Abstract:
A hydraulic valve is adapted to be connected between a pressurized supply line and first and second lines feeding respective first and second circuits with different functions, such as the steering and braking functions of an automobile vehicle. It comprises a first control member adapted to connect the supply line to the first feed line, a two-way distributor device for the second feed line and a second control member adapted to apply to the second feed line a pressure proportional to the force exerted by the user damped by virtue of a dashpot effect.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns a hydraulic control valve that can be used in a hydraulic circuit to perform two functions using a single hydraulic pump. It is more particularly, although not exclusively, concerned with a valve designed to be fitted to the hydraulic circuit of an automobile vehicle to enable simultaneous or independent supply of a hydraulic steering system and a system for braking the wheels of the vehicle. 
     2. Description of the prior art 
     In known hydraulic circuits it is common practise to use a hydraulic pump for each of the functions to be performed. This results in a relatively high unit cost for the installation. 
     The object of the invention is to avoid these disadvantages by providing a valve for controlling one of the two functions (braking, for example) of a two-function circuit supplied by a single hydraulic pump. 
     The device in accordance with the invention is naturally designed to be 100% safe, guaranteeing independent functioning of the two circuits. 
     SUMMARY OF THE INVENTION 
     The present invention consists in a hydraulic valve adapted to be connected between a pressurized supply line and first and second lines feeding respective first and second circuits with different functions, said valve comprising: 
     a first control member adapted to connect said supply line to said first feed line; 
     a two-way distributor device for said second feed line; and 
     a second control member adapted to apply to said second feed line a pressure proportional to the force exerted by the user damped by virtue of a dashpot effect. 
     The invention will now be described in more detail and by way of non-limiting example only with reference to the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a hydraulic circuit diagram showing the principle of the connection provided by a control valve in accordance with the invention. 
     FIG. 2 is a longitudinal cross-section through the valve in question when it is in a neutral position, that is to say when the steering circuit is connected continuously and the braking circuit is not operated. 
     FIG. 3 is an analogous cross-section when the user operates the braking circuit, the steering circuit continuing to be supplied as usual. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The equipment shown in the drawings comprises a hydraulic pump 1 adapted to feed oil under pressure into an outlet line 2 from which it can be distributed to a line 3 controling the steering circuit of a vehicle and/or to a line 4 controling the braking circuit of the same vehicle. 
     The pump 2 takes up oil from a reservoir 5 and discharges it towards a point 6, at a pressure with a maximum value in the order of 140 bars, for example. An adjustable pressure relief valve 7 is provided on a branch connection from the point 6: if operated because of excess pressure, the excess oil is returned to a reservoir 8. Beyond the point 6 the link 2 feeds the control valve 9 in accordance with the invention to feed the steering line 3 and/or the braking line 4. 
     The control valve 9 (see FIGS. 2 and 3) comprises three functional subsystems: 
     a steering control member 10 which connects the supply line 2 to the steering circuit 3 according to the known principle of an open center upstream circuit; 
     a two-position distributor device 11 for braking; 
     a braking control member 12 adapted to apply to the braking circuit 4 a pressure proportional to the force exerted by the driver on the brake pedal, with a dashpot type damper. 
     To this end the control valve 9 comprises a body 13 inside a bore 44 within which a hollow cylindrical main piston 14 can slide. The main piston ends with a head 15 around which slides the sleeve of a valve member 16 the rear end of which has a helical compression spring 17 bearing against it. The spring has thrust applied to it by a ring 18 in abutting engagement with a flange 19 on a plunger 20 whose rear end passes out through a fixed cap 21 closing off the body 13. 
     A seal 22 ensures that the sliding of the plunger 20 in the cap 21 is fluid-tight. 
     Inside the ring 18 a calibrated helical spring 23 is compressed between the flange 19 of the plunger 20 and the rear end 24 of the head 15 of the main piston 14. 
     A piston 25 slides inside the cylindrical front part of the main piston, its cross-section being calculated to balance the annular cross-section of the valve member 16 lying between: 
     its guide diameter 26 on the main piston 14, and 
     its guide diameter 27 in the body 13. 
     The piston 25 also delimits a damper chamber 28 at the back of the blind bore within which it slides inside the main piston 14. Its foot 29 bears against a fixed screwthreaded plug 30 which closes off the body 13. 
     Four annular grooves are formed in the body 13 along the length of the main piston 14, namely: 
     a groove 31 connected to a brake return line 32; 
     a groove 33 connected to the brake line 4; 
     a groove 34 connected to the pressure inlet line 2; and 
     a groove 35 connected to the steering line 3. 
     Lateral holes 36 and 37 formed in the hollow cylindrical wall of the main piston 14 are provided at the locations of the grooves 31 and 33, respectively, and they can be closed off in whole or in part by fluid-tight sliding within the bore of the stator body 13. 
     A circular edge 38 is provided on the outside of the main piston 14 to maintain communication between the grooves 34 and 33 to a more or less restricted degree (FIG. 3) or to isolate them from each other (FIG. 2), by virtue of fluid-tight sliding within the body 13. 
     Operation is as follows: 
     The equipment makes it possible to perform two functions using a single pump: 
     (1) to feed a steering system 3 with a specified maximum pressure, for example 140 bars; 
     (2) to feed a brake circuit 4 with a pressure: P break  =f (force on pedal), with a maximum brake pressure that can be less than the steering system pressure, for example 90 bars. 
     These two functions may be performed independently or simultaneously. 
     The pressure feed to the brakes is obtained at 4 by means of a calibratable pressure reduction member 12. The upstream circuit 2 which feeds the steering function being of the open center kind, the feed to the pressure reducer 12 is obtained by means of a calibratable valve type system (FIG. 1). 
     FIG. 2 shows the valve 9 in the unoperated position. In the absence of any force on the plunger 20 the groove 33 of the brake circuit is connected to the brake return groove 32 through the intermediary of the lateral holes 36 and 37 in the main piston 14. The valve member 16 bears against the cap 21. There is thus a free passage between the pressure inlet groove 34 and the groove 35 connected to the steering function 3, whereas the passage between the pressure inlet groove 34 and the brake groove 33 is closed off by the main piston 14. 
     In this configuration passage is provided from the pump 1 to the steering function 3, the brake function 4 being connected to the return line 32 (FIG. 1). The piston 25 serves to balance the annular cross-section of the valve 16 between the diameters 26 and 27. Also, the piston 25 procures dynamic balancing of the main piston 14 by virtue of the dashpot effect. 
     The whole corresponds to a dead travel 39 (FIG. 2). 
     FIG. 3 shows the valve in the braking position. When a force is applied to the plunger 20 the compression of the spring 17 situated between the ring 18 and the valve member 16 causes a rise in pressure in the pressure inlet groove 34 such that: 
     
         Pe×Sc=Kl×X 
    
     in which: 
     Pe=inlet pressure in groove 34; 
     Sc=annular cross-section of valve member 16 between guide diameters 26 and 27; 
     K1=thickness of spring 17; 
     X=travel of plunger 20 - dead travel 40. 
     At the same time, compression of the spring 23 displaces the main piston inside the body 13. The lateral holes 36 in the main piston 14 are then closed off, preventing coupling of the brake groove 33 to the brake return groove 31/32. The lateral holes 37 continue to provide a coupling between the brake groove 33 and the chamber 31 formed in the body 13 around the foot 29. The hydraulic braking of the edge 38 then authorizes movement of the pressure inlet groove at the orifice 34 towards the braking groove 33, and this in such a way that: 
     
         P.sub.break ×ST=K2×X 
    
     where: 
     ST=annular cross-section of main piston 14 between the outside diameter of main piston and the diameter of piston 25; 
     K2=thickness of spring 23. 
     When this condition is satisfied, the main piston 14 moves back and the edge 38 cuts off the passage from 34 to 33. The lateral holes 36 are still not uncovered and so continue to close off the passage from 33 to 31. The brake pressure is therefore proportional to the force on the plunger 20. 
     In the braking position the connection from the pressure inlet 34 to the steering function 35 is still provided by the passage corresponding to lifting of the valve 16 relative to the edge 42 of the body 13. 
     The equipment in accordance with the invention has the following advantages: 
     it enables simultaneous or independent supply of a hydraulic steering system and a braking system using a single pump, 
     it enables pressure limiting in the braking circuit to a known valve, compatible with the durability of the braking system seals; and 
     it enables progressive braking according to the force on the pedal.