DE102006022806A1 - Regulation of the brake pressure by means of a pressure relief valve II - Google Patents

Abstract

The invention relates to a device for adjusting a pressure limiting valve (7) of a hydraulic brake system, which limits the brake pressure (p) to a predetermined threshold. The positioning accuracy can be significantly improved if a estimation unit (4) for estimating the brake pressure (p) includes a sensor (11) for measuring the brake pressure, a unit (5) for determining a differential pressure (deltap) from the measured one (p <SUB> mess </ SUB>) and the estimated brake pressure (p <SUB> est </ SUB>) and a control unit (3) is provided, which controls the pressure relief valve in dependence on the differential pressure (delta-pap).

Description

State of technology

The The invention relates to a device for regulating the brake pressure in a hydraulic brake system, and a corresponding method.

modern Vehicles often include so-called driving support systems, automatically in driving situations in certain driving situations intervene to stabilize the vehicle or the driver otherwise to support. Which includes in particular vehicle dynamics control systems, such as e.g. ESP, as well so-called driver assistance systems, such as ACC (Adaptive Cruise Control), as well as value-added functions, such as APB (automatic parking brake) or a Hill Hold function (HHC). These systems usually use the brake system to intervene in the driving operation. in case of a Brake intervention is a control unit usually a target pressure before and controls a hydraulic pump to on a certain wheel the wished Build up brake pressure. The height of the Brake pressure is set essentially over the pump running time. The activation time is i. d. R. by a deposited in the software Model defined.

by virtue of tolerances in the overall system of the brake system, in particular during the In the first phase of pressure build-up, it is only possible to a limited extent desired Target pressure alone over to achieve the duration of the pump running time exactly. The actually achieved Brake pressure can therefore deviate relatively strongly from the target pressure. Known Brake systems therefore include a pressure relief valve, which serves the prevailing pressure in the brake circuit to a predetermined value to limit. When the brake pressure generated by the hydraulic pump reached the threshold set on the valve, the valve is overflowed and thus the pressure is limited. The pump only needs to run for at least that long until the brake pressure reaches the pressure threshold. The pressure threshold will i. A. over the controlled electric valve current.

at Systems with a pressure relief valve, however, is problematic that also the adjustment of the valve can be faulty. The set pressure threshold may therefore deviate from the target pressure. In known systems such Deviation from the target pressure by a higher-level vehicle controller corrected. However, this control process may be at delays in the partial braking area too for reactions perceivable to the driver (e.g., deceleration fluctuations, noises) to lead, whereby the control comfort impaired becomes.

epiphany the invention

It is therefore the object of the present invention, a method and to provide a device with the accuracy the pressure setting significantly improved and thus a desired Target pressure can be achieved more accurately.

Is solved this task according to the invention by the specified in claim 1 and in claim 7 Characteristics. Further embodiments of the invention are the subject of dependent claims.

One essential aspect of the invention is the brake pressure in the brake circuit to regulate a variation of the pressure threshold, wherein the pressure relief valve forms the actuator of the control. This has the significant advantage that the desired one Target printing can be achieved much more accurate.

The control arrangement according to the invention comprises a control unit to which a control difference is supplied and which adjusts the pressure relief valve depending on the control difference. The control difference is not formed as usual from a target pressure p _soll and a measured actual pressure p _mess , but preferably from an estimated pressure p _est and the actual pressure p _mess . If, instead of the estimated pressure p _est, a target pressure specification of a higher-level vehicle controller would be fed back, this would result in a very high system deviation at the beginning of the control, and there would be the risk that the brake pressure regulator could adversely affect a higher-level vehicle controller.

To the Estimate The brake pressure is preferably an estimation unit with a corresponding estimation algorithm intended. The estimation unit is calculated the current brake pressure, preferably taking into account the pump running time, the pump speed and / or the fluid temperature and possibly further Parameter.

Of the Actual pressure is measured by means of suitable sensors. With nominal pressure specifications with not too high dynamics this can be a circular pressure sensor as well how to use a wheel pressure sensor. The term "wheel pressure sensor" is intended to mean a pressure sensor Be understood behind the valves of the brake circuit, on the side of the wheel is arranged. This can actually on Wheel-acting pressure can be accurately detected. A "circular pressure sensor", however, is present arranged the valves of the brake circuit.

The regulator unit preferably comprises a valve characteristic that represents the valve current above a setpoint pressure (p / I characteristic curve). Of course, the valve characteristic could also be stored analytically. The term "valve characteristic" should therefore be understood to mean any corresponding functional relationship, regardless of the implementation.

According to one special embodiment of the Invention, the controller unit is designed so that it depends on the control difference a correction value (eg a current change) determines with which the control variable (eg the valve current) for the pressure relief valve is modified. To calculate the Correction value can be z. B. also used the valve characteristic become. By appropriate modification of the control variable can thus a pressure deviation from the target pressure can be compensated.

According to one preferred embodiment the control unit designed as a pure P or Pl controller, which the Deviation between estimated pressure and actual pressure supplied is and dependent of which a correction value for the control variable of the pressure relief valve generated.

There many disturbances usually only temporarily Influence on the valve control usually, it is not necessary to change the correction value to save in the system. Alternatively, the correction factor could of course permanently stored in the system and over several control cycles be adapted. The control system is thus able to do some the valve-specific disturbance factors "to learn", whereby the control quality for subsequent control cycles improved becomes.

The called estimation unit, the prevailing in the brake circuit pressure by means of a corresponding Algorithm estimates, usually calculates the brake pressure under consideration of Pump running time, the pump power and / or the fluid temperature and possibly further parameters. This estimation is also systemic relatively inaccurate. The treasure unit Therefore, it is preferably also corrected based on the differential pressure.

embodiments the invention

The Invention will be exemplified below with reference to the accompanying drawings explained in more detail.

1 shows a schematic representation of the controller structure of a control loop for controlling the brake pressure p in a hydraulic brake system. The arrangement includes a vehicle system 1 with a superordinate vehicle controller, such as ESP or ACC, which is able to intervene in the driving mode by means of an automatic brake control or in a controlling manner. When the vehicle system 1 becomes active, it generates a setpoint pressure value p _soll , which is sent to a pressure regulator 2 is issued. The vehicle system 1 and the printing plate 2 are realized here as software modules that can be stored in one or in different control devices.

The printing plate 2 includes a controller 3 with a valve characteristic 10 (p / I characteristic), which converts the target pressure p _soll in a corresponding valve current I _soll . The valve current I _soll forms the control variable for a pressure relief valve 7 , which serves to limit the brake pressure to a predetermined threshold. The height of the maximum brake pressure p is determined by the valve current I _soll .

The arrangement further comprises a hydraulic pump 14 for building up brake pressure. The hydraulic pump 14 is from the printing plate 2 activated on request and usually operated until the wheel brake pressure at the limiting valve 7 set threshold and the valve overflows. The wheel brake pressure is thereby limited to the predetermined threshold.

To the of the vehicle system 1 required target pressure p _{should set} as accurately as possible, the brake pressure is controlled here. For this purpose is a regulator 12 provided that a control difference from a measured brake pressure p _mess and an estimated brake pressure p _{est is} supplied. The pressure difference Δp is at a subtracting node 5 educated. The regulator 12 can z. B. be implemented as P or Pl controller.

The actual prevailing brake pressure is determined by means of a wheel pressure sensor 11 measured. For estimating the brake pressure p is further an estimation unit 4 provided in the control unit 2 is deposited as an algorithm.

The regulator 12 is designed so that depending on the differential pressure Ap it _should .DELTA.I a correction value determined (.DELTA.I _to here, the valve current) at which the control variable for the pressure relief valve 7 is modified. For this, the control variable I _{soll is} at a node 13 with the correction value .DELTA.I _{should be} added. As a result of this modification of the control variable, a pressure deviation of the actual brake pressure from the setpoint pressure p _soll can thus _be compensated.

The treasure unit 4 is preferably designed to estimate the brake pressure from various variables, in particular the pump running time, the pump speed, fluid temperature, etc. The associated estimation algorithm is a mathematical model in the pressure controller 2 deposited.

The output of the estimator 4 becomes the adjuster 3 fed. It forms in particular a switch-off criterion for the hydraulic pump 12 , The latter is preferably switched off when the estimated pressure p _{est has reached} a predetermined threshold.

The illustrated scheme allows a significant improvement in pressure accuracy in a simple Wise.

Claims (9)

Device for regulating the brake pressure (p) in a brake system, in particular a hydraulic brake system, by means of a pressure limiting valve ( 7 ), which limits the brake pressure to a predetermined threshold and for this purpose from an electronic device ( 2 ), comprising: - an estimation unit ( 4 ) with an estimation algorithm for estimating the brake pressure (p), - a sensor system ( 11 ) for measuring the brake pressure (p _mess ), - a unit ( 5 ) for determining a differential pressure (Δp) from the measured (p _mess ) and the estimated pressure (p _est ), and - a regulator unit ( 12 ), which determines a correction value (ΔI _soll ) in dependence on the differential pressure (Δp), with which a control variable (I _soll ) of the valve ( 7 ) is corrected. Device according to Claim 1, characterized in that the correction value (Δp) is added to the control variable (I _soll ). Device according to claim 1 or 2, characterized in that the control unit ( 12 ) comprises a P or Pl controller. Device according to one of the preceding claims, characterized in that the sensors ( 11 ) comprises a wheel pressure sensor. Device according to one of the preceding claims, characterized in that the control unit ( 12 ) comprises a p / I characteristic. Device according to one of the preceding claims, characterized in that an actuator ( 3 ) is provided, which generates a valve control variable (I _soll ) as a function of a desired value (p _soll ). Device according to claim 6, characterized in that the actuator ( 3 ) comprises a p / I characteristic. Method for regulating the brake pressure (p) in a brake system, in particular a hydraulic brake system, by means of a pressure limiting valve ( 7 ), which limits the brake pressure to a predetermined threshold and for this purpose from an electronic device ( 2 ), comprising the following steps: estimating the brake pressure (p) by means of an estimating unit ( 4 ), - measuring the brake pressure (p) by means of a sensor system ( 11 ), - calculating a differential pressure (Δp) from the estimated (p _est ) and the measured pressure (p _mess ), - determining a control variable (I _soll ) for the pressure relief valve ( 7 ), - calculating a correction factor (ΔI _soll ) for the valve control variable (I _soll ), and - correcting the valve control variable (I _soll ) by means of the correction factor (.DELTA.I _soll ). Method according to claim 8, characterized in that that the brake pressure (p) is controlled.