WO2019101669A1

WO2019101669A1 - Braking system for motor vehicles and operating method

Info

Publication number: WO2019101669A1
Application number: PCT/EP2018/081697
Authority: WO
Inventors: Stefan Drumm
Original assignee: Continental Teves Ag & Co. Ohg
Priority date: 2017-11-24
Filing date: 2018-11-19
Publication date: 2019-05-31
Also published as: DE102017221058A1

Abstract

The invention relates to a braking system (2) for motor vehicles having: a master brake cylinder (41) comprising a master brake cylinder housing (42) with a master bore, in which at least one master cylinder piston (48) having a hydraulic active area (A1) which delimits a pressure chamber (50) that is placed under a braking system pressure in the event of actuation of the master brake cylinder (41) is guided axially, and with a hydraulic connection (80, 84) in which pressure medium placed under this braking system pressure is fed into at least one associated braking circuit (I, II); a brake pedal (44) for actuating the master brake cylinder (41); a hydraulic drive stage (40) arranged upstream of the master brake cylinder (41), having a drive piston (48; 48, 200) that can be acted on both by the pedal force and hydraulically via an effective active area (A2); hydraulically actuatable wheel brakes (8, 10, 12, 14); a path detection device (s/U), which detects the actuation path of the brake pedal (44) or of a piston (48) connected to the brake pedal (44); a pressure-providing device (60) which is designed to generate a drive circuit pressure in a hydraulic drive circuit (A), which comprises a drive chamber (90), in which the drive circuit pressure acts on the drive piston (48; 48, 200) with a force in the actuation direction; an electrohydraulic unit (30), which per wheel brake (8, 10, 12, 14) has a separation valve and an outlet valve for adjusting braking pressures individual to each wheel, wherein hydraulic means (200, 244) are provided in order to vary the effective active area (A2) of the drive piston (48; 48, 200) depending on the pedal path. The invention also relates to methods for operating a braking system (2).

Description

Brake system for motor vehicles and operating procedures

The invention relates to a braking system for motor vehicles according to the preamble of claim 1. It further relates to an operating method.

In the vast majority of today's braking systems for motor vehicles, the hydraulic pressures are provided for actuating the wheel brakes by means of the combination of a vacuum brake booster with a tandem master cylinder. In the future, the vacuum brake booster will be replaced by an electric brake booster, because in modern vehicles, especially cars, on the one hand no vacuum is available and on the other for driver assistance functions such as congestion and parking assistance and for au tomatized driving an electrical controllability of the brake booster is required which, of course, is technically easier to re-assemble in the electric brake booster.

The known vacuum brake booster are usually equipped with a special gain characteristic, which has been found to be particularly comfortable to use for the driver. Upon actuation of the brake pedal of a car with vacuum brake booster and brake master cylinder, the output brake circuit pressures for small pedal travel are controlled in response to this pedal travel, the pressures in the initial road range increase very rapidly and the pedal force hardly increases. For more severe braking, the pedal characteristic transitions to a proportionality between the pedal force and the released pressure.

Electromechanical-hydraulic brake booster are known for example from DE 10 2011 086 916 Al. In boosting assisted braking processes, the pressure medium volume supplied to the wheel brakes is composed of a first volume of pressure medium delivered by the master brake cylinder and a second volume of pressure medium volume. which is controlled by a means for generating the boosting force. This makes it possible to assign a pressure value to each signal value of a detected pedal travel according to a predetermined characteristic curve, with which the wheel brakes are acted upon and at the same time causes a hydraulic portion of the pedal restoring force. Thus, the known from Vakuumbrems power amplifier steep increase in brake pressure in the initial pedal travel range can be realized. The disadvantage here is that the pedal force is due to the design in fixed proportional relation to the brake pressure. For a more comfortable pedal feel, the pedal return force in the initial pedal travel range would have to be reduced.

The invention has for its object to provide a brake system with an electro-hydraulic brake circuit pressure supply, which has approximately the proven, known from the vacuum brake booster to be detached characteristic and exerts a pedal restoring force, which reduces ver in the beginning Pedalweg area compared to the prior art is. Furthermore, a corresponding operating method should be provided.

This object is achieved with respect to the brake system according to the invention in that hydraulic means are provided to make the effective effective surface of the drive piston pedal path dependent variable.

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

The invention is based on the consideration that it is also desirable in hydraulic systems to realize the abovementioned actuation characteristics known from vacuum brake boosters, also in motor vehicles without a vacuum, in which an electrohydraulic brake system is used. As has now been recognized, this objective can be achieved by means of a pedal path-dependent effective surface area change.

The component connected to the main brake piston is preferably the hydraulic primary and drive piston.

Advantageously, the hydraulic means comprise a Wirkflächenvergrößerungskörper which is acted upon in the direction of actuation of the drive circuit pressure, wherein the corresponding reaction force on the Wirkflächenvergrößerungskörper against the operating direction consists of the sum of two forces, one of which is supported on the drive piston and the other on Antriebsstufen- and master cylinder housing and these support forces being path-dependent and / or differential-dependent.

The force supporting the active surface enlargement body against the drive piston is preferably a contact force due to a stop. That is, it is zero when the travel piston is larger than the effective-area increasing body path, and this same-path force assumes values greater than zero, which cause the effective-area enlargement body to not overtake the drive piston.

The Wirkflächenvergrößerungskörper against the drive step and master cylinder housing supporting force depends on the path of Wirkflächenvergrößerungskörpers relative to the housing. In a first, subsequent to the initial position path section, this support force is preferably zero. Thereafter, it grows in a second path section, preferably by placing it on a spring, and may eventually be in a third path section a contact force which causes another path of the Wirkflächenvergrößerungskörpers is blocked relative to the Antriebsstufen- and master cylinder housing. Preferably, the hydraulic means are designed such that the effective effective area decreases starting from an unactuated position of the brake pedal with increasing pedal travel.

The effective effective area in the first path section is preferably constant (and enlarged relative to an active surface in the third section) and also constant in the third path section (unenlarged). In between, there is preferably a continuous transition in the second path section. Because a fact neuter area change with automotive technology usual means is not feasible, the concept of path-dependent support of Wirkflächenvergrößerungskörpers was selected. Its hydraulically effective surface always remains the same. In the first path section, the effective area enlarging body is preferably supported solely on the drive piston. In the third path section, he preferably relies alone on the drive stage and master cylinder housing.

The active surface enlarging body advantageously has a pressure in the drive chamber, d. H. the drive circuit pressure acted upon additional effective area, wherein the Wirkflächenvergrößerungskörper is supported to a predetermined Pe dalweg on the hydraulic drive piston and beyond outgoing pedal travel on Antriebsstufen- and Hauptbremszy cylinder housing.

When pedal travel, which are greater than a predetermined pedal wegschwelle, preferably carried out a support of the Wirkflä chenvergrößerungskörpers the master cylinder housing by a support spring. Starting from this pedal path, the support begins, first with a small, then increasing with the way force. There is no power jump. The reaching of the Pedalwegschwelle corresponds to the end of the first section and the beginning of the second section. In a preferred embodiment, the support spring is formed as a plate spring or comprises at least one plate fields. In particular, it may be formed as a plate spring package. A stack of individual disc springs has the advantage of requiring little space.

In a further preferred embodiment, the Ab-support spring is formed as a helically wound compression spring or comprises a helically formed compression spring. A helically wound compression spring has a more linear characteristic than a diaphragm spring and has less hysteresis.

The effective area enlarging body is preferably designed as a sleeve penetrated by the drive piston.

Preferably, the brake system comprises at least two brake circuits and the master cylinder at least two pressure chambers, each brake circuit is associated with one of the pressure chambers.

The pressure medium reservoir preferably has connections assigned to the respective pressure chambers.

Advantageously, valve means are provided by which the brake circuits can be connected separately to the drive circuit.

Advantageously, normally open valve means are seen easily, which allow for unoperated brake pedal pressure buildup in the brake circuits by their activation, a flow of pressure medium is prevented in the pressure fluid reservoir. Advantageously, a pressure sensor for detecting the pressure in the drive circuit is provided.

Preferably, at least one pressure sensor is provided for detecting at least one brake circuit pressure.

Advantageously, an analog controllable valve to be may be required to reduce the pressure in the drive circuit.

With regard to the method, the above-mentioned object is achieved according to the invention by opening the valve means designed as switching valves in a normal operation with a ready-to-use pressure supply device for pedal-controlled and automated braking and adjusting a hydraulic pressure with the aid of the pressure supply device the open booster valve is ready in both brake circuits as well as in the drive chamber.

In normal operation, the primary circuit, secondary circuit and drive circuit are interconnected hydraulically. The common pressure is called braking system pressure and is provided via the pressure supply device, which is controlled by a elec tronic unit. For non-interconnected hydraulic circuits, however, the two brake circuit pressures and the working circuit pressure may be different.

Preferably, to perform a pedal-operated braking as Rekuperationsbremsung a Radbremsdruckaufbau is reduced or prevented and provided the same pedal behavior as without recuperation. The driver does not have to get used to a new braking behavior or pedal feel during a recuperation braking. In the case of a recognized leakage and / or non-functioning pressure supply device, the switch valves are preferably not opened. In this way, the present in the unactuated state Kreistrennung remains and a possible leakage has no effect on the other brake circuit.

The described brake system fulfills further tasks in preferred embodiments.

A brake circuit pressure supply compatible with an ESC module is realized. In order to continue to use as many components of the brake system at the transition from a vacuum-based to an electro-hydraulic brake booster, the new brake circuit pressure generating device described a conventional ESC module downstream and operated with the usual range of functions.

This includes one of the Bremskreisdruckbereitstel treatment device independent brake pressure generation - for example, if the required pressures are higher than the pressure currently supplied by the Bremskreisdruckbereitstellungseinrichtung. For this purpose, it is necessary that the ESC module can suck pressure medium via the brake circuit pressure supply device from the container.

Therefore, the task arises to get along in a new brake circuit pressure supply device without so-called isolation valves, as some brake system hydraulic layouts are used to decouple the Bremskreisdruckbereitstellungsein direction hydraulically from the modulator (eg in an ESC module). The pressure fluid flow rates permitted by such isolation valves in their open state are insufficient.

This task is easy to solve, since the ESC module itself is already provided, with arbitrary specifiable Circular press to work. Critical is only the operation of the ESC module when it should provide wheel brake pressures and at the same time a circular pressure drops to the value of the atmospheric pressure. In this case, the ESC "sucks" at the corresponding brake circuit, the circuit pressure drops below the atmospheric pressure and the ESC module requires a possible unhindered flow of pressure medium from the container into the brake circuit.

In conventional tandem master cylinders (THZ) two pressure chambers for the two brake circuits are arranged one behind the other. A floating piston separates the two chambers from each other and the primary pressure chamber is limited by a mechanically coupled to the brake pedal primary piston. In the two chambers springs are arranged, which position the piston in the unactuated state. The two springs are dimensioned differently. In the conventional brake system, the spring of the primary chamber is stronger, in order to achieve that at a pedal operation initially both pistons are moved simultaneously to close the two pressure equalization connections between THZ chambers and containers as possible simultaneously. Due to the different springs and different contributions of the seal ring friction on the balance of forces of the two pistons, the pressures in both brake circuits are always slightly different. In vehicles with diagonal brake circuit distribution, this leads to an undesirable skewing of the vehicle during braking.

Therefore, the task arises in the described brake circuit pressure generating device in a Normalbe mode to produce two exactly the same circular pressures Be the provision of exactly the same pressures in both circuits is preferably achieved in that both circuits are connected via Zuschaltventile in normal braking operation.

The braking system is also capable of providing a brake pedal travel during recuperation braking. A disadvantage of known brake system layouts is that a complex Electro-hydraulic cylinder-piston assembly must also be included in the system scope of the brake system to allow Rekuperationsbremsungen. Therefore, the task is to design a new Bremskreisdruckbereitstellungseinrichtung so that no additional components are required for Rekuperationsbremsungen, but on the other hand in brake system layouts that are not intended for Rekuperationsbremsungen no unnecessary components Vorhalten to brake systems for the same vehicle with Recuperation to be compatible.

This object is preferably achieved in that the piston of the actuator in the standby mode not in a

With recuperation braking, the ESC module with the aid of the wheel brake pressure modulation valves advantageously prevents pressure fluid from flowing into the wheel brakes or, in the case of partial recuperation, from the wheel brakes be recorded

Pressure fluid volume. The fact that the actuator is now able to accommodate a corresponding volume of pressure medium, the usual Pedalcha characteristic can be maintained even during recuperation.

A conventional vacuum brake booster is not electronically controlled. Therefore, in the vehicles equipped therewith, if necessary, a brake pressure build-up for a driver-independent braking by means of the ABS pump is performed. This pump is configured primarily for the return of pressure medium in ABS operation and not for performing a Nor mal braking, which is consequently associated with pressure pulsations, vibration and insufficient pressure build-up dynamics. In the past, a special, complex and voluminous "active booster" had to be used to carry out a comfortable automated braking system, which carries the pedal with it during "active braking". In this way, the driver receives a haptic information on a simultaneous active braking when pressing the brake pedal. Such But pedal behavior also has the consequence that the driver finds the additional braking by pedal in an automatic braking a correspondingly biased and thus "ver hardened" pedal.

In contrast, in brake systems with pedal decoupling and simulator pedal behavior is independent of a simultaneous Ak tive braking. The braking demand to be implemented by the braking system corresponds to the respective higher value of

Driver braking request and assistance brake request. If the assistance braking request is higher, the effect unpleasant for the driver is that the pedal position does not correspond to the actually executed deceleration.

Therefore, the task is to make the pedal behavior in superimposed driver and assistant braking as a compromise of the two approaches mentioned, such that the driver finds not too intensive assistance braking the brake pedal in the usual unactuated position and with the usual to speech behavior and that with intensive assistance braking the brake pedal the driver

haptically signaled by a corresponding movement that is braked just assisting.

The yielding of the pedal when pressed during an auto-matic braking is realized in the brake system described in that the pedal is not reset at low actuation paths by a system pressure or at least reduced power. So the driver can adjust the pedal travel with his foot in this area and the Bremssyste melektronik can take the driver's brake request via the pedal travel

The braking system of a motor vehicle is located during driving predominantly in a mode in which is not braked. The contribution of energy consumption in this phase is significant for an overall energy balance. Therefore, it is unfavorable when, as in some electrohydraulic simulator braking systems in the Standby mode, a solenoid valve (simulator valve) is constantly energized. Therefore, the task of designing a new brake circuit pressure providing device so that no permanently energized solenoid valves are needed.

This minimization of the electrical energy consumption in the standby mode is achieved by not requiring a simulator valve that is permanently energized during the journey.

The advantages of the invention are, in particular, that in an electro-hydraulic brake system, a characteristic of a Vakems umbremsverstärker pedal characteristic is displayed. Further advantages are described above.

An embodiment of the invention will be described with reference to a

Drawing explained in more detail. Therein, the single FIGURE shows a schematic representation of a brake system in a preferred embodiment.

This is shown in FIG. shown brake system 2 has four hydraulically actuated wheel brakes 8, 10, 12, 14 and sensors 16, 18, 20, 22 for detecting the rotational movement of the wheel brakes 8, 10, 12, 14 associated wheels. The brake system 2 comprises a

Hydraulic unit 30 or ESC HCU, which may be formed in a known manner. The hydraulic unit 30 comprises per wheel brake 8-14 an isolation valve and an exhaust valve. The brake system 2 further comprises an electronic control unit 34 for controlling the separating and exhaust valves. The control unit 34 preferably applies methods such as ESC, ABS, ASR, etc. These cause during a ent speaking engagement targeted control of the separation and exhaust valves for adjusting wheel-specific brake pressures.

The brake system 2 comprises a drive stage 40 and a master cylinder 41 with a drive stage and main brake cylinder housing 42 with a main bore in which a drive piston and a primary piston are guided or designated as a main piston 48 combined primary and operating piston is guided, which is both mechanically by means of a brake pedal 44 via a coupling rod 46 and hydraulically actuated, that is displaceable along the main bore axis. During a displacement in the direction of actuation, the primary piston side of the main piston 48 dips into a primary chamber 50 and displaces from this pressure medium into a primary circuit I or into the brake circuit line 80 belonging to the primary circuit.

The brake system 2 may also include a secondary piston 58, a secondary chamber 54 and a secondary circuit II with a second brake circuit line 84 connected to the secondary chamber 54. Upon actuation of the brake pedal 44, the main piston 48 moves into the primary chamber 50 and displaces pressure medium from the primary chamber. The resulting hydraulic pressure or in the event of failure of a lack of pressure buildup in the primary circuit I mechanical contact between the primary and secondary pistons be hit the secondary piston 58 with a force, whereby this is displaced in the direction of actuation. The secondary chamber 54 is limited on its side facing the primary chamber 50 side of the floating-mounted secondary piston 58, whereby a displacement of the secondary piston 58 in the direction of actuation pressure buildup of the secondary chamber 54 and the secondary circuit connected thereto II and belonging to the secondary circuit brake circuit 84 causes.

The primary circuit I and thus the primary chamber 50 is connected via the brake circuit line 80 and the secondary circuit II and thus the secondary chamber 54 is connected via the brake circuit line 84 to the hydraulic unit 30. Within the hydraulic unit 30, the two brake circuits I, II are strictly separated. This means that there is no possibility for the exchange of pressure medium between the components belonging to primary circuit I (ie hydraulic components connected or connectable to primary brake circuit 80) and secondary components II (ie hydraulic components connected or connectable to secondary brake circuit line 84). By way of example, the wheel brakes 8, 10 are associated with the first brake circuit I. By way of example, the wheel brakes 10, 12 are associated with the secondary secondary brake circuit II. According to the vehicle configuration with axle-wise or diagonal brake circuit division one of the brake circuits I, II associated wheel brakes of a vehicle axle or a driving zeugdiagonalen are assigned.

The brake system 2 has a hydraulic drive circuit A on which the components 66, 94, 90 comprises, as well as a device 60 for spreading an electrically controllable pressure in this hydraulic drive circuit A, which presented in the Darge embodiment of the brake system according to the invention as a driven by a linear actuator Piston-cylinder unit is formed. Alternatively, means 60 for providing an electrically controllable drive circuit pressure may comprise a pump driven by an electric motor and electrically controlled valves. Furthermore, pressure supply facilities with pump, pressure accumulator and valves are possible.

The pressure supply device 60 comprises a hy cally to the drive circuit A scoring pressure chamber 66, in which by means of an electric motor 68 and a coupled thereto Rotati ons translation gear 70, which is preferably designed as Kugelge wind operation, a pressure piston 74 is movable. A preferably redundantly designed pressure sensor measures the hydraulic pressure in the drive circuit A. For this purpose, it is connected to any component 66, 94, 90 of the drive circuit A is connected.

The drive stage 40 has a drive chamber 90, which counts hydraulically with respect to the drive circuit A, in which the drive circuit pressure exerts a force on the drive side of the main piston 48. Between drive stage 40 and master cylinder 41, the drive stage and master cylinder housing 42 in the central region of the combined primary and drive piston 48, ie between its drive piston side and its Primärkolben- Side, an annular chamber, which is aerated like the tank at atmospheric. Conveniently, this chamber is connected for this purpose with a hydraulic connection 170 to the container. Thus prevails in this chamber, the same hydraulic pressure as in the container.

A Nachsaugleitung 100 with a compared to the hyd raulischen pressure lines 80, 84 significantly larger cross-sectional area leads from the pressure fluid reservoir 102 in the vicinity of the pressure chamber 66. There is arranged between the Nachsaugleitung 100 and the drive circuit, a check valve 108, which is a suction of pressure medium made possible from the container and prevents backflow of pressure medium from the drive circuit A in the pressure medium reservoir 102.

Such a volume flow of pressure medium from the drive circuit A in the pressure medium reservoir 102 is necessary only in special operating situations of the brake system. Therefore, an analog controllable, normally closed electrohydraulic degradation valve 176 is provided, via which such a volume flow can be controlled Vo. In the Fig. From the construction valve 176 is preferably shown parallel to the check valve 108. There is no functional need for this parallel connection. It is only for technical reasons. The same function would have for example a valve between the drive chamber 90 and the space in which the spring 244 is located.

When pressure is reduced, it can occur that the actuator 70 retreats faster than pressure medium flows from the wheel brakes 8-14. Then he sucks over the check valve 108 pressure fluid from the pressure fluid reservoir 102 after. After the end of the braking, the sucked pressure medium can be drained tank with dissolved brake pedal 44 via equalizing connections between the master cylinder chambers and loading again. However, it can also occur that accumulates during a braking operation, the pressure medium amount in the system. In this situation, the degradation valve 176 is activated. It is preferably currentless. formed trained and the passage of permissible volume flow is steplessly controlled.

A preferably redundantly designed pressure sensor 114 measures the pressure in the primary circuit. Between drive circuit A and primary circuit I, a connection valve 120 is arranged, which blocks a flow of pressure medium from the primary circuit I in the drive circuit A in the electrically de-energized state and releases in the opposite direction and releases the hydraulic flow in both directions in the electrically energized state.

A preferably redundantly designed pressure sensor 130 measures the pressure in the secondary circuit. Between drive circuit A and seconds därkreis II a Zuschaltventil 136 is arranged, which locks in the electrically de-energized state, a flow of pressure medium from the secondary circuit II in the drive circuit A and releases in the opposite direction and releases the hydraulic flow in both directions in the electrically energized state ,

The master cylinder 40 has a hydraulic equalization connection, via which the primary circuit I is hydraulically connected to the container when the master cylinder 40 is unoperated. In addition, a solenoid valve 154 is provided, with which this compensation connection can be blocked in the outflow direction to the container, regardless of the actuation state of the master cylinder. In the illustrated embodiment from the guide, the primary chamber 50 is connected by an equalization line 150 to the pressure medium reservoir 102 for this purpose. In the compensation line 150, a normally open check valve 154 is arranged, which in the locked state, a flow of pressure medium from the primary chamber 50 into the pressure medium reservoir 102 blocks and releases in the reverse direction.

The master cylinder 40 has a hydraulic equalization connection, via which the secondary circuit II is hydraulically connected to the container when the master cylinder 40 is not actuated. In addition, a solenoid valve 166 is provided with which can be blocked in the outflow direction to the container, regardless of the actuation state of the master cylinder, this compensation connection. In the illustrated embodiment, the secondary chamber 54 is connected by a compensation line 160 to the pressure medium reservoir 102 for this purpose. In the compensation line 160, a normally open check valve 166 is arranged, which in the locked state, a flow of pressure medium from the secondary chamber 54 into the pressure medium reservoir 102 blocks and releases in the reverse direction.

With the help of the two check valves 154, 166, it is possible, even with unoperated brake pedal 44, a pressure build-up in the

To achieve brake circuits I and II, by their activation, a flow of pressure medium into the pressure medium reservoir 102 is prevented. With activated check valves 154, 166 can pressure medium, which is shifted via the connection valves 120, 126 from the drive circuit A in the brake circuits I, II does not flow to the container, resulting in the intended pressure build-up in the brake circuits I, II. The pressurized area of the drive piston is less than or equal to the pressurized area of the primary piston, so that the pressure applied to both sides of the main piston 48 does not cause this piston to move.

Even with a pedal-operated braking, pressure is built up in the drive circuit. This has the consequence that this drive circuit pressure beat the drive piston in the direction of actuation beauf and thus supports the driver in his pedaling. Normally, the connection valves 120, 126 are thereby opened and the pressure is adjusted or adjusted via the pressure supply device 60 in accordance with a predetermined actuation-pressure curve.

The brake system 2 is adapted to dalbetätigung at a Bremspe by the driver, this pedal via the pedal return force to signal the current brake system pressure. It has been shown that this function of the braking system for a pleasant brake pedal behavior depending on the degree of brake pedal operation must be designed differently. For stronger braking with larger pedal travel, the increase in the restoring force should be proportional to the increase in brake pressure, while for small pedal travel a pedalweggesteuerte increase in brake pressure should lead to no or only a small increase in pedal force. In order to realize this function, an effective surface enlargement body 200 is arranged in the drive chamber 90, which surrounds the main piston 48 in regions. The effective area enlarging body 200 has a stop 204 for the main piston 48, so that it is entrained in a movement of the effective area increasing body 200 in the actuating direction. The Wirkflächenvergröße is driven body 200 by the effect of the pressure in the hydraulic drive circuit A.

The Wirkflächenvergrößerungskörper 200 is formed in the illustrated embodiment as a sleeve or sleeve-shaped and is penetrated by the main piston 48 and has an annular surface hydraulically effective, which is acted upon by the pressure in the drive chamber 90. There are other events conceivable as long as its func tionality described below with regard to the switching of the hydraulic

Acting surface is given in the drive chamber 90.

The main piston 48 is both mechanically on the brake pedal and hydraulically via the pressure in the drive chamber 90 be tätigbar. The hydraulically effective area, which represents the proportionality factor between pressure and force, is not constant but is dependent on the path of the main piston 48. In a first, to the unactuated position at closing section, the effective area is to be increased, then a transition section and adjoin it a path section with not increased effective area. To realize the Wirkflächenvergrößerungskörper 200 is seen with an acted upon by the pressure in the drive chamber additional effective area, which is supported within the first Wegabschnitts only on the main piston 48, in the second path portion proportionately on Main piston and the housing 42 and in the third path section exclusively on the housing 42nd

The sleeve-shaped Wirkflächenvergrößerungskörper 200 has an annular hydraulic active surface, which of the pressure in the drive circuit A, d. H. the Aktuatordruck beauf is beat and which at a shift in Actuate supply direction, the main piston 48 can mechanically take 48 via a first stop between the sleeve and the main piston 48. Relative to the housing 42, the sleeve in a first path interval Si in the direction of actuation of the drive piston 48 is freely displaceable.

In a further displacement, the sleeve compresses in a second path interval S2 a on the sleeve and the housing 42 supporting spring 244, which is for example designed as a plate spring or a helical compression spring, until a further movement of the sleeve in the direction of actuation by a second Stop between sleeve and housing 42 or a "put on block" of the spring 244 is blocked.

In contrast, a displacement of the main piston 48 in Actuate supply direction over all three path sections mechanically unge prevents possible without a take-along of the sleeve he would be necessary, which not only the operation in the third path section d. H. without Wirkflächenvergrößerung but also an unamplified operating mode of the brake system with non-functional Aktuatordruckbereitstellung, ie without a structure of drive circuit pressure is possible.

During normal operation, the actuator pressure is switched to the two brake circuits I, II using the on-off valves 120, 136. With the help of the connection valves 120, 136, the brake circuits I and II can be connected separately to the drive circuit A.

In addition, the pressure of the drive circuit A acts in the drive chamber 90 to the hydraulically effective annular surface of the Main piston 48 and the hydraulically effective annular surface of the sleeve. In this case, the sum of these two hydraulically effective annular surfaces is slightly smaller and at most equal to the primary chamber in the Pri märkammer 50 dipping surface of the primary piston or

Primary piston portion of the combined drive and primary piston designed. As a result, when the primary and drive circuits are hydraulically connected, the hydraulic drive and return forces are essentially neutralized in the path interval Si of the main piston 48. Increasing the pressure will result in no increase in the hydraulically related portion of the pedal force for only a small amount or for equally designed areas.

Thus, the pedal force in the path interval Si is essentially determined by the mechanical pedal return springs which, as shown, are preferably arranged within the pressure chambers 50, 54. To support this spring action, a further "dry" spring arranged outside the hydraulic chambers can be provided.

In the path interval S3, the sleeve is not supported on the main piston 48 but on the housing 42. The sum of the hydraulic forces therefore gives the main piston 48 proportional to the brake system pressure against the direction of actuation loading

Restoring force. In the interval S2, the increasing with increasing piston travel spring force causes a transition of "no restoring force" at the boundary to the interval Si and full of formed restoring force at the boundary to the interval S3.

In normal operation, primary circuit I, secondary circuit II and drive circuit A are hydraulically interconnected. The common pressure is called brake system pressure and is set by the pressure supply device 60, which is controlled by an electronic control unit 260. Therefore, the brake system pressure can be specified as a function of the pedal travel or it can be set free for the purpose of representing other functions such as an automated braking or a brake assist function. When carrying out pedal-operated braking as retraining braking, the control and regulating unit (34) and the hydraulic module (30) preferably prevent a wheel brake pressure buildup from being prevented. In this case, the driver is provided with a pedal behavior, as it would be without recuperation braking. This means preferably that the ratio of pedal travel to braking torque is realized as in a normal braking. In order to ensure this, the boost ECU or the control unit 260 that controls the pressure supply device 68 and the ESC ECU or control unit 34 for controlling the separation and exhaust valves via a communication link 300 digital information.

Claims

claims

1. brake system (2) for motor vehicles, which can be controlled by both the driving zeugführer and independent of the driver, with

• A master cylinder (41) comprising a Hauptbremszy cylinder housing (42) having a main bore in which at least one master cylinder piston (48) having a hydraulic active surface (Ai) is guided axially, which limits a pressure chamber (50), which upon actuation the brake master cylinder is placed under a braking system pressure with a hydraulic connection, in which pressurized medium set under this braking system pressure is fed into at least one associated brake circuit (I, II);

A brake pedal (44) for actuating the master cylinder by applying a force to a master cylinder piston (48) or to a component connected to the master cylinder piston;

• with a the master cylinder (41) upstream hyd raulischen drive stage (40) with a drive piston (48) which can be acted upon both with the pedal force and hydraulically via an effective effective area (A2);

• Under pressure at atmospheric pressure fluid reservoir (102) having at least one of the pressure chamber (50) associated with connection;

• the at least one brake circuit (I, II) associated hyd raulisch controllable wheel brakes (8, 10, 12, 14);

• path detection means (98) for detecting the actuation travel of the brake pedal (44) or a piston (48) connected to the brake pedal (44);

A pressure supply device (60) which is set up to generate a drive circuit pressure in a hydraulic drive circuit (A) having a drive chamber (90) comprises, in which the drive circuit pressure applied to the drive piston (48) with a force in the direction of actuation;

• An electro-hydraulic unit (30) having a elekt electronic controller (34) and per wheel brake (8, 10, 12, 14) an isolation valve and an outlet valve for setting radin personal brakes brake pressure;

characterized in that

Hydraulic means are provided to make the effective effective surface (A ₂ ) of the drive piston (48) pedal path dependent variable.

2. brake system (2) according to claim 1, wherein the hydraulic means comprise a Wirkflächenvergrößerungskörper (200) which is pressurized by the drive circuit pressure in the direction of actuation drive circuit, wherein the corresponding reaction force on the Wirkflächenvergrößerungskörper (200) against the actuation direction consists of the sum of two forces, one of which is supported on the drive piston (48) and the other on Antriebsstufen- and master cylinder housing (42), and wherein these support forces are path-dependent and / or diffe renzwegabhängig.

3. brake system (2) according to claim 1 or 2, wherein the active surface enlargement body (200) acts on a pressure in the drive chamber to (90) acted upon additional effective area, and wherein the Wirkflächenvergrößerungskörper (200) up to a predetermined pedal travel on the hydraulic drive piston ( 48) and in the case of pedaling paths beyond the drive stage and master cylinder housing (42) is supported.

4. brake system (2) according to claim 3, wherein at pedal paths which are greater than a predetermined pedal travel threshold, a support from the effective area increasing body (200) at the arrival drive stage and master cylinder housing (42) by a support spring (244).

5. brake system (2) claim 4, wherein the support spring (244) is designed as a plate spring.

6. brake system (2) claim 4, wherein the support spring (244) is designed as a helically wound compression spring.

7. brake system (2) according to one of the preceding claims, wherein the Wirkflächenvergrößerungskörper (200) as a drive piston (48) penetrated sleeve is formed.

8. brake system (2) according to any one of the preceding claims, wherein valve means (120, 136) are provided, through which the brake circuits (I, II) can be separately connected to the drive circuit (A)

9. brake system (2) according to any one of the preceding claims, wherein normally open valve means (154, 166) are provided, which allow an actuator-controlled pressure build-up in the brake circuits (I, II) with unconfirmed brake pedal by by their activation an outflow of pressure medium in the

Pressure medium reservoir (102) is prevented.

10. brake system (2) according to any one of the preceding claims, wherein a pressure sensor (98) for detecting pressure in the drive circuit (A) is provided.

11. Brake system (2) according to one of the preceding claims, wherein at least one pressure sensor (114, 130) is provided for detecting at least one brake circuit pressure.

12. brake system (2) according to any one of the preceding claims, wherein an analog controllable valve (176) for reducing the pressure in the drive circuit (A) is provided as needed.

13. A method for operating a brake system (2) according to claim

8, wherein in a normal operation for pedal-controlled as well as for automated braking valve connecting means (120, 136) are opened and with the aid of the pressure supply device (60) a brake system pressure is adjusted by virtue of the opened Zuschaltventile (120, 136) in both brake circuits (I, II) and in the drive chamber (90) ready.

14. The method of claim 13, wherein carried out to perform a pedal-operated braking as Rekuperationsbremsung a wheel brake pressure build-up to a reduced extent or completely prevented and provides the same pedal behavior as without recuperation.

15. The method of claim 13 or 14, wherein in a recognized

Leakage and / or a non-functional Druckbereit positioning device (60) the Zuschaltventile (120, 136) are not opened.