DE102011086737A1 - Method for improving pre-pressure estimation in hydraulic strand of slippage-controlled motor car brake assembly, involves regulating level of low pressure storage units at constant or variable value above threshold level by pressure drop - Google Patents

Abstract

The method involves enabling a filling of low pressure storage units (46, 56) with hydraulic volume by pressure drop in wheel brake cylinders (49, 59). Pressure is estimated by a pressure estimation based on generator voltage. A level of the low pressure storage units is estimated by a low pressure storage estimation. The level of the low pressure storage units is regulated during a slippage regulation operation at a constant or a variable value above a threshold level by a pressure drop and/or by conveying of hydraulic volumes to the low pressure storage units. An independent claim is also included for a hydraulic strand for a slippage-controlled motor car brake assembly.

Description

The invention relates to a method for improving an admission pressure estimation in a hydraulic train of a slip-controlled motor vehicle brake system according to the preamble of claim 1 and a hydraulic train of a slip-controlled motor vehicle brake system according to the preamble of claim 10.

With increasing comfort requirements of electronic brake systems in a motor vehicle, among other things, ever higher demands are placed on the noise. In particular, the control noise of the valves perceptible by the driver, for example in the case of an ABS control, presents a problem in this respect since they are perceived as unpleasant and are not accepted by the driver. In addition, such noise-causing valve vibrations can even be associated with a clearly perceptible by the driver longitudinal vibration of the vehicle speed. This can only be avoided by an exact control of the currently used analogized digital valves. However, in order to be able to control the analogized digital valves exactly with a respective suitable current, it is necessary to know the pressure difference across the valve as precisely as possible in addition to the opening current characteristic of the valve. However, in view of a cost-effective production of the motor vehicle brake system, no pressure sensors are often present, so that the knowledge of the necessary for the regulation current form must be determined via a form model.

In this context, the DE 10 2010 028 083 A1 a method for individual calibration of a pump motor in a pressure control system of a motor vehicle. After the production of the pressure control system, the delivery rate or speed of the pump is measured as a function of the electrical control under defined pressure conditions and the measured data stored in the pressure control system. By means of, for example, a structure-borne noise sensor, the speed is determined at a known motor current during operation of the pump, and a conclusion is drawn on the form based on the measurement data stored as part of the individual calibration.

In the WO 2005/007475 A1 describes a method which allows an estimate of the current form on the run-off behavior of a motor-pump unit. An electronic unit controls the motor of the motor-pump unit as required electrically pulse width modulated, wherein during a turn-off phase generator voltage generated by the motor is tapped. The generator voltage is supplied to the electronic unit, which estimates the present in the brake system form based on the generator voltage. In this case, a detected via the generator voltage speed reduction, which undergoes the motor-pump unit during a switch-off due to the admission pressure load, used as a yardstick for the form.

The DE 10 2007 032 588 A1 proposes a motor vehicle brake system in which a fill level of a low-pressure accumulator is calculated model-based. The level of the low-pressure accumulator results according to the model of the volume which is discharged from the exhaust valves in the low pressure accumulator, and the flow rate of the return pump, which empties the low-pressure accumulator. The outlet volume of the outlet valves can be determined by the activation time and the opening width of the outlet valves as well as the pressure difference. The driving time and the opening width of the exhaust valves are known. The pressure difference can, for example, according to a method as it is generically in the DE 10 2010 028 083 A1 or the WO 2005/007475 A1 is disclosed. Thus, according to the model described, the level of the low pressure accumulator can be determined.

However, the pressure estimation methods known in the prior art are disadvantageous in that a pressure estimation of the admission pressure on the run-out behavior of the motor-pump unit is only possible if a low-pressure accumulator arranged on the suction side of the motor-pump unit provides sufficient fluid volume , When the low-pressure accumulator is empty, it is not possible to estimate the pressure from the behavior of the motor-pump unit. For this reason, in the slip control mode, the control of the motor-pump unit must always be selected and adjusted so that an empty delivery of the low-pressure accumulator is prevented. Thus, the control timing of the motor-pump unit is continuously adapted to the level of the low-pressure accumulator. However, as a meaningful form pressure estimation is not possible over a certain period as a result of a change in the actuation timing, no pre-pressure values are available for this period. This results in an unadapted control of the analogized digital valves, which can lead from noise to a longitudinal vibration of the vehicle speed.

The object of the invention is therefore to propose an improved admission pressure estimation method which avoids an empty delivery of a low-pressure accumulator during a slip control operation of a motor vehicle brake system without changing a drive timing of a motor-pump unit.

This object is achieved by the method for improving a Vordruckschätzung in a hydraulic train of a slip-controlled motor vehicle brake system according to claim 1 and the hydraulic train of a slip-controlled motor vehicle brake system according to claim 10.

The invention relates to a method for improving a Vordruckschätzung in a hydraulic train of a slip-controlled motor vehicle brake system, in which an electrically clocked control of an electric motor of a motor-pump unit is carried out. From the motor-pump unit hydraulic volume is discharged in accordance with the electrically clocked control of at least one low-pressure accumulator and pressurized on the outlet side of the motor-pump unit. By means of a pressure reduction in at least one wheel brake cylinder, a filling of the at least one low-pressure accumulator is effected with hydraulic volume, wherein in an electrical cycle break a pressure-loaded flow behavior of the motor-pump unit is detected in the form of a generator voltage applied to the electric motor. On the basis of the generator voltage, a pressure is estimated by means of a pressure estimation and by means of a low-pressure accumulator estimation, a level of the at least one low-pressure accumulator is estimated. The method according to the invention is characterized in that, by means of the pressure reduction and / or by introducing hydraulic volume into the at least one low-pressure accumulator, a fill level of the at least one low-pressure accumulator during a slip control operation is adjusted to a constant or variable value above a fill level threshold. According to the method of the invention, therefore, the control of the electric motor of the motor-pump unit is not changed, but rather held the level of the low-pressure accumulator above a level threshold, reaching or falling below an adaptation of the control of the electric motor of the motor-pump unit would make necessary , The level of the low pressure accumulator can be estimated, for example, based on opening times, opening widths and taking into account the diaphragm equations of an intake valve and an exhaust valve and a differential pressure. Thus, a substantially faster and more accurate estimation of the form is made possible by largely avoiding changes in the control of the electric motor. Such an improved estimation of the form also allows an improvement of a wheel pressure estimation by means of a wheel pressure model. This is particularly advantageous in brake systems that have no pressure sensor. But also in brake systems with pressure sensor (such as ESC systems), the inventively improved pressure estimation method can be used. The invention can then be used advantageously for securing or checking the pressure signal of a pressure sensor. The described pressure reduction or pumping can be done by all a low-pressure accumulator associated wheel brake cylinder or only by a low-pressure accumulator associated wheel brake cylinder.

It is preferably provided that, for conveying in, both an inlet valve assigned to the at least one wheel brake cylinder and an outlet valve assigned to the at least one wheel brake cylinder are controlled and / or regulated to an open position and / or an intermediate position, in particular during a simultaneous pressurization by the motor pump Aggregate or a pressure transducer. For the purposes of the invention, the term pressure transmitter means a master cylinder filled with hydraulic volume and a driver-actuated pressure-control device connected to the master cylinder, e.g. a brake pedal, understood. By simultaneous, at least proportionate opening of the exhaust valve and the inlet valve, a direct hydraulic short circuit of the low pressure accumulator can be made with the pressure transducer, which allows an immediate conveying of hydraulic volume from the pressure transducer into the low pressure accumulator. Likewise, a direct hydraulic short circuit is made with the output side of the motor-pump unit, which alternatively or additionally allows a continuation of the pumped from the motor-pump unit hydraulic volume in the low-pressure accumulator. The hydraulic volume delivered by the motor-pump unit into the low-pressure accumulator may be e.g. be discharged from the pressure transducer when the switching valve is open. Thus, the level of the low-pressure accumulator can be controlled or regulated.

It is particularly preferably provided that the inlet valve and the outlet valve are controlled and / or regulated so that a form in the at least one wheel brake cylinder is kept constant during the feed, in particular by the hydraulic resistances of the inlet valve and the exhaust valve are adapted to the form. By keeping the pre-pressure in the brake cylinder constant, there is the advantage that a currently performed slip control is influenced as little as possible, although at the same time hydraulic volume is fed into the wheel brake cylinder through the inlet valve and is discharged through the exhaust valve. The control or regulation of the intake valve and / or the exhaust valve is adapted to the currently existing form, since the form during the delivery and outflow characterized by the difference of the hydraulic resistances of the intake valve and the exhaust valve becomes. The term adaptation of the hydraulic resistance according to the invention means both the adaptation of the opening width of a valve and additionally or alternatively the adjustment of its opening time. For example, the hydraulic resistance of a digital valve can be adjusted by specifying on-off modulation with a certain duty cycle.

Appropriately, it is provided that the conveying is carried out at a time at which the currently performed slip control operation is substantially not affected, in particular at a time when no pressure reduction and / or pressure build-up in at least one wheel brake cylinder is made. This results in the advantage that a disadvantageous influence on the slip control operation can be avoided particularly reliably. Since the slip control operation is particularly easily influenced during a pressure reduction or a pressure build-up, the conveying-in can be carried out, for example. be made during a pressure maintenance phase.

In particular, it is expediently provided that the conveying in at a time after a pre-pressure reduction phase, in particular in a Radbeobachtungsphase, is made. During the Radbeobachtungsphase takes place neither a pressure build-up nor a pressure reduction. Instead, only the behavior of the vehicle wheel associated with the wheel brake cylinder is monitored. This results in the advantage that an introduction of hydraulic volume into the low-pressure accumulator during the wheel monitoring phase avoids particularly reliably influencing the slip control operation.

In addition, it is advantageous that the fill level threshold is set or determined in such a way that no adaptation of the control of the motor-pump assembly due to insufficient fill level is necessary. This results in the advantage that the low-pressure accumulator according to the idea of the invention always stores sufficient hydraulic volume to make an adjustment of the control of the electric motor of the motor-pump unit unnecessary. Thus, at any time a reliable pressure estimate can be made, which in turn allows at any time accurate control or regulation of the valves in the brake circuit.

According to a further preferred embodiment of the invention, it is provided that the pressure reduction takes place by opening the exhaust valve associated with the at least one wheel brake cylinder and that a pressure build-up by opening the inlet valve associated with the at least one wheel brake cylinder and simultaneous activation of pressure generated by the pressure transducer and / or by Opening of the inlet valve and simultaneous control of generated by the motor-pump unit pressure is carried out. Opening the exhaust valve is an equally simple and effective method of inducing pressure reduction in the wheel brake cylinder. In addition, there is the further advantage that an opening of the outlet valve also leads to a filling of the low-pressure accumulator with hydraulic fluid. A pressure build-up by opening the inlet valve and controlling pressure generated by means of the motor-pump unit or the pressure transducer is a simple and reliable way of increasing the pressure in the wheel brake cylinder. The exhaust valve may be closed during pressure build-up or at least be controlled to have a higher hydraulic resistance than the intake valve.

It is preferably provided that the low-pressure accumulator estimation be taken into account taking into account the hydraulic resistances and the opening times of the intake valve and the exhaust valve and taking into account the pressure, wherein the hydraulic resistances are characterized by valve opening widths and / or valve opening times. This results in the advantage that all factors influencing the fill level of the low-pressure accumulator are taken into account for the low-pressure accumulator estimation. The low-pressure accumulator estimation thus delivers a result which corresponds optimally to the actual fill level.

It is expediently provided that the admission pressure estimation and the low-pressure accumulator estimation are carried out in an electronic control unit, wherein the electronic control unit controls and / or regulates the engine-pump assembly, the exhaust valve and the inlet valve. The pre-compression estimation and the low-pressure accumulator estimation are significantly influenced by the behavior of the engine-pump unit, the exhaust valve and the intake valve. By controlling these devices in the same control unit which also performs the pre-pressure estimation and the low-pressure memory estimation based thereon, the output values used for the estimates are directly available. The integration of the estimation methods and the control in a single electronic control unit also leads to a cost savings compared to an estimate and control by means of separate control units due to the reduced hardware cost.

The invention further relates to a hydraulic train of a slip-controlled motor vehicle brake system, the at least one wheel brake cylinder, which is hydraulically connected between an inlet valve and an outlet valve, at least one low-pressure accumulator, which hydraulically connected behind the exhaust valve, a motor-pump unit, which is hydraulically connected behind the at least one low-pressure accumulator and in accordance with an electrically clocked control hydraulic volume from the at least one low-pressure accumulator in the direction of the inlet valve promotes and the outlet side of the motor-pump unit with pressure acted upon and an electronic control unit, which controls the exhaust valve and the inlet valve and / or regulates and controls an electric motor of the motor-pump unit electrically clocked comprises. The electric motor runs in an electrical cycle break pressure loaded and generates a generator voltage. When opening the exhaust valve hydraulic volume flows into the at least one low-pressure accumulator and fills it. The electronic control unit reads the generator voltage and estimates a pre-pressure based on the generator voltage. In addition, it estimates a fill level of the at least one low-pressure accumulator based on the hydraulic volume delivered from the at least one low-pressure accumulator and the hydraulic volume which has flowed into the at least one low-pressure accumulator. The hydraulic line according to the invention is characterized in that the electronic control unit controls and / or regulates the outlet valve and / or the inlet valve and / or the motor-pump unit such that the level of the at least one low-pressure accumulator during a slip control operation is at a constant or variable Value above a level threshold remains. The hydraulic line according to the invention thus comprises all the necessary devices for carrying out the method according to the invention and thus makes it possible to keep the level of the low-pressure accumulator above a certain level threshold. This results in the advantages already described.

It is preferably provided that the inlet valve and / or the outlet valve is an analogized digital valve. Analogized digital valves allow not only to set an open position and a closed position but also to set or adjust intermediate positions. Thus, by means of an analogized digital valve, a certain opening width can be set, which allows a comparatively precise control of the hydraulic resistance influenced by the opening width.

Further preferred embodiments will become apparent from the subclaims and the following description of an embodiment with reference to figures.

It shows

1 schematically four inventive hydraulic strands in two separate brake circuits of a motor vehicle and

2 a flowchart illustrating the individual steps of a possible embodiment of the method according to the invention.

1 shows a possible schematic structure of four hydraulic strands according to the invention in two separate brake circuits 4 . 5 of a motor vehicle. thruster 1 is via hydraulic lines 2 . 3 with brake circuits 4 . 5 hydraulically coupled. Every brake circuit 4 . 5 each includes a switching valve 41 . 51 , a separating valve 42 . 52 , as well as two wheel brake cylinders 49 . 410 . 59 . 510 , Each of the wheel brake cylinders 49 . 410 . 59 . 510 is each an inlet valve 45 . 48 . 55 . 58 and one outlet valve each 44 . 47 . 54 . 57 assigned. Furthermore, each brake circuit includes 4 . 5 each a low-pressure accumulator 46 . 56 and in each case a motor-pump unit 43 . 53 , A single, in brake circuits 4 . 5 contained, according to the invention hydraulic train includes pressure transducer 1 , an inlet valve 45 . 47 . 55 or 58 , a wheel brake cylinder 49 . 410 . 59 or 510 , an outlet valve 44 . 47 . 54 or 57 , a low pressure accumulator 46 or 56 , a motor pump unit 43 or 53 and an electronic control unit 7 , Some of the devices described are used, for example, for more than just one of the hydraulic strands according to the invention. For example, will pressure transducer 1 used in all four hydraulic strands, while low pressure accumulator 56 used in two hydraulic strands. In a slip control operation, the wheel rotation speed of the wheel brake cylinders becomes 49 . 410 . 59 and 510 monitored wheels and by means of pressure reduction and pressure build-up in wheel brake cylinders 49 . 410 . 59 and 510 regulated. In the following, for the sake of clarity, only a single hydraulic brake train is considered. However, the method is transferable without limitation to each of the four illustrated hydraulic brake strands.

The form in wheel brake cylinder 59 is by electronic control unit 7 from the discharge behavior of the electric motor of motor-pump unit 53 estimated. Likewise, electronic control unit appreciates 7 the level of low-pressure accumulator 56 , The level is reduced when engine-pump unit 53 Hydraulic volume from low-pressure accumulator 56 it is evacuated and it increases when by opening the exhaust valve 54 Hydraulic volume in low pressure accumulator 56 flows. To the current form from the behavior of motor-pump-aggregate 53 To be able to estimate, it is important that engine pump unit 53 is operated with a constant electrically clocked control. The electrically clocked control is from electronic control unit 7 specified. A constant adjustment of the electrically clocked control to a changing level of low-pressure accumulator 56 would lead to an estimate of the form by means of motor-pump unit 53 unreliable or even impossible. However, the most accurate knowledge possible of the prevailing form is an essential prerequisite for avoiding squeaking noises of the valves and longitudinal vibrations of the vehicle speed. To estimate the form intake valve 55 be opened so that a hydraulic short circuit between wheel brake cylinder 59 and motor-pump unit 53 arises.

In electronic control unit 7 is a level threshold for the level of hydraulic volume in low-pressure accumulator 56 stored, which should not be fallen below during the slip control operation, in order to avoid an adjustment of the electrically clocked control. Because electronic control unit 7 the electrically timed control for motor-pump unit 53 pretends, has electronic control unit 7 about information concerning the Niederuckspeicher 56 from motor-pump unit 53 Extracted amount of hydraulic volume. In order to keep the level constant, the same amount of discharged hydraulic volume must be returned. This happens, for example, first by means of a pressure reduction in the wheel brake cylinder 59 by opening exhaust valve 54 , as it was detected in the slip control operation that the corresponding form is too large and must be reduced. Thus flows one of electronic control unit 7 calculable amount of hydraulic volume in low pressure accumulator 56 from. intake valve 55 remains closed during this time. As the level of low pressure accumulator 56 according to the electronic control unit 7 However, running low pressure estimation further reduced, are now both exhaust valve 54 as well as inlet valve 55 opened and by means of pressure transducer 1 generated pressure directly in low-pressure accumulator 56 be controlled. Because at the same time a certain form in wheel brake cylinder 59 present by the introduction of hydraulic volume in low-pressure accumulator 56 should not be changed in order not to influence the braking force acting on the corresponding vehicle wheel, the hydraulic resistance of the exhaust valve 54 and inlet valve 55 to the wheel brake cylinder 59 adapted to existing pressure. Because a comparatively high pressure in wheel brake cylinder 59 is to be held, inlet valve 55 , which can be controlled analogously, almost completely open. With this large opening, the hydraulic resistance of the inlet valve 55 comparatively small. outlet valve 54 however, is a pure digital valve and is adjusted by means of a suitable choice of an up-to-modulation in such a way that compared to inlet valve 55 high hydraulic resistance is effected. Thus, the form in wheel brake cylinder 59 be kept constant while filling a low-pressure accumulator 56 with hydraulic volume is made. Therefore, the electrically timed control of motor-pump unit 53 are not changed and there are continuously good estimates of the form in wheel brake cylinder 59 in front.

2 shows a flowchart representing the individual process steps of a possible embodiment of the method according to the invention. In step 21 a slip control operation is started on the vehicle tire. In accordance with the requirements of the wheel rotational speeds, an electrically clocked control of a motor-pump unit takes place in method step 23 and a control of the intake and exhaust valves in process step 22 , From the control of the motor-pump unit and its discharge behavior is in step 25 Estimated pressure according to a pressure estimate. Furthermore, from the control and the discharge behavior of the motor-pump unit in step 24 the level of the low pressure accumulator estimated. In the estimation of the low pressure accumulator level in step 24 Also flows in step 22 selected valve control, which affects the amount of hydraulic fluid in the low-pressure accumulator. Depending on the estimated pressure in step 25 and the estimated level of the low pressure accumulator 24 is the valve control in step 22 and also the electrically clocked control of the motor-pump unit in process step 23 customized.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102010028083 A1 [0003, 0005]
• WO 2005/007475 A1 [0004, 0005]
• DE 102007032588 A1 [0005]

Claims (11)

Method for improving an admission pressure estimation in a hydraulic train of a slip-controlled motor vehicle brake system, - in which an electrically clocked control of an electric motor of a motor-pump unit ( 43 . 53 ), - whereby the engine-pump unit ( 43 . 53 ) in accordance with the electrically clocked activation of at least one low pressure accumulator ( 46 . 56 ) Hydraulic volume discharged and the outlet side of the motor-pump unit ( 43 . 53 ) is used for generating pressure, - wherein by means of a pressure reduction in at least one wheel brake cylinder ( 49 . 410 . 59 . 510 ) filling the at least one low-pressure accumulator ( 46 . 56 ) is effected with hydraulic volume, - wherein in an electrical cycle break a pressure-loaded flow behavior of the motor-pump unit ( 43 . 53 ) is detected in the form of a generator voltage applied to the electric motor, - wherein based on the generator voltage by means of a pressure estimation a pressure is estimated and - wherein by means of a low-pressure memory estimation a level of the at least one low-pressure accumulator ( 46 . 56 ), characterized in that - by means of the pressure reduction and / or by conveying hydraulic volume into the at least one low pressure accumulator ( 46 . 56 ) a level of the at least one low pressure accumulator ( 46 . 56 ) is adjusted to a constant or variable value above a level threshold during a slip control operation. A method according to claim 1, characterized in that for conveying both a the at least one wheel brake cylinder ( 49 . 410 . 59 . 510 ) associated intake valve ( 45 . 48 . 55 . 58 ) as well as an at least one wheel brake associated exhaust valve ( 44 . 47 . 54 . 57 ) are controlled and / or regulated to an open position and / or an intermediate position, in particular during a simultaneous pressurization by the motor-pump unit ( 43 . 53 ) or a pressure transducer ( 1 ). Method according to claim 2, characterized in that the inlet valve ( 45 . 48 . 55 . 58 ) and the exhaust valve ( 44 . 47 . 54 . 57 ) are controlled and / or regulated such that a pre-pressure in at least one wheel brake cylinder ( 49 . 410 . 59 . 510 ) is kept constant during conveyance, in particular by the hydraulic resistances of the inlet valve ( 45 . 48 . 55 . 58 ) and the exhaust valve ( 44 . 47 . 54 . 57 ) are adapted to the form. Method according to at least one of claims 1 to 3, characterized in that the conveying is carried out at a time at which the currently performed slip control operation is substantially not affected, in particular at a time at which no pressure reduction and / or pressure build-up in at least one wheel brake cylinder ( 49 . 410 . 59 . 510 ) is made. A method according to claim 4, characterized in that the conveying is carried out at a time after a Vordruckabbauphase, in particular in a Radbeobachtungsphase. Method according to at least one of claims 1 to 5, characterized in that the level threshold is set or determined such that no adjustment of the control of the motor-pump unit ( 43 . 53 ) is necessary due to low level. Method according to at least one of claims 1 to 6, characterized in that the pressure reduction by means of opening the at least one wheel brake cylinder associated exhaust valve ( 44 . 47 . 54 . 57 ) takes place and that a pressure build-up by opening the at least one wheel brake cylinder associated intake valve ( 45 . 48 . 55 . 58 ) as well as simultaneous control of by the pressure transducer ( 1 ) and / or by opening the inlet valve ( 45 . 48 . 55 . 58 ) as well as simultaneous control of the motor-pump unit ( 43 . 53 ) generated pressure takes place. Method according to at least one of claims 1 to 7, characterized in that the low pressure accumulator estimation taking into account the hydraulic resistances and the opening times of the intake valve ( 45 . 48 . 55 . 58 ) and the exhaust valve ( 44 . 47 . 54 . 57 ) taking into account the pressure, wherein the hydraulic resistances are characterized by valve opening widths and / or valve opening times. Method according to at least one of claims 1 to 8, characterized in that the pre-pressure estimation and the low-pressure accumulator estimation in an electronic control unit ( 7 ), wherein the electronic control unit is the engine-pump unit ( 43 . 53 ), the exhaust valve ( 44 . 47 . 54 . 57 ) and the inlet valve ( 45 . 48 . 55 . 58 ) controls and / or regulates. Hydraulic train of a slip-controlled motor vehicle brake system, in particular for carrying out the method according to at least one of claims 1 to 9, comprising at least one wheel brake cylinder ( 49 . 410 . 59 . 510 ), which hydraulically between an inlet valve ( 45 . 48 . 55 . 58 ) and an outlet valve ( 44 . 47 . 54 . 57 ), at least one low pressure accumulator ( 46 . 56 ), which hydraulically behind the exhaust valve ( 44 . 47 . 54 . 57 ), a motor-pump unit ( 43 . 53 ), which hydraulically behind the at least one low-pressure accumulator ( 46 . 56 ) is switched and according to an electrically clocked control hydraulic volume from the at least one low-pressure accumulator ( 46 . 56 ) in the direction of the inlet valve 45 . 48 . 55 . 58 ) and on the outlet side of the motor-pump unit ( 43 . 53 ) and an electronic control unit ( 7 ), which the exhaust valve ( 44 . 47 . 54 . 57 ) and the inlet valve ( 45 . 48 . 55 . 58 ) controls and / or regulates and an electric motor of the motor-pump unit ( 43 . 53 ) clocked electrically controlled, wherein the electric motor in an electrical clock break expires under pressure load and thereby generates a generator voltage, wherein upon opening of the exhaust valve ( 44 . 47 . 54 . 57 ) Hydraulic volume in the at least one low-pressure accumulator ( 43 . 53 ) flows and this filled and wherein the electronic control unit ( 7 ) reads out the generator voltage and estimates a pressure based on the generator voltage and a fill level of the at least one low-pressure accumulator ( 46 . 56 ) on the basis of the at least one low-pressure accumulator ( 46 . 56 ) conveyed hydraulic volume and in the at least one low-pressure accumulator ( 46 . 56 ) estimated hydraulic volume, characterized in that the electronic control unit ( 7 ) the outlet valve ( 44 . 47 . 54 . 57 ) and / or the inlet valve ( 45 . 48 . 55 . 58 ) and / or the motor-pump unit ( 43 . 53 ) controls and / or regulates such that the level of the at least one low-pressure accumulator ( 46 . 56 ) remains at a constant or variable above a level threshold during a slip control operation. Hydraulic line according to claim 10, characterized in that the inlet valve ( 45 . 48 . 55 . 58 ) and / or the outlet valve ( 44 . 47 . 54 . 57 ) is an analogized digital valve.

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