GB2071243A

GB2071243A - Dual-circuit Proportioning Valves for Brakes

Info

Publication number: GB2071243A
Application number: GB8104897A
Authority: GB
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1980-03-11
Filing date: 1981-02-17
Publication date: 1981-09-16
Also published as: ES500230A0; JPS56142741A; FR2478001A1; SE447229B; GB2071243B; ZA811080B; SE8100686L; DE3009292A1; BR8101340A; DE3009292C2; ES8202298A1; IT1139022B; JPH0134810B2; FR2478001B1; IT8120287A0

Abstract

A dual-circuit brake-pressure proportioning valve for a vehicle comprising a yoke (15) loaded by a spring (16) and acting on the tappets (11) of a pair of valve control pistons in a housing (13), includes adjustable screws (18) engaging extensions (14) of the yoke to limit tilting movement of the latter in the event of failure of one brake circuit. Holes (17) are provided in the extensions to permit the insertion of an adjusting screw driver. <IMAGE>

Description

SPECIFICATION Brake Pressure Control Valve This invention relates to a brake pressure control valve, for use in the hydraulic dual-circuit brake system of an automotive vehicle of the kind in which a change-over point is determined from the outside by a control force, which has two cylinders each connected in a respective one of the brake circuits, which are arranged in parallel to each other and which house the control pistons, and whose actuating tappets project outwardly on the same end face of the cylinder and abut a joint yoke which is acted upon by the control force from the opposite side.

In a known dual-circuit pressure control valve (as shown, for example, in German Patent Specification GB--OS 20 08 216), the two control pistons are acted upon by the pressure of two separate rear-wheel brake circuits. As soon as the pressure exceeds a predetermined value (change-over point), the two control pistons are moved in opposition to the control force which is preferably generated by a helical spring, thereby causing closure of a valve which is located between the master cylinder and the wheel cylinder. In this way it is achieved that the pressure in the rear-wheel brake cylinders rises more slowly beginning from the change-over point than in the master brake cylinder.

The disadvantage of the known dual-circuit pressure control valves is that the valve closure travels up to the exceeding of the change-over point are comparatively long so that a comparatively large volume is involved for actuating the control piston.

It is, therefore, an object of the present invention to provide a dual-circuit pressure control valve of the kind referred to, in which the valve closure travels of the control valve can be reduced to a minimum in order to decrease the volume input of the control valve to a value as low as possible and, in addition, to guarantee in the event of failure of one circuit an increase of the change-over point of the intact circuit in a simple way.

According to the invention in its broadest aspect there is provided a brake pressure control valve, for use in the hydraulic dual-circuit brake system of an automotive vehicle of the kind in which a change-over point is determined from the outside by a control force, which has two cylinders each connected in a respective one of the brake circuits, which are arranged in parallel to each other and which house the control pistons, and whose actuating tappets project outwardly on the same end face of the cylinder and abut a joint yoke which is acted upon by the control force from the opposite side, characterised in that adjustable stops are located in the housing at a predetermined lateral distance from the actuating tappets in the direction of the connecting line between said tappets, which stops cooperate with corresponding extensions of the yoke in such a manner that the extensions move into abutment with the assigned stop when the associated control valve has been opened and the actuating tappet has descended accordingly.

In this arrangement, the stop is so located that the associated extension comes into abutment with the assigned stop immediately after opening of the valve. Without such stops, comparatively large closure travels of 2,5 to 3 mms, for example, are necessary in order to safeguard a reliable opening even in an unfavourable tolerance situation in case of a change-over pressure increase of the intact circuit being required upon failure of the other circuit. By suitably arranging the stop in accordance with the present invention, the valve closure travel may be adjusted to approximately 0,5 mms without the change-over pressure increase being impaired thereby. This results in an essentially reduced volume input.

With the control valve operating normally, the closure travel is always covered by both pistons at the same time.

The yoke is preferably acted upon by the control force in the middle between the two actuating tappets, the control force being suitably generated by a helical spring acting on the yoke.

When an extension abuts its assigned stop, there is, in accordance with an embodiment of the present invention, an amplification of the control force at the actuating tappet assigned to the other stop. In an expedient manner, this produces an effect to the end that there occurs a simultaneous opening of both valves. This effect is particularly advantageous in the event of failure of the one brake circuit, as a higher braking force is thereby effective in the remaining brake circuit by increasing the change-over force.

The amplification factor brought about by abutment of one of the extensions at the assigned stop should range suitably between 1,2 and 1,4 and amount preferably to about 1,3.

In a preferred arrangement, both stops are spaced equidistantly from the associated actuating tappet, so that equal amplification factors prevail for both control pistons, if the extension remote from said control pistons bears against the assigned stop.

It is particularly advantageous, if the stops are adjustable stop screws which are able to be screwed in corresponding bores of the housing as far as a predetermined depth. Thus, the closure travel of the control piston may be adjusted to the lowest possible value even after assembly of the device. The method of adjustment will be described in detail later on.

To facilitate such adjustment, according to an advantageous embodiment of the present invention, each extension has opposite to the stop screw a bore having a smaller diameter than the screwhead. A screw driver is, for instance, able to be passed through said bore, which screw driver is able to engage in a corresponding slot in the screwhead.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing, which shows a schematical axial sectional view of a dual-circuit pressure control valve outside the control valve's housing in accordance with this embodiment of the present invention.

Located side by side and in parallel to each other in the control valve housing 13 are two control pistons (not shown) whose actuating tappets 11 project from the same wall of the housing 13. Bearing against these tappets are two indentations 19 of a yoke 1 5 which are spaced from each other, the yoke being acted upon symmetrically with respect to the two tappets 11 by a helical spring 1 6 extending between the area of the yoke 1 5 remote from the tappets and a spring abutment 20 secured to the housing 1 3. The spring 1 6 thus exerts a control force K on the yoke 15, the line of application of which force lies midway between the two tappets 11.

Provided on both sides of the yoke 1 5 are extensions 14, which extend beyond the tappets 11 and which co-operate with stop screws 12 screwed into tapped holes of the housing 13. The heads of the stop screws 12 have slots 18 for the insertion of a screw driver. Opposite to the slots 18, bores 17 are provided in the extensions 14 to enable a screw driver to be passed through.

According to this embodiment of the present invention, the distance s between the head of the stop screws 12 and the extensions 14 of the yoke 1 5 is adjusted the following way: Firstly, the valves are urged to their closed position by pressure build-up. In this position, the stop screws 12 are turned, by means of a screw driver inserted through the bores 17, until the defined distance s relative to the extensions 14 of the yoke 1 5 is brought about. The pressure is then decreased, whereupon the extensions 14 of the yoke abut the heads of the stop screws 12. As a result, the valve closure travel of both valves is defined exactly.

The distance of the actuating tappets 11 from the line of application of the control force K is designated by 1,, and the distance of the stops 12 from this line of application is designated by 12 When one of the extensions 14 abuts the associated stop screw 12, the control force acting on the other tappet 11 will increase accordingly by the amplification factor 2.12 V= 12+11 By suitably choosing the distance 12, in particular, it is thus possible to select the desired amplification factor which is important also in the event of failure of one brake circuit, because the braking force in the remaining brake circuit will be increased accordingly above the change-over point.

Claims

1. A brake pressure control valve, for use in the hydraulic dual-circuit brake system of an automotive vehicle of the kind in which a changeover point is determined from the outside by a control force, which has two cylinders each connected in a respective one of the brake circuits, which are arranged in parallel to each other and which house the control pistons, and whose actuating tappets project outwardly on the same end face of the cylinder and abut a joint yoke which is acted upon by the control force from the opposite side, characterised in that adjustable stops are located in the housing at a predetermined lateral distance from the actuating tappets in the direction of the connecting line between said tappets, which stops co-operate with corresponding extensions of the yoke in such a manner that the extensions move into abutment with the assigned stop when the associated control valve has been opened and the actuating tappet has descended accordingly.

2. A brake pressure control valve as claimed in claim 1, characterised in that the yoke is acted upon by the control force in the middle between the two tappets.

3. A brake pressure control valve as claimed in claim 1 or 2, characterised in that the control force is generated by a helical spring acting on the yoke.

4. A brake pressure control valve as claimed in any one of the preceding claims, characterised in that the two stops are spaced equidistantly from the associated actuating tappet.

5. A brake pressure control valve as claimed in any one of the preceding claims, characterised in that the stops are adjustable stop screws which can be screwed into corresponding bores of the housing to a predetermined depth.

6. A brake pressure control valve as claimed in claim 5, characterised in that the extensions are provided opposite to the stop screws with bores having a smaller diameter than the screw head.

7. A brake pressure control valve as claimed in any one of the preceding claims, characterised in that the amplification factor occasioned by abutment of one of the extensions at the associated stop ranges between 1,2 and 1,4 and preferably amounts to 1,3.

8. A brake pressure control valve, for use in the hydraulic dual-circuit brake system of an automotive vehicle substantially as described with reference to the accompanying drawings.