DE102007039332B4 - Method and steering assistance system for detecting the contact state of at least one hand of a driver on the steering handle of a vehicle - Google Patents

Abstract

Method for detecting the contact state of at least one hand of a driver on the steering handle of a vehicle,
characterized by the steps
1. the steering movement of the steering handle is detected by means of at least one torque sensor and at least one angle sensor,
2. the free steering movement of the steering handle is modelled using experimental measurement data, taking non-linear friction effects into account,
3. the driver steering torque is determined as a state by means of the state observer, whereby the state is a disturbance variable,
4. that a state observer is used to estimate the driver steering torque and the contact state between the hands and the steering handle is detected by means of the estimated driver steering torque, wherein the state observer is a disturbance observer.

Description

The invention relates to a method and a steering assistance system for detecting the contact state of at least one hand of a driver on the steering handle of a vehicle.

A steering handle with the above-mentioned features is known from DE 196 31 502 C1 known. With the introduction of modern driver assistance systems such as braking or lane-keeping support, as well as modern safety systems, information about the driver's behavior in emerging driving situations is increasingly required. The generic publication describes the attachment of a fiber-optic sensor to the steering handle, which can detect the elastic deformation of the steering handle's casing due to the driver's grip. This sensor is used as a measurement signal to control vehicle-side functions via an activated evaluation device.

With the progressive development of vehicle dynamics control and driver assistance systems, the detection of the contact state of the driver's hands with the steering handle is becoming increasingly important. For example, it is known from µ-split braking with active superimposed steering, or from DSR (Driver Steering Recommendation), that depending on the detected contact state between the driver's hands and the steering handle, the controller parameters are adjusted to eliminate or minimize potential vibrations of the steering handle and the resulting impaired handling of the vehicle. Even in driver assistance systems with lane guidance support, it is necessary to continuously monitor the contact state of the hands with the steering handle to avoid a driving situation in which the driver removes their hands from the steering handle while driving.

DE 100 48 956 C1 discloses a steering handle with a measuring device for determining the hand support of the vehicle driver and with an evaluation circuit coupled to the measuring device, which controls at least one vehicle-specific device, wherein a conductive surface is arranged on the steering handle which, together with the hand support surface of the vehicle driver and with a steering handle cover forming the dielectric, forms a capacitor, wherein the conductive surface of the steering handle is connected to a measuring circuit connected to a voltage supply in such a way that when the vehicle driver's hand is resting on the steering handle, a measuring variable is recorded due to the capacitive coupling between the steering handle and the vehicle body of the measuring current flowing from the output of the measuring circuit to the vehicle ground, and a corresponding measuring signal is transmitted to the evaluation circuit.

The DE 10121693 A1 and DE 10027922 A1 disclose methods and devices for detecting the contact between the hands and the steering handle based on sensors specifically provided for this purpose, which are to be attached to the steering handle.

In the US 6 219 603 B1 It is disclosed that contact between the hands and the steering handle is detected using an estimated driver steering torque calculated using a torque equation. However, this method does not account for the strong influence of nonlinear friction effects on the steering column. As a result, this method cannot clearly detect the contact state at small driver steering torques.

The invention is based on the object of providing a method for more reliably detecting the contact state between the hands of a driver and the steering handle.

The object is achieved by the features of claim 1 and the features of claim 7. Further advantageous embodiments are specified in the dependent claims.

It is understood that the term steering handle includes all devices that can be used to steer a vehicle.

In one embodiment of the method for detecting the contact state of at least one hand of a driver on the steering handle of a vehicle, the steering movement of the steering handle is detected by means of at least one torque sensor and at least one angle sensor, the free steering movement of the steering handle is modeled taking non-linear friction effects into account using experimental measurement data, the driver steering torque is determined as a state by means of the state observer, a state observer is used to estimate the driver steering torque and the contact state between the hands and the steering handle is detected by means of the estimated driver steering torque.

In a further embodiment, the dynamic model is a nonlinear differential equation that describes the free steering movement of the steering handle.

A particularly advantageous embodiment is characterized by the fact that the non-linear dynamic model of the steering handle is transformed into a linear model by numerical treatment.

In a further particularly advantageous embodiment, the detection of the hand-on/off state is carried out by comparing the moving average of the amount of the estimated driver steering torque in a predefined time window τ with a predefined threshold value ε1 and a comparison of the moving average of the amount of the quotient |x ₂ /M _s | with a predefined threshold value ε2.

A further advantageous embodiment is characterized in that when the measured moment M _s passes through zero, the modified quotient |x ₂ /M̃ _s | is used to calculate the moving average of the quotient |x ₂ /M _s |.

In a further advantageous embodiment, an active detection of the hand-off state is carried out if the estimated driver steering torque in a predefined time window τ is smaller than a predefined threshold value ε1 and the quotient |x ₂ /M _s |, optionally |x ₂ /M̃ _s |, is greater than a predefined threshold value ε2.

The object is also achieved by a steering assistance system which comprises a steering handle (1), a steering rod (2), means for detecting and determining steering movement signals (3, 4), means for filtering the steering signals (5, 6), means for forming mathematical derivatives (7), an observer for the driver's steering torque (8) and a hand-off detector (9).

The steering movement of a steering handle is advantageously represented with a nonlinear dynamic model taking into account both viscous and Coulomb friction, which advantageously reduces the estimation error.

The method according to the invention uses a disturbance variable observer to estimate the driver's steering torque. This eliminates the need for two explicit differentiations of the steering angle signal and advantageously reduces the computational effort required to estimate the driver's steering torque.

Furthermore, the method according to the invention does not directly detect the contact state, but rather determines the current driver steering torque. This allows, in certain safety-critical applications, the controller parameters to be configured not only based on the contact state of hands on the steering handle, but also based on the current driver steering torque.

Steering angle and steering torque sensors are often already present in a steering assistance system. The method according to the invention can advantageously use these sensor signals, which are not specifically intended for detecting the contact state between hands and the steering handle, to detect the contact state between hands and the steering handle. The steering handle thus remains unchanged, like a conventional steering wheel, and it is not necessary, as in the DE 196 31 502 C1 stated that the steering wheel should be modified accordingly.

An embodiment of the invention is illustrated in the drawings and is described in more detail below.

• 1 Einen schematische Aufbau eines erfindungsgemäßen Lenkassistenzsystems
• 2 Ein Vergleich zwischen Messung und Simulation
• 3 und 4 Der Einfluss des Zeitfensters τ auf Hand-Off-Detektion

It shows

• 1 A schematic structure of a steering assistance system according to the invention
• 2 A comparison between measurement and simulation
• 3 and 4 The influence of the time window τ on hand-off detection

The invention is based on the idea that the driver constantly makes steering corrections while driving. Even when driving straight ahead, a certain amount of "holding torque" is still present when holding the steering handle.

• • Durch das vom Fahrer auf die Lenkhandhabe ausgeübte Lenkmoment M_h.
• • Durch die Momente, die durch aktives Lenken von Aktuatoren wie EPS etc., oder durch unebenen Fahrbahn hervorgerufene Störmoment, oder als ein Gegenmoment des Lenkmomentes M_h. All diese Momente werden an dem Wirkungspunkt A, wo sich der Momentsensor befindet, als M_s zusammengefasst und lassen sich mit dem Momentsensor (4) ermitteln.
• • Durch das durch Reibung verursachte Moment M,. Dieses Moment wirkt ständig als Widerstand gegen die Rotationsbewegung der Lenkhandhabe (1).

In the 1 It is schematically shown that the rotational movement of the steering handle (1) can be caused and influenced by the following moments:

• • By the steering torque M _h exerted by the driver on the steering handle.
• • Through the moments caused by active steering of actuators such as EPS etc., or by uneven road surfaces, or as a counter-torque of the steering torque M _h . All these moments are summarized as M _s at the point of action A, where the torque sensor is located, and can be determined using the torque sensor (4).
• • By the moment M caused by friction. This moment constantly acts as a resistance against the rotational movement of the steering handle (1).

The rotational movement of the steering handle can be described by the following moment equation $$\ddot{\varphi }=\frac{1}{J}\left(M_s+M_r+M_h\right)$$

Where J is the moment of inertia of the steering handle (1) and the handlebar (2) above the torque sensor (4) and ϕ̈ is the angular acceleration of the steering handle.

In a hand-off condition, where the driver does not place his hands on the steering handle, the driver steering torque M _h is zero and Eq. (1) can be written as $$\ddot{\varphi }=\frac{1}{J}\left(M_s+M_r\right)$$ describe. In the following, this is referred to as "free steering movement of the steering handle."

1. 1. Die nicht durch Fahrer beeinflusste „freie Lenkbewegung der Lenkhandhabe“ möglichst genau mit einem nichtlinearen dynamischen Modell darzustellen.
2. 2. Das aus experimentellen Messdaten ermittelte nichtlineare Lenkhandhabemodell in ein numerisch behandelbaren linearen Modell zu transformieren.
3. 3. Das vom Fahrer ausgeübte Lenkmoment als eine Störgröße in dieses Modell einzubeziehen, wobei dies mit einem Zustandsbeobachter ermittelt wird.

The process according to the invention is preferably divided into three phases, whereby the individual phases can be further divided:

1. 1. To represent the “free steering movement of the steering handle” not influenced by the driver as accurately as possible using a non-linear dynamic model.
2. 2. To transform the nonlinear steering handling model determined from experimental measurement data into a numerically treatable linear model.
3. 3. To include the steering torque exerted by the driver as a disturbance in this model, which is determined using a state observer.

The friction moment in Eq.(1) and Eq.(2) is modeled as follows: $$M_r=-{\gamma }_v\cdot \dot{\varphi }-sign\left(\dot{\varphi }\right)\cdot {\gamma }_c\cdot \left(1-e^{v\cdot \left|\dot{\varphi }\right|}\right)$$

Here, γ _v is the coefficient of viscous friction and γ _c is the coefficient of Coulomb friction. Coulomb friction can be represented solely by sign(ϕ̇)·γ _c ; the term (1-e ^{v ·|ϕ̇|} ) included here improves the numerical treatment of Eq. (3). For the further description, Eq. (2) and Eq. (3) are combined as follows: $${\dot{x}}_1=a\cdot x_1+b_c\cdot sign\left(x_1\right)\cdot \left(1-e^{v\cdot \left|x_1\right|}\right)+b\cdot M_s$$ where x ₁ is the steering angle velocity and $a=\frac{{\gamma }_v}{J},b_c=-\frac{{\gamma }_c}{J},b=\frac{1}{J}.$ $$ The equation of state Eq. (4) represents the model structure of the steering handle dynamics. The unknown parameters a, b, b _c and v in this model are determined from experimental measurement data using parameter identification methods.

2 shows a comparison between a measurement and a simulation result of a model identified from measured data. It can be seen that the model represents the steering movement of the steering handle very well.

The steering handle model Eq. (4) describes a nonlinear dynamics of the steering handle and is not suitable for the design of a linear disturbance observer. In order to treat the model as a linear model, the steering speed x ₁ is included in the nonlinear term $$sign\left(x_1\right)\cdot \left(1-e^{v\cdot \left|x_1\right|}\right)$$ is replaced by the ϕ̇ calculated from the measured ϕ and this is defined together with the coefficient γ _c as Mc: $$M_c=-{\gamma }_c\cdot sign\left(\dot{\phi }\right)\cdot \left(1-e^{v\cdot \left|\dot{\varphi }\right|}\right)$$

Since M _c no longer depends on the model state x ₁ , it can be considered an independent input signal of the model. Thus, the model Eq. (4) can be transformed into a linear model: $${\dot{x}}_1=a\cdot x_1+b\cdot M_c+b\cdot M_s$$

Another way to decouple Mc from x ₁ is to not use x ₁ (t _k ) when calculating Mc(t _k ), but always use x̂(t _k-1 ) estimated with the observer (8): $$M_c\left(t_k\right)=-{\gamma }_c\cdot sign\left({\widehat{x}}_1\left(t_{k-1}\right)\right)\cdot \left(1-e^{v\cdot \left|{\widehat{x}}_1\left(t_{k-1}\right)\right|}\right)$$

Because the observed state at sampling point t _{k -1} is available for calculating Mc(t _k ), Mc(t _k ) can be considered as a known input signal of the model.

To determine the driver steering torque, the transformed linear steering model Eq. (6) is extended by an observable state: $$\left(\begin{array}{l}{\dot{x}}_1\\ {\dot{x}}_2\end{array}\right)=\left(\begin{array}{cc}a& b\\ 0& \xi \end{array}\right)\left(\begin{array}{l}{x}_1\\ x_2\end{array}\right)+\left(\begin{array}{cc}b& b\\ 0& 0\end{array}\right)\left(\begin{array}{l}{M}_c\\ M_s\end{array}\right),$$ where the extended state variable x ₂ represents the driver steering torque. ζ describes the linear dyna Mechanical behavior of the driver's steering torque. In a hand-off condition, where the driver does not place his hands on the steering handle, the driver's steering torque is 0 and remains unchanged. Therefore, x ₂ can be considered a constant, and ζ has a value of 0 in a hand-off condition.

Even in a hands-on state, where the driver has his hands on the steering handle and the driver's steering torque does not change quickly, this can be approximated with a constant in a certain time interval and ζ can be considered as 0. Thus, the extended state equation can be represented as follows: $$\left(\begin{array}{l}{\dot{x}}_1\\ {\dot{x}}_2\end{array}\right)=\left(\begin{array}{cc}a& b\\ 0& 0\end{array}\right)\left(\begin{array}{l}{x}_1\\ x_2\end{array}\right)+\left(\begin{array}{cc}b& b\\ 0& 0\end{array}\right)\left(\begin{array}{l}{M}_c\\ M_s\end{array}\right)$$

Using the extended state model Eq. (9), a state observer can be designed that estimates the driver steering torque.

The driver steering torque determined by the observer (8) does not exactly reflect the actual driver steering torque, as the model is only an approximation of the actual steering dynamics, and transforming the model using Eq. (5) or Eq. (7) affects the model's accuracy to a greater or lesser extent. The observer itself also has its own dynamics and provides the estimated value x ₂ for M _h with a certain time delay. In the extended steering model Eq. (9), the driver steering torque is considered constant, which is generally not the case in a hands-on condition.

Therefore, in a hand-off condition, it is possible that the driver steering torque estimated by the observer is not zero. To detect the hand-off condition as reliably as possible, the following criterion for hand-off detection is used:

If the moving average of the magnitude of the estimated driver steering torque x ₂ in a given time window τ is smaller than a given positive threshold ε1, and the moving average of the quotient |x ₂ /M _s | is smaller than positive ε2, then the hand-off condition (11) is true.

If the quotient |x ₂ /M _s | is greater than ε2 and |M _s | is less than ε3 (zero crossing of the measured moment M _s ), then it is checked whether the quotient |x ₂ /M̂ _s | is less than ε2. Here, M̂ _s = M _s + dM _s / dt · Δt Eq. (10). If the condition |x ₂ /M̂ _s |<ε2 is met, then the quotient |x ₂ /M̂ _s | modified according to Eq. (10) is used to calculate the moving average instead of |x ₂ /M _s |.

If the moving average of the magnitude of the estimated driver steering torque x ₂ in a given time window τ is less than ε1 and the moving average of the quotient |x ₂ /M _s | is greater than ε2, then active hand-off detection is performed. A predefined torque is applied by the actuator to the steering system, causing the steering angle of the steering handle to change, for example, sinusoidally with a predefined amplitude and frequency. For this active steering movement, hand-off detection is performed again as described above.

If the time delay of hand-off detection is not critical for the individual application, the time window τ will take a relatively large value. Preferably, the time window τ should be selected between 50 ms and 200 ms.

3 and 4 show the influence of the time window on the detection of the hand-off state. It can be seen that with a larger time window τ, the method detects the hand-off state with greater certainty, but also with a larger time delay.

Claims (7)

Method for detecting the contact state of at least one hand of a driver on the steering handle of a vehicle, characterized by the steps 1. the steering movement of the steering handle is detected by means of at least one torque sensor and at least one angle sensor, 2. the free steering movement of the steering handle is modeled taking non-linear friction effects into account on the basis of experimental measurement data, 3. the driver steering torque is determined as a state by means of the state observer, wherein the state is a disturbance variable, 4. that a state observer is used to estimate the driver steering torque and the contact state between the hands and the steering handle is detected by means of the estimated driver steering torque, wherein the state observer is a disturbance variable observer. Procedure according to Claim 1 characterized in that the dynamic model which describes the free steering movement of the steering handle is a non-linear differential equation. Procedure according to Claim 1 and 2 characterized in that the non-linear dynamic model of the steering handle is transformed into a linear model by numerical treatment. Method according to one of the preceding claims, characterized in that the detection of the hand-on/off state is carried out by a comparison of the moving average of the amount of the estimated driver steering torque in a predefined time window τ with a predefined threshold value ε1 and a comparison of the moving average of the amount of the quotient |x ₂ /M _s | with a predefined threshold value ε2. Method according to one of the preceding claims, characterized in that when the measured moment M _s passes through zero, the modified quotient |x ₂ /M̂ _s | is used to calculate the moving average of the quotient |x ₂ /M _s |. Method according to one of the preceding claims, characterized in that the estimated driver steering torque in a predefined time window τ is smaller than a predefined threshold value ε1 and the quotient |x ₂ /M _s |, optionally |x ₂ /M̂ _s |, is greater than a predefined threshold value ε2, an active detection of the hand-off state is carried out. Steering assistance system for detecting the contact state of at least one hand of a driver on the steering handle of a vehicle, characterized in that the steering assistance system comprises a steering handle (1), a handlebar (2), means for detecting and determining steering movement signals (3, 4), means for filtering steering signals (5, 6), means for forming mathematical derivatives (7), an observer for the driving steering torque (8) and a hand-off detector (9).