DE102012002771B4 - Electromechanical vehicle steering system - Google Patents

Abstract

Electromechanical vehicle steering system for steering assistance in a vehicle, with at least one torque sensor (3), wherein to compensate for the frictional forces and/or the mass inertia of a steering mechanism (1) of the vehicle steering system, a current frictional torque and/or a current mass moment of inertia during operation of the vehicle by means of the torque sensor (3 ) can be determined, characterized in that the steering mechanism is located between the vehicle driver (4) and the torque sensor (3) of the vehicle steering system, with freehand driving of the vehicle by measuring the total torques of the steering mechanism (1) depending on three driving situations, namely a steering standstill , a steering with constant steering angular speed and a steering with steering angular acceleration, can be seen, wherein in a driving situation of the steering with constant steering angular speed a freehand drive of the vehicle through a time integral of the determined friction force and / or or in a driving situation of the steering with steering angular acceleration a freehand drive of the vehicle a time integral of the determined mass inertia can be seen.

Description

The invention relates to an electromechanical vehicle steering system for steering assistance in a vehicle, with at least one torque sensor according to the preamble of claim 1 or a method for implementing such a vehicle steering system according to the preamble of claim 7, in order to measure inertia and frictional forces of a steering mechanism that are between the vehicle driver and the torque sensor of the vehicle steering system.

Nowadays, electromechanical vehicle steering is being used more and more in motor vehicles. An electromechanical vehicle steering system usually contains a torque sensor attached to the steering shaft, which can detect the steering torque applied by the driver. In addition to the steering torque applied by the driver, the kinematic parameters of the steering mechanics also have an effect, such as the moments of inertia, inertia and friction depend on the design of the steering system, in particular the components between the driver and the torque sensor, i.e. the detection results are strongly influenced. Such kinematic parameters must therefore be determined and compensated for.

Previous compensation methods, such as in the DE 10 2004 041 616 B4 described, were based on a predetermined, stored friction and mass inertia value. The disadvantage here is, on the one hand, that the stored friction and inertia can deviate greatly from their actual values; on the other hand, for every different construction or every changed structure of the steering wheel mechanics, a new determination and storage of the friction and inertia is necessary for every changed structure, which means a new one Friction and mass inertia value must be provided. A learning process, namely a determination via an integral function that lacks friction and inertia.

The DE 10 2008 021 848 A1 discloses a generic method for taking static and dynamic friction into account and a corresponding steering system, in which the influence of the steering speed on the friction of the steering system is corrected using a friction model.

The DE 10 2008 051 551 A1 discloses a vehicle control device in which an inertia compensation torque is determined to compensate for the influences of inertia in order to control the force on steerable wheels and the support torque of the steering system described there is adjusted accordingly.

The DE 10 2004 041 616 B4 discloses a method for steering assistance in a vehicle, in which a motor acting on a steering gear is controlled depending on a steering torque measured by a steering torque sensor. The measured steering torque is reduced by a correction variable that is formed from the moment of inertia and the rotational acceleration of the steering wheel.

The DE 10 2009 028 647 A1 discloses a method in which a driver hand torque currently applied by the driver is determined depending on the steering wheel angle and the steering torque. Depending on the course of the driver's hand torque, it is recognized whether the driver has his hands on the steering wheel or not.

The DE 10 2010 036 655 A1 discloses a method for operating a steering system and a steering system, wherein a control loop that regulates a steering assistance torque of the steering system takes the inertia of the steering column into account.

It is also of interest whether the driver controls the steering system specifically or drives hands-free, because hands-off driving often occurs when the steering wheel returns and represents a safety risk at high speeds. On the other hand, a hands-off with the parking steering assistant represents a safe state. A vehicle steering system should try to perceive hands-free driving and react accordingly.

The invention is then based on the object of improving an electromechanical vehicle steering system and its steering assistance in order to determine or compensate for the kinematic variables of the steering mechanism, in particular the frictional forces and inertia, which can affect the accuracy of the steering assistance, and thereby in particular to achieve freehand driving recognize.

This object is achieved according to the invention by an electromechanical vehicle steering system with the features of patent claim 1 or a method for steering assistance for a vehicle with the features of patent claim 7. Further advantageous embodiments of the invention result from the respective subclaims.

The invention is based on the idea of forming a friction function with variable values depending on the steering angular speed and steering angle, with the mass inertia also being determined accordingly. According to the invention, an electromechanical vehicle steering system for steering assistance in a vehicle is provided with at least one torque sensor. To compensate for the frictional forces and/or the mass inertia of a steering mechanism (e.g. component groups) of the vehicle steering system, which is located between the vehicle driver and the torque sensor of the vehicle steering system, a current frictional torque and/or a current mass moment of inertia are determined during operation of the vehicle using the torque sensor. This allows the friction and the mass inertia for the steering mechanism between the vehicle driver and the torque sensor to be determined individually for each steering angle and each steering angular speed in order to be able to better compensate for the corresponding moments of friction and moments of inertia that also act on the torque sensor.

According to an advantageous embodiment of the invention, a friction force and/or mass inertia of the steering mechanism to be compensated is determined by means of the torque sensor in such a way that a steering angular velocity-dependent friction function is determined by determining a current friction torque for individual steering angular velocity intervals, each of which has an almost constant steering angular velocity. A constant mass inertia, which is independent of the steering angle, between two different steering angular velocities is determined by a steering angular velocity-dependent friction force determined between the two steering angular velocities. In addition, a steering angle-dependent friction function can be determined by determining a current friction torque for individual steering angle intervals, each of which has an almost identical steering angle.

Alternatively, a constant mass inertia can be determined by torques that are measured by means of the torque sensor in a current steering angular velocity when braking and accelerating the vehicle steering (e.g. the steering wheel).

Since the electromechanical vehicle steering system is suitable for different vehicles or can be installed in different arrangements, instead of the constant mass inertia, there may be a steering angle-dependent mass inertia in the vehicle steering system. Such a mass inertia between two different steering angles can be determined by a steering angle-dependent friction force determined between the two steering angles.

A steering angle acceleration required for the calculations can be determined by a first derivative of the steering angular velocity or a second derivative of the steering angle. In order to compensate better and more precisely than a predetermined target value for the frictional force and mass inertia, which oscillate strongly depending on different current steering angular speeds and steering angles and thus deviate far from a predetermined target value, they are used by one of the above two methods for a range of the steering angular speed and the steering angle is determined. This means that a value of the friction force or mass inertia that needs to be compensated is measured more precisely.

In a hands-off case, no steering torque is applied by the driver against the influence of road stimuli, and driving at a high speed is therefore very dangerous. Therefore, hand-off driving of the vehicle can be detected by measuring the total torques between the vehicle driver and the torque sensor of the vehicle steering system depending on three driving situations, steering standstill, steering with constant steering angular velocity and steering with steering angular acceleration. Because the hands-off detection is integrated into the vehicle steering system, a hands-off case can then be recognized automatically. No other devices or mechanisms are required to determine the hands-off information; instead, hands-off information is determined and currently provided by the steering system.

According to the invention, freehand driving of the vehicle is recognized by measuring the total torques of the steering mechanism depending on three driving situations, namely a steering standstill, a steering with a constant steering angular velocity and a steering with a steering angular acceleration. In a steering driving situation with constant steering angular speed, freehand driving is achieved by a Time integral of the determined current friction force recognized. In a steering driving situation with steering angle acceleration, freehand driving of the vehicle is recognized by a time integral of the determined current mass inertia. Through the time integral of the frictional moments and the mass inertia, namely the current frictional moments and mass inertia have been learned, the difference or deviation between the determined current values and the frictional moments or the mass inertia then approaches zero.

To protect the electromechanical vehicle steering system, the determined kinematic parameters of the steering mechanism, such as the frictional force and the mass inertia, can each be compared with a pre-stored corresponding setpoint. If the determined parameters deviate from their corresponding target values, an appropriate error response must be carried out. Depending on the severity of the risk, this leads to a reduction or deactivation of steering angle-dependent functionalities or even to a reduction or deactivation of the steering assistance.

Furthermore, a method according to the invention is a method for steering support for a vehicle with an electromechanical vehicle steering system. In this method, a current frictional torque and/or a current mass moment of inertia for compensating for the frictional forces and/or the mass inertia of a steering mechanism of the vehicle steering system, which is located between the vehicle driver and the torque sensor of the vehicle steering system, is determined during operation of the vehicle by means of the torque sensor.

• 1: die schematische Darstellung eines erfindungsgemäßen Fahrzeuglenksystems,
• 2: Ermittlung eines kinematischen Kennwertes bei Hands-Off und bei Fahrereingriff.

The invention is explained in more detail below in the context of the exemplary embodiments using the figures. It shows:

• 1 : the schematic representation of a vehicle steering system according to the invention,
• 2 : Determination of a kinematic characteristic value during hands-off and driver intervention.

1 shows a schematic representation of a vehicle steering system according to the invention in a vehicle. The electromechanical vehicle steering system includes at least one torque sensor 3. It should be noted that the manual torque measured by the steering system via the torque sensor 3 does not only consist of the manual torque applied by the vehicle driver 4, but also of other kinematic parameters, such as the moments of inertia and friction from a steering mechanism 1, which has a steering wheel 5, or the components between the vehicle driver 4 and the torque sensor 3. To determine and compensate for such frictional forces and the mass inertia, a friction function is formed by means of the torque sensor 3 in such a way that a steering angle speed-dependent friction function R(v ) is determined for individual steering angular velocity intervals, each of which has an almost constant steering angular velocity.

To determine the mass inertia, the influence of friction must be negligibly small or must be taken into account. If the friction is already determined, a constant mass inertia function M, which is independent of the steering angular speed, is determined during acceleration between two different steering angular speeds v1, v2 with known friction. The mass inertia M can be determined by an integral between the two steering angular velocities from the specific friction function R(v,t).

It is shown mathematically, where the times t1 and t2 correspond to v1 and v2, respectively: $$M=\frac{1}{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="DE102012002771B4\_0007.png"\; state="\{\{state\}\}">t</figure-callout>}2-\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="DE102012002771B4\_0007.png"\; state="\{\{state\}\}">t</figure-callout>}1}{\displaystyle {\int }_{t1}^{t2}R\left(v,t\right)dt}$$

If friction has not yet been determined, or in order to enable independence from the friction calculation, a constant mass inertia M can be determined in an alternative way so that a moment M _Abbr measured when braking the steering wheel 5 is inverted and with the moment applied when accelerating the steering wheel 5 M _damage is averaged. The averaged torque is then divided by the acceleration α(t) of the steering angular velocity v. For the corresponding friction, it is important that the steering angular velocities in a range under consideration do not differ between braking and accelerating. This can be represented by a mathematical equation. $$M=\frac{1}{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="DE102012002771B4\_0007.png"\; state="\{\{state\}\}">t</figure-callout>}2-\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="DE102012002771B4\_0007.png"\; state="\{\{state\}\}">t</figure-callout>}1}{\displaystyle {\int }_{t1}^{t2}\frac{M_{bescH}\left(t\right)-M_{Abbr}\left(t\right)}{2\times \alpha \left(t\right)}}dt$$

ebenfalls lenkwinkelabhängig zu bestimmen. Idealerweise sind die Lenkwinkelgeschwindigkeit- und Lenkwinkelintervalle zur Erfassung einer momentanen Reibungskraft zu einer bestimmten Lenkwinkelgeschwindigkeit oder einem bestimmten Lenkwinkel möglichst oder sogar unendlich klein zu wählen, die prinzipiell einer Differenz der Lenkwinkelgeschwindigkeit Δv oder des Lenkwinkels Δθ entsprechen. Dabei wird eine für die Berechungen benötigte Lenkwinkelbeschleunigung durch eine erste Ableitung der Lenkwinkelgeschwindigkeit oder eine zweite Ableitung des Lenkwinkels ermittelt.If the steering angle dependence of the friction is not negligible, the friction must be determined accordingly via the steering angle θ. The areas in which the mass inertia is determined must then also be selected depending on the steering angle. A steering angle-dependent friction function R(θ) for individual steering angle intervals, which also each have an almost identical steering angle, can be determined, whereby the steering angle dependence must be taken into account when determining the mass inertia. If the mass inertia is dependent on the steering angle, the mass inertia function is $M|\begin{array}{c}\mathrm{<figure-callout\; id="2"\; label="\theta "\; filenames="DE102012002771B4\_0007.png"\; state="\{\{state\}\}">\theta </figure-callout>}2\\ \mathrm{<figure-callout\; id="1"\; label="\theta "\; filenames="DE102012002771B4\_0007.png"\; state="\{\{state\}\}">\theta </figure-callout>}1\end{array}$

also to be determined depending on the steering angle. Ideally, the steering angular velocity and steering angle intervals for detecting a momentary friction force at a specific steering angular velocity or a specific steering angle should be chosen as small as possible or even infinitely small, which in principle correspond to a difference in the steering angular velocity Δv or the steering angle Δθ. A steering angle acceleration required for the calculations is determined by a first derivative of the steering angular velocity or a second derivative of the steering angle.

Because a current moment of friction and/or moment of inertia is determined during operation of the vehicle by an integral function, the difference or deviation between the current values and the measured values of the moment of friction and/or moment of inertia can be significantly reduced, so that the frictional forces and/or to be able to compensate the mass inertia of the first steering mechanism 1 of the vehicle steering system more precisely.

In addition, the torque sensor 3 also detects moments or forces that are initiated by a road stimulus 5 and a support machine 6, for example an electric motor, via a lower steering mechanism 2 under the torque sensor 3, this steering mechanism 2 being between the torque sensor 3 and the Vehicle wheels 5 is located. The torque applied by the driver 4 is transmitted together with the moments of friction and inertia to the torque sensor 3 and counteracts the moments introduced from below.

The torque measured by the steering system, which was introduced above the torque sensor 3, therefore represents a sum of the driver's hand torque, inertia and friction, namely $$\text{Measuring torque}=\text{Hand moment}+\text{Mass tr}\ddot{\text{a}}\text{ghness moment}+\text{Friction torque}$$

In a hands-off case, no driver's hand torque is applied, hand torque = 0. Moments from the road excitation and the support machine 6 only counteract the moment of inertia and the moment of friction above the torque sensor 3 in the direction of the driver 4. The steering system enables hands-off detection to be distinguished in three driving situations:

1) Steering standstill:

When the steering is at a standstill, the mass inertia can be neglected, i.e. measuring torque = friction torque. If a measurement torque is greater than the friction, the driving situation can be assumed to involve driver intervention. However, if a measurement torque is smaller than the friction torque, no statement can be made about driver intervention because there is no counter-torque. However, the information about driver intervention can be determined if a limit torque is exceeded.

2) Steering movement with a constant steering angular velocity:

In the hands-off case, only the moments from inertia and friction act on the torque sensor 3. If the steering angular speed remains the same, the mass moment of inertia is negligible, that is, the measuring torque is approximately equal to the current frictional torque, namely $$\text{Measuring torque}\left(\text{t}\right)\approx \text{friction}\left(\text{t}\right).$$

If the driver 4 holds or guides the steering wheel 5, an additional torque is applied at least twice and is detected by the torque sensor 3. As in 2 displayed, the current friction torque can be precisely determined using a time integral. During hands-off, the difference between the measuring torque and the determined current friction torque (learning value) gradually decreases. Only when the learning value of the friction torque 8 remains constant over a certain time range and the difference between the measurement torque and the friction torque 9 approaches zero can it be assumed that hands-off occurred in this time range. With guided steering, however, the measuring torque is often determined by the current friction mo ment differ. The friction torque will not run in or will only occur with very strong fluctuations.

If the friction depends on the steering angle, the hands-off detection must be designed to be dependent on the steering angle.

3) Steering movement with steering angle acceleration:

If the steering angle acceleration remains the same, the moment from the mass moment of inertia is almost constant, ie, in the hands-off case, the measuring torque is approximately equal to the sum of the current friction torque and the moment from the mass inertia, namely $$\text{Measuring torque}\left(\text{t}\right)\approx \text{friction}\left(\text{t}\right)+\text{Mass tr}\ddot{\text{a}}\text{ghness moment}\left(\text{t}\right).$$

For steering movements with steering angle acceleration, the determination of the mass inertia including hands-off detection must be carried out analogously to the determination of the frictional torque using a time integral explained above. The moments from the current mass inertia are compared with the measurement torque minus the current friction torque. From the comparison, the mass moment of inertia of the steering mechanism 1 between the torque sensor 3 and the vehicle driver 4 can be reduced. Only when the current values of the mass moment of inertia 11 remain constant over a certain time range and the difference between the theoretical mass moment of inertia and the measurement torque minus the friction torque (characteristic curve 10) approaches zero, is it assumed that a hands-off occurred in this time range.

Because the total torques between the vehicle driver 4 and the torque sensor 3 of the vehicle steering system are measured depending on three driving situations, steering standstill, steering with constant steering angular velocity and steering with steering angular acceleration, hands-off driving of a vehicle can be automatically recognized. It does not require any other devices or mechanics to determine the hands-off information, but rather determines and provides current hands-off information.

In addition, steering systems are often manufactured variably on the same production line. The resulting variants differ, for example, in the design, the connection to the steering wheel 5, the translation from the steering pinion to the rack and the control electronics. In right-hand drive systems, the connection between the steering system and the driver is usually designed differently than in left-hand drive systems. If additional shafts and joints are used, the inertia or friction force of the components between the steering system and the driver 4 can be higher. Therefore, the determined friction force and/or mass inertia of the steering mechanism 1 and/or 2 are each compared with their pre-stored corresponding target values in order to protect the electromechanical vehicle steering system from an error. If the determined parameters deviate from their target values, an appropriate error response must be carried out. Depending on the severity of the risk, the steering angle-dependent functionalities or the steering support are reduced or switched off. If a kinetic parameter (e.g. steering angle) is influenced by the assumption of an incorrect variant (e.g. gear ratio), the kinematic parameter determined from this is falsified. If the comparison is carried out for every variant of the steering system that occurs, the incorrect assumption of the variant can be recognized or a correct variant can be determined via the multiple comparison. This method can also be transferred to other kinematic parameters of the steering mechanism 1, for example the natural frequency is changed by installing additional components.

Claims (12)

Electromechanical vehicle steering system for steering assistance in a vehicle, with at least one torque sensor (3), wherein to compensate for the frictional forces and/or the mass inertia of a steering mechanism (1) of the vehicle steering system, a current frictional torque and/or a current mass moment of inertia during operation of the vehicle by means of the torque sensor (3 ) can be determined, characterized in that the steering mechanism is located between the vehicle driver (4) and the torque sensor (3) of the vehicle steering system, with freehand driving of the vehicle by measuring the total torques of the steering mechanism (1) depending on three driving situations, namely a steering standstill , a steering system with constant steering angular velocity and a steering system with steering angular acceleration, can be seen, wherein in a driving situation of the steering system with constant steering angular velocity, a freehand drive of the vehicle is achieved by a time integral of the determined friction force and/or or in a driving situation of the steering with steering angle acceleration, freehand travel of the vehicle can be recognized by a time integral of the determined mass inertia. Electromechanical vehicle steering system Claim 1 , characterized in that a frictional force and/or mass inertia of the steering mechanism (1) to be compensated can be determined by means of the torque sensor (3) in such a way that - a steering angular velocity-dependent friction function by determining a current friction torque for individual steering angular velocity intervals, each of which has an almost constant steering angular velocity, is determined, and -a constant mass inertia between two different steering angular velocities is determined by a steering angular velocity-dependent friction force determined between the two steering angular velocities. Electromechanical vehicle steering system Claim 1 , characterized in that a constant mass inertia is determined by torques which are measured by means of the torque sensor (3) in a current steering angular velocity when braking and accelerating the vehicle steering. Electromechanical vehicle steering system according to one of the Claims 1 until 3 , characterized in that a steering angle-dependent friction function is determined by determining a current friction torque for individual steering angle intervals, each of which has an almost identical steering angle. Electromechanical vehicle steering system Claim 4 , characterized in that a steering angle-dependent mass inertia between two different steering angles is determined by a steering angle-dependent friction force determined between the two steering angles. Electromechanical vehicle steering system according to one of the preceding claims, characterized in that the determined frictional force and/or mass inertia of the steering mechanism (1) are each comparable to a corresponding target value in order to protect the electromechanical vehicle steering system from an error. Method for steering assistance for a vehicle with an electromechanical vehicle steering system, wherein a current frictional torque and/or a current mass moment of inertia during operation of the vehicle are determined by means of the torque sensor (3) in order to compensate for the frictional forces and/or the mass inertia of a steering mechanism (1) of the vehicle steering system, characterized in that the steering mechanism (1) is located between the vehicle driver (4) and the torque sensor (3) of the vehicle steering system, with freehand driving of the vehicle by measuring the total torques of the steering mechanism (1) depending on three driving situations, namely a steering standstill, a steering with constant steering angular speed and a steering with steering angular acceleration, is recognized, wherein in a driving situation of the steering with constant steering angular speed a freehand drive of the vehicle by a time integral of the determined friction force and / or in a driving situation of the steering with steering angular acceleration a freehand drive of the vehicle by a time integral the determined mass inertia is recognized. Procedure according to Claim 7 , characterized in that a friction force and/or mass inertia of the steering mechanism (1) to be compensated are determined by means of the torque sensor (3) in such a way that - a steering angular velocity-dependent friction function by determining a current friction torque for individual steering angular velocity intervals, each of which has an almost constant steering angular velocity, is determined, -a constant mass inertia between two different steering angular speeds is determined by a steering angular speed-dependent friction force determined between the two steering angular speeds. Procedure according to Claim 7 or 8th , characterized in that a constant mass inertia is determined by torques which are measured by means of the torque sensor (3) in a current steering angular velocity when braking and accelerating the vehicle steering, Procedure according to one of the Claims 7 until 9 , characterized in that a steering angle-dependent friction function is determined by determining a current friction torque for individual steering angle intervals, each of which has an almost identical steering angle. Procedure according to Claim 10 , characterized in that a steering angle-dependent mass inertia between two different steering angles is determined by a steering angle-dependent friction force determined between the two steering angles. Method according to claim one of the previous ones Claims 7 until 11 , characterized in that the determined frictional force and/or mass inertia of the steering mechanism (1) are each compared with a corresponding target value in order to protect the electromechanical vehicle steering system from an error.

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