of the brake pedals (10, 15) and is operatively associated with the trailer brake (48), characterised in that the brake pedals (10, 15) are operable individually, that a commutating valve (23) is arranged between a first brake cylinder (12) and the trailer brake valve (40) and that the commutating valve (23) is controllable by a second brake cylinder (17).

2. Apparatus according to Claim 1, characterised in that the commutating valve (23) is an unblockable non-return valve.

3. Apparatus according to Claim 1 and/or 2, characterised in that a blind bore (25) having sections (27 to 30) of different diameters is constructed in the commutating valve (23), that an unblocking piston (32) pressure-loaded by the second brake cylinder (17) is guided slidingly in a first section (28), and that it influences by a tappet (33) a closure element (36) pressure-loaded by the first brake cylinder (12) and resting upon a valve seat (35) formed between sections (27, 29).

4. An apparatus according to one of Claims 1 to 3, characterised in that two brake pedals (10, 15) are provided which are operable in common.

5. An apparatus according to one of Claims 1 to 4, characterised in that the traction vehicle brakes (14, 1 9) are operable individually via the brake pedals (10, 15).

6. An apparatus according to one of Claims 1 to 5, characterised in that the sto rage tanks for the pressurised medium of the brake cylinders (1 2, 1 7) are mutually con nected by a pipe.

7. An apparatus according to one of Claims 1 to 6, characterised in that a common storage tank for the pressurised medium is arranged for the brake cylinders (1 2, 1 7).

8. A hydraulic brake apparatus substantially as herein described with reference to the accompanying drawing.