Damper control

A vehicle comprising: a vehicle body; a plurality of wheel assemblies each having a rotation axis; at least one suspension linkage, each suspension linkage coupling a respective wheel assembly to the vehicle body to permit motion of the rotation axis of each respective wheel assembly relative to the vehicle body; a damper coupled to a respective suspension linkage to constrain the motion of the associated wheel assembly by applying a damper reaction force to the suspension linkage, the damper being configured to be responsive to a damper force control output to vary the damper reaction force being applied to the suspension linkage; at least one vehicle sensor configured to provide vehicle condition data; and a damper control unit configured to generate the damper force control output that causes the damper to generate respective damper reaction forces to act against the suspension linkage to control the motion of the wheel assembly towards a set position for the wheel assembly relative to the vehicle body, adjust the set position based on a change in the vehicle condition data, and calculate the set position based on variations in the vehicle condition data over time.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present Application claims the benefit of International Application No. PCT/GB2018/050020, entitled “DAMPER CONTROL,” filed Jan. 5, 2018, which claims the benefit of Great Britain Patent Application No. 1700149.6, entitled “DAMPER CONTROL” field on Jan. 5, 2017. The contents of International Application No. PCT/GB2018/050020 and Great Britain Patent Application No. 1700149.6 are hereby incorporated by reference.

FIELD OF DISCLOSURE

This invention relates to a vehicle comprising a damper control unit.

BACKGROUND OF THE INVENTION

A typical road vehicle comprises a suspension system between each wheel of the vehicle and a vehicle body. The suspension system may comprise a suspension linkage for each wheel of the vehicle which supports the body of the vehicle by connecting between the respective wheel and the body of the vehicle. Each wheel is typically mounted on bearings and the bearings are attached to the body of the vehicle via the suspension linkages. The suspension linkages support the body against those bearings and thus against the wheels.

Each suspension linkage is designed to permit the wheels of the vehicle to move relative to the body of the vehicle. This movement of the wheels enables the vehicle body to be at least partially isolated from displacements of the wheels relative to the vehicle body. The displacement range provided by the suspension linkages of each wheel, relative to the vehicle body, is generally limited. This limitation normally stems from the packaging of the suspension systems in the vehicle. For example, the wheels are normally located in wheel arches of the vehicle body and thus the wheels can only move upwards a certain distance before coming in to contact with the interior of the wheel arches. Therefore, the motions of the wheels are generally constrained to avoid this happening.

If a suspension linkage is allowed to reach the end of its travel then this can result in a hard stop in the motion range of the linkage and thus the wheel attached to it. Such a hard stop may provide a large force on the suspension linkage, wheel and/or vehicle body. This, at a minimum, can lead to discomfort for the occupants of the vehicle or worse lead to damage to the vehicle. Therefore, vehicles typically comprise at least one damper which is used to control the motion of the suspension linkages. The dampers control the motion of the suspension linkages by generating a force on the respective suspension linkage. This force generally acts against the motion direction of the suspension linkage to thus restrict the motion of the suspension linkage as it reaches its end points.

The suspension linkage may also include components such as springs to also control the motion of the vehicle's body relative to the wheels and assist in supporting the vehicle body. For example, the vehicle may have four wheels and be provided with a double wishbone suspension at each of the four wheels. The double wishbone suspension will be coupled between the bearing of the wheel and the body of the vehicle to allow the wheel to move relative to the body of the vehicle. A damper may be connected between one of the wishbones of the suspension and the body of the vehicle to control the movement of the wheel relative to the body of the vehicle.

It is common for at least one damper to be provided per suspension linkage so that the motion of that suspension linkage can be controlled independently of the other suspension linkages. By controlling the motion of the suspension linkage, the at least one damper in effect controls the motion of the associated wheel. The dampers, by controlling the motion of suspension linkages and thus the wheels, therefore can influence the ride quality of the vehicle, the grip of the tyres because the tyre contact with the ground is influenced by the damper, and/or the handling of the vehicle because the motion of the body of the vehicle is influenced by the damper. Therefore, the way in which the dampers operate to control the motion of their associated suspension linkages, and thus the suspension system, influences the balance between ride quality, tyre grip and handling of the vehicle.

The dampers that control the motion of the suspension linkages may be configured so that the force that the at least one damper generates on its respective suspension linkage can be varied according to the mode and size of motion that the wheels are currently undergoing. The modes of motion may be heave, pitch, roll and warp and the one or more dampers in the suspension linkages may be capable of being controlled to provide independent stiffness and damping for each of those modes of motion. Examples of such systems are described in WO2011/039498 and EP2769860, the technical descriptions of which are incorporated by reference where permitted by law although the present application should be interpreted without reference to these documents. In these systems the chambers on either side of a damper piston comprised in a damper unit are connected to chambers of other damper units to permit fluid flow there between. These connections may also comprise restrictions and accumulators. The damper piston can move within the damper unit to vary the volume of the chambers and thus cause fluid to be drawn in or forced out of respective chambers. The damper units may have more than one damper piston and separate chambers associated with each damper piston. The interconnection of the damper chambers permits the damping forces associated with each damper to be controlled. The damper unit that has more than one damper piston, together with the fluid interconnections, enables damping of roll motion of the vehicle to be decoupled from the damping of heave.

The dampers may comprise variable restrictions to the fluid connections between the damper chambers and the exterior of the damper which enable the damper forces, for a given position and motion of the suspension linkage, generated by the damper to be altered. Such adjustments are generally known as semi-active damping because the dampers can be controlled to alter the restraint of the motion of the suspension linkages without actively urging the suspension linkage to move in a particular direction. The dampers may also be capable of actively urging the suspension linkage to move in a particular direction. In this case, the adjustments are generally known as active damping because the dampers are active dampers and can operate as actuators to both actively urge the suspension linkage and resist the suspension linkage's motion.

The motion of the vehicle body, the wheels and suspension linkages together with the damper forces can be modelled to attempt to calculate the optimal force that a damper should generate at a given moment. Examples of such modelling are described in:Brezas, P. and Smith, M. C. (2012)LQ optimal and risk-sensitive control for vehicle suspensions. Proc. IEEE 51st Annu. Conf. Decision Control, pp. 2465-2470;Brezas, P (2013)Time-domain optimal control for vehicle suspensions. PhD Thesis, University of Cambridge. EThOS ID: uk.bl.ethos.607986;Brezas, P and Smith, M C (2014)Linear Quadratic Optimal and Risk-Sensitive Control for Vehicle Active Suspensions. IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY, VOL. 22, NO. 2, pp 543-556; andBrezas, P and Smith, M C and Hoult, W (2015)A clipped-optimal control algorithm for semi-active vehicle suspensions: Theory and experimental evaluation. Automatica, 53. pp. 188-194. ISSN 0005-1098;
the technical descriptions of which are incorporated herein by reference where permitted by law although the present application should be interpreted without reference to these documents. However, such modelling is complex and there are therefore significant challenges in applying such modelling to a real-time damping control system. For example, if the control of the damper forces and/or the inputs into the model are incorrect then instability in the vehicle suspension system can result.

It would therefore be desirable for there to be improved methods of control of the forces generated by dampers in suspension systems.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a vehicle comprising: a vehicle body; a plurality of wheel assemblies each having a rotation axis; at least one suspension linkage, each suspension linkage coupling a respective wheel assembly to the vehicle body to permit motion of the rotation axis of each respective wheel assembly relative to the vehicle body; a damper coupled to a respective suspension linkage to constrain the motion of the associated wheel assembly by applying a damper reaction force to the suspension linkage, the damper being configured to be responsive to a damper force control output to vary the damper reaction force being applied to the suspension linkage; at least one vehicle sensor configured to provide vehicle condition data; and a damper control unit configured to generate the damper force control output that causes the damper to generate respective damper reaction forces to act against the suspension linkage to control the motion of the wheel assembly towards a set position for the wheel assembly relative to the vehicle body, adjust the set position based on a change in the vehicle condition data, and calculate the set position based on variations in the vehicle condition data over time.

The change in vehicle condition data may indicate that the mass of the vehicle has changed. The change in vehicle condition data may indicate a change in the aero-loading on the vehicle. The change in vehicle condition data may indicate a change in vehicle speed. The damper control unit may be configured to calculate an adjustment to a normal position of the at least one suspension elements based on the change in vehicle condition data and adjust the set position based on that calculated adjustment.

The damper control unit may be configured to calculate the set position based on variations in the vehicle condition data over time by detecting a steady-state motion condition for the vehicle based on the vehicle condition data; and obtaining an average of the position of the wheel assembly relative to the vehicle body from the vehicle condition data over a period of steady-state motion of the vehicle. The damper control unit may be configured to calculate the damper force control output based on the vehicle condition data. The damper control unit may be configured to calculate the damper force control output based on an average of at least one sensed vehicle parameter comprised in the vehicle condition data over time and calculate the set positions of the suspension linkages based on that average. The damper coupled to a respective suspension linkage may constrain the motion of the associated wheel assembly by applying a damper reaction force in a direction opposite to the motion of the associated wheel assembly.

The dampers may be fluid dampers and the dampers may be configured to produce the damper reaction force by controlling fluid flow between at least one damper chamber and the exterior of the damper. The at least one vehicle sensor may comprise pressure sensors for each damper configured to sense the pressure of fluid within the at least one chamber of the dampers; the damper control unit may be configured to generate the damper force control output based on the current damper reaction force of the dampers, and may be configured to calculate the current damper reaction forces based on the pressure of fluid within the at least one chamber of the dampers. The dampers may be connected together by a fluid interconnection system; the damper control unit may be configured to calculate the current damper reaction forces based on the pressure of fluid within the at least one chamber of the dampers by removing the fluid pressure due to the fluid interconnection system.

According to a second aspect of the present invention there is provided a vehicle comprising: a vehicle body; a plurality of wheel assemblies each having a rotation axis; at least one suspension linkage, each suspension linkage coupling a respective wheel assembly to the vehicle body to permit motion of the rotation axis of each respective wheel assembly relative to the vehicle body; a damper coupled to a respective suspension linkage to constrain the motion of the associated wheel assembly by applying a damper reaction force to the suspension linkage, the damper being configured to be responsive to a damper force control output to vary the damper reaction force being applied to the suspension linkage; at least one vehicle sensor configured to provide vehicle condition data; and a damper control unit configured to generate the damper force control output that causes the damper to generate respective damper reaction forces to act against the suspension linkage to control the motion of the wheel assembly towards a set position for the wheel assembly relative to the vehicle body, the damper force control output being calculated based on the current velocity of the vehicle and the vehicle condition data.

The damper control unit may be configured to calculate the damper force control output based on the vehicle condition data and sets of adjustment factors, the damper control unit may select a set of adjustment factors to calculate the damper force control output based on the current velocity of the vehicle. The damper control unit may select a first set of adjustment factors to calculate the damper force control output when the current vehicle velocity is between first and second vehicle speeds. The damper control unit may select a second set of adjustment factors to calculate the damper force control output when the current vehicle velocity is between second and third vehicle speeds. The value of the second vehicle speed may be different depending on whether the vehicle speed is increasing or decreasing.

The vehicle may be capable of moving at speeds within a speed range and the speed range may be divided into a plurality of speed bands, the damper control unit may be configured to select a respective one of the sets of adjustment factors in dependence on the speed band that the current velocity falls within. The sets of adjustment factors may each cause the vehicle to have different handling characteristics. The damper coupled to a respective suspension linkage may constrain the motion of the associated wheel assembly by applying a damper reaction force towards the set position of the suspension linkage. The dampers may be fluid dampers and the dampers may be configured to produce the damper reaction force by controlling fluid flow within the damper.

The present invention will now be described by way of example with reference to the accompanying drawings. In the drawings:

DETAILED DESCRIPTION OF THE INVENTION

The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art.

The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

The present invention relates to a vehicle that comprises a vehicle body and a plurality of wheel assemblies each having a rotation axis. The vehicle has at least one suspension linkage, each suspension linkage coupling a respective wheel assembly to the vehicle body to permit motion of the rotation axis each wheel assembly relative to the vehicle body. Each suspension linkage couples a respective wheel assembly to the vehicle body to permit motion of the rotation axis each wheel assembly relative to the vehicle body in a direction generally perpendicular to the rotation axis. The motion may cause the orientation of the rotation axis of the wheel to rotate over the movement range of the suspension linkage. The motion of each rotation axis relative to the vehicle body of each wheel is constrained to move in a generally vertically orientated direction. The vehicle has at least one suspension linkage, each suspension linkage coupling a respective wheel assembly to the vehicle body to permit translational motion of each wheel assembly relative to the vehicle body.

Coupled to a respective suspension linkage the vehicle has a damper to constrain the motion of the associated wheel assembly by applying a damper reaction force to the suspension linkage. The damper being configured to be responsive to a damper force control output to vary the damper reaction force being applied to the suspension linkage. The vehicle also comprises at least one vehicle sensor configured to provide vehicle condition data. The vehicle may also comprise a damper control unit configured to generate the damper force control output that causes the damper to generate respective damper reaction forces to act against the suspension linkage to control the motion of the wheel assembly towards a set position for the wheel assembly relative to the vehicle body, adjust the set position based on a change in the vehicle condition data, and calculate the set position based on variations in the vehicle condition data over time. The vehicle may also comprise a damper control unit configured to generate the damper force control output that causes the damper to generate respective damper reaction forces to act against the suspension linkage to control the motion of the wheel assembly towards a set position for the wheel assembly relative to the vehicle body, the damper force control output being calculated based on the current velocity of the vehicle and the vehicle condition data.

FIG.1shows a vehicle1. The vehicle1comprises a plurality of wheels2for supporting the vehicle body3. The vehicle1comprises a suspension system for supporting the vehicle body3on wheels2. The suspension system comprises a suspension linkage4coupled between a wheel2and at least one mounting point5on the vehicle body3. A suspension linkage4couples a respective wheel2to the vehicle body3. Therefore, there may be one suspension linkage4per wheel2. Each wheel2is typically mounted on bearings6, and thus suspension linkage4may be coupled between a wheel bearing6and a vehicle body mounting point5. The wheel2can rotate about a rotation axis to permit movement on a motion surface such as a road. This rotation axis may be defined by wheel bearing6. The wheel2together with ancillary items such as bearings6and, for example, a wheel brake together may form a wheel assembly. Thus each wheel assembly may have a rotation axis associated with it about which the wheel assembly turns to permit movement on the motion surface.

Suspension linkage4may be constituted by a single link. It will be appreciated that suspension linkage4may be constituted by a more complicated arrangement of linkages to couple each wheel2to the vehicle body3as required by the particular motion requirements of wheels2. For instance, suspension linkage4may be a wishbone linkage as illustrated inFIG.1or alternatively suspension linkage4may be a double wishbone linkage.

Each suspension linkage4permits motion of the suspension linkage's4respective wheel2relative to vehicle body3. Each suspension linkage4has a movement range which is the total motion range of the wheel2relative to the vehicle body3. Generally, suspension linkage4permits the wheel2to move in with a generally vertical movement. Other motions of the wheel2may also be permitted by suspension linkage4, for instance the camber of wheel2may be permitted to alter and/or the position of the hub/bearing6of the wheel may be permitted to move in a lateral direction over the movement range of the suspension linkage4.

To control the motion of the wheel2, relative to the vehicle body3, over the suspension linkage's4motion range, the vehicle1comprises at least one damper7associated with the suspension linkage4. The damper7is coupled to the suspension linkage4to constrain the motion of the suspension linkage4over the motion range. The at least one damper7may be coupled between suspension linkage4and vehicle body3as shown inFIG.1to constrain the motion of suspension linkage4. Alternatively, or as well as, at least one damper7may be coupled between elements of the suspension linkage4to constrain the motion of suspension linkage. The at least one damper7is configured to produce a reaction force against the suspension linkage4. The reaction force causing control of the motion of the suspension linkage4and thus of the wheel2coupled to the respective suspension linkage4.

Vehicle1may also comprise one or more springs8, or other resilient biasing means, coupled to the suspension linkage4. Springs8may be physical springs such as a wound metal spring or may be formed from part of the motion resistance provided by dampers7. As with dampers7, the springs8may be coupled between suspension linkage4and vehicle body3and/or may be coupled between elements of the suspension linkage4. Springs8provide support to the suspension linkages4and thus to vehicle body3. Springs8bias the suspension linkages4so that at rest the suspension linkages4tend to a normal position. This normal position is the point in the motion range of the suspension linkage4that the suspension linkage4tends towards when there are no external motion forces acting on the vehicle1. No external motion forces may be acting on the vehicle1when the vehicle is at rest or when the vehicle1is moving with constant velocity that generates substantially no force on the vehicle1due to air resistance. The normal position may be a range of positions centred around the normal position. This may be due to internal resistances in the suspension system and/or the direction from which the suspension linkage4approaches the normal position.

Dampers7may be fluid dampers, i.e. the reaction forces generated by dampers7may be derived from the damper controlling the flow of a fluid. The fluid may be air or liquid. The liquid may be a hydraulic liquid such as oil or water. Dampers7may generate reaction forces by some other means, for instance they may comprise electromagnetics which generate the reaction forces by magnetic interaction between elements comprised by the damper7. The dampers7may be any combination of types of dampers7.

Dampers7may have a way in which the reaction force generated by the damper at a particular point in the dampers damping range can be varied. As discussed above, this may be by varying the magnetic interaction between elements comprised by the damper7. Alternatively, the damper7may comprise at least one piston9located in a damper cylinder (shown by11and12together). The piston9divides the respective damper chamber into two damper chambers11,12. Piston9can move through damper cylinder altering the volume of the two damper chambers11,12as it does so. As one damper chamber11,12increases in volume the other damper chamber11,12decreases in volume. The piston9acts on fluid contained in the damper chambers11,12. Thus the reaction force generated by damper7corresponds to the force generated by piston9acting on the fluid contained in the damper chambers11,12.

Fluid can flow in and out of first and second damper chambers11,12via first and second controllable valves13,14. Controllable valves13,14are configured to vary the size of an opening through which fluid can pass. In other words, the size of the restriction in the fluid path between each damper chambers11,12and the exterior of the respective chamber is variable, this variation being provided by each of the controllable valves13,14. The controllable resistance to fluid flow provided by controllable valves13,14can alter the force on piston9as it moves through the damper cylinder and thus alter the reaction force provided by damper7. Each controllable valve13,14may be responsive to a valve control input to control the opening of the valve and thus the size of the restriction.

The damper chambers11,12may be connected to each other, and/or other dampers of vehicle1by a fluid interconnection system15. The fluid interconnection system15may comprise one or more fluid springs16. Fluid spring16may be a fluid accumulator. The fluid interconnection system15can provide a more static element to the reaction force generated by the dampers7by restricting the flow of fluid between the damper chambers11,12.

The damper7may comprise more than one damper cylinder. Each damper cylinder may have controllable valves, or alternatively the variation in the damper reaction force may be provided by controllable valves being present on only one damper cylinder of the damper.

The damper7may be semi-active in its operation: the damper7may be capable of generating a reaction force only in a direction against the current motion direction of the suspension linkage. In other words, the damper may be capable of generating a reaction force only opposite to the damper velocity. The damper velocity being the velocity at which the damper's components are moving due to the motion of the suspension linkage. In this way, the damper can provide resistance to the suspension linkage's motion but not actively induce motion in the suspension linkage.

The damper7may be active in its operation: the damper7may be capable of generating a reaction force in a direction both against the current motion direction of the suspension linkage and with the current motion direction of the suspension linkage. Where the damper7is active, the active damper7can act as both an impedance to the suspension linkage motion and also as an actuator to the suspension linkage motion. In other words, the damper may be capable of generating a reaction force in both directions: opposite to the damper velocity and in the same direction as the damper velocity. The damper7may also generate a force in those two directions when the suspension linkage is stationary and so the damper velocity is zero. In the case of a fluid dampers, the fluid entering the damper through valves may be under pressure which permits the damper to exert a force irrespective of the direction of the damper velocity or if it is zero. In the case of an electromagnetic damper, the damper7may generate an electromagnetic field that permits the damper to exert a force irrespective of the direction of the damper velocity or if it is zero. In this way, the damper force may be positive or negative relative to the motion direction of the suspension linkage.

The vehicle1may comprise a damper reaction force measuring device for each suspension linkage4. This damper force measuring device may be configured to measure the instant damping force being provided by the dampers coupled to that suspension linkage4.

In the case of a fluid damper system, the vehicle1may comprise damper pressure sensors17,18configured to sense pressure in a respective damper cylinder. The vehicle may comprise damper pressure sensors17,18for each suspension linkage5. One damper pressure sensor18may sense the pressure of fluid in the first damper chamber11and one damper pressure sensor17may sense the pressure of fluid in the second damper chamber12. Two pressure sensors, one to each side of piston9enables the sensing of the pressure during both travel directions of the piston9. As the pressure of the fluid that the piston9acts against provides a force against that piston, the pressure sensors can be used to calculate the reaction force being generated by the damper at that time. The use of two pressure sensors provides for an accurate calculation of the damper reaction force in each motion direction of the damper. However, it will be appreciated that as the piston separates fluid in each damper chamber that one pressure sensor could be used in one damper chamber and the pressure to each side of the piston be derived from this one pressure sensor. Where a damper7comprises multiple damper cylinders (shown at11and12), it may be sufficient for only one damper cylinder to have pressure sensor(s) attached to it to be able to calculate the damper reaction force.

The operation of the dampers7to provide variable reaction forces is regulated by a damper control unit19. The damper control unit19may form part of, or may be comprised within, a vehicle management unit. The vehicle management unit may comprise other control systems such as an engine control unit. The damper control unit19comprises a processor20and a non-volatile memory21. The memory21stores a set of program instructions that are executable by the processor, and reference data such as look-up tables that can be referenced by the processor in response to those instructions. The processor20may be configured to operate in accordance with a computer program stored in non-transitory form on a machine readable storage medium. The computer program may store instructions for causing the processor to perform the operations of the damper control unit in the manner described herein.

The damper control unit19is coupled to damper(s)7, that are coupled to each suspension linkage4, to receive from them data that can be used to generate the current generated damper reaction force. The damper control unit19may be coupled to each of the pressure sensors17,18to receive readings of the current pressure in damper chambers11,12. The damper control unit19may be configured to derive the current damper reaction force of each suspension linkage4based on the received current pressure readings. The damper control unit19may utilise one or more look-up tables to derive the damper reaction forces from the pressure readings.

Where pressure sensors17,18are being used to derive the current damper reaction force for each suspension linkage4, the damper control unit19may remove from the pressures output by the pressure sensors the element of the sensed pressure that is due to the fluid interconnection system15. The fluid interconnection system15may comprise fluid springs or accumulators16as well as other components that control and influence the pressure within the fluid interconnection system. These components cause a resistance to the flow of fluid and thus contribute to the pressure generated within the damper chambers11,12. Therefore, for the damper control unit19to accurately derive the current damper reaction force being generated by a respective damper7, the pressure due to the fluid interconnection system15may be removed by the damper control unit19prior to calculating the current damper reaction force. The pressure due to the fluid interconnection system15may be calculated based on the current damper displacement, i.e. the position of the piston within the damper cylinder (shown at11and12) using a model of the fluid interconnection system15. The damper control unit19may utilise one or more look-up tables to derive the pressure due to the fluid interconnection system15at a particular damper displacement.

The vehicle may also comprise a rotation sensor22associated with each suspension linkage4. The rotation sensor22detects the current rotational position of the suspension linkage4within the movement range of the suspension linkage4. The damper control unit19is coupled to the rotation sensors22to receive from them a current rotational position input which indicates the current rotational position of the respective suspension linkage4. The rotational position of the suspension linkage4can be used by the damper control unit19to derive the position of wheel2, associated with that respective suspension linkage4, within the limits of possible travel of wheel2. The damper control unit19may utilise one or more look-up tables to derive the damper reaction forces from the rotational position inputs from the rotation sensors22.

The vehicle may also comprise an acceleration sensor23associated with each wheel2. The acceleration sensor23may be coupled to wheel hub or wheel bearing6so that the acceleration sensor23can sense the vertical acceleration of the wheel2relative to the vehicle body3. The acceleration sensor23may be a one-axis accelerometer configured to sense accelerations in the vertical direction. The damper control unit19is coupled to the acceleration sensors23to receive from them a wheel acceleration input which indicates the current acceleration of the respective wheel2.

The vehicle1may also comprise acceleration sensor(s) which measure at least one of heave, pitch and roll of the vehicle body. As illustrated inFIG.1, the vehicle1may comprise:a heave acceleration sensor24which measures the vertical acceleration of the vehicle body3;a roll acceleration sensor25which measures the acceleration of the vehicle body about a longitudinal centreline of the vehicle3;a pitch acceleration sensor26which measures the acceleration of the vehicle body about a lateral centreline of the vehicle3.

The damper control unit19is coupled to the one or each of the heave acceleration sensor24, the roll acceleration sensor25, the pitch acceleration sensor26to derive, respectively, the current vertical displacement of the vehicle body relative to the wheels2, the current rotational position of the vehicle body about the longitudinal centreline of the vehicle body relative to the wheels2, the current rotation position of the vehicle body about the lateral centreline of the vehicle body relative to the wheels2.

The damper control unit19can use the various inputs describing the current vehicle conditions to derive the current damper reaction forces that the dampers7should be controlled to provide to the respective suspension linkages. These damper reaction forces are selected to provide the required control to the motion of the wheels2with respect to the vehicle body to optimise the ride quality, tyre grip and/or handling of the vehicle. The damper control unit19is coupled to the dampers7to provide the damper force control output to the dampers7associated with each of the suspension linkages4. The damper force control output informs the damper7of the current damper reaction force that the damper(s)7associated with that suspension linkage should produce at that given point in time. In the case of the fluid dampers7described above, the damper control unit19is coupled to the controllable valves13,14. The damper control unit19may provide the controllable valves13,14with an input that controls the opening of each of the valves13,14. The damper reaction force output in this case may be in the form of valve opening output. The valve opening output may supply a current level to the valve which is associated with a particular size of valve opening. The damper control unit19may derive that required opening from the desired damper reaction force. The damper control unit19may use one or more look-up tables to convert the desired damper reaction force in to the required opening for each of the controllable valves13,14.

As discussed above, the dampers7are configured to provide reaction forces to constrain the motion of the suspension linkage towards a normal position. This normal position can vary during use of the vehicle. Instability or undesirable control action can occur when the damper control unit19is attempting to control the suspension linkage by variation of the damper reaction force towards a set position that is different to the current normal position of the suspension linkage. Undesirable control action may be force demands that are undesirable but do not lead to instability in the system. For instance, a jacking motion of the vehicle as it moves along. Such a deviation can occur when the sensed conditions affecting the normal position of the suspension linkage change. A change in conditions affecting the vehicle1may occur generally in two broad types: (i) changes to the vehicle parameters; and (ii) changes to conditional parameters not associated directly with changes to physical properties of the vehicle. The damper control unit19can sense changes associated with the static vehicle parameters and/or changes to the conditional parameters using any number of vehicle sensors such as those described above with reference toFIG.1. Those vehicle sensors may each be configured to generate vehicle condition data.

Changes to vehicle parameters may include:change in fuel level which changes the vehicle mass;change in vehicle mass, for instance: due to an increase or decrease in the number of passengers the vehicle is carrying, due to an increase or decrease in the cargo the vehicle is carrying;change in aero-loading on the vehicle, for instance: due to a change in speed of the vehicle, alteration of aerodynamic elements of the vehicle such as spoilers.

Changes to conditional parameters may include:sensor drift: the vehicle condition data output by the vehicle sensor may alter over time for a given value of a measured vehicle condition;calibration errors: the vehicle condition data output by the vehicle sensor may be offset from the actual value of a measured vehicle condition;the vehicle condition data output by the vehicle sensor may vary in a manner different to that of the variation of the measured value of a measured vehicle condition. For instance, the vehicle condition data output by the vehicle sensor may vary non-linearly as there is a linear variation in the measured value.

The damper control unit19may be configured to adjust the set position in response to a change in the vehicle condition data. A change in vehicle condition data can indicate that there has been an alteration to the vehicle parameters as given above. The set point may alter because the vehicle is now, for example, more heavily loaded than it was before and so the vehicle may sit lower on the suspension system than it did previously, i.e. the normal position of the wheels2relative to the vehicle body3may be higher than before. Thus the damper reaction forces that are calculated need to take in to account this change.

Another example is the change in the aero-loading on the vehicle. For instance, as the speed of the vehicle1changes, the downforce on the vehicle1may alter. This alteration in the downforce may, in effect, cause a variation in the weight of the vehicle body and thus change the normal position of the wheels2relative to the vehicle body3. Therefore, the damper control unit needs to take in to account this change in the set position of the suspension elements4.

The damper control unit19may calculate how the change in vehicle condition data effects the normal position of the suspension elements4and adjust the set position in response to that calculation. This adjustment can occur in response to the change in vehicle condition data. Such an adjustment can occur on a feed-forward basis in that the adjustment occurs soon after the change in vehicle condition data has been sensed.

The damper control unit19may also be configured to calculate the set position based on variations in the vehicle condition data over time. Variations in the vehicle condition data over time may be indicative of changes to conditional parameters not associated directly with changes to physical properties of the vehicle1. The damper control unit19may be configured to calculate an average of at least one sensed vehicle parameter over time and based on that average adjust the set positions of the suspension elements4.

The damper control unit19may be configured to calculate the set position by detecting a steady state motion condition for the vehicle1based on the vehicle condition data. Such a steady state motion condition may be when the vehicle is moving but with a motion which means the average position of the suspension element is at the normal position. Such a motion may occur when the vehicle1is moving with, for example, low speed, in a straight line, and/or with minimal steering input. The damper control unit19can therefore calculate the set position based on variations in the vehicle condition data over time. Such a calculation can help avoid the changes to the conditional parameters detailed above because the damper control unit19assesses the data over a period of time during which it is likely that any changes to the conditional parameters due to errors will be averaged out.

As discussed herein, the dampers7are configured to provide reaction forces to constrain the motion of the suspension linkage4towards a normal position. The size of the reaction forces generated by the dampers7effects the rate at which the suspension linkages are controlled towards the normal position, or set position. The reaction forces generated by the dampers7are generally proportional to the distance of the wheel2from the set position or, at least, calculated based on the distance of the wheel2from the set position. The reaction forces generated by the dampers7may also be calculated based on the velocity of the motion of wheel2relative to the set position. Using the distance of the wheel2from the set position and/or the velocity of the motion of the wheel2relative to the set position allows for variations in the reaction forces dependent on current motion state of the vehicle. For instance, this permits different damping to be applied depending on whether a wheel is experiencing movement due to bump or roll. In addition, if the wheel2is moving towards the set point and with a velocity that, knowing the current amount of damping in the system, will take the wheel past the set point then a damping force may be applied to attempt to slow the motion of the wheel2past the set point.

The direction that the reaction forces is applied is opposite to the motion direction of the wheel2and thus the wheel assembly. Thus, when the wheel2is moving towards the set point the reaction force is applied away from the set point and when the wheel2is moving away from the set point the reaction force is applied towards the set point. The reaction forces are applied is so as to be dependent on whether the wheel2is moving towards or away from the set point.

More generally, the reaction forces may be calculated based on the vehicle condition data, for example as discussed herein.

The rate at which the suspension linkages are controlled towards the set point effects the balance between ride quality, tyre grip and handling of the vehicle. There may be situations where the balance between those factors is chosen to be weighted in a particular way, for example if the vehicle is to be driven enthusiastically on a track, or driven in a comfortable manner.

The rate at which the suspension linkages are controlled towards the set position may be set based on the current velocity of the vehicle1. This is because the desired balance between the above factors generally alters as the speed of the vehicle1changes. Therefore, the way in which the damper control unit19may be configured to calculate the damper reaction forces at low speeds may be different to the way in which the damper control unit19may be configured to calculate those damper reaction forces at higher speeds. This can be because at lower speeds ride quality, i.e. the way in which the vehicle1suspension system handles bumps and turns, can be more important, but at higher speeds tyre grip and handling can become more important. Therefore, the damper control unit19can be configured to calculate the damper reaction forces based on the current velocity of the vehicle. As there are bands of vehicle speeds within which common vehicle handling characteristics are desirable, the damper control unit19may be configured to use a first set of adjustment factors to calculate the damper reaction forces based on the vehicle condition data when the current vehicle speed is between first and second vehicle speeds and configured to use a second set of adjustment factors to calculate the damper reaction forces based on the vehicle condition data when the current vehicle speed is between second and third vehicle speeds. The damper control unit19may be configured to apply hysteresis to the transition between the use of different sets of adjustment factors. The intermediate vehicle speed, in the above case second vehicle speed, where the transition occurs between the damper control unit19using the first set of adjustment factors and the second set of adjustment factors, may be different depending on whether the vehicle speed is increasing or decreasing.

Any number of blocks of vehicle speeds may be used to obtain the required vehicle handling characteristics. For example:a first set of adjustment factors may be used when the current vehicle speed is between zero and a first vehicle speed;a second set of adjustment factors may be used when the current vehicle speed is between a first vehicle speed and a second vehicle speed;a third set of adjustment factors may be used when the current vehicle speed is between a second vehicle speed and a third vehicle speed; anda fourth set of adjustment factors may be used when the current vehicle speed is between a fourth vehicle speed and maximum vehicle speed.

The blocks of vehicle speeds may be a plurality of speed bands. This plurality of speed bands each being a portion of the range of speeds at which the vehicle can travel. I.e. the vehicle may be capable of moving at all the speeds within a speed range and the speed range is divided into a plurality of speed bands. This speed range may be from zero to a maximum forward speed. There may also be a speed range from zero to a maximum reverse speed. There may be a set of adjustment factors associated with each of the speed bands. The set of adjustment factors associated with the current speed band of the vehicle may be used during the period that the vehicle has a current vehicle speed within that speed band.

As discussed above, the second, and third vehicle speeds may have different values depending on whether the vehicle speed is decreasing or increasing.

Each set of adjustment factors may have a specific balance between ride quality, tyre grip and handling of the vehicle. This balance being obtained by variation in the way in which the dampers7control the motion of the suspension linkages4by generating reaction forces towards the set position.

The current velocity of the vehicle1may be sensed by a vehicle sensor or calculated by the vehicle management system based on the inputs such as the engine speed, wheel size, and gear ratio of the vehicle1. The damper control unit19may be configured to receive a vehicle speed input indicating the current speed of the vehicle.