EP1077848A1

EP1077848A1 - Method for determining parameters

Info

Publication number: EP1077848A1
Application number: EP00914144A
Authority: EP
Inventors: Michael Latarnik; Helmut Fennel
Original assignee: Continental Teves AG and Co OHG
Current assignee: Continental Teves AG and Co OHG
Priority date: 1999-03-17
Filing date: 2000-03-16
Publication date: 2001-02-28
Also published as: WO2000055022A1

Abstract

The invention relates to a method for determining parameters for the viscosity or temperature of a vehicle brake fluid that is supplied to the wheel brakes via brake valves which are actuated by controllable coils. According to the invention, the parameters are determined using the temperature-dependent change in resistance of at least one coil in order to ensure good control dynamics even at low temperatures.

Description

Method for determining parameters

The invention relates to a method for determining parameters for the viscosity and / or temperature of a brake fluid of a vehicle.

As is known, the viscosity of a brake fluid or hydraulic fluid is highly temperature-dependent. The high viscosity at low fluid temperature, namely at low temperature, for example below -10 degrees C, in the starting phase of a motor vehicle, impairs the controllability of the brake pressure of a regulated hydraulic brake system. It is problematic if brake fluid is to be shifted from the brake fluid reservoir to a wheel brake particularly quickly, for example as part of a driving stability control function, ie without being influenced by the driver. With falling temperatures, the viscosity of the brake fluid increases disproportionately. At very low temperatures, this means that the brake fluid cannot be sucked in quickly enough, with the fact that the pressure loss in the pipeline increases with increasing viscosity. These obstacles lead to slow braking intervention. In the case of a driving stability control, however, there is a general requirement to effect a quick brake intervention. To solve the problem, devices have already been proposed which provide an auxiliary pressure source or a precharging pump (WO 96/20102). Because this is associated with considerable additional costs, people are increasingly refraining from these facilities. The object of the present invention is therefore to ensure the function of a hydraulic vehicle brake system with all its sub-functions, such as anti-lock function, traction slip function and driving stability function, with little effort, even at very low outside temperatures.

This object is solved by the features of claim 1.

Advantageous developments of the invention are specified in the subclaims.

The method is advantageously used in a driving dynamics control system which serves to support the driver of a vehicle in critical driving situations. In this context, a vehicle is a motor vehicle with four wheels, which is equipped with a hydraulic brake system. The driver can build up brake pressure in the hydraulic brake system using a pedal-operated master cylinder. Each wheel has a brake, which is assigned at least one inlet valve and one outlet valve. The wheel brakes are connected to the master cylinder via the inlet valves, while the outlet valves lead to an unpressurized container or low-pressure accumulator. Finally, there is an auxiliary pressure source, usually a motor-pump unit, which can also build up pressure in the wheel brakes regardless of the position of the brake pedal. The inlet and outlet valves and the further valves arranged in the brake circuit can be actuated electromagnetically for controlling the pressure in the wheel brakes by actuating valve coils. For the detection of dynamic driving conditions Four speed sensors, one for each wheel, a yaw rate sensor, a lateral acceleration sensor, a steering angle sensor and at least one pressure sensor for the brake pressure generated directly or indirectly by the brake pedal. An electronic control system, which usually forms a structural unit together with a hydraulic block that receives the valves and pump, and on one side of which the pump motor is arranged, regulates the driving dynamics of the vehicle during unstable driving. The function of the driving stability control therefore consists in giving the vehicle the vehicle behavior desired by the driver within the physical limits in critical (unstable) situations.

In ESP control systems (ESP = electronic stability program), the instability of the vehicle is used to calculate a wheel-specific pressure requirement that is necessary in order to get the vehicle back on the course desired by the driver. A yaw moment control ensures stable driving conditions when driving through a curved track. Different vehicle reference models can be used for yaw moment control, for example the single-track model. In the ESP control systems, input variables which result from the route desired by the driver (for example the steering wheel angle, speed and the like) are always fed to the vehicle model circuit, but also from these input variables and parameters characteristic of the driving behavior of the vehicle Properties of the environment predefined variables (coefficient of friction of the road, lane inclination) determines a target value for the yaw rate, which is compared with the measured actual yaw rate. The yaw rate difference is determined by means of a so-called yaw moment controller - or more precisely - a yaw moment Control law, converted into a yaw moment, which forms the input variable of a distribution logic. The distribution logic itself, depending on a brake pressure model, determines the brake pressure to be applied to the individual wheel brakes. The control of the intake and exhaust valves takes place via a pressure control, which converts pressure variables into valve switching signals depending on the real pressure build-up and pressure reduction characteristics in the wheel brakes, which are modeled in the pressure model. The pressure model receives the input variables required for this and, based on it and in accordance with system parameters, simulates the pressure prevailing in the brake. In particular, the pressure model can receive the control signals that influence the brake pressure on the brake under consideration, that is to say, for example, signals for the intake valves, the exhaust valves, for the hydraulic pump or the like. From these signals and from system parameters (e.g. line cross-sections, switching characteristics, etc.), the pressure model can simulate the pressure in the wheel brakes parallel to the build-up of the wheel pressure, so that the control loop can be closed by outputting the pressure determined in this way using the pressure model.

One difficulty with existing systems is taking into account the influence of fluctuating temperatures. At low temperatures, the viscosity of the brake fluid drops. This changes an input variable, the pump delivery rate or the delivery volume of the pump, which is included in the simulation of the wheel pressure in the pressure model and which increases or decreases as a function of the temperature-dependent viscosity of the brake fluid.

To avoid deviations between the wheel pressure simulated in the pressure model and the actual wheel pressure, would be an adjustment of the parameters stored in the pressure model or of the parameters made available to the pressure model, in particular the pump delivery volume, is desirable.

The design according to the invention therefore proposes a method for determining parameters for the viscosity and / or temperature of a brake fluid of a vehicle, which brake valves, which can be actuated via controllable coils, are fed to the wheel brakes, the parameters being determined via the temperature-dependent change in resistance of at least one coil. The temperature-dependent change in resistance of the valve coil can vary according to the relationships

R ₃ = R ₂₀ [l + α (5 - 20 ° C)] and

• _ Venti, l = 20 ° C ₊ ^ ^R ™ a * R 20 with R _θ = resistance at temperature &, α = temperature¬

coefficient (a = 3.9 for Cu), R ₂₀ = resistance at the temperature of 20 ° C and & _VeMύ = temperature in the controller. According to the invention, the parameters for the viscosity or temperature of the valve coil arranged in the controller are then determined in the evaluation unit. The evaluation unit can be designed as a microprocessor and can be part of the print model. The pump delivery capacity stored in the pressure model can be determined in the evaluation unit as a function of the temperature profile determined via the change in resistance of the valve coil or of a temperature threshold value, including correction factors. The temperature value is determined when the vehicle starts or immediately after the vehicle starts. The- In the further course, this start temperature value is corrected as a function of the controller current consumption, in particular the valve current consumption, and the heating or cooling of the hydraulic block through which the brake fluid flows. The temperature difference between the hydraulic block (HCU = Hydraulic Control Unit) and the control system or the controller (ECU = Electronic Control Unit) with the valve coil used as the temperature sensor is constant when the valve control or pump control is not actuated. This constant temperature difference value 3 _τ _ ₀ f tset of a controller / hydraulic block unit is used to correct the 9 _valve value determined by the change in resistance of the valve coil. The correction of the temperature $ can be followed by means of a correction factor k, which represents the course of the temperature difference between the measuring location (the controller), the temperature and the hydraulic block

$ ve _n m * ^{k = &} τ_ _H cu ^{or according to &} vemi ^{~ &} o _ff se, = T HCU ^{in the} evaluation unit. In addition, the temperature value 3 _brake can be determined in the evaluation unit, including correction values or correction values that are stored, calculated or estimated in tables, characteristic curves or models and reflect the valve _{current consumption} . According to one embodiment, the temperature value is a function of the hydraulic block through which the brake fluid flows according to the relationship

d & brake

^- / valve T_HCU offset>' ^■ ' - \ JT environment) dt d & _B with ^≡ - = temperature of the brake fluid (via the temperature of the hydraulic _block ), θ _VeMll = temperature via the change in resistance of the valve _coil arranged in the controller, & τ new = temperature of the hydraulic _block , 3 _0ffsel = controller / hydraulic _block temperature difference, t = time, V = valve _{current consumption} and ι _{r [/ mgetoπg} = ambient temperature, determined.

The temperature values determined in this way reflect the temperature of the brake fluid with sufficient accuracy. Using a correction factor ki, temperature deviations between the temperature of the hydraulic block and the brake fluid can be taken into account.

These parameters are provided as input variables for the pressure model that simulates the actual pressures of the brake fluid in the wheel brakes. The pressure build-up and / or pressure reduction characteristics of the pressure model are modified as a function of the parameters, in particular the temperature values. This modification via the parameters provided to the brake pressure model is carried out by means of a temperature-dependent determination of the pump delivery rate or variables derived therefrom. The pump delivery rate is modified by a predetermined amount when the temperature falls below a predetermined temperature, in particular when the temperature falls below -10 ° C., in particular increased or continuously modified depending on the temperature value.

According to the modified pressure curves of the pressure model, valve switching signals are calculated, via which the brake valves on the wheels are controlled and the pressure in the individual wheel brakes is individually regulated.

An embodiment of the invention is shown in the drawing and is described in more detail below: Show it

Fig. 1 shows an inventive motor-pump unit with valves actuated by valve coils

2 shows the circuit according to the invention for temperature-dependent resistance measurement on the coil according to FIG. 1.

Fig. 3 shows a valve block temperature model

Fig. 4 shows the dependence of the pump delivery rate on the temperature of the brake fluid

Fig. 1 shows a pressure control device which consists essentially of a hydraulic or valve block 24 or valve receiving body and a cover or housing 29. From this hydraulic block 24, the individual valve domes or valve housings 25, in which the valve parts (not shown) which are movable by magnetic force, protrude in a known manner. Such a valve block for an ABS with wheel-specific control generally contains 8, a valve block for an ESP with wheel-specific control generally contains 12 such valves, namely four inlet and four outlet valves as well as two separating valves and two changeover valves. As is known, the valve actuation force is generated by a magnetic field, which acts from a valve coil 26 through the valve housing 25 on valve bodies (not shown) arranged inside the valve housing 25.

The valve coils 26 are arranged and held elastically in the cover or housing 29 such that they are in place when they are put on of the housing 29 come to rest on the valve block 24 on the associated valve housings 25 and on the base 30 of the valve receiving body 24. With the aid of flexible connecting wires 31, the valve coils 26 are connected to a power board 32 and a printed circuit board 33 carrying the control electronics.

The individual valve coils 26 consist of a winding (not shown), in particular a copper winding, and a steel jacket which influences the course of the magnetic field lines.

An element 21 connects the electronic control system 22 (the regulator), in which the electronic stability program (ESP) is stored, with the pump motor 23 arranged opposite the regulator on the hydraulic block 24. The connecting element 21 is designed as an electrically pluggable supply element which holds the pump motor 23 and / or the valves of the brake system are supplied with the electrical energy made available by the electronic control system. Motor-pump units are known and therefore do not need to be described in more detail. The connecting element 21 is, for example, cylindrical and has a plug-in contact element 27 for electrically conductive fastening, which is inserted into a terminal assigned to the pump motor. The connecting element 21 is arranged within an opening 28 of the hydraulic block 24 and contacts the through-hole 28 of the hydraulic block 24 via elastic elements 34 provided on the circumference. In FIG. 2, a device for controlling the valve coils is shown schematically, which essentially consists of a microprocessor 40 or corresponding signal processing unit or evaluation unit with an analog / digital converter 41, which NEN voltage regulator 42 is connected to the power supply 43 of the vehicle. The input 55 of the A / D converter 41 is connected to the supplier 43 via a parallel connection. The supply voltage digitized in the A / D converter is fed to the microprocessor as a reference voltage via input 55. The supplier 43 is connected to the coil 26 via a supply line 44. The coil 26 is the valve coil mentioned in FIG. 1. Two electronic switches 46, 47 (semiconductor switches) are provided in the line between the ground connection 48 and the coil and in front of the supply connection 49 in the line 44. If the valve coil is supplied with current due to a control process via the switches 46, 47, a voltage dependent on the current drops at the coil 26. By means of the input AI and the input A2 of an operational amplifier 50, the differential input voltage of the valve coil is tapped and the output voltage signal, which is dependent on the temperature-dependent resistance value of the coil 26, is fed to the A / D converter of the microprocessor. In the microprocessor 40, the supply voltage supplied via input 55 is correlated with the output signal of the operational amplifier 50 and a temperature 3 _VeMi , which is dependent on the temperature-dependent change in resistance of the valve _{coil 26} , is formed. The temperature-dependent change in resistance of the valve coil can vary according to the relationships

^R 9 ^{~ R} 2d 1 + α (, - 20 ° c) and

R _Q - R 20

> S> "•, = 20 ° C +

^Va ""^"~ a * R ₂₀ with R ₅ = resistance at temperature 3, α = temperature coefficient (a = 3.9 for Cu j, R ₂₀ = resistance at the temperature of 20 ° C. and 3 _VeMύ = temperature in the controller). The parameters for the viscosity or temperature of the controller are arranged in the microprocessor 40 The microprocessor can be part of the pressure model. The pump delivery rate stored in the pressure model can be modified in the microprocessor depending on the temperature curve determined by the change in resistance of the valve coil or on a temperature threshold value including correction factors. Figure 4 shows the relationship the pump delivery capacity, which is influenced by the temperature of the brake fluid and thus the viscosity. If the temperature of the brake fluid falls below -10 ° C, the performance of the pump decreases almost proportionally to the temperature.

As FIG. 3 shows, the temperature value is determined when the vehicle starts or immediately after the vehicle starts. This start temperature value is subsequently corrected as a function of the controller current consumption, in particular the valve current consumption, and the heating or cooling of the hydraulic block through which the brake fluid flows. The temperature difference between the hydraulic block (HCU = hydraulic control unit) and the control system or the controller (ECU = electronic control unit) with the valve coil used as the temperature sensor is constant when the valve control or pump control is not actuated. This constant temperature difference value 3 _τ __ ₀ ffset of a controller / hydraulic block unit is used to correct the temperature _value 3 _Vmύ determined by the change in resistance of the valve _coil . The correction of the temperature, 9 valve can be done by means of a correction factor k, the course the temperature difference between the measuring point (the controller), the temperature and the hydraulic block, in the microprocessor. In addition, the temperature value 3 _brake can be determined in the microprocessor, including correction values or correction values which are stored, calculated or estimated in tables, characteristic curves or models and reflect the valve _{current consumption} . According to one embodiment, the temperature value is a function of the hydraulic block through which the brake fluid flows according to the relationship

d $ brake dt f [* &? Valve ^ T _^ HCU "Offset ''» '' \ J T_environment) d3 with brake = temperature of the brake fluid (via the temperature of the hydraulic block), 3 _valve = temperature via the change in resistance of the valve coil arranged in the controller, & τ _HCU = Temperature of the hydraulic _block , 3 _0ffiel = controller / hydraulic _block temperature difference, t = time, V = valve _{current consumption} and # _{r ü έ} ambient temperature, determined.

Depending on the temperature values, the pump delivery rate stored in the pressure model is corrected and the pressure build-up and pressure reduction curves are modified, by means of which the actual wheel pressures are simulated. As a result of the changed pressure build-up and pressure reduction curves of the pressure model, the valves of the brake system are activated for a longer time when the brake pressure builds up, for example, when the brake fluid has a higher viscosity, especially below a temperature of -10 ° C or -15 ° C. The actual wheel pressure thus reaches the brake pressure requested by the driving dynamics control earlier in time. A timer ensures that a cooling down period is available between the end of the old driving cycle and the resumption of a new driving cycle, within which the valve coil reaches ambient temperature.

Claims

claims

1. A method for determining parameters for the viscosity or temperature of a brake fluid of a vehicle which is supplied to the wheel brakes via brake valves which can be actuated by controllable coils, characterized in that the parameters are determined via the temperature-dependent change in resistance of at least one coil (26).

2. The method according to claim 1, characterized in that temperature-dependent change in resistance of the valve coil according to the relationships

and

with R _s = resistance at temperature 3, α =

Temperature coefficient (a = 3.9 for Cu), R ₂₀ = resistance at the temperature of 20 ° C and 3 _{Veι l} = temperature in the controller

Method according to one of claims 1 to 3, characterized in that the temperature value as a function of the hydraulic block flowed through by the brake fluid according to the relationship

d3 B _R rems dt ^~ J & Ventil ^ T HCU ^ Offset d ^'' X \ _T environment) with - ^s∑s≡ - = temperature of the brake fluid (above the temperature of the hydraulic block), 5 ^, = temperature above the

Change in resistance of the valve coil arranged in the controller, 3 _{T HCU} = temperature of the hydraulic block,

& o _{ffs t} = controller / hydraulic _block temperature difference, t =

Time, V = valve current consumption and

3 _{T ymgeÄung} ambient temperature, is determined.

Method according to one of claims 1 to 3, characterized in that the parameters are made available as input variables to a pressure model emulating the actual pressures of the brake fluid in the wheel brakes and that the pump delivery rate is modified as a function of a temperature limit value.

A method according to claim 1, characterized in that the parameters are measured at the start of the vehicle or immediately after the start of the vehicle and that the temperature determined from the temperature-dependent change in resistance of at least one valve coil is modified as a function of heating and cooling curves stored in an evaluation unit and Valve switching signals are calculated as a function of the modified temperature, via which brake valves on the wheels are controlled and the pressure in the individual wheel brakes is regulated individually.