STEERING INPUT DEVICE

In steer-by-wire systems in vehicles, it is desirable to provide the same accuracy and comfort as vehicles with a steering column and EPS. Most of the known steer-by-wire systems control an element either by applying a torque or by the input of a desired position, usually the angle of the element to be controlled.

In systems where a torque is applied to control an element the steering input devices rely on sensing an input torque or force applied by an operator to an operating element and providing an output force through an actuator to a controlled element, such as a wheel. When the controlled element moves in response to the resultant active force, which is the sum of the output force and the external forces acting on the controlled element, a position sensor transmits the resultant movement to a controller, which controls an actuator that triggers a corresponding movement on the operating element. As a result, the operator experiences a reaction force that corresponds to the external forces acting on the controlled element. Such systems require a steering input device capable of measuring a force input and allowing the controller to control the position of the element.

Control systems in which input of a desired position of an element is used to control the position of that element generate feedback to the operator by applying a force to the operating element. The latter system requires a steering input device that allows the operator to change the position of an operating element and a control device that can apply a force to the operating element through an actuator.

Depending on the application, a system with force input on an operating element or a system with position input of the element to be controlled may be preferable. Hybrid solutions are also possible for some applications. Fly-by-wire control of a commercial aircraft using a control stick is an example of an application where a hybrid solution is preferable. Fly-by-wire systems typically use position inputs for the elements being controlled and in some cases provide force feedback to a control stick. Commercial aircraft are flown by two pilots, each with a control stick, with the two sticks operating independently so that the two sticks can be operated in conflict. Pilots switch control from one stick to the other, which means that the other pilot does not receive feedback when one pilot is in control. Also, in some flight control systems, the flight control computer may switch the active control stick from one pilot to the other if the computer considers the steering inputs of the non-controlling pilot to be a more appropriate response to a particular situation than the steering inputs of the controlling pilot. This can cause confusion between pilots if they miss the visual indication of who is in control. A system where the active stick operates in position input mode and the non-active stick operates in position feedback mode would allow the non-active pilot to sense what the controlling pilot is doing. By introducing a force threshold, control can be taken over by the non-active pilot if the non-active pilot applies a significant force to override the active pilot's input. In the event that the flight control computer overrides the pilot's input, both control sticks could be switched to position feedback, and the controlling pilot would know immediately when the flight control computer overrides its input. The same applies to vehicles with steer-by-wire systems, where automatic driving assistance systems can temporarily take over control, or when switching to autonomous driving.

Vehicles equipped with two steering wheels for driver training would also benefit from a hybrid system in which the student driver operates the car through position control and force feedback, while the instructor can sense these control inputs through position feedback. If the instructor sees the need to intervene and exceeds a threshold force on the instructor steering wheel, control of the car is shifted to the instructor steering wheel and the instructor takes control with position control and force feedback on his steering wheel, while the student driver can now feel the instructor's control inputs through position feedback in the student steering wheel.

However, no solution is known from the prior art for a steering input device that can operate in both force input/position feedback mode and position input/force feedback mode.

EP 1 954 547 B1 shows a steering input device suitable for receiving a force input from an operator to an operating element and providing the operator with a position feedback of the element to be controlled. However, the proposed solution is not suitable for operation based on a position input and a force feedback because a self-locking gear between the actuator for the element to be controlled and the operating element prevents the operator from making a position input.

From EP 1 598 726 A2 an input device is known that allows position input and provides force feedback to the operator. However, this solution is not designed to provide the force feedback required in cars, aircraft and heavy machinery. The problem of motor ripple and inertia is also not addressed.

US 2016/179128 A1 discloses a joystick for controlling the speed of driven machine elements. A position detection system is provided that is capable of detecting the position of the joystick handle at a given time and using this information to control the speed or position of an element by a control unit and an actuator that operates the controlled element. A first feedback unit is capable of causing the joystick to vibrate when pre-programmed trigger events occur. A second feedback system consists of two motors that actuate two opposing racks connected to the joystick, with a spring between the racks. Although the application mentions the possibility of using the two motors to provide force feedback to the joystick, the primary purpose of the feedback system is to compensate for the neutral position of the joystick, the neutral position being the position to which the joystick returns when the operator is not applying force. However, this document does not describe that the force applied by the operator is determined and used to control the element.

Another desired feature of steer-by-wire systems is a realistic feedback of road forces to an operating element, for example a steering wheel or a joystick. For this purpose, a force feedback actuator must be provided, that generates a considerable force and transmits it to the operating element.

In principle, DC electric motors that provide sufficient torque for a direct drive can be used as force feedback actuators. However, these motors require a large installation space and are expensive. In addition, DC motors are usually designed to provide uniform torque during rotation, but not uniform torque during small angular movements. As a result, commercial motors deliver only a fraction of their nominal torque when not rotating, and exhibit significant torque variations (ripple) during very small movements and at low speeds. A high ratio gear could reduce the ripple and increase the speed and angular movement of the motor, but this would add significant inertia to the steering input device.

Stepper motors are designed to move in small steps and can be controlled very precisely in terms of both speed and position, but not in terms of torque. Because the stepper motor is designed to move in small specific steps, this type of motor also provides significant torque ripple.

Therefore, the objective of the invention is to provide a solution for a steering input device that can operate in both modes: force or torque input/position feedback mode and position input/force feedback mode, and that avoids ripple effects in the feedback force.

The problem is solved by a steering input device according to claim 1. The subclaims indicate advantageous further embodiments of the invention.

The steering input device according to the invention can be operated in both modes. It can be used to apply a force on the element to be controlled or the desired angular position of the element can be specified. Furthermore, the input device avoids the need for bulky motors because a quick provision of torque does not require a high torque from low or zero angular speed, as the motor will be allowed to move at high speed to increase the angular difference. This effect can be enhanced by providing a gear. A gear is amplifying both, the torque and the movement of the motor itself. At the same time, the at least one elastic element will allow a little spring loaded slack if the user applies a sudden steering correction to the input device, reducing the impact of high inertia resulting from the gear.

The input device according to the invention is balancing between the need for a bulky, expensive DC-motor and a stepper motor that has significant ripple and poor torque control options. The input device uses only position control for the motor and no torque control and therefore avoids problems with ripple effects. The ripple effect is reduced for all kinds of electric motors used as a feedback motor. If a hydraulic motor is used problems with ripple effects can be avoided completely.

The drawing shows preferred embodiments of steering input devices according to the invention, wherein

Figs. 1a - 1e

are various detailed views of elements of a coupling unit of the steering input device shown in Fig. 2;

Fig. 2

is a cross-section through a steering input device;

Fig. 3

is a view of a second steering input device with a steering wheel as operating element.

The steering input device 200 according to the invention, which is shown in Fig. 2, comprises an operating element 204 - in this case a joystick - with which an operator can exert control inputs for an element to be controlled (not shown) and via which he can receive feedback signals from the controlled element. The operating element 204 is connected to an input shaft 203, so that movement of the operating element 204 results in a corresponding movement of the input shaft 203. Further provided is a coupling unit 100 comprising two housing parts 101A, 101B axially connected such that each part 101A, 101B can rotate relative to the other. The coupling unit 100 has an elastic member in the form of a torsion spring member 102, the ends of the spring member 102 each being rotatably mounted in a groove in one of the housing parts 101A,101B. The housing part 101B of the coupling unit 100 is rotationally fixed to the input shaft 203. The opposite housing part 101A of the coupling unit 100 is non-rotatably connected to the output shaft 201a of a feedback motor 201.

A first angle sensor 202 measures the angular position θ1 of the motor output shaft 201a. The first angle sensor may be an external angle sensor or an angle sensor built into the motor 201. A second angle sensor 205 measures the angular position θ2 of the input shaft 203.

When no torque is transmitted through the coupling unit 100, the angular position θ₁ of the motor output shaft 201a corresponds to the angular position θ₂ of the input shaft 203.

On the other hand, when a torque T is transmitted through the coupling unit 100, the elastic deformation of the spring element 102 results in an angular displacement between the two shafts 202a and 203 of Δ θ=T/k, where k is the spring constant. The angular displacement can be determined as Δ θ= θ₂- θ₁ using the angular sensors 202, 205.

Since there is a relationship between the angular displacement Δ θ and the torque transmitted between the motor output shaft 201a and the input shaft 203, the steering input device 200 can be used to determine a torque from a given angular displacement Δ θ or to obtain torque feedback at the operating element 204 by applying a presettable angular displacement Δ θ.

The distinguishing feature of the steering input device according to the invention is the implementation of an elastic element 102 between an operating element 204 and a feedback motor 201, combined with a first angle sensor measuring the angular position of the output shaft of the feedback motor and a second angle sensor measuring the angular position of the input shaft. This allows to operate the steering input device in both modes: force input/position feedback mode and position input/force feedback mode. Further, ripple effects in the feedback force created by the motor 201 can be avoided. The motor 201 can be an electric motor or a hydraulic motor.

Fig. 1 shows the individual components of the coupling unit 100. The coupling unit 100 consists of the two housing parts 101A, 101B. Fig. 1a shows the internal details of the housing part 101A. A protrusion 104 provides axial alignment with the housing part 101B, ensuring adequate spacing between the two and centering of the spring element 102. The protrusion 104 may have a smaller protrusion that engages a recess on the opposite housing part 101B, or both protrusions may be in the form of a cylinder that receives a locking and alignment pin.

A groove 103 is provided in both housing parts 101A, 101B, in each of which one end of the spring element 102 is rotatably supported, as shown in Figs. 1b and 1d. Both housing parts 101A, 101B have shaft extensions on the outside, as shown in Fig. 1c, each of which can be rotationally connected to the motor output shaft 201a and the input shaft 203, respectively. In the illustrated example, the housing parts 101A, 101B each have a disk with hole patterns 105 for use with an optical angle sensor 202, 205.

In Fig. 1e, the housing part 101A facing away from the viewer remains fixed, while the housing part 101B facing the viewer is rotated by θ degrees. The angular displacement between the two housing parts is given by: Δθ= θ₂- θ₁, where θ₁ is the rotational position of the housing part 101A and θ₂ is the rotational position of the housing part 101B, measured from a common reference and in a common positive direction. Since the housing part 101A is not rotated, this results in an angular displacement of Δθ= θ₂-0= θ₂. For a given spring constant of k[Nm/deg] of the spring element 102, the illustrated rotation requires a torque of: T= Δθ·k= θ₂·k.

It is understood that the spring element 102 may be made of metal or a composite material. The spring element 102 may also have a different shape. A rubber part or a part made of a similar elastic material may also be used to achieve the characteristics of a torsion spring element.

The steering input device 200 according to the invention, shown in Fig. 2, comprises the operating element 204 with which the operator can make inputs and receive feedback. The operating element 204 may be in the form of a joystick, a steering wheel 206 (Fig. 3), or any other form suitable for the control task. The operating element 204 is connected to an input shaft 203, such that movement of the operating element 204 results in corresponding movement of the input shaft 203. In Fig. 2, the input shaft 203 and a portion of the operating element 204 are shown as a common component, but it may also be an assembly comprising multiple elements. A coupling unit 100 comprising two housing parts 101A, 101B is axially connected such that each part 101A, 101B can rotate relative to the other. Each end of a spring element 102 is rotatably fixed in a groove 103 in the housing part 101A, 101B of the respective ends of the spring element 102. One end of the coupling unit 100 is rotationally fixed to the input shaft 203. The housing 101B of the resilient member 102 may be an integral part of the input shaft 203. The opposite end of the coupling unit 100 is rotationally fixed to the output shaft 201a of the motor 201. The housing 101A of the elastic member 102 may be an integral part of the motor output shaft 201a.

A first angle sensor 202 measures the angular position θ₁ of the motor output shaft 201a. The first angle sensor can be an external angle sensor or an angle sensor built into the motor. A second angle sensor 205 measures the angular position θ₂ of the input shaft 203. There can also be at least one strain gauge attached to the input shaft 203 and/or to the operating element 204.

When no torque is transmitted through the coupling unit 100, the angular position θ₁ of the motor output shaft 201a corresponds to the angular position θ₂ of the input shaft 203.

When torque T is transmitted through the coupling unit, elastic deformation of spring 102 results in an angular displacement between the two shafts 202a and 203 of Δ θ=T/k, where k is the spring constant. The angular displacement can be determined from the inputs of the encoders 202, 205 as Δ θ= θ₂- θ₁. Thus, the steering input device can be used in a control system that uses position input by measuring the position θ₂ to which the operator moves the operator input shaft 203 over the operating element 204. A controller then controls an actuator that moves the controlled element to a corresponding position. A force feedback may be estimated by the controller. This may be based on measuring the current used by the actuator or measuring the force required. The controller can then calculate a suitable torque T to be applied to the input shaft 203. The desired feedback torque can then be applied by the controller by moving the motor output shaft 201a to an angular position of: θ₁= θ₂-T/k.

However, the steering input device can also be used in a control system that uses the applied force as a control input parameter and provides position feedback to the operator. In such a system, the operator applies a force to the operating element 204, causing a torque T1 to be applied to the input shaft 203. Since the controlled element does not move, the controller maintains the position θ₂₁ by driving the motor output shaft 201a in the opposite direction so that the position θ₂₁ is maintained. Equilibrium is reached at a motor output shaft position of θ₁₁, and the torque applied by the operator can be calculated as T1= (θ₂₁- θ₁₁)·k, which is used by the controller to apply an appropriate force to the controlled element.

When the operator increases the torque to a value T2 and the controller then applies a corresponding force to the controlled element, the controlled element starts to move. This is detected by an angle sensor on the controlled element and transmitted to the controller. The controller then allows the input shaft 203 of the operating element to move to a position θ₂₂ corresponding to the new position of the controlled element by driving the motor output shaft 201a to the position θ₁₂ given by: θ₁₂= θ₂₂-T2/k.

It is understood that the loop of transmitting input signals to the controller and receiving feedback signals from the controller is repeated at a high frequency (more than 100 Hz) and therefore the changes in rotational positions and applied forces are incremental and occur in very small steps.

The operating element can be any element suitable to manually control the movement of a part not only a steering wheel or a joystick.