WO2018054572A1

WO2018054572A1 - Method and device for operating a power-steering system of a motor vehicle, and power-steering system

Info

Publication number: WO2018054572A1
Application number: PCT/EP2017/068103
Authority: WO
Inventors: Marian Eirich; Reinhard Grossheim; Arnulf Heilig
Original assignee: Robert Bosch Automotive Steering Gmbh
Priority date: 2016-09-21
Filing date: 2017-07-18
Publication date: 2018-03-29
Also published as: CN109715475A; DE102016117748A1; CN109715475B

Abstract

The invention relates to a method for operating a power-steering system (1) of a motor vehicle, comprising a steering element (9) and an electric motor (10) for actuating at least one steerable wheel (2) of the motor vehicle with a steering torque, a supporting target motor steering torque (M_M) being predefined for the electric motor (10) according to a manual steering torque (M_H) applied to the steering element (9). According to the invention, the manual steering torque (M_H) is monitored and the target motor steering torque (M_M) is adjusted according to the manual steering torque (M_H) in such a way that the manual steering torque (M_H) does not exceed a predefinable threshold value (M_HG) during normal operation, the target motor steering torque (M_M) being limited to a predefinable maximum value (M_{M_max}).

Description

Description title

Method and device for operating a power steering system of a motor vehicle, power steering system

The invention relates to a method for operating a power steering system of a motor vehicle, the steering handle and an electric motor for

Actuation of at least one steerable wheel of the motor vehicle having a steering torque, wherein the electric motor is given a supporting motor steering torque depending on a hand steering torque applied to the steering handle.

Furthermore, the invention relates to an apparatus for operating such a power steering system and such a power steering system.

State of the art

Methods, devices and power steering systems of the type mentioned are known from the prior art. In order to assist the driver of a motor vehicle in steering, it is known to generate an assist steering torque in addition to a manual steering torque applied by the driver in order to simplify the steering of the vehicle for the driver.

As a result, it is achieved, in particular, that the driver only has to expend a smaller amount of force in order to adjust or pivot the steering wheel or wheels of the motor vehicle about a desired steering angle. For a long time, a hydraulic system was usually used to generate the assist steering torque, assisting the driver in steering by hydraulic pressure. With the increasing electrification of motor vehicles now also electromotive assistance devices are being developed and used which an electric assistive steering torque produce. The use of the electric motor has the advantage of simplified wiring and increased reliability compared to hydraulic systems. However, the reliability is also highly dependent on the control of the electric motor or a corresponding software programming, the failure of the

To avoid steering assistance. In particular, it is to be avoided that in the event of a sudden failure of the electromotive assistance device, the driver is confronted with a suddenly occurring counter-torque on the steering handle.

Disclosure of the invention

The inventive method with the features of claim 1 has the advantage that overcomes the disadvantage described above and the

Driving safety of the motor vehicle is increased. In particular, it is achieved that the driver is not affected by a sudden failure of the electromotive

Support can be surprised. According to the invention, it is provided for this purpose that the manual steering torque is monitored and the setpoint engine steering torque is set as a function of the manual steering torque such that the manual steering torque does not exceed a predefinable limit value, the setpoint engine steering torque being limited to a predefinable maximum value.

This ensures that the supporting motor steering torque is adjusted when the manual steering torque exceeds the specified limit or threatens to exceed. Until the limit value is reached, no desired engine steering torque is set, since in this case there is no faulty behavior in the electromotive assistance system and the steering torque can be well controlled by the driver. If the limit value of the driver's manual torque is exceeded, a target engine steering torque is set if the already set engine torque of the electromotive assistance system is less than a maximum value of, for example, 2 Nm, this is the case in the case of a malfunction of the electromotive assistance system, in normal operation, this case does not occur , The target engine torque is set so that the limit of the driver's manual torque is not significantly exceeded. The limit value of the driver's manual torque is chosen so that the driver can still master this moment well. The limitation of the nominal motor steering torque to a predefinable value takes place, since the functionality is intended to provide the desired engine steering torque only in the event of a fault, and influencing the steering feel during normal operation is not desired. In addition, with a limited target engine steering torque to, for example, 1/3 of the maximum engine torque, the vehicle at speeds greater than 0 km / h is still manageable in any situation. In particular, it is provided that as a limit for the

Hand steering torque 5Nm to 15Nm, in particular 8Nm be specified.

Due to the fact that with this functionality driver's torques> 8 Nm are prevented in the case of a support failure due to, for example, a software error, one after a fault is also abrupt

reintroduced support controllable by the driver, since then changes the driver's manual torque only from 8Nm to, for example, 3Nm, without the advantageous embodiment of the invention, a short-term software support failure would suddenly cause very high hand moments of> 30 Nm, a sudden onset of support could be a sudden reduction the driver's hand torque from 30 Nm to 3 Nm, both situations are difficult to control by the driver.

According to a preferred development of the invention, it is provided that the maximum value for the nominal motor steering torque 0.5Nm to 4Nm, in particular l, 5Nm be specified. The desired engine steering torque is thus limited so that this moment is sufficient to control the vehicle while driving in any driving situation with a driver's manual torque of less than 8 Nm, for example.

According to an advantageous development of the invention, it is preferably provided that the desired engine steering torque is reduced when a maximum steering angle of the steerable wheel is reached. This prevents that in the Endanschlagsbereich the wheel is not a real end stop

is exceeded or deflected. As a result, the steering system is protected, for example, from damage. Furthermore, it is preferably provided that the motor steering torque is reduced when reaching the maximum steering angle with a predetermined gradient. As a result, when the maximum steering angle is reached, the driver feels an increased counter-torque or has to increase the manual steering torque. This gives the driver a simple way that the maximum steering angle is reached or will be reached shortly.

Preferably, the target engine steering torque by a

predetermined / predeterminable gradient increases when the driver wants to reset from the maximum steering angle out the wheel by applying a corresponding manual steering torque.

Furthermore, it is preferably provided that the reduction of

Motor steering torque before reaching the maximum steering angle begins. This ensures that the driver is alerted in good time to the speed of reaching the maximum steering angle.

According to a preferred embodiment of the invention is also

provided that the electric motor is driven to a

To generate damping torque when the manual steering torque is below the limit, in particular below a further limit below the one limit. Thus, a damping torque is provided in the range of low manual steering torque, which allows comfortable operation of the steering system for the driver even at low manual steering torque. The electric motor is thus controlled in particular also at manual steering torque below the predetermined limit value to provide a supportive, in this case damping, engine steering torque available. Preferably, the provided damping torque is set lower than the assisting engine steering torque. If, due to a correspondingly high manual steering torque, the electric motor is already activated anyway, then advantageously no additional damping torque is generated so as not to influence the desired steering behavior.

The device according to the invention with the features of claim 8 is characterized by a specially prepared control unit, which is designed, when used as intended, the inventive method perform. This results in the already mentioned advantages. For detecting the manual steering torque, the device has in particular a torque sensor, in particular a torque sensor of the steering system, in order to detect the manual steering torque.

The steering system according to the invention with the features of claim 9 is characterized by the device according to the invention. This results in the already mentioned advantages.

Further advantages and preferred features and combinations of features emerge in particular from the previously described and from the claims. In the following, the invention will be explained in more detail with reference to an embodiment. Show this

1 shows a steering system of a motor vehicle in a simplified representation,

2 shows a method for operating the motor vehicle in a simplified representation and

3 shows the advantageous method in a flowchart.

FIG. 1 shows, in a simplified representation, a power steering system 1 for two steerable wheels 2 of a wheel axle of a wheel axle not shown here

Motor vehicle. The wheels 2 are supported by a respective suspension 3 pivotally mounted on the motor vehicle. By a respective

Articulated rod 4, each of the wheels is also connected to a steering gear 5. The steering gear 5 has a rack 6, which is coupled at its two ends with one of the hinge rods 4. With the rack 6 is a pinion 7 is engaged, which is rotatably connected to a handlebar 8, which also carries a steering handle 9 in the form of a usable by a driver steering wheel. As soon as the driver exerts a manual steering torque MH on the steering handle 9, as shown by a double arrow, he turns the handlebar 8 at an adequately high manual steering torque by an angle α and thus the pinion 7, whereby the rack 6 of the steering gear 5 is displaced and the wheels 2 are pivoted about a steering angle corresponding to the translation ß.

The power steering system 1 is designed as an electromotive power steering system 1 and has for this purpose an electric motor 10 as an actuator A, whose

Rotor with the handlebar 8 is directly or indirectly operatively connected. Of the

Electric motor 10 has a power electronics 11, which is controlled by a control unit 12 for operating the electric motor 10. The control unit 12 also detects data of a torque sensor 13, which is assigned, for example, the handlebar 8 to detect the applied by the driver on the steering wheel manual steering torque MH ZU. In response to the detected manual steering torque MH, the control unit 12, the electric motor 10 by the power electronics 11, a target engine steering torque MM before that of the

Electric motor 10 generates and transmitted directly or via a transmission to the handlebar 8 and thus superimposed on the manual steering torque. That of the

Control unit 12 performed method thus facilitates the driver driving the power steering system 1 having motor vehicle. Furthermore, the control unit 12 detects output signals of a sensor device 14 for detecting a rotational angle of a rotor R of the electric motor 10, wherein the rotational angle is used for controlling and regulating the electric motor 10.

The structure of the power steering system 1 presented here is to be understood as purely exemplary. Of course, the sensors and also the electric motor can be arranged elsewhere in the power steering system 1.

According to the present embodiment, the controller 12 performs the method illustrated in FIG. This method according to FIG. 2 is used, for example, as protection of systematic software errors in the

Steering support algorithm, parallel to the actual

Steering support algorithm performed. The procedure begins in step

Sl with the commissioning of the power steering system 1. By means of the

Torque sensor 13 detected data monitors the control unit 12 applied to the steering handle 9 manual steering torque MH and compares it in a step S2 with a predetermined limit MHG. Approaches the manual steering torque MH to the predetermined limit MHG, in this case of At a subsequent step S3, the control unit 12 controls the electric motor 10 to generate an assisting setpoint engine steering torque MM, so that the manual steering torque MH does not exceed the predetermined limit value MHG. In addition, it is monitored whether the sum of steering assistance and additional setpoint engine steering torque MM exceeds a predefinable maximum value MM_max. In the present case, the maximum value given is a maximum value of MM_max = 2Nm. Subsequently, the method is continued in a step S4, in which a current steering angle ß of the steerable wheels 2 is monitored. In this case, the current steering angle ß is compared with a maximum steering angle stop ß _ma x. Achieved the set steering angle ß the steering angle stop ß _ma x, the target motor steering torque MM is reduced in a subsequent step S5, the reduction is preferably not abruptly, but gradient-related, and wherein the reduction is in particular already started before reaching the maximum steering angle, so that the driver gets a feeling early by an increased counter-torque on the steering handle 9, that the maximum steering angle ß _ma x is reached soon.

If the permissible maximum value MM_max for the setpoint engine steering torque MM is exceeded in step S3, a warning message is advantageously output in step S6, which alerts the driver that an error has occurred, such as one of the wheels 2 against a Curb is pivoted. It is assumed that in

Normal operation of the motor vehicle or the power steering system 1 is a Stützungslenkmoment or motor steering torque of more than l, 5Nm is not necessary. However, if the engine steering torque MM exceeds the predetermined maximum value MM_max, it is recognized that an exceptional case must be present, whereupon the driver is alerted.

The method therefore provides that a manual steering torque MH, which exceeds the predetermined limit value MHG, in driving operation by the

Power steering system 1 is actively prevented by driving the electric motor 10 by an additional motor steering torque MM is generated in the direction of support. The manual steering torque is in particular by a PID controller adjusted. The manipulated variable with respect to the steering angle β, ie the target engine steering torque MM, is reduced in the end-stop range, ie in the region of the maximum steering angle β _ma , so that it is not deflectable

End stop is realized. In particular, the manipulated variable is reduced by an overall reduction factor, thereby enabling deceleration and ramp-in

System startup or system shutdown can take place. For this purpose, a gradient monitoring of the manipulated variable signal is preferably carried out. It is thereby achieved that for the sudden failure of the electromotive support, for example, by a systematic software error, no risk to the driving occurs, because then any possibly occurring counter-torque can be easily overcome by the driver.

The fact that a manual steering torque MH of more than 8 Nm is not allowed, is also a sudden activation of the electromotive

Support no longer critical. With correspondingly high hand steering torque causes the sudden addition of the electric motor no

safety-critical effect, the driver can do the extra

Just compensate the moment of support. In addition, the provision of a Dämpfungslenkmoments at low hand steering torque ensures a comfortable operation, in which case if a high

Manual steering torque is detected, and the electric motor 10 is driven towards generating a motorized steering torque to an additional

Damping torque is omitted so as not to influence the desired steering behavior. This is also the loss of damping by the

Power steering system counteracted in case of an error in the control.

FIG. 3 shows in a further flowchart the integration of the advantageous method into a conventional drive structure of a power steering system. In a first step AI, the manual steering torque MH and the setting angle α of the steering handle 9 and optionally further input signals X are detected and evaluated to determine the desired engine steering torque MM. Usually, the target engine steering torque is provided directly to the engine control B available, which depending on the target engine steering torque MM

Electric motor 10 drives. To implement the advantageous method, an additional security controller C is provided, which also by the

Steering controller A certain target engine steering torque MM and the

Manual steering torque MH receives. The security controller is the control unit 12, which performs the method described above and in

Dependence of the manual steering torque MH sets the desired engine steering torque MM such that the manual steering torque MH does not exceed the predefinable limit value MHG in normal operation, and limits the desired engine deflection torque MM to the predefinable maximum value MM_max, as already described above. The output torque of the safety controller C is output only when the output torque of the steering controller A is smaller than the calculated

The output torque of the safety controller is, thus ensuring that the safety controller normally does not intervene, but only in the case of, for example, a systematic software error in the steering controller A. Das

Output torque of the safety controller is added to the output torque of the steering controller.

Claims

claims

1. A method for operating a power steering system (1) of a motor vehicle having a steering handle (9) and an electric motor (10) for applying at least one steerable wheel (2) of the motor vehicle with a

Steering torque, wherein, depending on one of the

Steering handle (9) applied hand steering torque (MH) the electric motor (10) is given a supporting target engine steering moment (MM), characterized in that the manual steering torque (MH) monitors and the target engine steering torque (MM) in dependence of the manual steering torque (MH) is set such that the manual steering torque (MH) does not exceed a predeterminable limit value (MHG) in normal operation, wherein the setpoint motor steering torque (MM) is limited to a predefinable maximum value (MM_max).

2. The method according to claim 1, characterized in that as limit value (MHG) for the manual steering torque (MH), a limit value (MHG) of 5 to 15Nm, in particular 8Nm, is specified.

3. The method according to any one of the preceding claims, characterized

in that a value (MM_max) of 0.5 to 4 Nm, in particular 1.5 Nm, is specified as the maximum value (MM_max) for the setpoint engine steering torque (MM).

4. The method according to any one of the preceding claims, characterized

in that the setpoint engine steering torque (MM) is reduced when a maximum steering angle (β _ma x) is reached.

5. The method according to any one of the preceding claims, characterized

in that the setpoint engine steering torque (MM) is reduced when the maximum steering angle (βmax) is reached with a predefinable gradient.

6. The method according to any one of the preceding claims, characterized

characterized in that the reduction of the desired engine steering torque (MM) before reaching the maximum steering angle (ß _ma x) begins.

7. The method according to any one of the preceding claims, characterized

in that the electric motor (10) is activated to generate an attenuation torque (MMD) if the manual steering torque (MH) is below the limit value (MHG), in particular below a further limit value lying below the one limit value (MHG).

8. An apparatus for operating a power steering system (1) of a motor vehicle having a steering handle (9) and an electric motor (10) for applying a steerable wheel (2) of the motor vehicle with a steering torque, characterized by a specially prepared control unit (12), which is adapted to carry out the method according to one of claims 1 to 7 under normal use.

9. power steering system (1) for a motor vehicle, with a steering handle (9) and an electric motor (10) for applying at least one steerable wheel (2) of the motor vehicle with a steering torque, characterized by the device according to claim 8.