Steering system and method of controlling a steering system

Abstract

An electro-hydraulic steering system (1) comprises a hydraulic steering actuator (11) and a hydraulic-mechanical steering unit (6) for actuating the hydraulic steering actuator in response to a steering demand from a steering wheel (2) connected to the hydraulic-mechanical steering unit by a steering shaft (3). An electric motor (5) is operable to apply torque to the steering shaft and is controlled to provide haptic steering torque feedback to a user through the steering wheel. The electric motor (5) is controlled to provide haptic steering torque feedback during a dead range of movement of the steering member (2) before the hydraulic-mechanical steering unit begins to supply fluid to the steering actuator. The electric motor (5) may be controlled to provide haptic steering torque feedback that follows a predetermined profile to compensate for the effect of a spring in the hydraulic-mechanical steering unit that resists movement of the steering member.

Description

Technical Field

[0001] Embodiments of the present disclosure generally relate to hydraulic steering systems and methods of controlling hydraulic steering systems. Background Art

[0002] In a steering system, rotating a steering component (such as a steering wheel) generates a steering demand that indicates that the steered wheels should be turned by an angle corresponding to the direction and magnitude of the steering wheel rotation.

[0003] Hydraulic steering systems are commonly used in vehicles that may require high steering forces, such as agricultural vehicles or other types of utility vehicles. In a hydraulic steering system, a hydraulic steering actuator is coupled to a steered wheel, causing the steered wheel to rotate when the hydraulic steering actuator is actuated in response to a steering demand. The steering system includes a fluid supply device and a working port device, the fluid supply device including a pressurized fluid source and a tank, the working port device having two working ports (e.g., a left turn port and a right turn port) that are fluidly connected to the hydraulic steering actuator. The steering wheel is operably connected to a hydraulic-mechanical steering unit (also known as a manual metering unit) via a steering shaft. The hydraulic-mechanical steering unit is configured to connect one working port to a pressurized fluid source and another working port to a tank according to the direction and angle of rotational movement of the steering wheel.

[0004] It is also known to provide an electric-hydraulic steering system in which a steering supply valve device is connected to a controller (e.g., an electronic controller or ECU). The steering supply valve device is fluidly connected to a pressurized fluid source, a tank, and a working port, and is arranged to adjust the volume of fluid provided by a hydraulic-mechanical steering unit to a hydraulic steering actuator. This arrangement can be used to actively change the steering ratio R. For example, the steering ratio R can vary based on vehicle speed, steering wheel position, and / or steering angle. This arrangement is sometimes referred to as a superimposed hydraulic steering system. In a superimposed hydraulic steering system, a controller determines a suitable steering ratio based on at least one parameter of the vehicle and controls the steering system to operate with the steering ratio. For example, when an agricultural vehicle such as a tractor is operated at a low driving speed, it may be desirable to operate with a low steering ratio to achieve relatively fast turns, thereby obtaining better maneuverability. At high speeds, a higher steering ratio may be appropriate in order to maintain stability. By using a steering system supply valve device to increase the volume flow of fluid provided by the hydraulic-mechanical steering unit to the steering actuator, the steering ratio R can be reduced compared to the steering ratio provided by the hydraulic-mechanical steering unit itself.

[0005] The force that needs to be provided by the hydraulic steering actuator depends on the size and weight of the vehicle and the size of the tires. Vehicle manufacturers that produce a range of small and large vehicles offer different sizes of hydraulic steering actuators for the steering system, which are selected to meet the requirements of the specific vehicle design. Larger hydraulic steering actuators require higher fluid volume flows to provide an effective steering response compared to smaller actuators. Therefore, a hydro-mechanical steering unit that can deliver an appropriate volume flow to the hydraulic steering actuator is usually selected.

[0006] Hydraulic steering systems provide the driver with a different steering feel than the mechanical steering systems used in conventional motor vehicles such as cars. In mechanical steering systems, the forces from the steered wheels are transmitted back to the driver through the steering wheel as tactile steering torque feedback. Even in hydraulic power-assist systems, the forces from the steered wheels are transmitted to and through the steering wheel. In hydraulic steering systems, the steering wheel is largely isolated from the forces developed at the steered wheels. Summary of the invention

[0007] Aspects of the invention relate to an electro-hydraulic steering system, a method of operating an electro-hydraulic steering system, a vehicle (which may be a utility vehicle, such as an agricultural vehicle), and a method of operating a vehicle (which may be a utility vehicle, such as an agricultural vehicle).

[0008] According to one aspect of the present invention, there is provided an electric-hydraulic steering system for a vehicle, the electric-hydraulic steering system comprising a hydraulic steering actuator and a hydraulic-mechanical steering unit, the hydraulic-mechanical steering unit being used to actuate the hydraulic steering actuator in response to a steering demand from a steering component connected to the hydraulic-mechanical steering unit via a steering shaft, the system comprising an electric motor for applying torque to the steering shaft and an electronic controller for controlling the actuation of the electric motor, the controller being configured to control the actuation of the electric motor to provide tactile steering torque feedback to a user via the steering component.

[0009] In an embodiment, the controller is configured to control the electric motor to provide haptic steering torque feedback during a deadband range of movement of the steering component before the hydro-mechanical steering unit begins supplying fluid to the steering actuator.

[0010] In an embodiment, the controller is configured to control the electric motor to provide tactile steering torque feedback sensed by a user, which follows a predetermined profile within the range of movement of the steering component from an initial position to compensate for the influence of a biasing component (such as a spring) in the hydro-mechanical steering unit that resists movement of the steering component.

[0011] According to another aspect of the present invention, there is provided an electric-hydraulic steering system for a vehicle, comprising:

[0012] A hydraulic steering actuator, the hydraulic steering actuator is used to turn the steered wheel through a rotation angle;

[0013] a fluid supply device including a pressurized fluid source and a storage tank;

[0014] a workport device having two workports fluidly connected to the hydraulic steering actuator;

[0015] a hydraulic-mechanical steering unit fluidly connected between the fluid supply device and the workport device and configured to connect one of the two workports to a source of pressurized fluid and the other workport to a tank according to a steering demand;

[0016] A steering component, the steering component is connected to the hydraulic-mechanical steering unit through a steering shaft, and the steering component can be moved by a user to rotate the steering shaft to generate a steering demand;

[0017] a steering component sensor coupled to the controller for detecting position and / or movement of the steering component;

[0018] a steering supply valve assembly fluidly connected to the source of pressurized fluid, the reservoir, and the two working ports, the steering supply valve assembly being connected to the controller;

[0019] an electric motor operative to apply torque to rotate the steering shaft when actuated, the electric motor operatively connected to the controller;

[0020] wherein the controller is configured to provide a control output upon detecting movement of the steering component to actuate the steering supply valve device so as to supply fluid to one of the two working ports of the working port device according to the movement direction of the steering component at least during movement of the steering component from an initial position through a dead band range of movement, in which the hydraulic-mechanical steering unit does not supply fluid to the one of the two working ports;

[0021] Wherein, the controller is configured such that when the steering component moves from an initial position through at least a portion of the dead band range of movement, the controller provides a control output to control actuation of the electric motor to apply a torque to rotate the steering shaft in a direction opposite to the rotation direction applied to the steering shaft by a user.

[0022] Using a steering supply valve arrangement to supply fluid to the steering actuator within the deadband allows the steering system to respond more quickly to steering demands. However, during this deadband, the steering system does not inherently provide any significant resistance to the steering component being turned. Therefore, using an electric motor to apply torque to rotate the steering shaft in a direction opposite to the direction of rotation applied to the steering shaft by the user provides tactile steering torque feedback to the user, thereby improving the driving experience.

[0023] According to another aspect of the present invention, there is provided an electric-hydraulic steering system for a vehicle, comprising:

[0024] A hydraulic steering actuator, the hydraulic steering actuator is used to turn the steered wheel through a rotation angle;

[0025] a fluid supply device, the fluid supply device including a pressurized fluid source and a storage tank;

[0026] a workport device having two workports fluidly connected to the hydraulic steering actuator;

[0027] a hydraulic-mechanical steering unit fluidly connected between the fluid supply device and the workport device and configured to connect one of the two workports to a source of pressurized fluid and the other workport to a tank according to a steering demand;

[0028] A steering component, the steering component is connected to the hydraulic-mechanical steering unit through a steering shaft, and the steering component can be moved by a user to rotate the steering shaft to generate a steering demand;

[0029] a steering component sensor coupled to the controller, the steering component sensor for detecting a position and / or movement of a steering component;

[0030] a steering supply valve assembly fluidly connected to the source of pressurized fluid, the reservoir, and the two working ports, the steering supply valve assembly being connected to the controller;

[0031] an electric motor operative to apply torque to rotate the steering shaft when actuated, the electric motor operatively connected to the controller;

[0032] wherein the controller is configured to control actuation of the electric motor by providing a control output to apply a torque to rotate the steering shaft, thereby modifying tactile steering torque feedback sensed by a user through the steering component, wherein the controller is configured to control actuation of the electric motor based on at least one parameter indicative of an operating condition of the vehicle so that the tactile steering torque feedback sensed by the user follows a predetermined profile within a range of movement of the steering component from an initial position.

[0033] This is advantageous because the electric motor can be used to control the haptic steering torque feedback experienced by the user, thereby providing a haptic steering torque feedback profile that more closely matches the haptic steering torque feedback profile of a conventional motor vehicle having a mechanical steering system or a fluid power assisted mechanical steering system. The arrangement can also be used to provide a similar driver experience across a range of vehicles of different sizes.

[0034] In some embodiments, the controller is configured to control actuation of the electric motor to modify the user-sensed haptic steering torque feedback based on at least one of:

[0035] Steering angle of the steered wheels;

[0036] Steering angle of the steering component;

[0037] a steering torque applied to the steering member by a user;

[0038] The ground speed of the vehicle;

[0039] Fluid pressure differential between chambers of the steering actuator;

[0040] The speed at which the steering component moves.

[0041] In some embodiments, the controller is configured such that when the steering component moves from an initial position through at least a portion of a dead band range of movement, the controller actuates the electric motor to apply a torque to rotate the steering shaft in a direction opposite to a direction of rotation applied to the steering shaft by a user, in which dead band range the hydraulic-mechanical steering unit does not supply fluid to the one working port.

[0042] In some embodiments, the controller is configured to actuate the electric motor to apply an increasing level of torque that rotates the steering shaft in a direction opposite to the direction of rotation applied by the user during a first phase of movement of the steering component from an initial position to an intermediate position between the initial position and an end of the dead band range of movement, and to apply a decreasing level of torque that rotates the steering shaft in the same direction during a second phase of movement of the steering component beyond the intermediate position within the dead band range of movement.

[0043] In some embodiments, the hydraulic-mechanical steering unit includes a resilient biasing device that biases the hydraulic-mechanical steering unit to a neutral position in which no fluid is supplied to the working port device, the hydraulic-mechanical steering unit is movable to a first working position in response to movement of the steering component from an initial position in a first rotational direction, in which a first working port of two working ports is connected to a pressurized fluid source and a second working port of the two working ports is connected to a tank, and the hydraulic-mechanical steering unit is movable to a second working position in response to movement of the steering component from the initial position in a second rotational direction opposite to the first rotational direction, in which the first working port of the two working ports is connected to the tank and the second working port of the two working ports is connected to the pressurized fluid source, when the hydraulic-mechanical steering unit is moved from the neutral position to the working position. When the steering wheel is moved from the initial position to any one of the first and second working positions, the elastic biasing device generates a torque on the steering shaft opposite to the rotational direction applied to the steering component by the user, wherein, during a first range of movement of the steering component from the initial position, the elastic biasing device generates substantially no torque, during a transition range of rotational movement of the steering component after the first range of movement, the elastic biasing device generates an increasing level of torque on the steering shaft, and during movement of the steering component beyond the transition range, the elastic biasing device generates a substantially stable level of torque; wherein the controller is configured to control actuation of the motor so that, during the transition range of movement of the steering component, the torque applied by the electric motor to rotate the steering shaft in a direction opposite to the rotational movement applied to the steering component by the user decreases as the torque applied to the steering shaft by the elastic biasing device increases.

[0044] In some embodiments, the controller is configured to control actuation of the electric motor so as to adjust the magnitude and direction of the torque applied by the electric motor to the steering shaft as the steering member moves from an initial position during a steering maneuver, thereby maintaining a predetermined profile of tactile steering torque feedback to compensate for any torque applied to the steering shaft due to operation of the hydro-mechanical steering unit, including, for example, torque applied to the steering shaft by a resilient biasing device of the hydro-mechanical steering unit.

[0045] According to one aspect of the invention, there is provided a vehicle having an electro-hydraulic steering system according to any aspect of the invention described above. The vehicle may be a multi-purpose vehicle or an agricultural vehicle, such as a tractor. The term "vehicle" should be understood to include self-propelled mobile machines, such as harvesters, sprayers, etc.

[0046] Methods corresponding to the various aspects of the invention described above may also be claimed.

[0047] According to one aspect of the present invention, a method for operating an electric-hydraulic steering system for a vehicle is provided, the system comprising a hydraulic steering actuator and a hydraulic-mechanical steering unit, the hydraulic-mechanical steering unit being used to actuate the hydraulic steering actuator in response to a steering demand from a steering component connected to the hydraulic-mechanical steering unit via a steering shaft, the system comprising an electric motor for applying torque to the steering shaft and an electronic controller for controlling actuation of the electric motor; the method comprising controlling the actuation of the electric motor to provide tactile steering torque feedback to a user via the steering component.

[0048] In an embodiment, the method comprises controlling actuation of the electric motor to provide haptic steering torque feedback during a deadband range of movement of the steering component before the hydro-mechanical steering unit begins supplying fluid to the steering actuator.

[0049] In an embodiment, the method includes controlling actuation of an electric motor to provide tactile steering torque feedback sensed by a user that follows a predetermined profile over a range of movement of a steering component from an initial position to compensate for the effect of a spring in a hydro-mechanical steering unit that resists movement of the steering component.

[0050] According to another aspect of the present invention, there is provided a method of operating an electric-hydraulic steering system for a vehicle, the system comprising:

[0051] A hydraulic steering actuator, the hydraulic steering actuator is used to turn the steered wheel through a rotation angle;

[0052] a fluid supply device, the fluid supply device including a pressurized fluid source and a storage tank;

[0053] a workport device having two workports fluidly connected to the hydraulic steering actuator;

[0054] a hydraulic-mechanical steering unit fluidly connected between the fluid supply device and the workport device and configured to connect one of the two workports to a source of pressurized fluid and the other workport to a tank according to a steering demand;

[0055] A steering component, the steering component is connected to the hydraulic-mechanical steering unit through a steering shaft, and the steering component can be moved by a user to rotate the steering shaft to generate a steering demand;

[0056] a steering component sensor coupled to the controller for detecting position and / or movement of the steering component;

[0057] a steering supply valve assembly fluidly connected to the source of pressurized fluid, the reservoir, and the two working ports, the steering supply valve assembly being connected to the controller;

[0058] an electric motor operative to apply torque to rotate the steering shaft when actuated, the electric motor operatively connected to the controller;

[0059] The method includes:

[0060] detecting at least an initial movement of the steering member, and in response to the detection, actuating the steering supply valve device to supply fluid to one of two workports of the workport device according to the direction of movement of the steering member at least during movement of the steering member from the initial position through a dead range of movement in which the hydraulic-mechanical steering unit does not supply fluid to the one of the two workports;

[0061] The method also includes actuating the electric motor to apply a torque to rotate the steering shaft in a direction opposite to a rotation direction applied to the steering shaft by a user when the steering member moves from the initial position through at least a portion of the deadband range of movement.

[0062] According to another aspect of the present invention, there is provided a method of operating an electric-hydraulic steering system for a vehicle, the system comprising:

[0063] A hydraulic steering actuator, the hydraulic steering actuator is used to turn the steered wheel through a rotation angle;

[0064] a fluid supply device, the fluid supply device including a pressurized fluid source and a storage tank;

[0065] a workport device having two workports fluidly connected to the hydraulic steering actuator;

[0066] a hydraulic-mechanical steering unit fluidly connected between the fluid supply device and the workport device and configured to connect one of the two workports to a source of pressurized fluid and the other workport to a tank according to a steering demand;

[0067] A steering component, the steering component is connected to the hydraulic-mechanical steering unit through a steering shaft, and the steering component can be moved by a user to rotate the steering shaft to generate a steering demand;

[0068] a steering component sensor coupled to the controller for detecting position and / or movement of the steering component;

[0069] a steering supply valve assembly fluidly connected to the source of pressurized fluid, the reservoir, and the workport, the steering supply valve assembly being connected to the controller;

[0070] an electric motor operative to apply torque to rotate the steering shaft when actuated, the electric motor operatively connected to the controller;

[0071] The method includes modifying tactile steering torque feedback sensed by a user through a steering member by actuating an electric motor to apply a torque to rotate a steering shaft, the actuation of the electric motor being performed based on at least one parameter indicative of an operating condition of a vehicle such that the tactile steering torque feedback sensed by the user follows a predetermined profile over a range of movement of the steering member from an initial position.

[0072] In some embodiments, the method includes controlling the electric motor to modify the user-sensed haptic steering torque feedback based on at least one of:

[0073] Steering angle of the steered wheels;

[0074] Steering angle of the steering component;

[0075] a steering torque applied to the steering member by a user;

[0076] The ground speed of the vehicle;

[0077] Fluid pressure differential between chambers of the steering actuator;

[0078] The speed at which the steering component moves.

[0079] In some embodiments, the method includes controlling actuation of the electric motor to apply a torque to rotate the steering shaft in a direction opposite to a rotation direction applied to the steering shaft by a user when the steering component moves from an initial position through at least a portion of a dead band range of movement, wherein the hydraulic-mechanical steering unit does not supply fluid to the one working port.

[0080] In some embodiments, the method includes controlling actuation of the electric motor to apply an increasing level of torque to rotate the steering shaft in a direction opposite to the direction of rotation applied by a user through the steering member during a first phase of movement of the steering member from an initial position to an intermediate position between the initial position and an end of a dead band range of movement, and to apply a decreasing level of torque to rotate the steering shaft in the same direction during a second phase of movement of the steering member beyond the intermediate position within the dead band range of movement.

[0081] In some embodiments, the hydraulic-mechanical steering unit includes a resilient biasing device that biases the hydraulic-mechanical steering unit to a neutral position in which no fluid is supplied to the working port device, the hydraulic-mechanical steering unit is movable to a first working position in response to movement of the steering component from an initial position in a first rotational direction in which a first working port of two working ports is connected to a pressurized fluid source and a second working port of the two working ports is connected to a tank, and the hydraulic-mechanical steering unit is movable to a second working position in response to movement of the steering component from an initial position in a second rotational direction opposite to the first rotational direction in which a first working port of the two working ports is connected to the tank and a second working port of the two working ports is connected to a pressurized fluid source, when the hydraulic-mechanical steering unit When the element moves from the neutral position to any one of the first and second working positions, the elastic biasing device generates a torque on the steering shaft opposite to the rotational direction applied to the steering component by the user, wherein during a first range of movement of the steering component from the initial position, the elastic biasing device generates substantially no torque, during a transition range of rotational movement of the steering component after the first range of movement, the elastic biasing device generates an increasing level of torque on the steering shaft, and during movement of the steering component beyond the transition range, the elastic biasing device generates a substantially stable level of torque; wherein the method includes controlling the actuation of the electric motor so that during the transition range of movement of the steering component, the torque applied by the electric motor to rotate the steering shaft in a direction opposite to the rotational movement applied to the steering component by the user decreases as the torque applied to the steering shaft by the elastic biasing device increases.

[0082] In some embodiments, the method includes controlling actuation of the electric motor to adjust the magnitude and direction of the torque applied by the electric motor to the steering shaft when the steering component moves from an initial position during a steering maneuver, thereby maintaining a predetermined profile of tactile steering torque feedback to compensate for any torque applied to the steering shaft due to operation of the hydraulic-mechanical steering unit, including, for example, torque applied to the steering shaft by a resilient biasing device of the hydraulic-mechanical steering unit.

[0083] According to one aspect of the present invention, there is provided a computer program product comprising instructions, which, when a computer executes the program, cause the computer to perform one or more of the above methods.

[0084] According to one aspect of the present invention, a computer readable medium storing the above-mentioned computer program product is provided.

[0085] It should be understood that within the scope of the present application, the various aspects, embodiments, examples and alternatives described herein and their individual features may be used independently or in any possible and compatible combination. Where features are described with reference to a single aspect or embodiment, it should be understood that these features apply to all aspects and embodiments unless otherwise specified or these features are incompatible. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0087] Figure 1 is a schematic diagram showing a portion of a vehicle having an embodiment of an electric-hydraulic steering system according to one aspect of the present invention;

[0088] Figure 2 Schematic diagram showing the formation Figure 1 A fluid volume flow rate provided by a hydraulic-mechanical steering unit and a steering supply valve device as part of a steering system of the vehicle under two different ranges;

[0089] Figure 3 and Figure 4 Schematic diagram showing the formation Figure 1 The volume flow of fluid delivered by a hydraulic-mechanical steering unit and a steering supply valve arrangement that are part of a steering system, showing how the fluid flow changes as the steering wheel is rotated from an initial position;

[0090] Figure 5 Shown is the Figure 1 A device for providing tactile steering torque feedback to a user of a steering system;

[0091] Figure 6 shows how the level of tactile steering torque feedback can be adjusted according to Figure 1 The pressure difference between the first chamber and the second chamber of the hydraulic steering actuator of the steering system changes;

[0092] Figure 7 shows how the level of haptic steering torque feedback can vary depending on the speed of the vehicle;

[0093] Figure 8 shows how the level of haptic steering torque feedback can vary depending on the steering angle from any given starting position;

[0094] Fig. 9 shows how the level of tactile steering torque feedback can be adjusted according to Figure 1 The rotation speed of the steering wheel of the steering system and / or the torque applied to the steering wheel by the user vary; and

[0095] Fig.10A variety of different haptic steering torque feedback profiles are shown. DETAILED DESCRIPTION

[0096] According to an example of one aspect of the present invention, there is provided an electric-hydraulic steering system 1 for a vehicle 100, comprising at least one steered wheel (here, steered wheels 14, 16), such as Figure 1 The steering system 1 includes a steering component 2 and a hydraulic steering actuator 11. The steering component 2 may be in the form of a steering wheel for setting a desired steering angle (i.e., angular position) of steered wheels 14, 16. The hydraulic steering actuator 11 is operably connected to the steered wheels 14, 16 to rotate the steered wheels 14, 16 when actuated in response to a steering demand from the steering wheel 2.

[0097] The steering wheel 2 is coupled to a steering shaft 3, which is arranged to transmit the rotational movement of the steering wheel 2 to a hydro-mechanical steering unit 6 (sometimes also referred to as a manual metering unit). In a non-limiting example, the hydro-mechanical steering unit 6 may be an Orbitrol(R) hydrostatic valve available from Danfoss Power Solutions APS.

[0098] The hydraulic-mechanical steering unit 6 is hydraulically connected to a fluid supply arrangement comprising a pressurized fluid source 7 and a tank or reservoir 8. The pressurized fluid source 7 may be in the form of a pump arranged to pump hydraulic fluid from the tank 8 to the hydraulic-mechanical steering unit 6. The hydraulic-mechanical steering unit 6 is also hydraulically connected to a hydraulic steering actuator via a workport arrangement comprising a first workport 30 and a second workport 32, and via a first hydraulic line 9 connected to the first workport 30 and a second hydraulic line 10 connected to the second workport 32. In this embodiment, the hydraulic steering actuator 11 is a double-acting hydraulic cylinder accommodating a piston 12, which divides the cylinder into a first chamber 34 and a second chamber 36. The first hydraulic line 9 is fluidly connected to the first chamber 34 and the second hydraulic line 10 is fluidly connected to the second chamber 36. The piston 12 is arranged to move axially in the steering cylinder 11 in response to a pressure difference ∆p between the first and second chambers 34, 36, and is coupled to a steering device 25 of the vehicle 100. Movement of the piston 12 in response to changes in pressure in the first and second chambers 34, 36 exerts a steering force on the steering device 25, thereby turning the steered wheels 14, 16. The pressure sensors 19, 20 are arranged to sense the pressure of the hydraulic fluid in the hydraulic lines 9, 10 (and the pressure in the respective chambers 34, 36).

[0099] The first working port 30 and the first chamber 34 may be designated as a left port (left turn port) and a left chamber (left turn chamber), respectively, because the working port 30 and the chamber 34 are connected to a pressurized fluid source to turn the vehicle to the left when traveling forward. Similarly, the second working port 32 and the second chamber 36 may be designated as a right port (right turn port) and a right chamber (right turn chamber), respectively, because the working port 32 and the chamber 36 are connected to a pressurized fluid source to turn the vehicle to the right when traveling forward. It should be understood that, according to this definition and the steering arrangement, the left turn chamber and the right turn chamber may not be arranged on the left and right sides of each other.

[0100] In use, the user rotates the steering wheel 2 to generate a steering demand, thereby steering the steered wheels 14 and 16. The rotational movement of the steering wheel 2 is transmitted to the hydraulic-mechanical steering unit 6 via the steering shaft 3. Depending on the direction of rotation of the steering wheel 2, the hydraulic-mechanical steering unit 6 operates in response to the steering demand to connect one of the workports 30, 32 to the pressurized fluid source 7 and to connect the other workport 30, 32 to the tank 8. In the embodiment shown, rotation of the steering wheel 2 indicating a desired left turn causes the hydraulic-mechanical steering unit 6 to connect the first workport 30 and the first hydraulic line 9 to the pressurized fluid source 7, and to connect the second workport 32 and the second hydraulic line 10 to the tank 8. As a result, the fluid pressure in the first chamber 34 increases to be higher than the pressure in the second chamber 36, causing the piston to move to the left. Figure 1 . This in turn causes the steered wheels 14, 16 to turn left, as shown, and causes the vehicle to make a left turn when traveling in the forward direction indicated by arrow X with the steered wheels 14, 16 initially in the straight ahead position. Conversely, in response to rotation of the steering wheel 2 indicating a right turn requirement, the hydraulic-mechanical steering unit 6 operably connects the second working port 32 and the second hydraulic line 10 to a pressurized fluid source, and connects the first working port 30 and the first hydraulic line 9 to the tank 8. This causes the fluid pressure in the second chamber 36 to increase to a level higher than the pressure in the first chamber 34, causing the piston 12 to move to the position as shown in FIG. Figure 1 This in turn causes the steered wheels 14, 16 to turn to the right, as shown, so that the vehicle achieves a right turn when traveling in a forward direction with the steered wheels initially in a straight ahead position.

[0101] It should be understood that the steering actuator 11 and the steering device 25 can be constructed in a variety of different ways, and the hydraulic-mechanical steering unit 6 can be connected to the steering actuator 11 in any suitable manner to cause the steered wheels 14, 16 to be steered in the desired direction indicated by the rotation direction of the steering wheel 2. For example, instead of a single double-acting hydraulic cylinder, the steering actuator 11 may include a pair of double-acting hydraulic cylinders operably connected to the steered wheels 14, 16, so that extension of a first hydraulic cylinder and retraction of a second hydraulic cylinder in the hydraulic cylinders causes the steered wheels to rotate in one direction, while extension of the second hydraulic cylinder and retraction of the first hydraulic cylinder causes the steered wheels to rotate in the opposite direction. In this case, the working ports 30, 32 are connected to the chambers in the hydraulic cylinders in a cross-wise manner known in the art.

[0102] The hydro-mechanical steering unit 6 comprises a resilient biasing means, typically a spring means, schematically indicated at 40, which biases the unit to a neutral position in which no fluid is supplied to the working ports 30, 32. In response to rotation of the steering shaft 3 in a first rotational direction, the hydro-mechanical steering unit moves from the neutral position to a first working position in which a first of the working ports 30, 32 is connected to a source of pressurized fluid 7 and a second of the working ports 30, 32 is connected to a reservoir 8. In response to rotation of the steering shaft 3 in a second rotational direction opposite to the first rotational direction, the hydro-mechanical steering unit 6 moves to a second working position in which a first of the working ports 30, 32 is connected to a reservoir 8 and a second of the working ports 30, 32 is connected to a source of pressurized fluid 7. When the steering shaft 3 is rotated to move the hydro-mechanical steering unit to one of the first and second working positions, the resilient biasing means applies a restoring force which tends to move the hydro-mechanical steering unit back to the neutral position. This results in a reaction torque being applied to the steering shaft 3 that is opposite to the direction of rotation of the steering shaft 3 applied by the user via the steering wheel 2. When the steering wheel 2 is first moved from any initial position, the resilient biasing device 40 generates substantially no torque within a first range of movement of the steering wheel 2. After the first range of movement, the resilient biasing device 40 generates an increasing level of reaction torque on the steering shaft 3 within a transition range of rotational movement of the steering component. At the end of the transition range, the resilient biasing device generates its maximum level of reaction torque, which remains substantially constant for any continued movement of the steering wheel 2 beyond the transition range. If the user stops turning the steering wheel 2, the resilient biasing device 40 moves the hydraulic-mechanical steering unit back to the neutral position so that the hydraulic-mechanical steering unit no longer supplies fluid to the steering actuator 11, and the steering actuator 11 is held in place until the steering wheel 2 is turned again.

[0103] In a typical arrangement, the hydro-mechanical steering unit 6 has a rotating core (not shown) located within a sleeve (not shown), the valve core and sleeve having complementary ports. When the steering wheel 2 is turned, the steering shaft 3 rotates the valve core within the sleeve to move from the neutral position to one of the working positions against the action of the hydro-mechanical steering unit spring 40, which biases the valve core relative to the valve sleeve back to the neutral position. However, the hydro-mechanical steering unit 6 may take other forms.

[0104] As used herein, the "initial position of the steering wheel" in relation to the movement of the steering wheel that generates a steering demand is to be understood as the resting position of the steering wheel 2 in which the hydraulic-mechanical steering unit 6 is in the neutral position. Movement of the steering wheel 2 away from the initial position causes the hydraulic-mechanical steering unit 6 to move from the neutral position to one of the working positions. The term "initial position of the steering wheel" should not be interpreted as referring to the absolute position of the steering wheel 2. For example, if the steering wheel 2 is in the straight ahead position and is turned 10 degrees to the left and then remains in that position, then the straight ahead position will be the initial position of the steering wheel 2 for this first steering wheel movement. However, if the steering wheel remains in the position 10 degrees to the left and the hydraulic-mechanical steering unit returns to the neutral position, then the position 10 degrees to the left will be the initial position of the steering wheel for subsequent movements of the steering wheel away from the position 10 degrees to the left.

[0105] Typically, there will be some free play or clearance in the mechanical connection between the steering wheel 2 and the hydro-mechanical steering unit 6. In addition, the hydro-mechanical steering unit 6 typically has a hydraulic dead band in which the hydro-mechanical steering unit does not supply fluid to the associated working ports 30, 32 as the hydro-mechanical steering unit 6 moves from the neutral position to one of the working positions. As a result, when the steering wheel 2 is rotated from the initial position, the hydro-mechanical steering unit 6 will not begin to supply fluid to the associated working ports 30, 32 and the steering actuator 11 until the steering wheel 2 has rotated through the initial range of movement, which will be referred to as the "dead range of movement". The transition range of rotational movement of the steering wheel 2 (in this transition range, the torque applied by the hydro-mechanical steering unit spring 40 increases) will typically begin within the dead range of movement of the steering wheel 2, but may not end until after the dead range of movement.

[0106] The steering supply valve device 26 is hydraulically connected to the pressurized fluid source 7, the tank 8, and the first and second working ports 30, 32. The steering supply valve device 26 is an electronically controllable valve device that can be operated to selectively connect any one of the working ports 30, 32 to the pressurized fluid source 7 and connect the other of the working ports 30, 32 to the tank 8. The steering supply valve device 26 may include one or more solenoid valves and may be a proportional valve device. The steering supply valve device 26 is capable of bypassing the hydraulic-mechanical steering unit 6 (and the hydraulic-mechanical steering unit flow) to actuate the steering actuator 11, and therefore may be referred to as a steering supply bypass valve device. The steering supply valve device 26 can be used to actuate the steering actuator 11 independently of the hydraulic-mechanical steering unit 6, but may also be used in conjunction with the hydraulic-mechanical steering unit 6 to amplify the volume flow of the fluid provided by the hydraulic-mechanical steering unit 6 to the steering actuator.

[0107] The steering supply valve device 26 may be provided separately from the hydraulic-mechanical steering unit 6, or may be integrated into a combined unit with the hydraulic-mechanical steering unit 6, as shown. When the steering supply valve device 26 and the hydraulic-mechanical steering unit 6 are combined into a single unit, they may share fluid connections to the pressurized fluid source 7 and the reservoir 8 as well as the working port. An example of a suitable combined hydraulic-mechanical steering unit 6 and steering supply valve device 26 is the Danfoss OSPEC400 LSRM from Danfoss Power Solutions APS of Denmark.

[0108] The steering system 1 may be part of an open center hydraulic system or a closed center hydraulic system.

[0109] like Figure 1 As shown, the steering system 1 may further include an electric motor 5, which is arranged to selectively apply torque to rotate the steering shaft 3 in either rotation direction of the steering shaft 3. Thus, the electric motor may rotate the steering shaft to the left or to the right (that is, in a clockwise and counterclockwise direction), wherein clockwise movement corresponds to movement of the steering wheel 2 to the right, and counterclockwise movement corresponds to movement of the steering wheel 2 to the left, as shown in FIG. Figure 1 The electric motor 5 is operable to modify the tactile steering torque (force) feedback sensed by the user through the steering wheel 2 by applying a torque to rotate the steering shaft 3. In other words, the electric motor 5 is operable to adjust the steering feel applied to the user by modifying the torque that is opposite to the rotational movement of the steering wheel 2 implemented by the user to achieve the steering maneuver.

[0110] The steering system 1 has a control unit 21 (e.g., an electronic control unit ECU), which includes a controller or processor 22 and a memory 23. The controller 22 is configured to receive and process sensor signals / data, which may include any one or more of the following: signals / data representing the angular position of the steering wheel 2, the angular position of the steered wheels 14, 16, the vehicle speed v (i.e., the ground speed), the fluid pressure difference ∆p between the first and second chambers 34, 36 in the steering actuator, the steering torque applied to the steering wheel 2 by the user, and the movement speed of the steering wheel 2.

[0111] In one embodiment, the control unit 21 is an ECU, which includes one or more controllers or processors 22, input / output (I / O) interfaces and memory 23, all of which are connected to one or more data buses. The memory 23 may include any one or combination of volatile storage elements (e.g., random access memory RAM, such as DRAM and SRAM, etc.) and non-volatile storage elements (e.g., ROM, hard disk drive, tape, CDROM, etc.). The memory 23 may store a local operating system, one or more local applications, a simulation system, or a simulation application for any of various operating systems and / or simulation hardware platforms, simulation operating systems, etc. In one embodiment, the memory includes an operating system and software for executing various control strategies described herein (e.g., those for controlling the actuation of the steering supply valve device 26 and the electric motor 5). Those of ordinary skill in the art should be aware that in some embodiments, additional or fewer software modules (e.g., combined functions) may be used in the memory 23 or additional memory. In some embodiments, a separate storage device may be connected to the data bus, such as a permanent memory (e.g., optical, magnetic and / or semiconductor memory and associated drivers).

[0112] The controller 22 may be implemented as a custom or commercially available processor, a central processing unit (CPU) or a secondary processor among several processors, a semiconductor-based microprocessor (in the form of a microchip), a macroprocessor, one or more application-specific integrated circuits (ASICs), a plurality of appropriately constructed digital logic gates, and / or other well-known electrical constructions that include discrete components, both individually and in various combinations, to coordinate the overall operation of the control unit 21.

[0113] The steering system 1 includes various sensors that provide signals / data to the controller 21. These include a speed sensor 17, which is arranged to sense the speed of the vehicle (e.g., the speed of the vehicle on the ground). The steering system 1 also includes a steering wheel sensor 4 and a wheel angle sensor 18. The steering wheel sensor 4 is arranged to continuously sense the angular position of the steering wheel 2 (and therefore the movement and / or angular velocity of the steering wheel), and send data representing the position and speed of movement of the steering wheel to the control unit 21. The steering wheel sensor 4 is mounted at a position with minimal free play between the sensor 4 and the steering wheel 2, so that the sensor 4 detects the position and / or movement of the steering wheel 2 with an acceptable level of accuracy. The steering wheel sensor 4 may be configured to detect the angular position and / or rotational movement of the steering shaft 3 as a means of detecting the angular position and / or rotational movement of the steering wheel 2. The wheel angle sensor 18 continuously senses the angular position of at least one of the steered wheels 14, 16, and sends the sensed information to the control unit 21. The pressure sensors 19, 20 are also configured to send signals / data representative of the fluid pressures in the first and second hydraulic lines 9, 10 and the first and second chambers 34, 36 in the hydraulic steering actuator 11. The signals / data from the sensors may be stored in the memory 23. A sensor 27 for determining the torque applied to the steering wheel 2 by the user may also be provided, the sensor 27 being configured to send signals / data representative of the applied torque to the controller 21.

[0114] The steering system 1 is designed to operate at a maximum operating volume flow Qop of the fluid supplied to the hydraulic steering actuator 11 in order to provide an effective steering function under normal operating conditions. The maximum operating volume flow Qop may not be the maximum volume flow Qmax that the system can handle, which is usually set higher than the maximum operating volume flow Qop for safety reasons. The maximum operating volume flow Qop will be referred to as the first threshold value of the volume flow. However, in order to ensure that the steering system 1 can operate in an emergency mode, for example in the event of failure of the normal supply of pressurized fluid, the steering system 1 may be designed to operate at least in a limited manner to provide some steering function when the volume flow of the fluid supplied to the steering actuator 11 is higher than a minimum value Qe, which is less than the maximum operating volume flow Qop. The minimum volume flow Qe required to provide the emergency steering function will be referred to as the second threshold value Qe. The actual values ​​of the maximum operating volume flow Qop and the minimum emergency steering volume flow Qe depend on the specific characteristics of the steering system 1 and the vehicle, including parameters such as the size of the steering actuator 11, the weight of the vehicle 100 and the size of the steered wheels 14, 16, and may depend on the steering system meeting legal requirements in some jurisdictions. However, for any given application, a person skilled in the art will be able to determine appropriate values ​​of the maximum operating volume flow Qop and the minimum emergency steering volume flow Qe.

[0115] In one embodiment, the hydraulic-mechanical steering unit 6 in the steering system 1 is calibrated or specified so that it can deliver a maximum flow rate Qorbmax, which is less than the maximum operating volume flow rate Qop, but greater than the minimum emergency steering volume flow rate Qe. In other words, the hydraulic-mechanical steering unit 6 can only deliver a maximum volume flow rate Qorbmax that is less than a first threshold value but greater than a second threshold value. In order to enable the steering system 1 to operate effectively under normal operating conditions, the controller 21 is configured to actuate the steering supply valve device 26 according to one or more management programs or algorithms to increase the volume flow rate of the fluid provided to the hydraulic steering actuator 11 until the maximum operating volume flow rate Qop, which is required to meet the steering demand. Therefore, the fluid flow rate Qs from the steering supply valve device 26 is combined with the fluid flow rate Qorb from the hydraulic-mechanical steering unit 6 to provide a combined fluid flow rate Qsum delivered to the steering actuator 11 through the working port devices 30, 32. In the event of failure of the normal fluid supply of the steering system 1, the controller 21 or the steering supply valve device 26, the hydraulic-mechanical steering unit 6 is still able to deliver a volume flow rate Qorbmax of fluid, which is sufficient to provide an emergency steering function. This is advantageous because it enables the hydro-mechanical steering unit 6 to be used in a steering system 1 having a smaller volume flow capacity than is required to meet the demands of the steering system 1 under normal operating conditions, wherein the shortfall is compensated by the fluid flow Qs from the steering supply valve arrangement 26. This enables the use of a lower cost hydro-mechanical steering unit 6 without loss of steering performance or safety.

[0116] Furthermore, this arrangement enables a common hydraulic-mechanical steering unit 6 to be used in the steering systems 1 of a range of vehicles, even if at least some of the steering systems are designed to operate with different maximum operating volumetric flows Qop. Assuming that the hydraulic-mechanical steering unit 6 is capable of delivering a maximum volumetric flow Qorbmax that is higher than the required minimum emergency steering volumetric flow Qe (second threshold) for each of the various steering systems / vehicles in one or more ranges, the controller 21 can be configured to adjust the actuation of the steering supply valve 26 to ensure that the required maximum operating volumetric flow Qop at the steering actuator for each steering system / vehicle can be met. This enables common parts (such as the hydraulic-mechanical steering unit and the steering supply valve device 26) to be used in a range of vehicles, requiring only the controller algorithm to be changed to adapt the maximum operating volumetric flow Qop of the fluid delivered to the steering actuator 11 to the requirements of any given steering system / vehicle. This results in a reduction in the number of parts that the vehicle manufacturer must maintain, thereby saving manufacturing costs.

[0117] The layout in Figure 2 As schematically shown in Figure 2Included are curves showing the volumetric fluid flow for two different tractor ranges using a generally specified hydro-mechanical steering unit 6 , a hydro-mechanical steering unit 6 and a steering supply valve arrangement 26 . Figure 2 The volumetric fluid flow rates under normal operating conditions and under emergency steering conditions are shown. Lines 50 and 52 represent a first threshold value for a maximum operating volumetric flow rate Qop1 and a second threshold value for a minimum emergency steering volumetric flow rate Qe1, respectively, for a first range of tractors. Lines 54 and 56 represent a first threshold value for a maximum operating volumetric flow rate Qop2 and a second threshold value for a minimum emergency steering volumetric flow rate Qe2, respectively, for a second range of tractors less than the first range.

[0118] Both ranges of tractors use a commonly specified hydro-mechanical steering unit 6. Curve 58 represents the volume flow Qorb provided by the hydro-mechanical steering unit 6 during steering actuation. In the initial deadband region, shown by the left box (which ends at line 59), there is no fluid flow from the hydro-mechanical steering unit 6. After the deadband, the fluid flow from the hydro-mechanical steering unit increases until a maximum value Qorbmax. It should be noted that for both the first range and the second range of tractors, the maximum volume flow Qorbmax provided by the hydro-mechanical steering unit 6 is above the second threshold value 52, 56. Figure 2 The right-hand box starting from line 60 shows the emergency steering mode. In the emergency steering mode, the fluid flow from the hydro-mechanical steering unit 6 is maintained at its maximum value Qorbmax and is sufficient to provide the emergency steering function in any tractor range.

[0119] Curve 61 shows the volume fluid flow Qs1 provided by the steering supply valve device 26 in the first range of tractors, and curve 62 shows the total volume fluid flow Qsum1 provided to the steering actuator 11 in the first range of tractors, which is the sum of the fluid flow Qorb 58 from the hydraulic-mechanical steering unit and the fluid flow Qs 61 from the steering supply valve device 26. Figure 2 , it can be seen that the supply valve device 26 starts to supply fluid to the steering actuator during the dead band range of movement of the steering wheel 2, which will be described in more detail later. Within the dead band region, curve 62 follows curve 61. After the dead band region and once the hydraulic-mechanical steering unit 6 starts to supply fluid to the steering actuator 11, the total fluid flow Qsum1 supplied to the steering actuator indicated by curve 62 is increased by the additional flow Qorb 58 from the hydraulic-mechanical steering unit 6. As shown in the figure, the fluid supply Qs from the steering supply valve device 26 is regulated by the controller 21 so that the total fluid flow Qsum1 supplied to the steering actuator 11 (as shown by curve 62) increases until the first threshold value 50 for the tractor for the first range. In an emergency steering situation (in Figure 2 ), the fluid flow Qs provided by the steering supply valve device 26 is lost, causing curve 61 to drop to zero, but the total fluid flow Qsum1 provided to the steering actuator shown by curve 62 only drops to the maximum flow Qorbmax provided by the hydraulic-mechanical steering unit, thereby maintaining the emergency steering function.

[0120] Curve 64 shows the volumetric fluid flow Qs provided by the steering supply valve arrangement 26 for the second range of tractors, and curve 66 shows the total volumetric fluid flow Qsum2 provided to the steering actuator 11 in the second range of tractors, which is the sum of the fluid flow 58 from the hydraulic-mechanical steering unit 6 and the fluid flow 64 from the steering supply valve arrangement 26. Curves 64 and 66 follow a similar pattern to curves 61 and 62 as described above, and will not be described in detail, except that it should be noted that for the second range of tractors, the steering supply valve arrangement 26 is regulated by the controller 21 so that the total fluid flow provided to the steering actuator (as shown by curve 66), for the second range of tractors, only increases up to the lower first threshold value 54 under normal operating conditions.

[0121] It should be understood that Figure 2 The schematic diagram is intended to provide an illustration of the principles of this aspect of the invention and does not represent the actual flow of fluid from the hydro-mechanical steering unit 6 and / or the steering supply valve arrangement 26 during a steering maneuver.

[0122] As described above, a person skilled in the art will be able to determine appropriate values ​​for the maximum operating volume flow Qop and the minimum emergency steering volume flow Qe for any given vehicle application, thereby determining a suitable hydraulic-mechanical steering unit 26 and steering supply valve arrangement 26 to meet these requirements. However, as a guide, the following non-binding examples are provided:

[0123] Example 1.

[0124] The steering system has a first threshold value for a maximum operating volume flow Qop of 18 l / min and a second threshold value for a minimum emergency steering volume flow Qe of approximately 6 l / min. The steering system uses a hydraulic-mechanical steering unit with a maximum flow Qorbmax of approximately 11.25 l / min. This can be achieved, for example, by using a 250 cm3 (ccm) hydraulic-mechanical steering unit. In this example, the hydraulic-mechanical steering unit 6 is capable of meeting the second threshold value for the minimum emergency steering volume flow Qe to provide an emergency steering function. For use under normal operating conditions, the steering supply valve device 26 is capable of providing a volume fluid flow of up to at least 6.75 l / min so that the system can meet the required maximum operating volume flow Qop of 18 l / min.

[0125] Example 2.

[0126] The steering system has a first threshold value for the maximum operating volume flow Qop of 22.5 l / min and a second threshold value for the minimum emergency steering volume flow Qe of approximately 8.5 l / min. The steering system uses the same hydraulic-mechanical steering unit as in Example 1, with a maximum flow Qorbmax of approximately 11.25 l / min. In this example, the hydraulic-mechanical steering unit 6 is still able to meet the second threshold value for the minimum emergency steering volume flow Qe to provide the emergency steering function. For use under normal operating conditions, the steering supply valve device 26 is able to provide a volume fluid flow of up to at least 11.25 l / min so that the system can meet the required maximum operating volume flow Qop of 22.5 l / min.

[0127] The above examples are for illustration purposes only.

[0128] In an embodiment, the maximum flow rate Qorbmax of the hydraulic-mechanical steering unit 6 may not exceed 40%, or not exceed 50%, or not exceed 60%, or not exceed 70%, or not exceed 80%, or not exceed 90% of the first threshold value for the maximum operating volume flow rate Qop. However, in a specific embodiment, the maximum flow rate Qorbmax of the hydraulic-mechanical steering unit 6 may not exceed 50%, or not exceed 60%, or not exceed 70% of the first threshold value for the maximum operating volume flow rate Qop.

[0129] In addition to modifying the fluid flow to the actuator 11 so as to change the overall steering ratio R of the steering system in a superimposed steering system manner, the steering supply valve device 26 can also be used to amplify the output of the hydraulic-mechanical steering unit 6 to meet the maximum operating volume flow Qop requirement of the hydraulic steering actuator 11 under normal operating conditions.

[0130] As described above, since the steering supply valve device 26 is capable of supplying fluid to the working ports 30, 32 and the steering actuator 11 independently of the hydraulic-mechanical steering unit 6, the controller 21 is capable of regulating the steering supply valve device 26 so as to start supplying fluid to the steering actuator as long as the steering wheel 2 is turned before the steering wheel 2 has moved through the dead band range of movement and the hydraulic-mechanical steering unit 6 starts supplying fluid to the steering actuator. The movement of the steering wheel 2 is sensed by the steering wheel sensor 4, which sends a signal / data to the controller 21, and the controller 21 analyzes the steering wheel position signal / data and other data (such as the position of the steered wheels 14, 16 detected by the wheel angle sensor 18 and the vehicle speed detected by the speed sensor 17), and provides a signal to the steering supply valve device 26 to actuate the steering supply valve device 26 according to one or more management programs or algorithms.

[0131] This is Figure 3 and Figure 4 It is shown in Figure 3 and Figure 4 The flow of fluid from the hydraulic-mechanical steering unit 6 and the steering supply valve 26 relative to the change in the steering wheel angle during the steering maneuver is shown. The horizontal axis represents the change in the steering wheel angle starting from the initial position O of the steering wheel 2. The dotted line 59 represents the end of the deadband range of movement of the steering wheel 2, and the dotted line 68 represents the threshold value 1 for the maximum operating volume flow Qop. Curve 70 represents the volume fluid flow Qorb provided by the hydraulic-mechanical steering unit 6. Curve 72 represents the volume fluid flow Qs provided by the steering supply valve device 26. Curve 74 represents the total volume fluid flow Qsum provided to the steering actuator 11 through the working ports 30, 32, which is a combination of the fluid flow 70 provided by the hydraulic-mechanical steering unit 6 and the fluid flow 72 provided by the steering supply valve device 26. When the steering wheel sensor 4 detects movement of the steering wheel 2, the controller 21 operates in response to the control actuation of the supply valve device 26 to immediately begin delivering fluid Qs to the steering actuator 11, so that the steering system 1 reacts to the movement of the steering wheel 2 to begin turning the steered wheels 14, 16 without the usual delay caused by the dead band. This provides a faster response to steering demands that are more similar to steering demands of mechanical steering systems such as those found in conventional motor vehicles (such as automobiles). Continued movement of the steering wheel 2 beyond the dead band causes the hydraulic-mechanical steering unit 6 to also supply fluid Qorb to the steering actuator 11. In this embodiment, the controller 21 continues to actuate the steering supply valve device 26 outside the dead band so that the volume flow Qsum (curve 74) of the fluid provided to the steering actuator is the sum of the volume flow Qorb (curve 70) from the hydraulic-mechanical steering unit 6 and the volume flow Qs (curve 72) from the steering supply valve device 26. As shown, the controller 21 regulates the fluid flow from the steering supply valve device 26 so that the volume flow Qsum of the fluid provided to the steering actuator 11 increases until the maximum operating volume flow Qop (threshold 1 - line 68) required for effective steering control of the steering system under normal operating conditions.

[0132] Figure 3 and Figure 4 It is shown how the steering supply valve arrangement 26 can be controlled to provide different steering profiles. Figure 3 In the embodiment, the steering supply valve device 26 is actuated so that the volume flow rate Qs of the fluid supplied to the steering actuator 11 gradually increases within the dead band range, and only after the steering wheel 2 has moved beyond the dead band range of movement, the fluid flow rate from the steering supply valve device 26 rises to the level required to meet the maximum operating volume flow rate Qop (threshold 1). On the contrary, Figure 4 The steering supply valve device 26 is shown being actuated to provide a more rapid initial increase in fluid flow Qs to the steering actuator 11, thereby reaching a level of fluid flow from the steering supply valve device 26 within the dead band of steering wheel movement, which level is required to subsequently meet the maximum operating volume flow Qop (threshold 1) once the fluid supply from the hydraulic-mechanical steering unit 6 reaches its maximum value. Figure 3 The control strategy shown will provide a relatively slow steering response to small initial movements of the steering wheel 2. This may be suitable for a vehicle travelling at high speed on a highway. Figure 4 The control strategy shown will provide a faster steering response to a small initial movement of the steering wheel 2. This may be suitable for vehicles operating at low speeds in off-road environments, such as tractors, where it may provide increased maneuverability without compromising safety. The controller 21 may consider data such as vehicle speed v and / or steered wheel position to determine an appropriate control strategy to apply in response to steering wheel movement. Suitable management routines and / or algorithms may be stored in the memory 23 or may be available to the controller 21.

[0133] A potential problem with using the steering supply valve device 26 to begin supplying fluid to actuate the steering actuator 11 within the deadband region is that the steering system 1 inherently does not provide much resistance to the steering wheel 2 being turned within this range of steering wheel movement. Steering within the deadband range feels very light and therefore unnatural to the user, especially to a user familiar with the non-hydraulic steering systems used in most motor vehicles (such as automobiles). To address this issue, and in accordance with another aspect of the present invention, the controller 21 is configured to actuate the motor 5 to apply torque to the steering shaft 3 to produce appropriate tactile steering torque feedback to the user turning the steering wheel 2. This is in Figure 5 Shown in.

[0134] Figure 5 The torque opposing the rotation of the steering wheel 2 from the initial position 0 during the steering maneuver is shown, and the user will feel this torque as resistance to the movement of the steering wheel. As previously mentioned, the initial position is the starting position before the steering wheel 2 is rotated, and is not necessarily the neutral or straight ahead position of the steered wheels 14, 16 or the steering wheel 2. It can be any angular position. This torque creates the feeling of steering and can be described as tactile steering torque feedback. The end of the dead band range of movement of the steering wheel from the initial position is represented by line 59. The beginning of the transition range of movement (where the hydraulic-mechanical steering unit spring 40 begins to apply a reaction torque to the steering wheel shaft 3) is represented by line 82, which is opposite to the torque applied by the user through the steering wheel 2, and the end of the transition range of movement (at which the torque applied by the hydraulic-mechanical steering unit spring is at its maximum value) is represented by line 84.

[0135] The torque that the user must apply to the steering wheel to overcome the resistance of the steering system itself (i.e., if the electric motor 5 is not used to apply torque to the steering shaft 3) is represented by curve 86. During the initial range of movement of the steering wheel 2 within the dead band until the beginning of the transition range 82, the steering system 1 provides very little resistance to the turning steering wheel 2. Therefore, the steering will feel very light, which may feel unnatural, considering that the steering supply valve device 26 is operated to turn the steered wheels 14, 16 within this range of movement.

[0136] In the transition range of movement (between lines 82 and 84), the hydraulic-mechanical steering unit spring 40 will apply an increased reaction torque to the steering shaft 3, which is opposite to the torque applied to the user. As shown in the figure, the reaction torque applied by the hydraulic-mechanical steering unit spring 40 rises very quickly in the transition range, so that the user will feel the sudden increase of steering weight. This feels very unnatural, especially for people who are not used to driving a car with such a steering system. At the end of the transition range (line 84), the torque applied by the hydraulic-mechanical steering unit spring 40 is at its maximum value. In this embodiment, the transition range ends outside the dead zone range, so at this stage, the hydraulic-mechanical steering unit will supply fluid to the hydraulic steering actuator, which may increase the resistance felt by the user when turning the steering wheel 2. After the transition range 84 ends, as long as the user continues to move the steering wheel, the hydraulic-mechanical steering unit spring applies a substantially constant reaction torque to the steering shaft 3, which is opposite to the torque applied to the steering wheel by the user. During this continuous rotation movement of the steering wheel 2, steering will feel relatively heavy.

[0137] The tactile steering torque profile that is inherently generated by the steering system (especially the hydraulic-mechanical steering unit) and felt by the user at the steering wheel 2 is very different from the torque profile felt at the steering wheel of the conventional mechanical automotive steering system used in a typical motor vehicle. Such conventional steering systems typically provide resistance to turning the steering wheel, which increases rapidly when the steering wheel is first moved and then decreases as the user continues to turn the steering wheel. This is primarily caused by mechanical friction and mechanical resistance in the mechanical steering system. According to this aspect of the invention, the controller 21 is configured to adjust the magnitude and direction of the torque applied to the steering shaft 3 by the electric motor 5 so that the user feels a tactile steering torque feedback that follows a predetermined profile. The profile can be configured to more closely replicate the steering feel in a motor vehicle or other vehicle having a mechanical steering system (including a fluid power assisted mechanical steering system).

[0138] exist Figure 5, curve 88 shows an embodiment of a desired haptic steering torque feedback profile at the steering wheel 2 provided to the user, and curve 90 shows the torque profile applied by the motor 5 to the steering shaft 3 to achieve the desired haptic steering torque feedback profile 88. During the movement of the steering wheel 2 until the beginning of the transition range 82, the torque profile 90 applied by the electric motor 5 to the steering shaft 3 provides substantially the only resistance to turning the steering wheel 2 felt by the user, and thus profiles 88 and 90 follow the same path over this range of movement of the steering wheel.

[0139] like Figure 5 As shown, the desired tactile steering torque feedback profile 88 may include a relatively steep increase (a) in torque opposing the torque applied by the user to the steering wheel, which increases (a) after a relatively small change in the steering wheel angle, reaching a peak 92 at a position between the initial position 0 of the steering wheel and the end 59 of the deadband range. As the steering wheel 2 is further turned, the desired tactile steering torque feedback profile 88 includes a gradual decrease (b) in torque opposing the torque applied by the user to the steering wheel until the end 59 of the deadband range. After the deadband range, the desired tactile steering torque feedback profile 88 includes a slightly steeper decrease in torque opposing the torque applied by the user until the end 84 of the transition range, as shown in (c). Thereafter, the desired tactile steering torque feedback profile 88 includes a substantially constant torque (d) that is opposite to the torque applied by the user to the steering wheel 2, but at a level lower than the torque applied by the hydraulic-mechanical steering unit spring 40 within this range of movement of the steering wheel 2.

[0140] In order to generate the desired haptic steering torque feedback profile 88, the controller 21 is configured to actuate the electric motor 5, as appropriate, so as to generate a torque profile according to the curve 90. In the initial movement of the steering wheel 2 from the initial position 0 to the beginning 82 of the transition range, the controller 21 adjusts the motor to apply a torque to the steering shaft 3 in a direction opposite to the torque applied to the steering shaft by the user through the steering wheel 2. For this range of movement of the steering wheel 2, the level of torque applied by the motor 5 varies in accordance with the desired haptic steering torque feedback profile 88. Thus, with the initial movement of the steering wheel 2, the motor 5 is actuated to apply a fairly rapidly increasing torque to the steering shaft 3 (a), increasing to a maximum value at 92 when the steering wheel is in an intermediate position between the initial position 0 and the end 59 of the deadband range. During the movement of the steering wheel from this intermediate position 3 until the beginning 82 of the transition range, the torque applied to the steering shaft by the electric motor 5 decreases following the profile of the desired haptic steering torque feedback profile 88 (b). During the transition range, the hydraulic-mechanical steering unit spring 40 begins to apply a reaction torque to the steering shaft 3 that is opposite to the torque applied by the user through the steering wheel. The reaction torque increases rapidly throughout the transition range before reaching a maximum value at the end 84 of the transition range. Once the hydraulic-mechanical steering unit spring 40 is activated, the torque felt by the user at the steering wheel 2 is the sum of the torques applied to the steering shaft 3 by the hydraulic-mechanical steering unit spring 40 and the electric motor 5. In order to maintain the desired tactile steering torque feedback profile 88, the controller 21 adjusts the electric motor 5 so that the torque applied to the steering shaft 3 by the electric motor 5 compensates for the reaction torque applied by the hydraulic-mechanical steering unit spring 40. As the reaction torque applied by the hydraulic-mechanical steering unit spring 40 increases in the transition range, the torque applied by the electric motor 5 initially remains in the opposite direction to the torque applied by the user, but decreases in accordance with the increase in the reaction torque from the hydraulic-mechanical steering unit spring 40. As the reaction torque applied by the hydraulic-mechanical steering unit spring 40 increases, at a certain point, the torque applied by the electric motor 5 decreases to zero, and the motor is then actuated to apply a torque to the steering shaft that rotates the steering shaft 3 in the same direction as the user, thereby assisting the user in overcoming the torque applied by the hydraulic-mechanical steering unit spring 40. In this embodiment, the torque applied by the electric motor 5 decreases to zero at or near the end of the deadband range (as shown by line 59). Thereafter, the direction of the motor 5 is reversed to apply a torque to the steering shaft 3 in the same direction as the user, thereby counteracting the reaction torque applied by the hydraulic-mechanical steering unit spring 40. The torque applied by the motor 5 to the steering shaft 3 to assist the user increases in the remainder of the transition range. Once the transition range has ended 84 and the hydraulic-mechanical steering unit spring 40 is providing its maximum reaction torque, the torque applied by the electric motor 5 to assist the user remains substantially constant.As a result, the haptic steering torque feedback 88 felt by the user remains substantially constant for further movement of the steering wheel 2 , but at a level below the reaction torque of the hydro-mechanical steering unit spring 40 .

[0141] It should be appreciated that the desired haptic steering torque feedback profile 88 may differ from Figure 5 It will also be appreciated that the electric motor 5 may be controlled to apply a torque to the steering shaft 3 that is also variable in magnitude and / or direction to account for other effects of the steering system as the steering wheel 2 is rotated during a steering operation.

[0142] Additionally, the actual value of the torque applied with the desired haptic steering torque feedback profile 88 may also differ from Figure 5 The value shown. The controller 21 may be configured to change the desired tactile steering torque feedback profile 88 or select from a series of different desired tactile steering torque feedback profiles according to one or more operating parameters of the vehicle. For example, the controller 21 may be configured to adjust the actuation of the electric motor 5 so that when the vehicle is traveling at a relatively high speed (e.g., on a road), the user is subjected to a higher level of torque opposite to the movement of the steering wheel 2. This results in greater safety, stability, and controllability when operating at higher speeds. Conversely, if the vehicle is operated at a low speed in an off-road situation, a lower level of tactile steering torque feedback may be required. For example, this may be desirable for an agricultural tractor operating off-road in order to increase maneuverability and reduce user fatigue when performing repeated large steering operations. The controller 21 may adopt the desired tactile steering torque feedback profile 88 and / or control of the electric motor 5 in response to one or more parameters indicating the operating state of the vehicle. These may include any one or more of the following:

[0143] a. The steering angle of the steered wheels;

[0144] b. Steering angle of the steering component;

[0145] c. a steering torque applied to the steering member by a user;

[0146] d. The ground speed of the vehicle;

[0147] e. Fluid pressure differential between chambers of the steering actuator;

[0148] f. Speed ​​of movement of the steering wheel.

[0149] Figure 6 , 7 , 8 and 9 show how the desired feedback torque at the steering wheel 2 varies according to changes in various parameters.

[0150] Figure 6It is shown that the haptic steering torque feedback can be varied according to the pressure difference between the first and second chambers 34, 36 in the steering actuator, so that the torque increases as the pressure difference ∆p increases. The relationship can be linear / logarithmic / parabolic. This simulates the user's reaction force when the pressure difference increases (for example, when driving over a large rock in a field).

[0151] Figure 7 It is shown that the tactile steering torque feedback can increase with increasing vehicle speed v. Generally, as the vehicle speed increases, it is desirable to increase the steering resistance. This results in greater safety, stability and controllability at higher speeds. In this regard, after the transition range, when the hydraulic-mechanical steering unit spring 40 produces the maximum reaction torque that resists the user's steering movement and the electric motor 5 is used to assist the user, the torque applied by the electric motor 5 can be reduced to increase the tactile steering torque feedback. It is also possible that if the reaction torque from the hydraulic-mechanical steering unit spring is insufficient, the electric motor 5 can also be reversed at this stage, thereby further increasing the resistance to the steering movement.

[0152] Figure 8 How to change the tactile steering torque feedback torque generated by the electric motor in response to the movement of the steered wheels 14, 16 is shown. It should be noted here that the 0 position is not necessarily the straight ahead position, but any initial position of the steered wheels when the steering wheel 2 is moved. Whenever the steering wheel 2 is moved to generate a new steering demand, the steering system always has to pass through a dead zone range to the left or right. Within this dead zone, the electric motor 5 can be used to provide an initial high torque resistance to the movement of the steering wheel 2, otherwise the steering wheel 2 will feel very loose in the first 1-3° or so of the steering. After the steering passes through the dead zone range, the tactile steering torque feedback torque can be reduced, making the steering wheel easier to move and allowing the steering movement to continue. However, the tactile steering torque feedback should not be too low, and it may be desirable to provide a substantially constant resistance to the movement of the steering wheel after the dead zone, similar to an automotive steering system. This can be achieved by using a constant torque applied by the electric motor 5 to partially balance the reaction steering force generated by the hydraulic-mechanical steering unit spring 40.

[0153] Fig. 9It is shown how the haptic steering torque feedback torque can be varied depending on the speed at which the steering wheel 2 is moved and / or the torque applied to the steering wheel by the user. Generally speaking, as the speed at which the user moves the steering wheel increases or the torque applied to the steering wheel 2 by the user increases, it is desirable to increase the resistance to the steering wheel 2 being rotated. Alternatively, depending on the circumstances, instead of using the electric motor 5 to apply a resistance torque, the electric motor may be used to support the steering wheel movement, thereby supporting the user by applying a torque in the same direction as the user. This may be beneficial when the tractor is in a stationary position (zero ground speed) and the driver wishes to move the steering wheel from left to right as quickly as possible due to a particular field work application. Therefore, the controller 21 may be configured to use several different parameters to determine a suitable haptic steering torque feedback profile to be applied.

[0154] Fig.10 Modified haptic steering torque feedback profiles 88a, 88b, 88c are shown, which can be adjusted using the principles described above. It will be noted that while these different profiles 88a, 88b, 88c differ in the actual torque level applied at the steering wheel, the overall shape of these profiles remains largely similar, with a rapid increase in haptic steering torque feedback during initial movement of the steering wheel 2, and then a gradual decrease in haptic steering torque feedback to a lower and substantially constant torque outside the deadband range.

[0155] This aspect of the invention not only allows the haptic steering torque feedback profile to be customized to provide an improved driving experience, but can also be used to provide similar steering feel across a range of different sized vehicles.

[0156] This aspect of the present invention in providing a desired tactile steering torque feedback profile 88 can be applied independently of the first aspect of the present invention. That is, the above teachings on tactile steering torque feedback can be applied to a steering system in which the hydraulic-mechanical steering unit 6 is capable of delivering a maximum flow Qorbmax that is capable of at least meeting the system's maximum operating volume flow Qop (threshold 1). In such an embodiment, the steering supply valve device 26 can be used to supply fluid to the steering actuator 11 only during the dead band range of movement of the steering wheel 2. In particular, in this case, the concept of using the electric motor 5 to provide tactile steering torque feedback during the dead band range will be particularly beneficial.

[0157] The steering system 1 and control method described above are particularly, but not exclusively, applicable to utility vehicles, including agricultural vehicles such as agricultural tractors and the like.

[0158] All references cited herein are incorporated herein in their entirety. If there is a conflict between a definition herein and a definition in a cited reference, the definition herein shall prevail.

Claims

1. An electric-hydraulic steering system for a vehicle, characterized in that: The electric-hydraulic steering system comprises: A hydraulic steering actuator, the hydraulic steering actuator being used to turn the steered wheel through a rotation angle; a fluid supply device, the fluid supply device comprising a pressurized fluid source and a storage tank; a workport device having two workports fluidly connected to the hydraulic steering actuator; a hydraulic-mechanical steering unit fluidly connected between the fluid supply and the workport arrangement and configured to connect one of the two workports to the source of pressurized fluid and the other workport to the tank according to steering requirements; A steering component connected to the hydraulic-mechanical steering unit via a steering shaft, wherein the steering component can be moved by a user to rotate the steering shaft to generate a steering demand; a steering component sensor connected to the controller and arranged to detect the position and / or movement of the steering component; an electric motor operatively connected to the controller and, in use, operative to apply torque when actuated to rotate the steering shaft to provide tactile steering torque feedback to a user through the steering member; wherein the controller is configured to provide a control output upon detecting movement of the steering component to control actuation of the electric motor so as to apply a torque to rotate the steering shaft in a direction opposite to a rotation direction applied to the steering shaft by a user during at least a portion of a dead band range of movement of the steering component as the steering component moves from an initial position, wherein within the dead band range, the hydraulic-mechanical steering unit does not supply fluid to the one of the two working ports.

2. The electric-hydraulic steering system according to claim 1, characterized in that: The electric-hydraulic steering system includes a steering supply valve device connected to the pressurized fluid source, the tank and the two working port fluids, and the steering supply valve device is connected to the controller; wherein the controller is configured to provide a control output when the movement of the steering component is detected to actuate the steering supply valve device, thereby supplying fluid to one of the two working ports of the working port device according to the movement direction of the steering component, at least during the period when the steering component moves from the initial position through the dead zone range of the movement of the steering component.

3. The electric-hydraulic steering system according to claim 1 or claim 2, characterized in that: The controller is configured to actuate the electric motor to apply an increasing level of torque to rotate the steering shaft in a direction opposite to a rotation direction applied to the steering shaft by a user through the steering member during a first stage of movement of the steering member from an initial position to an intermediate position between the initial position and an end of the dead band range of movement, and to apply a decreasing level of torque to rotate the steering shaft in the same direction during a second stage of movement of the steering member beyond the intermediate position within the dead band range of movement.

4. The electric-hydraulic steering system according to any one of claims 1 to 3, characterized in that: The hydraulic-mechanical steering unit comprises a resilient biasing device, which biases the hydraulic-mechanical steering unit to a neutral position in which no fluid is supplied to the working port device, the hydraulic-mechanical steering unit is movable to a first working position in response to movement of the steering component in a first rotational direction from an initial position, in which a first working port of the two working ports is connected to the pressurized fluid supply device and a second working port of the two working ports is connected to the tank, and the hydraulic-mechanical steering unit is movable to a second working position in response to movement of the steering component in a second rotational direction opposite to the first rotational direction from the initial position, in which the first working port of the two working ports is connected to the tank and the second working port of the two working ports is connected to the pressurized fluid source, when the hydraulic-mechanical steering unit is moved from the neutral position to the second working position. When the steering wheel is in any of the first working position and the second working position, the elastic biasing device generates a torque on the steering shaft, and the torque is opposite to the rotational direction applied to the steering component by the user, wherein during a first range of movement of the steering component from an initial position, the elastic biasing device generates substantially no torque, during a transition range of rotational movement of the steering component after the first range of movement, the elastic biasing device generates an increasing level of torque on the steering shaft, and during movement of the steering component beyond the transition range, the elastic biasing device generates a substantially stable level of torque; wherein the controller is configured to control actuation of the electric motor so that during the transition range of movement of the steering component, the torque applied by the electric motor to rotate the steering shaft in a direction opposite to the rotational movement applied to the steering component by the user decreases as the torque applied to the steering shaft by the elastic biasing device increases.

5. The electric-hydraulic steering system according to claim 4, characterized in that: The controller is configured to control actuation of the electric motor to apply a torque to rotate the steering shaft in the same direction as a user-applied rotation direction to the steering shaft during movement of the steering member beyond a dead band range of movement of the steering member.

6. The electric-hydraulic steering system according to any one of claims 1 to 5, characterized in that: The controller is configured to control actuation of the electric motor so that, during a steering maneuver, as the steering member moves from an initial position, a magnitude and direction of a torque applied by the electric motor to the steering shaft is adjusted to maintain a predetermined profile of tactile steering torque feedback to compensate for torque applied to the steering shaft by operation of the hydro-mechanical steering unit.

7. An electric-hydraulic steering system for a vehicle, characterized in that: The electric-hydraulic steering system comprises: A hydraulic steering actuator, the hydraulic steering actuator being used to turn the steered wheel through a rotation angle; a fluid supply device, the fluid supply device comprising a pressurized fluid source and a storage tank; a workport device having two workports fluidly connected to the hydraulic steering actuator; a hydraulic-mechanical steering unit fluidly connected between the fluid supply device and the workport device and configured to connect one of the two workports to the pressurized fluid source and the other workport to the tank according to steering requirements; A steering component connected to the hydraulic-mechanical steering unit via a steering shaft, the steering component being movable by a user to rotate the steering shaft to generate a steering demand; a steering component sensor connected to the controller and arranged to detect the position and / or movement of the steering component; a steering supply valve assembly fluidly connected to the pressurized fluid source, the reservoir, and the two working ports, the steering supply valve assembly being connected to the controller; an electric motor operative to apply torque when actuated to rotate the steering shaft to provide tactile steering torque feedback to a user through the steering member, the electric motor operatively connected to the controller; wherein the controller is configured to provide a control output upon detecting movement of the steering component to actuate the steering supply valve device, thereby supplying fluid to one of the two working ports of the working port device according to the moving direction of the steering component at least during a period in which the steering component moves from an initial position through a dead band range of movement of the steering component, wherein the hydraulic-mechanical steering unit does not supply fluid to the one of the two working ports in the dead band range of movement; Wherein, the controller is configured such that when the steering component moves from the initial position through at least a portion of the dead band range of movement, the controller is configured to provide a control output to control actuation of the electric motor to apply a torque to rotate the steering shaft in a direction opposite to the direction of rotation applied to the steering shaft by a user.

8. A vehicle, characterized in that: The vehicle comprises an electro-hydraulic steering system according to any one of the preceding claims, wherein, optionally, the vehicle is a utility vehicle or a self-propelled mobile machine.

9. A method of operating an electric-hydraulic steering system for a vehicle, characterized in that The electric-hydraulic steering system includes: a hydraulic steering actuator; a hydraulic-mechanical steering unit, the hydraulic-mechanical steering unit being used to actuate the hydraulic steering actuator in response to a steering demand from a steering component connected to the hydraulic-mechanical steering unit via a steering shaft; an electric motor for applying torque to the steering shaft; an electronic controller for controlling actuation of the electric motor to provide tactile steering torque feedback to a user via the steering component; the method including controlling actuation of the electric motor to provide tactile steering torque feedback during a dead zone range in which the steering component moves from an initial position before the hydraulic-mechanical steering unit starts to supply fluid to the hydraulic steering actuator.

10. The method according to claim 9, characterized in that The method includes controlling actuation of the electric motor to provide tactile steering torque feedback sensed by a user, the tactile steering torque feedback following a predetermined profile over a range of movement of the steering component from an initial position to compensate for the effect of a biasing member in the hydro-mechanical steering unit that resists movement of the steering component.

11. The method according to claim 9 or claim 10, characterized in that: The electric-hydraulic steering system comprises: a fluid supply device, the fluid supply device comprising a pressurized fluid source and a storage tank; a workport device having two workports fluidly connected to the hydraulic steering actuator; The hydraulic-mechanical steering unit is fluidly connected between the fluid supply device and the workport device and is configured to connect one of the two workports to the pressurized fluid source and the other workport to the tank according to steering requirements; a steering supply valve assembly fluidly connected to the pressurized fluid source, the reservoir, and the two working ports, the steering supply valve assembly being connected to the controller; The method comprises: At least during the movement of the steering member from the initial position through the dead band range of movement, the steering supply valve device is actuated according to the movement direction of the steering member to supply fluid to one of the two working ports of the working port device.

12. A method of operating an electric-hydraulic steering system for a vehicle, characterized in that The electric-hydraulic steering system comprises: A hydraulic steering actuator, the hydraulic steering actuator being used to turn the steered wheel through a rotation angle; a fluid supply device, the fluid supply device comprising a pressurized fluid source and a storage tank; a workport device having two workports fluidly connected to the hydraulic steering actuator; a hydraulic-mechanical steering unit fluidly connected between the fluid supply device and the workport device and configured to connect one of the two workports to the pressurized fluid source and the other workport to the tank according to steering requirements; A steering component connected to the hydraulic-mechanical steering unit via a steering shaft, the steering component being movable by a user to rotate the steering shaft to generate a steering demand; a steering component sensor connected to the controller and arranged to detect the position and / or movement of the steering component; a steering supply valve assembly fluidly connected to the pressurized fluid source, the reservoir, and the two working ports, the steering supply valve assembly being connected to the controller; an electric motor operative to apply torque to rotate the steering shaft when actuated, the electric motor operatively connected to the controller; The method comprises: detecting at least an initial movement of the steering component, and in response to the detection, actuating the steering supply valve device to supply fluid to one of the two working ports of the working port device according to the direction of movement of the steering component at least during movement of the steering component from the initial position through a dead band range of movement of the steering component, wherein the hydraulic-mechanical steering unit does not supply fluid to the one of the two working ports; The method also includes actuating the electric motor to apply torque to rotate the steering shaft in a direction opposite to a rotation direction applied to the steering shaft by a user when the steering member moves from the initial position through at least a portion of the deadband range of movement.

13. The method according to any one of claims 9 to 12, characterized in that: The method includes modifying the tactile steering torque feedback sensed by a user through the steering member by actuating the electric motor to apply a torque to rotate the steering shaft, the actuation of the electric motor being performed based on at least one parameter indicative of an operating condition of the vehicle such that the tactile steering torque feedback sensed by the user follows a predetermined profile within a range of movement of the steering member starting from an initial position.

14. The method according to any one of claims 9 to 13, characterized in that The method includes controlling actuation of the electric motor to apply an increasing level of torque to rotate the steering shaft in a direction opposite to a direction of rotation applied by a user via the steering member during a first phase of movement of the steering member from an initial position to an intermediate position between the initial position and an end of the dead band range of movement, and to apply a decreasing level of torque to rotate the steering shaft in the same direction during a second phase of movement of the steering member beyond the intermediate position within the dead band range of movement.

15. The method according to any one of claims 9 to 14, characterized in that: The hydraulic-mechanical steering unit includes an elastic biasing device, which biases the hydraulic-mechanical steering unit to a neutral position, in which no fluid is supplied to the working port device, the hydraulic-mechanical steering unit is movable to a first working position in response to the movement of the steering component in a first rotational direction from an initial position, in which the first of the two working ports is connected to the pressurized fluid source, and the second of the two working ports is connected to the tank, and the hydraulic-mechanical steering unit is movable to a second working position in response to the movement of the steering component in a second rotational direction opposite to the first rotational direction from the initial position, in which the first of the two working ports is connected to the tank, and the second of the two working ports is connected to the pressurized fluid source, when the hydraulic-mechanical steering unit moves from the neutral position to the second working position. When the position is moved to any one of the first working position and the second working position, the elastic biasing device generates a torque on the steering shaft in the opposite direction to the rotational movement applied to the steering component by the user, wherein during a first range of movement of the steering component from the initial position, the elastic biasing device basically does not generate torque, during a transition range of rotational movement of the steering component after the first range of movement, the elastic biasing device generates an increasing level of torque on the steering shaft, and during movement of the steering component beyond the transition range, the elastic biasing device generates a substantially stable level of torque; wherein the method includes controlling the actuation of the electric motor so that during the transition range of movement of the steering component, the torque applied by the electric motor to rotate the steering shaft in the direction opposite to the rotational movement applied to the steering component by the user decreases as the torque applied to the steering shaft by the elastic biasing device increases.

16. The method according to any one of claims 9 to 15, characterized in that: The method includes controlling actuation of the electric motor to adjust the magnitude and direction of torque applied by the electric motor to the steering shaft as the steering member moves from an initial position during a steering maneuver to maintain a predetermined profile of haptic steering torque feedback to compensate for any torque applied to the steering shaft due to operation of the hydro-mechanical steering unit.

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