DE102015007927A1 - Automotive brake system - Google Patents

Abstract

A vehicle braking system includes at least one wheel brake cylinder (17-20), a source of pressurized fluid (23-25) and a stepped piston (27) from which a first piston surface (42) defines a first working chamber (28) communicating with the source of pressurized fluid (25) and a second piston surface (43) defining a second working chamber (29) communicating with the wheel brake cylinder (17-20) and a valve (32) for controllably opening and closing a connection between the working chambers (28, 29). On an input instrument (1), a sensor (21) for detecting the amount of operation of the input instrument (1) by a driver is arranged, and an electronic control unit (22) is arranged to connect the pressure fluid source (25) in accordance with the operation of the input instrument (1 ) to control.

Description

The present invention relates to a brake system for a motor vehicle having at least one engaging on a wheel of the motor vehicle wheel brake cylinder, a pressure fluid source and a stepped piston, of which a first piston surface defining a communicating with the pressure fluid source first working chamber and of which a second piston surface communicating with the brake cylinder limited second working chamber, as well as with a valve for controlled opening and closing of a connection between the working chambers. Such a brake system is out EP 2 460 717 A1 known.

As a source of pressurized fluid which supplies pressurized fluid needed to adjust the step piston to the working chambers, a conventional brake handle is proposed.

Conventionally, in such brake systems, a restoring force of the brake handle, which the driver has to overcome during braking, provides this with information about the vehicle deceleration to be expected in the current position of the brake handle. The higher the force applied to actuate the brake handle, the higher the pressure of the pressure fluid in the brake system, and the stronger the frictional force between a brake lining of the wheel brake cylinder and the wheel braked thereby.

Off at the brake system EP 2 460 717 A1 can be realized by opening and closing the valve different ratios between the brake lever and the wheel brake cylinder. This makes it possible to initially move the brake cylinder relatively far with a small movement of the brake handle and to close a gap between brake pads and brake disc quickly. However, as soon as this gap is closed, the pressure of the pressure fluid and consequently also the counterforce of the brake handle increases sharply until the valve closes and the transmission ratio thereby abruptly decreases. Corresponding to the reduced transmission ratio, the counterforce of the brake handle increases more slowly, giving the driver the impression that the brake is not engaged, and can cause a feeling of uncertainty. In addition, the brake is already effective even when the valve is open and the driver experiences a relationship between the force exerted by him on the brake lever force and the resulting vehicle deceleration in this state and involuntarily assumes that this relationship still applies even if he the force on the brake handle increases. However, if the increase in force causes the valve to close, then there is more vehicle deceleration than expected.

The advantages of the known brake system, early onset of braking due to the rapid closing of the gap between the brake disc and brake pads and at the same time the ability to build a strong braking force between the brake pads and brake disc, therefore, with an increased probability that the driver by the effect of Brake system is irritated and reacts incorrectly.

An object of the present invention is to develop such a brake system so that an irritation of the driver is excluded.

The object is achieved according to an embodiment of the invention by limiting in a motor vehicle brake system with at least one wheel brake cylinder, a pressure fluid source and a stepped piston, of which a first piston surface communicates with the pressurized fluid source first working chamber and of which a second piston surface with a Wheel valve associated with the second working chamber limited, and with a valve for controlled opening and closing a connection between the working chambers on an input instrument, a sensor for detecting the extent of operation of the input instrument is arranged by a driver and an electronic control unit is set, the pressure fluid source according to the operation of the input instrument. The electronic control unit thus decouples the counterforce that the driver senses when operating the input instrument, the pressure of the pressure fluid, so that a change in the ratio of the stepped piston when closing or opening the valve is not perceived by the driver and thereby not cause irritation can.

The source of pressurized fluid should suitably be driven by a motor controlled by the electronic control unit.

The valve may conveniently be controlled by the pressure in one of the working chambers.

The degree of actuation of the input instrument detected by the sensor may be given by the deflection of the input instrument from a rest position or by a restoring force acting on the input instrument in the rest position. In one case, for example, the sensor may be a displacement sensor disposed on the input instrument or on a mechanical component moved by the input instrument; in the other case, it could also be a pressure sensor which detects the pressure of a fluid pressurized by the operation of the input instrument.

While the amount of actuation sensed by the sensor may optionally be a displacement or a force, the haptic feedback required by the driver on the extent of actuation should preferably be in the form of a force. To provide them, therefore, a return element should be provided which exerts a return force acting on the input instrument in its rest position, this restoring force increasing with the extent of the actuation over the entire actuation path of the input instrument.

The second working chamber may, in particular in a vehicle with more than two wheels, communicate with brake cylinders on a plurality of wheels of the vehicle.

The source of pressurized fluid and the stepped piston are preferably integrated into a common assembly which may be provided on a chassis of the vehicle, separate from the wheels.

In particular, a master cylinder with a piston driven by a motor is considered as the source of pressure fluid. In particular, the piston can be driven by a threaded spindle.

The control unit can then each set a desired position of the piston, to which the piston is driven at a given extent of the operation of the input instrument. This determination may be based on a characteristic curve that sets the target position as a function of the operation of the input instrument so that a substantially linear relationship between actuation and vehicle deceleration results. For this purpose, the characteristic curve must have different slopes on both sides of and beyond the position at which the valve switches.

According to a preferred alternative, instead of a set position of the piston, the control unit sets a target torque of the piston driving motor, or technically equivalent, a set pressure in the master cylinder as a function of the amount of actuation. The target torque is particularly easy to set by controlling the power supply of the motor. Again, a substantially linear relationship between actuation and vehicle deceleration can be realized by the characteristic curve has different slopes on different sides of the torque or pressure at which the valve switches.

The input instrument may comprise a cylinder having a third working chamber connected to at least one of the wheel brake cylinders via a valve which is closed upon application of supply energy and open in the absence of supply energy. As long as the supply energy is applied, the valve keeps the third working chamber separated from the wheel brake cylinder. In the case of a loss of supply energy, however, it establishes such a connection, so that in the event of a fault, the wheel brake cylinder can be actuated directly via the cylinder of the input instrument.

Between the second working chamber bounded by the stepped piston and the wheel brake cylinders, a valve should then be provided which is open when supply energy is present but closed in the absence of the supply energy in order to prevent an outflow of pressurized fluid from the wheel brake cylinders to the second working chamber in the event of a malfunction.

The input instrument may further include a relief chamber into which pressurized fluid may escape from the third working chamber upon actuation of the input instrument.

In a line which connects the discharge chamber to the third working chamber, a valve should then be arranged which, although open in the presence of supply energy, is closed in the absence of the supply energy, in this case the transition of pressurized fluid displaced from the third working chamber to force the at least one wheel brake cylinder.

Two third working chambers, each associated with different wheel brake cylinders, may be housed together in the cylinder of the input instrument and separated from each other by a movable partition.

The object is further achieved by a motor vehicle, in particular a four-wheeled motor vehicle, with a brake system of the type described above.

Further features and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying figures. Show it:

1 a block diagram of the vehicle brake system according to the invention with a stepped piston in the rest position;

2 the stepped piston in a low-deflected state, with an open valve; and

3 the stepped piston in a widely deflected state, with a closed valve.

1 shows a block diagram of a vehicle brake system according to the invention. An input instrument 1 with which the driver sets a desired vehicle deceleration, here includes a brake pedal 2 and a control cylinder 5 , The brake pedal 2 is via a piston rod 3 with an outer piston 4 of the control cylinder 5 connected. The control cylinder 5 has two working chambers, an outer working chamber 6 between the outer piston 4 and an inner piston 7 , and an inner working chamber 8th beyond the inner piston 7 ,

At least one of the two working chambers 6 . 8th , in the case of 1 the outer working chamber 6 , is over a normally open valve 9 with a discharge chamber 10 connected in the case of actuation of the brake pedal 2 from the outer working chamber 6 displaced pressurized fluid can flow out. A feather 11 on a moving piston 12 the discharge chamber 10 acts, generates one of the operation of the brake pedal 2 counteracting, proportional to the amount of the displaced pressure fluid restoring force.

The outer working chamber 6 is also a valve 13 with a branch 46 connected, from which the lines of the brake system each have a further valve 35 to a wheel brake cylinder 17 a left rear wheel or via a valve 36 to a wheel brake cylinder 18 a right front wheel of the vehicle extend. Accordingly, a line extends with a closed valve in normal operation 14 from the inner working chamber 8th to a branch 47 and from there via a valve 37 to a wheel brake cylinder 19 a right rear wheel or via a valve 38 to a wheel brake cylinder 20 a left front wheel of the vehicle. The valves 13 . 14 are closed in normal operation; Therefore, in normal operation, the inner piston 7 immovable, and only the volume of the outer working chamber 6 is by pressing the brake pedal 2 variable.

Every wheel brake cylinder 17 - 20 is a valve 48 - 51 assigned to him with a low pressure reservoir 44 combines. The valves 48 - 51 can be individually opened in a conventional manner to reduce the braking force on a single wheel brake cylinder as part of an ESP or ABS function; at the same time then the same wheel brake cylinder associated valve from the group of valves 35 - 38 closed to prevent a system-wide drop in brake pressure.

A sensor 21 is at the steering cylinder 5 attached to by measuring the displacement of the outer bulb 4 in or by measuring it in the chambers 6 . 8th resulting pressure the extent of operation of the brake pedal 2 to be detected by the driver and sent to an electronic control unit 22 to hand over.

An output of the control unit 22 feeds and controls an electric motor 23 , The rotation of the electric motor 23 drives a threaded spindle 24 at the same time the piston rod of a master cylinder 25 is.

In a housing 26 is a cavity formed with two sections of different cross-sectional area. A stepped piston 27 divides this cavity into a first working chamber 28 with large cross-section, on one side by a large cross-sectional area 42 of the stepped piston 27 is limited, a second working chamber 29 with a small cross-section, bounded by a small cross-sectional area 43 of the stepped piston 27 , and an equilibrium volume maintained at ambient pressure 30 , which has a central area of the stepped piston 27 surrounds. The first working chamber 28 communicates with the master cylinder 25 , so from the master cylinder 25 displaced pressurized fluid into the first working chamber 28 overflow and while the stepped piston 27 against the force of one in the equalization volume 30 accommodated coil spring 31 can push back. The second working chamber 29 is over open valves in normal operation 15 . 16 with the branches 46 respectively. 47 connected.

One the working chambers 28 . 29 connecting valve 32 is formed by a axially through the stepped piston 27 extending passage 33 and one in the passage 33 extending, axially movable pin 39 ,

In the position of 1 is the valve 32 open, so in both working chambers 28 . 29 the same pressure prevails. To the extent that in the pressure fluid from the master cylinder 25 in the first working chamber 28 pumped in, it flows out of the second working chamber 29 over the valves 15 . 16 and 35 - 38 to the wheel brake cylinders 17 to 20 from. The pressure of the pressurized fluid remains low as long as the wheel brake cylinders 17 to 20 can yield to the influx of pressurized fluid by narrowing a gap between the brake disc and brake pads. If this is no longer possible, because the brake pads of the wheel brake cylinder 17 to 20 begin to touch their associated brake discs, is the capacity of the wheel brake cylinder 17 to 20 essentially exhausted. Pressure fluid, which is still out of the wheel brake cylinder 25 is displaced, can only find space by the elastic lines of the brake system and expands in the housing 26 the stepped piston 27 shifts so that the volume of the first working chamber 28 at the expense of the second working chamber 29 and the compensation volume 30 increases.

The one in the passage 33 of the stepped piston 27 recorded pen 39 carries at his second working chamber 29 facing the end of a thickened head 40 , The passage 33 is locally constricted to a valve seat 41 to build. The pencil 39 follows, as in 2 to see the relocation of the stepped piston 27 initially, with increasing pressure of the pressure fluid, so that the passage 33 remains open and the pressures in the working chambers 28 . 29 stay the same.

Only when as in 3 shown the head 40 to the valve seat 41 abuts, the valve closes 32 , so that different pressures in the working chambers 28 . 29 can adjust. The pencil 39 gets from that towards the working chamber 29 advancing step piston 27 taken; at the same time, by the pressure, which is now in the second working chamber 29 is higher than in the first one 28 , the head 40 at the valve seat 41 kept pressed tight. A balance arises when the pressure in the working chamber 29 by a factor higher than the pressure in the working chamber 28 that is the ratio of large cross-sectional area 42 to the small cross-sectional area 43 of the stepped piston 27 equivalent. The torque that the electric motor 23 must apply to a predetermined pressure in the wheel brake cylinders 17 to 20 to generate, is therefore with closed passage 33 according to the ratio of the to the chambers 28 . 29 adjacent areas 42 . 43 of the stepped piston 27 reduced, so even with limited torque of the engine 23 a high brake pressure in the wheel brake cylinders 17 to 20 can be built.

On the restoring force, the driver when pedaling the brake pedal 2 feels, this has no effect, as this restoring force in the spring 11 is produced.

In case of a fault, because of the electrical supply to the valves 9 . 13 - 16 . 35 - 38 . 48 - 51 due to a failure of the electrical system is omitted or because it is interrupted by a control unit due to a otherwise diagnosed defect, the valve closes 9 , so in case of operation of the brake pedal 2 a drainage of pressurized fluid to the discharge chamber 10 is no longer possible. At the same time the valves open 13 . 14 , and the valves 35 - 38 stay in their normally open state, allowing the pressurized fluid from both working chambers 6 . 8th of the cylinder 5 to the wheel brake cylinders 17 to 20 can drain away. The simultaneously closed valves 48 - 51 prevent escape of the pressurized fluid to the low pressure reservoir 44 , So a purely hydraulic braking is possible.

To simplify the installation of the brake system in a motor vehicle, the electric motor 23 , the master brake cylinder 25 , the case 26 and the valves 9 . 10 . 13 - 16 . 35 - 38 . 48 - 51 , preferably also the control unit 22 in a unit 45 be summarized, which can be pre-assembled outside the vehicle and then installed as a whole. Possibly. can also control the cylinder 5 and / or the discharge chamber 10 in this unit 45 be included. In particular, the assembly may comprise a metal block in which the working chambers 6 . 8th . 28 . 29 and possibly the control cylinder 5 or the discharge chamber 10 and the valves receiving chambers are formed as holes.

It should be understood that the foregoing detailed description and drawings, while indicating certain exemplary embodiments of the invention, are intended for purposes of illustration only and are not to be construed as limiting the scope of the invention. Various modifications of the described embodiments are possible without departing from the scope of the following claims and their equivalence range. While it has been assumed in the foregoing description that the wheel brake cylinders cooperate with disc brakes, drum brakes or brakes, of course, are contemplated in which a brake pad of a wheel brake cylinder is separated at rest from a rotating friction surface of the wheel through a gap and brakes the gap is closed and the brake pad is pressed against the friction surface.

In particular, this description and the figures also show features of the embodiments which are not mentioned in the claims. Such features may also occur in combinations other than those specifically disclosed herein. Therefore, the fact that several such features are mentioned in the same sentence or in a different type of textual context does not justify the conclusion that they can occur only in the specific combination disclosed; instead, it is generally to be assumed that it is also possible to omit or modify individual ones of several such features, provided this does not call into question the functionality of the invention.

LIST OF REFERENCE NUMBERS

1

input tool

2

brake pedal

3

piston rod

4

outer piston

5

control cylinder

6

third / outer working chamber

7

inner piston

8th

third / inner working chamber

9

Valve

10

relief chamber

11

feather

12

piston

13

Valve

14

Valve

15

Valve

16

Valve

17

wheel brake cylinder

18

wheel brake cylinder

19

wheel brake cylinder

20

wheel brake cylinder

21

sensor

22

control unit

23

electric motor

24

screw

25

Master Cylinder

26

casing

27

stepped piston

28

first working chamber

29

second working chamber

30

compensating volume

31

coil spring

32

Valve

33

passage

34

35

Valve

36

Valve

37

Valve

38

Valve

39

pen

40

head

41

valve seat

42

large cross-sectional area

43

small cross-sectional area

44

Low pressure reservoir

45

module

46

branch

47

branch

48

Valve

49

Valve

50

Valve

51

Valve

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2460717 A1 [0001, 0004]

Claims (15)

Vehicle braking system with at least one wheel brake cylinder ( 17 - 20 ), a source of pressurized fluid ( 23 - 25 ) and a stepped piston ( 27 ), from which a first piston surface ( 42 ) one with the pressure fluid source ( 25 ) communicating first working chamber ( 28 ) and of which a second piston surface ( 43 ) one with the wheel brake cylinder ( 17 - 20 ) communicating second working chamber ( 29 ), as well as with a valve ( 32 ) for controlled opening and closing of a connection between the working chambers ( 28 . 29 ), in which on an input instrument ( 1 ) a sensor ( 21 ) for detecting the extent of an operation of the input instrument ( 1 ) is arranged by a driver and an electronic control unit ( 22 ), the pressure fluid source ( 25 ) according to the operation of the input instrument ( 1 ) to control. A vehicle braking system according to claim 1, wherein the source of pressurized fluid ( 25 ) by a motor ( 23 ) is driven. Vehicle braking system according to claim 1 or 2, wherein the valve ( 32 ) by the pressure in one of the working chambers ( 28 . 29 ) is controlled. A vehicle braking system according to claim 1, 2 or 3, wherein the amount of actuation is given by the deflection of the input instrument ( 1 ) from a rest position or through an input instrument ( 1 ) in the rest position acting restoring force. Vehicle braking system according to one of the preceding claims, in which a restoring element ( 11 ) one the input instrument ( 1 ) restoring force acting on the rest position, which over the entire actuating travel of the input instrument ( 1 ) increases with the extent of the operation. Vehicle braking system according to one of the preceding claims, in which the second working chamber ( 29 ) with wheel brake cylinders ( 17 - 20 ) communicates at several wheels of the vehicle. A vehicle braking system according to claim 6, wherein the source of pressurized fluid ( 25 ) and the stepped piston ( 27 ) into a common assembly ( 45 ) are integrated. Vehicle braking system according to one of the preceding claims, wherein the source of pressurized fluid comprises a master cylinder ( 25 ) comprising a piston driven by a motor. Vehicle braking system according to claim 8, in which the control unit ( 22 ) is set, a target position of the piston or a target pressure of the wheel brake cylinder ( 17 - 20 ) according to the extent of the operation. A vehicle braking system according to claim 9, wherein the desired position or pressure is linearly related to the amount of operation. Vehicle braking system according to one of the preceding claims, in which the input instrument ( 1 ) a cylinder ( 5 ) with a third working chamber ( 6 . 8th ) provided with at least one of the wheel brake cylinders ( 17 - 20 ) via a valve ( 13 . 14 ), which is closed in the presence of supply energy and open in the absence of supply energy. A vehicle braking system according to claim 11, wherein the second working chamber ( 29 ) with each wheel brake cylinder ( 17 - 20 ) via a valve ( 15 . 16 ), which is open in the presence of supply energy and closed in the absence of supply energy. Vehicle braking system according to claim 11 or 12, in which the input instrument ( 1 ) a discharge chamber ( 10 ) and that in a conduit containing the discharge chamber ( 10 ) with the third working chamber ( 6 ) connects a valve ( 9 ) is arranged, which is open in the presence of supply energy and closed in the absence of supply energy. Vehicle braking system according to claim 13, in which two third working chambers ( 6 . 8th ) in a common cylinder ( 5 ) and separated from each other by a movable partition ( 7 ) are separated. Motor vehicle with a braking system according to one of the preceding claims.

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