DE102006040127A1 - Electronic motor vehicle brake control system`s hydraulic pump calibrating method, involves predetermining generator voltage, and determining correction values, while reaction of engine is evaluated based on controlled electrical signal - Google Patents

Abstract

The method involves determining correction values with which an electrical reference control signal for a regulated pump engine that is a component of a brake system (1), is corrected for increasing dosing accuracy. A temporally limited pump test cycle is accomplished with which an electrical parameter i.e. desired value for a generator voltage, of the engine is firmly predetermined. The values are determined while a reaction of the engine is evaluated based on electrical signal controlled by the engine in a control loop.

Description

The The invention relates to a method for calibrating a hydraulic pump according to the preamble of Claim 1 and an electronic motor vehicle brake control system according to claim 8, in which this method is used.

Today's standard electronically controlled motor vehicle brake systems comprise at least one hydraulic pump for returning brake fluid into a brake fluid reservoir or for the purpose of active pressure build-up, when the brake system includes functions such as vehicle dynamics control (ESP) or automatic distance control (ACC) etc. For driving the pump, a DC electric motor with brushes is usually used, which is clocked, for example, controlled by a PWM control. The basic structure of a corresponding brake system is shown in the block diagram in FIG 1 seen.

From the EP 0 662 051 B1 (P 7386) a corresponding brake system is known in which a method is used, in which the delivery rate of the hydraulic pump is electronically controlled. The pump is controlled by a PWM controller. To estimate the flow rate, the generator voltage of the pump is measured during the pulse pause times.

The older German patent application DE 10 2005 041 556 (P 11192) describes a method for determining a form in the aforementioned motor vehicle brake system. According to this method, the tracking voltage of the motor is also considered after a drive pulse of the clocked drive in the pulse pauses.

The The object of the present invention is now a method indicate with which the delivery rate the pump with increased Accuracy without the use of additional speed or pressure sensors carried out can be.

These The object is achieved by the method according to claim 1.

The The present invention is based on the consideration that it is production-related in a production series of the above mentioned motor / pump arrangements with the same electrical motor control to different Funding comes. It has been shown that this behavior is essentially through Characteristics scattering caused by the pump motor. It can be Observe that the speed with the same electrical control individually varies. Although you can Differences in the support line in principle also caused by mechanical-structural pump differences However, this cause does not play a major role in practice.

According to the method of the invention, at least one correction value is calculated in order to be able to correct the setpoint voltage V _{DES of} the clocked control loop for the electric motor individually upwards or downwards.

To At least once a time-limited pump test cycle is performed. This Cycle can be done in the field (in the vehicle, at the vehicle manufacturer) and / or be carried out after production. Preferably, the test cycle is automatically at regular intervals by the Electronics of the braking system for the formation of a current correction value / n called. This offers the advantage that no staff or no additional Devices for the calibration process needed will be.

During the Test cycle, an electrical parameter of the pump motor becomes fixed specified. Thereafter, it is preferred to wait until the pump control loop has settled. Then the calibration value (s) is / are determined by the reaction of the pump motor on the hand of the pump motor on the Control influenced electrical control signal evaluated becomes.

The test cycle therefore preferably includes at least one transient phase and one measurement phase. In the transient phase, the pump motor is expediently operated for a specific time of, for example, 2 s in the control loop. For this purpose, for example, the entire time, in particular in both phases, always a suitably predetermined target voltage V _DES maintained constant.

In the measurement phase, when the control loop has settled and the engine speed remains constant over time, then preferably a predetermined number of values of the controller output are collected. These values are in particular the ratio of pulse duration to the period of the PWM signal. These values are preferably measured at fixed time intervals of 10 ms. Thereafter, an averaging of these values is preferably carried out, for example by formation of the arithmetic mean p _DC . This value indicates the average pulse duration of the PWM signal, which differs from motor to motor.

Out this electrical parameter will / will be the correction value (s) certainly.

This is preferably done by a suitable, fixed predetermined value relationship, for example via a correction value table, in which the electrical parameter is assigned to suitable correction values or via an assignment formula With. The assignment formula preferably has more than one, for example, exactly two constants determined by preliminary experiments. In the case of an assignment formula, this can be done, for example, by the assignment rule y A = a · p DC + b, be realized
where the constants a and b are suitable constants to choose.

As already mentioned, the parameters a and b are expediently taken over series of measurements by laboratory experiments determined with several engines.

The correction value y _A is preferably used to calculate the closed loop target voltage V _DES to set a predetermined speed n _{DES of} the motor.

This is done in particular by applying the formula:

By the adaptation of the nominal voltage with the help of the unloaded and stationary Operating the measured value of the controller output variable, the Druckstellgenauigkeit the brake system opposite be increased in the case in which only a nominal parameter used to calculate the setpoint voltage from a speed request becomes. The advantage of this method is that no sensors must be used so that in a mass production the pump control can be calibrated particularly cost-effectively.

Prefers In the test phase, the pump motor or the pump is operated in such a way, that essentially no delivery load is applied to the pump. This is achieved in particular by the fact that the valves of the brake system are brought into positions at which the outlet of the pump with an open volume, e.g. the Master cylinder or the wheel brake cylinder is hydraulically connected. This is particularly preferred then the case when the coils of Valves of the brake system are not energized. In this condition is then, for example, the usual Brake systems existing electronic switching valve closed, so that the pump is no brake fluid can promote.

Preferably becomes the method according to the invention for calibrating hydraulic pumps in regulated motor vehicle brake systems used. By the pump calibration, for example, automatic brake interventions, where no pressure is manually controlled by the driver, the Brake pressure in the wheel brakes are controlled particularly sensitive. This is among others in distance control systems, such as ACC of particular Advantage.

During the execution the method according to the invention is expediently the supply voltage kept constant by an additional circuit. That way improve the accuracy of the process. Alternatively, it is also appropriate, the Influence of voltage fluctuations on the measured duty cycle in suitable way to compensate.

Further preferred embodiments emerge from the dependent claims and the following description of an embodiment with reference to Characters.

It demonstrate

1 3 is a block diagram of an electronically controlled braking system in which the exemplary method is carried out.

2 a diagram illustrating the speed differences of pump motors in a series and

3 the control principle for the pump motor.

This in 1 illustrated brake system 1 consists of a hydraulic valve block 2 (HCU) and a firmly connected electronic controller housing 3 (ECU). The brake system comprises two brake circuits I. and II. In the following, only circuit I will be explained in more detail. With tandem master cylinder 4 can brake fluid via hydraulic line in accordance with the brake pedal operation 5 in block 2 be initiated. Via inlet valve 6 and exhaust valve 7 can the pressure in the wheel brake cylinders 8th be set. The brake system shown is each with an additional pressure sensor 9 equipped per wheel brake circuit. In a variant of the brake system are no pressure sensors 9 available. hydraulic pump 10 is output side with inlet valve 6 connected. pump 10 is powered by a DC electric motor, which is electrically connected to the control unit 3 connected is. pressure line 5 leads via a hydraulic line to the upstream side of electrical switching valve 11 and isolation valve 14 , The second output of diverter valve 11 is with the inlet of pump 10 and exhaust valve 7 connected. The second side of isolation valve 14 is with the pump outlet and inlet valve 6 connected.

By switching on the electric motor promotes hydraulic pump 10 Hydraulic fluid upstream of inlet valve 6 so that the pressure rises there. This will be switching valve 11 opened, allowing brake fluid from storage tank 12 to the suction side 13 the pump 10 can flow. isolation valve 14 is closed. The electric motor of the pump is controlled by the control unit 3 electrically driven with a rectangular voltage signal with variable pulse width (PWM signal).

Inside electronic control unit 3 There is a microprocessor system in which various control and test programs are executed. control unit 3 In addition to internal printing requirements, it can also print requests from external ECUs, such as an automatic controller 15 (ACC). According to the existing pressure requirement valves are 6 . 7 and pump 10 activated so that the requested pressure rests as accurately as possible on the brake disc.

To do so during a corresponding, not through master cylinder 4 initiated, pressure demand the Sollradbremsdruck the brake pressure to meter with sufficient accuracy, among other things, an accurate adjustment of the pump delivery is necessary. Unfortunately, due to the manufacturing process, not every pump motor is exactly the same as the other, so that at least one individual engine calibration is required in order to set its speed with the required accuracy over the setpoint value of the engine control via the electrical control of the engine.

In the diagram in 2 the pump speed n of various pumps is shown with respect to time t. The pump motor is in a closed loop, as in 3 shows, operated. The setpoint for the controller is a constant voltage. The motor is controlled by a pulse width modulated signal with a fixed period from the motor controller. A PWM signal is a periodic square wave signal with a constant period within which the duration of a square pulse is varied. This allows the signal to be divided into two phases: in the time t _AN , a voltage is applied to the terminals of the motor; In the time t _OFF , no voltage is applied to the motor and it rotates due to the moment of inertia of its rotating components. In time t _OFF , generator voltage V _GEN is generated by the electronics 3 measured. The signal V _GEN is also filtered. This filtered voltage forms the actual size of the motor control loop and is adjusted by the controller in accordance with the predetermined target voltage V _DES . In this way, the motor can be operated at a constant speed because it is linearly related to the generated voltage.

curves 16 and 17 represent speed curves of two different motors at the same setpoint voltage. The dashed lines 18 . 19 represent the voltage applied to each of the motors target voltages. The differences in speed different engines with substantially the same nominal voltage are due to the deviation of the curves 18 and 19 clear. These speed differences cause different pressures to be set during operation of the pump, since different amounts of brake fluid are delivered into the brake cylinders depending on the engine used.

3 schematically represents the mode of action of the motor control circuit. Electric motor 20 , which with pump 10 is mechanically connected, is by means of an electrical PWM signal via line 21 driven. motor controller 22 is in the electronic control unit 3 integrated. engine 20 generated in the freewheeling phase (pulse pause of the PWM voltage line 21 ) a generator voltage V _GEN , via line 23 a differential element 24 is supplied, in which the generator voltage is subtracted from the target voltage V _DES . According to the input signal 25 sets PI controller 22 then a corresponding value of V _GEN , which corresponds to a specific pump speed n depending on the type of engine.

For the intended engine-specific calibration, a test cycle is carried out in which first the control circuit in 3 a suitable setpoint voltage V _{DES is} specified. When the control circuit has settled after a certain time (V _GEN remains essentially constant), approximately 100 values of the duty cycle, ie the ratio of pulse duration to the period of the PWM signal, are measured at fixed time intervals of 10 ms and summed up. Thereafter, this sum is divided by the value 100 to form the arithmetic mean. This value p _DC , which describes the average pulse duration of the PWM signal, now differs from motor to motor. It is converted to percent and used in the following straight-line equation: y A = a · p DC + b,

The parameters a and b in this equation have previously been determined by laboratory experiments with several motors. The value y _A is now used to calculate the closed loop target voltage V _DES to set a predetermined speed n _DES .

By adjusting the setpoint voltage using the value of the controller output variable measured in unloaded and stationary operation, the pressure setting accuracy of the brake system can be increased compared to the case in which only one nominal parameter is used to calculate the setpoint voltage from a speed request. The advantage of this method is that no separate measuring equipment has to be used. The properties of the pump motor can be determined in a ready-to-use brake system and evaluated directly in the controller software to increase the pressure setting accuracy.

Claims (8)

Method, in which one or more correction values are determined with which a nominal electrical drive signal for a controlled pump motor, which is in particular part of a controlled motor vehicle brake system, is corrected for an increase in the dosing accuracy, characterized in that carried out at least once a time-limited pump test cycle in which an electrical parameter of the pump motor is fixed and the correction value (s) are determined by evaluating the response of the pump motor based on at least one electrical signal influenced by the pump motor in the control loop. A method according to claim 1, characterized in that the evaluated influenced electrical signal is the generator voltage (V _GEN ) of the pump motor. A method according to claim 1 or 2, characterized in that the fixed predetermined electrical parameter is a desired value (V _DES ) for the generator voltage. Method according to at least one of the preceding claims, characterized in that the pump motor is controlled by a control circuit which generates a PWM signal and in which the generator voltage (V _GEN ) is used in the pulse pauses as the actual size of the control. Method according to at least one of the preceding Claims, characterized in that for determining the calibration value (s) the PWM signal over a longer one Period is evaluated. A method according to claim 5, characterized in that the evaluation of the PWM signal is carried out by the average of the ratio of the on times to the off times of the PWM signal is formed over a certain period of time and with the mean of a correction value (y _A ) is calculated for the setpoint. Method according to at least one of the preceding Claims, characterized in that during the Pumpentestzyklusses substantially no load on the hydraulic pump is applied. Electronic motor vehicle brake control system with at least one regulated pump for an active brake pressure build-up, characterized in that the pump control with the method according to at least one of claims 1 to 7 is calibrated.