EP1646541A1

EP1646541A1 - Electronic control method for a slip-controlled motor vehicle brake system

Info

Publication number: EP1646541A1
Application number: EP04766161A
Authority: EP
Inventors: Guntjof Magel; Rüdiger MAHLO; Frank Sikorski; Faouzi Attallah; Lukas Kroh
Original assignee: Continental Teves AG and Co OHG
Current assignee: Continental Teves AG and Co OHG
Priority date: 2003-07-11
Filing date: 2004-07-08
Publication date: 2006-04-19
Also published as: WO2005007475A1; US20060202552A1

Abstract

The aim of the invention is to be able to estimate an admission pressure in a slip-controlled motor vehicle brake system by using little sensory effort. Said aim is achieved by the fact that a) an electronic unit (7) supplies the motor (15) with modulated electrical starting and/or shut-off phases (PWM) in order to control the rotational speed, b) a generator voltage generated by the motor (15) is tapped during a shut-off phase, c) the generator voltage (15) is fed to the electronic unit (7) which estimates the admission pressure prevailing in the brake system based on the determined generator voltage, so as to d) be able to trigger the electrohydraulic valves (9) in a noise-optimized manner.

Description

Electronic control method for a slip-controlled motor vehicle brake system

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 with a hydraulic unit (HCU) comprising a receiving body for hydraulic components such as in particular electrohydraulic inlet and outlet valves for wheel brakes, which are organized in brake circuits, and with a Motor-pump unit with an electric motor, in particular for returning hydraulic fluid from wheel brakes in the direction of a pressure transducer, with an anti-lock control system using pressure build-up, pressure maintenance and pressure reduction switch positions of the electrohydraulic inlet and pressure switch positions evaluated by a vehicle driver using the pressure transducer in the brake system Exhaust valves is enabled.

Known electronically controlled motor vehicle brake systems suffer during ABS control processes from the disadvantage that pressure pulsations occur as a result of the operation of a so-called return pump and as a result of valve opening and valve closing processes, which lead to noise pollution and, as a result, to a greater or lesser degree of comfort. To improve this situation, among other things, the aim is to use valves which enable reduced noise emissions. In this context, the use of so-called analogue adjustable seat valves seems promising. To improve the noise behavior, a somewhat analogized control of the valves, in particular of analogically controllable, normally open inlet valves (AD / SO valves) is to be made possible. The evaluation of a physical relationship between a valve opening cross section in the area of a valve body of the valve, in conjunction with the pressure difference acting on the valve body and the induced current in an electrical valve coil

(/ ~ kp _Venta ) exploited. The noise optimization happens as follows. To enable a defined, calm pressure build-up gradient during a valve opening process, the coil current of the wheel inlet valve is set as a function of the differential pressure on the valve body in such a way that an opening gap on the valve body initially allows a metered throttling effect, and only then reaches an open position. In contrast to known valves, there is no sudden valve opening. The throttling effect described avoids high and consequently noise-intensive pressure build-up gradients. The noise level is reduced. High differential pressures on the valve body require a relatively high residual current in the valve coil in order to pass through the pressure gradient on the valve body to limit the throttle effect to an adequate level.

Because the pressure difference at the valve body is variable depending on the operating conditions, pressure sensors must be provided on both sides of the valve body for detection (_? _ _/ __ _, _? _„ __)

Driver in a brake circuit upstream of the intake valve pressure can be compared to form the differential pressure 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 derived exactly and consequently the pressure build-up gradient can be set exactly. It goes without saying that, in addition to noise-optimized pressure build-up control, other applications can exist. An ABS brake system for carrying out the described method requires at least four pressure sensors in the area of the wheel brakes and at least one pressure sensor to record the pressure applied by the driver, as well as a correspondingly complex data processing.

The invention is based on the object of specifying a method which allows a sufficiently precise estimate of the pressure difference at the valve body without complex pressure measurement. In other words, it is an object of the present invention to enable noise-optimized operation of the brake system and in particular to reduce the number of pressure sensors required in the brake system.

The object is achieved in accordance with the invention by the electronics unit supplying the motor with modulated electrical switch-on and / or switch-off phases for the purpose of speed control, wherein during a switch-off phase a generator voltage generated by the motor is tapped which is supplied to the electronic unit on the basis of the determined values Generator voltage estimates the upstream pressure in the brake system to enable noise-optimized control of the electrohydraulic intake and exhaust valves. As far as a modulated motor control is addressed in the present application, this should in principle be understood to mean a PWM control.

The invention is based on the basic idea of using a change in speed (speed reduction) which the motor-pump unit experiences during a switch-off phase of the motor as a yardstick for the system form, and to use the information and knowledge obtained in this way for noise-optimized control of the electromagnetic valves. The change in speed is simply recorded using the generator voltage output. According to the invention, neither an engine speed sensor nor a pressure sensor in the area of a master brake cylinder is required. In an advantageous development of the invention, it is provided that the tapped generator voltage is viewed and evaluated in a defined time interval in order to assess the stopping behavior of the motor-pump unit. It has been shown that the measurement of the generator voltage within the predetermined time interval is sufficient to enable a noise-optimized special control of the electro-hydraulic valves.

In a preferred control method, the stopping behavior of the motor-pump unit is assessed solely by evaluating the amount of the generator voltage gradient within the defined time interval. This limits the influence of measurement errors, outliers or other short-term disturbances in the voltage curve, and still enables a meaningful, quantified statement.

The surprisingly simple but hitherto unrecognized relationship is further exploited that - assuming constant boundary conditions, such as the degree of filling of a pressure medium reservoir, which is arranged in the intake tract of the pump - the magnitude of the speed gradient increases proportionally with the admission pressure. In other words, the speed of the motor-pump unit is braked faster during a switch-off phase due to a high admission pressure than due to a low one Admission pressure. These considerations are based on the assumption of constant boundary conditions.

In order to improve the quality of the control, it is conceivable to observe the pulse width of the electrical switch-on phases and / or switch-off phases, with switch-off phases primarily being selected for tapping the generator voltage which, in comparison with one or more adjacent switch-on phases and / or switch-off phases have a matching pulse width. As a result of this and, for the rest, largely constant boundary conditions - such as, for example, a stationary brake actuation - it is ensured that a sufficiently stabilized speed of the motor-pump unit was present at the beginning of the relevant interval.

Further details of the invention emerge from subclaims in connection with the description and the drawing. The drawing shows schematically:

1 is a vehicle brake system with only one wheel brake circuit shown,

2 speed curves n _M pA of a motor-pump unit (MPA) at different delivery pressures, 3 diagrams to illustrate pulse-width-modulated on and off phases of the motor-pump unit for the purpose of motor speed control,

4 tapped generator voltage curves U ₀ __ during a switch-off phase until the motor-pump unit comes to a standstill, in each case as a function of different delivery pressures,

Fig. 5 is a graph showing the relationship between system voltage U, terminal voltage O _oa U___ generator voltage and rotational speed of a motor-pump unit n,

Fig. 6 is a diagram to illustrate terminal voltage

U _on and generator voltage U _off during an interval Δt, and

Fig. 7 is a graph to illustrate the relationship between voltage U and pressure increase Δp.

1 shows an example of a brake circuit of a slip-controlled motor vehicle brake system 1, only one wheel brake circuit being shown. The brake system 1 comprises a brake device with a hydraulic pressure transmitter 3 in the form of a master brake cylinder, which comprises a hydraulic unit 6 and an electronic unit 7 with a hydraulic unit 4 and a distribution device 5 Wheel brake 8 is connected. The hydraulic unit 6 has a receiving body for hydraulic and electrohydraulic components such as electromagnetically actuated inlet and outlet valves 9, 10 for each wheel brake 8. In the connection - before an inlet valve for the said wheel brake, which is open when de-energized - there is a branch 11 to a second one Wheel brake circuit. Starting from the wheel brake 8, a return connection 12 leads via the exhaust valve 10, which is closed when de-energized, to a low-pressure accumulator 13, which can hold a volume drained from the wheel brake 8 as a result of ABS control cycles. The low-pressure accumulator 13 feeds a suction side of a motor-driven pump 14. This is preferably of the radial piston pump type and has a suction valve on the suction side and a pressure valve on one pressure side. Motor 15 and pump 14 are designed as a unit (motor-pump unit = MPA) and allow a return flow of drained hydraulic fluid in the direction of pressure transmitter 3. This makes it possible for a brake pedal to remain essentially in its place during ABS control with constant brake actuation and does not fail. It goes without saying that the brake system can have additional functionalities, such as traction control (ASR) or driving stability control (ESP), which requires a solenoid valve that is upstream of the inlet valve 9 and can be opened electromagnetically and de-energized. The following description is based on the example of a noise-optimized control of A / D inlet valves 9, although other possible uses are also 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 is required to empty the low-pressure accumulator. This prevents noise and irritation to the driver. A completely empty low-pressure accumulator is advantageous, for example, if an EBV control intervention (EBV = electronic brake force distribution) is required, with a certain volume to be absorbed, for example, from the wheel brakes of a rear axle in low-pressure accumulators. The return pump can thus - depending on the storage level - enable the empty delivery of the low pressure accumulator.

As a result of pressure reduction processes, an ABS regulation occurs via the outlet valve SG, 10

Pressure difference (Δp _profitable = Pτm ^~ P _ROΛ ^ ^a inlet valve SO, 9. The volume _escaping from the wheel brake 8 reaches the low-pressure accumulator 13, NDS. At the same time, the pump 14 is activated and promotes the drained volume - against the driver pre-pressure applied as a result of brake actuation - back again in the direction of pressure transmitter 3 and in front of the inlet valve 9. In this situation, the driver pre-pressure causes a resistance that increases affects the flow of the pump. With increasing pressure difference between pressure sensor 3 and wheel brake 8

(& P _pump ~ Pmz) the resistance increases, and at constant

_Pump output P _Pump and increasing pressure difference ψ _Pump the volume flow (V) drops. This relationship follows the relationship

"pump ⁼ AP pump ^' " ⁼ AP' umpe ^'n' * H '1)

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

Assuming low leakage losses, the speed n of the motor-pump unit (MPA) decreases with increasing pressure Ap _pump according to (1) with the same power P supplied. In other words, the maximum speed of the motor-pump unit is inversely proportional to the pressure increase. ⁿ MPA, mm ~ ^ 'AP' pump ( ² ) As can be seen from FIG. 2, this also applies to the stopping behavior of the motor-pump unit within a switch-off phase from the time Uk_ = 0. The amount of speed change per unit of time - that is, the speed gradient - increases with increasing pressure

^ Ψ Pump ^CLOSED -

Δn MPΛ ύφ At pump

As can be seen from the explanations below, the relationships described are used to form a pressure model by evaluating speed-equivalent information, which permits noise-optimized control. A direct measurement of pressure values can be avoided by using speed-proportional, electrical quantities of the motor in generator operation for modeling, in particular the gradient of the generator voltage, which is proportional to the gradient of the motor speed.

The electric motor 15 of the pump 14 is basically based on an externally excited direct current machine - in particular a permanent magnet excited commutator machine - the speed of which is controlled via pulse width modulation (PWM) of a constant terminal voltage U _κ ι. For speed control, the duration of the switch-on and switch-off phases according to the speed specification (= Requested_Pump_Speed) modulated in steps. A 12-stage speed control can be seen from FIG. 3, a full control of 100% corresponding to a so-called Requested_Pump_Speed of 12 with a switch-on phase over the entire aforementioned interval. From Requested_Pump_Speed <= 10, the motor 15 is controlled in a modulated manner. The armature voltage is interrupted cyclically. As Requested_Pump_Speed decreases, 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 operation (and thus the delivery capacity 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 _κ _) is generated as an regulator signal by means of an analog-digital converter. In the PWM switch-on phase, this signal corresponds approximately to the maximum available vehicle voltage. However, during a PWM switch-off phase, the motor 15 acts as a generator and, for example, a generator voltage U can be tapped from carbon brushes, the magnitude of which can provide information about the speed level. To evaluate the relationship

U _A = C _MaaΛ -. n + R _A -I _A (4)

the following assumptions are made: 1. The proportion of the armature current (I _Λ ) during generator operation is low and can therefore be neglected. 2. The excitation flow (Φ) and the motor constant (C _Masch ) are constant as design-related influencing variables, so that the equation (4) shows a proportionality between speed n and generator voltage U in generator mode:

^• UM: PΛflff

The above-mentioned relationship is confirmed by FIG. 4, in which the voltage U is plotted over time t. It also applies to the generator voltage that it is directly dependent on the speed of the motor 15 in a first deenergized loop (a certain subinterval of the aforementioned interval of 60 ms). The speed of the motor 15 is in turn influenced by the driver admission pressure and the pump load exerted thereby. As the driver admission pressure rises, the pump works against an increased resistance, and the speed and the associated tapped generator voltage U _OFF decrease. Because both U ₀ _ and U ₀ _ _{F are} pressure-dependent, the difference Δu = U _0N ^_ U _{0FF also} assumes characteristic, quasi- _{proportional values} for different admission pressures. The voltage difference is proportional to the driver pressure or the pressure increase to be applied. A value U _{0FF MIN} corresponds to the generator voltage in a last deenergized loop of an engine 15 _{shutdown phase} . From the values U ₀ FF, U _.FF MIN and the time Δt is the pressure-dependent gradient of the generator voltage t, anα “, U _{τ τOFF} = '-' OFF U OFF MIN ab, l.ei.t,, bar. .delta.t

In order to obtain the most meaningful statements possible for the noise-optimized control, it is advisable to take the following boundary conditions into account.

• Changing the speed of rotation: With frequently changed modulation of the PWM switch-on and switch-off phases (Requested_Pump_Speed), there are only short phases of a steady, constant speed level. This leads to a reduction in the evaluable database and thus to a deterioration in the quality of the model. The PWM modulation to be taken into account should be characterized by repeated intervals with largely identical modulation.

• Load state of the pump: Depending on the delivery state of the pump 14 (delivery in 2 brake circuits, delivery in one brake circuit or empty delivery, different motor loads occur, which leads to correspondingly changed speed and voltage constellations. Because of the differences between them However, load levels are striking, they can be recognized - for example via the amount of values recorded - and taken into account in the evaluation.

• Temperature: The decreasing kinematic viscosity of the brake fluid as the temperature rises means that the fluid becomes increasingly thin as the temperature rises and thus a lower load moment is generated on the pump than due to the tough brake fluid present in the cold. The lower load torque leads to higher speeds and thus lower voltage drops. The influence of temperature can also be recognized and taken into account.

The inversely proportional relationship between the values of U _on , U _of _, u _o f £ _min and the pressure increase Δp and the proportional relationship between the generator voltage gradient tan α U ₀ __ and the pressure increase Δp can be seen in FIG. 7.

Claims

claims

1. Electronic control method for a slip-controlled motor vehicle brake system (1) comprising a distribution device (5) with an electronics unit (7, ECU) and with a hydraulic unit (6, HCU) comprising a receptacle for hydraulic components such as, in particular, electro-hydraulic inlet and outlet valves (9 , 10) for wheel brakes (8), which are organized in brake circuits, and with a motor-pump unit with an electric motor (15), in particular for returning hydraulic fluid from wheel brakes (8) in the direction of a pressure sensor (3), taking into account an anti-lock control by means of pressure build-up, pressure maintenance and pressure reduction switch positions of the electrohydraulic inlet and outlet valves (9, 10) is made possible by a vehicle driver on the basis of the pressure transmitter (3) in the brake system, characterized in that a) the electronics unit (7) the motor (15) for speed control with defined electris Chen switched on and / or off phases, b) during a switch-off phase, a generator voltage generated by the motor (15) is tapped, c) the generator voltage (15) is supplied to the electronics unit (7), which is based on the determined generator voltage estimates the upstream pressure in the brake system in order to d) enable noise-optimized control of the electrohydraulic valves (9).

2. Control method according to claim 1, characterized in that the tapped generator voltage is viewed and evaluated in a defined time interval in order to assess the run-down behavior of the motor-pump unit, and that from the evaluated run-down behavior on the admission pressure load of the motor-pump unit is closed.

3. Control method according to claim 2, characterized in that the stopping behavior of the motor-pump unit is assessed by evaluating the amount of the generator voltage gradient within the defined time interval.

4. _Control method according to claim 3, characterized in that a time interval is defined via the relationship Δt = A * loop time - t _F , _ιnscha ι_ _{p ase} with, for example: loop time = 10 ms A = constant = 6 tRI n switching phase ⁼ 3 ms.

5. Control method according to claim 4, characterized in that the relationship t _E insohait _P hase <A * loop time is used for the time interval.

6. Control method according to claim 1, characterized in that the generator voltage gradient is proportional to the speed gradient.

7. Control method according to claim 1, characterized in that the speed gradient in generator operation increases proportionally with the form.

8. Control method according to claim 1, characterized in that the pulse width of electrical switch-on and / or switch-off phases is observed, and that switch-off phases are selected for tapping the generator voltage which have a matching pulse width in comparison with one or more adjacent switch-on phases and / or switch-off phases exhibit.