DE102014116235B4 - 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, wherein a power steering (4) an assist torque (36) in a steering gear (8) brings, wherein a base steering torque (44) in response to a manual torque-assist torque characteristic (42) and A manual torque (34) is determined, characterized in that a total torque (52) results from the addition of the base steering torque (44) and further partial torques (49a, 49b) such that the total torque (52) depends on the manual torque assistance torque. Characteristic (42) is limited, and that the assist torque (36) results in dependence on the limited total torque (52).

Description

The invention relates to a method for operating a steering system of a motor vehicle according to the preamble of claim 1, a computer program for carrying out such a method, a control unit on which such a computer program is executable and a memory element on which such a computer program is stored.

From the DE 10 2009 000 165 A1 a method for operating a power steering system is known in which calculated with an electronic computing unit, an engine torque and adjusted by a suitable motor drive. An intrinsically safe motor torque limit curve is described. If an integrator reaches an adjustable threshold, the motor torque is limited to the limit curve.

From the WO 2012/037995 A1 For example, a method of operating an electric steering system is known in which an absolute value of an intermediate correction value is compared with an assistance limit. If the absolute value exceeds the assist limit, the intermediate correction value is multiplied by a limiting factor.

From the generic DE 10 2009 048 091 A1 For example, a control method for a power assisted steering system is known. A sensor device determines a control variable introduced into the steering wheel. It is determined with the aid of the control variable, a default value for a motor torque of a power engine. For a case where the default value exceeds an upper limit, a limiting member outputs the upper limit value as the target engine torque. The upper limit depends on the introduced control quantity.

From the WO 2004/005112 A1 a hydraulic power steering is known in which by means of an additional torque actuator, an additional steering torque is actively applied. A total value for the application of the additional steering torque is determined taking into account a determined steering torque or a derived magnitude and a selected basic steering characteristic curve. The characteristic can represent a gain basic characteristic. A scaling factor or gain factor can be limited to a given value depending on the torque.

The object of the invention is thus to improve the operation of a power steering system.

The problem underlying the invention is solved according to claim 1. Furthermore, the solution of the problem by a computer program with the features of claim 8, by a control device having the features of claim 9 and by a memory element having the features of claim 10. Advantageous further developments are specified in the dependent claims.

The fact that a total torque is limited as a function of a manual torque assistance torque characteristic curve advantageously achieves a lower steering response in the event of a fault since a better adaptation to the respective driving situation is possible through the use of the manual torque assistance torque characteristic curve. The manual torque assist torque characteristic has a large proportion of a calculated total torque, whereby a fault can be detected from a strong deviation from this characteristic. Advantageously, in particular software implementation errors can be better treated by the use of the manual torque support torque curve, whereby a faulty calculated torque component is limited. At the same time, driver assistance functions and / or functions for autonomous driving can be integrated much better into the error handling since injuries to the resulting limitation due to the proximity to the manual torque assistance torque characteristic curve do not lead to unnecessary fluctuations in the engine torque or the assist torque. Thus, a better steering feel is achieved. In comparison to a fixed limiting characteristic, a corresponding determination within the scope of the application as well as a rating of the series products are no longer necessary.

In an advantageous embodiment, the total torque is limited as a function of a limiting characteristic. The limiting characteristic is determined as a function of the manual torque assist torque characteristic.

The limiting characteristic is spaced apart from the manual torque assist torque characteristic by an assist torque distance. By Stützungsmoment distance can be advantageously covered a torque proportion of other steering functions.

In an advantageous embodiment, the limiting characteristic is determined with a fixed assisting torque distance from the manual torque-assisting torque characteristic. This provides a simple way to find the boundary curve.

In an advantageous embodiment, the assist torque distance of the limiting characteristic of the manual torque increases. Support torque characteristic with an increasing amount of manual torque.

In an advantageous embodiment, the assist torque distance of the limiting characteristic from the manual torque assist torque characteristic is reduced with increased vehicle speed. This results in advantageous at increased vehicle speeds, a stronger limitation in the sense that the tolerance is reduced with respect to unwanted momentary jumps. This increases driving safety at high speeds.

In an advantageous embodiment, the limiting characteristic is shifted in dependence on a steering angle by an assist torque distance. This makes it possible that driver assistance functions and / or functions for autonomous driving can be operated at an operating point in which no unnecessarily high error torque is possible and the driver always encounters a steering feel corresponding to the driving situation when engaging the steering wheel.

Depending on a speed of the motor vehicle, the manual torque-assisting torque characteristic curve is advantageously determined. Due to the dependence on the speed is advantageously achieved that a driving situation, for example, a parking or a highway ride in the limitation of the assist torque are taken into account. The position of a fault torque is therefore avoided depending on the driving situation.

Further applications and advantages of the invention will become apparent from the following description of embodiments of the invention, which are illustrated in the figures of the drawing. For functionally equivalent sizes and features, the same reference numerals are used in all figures, even in different embodiments.

• 1 ein Lenksystem in schematischer Form;
• 2 ein schematisches Blockdiagramm und
• 3 ein schematisches Handmoment-Unterstützungsmoment-Diagramm.

Hereinafter, exemplary embodiments of the invention will be explained with reference to the drawings. In the drawing show:

• 1 a steering system in schematic form;
• 2 a schematic block diagram and
• 3 a schematic hand moment assist torque 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 is predominantly assumed by 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 carrying out the method according to the invention suitable devices. Other embodiments may be carried out for example 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 18 also a steering column between the steering means 28 and the superposition steering 6 be arranged. In this embodiment, the torsion bar 18 between the superposition steering 6 and the power steering system 4 arranged.

The power steering system 4 includes a motor 22 and a gearbox 24 , A control unit 26 is the power steering system 4 assigned. The motor 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 hand moment 34 fed. Depending on the supplied manual torque 34 determines the control unit 26 a support moment 36 , for example, as a manipulated variable to the engine 22 is supplied. The support moment 36 is through the control unit 26 limited as a function of a manual torque support torque characteristic.

2 shows a schematic block diagram for determining the assist torque 36 , A block 38 determined as a function of a speed 70 of the motor vehicle, the manual torque-assist torque characteristic 42 , The manual torque assist torque characteristic 42 is determined from a rack force manual torque characteristic.

A basic steering torque 44 is from a block 46 depending on the manual torque support torque characteristic 42 and the hand moment 34 determined. More blocks 47 to 48 determine respective partial moments 49 which is an addition point 50 be supplied. A total moment 52 results from the addition of the moments 44 . 49a and 49b ,

Depending on the manual torque support torque characteristic 42 determines a block 54 a limiting characteristic 60 , In one embodiment, the block 54 a steering angle 62 supplied to the limiting characteristic 60 depending on the steering angle 62 to investigate. Depending on the steering angle 62 becomes the limiting characteristic 60 widened for higher hand moments.

A block 64 determined as a function of the total torque 52 , the moment of hand 34 and depending on the limiting characteristic 60 the support moment 36 and thus limits the moment of support 36 starting from the total moment 52 to values determined by the limiting characteristic 60 and the hand moment 34 be specified. In particular, this can result in excessive torque requirements resulting from the total torque 52 arise, be prevented. Through the block 64 This will cause unpredictable software errors in the blocks 46 to 48 intercepted.

In not shown form is the block 54 from one of the blocks 47 to 48 an assist torque distance supplied to the limiting characteristic 60 to move the assist torque distance. The corresponding function that creates this assist torque distance, one of the blocks 47 to 48 , is in particular a driver assistance function and / or a function for an autonomous driving, in which by the block 54 supplied assist torque distance advantageously a steering feeling is given, which expects the driver in an intervention in the steering means. On the other hand, the limit of the support torque 36 is advantageously shifted. Under the limit of the assist torque 36 is a limit on the total moment 52 to understand, with unwanted missing moments, resulting in the total moment 52 beneficial, not in the moment of support 36 are included. The limitation can take place in such a way that when the limiting characteristic is exceeded as the desired torque, the torque of the hand 34 corresponding value of the support torque 36 the limiting characteristic to the motor 22 is given.

3 shows a schematic hand moment assist torque diagram 66. The hatched area 68 sets permissible values for the assisting torque 36 as a function of the manual torque 34 dar. The limiting characteristic 60 is made up of parts 60a and 60b together. In positive manual torque direction 34 is the limiting characteristic 60a by an assist torque distance 70a from the manual torque assist torque characteristic 42 spaced. The assist torque distance 70 can be fixed or variable depending on the hand moment 34 and / or the vehicle speed are determined.

In negative hand moment direction 34 the limiting characteristic runs 60a in one area 72a parallel and by the distance 70a spaced apart from the hand moment axis 34 , In one area 74a the limiting characteristic falls 60a to a value of zero Nm of the assist torque 36 from. In an analogous manner, the limiting characteristic results 60b ,

In one embodiment, the assist torque distance becomes 70 with an increasing amount of hand moment 34 increased.

In one embodiment, the assist torque distance becomes 70 reduced at an increased vehicle speed. Dependent on a steering angle 62 becomes the limiting characteristic 60 moved along the manual torque axis 34. The steering angle refers to a steering angle of the wheels 16. In another embodiment, instead of the steering angle, a steering wheel angle can be used.

The limit by the block 64 takes place in such a way that the total moment 52 as a support moment 36 within the range 68 lies. Is the total moment 52 outside the range 68 , so for example, the support moment 36 limited to 0 Nm. In another embodiment, the assist torque becomes 36 on a current hand moment 34 corresponding value of the limiting characteristic 60 selected. In another embodiment, a filter may cause the assist torque to settle 36 be used to the predetermined limit value.

At a high vehicle speed, that is, from a speed of 20 km / h, for example, a support torque distance in the range of 0.3 Nm to 0.5 Nm is selected. At a low vehicle speed below 20 km / h becomes a support torque distance 70 in the range of 1 Nm up to 1.5 Nm.

Claims (10)

A method for operating a steering system (2) of a motor vehicle, wherein a power steering (4) an assist torque (36) in a steering gear (8) brings, wherein a base steering torque (44) in response to a manual torque-assist torque characteristic (42) and A manual torque (34) is determined, characterized in that a total torque (52) results from the addition of the base steering torque (44) and further partial torques (49a, 49b) such that the total torque (52) depends on the manual torque assistance torque. Characteristic (42) is limited, and that the assist torque (36) results in dependence on the limited total torque (52). The procedure according to Claim 1 characterized in that the total torque (52) is limited in response to a limiting characteristic (60), wherein the limiting characteristic (60) is determined as a function of the manual torque assist torque characteristic (42), and wherein the breaking limit characteristic (60) is spaced apart from the manual torque assist torque characteristic (42). The procedure according to Claim 2 characterized in that the limiting characteristic (60) is determined with a fixed assisting torque distance (70) from the manual torque assisting torque characteristic (42). The procedure according to Claim 2 characterized in that an assist torque distance (70) of the limiting characteristic (60) from the manual torque assist torque characteristic (42) increases with an increasing amount of the manual torque (34). The procedure according to Claim 2 characterized in that an assist torque distance (70) between the limiting characteristic (70) and manual torque assist torque characteristic (42) is reduced at increased vehicle speed (40). The method according to one of Claims 2 to 5 , characterized in that the limiting characteristic (60) is shifted in dependence on a steering angle (62) by an assist torque distance. The method according to one of the preceding claims, characterized in that the manual torque assistance torque characteristic curve (42) is determined as a function of the speed (40) of the motor vehicle. A computer program for a digital computing device configured to perform a method according to any one of the preceding claims. A control device (26) for operating a steering system (2) of a motor vehicle, which is provided with a microprocessor (28) on which a computer program according to the Claim 8 is executable. A memory element (30) for the control unit (26) after the Claim 9 on which a computer program after Claim 8 is stored.

Images