DE102017216504A1 - A method of operating a power steering system and power steering system - Google Patents

Abstract

A method for operating a power steering system, in particular an electromechanically assisted power steering system, is proposed. The power steering system includes a steering wheel, a steering column, and a servomotor that temporarily assists manual torque (M _H ) with additional assist torque during steering by additional servo torque and in predefined vehicle conditions. First, an entire current torque acting on the steering column is determined. Furthermore, an assistance torque is determined with which at least one assistance system acts on the steering column via the servomotor. An operating point (P) is determined from the total torque acting on the steering column and the assistance torque. Subsequently, a maximum and a minimum allowable servo motor torque (M _{M, max} , M _{M, min} ) is determined and the current servo motor torque (M _M ) is reduced to at most the determined maximum allowable servo motor torque (M _{M, max} ) via driving the servomotor. Further, a power steering system is proposed.

Description

The invention relates to a method for operating a power steering system, in particular an electromechanically assisted power steering system. The invention further relates to a power steering system, in particular an electromechanically assisted power steering system.

In partially self-propelled motor vehicles, assistance systems apply torque to the steering column via a servomotor, so that the vehicle is assisted or partially autonomously steered. In cooperative driving, ie in vehicles of the autonomy levels 2 and 3 according to BASt (assisted driving or semi-automated driving), the servo motor torque must be limited so that the torque applied to the steering wheel remains manageable for the driver.

According to a method of the prior art, for this purpose, an upper and a lower limit of the servomotor torque is determined empirically in a driving test and applied across driving situations.

However, the effect of the servomotor torque varies depending on the driving situation (e.g., cornering or straight ahead) and the characteristic of the steering assistance, whereby optimal servomotor support is not achieved in all driving situations.

The object of the invention is therefore to provide a method for operating a power steering system, is provided in the driving situation across optimal support by the servo motor.

• Bestimmen eines gesamten auf die Lenksäule wirkenden aktuellen Drehmoments,
• Bestimmen eines Assistenzdrehmoments, mit dem wenigstens ein Assistenzsystem die Lenksäule über den Servomotor beaufschlagt,
• Bestimmen eines Arbeitspunktes aus dem gesamten auf die Lenksäule wirkenden Drehmoment und dem Assistenzdrehmoment,
• Bestimmen eines maximal und eines minimal erlaubten Servomotordrehmoments, und
• Reduzieren des aktuellen Servomotordrehmoments auf höchstens das bestimmte maximal erlaubte Servomotordrehmoment über Ansteuern des Servomotors.

The object is achieved by a method of the type mentioned above, wherein the power steering system comprises a steering wheel, a steering column and a servo motor, which supports the manual torque when steering by an additional servo torque and in predefined vehicle states temporarily by an additional assist torque, with the following steps:

• Determining an entire current torque acting on the steering column,
• Determining an assistance torque with which at least one assistance system acts on the steering column via the servomotor,
• Determining an operating point from the total torque acting on the steering column and the assist torque,
• Determining a maximum and a minimum allowable servo motor torque, and
• Reducing the current servo motor torque to at most the certain maximum allowed servo motor torque via driving the servomotor.

This ensures that the torque expressed on the steering wheel, which is applied by the servomotor, always lies in an area which can be controlled by the driver. In particular, it is prevented that the servomotor applies too much torque and the steering wheel is twisted against the will of the driver.

Preferably, for determining the maximum and the minimum allowable servo motor torque, a steering gain curve and the determined operating point are used. As a result, it is possible to prevent driving situation-spanning that the servomotor acts on the steering column and thus the steering wheel with excessive torque. In addition, the maximum and the minimum allowable servo motor torque are determined depending on the driving situation (for example, cornering or straight-ahead driving), whereby the steering assistance by the servomotor can be optimally adapted to any driving situation.

According to one aspect, it is provided that, based on the determined minimum allowable servo motor torque, the servomotor is driven such that the current servo motor torque does not fall below the minimum allowable servo motor torque. This additionally prevents the servomotor from providing too little torque to assist the driver in steering the motor vehicle.

A further aspect provides that, to determine the operating point, the difference is formed from the specific total torque acting on the steering column and the determined assistance torque. The difference between the two quantities gives the sum of manual torque, with which the driver acts on the steering wheel, and servo torque. Each operating point is unambiguously, in particular one-to-one, assigned to such a sum, so that the operating point can be determined particularly easily in this way.

According to one embodiment, the gain curve of the steering system is used to determine the operating point. The particular operating point corresponds to the point on the gain curve associated with the manual torque currently applied by the driver. On the other hand, the specific operating point corresponds to the point which is assigned to the servo torque, that is to say the servomotor torque adjusted by the assistance torque. By using the gain curve to determine the operating point, Depending on the driving situation, the optimum steering assistance can be set by the servomotor.

Preferably, a predefined maximum controllable torque is used to determine the maximum and minimum allowed servo motor torque. This ensures that the driver can control a torque which manifests itself on the steering wheel, with which the servomotor acts on the steering column, across driving conditions.

It is further preferred that, starting from the manual torque assigned to the operating point, the predefined maximum controllable torque is added or subtracted in order to determine the maximum or the minimum permitted servo motor torque, wherein the minimum permitted servo motor torque corresponds to the servo motor torque that is in the gain curve of the difference Hand torque is assigned at the operating point and predefined maximum controllable torque, and wherein the maximum allowable servo motor torque corresponds to the servo motor torque that is assigned in the gain curve of the sum of manual torque at the operating point and predefined maximum controllable torque. As a result, depending on the driving situation, the optimal limits for the servomotor torque are always determined, so that the servo motor torque set by the servomotor is always in an optimum range that can be controlled by the driver.

In one aspect of the invention, the total torque acting on the steering column is measured by means of a torque sensor of the steering system. As a result, the entire torque acting on the steering column is available as a measured variable for the steps of the method and does not have to be determined from data from other sensors of the steering system.

Another aspect provides that the steps of the method are repeated at certain intervals, in particular wherein the time intervals are selected such that the steps of the method are repeated continuously. In other words, it is continuously checked whether the current servo motor torque is within a permitted range defined by the maximum and minimum permitted servo motor torque. As a result, the servo motor torque can be quickly adapted to changes in the driving situation (for example, transition from cornering to straight ahead driving).

The object is further achieved according to the invention by a power steering system of the type mentioned, wherein the steering system comprises a steering wheel, a steering column and a servo motor, and wherein the steering system is adapted to carry out the method described above. With regard to the advantages, reference is made to the above explanations.

• - 1 ein schematisches Ablaufdiagramm der Schritte eines erfindungsgemäßen Verfahrens; und
• - 2 eine Verstärkungskurve eines erfindungsgemäßen Servo-Lenksystems, mit der auch das erfindungsgemäße Verfahren arbeitet.

Further advantages and features of the invention will become apparent from the following description and the drawings, to which reference is made. In these show:

• - 1 a schematic flow diagram of the steps of a method according to the invention; and
• - 2 a gain curve of a servo steering system according to the invention, with which also the inventive method works.

The following is based on the 1 and 2 a method for operating a power steering system, in particular an electromechanically assisted power steering system described.

The power steering system includes a steering wheel, a steering column, and a servomotor. The power steering system is intended for use in a motor vehicle having additional assistance systems for at least partially autonomous driving. An example of such an assistance system is a lane keeping assistance system that assists the driver in maintaining a lane.

Such assistance systems apply an assist torque to the steering column in predefined vehicle states via the servomotor to assist the driver in steering the motor vehicle.

The assist torque acts in addition to the servomotor also applied servo torque on the steering column, which assists the driver when driving the motor vehicle. An entire torque acting on the steering column is thus given by the sum of the manual torque with which the driver acts on the steering column, the servo torque and the assist torque.

So that a total servo motor torque exerted by the servomotor on the steering column M _M (Sum of servo torque and assist torque) is always within a range that is manageable and surmountable by the driver, the following steps are performed:

First, the total torque acting on the steering column is determined (step S1 , please refer 1 ). This can be done by means of a torque sensor of the servo steering system. Alternatively, the entire torque acting on the steering column from a relative rotation angle between a upper and a lower end of a torsion bar of the steering column can be determined.

In addition, an assist torque is determined with which at least one assistance system acts on the steering column via the servomotor (step S2 ). If several assistance systems actuate the steering column via the servomotor with an assistance torque, the total assist torque is determined, ie the sum of the individual assist torques.

In the following, the assistance torque is mentioned, so it is always meant the entire assistance torque.

In a correspondingly operating control, the above and subsequent steps are carried out.

The assistance torque is determined, for example, from control data of the at least one assistance system. For this purpose, it may be provided that control cams and / or control tables are stored in a control unit of the at least one assistance system which, depending on the driving situation, contains, in particular depending on operating parameters of the motor vehicle, the assistance torque applied by the assistance system via the servomotor.

The operating parameters may include a speed of the motor vehicle, a longitudinal acceleration of the motor vehicle, a lateral acceleration of the motor vehicle, a steering angle, a steering angular acceleration and / or signals from optical systems (for example an external camera) of the motor vehicle.

Now, an operating point P is determined from the determined total torque acting on the steering column and the determined assist torque (step S3 ). In addition the in 2 shown gain curve 10 used. The gain curve 10 describes the relationship between manual torque M _H and the additional servo motor torque applied by the servo motor M _M , The gain curve 10 can be stored in a control of the power steering system.

The particular operating point P corresponds to the point on the gain curve 10 , the manual torque currently applied by the driver M _H assigned. On the other hand, the specific operating point P corresponds to the point which is assigned to the servo torque, that is to say the servomotor torque adjusted by the assistance torque M _M ,

In order to determine the operating point P, the difference may be formed from the determined total torque acting on the steering column and the assist torque. Because every point on the gain curve 10 clearly, especially one-to-one, a sum of manual torque M _H and Servo torque represents, can be determined from this difference clearly the operating point.

Now, a maximum allowable servo motor torque will be M _{M, max} and a minimum allowable servo motor torque M _{M, min} determined (step S5 ). For this purpose, a predefined maximum controllable torque M _{H, max} used. The predefined maximum controllable torque M _{H, max} refers to the torque that the driver can still control, ie the torque to which the hand torque M _H maximum of the working point P associated with manual torque M _H may deviate. The predefined maximum controllable torque M _{H, max} For example, 1 Nm to 10 Nm, in another example 2 Nm to 5 Nm. The maximum and minimum allowed servo motor torque M _{M, max} respectively. M _{M, min} define a permitted torque range.

Around the maximum and minimum allowable servo motor torque M _{M, max} respectively , M _{M, min} in the control, accordingly, the predefined maximum controllable torque M _{H, max} to the working point P associated with manual torque M _H added or from the working point P associated with manual torque M _H subtracted. The maximum allowed servo motor torque M _{M, max} is then the servo motor torque M _M that in the boost curve 10 the sum of manual torque M _H at the specific operating point P and the predefined maximum controllable torque M _{H, max} assigned. Analog is the minimum allowable servo motor torque M _{M, min} the servo motor torque M _M that in the boost curve 10 the difference between manual torque M _H at the specific operating point P and the predefined maximum controllable torque M _{H, max} assigned.

The current servo motor torque M _M Will now with the maximum and minimum allowable servo torque M _{M, max} respectively. M _{M, min} compared.

Exceeds the current servo motor torque M _M the maximum allowed servo motor torque M _{M, max} , so the servo motor is driven so that the servo motor torque M _M at most the maximum allowed servo motor torque M _{M, max} is reduced (step S5 ). The servo motor is thus controlled such that the current servo motor torque M _M is brought into the permitted torque range.

Below the current servo motor torque M _M the minimum allowable servo motor torque M _{M, min} , so the servo motor is driven so that the servo motor torque M _M to at least the minimum allowable servo motor torque M _{M, min} is increased. The servomotor is thus controlled such that the current servo motor torque is brought into the permitted torque range.

The above-described steps of the method can be repeated at certain fixed time intervals. In particular, the time intervals are selected such that the steps of the method are continuously repeated so that it is continuously checked whether the current servo motor torque M _{M is} within the permitted range.

Is the current servo motor torque M _M outside the allowable torque range, so the servo motor is driven such that the current servo motor torque M _M is brought into the allowed range.

Claims (10)

A method of operating a power steering system, particularly an electromechanically assisted power steering system, wherein the power steering system includes a steering wheel, a steering column, and a servo motor that temporarily transposes the manual torque (M _H ) while steering through an additional servo torque and in predefined vehicle conditions Supports an additional assist torque, comprising the following steps: determining an overall torque acting on the steering column, determining an assisting torque by which at least one assistance system acts on the steering column via the servomotor, determining an operating point (P) from the total to Steering column acting torque and the assist torque, - determining a maximum and a minimum allowable servo motor torque (M _{M, max} , M _{M, min} ), and - reducing the current servo motor torque (M _M ) to at most the certain maximum allowable servo motor torque (M _{M, max} ) above Activation of the servomotor. Method according to Claim 1 , characterized in that for determining the maximum and the minimum allowable servomotor torque (M _{M, max} , M _{M, min} ) a gain curve (10) of the steering system and the specific operating point (P) are used. Method according to one of the preceding claims, characterized in that based on the determined minimum allowable servo motor torque (M _{M, min} ), the servo motor is controlled such that the current servo motor torque (M _M ) does not fall below the minimum allowable servo motor torque (M _{M, min} ) , Method according to one of the preceding claims, characterized in that for determining the operating point (p), the difference is formed from the determined total torque acting on the steering column and the determined assistance torque. Method according to one of the preceding claims, characterized in that for determining the operating point (P), the amplification curve (10) of the steering system is used. Method according to one of the preceding claims, characterized in that a predefined maximum controllable torque (M _{H, max} ) is used for determining the maximum and the minimum permitted servo motor torque (M _{M, max} , M _{M, min} ). Method according to Claim 6 , characterized in that starting from the operating point (P) associated manual torque (M _H ) the predefined maximum controllable torque (M _{H, max} ) is added or subtracted by the maximum or the minimum allowable servo motor torque (M _{M, max} , M _{M, min} ), wherein the minimum allowable servo motor torque (M _{M, min} ) corresponds to the servo motor torque (M _M ) present in the gain curve (10) of the difference between manual torque (M _H ) at the operating point (P) and predefined maximum controllable torque (M _{H, max)} is associated, and wherein the servo motor torque maximum allowed (M _{M, max)} that of the servo motor torque (M _M) corresponds to that in the gain curve (10) the sum of the manual torque (M _H) at the operating point (P) and predefined maximum controllable torque (M _{H, max} ) is assigned. Method according to one of the preceding claims, characterized in that the entire torque acting on the steering column by means of a torque sensor of the steering system is measured. Method according to one of the preceding claims, characterized in that the steps of the method are repeated at certain time intervals, in particular wherein the time intervals are selected such that the steps of the method are repeated continuously. Servo steering system, in particular electromechanically assisted power steering system, wherein the Steering system comprises a steering wheel, a steering column and a servo motor, and wherein the steering system is adapted to perform a method according to any one of the preceding claims.

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