DE102016100980B4 - Method for operating a steering system of a motor vehicle - Google Patents

Abstract

A method for operating a steering system (2) of a motor vehicle with a power steering system (4), wherein a support torque (36) by means of a drive unit (22) of the power steering system (4) in a steering gear (8) is introduced, wherein a torsion bar moment (34) is determined by means of a torque sensor (32), wherein an actual rotational speed (90) of the drive unit (22) is determined, wherein a vibration signal (44) for generating vibrations in the steering gear (8) is determined, and wherein the vibration signal (44 ) is linked to the assistance torque (36) when the actual speed (90) of the drive unit (22) falls below a minimum speed (86; 66) for the drive unit (22), characterized in that the minimum speed (86; 66) for the drive unit (22) is determined as a function of an effective torque (64) of the drive unit (22).

Description

The invention relates to a method for operating a steering system of a motor vehicle according to the preamble of claim 1.

In addition, the invention relates to a computer program for carrying out such a method, a control unit with such a computer program and a storage medium for such a control unit.

Steering systems, with power steering, in which by means of a drive unit, an assisting force is introduced into a steering gear of the steering system, are known. For the driver, the steering feel is realized, for example, by specifying a desired driver torque on a torsion bar of the steering system.

From the DE 10 2009 000 638 A1 a method for determining a target steering torque for a steering means of a steering device in a vehicle is known.

Furthermore, so-called stick-slip effects are known in steering systems, which are characterized by an increased adhesive friction. These stick-slip effects cause the driver of the vehicle to feel that the steering system is jerky and thus to assume a defect in the steering system. The resulting complaints can be correspondingly high.

Such a steering system is for example from the DE 10 2014 113 614 B3 known.

Furthermore, from the DE 10 2009 057 166 A1 a generic method for operating a steering system of a motor vehicle, in which a vibration excitation is activated when a motor angular velocity of a drive unit is smaller than a predetermined limit value for the motor angular velocity.

In addition, from the DE 101 38 540 A1 discloses a method for operating a steering system of a motor vehicle with a power steering system, wherein a Stromdithersignal is generated when a motor angular velocity of a drive unit is in a predetermined range.

Thus, it is an object of the invention to effectively reduce the friction in the steering system.

The object is achieved by a method according to claim 1, a computer program according to claim 7, a control device according to claim 8 and a storage medium according to claim 9. Advantageous developments are specified in the subclaims. Aspects important to the invention can be found in the following description, in the drawings, wherein the aspects, both alone and in various combinations, may be important to the invention without again being explicitly pointed out.

It is proposed that a vibration signal for generating vibrations in the steering gear is determined. A minimum speed for the drive unit is determined as a function of an effective torque of the drive unit. The vibration signal is linked to a support torque when the actual speed of the drive unit falls below the minimum speed. Advantageously, there is thus a reduction of the friction in the steering system. In particular, the stick-slip effect can be reduced depending on the determined effective moment and thus independently of the particular application of the steering feel. Thus, for example, it is possible to switch over between different driving characteristics or different steering-feel adjustments, without the procedure for reducing the friction having to be adapted to these driving or steering characteristics. There is thus achieved a decoupling of the introduction of the vibration signal from other steering functions in the sense of a voting independence and it can thus be an improved adaptation of the vibration signal to the vehicle and the respective driving situation. Consequently, the steering feel, in particular the steering can be improved despite high friction in the steering system and at the same time greatly reduce the hooking of the steering.

In an advantageous development, the minimum rotational speed is determined by means of an applied characteristic field as a function of the effective torque. This advantageously results in an adaptation to the respective steering system type.

In an advantageous development, the effective torque is determined as a function of the torsion bar torque, as a function of the assist torque and as a function of the vibration signal.

In an advantageous development, the vibration signal is subtracted in the determination of the effective torque. Thus, latching, i. a detection of a stick-slip state by the switched-vibration signal avoided.

In an advantageous embodiment, a further minimum rotational speed is determined by means of a further applied characteristic map as a function of a steering angle or as a function of a manual torque gradient. A maximum minimum speed is determined as a function of the minimum speed and the additional minimum speed. It Thus, a maximum value formation takes place from individual minimum speeds of the applied maps. The vibration signal is linked to the assist torque when the actual speed of the drive unit falls below the maximum minimum speed. In this way, different stick-slip states can be reliably detected in a simple manner.

In an advantageous embodiment, an amplitude of the vibration signal is determined as a function of the steering angle and in dependence on a vehicle speed. Advantageously, this can also be a hakeln the steering can be reduced during cornering. So it can be done to adapt the vibration amplitude to different driving situations.

Other aspects, applications and advantages of the invention will become apparent from the following description of embodiments of the invention, which is illustrated in the figures of the drawing. All described or illustrated aspects, alone or in any combination, constitute the subject matter of the invention, independently of their summary in the claims or their dependency, and independently of their wording or representation in the specification or the drawings. It will be used for functionally equivalent sizes in all figures, even with different embodiments, the same reference numerals.

• 1 in schematischer Form ein Lenksystem;
• 2 und 4 jeweils ein schematisches Blockdiagramm; und
• 3 ein schematisches Berechnungsdiagramm.

Embodiments of the invention will now be described by way of example with reference to the drawings. In the drawing show:

• 1 in schematic form, a steering system;
• 2 and 4 each a schematic block diagram; and
• 3 a schematic calculation diagram.

1 shows in schematic form a steering system 2 with a power steering system 4 , Furthermore, the steering system 2 As shown also include a superposition steering 6. The steering system 2 has a steering gear 8th on, which is designed for example as a rack and pinion steering gear. The steering gear 8th can also be designed as recirculating ball or ball nut transmission. In this description, it is mainly assumed that a rack and pinion steering, wherein the steering gear is a pinion 10 and a rack 12 includes. The steering gear 8th is over the pinion 10 and the rack 12 on each side of the vehicle with a steering linkage 14 connected, each cooperating with a wheel 16. Basically, the steering system provides 2 one of a variety of possible embodiments for performing the method according to the invention suitable devices. For example, a drive unit can also be located on the steering column. Other embodiments may thus be implemented by other steering gear or by a different arrangement of drives. Furthermore, further sensors may be arranged in the steering system, the arrangement and execution of which is not discussed here.

On a torsion bar 18 is a steering means 20 , For example, arranged a steering wheel. By means of the superposition steering 6 can the applied by the driver Lenkmittelwinkel in a normal operation of the steering system 2 towards the steering gear 8 are increased or decreased. This steering angle difference caused by the superposition steering 6 in the steering gear 8th is introduced, is also referred to as additional steering angle.

Of course, instead of a torsion bar 26 also a steering column between the steering means 28 and the superposition steering 6 be arranged. In this embodiment, the torsion bar is between the superposition steering 6 and the power steering system 4 arranged.

The power steering system 4 includes a motor, also called a drive unit 22 more significant, and a gearbox 24 , A control unit 26 is assigned to the power steering 4. The drive unit 22 acts via the gearbox 24 on the rack 12. The control unit 26 has a microprocessor 28 on top of a data line with a storage element 30 connected is. The microprocessor 28 is also denominated as a digital computing device on which the methods described herein can be performed. The storage element 30 is also signifiable as a storage medium. On the storage element 30 can one on the microprocessor 28 to be executed computer program.

The control unit 26 becomes one of a sensor 32 determined torsion bar torque 34 fed. Depending on the supplied torsion bar torque 34 determines the control unit 26 a support moment 36 , Which represents a desired value for a contribution of the assisting torque and, for example, converted accordingly as a manipulated variable of the drive unit 22 is supplied.

2 shows a schematic block diagram 40 for execution in the control unit 26 , By means of a block 42 becomes a vibration signal 44 determined and a block 46 fed. The block 46 decides on the basis of a signal 48 whether the vibration signal 44 to the addition point 50 according to a signal 52 is forwarded. At the addition point 50 become a pre-calculated support moment 54 and the signal 52 , For example, the vibration signal 44, added. The sum is the addition point 50 the support moment 36 ,

The vibration signal 44 is used to avoid stick-slip effects, which is a hiccup of the steering system 2 cause. The vibration signal 44 is, for example, a square wave signal or a sine wave signal and may have a frequency of 60 Hz and an amplitude of 0.1 Newton meters.

An applied map 56 becomes a vehicle speed 58 fed and a factor 60 determined. An applied map 62 an effective torque 64 is applied to a first minimum speed 66 to investigate. The map 62 is independent of the vehicle speed. The effective moment 64 corresponds essentially to the steering gear 8th applied calculated rack power and thus is essentially independent of the application of the steering system 2 , The map 62 can be designed differently for different vehicle speeds and thus applied differently.

An applied map 68 becomes a steering angle 70 for determining a second minimum speed 72 fed. An applied map 74 becomes a gradient 76 of the torsion bar torque 34 supplied to a third minimum speed 78 to investigate. The minimum speeds 66 . 72 . 78 become a block 80 fed, the block 80 the largest of the supplied minimum speeds 66 . 67 . 78 as the largest minimum speed 82 forwards and a block 84 supplies. The block 84 multiplies the factor 60 with the highest minimum speed 82 and passes this comparison value, which is also the minimum speed 86 can be labeled, to a block 88 on. The block 88 compares the minimum speed 86 with an actual speed 90 the drive unit 22 and determines the signal 48 depending on the comparison.

Thus, the vibration signal 44 then on the support moment 36 switched on or is the vibration signal 44 with the support moment 54 to the in the steering gear 8th support moment to be introduced 36 linked when the actual speed 90 below the minimum speed 86 falls and thus a detection of a possible stick-slip effect occurs. Through the activated vibration signal 44 then this possible stick-slip effect can be eliminated. The vibration signal 44 on the other hand, it is switched off, ie deactivated, if the actual speed 90 over the minimum speed 86 increases. The vibration signal is preferred 44 not hard on and off, but there is a ramping and ramping over an applied ramp slope instead.

3 shows a schematic calculation diagram 92 for determining the effective torque 64 , The effective moment 64 results from a multiplication of the torsion bar torque 34 with a gear ratio 96 at the multiplication point 94. The product 98 and the support moment 36 be at an addition point 100 added. Furthermore, at the addition point 100 the vibration signal 44 , which also represents a moment, subtracts. As a result, from the addition point 100 the effective moment 64 output.

4 shows a schematic block diagram 102 for determining an amplitude 104 of the vibration signal 44 , The vehicle speed 58 becomes an applied map 106 to determine a factor 108 fed. The steering angle 70 becomes an applied map 110 supplied to determine an amplitude 112. A block 114 multiplies the factor 108 with the amplitude 112 and gives the amplitude 104 out. In a position of the steering wheel for a straight ahead travel low amplitudes 104 to keep the steering free. For larger steering angles, however, such as when cornering with constant steering angle and small steering angle corrections taking place, on the other hand, larger amplitudes 104 necessary to the steering system 2 to keep free.

Claims (9)

A method for operating a steering system (2) of a motor vehicle with a power steering system (4), wherein a support torque (36) by means of a drive unit (22) of the power steering system (4) in a steering gear (8) is introduced, wherein a torsion bar moment (34) is determined by means of a torque sensor (32), wherein an actual rotational speed (90) of the drive unit (22) is determined, wherein a vibration signal (44) for generating vibrations in the steering gear (8) is determined, and wherein the vibration signal (44 ) is linked to the assistance torque (36) when the actual speed (90) of the drive unit (22) falls below a minimum speed (86; 66) for the drive unit (22), characterized in that the minimum speed (86; 66) for the drive unit (22) is determined as a function of an effective torque (64) of the drive unit (22). The procedure after the Claim 1 , characterized in that the minimum speed (86) by means of an applied characteristic field (62) in dependence on the effective moment (64) is determined. The procedure after the Claim 2 , characterized in that the effective torque (64) in dependence on the torsion bar torque (34), in dependence on the assisting torque (36) and is determined as a function of the vibration signal (44). The procedure after the Claim 3 , characterized in that the vibration signal (44) in the determination of the effective torque (64) is subtracted. The method according to one of the preceding claims, characterized in that a further minimum speed (72; 78) is determined by means of a further applied characteristic map (68; 74) as a function of a steering angle (70) or as a function of a manual torque gradient (76) of the torsion moment ( 34), wherein a maximum minimum speed (82) is determined in dependence on the minimum speed (66) and the further minimum speed (72; 78), and wherein the vibration signal (44) is associated with the assist torque (36) when the Actual speed (90) of the drive unit (22) below the maximum minimum speed (82). The method according to one of the preceding claims, characterized in that an amplitude (104) of the vibration signal (44) in dependence on the steering angle (70) and in dependence on a vehicle speed (58) is determined. A computer program for a digital computing device configured to perform the method of any one of the preceding claims. A control device (26) for a steering system (2) of a motor vehicle, which is provided with a digital computing device on which the computer program Claim 7 is executable. A storage medium for the control unit of a steering system (2) after the Claim 8 on which the computer program after the Claim 7 is stored.

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