DE102007050866A1 - Method for monitoring malfunction in steering system, particularly castor steering system, involves measuring actual value for steering angle of secondary steering axle by sensor - Google Patents

Abstract

The method involves measuring an actual value for the steering angle of a secondary steering axle by a sensor. A modified steering angle limit value is determined from a steering angle limit during a change in the steering angle target value of the secondary steering axle, taking into consideration a predetermined minimum steering speed, which replaces the assigned steering angle limit value, so that a modified tolerance band emerges. An alarm is produced, if the steering angle-actual value depends on the modified tolerance band.

Description

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

Battery powered Steering systems comprising a primary steering axle coupled to a vehicle steering wheel and a hydraulically driven, secondary steering axle include already generally known from the prior art, so that the principal Design and operation does not need to be discussed in detail. The advantage This steering is that the steering behavior of Improved vehicles with more than two axles and reduced tire wear becomes.

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

Usually Fixed tolerance values are given by which the steering angle actual value is the steering angle reference value maximum or may fall short of. If the steering angle feedback is on This tolerance value leaves the defined tolerance band Alarm triggered, in which the steering system is deactivated and a system error is displayed becomes. When the steering system is deactivated, the secondary steering axle becomes transferred to a position that no impairment the safety of the steering behavior is expected. The behavior of the secondary steering axle approaches to an unguided axle.

As a result inadequate supply to one of the secondary steering axles, secondary Steering circuit can be the steering angle feedback of the secondary steering axle with this circuit not always with the necessary speed be adjusted to the steering angle setpoint, so that the steering angle actual value the tolerance band leaves and thus triggers an alarm. However, this alarm can be called a false alarm because it no system error, just a lack of setting speed underlying. This makes this false alarm fundamentally different of real system errors, where a deactivation of the steering system and a corresponding display for security reasons necessary is. Such real alarms are desired, for example, in the event that the amount of the actual steering angle value to the amount of the steering angle command value by more as a small predetermined tolerance value leads, or at a development of the steering angle actual value and steering angle target value in opposite directions. An example of the possibility of the occurrence of inadequate Hydraulic supply are steering systems in which a common Pump both one of the primary Steering axle associated, primary Steering circuit as well as the secondary Powered steering circuit, with a priority circuit first a minimum Supply of the primary Steering circuit ensures. For losses in performance the pump (for example, by wear) is therefore exclusively the first secondary Steering circuit affected by insufficient hydraulic supply.

task The invention is therefore an improvement of fault monitoring in electrohydraulic steering systems.

• a) mittels eines Sensors wird ein Istwert für den Lenkwinkel der sekundären Lenkachse gemessen;
• b) es wird ein 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, so daß 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) an actual value for the steering angle of the secondary steering axle is measured by means of a sensor;
• b) a target value 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) upon a change in the steering angle setpoint of the secondary steering axle, a modified steering angle limit value is determined from at least one steering angle limit taking into account a predetermined minimum steering angle speed, which replaces the associated steering angle limit, so that a modified tolerance band is formed;
• e) an alarm is triggered when the actual steering angle value leaves the modified tolerance band.

By This procedure will trigger the Alarms for apparent system errors during fast steering movements caused by a slow system reaction, avoided. As a result a dependency the steering angle limit values of the steering angular velocity becomes The tolerance band is not generally expanded so that the system sensitivity in the case of "real" system errors in the Maintained and early alarm is triggered.

Advantageous embodiments of the invention and their advantages will be apparent from the Unteran 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 limit values α _{O, mod} , α _{U, mod} together form the modified tolerance band T _mod for an 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 desired value α _soll in a tolerance band T _mod , taking into account a predetermined minimum steering angular velocity v _{α, min} .

To determine the current modified tolerance band, the following method is repeated continuously, where T _x-1, T _x of successive procedures between two points in time, a time interval AT = T _x - is predetermined T _x-1, preferably in the order of well under a 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, min2 . otherwise α O, mod (T x ) = α O, mod (T x-1 ) - ΔT · v α, min2 ,

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, min2 . otherwise α U, mod (T x ) = α U, mod (T x-1 ) + ΔT · v α, min2 ,

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 determination of a pump power, which should at least for the adjustment of the steering angle actual value α _is the secondary steering axle available, resulting from the influence of the centering _device so two minimum steering angle _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, taking into account a predetermined second steering angle speed 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} determined, 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. With this silent alarm, for example, a decrease in pump performance due to signs of wear is indicated as part of the inspection, so that a pump replacement can already be carried out before an actual alarm due to pump wear occurs.

The inventive method is applicable to steering systems which, in addition to a primary steering axle, mostly a primary steered front axle, have at least one secondary steering axle, wherein These are secondary Axis are located on motor vehicles or on trailers or semi-trailers can. In some embodiments are several secondary Steering axles provided, which can be actuated simultaneously, wherein with the procedure 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 comes in so-called tracking systems for use in which the secondary steering axle is a steered, non-driven trailing axle behind the driven axle is. Furthermore, the method can of course also in steering systems for Are used in which the secondary steering axle 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) sensing an actual value (α _ist ) for the steering angle (α) the secondary steering axle measured; b) a target value (α _soll ) for the steering angle (α) of the secondary steering axle is determined; 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 that 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 predefined 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} ) in step c) is predetermined as a function of 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 into the center position is set greater than when steering out of the center position. 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 angle speed (v _{α, min),} a second modified steering angle limit value (α _{O , mod2} , α _{U, mod2} ) is determined, so that a second modified tolerance _band (T _{mod, 2} ) is produced, wherein in step e) a silent alarm is triggered if the steering angle actual value (α _is ) the second modified tolerance band ( T _{mod, 2} ) leaves.