Patent Application
20250042465
The present invention relates to a steering system having the features of the first part of claim 1. The invention also relates to a steering system feedback arrangement and to a method for providing steering feedback in a steering system having the features of the first part of claims 14 and 17 respectively, and to a vehicle comprising such a steering system.
Traditionally the steering system of e.g. a road vehicle comprises a mechanical connection between the steering wheel and the steerable wheels. Other steering systems, not having a mechanical connection, are also known, which often are referred to as SbW, steer-by-wire, systems. In a SbW, steer-by-wire, system, one or more sensors register physical properties, e. g. forces and movements of the steering wheel or other steering input device, such as a yoke or joystick or other means, and generate signals. These signals of the registered physical properties can be provided to an ECU,
Electronic Control Unit, and transformed by the ECU into a desired action to be provided on the steerable wheels. A power assisted steering actuator that is electrically connected to the ECU and mechanically linked to the steerable wheels will then execute the desired action and apply desired forces to the said steerable wheels.
The feedback to the driver is typically provided by means of an electric motor, creating forces and/or movements to the steering wheel, otherwise transmitted via the mechanical connection.
SbW systems offer many advantages compared to conventional mechanical steering, such as allowing energy absorption in collisions, flexible location of a steering wheel, handling of left- and right-hand drive variants, removable steering wheel, variations in steering input devices, autonomous drive and advanced driving aid being some examples. Also, SbW systems offer several opportunities for the driving experience itself, e.g. variable steering ratio and immunity to road disturbances.
To obtain a desired feedback force, a feedback actuator, typically an electric motor, must be able to deliver a certain torque, either directly or via a gear. It very important that the performance of the motor is sufficient, otherwise it is not possible to create a good driving experience. On the other hand, a high performance of an electric motor generally is associated with significant penalties such as cost, weight, volume and use of raw materials like copper and rare earth metals. The latter materials are often mined and having to rely on such raw materials can have a severe negative impact on the environment and constitutes a disadvantage as far as the goal of allowing a sustainable production is concerned.
Since the feedback force is generated solely by an electric motor, the use of electric energy is required, which is undesired, especially in an electric car where every saving in electric consumption is preferred in favour of a greater range.
If there is a failure in the steering system, a desired functionality, or even a legal requirement, is that the vehicle still shall be controllable. An example of providing such a functionality is through the steering having a self-centring effect. When the steering wheel is connected mechanically to the steerable wheels of the vehicle, the self-centring forces are transmitted from the tyres via the suspension geometry to the steering wheel. When the force in the steering wheel is solely dependent on a feedback motor, the self-centring effect will be lost if the motor fails.
The use of an electric motor is not optimal for creating all properties needed for a good steering feel. One property needed for a good steering feel is friction feel, especially for slow, zero and reversing angular speed of the motor and hence, the steering wheel.
A certain torque output from the electric motor is needed. One way of reducing the torque requirement of the electric motor is to use a gear to increase the produced torque. This will make the motor to spin at higher speeds which can cause steering feel defects usually referred to as inertia feel. Another disadvantage of using a gear is that gears often are prone to lash and/or friction which in turn also can affect the steering feel in an adverse manner. In addition, through the use of a gear, the complexity will be enhanced which increases the risk of failures and raises costs, making the use of a smaller motor not to be obviously favourable. Also, even though a gear itself can reduce the torque output needed from the motor, the energy consumption will not be lowered since the motor instead must run at higher revolutions.
There is technology available for permanent magnet free electric motors, such as reluctance motors and inductions motors. However, these are typically plagued with high torque ripple and/or require much space, a large volume, and they are thus not suited for automotive steering applications.
So far, cars with SbW are equipped with a mechanical backup in the case of failure. An intermediate shaft is then required, resulting in that the location of the steering wheel is not as flexible as would be desirable, it cannot be removed, it is unnecessarily complicated to handle left- and right-hand drive variants and it also is an obstacle in enhancing energy absorption in collisions, and does not allow for variations in steering input devices.
Further, for a good steering feel a certain amount of friction feel is desirable. The control of electric motors for creating a friction feel, however, can be cumbersome, especially for slow, zero and reversing angular speed of the motor and, hence, the steering wheel. To reduce the need for friction feel created by the motor it is possible to create the steering feel using mechanical components. Such solutions are known from other steering applications with a specially designed axial bearing where a certain friction level is provided.
Cars with SbW having a system relying on an electric motor for feedback are well known but all so far known solutions suffer from one or more of the above mentioned disadvantages.
US20180319422 shows a power assisted steering system for a vehicle with a feedback arrangement comprising an electric feedback motor and a mechanical feedback arrangement comprising a preloaded belt. However, the solution suffers from several drawbacks, it is space demanding, complex and sensitive. Also, the lifetime is limited through the use of a belt comprising a pre-loaded cable pull. It also does not offer a sufficient steering safety.
All so far known steering systems with feedback arrangements are associated with drawbacks and suffer from several shortcomings.
It is therefore an object of the present invention to provide a steering system, a steering system feedback arrangement and a method in a steering system respectively through which one or more of the above-mentioned problems can be solved and through which one or more of the shortcomings can be overcome.
It is an object of the present invention to provide an improved power assisted wired or wireless steering system, particularly an improved power assisted Steer-by-Wire (SbW) steering system.
It is a particularly an object to provide a steering system for providing steering feedback in a vehicle steering system through which steering safety can be enhanced.
More particularly it is an object to provide a steering system through which steering safety can be upheld also when there is a loss in steering assistance or a failure in the steering system, and particularly steering facilitated in case of a loss in steering assistance.
Further it is a particular object to provide a steering system through which a desired steering feel can be provided, and most particularly which is capable of providing more properties needed for constituting a good steering feel than so far known steering systems, particularly friction feel, also under varying circumstances.
Another particular object is to provide a vehicle steering system, a vehicle steering method and a vehicle steering system arrangement respectively through which steering safety as well as steering feel can be upheld also when there is a steering failure, e.g. loss in steering assistance.
A most particular object is to provide a SbW steering system through which one or more of the above-mentioned objects can be achieved.
It is particularly an object to provide a steering system arrangement providing feedback in a wired steering system, e.g. a SbW steering system, or in a wireless steering system, and through which one or more of the above mentioned objects can be achieved.
Yet another particular object is to provide a vehicle steering system and a steering system arrangement respectively which is cheap and easy to implement and fabricate.
Another particular object is to provide a vehicle steering system and a steering system arrangement respectively which is compact, reliable and robust and which has a long lifetime.
Yet another particular object is to provide a vehicle steering system and a steering system arrangement respectively which is environmental friendly and allows for a sustainable production.
Another particular object is to provide a vehicle steering system and a steering system arrangement respectively through which energy consumption for steering (feedback) is low, and is reduced compared to for known steering methods, allowing saving in electric consumption.
Still another object is to provide a vehicle steering system and a steering system arrangement respectively through which steering safety and steering feel can be improved in a wired, particularly a SbW steering system, or a wireless steering system without requiring a large volume, adding in weight or in cumbersomeness.
Still further it is a particular object is to provide a vehicle steering method and a vehicle steering system arrangement respectively which is reliable, safe and at the same time provides a good steering feel and steering response (vehicle reaction to steering input) under varying conditions.
Most particularly it is an object to provide for improved steering feedback in a steering system, particularly a steer-by-wire (SbW) steering system.
It is also an object of the present invention to provide a vehicle with a steering system through which one or more of the above mentioned objects are achieved.
Therefore a steering system as initially referred to is provided which has the characterizing features of claim 1. A steering system arrangement and a method in a steering system respectively as initially referred to having the characterizing features of the respective independent claims 14 and 17 are therefore also provided as well as a vehicle comprising such a steering system.
Advantageous embodiments are given by the respective appended dependent claims and are described in the detailed description respectively.
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 as defined by the accompanying claims.
The invention will in the following be further described, in a non-limiting manner, and with reference to the accompanying drawings, in which:
For the purposes of describing the present invention, and to facilitate the understanding thereof, the following definitions are given, some of which will be relied upon in the detailed description of advantageous embodiments:
Torque and/or angle reference control (TAC) comprises steering feel control (SFC) and/or steering position control (SPC), respectively. For the steering feel control, it is the control of the steering-wheel torque that the driver feels that is the subject matter, and in steering position control, it is the control of the road-wheel angles, and specifically for a front-wheel steered vehicle, the control of the front axle road-wheel angle, here referred to as the steering angle (see the definition below).
A steering angle is an angle in the steering system that influences the lateral acceleration or curvature of the vehicle, measured somewhere in the steering system, where such steering angles can be:
Power steering will also provide a means for to modulate steering feedback.
A steering position actuator is an actuator which can be used for SPC, i.e. to influence one or more of the steering angle, such as the front wheel steering angle, rear wheel steering angle, the individual steering angles of the wheels, the axle braking torque or force, the wheel braking torque or force, the driving torque or force on the individual axles, the driving torque or force on the individual wheels, the camber angle on each axle, or the camber angle on each wheel.
A specific type of steering position actuator is an angle overlay actuator. An angle overlay actuator is an actuator that is used to achieve a relative angle somewhere in the steering column. Two hardware concepts are dominating the angle overlay actuator scene, namely planetary gears (such as in the BMW concept for “Front Active Steering”) and harmonic drives (such as in the Audi variable steering gear ratio).
A state is defined as a translational or rotational position, velocity or acceleration, or from these before-mentioned states derived states such as e.g. a vehicle slip angle, which is the angle between the vehicle local x-axis and the vehicle speed vector.
For SFC, Hydraulic Power Steering (HPS) has been widely used, and now Electric Power Steering (EPS) is used. In order to give the driver feedback in the SFC, the EPS is used, and will in this document be called a feedback torque actuator or only torque actuator.
Heavy vehicles and farming vehicles such as e.g. tractors require great steering assistance levels. Therefore, the assistance actuators of today are predominantly hydraulic assistance driven (because the fact that hydraulics has high power density). That means that if one would like greater controllability than standard hydraulic assistance valves result in, for functions such as e.g. Lane Keeping Aid (LKA), it is possible to add an EPS actuator above the HPS actuator, i.e. towards the steering wheel side. Therefore, for farming equipment and heavy vehicles, a combination of HPS and EPS is now emerging, where the EPS is mounted on the steering wheel side of the HPS system. The HPS actuator is used to achieve a torque reduction, an assistance, and is therefore called hydraulic assistance actuator.
An actuator is a mechanism or system that is operated mechanically or by an ECU and converts a source of energy, typically electric current, hydraulic fluid pressure, or pneumatic pressure, into a motion, force or torque.
Variable Gear Ratio (VGR) or variable steering gear ratio is a function to control the steering gear in such a way that the ratio between the steering wheel and the road wheels follows a defined function, usually speed dependent, but other functions are also possible
Also other functions, such as e.g. safety functions can benefit from an angle overlay actuator. Such safety functions are e.g. oversteer compensation, where the steering angle is controlled in such a way that the oversteering is reduced by a counter steering, or understeer compensation, where the function controls the steering angle in such a way that the tyre-to-road friction is used in an optimal way, reducing otherwise over-exaggerated steering angles. By these examples of steering angle control, the steering wheel does not necessarily need to move, as the angle overlay actuator adds the angle necessary to move the steering angle without moving the steering-wheel angle.
A torsion-bar torque is a torque measured by the use of a sensor that is sensitive to a twist of a specific torsion bar that is mounted somewhere in the steering column.
A steering-wheel torque is the torque resulting from the force applied by the driver to the steering wheel. This steering-wheel torque is normally approximated by the torsion-bar torque.
A driver torque is equal to the steering-wheel torque.
A signal bus is a transmission path on which signals can be read and/or transmitted.
An input signal can for example be the measure of a torque resulting from the force applied by the driver via the steering wheel, measured somewhere between the steering wheel and the wheel, or a signal from which this quantity can be derived from.
An ECU is an electric control unit that is used to read analogue sensor signals and digital signals, that can come over e.g. a signal bus, perform any type of computations, such as e.g. perform a control task and actuate actuators, either via a sent analogue or digital signal or by directly controlling e.g. an electric motor from a motor control stage.
Controllability describes the ability of an external input to move the internal state, an actual value, of a system from any initial state to an arbitrary other final state, a target value, in a finite time interval, thus minimising the difference between the target value and the actual value, i.e. the control error.
A lateral acceleration feedback torque is a torque felt by the driver that corresponds to the lateral acceleration of the vehicle.
The lateral acceleration can be calculated from a vehicle model, which uses vehicle speed and steering angle as input. The lateral acceleration feedback torque, in turn, is a function (e.g. calculated, obtained from a table or a matrix) or similar of the lateral acceleration calculated from the vehicle model.
A tyre friction torque is the torque generated by friction between the tyres and the road or a model of this friction. When turning a wheel, the friction between the tyre and road must be overcome, being the tyre friction torque.
The mathematical model of the tyre friction torque is a model of an angle or angular speed driven hysteresis. The mathematical model of the tyre also contains a relaxation part such that as the tyre rolls, the torque of the hysteresis will have a relaxation length so that the hysteresis torque decreases with the rolling length of the tyre. The relaxation can preferably be the well-known half-life exponential decay function. The model of the tyre friction is the combination of the hysteresis and the relaxation so that e.g. an increase owing to the hysteresis torque can happen at the same time as the torque decrease owing to the relaxation. The resulting torque of the model is the sum of the two parts.
A steering system friction or a friction torque is the friction of the parts of the components of the steering system or a model of this friction.
The mathematical model of the steering system friction torque is a model of an angle or angular speed driven hysteresis. The maximum torque in the hysteresis can be shaped by a function so that the maximum torque is different on centre compared to off centre.
A damping torque occurs owing to damping of the tyres and the steering system or a model of this damping.
A mathematical model of the damping torque consists of some damping constant times an angular speed or translational speed, such as e.g. the rack velocity, measured somewhere in the linkage between the road wheels and the steering wheel. The damping constant can be such that the damping has a blow-off, such that the damping constant decreases for great angular or translational speeds. The damping constant can be vehicle speed dependent as well as different for steering outwards compared to inwards. The damping constant can also be a function of the steering-wheel or torsion-bar torque.
A returnability torque comes from the geometry and components of the steering system or a model of the steering system.
A returnability torque is a vehicle speed dependent and steering-wheel angle dependent torque.
The above mentioned torque contributions can all be vehicle speed dependent. The torque contributions can also be calculated via mathematical models or sensed via sensors in the vehicle or steering system.
A compensation torque is the sum of the above-mentioned tyre friction torque, the friction torque, the damping torque and the returnability torque. The parts of the compensation torque are calculated from mathematical models of the different torque parts.
A reference generator concept for steering feel is a closed loop control method where first a reference or target value is calculated and then the steering assistance is controlled to minimize the error between the reference or target value and a corresponding measured value. Reference generator concepts for steering can be of two kinds, namely torque reference generator concepts and angle reference generator concepts.
A torque reference generator is used in a steering feel control concept where the steering-wheel torque is calculated in a reference generator, giving a reference steering-wheel torque, this reference steering-wheel torque is then compared to a measured steering-wheel torque and the difference, forming a steering wheel torque error, is fed to a controller so that the steering wheel torque error can be minimized. The reference steering-wheel torque is in other words used to control, by the use of closed loop control, the feedback torque actuator.
A target steering-wheel torque is the sum of the lateral acceleration feedback torque, the above-mentioned tyre friction torque, the friction torque, the damping torque and the returnability torque.
An angle reference generator is used in a steering feel control concept where the steering-wheel angle is calculated in a reference generator, giving a reference steering-wheel angle; this reference steering-wheel angle (reference feedback torque actuator angle) is then compared to a measured steering-wheel angle and the difference, a steering-wheel angle error, is fed to a controller so that this error can be minimised. In other words the reference torque actuator angle can be said to be used to control the feedback torque actuator to this reference angle.
A target steering angle, in the angle reference generator, is based on the equation of the target steering-wheel torque, where the target steering-wheel torque is the sum of the lateral acceleration feedback torque, the above-mentioned tyre friction torque, the friction torque, the damping torque and the returnability torque. If the target steering-wheel torque, in this equation is changed to the sensed or estimated driver torque, the steering angle can be derived out of this steering angle dependent equation. This derived steering angle is the target steering angle of the angle reference generator.
The parts of the target steering-wheel torque are calculated from mathematical models of the different torque parts.
A target steering-wheel angle can be calculated from the equation of steering feel, where the torsion-bar torque should be equal to the target steering-wheel torque as described above. Now, from this equation, a target steering-wheel angle can be calculated.
The parts of the target steering-wheel angle are calculated from mathematical models of the different torque parts.
A vehicle state controller, is defined as a dynamic function for achieving a target state in a vehicle in a controlled manner. That is, to minimise the difference between the target state and the actual state, i.e. the control error, in a controlled way.
A PID controller is a proportional-integral-derivative controller, which is a control loop feedback mechanism widely used in industrial control systems and a variety of other applications requiring continuously modulated control. A PID controller continuously calculates an error value, e (t), as the difference between a target value and a measured process value and applies a correction based on proportional, integral, and derivative terms (denoted P, I, and D respectively) which give their name to the controller. In practical terms it automatically applies accurate and responsive correction to a control function. An everyday example is the cruise control on a road vehicle; where external influences such as gradients would cause speed changes, and the driver has the ability to alter the desired set speed. The PID algorithm restores the actual speed to the desired speed in the optimum way, 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.
A vehicle state actuator, is an actuator that when actuated influences one or several vehicle states.
Vehicle state actuators are brakes, engine, controllable four-wheel-drive clutches, controllable differentials, active dampers, electric or hydraulic wheel motors and electrically or hydraulically driven axles.
A target value, reference value or request is a set point for the actuator that is achieved by the use of either a closed loop controller and/or a feed-forward controller.
A vehicle model is a mathematical model that transforms a road-wheel angle and a vehicle speed to a number of vehicle yaw and/or lateral states, namely vehicle yaw rate and acceleration, vehicle lateral speed and acceleration and vehicle body sideslip angle.
Transformation is defined as a mathematical function or lookup table with one input value used to produce one output value. That means that a transformation can be used, with its tuneable parameters, to create a relation between the input value and the output value with arbitrary tuneable shape. A transformation can have time-varying parameters that are even dependent on other values, a so-called gain scheduling, so that the transformation is a function with parameters that themselves are functions. An example of such a transformation is a vehicle state to driver torque relation where the relation is a vehicle speed dependent continuously rising, degressive shaped function.
A steering-wheel torque measurement is a torque measured in the steering column or in the steering wheel.
A vehicle axis 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 point to the left. Z points upward.
A Torque and Angle Sensor (TAS) is a sensor for sensing torque and angle.
An ABS sensor or wheel speed sensor is a sensor measuring wheel speed.
A rate gyro sensor measures angular speed around an axis in yaw, pitch or roll direction.
An acceleration sensor measures acceleration in longitudinal, lateral or vertical direction.
A position sensor measures the position. It can be a local, regional or worldwide coverage, generally referred to as GPS.
A brake pedal sensor indicates if the pedal is pressed.
A break pressure sensor measures the pressure in the brake system.
The term TAC (Torque and/or Angle reference generator control concept) is used for the SFC and/or for the SPC.
The steering wheel 1 is connected to steering shaft 2 which in turn is connected to the electric feedback motor 3. The electric feedback motor 4 is connected to the mechanical feedback arrangement 4.
The feedback motor 3 is via electric connection 6 controlled by the ECU 5 via regulation of a current provided to the electric feedback motor 3 to provide a controlled, desired, torque to the steering wheel 1. In the shown embodiment the steering wheel 1 and the electric feedback motor 3 are directly connected, without any torque or angle sensor or any torque and angle sensor (TAS) arranged on the shaft 2 for providing a control signal to the ECU 5. In alternative embodiments a sensor (torque or angle or torque and angle sensor) may be provided for sensing torque and/or angle in the steering shaft 2, in addition to the estimation of torque provided by the electric motor, i.e. torque estimated based on currents in the electric motor, e.g. for redundancy reasons and/or further increasing torque value accuracy for improving the steering feedback control even more. As an example a torsion bar with a torque sensor may be used for measuring the driver torque, i.e. the torque caused by the force applied by the driver on the steering wheel 1, which torque is transmitted through the steering shaft 2 to the torsion bar.
The ECU 5 via connection 7 controls a current provided to the electrically controllable actuator, e.g. assistance motor, 8, and preferably receives sensor information from angle sensors (not shown), or torque and/or angle sensors; of, or in communication with, the electric assistance motor 8.
According to the present invention, the feedback arrangement 10, as referred to above, comprises a feedback motor 3 combined with a mechanical feedback arrangement 4. The mechanical feedback arrangement 4 comprises a PFFE, passive force feedback element. The mechanical feedback arrangement (PFFE) 4 may comprise any kind of spring, i.e. an element that builds up force in a direction which is opposite to the direction of movement, without any input of energy than the energy provided by the movement itself. The mechanical feedback arrangement (PFFE) 4 will generate a force in the steering wheel 1 opposite to the direction of the movement when turning away from the centre, i.e. straight ahead position. If the electric feedback motor 3 fails, the mechanical feedback arrangement (PFFE) 4 will generate a force that will try to return the steering wheel 1 to centre, i.e. normally the straight-ahead position.
The force generated by the mechanical feedback arrangement (PFFE) 4 will provide an addition of force to the force generated by an electric feedback motor 3. This means that a certain maximum amount of feedback force can be generated with a smaller electric feedback motor which is very advantageous for several reasons since less space is required, less energy will be needed which is particularly advantageous in an electric vehicle, e.g. a car, wherein every saving in electric consumption is preferred in favour of a greater range.
The electric feedback motor 3, in turn, can add or reduce forces to the mechanical feedback arrangement (PFFE) 4 to exactly shape the desired steering feedback for every situation.
Depending on the design of the mechanical feedback arrangement (PFFE) 4 and how it interacts with the steering wheel 1, it is also, in advantageous embodiments to which the invention, however, is not restricted, possible to create a certain amount of desirable friction force. For example when the feedback force is created using cam profiles attached to, or otherwise formed in, the steering shaft 2 interacting with e.g. roller bearings 47B,47B′ as in the embodiment shown in
It is also possible to, relevant to embodiments described below with reference e.g. to
In still other embodiments other types of springs can be used in the mechanical feedback arrangement, e.g. leaf springs, washer shaped springs or any other type of spring being elastic and providing a force when the spring element is deformed. Thus, the coil springs shown in
A spring (or springs) (or more generally spring element(s)) may according to the invention be made of steel or any other appropriate metal or metal composition. Alternatively the spring element(s) may be made of an elastic material such as rubber or an elastomer. Still further the, or each, spring element may be a gas spring.
The seats 44B, 44B′ are in the shown embodiment arranged on opposite sides, oppositely directed, although they can also be arranged in other manners. Through being oppositely located, any resulting bending force exerted on the steering shaft 2B by bushings 47B,47B′ (as explained below) can be evened out.
The other ends of the springs 43B,43B′, distant from ends connected at the seats 44B,44B′, each can act on a respective outer rocker arm 451B,451B′ of a respective rocker arrangement 45B,45B′. Each rocker arrangement 45B,45B′ is pivotally mounted around a respective pivot shaft 46B,46B′ attached to an inner wall, protruding portion or similar (not shown) in any appropriate manner at an inner portion of the mechanical feedback arrangement 4B. At a free end of an inner arm 452B,452B′ of each respective rocker arrangement 45B,45B′, a respective bearing shaft 48B,48B′ with a bearing 47B,47B′ is attached which is movable with the inner arm 452B,452B′ between the respective seat 44B,44B′ and the respective cam surface 21B,21B′. Thus, when the steering shaft 2B is rotated, a cam surface 21B,21B′ will actuate upon a respective bearing 47B,47B′, actuating upon the respective inner rocker arm 452B,452B′, such that the rocker arrangement 45B,45B′ will rotate around the pivot shaft 46B,46B′ and the respective spring 43B,43B′ will be actuated upon by the respective outer rocker arm 451B,451B′ and vice versa.
In this embodiment a reaction force is provided in which in addition each inner rocker arm 49B,49B′ and each bearing 47B,47B′ will act on one of the cam profiles 21B,21B′; inner rocker arm 49B and bearing 47B on cam profile 21B and inner rocker arm 49B′ and bearing 47B′ on cam profile 21B′. An advantage is that through the use of cam profiles and through shaping the cam profiles a very precise design of the steering feedback can be provided. Another advantage of using cam profiles connected to or forming part of a steering shaft in combination with a spring arrangement as described is that the steering stroke can be up to one full revolution to both left- and right steering inputs. Particularly the cam profiles can be shaped in different manners to provide a desired torque build-up.
Through the arrangement of the mechanical feedback arrangement according to the present invention a feedback torque can be built up also for a limited turning of the steering wheel, also for the first turning degrees and the spring(s) 43;43A,43A′ act tangentially to the moving direction of the actuation element(s), e.g. lever 21 or cam profile 21B,21B′, and hence not directed towards the centre of the steering column. It is an advantage that also for small angles a considerable feedback torque can be generated.
In the embodiments discussed with reference to
In another embodiment, not shown, which is a simplification of the embodiment described with reference to
In still another alternative embodiment, also not shown, comprising one or more cam profiles as more thoroughly described with reference to the embodiment shown e.g. in
In particular embodiments (not shown) existing or additional electrical coils in the feedback motor can be used to create a damping feel. If there is a malfunction in the steering system or if there is any other reason to shut the steering down, the mechanical feedback will return the steering wheel to centre position. However, the return speed can be perceived to be to strong and unwanted overshoot and oscillations can occur. According to these embodiments of the invention, to counteract these effects, the coils in the feedback motor are connected to each other to create magnetic fields that will dampen the rotation of the steering wheel. The connection of the coils can advantageously also be done via resistors, fixed or a potentiometers, so that the dampening effect can be regulated.
In particular embodiments (not shown) a mechanical feedback arrangement as described above may comprise or be connected to an additional unit containing electric coils and a rotor which is primarily designed for providing a dampening torque. The dampening torque can be applied during faulty operation or as an addition to normal operation. The coils can also be connected via resistors, fixed or potentiometers, to allow for regulation of the dampening effect. The advantage of having an additional device for dampening torque instead of using the electric motor is that it will work also with a faulty motor.
In alternative embodiments (not shown) a mechanical feedback arrangement as described above is connected to the steering shaft instead of being connected to the electric feedback motor. This alternative allows for a high flexibility to fit different package solutions.
In yet other alternative embodiments (not shown) a mechanical feedback arrangement as described above is connected directly to the steering wheel instead of being connected to the electric feedback motor, which allows for a flexibility to fit different package solutions.
It should be clear that the invention is not limited to the specifically illustrated embodiments but that features of different embodiments can be combined in an arbitrary manner within the scope of the appended claims.
It should also be clear that the inventive concept also covers embodiments with a steering arrangement comprising for example a yoke, joystick or any other input device instead of a steering wheel. This is applicable for all embodiments of a feedback arrangement and locations of a feedback arrangement, or part thereof, as described in the present application.
It is an advantage of the present invention that, through the provisioning of a feedback arrangement comprising an electric feedback motor and a mechanical feedback arrangement to provide a feedback torque, the desired maximum feedback torque will be built by the sum of the electric feedback motor and the mechanical feedback arrangement, since the electric feedback motor can have a smaller torque rating than if it were the sole source of feedback. This will reduce fabrication costs, and the size (weight and volume) of the electric feedback arrangement can be reduced as compared to if it were the sole source of feedback. It is also an advantage to be able to have an electric feedback motor of a small size since for fabrication of an electric motor raw materials like copper and rare earth metals and other critical minerals are needed, and it is an imperative to contribute in holding down the increased demand for mining production which can have severe negative impacts on the environment, and to support a sustainable production.
It is also an advantage of the present invention that, since the feedback force is generated not only by an electric feedback motor, but also with a mechanical feedback arrangement, less energy will be used, which is of large importance, especially in an electric vehicle where every saving in electric consumption is preferred in favour of a greater range.
Another advantage of the invention is that it is easier to meet requirements as to a vehicle having to be controllable despite a failure in the steering system, which even is a legal requirement and a required functionality is that the steering shall have a self-centring effect. (Uniform provisions concerning the approval of vehicles with regard to steering equipment, UN Regulation No. 79, which must be complied with for any party seeking a UN type approval for a vehicle.)
Another advantage of the present invention is that the suggested arrangement is axially compact allowing the steering wheel (steering column) to move axially e.g. in case of an accident, enabling an good collision safety.
Since according to the invention, the steering wheel, or more generally the steering arrangement, is connected mechanically to the steerable wheels, self-centring forces are transmitted from the tyres via the suspension geometry to the steering arrangement. When the force in the steering wheel is solely dependent on an electric feedback motor, the self-centring effect will be lost if the electric feedback motor fails, but with addition of the mechanical feedback arrangement this self-centring effect will be maintained.
Still another advantage of the present invention is that an improvement in creation of properties constituting a good steering feel is made as compared to when only an electric feedback motor is used. One such property is friction feel, for which the use an electric motor is not optimal, especially for slow, zero and reversing angular speed of the motor and hence, the steering wheel. A mechanical feedback arrangement according to the present invention can be designed to achieve the desired friction feel, also for instance by replacing the bearings shown in
If the feedback would be generated only by a mechanical feedback it would be not be possible to achieve different feedback characteristics for different speeds and parking, but through the exact control of feedback torque contribution form the electric feedback motor this is enabled, which is very advantageous.
The inventive concept with the use of a feedback arrangement as described above is applicable for wired or wireless steering systems for steering of different vehicles, cars, trucks, buses, but also other vehicles such as aircrafts, boats, remotely operated vehicles and radio-controlled models and toys. It can also be used for steering of vehicles in simulators and computer games while providing a feedback, e.g. a desired feedback.
It should be clear that the invention is not limited to the specifically illustrated embodiments, but that it can be varied in a number of ways within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2250146-4 | Feb 2022 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2023/050003 | 1/2/2023 | WO |
