WO1997015479A1

WO1997015479A1 - Braking force distributing device for a motor vehicle

Info

Publication number: WO1997015479A1
Application number: PCT/SE1996/001362
Authority: WO
Inventors: Lars Bruhn
Original assignee: Feal Ab
Priority date: 1995-10-23
Filing date: 1996-10-23
Publication date: 1997-05-01
Also published as: SE9503713L; SE9503713D0; NO981812D0; SE509013C2; NO981812L

Abstract

The device is intended for a vehicle equipped with fluid operating suspension means, preferably pneumatic suspension means. At least one of the wheel axles of the vehicle is provided with a regulating valve (2) for the supply of brake fluid to the wheels on this axle. According to the invention, the regulating valve (2) is controlled by a control means (1) that includes a pressure chamber (13) which communicates with the suspension means. A pressure surface (20) exposed to the pressure in the chamber (13) can be moved by this pressure, wherein the pressure surface is mechanically connected (16, 18) to the regulating valve (2) for the purpose of adjusting the valve in accordance with the pressure in the suspension means.

Description

BRAKING FORCE DISTRIBUTING DEVICE FOR A MOTOR VEHICLE

The present invention relates to a braking force distributing device of the kind defined in the preamble of Claim 1.

In automotive vehicle braking systems, for instance car braking systems, the brake circuits are normally adapted to achieve a predetermined distribution of the braking force on the front and rear pairs of vehicle wheels, this distribution being adapted to an assumed normal distribution of the vehicle load. However, if the car is loaded in a manner which deviates radically from this assumed normal distribution, e.g. if the vehicle is heavily loaded at its rear, this normalized braking force distribution will not provide the best possible braking effect. In this case, a relatively larger braking effect is desired on the rear wheels of the car.

Devices for compensating uneven loading of a vehicle are known in respect of cars fitted with mechanical suspensions. These devices function to sense load distribution mechanically and actuate mechanical valves in the brake circuits in accordance with the sensed load distribution.

These known devices, however, are relatively complicated and do not provide a satisfactory solution in respect of cars fitted with suspension means that function through the medium of a fluid, for instance pneumatic suspensions.

Accordingly, the object of the present invention is to provide a braking force distributing device which is of simple construction and which is effective in vehicles fitted with this type of suspension.

This object has been achieved in accordance with the invention with a braking force distribution device of the kind defined in the preamble of Claim 1 that includes the special features set forth in the characterizing clause of said Claim.

The control devices are adapted to utilize the pressure increase obtained from the pneumatic suspension devices on that wheel axle which is subjected to an elevated load. The elevated pressure acts on the pressure surface causing the surface to be displaced and to activate, through connecting devices, the brake fluid regulating valve that serves the brakes on the wheels mounted on this axle, so as to obtain an elevated braking action. The use of the pressure increase in the pneumatic springs in this manner provides an immediate and simple solution to the problem of adapting the relative braking force in accordance with load distribution.

The control system of respective axles is suitably activated by the pressure in the springs mounted on the same axle, although it is conceivable to allow the control system to be actuated by the springs adjacent the other axle and to include some form of inverting function in the system.

In one preferred embodiment, the pressure surface is disposed on- a piston, which is preferably connected to the regulating valve via a piston rod.

The aforedescribed embodiments and other advantageous embodiments of the invention will be evident from the dependent Claims.

The invention will now be described in more detail with reference to a preferred embodiment thereof and also with reference to the accompanying drawing, which shows a longitudinal section view of the control device. The illustrated device is intended to be mounted in the proximity of the rear axle of a motor vehicle, for instance a minibus. Shown at the top of the drawing is the actual control device 1 that actuates the schematically illustrated brake fluid regulat- ing valve 2, shown at the bottom of the drawing.

A housing 3 defines together with a cap connected to said housing a cylindrical cavity that has a first large diameter nearest the cap 4 and a smaller diameter spaced therefrom. The cap 4 has an outer diameter which corresponds to the larger diameter of the cylindrical cavity and which seals against the inner wall of the housing 3 through the medium of an O-ring arranged in a groove in the periphery of the cap . The axially outer part of the cap 4 has a smaller diameter such as to form an annular space 6 between the cap 4 and the housing 3 on the outside of the cap. This part of the housing includes a groove on the inside of the housing 3. The annular space 6 between the outer part of the cap 4 and the housing 3 accommodates a locking ring 8 which is snapped into the groove 7 on the inner wall of the housing 3, so as to hold the cap 4 in position.

A piston 9 is mounted displaceably in the cylindrical space of larger diameter between the cap 4 and the housing 3, said piston sealing against the inside of the housing through the medium of an O-ring 10 in a peripheral groove in the piston 9.

Provided on the outer side of the cap 4 is a compressed air connector 11 which is connected to the inside of the cap by means of a passage 12 and thus discharges into the cylindrical space between the piston 9 and the cap 4, this space thus forming a pressure chamber 13 to which the upper side of the piston is exposed, this upper piston side forming a pressure surface 20. The cap 4 is provided on its inner side with a shallow recess or hollow so that the chamber 13 will have a certain volume even when the piston 9 is in its outer position in abutment with the cap 4. Provided on the opposite side of the piston 9 is a mechanical spring 14 which supports against the bottom of the cylindrical space of smaller diameter. The spring 14 presses against the piston 9 via a bushing 15 and thus strives to press the piston into abutment with the cap 4.

Connected to the piston 9 is a piston rod 16 which extends through a transit 17 in the end of the housing 3 distal from the cap 4. The piston rod 16 is connected to an operating rod 18 of the regulating valve 2.

A compressed air conduit 19 connects the compressed-air connector 11 to the pressure cylinder (not shown) of the pneumatic suspen- sion of that wheel axle to which the supply of brake fluid shall be controlled by the valve 2.

The described device functions in the following manner: In the case of normal load distribution, the pressure forwarded from the suspension through the conduit 19 and the passage 12 to the pressure chamber 13 is too low for the downwardly acting force on the upper side of the piston 9 to overcome the upwardly directed force exerted by the spring 14. In this case, the piston will have the position shown in the drawing, which corresponds to a first position of the valve body (not shown) of the valve 2, which represents a brake fluid pressure for normal braking action.

If the load on an axle, in the illustrated case the rear axle, is increased considerably, this will result in a pressure increase in the pneumatic suspension of this axle, which results in a greater downwardly acting force on the piston 9 generated by the aforedescribed system. With a suitably dimensioned spring 14, this force is able to move the piston 9 downwards in the drawing, against the action of the spring. This movement is transmitted via the piston rod 16 to the valve operating rod 18, which therewith moves the valve body to a position corresponding to a higher brake fluid pressure and therewith an elevated braking action on the wheels on this axle, as compared with the normal braking action. The valve may, for instance, have a control range which provides a brake fluid pressure of about 40 bars with respect to the rear wheels when the load on this axle is low and the piston 9 is in its upper position, wherein said pressure can be increased continuously to about 80 bars when the piston is moved downwards as a result of an increasing, sensed axle load. The pressure in the brake circuit for the front wheels is at a constant pressure of about 80 bars.

The brake force is distributed on respective wheel pairs in this way, in accordance with how the load is distributed in the vehicle.

The valve 2 has not been described in detail, because it repre- sents no decisive aspect of the invention. Valves of this kind are well known and constitute standard components that can be used in applying the present invention. Naturally, this does not exclude the use of a valve that has been designed particularly for use in the present context.

The aforedescribed embodiment of the invention is intended solely as an example that illustrates the concept and function of the invention. Different modifications and other concrete solutions are, of course, possible. For instance, the piston may be replaced with a bellows device within the scope of the invention, the limitation of which is defined exclusively by the scope of the following Claims.

Claims

1. A device for distributing the braking force between the wheel axles of a motor vehicle that includes fluid-operating suspension means and has at least two wheel axles, wherein at least one of said axles is allocated a brake-fluid regulating valve (2) which is actuated by control means (1) , wherein said control means (1) includes a pressure chamber (13) which communicates with said fluid-actuated suspension means via conduit means (19) , and which further includes a displaceable pressure surface (20) which is exposed to said pressure chamber (13) , and mechanical connector means (16, 18) which connect said pressure surface (20) with said regulating valve (2) , characterized in that said suspension means include suspension units that are individual for each wheel axle, wherein the pressure chamber (13) of said control means (1) communicates with the suspension unit that is arranged adjacent the wheel axle to which the regulating valve (2) actuated by the control means is allocated.

2. A device according to Claim 1, characterized in that the suspension means are pneumatic.

3. A device according to Claims 1-2, characterized in that the pressure surface (20) is disposed on a piston (9) .

4. A device according to any one of Claims 1-3, characterized in that the connector means includes a rod (16) .

5. A device according to any one of Claims 1-4, characterized in that the pressure surface (20) is actuated by at least one spring

(14) in a direction opposite to the direction of the pressure force exerted by said fluid on said pressure surface (20) .

6. A device according to Claim 5, characterized in that the spring (14) is mechanical.

7. A device according to any one of Claims 1-6, characterized in that the regulating valve adjusts the brake fluid pressure between pressure levels having a pressure ration in the range 1:1.5 to 1:4, preferably 1:2.

8. A device according to Claim 7, characterized in that the pressure levels are 25-50 and 60-100 bars respectively, preferably about 40 bars and about 80 bars respectively.