DE102006007250A1 - Method for steering a vehicle and vehicle steering - Google Patents

Abstract

The invention relates to a method for steering a vehicle with a superposition steering system, wherein by means of the superposition steering system, a target steering angle, which is determined from a predetermined steering angle of the driver and at least one additional steering angle, is set. DOLLAR A According to the invention, the method is carried out so that a rate of change of the target steering angle is limited to a situation-dependent determined maximum value, in particular to avoid that due to high steering angle speeds sufficient support can be provided by a power steering system. DOLLAR A The invention further relates to a suitable for carrying out the method vehicle steering.

Description

The The invention relates to a method for steering a vehicle a superposition steering system as well as a vehicle steering.

Under the name superposition steering Electromechanical actuators are known which have a steering angle, by the driver of a vehicle through a steering wheel is predetermined, superimpose with another steering angle. Other names for such Systems are ESAS (English: "Electronic Steer Assistant Steering ") and AFS (English: "Active Front Steering ").

The superposition steering allows a free assignment of steering wheel position and wheel steering of the steerable front wheels of the vehicle. This includes both variable steering ratios and driver-independent steering interventions represented, for example, generated by a driver assistance system become. As driver assistance systems are, for example, vehicle dynamics regulations such as ESP (English: "Electronic Stability Program ") or Lane keeping systems in question.

The possibility a variable steering ratio allows the ratio between the steering angle set by the driver on the steering wheel and the wheel steering angle depending on Speed and steering angle vary, these sizes being from corresponding sensors are detected. At low speeds in city traffic or when parking allows a direct translation the driver to maneuver the vehicle with low steering angle, without the hands have to embrace on the steering wheel. In contrast, at high speed, for example while a highway trip, an indirect translation chosen the a more precise one Straight running of the vehicle allowed.

Especially with a direct steering ratio now arises the difficulty that a change made by the driver the steering wheel angle or the driver steering angle in conjunction with that of a control unit predetermined steering ratio the resulting setpoint curve of the sum steering angle, the off the superposition of the Driver steering angle and overlay steering angle arises, exceeds a certain limit for the steering angular velocity. This limit value of the steering angular velocity is defined by that for greater steering angle speeds the power steering does not provide sufficient support due to its design can, so the desired relationship between transmission input side and transmission output side steering angle is no longer dynamically adjustable.

For the driver expresses himself This circumstance in a perceived as unpleasant "hardening" of the steering wheel, because he a bigger hand moment on Steering wheel must apply. The cause of the "hardening" is that a power steering usually so is designed to be within a certain speed range the vehicle the full steering assistance only up to a certain Steering angle speed makes.

In The rule is, for example, in the state or rolling of the vehicle the sizing chosen so that up to a maximum steering speed of 500 ° / second the maximum steering torque to be applied by a driver is a value from 5 to 6 Newton meters. An exact specification for different vehicle speed ranges will be provided by the vehicle manufacturer for vehicle types individually determined. This specification describes up to which Steering speed must support the power steering so that the of the Driver maximum applied hand torque is not exceeded.

If the overlay steering system a more direct steering ratio due to a present driving situation and the driver simultaneously makes a quick steering movement, the resulting setpoint course of the transmission output side total steering angle as described above Significantly exceed the limit value of the steering angle velocity, what about the already mentioned undesirable hardening the steering behavior leads.

Around this hardening of the ride significantly impairing the hardening of the Can prevent steering behavior, for vehicle models with superposition steering be provided a modified power steering, if necessary a higher one power steering can muster. However leads this remedy usually higher Production costs for the power steering.

Of these, It is an object of the present invention to provide a method for steering a vehicle with a superposition steering and a To provide vehicle steering, where a possible hardening of the steering behavior to others Way is avoided.

These Object is according to the invention by a method having the features of claim 1 and by a vehicle steering with the features of claim 8 solved.

Accordingly, a Method for steering a vehicle with a superposition steering system proposed, in which by means of the overlay steering system a target steering angle, which consists of a predetermined by the driver steering angle and is determined at least one additional steering angle is set. Draws according to the invention the method is characterized in that a rate of change of the target steering angle amount to a situation-dependent determined maximum value is limited.

hereby is the setpoint course of the means of the overlay steering system Adjusted steering angle adjusted so that the steering angle speed is limited to values for the power steering system a sufficient and by the driver usual support can provide. A hardening the steering due to the particular in a direct steering ratio occurring high steering angle speeds is thus avoided.

Further the invention provides a suitable for carrying out the method Vehicle steering before. The vehicle steering system includes a superposition steering system, with a target steering angle, which is predetermined by a driver Steering angle and at least one additional steering angle can be determined, adjustable is. The vehicle steering is characterized according to the invention it contains a function module with a rate of change of the target steering angle amount to a situation-dependent determined Maximum value can be limited.

at An advantageous embodiment of the invention is provided that a first additional steering angle in accordance with the vehicle speed is determined such that a speed-dependent transmission ratio between the predetermined by the driver steering angle and the target steering angle results.

A further particularly advantageous embodiment the invention includes that the first additional steering angle in accordance with determined by the driver steering angle is determined.

A particularly preferred embodiment The invention is further characterized in that the rate of change of the target steering angle is limited to a maximum value in dependence is determined by the vehicle speed.

hereby in particular at a function of the vehicle speed adjusted direct steering ratio, too high rates of change avoided the desired steering angle.

Further is a particularly advantageous embodiment of the invention thereby characterized in that the rate of change the target steering angle is limited to a maximum value, as a maximum of dependence from the vehicle speed determined maximum value and the rate of change determined by the driver steering angle is determined.

On This way is achieved by limiting the steering angular velocity the target steering angle not below that set by the driver Steering wheel angular velocity is.

moreover it is provided in a further advantageous embodiment of the invention, that is another additional steering angle in a vehicle dynamics control system and / or in a lane keeping system, wherein only the rate of change a proportion of the desired steering angle, that of the first additional steering angle and the steering angle given by the driver results limited becomes.

In order to is achieved that for safety-relevant portions of the target steering angle, in a vehicle dynamics control system and / or a lane keeping system, no limit the steering angle velocity takes place, and these shares with a high dynamics are set.

A particularly expedient embodiment The invention is also characterized by the fact that by means of the overlay steering system due the setting of the target steering angle a steering torque on a steering line of the vehicle that's on steerable wheels the vehicle acts, and wherein the effect of the steering torque means a power steering system is amplified.

Further Advantages, special features and expedient embodiments of the invention emerge from the dependent claims and the following description of preferred embodiments the invention with reference to the figures. In the figures are the same or Corresponding elements provided with the same reference numerals.

From the figures shows:

1 a schematic representation of the basic structure of a superposition steering;

2 a block diagram of a steering control system for determining a desired steering angle to be set by means of a superposition steering system;

3 a block diagram of a module for determining a speed-dependent over scan rate;

4 a block diagram of a steering control system according to the invention, in which a situation-dependent adaptation of the variable steering ratio is made, and

5 the function module for situation-dependent adaptation of the variable steering ratio 4 in greater detail.

1 shows a schematic diagram of an inventive superposition steering for a motor vehicle. In 1 are shown in addition to the schematic apparatus design and sensor information that are necessary to realize the function of the superposition steering.

In the 1 shown superposition steering comprises a steering wheel 1 and one with the steering wheel 1 connected steering column 2 , the two universal joints 3 . 4 having. The steering column 2 is with a steering wheel shaft 6 connected or forms part of the steering wheel shaft 6 , The steering wheel shaft 6 is drivingly with a steering wheel gearbox 7 positively coupled, which is the rotational movement of the steering wheel shaft 6 in a translatory movement of a handlebar 8th transforms. The handlebar 8th is in 1 as a rack 8th formed, which the at the handlebar 8th arranged tie rods 11 . 12 actuated. The operation of the tie rods 11 . 12 causes a pivoting of steerable vehicle wheels 13 . 14 to control the direction of travel of the vehicle. Preferably, the steerable vehicle wheels 13 . 14 around the front wheels of the vehicle.

In the steering system shown here, a hydraulic power steering system is provided. This has a pump 16 which is driven by the drive motor. The pump 16 is in the illustrated embodiment via a belt drive 17 driven. Of course, however, all other suitable drive means are also conceivable for the realization of the present invention, which are known in the art. The hydraulic pump 16 generates pressure in a hydraulic fluid or a hydraulic fluid. The hydraulic fluid is via a pressure line 18 a hydraulic full bridge 19 supplied at a first terminal. A second connection of the hydraulic full bridge 19 is with a return line 21 connected in which the hydraulic fluid in a reservoir 22 can flow back. The storage tank 22 in turn is back with the pump 16 fluidly connected, so that the pump 16 from the reservoir 22 Hydraulic fluid can suck. Two pressure lines 23 . 24 lead from a third and fourth connection to a hydraulic cylinder 26 ,

The hydraulic cylinder 26 is from a sealed piston 27 in two working chambers 28 . 29 divided, the pressure line 23 to the cylinder chamber 28 leads and the pressure line 24 to the cylinder chamber 29 , The piston 27 sits firmly on the handlebar 8th so that the piston 27 directly on the handlebar 8th Force can exert if one of the two cylinder chambers 28 . 29 is subjected to a greater pressure than the other cylinder chamber.

In the steering wheel shaft 6 is a torsion bar 31 integrated. The torsion bar 31 twists under the action of one of the steering wheel shaft to the steering gear 7 transmitted steering torque M. By the rotation, which is proportional to the steering torque, the hydraulic full bridge 19 so controlled that a predetermined differential pressure in the working chambers 28 . 29 of the hydraulic cylinder 26 adjusts, so that the steering torque M is amplified.

Between the second universal joint 4 and the torsion bar 31 is also a superposition gear 32 arranged. The superposition gearbox 32 has two input shafts, one with the steering column 2 connected and the other with the servomotor 33 , The superposition gearbox 32 is suitable for superimposing a steering angle δ _H predefined by the driver with a superimposition angle φ _Mot , which is generated by a servomotor 33 is produced. For the driver's steering angle δ _H and the overlay steering angle φ _Mot are in the superposition gearing 32 different translation factors ν ₁ and ν _{2 are} provided. An output shaft of the superposition gear 32 is with the steering wheel shaft 6 coupled, wherein the driver's steering angle δ _{H is} coupled to the overlay angle φ _Mot taking into account the translation factors ν ₁ and ν ₂ additively to a resulting steering angle δ _R.

The driver's steering angle δ _H is in this case by an angle sensor 36 , the superposition angle φ _Mot from an angle sensor 37 and the resulting steering angle δ _R from an angle sensor 38 measured.

Basically, another structure of the superposition steering is conceivable in which the superposition gear between the torsion bar 31 and the steering gear 7 is arranged. However, this alternative structure has no influence on the essence of the invention and will therefore not be considered further below.

The control of the servomotor 33 or the determination of the overlay angle φ _Mot takes place in accordance with an additional steering angle in such a way that the resulting steering angle δ _{R is} a _sum steering angle δ _sum which is the sum of the driver's steering angle δ _H and the additional steering angle corresponds. In this case, the additional steering angle has a proportion determined as a function of the driver's steering angle δ _H and the vehicle speed v _Kfz , by means of which a variable steering ratio is realized. Furthermore, it can have further components which are determined, for example, by a vehicle dynamics control system or a lane keeping system. The total steering angle is determined in accordance with a desired steering angle, which is also referred to below as the _sum desired steering angle δ _{sum, CMD} and is determined in a steering control system.

In 2 a schematic block diagram of the steering control system is shown. The predetermined by the driver steering angle δ _H and the vehicle speed v _Kfz form the input variables for the block 41 , in which the translation factor ν _{δ, ESAS} for the desired steering ratio is determined. By multiplying the driver's steering angle δ _H by the ratio factor ν _{δ, ESAS} in the multiplier block 42 results in the desired value δ _{CMD, DRV of} the driver's steering angle. A control unit 43 , which is a driving dynamics controller in the embodiment of the invention shown by way of example, determines an additional steering angle Δδ _ESP , and an adding stage 45 forms from the setpoint δ _{CMD, DRV of} the driver steering angle and the additional steering angle Δδ _ESP , the setpoint δ _{sum, CMD of} the _sum steering angle δ _sum . The setpoint δ _{sum, CMD of} the cumulative steering angle is determined by means of a steering loop 44 set. The input variable is the steering loop 44 while the control deviation δ _{sum, CMD} - δ _sum supplied in the difference formation stage 46 formed and by means of the steering loop 44 is regulated.

Overall, a total additional steering angle is thus set with the overlay steering system, which consists of a first additional steering angle, with which the variable, speed-dependent steering ratio is achieved, as well as a second additional steering angle, the in the driving dynamics controller 43 determined additional steering angle Δδ _ESP corresponds.

As previously mentioned, instead of the vehicle dynamics controller 43 Alternatively or additionally, a lane keeping system or a further driver assistance system may be provided which determines a further additional steering angle. If such assistance systems are present, the assistant steering angles generated thereby are superimposed additively to the desired value δ _{CMD, DRV of} the driver steering angle as well as the additional steering angle Δδ _ESP .

In 3 is the block 41 out 2 shown in greater detail, in which the ratio factor ν _{δ, ESAS is determined} as a function of the present vehicle speed v _{motor vehicle} and the steering angle δ _H set by the driver.

Based on a predetermined characteristic is thereby in the block 47 an adapted to the vehicle speed v _Kfz translation factor ν _{δ, V} determined. Another, adapted to the driver's steering angle δ _H translation factor ν _{δ, H} is in the block 48 on the basis of a characteristic from that at the multiplication point 49 determined with the translation factor ν _{δ, V} driver steering angle δ _H to adjust the steering ratio to the driver's request. The translation factor ν _{δ, ESAS} , which is the output signal of the block 41 is formed by a multiplicative linkage of the two translation factors ν _{δ, V} and ν _{δ, H} at the multiplication point 50 determined.

As already explained at the beginning, can especially with a very direct translation of the steering a lot size Steering angle speeds occur where the dynamics of the Power steering system is insufficient to provide adequate steering assistance guarantee. The driver takes this as a hardening of the steering.

In order to avoid the problem of hardening of the steering, without having to modify the power steering, the invention proposes to adjust the course of the target value δ _{CMD, DRV of} the driver steering angle or the variable steering ratio so that situation-dependent rates of change of driver steering angle setpoint δ _{CMD, DRV} not be crossed, be exceeded, be passed. In this way, the steering angular velocities that occur are limited to values at which the power steering has sufficient dynamics to provide steering assistance. In particular, it can be achieved in this way that the steering torque to be applied by the driver always remains below a value of 5 to 6 Newton meters.

In 4 a schematic block diagram of a steering control system according to the invention is shown, compared to the in 2 system shown in particular by a functional module 51 is extended, which is used for situation-dependent adjustment of the steering ratio. Numerous components of in 4 The block diagram shown corresponds to the components associated with 2 have already been described, so that in connection with a repetition of the description 4 is waived.

The functional module 51 receives, as input variables in addition to the driver's desired steering angle δ _{CMD, DRV} the driver steering angle speed ω _H and the vehicle speed v _Kfz . The driver steering angle speed ω _H is thereby in a Differentiationstufe 52 determined from the driver steering angle signal δ _H. Output size of the function module 51 is a modified driver steering angle setpoint δ _{CMD, DRV, Mod} .

The setpoint δ _{sum, CMD} for the set total steering angle results in the inventive system from the addition of the modified driver steering angle setpoint δ _{CMD, DRV, Mod} and the additional steering angle Δδ _ESP and is by means of the steering loop 44 set as already related to 2 has been explained.

The modification of the driver steering angle setpoint δ _{CMD, DRV} results from a model for the maximum predefinable steering angle speed and essentially takes into account the limit values of the steering angle speeds at which the power steering still provides sufficient support.

The model for the maximum specifiable steering angular velocity is in the function module 51 For example, stored in the form of a characteristic or a table.

In 5 is a preferred embodiment of the functional module 51 for the situation-dependent adaptation of the steering ratio shown on the basis of a block diagram. According to 5 becomes with the function module 51 Essentially, a limitation of the rate of change of the driver steering _angle setpoint δ _{CMD, DRV} made, so that the modified setpoint δ _{CMD, DRV, MOD} results.

This is done in the block 53 The amount of a maximum _{steering angle speed} ω _{CMD, MAX, MODELL is} determined on the basis of a predetermined characteristic curve from the vehicle speed v _Kfz . The characteristic curve is given in particular taking into account the value of the speed-dependent transmission factor ν _{δ, ESAS} , so that in particular when at low vehicle speeds v _Kfz a very direct steering ratio is set, there is a sufficient limitation of the steering angular velocity.

In the block 54 becomes the maximum value of the amount of the maximum _{steering angular velocity} ω _{CMD, MAX, MODEL} and the magnitude | ω _H | the driver steering angle velocity ω _H , which is in the block 55 is determined determined. The determined maximum value | ω _{CMD, MAX} | is equal to the maximum steering angular velocity value to which the steering angular velocity in the limiting module 56 is limited.

By the maximum value formation in the block 54 is achieved that the limitation of the steering angle speed by the function module 51 not below the steering wheel speed ω _H set by the driver.

Within the boundary module 56 is the modified driver's desired steering angle signal δ _{CMD, DRV, MOD} on a time-discrete deadtime 57 fed back, which delays the signal by one clock period of the clock-wise operating digital controller. At the subtraction point 58 is then the value of the modified Sollfahrerenkwinkelsignals δ _{CMD, DRV, MOD of} the previous cycle step of the target value δ _{CMD, DRV of} the driver's steering angle subtracted. The thus determined difference δ _{CMD, DRV, MOD} -δ _{CMD, DRV} is then in the block 59 amount to the maximum value | ω _{CMD, MAX} | Limits the amount of steering angle speed. In the time-discrete integration module 60 the limited value of the difference δ _{CMD, DRV, MOD} - δ _{CMD, DRV is added} to the value of the nominal driving steering angle δ _{CMD, DRV, MOD} determined in the previous timing step. In this way, in each clock step of the discrete-time controller, an amount equal to | ω _{CMD, MAX} | limited rate of change for the desired driving steering angle δ _{CMD, DRV, MOD} , in which the power steering has sufficient dynamics to provide the driver with the usual steering assistance.

Claims (9)

A method for steering a vehicle with a superposition steering system in which a desired steering angle (δ _{CMD, DRV} ; δ _{sum, CMD} ) determined from a steering angle (δ _H ) predetermined by the driver and at least one additional steering angle is set by means of the superposition steering system, characterized in that a rate of change of the target steering angle (δ _{CMD, DRV} ) is limited to a maximum value determined by the situation (| ω _{CMD, Max} |). A method according to claim 1, characterized in that a first additional steering angle in accordance with the vehicle speed (v _{motor vehicle} ) is determined such that a speed-dependent gear ratio (ν _{δ, ESAS} ) between the predetermined by the driver steering angle (δ _H ) and the target steering angle ( δ _{CMD, DRV} ). A method according to claim 2, characterized in that the first additional steering angle in accordance with the predetermined by the driver steering angle (δ _H ) is determined. Method according to one of the preceding claims, characterized in that the rate of change of the target steering angle (δ _{CMD, DRV} ) to a maximum value (| ω _{CMD, Max, model} |) is limited, which is determined as a function of the vehicle speed (V _Kfz ). Method according to one of the preceding Claims, characterized in that the rate of change of the target steering angle (δ _{CMD, DRV} ) is limited in amount to a maximum value (| ω _{CMD, Max} |), which is a maximum of the determined in response to the vehicle speed (v _Kfz ) maximum value (| ω _{CMD, Max, model} |) and the rate of change (ω _H ) of the driver's steering angle (δ _H ) is determined. Method according to one of the preceding claims, characterized in that a further additional steering angle (Δδ _ESP ) in a vehicle dynamics control system ( 43 ) and / or in a lane keeping system, wherein only the rate of change of a proportion (δ _{CMD, DRV} ) of the target steering angle (δ _{sum, CMD} ) resulting from the first additional steering angle and the driver predetermined steering angle (δ _H ), limited becomes. Method according to one of the preceding claims, characterized in that by means of the superposition steering system due to the adjustment of the target steering angle (δ _{CMD, DRV} , δ _{sum, CMD} ) a steering torque is exerted on a steering line of the vehicle, which acts on steerable wheels of the vehicle, and that the effect of the steering torque is amplified by means of a power steering system. A vehicle steering system comprising a superimposed steering system with which a desired steering angle (δ _{CMD, DRV} ; δ _{sum, CMD} ), which can be determined from a steering angle (δ _H ) and at least one additional steering angle, is adjustable, characterized in that it is a functional module ( 51 ), with which a rate of change of the nominal steering angle (δ _{CMD, DRV} ) can be limited to a maximum value (| ω _{CMD, Max} |) determined as a function of the situation. A vehicle steering system according to claim 8, characterized in that by means of the superposition steering system due to the setting of the target steering angle (δ _{total, CMD} ) a steering torque to a steering line of the vehicle is exercisable, which acts on steerable wheels of the vehicle, and that it contains a power steering system, the is able to amplify the effect of the steering torque.