DE102018202311A1 - Simulator and braking system - Google Patents

Abstract

The invention relates to a simulator for generating a brake pedal characteristic of a fluid-operated brake system, wherein the simulator has an integrated valve function. The invention further relates to a brake system with such a simulator, which thus makes do with at least one valve less.

Description

The invention relates to a simulator for generating a brake pedal characteristic of a fluid-operated brake system.

Such a simulator has a simulator cylinder. The simulator cylinder has a piston which is arranged to be linearly movable in the simulator cylinder and divides the simulator cylinder into a first chamber and a second chamber. The simulator further includes a biasing arrangement that biases the piston to a rest position, wherein a size of the first chamber in the rest position is minimal. In the simulator cylinder, a first connection is formed, which leads in each position of the piston in the first chamber.

The invention further relates to a brake system for a motor vehicle, wherein the brake system comprises a brake cylinder, a brake pedal, at least one arranged in the brake cylinder brake cylinder piston and a simulator.

Motor vehicles typically have brake pedals by means of which a driver can actuate a brake of the motor vehicle. Typically, this is a service brake which serves to decelerate the vehicle while the vehicle is moving. Due to the increasing use of electronically controlled brake systems and also due to the transition to semi-autonomous or autonomous vehicle controls, it may be necessary to hydraulically decouple the brake pedal of the vehicle installed brakes, so that the driver no longer directly actuates the brakes, but detects the driver's brake request electronically and implemented accordingly.

In such a case, however, it is advantageous if the driver experiences the most natural and familiar characteristic of the brake pedal, which in the ideal case is not or only slightly different from a brake pedal characteristic, which occurs in an immediate actuation of the brakes by means of the brake pedal.

In order to produce such a brake pedal characteristic, simulators are used, which are coupled to a brake cylinder piston connected to the brake pedal and which generate a realistic characteristic by hydraulic means. However, this is still associated with a great deal of effort.

It is therefore an object of the invention to provide alternative, for example simpler, embodiments of a simulator and a braking system with a simulator in comparison with known from the prior art designs.

This is achieved according to the invention by a simulator according to claim 1 and by a braking system according to claim 5. Advantageous embodiments can be taken, for example, the respective subclaims. The content of the claims is made by express reference to the content of the description.

The invention relates to a simulator for generating a brake pedal characteristic of a fluid-operated brake system. The simulator has a simulator cylinder. The simulator has a piston which is arranged to be linearly movable in the simulator cylinder and divides the simulator cylinder into a first chamber and a second chamber. The simulator further includes a biasing arrangement that biases the piston to a rest position, wherein a size of the first chamber in the rest position is minimal. In the simulator cylinder, a first connection is formed, which leads in each position of the piston in the first chamber.

It should therefore be understood that the first chamber and the second chamber have no constant size or extent, but are different in size depending on the position of the piston. The ports, which lead in each position of the piston in a respective chamber, preferably have a respective opening, which is arranged at each position of the piston on a specific side of the piston, so that the aforementioned functionality is achieved.

According to the invention, it is provided that the simulator cylinder has a second connection, which leads into the second chamber at each position of the piston. The piston forms a third chamber between the first chamber and the second chamber in the simulator cylinder. The simulator cylinder further includes a third port which leads to the third chamber at each position of the piston.

The simulator cylinder further includes a first seal which isolates the first chamber and the third chamber from each other at each position of the piston. Alternatively, the piston has a first seal which, in each position of the piston, isolates the first chamber and the third chamber from each other.

In addition, the simulator cylinder has a second seal, which in the rest position of the piston, the third chamber and the second chamber against each other and isolated in all layers of the Pistons, which are different from the rest position, a fluidic connection between the third chamber and the second chamber releases. Alternatively, the piston has a second seal which, in the rest position of the piston, isolates the third chamber and the second chamber from one another and releases a fluidic connection between the third chamber and the second chamber in all positions of the piston which are different from the rest position.

The inventive design of the simulator, it is possible to produce by means of the second port, a pressure equalization between the two sides of the piston, so that it can be operated without a valve between the first port and a brake cylinder. This valve can thus be saved, which reduces the effort and costs.

By means of the third connection, the third chamber and the second seal can be realized in the described functionality additionally a valve function, which can be used in particular for a return line to a pressure equalization tank. At rest, this valve is closed, which in particular ensures that a backflow of hydraulic fluid can be prevented in a surge tank when a brake system is in a hydraulic fallback level.

Preferably, the piston forms the third chamber by at least one outer recess in the piston. Such a recess may, for example, be circumferentially circumferential. It can also be used several such recesses.

According to a preferred embodiment, the first seal is designed as a ring seal surrounding the piston.

According to a preferred embodiment, the second seal is designed as a ring seal and the piston has a sealing portion which rests in the rest position on the second seal and in all positions which are different from the rest position, does not abut the second seal. This allows a simple and reliable realization of the second seal.

Preferably, the biasing arrangement is designed as a spring. In particular, the biasing arrangement can be arranged in the second chamber. Such embodiments have proven themselves in practice, it being understood that other designs are possible. For example, the biasing arrangement may also be another elastic element, and it may also be disposed at other locations.

The invention further relates to a brake system for a motor vehicle. The brake system has a brake cylinder. It also has a brake pedal and a brake cylinder piston arranged in the brake cylinder, which delimits a pressure chamber in the brake cylinder and which is connected to the brake pedal, so that a pressure in the pressure chamber can be generated by means of the brake pedal. This corresponds to a proven embodiment of a brake cylinder with brake pedal for generating a pressure by means of the brake pedal.

The brake system furthermore has a simulator according to the invention. In this case, all embodiments and variants described herein can be used.

The brake system also has a connection between the pressure chamber and the first port of the simulator. It also has a connection between the pressure chamber and the second port of the simulator, wherein in the connection between the pressure chamber and the second port of the simulator, at least one pressure relief valve is arranged. Furthermore, the brake system has a surge tank and a connection between the third port of the simulator and the surge tank.

By means of the braking system according to the invention, the advantages described above can be achieved. In particular, it is possible to dispense with a valve between the pressure chamber and the first connection of the simulator. The connection between the pressure chamber and the first port of the simulator is thus preferably carried out directly, which may in particular mean that no valve is arranged in this connection. The connection can also be made so that it is not switchable.

In particular, the pressure relief valve may be used to selectively enable or disable communication between the pressure chamber and the second port, for example to prevent accidental flow of hydraulic fluid between the surge tank and other components of the brake system through the simulator.

In the connection between the pressure chamber and the second port of the simulator, a separating valve is preferably further arranged between the pressure chamber and the pressure relief valve. Thus, an additional switching function can be realized.

The pressure relief valve is preferably designed to be normally open. As a result, for example, a free flow of hydraulic fluid in a hydraulic fallback level to brakes mentioned below can be achieved.

Preferably, the separating valve is designed to be normally open, so that in a hydraulic fallback level, a pressure equalization between the first chamber and the second chamber of the simulator is possible, whereby the piston of the simulator is held in its rest position by means of the biasing arrangement. The already mentioned above, formed in the simulator valve thus remains closed.

In the connection between the pressure chamber and the first port of the simulator, preferably no valve and / or no further component is arranged. This corresponds, as already mentioned, a particularly simple and advantageous embodiment, whereby costs can be reduced.

Preferably, the brake system has a number of brakes, each brake being connected via a respective outlet valve to a central port. The central connection is preferably in the connection between the pressure chamber and the pressure relief valve and particularly preferably in the connection between the isolation valve and the pressure relief valve. Thereby, an immediate actuation of the brakes by the brake pedal by means of a pressure built up in the pressure chamber. This may be particularly useful in a hydraulic fallback mode of the braking system, i. if due to a failure of the power supply only a manual braking is possible.

The exhaust valves are preferably designed to be normally open, which has the advantage that they release a fluidic connection between the pressure chamber and brakes in a hydraulic fallback level, which allows manual braking of the vehicle.

The brake system preferably has an automatically operated pump, wherein each brake is preferably connected to the pump via a respective inlet valve. This allows an electrically actuated release of the brakes, for example, a detected by a driver of the vehicle via the brake pedal braking request is detected, for example by means of a displacement or pressure sensor, and the pump then generates the pressure to implement the braking request. Alternatively, however, the pump can also be controlled, for example, by a partially autonomous or autonomous vehicle control.

The inlet valves are preferably designed to be normally closed. As a result, in a hydraulic fallback mode, a pressure from the pressure chamber in a region of the brake system can act as far as the intake valves, so that no pressure which is supposed to act on the brakes is lost.

Preferably, the brake system has a controller configured to control at least the pump and the valves. Thus, various functionalities and operating modes can be realized.

The controller is preferably configured to close the isolation valve, open the pressure relief valve, and pressure modulate the brakes via the exhaust valves in at least one operating mode upon actuation of the brake pedal. Such a design allows each wheel to be braked individually, with pressure typically generated by a pump and selectively reduced by the exhaust valves on each wheel as needed.

Preferably, the controller is configured to open the isolation valve in at least one operating mode when the brake pedal is not actuated. It can thereby be achieved that a braking request given by the driver by pressing the brake pedal is not only detected and leads to a triggering of a braking process realized by means of a pump, but at the same time also the pressure generated by the driver in the pressure chamber and / or in the simulator is passed to the brakes, so that a faster response occurs. This can lead to a shortening of the braking distance, especially in the event of danger braking.

It should be understood that the braking system is in particular a vacuum-free braking system.

As a central element, for example, a pedal feel simulator can be considered, the simulator piston weggesteuert releases a hydraulic connection and thus fulfills a valve function. A characteristic of this switching simulator may be, in particular, that the hydraulic connection is closed in the unactuated state. Such a simulator makes it possible, in a suitable arrangement, to save a solenoid valve.

Further features and advantages will be apparent to those skilled in the embodiment described below with reference to the accompanying drawings.

• 1: ein Bremssystem gemäß einem ersten Ausführungsbeispiel,
• 2: ein Bremssystem gemäß einem zweiten Ausführungsbeispiel,
• 3 bis 5: das Bremssystem von 2 in unterschiedlichen Zuständen.

Showing:

• 1 a brake system according to a first embodiment,
• 2 a brake system according to a second embodiment,
• 3 to 5 : the brake system of 2 in different states.

1 shows a braking system 10 with a simulator 100 according to a first embodiment of the invention.

The brake system 10 has a total of four brakes B1 . B2 . B3 . B4 on. Each of these brakes B is associated with a respective wheel of a motor vehicle, wherein the brakes B1 . B2 Front wheels are assigned and the brakes B3 . B4 Rear wheels are assigned.

Associated with the brakes are four intake valves E1 . E2 . E3 . E4 and four exhaust valves A1 . A2 . A3 . A4 , Everybody is brake B1 . B2 . B3 . B4 one of the intake valves E1 . E2 . E3 . E4 and one of the exhaust valves A1 . A2 . A3 . A4 assigned. About these valves e . A can the brakes B be operated in more detail below to be described.

The brake system 10 has an automatically operated pump 20 on which by means of a motor M is operable. As a result, a pressure can be provided which can be selectively directed to the brakes B via the inlet valves E.

The brake system 10 also has a brake cylinder 30 on. This is a brake cylinder piston 32 arranged, which is linear in the brake cylinder 30 can move. The brake cylinder piston 32 borders in the brake cylinder 30 a pressure chamber 34 which corresponds to the position of the brake cylinder piston 32 has a variable size.

The brake system 10 has a brake pedal 40 on which with the brake cylinder piston 32 is coupled. By pressing the brake pedal 40 can the brake cylinder piston 32 a pressure in the pressure chamber 34 produce.

The pressure chamber 34 is about the exhaust valves A with the brakes B connected. This allows a driver directly by pressing the brake pedal 40 a pressure in the brakes B generate, so that a motor vehicle in which the braking system 10 is installed, can be braked manually.

Between the pressure chamber 34 and the exhaust valves A is a separating valve T arranged. After the isolation valve T is a central connection Z arranged, from which the individual exhaust valves A are connected.

Both the isolation valve T as well as the respective exhaust valves A are normally open when open. This allows a direct fluidic connection between the brake cylinder in a hydraulic fallback level 30 or its pressure chamber 34 and the brakes B exists, so that even in case of failure of any electrical power supply braking of the motor vehicle can take place.

The brake system 10 further includes a surge tank 50 on. This serves as a central reservoir for brake fluid.

The brake system 10 has a controller 15 on, which is shown here only schematically. This serves to control the components shown, in particular to achieve the functionality described herein.

The brake system 10 also has a simulator 100 on. This is used for the brake pedal 40 to produce a characteristic which corresponds in whole or in part to a characteristic which, when the brakes are applied directly B through the brake pedal 40 would arise, even if no immediate hydraulic connection between the pressure chamber 34 and the brakes B consists.

The simulator 100 has a simulator cylinder 110 on. In the simulator cylinder 110 is a piston 120 arranged in the simulator cylinder 110 is linearly movable.

Right from the piston 120 is a first chamber 121 educated. Left of the piston 120 is a second chamber 122 educated. Lateral or surrounding to the piston 120 is a third chamber 123 educated. The chambers are partially separated from each other but are also partially interconnected, as will be described further below. It should be understood that the chambers 121 . 122 . 123 have different positions and volumes, depending on the position in which the piston 120 located. This will be discussed further below.

In the second chamber 122 is a biasing arrangement 130 arranged, which in the present case is in the form of an elastic element. This pushes the piston 120 to the right in a rest position, in which the volume of the first chamber 121 is minimal. The piston 120 However, it can also be against the resistance of the biasing arrangement 130 be moved to the left, especially when a suitable pressure in the first chamber 121 is built.

In the simulator cylinder 110 are a first connection 141 , a second connection 142 and a third connection 143 educated. The first connection 141 is arranged so that it is at each position of the piston 120 in the first chamber 121 leads. The second connection 142 is arranged so that it is at each position of the piston 120 in the second chamber 122 leads. The third connection 143 is arranged so that it is at each position of the piston 120 in the third chamber 123 leads. Thus, each of the chambers 121 . 122 . 123 at every position of the piston 120 from outside the simulator 100 be addressed.

Between the first chamber 121 and the third chamber 123 is a first seal 111 arranged in the form of a ring seal. This is at every position of the piston 120 sealing between the first chamber 121 and the third chamber 123 , Thus, there is no case inside the simulator cylinder 110 a connection between the first chamber 121 and the third chamber 123 ,

Furthermore, between the third chamber 123 and the second chamber 122 a second seal 112 arranged. This is present as a ring seal within the simulator cylinder 110 arranged. She is in the rest position of the piston 120 sealing between the third chamber 123 and the second chamber 122 , so that in this rest position of the piston 120 no fluid exchange between the third chamber 123 and the second chamber 122 is possible. For this purpose, there is a trained sealing portion of the piston 120 at the second seal 112 on. However, is the piston 120 outside its rest position, so seals the second seal 112 no longer between the third chamber 123 and the second chamber 122 so that a fluid exchange between these two chambers 122 . 123 is possible and thus also a pressure equalization between the two chambers 122 . 123 takes place.

The first connection 141 is about a first connection V1 with the pressure chamber 34 connected. The pressure chamber 34 is also about the isolation valve T and a pressure relief valve D in a second connection V2 with the second connection 142 connected. The pressure relief valve D is designed normally open, and it is a first check valve R1 with flow direction from the second port 142 away in parallel.

The third connection 143 is about a third connection V3 with the expansion tank 50 connected.

The brake system 10 further comprises a number of sensors, which are each shown as square boxes with a diagonal bisection, each with the upper left of the letter " U Is indicated as an indicator that an electrical variable is generated as the output of the respective sensor. The electrical size can be implemented either as a voltage, current or as a digital signal. Diagonal bottom right is given in each case the size to be measured, where " p "Stands for a pressure," s "stands for a way, in particular that of the brake cylinder piston 32 , " δ "Stands for an angle, especially that of the engine M , and "?" for an equivalent amount of operating force on the brake pedal 40 is, for example, a pressure in the brake cylinder 30 or for a force on the brake cylinder 30 ,

The pump 20 is also a second check valve R2 with the expansion tank 50 connected, wherein the flow direction of the second check valve R2 to the pump 20 pointing. As a result, if necessary, brake fluid from the expansion tank 50 into the pump 20 be sucked to these then to build up pressure in the brakes B to use.

The described configuration of the brake system 10 and the simulator 100 allows different modes of operation.

For example, in an operating mode in which a direct control of the brakes B by manual operation by means of the brake pedal 40 is provided, the isolation valve T , the pressure balance valve D and the exhaust valves A be open while the intake valves E are closed. In this case, it is possible by pressure build-up in the brake cylinder 30 or in its pressure chamber 34 by means of the brake pedal 40 immediately the brakes B to press. Such a condition also automatically arises in a hydraulic fallback mode, which occurs in particular when a power supply fails and thus all valves assume their respective de-energized state. The described functionality allows in this case a manual braking of the motor vehicle.

In the state just described becomes a in the pressure chamber 34 generated pressure both over the first connection V1 in the first chamber 121 as well as the second connection V2 in the second chamber 122 directed. Thus, the first chamber 121 and the second chamber 122 the same pressure. The piston 120 is thus moved in such a state not due to any pressure differences, but only due to the biasing arrangement 130 biased into its rest position.

In this rest position both seals 111 . 112 closed. A loss of pressure from between the pressure chamber 34 and brakes B lines over the third connection V3 is thus prevented, whereby an efficient braking is possible.

Furthermore, it is also possible the intake valves e to open and either the isolation valve T or to close the exhaust valves A. In this case, the pump can 20 used to apply pressure in the brakes B to create. A wheel-specific pressure variation is, for example, by selectively opening the exhaust valves A possible.

A brake request may also be in such a state by means of the brake pedal 40 be triggered by the driver. Also in this case, a pressure in the pressure chamber 34 built, which, however, not or at least not alone for the buildup of pressure in the brakes B is responsible, but rather in the simulator 100 is directed. The first connection is used in particular for this purpose V1 , which is why a pressure in the first chamber 121 is increased. This then pushes the piston 120 against the resistance of the biasing arrangement 130 to the left, so that the pressure build-up a resistance is opposed. This leads to a realistic braking characteristic for the driver, which the brake pedal 40 actuated.

Details and functionalities will be described below with reference to the second embodiment and the 2 to 5 discussed in more detail. The embodiments are correspondingly applicable to the first embodiment.

2 shows a braking system 10 with a simulator 100 according to a second embodiment of the invention. As a difference from the first embodiment is the second seal 112 outboard on the piston 120 designed as a ring seal, as well as the first seal 111 , Otherwise, the components have the same structure and are interconnected.

2 shows a state which is that of 1 corresponds, ie all valves are in their respective de-energized position, which corresponds to a hydraulic fallback level.

3 shows the brake system 10 from 2 in a state in which the isolation valve T is closed, the pressure relief valve D is also closed, the exhaust valves A opened and the intake valves E1 . E2 the front brakes B1 . B2 opened as well as the inlet valves E3 . E4 the rear brakes B3 . B4 are closed. In this configuration, the pump can 20 as shown for pressure build-up in the two front brakes B1 . B2 be used by means of the motor M is pressed. The pressure is thereby in the two front brakes B1 . B2 directed. For example, these can be used separately in front of the rear brakes B3 . B4 to be activated.

One in the pressure chamber 34 a pressure built up by a driver is over the first connection V1 in the first chamber 121 passed, causing the piston 120 is moved to the left as shown. This opens a connection between the second chamber 122 and the third chamber 123 , The second chamber 122 thereby takes an atmospheric pressure of the expansion tank 50 one, causing the piston 120 in its position by the interplay between biasing arrangement 130 on the one hand and the pressure in the first chamber 121 on the other hand is determined. This produces a realistic braking characteristic for the driver using the brake pedal 40 actuated.

In the state which is in 4 is shown, the isolation valve T is closed, the pressure relief valve D opened, the exhaust valves A are closed and the inlet valves E are open. Thus, only the pump 20 used to generate a pressure in the brakes B. The exhaust valves A Although closed in the state shown, they can be selectively opened to provide a wheel-individual pressure variation on each one of the brakes B1 . B2 . B3 . B4 to enable. One thereby at the respective brake B derived pressure is via the opened pressure relief valve D in the second chamber 122 and from there to the third chamber 123 about inside the simulator cylinder 110 passed open connection. From the third chamber 123 will be the corresponding pressure over the third connection V3 in the expansion tank 50 derived.

It should be understood that alternatively also the exhaust valves A opened and both the isolation valve T as well as the pressure relief valve D can be closed. In this case, although also a pressurization by means of the pump 20 possible, a wheel-individual pressure setting is no longer possible because any excess pressure can not be derived individually. It would be in such a case only an overall lower pressure setting by opening the pressure relief valve D possible.

5 shows a state in which the isolation valve T opened and the pressure relief valve D is also open. The intake valves E are opened and the exhaust valves A are closed. This corresponds to a typical state during automatic braking, for example by an emergency brake assistant or a speed or distance control function. A wheel-individual Pressure adjustment is via selective actuation of the exhaust valves A possible.

It should be understood that the arrangement of intake and exhaust valves shown corresponds to a Radventilumkehr arrangement.

In the figures, a single-master cylinder is shown in each case. It is understood, however, that the corresponding embodiments are also executable with tandem master cylinders or other master cylinders. A particular advantage of the embodiments shown is to mention that the first connection V1 no separate valve needed. A corresponding valve function is rather within the simulator 100 provided. This saves effort.

In the respective hydraulic fallback level, the piston 120 defined by the pressure balance left and right by its spring force defined in the rest position and thus seals with the two seals 111 . 112 against the third connection 143 from. This makes it possible for the pressure medium volume to reach the brakes B without loss from the master brake cylinder.

• Hat der Fahrer das Bremspedal 40 und somit den Kolben 120 betätigt, dann wird zum radselektiven Druckabbau das Druckentlastungsventil D geöffnet. Das Volumen kann durch das geöffnete Auslassventil A, durch das Druckentlastungsventil D und dann durch die geöffnete Verbindung innerhalb des Simulators 100 in den Ausgleichsbehälter 50 fließen. Dies ist insbesondere in 4 dargestellt.

For wheel-selective pressure modulations, the respective required exhaust valves A can be closed and selectively reopened for pressure reduction. In order to discharge the pressure medium volume for the purpose of pressure reduction, it is possible, for example, to proceed as follows:

• Does the driver have the brake pedal? 40 and thus the piston 120 actuated, then the pressure release valve becomes wheel-selective pressure reduction D open. The volume can through the open exhaust valve A, through the pressure relief valve D and then through the open connection inside the simulator 100 in the expansion tank 50 flow. This is especially in 4 shown.

Does the driver have the brake pedal? 40 and thus the piston 120 not actuated, then according to one embodiment, the pressure relief valve remains D closed, however, is the isolation valve T open. Also is not shown breather hole in the brake cylinder 30 open. The volume can thus through the open exhaust valve A and then through the isolation valve T and the breather hole in the expansion tank 50 flow.

For very fast pedal operations of the brake pedal 40 can pressure medium volume from the simulator 100 over the first check valve R1 of the closed pressure relief valve D already prematurely flow into the brakes B and the latencies of a control of the pump 20 overcome. This can, as already described above, use the braking effect sooner.

As an advantage of the embodiments shown may be mentioned in particular that a simulator valve can be omitted and a total of only ten valves are needed. This reduces packaging costs and saves costs. Furthermore, better dynamics in driver-operated emergency braking maneuvers should be mentioned. In typical driving situations, for example in a brake-by-wire operation, for example, only three valves are switched active. For normal braking function, ie in particular for a desired actuation of the brakes B by the driver, for example, four valves are switched. As a result, energy can be saved compared to designs that require a circuit of more valves.

For circle separation in leaks, any number and combinations of wheel brakes on the brake cylinder 30 and the pump 20 be switched. This can be done for example in a black and white arrangement or in a diagonal arrangement.

The claims belonging to the application do not constitute a waiver of the achievement of further protection.

If, in the course of the procedure, it turns out that a feature or a group of features is not absolutely necessary, it is already desired on the applicant side to formulate at least one independent claim which no longer has the feature or the group of features. This may, for example, be a subcombination of a claim present at the filing date or a subcombination of a claim limited by further features of a claim present at the filing date. Such newly formulated claims or feature combinations are to be understood as covered by the disclosure of this application.

It should also be noted that embodiments, features and variants of the invention, which are described in the various embodiments or embodiments and / or shown in the figures, can be combined with each other as desired. Single or multiple features are arbitrarily interchangeable. Resulting combinations of features are to be understood as covered by the disclosure of this application.

Recoveries in dependent claims are not to be understood as a waiver of obtaining independent, objective protection for the features of the dependent claims.

These features can also be combined as desired with other features.

Features that are disclosed only in the specification or features that are disclosed in the specification or in a claim only in conjunction with other features may, in principle, be of independent significance to the invention. They can therefore also be included individually in claims to distinguish them from the prior art.

Claims (15)

A simulator (100) for generating a brake pedal characteristic of a fluid operated brake system (10), the simulator (100) comprising: - a simulator cylinder (110), - a piston (120) which is linearly movable in the simulator cylinder (110) and the simulator cylinder (110) into a first chamber (121) and a second chamber (122), - a biasing assembly (130) which biases the piston (120) in a rest position, wherein a size of the first chamber (121) in the Resting position is minimal, - wherein in the simulator cylinder (110), a first terminal (141) is formed, which leads in each position of the piston (120) in the first chamber (121), characterized in that - the simulator cylinder (110) second port (142) which leads into the second chamber (122) at each position of the piston (120), - the piston (120) a third chamber (123) between the first chamber and the second chamber (122) in the simulator cylinder (110 ), - the Simulator cylinder (110) has a third connection (143) which leads into the third chamber (123) in each position of the piston (120), - the simulator cylinder (110) or the piston (120) has a first seal (111), which at each position of the piston (120) the first chamber (121) and the third chamber (123) against each other, and - the simulator cylinder (110) or the piston (120) has a second seal (112) which in the rest position of Piston (120) the third chamber (123) and the second chamber (122) isolated from each other and in all positions of the piston (120), which are different from the rest position, a fluidic connection between the third chamber (123) and the second chamber ( 122) releases. Simulator (100) after Claim 1 , - wherein the piston (120) forms the third chamber (123) by at least one outer recess in the piston (120). Simulator (100) according to one of the preceding claims, wherein the first seal (111) is designed as a ring seal surrounding the piston (120), and or - Wherein the second seal (112) is designed as a ring seal and the piston (120) has a sealing portion which rests in the rest position on the second seal (112) and in all positions which are different from the rest position, not on the second seal (112) is present. Simulator (100) according to one of the preceding claims, - Wherein the biasing arrangement (130) is designed as a spring and / or in the second chamber (122) is arranged. A braking system (10) for a motor vehicle, the braking system (10) comprising: a brake cylinder (30), a brake pedal (40), - At least one in the brake cylinder (30) arranged brake cylinder piston (32) which in the brake cylinder (30) delimits a pressure chamber (34) and which is connected to the brake pedal (40), so that by means of the brake pedal (40), a pressure in the pressure chamber (34) is producible, a simulator (100) according to one of the preceding claims, a connection (V1) between the pressure chamber (34) and the first connection (141) of the simulator (100), a connection (V2) between the pressure chamber (34) and the second port (142) of the simulator (100), wherein in the connection (V2) between the pressure chamber (34) and the second port (142) of the simulator (100) at least one pressure relief valve (D) is arranged, - An expansion tank (50), and - A connection (V3) between the third port (143) of the simulator (100) and the surge tank (50). Brake system (10) after Claim 5 , wherein in the connection (V2) between the pressure chamber (34) and the second port (142) of the simulator (100) between the pressure chamber (34) and pressure relief valve (D) further comprises a separating valve (T) is arranged. Brake system (10) according to one of Claims 5 or 6 , - wherein the pressure relief valve (D) is designed to be normally open, and / or - wherein the separating valve (T) is designed to be normally open. Brake system (10) according to one of Claims 5 to 7 in the connection (V1) between the pressure chamber (34) and the first connection (141) of the Simulator (100) no valve and / or no further component is arranged. Brake system (10) according to one of Claims 5 to 8th in which the brake system (10) comprises a number of brakes (B), each brake (B) being connected to a central port (Z) via a respective outlet valve (A), the central port (Z) being in the connection (V2) between the pressure chamber (34) and the pressure relief valve (D) or in the connection between the separating valve (T) and the pressure relief valve (D) is arranged. Brake system (10) after Claim 9 , - Wherein the exhaust valves (A) are designed normally open. Brake system (10) according to one of Claims 9 or 10 in which the brake system (10) has an automatically operated pump (20), wherein each brake (B) is connected to the pump (20) via a respective inlet valve (E). Brake system (10) after Claim 11 , - wherein the inlet valves (E) are designed normally closed. Brake system (10) according to one of Claims 11 or 12 - wherein the brake system (10) comprises a controller (15) which is configured to control at least the pump (20) and the valves (D, T, A, E). Brake system (10) after Claim 13 as well as after Claim 6 or any claim dependent thereon, wherein the controller (15) is configured to close the isolation valve (T), open the pressure relief valve (D) in at least one operating mode upon actuation of the brake pedal (40) and apply pressure modulation of the brakes (B ) by means of the outlet valves (A). Brake system (10) according to one of Claims 13 or 14 as well as after Claim 6 or a dependent claim, - wherein the controller (15) is configured to open the isolation valve (T) in at least one mode of operation when the brake pedal (40) is not actuated.

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