DE102016219735A1 - Method for adapting a stored pressure-volume curve in a brake system and brake system - Google Patents

Abstract

Method for adapting a stored pressure-volume curve for pressure regulation in a brake system (2), wherein a system pressure (PSys) is built up in at least one wheel brake (42, 44, 46, 48, 250) by a pressure supply device (20, 278) is, for which the stored pressure-volume characteristic curve is used, indicating the given volume of the associated system pressure (PSYS), during a braking operation pressures and associated volumes are determined, with their help an adapted characteristic from the stored characteristic by a shift to the volume axis and an elongation of the stored characteristic curve is obtained.

Description

The invention relates to a method for adjusting a stored pressure-volume curve for pressure control in a brake system, in which constructed in at least one wheel of a pressure supply device, a system pressure, for which the stored pressure-volume curve is used to the given volume to the associated Indicates system pressure. It also relates to a braking system.

In automotive engineering, brake-by-wire brake systems are becoming increasingly widespread. Such brake systems often comprise, in addition to an actuatable by the driver master cylinder an electrically ("by-wire") controllable pressure supply device by means of which in the operating mode "brake-by-wire" takes place an actuation of the wheel brakes.

In these brake systems, in particular electro-hydraulic brake systems with the "brake-by-wire" mode, the driver is decoupled from the direct access to the brakes. Upon actuation of the pedal usually a pedal decoupling unit and a simulator are operated, which is detected by a sensor, the braking request of the driver. The pedal simulator serves to give the driver as familiar a brake pedal feel as possible. The detected braking request leads to the determination of a desired braking torque, from which then the target brake pressure for the brakes is determined. The brake pressure is then actively built up by a pressure supply device in the brakes.

The actual braking thus takes place by active pressure build-up in the brake circuits with the aid of a pressure supply device, which is controlled by a control and regulation unit. As a result of the hydraulic decoupling of the brake pedal actuation from the pressure build-up, many functionalities such as ABS, ESC, TCS, hill-start assist etc. can be comfortably realized for the driver in such brake systems.

The pressure-providing device in brake systems described above is also referred to as an actuator or hydraulic actuator. In particular, actuators are designed as linear actuators in which a piston is axially displaced into a hydraulic pressure chamber to build up pressure, which is built in series with a rotational-translation gear. The motor shaft of an electric motor is converted by the rotation-translation gear in an axial displacement of the piston.

From the DE 10 2013 204 778 A1 is a "brake-by-wire" -Bremsanlage for motor vehicles is known which a brake pedal operable tandem master cylinder, the pressure chambers are connected via an electrically actuated release valve separable with a brake circuit with two wheel brakes, a hydraulically connected to the master cylinder, switched on and off simulation device , And an electrically controllable pressure-supplying device, which is formed by a cylinder-piston arrangement with a hydraulic pressure chamber whose piston is displaceable by an electromechanical actuator includes, wherein the pressure-supplying device is connected via two electrically actuated Zuschaltventile with the intake valves of the wheel brakes.

In such brake systems, a mechanical or hydraulic fallback stage is usually provided, by means of which the driver can decelerate or stop the vehicle by muscular force when the brake pedal is actuated, if the "by-wire" mode of operation fails or is disturbed. While in normal operation by a pedal decoupling unit, the above-described hydraulic decoupling between brake pedal operation and brake pressure build-up, this decoupling is canceled in the fallback so that the driver can move brake means directly into the brake circuits. In the fallback level is switched when with the help of the pressure supply device no pressure build-up is possible.

In normal operation, the driver actuates a pedal simulator in such an external power brake system, wherein this pedal operation is detected by pedal sensors and a corresponding pressure setpoint for the linear actuator is determined to actuate the wheel brakes. A movement of the linear actuator from its rest position forward into the pressure chamber displaces brake fluid volume from the linear actuator via the open valves in the wheel brakes and thus causes a pressure build-up. In the opposite case, the movement of the linear actuator back in the direction of its rest position leads to a pressure reduction in the wheel brakes. The setting of a required system pressure is carried out with the aid of a suitable pressure regulator or a suitable pressure control system in which, for example, a speed controller is subordinate to the pressure regulator.

For the demand-driven and precise setting of the required pressures, a pressure-volume characteristic is stored in the brake system, which maps the ratio of volume and pressure, so that the associated pressure can be determined for each volume and vice versa. During operation of the vehicle, however, the distribution of volume and pressure expressed with the aid of the characteristic curve is in part subject to considerable fluctuations. Due to variant or item scattering, the state of wear of components, In particular the brake pads, the temperature and the operating state of the brake system, the pressure-volume relation changes dynamically.

The invention is therefore an object of the invention to provide a method by which these changes during operation can be taken into account. Furthermore, a braking system should be specified.

With regard to the method, this object is achieved in that pressures and associated volumes are determined during a braking process, with the aid of an adapted characteristic from the stored characteristic is obtained by a shift on the volume axis and an expansion or scaling of the stored characteristic ,

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

The invention is based on the consideration that precisely controlled braking processes are no longer possible due to the dynamic changes in the effective characteristic curve, that is to say the currently existing relationship between volume and pressure. It is therefore necessary to detect these fluctuations or operational or state-dependent changes during the normal braking operation and to model these changes in order to adjust the characteristic accordingly. It should be dispensed with the use of special test stimuli and consider only the waveforms that are present in a normal operation of the wheel brake.

As has now been recognized, a high-performance adaptation of the characteristic curve can be carried out, in which these changes can be parameterized in that the current characteristic curve can be determined from the stored characteristic curve by a displacement on the volume axis and an elongation of the basic characteristic curve. In this way, the essential changes occurring during operation of the brake system of the components involved can be parameterized, whereby the precision of the active pressure build-up is increased.

Preferably, the adapted characteristic curve or the adapted pressure-volume characteristic is then used to build up a system pressure.

Elongation involves a positive stretch as well as a negative strain or compression.

Advantageously, the stored characteristic curve is represented by a plurality of support points of the volume, to each of which a pressure value is assigned. The characteristic curve is represented in this way by a set of value pairs, each value pair including a volume value and an associated pressure value.

The volume value of a support point of the adapted or modified characteristic curve is preferably given by the multiplication of the volume value of the stored characteristic curve with a dilation factor and the addition of a constant volume. A multiplication with a strain factor greater than one corresponds to an expansion, while a multiplication with a strain factor smaller than one corresponds to a compression.

The expansion factor and the constant volume are chosen in a preferred embodiment of the method for all support points the same. In this way, only two parameters, namely the expansion factor and the constant volume need to be adjusted to obtain the modified characteristic, which can be done quickly during operation.

Preferably, the volume value of the modified support point is determined during a brake application at a point in time in which the system pressure assumes a pressure value of a support point of the stored characteristic curve. In this way, the use of special test cycles for updating can be dispensed with.

This determination during a pressure build-up is advantageously carried out when the pressure value is reached or exceeded for the first time.

A modification or adaptation of the characteristic curve preferably takes place when, during the determination of the volume value at a support point, the time derivative of the pressure is less than a predefined threshold value and / or when the engine speed of the engine of the pressure supply device is lower than a predefined rotational speed threshold value. Preferably, the pressure-providing device has a hydraulic pressure chamber, which is delimited by a hydraulic pressure piston, wherein the piston is moved in the pressure space with the aid of an electric motor and a rotation-translation gearbox interposed between the engine and the piston. The rotation-translation gear is preferably designed as a ball screw (KGT).

A modification or adaptation of the characteristic is advantageously carried out when the pressure exceeds a predetermined minimum pressure threshold value and / or when a number of interpolation points has been determined which is greater than a predefined one Minimum number of support points. This is preferably done with reliable detection of the pressure value.

Preferably, an adaptation of the characteristic curve is only carried out if the number of interpolation points for which the deviation of the determined volume value from the stored volume value is smaller than a predefined deviation value is greater than a number threshold value, preferably larger than the plurality of interpolation points. The number threshold value is preferably selected to be at least equal to or greater than two thirds of the total number of interpolation points.

If the characteristic is to be modified, the expansion factor and the constant volume are preferably calculated with the aid of the new interpolation points.

The adaptation of the characteristic curve preferably takes place by determination or estimation of the two change parameters constant volume and expansion factor, for example by means of the known least squares method.

The characteristic curve is preferably stored in a memory of a control and regulation unit. The adapted characteristic is preferably stored in a memory of the control unit. When driving, the adapted characteristic curve is used to control the pressure supply device for the active brake pressure buildup. Preferably, the volumes are determined during each braking operation or at regular intervals.

With respect to the braking system, the above object is achieved with means for carrying out a method according to one of the preceding claims. In particular, a control and regulating unit for carrying out the method is preferably provided.

The advantages of the invention are in particular that the precision and reliability of the active brake pressure build-up can be maintained even with changes in the brake system by a modification of the pV characteristic during braking operation. In particular, no additional test cycles are necessary, so that the brake system is available at any time as needed for braking operations.

An embodiment of the invention will be explained in more detail with reference to a drawing. In it show in a highly schematic representation:

1 a braking system in a preferred embodiment;

2 a wheel brake operable by a pressure supply device;

3 a pressure control system;

4 an exemplary pressure-volume characteristic; and

5 a diagram for adapting a tracking parameter.

Identical parts are provided with the same reference numerals in all figures.

In 1 is an embodiment of a brake system according to the invention 2 shown. The brake system comprises one by means of an actuating or brake pedal 6 actuated master cylinder 10 , one with the master cylinder 10 cooperating simulation device 14 , a master cylinder 10 assigned, under atmospheric pressure medium reservoir 18 , an electrically controllable pressure supply device 20 , which by a cylinder-piston arrangement with a hydraulic pressure space 26 is formed, whose pistons 32 is displaceable by an electromechanical actuator, an electrically controllable pressure modulation device for setting wheel-individual brake pressures and an electronic control and regulation unit 40 ,

The unspecified pressure modulation device comprises, for example hydraulically actuated wheel brakes 42 . 44 . 46 . 48 and each operable wheel brake 42 to 48 an inlet valve 50 . 52 . 54 . 56 and an exhaust valve 60 . 62 . 64 . 66 , the hydraulically interconnected in pairs via center ports and to the wheel brakes 42 to 48 are connected. The inlet connections of the inlet valves 50 to 56 be by means of brake circuit supply lines 70 . 72 supplied with pressures that are derived in a "brake-by-wire" mode from a system pressure in one to the pressure chamber 26 the pressure supply device 20 connected system pressure line 80 is present and corresponds to the pressure provided by the pressure supply device. The brake 42 . 44 are doing to a first brake circuit 84 , the brake 46 . 48 to a second brake circuit 88 hydraulically connected.

The inlet valves 50 to 56 is one to each of the brake circuit supply lines 70 . 72 opening check valve 90 . 92 . 94 . 96 connected in parallel. In a fallback mode, the brake circuit supply lines become 70 . 72 via hydraulic lines 100 . 102 with the pressures of the brake fluid from pressure chambers 120 . 122 of the master cylinder 10 applied. The outlet connections of the outlet valves 60 to 66 are via a return line 130 with the pressure medium reservoir 18 connected.

The master cylinder 10 points in a housing 136 two pistons arranged one behind the other 140 . 142 on top of the hydraulic pressure chambers 120 . 122 limit. The pressure chambers 120 . 122 on the one hand over into the piston 140 . 142 formed radial bores and corresponding pressure equalization lines 150 . 152 with the pressure medium reservoir 18 in conjunction, wherein the connections by a relative movement of the pistons 140 . 42 in the case 136 can be shut off. The pressure chambers 120 . 122 On the other hand, by means of the hydraulic lines 100 . 102 with the already mentioned brake circuit supply lines 70 . 72 in connection.

In the pressure compensation line 150 is a normally open valve 160 contain. The pressure chambers 120 . 122 take unspecified return springs on which the pistons 140 . 142 with unoperated master cylinder 10 position in a starting position. A piston rod 166 couples the pivoting movement of the brake pedal 6 due to a pedal operation with the translational movement of the first master cylinder piston 140 or primary piston, whose actuation path of a, preferably redundantly running, displacement sensor 170 is detected. As a result, the corresponding piston travel signal is a measure of the brake pedal actuation angle. It represents a braking request of the driver.

In the to the pressure chambers 120 . 122 connected line sections 100 . 102 is ever a separating valve 180 . 182 arranged, which is designed as an electrically actuated, preferably normally open, 2/2-way valve. Through the isolation valves 180 . 182 can the hydraulic connection between the pressure chambers 120 . 122 of the master cylinder 10 and the brake circuit supply lines 70 . 72 be shut off. One to the line section 102 connected pressure sensor 188 detects the in the pressure room 122 by a displacement of the second piston 142 built up pressure.

The simulation device 14 is hydraulic to the master cylinder 10 can be coupled and, for example, essentially comprises a simulator chamber 190 , a simulator spring chamber 194 and one the two chambers 190 . 194 mutually separating simulator piston 198 , The simulator piston 198 is supported by a in the simulator spring chamber 194 arranged elastic element (eg a spring), which is advantageously biased on the housing 136 from. The simulator chamber 190 is by means of an electrically operated simulator valve 200 with the first pressure chamber 120 of the master cylinder 10 connectable. When setting a pedal force and open simulator valve 200 flows pressure medium from the master cylinder pressure chamber 120 into the simulator chamber 190 , A hydraulic anti-parallel to the simulator valve 200 arranged check valve 210 allows independent of the switching state of the simulator valve 200 a largely unhindered backflow of the pressure medium from the simulator chamber 190 to the master cylinder pressure chamber 120 , Other designs and connections of the simulation device to the master cylinder 10 are conceivable.

The electrically controllable pressure supply device 20 is designed as a hydraulic cylinder-piston arrangement or a single-circuit electrohydraulic actuator whose / whose pressure piston 32 which the pressure room 26 limited, by a schematically indicated electric motor 220 with the interposition of a likewise schematically illustrated rotational-translation gear, which is preferably designed as a ball screw (KGT), can be actuated. One of the detection of the rotor position of the electric motor 220 Serving, only schematically indicated rotor position sensor is denoted by the reference numeral 226 designated. In addition, a temperature sensor can also be used 228 be used to sense the temperature of the motor winding.

The by the force effect of the piston 32 on the in the pressure room 26 enclosed pressure fluid generated actuator pressure is in the system pressure line 80 fed and with a preferably redundant pressure sensor 230 detected. With open pressure switch valves 240 . 242 the pressure medium enters the wheel brakes 42 to 48 for their operation. By pushing back and forth the piston 32 takes place with open pressure switch valves 240 . 242 in a normal braking in the "brake-by-wire" mode a Radbremsdruckaufbau and degradation for all wheel brakes 42 to 48 ,

During pressure reduction, this flows from the pressure chamber before 26 in the wheel brakes 42 to 48 shifted pressure medium on the same way back into the pressure chamber 26 back. On the other hand, when braking with different individual wheel flows, with the help of the intake and exhaust valves 50 to 56 . 60 to 66 regulated wheel brake pressures (eg in the case of anti-lock control (ABS control)) via the exhaust valves 60 to 66 drained pressure medium content in the pressure fluid reservoir 18 and thus initially stands the pressure supply device 20 for actuating the wheel brakes 42 to 48 no longer available.

In an alternative embodiment, the brake system 2 four in 2 illustrated wheel brakes 250 on. In a, preferably floating, caliper 254 are two brake elements 258 . 262 arranged on each one brake lining 266 . 270 is arranged, between which a brake disc 274 is arranged. A pressure delivery device 278 , which is designed as a linear actuator, has a hydraulic pressure chamber 282 in which a pressure piston 286 is shifted as needed. In this case, the rotational movement of the motor shaft of an electric motor 290 by a rotation-translation gear in a translational movement of the pressure piston 286 transformed. For detecting the piston position is a rotor position sensor 294 intended. Via a hydraulic line 300 is the pressure room 282 with a hydraulic room 304 hydraulically connected. The pressure in the pipe 300 is by a, preferably redundantly running, pressure sensor 310 measured.

The hydraulic room 304 is on the brake disc 274 facing side of a sliding pressure piston 316 limited. When moving the pressure piston 286 in the pressure room 282 Hydraulically fluid enters the hydraulic room 304 promoted, whereby the pressure piston the brake pad 270 against the brake disc 274 suppressed. The pressure room 282 is in the unactuated state of the pressure piston 286 via a hydraulic line 322 with a surge tank 326 connected. saddle 254 , Surge tank 326 and pressure delivery device 278 are preferably in a common housing 330 arranged. A control unit 340 is signal input side with the pressure sensor 294 connected and signal output side with the electric motor 290 connected. The control and regulating unit is preferred 340 with a wheel speed sensor 344 connected.

In the control unit 40 is software and / or hardware a pressure control system 360 implemented that in 3 is shown in more detail in a preferred embodiment. For pressure control is the pressure sensor 230 available, that of the linear actuator or the pressure-providing device 20 applied hydraulic pressure or system pressure P _Sys detected. The position of the linear actuator or the position of the pressure piston 220 is measured by the also in 1 illustrated motor angle sensor 226 ,

The pressure control system 360 has a pressure control module 366 to which the target system pressure P _{Sys, Soll} and the actual system pressure P _{Sys are} supplied. A calculation module 370 the _target system pressure P _{Sys, Soll is} supplied. The calculation module 370 calculated by means of the target system pressure P _Sys, in the context of a speed precontrol calculation _, a pilot control angular velocity ω _{Akt, Soll, DR, FFW of} the motor shaft or of the motor.

The target system pressure P _{Sys, Soll} becomes a subtraction module 374 supplied to the actual system pressure or system pressure P _{Sys is} supplied and is subtracted from the target system pressure P _{Sys, Soll} . The pressure difference determined in this way becomes a pressure regulator 378 which calculates therefrom a regulator manipulated variable ω _{Akt, Soll, DR, Ctrl} for the angular velocity. This regulator manipulated variable becomes the pilot angular velocity in an adder module 382 adds, whereby a target angular velocity ω _{Akt, Soll is} calculated. This becomes a limiting module 386 fed, which limits it to a predetermined range of values, resulting in the resulting angular velocity ω _{Alt, Soll, Result} results.

The limited target angular velocity ω _{Akt, Soll, Result} becomes a subtraction module 390 fed to the Istwinkelgeschwindigkeit ω _{Akt is} supplied and is subtracted from the target angular velocity ω _{Akt, Soll} . The angular velocity difference thus determined becomes a speed controller 396 fed, which calculates a target engine torque using this angular velocity difference, which in a limiting module 400 is limited to a predetermined motor torque value range. The limiting module 400 provides as output a target engine torque M _{Akt, Soll} , with which the electric motor 220 the print ready-to-use device 20 is controlled.

From the motor angle signal of the motor angle sensor 226 the engine speed signal z. B determined by differentiation. Output of the system pressure control system after 3 is the manipulated variable of the speed controller 296 a setpoint for the motor torque to be applied by the motor. To carry out the desired actuator movement or the movement of the piston 32 in order to apply defined brake pressures, this engine torque must be such that, in addition to the required actuator acceleration, a sufficient compensation of the counter torques acting on the actuator, essentially caused by friction and the load torque corresponding to the brake pressure, can take place. The commonly used governor structure for the governor to accomplish these tasks is therefore a proportional integral controller (PI controller).

Due to the non-linear behavior of the characteristic curve, the control loop dynamics can be optimized by raising the basic gain of the pressure regulator in the lower pressure range, in which the brake has a very soft behavior. The same applies to the also in 3 illustrated module 370 or the function block "Calculation of the speed precontrol", in which, on the basis of the requested setpoint pressure curve P _{Sys, setpoint} (t), an engine speed to be preselected is determined, wherein for setting a specific setpoint pressure gradient on the basis of the 4 a significantly higher engine speed is required in the range of small pressures shown, as in the region of high brake pressures, where the characteristic curve is almost linear.

In 4 By way of example, a pressure-volume curve or pV curve is shown in a diagram or Cartesian coordinate system. On the abscissa 444 the volume is applied. On the ordinate 448 the pressure or system pressure is plotted. For a given volume, the characteristic thus expresses the built-up pressure. The characteristic is preferably in a memory of the control unit 40 of the brake system 2 deposited.

Since a mathematical description of in 4 shown characteristic in an analytical form for an online implementation in a pressure control (eg according to an arrangement or a pressure control system 360 to 3 ) is too expensive and unsuitable due to the high computational time requirement, the preferred description of this characteristic is in the form of a table with nodes (P _i , V _{mod, i} ).

The characteristic curve is preferably deposited at discrete volume interpolation points V _i , ie for each of these interpolation points (i), of which schematically three interpolation points 450 . 452 . 454 are plotted and each of which a volume value V _{Mod, i is} assigned, a corresponding pressure value P _{i is} deposited. For volumes that lie between the interpolation points, the pressure value is interpolated. For volumes that are larger than the largest stored interpolation point value, the characteristic is extrapolated.

According to the invention, the pV characteristic curve is adapted or modified during the operating period of the brake system, so that the pressure supply device or the linear actuator can be precisely controlled. Due to variant or item scattering, the state of wear, in particular of the linings, the temperature, or the operating state, the brake characteristic curve or pV characteristic curve is sometimes subject to considerable fluctuations. For given pressure values new volume values are therefore determined.

As a model for these changes, the characteristic curve is adapted or modified so that the current or adapted characteristic curve results from the characteristic stored in the memory by a displacement on the volume axis as well as an expansion / compression of the basic characteristic curve. If one considers defined interpolation points of the pressure values P _I (with i = 1..N, where N indicates the number of interpolation points), then the values V _{Mod, I represent} the corresponding volume interpolation points of the basic characteristic curve. The currently present characteristic line then supplies the volume support points V _{Mess, I} for the same pressure values P _I. According to the assumption made with respect to the characteristic change is then obtained, the general approach that the determined, current _measuring volume _{V, Akt} from the associated volume value V _Mod the base curve according to the equation V _{measurement, Akt} = V ₀ + K _v * V _Mod where V ₀ includes the characteristic displacement on the volume axis and the parameter K _{v represents} the above-mentioned strain / compression of the characteristic.

During a braking operation during the pressurization phase, when a pressure value P _{i is} reliably detected and reached the first time, the associated brake volume is determined. That is, during the pressure build-up phase, the actuator volume value V _{Mess, Akt, i to} be assigned to this pressure value is stored in the event of a reliably recognized, first time exceeding of a pressure interpolation point value P _i . The actuator volume value V _{Mess, Akt, i} can, for example, from the actuator position X _Akt according to the relationship V = A _piston X _act be calculated, wherein A _{piston is} the cross-sectional area of the linear actuator _piston and the actuator position X _Akt from the 1 or 2 known motor angle signal can be determined. The size X _Akt is the displacement of the piston in the hydraulic pressure chamber.

A reliable detection of the pressure value preferably comprises the following operations. It is considered and evaluated whether there is a crossing of the pressure value P _i in a plurality of successive controller loops. If this is the case, then the exceeding of P _{i is} recognized and the volume value which was present when P _{i was} exceeded for the first time (within this observation interval) is stored.

After completion of the braking, the linear actuator is depressurized and is back in its rest position. In this state, it is now checked whether basis of the determined interpolation point values V _{measurement, Akt, i} is an update in the 4 shown, static characteristic can be done or must be made. For this purpose, it is first checked in which speed range the braking was carried out, whereby here too only the pressure build-up phase is considered. If the pressure build-up dynamics during the time interval in which the interpolation points were detected, below a threshold value (dP / dt) _{Est, Max} , so dynamic effects, such. B back pressures or pressure oscillations are neglected by a quick operation and the determination of the change parameters V ₀ and K _v can be allowed. Alternative to Pressure _build-up gradient (dP / dt) _{Est, Max} The engine speed can also be considered here, in which case a predefined maximum speed ω _{Est, Max may} not be exceeded.

In addition, it is now checked whether a predefined minimum pressure P _{Est, Min has been} reached, or a predefined minimum number N _{Est, Min} (preferably> 2) has been detected by interpolation points. This avoids that only the range of small brake pressures, in which the brake has a very soft behavior, is considered, and that a representative range of the characteristic curve 4 is detected. The minimum values mentioned should therefore in any case include an area in which the characteristic line starts to change into the linear range.

In addition, it is still checked whether an adjustment is required at all. This is done on the basis of the determined during the braking volume control point values V _{measurement, Akt, i} compared to the support point value V _{mod, i} currently used in the model. The need for an adaptation arises when the significant deviation is found for the majority of the intercepted interpolation points, that is to say: | V _{Mess, Akt, i} - V _{Mod, i} | > ε _i

The adaptation of the characteristic curve 4 then takes place by estimation or determination of the two change parameters V ₀ and K _v, z. B using the known method of least squares. For this purpose, these two parameters are determined such that the sum of the error squares is minimal: Σ (V _{Mess, Akt, i} - (V _{0, Est} + K _{v, Est} * V _{Mod, i} )) ² → Min, (i = 1..N _Est )

After a new parameter set has been determined, the interpolation points are tracked to the characteristic line, i. H. the modified characteristic is stored and used in operation for the control of the pressure supply device. In order to achieve sufficient robustness against disturbances in measurements or estimation results, it makes sense not to adopt the newly determined parameters 100%, but to consider prior knowledge of the possible changes in the characteristic curve and to make the determined change parameters plausible. For example, the determined parameters can change only with a certain speed.

To increase the robustness, therefore, a follow-up factor β is defined, which carries out a weighting between the last-used parameter set (table values V _{Mod, i} ) and the values newly determined on the basis of the last estimate (table values V _{Mess, Est, i} ). For each new table value (V _{Mod, New, i} ) then: V _{Mod, New, i} = β · V _{Meas, Est, i} + (1-β) · V _{Mod, i}

With a value of β = 0, the new value used is the previous value used. At a value of β = 1, the old value is completely replaced by the new value. For values between 0 and 1, the old value of the interpolation point contains an admixture with the new value. The volume V _{measurement, Est, i} represents, for pressure support point P _i associated new volume reference point, which can be calculated from the current characteristic point V _{Mod, i,} and the change in parameters determined V _{0, Est} and K _{v, Est:} V _{meas, Est, i} = V _{o, Est} + K _{v, Est} · V _{mod, i}

When determining the weighting factor β, a compromise must be found between a high adaptation dynamics, but weak filtering (β → 1) and a good filtering of errors, but only slow adaptation dynamics (β → 0). The weighting factor β can therefore be specified as a constant parameter according to the above-mentioned criteria. Alternatively, it is proposed to redetermine this parameter after each braking in which a characteristic adjustment is possible and found to be necessary, based on the pressure build-up speed and the number of points to consider in the estimation. A diagram of a method for determining the weighting factor β with 0 ≦ β ≦ β _Max ≦ 1 is shown 5 ,

In a first block 480 , which has the time derivative of the pressure as the input variable, a first weighting variable λ _{1 is} determined, the value of which depends on the amount of said time derivative. From the value zero up to a first limit of the value, λ _{1 is assigned} the value 1, after which the value of λ _{1 is} linearly reduced until it is and remains zero for magnitude values that are greater than a second limit value.

In a second block 486 whose input quantity is the number of nodes in which a modified volume could be determined during a braking operation, a second weighting quantity λ _{2 is} calculated. Beginning with a count value of zero, λ _{2 is increased} , preferably in stages, until it receives and retains the maximum value of 1 when a step number limit value is exceeded.

In a block 492 the two weighting quantities λ ₁ , λ ₂ are linked together, in particular multiplied together (ie λ = λ ₁ · λ ₂ ), in order to obtain a third weighting variable λ determine. This third weighting quantity λ is input quantity in one block 498 in which the weighting factor β is determined as a function of λ. Starting from a value of zero, β is increased linearly with increasing value of λ until it reaches and maintains the value 1 when a limit value is exceeded. Output size of block 498 is the above weighting factor or tracking factor β.

With the help of in the blocks 480 . 486 . 492 and 498 β is set to a value between 0 and 1. In this case, β is chosen to be substantially higher, the lower the time derivative of the pressure was to the detection period and the more nodes could be redetermined.

The described method is preferably implemented in software and / or hardware in the control and regulation unit.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102013204778 A1 [0006]

Claims (11)

Method for adapting a stored pressure-volume characteristic for pressure regulation in a brake system ( 2 ), in which in at least one wheel brake ( 42 . 44 . 46 . 48 ; 250 ) from a pressure delivery device ( 20 . 278 ) is set up a system pressure (P _Sys ), for which the stored pressure-volume curve is used, the given volume to the associated system pressure (P _Sys ) indicates, characterized in that during a braking operation pressures and associated volumes are determined, with their Help a matched characteristic from the stored characteristic by a shift on the volume axis and an elongation of the stored characteristic is obtained. The method of claim 1, wherein the stored characteristic is represented by a plurality of support points of the volume with volume values (V _i ), each of which a pressure value (P _i ) is assigned. The method of claim 2, wherein the volume value (V _i ) of a support point of the adjusted characteristic is given by the multiplication of the volume value (V _i ) of the stored characteristic with a strain factor (K) and the addition of a constant volume (V ₀ ). Method according to Claim 3, in which the expansion factor (K) and the constant volume (V ₀ ) are chosen to be the same for all reference points. Method according to one of claims 2 to 4, wherein the volume value (V _i ) of the modified support point during a brake operation is determined at a time in which the system pressure (P _Sys ) to the support point (i) the stored characteristic associated pressure value (P _i ). The method of claim 5, wherein the determination is performed during a pressure build-up, in particular when the pressure value (P _i ) is reached or exceeded for the first time. Method according to one of claims 4 to 6, wherein an adjustment of the characteristic occurs when during the determination of a volume value (V _i ) at a support point, the time derivative of the system pressure (P _Sys ) is less than a predetermined threshold and / or if the engine speed the engine of the pressure supply device ( 20 . 278 ) is less than a predetermined speed threshold. Method according to one of claims 4 to 7, wherein an adjustment of the characteristic occurs when the pressure exceeds a predetermined minimum pressure threshold (P _{Est, Min} ) and / or if a number of support points has been determined which is greater than a predetermined minimum support point number (N _{est , Min} ). Method according to one of claims 1 to 8, wherein an adjustment of the characteristic curve is only performed when the number of nodes, where the deviation of the determined volume value (V _{measurement, act, i} ) from the stored volume value (V _{mod, i} ) smaller is a predetermined deviation value greater than the number threshold. Method according to one of claims 1 to 9, wherein with the aid of the new support points, the expansion factor (K) and the constant volume (V ₀ ) are calculated. Brake system ( 2 ) with means for carrying out a method according to one of the preceding claims.

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