DE10355239A1 - Slip-controlled braking system for road vehicle estimates pressure in brake circuits and has PWM control of electric motor driving hydraulic pump pressurizing brake circuits - Google Patents

Abstract

The brake pedal in the road vehicle may be connected to a servo mechanism providing hydraulic pressure for a dual-circuit brake system. A hydraulic pump in the first brake circuit is driven by a separately excited DC motor. The operating system is as follows:- (A) An electronic control circuit supplies the motor with modulated PWM (Pulse Width Modulation) starting and/or shut-off phases to control the rotational speed. (B) A generator voltage produced by the motor is tapped during a shut-off phase. (C) The generator voltage is fed to the electronic control circuit which estimates the admission pressure prevailing in the brake system. (D) A hydraulic control valve is triggered with minimum noise to control the pressure in the brake cylinders.

Description

The The invention relates to an electronic control method for a slip-controlled Motor vehicle brake system, comprising a distribution device with an electronic unit (ECU) and a hydraulic unit (HCU) comprising a receiving body for hydraulic Components such as in particular electro-hydraulic intake and exhaust valves for wheel brakes, which are organized in brake circuits, and with a motor-pump unit with electric motor, in particular for the return of hydraulic fluid from wheel brakes in the direction of a pressure transducer, wherein under evaluation one, from a driver on the basis of the pressure transducer in the brake system input form Anti-lock control by means of pressure build-up, pressure maintenance and pressure shutdown settings the electro-hydraulic inlet and outlet valves is made possible.

Known electronically controlled motor vehicle brake systems suffer during ABS control processes the disadvantage that as a result of the operation of a so-called return pump as well as through valve opening and valve closing operations, pressure pulsations occur, which leads to a noise nuisance and as a result to a more or less strong comfort restrictions to lead.

To improve this situation, inter alia, the use of valves is sought, which allow a reduced noise emission. In this context, the use of so-called analogized adjustable seat valves appears promising. In order to improve the noise behavior, a somewhat analogized activation of the valves, in particular of analogously controllable normally open inlet valves (AD / SO valves), should be made possible. In this case, the evaluation of a physical relationship between a valve opening cross-section in the region of a valve body of the valve, used in conjunction with the pressure acting on the valve body pressure difference and the induced current in an electric valve coil (I ~ Δp _valve ). The noise optimization is done as follows. To enable a defined-calmed pressure increase gradient in a valve opening process, the coil current of the Radeinlassventils in response to the differential pressure on the valve body is set such that an opening gap on the valve body initially allows a metered throttling effect, and only then enters an open position. In contrast to known valves, there is no abrupt valve opening. The throttling effect described avoids high and consequently noise-intensive pressure buildup gradients. The noise level is reduced. High differential pressures on the valve body require a relatively high residual current in the valve spool in order to limit the pressure gradient on the valve body by the aforementioned throttling effect to an adequate level.

Because the pressure difference applied to the valve body is variable as a function of the operating conditions, pressure sensors must be provided for their detection on both sides of the valve body (p _THZ p _Rad ). As a result, the pressure applied by the driver in a brake circuit upstream of the intake valve to form the differential pressure can be compared with the actual pressure at the wheel brake. From this knowledge, the coil current required for the noise-optimized pressure build-up control can be precisely derived and consequently the pressure build-up gradient can be set exactly. It is understood that in addition to a noise-optimized pressure build-up control further applications may exist. An ABS braking system for carrying out the described method requires at least four pressure sensors in the region of the wheel brakes and at least one pressure sensor for detecting the driver-side applied pressure and a correspondingly complex data processing.

Of the Invention is now based on the object to provide a method that without elaborate pressure measurement a sufficiently accurate estimate the pressure difference allowed on the valve body. In other words It is an object of the present invention to provide a noise optimized one To allow operation of the brake system and in particular the number of required pressure sensors in the brake system to reduce.

The The object is achieved according to the invention by the electronics unit modulates the motor for the purpose of speed control powered on and / or off phases, wherein during a Shutdown tapped a generated by the motor generator voltage which is supplied to the electronic unit, which is based on the determined generator voltage present in the brake system Estimates form, a noise-optimized Control of electrohydraulic inlet and outlet valves to enable. So far in the present application a modulated motor drive is addressed, is basically a PWM control be understood.

The Invention is based on the idea, a speed change (Speed reduction) which the motor-pump unit during a shutdown phase of the engine, as a standard for the To use the system form and the information thus obtained and findings on noise-optimized Regulation of electromagnetic valves. The speed change is simply detected by means of the delivered generator voltage. According to the invention is neither an engine speed sensor or a pressure sensor in the region of a master cylinder required.

In Advantageous development of the invention is provided that the tapped generator voltage in a defined time interval is considered and evaluated to the run-out behavior of the motor-pump unit to judge. It has been shown that the metrological detection the generator voltage within the predetermined time interval is sufficient to make a noise-optimized Special regulation of electrohydraulic valves to allow.

at A preferred control method is the flow behavior of the motor-pump unit alone by evaluating the magnitude of the generator voltage gradient assessed within the defined time interval. This will the influence of measurement errors, outliers or other short-term Disturbances in limited to the voltage curve, and yet a meaningful, quantified Statement allows.

It will continue to be the surprising simple but hitherto unrecognized relationship exploited that - under the assumption of constant boundary conditions, such as the filling level a pressure medium accumulator, which arranged in the intake of the pump is the Amount of the speed gradient increases proportionally with the form. With In other words, the speed of the motor-pump unit during a Shutdown phase decelerated faster due to a high pre-pressure, as a result of a low form. These considerations are based on the Assumption of constant boundary conditions.

Around the quality To improve the scheme, it is conceivable, the pulse width of the electrical Switching phases and / or turn-off phases to observe, where for tapping the generator voltage primarily such Off phases selected which are compared with one or more adjacent ones Switch-on and / or switch-off phases have a matching pulse width. By and by the way largely constant boundary conditions - such as a stationary brake actuation - is ensured that a sufficiently stabilized speed of the motor-pump unit at the beginning of the relevant Interval has been present.

Further Details of the invention are subject of subclaims in connection with the Description and the drawing forth. In the drawing shows respectively schematically:

1 a vehicle brake system with only one illustrated wheel brake circuit,

2 Speed curves n _{MPA of} a motor-pump unit (MPA) at different delivery pressures,

3 Diagrams to illustrate pulse-width modulated switching on and off phases of the motor-pump unit for the purpose of controlling the engine speed,

4 tapped generator voltage curves U _off during a switch-off phase until the motor-pump unit is at a standstill, in each case depending on different delivery pressures,

5 a diagram to illustrate the relationships between on-board voltage U, terminal voltage U _on , generator voltage U _off and speed n of a motor-pump unit,

6 a diagram illustrating terminal voltage U _on and generator voltage U _off during an interval .DELTA.t, and

7 a diagram illustrating the relationships between voltage U and pressure increase Δp.

From the 1 exemplifies a brake circuit of a slip-controlled motor vehicle brake system 1 show, with only a wheel brake is shown. The brake system 1 includes a braking device with egg a hydraulic pressure transmitter 3 in the form of a master cylinder, which via a hydraulic connection 4 and a distribution device 5 comprising a hydraulic unit 6 and an electronics unit 7 with a wheel brake 8th connected is. The hydraulic unit 6 has a receiving body for hydraulic and electro-hydraulic components such as electromagnetically actuated intake and exhaust valves 9 . 10 for every wheel brake 8th , In the connection - even before a normally open inlet valve for said wheel brake - there is a branch 11 to a second wheel brake circuit. Starting from the wheel brake 8th leads a return connection 12 via the normally closed exhaust valve 10 to a low-pressure accumulator 13 which one, out of the wheel brake 8th as a result of ABS control cycles, it is possible to absorb The low pressure accumulator 13 feeds a suction side of a motor-driven pump 14 , This is preferably of the type radial piston pump and has in each case a suction valve on the suction side and a pressure valve on a pressure side. engine 15 and pump 14 are designed as an aggregate (motor-pump unit = MPA) and allow a return pumped hydraulic fluid in the direction of pressure transducer 3 , This allows a brake pedal to remain substantially in place during an ABS control during an ABS control and not fall through. It is understood that the brake system may have additional functionalities such as traction control (ASR) or driving stability control (ESP), which is an intake valve 9 upstream, electromagnetically controllable and normally open separating valve requires.

The following description is based on the example of a noise-optimized control of A / D inlet valves 9 although quite other uses are conceivable without departing from the invention. For example, it is conceivable to use the information obtained to estimate the degree of filling of low-pressure accumulators, and for example, to control the pump only as long as required to emptying the low-pressure accumulator. This prevents noise or irritation of the driver. A completely empty low-pressure accumulator is advantageous, for example, if an EBV control intervention (EBV = electronic brake force distribution) is required, wherein a certain volume is to be absorbed, for example, from the wheel brakes of a rear axle into low-pressure accumulators. The return pump can thus - depending on the storage level - allow empty conveying the low-pressure accumulator.

During an ABS control, as a result of depressurization processes, via the exhaust valve SG, 10 a pressure difference (Δp _valve = p _THZ - p _Rad ) at the intake valve SO, 9 one. That from the wheel brake 8th Escaped volume enters the low pressure accumulator 13 , NDS. At the same time the pump 14 Activates and delivers the drained volume back to the pressure transmitter against the driver pre-pressure applied as a result of the brake application 3 and in front of the inlet valve 9 , The applied driver pre-pressure causes a resistance in this situation, which affects the flow rate of the pump. With increasing pressure difference between pressure transducer 3 and wheel brake 8th (Δp _pump ≈ p _THZ ), the resistance increases, and at constant pump power P _pump and increasing pressure difference Δp _pump , the delivered volume flow (V) decreases. This relationship follows the relationship P pump = Δp pump · V = Δp pump * N * V H (1)

2 illustrates the relationship between the rotational behavior of the motor-pump unit with increasing pressure increase at a constant temperature, divided into a switch-on (U _KL = max.) And a switch-off (U _KL = 0). It should be noted that there is a rigid coupling between the engine and the pump, so that the engine speed coincides with the pump speed.

Assuming low leakage, decreases according to (1) with the same supplied power P, the speed n of the motor-pump unit (MPA) with increasing pressure increase Δp _pump from. In other words, the maximum speed of the motor-pump unit behaves inversely proportional to the pressure increase. n MPA, max ~ 1 / Δp pump (2)

How out 2 This also applies to the discharge behavior of the motor-pump unit within a switch-off phase from the time U _kl = 0. The amount of speed change per unit time - ie the speed gradient - increases with increasing pressure increase Δp _pump .

As will be seen from the explanations below, the relationships described will be omitted used to form by evaluation of speed-equivalent information, a pressure model, which allows a noise-optimized control. A direct measurement of pressure values can be avoided by resorting to modeling speed-proportional, electrical quantities of the motor in the generator mode, in particular to the gradient of the generator voltage, which is proportional to the gradient of the engine speed.

The electric engine 15 the pump 14 is basically based on a separately excited DC machine - in particular a permanent magnet-excited commutator machine - whose speed is controlled by a pulse width modulation (PWM) of a constant terminal voltage U _KL . For speed control, within a fixed interval (for example, t = 60 ms), the duration of the switch-on and switch-off phases is modulated stepwise in accordance with the speed specification (= Requested_Pump_Speed). Of the 3 is a 12-stage speed control refer to a full scale of 100 a so-called Requested_Pump_Speed of 12 corresponds to a switch-on phase over the entire aforementioned interval. From Requested_Pump_Speed <= 10 becomes the engine 15 modulated controlled. The armature voltage is interrupted cyclically. With decreasing Requested_Pump_Speed, the pulse width of the switch-off phases (motor off) increases, and the pulse width of the switch-on phases (motor on) decreases.

The speed control of the motor 15 in ABS mode (and thus the delivery rate of the pump 14 ) takes place as a function of the calculated volume throughput or the degree of filling of the low-pressure accumulator 13 (NDS) model. The pulse width modulated terminal voltage (U _Kl ) is generated by means of an analog-to-digital converter as a controller signal. In the PWM switch-on phase, this signal corresponds approximately to the maximum available on-board voltage in the vehicle. During a PWM switch-off phase, the motor acts 15 However, as a generator and it can, for example, on carbon brushes a generator voltage U are tapped, the height of which can provide information about the speed level. To evaluate the relationship U A = C Masch · Φ · n + R A · I A (4) The following assumptions are made: 1. The proportion of the armature current (I _A ) during generator operation is low and can therefore be neglected. 2. The excitation flux (Φ) and the motor constant (C _Masch ) are constant as design-related influencing variables, so that from the equation ( 4 ) in generator mode, a proportionality between speed n and generator voltage U results: n MPA ~ U MPA, Off

The above relationship is through 4 confirmed, in which the voltage U is removed over the time t. For the generator voltage further applies that this in a first de-energized loop (a certain subinterval of the aforementioned interval of 60 ms) directly from the speed of the motor 15 is dependent. The speed of the engine 15 is in turn influenced by the driver pressure and the pump load applied. With increasing driver pre-pressure, the pump works against increased resistance, and the speed and the corresponding tapable generator voltage U _OFF decrease. Because both U _ON and U _{OFF are} pressure-dependent, the difference ΔU = U _ON -U _{OFF also} assumes characteristic, quasi-proportional values for different feed pressures. The voltage difference is proportional to the driver pre-pressure or to the applied pressure increase. A value U _{OFF MIN} corresponds to the generator voltage in a last non-energized loop of a switch-off phase of the motor 15 ,

From the values U _OFF , U _{OFF MIN} and the time Δt is the pressure-dependent gradient of the generator voltage

• • Änderung der Pumpendrehzahl: Bei häufig geänderter Modulation der PWM-Einschalt- und Ausschaltphasen (Requested_Pump_Speed), existieren nur kurze Phasen eines eingeschwungenen, konstanten Drehzahlniveaus. Dies führt zu einer Verringerung der auswertbaren Datenbasis und damit zu einer Verschlechterung der Qualität des Modells. Die zu berücksichtigende PWM-Modulation sollte durch wiederholte Intervalle mit weitgehend identischer Modulierung gekennzeichnet sein.
• • Lastzustand der Pumpe: In Abhängigkeit von dem Förderzustand der Pumpe 14 (Förderung in 2 Bremskreisen, Förderung in einem Bremskreis oder Leerförderung treten unterschiedliche Motorbeanspruchungen auf, was zu entsprechend veränderten Drehzahl- und Spannungskonstellationen führt. Weil die Unterschiede zwischen diesen Laststufen jedoch markant sind, können diese – beispielsweise über den Betrag erfasster Werte – erkannt und bei der Auswertung berücksichtigt werden.
• • Temperatur: Die abnehmende kinematische Viskosität der Bremsflüssigkeit mit steigender Temperatur führt dazu, dass die Flüssigkeit mit steigender Temperatur immer dünnflüssiger wird und so ein geringeres Lastmoment auf die Pumpe erzeugt wird als durch bei Kälte vorliegender zäher Bremsflüssigkeit. Das geringere Lastmoment führt zu höheren Drehzahlen und damit zu geringeren Spannungsabfällen. Auch der Temperatureinfluss ist erkennbar und berücksichtigbar.

In order to obtain as meaningful statements as possible for the noise-optimized control, it is advisable to consider the following boundary conditions.

• • Changing the pump speed: With frequently changed modulation of the PWM switch-on and switch-off phases (Requested_Pump_Speed), only short phases of a steady, constant speed level exist. This leads to a reduction of the evaluable database and thus to a deterioration of the quality of the model. The PWM modulation to be considered should be characterized by repeated intervals with largely identical modulation.
• • Load condition of the pump: Depending on the pumping condition 14 (Promotion in 2 brake circuits, promotion in a brake circuit or idle promotion occur different engine loads, which leads to correspondingly changed speed and voltage constellations.HCLFHLBecause the differences between these load levels, however, are distinctive, they can - for example, the amount detected values - recognized and taken into account in the evaluation.
• • Temperature: The decreasing kinematic viscosity of the brake fluid as the temperature rises causes the fluid to become less viscous as the temperature rises, resulting in a lower load moment on the pump than when the brake fluid is cold. The lower load torque leads to higher speeds and thus lower voltage drops. The influence of temperature is also recognizable and can be considered.

The inverse proportional relationship between the values of U _on , U _off , uoff_min min and the pressure increase Δp, and the proportional relationship between the generator voltage gradient tan α U _off and the pressure increase Δp goes out 7 out.

Claims (8)

Electronic control method for a slip-controlled motor vehicle brake system ( 1 ) comprising a distribution device ( 5 ) with an electronic unit ( 7 , ECU) and with a hydraulic unit ( 6 , HCU) comprising a receiving body for hydraulic components such as in particular electro-hydraulic intake and exhaust valves ( 9 . 10 ) for wheel brakes ( 8th ), which are organized in brake circuits, and with a motor-pump unit with electric motor ( 15 ) in particular for the return of hydraulic fluid from wheel brakes ( 8th ) in the direction of a pressure transducer ( 3 ), taking into account, by a vehicle driver, the pressure transducer ( 3 ) in the brake system, an anti-skid control by pressure build-up, pressure holding and Druckabbauschaltstellungen the electro-hydraulic intake and exhaust valves ( 9 . 10 ), characterized in that a) the electronics unit ( 7 ) the engine ( 15 ) is supplied with defined electrical input and / or switch-off phases for the purpose of speed control, b) during a switch-off phase, a signal passed through the motor ( 15 ) generator voltage is tapped, c) the generator voltage ( 15 ) of the electronics unit ( 7 ), which estimates on the basis of the determined generator voltage the present in the brake system form to d) a noise-optimized control of the electro-hydraulic valves ( 9 ). Control method according to claim 1, characterized that the tapped generator voltage in a defined time interval is considered and evaluated to the run-out behavior of the motor-pump unit to judge, and that from the judged discontinuation on the admission pressure of the motor-pump unit is closed. Control method according to Claim 2, characterized that the leakage behavior of the motor-pump unit by evaluating the Amount of the generator voltage gradient within the defined time interval is judged. Control method according to claim 3, characterized in that a time interval over the relationship .DELTA.t = A · loop time - t _switch-on with, for example: loop time = 10 ms A = constant = 6 t _switch-on = 30 ms is defined. Control method according to Claim 4, characterized in that the relationship t _switch-on phase <A · loop time is used for the time interval. Control method according to claim 1, characterized the generator voltage gradient is proportional to the speed gradient is. Control method according to claim 1, characterized that the speed gradient in generator operation proportional to the form is growing. Control method according to claim 1, characterized the pulse width of electrical switch-on phases and / or switch-off phases is observed, and that for the tapping of the generator voltage such Ausschaltphasen be selected which in comparison with one or more adjacent switch-on phases and / or off phases a matching Have pulse width.