GB2147378A

GB2147378A - Braking pressure control unit

Info

Publication number: GB2147378A
Application number: GB08423321A
Authority: GB
Inventors: Ulrich Zutt
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1983-09-30
Filing date: 1984-09-14
Publication date: 1985-05-09
Also published as: FR2552724A1; FR2552724B1; IT8422910A0; DE3335479C2; BR8404681A; GB2147378B; IT1175761B; DE3335479A1; GB8423321D0

Abstract

A braking pressure control unit is of the kind in which the stepped pistons (14, 15) of the or each proportioning control valves (8, 9) has an effective surface (A1) exposed to the pressure of a control chamber (60, 61) which communicates with the inlet (4) of a brake circuit via a valve seat (32) engageable by an inertia element (33). The control chamber pressure acts on the effective surface (A1) in the control valve closing direction. The inertia element (33) is moved away from its associated valve seat (32) by a sufficient vehicle deceleration. One of the stepped pistons carries an extension (40) forming a stop (41) for the inertia element (33) so that, in the initial unpressurised state, the connection between the control chambers (60, 61) and the inlet (4) is held open, but is closed by the inertia element (33) as the stepped piston is displaced by increasing input pressure before closing of the control valve (8) and is opened again at the set deceleration. Depending on the pressurisation of the effective surface (A1) there will result an increased change-over pressure and a changed reduction ratio for the loaded vehicle and upon failure of the brake circuit. In Fig. 2 (not shown) the inertia value axis is perpendicular to the central valve axes. <IMAGE>

Description

SPECIFICATION Braking pressure control unit This invention relates to a braking pressure control unit for a vehicular pressure-mediumoperable dual-circuit brake system of the kind wherein there is arranged between an inlet connected with a pressure medium source and an outlet from a brake circuit connected with a wheel brake cylinder a control valve with a stepped piston which is pressure-dependently displaceable against a control force acting in the opening direction and which is provided with an effective surface exposed to the pressure of a control chamber, the control chamber communicating with an inlet chamber via a valve device with an inertia element.

Braking pressure control units of this kind serve to reduce the braking pressure at the rear wheel brakes of a vehicle relative to the pressure prevailing at the front wheel brakes and are provided for brake systems featuring a so-called 'diagonal allocation' of the two brake circuits where one rear brake on one side of the vehicle and one front wheel brake on the other side of the vehicle are connected to one brake circuit. As the braking pressure at the brakes on both sides of the vehicle must be the same so as to avoid a deviation of the vehicle during the braking action, it must be ensured in such a braking pressure control unit that, the reduced pressures of the two brake circuits will be the same each time.

What is further aimed at is that in the case of failure of one brake circuit the braking pressure control unit will not reduce the pressure of the remaining operative brake circuit to a greater extent than in the case of an intact brake system in order to ensure that the remaining braking action will be as strong as possible.

Such a braking pressure control unit is known from the German Patent Specification (DE-PS) No. 2,904,046. As shown in that specification, a control valve with a stepped piston is arranged between an inlet chamber connected with a pressure medium source and an outlet chamber of each brake circuit, the outlet chamber being connected with a wheel brake cylinder. The control valve is pressure-dependently displaceable into the closing position against a control force acting in the opening direction. The control force is applied by pressurisation of an effective surface of the stepped piston by the pressure active in a control chamber. The pressure of the control chamber is controlled via a valve device with an inertia element which in dependence on the vehicle deceleration establishes or interrupts the connection between the control chamber and an inlet chamber.If the vehicle deceleration has achieved a certain value the connection will be interrupted. The control valves are arranged in an opposite direction relative to each other, the confronting end surfaces of the two stepped pistons forming the effective surfaces with regard to the control force. The closing movement of the two stepped pistons will bring about a reduction of the volume in the control chamber. A compensating piston dispiaceable against the force of a spring serves to establish a compensation. Because of the deceleration-responsive closure of the connection towards the control chamber the level of the control chamber pressure, and thus the change-over pressure, is variable, yet not the reduction ratio of the control valves. Further, between the confronting stepped piston ends an auxiliary piston is arranged in the control chamber.Upon failure of the brake circuit ensuring pressure medium supply to the control chamber, the auxiliary piston will mechanically prevent the stepped piston of the intact brake circuit from moving into its closing position. The outlet-side pressure of the intact brake circuit will not be reduced. Upon failure of the other brake circuit the braking pressure to be generated for achieving the same deceleration must be doubled, i.e. there will be an increase in the change-over pressure at which the pressure reduction will set in in the intact brake circuit. Upon circuit failure, this braking pressure control unit thus shows a different braking behaviour depending on which of the two circuits has failed. Either, there will be no braking pressure reduction at all or, in case of an increased changeover pressure, there will be the same reduction ratio as in case of an intact brake system.

It is an object of this invention to provide a braking pressure control unit of the kind referred to having improved adaptation to the ideal braking pressure distribution curves.

According to the invention in its broadest aspect, a braking pressure control unit of the kind referred to is characterised in that the effective surface is arranged in such a way as to ensure that the stepped piston is pressurisable in the closing direction by the pressure of the control chamber, in that, in response to a certain vehicle deceleration, the inertia element may be moved away from the valve seat, and in that a device controls a connection between the control chamber and the inlet, which connection is open in the unpressurised state.

With the brake circuits intact, the pressurisation of the effective surface by the control chamber pressure will result in a force constituent opposing the control force. Thus, also due to the other pressurisable surfaces of the stepped piston, there will be a determination of the magnitude of the change-over pressure and of the reduction ratio. There will be an increase in the change-over pressure and in the reduction ratio if there is no pressurisation by the control chamber pressure as is the case, for example, in a loaded vehicle where the inertia element will not re-open the connection between the control chamber and the inlet upon a further deceleration, which connection at first was open and was caused to close by a deceleration still too small.

By means of the invention it will further be achieved that upon circuit failure the braking behaviour will always be the same in the remaining intact circuit irrespective of which of the two brake circuits has failed. Upon circuit failure there will be an increase in the change-over pressure in the remaining intact brake circuit. Further, there will be a change in the reduction ratio. The rate of increase of the reduced outlet-side pressure will exceed the rate of increase in an intact brake system and in an unloaded vehicle.

In an advantageous embodiment it is provided that the device is formed by a stop for a valve body, which stop is displaceable by the stepped piston and by means of which a distance may be established between the valve body and its associated valve seat, and in that the valve body may be caused to abut on its associated valve seat before the closing position of the stepped piston has been reached. Thus, in a simple way, it will be achieved that in the unpressurised state and at the onset of the stepped piston's movement the connection will reliably be kept open, especially if there is a rapid pressure build-up.

A particularly simple embodiment provides that the valve body is the inertia element. This will result in a compact braking pressure control unit with few components.

For the connection between the control chamber and the inlet there may be provided a first valve device with the inertia element and a second valve device operated in parallel with the first one and controlled by the stop.

In this embodiment, there will result a minimum displacement travel of the inertia element and thus a reduction in the response time of the control valves. In a further embodiment it is provided that the second valve device is formed by a spring-loaded ball-type seat valve.

A particularly simple structure with an even control of the two circuits will be achieved by connecting the two control chambers with the inlet of one of the two brake circuits. This will also apply to an embodiment where the two control chambers end in a joint pressure medium channel which may be connected with the inlet and which is provided at one end with the valve seat for the valve body arranged in a pressure medium chamber.

The stop is advantageously formed fast with the control chamber-side end of one of the stepped pistons, penetrates the valve seat and projects into the pressure medium chamber.

A particularly simple and compact structure will be achieved by arranging the stepped piston and the inertia element in alignment one behind the other or by arranging the stepped piston and the second valve device in alignment one behind the other. Further, it may be provided that the pressure medium channel is connected with one front face of a compensating piston whose other front fa.e is pressurised by atmospheric pressure. Thus it will be ensured that there will occur no vacuum in the control chamber which might influence the control behaviour.

In a further embodiment, the control valves are arranged in the same direction, side by side. This permits the application of the control force to the stepped pistons by means of a joint control force device.

A particularly simple embodiment will be provided where the device is designed as a pressure limiting valve arranged between the inlet and the control chamber.

The provision of a throttle between the inlet and the control chamber will improve the kinetic behaviour of the inertia element upon rapid actuation.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a sectional view of one embodiment of a braking pressure control unit; Figure 2 is a further embodiment of a braking pressure control unit; and Figure 3 is a braking pressure diagram of a braking pressure control unit according to Fig.

1 or Fig. 2.

Parts corresponding to one another have been assigned like reference numerals in the different embodiments.

The braking pressure control unit represented in Fig. 1 consists of a housing 1 with a first housing bore 2 having a diameter stepped several times and with a second housing bore 3 stepped several times and extending in parallel with the first one. Ending in the housing bores 2, 3 are bores essentially extending transversely in respect of the longitudinal axes of the housing bores 2, 3 and forming inlets 4, 5 and outlets 6, 7 for the pressure medium as well as a connection bore 28 between the two housing bores 2,3. A further cross bore 29 establishes a communication from the housing bore 3 to the atmosphere. The inlet 4 and the outlet 6 are connected to a first brake circuit I, the inlet 5 and the outlet 7 being connected to a second brake circuit Il of a vehicular pressure-medium-operable brake system. The inlets 4 and 5 each communicate with a front wheel brake and a pressure medium source, the outlets 6 and 7 communicating with the brake of a rear wheel. Between inlet 4, 5 and outlet 6, 7 of each brake circuit a control valve 8, 9 is arranged which acts as pressure reducing valve.

In the assembled braking pressure control unit's position represented in Fig. 1, the housing bores 2, 3 show an inclination towards the vehicle's driving direction indicated by an arrow.

Each control valve 8, 9 has a valve seat 10, 11 kept in rigid abutment on a step of the housing bore 2, 3 by means of a threaded sleeve 12, 1 3 screwed into the open end of the housing bore 2, 3. The step of the housing bore 2, 3 is formed in a section of reduced diameter at the transition of the first section of the housing bore 2, 3, the first section being provided with a thread. The valve seat 10, 11 and the threaded sleeve 12, 1 3 are sealed relative to the housing bore 2, 3. The inlet 4, 5 opens into the housing bore 2, 3 between the threaded sleeve 12, 1 3 and the valve seat 10, 11.

Within the bore of the threaded sleeve 12, 1 3 a portion of a stepped piston 14, 1 5 is guided displaceably and sealed by a gasket relative to the bore. Thus there results an effective surface A3 at each of the stepped pistons 14, 1 5. The control force is applied to the outwardly projecting end of the stepped piston 14, 1 5 by means of a control spring 16, 1 7. The control springs 16, 1 7 other end is supported at the threaded sleeve 12, 1 3. A smaller diameter portion of the stepped piston 14, 1 5 penetrates the valve seat 10, 11 and carries a cup-shaped component 18, 1 9 at the area lying in the smaller diameter section of the housing bore 2, 3.An elastic seal 20, 21 is arranged within the cup-shaped component 18, 19. The outlet 6, 7 ends in this smaller diameter area of the housing bore 2,3.

The seal 20, 21 lies opposite to the valve seat 10, 11. Together with the valve seat 10, 11, the seal 20, 21 forms a valve passage whose effective pressurisable diameter defining the effective surface A2 is larger than the diameter of the stepped piston's 14, 1 5 portion guided in a sealed manner within the threaded sleeve 12, 1 3. A sealing lip 22, 23 at the seal 20, 21 forms a non-return valve opening towards the inlet 4, 5.The stepped piston 14, 1 5 has a porion 24, 25 following the area with the cup-shaped component 18, 1 9. The portion 24, 25 has a diameter A which is smaller than the diameter of the stepped piston portion guided within the threaded sleeve 1 2, 1 3. The portion 24, 25 is guided in a sealed manner within a section of the housing bore 2, 3 whose area ending at the front face of the stepped pistons 14, 1 5 communicates with the inlet 4 of the first brake circuit I and forms a control chamber 60, 61. The housing bore 3 is connected with a pressure medium channel 30 by means of the connection bore 28 connecting the two housing bores 2, 3.The pressure medium channel 30 is formed by an extension of the housing bore 2 and ends in a pressure medium chamber 31. At the orifice, a valve seat 32 is provided which is associated with an inertia element 33 having the shape of a ball.

The ball is movable within the pressure medium chamber 31 in dependence on the deceleration. Via a connection channel 34 extending in parallel with the housing bore 2, the inlet 4 of the brake circuit I communicates with the pressure medium chamber 31 and with a port 35 which, on its part, ends in the pressure medium chamber 31. Connected to the port 35 is the pressure medium line coming from the pressure medium source of the brake circuit I. The port 35 is provided in a cover 36 sealing of the pressure medium chamber 31. Between the port 35 and the ball a guide plate 37 is inserted which is provided with openings 38 for a flow directed on the ball.

The housing bore 2, the valve seat 32, the pressure medium chamber 31, the ball, and the port 35 are arranged in alignment one behind the other.

As opposed to the stepped piston 15, the stepped piston 14 has an extension 40 at its end. The extension 40 penetrates the valve seat 32 with radial play, projects into the pressure medium chamber 31, and forms a stop 41 for the ball by means of which stop, in the unpressurised state, a distance will be established between the areas of contact of ball and valve seat 32.

The end-side portion of the stepped piston 1 5 carries two seals 50, 51, the cross bore 29 ending between them in this section of the housing bore 3. In this way, the demand is complied with which is made with regard to the separation of the media of the two brake circuits.

The connection bore 28 extends from the housing bore 2 to the housing's outside. Near its open end it is provided with a compensating piston 62 sealed relative to the wall of the connection bore 28. One front face communicates with the control chambers 60, 61, the other front face communicating with the atmosphere. The compensating piston 62 may be caused to abut on a stop 63 in the direction of the housing's outside.

In the braking pressure control unit's position represented in Fig. 1, the stepped pistons 14, 1 5 are pressed by the force of control springs 16, 1 7 against a support at the valve seat 10, 11, the support being formed fast with the housing. The valve passages of the control valves 8,9 are open. A distance is established between the ball and the valve seat 32.

A pressure being generated in the two brake circuits I, II of the intact brake system, this pressure will propagate through the inlets 4, 5, the valve passages, and the outlets 6, 7 to the wheel brakes of the rear wheels. Thus, the pressure increase at the outlets 6, 7 at first will follow the line O-A in Fig. 3. The pressure of brake circuit I will also propagate into the control chambers 60, 61 communicating with the inlet 4 and will pressurise the respective effective surface A1 of the stepped pistons 14, 15.

The pressure increasing, the stepped pistons 14, 1 5 will move in the closing direction.

The extension 40 will be moved so far into the pressure medium channel's 30 area surrounded by the valve seat 32 that, before reaching the control valve's 8 closing position, the ball will no longer be able to abut on stop 41 at the front face of the extension 40 but rather will abut on the valve seat 32.

Now, the connection between the control chambers 60, 61 may be interrupted by the abutting of the ball on the valve seat 32.

The vehicle being unloaded, the vehicle deceleration, which will have been achieved before the first closure of the control valves 8, 9 which is introducing the reduction phase, will already be so great that the ball will not have come into abutment on the valve seat 32, but will be found on the guideway inclined towards the driving direction in the pressure medium chamber 31, a distance being maintained in respect of the valve seat 32. The pressure reaching a value Put the change-over pressure for the unloaded vehicle, the control valve 8, 9 will close for the first time. Any further pressure increase at the outlet 6, 7 will take place with a reduced rate of increase m as compared with the pressure increase at the inlet 4, 5. The pressure build-up at the outlet 6, 7 is characterised by the line A-B in Fig. 3.

For the unloaded vehicle, the following ratios will apply: Pu = Control force / A3, with the inlet pressures of the two brake circuits being the same and cor responding to the pressures of the con trol chambers and, until reaching of Pu, also corresponding to the outlet pressures; for the reduction ratio: m = (A2-A3-A1) / (A2-A1) The vehicle being loaded, the vehicle deceleration achieved before the first closure of the pressure control valves 8, 9 will not suffice to lift the ball off the valve seat 32 on which it has come to abut after the displacement of the stepped piston 14. The displacement of the stepped pistons 14, 1 5 will cause a slight vacuum in the control chambers 60, 61. This vacuum will act on the one front face of the compensating piston 62 whose other front face is pressurised by the atmospheric pressure.The compensating piston 62 will therefore move in the direction of the control chambers 60, 61, the pressure in the control chambers 60, 61 thus substantially corresponding to the atmospheric pressure.

For the loaded vehicle, the following ratios will apply:for the change-over pressure: Put = Control force / (A3-A1), until reaching of Pu the inlet pres sures of the two brake circuits being the same and corresponding to the outlet pressures. The control cham bers, however, are not pressurised; for the reduction ratio: m = (A2-A3) / (A2-A1) Upon failure of brake circuit I no pressure will be built up in the control chambers 60, 61. Thus the change-over pressure and the reduction ratio in brake circuit Il will correspond to the change-over pressure Pu and m" of the loaded vehicle, irrespective of whether the vehicle is loaded or unloaded.

Upon failure of brake circuit Il a vehicle deceleration corresponding to the vehicle deceleration with intact brake circuits will not come about until there occurs a doubled pressure build-up by the pressure medium source of the brake circuit I. Thus, before the first closure of the control valve 8, the ball will rest at the valve seat 32, separating the connection between inlet 4 and control chambers 60, 61. In this case, also, there will result the change-over pressure Put and the reduction ratio m' applying to the loaded vehicle, irrespective of the actual loading of the vehicle.

Irrespective of which of the two brake circuits failed, upon circuit failure, altogether, there will always result the same change-over pressure Pu and the same reduction ratio m+.

As opposed to the braking pressure control unit according to Fig. 1, the braking pressure control unit represented in Fig. 2 has a valve device 70 operated in parallel with the inertia valve (valve seat 32), inertia element 33). The valve device 70 is arranged in a pressure medium chamber 74 and is designed as spring-loaded ball-type seat valve comprising the spring 71, the valve seat 72, and the valve ball 73. The housing bore 2 with the stepped piston 14 of the brake circuit I, the pressure medium chamber 74 with the valve device 70, and the port 35 are arranged in alignment one behind the other. The extension 40 of the stepped piston 14 forms a stop means for the valve ball 73. The pressure medium chamber 31 with the inertia element 33 is arranged transversely in respect of the axis of the stepped housing bore 2 and communicates with the port 35 via a connection channel 75. The valve seat 32 for the ball of the inertia valve 32, 33 is arranged at one end of a connection bore 28 between the housing bores 2 and 3, the connection bore 28 running transversely in respect of the axes of the housing bores 2, 3. The compensating piston may be arranged in an extension of the control chamber 61, at the end of the housing bore 3.

By means of the embodiment according to Fig. 2 it is achieved that, the vehicle being loaded, the ball of the inertia valve 32, 33 will not be moved away from the valve seat 32 and thus will not travel a distance until abutting on the valve seat 32 as is provided in the embodiment according to Fig. 1 due to the displacement of the stop 41. Alternatively it will travel but a small distance in the opening direction if there is a sufficient deceleration. This will result in a reduction in the response time. Further, there is no closing distance and thus no influence of closing distance tolerances. For the rest, the mode of operation will correspond to that of the braking pressure control unit according to Fig. 1.

Claims

1. A braking pressure control unit for a vehicular pressure-medium-operable circuit brake system of the kind wherein there is arranged between an inlet connected with a pressure medium source and an outlet from a brake circuit connected with a wheel brake sylinder a control valve with a stepped piston which is pressure-dependently displaceable against a control force acting in the opening direction and which is provided with an effective surface exposed to the pressure of a control chamber, the control chamber communicating with an inlet chamber via a valve device with an inertia element, characterised in that the effective surface (A,) is arranged in such a way as to ensure that the stepped piston (14, 15) is pressurisable in the closing direction by the pressure of the control chamber (60, 61), in that, in response to a certain vehicle deceleration, the inertia element (33) may be moved away from the valve seat (32), and in that a device (40) controls a connection between the control chamber (60, 61) and the inlet, which connection is open in the unpressurised state.

2. A braking pressure control unit as claimed in claim 1, characterised in that the device (40) is formed by a stop for a valve body (33, 73), which stop is displaceable by the stepped piston and by means of which a distance may be established between the valve body (33, 73) and its associated valve seat (32, 72), and in that the valve body (33, 73) may be caused to abut on its associated valve seat (32, 72) before the closing position of the stepped piston has been reached.

3. A braking pressure control unit as claimed in claim 2, characterised in that the valve body is the inertia element (33).

4. A braking pressure control unit as claimed in claim 2, characterised in that for the connection between the control chamber (60, 61) and the inlet there are provided a first valve device (33, 32) with the inertia element (33) and a second valve device (70) operated in parallel with the first one and controlled by the stop (41).

5. A braking pressure control unit as claimed in claim 4, characterised in that the second valve device (70) is formed by a spring-loaded ball-type seat valve (71, 72, 73).

6. A braking pressure control unit as claimed in any one of the preceding claims, characterised in that the two control chambers (60, 61) may be connected with the inlet (4 and 5, respectively) of one of the two brake circuits.

7. A braking pressure control unit as claimed in claim 6, characterised in that the two control chambers (60, 61) end in a joint pressure medium channel (30) which may be connected with the inlet (4) and which is provided at one end with the valve seat (32, 72) for the valve body (33, 73) arranged in a pressure medium chamber (31, 74).

8. A braking pressure control unit as claimed in claim 7, characterised in that the stop (41) is formed fast with the controlchamber-side end of one of the stepped pistons (14) and in that it penetrates the valve seat (32, 72) and projects into the pressure medium chamber (31, 74).

9. A braking pressure control unit as claimed in claim 8, characterised in that the stepped piston (14) and the inertia element (33) are arranged in alignment one behind the other.

10. A braking pressure control unit as claimed in claim 8, characterised in that the stepped piston (14) and the second valve device (70) are arranged in alignment one behind the other.

11. A braking pressure control unit as claimed in any one of the preceding claims, characterised in that the pressure medium channel (30) is connected with one front face of a compensating piston (62) whose other front face is pressurised by atmospheric pressure.

12. A braking pressure control unit as claimed in any one of the preceding claims, characterised in that the control valves (8, 9) are arranged in the same direction, side by side.

13. A braking pressure control unit as claimed in any one of the preceding claims, characterised in that the device is designed as a pressure limiting valve arranged between the inlet and the control chamber.

14. A braking pressure control unit as claimed in any one of the preceding claims, characterised in that a throttle is provided between the inlet and the control chamber.

1 5. A braking pressure control unit substantially as described with reference to the accompanying drawings.