DE102013009432A1 - Hydraulic brake system with a buffer - Google Patents

Abstract

A hydraulic brake system with an intermediate store is described. The braking system further comprises: at least one wheel brake; a master brake cylinder configured to shift hydraulic fluid into the at least one wheel brake; a pump that is configured to shift hydraulic fluid into the at least one wheel brake; a pressure relief valve which is set up to selectively block a hydraulic connection between the wheel brake and an inlet of the pump; a control unit which is set up to control the pump and the pressure relief valve. The intermediate storage of the brake system comprises a storage chamber, a piston, a reset element and a membrane. The storage chamber is set up to hold hydraulic fluid. The piston is movably arranged in the intermediate store. The restoring element generates a force which counteracts the absorption of hydraulic fluid in the storage chamber. The membrane is arranged between a wall of the storage chamber and the piston and is set up to seal the storage chamber from the environment when the piston is displaced.

Description

Technical area

Here, a vehicle brake system for a land vehicle will be described. The vehicle brake system includes a buffer for temporarily receiving hydraulic fluid provided with a membrane.

background

Land vehicles usually have a vehicle brake system in which a hydraulic fluid is conducted into the wheel brakes of the vehicle for braking. Increasingly, however, vehicles also have an electric machine which serves to drive the vehicle alternatively or at least in support of an internal combustion engine. The electric machine has the advantage over a combustion engine that it can be operated as a generator and as a motor. During generator operation of the electric machine, the kinetic energy of the vehicle is converted into electrical energy. The energy recovery from the kinetic energy of the land vehicle by means of the electric machine can be referred to as recuperation.

While in normal braking mode kinetic energy of the vehicle is converted into heat energy due to the frictional interaction of the brake shoes and brake discs on the wheel brakes, during recuperation the kinetic energy of the vehicle is used to charge the vehicle battery. The stored in the charged battery chemical energy is then used in a motor operation of the electric machine use for driving the land vehicle. The braking of the vehicle by means of the electric machine, so that the wheel brakes can remain unconfirmed. In general, this is even desirable because any kinetic energy converted to thermal energy at the wheel brakes is no longer available for charging the vehicle battery.

Since the wheel brakes are not actuated during recuperation, there is no or only a slight brake pressure in the brake system. Therefore, in the recuperation, the reaction of the brake pedal may deviate from a usual pedal feedback, so that the driver has the feeling that he would press the brake pedal empty. To avoid this, so as to continue to give the driver the usual brake feel, pedal depression simulators are often provided, which simulate a brake pressure build-up in the wheel brakes corresponding pedal return. However, such pedal return simulators increase the cost, volume and weight of the brake system, so that there are demands for brake systems that allow recuperation without additional components. In this regard, braking systems are known that differ only by minor changes in non-recuperation-compatible braking systems.

For example, in the document DE 10 2011 121 748 A1 proposed a brake system in which the driver builds the brake pressure in a conventional manner in the wheel brakes. The built-up brake pressure is then released during braking by the ABS or ESP pressure relief valves are opened. Due to the restoring force of the wheel brakes, the hydraulic fluid received in the wheel brakes is displaced via the open pressure reduction valves to a buffer store, which receives the hydraulic fluid during recuperation. Since the buffer is connected to the wheel brakes via the opened pressure reduction valve, approximately the same pressure is present in the wheel brakes and the buffer. Thus, there is still a small residual pressure in the wheel brakes even with open pressure reduction valves. This residual pressure generates a residual hydraulic braking torque. The converted by the residual braking torque into heat energy kinetic energy of the vehicle is thus no longer available for recuperation.

Underlying task

It is therefore an object to provide a simply constructed and inexpensive to produce vehicle braking system that allows hydraulic and regenerative braking. In addition, the braking system should give the driver a comfortable braking and braking feeling, with the largest possible portion of the kinetic energy of the land vehicle to be converted into electrical energy.

Suggested solution

To solve the problem, a hydraulic braking system for a land vehicle is proposed. The hydraulic brake system comprises at least one wheel brake associated with a wheel of the land vehicle; a master cylinder hydraulically connected to the at least one wheel brake, the master cylinder configured to displace hydraulic fluid into the at least one wheel brake upon actuation of the brake system by the driver; a pump whose output is hydraulically connected to the at least one wheel brake, the pump being configured to displace hydraulic fluid into the at least one wheel brake; a pressure relief valve, which is adapted to a hydraulic connection selectively lock between the wheel brake and an inlet of the pump; and a control unit configured to drive the pump and the pressure reduction valve. Furthermore, the brake system comprises a buffer with a storage chamber, a piston, a return element and a membrane. The storage chamber is hydraulically connected to the pressure relief valve and the inlet of the pump and adapted to receive hydraulic fluid. The piston is movably arranged in the buffer. The return element generates a force counteracting the absorption of hydraulic fluid into the storage chamber. The membrane is disposed between a wall of the storage chamber and the piston and is adapted to seal the storage chamber from the environment during a displacement of the piston.

According to a further aspect, a hydraulic unit is proposed to solve the problem. This hydraulic unit, the above-defined pump, the pressure reduction valve and the buffer are assigned.

With the proposed solution, the friction forces occurring during displacement of the piston can be reduced. For example, the membrane seal membrane may obviate the need for a conventional o-ring seal. Since an O-ring seal is usually clamped between a side wall of the storage chamber and a piston, the frictional resistance of the O-ring must be overcome to displace the piston. The proposed arrangement with the piston and the membrane can be moved almost without friction between the piston, diaphragm and the wall of the storage chamber. Accordingly, much lower forces are required to move the piston and the restoring element must apply a much lower restoring force to move the piston back to the starting position. The reset element of the buffer can therefore be significantly reduced. For example, softer springs, that is springs with smaller spring constants, can be used. This in turn means that the buffer can absorb hydraulic fluid even at very low pressure. Thus, the buffer with membrane allows a reduction of the residual brake pressure. In recuperation, therefore, a larger proportion of the kinetic energy can be converted into electrical energy. The increased recuperation power causes a significant CO ₂ savings. In addition, because the standard components of a braking system can be substantially maintained, the proposed solution can be implemented inexpensively.

Design and characteristics

The control unit of the brake system may be configured to control the pressure reduction valve, so that as a result of actuation of the brake system by the driver hydraulic fluid is displaced from the master cylinder via the at least one wheel brake and the opened pressure reduction valve in the buffer. The control unit may be configured to open the pressure relief valve during or after a brake pressure build-up by the driver. Further, the control unit may be configured to close an isolation valve during or after the brake pressure build-up by the driver.

The membrane may be, for example, a rolling membrane. The membrane may be disposed between the wall of the storage chamber and the piston such that a portion of a shell or shell surface of the membrane abuts a side wall of the storage chamber / sleeve and another portion of the shell or shell surface of the membrane abuts a side wall of the piston , The jacket or the lateral surface of the membrane can be arranged folded in a filled or an empty state of the buffer.

In the hydraulic connection between the buffer and the input of the pump, a first check valve may be arranged with an opening pressure of less than 0.3 bar. The opening pressure of the first shut-off valve may also be less than 0.1 bar.

The return element may be a spring. The force generated by the restoring element, counteracting the filling of the storage chamber, can correspond to a hydraulic pressure in the storage chamber of less than 1 bar. This pressure can also be referred to as recording pressure. The minimum absorption pressure of the intermediate storage tank can be less than 0.3 bar. The maximum intake pressure may be less than 0.9 bar. Although larger pressures may occur, however, the buffer is already completely filled at the maximum intake pressure, so that no additional hydraulic fluid volume can be absorbed.

The buffer can record a minimum hydraulic fluid volume even when empty. The membrane may be adapted to prevent drainage of hydraulic fluid from the accumulator to the inlet of the pump when the accumulator is empty. As an empty state of the buffer, a state may be referred to, in which the piston is held by the restoring force of the return element in a starting position. In the empty state of the Buffer, the pressure of the hydraulic fluid is not sufficient to move the piston from its initial position. The membrane may have a sealing lip. The sealing lip may be adapted to abut against a wall of the storage chamber in the empty state of the buffer. The sealing lip may be adapted to prevent the drainage of hydraulic fluid in the empty state of the buffer. The sealing lip may be configured to prevent an exchange of hydraulic fluid between an inlet and an outlet of the buffer.

Brief description of the drawings

Other objects, features, advantages and applications will become apparent from the following description of non-limiting embodiments to be understood and the accompanying drawings.

1 shows a schematic sectional view of a first embodiment of a buffer;

2 shows a schematic sectional view of a second embodiment of a buffer;

3 shows a schematic hydraulic circuit diagram of a brake system; and

4 shows a schematic view of a hydraulic unit.

Detailed description of embodiments

Embodiments of a hydraulic brake system of a land vehicle will be described below. Matching elements are denoted by the same reference numerals in the figures.

1 shows a schematic sectional view of a first embodiment of a buffer 10 , The cache 10 essentially comprises a storage chamber 12 , a piston 16 , a membrane 21 and a return element. The storage chamber 12 is provided for receiving hydraulic fluid of the brake system. The cavity of the storage chamber 12 may for example be formed by a hole in an aluminum block, wherein the wall 14 the bore the storage chamber 12 limited. The shape of in 1 illustrated storage chamber 12 is essentially cylindrical. However, there may be other forms for cache 10 and storage chamber 12 be provided. Further, an inlet 18 and an outlet 19 provided the storage chamber 12 connect with hydraulic fluid lines of the brake system.

The open side of the bore is through the piston 16 limited. The piston 16 is arranged movably. At the in 1 illustrated embodiment, the piston 16 be moved up or down. This is by the double arrow 20 indicated. As the material for the piston, for example, plastic can be used. The piston 16 is in a sleeve 17 guided. The sleeve 17 can be embedded in the hole and with the wall 14 the bore enclose a substantially cylindrical cavity. The sleeve 17 can an opening 17a exhibit. About the opening 17a can be carried out a pressure exchange with the environment, so that in the sleeve 17 Ambient pressure is present. As material for the sleeve 17 For example, steel can be used.

At the in 1 illustrated embodiment, the membrane 21 between the storage chamber 12 and the piston 16 arranged. Part of the jacket of the membrane 21 lies on an inner wall of the sleeve 17 and another part of the jacket of the membrane 21 lies on a side surface of the piston 16 at. Between the on the inner wall of the sleeve 17 adjacent part and on the side surface of the piston 16 adjacent part of the coat is a rolled pleat 21b arranged the membrane. An end face of the membrane 21 lies on an end face of the piston 16 at. Thus, the membrane is partially through the piston 16 supported. The membrane 21 is impermeable to the hydraulic fluid of the brake system and is provided to the storage chamber 12 seal. In particular, the membrane is provided to prevent a resulting from the movement of the piston leakage of the hydraulic fluid. At the in 1 illustrated embodiment, the storage chamber 12 strictly speaking, not by the piston 16 but through the piston 16 adjacent membrane 21 limited. However, other arrangements may be provided. Thus, in further embodiments, a membrane may be provided which only the gap between the wall 14 and pistons 16 seals, leaving the storage chamber 12 is limited by the piston and diaphragm.

As material for the membrane 21 For example, an elastomer can be used. The elastomer may be reinforced by a fabric. Because the membrane 21 the storage chamber 12 seals, is a conventional seal the storage chamber 12 not required by a piston and a clamped in the radial direction between the wall and piston O-ring.

The membrane 21 can on the wall 14 and / or on the sleeve 17 be attached. At the in 1 illustrated embodiment, the membrane 21 between the sleeve 17 and the wall 14 trapped. For example, a level 14a in the wall 14 be provided. The edge of the membrane 21 can at the stage 14a rest and the membrane 21 can from the sleeve 17 against the stage 14a be pressed. At the edge of the membrane 21 can also have a circumferential thickening 21a be provided. On the sleeve 17 can be a head start 17b be provided, which is the membrane 21 against the stage 14a pushes and thickening 21a the membrane 21 fixed. The lead 17b can, for example, in the radial direction between the thickening 21a the membrane and the storage chamber 12 be arranged. The lead 17b can prevent the thickening 21a from the gap between the sleeve 17 and wall 14 is pulled. The lead 17b can be formed circumferentially. For diaphragms that seal only the radial gap between the piston and the wall of the storage chamber, may be on the piston 16 one of the above-described attachment of the membrane corresponding attachment of the membrane may be provided on the piston.

At the membrane 21 can a sealing lip 23 be provided. The sealing lip 23 can, for example, at one of the storage chamber 12 facing side of the membrane 21 be arranged. At the in 1 illustrated embodiment is the sealing lip 23 on one of the front side of the membrane 21 arranged. Accordingly, the sealing lip protrudes 23 in the storage chamber 12 , The cross section of the sealing lip 23 may be semicircular or trapezoidal, for example. In a plan view of the end face of the membrane, the sealing lip 23 for example, have a round or circular shape. If the cache is empty, so the cache 10 no hydraulic fluid absorbs, lies the sealing lip 23 at the end face of the piston 16 opposite section of the wall 14 like this, for example 1 is shown. The end face of the piston 16 opposite section of the wall 14 can also be used as the bottom of the storage chamber 12 be designated. The sealing lip 23 can be arranged such that at the portion of the wall 14 fitting sealing lip 23 the junctions of admitting 18 and the outlet 19 separates each other. Through the sealing lip 23 can be in the empty state of the cache 10 a drain of hydraulic fluid through the outlet 19 be prevented. For example, if a pump of the brake system hydraulic fluid from the buffer 10 sucks, can through the sealing lip 23 prevents that in the space between wall 14 and pistons 16 absorbed hydraulic fluid from the buffer 10 is sucked. Through the sealing lip 23 is thus also in the empty state of the cache 10 a minimum hydraulic fluid volume in the storage chamber 12 is included. That in the storage chamber 12 enclosed minimum hydraulic fluid volume exerts a minimum pressure on the diaphragm 21 out. This can be prevented at the roll fold 21b the membrane 21 In comparison to the ambient pressure, a negative pressure is created.

In the embodiment of the 1 a rolling membrane is provided. The rolling diaphragm is arranged so that it attaches itself to the piston 16 , the Wall 14 and / or the inner wall of the sleeve 17 supported. By supporting the membrane 21 can damage the membrane 21 For example, if a high pressure occurs due to an error, it can be prevented. When moving the piston 16 rolls the membrane 21 at the rolled fold 21b from where the position of the rolled fold 21b with the piston 16 is moved up or down.

At the in 1 illustrated embodiment, the return element by a spring 22 educated. For example, a coil spring may be provided. The feather 22 can, for example, in 1 shown on the sleeve 17 be supported and the piston 16 press down. To ensure that the return element the piston 16 reliable in the 1 shifts position shown, is the spring 22 biased. The power of the spring 22 acts on the piston 16 on the one in the storage chamber 12 absorbed hydraulic fluid, wherein the spring 22 generates a force, which is the inclusion of hydraulic fluid in the storage chamber 12 counteracts.

The pressure of the hydraulic fluid creates one on the piston 16 Acting force. The force generated by the pressure of the hydraulic fluid exceeds the biasing force of the spring 22 the hydraulic fluid shifts the piston 16 upward, with hydraulic fluid in the storage chamber 12 is recorded. Moving the piston upwards turns the spring 22 curious; excited. When the pressure of the hydraulic fluid decreases and that of the hydraulic fluid on the piston decreases 16 applied force is less than that of the spring 22 generated restoring force, moves the spring 22 the piston 16 down, leaving the cache 10 the hydraulic fluid returns to the brake system.

In 2 is a cross section of a second embodiment of a buffer 10 shown. The basic structure of in 2 shown cache is similar to the in 1 illustrated cache. Unlike the in 1 shown cache is in the in 2 illustrated buffer a folded rolling diaphragm 25 intended. In this embodiment, it is for moving the piston 16 do not need membrane jacket on the inner wall of the sleeve 17 or on the wall 14 but is folded in a space between pistons and sleeve arranged. By this construction, the cache 10 be constructed more compact than the in 1 illustrated buffers.

The in the 1 and 2 illustrated cache 10 For example, they may be low pressure buffers. The reset element may for example be sized so that the cache 10 absorbs hydraulic fluid from a pressure of 0.3 bar, so that the minimum absorption pressure of the buffer is 0.3 bar. Furthermore, the restoring element can be set up so that the pressure required to completely fill the temporary storage tank with hydraulic fluid is less than 1.5 bar. For example, to completely fill the cache 10 required pressure less than 1 bar. Furthermore, the pressure required for complete filling can be 0.9 bar. Accordingly, brake systems can be implemented with the caches described, the residual brake pressure is less than 1 bar.

The 3 is a schematic hydraulic circuit diagram of a brake system 30 , This hydraulic brake system 30 includes in conjunction with the 1 or 2 described cache 10 ,

The brake system 30 allows recuperation, ie a deceleration process in which an electric machine of the land vehicle converts the kinetic energy of the land vehicle into electrical energy. The brake system 30 has two hydraulically separated brake circuits, hereinafter the brake system 30 is explained in terms of a brake circuit. What has been said for the components of this brake circuit applies in a corresponding manner to the other brake circuit. Even though only one brake circuit is considered below, there are interactions between the two brake circuits. This is done via a master cylinder 36 of the land vehicle pressure equalization, so that in both brake circuits usually the same brake pressure is applied.

This in 3 illustrated brake system 30 includes a brake pedal 32 , The brake pedal 32 is via a brake booster 34 with the master cylinder 36 connected. The master cylinder 36 is with a brake fluid reservoir 38 connected, in which hydraulic fluid is kept in stock.

Via supply lines 40 . 40a . 40b is the master cylinder 36 with a first wheel brake 48 and a second wheel brake 50 connected. In the supply line 40a to the first wheel brake 48 is a first isolation valve 42 provided, wherein the first isolation valve 42 is set up to the feed line 40a optionally lock to the first wheel brake. In the supply line 40b to the second wheel brake 50 is a second isolation valve 44 provided, wherein the second isolation valve 44 is set up to the feed line 40b to the second wheel brake 50 optionally lock. Between the master cylinder 36 and the wheel brakes is in the supply line 40 a third isolation valve 46 arranged that is adapted to the feed line 40 to lock. Thus, the third isolation valve isolates 46 in the closed switching state, the master cylinder 36 from the wheel brakes 48 . 50 ,

From the first and second wheel brakes 48 . 50 lead return lines 52 . 52a . 52b to an inlet of a pump 58 , In the return line 52a from the first wheel brake 48 is a first pressure reduction valve 54 arranged, wherein the first pressure reduction valve 54 is set up, the return line 52a from the first wheel brake 58 optionally lock. In the return line 52b from the second wheel brake 50 is a second pressure relief valve 56 arranged, wherein the second pressure reduction valve 56 is set up, the return line 52b from the second wheel brake 50 optionally lock.

The inlet 18 of the cache 10 is hydraulic with the first and second pressure relief valve 54 . 56 connected. The outlet 19 of the cache 10 is hydraulic with an inlet of the pump 58 connected. The cache 10 is for temporary admission of the wheel brakes 48 . 50 provided outflowing hydraulic fluid. In the connection between the cache 10 and the inlet of the pump 58 is a first check valve 67 intended. The check valve 67 may be a check valve, which already assumes the passage position with a small pressure difference. Thus, a check valve may be provided with an opening pressure of less than 0.3 bar. Furthermore, a check valve may be provided with an opening pressure of less than 0.1 bar. Also at the inlet of the pump 58 provided check valves may be constructed such that they assume their passage position even at low pressure differences. Other blocking valves for pressure limiting are parallel to the isolation valves 42 . 44 . 46 and the pressure relief valves 54 . 56 provided to bridge this when the applied pressure on one side of the check valves exceeds a predetermined value.

The pump 58 is adapted to hydraulic fluid in the wheel brakes 48 . 50 to promote. This is the outlet of the pump 58 with the supply line 40 connected. The inlet of the pump 58 is with a supply valve 60 connected so that the inlet of the pump 58 through the supply valve 60 with the brake fluid reservoir 38 is connectable. By opening the supply valve 60 can the pump 58 Hydraulic fluid from the brake fluid reservoir 38 suck. The pump 58 may be a radial piston pump whose flow rate is variable, the in 3 shown pump is a radial piston pump with six pistons.

The isolation valves 42 . 44 . 46 , Pressure relief valves 54 . 56 and the supply valve 60 may be, for example, electromagnetically operable 2/2-way valves. The isolation valves 42 . 44 . 46 are open in normal position valve assemblies that allow in normal position (no current) a flow of hydraulic fluid. The pressure relief valves 54 . 56 and the supply valve 60 are closed in normal position valve assemblies that prevent in normal position (no current) a flow of hydraulic fluid. However, it is also possible to use other valves to achieve the same effect.

The isolation valves 42 . 44 . 46 and the pressure relief valves 54 . 56 may be arranged to be wholly or partially addressed. In a partial control of the valves, the drive energy is not sufficient to fully open or close. The valves are therefore in a partially open switching state, in which a smaller volume of hydraulic fluid can flow through the valves, as in the fully open switching state. Thus, the valves throttle in the partially open switching state, the flow of hydraulic fluid. Further, the valves can be controlled, for example, with pulse width modulation (PWM) signals, which can be throttled by the PWM control over the valves effluent hydraulic fluid volume.

Moreover, in 3 a control unit 68 shown. The control unit 68 is with the isolation valves 42 . 44 . 46 the pressure relief valves 54 . 56 and the supply valve 60 electrically connected and adapted to specify these valves switching states. This activation of the valves can also be referred to as opening or closing of the valves. The control unit 68 is also with a motor of the pump 58 electrically connected and adapted to the flow rate of the pump 58 pretend. For example, the control unit 68 output a PWM signal and thereby the speed of the pump 58 pretend. For reasons of clarity, the respective electrical connections are not shown.

Further, on the brake pedal 32 a pedal travel sensor 66 for detecting the operation of the brake pedal 32 arranged, wherein the pedal travel sensor 66 one of the operation of the brake pedal 32 corresponding signal to the control unit 68 emits. The brake system may comprise further components, such as sensors, which are not absolutely necessary for the understanding of the present brake system and are not shown here for reasons of clarity.

In 3 is an electrical machine 70 indicated. The electric machine 70 is adapted to convert kinetic energy of the land vehicle into electrical energy during a deceleration process. The electric machine generates this 70 a regenerative braking torque. The electric machine 70 can be part of the drive train of the land vehicle. Likewise, the electric machine 70 be a generator that is independent of the drive train coupled to the wheels of the land vehicle and is specifically designed to convert kinetic energy into electrical energy. The operation of the electric machine 70 is through a control unit 72 controlled. The control unit 72 is with the control unit 68 connected to the brake system. Accordingly, data and / or control signals between the controller 72 the electric machine and the control unit 68 be replaced the brake system. In addition to two separate controls for braking system 30 and electric machine 70 can also be provided a common control.

Hereinafter, with reference to FIGS 3 an operation of the brake system in conjunction with recuperation explained. When recuperation is a part of the total braking torque through the braking system 30 and the other part by the electric machine 70 provided. So that the process of the braking process for the driver remains predictable and no unexpected effects occur, the composite of hydraulic braking torque and regenerative braking torque total braking torque during the entire braking process by the operation of the brake pedal 32 predetermined braking request of the driver correspond. The replacement of the hydraulic braking torque by a regenerative braking torque and vice versa can be referred to as diaphragms.

At the in 3 illustrated brake system 30 are in the initial phase of recuperation the isolation valves 42 . 44 . 46 open. Thus, the operation of the brake pedal 32 by the driver a volume displacement of the hydraulic fluid from the master cylinder 36 to the wheel brakes 48 . 50 , Accordingly, the driver builds by pressing the brake pedal 32 in the wheel brakes 48 . 50 a brake pressure and thus a hydraulic braking torque.

The blinding can be done after the brake pressure build-up or already during the brake pressure build-up. If the fading after the Driver has fully built the brake pressure, the initial phase of recuperation corresponds to a conventional braking operation. After the brake pressure has been built up, at least one of the isolation valves is closed and one or more of the pressure relief valves are opened. As a result, the brake pressure in the wheel brakes can be reduced, while the driver is given a familiar pedal reaction.

If the aperture already occurs during the brake pressure build-up, for example, the first and second isolation valve 42 . 44 or the third isolation valve 46 be partially controlled. The partial control of one of the isolation valves 42 . 44 . 46 causes the volume displacement from the master cylinder 36 in the wheel brakes 48 . 50 is throttled. By throttling the volume displacement of the pressure build-up in the wheel brakes 48 . 50 delayed. In addition, in the wheel brakes 48 . 50 applied brake pressure lower than that in the master cylinder 36 applied brake pressure. Thus, the hydraulic braking torque can be built reduced already during the construction of the total braking torque.

The control unit 68 can be the throttle effect of the or the isolation valves 42 . 44 . 46 predetermined such that the pedal reaction due to the throttle effect largely corresponds to the pedal reaction in a purely hydraulic braking operation. For example, the isolation valve (s) 42 . 44 . 46 be controlled such that an increasing deflection of the brake pedal 12 to an increasing closing of the isolation valve (s) 42 . 44 . 46 leads.

The pressure relief valves 54 . 56 may be open or closed by the driver during braking torque build-up, depending on how the transition from hydraulic braking torque to regenerative braking torque is implemented. For example, in the document DE 10 2012 023 345 A1 described dynamic pressure control be provided to the hydraulic braking torque in dependence on that of the electric machine 70 built regenerative braking torque to reduce. The disclosure of the document DE 10 2012 023 345 A1 is hereby fully incorporated by reference.

Due to the resistance caused by the throttling action of the isolation valves and / or the pressure reduction valves, a suitable counterforce can be generated on the brake pedal. Thus, the driver is not given the feeling that he would brake pedal 32 press empty. Since due to the throttling effect less hydraulic fluid is displaced into the wheel brakes, the pedal travel extension otherwise frequently occurring during recuperation can at least be reduced. The pedal reaction of the brake system designed in this way thus essentially corresponds to the pedal reaction of conventional brake systems or is at least closely approximated. A special pedal feedback simulation device can therefore be dispensed with. In addition, the partial closing of the isolation valves takes place 42 . 44 largely without noise.

Once the regenerative braking torque from the electric machine 70 has been constructed, the hydraulic braking torque can be completely hidden as a rule. In addition, this flows in the wheel brakes 48 . 50 absorbed hydraulic fluid through the open pressure relief valves 54 . 56 in the cache 10 , By receiving the hydraulic fluid is in the buffer 10 tensioned the return element.

With open pressure relief valves 54 . 56 lies in the wheel brakes 48 . 50 and in the cache 10 about the same pressure. This residual pressure generated even with open pressure reduction valves 54 . 56 a residual hydraulic braking torque. The in conjunction with the 1 and 2 described buffer, in particular compared to conventional buffers with O-ring seals, particularly low residual pressures. For example, the described buffers may allow residual brake pressures of less than 1 bar. Accordingly, the residual hydraulic braking torque can be significantly reduced during recuperation, so that a larger proportion of the kinetic energy through the electric machine 70 can be converted into electrical energy.

The 4 is a schematic representation of a hydraulic unit 80 , The hydraulic unit 80 includes a metal body 82 , which can be made of aluminum, for example. Inside the metal body 82 are at least the kegs of the pump 58 , the isolation valves 42 . 44 . 46 and pressure relief valves 54 . 56 added. In the 4 are just the engine 84 the pump 58 and the bobbins 86 visible for actuating the valves. In addition, in the hydraulic unit 80 other elements of in conjunction with 3 be recorded described brake circuit. These are, however, inside the metal body and are therefore not visible.

This in 4 illustrated hydraulic unit 80 also includes hydraulic connections 88 where the wheel brakes 48 . 50 and the master cylinder 36 can be connected. In addition, in or on the hydraulic unit 80 one or more buffers 10 be provided. In the hydraulic unit 80 recorded cache 10 can as a hole in the metal body 82 be executed. This in 4 through the two illustrated sleeves 17 indicated. Alternatively, on the hydraulic unit 80 also connections 88 for one or more buffers 10 be provided. Finally, on the hydraulic unit 80 the control unit 68 to be appropriate.

The variants of the brake system described above 30 and the cache 10 are only intended to improve understanding of the structure, operation and characteristics of the braking system 30 and the cache 10 ; they do not restrict the revelation to the exemplary embodiments. The figures are partially schematic, with essential properties and effects are shown partially enlarged significantly to illustrate the functions, principles of action, technical features and features. In this case, each mode of operation, every principle, every technical embodiment and every feature which is / are disclosed in the figures or in the text can be associated with all claims, every feature in the text and in the other figures, other modes of operation, principles, technical designs and features included in or resulting from this disclosure are freely and arbitrarily combined so that all conceivable combinations are consistent with the brake system described 30 and cache 10 attributable to. In this case, combinations between all individual versions in the text, that is to say in each section of the description, in the claims and also combinations between different variants in the text, in the claims and the figures.

Also, the claims do not limit the disclosure and thus the combination options of all identified features with each other. All disclosed features are explicitly disclosed herein individually as well as in combination with all other features.

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 102011121748 A1 [0005]
• DE 102012023345 A1 [0049, 0049]

Claims (10)

Hydraulic brake system ( 30 ) for a land vehicle, with at least one wheel brake associated with a wheel of the land vehicle ( 48 . 50 ); a master cylinder ( 36 ), which hydraulically with the at least one wheel brake ( 48 . 50 ), wherein the master cylinder ( 36 ) is adapted, upon actuation of the braking system ( 30 ) by the driver hydraulic fluid in the at least one wheel brake ( 48 . 50 ) to move; a pump ( 58 ) whose output is hydraulically connected to the at least one wheel brake ( 48 . 50 ), the pump ( 58 ) is adapted to hydraulic fluid in the at least one wheel brake ( 48 . 50 ) to move; a pressure relief valve ( 54 . 56 ), which is adapted to provide a hydraulic connection between the wheel brake and an inlet of the pump ( 58 ) optionally to block; a control unit ( 68 ), which is adapted to the pump ( 58 ) and the pressure relief valve ( 54 . 56 ) head for; and a cache ( 10 ) with a storage chamber ( 12 ), a piston ( 16 ), a return element and a membrane ( 21 ), the storage chamber ( 12 ) hydraulically with the pressure reduction valve ( 54 . 56 ) and the inlet of the pump ( 58 ) and adapted to receive hydraulic fluid, the piston ( 16 ) movable in the cache ( 10 ), the return element is one of the inclusion of hydraulic fluid in the storage chamber ( 12 ) produces counteracting force, and the membrane ( 21 ) between a wall of the storage chamber ( 12 ) and the piston ( 16 ) is arranged and is adapted to a displacement of the piston ( 16 ) the storage chamber ( 12 ) to seal against the environment. A hydraulic braking system according to claim 1, wherein the control unit ( 68 ) is adapted to the pressure reduction valve ( 54 . 56 ) that as a result of actuation of the brake system by the driver hydraulic fluid from the master cylinder ( 36 ) via the at least one wheel brake ( 48 . 50 ) and the opened pressure relief valve ( 54 . 56 ) in the cache ( 10 ) is moved. A hydraulic braking system according to claim 1, wherein the membrane ( 21 ) is a rolling membrane. Hydraulic brake system according to claim 1, wherein in the hydraulic connection between the buffer ( 10 ) and the inlet of the pump ( 58 ) a first check valve ( 67 ) is arranged with an opening pressure of less than 0.3 bar, and preferably less than 0.1 bar. Hydraulic brake system according to one of the preceding claims, wherein the pressure generated by the restoring element, the filling of the storage chamber ( 12 ) counteracting force a hydraulic pressure in the storage chamber ( 12 ) of less than 1 bar. Hydraulic brake system according to one of the preceding claims, wherein the minimum absorption pressure of the buffer ( 10 ) is about 0.3 bar. Hydraulic brake system according to one of the preceding claims, wherein the membrane ( 21 ) is set up in the empty state of the cache ( 10 ), a drainage of hydraulic fluid from the buffer ( 10 ) to the inlet of the pump ( 58 ) to prevent. Hydraulic brake system according to the preceding claim, wherein the membrane ( 21 ) a sealing lip ( 23 ) having. Hydraulic brake system according to the preceding claim, wherein the sealing lip ( 23 ) is set up in the empty state of the cache ( 10 ) an exchange of hydraulic fluid between an inlet ( 18 ) and an outlet ( 19 ) of the cache ( 10 ) to prevent. Hydraulic unit for a defined in the preceding claims brake system, wherein the hydraulic unit, the pump, the valve assemblies and the buffer are assigned.

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