GB2598586A - Controller for ePAS system - Google Patents

Abstract

A controller for an electric power assisted steering (ePAS) system, which permits articulation of one or more vehicle wheels within a steering angle range, is configured to adjust a maximum available steering lock for the ePAS system in dependence on a plurality of inputs (I1, I2, I3, I4, I5), which may include vehicle parameters such as vehicle speed and non-vehicle parameters such as terrain features and weather conditions. This may allow the amount of steering range to be adjusted according to conditions while avoiding damage to a tyre from contacting a wheel arch cavity. Haptic feedback may be provided if a driver exceeds a maximum available steering lock. A vehicle and control method are also provided.

Description

CONTROLLER FOR EPAS SYSTEM

TECHNICAL FIELD

The present disclosure relates to a controller for an electric power assisted steering system, a steering control method and a vehicle comprising the controller.

BACKGROUND

For an urban vehicle or a vehicle required to operating in confined surroundings, a small turning circle is highly desirable. This can be achieved in a number of ways but, primarily, by definition of steering lock angle. The steering lock angle is the maximum angle (with respect to a straight ahead position) that the steerable wheels of the vehicle can be turned under the control of a driver of the vehicle. Typically, the driver controls a steering angle by turning a steering wheel in a desired direction, by a desired amount. When the steering lock angle has been reached, the driver is unable to turn the steering wheel further, and the steerable wheels of the vehicle will not be able to turn further. The steering lock angle defined for a particular vehicle is influence by a large number of package parameters, including vehicle width, tyre width and diameter, suspension kinematic travel for ride and handling, structural elements of the vehicle body and chassis components. The definition of steering lock angle is constrained to ensure that the rotating tyre assembly cannot touch parts of the vehicle during all operating condition use cases, which may otherwise result in damage to the tyre. This is referred to as the wheel, or tyre, envelope. As a result of the fact that the effective tyre envelope is derived from a combination of all foreseeable loading conditions for the vehicle, the available lock angle is unlikely to be in its maximum potential condition in most operating conditions and the driver! operator will experience a restricted attribute performance in most use cases. In other words, the steering lock angle is generally constrained by a worst case scenario, and is thus overly conservative for most typical case scenarios.

It is an aim of the present invention to address one or more of the disadvantages associated

with the prior art.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a controller for an electric power assisted steering system, a method of performing steering control, and a vehicle, as claimed in the appended claims.

According to an aspect of the present invention there is provided a controller for an electric power assisted steering (ePAS) system, the system configured to permit articulation of one or more vehicle wheels within a steering angle range, the controller comprising control logic configured to adjust a maximum available steering lock for the ePAS system in dependence on a plurality of inputs.

The controller may comprise control means comprising one or more controllers, an electronic memory accessible to the one or more controllers and arranged to store the control logic, which when implemented by the one or more controllers carries out the adjustment of maximum available steering lock in dependence on the plurality of inputs, the controllers further provided with input means arranged to receive the inputs.

In this way, the wheel envelope can be adjusted dynamically to be as tight (close to the wheel arch cavity surrounding the wheel) as possible, thereby achieving, or at least approximating, a maximum possible steering articulation. In particular, this technique maximises the amount of maximum steering lock available taking into account the current state of the vehicle and its environment. This provides a way to make more of the potential available lock angle accessible to a driver more frequently, through a combination of control and system features.

In particular, through combining inputs for existing sensing in a new way or adding new sensing, it is possible to protect for against tyre contact and thus allow more lock angle in normal use.

The maximum available steering lock may be set to an upper value when the plurality of inputs satisfy predetermined criteria, and to a lower value otherwise. More than one lower value may be available, each lower value being associated with different criteria.

The plurality of inputs may comprise one or more detected events. An event may be a current event, or a predicted future event. In either case, two types of events can be distinguished -a first type which are incompatible with a large amount of steering lock, and a second type which require, or benefit from, a large amount of steering lock. In response to a detected event of the first type, the controller is configured to limit the maximum available steering lock.

In some cases, detection of an event of the first type will, without regard to other inputs, result in the maximum available steering lock being limited (that is, the upper limit being unavailable). In other cases, detection of an event of the first type is considered along with other inputs in determining a value for the maximum available steering lock. In response to a detected event of the second type, the controller is configured to maximise a value of maximum available steering lock subject, subject to one or more other inputs. Examples of events are described subsequently.

The plurality of inputs may comprise one or more parameters. The plurality of inputs may comprise either only events, only parameters, or both events and parameters. The input parameters may comprise one or more vehicle parameters and/or one or more non-vehicle parameters. The plurality of inputs may for example comprise vehicle speed and at least one other input (which may be an event, or a parameter).

The vehicle parameters may comprise one or more of a requested steering angle, vehicle mass, vehicle speed, vehicle yaw and/or roll angle or angular rate, amount of vertical wheel motion relative to the vehicle body, tyre pressure and steering torque, and lateral and longitudinal vehicle accelerations. The vehicle parameters may for example be obtained from one or more of a vehicle yaw sensor, suspension ride height angle sensor, magnetic rheology damping medium, ePAS steer assistance map, TPMS, proximity sensor and managed contact sensor. Indicator/turn signal operation, PDC parking sensors, or any indication the vehicle is towing can also be monitored (the latter making it possible to limit steering articulation to avoid jack-knifing).

The non-vehicle parameters may comprise one or more sensed environmental conditions.

These may include one or more of ambient temperature (using a temperature sensor), precipitation (using a rain sensor) and humidity (using a humidity sensor), used together or individually. For example, precipitation and temperature may together be used to determine that the conditions are likely to be icy (precipitation and low temperature) or wet (precipitation and higher temperature).

The non-vehicle parameters may also comprise the detection of stationary or moving obstacles, or terrain features, outside the vehicle (although these may in some cases be detected as events). Obstacles or terrain may detected using one or more of a stereoscopic camera, ultrasonic sensor, lidar and radar. The data pertaining to the environment and surroundings of the vehicle may be received from vehicle mounted sensors on the vehicle, or via V-2-I / V-2-V communications from another vehicle, or from stationary infrastructure. The non-vehicle parameters may include a location of the vehicle, with geofencing being used to provide a maximum possible steering lock available (potentially subject to other conditions) in one geofenced area but not outside of it.

The non-vehicle parameter may be obtained based on a current location of the vehicle (obtained for example using GPS) and a known location of road and/or terrain features (obtained for example from mapping data, or data received externally of the vehicle). The non-vehicle parameter may be obtained from another vehicle, for example a vehicle currently at, or previously at, a location ahead of the vehicle.

The control logic carries out a plurality of (concurrent or sequential) checks, and determine a maximum steering lock in dependence on the outcome of those checks. The outcome of these checks need not be limited to a simple maximum versus normal steering lock decision, but may be adjusted between those two (arbitrary) limits in real time to take wheel position versus wheel articulation envelope into account. In one example, a driver could start a turn by winding the wheel to full lock and then creeping forward from a parked location. If the road camber momentarily puts the wheel into a droop position, this may affords more lock, in which case the maximum available lock limit may be temporarily increased. The driver is able to hold the steering wheel against resistance provided by a variable / virtual end-stop. As the topography of the surface changes as the car continues to turn, the controller may determine that there is a risk of the wheel/tyre rubbing the inner arch, so it may reduce the position of the end stop to a position it determines to be a safe working limit and continues to adjust it based on the plurality of inputs until the driver completes the turn, at which point the system may return the position of the end stops to a default position (potentially quite a conservative one) until the inputs suggest the driver requires more steering lock than that default lock setting will give them. The process then starts all over again. All the time, the driver is able to simply hold the steering wheel against the resistance felt by the variable end stop. This process can be expected to feel quite intuitive to the driver, as if the driver is 'feeling' the road through the steering wheel.

If the control logic reduces the maximum available steering lock, if a current amount of steering lock exceeds the reduced maximum amount of steering lock, the controller may be configured to automatically reduce the current amount of steering lock.

In some cases, the limits may be controlled differently in some scenarios between left and right. For example, in the case where the system is operating in an area where vehicles drive on the left, the system might permit very tight right hand turns to negotiate mini-roundabouts or for turning around in the road, but limit the maximum lock turning left to mitigate against the wheels/tyres striking a kerb. It will be appreciated that these directions may be reversed for vehicles operating in areas where vehicles drive on the right. In one implementation, this may involve setting a maximum amount of available steering lock differently for each of left and right turning, dependent on a detection of obstacles and/or terrain externally of the vehicle.

The orientation of the vehicle may also be used (vehicle yaw and roll) may also be used to select different amounts of steering lock for different directions of steer.

The controller may be configured, when an amount of steering lock demanded by the driver exceeds a threshold, to provide feedback to the driver. The threshold may be static, or may vary in dependence on the current maximum available steering lock. In this way, the driver is, in effect, notified when they are close to the maximum extend of available lock. The feedback is preferably haptic feedback, enabling the driver to "feel" the proximity of the maximum extent of steering through the driving controls (steering wheel).

The control logic may comprise one or more look up tables which relate maximum available steering angle lock to the input parameters.

Various different checks may be applied in determining whether or not the maximum available steering lock should be limited. For example, if a detected or predicted amount of wheel motion exceeds a threshold value, the maximum available steering lock is limited and/or reduced. In another example, if a detected or predicted amount of steering torque (needs definition) exceeds a threshold value, the maximum available steering lock is limited and/or reduced. In another example, if a detected or predicted vehicle yaw and/or roll exceeds a threshold value, the maximum available steering lock is limited and/or reduced. In another example, if a detected tyre pressure exceeds a threshold value, the maximum available steering lock is limited and/or reduced.

According to another aspect of the present invention, there is provided a vehicle comprising a controller according to the above.

According to another aspect of the present invention, there is provided a control method for power assisted steering, the method permitting articulation of one or more vehicle wheels within a steering angle range, the method comprising obtaining a plurality of inputs and adjusting a maximum available steering lock in dependence on the plurality of inputs.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic representation of a vehicle according to an embodiment of the present invention; Figure 2 shows a schematic representation of a front-wheel pair undergoing articulation; Figure 3 shows a schematic representation of a steerable wheel at a zeroed (forward directed) position, and at a plurality of end stop positions; Figure 4 shows a control block diagram; and Figure 5 shows a process for controlling maximum steering lock.

DETAILED DESCRIPTION

Embodiments of the present invention are intended to operate primarily in an urban environment where streets may be narrow or made narrow by parked cars. In such an environment, there is a desire to keep the turning circle as small as possible so that, for example, the vehicle can turn 1800 in a typical two-lane road to help with picking up fares and reducing pick-up/drop-off times.

It is known for electric power assisted steering (ePAS) systems to have a variable or virtual end stops (maximum steering lock angles), but these typically only provide a small difference in steering lock in use due to the potential for the tyre to foul the wheel arch liner. In some vehicle architectures, such as an electric vehicle, the front end of the vehicle may have a relatively open nature due to the absence of an internal combustion engine. This makes it possible to provide for a wider range of steering angles without contacting the interior of the wheel arch cavity. However, constraints do still exist, both in terms of the wheels contacting the interior of the wheel arch cavity, and/or in terms of the wheels (particularly if tall and narrow) contacting obstacles external to the vehicle and/or representing a hazard to other road users.

Referring to Figure 1, a vehicle 2000 is shown which comprises a body 1, steerable front wheels 2, rear wheels 3, an electronic controller 4, an electric power assisted steering system (ePAS) 5, vehicle steering controls 6 (for example a steering wheel), forward-looking sensor(s) 7 (for example one or more of a camera, LIDAR, RADAR or ultrasonic sensor), rear sensors 8 (which may take the same or similar form to the forward-looking sensors(s) 7, GPS receiver 9, V2V/V2X (vehicle-to-vehicle, vehicle to anything) data transmitter/receiver 10 and a plurality of internal vehicle state sensors 11. The ePAS system 5 is configured to permit articulation of the vehicle wheels 2 within a steering angle range which is constrained by a maximum available steering lock. Each of the vehicle wheels 2 are provided within a respective wheel arch cavity 12, which is shaped and dimensioned to permit the wheel 2 to articulate (steer left and right) within, while also permitting vertical movement of the wheel according to the operation of the suspension system and its interaction with the underlying terrain.

Within the language of the present disclosure, an controller for an ePAS system may be an electronic controller forming part of the electric power assisted steering system 5 (with that controller implementing the method described herein, as well as its conventional operations), or a separate controller (for example the electronic controller 4) which provides control inputs to (and thus controls at least part of the functionality of) the electric power assisted steering system 5 (or fully electric in the case of drive by wire). Further, the control process carried out by the present technique may be distributed across several control units, one of which may be the controller 4, one of which may be part of the ePAS system 5, and others which may be provided elsewhere, and integrated within other systems within the vehicle 2000.

Referring to Figure 2, a front axle assembly 13 of the vehicle 1 is shown, with a left steerable wheel 2a and right steerable wheel 2b being provided thereon. A forwards direction of the vehicle is denoted by an arrow 14. Each of the left steerable wheel 2a and right steerable wheel 2b is able to articulate about a "straight ahead" position A, across a range from a position B in which a maximum steering lock is applied to the left, to a position C in which a maximum steering lock is applied to the right.

Referring to Figure 3, a close-up view of the wheel 2a is provided, in which a plurality of maximum steering lock angles (positions) 131, 132, B3 are provided when steering to the left.

Only three maximum steering lock angles are shown in Figure 3 in the interests of clarity, but in practice a larger number is likely to be used. It will be appreciated that there are a theoretically infinite number of theoretical stop position because the envelope is a full 3D shape. The present technique seeks to adjust the lock to maximise angle in any state of bump drop, humidity, tyre pressure and many others. There is a trade-off between highly flexible optimisation (very large number of possible maximum steering angles, or even a continuum) and simplicity and speed of processing. Equivalent positions (not shown) Cl, C2, C3 may be provided when steering to the right. Accordingly, there are three maximum steering lock positions available in this embodiment. At least positions IBI and B2 are virtual stop positions, with B3 either being a physical maximum steering lock position (constrained by the geometry of the steering assembly), or a virtual stop position itself. Virtual stop positions are governed by the ePAS system 5, which controls the steering angle in accordance with a steering angle request from the user (using the steering actuator, or wheel 6), and instructions from the controller 4. The position B3 represents a best case scenario, when no factors require a more conservative maximum steering angle to be used. The position B2 represents a more conservative maximum steering angle, and may be selected when one or more factors (indicated or represented by inputs to the controller 4) result in the position B3 representing an unacceptable risk of contact between the wheel 2a and the wheel arch cavity 12. The position B1 represents a maximum steering angle which is even more conservative than that of B2, and may be selected when one or more factors (indicated or represented by the inputs to the controller 4) result in the position B2 representing an unacceptable risk of contact between the wheel 2a and the wheel arch cavity 12. While the present embodiment utilises three candidate maximum steering angles, the present technique can be carried out using only two candidate maximum steering angles, and may also be carried out using more than three candidate maximum steering angles, or even by having a continuously variable maximum steering angle defined as a function of the input parameters.

Connectivity between the various parts of Figure 1 is shown in the block diagram of Figure 4. In particular, the controller 4 receives, as inputs, signals from the ePAS system 5, the vehicle steering controls 6, the forward-looking sensor 7, the rear sensors 8, the GPS receiver 9, the V2V data receiver 10 and the internal vehicle state sensors 11. The controller 4 comprises steering control logic 41 and one or more lookup tables 42, which are used, based on the input parameters, to adjust the maximum available steering lock in dependence on a plurality of the input parameters. The inputs may either be events (current or future predicted), or parameters. Both events and parameters can be taken into account in determining, and adjusting, the maximum available steering lock.

Events may be of a first type which are incompatible with a large amount of steering lock, and a second type which require, or benefit from, a large amount of steering lock. If an event of the first type is detected, the controller 4 is configured to limit the maximum available steering lock (that is, not permit a maximum possible value -for example denying position B3 in Figure 3. Examples of events of the first type are the detection of an object or terrain feature (ahead of the vehicle) which would be likely, if navigated by the vehicle, to generate a large amount of tyre motion, the proximity of a kerb to the vehicle, or the detection of nearby road users. In certain cases, detection of an event of the first type will, without regard to other inputs, result in the maximum available steering lock being limited (that is, the upper limit being unavailable).

In other cases, detection of an event of the first type is considered along with other inputs in determining a value for the maximum available steering lock.

If an event of the second type is detected, the controller is configured to maximise a value of maximum available steering lock subject, subject to one or more other inputs. Examples of events of the second type are the detection of a road layout (ahead) which may require a high amount of steering lock to navigate or manoeuvre on, or the detection of a transient object which may require full lock to navigate around. Even when these events are detected, this does not automatically result in the maximum possible value being available for the maximum available steering lock, since present and future factors may make wheel contract within the wheel arch cavity 12 probable, and thus full lock unachievable.

In addition to, or instead of events, the inputs may comprise one or more parameters. Generally, parameters are simply compared with threshold values, or combined with other parameters (and the result of that combination then compared with a threshold value) to determine if a large amount of steering lock is likely to be problematic. Input parameters may be vehicle parameters or non-vehicle parameters. The vehicle parameters may comprise one or more of a requested steering angle (demand), vehicle mass, vehicle speed, vehicle yaw and/or roll angle or angular rate, amount of vertical wheel motion relative to the vehicle body, tyre pressure and steering torque, and lateral and longitudinal vehicle accelerations of the vehicle. Some of these parameters may be obtained or derived from existing systems, such as the requested steering angle, which may either be obtained from the vehicle steering controls, or the ePAS system, and the vehicle speed, which may be computed based on wheel speed or GPS position over time, and steering torque, which again may be obtained from the ePAS system. Others of the parameters may be measured by dedicated sensors. For example, the internal vehicle state sensors 11 may comprise a vehicle yaw sensor (gyroscope), and one or more accelerometers or gyroscopes capable of detecting a current vehicle yaw and/or roll angle, as well as a rate of change of the vehicle yaw and roll angle, and also lateral and longitudinal accelerations of the vehicle. The internal vehicle state sensors 11 may also comprise one or more suspension ride height angle sensors, disposed for example in conjunction with a suspension system of the vehicle, for detecting an amount of vertical wheel motion relative to the vehicle body. This sensor, by monitoring the displacement of the suspension system when the vehicle is at rest, may also be able to determine the vehicle mass (including passengers and cargo). Tyre pressure may be monitored directly using a direct tyre pressure monitoring system (TPMS) 15 fitted to the wheels 2, 3 or indirectly, by being inferred based on vehicle handling behaviour.

The present technique may adjust maximum steering lock angle in a number of situations.

For example, during low speed manoeuvring (vehicle speed below a predetermined speed), maximum lock may be limited to protect for suspension deflection from high loads from impacts (for example dropping down kerbs, hitting pot holes).

Action to sensed condition -the predicted envelope growth can be mitigated through limitation or positive action to drive change the potential envelope to prevent tyre contact for example, steering angle can be limited or backed off automatically by the ePAS or the suspension compression can be limited or positively managed through actions on but not limited roll control system, damping control system, for example a reactive damping system, air suspension system or, air spring system.

The present technique does not directly adjust the amount of steering lock requested by a driver (unless the maximum available lock is less than the current amount of requested steering lock, in which case a reduction in the amount of steering lock requested may be imposed), but instead modifies the range of steering lock available to the driver.

Controller monitors inputs in real-time, and constantly adjusts the wheel movement envelope, and thus the maximum available steering lock, in dependence thereon. Thereby optimising (making full) mechanical lock available, in real-time.

In some cases, mitigating action may be taken if an event, combined with current steering lock, is predicted to cause a wheel to contact the inside of the wheel arch cavity. Such an event may be to dial back (reduce from a current steering position) the wheel steering lock, overriding driver input, or may be adjusting a suspension system to reduce deflection (increase stiffness) (or otherwise adjust the amount of deflection). Alternatively, the vehicle speed may be limited (reduced).

Predicted yaw/roll may be based on a sensed terrain (e.g. slope) around the vehicle, and a relative position and direction of travel (and optionally speed) of the vehicle.

The plurality of input parameters may comprise vehicle speed and at least one other input parameter. Vehicle speed is a key influencer of the required steering envelope which is safely available without risking contact with the interior of the wheel arch cavity 12. However, the present technique proposes the use of additional parameters as well, to in effect provide for a maximum available steering lock which varies as a function of a range of parameters to optimise the available steering available for a wide variety of operational conditions.

The non-vehicle parameters may comprise one or more sensed environmental conditions, for example ambient temperature, rainfall and humidity.

The non-vehicle parameters may comprise the detection of stationary or moving obstacles, or terrain features, outside the vehicle. For example a parameter may comprise an indication that a stationary obstacle is within a first predetermined distance of the vehicle, or an indication that a moving obstacle is within a second predetermined distance of the vehicle. The first and second predetermined distances may be the same, or different. Stationary objects may include kerb, lampposts, railings, parked vehicles and the like. Moving objects may include pedestrians, cyclists and other moving automotive vehicles. A parameter may also indicate a type of terrain on which the vehicle is current travelling, such as a driving surface type (road, grass, sand, rutted track). Various different sensors may be used to detect obstacles or terrain features, for example one or more of a stereoscopic camera, ultrasonic sensor, lidar and radar.

The non-vehicle parameter may be obtained based on a current location of the vehicle (for example determined by GPS) and a known location of road and/or terrain features (known in advance from mapping data).

The non-vehicle parameter (or event detection) may be obtained from another vehicle.

The control logic may carry out a plurality of checks, and determine a maximum steering lock in dependence on the outcome of those checks.

It will be appreciated that the controller 4 may continuously (or at intervals, or in response to a change) evaluate the input parameters as they vary over time, and as a result may reduce the maximum steering lock. In some cases, at the time of the reduction, the driver may already be utilising an amount of steering lock which is greater than the reduced maximum steering lock value. In this case, the controller is configured to automatically reduce the current amount of steering lock.

The controller may be configured, when an amount of steering lock demanded by the driver exceeds a threshold, to provide feedback, for example haptic feedback through the steering controls, to the driver. This lets the driver know that they are close to the maximum steering limit of the vehicle at the time. Since the maximum available steering lock varies in the present technique, the threshold for hapfic feedback will also vary. As a result, if conditions cause the maximum available steering lock to reduce, the threshold may in turn reduce past the current steering request of the driver, causing the feedback to be trigger. This lets the driver know that the conditions are changing in a manner which is reducing access to full lock. The driver may be able to take mitigating action as a result -for example by slowing down, moving off a slope, or moving onto smoother terrain.

The control logic comprises one or more look up tables which relate maximum available steering angle lock to the input parameters (or in some cases detected events).

While in some embodiment, the maximum available steering lock is set to an upper limit by default providing none of a set of predetermined limiting conditions are met, in other embodiments the maximum available steering lock is only set to the upper limit if none of the set of predetermined limiting conditions are met and if one or more full-lock required conditions are met. Explained differently, the maximum possible value for the maximum available steering lock is only made available when one or more full-lock required conditions are detected, and then only if none of the predetermined limiting conditions are met. The conditions may be the detection or absence of events, and/or input parameters satisfying respective threshold values.

In some cases the maximum available steering lock is set based on events or conditions detected at the time, using parameters indicative of the current state and/or environment of the vehicle. However, in other cases the maximum available steering lock is set based on predicted events or conditions. This enables the appropriate maximum available steering lock to be in place by the time the event occurs. Several example probable future events or conditions are described herein.

A first example is a detection of a known road layout which might potentially require, or benefit from, full lock. This may be determined based on a current location of the vehicle (for example based on GPS), a current route of the vehicle (for example based on navigation software operating on the vehicle) and road layouts on that route, and road layout characteristics (which might be available in a database or map tool operating on the vehicle, or available from another source utilising V2X (vehicle-to-everything). Such road layouts may include narrow roads, roads with tight turns, or dead ends where a turn in the road will be required.

A second example is a detection of any known objects or features which would be likely to generate large tyre motion is lock is applied. This detection could be made from sensor data from the vehicle, or obtained by another vehicle currently or previously at that location (utilising V2X -vehicle-to-vehicle data sharing) Referring to Figure 5, adjustment (or setting) of maximum available steering lock is carried out based on a number of inputs 11 to 15, and by carrying out a number of checks Cl to C5. In some cases, one or more of the inputs will be an event of the first type, and that event may be sufficient to immediately limit the available lock (without carrying out checks Cl to C5). It will be appreciated that a different number of checks and inputs may be used as may be desired.

Examples of the checks Cl to C5 may be as follows: Cl: Vehicle speed check -if the vehicle speed is likely to generate large tyre motion, or cause unacceptable levels of tyre scrub, if full lock is applied, lock limiting action may be taken. This determination may be made by comparison with a threshold speed value (which may be predetermined, or set based on other factors, such as the terrain ahead). For example, at very low speeds, lock may not be limited due to the likelihood of kerbs and pot holes while manoeuvring -low "manoeuvring" speeds are those at which a large steering lock would be most beneficial, for example for a 3 point turn. Accordingly, based on vehicle speed (for example when the vehicle speed is below 20km/h or another threshold), the maximum steering lock may be made available (subject to other factors).

02: Vehicle yaw/roll -if the vehicle yaw/roll is likely to generate large tyre motion, or cause unacceptable levels of tyre scrub, if full lock is applied, lock limiting action may be taken. This determination may be made by comparison of one or both of yaw and roll with a threshold value (or values), which may be predetermined, or set based on other factors). An example for this check is where a vehicle is travelling uphill/downhill or on a side-slope, in which case forces may be distributed unevenly, and unusually, on the wheels, requiring lock limiting action (potentially differently between right turn and left turn, particularly on a side slope. Additionally or alternatively, environmental conditions such as rain or snow can reduce the surface friction and make the roads slippers. In such conditions, the maximum available steering lock may be limited unless the vehicle is travelling below a lower speed threshold to avoid unwanted tyre slip and vehicle yaw.

3: Wheel motion -if the rate of change and amount of wheel displacement is high (compared with a predetermined or variable threshold), lock limiting action may be taken. For example, the threshold for an amount of displacement deemed to be problematic could be 50% of maximum (vertically or angular), or 50mm vertically.

4: Tyre pressure -if the rate of change and value of tyre pressure is high (compared with a predetermined or variable threshold, based for example on manufacturer specifications), lock limiting action may be taken.

5: Steering torque -if the rate of change and/or amount of steering torque is high (compared with a predetermined or variable threshold), lock limiting action may be taken. The threshold may correspond to an unexpected delta, for example from obstacles (for example > 20% Nm than normal dry high mu road).

In some cases, the event of the first type will simply be taken into consideration when carried out the checks Cl to C5 (and could influence the thresholds used -for example, if the event is indicative of forthcoming terrain requiring high amounts of tyre motion, smaller thresholds may be used for some of the tests, to provide a more conservative outcome). In some cases, the process of Figure 6 is only initiated upon detection of an event of a second type indicating that full steering lock may be beneficial. More generally, the inputs 11 to 15 may represent parameters to be checked, as well as parameters which influence the checks. For example, the input 11 may be steering angle, indicating whether there is a high steering angle demand from the driver. This may serve as a prerequisite to carrying out the other checks (since if the steering angle demand is low, full lock us unlikely to be required). It may also relate to setting thresholds for one of more of the checks Cl to 05.

Embodiments of the present invention may be considered as providing a driver with additional lock when (detected) circumstances (that is, detected or predicted events) require it, or would benefit it. For example, in the absence of such circumstances, the maximum available steering lock may correspond to a first predetermined number of turns of the vehicle steering wheel (three for example), whereas in the presence of such circumstances, an additional half turn or turn of the vehicle steering wheel may be made available. Preferably, even in the presence of such circumstances, the additional lock is only made available if a state of the vehicle satisfies predetermined criteria.

In some embodiments, the present technique monitors vehicle parameters such as speed along with external factors (for example events) using external cameras, lidar and the like, to determine that there are no other road users in the immediate vicinity before allowing maximum lock. In this way, cyclists passing close to the vehicle and the like will not find the extremes of wheel articulation a road hazard.

The present technique enables steering angle and thus vehicle turning circle to be maximised over and above what would normally be available in most use case situations. This is achieved by accounting in real-time for high input and/or low frequency perturbations that traditionally statically set the position of the steering lock stops to prevent unwanted contact between the rotating wheel assembly and the fixed parts of the vehicle structure for a worst-case combination of these.

Claims (27)

1. CLAIMS1. A controller for an electric power assisted steering (ePAS) system, the ePAS system configured to permit articulation of one or more vehicle wheels within a steering angle range, the controller comprising control logic configured to adjust a maximum available steering lock for the ePAS system in dependence on a plurality of inputs.
2. 2. A controller according to claim 1, wherein the maximum available steering lock is set to an upper value when the plurality of inputs satisfy predetermined criteria, and to a lower value otherwise.
3. 3. A controller according to claim 1 or claim 2, wherein the plurality of inputs comprise one or more detected events.
4. 4. A controller according to claim 3, wherein, in response to a detected event of a first type, the controller is configured to limit the maximum available steering lock.
5. 5. A controller according to claim 3 or claim 4, wherein, in response to a detected event of a second type, the controller is configured to maximise a value of maximum available steering lock subject, subject to one or more other inputs.
6. 6. A controller according to any preceding claim, wherein the plurality of inputs comprise one or more parameters.
7. 7. A controller according to claim 6, wherein the input parameters comprise one or more vehicle parameters and/or one or more non-vehicle parameters.
8. 8. A controller according to claim 6, wherein the plurality of inputs comprise vehicle speed and at least one other input.
9. 9. A controller according to claim 3, wherein the vehicle parameters comprise one or more of a requested steering angle, vehicle mass, vehicle speed, vehicle yaw and/or roll angle or angular rate, amount of vertical wheel motion relative to the vehicle body, tyre pressure and steering torque, and lateral and longitudinal vehicle accelerations.
10. 10. A steering controller according to claim 9, wherein the vehicle parameters are obtained from one or more of a vehicle yaw sensor, suspension ride height angle sensor, magnetic rheology damping medium, ePAS steer assistance map, TPMS, proximity sensor and managed contact sensor.
11. 11. A controller according to claim 8 or claim 9, wherein the non-vehicle parameters comprise one or more of sensed environmental conditions.
12. 12. A controller according to claim 11, wherein the sensed environmental conditions comprise one or more of ambient temperature, precipitation and humidity.
13. 13. A controller according to claim 8 or claim 9, wherein the non-vehicle parameters comprise the detection of stationary or moving obstacles, or terrain features, outside the vehicle.
14. 14. A controller according to claim 13, wherein the obstacles or terrain are detected using one or more of a stereoscopic camera, ultrasonic sensor, lidar and radar.
15. 15. A controller according to claim 7, wherein the non-vehicle parameter is obtained based on a current location of the vehicle and a known location of road and/or terrain features.
16. 16. A controller according to claim 7, wherein the non-vehicle parameter is obtained from another vehicle.
17. 17. A controller according to any preceding claim, wherein the control logic carries out a plurality of checks, and determines a maximum steering lock in dependence on the outcome of those checks.
18. 18. A controller according to any preceding claim, wherein if the control logic reduces the maximum available steering lock, if a current amount of steering lock exceeds the reduced maximum amount of steering lock, the controller is configured to automatically reduce the current amount of steering lock.
19. 19. A controller according to any preceding claim, wherein the controller is configured, when an amount of steering lock demanded by the driver exceeds a threshold, to provide feedback to the driver.
20. 20. A controller according to claim 19, wherein the feedback is haptic feedback.
21. 21. A controller according to any preceding claim, wherein the control logic comprises one or more look up tables which relate maximum available steering angle lock to the input parameters.
22. 22. A controller according to any preceding claim, wherein, if a detected or predicted amount of wheel motion exceeds a threshold value, the maximum available steering lock is limited and/or reduced.
23. 23. A controller according to any preceding claim, wherein, if a detected or predicted amount of steering torque (needs definition) exceeds a threshold value, the maximum available steering lock is limited and/or reduced.
24. 24. A controller according to any preceding claim, wherein, if a detected or predicted vehicle yaw and/or roll exceeds a threshold value, the maximum available steering lock is limited and/or reduced.
25. 25. A controller according to any preceding claim, wherein if a detected tyre pressure exceeds a threshold value, the maximum available steering lock is limited and/or reduced.
26. 26. A vehicle comprising a controller according to any preceding claim.
27. 27. A control method for power assisted steering, the method permitting articulation of one or more vehicle wheels within a steering angle range, the method comprising obtaining a plurality of inputs and adjusting a maximum available steering lock in dependence on the plurality of inputs.