DE102012022801B4 - Steering monitoring method and steering system - Google Patents

Abstract

Method for monitoring a steering system (200) for a motor vehicle (100), the steering system (200) having a toothed rack (240) which meshes with a steering pinion (230), a pressure piece (250) for the sliding bearing of the toothed rack (240) in the area of the steering pinion (230), a steering assistance motor (260) and a control unit (300) for the electromechanical conversion of a manual torque applied by the driver into steering assistance by the steering assistance motor (260), the method comprising:in normal operation of the motor vehicle (100) , detecting at least one operating variable of the steering system (200) available in the control unit (300); andon the basis of the at least one operating variable, determining a state of the pressure piece (250).

Description

The present invention relates to a steering monitoring method and a correspondingly designed steering system. Furthermore, the invention relates to a motor vehicle with such a steering system.

A typical embodiment of a steering system for a motor vehicle is based on a toothed rack, which is coupled to a steering pinion via a toothing engagement. In this way, a manual torque applied by the driver via a steering wheel can be converted into a steering movement of the wheels of the motor vehicle, e.g. by the rack acting on tie rods coupled to the wheels of the motor vehicle.

In such steering systems, a pressure piece is often used in the area of the toothed engagement between the rack and steering pinion, which serves as a slide bearing for the toothed rack and is intended to ensure correct toothed engagement between the toothed rack and steering pinion. With a suitable setting of the play between the pressure piece and the rack, for example, disturbing vibrations or noises in the steering system can be avoided. Furthermore, operating characteristics of the steering system, for example with regard to friction, can be adjusted.

In the event of an unsuitable setting of the pressure piece play or a defective pressure piece, it may no longer be possible to guarantee correct guidance of the rack and disturbing vibrations or noises may occur. Furthermore, even more serious faults in the steering system can occur, e.g. if a part of the defective pressure piece becomes wedged in the steering system and the steering locks up.

In this respect, there is a general need to detect incorrect adjustment of the pressure piece play or a defect in the pressure piece early and reliably.

The DE 10 2006 052 376 A1 describes a method for determining the pressure piece play in a rack and pinion steering system, in which a predetermined torque is applied to the rack about its longitudinal axis and the twisting angle of the rack caused thereby is measured. The pressure piece play is deduced from the size of the torsion angle.

The DE 10 2008 042 134 A1 describes a device for pressing a rack onto a pinion, in particular for a steering system of a motor vehicle. In this device, a pressure piece is slidably guided. Any play in the pressure piece that occurs in the steering is automatically compensated for by an adjustment device. The adjustment device is implemented mechanically using two washers and a torsion spring.

The DE 10 2010 002 685 A1 describes an adjustment element for a pressure piece in a rack and pinion steering gear, which is based on a wedge effect in the manner of a wedge gear.

The U.S. 2009/0249902 A1 describes a rack and pinion steering gear with an automatic pressure piece setting, which is implemented mechanically via a wedge element, a spring and an adjusting screw.

The EP 1 832 496 A1 describes a pressure piece unit for a steering gear, which is provided with a hydraulic damping unit. By readjusting the pressure in the hydraulic damping unit, the contact pressure of the pressure piece can be adjusted.

The DE 197 45 733 A1 describes a steering device for a motor vehicle, in which a compensation device is provided which transmits a compensation torque to a steering wheel of the motor vehicle. The compensation device can be controlled depending on the torque and steering angle on the steering wheel. Furthermore, the driving condition of the motor vehicle can also be taken into account, eg driving speed or yaw rate.

The DE 198 15 470 A1 discloses a method for determining the condition or the wear of a steering system of a motor vehicle.

The DE 10 2006 017 775 A1 also discloses a method for detecting a defect in a steering system.

The DE 10 2010 062 499 A1 shows a method for monitoring the function of a steering system in a vehicle.

The DE 10 2009 002 594 B3 shows a method for determining an increased internal friction of the steering mechanism of a vehicle.

The DE 102 06 474 A1 also discloses a method for detecting friction in an electric or mechanical steering device.

An object of the present invention is to address the above need and to provide methods and apparatus by which efficient monitoring Checking the condition of a pressure piece of a rack and pinion steering system is made possible.

According to the invention, this object is achieved by a method according to claim 1, by a steering system according to claim 8 and by a motor vehicle according to claim 10. The dependent claims define preferred or advantageous embodiments of the invention.

The method according to the invention serves to monitor a steering system for a motor vehicle. The steering system comprises a toothed rack, which meshes with a steering pinion, a thrust piece for the sliding bearing of the toothed rack in the area of the steering pinion, a power steering motor and a control unit for electromechanically converting a manual torque applied by the driver into power steering by the power steering motor. In the method according to the invention, at least one operating variable of the steering system that is available in the control unit is detected during normal operation of the motor vehicle, in particular while driving. A state of the pressure piece is determined on the basis of the at least one operating variable. On the one hand, this can include detecting a defect in the pressure piece. Alternatively or additionally, this can also include determining a play between the pressure piece and the toothed rack. This determined pressure piece play can also be used to control an actuating element for adjusting the pressure piece play. Furthermore, depending on the determined condition of the pressure piece, a warning message can be issued. The determined condition of the pressure piece or data derived from it can also be logged for later use.

By determining the state of the pressure piece using the operating variables that are available in the control unit of the steering system during normal operation of the motor vehicle, a defect in the pressure piece or too much or too little play in the pressure piece can be detected immediately after such a state occurs, without For example, a special diagnosis would be required as part of maintenance. Furthermore, a sensor system available to the control unit of the steering system can also be used in an efficient manner.

The at least one operating variable can include the manual torque, a position of the power steering motor, a speed of the power steering motor, a drive current of the power steering motor and/or a torque applied by the power steering motor. These operating variables are particularly suitable for estimating a force applied to the rack. From this, in turn, conclusions can be drawn about the condition of the pressure piece. For example, a degree of variation of the force applied to the toothed rack can be determined and the state of the pressure piece can be determined on the basis of this degree of variation. A defective condition of the pressure piece, e.g. excessive play or a defect in the pressure piece, can then be determined, for example, by comparing the degree of variation with a threshold value. Alternatively or additionally, the operating variables mentioned can also be used in order to estimate a frictional force occurring between the pressure piece and the toothed rack.

The steering system according to the invention comprises a steering pinion, a toothed rack which meshes with the steering pinion, a pressure piece for the sliding bearing of the toothed rack in the area of the steering pinion, a steering-assist motor for providing steering assistance, and a control unit for electromechanically converting a manual torque applied by the driver into steering assistance by the power steering motor. Furthermore, the steering system includes a monitoring device, which can be implemented, for example, in the control unit or via an on-board computer of the motor vehicle. The monitoring device is designed to detect at least one operating variable of the steering system that is available in the control unit during normal operation of the motor vehicle and to determine a state of the pressure piece based on the at least one operating variable. The steering system can be designed in particular to carry out the method according to the invention described above.

According to the invention, a motor vehicle is also provided with the steering system according to the invention described above.

• 1 veranschaulicht schematisch ein Kraftfahrzeug mit einem Lenksystem gemäß einem Ausführungsbeispiel der Erfindung.
• 2 zeigt schematisch den Aufbau des Lenksystems.
• 3 zeigt ein Blockdiagramm zur Veranschaulichung von Funktionen einer Druckstücküberwachung gemäß einem Ausführungsbeispiel der Erfindung.
• 4 zeigt ein Blockdiagramm zur Veranschaulichung von Funktionen einer Druckstücküberwachung gemäß einem weiteren Ausführungsbeispiel der Erfindung.
• 5 zeigt ein Flussdiagram zur Veranschaulichung eines Verfahrens zur Druckstücküberwachung gemäß einem Ausführungsbeispiel der Erfindung.
• 6 zeigt ein Blockdiagramm zur Veranschaulichung von Funktionen einer Druckstücküberwachung gemäß einem weiteren Ausführungsbeispiel der Erfindung.
• 7 zeigt ein Blockdiagramm zur Veranschaulichung von Funktionen einer Druckstücküberwachung gemäß einem weiteren Ausführungsbeispiel der Erfindung.

Exemplary embodiments of the invention are explained in more detail below with reference to the accompanying drawings.

• 1 FIG. 1 schematically illustrates a motor vehicle with a steering system according to an embodiment of the invention.
• 2 shows the structure of the steering system.
• 3 shows a block diagram to illustrate functions of a pressure piece monitoring according to an embodiment of the invention.
• 4 shows a block diagram to illustrate functions of a pressure piece monitoring according to a further embodiment of the invention.
• 5 shows a flow chart to illustrate a method for pressure piece monitoring according to an embodiment of the invention.
• 6 shows a block diagram to illustrate functions of a pressure piece monitoring according to a further embodiment of the invention.
• 7 shows a block diagram to illustrate functions of a pressure piece monitoring according to a further embodiment of the invention.

The following description of exemplary embodiments of the invention relates to an exemplary electromechanical steering system in a motor vehicle. In these exemplary embodiments, one or more operating variables of the steering system are detected during normal operation of the motor vehicle, in particular while driving, in order to draw conclusions about the state of a pressure piece of the steering system.

1 FIG. 1 schematically illustrates a motor vehicle 100 equipped with a steering system 200 according to an exemplary embodiment of the invention. The steering system 200 is designed as an electromechanical steering system, in which a manual torque applied by the driver of the motor vehicle via a steering wheel 210 is supported by a steering-assist motor. The steering assistance provided by the steering assistance motor is controlled via a control unit 300 . This takes place in a dynamic manner in that the manual torque is detected and the steering assistance is provided as a function of the manual torque. For this purpose, the steering system is provided in a known manner with sensors for detecting the manual torque. Furthermore, the steering system can also detect a position of the power steering motor, eg an angular position, a torque applied by the power steering motor, a drive current of the power steering motor, a speed of the power steering motor or the like. In addition, control unit 300 can be supplied with other measured variables that are available in the vehicle, for example driving speed, lateral acceleration, yaw rate, curve radius or the like. For this purpose, the control unit can be coupled to an on-board computer 150 of motor vehicle 100, as shown.

The structure of the steering system 200 is in 2 shown schematically. As shown, the steering system 200 includes the steering wheel 210, via which the driver manually generates the manual torque, a steering column 220, a steering pinion 230, which is coupled to the steering wheel via the steering column 220, a rack 240, which meshes with the steering pinion 230 and a pressure piece 250 for the sliding bearing of the rack in the area of the steering pinion 230. For this purpose, the steering pinion 230 is typically arranged on one side of the rack 240, while the pressure piece 250 is arranged on the opposite side of the rack 240 and the rack 240 in Direction of the steering pinion 230 presses.

Furthermore, the steering system 200 includes the steering assistance motor 260 and the control unit 300 for controlling the steering assistance provided by the steering assistance motor 260 . The steering assistance motor 260 can be implemented in a manner known per se via an electric motor. To control the power steering, the controller 300 provides control signals to the power steering motor 260, e.g., to adjust the drive current. Furthermore, the steering assistance motor 260 can supply measured variables to the control device, e.g. In the illustrated example, the power steering motor 260 acts on the rack 240, such as through a ball screw.

Furthermore, the steering system 200 can also include an actuating element 270, via which the positioning of the pressure piece 250 can be adjusted. In particular, the position of the pressure piece 250 relative to the toothed rack 240 can be adjusted via the actuating element 270, so that the play or the friction between the pressure piece 250 and the toothed rack 240 can be adjusted. The actuating element 270 can be implemented using a suitable electromechanical actuating mechanism, e.g. based on a stepper motor.

In steering system 200, operating variables available in the control unit are used to determine the state of the pressure piece, e.g. to detect excessive play between pressure piece 250 and the rack or to detect a defect in pressure piece 250. Various monitoring functions can be implemented for this purpose.

One approach is based on estimating a total force acting on rack 240, also referred to below as rack force, or a frictional force occurring between pressure piece 250 and rack 240 from the operating variables. Corresponding functions are shown in the block diagram of FIG 3 illustrated.

When implementing 3 several operating variables of the steering system 200 are fed to an observer algorithm 310 . The observer algorithm 310 is designed to adapt a system model depending on the operating variables supplied to the observer algorithm 310 in such a way that an approximation for a variable that cannot be observed directly, in this case the rack force FZ and/or the frictional force FR, is supplied. Methods known in control engineering can be used for this purpose. In the example shown, it is assumed that the operating variables supplied to the observer algorithm 310 include the manual torque, referred to as HM, the position of the power steering motor 260, referred to as MS, and the speed of the power steering motor 260, referred to as DZ. Alternatively or additionally, the drive current of the steering assistance motor 260 and/or the torque applied by the steering assistance motor 260 could also be used.

The output variable of the observer algorithm 310, ie the rack force FZ or the frictional force FR, is then supplied to a filter 320 in order to determine the extent of its variation. The degree of variation quantifies the extent of short-term deviations of the output variable FZ or FR from a mean value that varies only slowly, for example over periods of several seconds. In the output variable FZ or FR, such deviations typically manifest themselves as “ripples”. The variation strength of the force FZ is in 3 denoted as V(FZ). The variation strength of the frictional force FR is in 3 denoted as V(FR).

Another approach to pressure piece monitoring is based on first estimating a force FU applied by the power steering motor 260 to the rack 240 from the operating variables, also referred to below as the power steering, and considering the rack force FZ via a force balance on the rack 240. Corresponding functions are shown in the block diagram of FIG 4 illustrated.

When implementing 4 several operating variables of the steering assistance motor 260 are fed to an observer algorithm 330 . Observer algorithm 330 is designed to adapt a system model as a function of the operating variables supplied to observer algorithm 330 in such a way that an approximation for a variable that cannot be observed directly, in this case support force FU, is supplied. In the example shown, it is assumed that the operating variables supplied to the observer algorithm 330 include the position of the power steering motor 260, denoted as MS, and the speed of the power steering motor 260, denoted as DZ. Alternatively or additionally, the drive current of the steering assistance motor 260 and/or the torque applied by the steering assistance motor 260 could also be used.

zu berechnen, wobei FH die aus dem Handmoment resultierende manuell aufgebrachte Kraft, FR die zwischen dem Druckstück 250 und der Zahnstange wirkende Reibungskraft und FD eine durch die Massenträgheit der Zahnstange 240 verursachte dynamische Kraft darstellt.The balance of forces on the rack 240 can be used to calculate the rack force according to processing block 340 $$\text{car}=\text{FU}+\text{FH}+\text{FR}+\text{FD}$$

to be calculated, where FH represents the manually applied force resulting from the manual torque, FR represents the frictional force acting between the pressure piece 250 and the rack and FD represents a dynamic force caused by the mass inertia of the rack 240.

FH can be calculated from the manual torque HM and the gear ratio of the steering pinion 630 IR using: $$\text{FH}=\text{HM}\times \text{IR}.$$

The dynamic force FD can be calculated from the mass mZ of the rack 240 and the acceleration a acting on the rack via: $$\text{FD}=\text{mZ}\times \text{a}.$$

Various suitable friction models can be used for the frictional force, including simple models which, for example, only provide a fixed absolute value of FR, the sign of which varies depending on the direction of movement of the rack. More complex models, taking into account, for example, the instantaneous speed of movement of the rack 240 and/or temperature, can also be used and provide more accurate monitoring.

The according 3 or 4 A certain degree of variation can be used to detect a faulty state of the pressure piece 250 via a comparison with a threshold value. 5 shows a flowchart to illustrate a corresponding method.

In step 510, the operating variables required to determine the rack force FR and/or the frictional force FR are recorded. As explained above, a suitable sensor system of the steering system can be used for this purpose, for example a sensor for detecting the manual torque, as well as an internal sensor system of the power steering motor 260 for detecting the position MS and speed DZ.

In step 520, the rack force FZ and/or the frictional force FR is estimated from the detected operating variables, for example using an observer algorithm as in connection with FIG 3 or 4 explained.

Steps 510 and 520 can be repeated continuously while motor vehicle 100 is in operation in order to detect rack force FZ or the frictional force in real time.

In step 530, the degree of variation V(FZ) or V(FR) is determined, for example using a suitable filter as in connection with FIG 3 explained.

In step 540, the degree of variation V determined in step 530 is compared with a threshold value SW. If the degree of variation V exceeds the threshold value SW, a faulty pressure piece state is detected in step 550, for example too large a pressure piece game or a defect in the pressure piece 250. If the rack force FZ according to 4 is determined, it can be advantageous to select the threshold value SW to be correspondingly higher in order to hide any interference. Furthermore, disruptive influences can be avoided by restricting the evaluation to certain predefined driving situations, eg driving within a predefined speed window and with a yaw rate or lateral acceleration that is not too high. A suitable protective measure can then be initiated in step 560 , for example a warning can be issued to the driver of motor vehicle 100 or the play of pressure piece 250 can be adjusted via actuating element 270 . In addition, detected defective states of the pressure piece 250 can also be logged, for example to be used as an aid when adjusting the pressure piece 250 later as part of maintenance.

If, at step 540, the amount of variation V does not exceed the threshold, then at step 570 a non-faulty saddle condition is identified.

After step 560 or 570, the method can be repeated beginning with step 510.

Another way to evaluate the 3 estimated friction force FR is to compare it with a target value for the friction force. Corresponding functions are shown in the block diagram of FIG 6 illustrated.

At 6 will like related to 3 explains the observer algorithm 310 used to estimate the frictional force FR. The estimated frictional force FR is then fed to a processing block 350 which compares the estimated frictional force FR to a desired value for the frictional force, denoted S(FR). If an excessive deviation from the desired value S(FR) is determined, for example by a threshold value comparison, a faulty state of the pressure piece 250, for example excessive play or a defect in the pressure piece 250, can be inferred. In 6 the determined state of the pressure piece 250 is illustrated by an output signal STAT. The setpoint value S(FR) used here can be determined in advance in tests, for example. Furthermore, the setpoint S(FR) can also be determined using a more complex friction model, which also takes into account, for example, the speed of movement of the toothed rack 240 and/or the temperature.

To the reliability of the case 6 To increase the evaluation used, the current driving situation of motor vehicle 100 can also be taken into account in processing block 350 . For this purpose, the processing block 350 can be supplied with corresponding measured variables for characterizing the driving situation 6 illustrated by the input variable SIT. Here, for example, the driving speed, lateral acceleration or yaw rate can be taken into account. In this way, the evaluation can be limited to certain specified driving situations, for example driving within a specified speed window and with a yaw rate or lateral acceleration that is not too high.

Yet another possibility is to use the observer algorithm 310 of 3 estimated rack force in combination with the over the observer algorithm 330 of 4 evaluate the estimated rack force. Corresponding functions are shown in the block diagram of FIG 7 illustrated. In 7 is the one about the observer algorithm 310 of 3 estimated rack force denoted by FZ1, and via the observer algorithm 330 of 4 estimated rack force is denoted by FZ2.

The rack forces FZ1, FZ2 estimated in different ways are supplied to a further processing block 370, which draws conclusions about the state of the pressure piece 250 from a combined evaluation. In 7 the determined state of the pressure piece 250 is again illustrated by an output signal STAT. For example, the processing block 370 for determining the state of the pressure piece 250 can use a difference ΔFZ of the estimated toothed rack determine genetic forces FZ1, FZ2. If this difference exceeds a threshold value, it can be concluded that pressure piece 250 is in a faulty state. Alternatively, a correction value for the frictional force FR used as an input variable in processing block 340 can also be determined from the difference ΔFZ. If the rack forces FZ1 and FZ2 can be reconciled using this correction value, e.g. the newly determined difference ΔFZ is now below the threshold value, a changed friction characteristic between pressure piece 250 and rack 240 and thus a faulty state of pressure piece 250 can be inferred. Otherwise, an evaluation artifact can be concluded, and a warning or other protective measures can be omitted.

However, the evaluations of the operating variables described above can not only be used to identify faulty states of the pressure piece 250, but also to determine the play of the pressure piece. The pressure piece play determined in this way can be used in connection with 2 explained actuating element 270 to drive, so that the pressure piece game is adjusted to a suitable value during operation. In this way, a constant friction in the area of the teeth between the steering pinion 230 and the rack 240 can be achieved, for example, independently of the state of wear of the steering system 200 . Furthermore, the friction could be precisely adjusted depending on the driving situation, the driver's steering input, and/or other driver settings. In this way, the steering feel or the steering acoustics can be adjusted as required, e.g. by reducing the pressure piece play on poor roads, so that vibrations or rattling are avoided, or by increasing the pressure piece play when motor vehicle 100 is stationary or motor vehicle 100 is driving slowly, so that the Available power of the power steering motor 260 can be better utilized. The yoke clearance or sensed condition of the yoke 250 may also be used to determine data indicative of an amount and/or direction in which to increase or decrease the yoke clearance during a service intervention. Such data can, for example, be logged and made available via a suitable interface so that they can be called up and analyzed by workshop personnel.

Thus, as can be seen from the foregoing, the techniques presented herein make it possible to efficiently monitor the condition of a yoke of a rack-and-pinion steering system. In particular, operating variables of the steering system that are available while the motor vehicle is in operation can be used here, so that early detection of an unsuitable setting or a defect in the pressure piece is made possible.

It goes without saying that various modifications are possible in the exemplary embodiments presented above. In particular, the concepts used in these exemplary embodiments can be used in different vehicle types. The concepts can also be used in differently designed steering systems, e.g. in steering systems with several steering pinions that mesh with the toothed rack. In the case of such steering systems, a plurality of thrust pieces can also be provided, which are monitored in accordance with the concepts outlined above. Furthermore, the various monitoring methods presented here can be combined with one another and also with other monitoring methods. Furthermore, other types of operating variables can additionally or alternatively serve as a basis for the evaluations, for example a directly measured rack force, e.g. via a sensor system at the coupling point between rack 240 and steering support motor 260. In the exemplary implementations shown, which are based on threshold value comparisons, instead of a threshold value, several threshold values can be used in order to enable a more refined evaluation, e.g. a distinction between too much play in the thrust piece and a defect in the thrust piece. Furthermore, it goes without saying that the monitoring methods can be implemented by specially designed electronic hardware or by software for execution by a processor of a control unit of the steering system or an on-board computer.

Claims (10)

Method for monitoring a steering system (200) for a motor vehicle (100), the steering system (200) having a toothed rack (240) which meshes with a steering pinion (230), a pressure piece (250) for the sliding bearing of the toothed rack (240) in the area of the steering pinion (230), a steering assistance motor (260) and a control unit (300) for electromechanically converting a manual torque applied by the driver into steering assistance by the steering assistance motor (260), the method comprising: during normal operation of the motor vehicle (100) , detecting at least one operating variable of the steering system (200) available in the control unit (300); and based on the at least one operating variable, determining a state of the pressure piece (250). procedure after claim 1 , comprising: wherein the at least one operating variable comprises the manual torque, a position of the power steering motor (260), a speed of the power steering motor (260), a drive current of the power steering motor (260) and/or a torque applied by the power steering motor (260). procedure after claim 1 or 2 , comprising: on the basis of the at least one operating variable, determining a degree of variation of a force applied to the toothed rack (240); and determining the state of the pressure piece (250) on the basis of the degree of variation determined. procedure after claim 3 comprising: comparing the magnitude of the variation to a threshold; and upon exceeding the threshold, determining a faulty condition of the thrust pad (250). A method according to any one of the preceding claims, comprising: on the basis of the at least one operating variable, determining a frictional force occurring between the pressure piece (250) and the toothed rack (240). A method according to any one of the preceding claims, comprising: based on the at least one operating variable, determining a clearance between the pressure piece (250) and the rack (240). procedure after claim 6 , comprising: depending on the game of the pressure piece (250), controlling an actuating element (270) for adjusting the pressure piece game. Steering system (200) for a motor vehicle (100), comprising: a steering pinion (230); a rack (240) meshingly engaged with the steering pinion (230); a pressure piece (250) for the sliding bearing of the toothed rack (240) in the region of the steering pinion (230); a steering assist motor (260) for providing steering assist; a control unit (300) for the electromechanical conversion of a manual torque applied by the driver into a steering assistance by the steering assistance motor (260); and a monitoring device (150; 300), wherein the monitoring device (150; 300) is designed to detect at least one operating variable of the steering system (200) that is available in the control unit (300) during normal operation of the motor vehicle (100) and to use the at least one operating variable to determine a state of the pressure piece (250). determine. steering system claim 8 , wherein the steering system (200) for carrying out a method according to one of Claims 1 until 7 is designed. Motor vehicle (100) with a steering system (200). claim 8 or 9 .

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