Method for operating a braking system of a motor vehicle, in particular a motor car

Abstract

Method for operating a brake system (10) of a motor vehicle, in which the brake system (10) has a brake pressure sensor (20) having at least one master cylinder (22) and a brake circuit (26) connected to the master cylinder (22) and through which brake fluid flows, which has at least one brake line (44) connected to a wheel brake (30) actuated by means of the brake fluid and through which brake fluid flows, in which two inlet valves (48, 54) connected in series are arranged, via which the wheel brake (30) can be supplied with hydraulic fluid for actuating the wheel brake (30), characterized in that the inlet valves (48, 54) are designed as valves that can be supplied with electrical energy and are normally open.which are each switchable between an open state releasing the brake line (44) as the first state and a closed state blocking the brake line (44) as the second state, wherein after actuation of the master cylinder (22) by a person, at least one of the inlet valves (48, 54) is supplied with electrical energy and thereby switched from its open state releasing the brake line (44) to its closed state blocking the brake line (44), whereupon the respective inlet valve (48, 54) is switched back and forth several times between its respective states within a predetermined or predetermined time period.

Description

[0001] The invention relates to a method for operating a braking system of a motor vehicle, in particular a motor vehicle, according to the preamble of patent claim 1.

[0002] DE 10 2009 032 281 A1 discloses a braking system with means for controlling brake and traction slip and for autonomous brake pressure control, with a brake pressure sensor consisting of a master cylinder and a pressureless reservoir. Furthermore, DE 38 24 877 C2 discloses an anti-lock braking system with propulsion control for a motor vehicle.

[0003] The object of the present invention is to provide a method for operating a braking system of a motor vehicle, in particular a motor vehicle, so that a particularly advantageous operation of the braking system can be realized, while at the same time an excessive load on the braking system can be avoided.

[0004] This object is achieved by a method having the features of patent claim 1. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims.

[0005] The invention relates to a method for operating a braking system of a motor vehicle, also referred to simply as a vehicle, which is preferably designed as a motor vehicle, in particular as a passenger car. In particular, the method is carried out by means of an electronic computing device, also referred to as a control unit, of the braking system and thus of the motor vehicle. Very particularly, the method is carried out while the motor vehicle is traveling, for example while traveling, in particular along a surface, also referred to as the ground or roadway. In the method, the braking system has a brake pressure sensor, also referred to simply as a pressure sensor, which has at least one master cylinder. The master cylinder is also referred to as the master brake cylinder and can be actuated by a person, such as the driver of the motor vehicle.By operating the brake pressure sensor, the braking system can be activated, which can, for example, slow down the vehicle.

[0006] The braking system further comprises a brake circuit connected to the master cylinder, through which brake fluid can flow. The brake circuit comprises at least one brake line through which brake fluid can flow and which is connected, in particular fluidically, to a wheel brake. Thus, the wheel brake can be supplied with the brake fluid flowing through the brake line via the brake line, so that the wheel brake can be actuated by means of the brake fluid flowing through the brake line. The wheel brake is assigned, for example, to a vehicle wheel of the motor vehicle, also simply referred to as a wheel, wherein the vehicle wheel can be braked by means of the assigned wheel brake. This allows the motor vehicle as a whole to be braked. By actuating the brake pressure sensor, the wheel brake can be actuated via the brake fluid, whereby the vehicle wheel to which the wheel brake is assigned can be braked.As a result, the aforementioned person can brake the vehicle wheel and thus the motor vehicle by actuating the master cylinder. The wheel brake is preferably a friction brake, in particular a disc brake. Very particularly, the braking system and thus the wheel brake is a service brake of the motor vehicle. The vehicle wheel is a ground contact element of the motor vehicle which is or can be supported on the aforementioned ground via the ground contact element downwards in the vertical direction of the motor vehicle. If the motor vehicle is driven along the ground while the motor vehicle is supported on the ground via the ground contact element downwards in the vertical direction of the motor vehicle, the ground contact element rolls, in particular directly, along the ground. In particular, the ground contact element touches the ground, in particular directly.

[0007] At least or exactly two inlet valves of the brake circuit are arranged in the brake line, which thus has the inlet valves. With respect to a transmission direction in which, when the brake pressure sensor is actuated, brake pressure is transmitted or exerted via the brake fluid to the wheel brake in order to thereby actuate the wheel brake and thus brake the vehicle wheel, the respective inlet valve is arranged downstream of the master cylinder and upstream of the wheel brake. The inlet valves are fluidically connected to one another in the brake line so that, with respect to the transmission direction, the inlet valves follow one another, thus one of the inlet valves is arranged downstream of the other inlet valve and upstream of the wheel brake, so that the other inlet valve is arranged upstream of one inlet valve and downstream of the master cylinder. The wheel brake can be supplied with hydraulic fluid via the inlet valves to operate the wheel brake.In particular, by means of the respective inlet valve arranged in the brake line, a supply of the wheel brake with brake fluid can be adjusted, i.e. varied, whereby an actuation of the wheel brake can be adjusted, i.e. varied. For this purpose, for example, a respective flow cross-section of the respective inlet valve through which the brake fluid can flow can be adjusted, i.e. varied, in particular such that the respective flow cross-section of the respective inlet valve can be set to at least two, in particular to more than two, different values, wherein, for example, a first of the values ​​is greater than zero and a second of the values ​​is zero. Furthermore, it is conceivable that a third of the values ​​or the second value is greater than zero, wherein in particular the third value is different from the first value.

[0008] In order to be able to realize a particularly advantageous operation, in particular a particularly advantageous actuation or actuation, of the brake system, wherein at the same time an excessive load on the respective inlet valve and thus on the brake system can be avoided, it is provided according to the invention that the respective inlet valve is designed as a valve that can be supplied with electrical energy, that is to say in particular with an electrical current and / or an electrical voltage, and can thereby be controlled, in particular in a targeted and active manner, wherein the respective inlet valve is open when de-energized.The feature that the respective inlet valve is open when de-energized, i.e., that the respective inlet valve is a respective de-energized valve, is to be understood that the respective inlet valve is open in the respective de-energized state of the respective inlet valve and thus fluidically releases the brake line for a flow of brake fluid through the brake line. The respective de-energized state of the respective inlet valve is to be understood that in the respective de-energized state of the respective inlet valve, i.e., during the respective de-energized state of the respective inlet valve, the respective inlet valve is not supplied with electrical energy, in particular continuously and thus without interruption.In other words, when and in particular whenever the respective inlet valve is not supplied with electrical energy, that is to say, for example, when and in particular whenever no electrical voltage is applied to the respective inlet valve and / or when the respective inlet valve is not supplied with electrical current, the respective inlet valve is open, such that the respective inlet valve releases the brake line, in particular for brake fluid to flow through the brake line. Thus, the respective inlet valve, which fluidically releases the brake line when the respective inlet valve is de-energized, is also referred to as a normally open valve. In other words, the respective inlet valve is therefore normally open.

[0009] The respective inlet valve can thus be switched between a respective open state, which releases the brake line, and a respective closed state, which blocks the brake line. The respective open state is also referred to as the first state or is a first state of the respective inlet valve, and the respective closed position is also referred to as the second state or is a respective second state of the respective inlet valve. Since the respective inlet valve is open when de-energized, the respective inlet valve can be switched or is switched from its respective open state to its respective closed state by the fact that the respective inlet valve can be or is supplied with electrical energy. In other words, by supplying the respective inlet valve with electrical energy, the respective inlet valve can be switched from its respective open state to its respective closed state.

[0010] In the method according to the invention, it is further provided that after an actuation of the master cylinder by a person, in particular after an end of an actuation of the master cylinder by a person, at least one of the inlet valves is actively and thus specifically supplied with electrical energy and is thereby actively and thus specifically switched from its open state of the at least one inlet valve, which releases the brake line, to its closed state of the at least one inlet valve, which fluidically blocks the brake line.

[0011] Supplying the at least one intake valve with electrical energy comprises, for example, supplying the at least one intake valve with electrical current and / or applying an electrical voltage to the at least one intake valve. Supplying the at least one intake valve with electrical energy is also referred to as energizing or energizing the at least one intake valve. Thus, following the aforementioned actuation of the master cylinder by the person, the at least one intake valve is energized, thereby switching from the open state of the at least one intake valve to the closed state of the at least one intake valve.Since the inlet valves are arranged downstream of the master cylinder and upstream of the wheel brake, particularly with respect to the aforementioned transmission direction, the inlet valves are arranged in a braking operation flow path, also simply referred to as a flow path, between the master cylinder and the wheel brake, in particular a wheel cylinder of the wheel brake. By energizing the at least one inlet valve, the de-energized state of the at least one inlet valve is canceled or terminated, and the brake line is thereby fluidly blocked, so that the braking operation flow path is interrupted.In particular, it is provided that during the actuation of the master cylinder by the person, both inlet valves are open at the same time, thus that during the actuation of the master cylinder by the person, both inlet valves are in their open states at the same time, wherein after the actuation of the master cylinder by the person, in particular after the end of the actuation of the master cylinder by the person, at least one inlet valve is actively and thus deliberately closed, thus switching from its open state to its closed state. As a result, a low-flow resistance backflow of the brake fluid away from the actuation and towards the master cylinder is prevented, i.e. suppressed. If necessary, a possible backflow of the brake fluid away from the wheel brake into a return flow path associated with increased flow resistance is permitted or enforced.

[0012] Furthermore, the method according to the invention provides that - after the at least one inlet valve has been switched from its open state to its closed state - the respective inlet valve is actively and thus deliberately switched back and forth between its respective states within a predetermined or predeterminable period of time. In other words, the method according to the invention provides that - after the at least one inlet valve has been switched from its open state to its closed state and in particular after the at least one inlet valve has reached its closed state - both inlet valves arranged in the brake line are actively and thus deliberately switched back and forth between their respective states, so that when considering the respective inlet valve alone, the respective inlet valve is alternately switched back and forth between its respective states several times.In other words, after the at least one intake valve has been actively and thus specifically switched from its open state to its closed state, a first of the intake valves is alternately switched back and forth between the states of the first intake valve several times within the time period, and the second intake valve is alternately switched back and forth between the states of the second intake valve several times within the time period. This can prevent excessive, particularly mechanical, loading of the respective intake valve and thus the braking system.

[0013] The invention is based in particular on the finding that because the respective intake valve is designed as a normally open valve and, for example, as an electromagnetic valve, a high, in particular mechanical, load can occur on the respective intake valve if the respective intake valve is kept closed for a relatively long time, i.e. without interruption, and is supplied with electrical energy for this purpose. In other words, because the respective intake valve is designed as an advantageous normally open valve, it is necessary to supply the respective intake valve, in particular without interruption, with electrical energy, in particular with a current, in order to keep the intake valve open accordingly without interruption. Such continuous current supply to the respective intake valve can lead to an undesirably high load on the intake valve.However, since it is now provided according to the invention that after the switching of the at least one inlet valve from the open state of the at least one inlet valve to the closed state of the at least one inlet valve, both the first inlet valve and the second inlet valve are alternately switched back and forth between their respective states several times, it can be avoided that the respective inlet valve is kept closed for an excessively long period of time, so that excessive loading of the respective inlet valve can be avoided.

[0014] Further findings and considerations underlying the invention are in particular the following: The wheel brake, which is preferably designed as a disc brake and thus as a friction brake, has, for example, a brake disc that can rotate with the vehicle wheel, in particular is connected to the vehicle wheel in a rotationally fixed manner, a brake pad and a brake piston, also simply referred to as a piston, which is, for example, a component of the aforementioned wheel cylinder. The brake piston can be supplied with brake fluid via the brake line and thus via the inlet valves, i.e. can be pressurized, whereby the brake piston presses the brake pad against the brake disc by pressurizing the brake piston with hydraulic fluid, thereby braking the vehicle wheel. The brake piston can be actuated by actuating the master cylinder and subsequently press the brake pad against the brake disc, thus braking the vehicle wheel.In particular, by actuating the brake piston, i.e. by pressurizing the brake piston with brake fluid, the brake piston is moved towards the brake pad and towards the brake disc, whereby the brake pad is moved towards the brake disc and thereby into support engagement with the brake disc. A movement of the brake piston away from the brake pad and / or away from the brake disc is also referred to as resetting or resetting of the brake piston. Tilting of the brake disc, also referred to as brake disc tilting, as well as vibrations of a brake caliper of the wheel brake, also referred to as brake caliper vibrations, particularly when the brake caliper is designed as a floating caliper or floating caliper, can lead to an excessively high resetting of the brake piston.Brake disc tilting and brake caliper vibrations can be caused by high wheel contact forces, high tire lateral forces, and / or chassis and steering forces. If no countermeasures are taken, the excessive retraction of the brake piston can result in, for example, the person being able to move, in particular press, a brake pedal, which is used to actuate the master cylinder, all the way to or up to a stop during braking, without the wheel brake being applied or the vehicle wheel being decelerated. In order to decelerate the associated vehicle wheel using the wheel brake, the person must release or release the brake pedal and then depress, in particular press, the brake pedal again, possibly even several times.This allows brake fluid, which was previously forced into a reservoir due to excessive brake piston retraction, to be drained from the reservoir or returned to the reservoir via the re-opened openings in the master cylinder. Such excessive retraction of the brake piston occurs primarily with floating-caliper brakes on rough surfaces such as cobblestones, Belgian blocks, etc., or in terrain also known as off-road, such as gravel roads, field tracks, etc. Such excessive retraction of the brake piston can occur within a few hundred meters of travel or within a few seconds without actuating the master cylinder.Such excessive retraction of the brake piston is typically counteracted by actively building up pressure in the brake circuit, in particular by pumping brake fluid into the brake circuit using a pump located in the brake circuit and / or increasing the pressure of the brake fluid in the brake circuit. The pump is designed, for example, as an electric pump, i.e., as an electrically operated pump. However, this can lead to undesirable noises caused by the pump and / or undesirable emissions, because an air gap, particularly between the brake disc and the brake pad, is actively closed. Furthermore, it can reduce the service life of the pump.In order to avoid the problems and disadvantages mentioned above, in the method according to the invention, the at least one inlet valve is actively and thus specifically supplied with electrical energy after the actuation of the master cylinder by the person and is thereby actively and specifically switched from the open state of the at least one inlet valve to the closed state of the at least one inlet valve.In other words, the at least one inlet valve is actively and thus deliberately closed after the actuation of the master brake cylinder by the person and is thereby kept actively and thus deliberately closed, in particular during a particular subsequent predetermined or predeterminable time interval, in particular until the at least one inlet valve is switched back from its closed state to its open state, in order to switch the at least one inlet valve back and forth alternately between its states several times within and during the time period.By the targeted closing of the at least one inlet valve and in particular by the at least one inlet valve being kept closed during the time interval, in particular without interruption, a volume of the brake circuit arranged between the at least one closed inlet valve and the wheel brake, in whose volume the brake fluid is or can be accommodated, is kept at least substantially constant and / or enclosed, so that an excessively high resetting of the brake piston can be avoided. This volume is also referred to as the hydraulic volume and is kept at least substantially constant by the at least one inlet valve being actively and thus specifically closed and then kept closed, in particular during the time interval, in particular continuously and / or between two braking applications or actuations of the master brake cylinder by a person.As a result, the free travel by which the piston can move back and thus away from the brake disc and / or the brake pad can be limited and advantageously kept small, so that excessive resetting of the brake piston can be avoided. In particular, the aforementioned volume can be deliberately kept constant and / or closed during the aforementioned period and thus advantageously kept small, particularly between the aforementioned two braking applications or the actuation of the master cylinder by the person, so that excessive free travel by which the piston can move back and thus away from the brake disc and / or the brake pad can be avoided.

[0015] In other words, by selectively switching the intake valves back and forth between their states within and during the time period, so that when considering only the respective intake valve, the respective intake valve is alternately switched back and forth between its respective states several times within and during the time period, the free travel by which the piston can move back and thus away from the brake disc and / or the brake pad can be limited and thus advantageously kept small, so that excessive resetting of the brake piston can be avoided. At the same time, excessive loading of the intake valves can be avoided.

[0016] For example, for temperature equalization or in special situations, at least one intake valve can be opened briefly or even for a longer period if confining the volume is not necessary or if short-term pressure equalization is desired without significantly increasing the air gap. For this purpose, additional detections such as speed, lateral / longitudinal acceleration, yaw rate, and / or vertical acceleration may need to be evaluated to avoid opening at inopportune moments and thus missing the original goal of a quasi-constant air gap or volume.For example, a control or regulation is carried out by means of the electronic computing device, wherein the method is carried out by means of the control or regulation and thus in particular the at least one inlet valve is switched from its open state to its closed state and, for example, the inlet valves are switched back and forth between their states after the at least one inlet valve has been switched to the closed state. For example, a distinction is made by means of the electronic computing device, in particular by means of the control or regulation, between braking operation and non-braking operation of the braking system. Braking operation is brought about and thus carried out, for example, by actuating the master cylinder, so that the braking system is in braking operation, in particular when the person actuates the master cylinder.If the person stops operating the master cylinder or if the master cylinder is not operated, the braking system is in non-braking mode. The feature that at least one inlet valve is closed after the person has operated the master cylinder means that the person first operates the master cylinder and then stops operating the master cylinder, whereupon the inlet valve is actively and therefore specifically closed. By means of the electronic computing device, for example, the braking mode and then the non-braking mode of the braking system is first determined, in particular recorded. The end of the operation of the master cylinder therefore causes a change from braking mode to or onto non-braking mode.If this change or non-braking operation is determined, in particular by means of the electronic computing device, the at least one inlet valve is actively and thus deliberately closed, in particular by means of the electronic computing device, thus switching from the open state to the closed state of the at least one inlet valve. In particular, it is provided that the at least one inlet valve is closed, in particular without interruption and thus continuously, i.e., interrupted, during the time interval of the non-braking operation following a braking operation, in particular until the repeated alternating switching of the at least one inlet valve back and forth between its states begins.In particular, it is provided that the inlet valves are alternately switched back and forth between their respective states several times during the non-braking operation following the braking operation, in particular during the entire non-braking operation, in particular until a change from non-braking operation to or onto braking operation occurs. In this way, excessive resetting of the brake piston can be effectively and efficiently avoided without requiring operation of the aforementioned pump with the associated disadvantages and without excessive loading of the inlet valves occurring. Briefly opening the respective inlet valve, in particular without brake application, can lead to advantageous pressure equalization and / or be advantageous in that any residual pressure can be reduced, for example as a result of thermal expansion of the brake fluid.This can be possible and useful in the event of a standstill or other special situations.

[0017] In order to advantageously avoid excessive return of the brake piston and excessive loading of the inlet valves, particularly during non-braking operation, one embodiment of the invention provides that after the actuation of the master cylinder by the person, the at least one inlet valve is switched from its open state releasing the brake line to its closed state blocking the brake line, while the other inlet valve remains in its open state.

[0018] Another embodiment is characterized by the fact that, after the master cylinder is actuated by the person, both inlet valves are simultaneously switched from their open states to their closed states. This reliably prevents excessive retraction of the brake piston.

[0019] The respective switching of the respective intake valve from the respective open state to the respective closed state is also referred to as closing the respective intake valve, and the respective switching of the respective intake valve from its respective closed state to its respective open state is also referred to as opening the respective intake valve.

[0020] In order to advantageously avoid excessive resetting of the brake piston and excessive loading of the inlet valves after the at least one inlet valve has been closed, a further embodiment of the invention provides that after the at least one inlet valve has been switched over to its closed state, the inlet valves are switched back and forth between their closed states and open states within the time period such that the time period has at least or exactly two types of time phases, namely a first type and a second type. During the first type, a first of the inlet valves is in its closed state, while at the same time the second inlet valve is in its open state. During the second type, the second inlet valve is in its closed state, while at the same time the first inlet valve is in its open state.

[0021] It has proven particularly advantageous if, after switching the at least one intake valve to its closed state, the intake valves are switched back and forth between their closed states and open states within the time period in such a way that the time period has at least or exactly three types of time phases, namely the first type, the second type, and a third type, during which both intake valves are simultaneously in their closed states, wherein the first type and the second type alternate within the time period and the third type lies between the first type and the second type. This makes it possible to avoid excessive loading of the intake valves.

[0022] In order to be able to reliably avoid excessive resetting of the brake piston and excessively high loading of the brake system, it is provided in a further embodiment of the invention that after the switching of at least one inlet valve into its closed state, the inlet valves are switched back and forth between their closed states and open states within the time period in such a way that within the time period the respective inlet valve initially in its open state is switched to its closed state, while the respective inlet valve initially in its closed state is still in its closed state and the respective inlet valve initially in its closed state is only switched from its closed state to its open state when the respective inlet valve initially in its open state has reached its closed state,whereby the time period has at least or exactly three types of time phases, namely the first type, the second type and the third type, wherein within the time period the first type and the second type alternate and the third type lies between the first type and the second type, in particular always or always.

[0023] In order to reliably prevent excessive resetting of the brake piston and excessive wear of the brake system, a further embodiment of the invention provides that after the at least one inlet valve has been switched to its closed state, the inlet valves are switched back and forth between their closed states and open states within the time period such that the time period has at least or exactly two types of time phases, namely the first type and the second type, wherein the first type and the second type alternately follow one another and directly adjoin one another. Thus, for example, a respective start of the second type coincides with a respective end of the first type and vice versa, and a respective end of the second type coincides with a respective start of the first type and vice versa.

[0024] It has proven particularly advantageous if, after the at least one intake valve has been switched to its closed state, the intake valves are alternately switched back and forth between their closed states and open states within the time period in such a way that, within the time period, the respective switching of the respective intake valve from the respective closed state to the respective open state coincides in time with the respective switching of the respective intake valve from the respective open state to the respective closed state and vice versa, whereby the time period has at least or exactly two types of time phases, namely the first type and the second type, wherein the first type and the second type alternately follow one another and directly adjoin one another. This makes it possible to avoid excessive loading of the braking system and, at the same time, to avoid excessive loading of the intake valves.

[0025] A further embodiment is characterized in that after switching the at least one intake valve into its closed state, the intake valves are switched back and forth between their closed states and open states within the time period in such a way that the time period has at least or exactly four types of time phases, namely the first type, the second type, a third type during which both intake valves are simultaneously in their closed states, and a fourth type during which both intake valves are simultaneously in their open states.It is intended that, within the time period, the first type and the second type alternate, and the third type and the fourth type alternate, such that the third type is positioned between the first type and the second type, such that the third type follows the first type and precedes the second type, and the fourth type is positioned between the second type and the first type, such that the fourth type follows the second type and precedes the first type. This can particularly advantageously prevent excessive loading of the braking system.

[0026] Finally, it has been shown to be particularly advantageous in order to avoid excessive wear of the brake system and excessive resetting of the brake piston if, after the switching of at least one inlet valve into its closed state, the inlet valves are switched back and forth between their closed states and open states within the time period in such a way that the time period has at least or exactly two types of time phases, namely a first type during which the inlet valves are simultaneously in their closed states, and a second type during which the inlet valves are simultaneously in their open states, wherein the first type and the second type alternately follow one another and directly adjoin one another, so that an end of the first type coincides with a start of the second type and vice versa, and that an end of the second type coincides with a start of the first type and vice versa.As a result, excessive wear of the brake system can be avoided, and excessive return of the piston can be avoided, in particular in the non-braking operation which, for example, lies between two braking operations, in particular such that the non-braking operation begins with an end of a first of the braking operations and ends with a start of a second of the braking operations, wherein the second braking operation follows the first braking operation in time.

[0027] Also disclosed is a braking system for a motor vehicle, wherein the braking system is designed to implement a method according to the invention. Advantages and advantageous embodiments of the method according to the invention are to be regarded as advantages and advantageous embodiments of the braking system, and vice versa.

[0028] Furthermore, a motor vehicle, also referred to simply as a vehicle and preferably designed as a motor vehicle, in particular as a passenger car, is disclosed, which has the aforementioned disclosed braking system. Advantages and advantageous embodiments of the method according to the invention and the disclosed braking system are to be regarded as advantages and advantageous embodiments of the disclosed vehicle, and vice versa.

[0029] Further advantages, features, and details of the invention will become apparent from the following description of a preferred embodiment and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the single figure, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0030] The drawing shows in the only figure a schematic representation of a braking system of a motor vehicle.

[0031] The single figure shows a schematic representation of a braking system 10, in the present case designed as a service brake, of a motor vehicle, also simply referred to as a vehicle, which is designed, for example, as a motor vehicle, in particular as a passenger car. A method for operating the braking system 10 is described below with reference to the figure. The motor vehicle has, in particular precisely, two vehicle axles arranged one behind the other and thus consecutively in the longitudinal direction of the motor vehicle, which are also simply referred to as axles. The respective vehicle axle has, in particular precisely, two vehicle wheels, which are also simply referred to as wheels. The vehicle wheels are ground contact elements of the motor vehicle, which can be or is supported downwards on a ground in the vertical direction of the motor vehicle via the ground contact elements.The two vehicle wheels of a first of the vehicle axles are shown particularly schematically in the figure and designated 12 and 14 in the figure. In the present case, the first vehicle axle is a front axle, so that the vehicle wheels 12 and 14 are the front wheels of the motor vehicle. The two vehicle wheels of a second of the vehicle axles are shown particularly schematically in the figure and designated 16 and 18. For example, the second vehicle axle is a rear axle, which follows the front axle towards the rear in the vehicle's longitudinal direction. Thus, the vehicle wheels 16 and 18 are the rear wheels of the motor vehicle.The vehicle wheels 12 and 14 are arranged on opposite sides of the motor vehicle in the transverse direction of the motor vehicle, in this case such that the vehicle wheel 12 is arranged on the right side of the motor vehicle as viewed in the forward direction of travel of the motor vehicle and the vehicle wheel 14 is arranged on the left side of the motor vehicle as viewed in the forward direction of travel. Thus, the vehicle wheel 12 is a left front wheel and the vehicle wheel 14 is a right front wheel of the motor vehicle. The vehicle wheels 16 and 18 are arranged on the opposite sides of the motor vehicle in the transverse direction of the vehicle such that the vehicle wheel 16 is arranged on the left side and the vehicle wheel 18 is arranged on the right side of the motor vehicle, so that the vehicle wheel 16 is a left rear wheel and the vehicle wheel 18 is a right rear wheel of the motor vehicle.

[0032] The brake system 10 has a pressure sensor 20, also referred to as a brake pressure sensor, with a first master cylinder 22 and a second master cylinder 24, wherein the master cylinders 22 and 24 are also referred to as master brake cylinders. In the exemplary embodiment shown in the figure, the vehicle wheel 12 is referred to as the first vehicle wheel, the vehicle wheel 16 as the second vehicle wheel, the vehicle wheel 14 as the third vehicle wheel, and the vehicle wheel 18 as the fourth vehicle wheel. The brake system 10 also comprises a first brake circuit 26 connected to the first master cylinder 22 and a second brake circuit 28 connected to the second master cylinder 24. The brake circuit 26 has a first wheel brake 30 assigned to the vehicle wheel 12 and a second wheel brake 32 assigned to the vehicle wheel 16. The brake circuit 28 has a third wheel brake 34 assigned to the vehicle wheel 14 and a fourth wheel brake 36 assigned to the vehicle wheel 18.The respective wheel brake 30, 32, 34, 36 is designed here as a disc brake and thus as a friction brake and comprises a respective brake disc 38 which is connected in a rotationally fixed manner to the vehicle wheel 12, 14, 16, 18 to which the respective wheel brake 30, 32, 34, 36 is assigned. In addition, the respective wheel brake 30, 32, 34, 36 comprises a respective brake caliper 40, which can be designed, for example, as a floating caliper or floating caliper. In addition, the respective wheel brake 30, 32, 34 and 36 comprises, for example, at least one respective brake piston (not visible in the figure), which is also referred to as a wheel piston or piston and is movable, for example, relative to the respective brake caliper 40 and in particular also relative to the respective brake disc 38, in particular translationally.Furthermore, for example, the respective wheel brake 30, 32, 34, 36 has at least one respective brake pad, designed as a friction lining or having a friction lining, which can be pressed against the respective brake disc 38 of the respective wheel brake 30, 32, 34, 36 by actuating the respective brake piston of the respective wheel brake 30, 32, 34, 36, in order to thereby brake the respective vehicle wheel 12, 14, 16, 18 to which the respective wheel brake 30, 32, 34, 36 is assigned. This allows the motor vehicle as a whole to be braked. The respective brake piston can be actuated by supplying the respective brake piston with brake fluid from the brake system 10. By actuating the respective brake piston, the respective wheel brake 30, 32, 34, 36 is confirmed, whereby the respective vehicle wheel 12, 14, 16, 18, to which the respective wheel brake 30, 32, 34, 36 is assigned, can be braked.The respective brake piston and thus the respective wheel brake 30, 32, 34, 36 can be actuated by actuating the respective master cylinder 22, 24, wherein the respective master cylinder 22, 24 can be actuated by actuating the pressure sensor 20. The pressure sensor 20 comprises a brake pedal 42, which can be actuated by a person, such as the driver of the motor vehicle. By actuating the brake pedal 42, the pressure sensor 20 and thus the master cylinders 22 and 24 can be actuated, in particular simultaneously, whereby the vehicle wheels 12, 14, 16, and 18 can be braked. The pressure sensor 20 is also referred to as a brake pressure sensor.

[0033] The first brake circuit 26 has a first brake line 44, which is connected to the first master cylinder 22 and thus fluidically connected to the master cylinder 22. Furthermore, the second brake circuit 28 has a second brake line 46, which is connected to the second master cylinder 24 and thus fluidically connected to the master cylinder 24. A brake fluid can flow through the respective brake line 44, 46, wherein in particular the brake fluid can be received in the respective brake line 44, 46 or is already received. The respective friction brake 30, 32, 34, 36 can be actuated by actuating the respective master cylinder 22, 24 via the brake fluid received in the respective brake line 44, 46. In other words, if a person such as the driver of the motor vehicle actuates the brake pedal 42, the pressure sensor 20 and thus the master cylinders 22 and 24 are actuated.As a result, the wheel brakes 30, 32, 34, and 36 are actuated via the brake fluid contained in the brake lines 44 and 46, thereby braking the vehicle wheels 12, 14, 16, and 18. For this purpose, the brake line 44 is connected to the wheel brakes 30 and 32, so that the wheel brakes 30 and 32 can be actuated by the brake fluid flowing through the brake line 44 or contained in the brake line 44. The brake line 46 is connected to the wheel brakes 34 and 36, so that the wheel brakes 34 and 36 can be actuated by the brake fluid flowing through the brake line 46 or contained in the brake line 46. By or upon actuation of the respective wheel brake 30, 32, 34, 36, the respective brake piston of the respective wheel brake 30, 32, 34, 36 can be actuated with the brake fluid held in the respective brake line 44, 46, whereby the respective brake piston can be actuated.As a result, the respective brake piston presses the respective brake pad against the respective brake disc 38, whereby the respective vehicle wheel 12, 14, 16, 18 is braked or can be braked.

[0034] The wheel brake 30 is assigned a first supply valve 48, which is arranged in a first branch 51 of the brake line 44. The wheel brake 32 is assigned a second supply valve 50, which is arranged in a second branch 52 of the brake line 44. The branches 51 and 52 are connected in parallel to one another in terms of flow, so that the supply valves 48 and 50 are connected in parallel to one another in terms of flow. Since the supply valves 48 and 50 are arranged in branches 51 and 52 of the brake line 44, the supply valves 48 and 50 are arranged in the brake line 44. In addition, the branches 51 and 52 and the supply valves 48 and 50 are components of the first brake circuit 26. The first brake circuit 26 also has a third supply valve 54 which is common to the supply valves 48 and 50 and the wheel brakes 30 and 32 and the branches 51 and 52 and which is arranged in a third branch 56 of the brake line 44.Thus, the third supply valve 54 and the third branch 56 are components of the first brake circuit 26. The respective branch 51, 52 and thus the respective supply valve 48, 50 are, for example, connected in series with the branch 56 and thus with the supply valve 54 in terms of flow technology.

[0035] The third wheel brake 34 is assigned a fourth supply valve 58, which is arranged in a fourth branch 60 of the brake line 46. The wheel brake 36 is assigned a fifth supply valve 62, which is arranged in a fifth branch 64 of the brake line 46. The branches 60 and 64, and thus the supply valves 58 and 62, are connected in parallel to one another in terms of flow. Furthermore, the supply valves 58 and 62 and the branches 60 and 64 are components of the second brake circuit 28. The second brake circuit 28 also includes a sixth supply valve 66, which is common to the wheel brakes 34 and 36, the branches 60 and 64, and the supply valves 58 and 62 and is arranged in a sixth branch 68 of the brake line 46. The supply valve 66 and the branch 68 are thus components of the second brake circuit 28.For example, the respective branch 60, 64 and thus the respective supply valve 58, 62 are connected in series with the branch 68 and thus with the supply valve 66 in terms of flow technology.

[0036] It can be seen that the supply valves 48, 50, 58, and 62 are wheel-specific, and thus wheel-brake-specific, supply valves, such that the wheel brake 30 can be supplied with brake fluid via the supply valve 48, the wheel brake 32 via the supply valve 50, the wheel brake 34 via the supply valve 58, and the wheel brake 36 via the supply valve 62. In particular, the respective supply valve 48, 50, 58, and 62 can influence the supply of the respective wheel brake 30, 32, 34, 36 with brake fluid, thus a respective flow of the brake fluid to the respective wheel brake 30, 32, 34, 36, and in doing so, in particular, can adjust and thus vary this flow.In particular, the supply valves 48, 50, 58 and 62 are wheel-individual valves of an electronic stability program of the motor vehicle, also referred to as ESP, wherein by means of the respective supply valve 48, 50, 58 and 62 a respective brake pressure of the respective wheel brake 30, 32, 34, 36 can be modulated, i.e. adjusted and thus varied, individually and thus in particular independently of the other, remaining wheel brakes 30, 32, 34, 36.

[0037] The supply valve 54 is a valve common to branches 51 and 52, and thus to supply valves 48 and 50 and wheel brakes 30 and 32, through which the supply valves 48 and 50 can be supplied with brake fluid. Accordingly, the supply valve 66 is a supply valve common to supply valves 58 and 62 and wheel brakes 34 and 36, through which the supply valves 58 and 62 can be supplied with brake fluid.With respect to a transmission direction in which, when the respective master cylinder 22, 24 is actuated, a pressure can be transferred to the respective wheel brake 30, 32, 34, 36 via the brake fluid held in the respective brake line 44, 46 in order to thereby actuate the respective wheel brake 30, 32, 34, 36 and thus brake the respective, associated vehicle wheel 12, 16, 14, 18, the supply valve 58 is arranged downstream of the master cylinder 22 and upstream of the wheel brake 30 and downstream of the supply valve 54 and upstream of the wheel brake 30, wherein, with respect to the transmission direction, the supply valve 50 is arranged downstream of the master cylinder 22 and upstream of the wheel brake 32 and downstream of the supply valve 54 and upstream of the wheel brake 32. Accordingly, with respect to the transmission direction, the supply valve 54 is arranged downstream of the master cylinder 22, upstream of the supply valve 48 and upstream of the supply valve 50.With respect to the transmission direction, the supply valve 58 is arranged downstream of the master cylinder 24 and upstream of the wheel brake 34 and downstream of the supply valve 66 and upstream of the wheel brake 34. With respect to the transmission direction, the supply valve 62 is arranged downstream of the master cylinder 24 and upstream of the wheel brake 36 and downstream of the supply valve 66 and upstream of the wheel brake 36. With respect to the transmission direction, the supply valve 66 is arranged downstream of the master cylinder 24 and upstream of the supply valves 58 and 62. The supply valves 48, 50, and 56 are arranged in the brake line 44, with the supply valves 58, 62, and 66 being arranged in the brake line 46.

[0038] It can be seen that the supply valves 48, 50, and 54 are inlet valves, via which the respective wheel brake 30, 32 can be supplied with hydraulic fluid, i.e., can be pressurized with hydraulic fluid, in order to actuate the respective wheel brake 30, 32. This means that the respective brake piston of the respective wheel brake 30, 32 can be supplied with brake fluid via the inlet valves and can thus be pressurized with brake fluid. Accordingly, the supply valves 58, 62, and 66 are inlet valves, via which the respective wheel brake 34, 36, i.e., in particular the respective brake piston of the respective wheel brake 34, 36, can be supplied with hydraulic fluid and can thus be pressurized with hydraulic fluid, in order to actuate the respective wheel brake 34, 36.

[0039] In order to be able to realize a particularly advantageous operation of the brake system 10, for example, the respective supply valve 48, 50, 58, 62 and / or the respective supply valve 54, 66 is designed as a valve that can be supplied with electrical energy and is open when de-energized, which in the above-mentioned method for operating the brake system 10 is supplied with electrical energy after an actuation of the respective master cylinder 22, 24 by a person, that is to say in particular after an end of an actuation of the respective master cylinder 22, 24 by a person, and is thereby switched from an open state that fluidically releases the respective brake line 44, 46 into a closed state that fluidically blocks the respective brake line 44, 46.In the respective open state, the respective valve releases the brake line 44 so that, for example, the brake fluid can flow through the respective valve and through the respective brake line 44, 46. In the respective closed state, the respective valve fluidly blocks the brake line 44, 46 so that the brake fluid cannot flow through the respective valve and thus not through the respective brake line 44, 46. The method prevents an excessively high resetting of the respective brake piston, that is to say in particular an excessively far movement of the respective brake piston away from the respective brake pad. The aforementioned actuation of the respective master cylinder 22, 24 brought about by the person is also referred to as the first actuation of the respective master cylinder 22, 24.

[0040] Preferably, it is provided that, after the respective valve has been switched to the closed state, the respective valve is held in the closed state continuously and thus without interruption, i.e., continuously, for a period of time. Furthermore, it is preferably provided that, after the respective valve has been switched to the closed state, a further actuation of the respective master cylinder 22, 24, initiated by a person, following the first actuation of the respective master cylinder 22, 24, is detected by a sensor device 70 of the brake system 10.The further actuation of the respective master cylinder 22, 24 is also referred to as renewed actuation or second actuation of the respective master cylinder 22, 24 and is effected, for example, by the same person who also effected the first actuation of the respective master cylinder 22, 24, or the second actuation of the respective master cylinder 22, 24 is effected by a different, additional person. Depending on the detection of the further actuation of the respective master cylinder 22, 24 taking place after the respective valve has switched to the closed state, the respective valve is switched from the closed state to the open state. For this purpose, for example, the supply of electrical energy to the respective valve is terminated, so that the respective valve returns, in particular independently and thus automatically, from the closed state to its open state.In particular, it is provided that after the respective valve has been switched to the closed state, the respective valve is held in the closed state continuously and thus without interruption, that is to say continuously, until the further actuation of the respective master cylinder 22, 24 taking place after the respective valve has been switched to the closed state is detected by means of the sensor device 70.

[0041] In order to be able to precisely detect the further, renewed actuation of the respective master cylinder 22, 24, the sensor device 70 comprises, for example, a travel sensor 72, also referred to as a braking distance sensor, by means of which a distance traveled by the brake pedal 42 as a result of its actuation and thereby the further, renewed actuation of the respective master cylinder 22, 24 is detected. Alternatively or additionally, the sensor device 70 comprises a pressure sensor 74, also referred to as a pre-pressure sensor, by means of which a pressure prevailing in the respective master cylinder 22, 24 and / or in the respective brake circuit 26, 28, in particular in the respective brake line 44, 46, and thereby the further, renewed actuation of the respective master cylinder 22, 24 is detected.

[0042] From the figure, it can be seen that a respective bypass line 76 is assigned to the respective supply valve 48, 50, 58, and 62, which bypass line 76 is fluidically connected to the respective brake line 44, 46 at, in particular, exactly two connection points, namely at a respective first connection point and at a respective second connection point. With respect to the transmission direction, the respective first connection point is arranged downstream of the respective master cylinder 22, 24 and upstream of the respective supply valve 48, 50, 58, 62, and in particular downstream of the respective supply valve 54, 66, and the respective second connection point is arranged downstream of the respective supply valve 48, 50, 58, 62 and upstream of the respective associated wheel brake 32, 30, 34, 36, with respect to the transmission direction.A respective check valve 78 is arranged in the respective bypass line 76, which, for example, automatically opens the respective bypass line 76 for a flow of brake fluid from the second connection point to the first connection point and automatically fluidically blocks an opposite flow of brake fluid from the respective first connection point to the respective second connection point. If, for example, the respective supply valve 48, 50, 58, 62 is used as the aforementioned normally open valve, the respective bypass line 76 and the respective check valve 78 can be omitted, or the respective check valve 78 can be equipped with an increased differential pressure.

[0043] A respective second bypass line 80 is assigned to the respective supply valve 54, 66, in which a respective second check valve 82 is arranged. The respective bypass line 80 is fluidly connected to the respective brake line 44, 46 at, in particular, exactly two further connection points, namely at a third connection point and at a fourth connection point. The respective third connection point is arranged downstream of the respective master cylinder 22, 24 and upstream of the respective supply valve 54, 66, with respect to the transmission direction, and the respective fourth connection point is arranged downstream of the respective supply valve 54, 66 and upstream of the supply valves 48 and 50 or 58 and 62, with respect to the transmission direction.The respective check valve 82 automatically releases the respective bypass line 80 for a flow of brake fluid from the respective third connection point behind the respective fourth connection point and automatically blocks the respective bypass line 80 for an opposite flow of brake fluid from the respective fourth connection point towards the respective third connection point.

[0044] In order to be able to realize particularly advantageous operation of the brake system 10, it is preferably provided that the respective valve is actively and thus specifically switched from the open state to the closed state at the earliest half a second, in particular at the earliest or exactly one second, after the first actuation of the respective master cylinder 22, 24 by the person, i.e. after the end of the first actuation of the respective master cylinder 22, 24. Furthermore, it is preferably provided that the respective valve is actively and thus specifically switched from the open state to the closed state at most two seconds, in particular at most 1.5 seconds, after the first actuation of the respective master cylinder 22, 24, i.e. after the end of the first actuation of the respective master cylinder 22, 24. In this way, excessive resetting of the respective brake piston can be reliably avoided.

[0045] The respective open state of the respective supply valve 48, 50, 54, 58, 62, 66 is also referred to as the respective first state, and the respective closed state of the respective supply valve 48, 50, 54, 58, 62, 66 is also referred to as the respective second state.

[0046] It can be seen that the respective branch 51, 52 is fluidically connected in series with branch 56, and the respective branch 60, 64 is fluidically connected in series with branch 68. Thus, the supply valves 48 and 54, or the supply valves 50 and 54, are fluidically connected in series with one another. Accordingly, the supply valves 58 and 66, or the supply valves 62 and 66, are fluidically connected in series with one another. In the aforementioned method, for example, with respect to the wheel brake 30, at least one of the serially connected supply valves 48 and 54 is switched from its open state to its closed state. With respect to the wheel brake 32, at least one of the supply valves 50 and 54 is switched from its open state to its closed state.With respect to the wheel brake 34, at least one of the serially connected supply valves 58 and 66 is switched from its open state to a closed state during the method, and accordingly, with respect to the wheel brake 36, at least one of the serially connected supply valves 62 and 66 is switched from its open state to its closed state during the method. For example, the supply valves 48 and 54 form a first valve pair, the supply valves 50 and 54 form a second valve pair, the supply valves 58 and 66 form a third valve pair, and the supply valves 62 and 66 form a fourth valve pair. The respective supply valves of the respective valve pair are fluidically connected in series with one another.In the method, at least one of the supply valves of at least one of the valve pairs is activated and thus specifically switched from its open state to its closed state after the actuation of the main cylinder 22 by the person, in particular after the end of the actuation of the main cylinder 22 by the person.

[0047] In order to avoid, on the one hand, an excessively high return of the respective brake piston and, on the other hand, an excessively high load on the respective supply valves of the respective valve pair, it is preferably also provided in the method that - after the at least one supply valve of the at least one valve pair has been deliberately switched to its closed state - the supply valves of the at least one valve pair, which comprises the at least one supply valve which was deliberately switched to its closed state after the actuation of the master cylinder 22 by the person, in particular after the end of the actuation of the master cylinder 22 by the person, are switched back and forth between their respective closed and open states within a predetermined or predeterminable period of time in such a way thatthat when considering only the respective supply valve of the at least one valve pair, the respective supply valve of the at least one valve pair is switched back and forth several times within the time period, alternating between its respective states.

[0048] In relation to the wheel brake 30, this means, for example, the following: In the method, after the actuation of the master cylinder 22 by the person, in particular after the end of the actuation of the master cylinder 22 by the person, at least one of the supply valves 48 and 54 of the first valve pair assigned to the wheel brake 30 is specifically switched from the open state of the at least one supply valve 48, 54 to the closed state of the at least one supply valve 48, 54, whereupon both the respective supply valve 48 and the respective supply valve 54, each considered individually, are alternately switched back and forth between their respective states several times within the predetermined or predeterminable time period.As a result, excessive return of the brake piston can be avoided during the period of time, and at the same time, it can be avoided that, in particular during the period of time, the respective supply valve 48, 54 remains open for an excessively long time, so that excessive loading of the respective supply valve 48, 54 can be reliably avoided.

Claims

[1] Method for operating a brake system (10) of a motor vehicle, in which the brake system (10) has a brake pressure sensor (20) having at least one master cylinder (22) and a brake circuit (26) connected to the master cylinder (22) and through which a brake fluid can flow, which brake circuit has at least one brake line (44) connected to a wheel brake (30) actuated by means of the brake fluid and through which the brake fluid can flow, in which two inlet valves (48, 54) connected in series with one another are arranged, via which the wheel brake (30) can be supplied with the hydraulic fluid for actuating the wheel brake (30), characterized byin that the inlet valves (48, 54) are designed as valves which can be supplied with electrical energy and are open when de-energized, and which can each be switched between a respective open state releasing the brake line (44) as a first state and a respective closed state blocking the brake line (44) as a second state, wherein after actuation of the master cylinder (22) by a person, at least one of the inlet valves (48, 54) is supplied with electrical energy and is thereby switched from its open state releasing the brake line (44) to its closed state blocking the brake line (44), whereupon the respective inlet valve (48, 54) is alternately switched back and forth between its respective states several times within a predetermined or predeterminable period of time. [2] Method according to claim 1, characterized bythat after the actuation of the master cylinder (22) by the person, at least one inlet valve (48, 54) is switched from its open state releasing the brake line (44) to its closed state blocking the brake line (44), while the other inlet valve (54, 48) remains in its open state. [3] Method according to claim 1, characterized by that after the actuation of the master cylinder (22) by the person, both inlet valves (48, 54) are simultaneously switched from their open states to their closed states. [4] Method according to one of the preceding claims, characterized by that after switching the at least one inlet valve (48, 54) into its closed state, the inlet valves (48, 54) are switched back and forth between their closed states and open states within the time period in such a way that the time period has at least or exactly two types of time phases, namely: - a first mode during which a first of the intake valves (48, 54) is in its closed state and the second intake valve (54) is in its open state; and - a second mode during which the second inlet valve (54) is in its closed state and the first inlet valve (48) is in its open state. [5] Method according to claim 4, characterized by that after switching the at least one inlet valve (48, 54) into its closed state, the inlet valves (48, 54) are switched back and forth between their closed states and open states within the time period in such a way that the time period has at least or exactly three types of time phases, namely: - the first type; - the second type; and - a third mode during which both inlet valves (48, 54) are in their closed states simultaneously, the first mode and the second mode alternating within the time period and the third mode being located between the first mode and the second mode. [6] Method according to claim 5, characterized bythat after switching the at least one inlet valve (48, 54) into its closed state, the inlet valves (48, 54) are switched back and forth between their closed states and open states within the time period in such a way that within the time period the respective inlet valve (48, 54) initially in its open state is switched into its closed state, while the respective inlet valve (48, 54) initially in its closed state is still in its closed state and the respective inlet valve (48, 54) initially in its closed state is only switched from its closed state to its open state when the respective inlet valve (48, 54) initially in its open state has reached its closed state, whereby the time period has at least or exactly three types of time phases, namely: - the first type; - the second type; and - the third type, whereby within the time period the first type and the second type alternate and the third type lies between the first type and the second type. [7] Method according to claim 4, characterized by that after switching the at least one inlet valve (48, 54) into its closed state, the inlet valves (48, 54) are switched back and forth between their closed states and open states within the time period in such a way that the time period has at least or exactly two types of time phases, namely: - the first type; and - the second type, where the first type and the second type alternate and are directly connected to each other. [8] Method according to claim 7, characterized bythat after the switching of the at least one inlet valve (48, 54) into its closed state, the inlet valves (48, 54) are alternately switched back and forth between their closed states and open states within the time period in such a way that, within the time period, the respective switching of the respective inlet valve (48, 54) from the respective closed state to the respective open state coincides in time with the respective switching of the respective inlet valve (48, 54) from the respective open state to the respective closed state and vice versa, whereby the time period has at least or exactly two types of time phases, namely: - the first type; and - the second type, where the first type and the second type alternate and are directly connected to each other. [9] Method according to claim 4, characterized bythat after switching the at least one inlet valve (48, 54) into its closed state, the inlet valves (48, 54) are switched back and forth between their closed states and open states within the time period in such a way that the time period has at least or exactly four types of time phases, namely: - the first type; - the second type; - a third mode during which both inlet valves (48, 54) are in their closed states simultaneously; and - a fourth mode during which both inlet valves (48, 54) are in their open states simultaneously, wherein within the time period the first mode and the second mode alternately follow one another and the third mode and the fourth mode alternately follow one another such that: o the third species lies between the first species and the second species in such a way that the third species follows the first species and precedes the second species; and o the fourth species lies between the second species and the first species in such a way that the fourth species follows the second species and precedes the first species. [10] Method according to one of the preceding claims, characterized by that after switching the at least one inlet valve (48, 54) into its closed state, the inlet valves (48, 54) are switched back and forth between their closed states and open states within the time period in such a way that the time period has at least or exactly two types of time phases, namely: - a first mode during which the intake valves (48, 54) are simultaneously in their closed states; and - a second mode during which the inlet valves (48, 54) are simultaneously in their open states, the first mode and the second mode alternating and directly following one another.

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