DE102020202367A1 - Method for operating a braking system and braking system - Google Patents

Abstract

A method for operating a brake system which comprises • a driver brake request detection (25, 20) • hydraulically actuated wheel brakes (8a-d) • inlet valves (6a-d) and outlet valves (7a-d) assigned to the wheel brakes, each wheel brake (8a -d) each hydraulically connected to an inlet valve (6a-d) and an outlet valve (7a-d), and the respective inlet valve (6a-d) when a pressure value is exceeded, which is a function of a holding current of the inlet valve (6a-d ) is opened; an electronic control and regulation unit (12) for controlling the inlet (6a-d) and outlet valves (7a-d); the system pressure being determined, a differential pressure between the system pressure and the pressure in at least one wheel brake (8a-d) being determined, and a holding current being set in the inlet valve (6a-d) of this wheel brake (8a-d) which leads to the opening of the inlet valve (6a-d) when the differential pressure is exceeded.

Description

• • eine Fahrerbremswunscherfassung;
• • hydraulisch betätigbare Radbremsen;
• • den Radbremsen zugeordnete Einlassventile und Auslassventile, wobei jede Radbremse jeweils hydraulisch mit einem Einlassventil und einem Auslassventil verbunden ist, und wobei das jeweilige Einlassventil bei Überschreiten eines Druckwertes, welcher eine Funktion eines Haltestroms des Einlassventils ist, öffnet;
• • eine mittels eines Zuschaltventils hydraulisch mit den Radbremsen verbindbare Druckbereitstellungeinrichtung mit einer Druckkammer zur Bereitstellung eines Systemdruckes zum aktiven Druckaufbau in den Radbremsen;
• • einer elektronische Steuer- und Regeleinheit zur Ansteuerung der Einlass- und Auslassventile;

wobei der Systemdruck bestimmt wird. Sie betrifft weiterhin ein Bremssystem.The invention relates to a brake system for operating a brake system which comprises

• • a driver brake request detection;
• • hydraulically operated wheel brakes;
• Inlet valves and outlet valves assigned to the wheel brakes, each wheel brake being hydraulically connected to an inlet valve and an outlet valve, and the respective inlet valve opening when a pressure value that is a function of a holding current of the inlet valve is exceeded;
• A pressure supply device which can be hydraulically connected to the wheel brakes by means of a connecting valve and has a pressure chamber for providing a system pressure for actively building up pressure in the wheel brakes;
• • an electronic control and regulation unit for activating the inlet and outlet valves;

whereby the system pressure is determined. It also concerns a braking system.

In the case of electrohydraulic brake systems with the “brake-by-wire” operating mode, the driver is decoupled from direct access to the brakes. When the pedal is operated, a pedal decoupling unit and a simulator are usually operated, with the driver's braking request being detected by a sensor system. The pedal simulator is used to give the driver the most familiar feeling possible on the brake pedal. The detected braking request leads to the determination of a target braking torque, from which the target braking pressure for the brakes is then determined. The brake pressure is then actively built up in the brakes by a pressure supply device.

The actual braking thus takes place by actively building up pressure in the brake circuits with the aid of a pressure supply device that is activated by a control and regulating unit. Due to the hydraulic decoupling of the brake pedal actuation from the pressure build-up, many functionalities such as ABS, ESC, TCS, slope starting aid, etc. can be comfortably implemented for the driver in 5 such brake systems.

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

In such brake systems, a mechanical or hydraulic fallback level is usually provided through which the driver can brake or bring the vehicle to a standstill using muscle power when the brake pedal is pressed if the “by-wire” operating mode fails or is disturbed. In normal operation, the driver actuates a pedal simulator in such an external power brake system, this pedal actuation being detected by pedal sensors and a corresponding pressure setpoint for the linear actuator for actuating the wheel brakes being determined.

A movement of the linear actuator from its rest position forwards into the pressure chamber shifts the brake fluid volume from the linear actuator via the opened valves into the wheel brakes and thus creates 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 required system pressure is set using a suitable pressure regulator or a suitable pressure control system.

Brake systems are also known in which the brake pedal is provided with the aid of driver brake request recognition, in particular a pedal travel and / or pedal angle sensor, and no master brake cylinder that can be actuated with the brake pedal is provided. In this case, the brake pedal is designed to be “dry”.

From the DE 10 2017 219 598 A1 a brake system or a brake system with a master brake cylinder, a simulator and a pressure supply device, which can be hydraulically connected to the wheel brakes via a connecting valve, is known. The system pressure, which corresponds to the pressure in the pressure chamber of the pressure supply device, is measured by a system pressure sensor which, viewed from the pressure chamber of the pressure supply device, is located behind the connecting valve.

Such a positioning of the system pressure sensor outside the pressure chamber has the advantage that this sensor can be used for the pressure determination even in the case of non-by-wire operation. In addition, when the connection valve is closed, the system pressure can be monitored during refill, pressurehold, etc.

In known brake systems, the system pressure sensor is used for the opening algorithm of the connecting valve or valves. This will be after a pressurehold or after a refill. The aim of placing the system pressure sensor outside the pressure chamber of the pressure supply device is also to detect when the connecting valve has been pushed open on the basis of a pressure increase in the system. The increase in pressure should therefore be detected with the sensor. In this case, the connection valve can open when there is pressure equalization between the pressure supply device and the hydraulic system with the wheel brakes.

The disadvantage of the above-described arrangement of the system pressure sensor is that the pressure measurement is very dependent on external influences. When the connection valve is closed, there may be a pressure increase at the system pressure sensor due to the isolating valve hydraulically separating the master brake cylinder, recoil of the wheels, disc beating or the integrated parking brake (IPB). All inlet valves are closed during a suction process. A pressure reduction in the wheel brakes is still possible through the outlet valves. Since the sequence valve (PFV) is also closed during the close-up process, the system pressure sensor is located in the rigid space. This leads to enormous increases in pressure at the system pressure sensor when the outlet valve is switched, measurements have shown increases in pressure of up to 50 bat. Through the pressure peaks

This pressure increase due to the outlet valves is currently difficult to distinguish from a pressure increase due to a PFV forced on by the LAC. The result is currently an unsafe opening of the connection valve by the pressure regulator, which can endanger the entire by-wire braking.

Preventing the switching of the outlet valves during a refill and during the opening process of the connecting valve would have negative effects on the braking distance and vehicle stability.

The invention is therefore based on the object of preventing the system pressure measurement and thus the opening algorithm of the connecting valve from being influenced by pressure peaks, in particular by switching the outlet valves. Furthermore, a corresponding braking system should be specified.

With regard to the method, this object is achieved according to the invention in that a differential pressure is determined between the system pressure and the pressure in at least one wheel brake, and a holding current is set in the inlet valve of this wheel brake, which leads to the opening of the inlet valve when the differential pressure is exceeded .

Advantageous refinements of the invention are the subject matter of the subclaims.

The invention is based on the consideration that high pressure peaks can occur both during switching operations of the outlet valves during a suction operation and during fast control operations in the hydraulically rigid space between the pressure supply device and wheel brakes, which make it difficult for the pressure regulator to open the connection valve precisely, so that an accurate and reliable braking cannot be performed.

As has now been recognized, these pressure peaks can be prevented by, as it were, carrying out a system pressure control with the aid of the inlet valves. The inlet valves can be described with the aid of an opening current characteristic, which indicates the pressure at which the corresponding valve opens when a certain holding current is present. Depending on the desired system pressure and the applied wheel pressure, the holding current is set or reduced accordingly. In principle, the inlet valve remains closed, but due to the selected holding current, it would open when the admission pressure rises until the admission pressure falls back to the desired value.

The driver brake request recognition preferably comprises a pedal travel and / or pedal angle sensor and / or a pressure sensor for measuring the pressure in a camera of the master brake cylinder.

In a preferred embodiment, the brake system or the brake system comprises a master brake cylinder that can be actuated with a brake pedal. A master brake cylinder with only one pressure chamber or a tandem master brake cylinder with a primary chamber and a secondary chamber can be provided here.

The system pressure is preferably measured with the help of a system pressure sensor. In an advantageous embodiment, the system pressure sensor is arranged between the wheel brakes and the respective connection valve. In another embodiment, the system pressure can be determined with the aid of a model. For example, a relationship between engine torque and system pressure can be used for this.

The pressure in the respective wheel brake is preferably determined as follows. When the inlet valve is closed, the wheel pressure is determined using the pressure model. Before the inlet valve closes, the wheel pressure or pressure in the wheel brake is equal to the sensed or determined system pressure. After closing the inlet valve, the wheel pressure is stored and the Exhaust valve opening times are calculated with the stored wheel pressure, the PV characteristic curve and the orifice of the exhaust valve in a wheel pressure model in order to determine the resulting wheel pressure.

The holding current of the inlet valve is advantageously set only at a point in time at which the outlet valve hydraulically connected to the wheel brake is not open. In order to prevent or compensate for the increase in system pressure caused by closing the outlet valve, the inlet valve is advantageously supplied with an adapted holding current from the wheel on which the outlet valve has just been closed. As a result, the excess volume would flow back into the “right” wheel.

After an outlet valve has been switched, the new wheel volume, the wheel pressure and the differential pressure with respect to the system pressure are preferably recalculated, with these updated variables being used to determine a new holding current value. In this way, a precise determination of a suitable holder current is made possible.

The setting of the holding current is advantageously carried out during a refilling process of the pressure chamber of the pressure supply device and / or when all the inlet valves are closed. At this point all inlet valves are closed. The stiff space is created when all inlet valves are closed. The holding current is advantageously reduced when all the inlet valves are closed, particularly preferably only on the wheel brake on which the outlet valve has just been closed.

In a preferred embodiment of the method, the setting or lowering of the holding currents is carried out at several, in particular all or those on a common vehicle axle, inlet valves, in particular at the same time. In this way, an unwanted pressure peak caused by the LAC can be reduced effectively. In this way, the excess volume of the advancing piston of the pressure supply device can be distributed over several wheels, whereby overbraking of individual wheels can be prevented. When setting the holding currents on only one axle, overbraking on one side of the vehicle is avoided.

In another preferred embodiment, the lowering of the holding current is only carried out at the inlet valve of the wheel brake on which an outlet valve has just been closed. As a result, the excess volume is fed into the wheel brake, from which the corresponding volume had previously emerged.

The setting of the holding current in at least one inlet valve is preferably carried out by the pressure supply device during a rapid pressure build-up process. In this way, pressure peaks can be avoided during the control process, so that the control valve can be controlled precisely and as required during the control process.

In a further preferred embodiment, the holding current is set during a rapid pressure build-up process by the pressure supply device on all inlet valves or on two wheel brakes on the same vehicle axle. This increases the vehicle's stability and prevents overbraking on one wheel.

In a preferred embodiment, the connecting valve is opened by the control and regulation unit when at least one opening condition is present, and the lowering of the holding current is only carried out when this opening condition is met. In this way, accidental opening or opening in the event of incorrect pressure conditions can be avoided.

The opening condition is preferably a function of the pressure piston position of the pressure supply device and / or the engine torque.

In a preferred embodiment, the opening condition is met when the engine torque is high enough to produce a pressure equilibrium between the pressure chamber of the pressure supply device and the system pressure.

• • eine Fahrerbremswunscherkennung;
• • hydraulisch betätigbare Radbremsen;
• • den Radbremsen zugeordnete Einlassventile und Auslassventile, wobei jede Radbremse jeweils hydraulisch mit einem Einlassventil und einem Auslassventil verbunden ist, und wobei das jeweilige Einlassventil bei Überschreiten eines Druckwertes, welcher eine Funktion eines Haltestroms des Einlassventils ist, öffnet;
• • eine mittels eines Zuschaltventils hydraulisch mit den Radbremsen verbindbare Druckbereitstellungeinrichtung mit einer Druckkammer zur Bereitstellung eines Systemdruckes zum aktiven Druckaufbau in den Radbremsen;
• • einer elektronische Steuer- und Regeleinheit zur Ansteuerung der Einlass- und Auslassventile, in welcher ein Verfahren nach einem der vorherigen Ansprüche hardware- und/oder softwaremäßig implementiert ist.

With regard to the brake system, the above-mentioned object is achieved according to the invention by a brake system

• • a driver brake request recognition;
• • hydraulically operated wheel brakes;
• Inlet valves and outlet valves assigned to the wheel brakes, each wheel brake being hydraulically connected to an inlet valve and an outlet valve, and the respective inlet valve opening when a pressure value that is a function of a holding current of the inlet valve is exceeded;
• A pressure supply device which can be hydraulically connected to the wheel brakes by means of a connecting valve and has a pressure chamber for supplying a system pressure for active pressure build-up in the wheel brakes;
• • an electronic control and regulation unit for activating the inlet and outlet valves, in which a method according to one of the preceding claims is implemented in terms of hardware and / or software.

In a first preferred embodiment, the master brake cylinder is designed with exactly one pressure chamber.

In a second preferred embodiment, the master cylinder is designed as a tandem master cylinder with two pressure chambers each assigned to a brake circuit, a pump being provided in each brake circuit for building up and reducing pressure as required in the respective brake circuit.

A system pressure sensor is preferably provided and the system pressure is preferably measured with the aid of the system pressure sensor. In an advantageous embodiment, the system pressure sensor is arranged between the wheel brakes and the respective connection valve.

The advantages of the invention are in particular that the problems of the current system pressure sensor position and the problems resulting therefrom during refill can be limited and eliminated. High pressure peaks in the hydraulically rigid space between the connecting valve and the wheel brakes can be reduced, which enables precise control of the connecting valve.

• 1 ein erstes Ausführungsbeispiel eines erfindungsgemäßen Bremssystems,
• 2 ein zweites Ausführungsbeispiel eines erfindungsgemäßen Bremssystems, und
• 3 Haltestromkennlinien eines Einlassventils.

An embodiment of the invention is explained in more detail with reference to a drawing. They show in a highly schematic representation:

• 1 a first embodiment of a brake system according to the invention,
• 2 a second embodiment of a brake system according to the invention, and
• 3 Holding current characteristics of an intake valve.

The same parts are provided with the same reference symbols in all figures.

An in 1 The illustrated braking system for a motor vehicle comprises four hydraulically actuatable wheel brakes
8a-8d. The brake system comprises a means of an actuation or brake pedal 1 actuatable master cylinder 2 ,
one with the master cylinder 2 interacting path simulator or a simulation device 3 , a pressure medium storage container under atmospheric pressure 4th , an electrically controllable pressure supply device 5 , and wheel-specific brake pressure modulation valves, which, according to the example, as inlet valves 6a-6d and exhaust valves
7a-7d are executed. The brake system also includes an electronic control and regulation unit 12th to control the electrically operated components of the brake system.

The wheel brake is according to the example 8a the left front wheel (FL), the wheel brake 8b the right front wheel (FR), the wheel brake 8c the left rear wheel (RL) and the wheel brake 8d assigned to the right rear wheel (RR).

The master cylinder 2 has in a housing 16 a master cylinder piston 15th on, of a hydraulic pressure chamber 17th limited, and represents a single-circuit master cylinder. The pressure chamber 17th takes a return spring 9 on that the piston 15th when the main brake cylinder is not actuated 2 positioned in a starting position. The pressure chamber 17th stands on the one hand over in the piston 15th formed radial bores and a corresponding pressure equalization line 41 with the pressure medium reservoir 4th in connection, this by a relative movement of the piston 17th in the housing 16 are lockable. The pressure chamber
17 is on the other hand by means of a hydraulic line section (also referred to as the first supply line) 22 with a brake supply line 13th in connection to which the inlet connections of the inlet valves 6a-6d are connected. So is the pressure chamber 17th of the master cylinder 2 with all inlet valves 6a-6d tied together.

In the pressure equalization line 41 or in the connection between the pressure chamber 17th and the pressure medium reservoir 4th For example, no valve, in particular no electrically or hydraulically actuated valve and no check valve, is arranged.

Alternatively, in the pressure equalization line 41 or between the master cylinder 2 and the pressure medium reservoir 4th a diagnostic valve, in particular a normally open, diagnostic valve, preferably a parallel connection of a normally open diagnostic valve with one connected to the pressure medium reservoir 4th closing check valve.

Between the to the pressure chamber 17th connected supply line 22nd and the brake supply line 13th is an isolation valve 23 arranged or pressure chamber 17th is with the brake supply line 13th via the first supply line 22nd with a separation valve 23 tied together. The isolation valve 23 is
designed as an electrically operated, preferably normally open (SO), 2/2-way valve. Through the isolation valve 23 can be the hydraulic connection between the pressure chamber 17th and the brake supply line 13th be locked.

A piston rod 24 couples the pivoting movement of the brake pedal 1 as a result of a pedal operation with the translational movement of the master cylinder piston 15th , whose actuation travel is from a preferably redundant travel sensor 25th is captured. As a result, the corresponding piston travel signal is a measure of the brake pedal actuation angle. It represents a braking request from a vehicle driver.

One to the first supply line 22nd connected pressure sensor 20th detects the in the pressure chamber 17th by moving the piston 15th built-up pressure. This pressure value can also be evaluated to characterize or determine the driver's braking request. Alternative to a pressure sensor 20th can also be a force sensor 20th can be used to determine the driver's braking requirement.

The simulation facility 3 is carried out hydraulically according to the example and hydraulically to the master cylinder 2 coupled. The simulation facility 3 has, for example, essentially a simulator chamber 29 , a simulator back chamber 30th as well as one of the two chambers 29 , 30th separating simulator pistons 31 on. The simulator piston 31 is supported by a in the (for example dry) simulator back chamber 30th arranged elastic element 33 (e.g. simulator spring) on a housing. The hydraulic simulator chamber 29 is, for example, by means of a simulator release valve that is preferably electrically actuatable, preferably closed with a currentless condition 32 with the pressure chamber 17th of the master cylinder 2 tied together.

The brake system or the brake system includes each hydraulically actuated wheel brake 8a-8d an inlet valve 6a-6d and an exhaust valve 7a-7d , which are hydraulically interconnected in pairs via central connections and to the wheel brake 8a-8d are connected. The inlet valves 6a-6d is one to the brake supply line 13th opening, unspecified non-return valve connected in parallel. The outlet connections of the exhaust valves 7a-7d are via a common return line 14th with the pressure medium reservoir 4th tied together.

The electrically controllable pressure supply device 5 is designed as a hydraulic cylinder-piston arrangement (or a single-circuit, electrohydraulic actuator (linear actuator)), the piston of which 36 by a schematically indicated electric motor 35 with the interposition of a rotation-translation gear, also shown schematically 39 is actuatable. The piston 36 limits the only pressure space 37 the pressure supply device 5 .

One of the detection of the rotor position of the electric motor 35 Serving, only schematically indicated rotor position sensor is denoted by the reference symbol 44 designated.

To the printing room 37 the electrically controllable pressure supply device 5 a line section (also referred to as a second supply line) 38 is connected. The supply line 38 is via an electrically operated, preferably normally closed, connection valve 26th with the brake supply line 13th tied together. Through the sequence valve 26th can be the hydraulic connection between the pressure chamber 37 the electrically controllable pressure supply device 5 and the brake supply line 13th (and thus the inlet connections of the inlet valves 6a-6d ) can be opened and locked in a controlled manner.

The one by the force of the piston 36 on that in the print room 37 Trapped pressure medium generated actuator pressure is in the second supply line 38 fed in. In a “brake-by-wire” operating mode, in particular when the brake system is in a fault-free state, the supply line 38 via the sequence valve 26th with the brake supply line 13th tied together. In this way, during normal braking, the wheel brake pressure is built up and reduced for all wheel brakes 8a-8d by moving the piston back and forth 36 .

In the event of a pressure reduction by retracting the piston 36 that flows out of the pressure chamber beforehand 37 the pressure supply device 5 in the wheel brakes 8a-8d shifted pressure medium in the same way back into the pressure chamber 37 return.

Alternatively, different wheel brake pressures can be set individually for each wheel simply by means of the inlet and outlet valves 6a-6d , 7a-7d can be set. When the pressure drops accordingly, it flows through the outlet valves 7a-7d discharged pressure medium portion via the return line 14th in the pressure medium reservoir 4th .

A suction of pressure medium into the pressure chamber 37 is by retracting the piston 36 when the sequence valve is closed 26th possible by removing pressure medium from the container 4th over the line 42 with one in the direction of flow to the actuator
5 opening check valve 53 in the acuator pressure chamber or pressure chamber 37 can flow.
The example is pressure room 37 also in a non-actuated state of the piston 36 via one or more sniffing holes with the pressure medium reservoir 4th tied together. This connection between the pressure chamber 37 and pressure medium reservoir 4th becomes with a (sufficient) actuation of the piston 36 in the direction of actuation 27 separated.

In the brake supply line 13th is an electrically operated, normally open circuit isolating valve 40 arranged through which the brake supply line 13th in a first line section 13a , which (via the isolating valve 23 ) with the master cylinder 2 is connected, and a second line section 13b , which (via the sequence valve 26th ) with the pressure supply device 5 is connected, is separable. The first line section 13a is with the inlet valves 6a , 6b the wheel brakes 8a , 8b connected and the second line section 13b is with the inlet valves 6c , 6d the wheel brakes 8c , 8d tied together.

With the circuit separation valve open 40 the braking system is single-circuit. By closing the circuit isolation valve 40 the brake system, in particular controlled according to the situation, can be separated or divided into two brake circuits I and II. The master brake cylinder is in the first brake circuit I. 2 (via the isolation valve 23 ) with only the inlet valves 6a , 6b the wheel brakes 8a , 8b connected to the front axle VA, and the pressure supply device in the second brake circuit II 5 (when the sequence valve is open 26th ) with only the wheel brakes 8c and 8d connected to the rear axle HA.

The inlet connections of all inlet valves 6a-6d can with the circuit isolation valve open 40 by means of the brake supply line 13th be supplied with a pressure which, in a first operating mode (for example “brake-by-wire” operating mode), corresponds to the brake pressure that is provided by the pressure supply device 5 provided. The brake supply line 13th can in a second operating mode (e.g. in a currentless fallback operating mode) with the pressure of the pressure chamber 17th of the master cylinder 2 be applied.

The brake system advantageously includes a level measuring device 50 for determining a pressure medium level / level in the pressure medium storage container 4th . Advantageously, a situation recognition for the circuit separation takes place by means of the circuit separation valve 40 via the level measuring device 50 .

The hydraulic components, namely the master brake cylinder, are according to the example 2 , the simulation facility 3 , the print provision facility 5 who have favourited valves 6a-6d , 7a-7d , 23 , 26th , 40 and 32 as well as the hydraulic connections including the brake supply line 13th , together in one
(single) hydraulic control and regulation unit 60 (HCU) arranged. The hydraulic control and regulation unit 60 is the (only) electronic control and regulation unit (ECU) 12th assigned. Hydraulic and electronic control and regulation units are preferred 60 , 12th designed as one unit (HECU)

The braking system includes a pressure sensor 19th or system pressure sensor for detecting the pressure supply device 5 provided pressure. The pressure sensor 19th is here from the pressure chamber 37 the pressure supply device 5 seen behind the sequence valve 26th arranged.

In 2 a braking system is shown in a further preferred embodiment. The braking system consists of three modules 70 , 72 , 74 , each with a separate control and regulation unit 80 , 82 , 84 include. The module 70 includes the master cylinder 2 , which acts as a tandem master cylinder with a primary chamber 90 and a secondary chamber 92 is designed and the simulator or the simulation device 3 . With the help of the simulator release valve 32 is the primary chamber in by-wire mode 90 with the simulator chamber 29 connectable. The two chambers 90 , 92 of the master cylinder are hydraulic with a pressure medium reservoir 4a connectable. A partition 100 in this container ensures that, even in the event of a leak, one of the two is each connected to a chamber 90 , 92 connected brake circuit I, II is still pressure medium available for the other brake circuit. The control and regulation unit 80 of the module 80 essentially serves to control the valve 32 .

The brake system has a driver brake request detection, which a pedal travel sensor 25th includes as well as a pressure sensor 20th for measuring the pressure in the master brake cylinder.
The second module 72 with the control and regulation unit 82 comprises the pressure supply device 5 and two sequence valves 26a , 26b through which the pressure chamber 37 the pressure supply device 5 is hydraulically connectable to the wheel brakes. It also includes the one rotor position sensor 44 as well as a pressure sensor 20th for measuring the pressure in the primary chamber 90 . The two chambers 90 , 92 can be operated in brake-by-wire mode with the aid of isolating valves 23a , 23b are hydraulically separated from the wheel brakes so that the driver can do so when the simulator release valve is open 22nd Brake fluid from the primary chamber 90 into the simulator chamber 29 shifts.

The pressure chamber 37 is hydraulic with a pressure medium reservoir 4b connected and can suck in from this braking agent, whereby through a non-return valve 120 the return flow of pressure medium from the pressure chamber 37 into the container 4b is prevented.

When the isolation valves 23a , 23b are closed and the master cylinder 2 hydraulically from the wheel brakes during by-wire operation 8a-d can be separated via a line 124 and opening a drain valve 122 excess braking volume in the container 4b be promoted.

In the pressure medium reservoir 4b is a partition 130 provided, which defines two separate chambers when the level is below the height of the partition 130 sinks. The control and regulation unit 82 serves to control the pressure supply device 5 and the valves 26a , 26b , 23a , 23b , 122 .

The third module 74 with the control and regulation unit 84 includes the inlet valves assigned to the wheel brakes 6a-d and exhaust valves 7a-d . There is one pump in each brake circuit 140 , 142 provided, each via a pump sequence valve 160 , 162 can be hydraulically connected in the suction path to the pressure supply device.

With the help of overflow valves 150 , 153 the pressure can be set with the help of the respective pump 140 , 142 can be built. Promotes the pump 140 , 142 too much volume and the pressure increases, this valve becomes 150 , 152 pushed open and the pressure in the pump chamber remains through this valve 150 , 152 and its current controllable.

Furthermore, there is a low-pressure accumulator in each of the two brake circuits 164 , 166 intended. With the help of a check valve 168 , 170 is the flow of pressure medium from the delivery circuit of the pump 140 , 142 towards the exhaust valves 7a-d prevented. The control and regulation unit 84 is used to control the pumps 140 , 142 as well as the valves 67a-d , 7a-d 160 , 162 , 150 , 152 . The module 74 further includes the system pressure sensor 19th .

The two pressure medium storage tanks 4a , 4b are with the common pressure medium reservoir 4th hydraulically connected.

The pressure provision facility 5 is used in this brake system to provide a pre-pressure while the pumps 140 , 142 are used in particular for control processes and the pressure build-up by the pressure supply device 5 support.

The three control and regulation units 80 , 82 , 84 are connected to each other on the signal side, in particular via a CAN bus.

At least one of the control and regulation units 80 , 82 , 84 is designed to carry out a method described above, which is explained using an example.

At the beginning of a refill process or refill of the pressure chamber 37 the pressure supply device 5 is a system pressure (that of the system pressure sensor 19th is measured) from 70 bar. In the wheel brake 8a the pressure is 30 bar. So there should be a pressure difference of 40 bar. According to the upper opening curve (see 3 and the description below) a holding current of approx. 400mA must be selected to control the inlet valve at this differential pressure 6a keep closed.

If the system pressure were to rise to 100 bar, for example, due to the OV closing, this additional 30 bar would be the inlet valve 6a and to a volume flow into the wheel brake 8a to lead. Because it is a hydraulically stiff space in front of the inlet valve 6a acts,
the admission pressure would collapse even with very small volumes, and so would the inlet valve 6a close again at the pressure difference of 70 bar. Because of the small volume, the pressure would increase in the wheel brake 8a not significant.

In 3 is finally exemplary for an inlet valve 6a-d a family of opening characteristics a. On the x-axis is the pressure, on the y-axis 202 the holding current is removed. An upper opening characteristic shows at a given pressure how high the holding current of the inlet valve must be set so that the valve still closes at this pressure and opens at higher pressures. With the help of the other lines, it is possible to deduce which volume flow occurs when the pressure increases.

With the help of the characteristic 210 can the control and regulation unit 12th respectively. 80 , 82 , 84 thus set the appropriate holding current in each case.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was 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.

Patent literature cited

• DE 102017219598 A1 [0008]

Claims (13)

A method for operating a brake system, which comprises • a driver brake request detection (25, 20); • hydraulically actuated wheel brakes (8a-d); • Inlet valves (6a-d) and outlet valves (7a-d) assigned to the wheel brakes, each wheel brake (8a-d) being hydraulically connected to an inlet valve (6a-d) and an outlet valve (7a-d), and the the respective inlet valve (6a-d) opens when a pressure value which is a function of a holding current of the inlet valve (6a-d) is exceeded; • a pressure supply device (5) which can be hydraulically connected to the wheel brakes (8a-d) by means of a connecting valve (26) and has a pressure chamber (37) for providing a system pressure for actively building up pressure in the wheel brakes (8a-d); • an electronic control and regulation unit (12) for controlling the inlet (6a-d) and outlet valves (7a-d); the system pressure being determined, characterized in that a differential pressure between the system pressure and the pressure in at least one wheel brake (8a-d) is determined, and a holding current is set in the inlet valve (6a-d) of this wheel brake (8a-d) which leads to the opening of the inlet valve (6a-d) when the differential pressure is exceeded. Procedure according to Claim 1 , the system pressure being measured with a system pressure sensor (19) which is arranged in particular between the wheel brakes (8a-d) and the connection valve (24; 24a, 24b). Procedure according to Claim 1 or 2 , the new wheel volume, the wheel pressure and the differential pressure to the system pressure being recalculated after an outlet valve (7a-d) has been switched, and these updated variables are used to determine a new holding current value. Method according to one of the Claims 1 until 3 , wherein the setting of the holding current is carried out during a refilling process of the pressure chamber (37) of the pressure supply device (5) and / or when all inlet valves (6a-d) are closed. Procedure according to Claim 4 , whereby the lowering of the holding currents is carried out at all inlet valves (6a-d). Procedure according to Claim 4 The lowering of the holding current is only carried out at the inlet valve (6a-d) of the wheel brake (8a-d) on which an outlet valve (7a-d) has just been closed, or at two wheel brakes (8a-d) of an axle. Method according to one of the Claims 1 until 6th wherein the setting of the holding current in at least one inlet valve (6a-d) is carried out by the pressure supply device (5) during a rapid pressure build-up process. Method according to one of the Claims 1 until 7th , the connecting valve (26) being opened by the control and regulating unit when at least one opening condition is present, and the lowering of the holding current is only carried out when this opening condition is met. Procedure according to Claim 8 , wherein the opening condition is a function of the pressure piston position of the pressure supply device (5) and / or the engine torque. Procedure according to Claim 9 , wherein the opening condition is fulfilled when the engine torque is high enough to produce a pressure equilibrium between the pressure chamber (37) of the pressure supply device (5) and the system pressure. Brake system for automobiles, comprising • a driver brake request detection (25, 20); • hydraulically actuated wheel brakes (8a-d); • Inlet valves (6a-d) and outlet valves (7a-d) assigned to the wheel brakes, each wheel brake (8a-d) being hydraulically connected to an inlet valve (6a-d) and an outlet valve (7a-d), and the the respective inlet valve (6a-d) opens when a pressure value which is a function of a holding current of the inlet valve (6a-d) is exceeded; • a pressure supply device (5) which can be hydraulically connected to the wheel brakes (8a-d) by means of a connecting valve (26) and has a pressure chamber (37) for providing a system pressure for actively building up pressure in the wheel brakes (8a-d); • an electronic control and regulation unit (12) for controlling the inlet (6a-d) and outlet valves (7a-d), in which a method according to one of the preceding claims is implemented in terms of hardware and / or software. Braking system after Claim 11 , wherein the master cylinder (2) is designed with exactly one pressure chamber (17). Braking system after Claim 11 , with a master cylinder (2) designed as a tandem master cylinder with two pressure chambers (90, 92) each assigned to a brake circuit (I, II), with a pump (140, 142) in each brake circuit (I, II) for pressure build-up and Pressure reduction in the respective brake circuit (I, II) is provided.

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