DE102007050866B4 - Method for error monitoring in a steering system - Google Patents

Abstract

A method for fault monitoring in a steering system having a primary steering axle coupled to a vehicle steering wheel and a hydraulically controlled secondary steering axle, the method comprising the steps of: a) using a sensor to obtain a steering angle actual value (α ist) for the steering angle (α ) of the secondary steering axle measured; b) it is determined a steering angle setpoint (αsoll) for the steering angle (α) of the secondary steering axle; c) based on the steering angle reference value (αsoll), a tolerance band (T) with an upper steering angle limit value (αO) and a lower steering angle limit value (αU) is determined by means of predetermined tolerance values (x1, x2); d) upon a change in the steering angle target value (αsoll) of the secondary steering axle, a modified steering angle limit value (α0, α2, min, vα, min1, vα, min2) is calculated from at least one steering angle limit value (α0, αU) taking into account a predetermined minimum steering angle speed. mod, αU, mod) which replaces the associated steering angle limit value (αO, αU) so that a modified tolerance band (Tmod) is produced; e) an alarm is triggered when the actual steering angle value (α actual) leaves the modified tolerance band (Tmod).

Description

The invention relates to a method for error monitoring in a steering system, in particular in a tracking control system.

Electrohydraulic steering systems which comprise a primary steering axle coupled to a vehicle steering wheel and a hydraulically controlled secondary steering axle are already generally known from the prior art, so that the basic design and mode of operation need not be discussed in more detail. The advantage of these steering systems is that the steering performance of vehicles with more than two axles is improved and tire wear is reduced.

As a rule, two steering angle sensors are provided, one sensor determining the actual value for the steering angle of the primary steering axle (usually the front axle) and the other sensor determining the actual value for the steering angle of the secondary steering axle. From the actual steering angle value for the primary steering axle, which essentially corresponds to a manually applied steering wheel angle, a desired value for the steering angle of the secondary steering axle is determined by means of an electronic control unit. The secondary steering axle is then operated in the following so that the sensed steering angle actual value approaches the steering angle command value.

Usually, fixed tolerance values are predetermined, by which the actual steering angle value may exceed or fall short of the steering angle reference value. If the actual steering angle value leaves a tolerance band defined by these tolerance values, an alarm is triggered in which the steering system is deactivated and a system error is displayed. When deactivating the steering system, the secondary steering axle is transferred to a position that does not expect the safety of the steering behavior to be impaired. The behavior of the secondary steering axle approaches that of an unguided axle.

As a result of insufficient supply of a secondary steering axle associated, secondary steering circuit of the steering angle actual value of the secondary steering axle in this circuit can not always be adjusted with the necessary speed the steering angle setpoint, so that the actual steering angle value leaves the tolerance band and thus triggers an alarm. However, this alarm can be called a false alarm because it is not based on a system error, but only a lack of setting speed. Thus, this false alarm differs fundamentally from real system errors, in which a deactivation of the steering system and a corresponding display for security is necessary. Such real alarms are desired, for example, in the event that the amount of the actual steering angle value leads the amount of the steering angle command value by more than a small predetermined tolerance value, or in a development of the steering angle feedback value and steering angle command value in opposite directions. An example of the possibility of the occurrence of insufficient hydraulic supply are steering systems in which a common pump supplies both a primary steering shaft associated with the primary steering circuit and the secondary steering circuit, with a priority circuit first ensures a minimum supply of the primary steering circuit. If the performance of the pump is impaired (for example due to wear), only the secondary steering circuit is initially affected by insufficient hydraulic supply.

The DE 103 26 384 A1 relates to a control method and a steering system for multi-steering a motor vehicle. The steering of a steerable front axle and a steerable rear axle via a hydraulic power steering system, which includes an electronic processing unit for determining steering angle setpoints. Furthermore, the steering system detects steering angle actual values both on the steerable front axle and on the steerable rear axle. For commissioning of the motor vehicle, a basic adjustment of the rear axle is calibrated for the straight-ahead driving of the motor vehicle, wherein this basic adjustment of the rear axle is recalibrated during vehicle operation depending on the vehicle speed and depending on the steering angle at the front axle.

In the DE 198 39 951 C2 discloses a steering system for non-track-bound motor vehicles, with a driver-operated steering handle, an actuator for steering adjustment steerable vehicle wheels, an operable with the steering handle steering angle setpoint generator, an operable with the steerable vehicle wheels steering angle feedback, one of the actuator in response to a comparison the setpoint and actual values of the steering angle and constantly controlling for malfunction control system and a cooperating with them sensor control arrangement arranged between the steering handle and the steerable vehicle wheels mechanical or hydraulic positive coupling, which is open when correctly operating control arrangement and automatically closed in case of faulty control arrangement , The positive coupling is closed in particular when the deviation between the nominal value and the actual value of the steering angle exceeds a threshold value, wherein the threshold value can be changed depending on parameters such as the vehicle speed and / or a setting force of the actuator.

The object of the invention is to improve the error monitoring in electro-hydraulic steering systems.

• a) mittels eines Sensors wird ein Lenkwinkel-Istwert für den Lenkwinkel der sekundären Lenkachse gemessen;
• b) es wird ein Lenkwinkel-Sollwert für den Lenkwinkel der sekundären Lenkachse ermittelt;
• c) ausgehend von dem Lenkwinkel-Sollwert wird mittels vorgegebener Toleranzwerte ein Toleranzband mit einem oberen Lenkwinkelgrenzwert und einem unteren Lenkwinkelgrenzwert bestimmt;
• d) bei einer Veränderung des Lenkwinkel-Sollwerts der sekundären Lenkachse wird aus wenigstens einem Lenkwinkelgrenzwert unter Berücksichtigung einer vorgegebenen minimalen Lenkwinkelgeschwindigkeit ein modifizierter Lenkwinkelgrenzwert ermittelt, welcher den zugeordneten Lenkwinkelgrenzwert ersetzt, sodass ein modifiziertes Toleranzband entsteht;
• e) es wird ein Alarm ausgelöst, wenn der Lenkwinkel-Istwert das modifizierte Toleranzband verlässt.

According to the invention, the object is achieved by a method for fault monitoring in a steering system which has a primary steering axle coupled to a steering wheel and a hydraulically controlled, secondary steering axle, the method comprising the following step:

• a) a steering angle actual value for the steering angle of the secondary steering axle is measured by means of a sensor;
• b) a steering angle setpoint for the steering angle of the secondary steering axle is determined;
• c) based on the steering angle reference value, a tolerance band with an upper steering angle limit value and a lower steering angle limit value is determined by means of predetermined tolerance values;
• d) When the steering angle setpoint value of the secondary steering axle changes, a modified steering angle limit value is determined from at least one steering angle limit value, taking into account a predefined minimum steering angle speed, which replaces the assigned steering angle limit value, resulting in a modified tolerance band;
• e) An alarm is triggered when the actual steering angle value leaves the modified tolerance band.

This procedure avoids triggering the alarm in case of apparent system errors that occur during fast steering movements due to a slow system response. As a result of a dependence of the steering angle limit of the steering angle speed, the tolerance band is not generally widened, so that the system sensitivity for "real" system errors is essentially maintained and early alarm is triggered.

Advantageous embodiments of the invention and their advantages will be apparent from the dependent claims.

The invention will be described below with reference to a preferred variant of the method, which is illustrated in the accompanying drawing. In the single figure, a steering angle target value α _{soll of} the secondary steering axis and an associated modified tolerance band T _{mod are} plotted over the time T, wherein the modified tolerance band T _{mod was determined} by means of the method according to the invention.

The figure shows by a curve 10 the course of the steering angle target value α _{is intended} for a steering angle α of the secondary steering axle of an electro-hydraulic steering system, wherein the steering angle α is defined for a straight ahead to 0 °. In addition, in the figure is a curve 12 plotted, which indicates the course of a modified upper steering angle limit α _{O, mod} , and a curve 14 indicating the course of a modified lower steering angle limit α _{U, mod} . The curves 12 . 14 the modified steering angle limits α _{O, mod} , α _{U, mod} together form the modified tolerance band T _mod for a steering angle actual value α _is the steering angle α of the secondary steering axle. The illustrated modified tolerance band T _mod is based on a rigid tolerance band T of constant width (not shown) with an upper steering angle limit α _O = α _soll + x ₁ and a lower steering angle limit α _U = α _soll - x ₂ , where x ₁ and x _{2 are} predetermined Tolerance values (eg x ₁ = x ₂ = 4 °) are. This rigid tolerance band T is modified in a change in the steering angle target value α _soll in a tolerance band T _mod , taking into account a predetermined minimum steering angular velocity v _{α, min} .

To determine the respective modified tolerance band, the following procedure is repeated continuously, wherein between two times T _x-1 , T _x successive procedures, a time interval .DELTA.T = T _x -T _{x-1 is} given, which is preferably of the order of significantly less than one Second lies.

The following is the preferred algorithm for determining the modified tolerance band T _mod :

Modified upper steering angle limit α _{O, mod} :

For positively defined angles, ie for α _{O, mod} (T _x-1 )> 0, the following applies:
With an increasing steering angle limit value α _O (T _x )> α _{O, mod} (T _x-1 ) (steering out of the center position) α _{O, mod} (T _x ) = α _O (T _x ).

When the steering angle limit value α _O (T _x ) ≦ α _{O, mod} (T _x-1 ) decreases (steering in the direction of the center position), α _{O, mod} (T _x ) is determined as follows: α _{O, mod} (T _x ) = α _O (T _x ), if α _{O, mod} (T _x-1 ) - α _O (T _x ) <ΔT · v _{α, min1} , otherwise α _{O, mod} (T _x ) = α _{O, mod} (T _x-1 ) - ΔT · v _{α, min1} .

For negatively defined angles, ie α _{O, mod} (T _x-1 ) <0,
When the steering angle limit value α _O (T _x ) ≦ α _{O, mod} (T _x-1 ) (steering out of the center position) increases in magnitude, α _{O, mod} (T _x ) is determined as follows: α _{O, mod} (T _x ) = α _O (T _x ), if α _{O, mod} (T _x-1 ) - α _O (T _x ) <ΔT · v _{α, min 2} , otherwise α _{O mod} (T _x ) = α _{O, mod} (T _x-1 ) - ΔT · v _{α, min 2} .

When the steering angle limit decreases in absolute value α _O (T _x )> α _{O, mod} (T _x-1 ) (steering in the direction of the center position) α _{O, mod} (T _x ) = α _O (T _x ).

Modified lower steering angle limit α _{U, mod} :

For positively defined angles, ie α _{U, mod} (T _x-1 )> 0, the following applies:
When the steering angle limit value α _U (T _x ) ≥ α _{U, mod} (T _x-1 ) (steering out of the center position) increases in magnitude, α _{U, mod} (T _x ) is determined as follows: α _{U, mod} (T _x ) = α _U (T _x ), if α _U (T _x ) - α _{U, mod} (T _x-1 ) <ΔT · v _{α, min 2} , otherwise α _{U, mod} (T _x ) = α _{U, mod} (T _x-1 ) + ΔT · v _{α, min 2} .

When the steering angle limit decreases in absolute value α _U (T _x ) <α _{U, mod} (T _x-1 ) (steering in the direction of the center position) α _{U, mod} (T _x) = α _U (T _x).

For negatively defined angles, ie α _{U, mod} (T _x-1 ) <0, the following applies:
In the case of an increase in the steering angle limit value α _U (T _x ) <α _{U, mod} (T _x-1 ) (steering out of the middle position) is: α _{U, mod} (T _x ) = α _U (T _x ).

When the steering angle limit value α _U (T _x ) ≥ α _{U, mod} (T _x-1 ) (steering in the direction of the center position) decreases, α _{U, mod} (T _x ) is determined as follows: α _{U, mod} (T _x ) = α _U (T _x ), if α _U (T _x ) - α _{U, mod} (T _x-1 ) <ΔT · v _{α, min1} , otherwise α _{U, mod} (T _x ) = α _{U, mod} (T _x-1 ) + ΔT · v _{α, min1} .

In this calculation, different minimum steering angular velocities v _{α, min} have already been taken into account. As a rule, v _{α, min 1 is set greater} for steering angle _{limit values} falling in the direction of the center position than the minimum steering angle _velocity v _{α, min 2} for steering angle _{limit values} increasing in magnitude (steering out of the center position). This is based on the finding that in steering systems with a centering a steering movement to the center position (α = 0) out is usually supported by the centering, whereas a steering movement from the center position (α = 0) out against the force of the centering must be done , From the definition of a pump power that _is α least for setting the steering angle-actual value of the secondary steering axis to be available, that is resulting from the influence of the centering two minimum steering angular velocities v _{α, min1,} v _{α, min2.} The use of two different steering _{angular velocities} v _{α, min 1} , v _{α, min 2} is shown in the figure by different slopes in the curves 12 . 14 with decreasing or increasing steering angle limit values (see figure, circled areas A and B).

The tolerance values x ₁ , x ₂ for the initial determination of the fixed tolerance band T are preferably predefined as a function of a vehicle speed v, the tolerance values x ₁ , x ₂ in particular being able to be identical.

Particularly preferably, the tolerance values below a first predetermined vehicle speed v ₁ (eg 4 km / h) take a predetermined first value x ₁ * (eg 20 °) above a second predetermined vehicle speed v ₂ (eg. 45 km / h) a predetermined second value x ₂ * (eg 3 °) and interpolated linearly therebetween.

Also, the minimum steering angular velocity v _{α, min} can be specified as a function of the vehicle speed v.

In a particular _{variant of the} method, a second modified steering angle _limit α _{O, mod 2} , α _{U, mod 2 is} determined taking into account a predetermined second steering angle velocity v _{α, 2} that is greater than the predetermined minimum steering _{angular velocity} v _{α, min} , so that a second modified tolerance _band T _{mod, 2} arises, wherein a silent alarm is triggered when the steering angle actual value α _is the second modified tolerance band T _{mod, 2} leaves. Silent alarm in this case means that the driver does not receive an indication and the steering system is not deactivated. However, the incident is stored internally and read out in the event of an inspection. For example, this silent alarm alerts the inspection to a decrease in pump performance due to wear, so pump replacement may already be performed before an actual alarm due to pump wear occurs.

The method according to the invention can be used in steering systems which, in addition to a primary steering axle, usually a primary steered front axle, have at least one secondary steering axle, whereby this secondarily steered axle can be located on motor vehicles or on trailers or semitrailers. In some embodiments, a plurality of secondary steering axles are provided, which can be operated simultaneously, with the method described above for all secondary steering axles common setpoints and tolerance bands or for each secondary steering axle own setpoints and tolerance bands can be determined.

Preferably, the described method is used in so-called tracking control systems in which the secondary steering axle is a steered, non-driven trailing axle behind the driven axle. Furthermore, the method can of course also be used in steering systems in which the secondary steering axle is a steered, non-driven leading axle in front of the driven axle.

Claims (8)

A method of fault monitoring in a steering system having a primary steering axle coupled to a vehicle steering wheel and a hydraulically controlled secondary steering axle, the method comprising the steps of: a) using a sensor to obtain a steering angle actual value (α _ist ) for the steering angle ( α) the secondary steering axle measured; b) it is determined a steering angle target value (α _soll ) for the steering angle (α) of the secondary steering axle; c) based on the steering angle reference value (α _soll ), a tolerance band (T) with an upper steering angle limit value (α _O ) and a lower steering angle limit value (α _U ) is determined by means of predetermined tolerance values (x ₁ , x ₂ ); d) upon a change in the steering angle target value (α _soll ) of the secondary steering axle, at least one steering angle _{limit value} (α _O , α _U ) is taken into account taking into account a predetermined minimum steering _{angular velocity} (v _{α, min} , v _{α, min 1} , v _{α, min 2} ) a modified steering angle limit (α _{O, mod} , α _{U, mod} ) is determined, which replaces the associated steering angle limit (α _O , α _U ), so that a modified tolerance band (T _mod ) is formed; e) an alarm is triggered when the actual steering angle value (α _is ) leaves the modified tolerance band (T _mod ). Method according to Claim 1, characterized in that in step d) a modified steering angle limit value (α _{O, mod} , α _{U, mod} ) is determined only for those steering angle limit value (α ₀ , α _U ) which, viewed in the steering direction, corresponds to the steering angle actual value ( α _is ) trailing. Method according to one of the preceding claims, characterized in that the tolerance values (x ₁ , x ₂ ) in step c) are predefined as a function of a vehicle speed (v). A method according to claim 3, characterized in that the tolerance values (x ₁ , x ₂ ) in step c) below a first predetermined vehicle speed (v ₁ ) a predetermined first value (x ₁ *) and above a second predetermined vehicle speed (v ₂ ) assume a predetermined second value (x ₂ *) and interpolate linearly therebetween, the first value (x ₁ *) being greater than the second value (x ₂ *). Method according to one of the preceding claims, characterized in that the minimum steering angle speed (v _{α, min} ) in step c) is predetermined as a function of the vehicle speed (v). Method according to one of the preceding claims, characterized in that the minimum steering angle speed (v _{α, min} ) is predetermined in step c) depending on the steering direction in a center position or from a center position. A method according to claim 6, characterized in that the minimum steering angle speed (v _{α, min} ) in step c) when driving in the center position is set greater than when steering from the center position out. Method according to one of the preceding claims, characterized in that in step d), taking into account a predetermined second steering angular velocity (v _{α, 2} ), which is greater than the predetermined minimum steering angular velocity (v _{α, min} ), a second modified steering angle limit (α _{O , mod2} , α _{U, mod2} ) is determined, so that a second modified tolerance _band (T _{mod, 2} ) arises, wherein in step e) a silent alarm is triggered when the steering angle actual value (α _is ) the second modified tolerance band ( T _{mod, 2} ) leaves.

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