DE102009046118A1 - Method for operating an electrical power steering of vehicle, involves generating engine torque of electric motor over engine current which is calculated by engine controller - Google Patents

Abstract

The method involves generating an engine torque of an electric motor (5) over an engine current which is calculated by an engine controller (9). The engine controller so calculates the engine current that during the same directionality of the motor torque and motor rotation direction, motor torque is limited to a higher value than during opposite directionality of the motor torque and motor rotation direction.

Description

The invention relates to a method for operating an electric power steering system of a vehicle according to the preamble of claim 1 and an electric power steering system according to claim 13.

The DE 103 10 492 A1 describes a power steering, in particular for motor vehicles, with a servomotor formed as an electric motor, which drives a spindle formed with a toothed portion, axially displaceable component via a rotatably mounted in a frame formed as a steering gear housing, but axially non-displaceably mounted ball nut. The servo motor and the spindle and the ball nut are rotatably supported by means of an eccentric bearing, so that the center distance between the shaft of the servomotor and the spindle in the sense of adjusting a bias of a toothed belt, which connects the shaft of the servomotor with the recirculating ball nut variable.

The DE 100 52 275 A1 describes a power steering system for a motor vehicle, wherein a steering handle designed as a steering handle for pivoting a steerable wheel is used. The wheel is articulated in a known manner with wheel steering levers and tie rods connected to a movable component of the transmission. For a play-free connection of the electric servo motor to the transmission is a pulley on the motor shaft of the servomotor, which is operatively connected to an input side pulley on the transmission via a toothed belt.

From the DE 10 2004 037 599 A1 a recirculating ball gear for an electromechanical steering system of a motor vehicle is known.

The DE 103 33 909 A1 describes a steering nut for a ball screw and an electric power steering provided therewith.

In electric power steering systems with a traction mechanism transmission formed as a toothed belt transmission or with at least one toothed belt in a traction mechanism a certain minimum bias of the belt is required to transmit the engine torque of the electric motor safely. The preload can be determined by calculation or trial.

If the bias of the toothed belt is too low, then the toothed belt runs up in the toothing of the gears of the traction mechanism on the tooth flanks. The timing belt causes high tensile forces in the Riementrummen. At high engine torques, the timing belt even tends to skip the teeth of the gears of the traction mechanism.

To compensate for tolerances in a series production of electric power steering systems, it is necessary to increase the preload for the toothed belt in order to reliably prevent run-up or even skipping. However, this can be disadvantageous for the storage of the components of the toothed belt drive. In addition, irregularities in the pulling force of the belt drive can result.

The invention has for its object to provide a method for operating an electric power steering and power steering, with the help of the toothed belt tension is as low as possible adjustable and yet run up of the belt or even skipping the belt is prevented.

The object is achieved by a method for operating an electric power steering system of a vehicle according to claim 1 and with an electric power steering system having the features of claim 13.

Characterized in that the motor control for the electric motor of the servo motor drive limits the engine torque to a defined size when the torque direction of the components of the Zugmittelgetriebes, as the gears and shafts opposite to the direction of movement of a shaft or an armature of the electric motor is (electric motor brakes), the limited Engine torque is lower than the normal value of the electric motor with rectilinearity of the engine torque and the direction of rotation of the engine, a control measure is taken which causes that in a deceleration of the electric motor of the timing belt with its empty strand on the small pulley on the electric motor does not come up and skips.

Preferred embodiments emerge from the subclaims.

It is expedient to limit the maximum engine torques for both operating modes (same-direction and opposite orientation of the engine torque and the engine rotational direction) by the engine control.

It may nevertheless be expedient to provide an adaptive control of the engine torque with opposite engine torque to the direction of rotation of the other components of the traction mechanism in the sense that the rotational accelerations of the components of the traction mechanism or other representative component of the traction mechanism and measured by the Engine control are processed, so that the timing belt does not run up in this mode on the tooth flanks of a gear of the traction mechanism and skips a tooth.

The bias of the toothed belt is adjusted so that in the rectilinearity of the engine torque and the direction of rotation of the electric motor and in Gegengegengerheitheit the direction of rotation of the motor torque and the direction of rotation of the electric motor, the toothed belt does not skip the tooth flanks of the gears of the traction mechanism or runs up to the tooth flanks. In this case, in one embodiment of the electric power steering and the operating method, the slack side of the toothed belt is always preloaded with about 50 Nm.

In order to prevent oscillation of the system electric motor traction mechanism, it may be expedient to perform a change of the limitation of the engine torque over a time ramp by the engine control. The transition from the operation of the electric motor with limited engine torque to operate the electric motor with higher engine torque can preferably be done instead of a temporal hysteresis over a course depending on the rotation angle of the electric motor or other motion-dependent variables of the system electric motor - traction mechanism. It is expedient, the transition of the limitation of the maximum engine torque between the maximum engine torque for mode a with the same sense of engine torque and engine speed to mode b, with opposite direction of engine torque and engine speed within the passage of a rotation angle of the shaft of the electric motor of at most about 90 ° or to perform at most about 180 °. In the opposite direction of rotation of the engine torque to the direction of engine rotation, the engine control limits the engine torque to about 2 to 6 Nm. The hysteresis can be achieved by the fact that in a transition of the mode b to mode a, the engine torque remains above the value of the mode b over a certain angle of the shaft of the electric motor.

The invention will now be described in more detail with reference to an embodiment and reproduced with reference to the accompanying drawings. In the drawing shows:

1 a schematic, simplified representation of an electric power steering according to the invention,

2 a partial view of a gear on a shaft of an electric motor of the power steering system in engagement with a toothed belt in the same direction of motor rotation direction and engine torque,

3 a partial view of a gear on a shaft of an electric motor of the power steering system in engagement with a toothed belt in the opposite direction of rotation of engine torque and electric motor,

4 the transmittable engine torque in the same direction and unequal direction of rotation of engine torque and engine rotation direction plotted on the belt pretension,

5 the maximum engine torque at a transition from operating mode a to operating mode b with a dependence on the rotational angle of the shaft of the electric motor,

6 a partial view of a gear on a shaft of an electric motor of the power steering in engagement with a toothed belt in different directions of engine torque and engine rotation direction wherein the engine torque is limited by an engine control,

7 the transmittable engine torque at a transition from the mode b to the mode a with a function of the rotation angle of the shaft of the electric motor.

LIST OF REFERENCE NUMBERS

1

Power steering, electric

2

Steering handle

3

wheel

4

Servo drive, electric

5

electric motor

6

traction drives

7

toothed belt

8th

steering gear

9

motor control

10

tooth flank

11

gear

12

wave

13

rack

14

pinion

15

loose side

δ _S

steering wheel angle

δ

wheel steering angle

M _M

engine torque

δ _w

Rotation angle, v. 12

1 shows an electric power steering 1 a passenger car, which is formed as an electromechanical power steering system. The electric power steering 1 has a steering handle formed as a steering wheel 2 on. The steering wheel is via a steering shaft with a steering gear 8th operatively connected.

The steering gear 8th serves to a rotation angle or steering wheel angle δ _{S of} the steering shaft in a wheel steering angle δ of steerable wheels 3 of Implement motor vehicle. The steering gear 8th has a rack 13 and a pinion 14 on, which the steering shaft attacks. Through the steering wheel, the wheel steering angle δ of the steerable wheels 3 of the motor vehicle specified.

The electric power steering 1 also has an electric servo drive 4 on which of the variable torque assistance is used by a variable specification of a steering torque.

The electric servo drive 4 consists of an electric motor 5 , the engine torque M _M via a traction mechanism 6 with toothed belt 7 transfers to a recirculating ball nut. The ball nut is in a conventional manner with a threaded portion of the rack 13 engaged, wherein upon rotation of the ball nut the rack 13 axially displaced in one or the other direction.

As the 2 . 3 and 6 show, the traction mechanism 6 one on a wave 12 of the electric motor 5 rotatably mounted gear 11 on, over and over another gear on the ball nut of the timing belt 7 is curious.

Furthermore, an electric engine control 9 for controlling or regulating the motor current and motor torque of the electric motor 5 intended. The engine control 9 comprises a memory element on which a computer program for processing on a microprocessor of the engine control 9 with the purpose of the engine torque in opposite direction of rotation of the shaft of the servomotor 5 to reduce the engine torque, compared to the engine torque with the same direction of rotation of engine torque and shaft of the electric motor 5 ,

2 illustrated in a partial view of the traction mechanism 6 in particular of the gear 11 on the wave 12 of the electric motor 5 and the toothed belt mounted thereon 7 an operating situation or mode a, in which the engine torque M _M and the direction of rotation of the gear 11 or the wave 12 are rectified. In this situation, the leertrum runs 15 of the toothed belt 7 on the large gear, not shown on the ball nut. In the case of a sufficient pretensioning of the toothed belt, there is no risk of the toothed belt starting up on tooth flanks of one of the two toothed wheels.

In operating situations of the power steering 1 but, where the moment direction of the engine torque and the direction of movement of the electric motor 5 or its shaft 12 are opposite, (mode b), z. B. during rapid deflection, drives the electric motor 5 first at high speed in one direction. Then the electric motor has the ball screw in the steering gear 8th decelerate quickly to then drive it in the opposite direction. In this situation, the leertrum runs 15 on the gear 11 , so on the small pulley of the traction mechanism 6 one. The timing belt 7 tends to run up the tooth flanks 10 of the gear 11 (see. 3 ). The tendency to run up and skip the belt 7 can, how 5 shows, directly as a function of the engine torque M _M are shown.

If, however, the engine torque M _M in this operating situation in a certain time interval or over a predetermined rotational angle of the shaft 12 from the engine control 9 limited, (mode b), there is no run-up or skip (cf. 6 ).

The 4 shows in a diagram the necessity of limiting the motor torque in opposite direction of rotation of the motor torque and direction of rotation of the shaft 12 on. When the direction of rotation is opposite, the possible transmittable motor torque M _{M is} less than with the same direction of rotation, since it causes the toothed belt to run up and over 7 comes.

Another special case, which clarifies the necessity of limiting the engine torque by the engine control, occurs in a parking situation of a vehicle in the vicinity of the steering stop. In this operating or driving situation, the tire bladder acts according to a spring, which is biased by the engine torque. If the steering stop now steers in the opposite direction, the engine torque initially remains in the same direction, but the direction of movement turns around. If the engine torque M _{M is} reduced, the biased Lash pushes back the steering wheel. On the other hand, if the driver stops on the steering wheel, the direction of rotation of the engine may again be reversed, as a result of which the steering assistance force in turn increases and the lug is in turn pre-stressed. It can be in the system - electric motor 5 - traction mechanism 6 and tire vibrations occur. This applies in particular if the respective permissible maximum engine torques for the operating modes a, b are switched without transition behavior.

Therefore, in addition, a transient behavior between the provided for the respective mode a, b and limited engine torque by the engine control 9 intended. The 5 shows a transition of the maximum engine torque M _M of the mode a (directance of the engine torque and the engine rotation direction) to the mode b (opposing motive torque and direction of rotation of the electric motor) over a rotation angle of the shaft of the electric motor 5 , In another change of the mode b to the mode a is how 7 shows a hysteresis of the motor control 9 provided, wherein initially limited to a lower value engine torque M _M remains and angle-delayed transition to a higher, possible for the mode a engine torque is done, so that by this measure the engine control 9 a swinging of the system is prevented. As 6 shows, is also in the mode b, ie in the opposite direction of motor torque M _M and direction of rotation of the shaft 12 of the electric motor 5 the timing belt on the gear 11 without ramping up the tooth flanks 10 and without tendency to skip.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10310492 A1 [0002]
• DE 10052275 A1 [0003]
• DE 102004037599 A1 [0004]
• DE 10333909 A1 [0005]

Claims (13)

Method for operating an electric power steering ( 1 ) of a vehicle, comprising: - a steering handle ( 2 ) for specifying a steering wheel angle (δ _S ) as a measure of a desired steering angle (δ) for at least one steerable wheel ( 3 ) of the vehicle, and - an electric servo drive ( 4 ) with an electric motor ( 5 ) for providing at least one steering assist force via a traction mechanism transmission ( 6 ) with at least one toothed belt ( 7 ) on a steering gear ( 8th ), wherein an engine torque (M _M ) of the electric motor ( 5 ) via a motor current supplied by a motor control ( 9 ) is generated, characterized in that the engine control ( 9 ) calculates the motor current so that when motor torque (M _M ) and motor direction (mode a) are rectified, the motor torque (M _M ) is limited to a higher value than in the opposite direction of rotation of motor torque (M _M ) and motor rotation (mode b). Method according to claim 1, characterized in that by the motor control ( 9 ) a maximum engine torque (M _M ) for both modes (a, b) of the electric motor ( 5 ) is limited. Method according to Claim 1 or 2, characterized in that the engine torque (M _M ) in the operating mode b is determined by the engine control system ( _M ). 9 ), that the toothed belt ( 7 ) does not skip or on tooth flanks ( 10 ) of the gears ( 11 ) of the traction mechanism ( 6 ) starts up. Method according to one of claims 1 to 3, characterized in that the bias of the toothed belt ( 7 ) is set so that in the operating mode a at maximum engine torque of the toothed belt ( 7 ) does not skip or on tooth flanks ( 10 ) of the gears ( 11 ) of the traction mechanism ( 6 ) starts up. Method according to one of claims 1 to 4, characterized in that the bias of the toothed belt ( 7 ) is set so that in mode b the toothed belt ( 7 ) at maximum engine torque (M _M ) does not skip or at tooth flanks ( 10 ) of the gears ( 11 ) of the traction mechanism ( 6 ) starts up. Method according to one of claims 1 to 5, characterized in that the slack side of the toothed belt ( 7 ) is always biased to at least about 50N. Method according to one of claims 1 to 6, characterized in that the engine control ( 9 ) performs a switching over of the limitation of the engine torque (MM) between the two modes a, b over a time ramp. Method according to one of Claims 1 to 7, characterized in that the engine control ( 9 ) a switching between the limitation of the engine torque (M _M ) in both modes (a, b) in response to passing through a rotation angle (δ _W ) of a shaft ( 12 ) of the electric motor ( 5 ) or one with the electric motor ( 5 ) operatively connected rotary member of the power steering ( 1 ). Method according to one of claims 1 to 8, characterized in that the engine control ( 9 ) the transition of the limitation of the maximum engine torque (M _M ) between the maximum engine torque (M _M ) for the mode a to the mode b within the passage of a rotation angle of the shaft ( 12 ) of the electric motor ( 5 ) of about 90 °. Method according to one of claims 1 to 8, characterized in that the engine control ( 9 ) the transition of the limitation of the maximum engine torque (M _M ) between the maximum engine torque (M _M ) for the mode b and the mode a within the passage of a rotation angle (δ _W ) of the shaft ( 12 ) of the electric motor ( 5 ) of about 180 °. Method according to one of claims 1 to 10, characterized in that of the engine control ( 9 ) a hysteresis for the limitation of the engine torque (M _M ) for the transition between the modes a and b over a defined rotation angle (δ _W ) of the shaft ( 12 ) of the electric motor ( 5 ) is provided. Method according to one of claims 1 to 11, characterized in that the maximum engine torque (M _M ) in the mode b by the engine control ( 9 ) is limited to about 2 to 6 Nm. Electric power steering for a vehicle, with a steering handle ( 2 ) for specifying a steering wheel angle (δ _S ) as a measure of a desired steering angle (δ) for at least one steerable wheel ( 3 ) of the vehicle, and an electric servo drive ( 4 ) with an electric motor ( 5 ) for providing at least one steering assist force via a traction mechanism transmission ( 6 ) with at least one toothed belt ( 7 ) on a steering gear ( 8th ), wherein an engine torque (M _M ) of the electric motor ( 5 ) via a motor current supplied by a motor control ( 9 ) is generated, and by the engine control ( 9 ) the modes a, b according to one of claims 1 to 12 is performed.

Images