DE102006024361A1 - Process and assembly to regulate operation of an automobile brake valve in response to change in hydraulic target pressure value - Google Patents

Abstract

In a process to control the operation of an automotive hydraulic wheel brake (9) an initial pressure is generated and delivered at maximum pressure to an inlet valve (5). The valve is operated by an electrical control unit (11) whose current varies in response to a target pressure gradient or change in pressure gradient. The electrical current is reduced in response to an increase in the target pressure gradient, and increased in response to a decrease in the target pressure gradient. Also claimed is a commensurate brake control assembly.

Description

State of the art

The The invention relates to a method for controlling the wheel brake acting brake pressure in a brake system according to the preamble of the claim 1 and a control unit to carry out such a method according to claim 10th

As intake valves for wheel brakes today intake valves are used, which are closed at a certain closing current and open when not energized or energized with a lower driving current than the closing current. The degree of opening depends on the magnitude of the drive current. Depending on the drive current with which the inlet valve is energized, a pressure difference .DELTA.p between the pre-pressure p _before in the hydraulic line upstream of the inlet valve and the _wheel pressure p _wheel in the brake cylinder of the wheel brake would be set in the static state. The drive current, with which the inlet valve is acted upon, is set in the prior art as a function of the pressure on the master cylinder or as a function of the pressure in the brake circuit and as a function of the desired pressure in the wheel brake, ie the setpoint pressure p _soll . From a control unit, the difference .DELTA.p between the form p _before and the target pressure in the wheel brake p _{soll is} formed, whereupon determined by the control unit, for example based on a table, a polynomial or a characteristic of the associated drive current for controlling the intake valve. The activation takes place cyclically. In addition, it is known to take into account the gradient of the target pressure in the calculation or determination of the drive current for the intake valve. Particularly the drive current is reduced, thus further opening the intake valve, when the slope of the nominal pressure p _{is intended,} therefore, the gradient of the nominal pressure p _{is intended} to reach a predetermined value.

The Application of a driving strategy in which the inlet valve is continuous energized, that is not closed cyclically, has in contrast proven to be a driving strategy, in which the inlet valve is closed after each cycle since from the continuous energization a greatly reduced pressure build-up noise as well a low pedal reaction result. This is due to the fact that the intake valve not after each cyclic polling step, in particular of about 10 ms, is closed. Disadvantageous when using with continuously energized intake valves is the bad Pressure adjustment accuracy for dynamic target pressure requirements. Here, known, continuously energized intake valves have difficulties to find the working point.

From the DE 102 38 217 A1 A method for controlling the brake pressure at steep pressure increase gradient is known. In the known method, the threshold value which can be set on a pressure limiting valve of a brake system is set as a function of the pressure increase gradient.

Disclosure of the invention

Technical task

Of the Invention is based on the object, a method and a control device for carrying out the Propose method with which the Druckeinstellgenauigkeit of continuously energized intake valves with dynamically changing Target pressure requirements is improved.

Technical solution

These The object is achieved by a method having the features of the claim 1 and with a control unit solved with the features of claim 10.

advantageous Further developments of the invention are specified in the subclaims.

The invention is based on the idea, the drive electric current depending not only on the pressure difference Ap between the admission pressure p _before and the target pressure p _{is intended to} adjust, but additionally at least one of the dynamic variables such as the change of the nominal pressure gradient, which is the second derivative of the nominal pressure gradient, the gradient of Form, ie the first derivative of the form pressure curve, or the change in the gradient of the form, so the second derivative of the form pressure profile in the adjustment of the drive current for the intake valve to be considered. As a result of the configuration of the method according to the invention, dynamic setpoint pressure requirements of different controllers, such as BSC or FZR, or functions such as, for example, CBC or HAB, can be implemented with high comfort. Furthermore, results from the inventive design of the method, a low pressure build-up noise and a low pedal reaction. Under the form p _before the pressure in the hydraulic line is understood before the inlet valve.

The basic calculation of the control flow for the inlet valve is based on the DP-I characteristic curve or a corresponding table or a corresponding polynomial. This characteristic shows in the quasi-static case, the operating points of the intake valve, in which the intake valve just closes and there is an equilibrium of forces at the inlet valve. By taking into account the change in the target pressure gradient and / or the gradient the pre-pressure and / or the change of the gradient of the pre-pressure is an increase or decrease of the drive current with respect to the DP-I characteristic curve.

In Further development of the invention is advantageously provided that also the valve position when setting the electrical drive current considered becomes. If the inlet valve is found to be closed Position is and due to the desired pressure requirements, an opening of the inlet valve is necessary, then the drive current by an amount x on lowered than would actually be necessary on the basis of the DP-I characteristic curve. These measure is particularly effective with only small nominal pressure changes, because it can not be ruled out that with some border pattern intake valves for tolerance reasons the low current reduction, which is actually used to adjust the pressure difference would not be enough suffice, the inlet valve from its fully closed Position something out to open. When already partially open Intake valve is this extra Lowering of the drive current is required to a lesser extent.

Further can in development of the invention further valve properties, in particular the valve inertia, considered become. Similarly, in the calculation of the drive current, the knowledge with, that the inlet valve or the closing and opening behavior is not linear to the drive current behaves but that depending on the size of the set Pressure difference Δp with deviations in relation to the drive current is to be expected.

Brief description of the drawings

Further Advantages and expedient designs The invention are the other claims, the description of the figures and to take the drawings. Show it:

1 a schematic representation of a brake system,

2 a schematic representation of a control unit with the input variables p _before and p _soll ,

3a - 8b different diagrams from which the effect of various parameters on the determination of the drive current of an intake valve can be seen, in all diagrams, the course of the form p _before over time, the course of the desired pressure p _soll over time, ie the target pressure in the wheel brake, the History of the actual actual pressure in the wheel brake p _wheel over time and the drive current I _EV over time are shown.

embodiments the invention

1 shows a schematic representation of a brake system for four wheels 8th of a vehicle. In a braking operation where the driver depresses the brake pedal 1 actively actuated, the wheel brakes 9 the wheels 8th pressurized in accordance with the braking force applied by the driver. This is a brake fluid from the master cylinder 10 via hydraulic lines 7 , a control or switching valve (UPS) 2 and inlet valves 5 each to the wheel brakes 9 the vehicle wheels 8th directed.

In a brake application caused by a control, the brake pressure from a hydraulic pump 4 generated, which is controlled by the control device accordingly. During a pump cycle, a brake fluid is initially on the high-pressure resistant switching valve 2 sucked in and then the wheel brake 9 pressurized. After a pressure build-up phase lasting several pump cycles, finally, the required brake pressure p _Rad at the wheel brakes becomes 9 reached. For pressure reduction at the wheel brakes are exhaust valves 6 intended.

For controlling the intake valves 5 is a control unit 11 provided with a drive current I _EV1 to I _EV4 for each inlet valve 5 is adjustable. The arrow 14 indicates input variables for the control unit 11 at. This is primarily the form p _before in the hydraulic line 7 and to reach a target pressure p _soll at the wheel brakes 9 , which is usually given by a controller, such as an ESP or ABS controller.

How out 2 it can be seen in the control unit 11 several calculations performed. By subtraction ( 13 ), the pressure difference Δp at the inlet valve is calculated. Furthermore, the determination of the admission pressure gradient p _before / dt. In addition, the target pressure gradient p _soll / dt and the change of the target pressure gradient p _soll / (dt) ^{2 are} determined. In a calculation step 12 From these variables, the drive current I _EV for the intake valve (s) 5 calculated.

In 3a is the basic, known per se determination of the drive current I _EV as a function of the form p _before and the setpoint pressure p _{soll shown} in the wheel. It can be seen that due to the activation of the inlet valve with the drive current I _EV, the actual _wheel pressure p _Rad approximately follows the setpoint pressure curve. In the in 3a illustrated the simplest variant of the drive current I _EV is _present in dependence on the pressure difference Ap between the admission pressure p and target pressure p _{is intended to} set. The necessary queries of the form p _before and the target pressure p _soll and all Other influencing variables explained in the following diagrams occur cyclically, in particular at a time interval of 5 ms or 10 ms. Immediately thereafter, the control of the inlet valve with the drive current I _EV . It can be seen that in a first period A, the inlet valve is energized with an increased drive current (closing current) I _v , the inlet valve is thus shot. Target pressure p _soll and the actual _wheel pressure p _Rad are greater than 0 bar in the example. In a subsequent period B a higher target pressure is required by a controller not specified. The target pressure p _soll increases linearly, whereby the pressure difference .DELTA.p is lower. As the pressure difference Δp decreases, the drive current I _{EV is} lowered in accordance with valve characteristics (DP-I characteristic curves). In a subsequent period C an even steeper setpoint pressure curve is required. Thus, the drive current I _EV is lowered more linearly. This also increases the actual _wheel pressure p _Rad , but much flatter than the target pressure p _soll . In a subsequent period D, the pressure in the wheel brake should be maintained. Thus, a constant drive current I _{EV is} provided. The actual _wheel pressure p _Rad thus remains constant, but at a lower level than the predetermined target pressure p _soll .

At the in 3b In addition to the pressure difference Δp from the admission pressure p _before and the target pressure p _soll (dashed line in the time segments B and C), the gradient represented in the illustrated diagram is taken into account as well as the gradient of the target pressure. The form p _before is as in 3a in the entire time periods A, B, C, D constant. The slope of the setpoint pressure curve p _soll in the time segment B is less than in the time segment C, which results in a stronger reduction of the control current I _EV in the period C than in the period B. Also in the period B, the drive current I _{EV is} lower than in the comparable period B according to 3a since here too the magnitude of the setpoint pressure gradient has flowed into the calculation of the drive current I _EV . It can be seen that the actual pressure profile p _wheel follows the desired pressure profile p _soll much better than without the consideration of the gradient of the desired pressure profile.

4a corresponds exactly 3b , Thus, in addition to the pressure difference Δp, the magnitude of the gradient of the setpoint pressure profile p _{soll is} taken into account in the determination of the drive current I _EV .

The diagram 4b describes an embodiment of the present invention. In addition to the differential pressure Ap and the gradient of the desired pressure profile, in the determination of the driving current I _EV the change in the gradient of the target pressure curve p _should therefore take into account the second derivative of the desired pressure curve. In the transition from the period A to the period B, the gradient is increased. This is detected at a polling cycle and the drive current I _EV is lowered by the value a with respect to the characteristic without regard to the change of the target pressure gradient (dashed line). After lowering, the change decays again based on a predetermined function b, and the drive current again approaches the characteristic curve without taking into account the parameter of the change in the target pressure gradient. Also at the boundary between the period B and the period C is a change, again an increase, the gradient of the setpoint pressure curve p _soll . Again, the drive current I _EV is lowered by one value and the change decays again based on a predetermined function and approaches the curve of the characteristic without taking into account the parameter of the change of the target pressure gradient. It can be seen that the actual pressure in the wheel brake p _wheel follows the setpoint pressure curve p _soll much more precisely than in the diagram 4a where the change in the target pressure gradient is not taken into account in the determination of the drive current. As well in 4a as well as in 4b the form p _is constant over all time periods A, B, C and D _before .

At the in 5a shown diagram, both the pressure difference .DELTA.p and the gradient of the form in the calculation of the drive current are taken into account. In the period C, the course of the nominal pressure p is _{intended to} shallower than in the period B, whereby the drive current I _EV at the beginning of the period C is greater than at the end of the period B. In the period C, the target pressure p rises _will, however, continue to constant light, whereby Actuator current I _EV drops slightly, thus opening the valve slightly further. It can be seen that the actual pressure p _Rad in the wheel brake at the beginning of the period C overshoots the desired pressure p _soll and is kept constant at a higher level in the time period C.

At the in 5b In addition, the change in the target pressure gradient is taken into account, which leads to the fact that in the transition between the time period A and time period B, the drive current I by the value a in comparison to the characteristic according to FIG 5a or in comparison to the dashed characteristic according to 5b is abruptly lowered and in the course of the time period B after a predetermined function b again adapts to the course without taking into account the change in the target pressure gradient. In the transition from the period B to the period C, the gradient of the target pressure is lowered, whereby the drive current I _{EV is} suddenly increased by a certain value and in the course of the period C approaches the function again without taking into account the parameter of the Solldruckgradientenänderung. By this measure, the actual pressure curve p _{wheel is} partially even Coverage with the desired pressure curve p _soll .

In the diagrams according to 6a and 6b the admission pressure p rises _over the time t. In the diagram according to 6b was contrary to the diagram according to 6a the size of the gradient of the form p _before considered. Accordingly, the drive current I _EV compared to the characteristic (dashed line) was increased without consideration of the admission pressure gradient, the inlet valve thus further closed.

In the 7a and 7b the opposite case is shown. Here, the form drops over time. Proportional to the size of the admission pressure gradient p _before / dt, the drive current I _{EV was} lowered in comparison to the characteristic (dashed line) without taking into account the admission pressure gradient.

In both cases ( 6b and 7b ) in which the admission pressure gradient was taken into account in the determination of the drive current I _EV for the intake valve, the actual pressure p _wheel in the wheel follows much more accurately the target pressure setting p _soll .

In the diagram according to 8b has been the position of the intake valve in contrast to the diagram according to 8a with otherwise the same parameters for determining the drive current I _EV taken into account. During the period A, the inlet valve is closed, that is, energized with increased drive current (closing current) I _v . In the transition from the period A to the period B, a change in the target pressure specification. Without considering the valve position, a drive current would be as in 8a (or dashed line in 8b ) is provided for energizing the inlet valve. In order to ensure that borderline inlet valves (maximum production tolerance) open as required at the required small target pressure change, the drive current is additionally reduced by the value a. The course of the drive current I _{EV then} approaches the course of the characteristic without consideration of the valve position by means of a predetermined function.

Claims (11)

Method of controlling the wheel brake ( 9 ) acting brake pressure in a brake system with a pressure generating device for generating a pre-pressure (p _before ) and at least one closed when energized with a certain drive current inlet valve ( 5 ) for admitting a brake fluid in the wheel brake ( 9 ) and with a control unit ( 11 ) for adjusting the electrical drive current (I _EV ) for energizing the inlet valve ( 5 ) as a function of a setpoint pressure (p _soll ) and the admission pressure (p _before ), characterized in that the electrical drive current (I _EV ) additionally in dependence of the change in the target pressure gradient (p _soll / (dt) ² ) and / or in dependence Gradient of the pre-pressure (p _before / dt) and / or in response to the change of the gradient of the form (p _before / (dt) ² ) is set. A method according to claim 1, characterized in that the dependence of the electrical drive current (I _EV ) of the change in the target pressure gradient (p _soll / (dt) ² ) and / or of the gradient of the form (p _before / dt) and / or the change in the gradient of the form (p _before / (dt) ² ) in at least one table and / or at least one characteristic and / or at least one polynomial is deposited. A method according to claim 1 or 2, characterized in that the electrical drive current (I _EV ) at an increase of the target pressure gradient (p _soll / (dt)) is reduced. Method according to one of the preceding claims, characterized in that the electrical drive current (I _EV ) at a reduction of the target pressure gradient (p _soll / (dt)) is increased. Method according to one of the preceding claims, characterized in that the electrical drive current (I _EV ) is increased at a positive admission pressure gradient (p _before / (dt)). Method according to one of the preceding claims, characterized in that the electrical drive current (I _EV ) with a negative admission pressure gradient (p _before / (dt)) is reduced. Method according to one of the preceding claims, characterized in that the inlet valve position is taken into account in the adjustment of the electrical drive current (I _EV ). Method according to one of the preceding claims, characterized in that the electrical drive current (I _EV ) for controlling the inlet valve ( 5 ) in the closed position inlet valve ( 5 ) is set lower with otherwise identical control parameters than with the intake valve not in the closed position ( 5 ). Method according to one of the preceding claims, characterized in that the control of the electrical drive current while ASR, ABS, or ESP control. Controller, containing means for carrying out the method for controlling the brake pressure acting on a wheel brake in a brake system according to one of the preceding Control unit according to Claim 10, in which the dependence of the change in the electrical control current (I _EV ) on the change in the target pressure gradient (p _soll / (dt) ² ) and / or on the gradient of the primary pressure (p _vor / dt) and / or on the Changing the gradient of the form (p _before / (dt) ² ) in at least one table and / or at least one characteristic and / or at least one polynomial, in particular in a memory, is deposited.