WO2010015379A1

WO2010015379A1 - Method for controlling a power unit of a vehicle steering system

Info

Publication number: WO2010015379A1
Application number: PCT/EP2009/005637
Authority: WO
Inventors: Jochen Gessat
Original assignee: Trw Automotive Gmbh
Priority date: 2008-08-04
Filing date: 2009-08-04
Publication date: 2010-02-11
Also published as: DE102008036261A1; DE102008036261B4

Abstract

A method for controlling a power unit of a vehicle steering system provides in a first step that at least one steering-relevant parameter (v, φ, M_L) is determined. In a second step, an additional parameter (PA) is determined, which is dependent on a trailer load of the vehicle. In a third step, a controlled variable (S) for the steering system of the vehicle is determined as a function of the at least one steering-relevant parameter (v, φ, M_L) and the additional parameter (PA). The method according to the invention is used to maintain the familiar steering feel for the driver during trailer operation of the vehicle and improve control of the vehicle.

Description

Method for controlling a power unit of a vehicle steering system

The invention relates to a method for controlling a power unit of a vehicle steering system, in particular a steering system for a vehicle with a trailer hitch. In modern hydraulic or electric steering systems is the

Control of the steering system depending on various steering-relevant parameters such. Steering angle, steering torque or vehicle speed. The functional relationship is stored in maps and determines the steering behavior of the vehicle. If a trailer is attached to a vehicle, this can significantly change the steering behavior of the vehicle. The driver experiences a changed steering feel and must adapt to this change quickly.

The object of the invention is to easily and inexpensively the

Operation of a steering system to improve so that when the trailer operation the driver gives a familiar steering feel or control over the vehicle is improved

This object is achieved by a method having the features of claim 1. Advantageous developments of the invention are defined in the dependent claims. The method according to the invention serves to control a power unit of a vehicle steering system, and comprises the steps of determining at least one steering-relevant parameter or a mathematical derivative of such a parameter after the time, determining an additional parameter that is dependent on a trailer load, and determining a manipulated variable for the steering system of the vehicle as a function of the at least one steering-relevant parameter and the additional parameter. With this method, it is possible in a simple manner to change the control of a power unit of a steering system in response to a trailer coupled to the vehicle, whereby trailer operation created for the driver a familiar steering feel and / or the control of the vehicle is improved by the driver.

The power unit may be a pump unit that is mechanically driven, e.g. through the internal combustion engine of the vehicle. Such a pump unit comprises a solenoid valve, which then acts on the manipulated variable. By means of acting on the solenoid valve

Control value, the pump flow rate can be controlled.

Alternatively, the power unit may be a so-called motor-pump unit (MPA) in which the pump is driven by an electric motor. In this case, the manipulated variable may be a rotational speed and / or a drive torque for the electric motor.

According to a further variant, the power unit may be an electric motor which cooperates with an actuator of a steering gear. The actuator is e.g. a rack of the steering gear. The interaction of electric motor and actuator or steering gear can be done via a suitable coupling. In other words, the electric motor may be coupled to the actuator or to the rack. If the electric motor is permanently coupled to the actuator, then, for example. a "stand-by mode", in which no power steering assistance is exerted on the actuator, thereby realizable that the electric motor is not driven.

According to the invention, the manipulated variable may be a torque and / or a rotational speed for an electric motor which acts directly or indirectly on the steering gear. A direct effect of the electric motor on the steering gear is given in an electromechanical vehicle steering system. In this case, the manipulated variable may be a rotational speed, a torque, a support torque or a restoring torque acting on the rack of the steering system. If the steering system is based on an electro-hydraulic principle, the manipulated variable may be a volume flow which is conveyed by a pump for a hydraulic circuit of this steering system. Furthermore, in an electro-hydraulic steering system, the manipulated variable may be formed by an attenuation acting on the hydraulic circuit. Regardless of which type the steering system is, the manipulated variable can also cause an automatic active steering torque. The steering-relevant parameter can be formed from the speed of the vehicle and / or from a respectively selected steering angle. Optionally, the steering-relevant parameter can also be formed from a mathematical derivation of the aforementioned variables according to time, for example as steering angle speed. If the power unit has an electric motor which acts directly or indirectly on the steering system, the steering-relevant parameter can also be formed from a drive torque acting on the electric motor.

In a preferred embodiment of the invention, the additional parameter, which depends on the trailer load of the vehicle, is a binary quantity which assumes a first value for a trailer coupled to the vehicle and a second value for a trailer without a trailer. In this way, the control of the vehicle's steering system can be switched between a "no trailer" control and a "trailer" control. In an advantageous development of the invention, in step c) the determination of the manipulated variable can take place via a predefined characteristic field in which a plurality of data values are stored, which depend on the steering-relevant parameters. The predetermined map is retrieved in particular for the case when no trailer is coupled to the vehicle and thus the trailer load is zero. By calculating the manipulated variable based on the predetermined characteristic field, it is particularly easy to specify the desired steering behavior of the vehicle for the driver.

In the event that a trailer is actually coupled to the vehicle and thus the trailer load is not equal to zero, in an advantageous embodiment of the invention, a data value of the predetermined map can be linked to a correction value in order to determine the manipulated variable. The correction value may be a factor by which a corresponding data value of the characteristic map is multiplied, wherein the factor may be greater or less than 1. Alternatively, the correction value may be a summand with which a corresponding data value of the characteristic map is added, wherein the addend may be greater or less zero, ie positive or negative. The concrete value for the correction factor or the summand is dependent on a respective trailer load of the vehicle, to a corresponding manipulated variable for the steering system to determine. Regardless of the variant, whether a corresponding data value of the predetermined characteristic field is suitably adapted by means of multiplication or addition in order to determine therefrom the manipulated variable, this ensures a simple algorithm. Instead of a data value of the given map by means of a

It is also possible to generate the manipulated variable via an alternative characteristic field as described above. For this purpose, an alternative map is deposited from the outset, which also depends on the steering-related parameters as well as the additional parameters. If in fact a trailer load is coupled to the vehicle and thus the additional parameter is not equal to zero, the alternative map is retrieved in step c) to determine the manipulated variable therefrom.

Advantageously, the additional parameter is determined by a sensor, whereby no activation by the driver of the vehicle is needed. Alternatively, it is possible that the additional parameter by a manual

Input is determined. This can be done for example via a operated by the driver of the vehicle switch. In this way, a separate sensor for the determination of the additional parameter can be omitted.

According to one of the preferred embodiments, the steering system is an electro-hydraulic vehicle steering system. Preferably, the electro-hydraulic steering system comprises a hydraulic circuit with a pump or a

Motor pump unit as a power unit, depending on the

Actuating value of. the volume flow delivered by the pump varies. A control of the volume flow can easily via a motor pump unit with variable speed and / or variable displacement or a

Pump with a throttle valve, e.g. in the form of a solenoid valve, and or or a variable delivery volume happen.

According to a further preferred embodiment, the steering system is an electromechanical steering system in which the power unit is coupled in the form of an electric motor directly to the steering gear. In this way, a steering torque can be calculated as the manipulated variable and its calculation can be made dependent on the additional parameter in a variety of ways. The invention will be described below with reference to the accompanying drawings.

Show it:

1 is a schematic view of an electro-hydraulic steering system controlled by a method according to the invention,

Fig. 2. a method for controlling a steering system according to a

Embodiment of the invention, and

FIG. 3 shows a method for controlling a steering system according to a further embodiment of the invention. FIG

Figure 1 shows an electro-hydraulic vehicle steering system 10. A steering wheel 12 is connected via a steering column 14 with a servo valve 16 and a pinion 18 which meshes with a rack 20. The servo valve 16 is connected via a hydraulic circuit 21 to a power unit in the form of a motor / pump unit 22, a reservoir 24 and a hydraulic actuating cylinder 26. The motor pump unit 22 includes an electric motor 36 and a pump 23 that is driven by the electric motor 36. The function of the vehicle steering system 10 is determined by the position of the servo valve 16 and the volume flow delivered by the pump 23 of the motor / pump unit 22.

There is a steering sensor 32 is provided, which is attached to the steering column 14 and a steering angle! φ or a steering angle speed φ and / or a steering torque M _L determined, and a speed sensor 33 which determines a vehicle speed v. The motor pump unit 22 has a control unit 28 which controls the motor pump unit 22 in accordance with a method according to the invention. For this purpose, the control unit 28 receives a signal from a trailer sensor 34, which is arranged for example on the trailer hitch of the vehicle, from this signal, the trailer-dependent additional parameter P _{A is} determined. In addition, the control unit 28 receives at least one steering-relevant parameter, the vehicle speed v, steering angle φ and / or Steering torque M _L can be formed. Alternatively, the steering-relevant parameter may also be formed from a mathematical derivation of vehicle speed v and / or steering angle φ according to time, eg as steering angular velocity ψ. An advantageous variant of the method for controlling the electrohydraulic vehicle steering system 10 is shown in FIG. In a first method step, a vehicle speed v, a steering angle φ and a steering torque M _{L are determined} as steering-relevant parameters v, φ, M _L. It is possible to determine further less steering-relevant parameters, whereby certain steering-relevant parameters can be replaced by other steering-relevant parameters.

In a second step 30, an additional parameter P _{A is} determined, which is dependent on a possibly trailer load of the vehicle and transmitted to the control unit 28. The additional parameter P _A is determined, for example, by an automatic parameter detection by the trailer sensor 34. The additional parameter P _A can be a binary variable which assumes a first value for a trailer coupled to the vehicle and a second value without a trailer. Alternatively, it is also possible that the additional parameter P _{A is} not detected sensory, but by the driver of the vehicle manually, for example via a switch is specified. The manual parameter specification is particularly useful when the additional parameter P _{A is} a binary size that only distinguishes between a driving with or without trailer. The additional parameter P _A can also be of a different kind, for example a continuous variable as a function of the load on the trailer hitch. In a symbolized in Figure 2 by the rhombus 40 third step is the

(binary) additional parameters P _A checked. Depending on the value of the additional parameter P _A , a map K ₀ or K _{1 is} selected for the calculation of the manipulated variable S.

If no trailer is coupled to the vehicle, the map K _{0 is} selected in step 42 (FIG. 2) which depends on the steering-relevant

Parameters v, φ, M _{L determines} the manipulated variable S for the vehicle steering system 10.

The map K ₀ may contain a plurality of data values that make up in

Dependence of the parameters v, φ, M _L then the manipulated variable for the steering system is determined suitably. It is also possible for a plurality of characteristic maps K _{0 to be} provided if different steering modes are provided for the vehicle steering system 10, for example a comfort or sports mode selectable by the driver. If a trailer is attached to the vehicle, instead of the

Map K ₀ in step 44 (Fig. 2) selected the map Ki, which in turn depends on the steering-related parameters v, φ, M _L , but differs from the map K ₀ . The maps K ₀ and / or K ₁ can be formed with the aid of empirical driving tests. If both characteristic maps K ₀ and K _{1 are} empirically formed with the aid of such driving tests, the respective driving tests may differ from one another, ie driving test without or with trailer load. It is not necessary for the two maps K ₀ and K ₁ that they are both dependent on the same steering-relevant parameters. It is therefore also possible that a map K ₀ or K ₁ is independent of one or more parameters.

In the case of the vehicle steering system 10 shown in FIG. 1, the manipulated variable S corresponds to the volume flow in the hydraulic circuit 21 conveyed by the motor pump unit 22. However, the manipulated variable S can also be formed from other physical values as a function of a corresponding embodiment of the steering system. For example, the manipulated variable, a pressure in a cylinder chamber of the hydraulic actuating cylinder 26 or the torque for the electric motor 36th

FIG. 3 shows an alternative embodiment of the method according to the invention. Step 30 corresponds to the representation of FIG. 2. If it is determined in step 40 that the trailer load and thus the additional parameter are not equal to zero, the method continues with step 46, in which the data of the predetermined characteristic field K ₀ are used becomes. Subsequently, in step 48, a corresponding data value of this characteristic field is combined with a correction value W _{K in} order then to determine the desired manipulated variable as a result. The steps 46 and 48 correspond to the step c), according to the definition of claim 1. The correction value W "can be formed from a factor with which a corresponding data value of the predetermined characteristic field K _{0 is} multiplied. Depending on a particular driving situation of the vehicle, this factor is greater or smaller 1. Alternatively, the correction value may be formed from a summand with which a corresponding data value of the predetermined characteristic K _{0 is} added. Depending on a respective driving situation of the vehicle, the summand may be greater or less zero, ie positive or negative. From the result of such a multiplication or addition of a corresponding data value of the map K ₀ , the manipulated variable S can then be determined.

Claims

claims

A method for controlling a power unit for a vehicle steering system, comprising the steps of: a) determining at least one steering-relevant parameter (v, φ, M _L ) or a mathematical derivative (v, φ) of such a parameter after

Time, b) determining an additional parameter (P _A ), which is dependent on a trailer load, and c) determining a manipulated variable (S) for the steering system of the vehicle as a function of at least one steering-relevant parameter (v, φ, M _L ) and Additional parameters (P _A ).

2. The method according to claim 1, characterized in that the additional parameter (P _A ) is a binary size, which assumes a second value with an existing trailer load a first value and without a trailer load.

3. The method according to claim 1 or 2, characterized in that in step c) the determination of the manipulated variable (S) via a predetermined characteristic field (K ₀ ), which depends on the at least one steering-relevant parameter (v, φ, M _L ) ,

4. The method according to claim 3, characterized in that in step c) a data value of the characteristic field (K ₀ ) with a correction value (W _κ ) is linked to determine therefrom the manipulated variable (S).

5. The method according to claim 4, characterized in that the correction value (W _κ ) is a factor with which a corresponding data value of the characteristic map (K ₀ ) is multiplied.

6. The method according to claim 4, characterized in that the correction value (W _κ ) is a summand with which a corresponding data value of the characteristic map (K ₀ ) is added.

7. The method according to claim 1 or 2, characterized in that in step c) the determination of the manipulated variable (S) via an alternative map (K ₁ ) takes place, which depends on the at least one steering-relevant parameter (v, φ, M _L ) and on the additional parameter (P _A ).

8. The method according to any one of claims 1 to 7, characterized in that the additional parameter (P _A ) by a sensor (34) is determined.

9. The method according to any one of claims 1 to 8, characterized in that in step b) the trailer-dependent additional parameter (P _A ) is determined by a manual input.

10. The method according to any one of claims 1 to 9, characterized in that the manipulated variable (S) is a rotational speed, a geometric pump delivery volume, a torque, a Unterstüzungsmoment and / or a restoring torque for the power unit.

11. The method according to any one of claims 1 to 10, characterized in that the power unit is a pump unit comprising a solenoid valve.

12. The method according to any one of claims 1 to 10, characterized in that the power unit is a motor pump unit, wherein the pump is driven by an electric motor.

13. The method according to any one of claims 1 to 10, characterized in that the power unit is an electric motor which can be coupled to an actuator of a steering gear.

14. Steering system with a power unit which is operable by a method according to one of claims 1 to 13.