WO2016105316A1

WO2016105316A1 - Steering feel generating system for steer-by-wire systems

Info

Publication number: WO2016105316A1
Application number: PCT/TR2015/050252
Authority: WO
Inventors: Mehmet Selçuk ARSLAN
Original assignee: Arslan Mehmet Selçuk
Priority date: 2014-12-24
Filing date: 2015-12-17
Publication date: 2016-06-30

Abstract

This invention is related to a system (10) providing instantly feedback to determine the next motion of the steering wheel (1) by using the hysteresis curve model to generate steering feel in the steer-by-wire systems.

Description

DESCRIPTION

STEERING FEEL GENERATING SYSTEM FOR STEER-BY- WIRE

SYSTEMS

Related technical field of the invention This invention is related to a system providing steering wheel turning feel to the driver by generating steering wheel reaction torque.

Prior Art

The steering wheel motion is created by providing a mechanical connection between the steering wheel and wheels in the vehicles. However, there is not any mechanical connection between wheels and the vehicle's steering wheel which is used by the driver in the steer-by- wire systems. Instead of this, for example, the angle of the steering wheel is transmitted to the control unit by a sensor measuring the rotational motion of the steering wheel and in accordance with this information, the control rack which the wheels are connected to is driven with an electric motor. While the torque occurring in wheels in case of turning the wheels right and left can be transmitted directly to the steering wheel with the mechanical connection in the vehicles without steer-by- wire, production of a reaction torque in the steering wheel is required in the steer-by-wire systems whose mechanical connection does not exist with the wheels.

When the steering wheel is turned in the conventional type vehicles without steer-by- wire, a reaction torque mainly based on SAT (Self Aligning Torque - wheel aligning torque) occurs and therefore, the driver senses steering wheel turning feel. In other words, the motion of the wheels is fed to the driver back with SAT. Thereby; because the steering wheel turning feel or steering feel affects usage quality, it is defined as the most basic and important feedback provided to the driver. In the SBW (Steer By Wire) systems, because direct connection to the steering wheel is not carried out and the connection between the front axle electric motor and steering wheel (handwheel) is provided electrically, generating a force-feedback system is inevitable to create steering feel for the driver. The relation between the steering wheel angle and the steering wheel reaction torque transmitted from the steering wheel in the conventional vehicles is in the form of a hysteresis curve as shown in the Figure 3. In between the points where this curve intersects the horizontal axis, in between the points where it intersects the vertical axis, maximum and minimum values and inclination of this curve depends on the dynamics conditions of the vehicle.

SAT information which is estimated is used to create conventional steering feel in this systems in the prior art. To use the estimated SAT information causes some difficulties and complicated structure. Also, while the vehicle goes with a low velocity or stops, the SAT model cannot be used in these systems. Usage of an additional approach to the SAT model is required to be able to create steering feel in case of that the vehicle stops or goes with a low velocity. In addition, usage of the SAT model for a better steering feel creates a problem in the maneuver skill of the driver while the active steering control or SBW control is in use. The interference of corrective control command of the active steering control to correct the dynamic behavior of the vehicle causes a different steering motion of the wheels apart from the driver's steering command. In addition, feeding the SAT back to the driver would have a disturbing effect on the driver during the maneuver. The reaction torque of the wheel is calculated by real time measuring of the tire lateral force to provide torque feedback to the driver in some works in the prior art. However, these methods are not feasible because of the cost of the sensors used in these methods, lifetime limitedness and calibration necessity in change.

While the steering wheel turning feel is produced, the steering wheel torque feedback is produced according to the force signal taken from the load cells positioned into the control rack in some embodiments of the prior art. One of these embodiments is disclosed in the United States patent document with the number of US6678596. There is a load sensor measuring the load in the actuator in this embodiment. In addition, a series of equations is used to calculate the torque applied to the user with the electric motor. Brief description of the invention

The aim of this invention is to realize a system generating steering feel effectively for the driver in the steer-by-wire systems.

The disclosed system generating steering feel for steer-by-wire systems of the invention comprises a steering wheel, a steering wheel motor rotating the steering wheel, a steering wheel angle sensing unit which senses the rotation angle of the steering wheel, a vehicle dynamics sensing unit providing sensing of dynamics like longitudinal velocity, yaw velocity, lateral acceleration of the vehicle. Also, the disclosed system of the invention comprises a control unit adapted such that it provides instantly feedback to determine next motion of the steering wheel via using the hysteresis curve model by calculating the reaction torque that is to be transmitted to the steering wheel according to the information taken from the steering wheel angle sensing unit and vehicle dynamics sensing unit and by transmitting this reaction torque to the steering wheel.

In the invention,

the steering feel is generated by the control unit (4) by using this equation in which:

"Tsw" is the steering wheel reaction torque namely control signal applied onto the motor attached to steering wheel,

K_w, σ, n " are constant values, "pfuj " is the parameter related to the longitudinal (linear) velocity of the vehicle on which the system is applied, is the normalized steering wheel angle,

"ω" is the hysteretic displacement and " " and "0_n" are respectively first order derivatives of ω and θ_η with respect to time,

"7V" is "reduction in the steering wheel reaction torque" value which be calculated depending on the longitudinal velocity and pneumatic trail dynamics and steering wheel angle (θ_η) of the vehicle by the control unit of the moving vehicle.

When T_r =0 is taken in this equation, this equation is used in a more simplified form for low velocity systems. In an embodiment of the invention, the values in the equation (1) are selected as κ_χ = 0.01, K_W = 1, σ = 0.05 and n=2.

Also, the system comprises a pneumatic trail estimation unit which gives the distance between lateral axis of the tire and the point on which the resultant lateral tire force which occurs depending on the tire motion in the contact patch of the tire acts. Thus, while the control unit calculates the reaction torque transmitted to the steering wheel, it includes also the information which it takes from the pneumatic trail estimation unit together with the information which it takes from the steering wheel angle sensing unit and vehicle dynamics sensing unit.

In the invention, pneumatic trail is calculated by pneumatic trail estimation calculation unit and used in this equation:

in which normalized velocity parameter is "M«", pneumatic trail parameter is "ξ".

In the preferred embodiment of the invention, the steering wheel motor rotating the steering wheel is an electric motor. The invention can be used in the steer-by- wire (steer-by- wire) systems, in the steering simulators and in all systems where generation of the reaction torque transmitted to the steering wheel is required like game steering wheels.

Detailed description of the invention

Figure 1: It is the schematic view of the invention.

Figure 2: It is the schematic view of a steer-by- wire system where the invention is used in an embodiment. Figure 3: It is the graph showing the condition of the reaction torque which is felt in the steering wheel according to the steering wheel angle in the conventional (without steer-by- wire) vehicles.

Figure 4: It is the graph showing the condition of the reaction torque generated in the control unit according to the steering wheel angle in the invention.

Description of the references in the figures:

The parts in the attached figures are numbered respectively for the purpose of this invention and the equivalents of these numbers are given below.

10. System generating steering feel

1. Steering wheel

2. Steering wheel motor

3. Steering wheel angle sensing unit

4. Control unit

5. Vehicle dynamics sensing unit

6. Pneumatic trail estimation calculation unit

M. Wheel driving motor

T. Wheel

K. Control rack

The disclosed system generating steering feel (10) for electronic wheel systems of the invention comprises a steering wheel (1), a steering wheel motor (2) rotating the steering wheel (1), a steering wheel angle sensing unit (3) which senses the rotation angle of the steering wheel (1), a vehicle dynamics sensing unit (5) providing sensing vehicle dynamics like longitudinal velocity, yaw velocity, lateral acceleration of the vehicle, a pneumatic trail estimation calculation unit (6) which gives the distance between the lateral axis of the tire and the point on which the resultant lateral tire force occurring depending on the tire motion in the contact patch of the tire acts, a control unit (4) providing instantaneously feedback to determine next motion of the steering wheel (1) by calculating the reaction torque which is about to be transmitted to the steering wheel (1) according to the information that the control unit (4) takes from the steering wheel angle sensing unit (3), vehicle dynamics sensing unit (5) and pneumatic trail estimation unit with the usage of hysteresis curve model and by transmitting it to the steering wheel (1).

In an embodiment, the disclosed system generating steering feel (10) of the invention is used in a system comprising wheels (T) where the motion of the steering wheel (1) is transmitted, a wheel driving motor (M) moving the wheels (T), a control rack (K) connecting the wheels (T) with each other.

In the invention, a hysteresis model is used to generate the reaction torque. The steering wheel reaction torque developed based on the Bouc-Wen hysteresis model is used in the invention. Said used model is given in the equation (1) below.

Tsw is the steering wheel reaction torque namely the control signal applied onto the motor (2) attached to the steering wheel (1) in the equation (1). In other words, it expresses the torque applied onto the driver and it is the quantity which we mention as steering feel. κ_%, K_w, σ, n, and p(u) are the parameters of the hysteresis curve and the parameter of p(u) is a function depending on the longitudinal (linear) velocity (u) of the vehicle. The parameters of κ_χ, K_w, σ, n are constants and they are determined according to the need. These constant parameters are expressed with real numbers. θ_η is the normalized steering wheel angle namely the normalized angular rotation quantity of the steering wheel (1). This value is obtained by dividing the steering wheel angle by the maximum steering wheel angle: θ_η = Θ / θ_η. ώ and θ_η are respectively first order derivatives of ω (hysteretic displacement) and θ_η with respect to time in the equation (1).

Rotation of the steering wheel (1) (θ_η) and the velocity of the vehicle p(u) are the variables and the generated T_sw(t) torque changes in case of their change. The main input of the system is the steering wheel angle (#„) and while the output torque can be generated even if the vehicle velocity remains constant, its opposite is not true. The term specified as T_r depends on the longitudinal velocity of the vehicle and the pneumatic trail dynamics, also it is generated with calculation by the control unit (4) of the moving vehicle depending on the steering wheel angle (#„). After the control unit (4) calculates this value, it sends this value to the related unit as a control signal.

It is known that how the parameters of κ_χ, K_w, σ, n affect the relation between the input (the steering wheel angle) and the output (the torque applied onto the steering wheel (1)). The changes made by the producer are made in the direction of these information according to where the system is used. A hysteresis curve which gives this input (horizontal axis), output (vertical axis) is given in the Figure 4. This graph shows the reaction torque, depending on the steering wheel angle, generated by using Equation (1) in response to an order of sinusoidal steering wheel angle applied while a sedan type passenger car whose front wheels (T) can only be steered moves at a speed of 100 km/h and it can have different forms for the same variables via the constants in the equations. Namely, a change in the parameters for a specific sinusoidal input causes creating different hysteresis forms.

The control unit (4) signal which is generated with the invention and which makes the driver feel the real condition of the vehicle (wheels) is as seen in the Figure 4. The constant parameters creating the control unit (4) signal transmitted to the steering wheel, namely the hysteresis curve, can be changed according to the vehicle steering characteristics and the driver's like by the vehicle producer.

The term of T_r has a special importance in the Equation (1). It represents the reduction in the steering wheel reaction torque which is felt by the driver according to the dynamic behavior of the vehicle and this term is optional. Especially in low speed vehicles like agricultural vehicles or construction equipment, this term does not have any importance. If it is demanded that the interaction between the tire and road is reported to the driver in the form of torque feedback, this term can be added to the right side of the equation as negative signed as in Equation(l). In other cases, it is taken as 7V =0. A change in the steering wheel reaction torque acting on the driver occurs in case of that the tire approaches to the gripping limits and passes them while the vehicle is maneuvered by rotating the steering wheel in the conventional vehicles. Even if the lateral tire forces increase, the self-aligning torque and related to this, the steering wheel reaction torque decrease as the tire approaches to its limits. This reduction in the reaction torque is important in the sense that the driver can make corrective maneuvers or at least the driver is informed about the dynamic condition of the vehicle. In the disclosed system of the invention, the relations of the normalized steering wheel angle and the steering wheel reaction torque which are calculated by including and not including the term of T_r is indicated in the Figure 4. A sharp drop is seen in the torque value in the graph of the steering wheel reaction torque where the term of T_r is effective. This drop indicates an effective feedback to the driver.

The self-aligning torque is equal to the product of the lateral tire force and a length which changes according to the dynamic behavior of the tire in the contact patch of the tire and which is called as pneumatic trail. While the aligning torque decreases, the pneumatic trail decreases theoretically. For this reason, the term of T_r can be given as the following, especially depending on the pneumatic trail (ξ) and the longitudinal velocity of the vehicle in addition to its dependence on the hysteresis curve parameters:

Here, the normalized velocity, u_n, is defined as:

Here, the variable of ξ is the pneumatic trail and it is found by estimation in the pneumatic trail estimation unit (6). Various estimation methods can be used while the pneumatic trail is calculated. As shown in the Figure 1 and 2, the pneumatic trail estimated by using analytical approximations together with the sensor data which gives dynamic condition of the vehicle is used by the control unit (4) and the steering wheel reaction torque namely, equation (1) signal is generated by combining the pneumatic trail with the data of other sensing units (3, 5). This invention can be used to generate the reaction torque transmitted to the steering wheel (1) in the steer-by- wire (steer-by- wire) systems, steering simulators and game steering wheels.

In the disclosed system (10) of the invention, the motor (2) which is used is an electric motor in the preferred embodiment.

In the disclosed system (10) of the invention, the parameters in the mathematical formula creating the control signal which is sent to the steering wheel motor (2) by the control unit (4) to form the steering feel can be changed in wide ranges by the producer. In order to provide the steering feel aimed by the producer, adjusting the parameters is possible depending on the dynamic characteristics of the vehicle and/or offering different steering feelings optionally.

The adjustment process is based on that the producers adjust the parameters of the model with the tests that they perform on the vehicles to obtain the desired steering feel. Mainly, which properties belonging to the hysteresis figure that these parameters change can be given such that: κ_χ controls the hysteresis gradient, K_W controls the distance between the points where the hysteresis curve intersects the vertical axis, p controls the ductility of the figure and the gradient of the figure without changing its limits, σ controls the hardening and softening of the figure and also the distance between the points where the hysteresis curve intersects the horizontal axis, and n controls passing from linear behavior to plastic behavior. If it is desired that the limits of the hysteresis curve stay at the unit value, the parameters of /¾and K_W can be changed depending on each other. For example; when K_W - 1 is selected, κ_χ - 0.01 can be selected. If the value of κ_χ is increased, to decrease the value of K_W is required. The parameter of n is a greater number than zero. The parameters used in the calculation of the Figure 4 are selected as κ_χ = 0.01, K_w = 1, σ= 0.05 and n=2.

It is prevented that the undesired effects like vibrations at high or low speeds in the wheels (T) are reflected to the driver due to the mathematical model used in the control unit (4) in the disclosed system (10) of the invention. In addition, a system (10) where the output type of the signal which outputs from the control unit (4) can be changed easily is created with said method.

In the invention, the simple model which is mentioned in the Equation (1) and where Tr =0 is taken can be used in the vehicles like agricultural machinery working at low speeds, steering and game simulators. In addition, the extensive model can be used in every type of vehicle. In the invention, since the interaction of road and wheel is also reflected to the driver, the feedback that the driver takes is richer and more important.

The invention is not limited with the embodiments disclosed above and a skilled person in the art can perform different embodiments of the invention easily. They should be evaluated within the scope of the invention protection demanded with claims.

Claims

A steering feel generating system (10) for steer-by-wire systems comprising a steering wheel (1), a steering wheel motor (2) rotating the steering wheel (1), a steering wheel angle sensing unit (3) which senses the rotation angle of the steering wheel (1), a vehicle dynamics sensing unit (5) providing sensing of dynamics like longitudinal velocity, yaw velocity, lateral acceleration of the vehicle; characterized by a control unit (4) adapted such that it provides instantly feedback to determine next motion of the steering wheel (1) by calculating the reaction torque which is about to be transmitted to the steering wheel (1) via using the hysteresis curve model according to the information which the control unit (4) takes from said steering wheel angle sensing unit (3) and vehicle dynamics sensing unit (5) and by transmitting the reaction torque to the steering wheel (1).

A system (10) according to claim 1 characterized by a control unit (4) generating steering feel by using this equation;

in which "T_Sw" is the steering wheel reaction torque namely the control signal applied onto the motor (2) connected to the steering wheel, " _¾ K_W, , n" are constant values, "p(u) " is the parameter depending on the longitudinal (linear) velocity of the vehicle on which the system is applied, "θ„" is the normalized steering wheel angle, "ω" is the hysteretic displacement and " " and "0_n" are respectively first order derivatives of ω and 9_n with respect to time, "TV" is the value of "drop in the steering wheel reaction torque" which can be calculated by the control unit (4) of the moving vehicle depending on the longitudinal velocity of the vehicle and pneumatic trail dynamics and steering wheel angle (ft).

A steering feel generating system (10) according to claim 2 wherein T_r =0 is taken when it is used in the low speed systems.

4. A steering feel generating system (10) according to claim 2 or 3 wherein κ_χ = 0.01, K_w - 1, σ = 0.05 and n-2 are selected.

5. A steering feel generating system (10) according to any of claims above characterized by comprising a pneumatic trail estimation calculation unit (6) which calculates the distance between the lateral axis of the tire and the point on which the resultant lateral tire force occurring depending on the tire motion in the contact patch of the tire acts and a control unit (4) including also the information that it takes from the tire trail estimation unit (6) to the calculation while it calculates the reaction torque transmitted to the steering wheel (1).

6. A system (10) according to Claim 5 characterized by a pneumatic trail estimation calculation unit (6) calculating pneumatic trail by using this equation;

in which the normalized velocity parameter is "««", the pneumatic trail parameter is "ξ".

7. A system (10) according to any of claims above wherein the steering wheel motor (2) rotating the steering wheel (1) is an electric motor.

8. A system (10) according to any of claims above which is used to generate the reaction torque transmitted to the steering wheel (1) in the steer-by- wire systems, steering simulators and game steering wheels.

Figure 1

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Figure 2

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