FR2565184A1 - Hydraulic servo brakes with antiskid control - Google Patents

Abstract

The servo brake pressure is applied to the brake circuits via a control valve (2) operated by the brake pedal linkage. The separate brake circuits are connected to the pressure reservoirs (22) via control valves, with the stored pressure applied to the circuits via non return valves (24). During braking the stored pressure shortens the return path of the brake control piston and hence improves the response of the brake circuit.

Description

 The present invention relates to vehicle braking equipment with an anti-lock system, consisting of a pressure source, a brake pressure control valve actuated by a pedal and a race simulator, at least one closed braking circuit and at at least one master cylinder connected to said circuit and comprising a main piston, a primary chamber connected by a reversing valve to the brake pressure control valve and, in the event of anti-lock, isolated from the latter and connected to a return tank, as well as Jar an emergency brake plunger which, in an emergency, allows the main piston to be moved using the pedal, and a secondary chamber.

 The patent application of the Federal Republic of Germany published under the number 25 31 264 describes an example of embodiment of a vehicle braking equipment for this TV. In this exemplary embodiment, the stroke simulator and in brake pressure control valve are housed in an emergency braking sound, and the emergency braking pusher, entering the primary chamber to move the main piston is t ::; - é on the emergency piston. Such vehicle brake equipment is characterized by high operational safety. t patent application of the Federal Republic of Germany published under number 31 51 292 shows that it is possible to have a race simulator and a brake pressure control valve c next to a spare piston, and to bring together in one piece an emergency brake push button for a main track and a push button for a spare piston. In the aforementioned first brake equipment, excessive slippage of the wheels braked by the firm brake circuit is reduced by reducing 1. pressure in the primary chamber of a master cylinder. The pressure is reduced by controlling a reversing valve, supplying the primary chamber with pressure delivered by a control valve, ie the braking pressure, and causing a translation of the main piston towards the brake plunger. rescue. The brake pressure thus decreases in the secondary chamber. When this pressure reduction the pedal is fully depressed, due to brutal braking in case of panic for example, so that the emergency piston is moved for example main piston hits the emergency brake plunger penetrating deep into the primary chamber. The latter limits the stroke of the main piston with the disadvantage that no sufficient reduction in the braking pressure occurs, in particular in the case of very variable grip of the road. It would certainly be possible to increase by construction the initial distance between the emergency brake plunger and the main piston, but this would result in much longer strokes of the pedal in the event of failure of the pressure source. The guard is then particularly unfavorable.

 According to an essential characteristic of the invention, the braking equipment comprises for each closed braking circuit an accumulator which a filling valve connected to the closed braking circuit makes it possible to fill at least during a risk of blockage, and which '' a non-return valve allows emptying into the closed braking circuit.

The braking equipment according to the invention has the following advantage: a partial volume of the pressure fluid in the closed braking circuit flows in the accumulator, at the latest at the time of a risk of blockage, so that the main piston does not come into contact with the emergency brake plunger in the event of a pressure decrease necessary to reduce the slip of the wheels.

At the end of braking, the accumulator discharges the partial volume into the closed braking circuit. The only hole in the closed brake circuit is a master cylinder breather, closed during braking.

The braking equipment according to the invention thus has great operational safety.

 According to another characteristic of the invention, the filling valve is made in the form of a 2/2 distributor with a hydraulic control input; and said inlet is connected directly to the pressure source. Hydraulic control according to this characteristic is particularly convenient and economical.

 According to another characteristic of the invention, the filling valve is made in the form of a 2/2 distributor with a hydraulic control input and connected to the pressure source and to a return pipe leading to said source. The braking equipment according to this characteristic provides increased braking safety in the event of a failure of the pressure source during normal braking.

 According to another characteristic of the invention, the reversing valve supplying the primary chamber is hydraulically controlled and connected to the pilot valve of the filling valve. This results in economical control of the reversing valve.

 According to another characteristic of the invention, the accumulator consists of a cylinder, a piston and a return spring, and comprises an adjustment piston acting on the piston, against the action exerted by the return spring, and is moving in an adjustment cylinder connected to the pilot valve. This results in a very rapid decrease in the braking pressure in the event of blockage protection.

 Other characteristics and advantages of the invention will be better understood with the aid of the detailed description below of two embodiments and of the appended drawings in which FIG. 1 represents a first embodiment of the braking equipment. vehicle according to the invention; and Figure 2 shows a second embodiment.

 The first exemplary embodiment of the braking equipment 2 represented in FIG. T comprises a known pressure source 3, a valve 4 for controlling the braking pressure, a stroke simulator 5, a cross-member 6, a pusher 7 of pedal, a pedal lever 8, a pedal 9, a cylinder 10, an emergency brake piston '1, a pusher 12, a master cylinder 13, a main piston 1', a spring 15 for returning the main piston, an emergency brake plunger 16, a return tank 17, a first anti-blocking valve 18, a reversing valve 19, two other anti-blocking valves 20, 21, an accumulator 22, a filling valve 23 and a non-return valve return 24. The master cylinder 13, the valves 19, 20, 21 and the accelerator 22 form part of a closed brake circuit I. The emergency brake piston 11 and the anti-lock valve 18 are part of an open brake circuit II.

 A pipe 25 connects the pressure source 3 to a non-return valve 26, which opens towards the valve 4 for controlling the brake pressure, on which it is for example fixed. The brake pressure control valve 4 comprises a control cylinder 27, in which a control piston 28 of known type is movable against the action exerted by a spring 29. A pusher 30 is housed on the side opposite the spring 29. It is movable longitudinally in a guide tube 31 penetrating into the control cylinder 27.

The spring guide tube is fixed on the cross-member 6. Between the latter and the pusher 30 is the stroke simulator 5, produced in the form of a compression spring 32. A seal 33 prohibits the loss of fluid pressure between the tube 31 for guiding the spring and the control cylinder 27. The cross-member 6 is coupled by the pedal plunger 7 to the pedal lever 8, so that the pedal 9 can, by means of the compression spring 32 of the race simulator 5, move the control piston 28 against the action exerted by the spring 29.

 A channel 34 connects the control cylinder 27 to the cylinder 10. The emergency brake piston 11 is movable in the cylinder 10 and provided with seals 35, preventing any loss of pressure fluid. The cylinder. 10 is arranged parallel to the control cylinder 27. The pusher 12 is arranged coaxially with the emergency brake piston 11 and in the extension of the latter, and fixed to the cross-member 6. The cross-member is shown in an initial position, established by a spring 36. The emergency brake plunger 16, of smaller diameter, is arranged coaxially with the plunger 12 and in the extension of the latter. The emergency braking plunger 16 passes through the emergency braking piston 11, with respect to which a seal 37 seals. The master cylinder 13 is disposed in the extension of the cylinder 10 from which it is separated by a partition 38. The emergency brake plunger 16 passes through this partition 38 with respect to which a seal 39 seals. The master cylinder 13 is connected to the return tank 17 by breathers 40, 41.

 The braking circuit II is connected to the cylinder 10 and comprises pipes 42, 43 which, seen from the cylinder 10, are arranged downstream of the anti-lock valve 18 and lead to wheel brake cylinders not shown, assigned for example to a rear axle.

 The reversing valve 19 is produced in the form of a controlled 3/2 electromagnetic distributor and connects, in its neutral position1 the braking circuit II to a primary chamber 44. The latter is located between the partition 38 and the main piston 14 On the side opposite the latter, the master cylinder 13 defines a secondary chamber 45 in which is housed the return spring 15 of the main piston.

The braking circuit I is connected to this secondary chamber 45 and comprises pipes 46 and 47, arranged downstream of its anti-lock valves 20, 21 and leading to wheel brake cylinders not shown, assigned for example to a front axle.

 The accumulator 22 is for example constituted in a known manner by a cylinder 48, a piston 49 movable in the latter and a spring 50 loading the piston 49. The filling valve 23 is made in the form of a 2/2 distributor hydraulically controlled and to do this comprises a hydraulic control input 51. A spring 52 causes the filling valve 23 to pass into its isolation position.

When sufficient hydraulic pressure is applied to the hydraulic control input 51, this filling valve 23 connects the braking circuit I to the accumulator 22. The non-return valve 24 is mounted in bypass on the filling valve 23 and, seen from the accumulator 22, opens towards the braking circuit I. The hydraulic control input 51 is connected by a pipe 53 to the pressure source 3.

 The operation of the vehicle braking equipment is as follows. The pressure source 3 of the braking equipment 2 is connected when the vehicle is put into service. A pressure thus appears in the source 3, propagates through the pipe 53 to the hydraulic control input 51 of the filling valve 23 and brings the latter into its passage position. When the pedal 9 is depressed, the stroke simulator 5 moves the control piston 28 by its spring 32, so that the pressure prevailing in the pipe 25 reaches totally or partially the channel 34 and the cylinder 10, depending on the position of the pedal 9. When the roadway on which the vehicle is traveling has sufficient grip for the instantaneous pressure applied, the pressure prevailing in the cylinder 10 acts in the wheel brake cylinders by the braking circuit II, its anti-lock valve 18 located in the neutral position and the connecting pipes 42 and 43. The reversing valve 19 is in the neutral position shown as long as there is no risk of blockage and thus connects the braking circuit II to the chamber primary 44. The main piston 14 is consequently loaded and moved against the action exerted by the return spring 15. The breather 40 is thus crossed, so that a braking pressure finally appears in the secondary chamber 45.

This pressure propagates in the braking circuit I, crosses the anti-lock valves 20 and 21, then reaches via the lines 46 and 47 of the wheel brake cylinders not shown. Increasing pressure in the circuit. braking I leads the filling valve 23, controlled in its passage position, to apply the braking pressure on the piston .49. This pressure moves the piston 49 against the action of the spring 50. The accumulator 22 then absorbs a volume corresponding to the translation travel of the piston 49 and to its section. After closing the breather 40, the main piston 14 consequently performs a stroke imposed by the capacity of the wheel brake cylinders and by the aforementioned volume, absorbed by the accumulator 22. It is thus easily seen that the main piston 14 must , to produce a well-defined braking pressure, perform a stroke greater than that necessary in the absence of accumulator 22.

There is a distance 54 between the emergency brake plunger 16, also moved by the pedal 9, and the main piston 14 so that the brake valve applies pressure without the pedal plunger 16 reaching the piston 14. When the pedal 9 is released, the main piston 14 returns to the initial position shown and, as a result of the force exerted by the spring 50, the accumulator 22 is emptied into the secondary chamber 45 by the filling valve 23 and / or the non-return valve 24 and the braking circuit I.

 In the event of failure of the pressure source 3 in operation, the spring 52 causes the filling valve 23 to pass into its isolation position. When braking is initiated, the pedal 9 moves, by means of the pedal lever 8, the pedal push button 7 and the emergency brake push button 16, the main piston 14 in order to establish a braking pressure. The filling valve 23 being closed, as previously indicated, the stroke of the main piston 14 is then the same as in conventional type of braking equipment.

 When one of the wheels belonging to the closed brake circuit I tends to lock, that of the anti-lock valves 20, 21 whose corresponding wheel does not risk blocking closes. The reversing valve 19 is simultaneously controlled to pass into its second position.

In the latter, it isolates the primary chamber 44 from the open brake circuit II and establishes a connection between the primary chamber 44 and the return tank 17. This operation of the valves 20 or 21 and 19 however occurs only when a pressure controller 55 incorporated in the source 3 indicates a sufficiently high pressure.

The operation of the reversing valve 19 produces a reduction in the pressure in the primary chamber 44 and consequently a displacement of the main piston 14 towards the emergency brake plunger 16. The braking pressure consequently also decreases in the secondary chamber 45 and that of the anti-lock valves 20, 21 assigned to the wheel presenting a risk of blocking also reduces the pressure in the wheel brake cylinder. As previously indicated, the accumulator 22 absorbs, when the pressure source is operating normally, a volume of the pressure fluid located in the braking circuit I. The distance 54 is therefore greater than in braking equipment not comprising accumulator 22, so that the risk of the main piston 14 drawing on the emergency braking plunger 16, even when, as a result of abrupt depressing of the pedal 9 from its rest position, said plunger 16 performs a stroke relatively large towards the secondary chamber 45. High strokes of the emergency brake plunger 16 may appear in particular in the case of vigorous braking on roads with good grip. The capacity of the accumulator 22 is dimensioned so that even in the case of relatively high translational strokes of the emergency brake plunger 16, the main piston 14 has a sufficient return stroke for a reduction in pressure allowing a new acceleration of the wheel presenting a risk of blocking. The reversing valve 19 is returned to its initial position when this wheel has reached a sufficiently high speed of rotation. As a result, pressure is again directed from the open brake circuit II in the primary chamber 44 and that the anti-lock valve 20 or 21 still open in the brake circuit I provides increased braking force. The other anti-lock valve 2f or 20 is opened again when no risk of blockage is observed. The control of the anti-lock valve 18 of the braking circuit II is carried out in a known manner.

 In the event of failure of the pressure source 3, and for sufficient depressing of the pedal 9, the pusher 12 reaches the emergency braking piston 11, so that an emergency braking pressure also appears in the braking circuit II.

 The second exemplary embodiment of a vehicle braking equipment 2a according to FIG. 2 differs from the example previously described by a pipe 53a connecting the pressure source 3 to a 2/2 electromagnetic distributor 56, serving as a pilot valve.

The hydraulic control input of the filling valve 23 is connected by a pipe 53b to the pilot valve 56. The accumulator 22 of the first embodiment could be connected to this valve 23. The accumulator 22a shown is a development of the accumulator 22 and comprises a cylinder 48a, a piston 49a, a spring 50a and furthermore an adjustment piston 57 housed in an adjustment cylinder 58. The diameter of the adjustment cylinder 58 is greater than that of the cylinder 48a and the adjustment piston 57 is connected to piston 49. The adjustment cylinder 58 has two connections 59 and 60. The connection 59 is connected by a pipe 61 to the pipe 53b. A pipe 62 connects the fitting 60 to a hydraulic control input 63 of a hydraulically controlled reversing valve 19a. This reversing valve 19a is again produced in the form of a 3/2 distributor and is used to transmit the pressure of the circuit braking II to the primary chamber 44 in the case of normal braking or to connect the primary chamber 44 to the return tank 17 in the case of protection against blocking. When a risk of blockage appears on wheels assigned to the closed braking circuit I, the control valve 56 is electromagnetically controlled to its passage position. The pressure source 3 is thus connected by the pipes 53a and 53b to the hydraulic control input 51 of the reversing valve 19, so that the pressure of the braking circuit I loads the piston 48a. The adjustment piston 57 is simultaneously loaded into the adjustment cylinder 58 via the pipe 61 and the connector 59. The two loads produce compression of the spring 50a and the accumulator 22a, as well as the accumulator 22 of the first embodiment, consequently absorbs a volume of pressure fluid, so that in order to achieve a determined decrease in the braking pressure, the main piston 14 must perform a shorter stroke towards the emergency brake plunger 16. The accumulator 22a has the following advantage: a determined volume is necessarily drawn into the closed braking circuit I as a result of the forced translation of its piston 48a by the adjusting piston 57. Simultaneously with the load of the adjusting piston 57, the input 63 for hydraulic control of the reversing valve 19a is loaded by the connector 60 and the pipe 62. Said valve, like the reversing valve 19 of the first embodiment, ensures a decrease ion of sufficient pressure to accelerate a wheel presenting a risk of blocking. The braking equipment 2a has the advantage that the accumulator 22a is only filled in the event of protection against blocking. A relatively short stroke of the pedal 9 is therefore sufficient for emergency braking in the event of failure of the pressure source 3 during braking. The hydraulic control of the reversing valve 19a has the advantage of allowing the use of an electrical circuit, used to actuate in the first embodiment the reversing valve 19 with electromagnetic control. In the second embodiment, an electromagnet 64 of the pilot valve 56 is connected, instead of an electromagnet of the reversing valve, to an electrical control.

When a risk of blocking disappears, the pilot valve 56 returns to its initial position, so that the valves 19a, 23 and the piston 48a each return to its initial position. The pressure fluid which is no longer needed is returned to the pressure source 3 by the pilot valve 56 and a return line 65. After the end of braking, the accumulator 22a is emptied by the non-return valve 24 in the circuit. brake I and the secondary chamber 45.

 Finally, it should be specified that, in addition to the master cylinder 13, it is possible to incorporate a master cylinder for another closed braking circuit, with an accumulator 22. The master cylinder 13 can then for example be connected to a left front wheel brake and the master cylinder added to a right front wheel brake.

The two master cylinders can be arranged one behind the other, as indicated for example in the patent application of the
Federal Republic of Germany published under number 29 08 480. It is also possible to have three master cylinders one behind the other for three closed brake circuits and to equip each of these circuits with an accumulator 22.

 Of course, various modifications can be made by those skilled in the art to the principle and to the devices which have just been described only by way of nonlimiting examples, without departing from the scope of the invention.

Claims (5)

Claims 1. Vehicle braking equipment with an anti-lock system, consisting of a pressure source, a brake pressure control valve actuated by a pedal and a racing simulator, at least one closed braking circuit and at least one cylinder connected to said circuit and comprising a main piston, a primary chamber connected by a reversing valve to the brake pressure control valve and, in the event of anti-lock, isolated from the latter and connected to a return tank, thus only by an emergency braking plunger which, in an emergency, makes it possible to move the main piston using the pedal, and a secondary chamber, said braking equipment (2, 2a) being characterized in that it comprises for each closed braking circuit an accumulator (22, 22a) which a filling valve (23) connected to the closed braking circuit (I) makes it possible to fill at least during a risk of blocking and a non-return valve -back (24) allows vacuum r in the closed braking circuit (I). 2. Vehicle braking equipment according to claim 1, characterized in that the filling valve (23) is produced in the form of a 2/2 distributor with a hydraulic control input (51); and said inlet (51) is connected directly to the pressure source (3). 3. Vehicle braking equipment according to claim 1, characterized in that the filling valve (23) is produced in the form of a 2/2 distributor with a hydraulic control input (51) and connected to an electromagnetic pilot valve (56), connected to the pressure source (3) and to a return line (65) leading to said source. 4. Vehicle braking equipment according to claim 3, characterized in that the reversing valve (19a) supplying the primary chamber (44) is hydraulically controlled and connected to the pilot valve (56) of the filling valve (23 ). 5. Vehicle braking equipment according to claim 3, characterized in that the accumulator (22a) consists of a cylinder (48a), a piston (49a) and a return spring (50a) and comprises an adjustment piston ( 57) acting on the piston (49a), against the action exerted by the return spring (50a), and moving in an adjustment cylinder (58) connected to the pilot valve (56).