DE102017221019A1 - Braking system for motor vehicles - Google Patents

Abstract

Braking system (2), comprising hydraulically actuable wheel brakes (42-48), - a master brake cylinder (10) which can be actuated by means of a brake pedal (6) with at least one pressure chamber (120, 122) connected to the wheel brakes (42-48); a pressure supply device (20) having a pressure chamber (26) which is delimited by a pressure piston (32), wherein in each case an inlet valve (50-56) is provided in a hydraulic connection between the pressure chamber (26) and a wheel brake (42-48) is arranged, wherein at least one inlet valve (50-56) is designed as a normally closed pressure reducing valve.

Description

The invention relates to a brake system, comprising hydraulically actuated wheel brakes, an operable by means of a brake pedal master cylinder with at least one connected to the wheel brake pressure chamber, a pressure supply device with a pressure chamber, which is delimited by a pressure piston, each in a hydraulic connection between the pressure chamber and a wheel brake is arranged in each case an inlet valve.

In automotive engineering, brake-by-wire brake systems are becoming increasingly widespread. Such brake systems often comprise, in addition to an actuatable by the driver master cylinder an electrically ("by-wire") controllable pressure supply device by means of which in the operating mode "brake-by-wire" takes place an actuation of the wheel brakes.

In these brake systems, in particular electro-hydraulic brake systems with the "brake-by-wire" mode, the driver is decoupled from the direct access to the brakes. Upon actuation of the pedal usually a pedal decoupling unit and a simulator are operated, which is detected by a sensor, the braking request of the driver. The pedal simulator serves to give the driver as familiar a brake pedal feel as possible. The detected braking request leads to the determination of a desired braking torque, from which then the target brake pressure for the brakes is determined. The brake pressure is then actively built up by a pressure supply device in the brakes.

The actual braking thus takes place by active pressure build-up in the brake circuits with the aid of a pressure supply device, which is controlled by a control and regulation unit. As a result of the hydraulic decoupling of the brake pedal actuation from the pressure build-up, many functionalities such as ABS, ESC, TCS, hill-start assist etc. can be comfortably realized for the driver in such brake systems.

The pressure-providing device in brake systems described above is also referred to as an actuator or hydraulic actuator. In particular, actuators are designed as linear actuators in which a piston is axially displaced into a hydraulic pressure chamber to build up pressure, which is built in series with a rotational-translation gear. The motor shaft of an electric motor is converted by the rotation-translation gear in an axial displacement of the piston.

From the DE 10 2013 204 778 A1 is a "brake-by-wire" -Bremsanlage for motor vehicles is known which a brake pedal operable tandem master cylinder, the pressure chambers are connected via an electrically actuated release valve separable with a brake circuit with two wheel brakes, a hydraulically connected to the master cylinder, switched on and off simulation device , And an electrically controllable pressure-supplying device, which is formed by a cylinder-piston arrangement with a hydraulic pressure chamber whose piston is displaceable by an electromechanical actuator includes, wherein the pressure-supplying device is connected via two electrically actuated Zuschaltventile with the intake valves of the wheel brakes.

In such brake systems, a mechanical or hydraulic fallback stage is usually provided, by means of which the driver can decelerate or stop the vehicle by muscular force when the brake pedal is actuated, if the "by-wire" mode of operation fails or is disturbed. While in normal operation by a pedal decoupling unit, the above-described hydraulic decoupling between brake pedal operation and brake pressure build-up, this decoupling is canceled in the fallback so that the driver can move brake means directly into the brake circuits. In the fallback level is switched when with the help of the pressure supply device no pressure build-up is possible.

In normal operation, the driver actuates a pedal simulator in such an external power brake system, wherein this pedal operation is detected by pedal sensors and a corresponding pressure setpoint for the linear actuator is determined to actuate the wheel brakes. A movement of the linear actuator from its rest position forward into the pressure chamber displaces brake fluid volume from the linear actuator via the open valves in the wheel brakes and thus causes a pressure build-up. In the opposite case, the movement of the linear actuator back in the direction of its rest position leads to a pressure reduction in the wheel brakes. The setting of a required system pressure is carried out with the aid of a suitable pressure regulator or a suitable pressure control system in which, for example, a speed controller is subordinate to the pressure regulator. For the demand-driven and precise setting of the required pressures, a pressure-volume characteristic is stored in the brake system, which maps the ratio of volume and pressure, so that the associated pressure can be determined for each volume and vice versa.

Upon actuation of the brake pedal to request a brake pressure, the driver is no longer directly connected to the brake system, but actuates a pedal simulator, which has a suitable pedal characteristic, so that the driver a sufficiently accurate dosage of the requested braking request is made possible. This pedal operation is detected by pedal sensors and determined therefrom a desired braking request of the driver pressure setpoint for the linear actuator to actuate the wheel brakes.

A disadvantage of known brake system are the necessary when Druckeinstelen the energy consumption when switching the valves and the associated noise.

The invention is therefore based on the object to improve a brake-by-wire braking system in terms of its energy requirements and its flexibility.

This object is achieved in that at least one inlet valve is designed as a normally closed pressure reducing valve.

Advantageous embodiments of the invention are the subject of the dependent claims.

The invention is based on the consideration that modern requirements for brake systems include low-noise, precise pressure adjustment and low energy consumption, which should as far as possible be fulfilled simultaneously. A system without additional permanently switched or audibly switching valves, which hydraulically disconnect the wheel brakes from the actuator in case of loss of electrical power supply, in conjunction with Radeinlassventilen that are not connected digitally, this is particularly true.

As has now been recognized, these advantages can be represented by forming an inlet valve as a normally closed pressure reducing valve. The brake pressure in the wheel brake assigned to the intake valve can be realized without a shift only on the basis of the pressure applied to the intake valve.

As a pressure reducing valve is in this case a valve understood, which locks in one direction and opens in the other direction as soon as a threshold pressure is exceeded. By energizing the pressure reducing valve, the height of the threshold pressure can be controlled. In particular, the higher the current value, the higher the desired pressure difference.

Advantageously, each of the inlet valves is designed as a pressure reducing valve, whereby one of the wheel pressure build-up can be made particularly simple. In particular, all intake valves can be controlled with the same method in order to adjust all wheel pressures independently and quietly to the desired value.

The pressure-providing device is advantageously designed to convey pressure medium from the pressure chamber without a delivery break in one direction. This means in particular, it is always promoted pressure medium in the direction of the wheel brakes, but this is done without a Nachsaugzyklus.

In a preferred embodiment, the pressure supply device to a second pressure chamber, which is arranged with respect to the pressure piston on the other side and which is hydraulically connected via a Nachsaugleitung with the pressure fluid reservoir, wherein in the pressure piston, a check valve is arranged, which a pressure medium flow of allowed the further pressure chamber in the first pressure chamber and locks in the other direction.

Each wheel brake is preferably associated with an outlet valve, wherein at least one outlet valve is designed as a normally open overflow valve.

The at least one pressure chamber of the master cylinder is preferably connected or connectable via a respective outlet valve with a wheel brake. As a result, a so-called Radventilumkehr is realized in which are used during the pressure build-up with the help of the pressure supply device, the exhaust valves for Raddruckabbau, but act in the fallback level as intake valves.

The master cylinder preferably has two pressure chambers and a further pressure chamber, which is hydraulically connected to a simulation device.

One of the pressure chambers is preferably connected via a hydraulic line to the pressure medium reservoir, in which a pressure compensation valve is arranged.

In a preferred embodiment, the master brake cylinder has exactly one pressure chamber and a further pressure chamber, which is hydraulically connected to a simulation device. In this case, the braking system is preferably single-circuited in the fallback mode.

The further pressure chamber is preferably connected via a hydraulic line to the pressure medium reservoir, in which a pressure compensation valve is arranged.

The respective inlet valve is designed to be particularly advantageous as a solenoid valve, in particular for slip-controlled motor vehicle brake systems, with a valve stem arranged in a valve stem, which is able to open or close a valve passage in a valve seat of the valve housing, with a valve provided for actuating the valve stem magnetic drive, consisting of an axially movably received in the valve housing magnet armature, which is electromagnetically actuated by means of a valve core, a valve core formed in the magnetic core, which faces the armature, and with a compression spring for positioning the valve stem in a valve passage in the valve seat occluding basic position, wherein in the Electromagnetically excited position of the magnetic drive, the actuating direction of the armature is rectified with the effective direction of the compression spring.

The advantages of the invention are in particular that known normally open AD (analog / digital) valves can be used as exhaust valves in the brake system described. The intake valves used as pressure reducing valves described during the Radbremsdruckaufbau need during normal braking no energy or no energization. You still need no strong compression spring with high switching and holding current. There are therefore no switching noises. The use of the brake system described allows stepless and independent control of all wheel pressures, as can be used for functions such as yawing momentary control or axial blending or combinations thereof.

• 1 ein Bremssystem in einer ersten bevorzugten Ausführungsform; und
• 2 ein Bremssystem in einer zweiten bevorzugten Ausführungsform.

An embodiment of the invention will be explained in more detail with reference to a drawing. In it show in a highly schematic representation:

• 1 a brake system in a first preferred embodiment; and
• 2 a brake system in a second preferred embodiment.

Identical parts are provided in both figures with the same reference numerals.

An in 1 illustrated brake system 2 , which is designed as a foreign-power brake system, comprises one by means of an actuating or brake pedal 6 actuated master cylinder 10 , one with the master cylinder 10 cooperating simulation device 14 , a master cylinder 10 assigned, under atmospheric pressure medium reservoir 18 , an electrically controllable pressure supply device 20 , which by a cylinder-piston arrangement with a hydraulic pressure space 26 is formed, whose pistons 32 by an electromechanical actuator 34 which is an electric motor and a rotational translation thread, which is preferably designed as a ball screw, is displaceable, an electrically controllable pressure modulation device 36 for adjusting wheel-specific brake pressures and an electronic control unit 40 ,

The pressure modulation device 40 includes, for example, hydraulically actuated wheel brakes 42 . 44 . 46 , 48 and each operable wheel brake 42 - 48 an inlet valve 50 . 52 . 54 . 56 and an exhaust valve 60 . 62 . 64 . 66 , The inlet connections of the inlet valves 50 to 56 be by means of a brake circuit supply line 70 supplied with pressures that are derived in a "brake-by-wire" mode from a system pressure in a pressure chamber to a 26 the pressure supply device 20 connected system pressure line 80 present and that of the pressure supply device 20 provided pressure corresponds. The brake 42 . 44 are doing to a first brake circuit I , the brake 46 . 48 hydraulically connected to a second brake circuit II.

The master cylinder 10 points in a housing 70 two pistons arranged one behind the other 140 . 142 on, the hydraulic pressure chambers 120 . 122 limit. The pressure room 122 is over in the piston 142 or secondary piston formed radial bores and equalization holes and a pressure medium equalization line 138 with the pressure medium reservoir 18 hydraulically with unactuated piston 142 in connection. The one from the piston 140 or primary piston and the floating secondary piston 142 limited pressure chamber 140 or the primary chamber is via a pressure equalization line 136 with the pressure medium expansion tank 18 connected. With the help of one in the pressure equalization line 136 arranged, in particular normally closed, pressure compensation valve 134 This connection can be blocked if necessary.

The master cylinder 10 has a third pressure chamber 128 on, which is in particular designed as an annular chamber annular around the primary piston. This corresponds to a pressure effect in the pressure chamber 128 a force acting on the first master cylinder piston 140 acts counter to the direction of actuation. In the inoperative state of the master brake cylinder piston, the primary / secondary chamber via a radial bore with the chamber 128 connected. The connection through the radial bores is by an operation (a displacement) of the piston 140 or. 142 locked in the housing. The first pressure room 140 and the hydraulic chamber 128 are thus in an actuated state of the first master cylinder piston hydraulically sealed against each other.

In a normal braking in the normal mode of the brake system ("brake-by-wire" mode) is when the brake pedal 6 operated by the driver of the primary piston, wherein the piston movement is detected by means of the displacement sensor. By means of the electronic control unit, the simulator valve and the isolating valve are closed and the drain valve is opened. Pressure builds up in the (ring) chamber according to the simulator characteristic of the simulation device. Since no pressure build-up in the (primary) pressure chamber is possible due to the opened drain valve, the only static counterforce is the simulator pressure force. A hydraulic damping effect can be achieved by the opening characteristic of the drain valve. Thus, primary piston travel-dependent damping values can also be implemented (hydraulically / mechanically and / or electronically). Due to the non-pressurized primary chamber, the secondary chamber also remains depressurized or almost depressurized.

The pressure chamber 128 is via a pressure equalization line 126 with the pressure medium expansion tank 18 connected. In the pressure compensation line 126 is a, preferably normally open, pressure compensation valve 150 arranged, with the help of which, if necessary, the connection between the pressure chamber 128 and pressure fluid reservoir 18 can be locked. To the pressure balance valve 150 is a check valve 152 connected in parallel, which is a return flow of pressure medium from the pressure chamber 128 in the pressure medium reservoir 18 locks and releases in the opposite direction.

By opening the pressure compensation valve 134 can the pressure room 120 be switched without pressure, ie it is hydraulically with the pressure medium reservoir under atmospheric pressure 18 connected, so that it also sets in it atmospheric pressure. By opening the pressure compensation valve 150 can the pressure chamber 128 be depressurized in the same way.

The pressure room 120 or the primary pressure chamber is via a brake line 160 with the wheel brakes 42 . 44 the brake circuit I connected or connected. The pressure room 122 or the secondary pressure chamber is via a brake line 162 with the wheel brakes 46 . 48 the brake circuit II connected or connected.

A piston rod 166 couples the pivoting movement of the brake pedal 6 due to a pedal operation with the translational movement of the first master cylinder piston 140 or primary piston, whose actuation path of a, preferably redundantly running, displacement sensor 170 is detected. As a result, the corresponding piston travel signal is a measure of the brake pedal actuation angle. It represents a braking request of the driver.

The simulation device 14 or the simulator is hydraulically via a pipe 192 to the master cylinder 10 coupled and includes, for example, essentially a hydraulic simulator chamber 190 , a simulator spring chamber 194 and one the two chambers 190 . 194 mutually separating simulator piston 198 , The simulator piston 198 is supported by a in the simulator spring chamber 194 arranged elastic element 196 (For example, a spring), which is advantageously biased, on a housing 204 of the simulator.

A preferably redundantly designed pressure sensor 240 measures the system pressure in the system pressure line 80 prevails. A preferably redundantly designed pressure sensor 244 measures the pressure in the pipe 192 ,

The electrically controllable pressure supply device 20 is designed as a hydraulic cylinder-piston arrangement or a single-circuit electrohydraulic actuator whose / whose pressure piston 32 which the pressure room 26 limited, by a schematically indicated electric motor 220 with the interposition of a likewise schematically illustrated rotational-translation gear, which is preferably designed as a ball screw (KGT), can be actuated. One of the detection of the rotor position of the electric motor 220 Serving, only schematically indicated rotor position sensor is denoted by the reference numeral 226 designated. In addition, a temperature sensor can also be used 228 be used to sense the temperature of the motor winding. A pressure room 270 is via a hydraulic suction line 260 into which a check valve 262 is switched, with the pressure fluid reservoir 18 connected.

The pressure delivery device 20 is designed as a reversing linear actuator to move in a direction without Nachsaugpause / feeding break hydraulic fluid or liquid volume z. This is one in the piston 32 arranged check valve 274 arranged, which flow of pressure medium from the pressure chamber 270 in the pressure room 26 allowed and locks in the opposite direction. When the piston 32 in the picture to the right in the pressure room 26 moves, promotes the brake fluid in the direction of the wheel brakes. The pressure room 270 is due to the resulting negative pressure in the Nachsaugleitung 160 filled with pressure medium. The piston 32 can then be reversed so that it enters the pressure chamber 270 moves. In this case, pressure medium from the pressure chamber 270 by the check valve 274 in the pressure room 26 promoted, so that even with this direction of movement of the piston 32 Pressure medium from the pressure chamber 26 is moved. Since in both piston directions pressure fluid in the direction of the wheel brakes 42 - 48 is promoted, pressure medium from the wheel brakes is always using the exhaust valves 60 - 66 dismiss.

The brake system 2 is designed to allow noise and low energy individual pressure build-up.

This is the respective inlet valve 59 . 52 . 54 . 56 designed as a pressure reducing valve. It is preferably designed in each case as a normally closed analog-digital valve (SG-AD valve), in particular with an increasing characteristic curve.

The respective outlet valve 60 - 66 is preferably designed as a normally open analog / digital valve. The respective outlet valve 60 - 66 In each case, a check valve is connected in parallel, which is a return flow of pressure medium from the respective wheel brake 42 - 48 prevented.

In normal braking operation builds the pressure supply device 20 via the brake circuit supply line 70 Brake pressure in the wheel brakes on. The inlet valves are not energized, but open when the pressure in the brake circuit supply line 70 exceeds the low opening pressure of the compression spring in the valve. To achieve a uniform brake force distribution and valve design, the lowest possible value for this opening pressure is sought.

During normal braking, the respective exhaust valve is closed or overflowed to control the wheel pressure according to the exhaust valve 60 . 62 . 64 . 66 characterizing current-pressure characteristic. By overflow of the respective exhaust valve 60 - 66 can in the wheel brakes 42 - 48 wheel-individually brake pressure can be reduced and thus adjusted. By combination with the master cylinder 10 , the next primary chamber and secondary chamber still the other, with the simulation device 14 hydraulically connected pressure chamber 128 has, it can be ensured that in the normal braking mode, a return of pressure medium from the exhaust valves 60 - 66 to the pressure fluid reservoir 18 is possible.

Lowering the wheel pressure in the respective wheel brake 42 - 48 takes place in the present embodiment by means of the respective associated outlet valve 60 - 66 because the intake valves 50 - 56 do not allow backflow of pressure medium. This allows the use of a pressure delivery device 20 or a linear actuator, which can only move brake fluid in one direction (from the pressure chamber 26 to the wheel brakes 42 - 48 ), but in both directions of the piston movement and without feeding break by vacuuming.

The modulation of the wheel pressure can be carried out both on the wheel and on the axle. When a pressure differential is to be set between the wheels (or axles), the intake valves become 50 - 56 more closed by increasing the current at the wheel brakes with the lower pressure. Thus it is with the help of the pressure supply device 20 possible to set a higher wheel brake pressure in the other wheel brakes.

In a fallback, in which the pressure delivery device 20 not used to build up pressure, the driver can by pressing the brake pedal 6 Build up wheel brake pressure. The intake valves 50 . 56 are / are closed because they are no longer opened by pressure built up by the linear actuator. On the other hand, since they no return flow of pressure medium from the wheel brakes 42 - 48 The linear actuator does not have to be hydraulically separated from the wheel brakes by separate isolation valves 42 - 48 be separated. By pressing the brake pedal 6 become the pistons 140 . 142 each in the appropriate pressure chamber 120 . 122 in the direction of the wheel brakes 42 - 48 postponed. The exhaust valves 60 - 66 assume the function of intake valves in this mode in the sense of a Radventilumkehr.

In 2 is a braking system 2 shown in a second preferred embodiment. This braking system 2 is essentially different from the one in the 1 illustrated embodiment by the design and hydraulic connection of the master cylinder 10 to the brake circuits I, II. The master cylinder 10 is single-circuit formed with a pressure piston 140a when pressing the brake pedal 6 in a pressure room 120a is movable.

Via a pressure line 310 is the pressure room 120a with the exhaust valves 60 . 62 the wheel brakes 42 . 44 connected. The pressure room 120a is preferred and as shown not with the wheel brakes 46 . 48 the other, the rear axle associated, brake circuit II connected or connectable. In the present embodiment, the two wheel brakes correspond 42 . 44 the brake circuit I the front brakes and the two wheel brakes 46 . 48 the brake circuit II the rear brakes.

In a fallback mode, the driver can by pressing the brake pedal 6 Pressure medium from the pressure chamber 120a in the direction of the wheel brakes 42 . 44 shift the front axle, wherein in the sense of a wheel reversal the exhaust valves 60 . 62 when Exhaust valves act. The driver thus receives no direct access to the wheel brakes on the rear axle, which prevents overbraking the rear axle.

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

• DE 102013204778 A1 [0006]

Claims (10)

Braking system (2), comprising - hydraulically actuated wheel brakes (42-48); - a master brake cylinder (10) operable by means of a brake pedal (6) with at least one pressure chamber (120, 122) connected to the wheel brakes (42-48); - A pressure supply device (20) having a pressure chamber (26) which is bounded by a pressure piston (32), wherein in each case in a hydraulic connection between the pressure chamber (26) and a wheel brake (42-48) each have an inlet valve (50-56 ) is arranged, characterized in that at least one inlet valve (50-56) is designed as a normally closed pressure reducing valve. Brake system (2) after Claim 1 wherein each inlet valve (50-56) is designed as a pressure reducing valve. Brake system (2) after Claim 1 or 2 wherein the pressure-providing device (20) is adapted to convey pressure medium from the pressure chamber (26) in one direction without a delivery break. Brake system (2) after Claim 3 wherein the pressure providing means (20) comprises a second pressure space (270) disposed on the other side with respect to the pressure piston (32) and hydraulically connected to a pressure medium reservoir (18) via a suction line, and in the pressure piston (32) a check valve (274) is arranged, which allows a pressure medium flow from the second pressure chamber (270) in the first pressure chamber (26) and blocks in another direction. Braking system (2) according to one of Claims 1 to 4 , wherein each wheel brake (42-48) is associated with an outlet valve (60-66), and wherein at least one outlet valve (60-66) is designed as a normally open overflow valve. Brake system (2) after Claim 5 , wherein the at least one pressure chamber (120, 122) of the master cylinder (10) via a respective outlet valve (60-66) with a wheel brake (42-48) is connected or connectable. Braking system (2) according to one of Claims 1 to 6 wherein the master brake cylinder (10) has two pressure chambers (120, 122) and a further pressure chamber (128) which is hydraulically connected to a simulation device (16). Brake system (2) after Claim 7 wherein one of the pressure chambers (120, 122) is connected via a hydraulic line to a pressure fluid reservoir (18) in which a pressure compensation valve (134) is arranged. Brake system (2) after Claim 6 wherein the master brake cylinder (10) has exactly one pressure chamber (120a) and a further pressure chamber (128a) which is hydraulically connected to a simulation device (16). Brake system (2) after Claim 9 , wherein the further pressure chamber (128, 128a) is connected via a hydraulic line to a pressure medium reservoir (18) in which a pressure compensation valve (150) is arranged.

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