Method and system arrangement for vehicle steering and vehicle having such a system

Abstract

The invention relates to a vehicle steering system arrangement (100) comprising a vehicle suspension allowing wheel steering and a power-assisted vehicle steering having a feedback torque actuator (130), with steering feel being controlled by means of a torque and / or angle control system TAC (132). The vehicle suspension having steerable wheels comprises a plurality of vehicle suspension parameters, and the geometry and / or dimensions of one or more vehicle suspension parameters or elements are designed to reduce or minimize the steering effort required to steer the vehicle while being driven. The torque and / or angle control TAC (132) is used to control the wheel steering angle based at least on a directly or indirectly sensed and / or calculated steering wheel angle, and to provide feedback control by controlling the feedback torque actuator to generate a target feedback torque and a target steering feel, and thereby reduce or eliminate driver feedback provided by the vehicle suspension, so that if there is a fault in the steering control and assistance is lost, the steering effort will be low enough for the driver to handle safely, so that a fail-operating steering gear is not required.

Description

Technical Field

[0001] The invention relates to a method for steering a vehicle. The invention also relates to a vehicle steering arrangement, and a vehicle comprising such a steering arrangement. Background Art

[0002] The steering and front suspension of a vehicle are usually designed to give a certain feedback and steering effect based on the torque caused by the driver's hand force on the steering wheel, with or without amplification by power steering (BCPS, boost-curve power steering). For BCPS, the steering feel is purely a small fraction of the rack force, with all its perturbations, friction, etc. This severely limits the freedom of vehicle design and the optimization of vehicle characteristics.

[0003] The suspension design will also resist undesired steering effects from external forces, i.e. changes in wheel steering angle (between the wheels in a top view, relative to the forward direction of travel) not introduced by the driver, while providing the desired steering effect from external forces. This often results in severe compromises and, as mentioned above, increased constraints on the suspension design and overall vehicle performance.

[0004] Even if the suspension parameters can be adjusted to minimize steering forces, they may not usually be low enough to allow comfortable driving with good steering feel. The need for power assistance usually increases with front axle load.

[0005] Another topic surrounding modern vehicles and their power assisted steering is that steering may be too difficult if the assistance is lost. To overcome this, the power steering of vehicles with high steering rack loads would need to be fail-safe, i.e., maintain assistance even during a failure, which would be very expensive.

[0006] Therefore, the current design of suspension and power steering system must meet many conflicting goals.An important criterion for designing a good steering system with good feedback is to provide increased torque feedback and self-centering of the steering wheel when the vehicle turns more difficultly, that is, when accelerating laterally. The means to do this is to have a certain caster offset value at the ground. The caster offset at the ground is a lever between the longitudinal center point of the steering axis and the wheel contact patch. The increase of the caster offset at the ground will give clear torque feedback to the driver, thereby overcoming the friction and force reduction of the power steering. If the feedback from the caster offset at the ground is strong, it will also reduce the disturbance around the steering axis (such as the steering effect from the acceleration of the vehicle) except the disturbance in the lateral direction, thereby becoming relatively small.

[0007] This self-aligning design will also increase the steering effort required when driving slowly to some extent. At higher speeds, this effect is often significant with respect to other forces.

[0008] Another criterion is to have steering wheel self-centering at very slow speeds where the lateral acceleration forces are too low to provide this self-centering. The amount or value of the normal force lever and inclination of the steering axis towards the vehicle centerline will create a lifting effect of the vehicle when turning away from the straight ahead position. This will create a self-centering effect when the steering wheel is released after turning.

[0009] Unfortunately, this self-aligning design will also increase the steering effort required when stationary and driving slowly. At higher speeds, this effect generally loses significance with respect to other forces.

[0010] The normal forces acting on the tires will also give a turning torque about the steering axis. In an ideal situation, the sum of these forces from the left and right sides will balance each other. When driving on uneven roads, driving with an asymmetrically loaded vehicle, or driving on roads with lateral inclinations, the sum of the forces will not be zero, creating a perturbation torque in the steering wheel.

[0011] Furthermore, when the vehicle is driving in a curve, the outer wheel has a higher normal load than the inner wheel, thereby increasing or decreasing feedback to the driver.

[0012] A special case is a tire explosion which can suddenly lead to asymmetric normal forces and therefore sudden steering torque changes which can seriously affect the driver's ability to maintain the intended course. In the case of heavy vehicles, this situation often results in the death of the driver, or of people in cars in oncoming traffic, if the vehicle goes off the road.

[0013] The lever for the normal force can be set to zero, at least in theory, to overcome the above mentioned problems. However, in practice, due to other factors and constraints imposed by practical situations, the lever is not designed to be zero.

[0014] Even though the lever may be set to zero, the effective lever will change anyway as the actual contact point between the road and the wheel changes.

[0015] Attempts to reduce the problem of high steering forces to some extent based on a compromise in the case of steering feedback and returnability as described above have not been satisfactory.

[0016] Power steering itself is the primary solution for overcoming the high hand force of the driver, especially when parking. There is a conflict between the desire to have low amplification at higher speeds close to straight ahead and high amplification at lower speeds. This is solved by highly non-linear amplification, boost-curves, which are U-shaped, which try to compromise between the goals, but may result in non-linear steering feel or steering forces that are too high or too low at different speeds.

[0017] To overcome this speed dilemma, different ways have been proposed to steer the power assist bend as a function of speed. For hydraulic steering, Honda has proposed a hydraulic solution, while ZF AG has an electronic solution. This design suffers from the disadvantages of being complex and expensive, and can lead to increased sensitivity to disturbances when lower assist is desired. It can also sometimes compromise steering feel and performance.

[0018] In the case of EPS (Electric Power Steering), power steering is handled via software at a much smaller cost and complexity penalty than in the hydraulic case. Still, it does not solve the problem of increased sensitivity to disturbances.

[0019] High steering forces mean that the power steering must be able to handle higher loads. Therefore, placing higher demands on the power steering itself will increase cost, weight, maximum current demand and overall power consumption.

[0020] In order to obtain a sufficiently low, legal steering effort for the driver when the power steering fails, the steering ratio can be increased or a larger steering wheel can be used. However, these two solutions significantly impair the driver's steering experience.

[0021] Another means of dealing with power assist failures is to add redundancy to the system. In the case of heavy vehicles, the power steering pump can be duplicated, however this will significantly increase cost and complexity.

[0022] For EPS, several subsystems can be doubled or even tripled to achieve adequate redundancy in the power steering system. However, using redundant subsystems to this extent will increase cost and complexity, and is space-demanding. Summary of the invention

[0023] It is therefore an object of the present invention to provide a vehicle steering method and a vehicle steering system arrangement, respectively, by which one or more of the above-mentioned problems can be solved and by which one or more disadvantages can be overcome.

[0024] In particular, the object is to provide a vehicle steering method and a vehicle steering system arrangement by which steering safety can be increased.

[0025] Even more particularly, the object is to provide a method and a vehicle steering system arrangement by which steering safety can be increased in the event of a loss of steering assistance and in particular steering can be facilitated in the event of a loss of steering assistance.

[0026] Another specific object is to provide a method and a vehicle steering system arrangement, respectively, by which steering safety can be increased at normal or high speeds and even more particularly at least to some extent also at low or very low driving speeds (e.g. down to parking speed).

[0027] Further, a specific object is to provide a vehicle steering method and a vehicle steering system arrangement, respectively, by which braking stability can be increased.

[0028] Another specific object is to provide a vehicle steering method and a vehicle steering system arrangement, respectively, by means of which steering safety can be increased in the event of a loss of steering assistance and braking stability can be achieved.

[0029] Another specific object is to provide a vehicle steering method and a vehicle steering system arrangement, respectively, by which steering safety can be enhanced in the event of uneven forces, which are caused, for example, by ice or clay or unevenly distributed slippery conditions on the road generally under one side of the vehicle and not on the other side, or by sudden yaw disturbances.

[0030] Yet another specific object is to provide a vehicle steering method and a vehicle steering system arrangement, respectively, which are cheap and easy to implement and manufacture.

[0031] Another specific object is to provide a vehicle steering method and a vehicle steering system arrangement, respectively, by which steering safety can be enhanced in the event of a failure in the steering performed by a wire steering system. The steering performed by a wire steering system comprising at least two motors, one for driver feedback and the other for turning the wheels, can have a moderate degradation in the event of a failure of one motor. With the failure of one motor, the steering arrangement essentially becomes a conventional power steering system via a mechanical connection. With the present invention, either motor can assist the driver in steering safely under reduced steering forces, even if it is a motor intended for torque feedback - typically having a lower capacity than a motor intended for turning the wheels.

[0032] Further, a specific object is to provide a vehicle steering method and a vehicle steering system arrangement, respectively, which are reliable, safe and at the same time provide good steering feel and steering response (how the car reacts to steering inputs) at high speeds, but preferably also at low speeds, and in particular at all speeds above a parking maneuver speed.

[0033] It is also an object of the present invention to provide a vehicle by means of which one or more of the above-mentioned objects can be achieved.

[0034] Hence, a vehicle steering method and a vehicle steering system arrangement, respectively, as initially mentioned are provided.

[0035] Advantageous embodiments are described in the detailed description.

[0036] It will be appreciated that features of the invention are susceptible to being combined in any combination without departing from the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The invention will be further described below in a non-limiting manner and with reference to the accompanying drawings, in which:

[0038] Figure 1Schematically illustrates a steering system arrangement with TAC - Torque and / or Angle Control and front suspension of a ground vehicle according to an exemplary embodiment of the present invention,

[0039] Figure 2 Schematically illustrates a front view of the steering wheel and Figure 1 The main influencing parameters of the steering system layout in Figure 3 Schematically illustrates a side view of a steered wheel and Figure 1 The main influencing parameters of the steering system layout. DETAILED DESCRIPTION

[0040] For the purpose of describing the present invention, and to facilitate understanding of the present invention, the following definitions are given, which will be relied upon in the detailed description of advantageous embodiments:

[0041] definition:

[0042] Torque and / or angle reference control (TAC) includes steering feel control (SFC) and / or steering position control (SPC), respectively. For steering feel control, the control of the steering wheel torque felt by the driver is the subject, and in steering position control, it is the control of the wheel angles, and specifically for front wheel steer vehicles, the control of the front axle wheel angle, which is here called steering angle (see definition below).

[0043] The steering angle is the angle in the steering system that affects the lateral acceleration or curvature of the vehicle. This angle is measured somewhere in the steering system. This steering angle can be:

[0044] - the front wheel angle, and in case of e.g. Ackermann steering the steering angle is defined as the average of the angles of the two front wheels;

[0045] - articulation angle for articulated vehicles;

[0046] - rear wheel steering angle in case of a rear wheel steering vehicle;

[0047] - In case of an all-wheel steering vehicle, the combination of the front wheel angle and the rear wheel angle.

[0048] The power steering will also provide a means for adjusting steering feedback.

[0049] A steering position actuator is an actuator that can be used for SPC, which affects one or more of the following: steering angle (such as, front wheel steering angle, rear wheel steering angle, individual steering angles of wheels), axle braking torque or force, wheel braking torque or force, driving torque or force on individual axles, driving torque or force on individual wheels, camber angle on each axle, or camber angle on each wheel.

[0050] A specific type of steering position actuator is an angle overlay actuator. An angle overlay actuator is an actuator used to achieve a relative angle somewhere in the steering column. Two hardware concepts dominate the angle overlay actuator scene, planetary gears (such as the concept in BMW for "Front Active Steering") and harmonic drives (such as the variable steering gear ratio in Audi).

[0051] State is defined as translational or rotational position, velocity or acceleration, or a state derived from these previous states, such as, for example, the vehicle slip angle, which is the angle between the vehicle's local x-axis and the vehicle's velocity vector.

[0052] For SFC, hydraulic power steering (HPS) has been widely used, and electric power steering (EPS) is now used. In order to give driver feedback in SFC, EPS is used, and EPS will be referred to as feedback torque actuator or just torque actuator in this document.

[0053] Heavy vehicles and agricultural vehicles (such as for example tractors) require a high level of steering assistance. Therefore, today's auxiliary actuators are mainly hydraulically assisted driven (due to the fact that hydraulics have a high power density). This means that if for functions such as for example lane keeping assist (LKA) one wants to get better controllability than what can be obtained with a standard hydraulic auxiliary valve, it is possible to add an EPS actuator above the HPS actuator, i.e. towards the steering wheel side. Therefore, for agricultural equipment and heavy vehicles, a combination of HPS and EPS is now emerging, in which the EPS is mounted on the steering wheel side of the HPS system. The HPS actuator is used to achieve torque reduction, assistance, and is therefore called a hydraulic assisted actuator.

[0054] An actuator is a mechanism or system that is operated mechanically or by an ECU and that converts an energy source (usually electrical current, hydraulic fluid pressure, or pneumatic pressure) into motion, force, or torque.

[0055] Variable gear ratio (VGR) or variable steering gear ratio is a function for controlling the angle overlay actuator in such a way that the gear ratio between the steering wheel and the wheels follows a speed-dependent function. By controlling the angle overlay actuator in this way, the steering response can be made vehicle speed dependent.

[0056] Other functions, such as safety functions, may also benefit from the angle superposition actuator. Such safety functions are for example oversteer compensation, in which the steering angle is controlled in such a way that oversteer is reduced by counter steering, or understeer compensation, in which the function controls the steering angle in such a way that the tire-road friction is used in an optimal way, thereby reducing the steering angle that would otherwise be over-exaggerated. With these examples of steering angle control, the steering wheel does not necessarily need to be moved, since the angle superposition actuator increases the angle necessary to move the steering angle without moving the steering wheel angle.

[0057] Torsion-bar torque is the torque measured by using a sensor that is sensitive to the twisting of a specific torsion bar mounted somewhere in the steering column.

[0058] Steering wheel torque is the torque resulting from the force applied by the driver to the steering wheel. This steering wheel torque is usually approximated by the torsion bar torque.

[0059] Driver torque is equal to steering wheel torque.

[0060] A signal bus is a transmission path over which signals can be read and / or transmitted.

[0061] The input signal may for example be a measure of the torque resulting from the force applied by the driver via the steering wheel - the torque being measured somewhere between the steering wheel and the wheels, or a signal from which this quantity can be derived.

[0062] An ECU is an electronic control unit that is used to read analog sensor signals and digital signals that may arrive via, for example, a signal bus, perform any type of calculation, such as, for example, control tasks and actuate actuators either via the analog or digital signals sent or by directly controlling, for example, an electric motor from a motor control stage.

[0063] Controllability describes the ability of an external input to move the internal state of the system (actual value) from any initial state to any other final state (target value) within a finite time interval, thereby minimizing the difference between the target value and the actual value, i.e., the control error.

[0064] The lateral acceleration feedback torque is the torque felt by the driver that corresponds to the lateral acceleration of the vehicle.

[0065] The lateral acceleration may be calculated from a vehicle model that uses vehicle speed and steering angle as inputs. The lateral acceleration feedback torque is in turn a function of the lateral acceleration calculated from the vehicle model (eg, a function calculated, obtained from a table or matrix).

[0066] Tire friction torque is the torque generated by the friction between the tire and the road or a model of this friction. When the wheel is turned, the friction between the tire and the road must be overcome, which is the tire friction torque.

[0067] The mathematical model of tire friction torque is a model of angle or angular speed driven hysteresis. The mathematical model of the tire also contains a relaxation part, so that when the tire rolls, the hysteretic torque will have a relaxation length, so that the hysteresis torque decreases with the rolling length of the tire. The relaxation can preferably be a well-known half-life exponential decay function. The model of tire friction is a combination of hysteresis and relaxation, so that, for example, an increase in torque due to hysteresis can occur simultaneously with a decrease in torque due to relaxation. The resulting torque of the model is the sum of these two parts.

[0068] Steering system friction or friction torque is the friction of a part of the linkage of the steering system or a model of that friction.

[0069] The mathematical model of the steering system friction torque is a model of the angular or angular velocity drive hysteresis. The maximum torque in hysteresis can be shaped by a function so that the maximum torque is different on centre compared to off centre.

[0070] The damping torque occurs due to the damping of the tire and steering system or a model of this damping.

[0071] The mathematical model of the damping torque consists of some damping constant multiplied by the angular velocity or translational velocity (such as, for example, the rack velocity) measured somewhere in the linkage between the wheels and the steering wheel. The damping constant may be such that the damping has a blow-off so that for large angular or translational velocities the damping constant decreases. The damping constant may be vehicle speed dependent and different for outward steering than for inward steering. The damping constant may also be a function of the steering wheel or torsion bar torque.

[0072] The return torque comes from the geometry of the steering system or the model of the steering system.

[0073] The return torque is the torque that is vehicle speed dependent and steering wheel angle dependent.

[0074] These torque contributions may all be vehicle speed dependent. These torque contributions may also be calculated via mathematical models or sensed via sensors in the vehicle or steering system.

[0075] The compensation torque is the sum of the tire friction torque, friction torque, damping torque and return torque mentioned above. The compensation torque components are calculated from the mathematical model of the different torque components.

[0076] The reference generator concept for steering feel is a closed-loop control method in which a reference value or target value is first calculated and then the steering assistance is controlled to minimize the error between the target value and the corresponding measured value. The reference generator concept for steering can be of two kinds, namely the torque reference generator concept and the angle reference generator concept.

[0077] The torque reference generator is a steering feel control concept in which the steering wheel torque is calculated in a reference generator, giving a reference steering wheel torque, and this reference steering wheel torque is then compared with the measured steering wheel torque, and the difference - the steering wheel torque error - is fed to the controller so that the steering wheel torque error can be minimized. In other words, the reference steering wheel torque is used to control the feedback torque actuator by using closed-loop control.

[0078] The target steering wheel torque is the sum of the lateral acceleration feedback torque, the tire friction torque mentioned above, the friction torque, the damping torque and the return torque.

[0079] Angle reference generator is a steering feel control concept in which the steering wheel angle is calculated in the reference generator, giving a reference steering wheel angle, and this reference steering wheel angle (reference feedback torque actuator angle) is then compared with the measured steering wheel angle, and the difference - the steering wheel angle error - is fed to the controller so that the error can be minimized. In other words, it can be said that the reference torque actuator angle is used to control the feedback torque actuator to this reference angle.

[0080] In the angle reference generator, the target steering angle is based on an equation for the target steering wheel torque, in which the target steering wheel torque is the sum of the lateral acceleration feedback torque, the tire friction torque mentioned above, the friction torque, the damping torque, and the return torque. If the target steering wheel torque in the equation is changed to the sensed or estimated driver torque, the steering angle can be derived from the steering angle related equation. The derived steering angle is the target steering angle of the angle reference generator.

[0081] The target steering wheel torque components are calculated from a mathematical model of the different torque components.

[0082] The target steering wheel angle can be calculated from the equation for steering feel, where the torsion bar torque should be equal to the target steering wheel torque as described above. Now, from this equation, the target steering wheel angle can be calculated.

[0083] The target steering wheel angle components are calculated from a mathematical model of the different torque components.

[0084] The vehicle state controller is defined as a dynamic function used to achieve a target state in the vehicle in a controlled manner. That is, the difference between the target state and the actual state, i.e., the control error, is minimized in a controlled manner.

[0085] A PID controller is a proportional-integral-derivative controller, which is a control loop feedback mechanism widely used in industrial control systems and various other applications where continuous adjustment of control is required. A PID controller continuously calculates an error value e(t) as the difference between a target value and a measured process value, and applies corrections based on proportional, integral, and derivative terms (denoted P, I, and D, respectively), which give their names to the controller. In effect, it automatically applies accurate and responsive corrections to the control function. An everyday example is cruise control on a road vehicle; where external influences such as slope will cause speed changes, and the driver has the ability to change the desired set speed. The PID algorithm restores the actual speed to the desired speed in an optimal manner without delay or overshoot by controlling the power output of the vehicle's engine. A PID controller, the I part of a PID controller, can sometimes suffer from integral windup.

[0086] Integral windup (also known as integrator windup or reset windup) refers to the situation in a PID feedback controller where a large change in the target value (such as a positive change) occurs and the integral term accumulates significant error during this ramp-up (windup), overshooting and continuing to increase as this accumulated error is unwinded (offset by the error in the other direction). A specific problem is excessive overshoot.

[0087] Anti-windup is a term for a group of solutions to the integral windup problem. The problem can be solved by:

[0088] - Initialize the controller integral to a desired value, such as the value before this problem;

[0089] - Increase the target value with a suitable ramp;

[0090] - disable the integration function until the process variable to be controlled has entered the controllable region;

[0091] -Prevent the integral term from accumulating above or below a predetermined limit;

[0092] -Back-calculate the integral term to constrain the process output to within feasible bounds.

[0093] Vehicle state actuators are actuators that influence one or several vehicle states when actuated. Vehicle state actuators are brakes, engine, controllable four-wheel drive clutch, controllable differential, active dampers, electric or hydraulic wheel motors and electric or hydraulic drive axles.

[0094] The target value, reference value or request is the set point of the actuator achieved by using a closed loop controller and / or a feedforward controller.

[0095] The vehicle model is a mathematical model that transforms the wheel angles and vehicle speed into a plurality of vehicle yaw and / or lateral states, namely, vehicle yaw rate and acceleration, vehicle lateral speed and acceleration, and body slip angle.

[0096] A transformation is defined as a mathematical function or lookup table where one input value is used to produce one output value. This means that a transformation with its adjustable parameters can be used to create a relationship between input and output values ​​with an arbitrary adjustable shape. A transformation can have time-varying parameters that even depend on other values, a so-called gain scheduling, making the transformation a function with parameters that are themselves functions. An example of such a transformation is the relationship of vehicle state to driver torque, where the relationship is a continuously rising degressive shaped function with respect to vehicle speed.

[0097] The steering wheel torque measurement is the torque measured in the steering column or steering wheel or the force measured in the steering rack multiplied by the torque ratio between the steering rack and the steering wheel.

[0098] Steering angle here refers to any angle between the steering wheel and the wheels multiplied by the ratio between the angular freedom and the steering wheel angular freedom. It can also be the rack position multiplied by its ratio between the rack translational freedom and the steering wheel angular freedom.

[0099] Vehicle axes and coordinate system where X is in the horizontal plane and in the forward direction of travel. Y is in the horizontal plane, perpendicular to X, and pointing to the left. Z points up.

[0100] sensor:

[0101] ABS sensors or wheel speed sensors are sensors that measure the speed of the wheels.

[0102] A rate gyro sensor measures angular velocity about an axis in the yaw, pitch, or roll directions.

[0103] Accelerometers measure acceleration in the longitudinal, lateral or vertical direction.

[0104] Location sensors measure location. It can be local, regional or global coverage. Commonly referred to as GPS.

[0105] The brake pedal sensor indicates whether the pedal is pressed.

[0106] The brake pressure sensor measures the pressure in the brake system.

[0107] The term TAC (Torque and / or Angle Reference Generator Control Concept) is used for SFC and / or for SPC.

[0108] Figure 1 is a schematic diagram of a steering system 100. There is a linkage between the front axle steered wheels 4 and a torque actuator 130. The linkage consists of a steering rack 124 with an associated tie rod 125, which is connected to a column shaft 135 to the torque actuator 130 via a pinion 122. The feedback torque is actuated by the torque actuator 130, which consists of an auxiliary motor controlled by a TAC 132 (torque and / or angle controller). The TAC 132 will control the torque feedback to the driver and control the angle of the steered wheels 4.

[0109] An example of torque and / or angle control is described in WO2010144049, the contents of which are hereby incorporated by reference herein. An example of torque and / or angle control is also described in WO2019182496 of the same applicant, the contents of which are hereby incorporated by reference herein, in which the steering angle and vehicle speed are used to achieve the target steering wheel torque. The target steering wheel torque is calculated using a mathematical model. As an example, the target steering wheel torque includes one or more of the following torque contributions: lateral acceleration feedback torque, steering system friction torque, tire friction torque, damping torque, and steering wheel self-alignment torque. Then, the feedback torque actuator mentioned is controlled via closed-loop current control to achieve the target steering wheel torque. Here, the target steering wheel torque is first converted into a target motor current, and the target motor current is compared with the actual motor current, where the difference between the two will form a control error. Then, a controller is used to minimize the control error to achieve the target current, and thus the target steering wheel torque.

[0110] exist Figure 1 In the embodiment, above the torque actuator 130, there is a torsion bar 128 with a torque sensor for measuring the driver torque, ie the force T applied by the driver in the steering wheel 120. DThe resulting torque is transmitted to the torsion bar 128 via the steering wheel shaft 121. The steered wheels 4 are attached to the vehicle and are arranged so that they can turn around the steering shaft 3. The orientation of the steering shaft 3 is determined by the design of the suspension 131.

[0111] Figure 2 is a schematic back to front view of a steered wheel 4 illustrating the main parameters influencing the steering characteristics. The wheel 4 is steered about a steering axis 3. There is a distance between the wheel center 1 and the normal to the steering axis 3, which is indicated as the normal steering axis offset 6 at the wheel center. The normal steering axis offset 7 at the ground is the distance from the wheel contact center 2 perpendicular to the steering axis 3. There is a steering axis tilt angle 5 between the Z axis and the normal projection of the steering axis 3 onto the YZ plane.

[0112] Figure 3 is a schematic side view of the steered wheel 4 and the main influencing parameters mentioned above. The steered wheel 4 rotates around the steering axis 3. There is a kingpin caster angle 9 between the Z axis and the normal projection of the steering axis 3 on the XZ plane. The intersection of the steering axis 3 and the road plane is the steering axis road intersection 13. The kingpin caster offset 8 at the wheel center is the distance between the wheel center 1 and the projection of the steering axis 3 onto the following plane: the plane is perpendicular to the XY plane and parallel to the intersection of the wheel plane and the XY plane. The kingpin caster offset 10 at the ground is the distance in the X direction from the steering axis road intersection 13 to the wheel contact center 2. The wheel ground lateral force point 12 is the point where the sum of the lateral forces between the wheel and the ground is located. The pneumatic trail 11 is the distance between the wheel contact center 2 and the wheel ground lateral force point 12 in the X direction.

[0113] As mentioned above, the object of the present invention is to achieve an improvement in characteristics by using TAC instead (or TAC in combination with BCPS), thereby at least partially eliminating or minimizing one or more constraints that limit the design of vehicles that usually use BCPS. The use of TAC will also enable the desired steering effect for different vehicle states, giving opportunities that are not even possible for conventional BCPS and suspension layouts that are severely limited by external forces and geometry.

[0114] By using TAC to provide feedback and wheel angle control and simultaneously reducing the caster offset 10 (castor trail) plus aerodynamic trail 11 at the ground to near zero, very low or zero (even negative) steering forces can be achieved even with high lateral forces at the tire contact patch while providing the desired steering feedback to the driver. The caster offset 10 at the ground is dominated by three parameters, and to some extent by a combination of these parameters, namely the caster angle 9, the caster offset 8 at the wheel center, and the wheel diameter. As the caster angle 9 increases, there will be a greater caster offset 10 at the ground. Under the condition that there is a certain amount of caster angle 9 (i.e., the angle ≠ 0), larger wheels will also increase, or more precisely amplify, the caster offset 10 at the ground. As the caster offset 8 at the wheel center increases, the caster offset 10 at the ground will also increase subsequently, but is independent of the caster angle 9 and the wheel diameter. When the combination of castor angle 9, castor offset 10 at the ground and wheel diameter is set for low steering forces in general and for low hand forces in case of power steering failure in particular, certain drawbacks will occur for normal driving. The main drawback is that the feedback force from the wheel - which provides feedback from lateral acceleration etc. - will be very low and the assistance provided from the conventional BCPS will feel over-assisted, with too low lateral feedback to the driver. The legal requirements for hand forces in case of power steering failure are only for very low speeds, at which the lateral forces are low. At higher speeds, it is easier to end up with higher lateral forces for normal driving. In this case, the power steering failure is more severe due to the speed itself, giving less time to react quickly and efficiently, and the kinetic energy is greater, which in turn will lead to accidents with higher collision violence. The present invention will be particularly good at improving this situation. It will be effective for steering in case of failure for normal steering gear and steer-by-wire systems with mechanical backup. Bonuses from lower steering effort are less expensive power steering, less maximum current demand, lower overall energy consumption, and a lighter steering system.Another advantage of having a small castor offset 10 at ground level is that the vehicle will be less prone to front end vibrations known as shimmy.

[0115] Another source of feedback to the driver via the steering wheel comes from the normal steering axis offset 6 at the center of the wheel, which is a lever around the steering axis 3 that feeds the normal force from the tire into the steering linkage. In the ideal case of driving straight ahead, the sum of the normal forces from the left and right cancel each other out. When turning, the normal force will not be canceled out, because the outer tire will bear more normal forces than the inner tire. In the more common suspension design (i.e., the positive value of the normal steering axis offset 6 at the center of the wheel and the positive value of the caster angle 9), the normal force during the turn will give negative feedback to the driver, thereby offsetting the force from the lateral direction at the wheel ground lateral force point 12 to some extent. In theory, the force from the feedback from the lateral force and the normal force can be balanced, thereby giving low steering force when the power steering (PS) fails. However, this is impossible in the case of BCSP, because when driving normally, it will give the driver very poor quality feedback, this is because the expected signal is very low and is sensitive to unwanted disturbances. This would require the normal steering axis offset 6 at the wheel center to have a certain value ≠ 0, which in turn would lead to some negative effects. The normal steering axis offset 6 at the wheel center would itself also contribute to disturbances, such as feedback from a vehicle loaded asymmetrically from left to right, load shifts due to cambered roads, vertical force inputs from uneven roads, sensitivity to vibrations caused by unbalanced wheels, etc. A very special case is when the vehicle has had a front tire explosion. A sudden and strong difference in the normal force will generate a steering effect that may be impossible for the driver to fully counteract and thus lead to a deviation from the intended path. If it is a heavy vehicle, this usually leads to running off the road or into oncoming traffic, both of which involve a high risk of fatal consequences.

[0116] In general, for a BCPS, the normal steering axis offset 6 at the wheel center may be desired to be kept zero or low for many reasons, but for other properties and practical reasons, it is better to have a higher value. This leads to a compromise that severely limits the optimal performance for both normal driving and safe handling during PS failure. All these drawbacks will be overcome when a low force feedback suspension geometry is used in combination with TAC, thereby providing the desired feedback in normal driving situations, while the geometry itself will provide sufficiently low steering forces with acceptable feedback quality in the event of PS failure. As described above, the TAC principle of assisting the driver to achieve the desired steering angle and resulting path, rather than just giving some increased force as in BCPS, will effectively support the driver to stay on track, even in the event of a tire blowout.

[0117] As described in the text above, for a BCPS, in order to achieve low steering efforts in the event of a PS failure, the normal steering axis offset 6 at the wheel center will typically be required to have a value ≠ 0. If the normal steering axis offset 6 at the wheel center is optimized for low steering efforts, i.e. the normal steering axis offset 6 at the wheel center is close to zero, then due to the value of the steering axis inclination angle 5, the following effect is typically given: a negative normal steering axis offset 7 at the ground. Although the normal steering axis offset 7 at the ground can generate a steering effect that is beneficial for braking in split-mu, it may have a steering effect that is detrimental to stability when braking in a curve, which typically results in a compromise between these two properties, and is also used to generate some steering wheel self-centering at low speeds. When a TAC is used instead of a BCPS, the steering effect is shaped using an algorithm within the angle controller.

[0118] For braking in a curve, it is desirable to have a counter-steering effect, i.e., to reduce the steering angle when applying the brakes. When braking in a curve is detected, the angle controller will reduce the steering angle. The controller will detect braking by monitoring one or more sensors in combination. The sensor is, for example, one or more of the following: a switch for brake pedal application, a brake pressure sensor, an (ABS) wheel speed sensor, a longitudinal acceleration sensor, a pitch gyro sensor, and a positioning sensor (such as GPS). The vehicle's travel in a curve will be detected by monitoring one or more sensors in combination. These sensors are (ABS), such as wheel speed sensors, lateral acceleration sensors, yaw rate gyro sensors, steering wheel angle sensors, steering wheel torque sensors.

[0119] A similar situation is deceleration in a curve, but without applying the brake pedal. In this case, the signals from the brake pedal application and brake pressure sensors are not used.

[0120] For braking in split-mu, that is, when one side of the vehicle's wheels has good grip and the wheels on the other side of the vehicle exhibit poor grip, the different braking forces from the left to the right will create a turning moment on the vehicle in the direction of the side with good grip. In this case, it is desirable to have the steering effect on the side with poor grip offset the turning moment, thereby achieving the path indicated by the driver through the steering wheel input. When braking on split-mu is detected, the angle controller will increase the offset steering angle. The controller will detect braking by monitoring one or more sensors in combination. The sensor is, for example, one or more of the following: a switch for brake pedal application, a brake pressure sensor, an (ABS) wheel speed sensor, a longitudinal acceleration sensor, a pitch gyroscope sensor, and a positioning sensor (such as GPS).

[0121] For good cornering, i.e. making a step steer input on the steering wheel, it is desirable to have a higher steered wheel response in the transient phase than in steady-state cornering. This will make the car feel more responsive because the phase lag between the steering input and the response in the vehicle will be lower. The traditional way to achieve this is to have some roll understeer from the suspension geometry during rolling, which reduces the steered wheel angle when the vehicle rolls, i.e. leans to one side or the other. The drawback is that this usually leads to a change in toe-in when going over bumps, etc., which may cause route instability. Since it also depends on the roll angle of the vehicle, it may be difficult to get the desired effect, since it is also desirable to have a flat vehicle behavior, i.e. a low roll angle when turning. In the case of TAC, the steered wheel angle can be set higher for the transient cornering phase and lower for steady-state cornering without having a perturbation steering effect for other conditions. The controller will detect the instantaneous turn by monitoring one or more sensors in combination, such as one or more of a steering wheel angle sensor, a steering wheel torque sensor, a lateral acceleration sensor, a yaw rate gyro sensor. The effect will be speed dependent by also using vehicle speed information from (ABS) wheel speed sensors and / or positioning data from a positioning system (e.g. GPS).

[0122] When TAC is used instead of BCPS, the steering effect is accurately achieved within the control algorithm as described above, because the steering wheel returnability, the normal steering axis offset 6 at the center of the wheel, and the steering axis tilt angle 5 can be optimized for reducing the steering force. Traditionally, a low steering axis tilt angle 5 must be selected to some extent to reduce the steering force, but then there can only be a compromise of poor returnability at low speeds. In addition, due to packaging reasons, low steering axis tilt angle 5 may be difficult to achieve, and complex front suspension designs with several ball joints have been used to achieve low steering axis tilt angle 5, which has the normal steering axis offset 7 at the desired ground and the normal steering axis offset 6 at the center of the wheel. Like other low steering axis tilt angle 5 designs, these designs will also suffer from poor returnability, but may also experience cost, damage, friction or impact. In the case of the present invention, a low steering force design with a low steering axis tilt angle 5 will rely on a control function for returnability. Since the steering effect from the longitudinal forces is also controlled by the function, rather than by the normal steering axis offset at the ground 7 and the normal steering axis offset at the wheel center 6, this will allow a simpler suspension design that can still be optimized for low steering forces and thus achieve good handling in the event of PS failure.

[0123] Another reason to keep the normal steering axis offset 6 at the wheel center low is that this will also make the suspension geometry less sensitive to transmitting torque disturbances to the driver originating from asymmetric left and right wheel drive torques. Unequal drive torques may have unwanted properties, such as friction in the differential or desired differences in drive torque from a torque vectoring system. However, as mentioned earlier, keeping the normal steering axis offset 6 at the wheel center low or zero will not minimize steering forces. Thanks to the control design for steering angle and driver feedback, the present invention, in which TAC can be combined with the normal steering axis offset 6 at the wheel center that provides low steering forces, still provides almost complete insensitivity to any resulting torque steer effects. It will also be insensitive to the wheel contact center 2 wandering in the lateral direction of the tire, which is not even possible with a conventional front suspension. It is particularly important that the combination of steering geometry is optimised for low rack forces but still has self-centring force to comply with the uniform provisions concerning the approval of vehicles with respect to steering equipment, UN Regulation No. 79, which must be complied with by any party seeking UN type approval for its vehicle, will make it possible for the driver to safely deal with loss of assistance over a much wider range of front axle loads at the same time, thanks to the extremely good steering feel provided by TAC.

[0124] It is clear that the invention is not limited to the specifically described embodiments, but it can be varied in many ways within the scope of the invention.

Claims

1. A method for vehicle steering in a vehicle having a vehicle suspension allowing wheel steering and comprising a power-assisted vehicle steering system having one or more feedback torque actuators and wherein the steering feel is controlled by means of a torque and / or angle control system which directly or indirectly senses and / or calculates at least a steering wheel angle and a steering wheel torque and controls the feedback torque actuators, wherein the vehicle suspension allows steering of the front and / or rear wheels of the vehicle and comprises or is defined by a plurality of vehicle suspension parameters or elements, It is characterized in that The method comprises: - selecting or designing the geometry and / or dimensions of one or more of the vehicle suspension parameters or elements to reduce or minimize the steering effort required to steer the vehicle while driving, in combination with: - Use of said torque and / or angle control system including a torque or angle reference generator for controlling a feedback torque actuator by calculating a target steering angle and / or a target feedback torque, and for controlling a wheel steering angle based at least on a directly or indirectly sensed and / or calculated steering wheel angle and / or steering wheel torque, and providing feedback control by minimizing the error between the calculated target steering angle and / or the calculated target feedback torque and the directly or indirectly sensed and / or calculated steering wheel angle and / or steering wheel torque, and thereby also reducing or eliminating the need for driver feedback provided by said vehicle suspension, so that if there is a fault in the steering control resulting in a loss of steering assist, the steering effort will be low enough for the driver to handle safely, thereby rendering the need for a fail-safe steering gear redundant.

2. The method according to claim 1, characterized in that: A compensation torque comprising one or more of the following compensation torque components is subtracted from the torque value caused by the force applied by the driver via the steering wheel: - tire friction torque, which is a function of the sensed or estimated yaw and / or lateral vehicle state, - steering system friction torque, which is a function of sensed or estimated yaw and / or lateral vehicle state, - a damping torque which is a function of the derivative of the sensed or estimated yaw and / or lateral vehicle state, and - A self-aligning torque which is a function of the sensed or estimated yaw and / or lateral vehicle state.

3. The method according to claim 1 or 2, characterized in that: The vehicle suspension parameters or elements include steering axis orientation definition parameters.

4. The method according to claim 3, characterized in that: At least one of the vehicle suspension parameters or elements includes a caster offset distance at the ground and a caster trail, and the caster trail is designed to be between -40 mm and +20 mm, and the suspension influencing parameters that dominate the caster trail are the caster angle, the caster offset at the wheel center, and the wheel radius.

5. The method according to claim 1 or 2, characterized in that: At least one of the vehicle suspension parameters or elements includes steering axis inclination, and the steering axis inclination is designed to be between -2° and +8°.

6. The method according to claim 1 or 2, characterized in that: The reference generator is a feedback torque reference generator for calculating a target feedback torque, and the assist torque is controlled so that a feedback torque error is minimized, and at least one of the feedback torque actuators is closed-loop controlled.

7. The method according to claim 1 or 2, characterized in that: The reference generator is a steering angle reference generator for calculating a target steering angle, and the assist torque is controlled to minimize a steering angle error, and at least one of the feedback torque actuators is closed-loop controlled.

8. The method according to claim 1 or 2, characterized in that: - the measuring of at least one input signal comprises using a wheel speed sensor or a drive shaft speed sensor, and the method further comprises the steps of: - calculating the vehicle speed using the at least one input signal.

9. The method according to claim 1 or 2, characterized in that: The method comprises the following steps: -Determining the steering angle based on additional input signals from the at least one sensor, including any angle or rack position in the steering system, the at least one sensor including an angle or position sensor located in the steering column or elsewhere in the steering system, the steering angle being the sensed angle multiplied by the ratio between the rotation or translation of the sensor element of the sensor and the rotation at a reference steering angle.

10. The method according to claim 1 or 2, characterized in that: The one or more feedback torque actuators provide all steering assist actuator functions.

11. A vehicle steering system arrangement in a vehicle having a vehicle suspension allowing wheel steering and comprising a power assisted vehicle steering system having one or more feedback torque actuators and wherein the steering feel is controlled by means of a torque and / or angle control system which directly or indirectly senses and / or calculates at least a steering wheel angle and a steering wheel torque and controls the feedback torque actuators, wherein the vehicle suspension allows steering of the front and / or rear wheels of the vehicle and comprises or is defined by a plurality of vehicle suspension parameters or elements, Features: - the geometry and / or dimensions of one or more vehicle suspension parameters or elements are designed or selected to reduce or minimize the steering effort required to steer the vehicle while driving, - the torque and / or angle control system comprises a torque or angle reference generator for controlling a feedback torque actuator by calculating a target steering angle and / or a target feedback torque, and for controlling a wheel steering angle based at least on a directly or indirectly sensed and / or calculated steering wheel angle and / or steering wheel torque, and providing feedback control by minimizing an error between the calculated target steering angle and / or the calculated target feedback torque and the directly or indirectly sensed and / or calculated steering wheel angle and / or steering wheel torque, and thereby reducing or eliminating the need for driver feedback provided by the vehicle suspension, Such that if there is a fault in the steering control such that steering assist is lost, the steering effort will be low enough for the driver to handle safely, thereby eliminating the need for a fail-operation steering gear.

12. The vehicle steering system arrangement according to claim 11, characterized in that: A compensation torque comprising one or more of the following compensation torque components is subtracted from the torque value caused by the force applied by the driver via the steering wheel: - tire friction torque, which is a function of the sensed or estimated yaw and / or lateral vehicle state, - steering system friction torque, which is a function of sensed or estimated yaw and / or lateral vehicle state, - a damping torque which is a function of the derivative of the sensed or estimated yaw and / or lateral vehicle state, and - A self-aligning torque which is a function of the sensed or estimated yaw and / or lateral vehicle state.

13. A vehicle steering system arrangement according to claim 11 or 12, characterised in that: The vehicle suspension parameters or elements include steering axis orientation definition parameters.

14. The vehicle steering system arrangement according to claim 13, characterized in that: At least one of the vehicle suspension parameters or elements includes a caster offset distance at the ground and a caster trail, and the caster trail is designed to be between -40 mm and +20 mm, and the suspension influencing parameters that dominate the caster trail are the caster angle, the caster offset at the wheel center, and the wheel radius.

15. The vehicle steering system arrangement according to claim 11 or 12, characterized in that: At least one of the vehicle suspension parameters or elements includes steering axis inclination, and the steering axis inclination is designed to be between -2° and +8°.

16. The vehicle steering system arrangement according to claim 11 or 12, characterized in that: The reference generator is a feedback torque reference generator for calculating a target feedback torque, and the assist torque is controlled so that a feedback torque error is minimized, and at least one of the feedback torque actuators is closed-loop controlled.

17. A vehicle steering system arrangement according to claim 11 or 12, characterised in that: The reference generator is a steering angle reference generator for calculating a target steering angle, and the assist torque is controlled to minimize a steering angle error, and at least one of the feedback torque actuators is closed-loop controlled.

18. A vehicle steering system arrangement in a vehicle having a vehicle suspension allowing wheel steering and comprising a power assisted vehicle steering system having one or more feedback torque actuators and wherein steering feel is controlled by means of a torque and / or angle control system which directly or indirectly senses vehicle state parameters and / or calculates a steering effect introduced by a driver including steering wheel angle and steering wheel torque and controls the feedback torque actuators, Features: The torque and / or angle control system includes one or more vehicle state sensors for monitoring and measuring one or more vehicle states; The torque and / or angle control system comprises an algorithm for determining an additional steering effect in addition to the steering effect introduced by the driver to enhance the degree to which the vehicle follows the driver's intention, wherein the value of the additional steering effect is derived from the monitored and measured vehicle states using a mathematical model describing the vehicle's behavior; The torque and / or angle control system comprises a torque or angle reference generator and is arranged to control the wheel steering angle based on measurements made by one or more sensors monitoring one or more vehicle state parameters, and to provide feedback control by controlling the one or more feedback torque actuators to generate feedback torque as well as a target steering feel and the additional steering effect, and the additional steering effect is therefore substantially independent of the vehicle suspension.

19. A vehicle having a vehicle suspension that allows wheel steering and a power-assisted vehicle steering system, characterized in that: The vehicle comprises a vehicle steering system arrangement as claimed in any one of claims 11-18.

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