Determination of traction forces by changing wheel normal forces

Abstract

A control system (300) for controlling an active suspension system (104) of a vehicle (100) to determine a relative traction level, the control system comprising one or more controllers (301), wherein the control system is configured (908) to: control the active suspension system to change a normal force through a first subset of one or more wheels; determine a traction-related variable at each of the wheels of the first subset of wheels to which a known torque is applied; control the active suspension system to change a normal force through a second subset of one or more wheels; and determine a traction-related variable at each of the wheels of the second subset of wheels to which a known torque is applied, wherein the traction-related variable is indicative of the relative traction level.

Description

Technical Field

[0001] This disclosure relates to determining traction force by changing the normal force of the wheels. In particular, but not exclusively, this disclosure relates to determining traction force by changing the normal force of multiple wheels of a vehicle. Background Technology

[0002] If the individual wheels of a vehicle are on a surface offering different coefficients of friction μ, the options for maximizing traction are limited. A limited-slip differential, or locking differential, is a mechanism that prevents or limits differential slippage between the wheels coupled to the differential to mitigate traction loss through the wheel with the lowest μ contact area with the ground.

[0003] The traction control system can detect wheel slippage and reduce the speed of the slipping wheel by applying braking force and / or reducing torque. Due to the mechanical action within the differential, braking the slipping wheel will cause torque to be transferred through the differential to the wheel with greater traction. Summary of the Invention

[0004] The purpose of this invention is to provide an improved method for measuring traction force levels.

[0005] According to one aspect of the invention, a control system for controlling an active suspension system of a vehicle to determine a relative traction level is provided, the control system comprising one or more controllers, wherein the control system is configured to:

[0006] The active suspension system is controlled to change the normal force passing through one or more wheels of the first subgroup;

[0007] Determine the variables related to traction force at each wheel in the first subgroup of wheels to which a known torque is applied;

[0008] The active suspension system is controlled to alter the normal force passing through one or more wheels of the second subgroup; and

[0009] Determine the variables related to traction force at each wheel in the second subgroup of wheels to which a known torque is applied.

[0010] Among them, the traction-related variables indicate the relative traction level.

[0011] In some examples, traction-related variables include wheel speed.

[0012] In some examples, the control system is configured to obtain an initial approximation of the relative traction level based on wheel speed measurements of the wheels of the first and second subgroups before changing the normal force passing through the wheels of the first and second subgroups.

[0013] The traction-related variables determined during the change of normal force improve the initial approximation.

[0014] In some examples, the traction-related variables indicate the average traction level measured over multiple repeated variations of the normal force.

[0015] In some examples, the wheels of the first subgroup include a first pair of wheels at the opposite corner on the first diagonal of the vehicle, and the wheels of the second subgroup include a second pair of wheels at the opposite corner on the second diagonal of the vehicle.

[0016] In some examples, the control system is configured to repeatedly pulsate the normal force of the wheels passing through the first subgroup in a first phase and repeatedly pulsate the normal force of the wheels passing through the second subgroup in a second phase while determining traction-related variables.

[0017] In some examples, the second phase is offset by approximately 180 degrees relative to the first phase.

[0018] In some examples, the first subgroup is the first wheel at the first corner of the vehicle, and the second subgroup is the second wheel at the second adjacent corner of the vehicle.

[0019] In some examples, the first corner is located at the first lateral side of the vehicle and at the first longitudinal end of the vehicle, and the second corner is located at the second lateral side of the vehicle and at the first longitudinal end of the vehicle.

[0020] In some examples, the control system is configured as follows:

[0021] The active suspension system is controlled to change the normal force through a third wheel, which is located at the second lateral side of the vehicle and at the second longitudinal end.

[0022] Determine the variables related to the traction force at the third wheel where a known torque is applied;

[0023] The active suspension system is controlled to alter the normal force passing through a fourth wheel, which is located at the first lateral side and at the second longitudinal end; and

[0024] Determine the variables related to the traction force at the fourth wheel where a known torque is applied.

[0025] Among them, the traction-related variables at the first, second, third, and fourth wheels indicate the relative traction levels among the first, second, third, and fourth wheels.

[0026] In some examples, the control system is configured to repeatedly pulsate the normal force through the first wheel in a first phase, repeatedly pulsate the normal force through the second wheel in a second phase, repeatedly pulsate the normal force through the third wheel in a third phase, and repeatedly pulsate the normal force through the fourth wheel in a fourth phase while determining traction-related variables.

[0027] In some examples, the second phase lags behind the first phase by approximately 90 degrees, the third phase lags behind the second phase by approximately 90 degrees, and the fourth phase lags behind the third phase by approximately 90 degrees.

[0028] In some examples, altering the normal force involves repeatedly pulsating the normal force at a rate corresponding to a frequency between about 0.25 Hz and about 15 Hz.

[0029] In some examples, the control system is configured to calculate the rate of each subgroup of wheels, including compensating for differences between at least one of the following:

[0030] The weight on each wheel;

[0031] The travel height at each wheel; and

[0032] Tire pressure at each wheel.

[0033] In some examples, altering the normal force involves repeatedly pulsating the normal force outside the range that causes wheel bounce.

[0034] In some examples, the control system is configured to change the normal force and determine traction-related variables based on received indications of traction loss of the vehicle.

[0035] In some examples, the indication of a vehicle's traction loss is based on information from wheel speed sensors.

[0036] In some examples, the control system is configured to change the normal force and determine traction-related variables based on received ground information.

[0037] In some examples, ground information depends on one or more of the following:

[0038] The vehicle's selected terrain mode; and

[0039] Information obtained from one or more sensors.

[0040] In some examples, the control system is configured to cause at least one of the following based on the relative traction level:

[0041] Control the torque supplied to the wheels;

[0042] Control the friction braking at the wheels;

[0043] Controlling the spring stiffness of the active suspension;

[0044] Control the damping rate of the active suspension;

[0045] Control regenerative braking settings;

[0046] Control the steering at the steerable wheels; or

[0047] Control the selection of terrain patterns.

[0048] According to one aspect of the present invention, an active suspension system including the control system is provided.

[0049] According to one aspect of the present invention, a vehicle is provided that includes the control system or the active suspension system.

[0050] According to one aspect of the present invention, a method is provided for controlling an active suspension system of a vehicle to determine a relative traction level, the method comprising:

[0051] The active suspension system is controlled to change the normal force passing through one or more wheels of the first subgroup;

[0052] Determine the variables related to traction force at each wheel in the first subgroup of wheels to which a known torque is applied;

[0053] Control the active suspension system to alter the normal force passing through one or more wheels of the second subgroup; and

[0054] Determine the variables related to traction force at each wheel in the second subgroup of wheels to which a known torque is applied.

[0055] Among them, the traction-related variables indicate the relative traction level.

[0056] According to one aspect of the invention, computer software is provided that, when executed, is configured to perform the methods described herein. According to another aspect of the invention, a non-transitory computer-readable medium is provided, comprising computer-readable instructions that, when executed by a processor, cause any one or more of the methods described herein to be performed.

[0057] The one or more controllers may collectively include: at least one electronic processor having an electrical input for receiving information; and at least one electronic memory device electrically connected to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon to cause the control system to perform the method.

[0058] Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples, and alternatives set forth in the foregoing paragraphs, claims, and / or the following description and drawings, and in particular the various features of said aspects, embodiments, examples, and alternatives, may be adopted individually or in any combination falling within the scope of the appended claims. That is, the features of all embodiments and / or any embodiments may be combined in any manner and / or combination falling within the scope of the appended claims, unless such features are incompatible. The applicant reserves the right to amend any originally filed claim or accordingly file any new claim, including the right to modify any originally filed claim to any feature subordinate to and / or incorporated into any other claim, although not initially claimed in this manner. Attached Figure Description

[0059] One or more embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which:

[0060] Figure 1 The illustration shows an example vehicle and coordinate system;

[0061] Figure 2A , Figure 2B The diagram illustrates the forces acting on the wheels and the road.

[0062] Figure 3 The illustration shows an example control system;

[0063] Figure 4 An example of a non-transitory computer-readable storage medium is illustrated;

[0064] Figure 5 An example of a vehicle's active suspension system is illustrated.

[0065] Figure 6A , Figure 6B , Figure 6C The illustration shows an example of diagonal out-of-phase normal force variation used to estimate relative traction force levels;

[0066] Figure 7A , Figure 7B , Figure 7C , Figure 7D , Figure 7E The illustration shows an example of 90-degree out-of-phase normal force variation used to estimate relative traction force levels; and

[0067] Figure 8 The example method is illustrated. Detailed Implementation

[0068] Figure 1 An example of a vehicle 100 that can implement embodiments of the present invention is illustrated. In some, but not necessarily all, examples, vehicle 100 is a passenger vehicle, also referred to as a bus or automobile. In other examples, embodiments of the present invention can be implemented for other applications, such as industrial vehicles or commercial vehicles. Vehicle 100 has a vehicle body 102 (sprung mass) supported by suspension.

[0069] Figure 1 The diagram also illustrates a coordinate system. The x-axis is the longitudinal axis. The rotation of the vehicle body around the x-axis, "R", represents roll. The y-axis is the lateral axis. The rotation of the vehicle body around the y-axis, "P", represents pitch. The z-axis is the vertical axis. The rotation of the vehicle body around the z-axis, "Y", represents yaw.

[0070] Figure 2A The diagram schematically illustrates the wheel and the road surface, as well as the forces acting on the wheel and the road. F T The traction force depends on the torque Tq applied by a torque source such as an internal combustion engine or electric motor, and also on the available traction force. F F is the frictional force. W For the weight of vehicle 100 supported by wheels, if vehicle 100 has one wheel at each corner, then F W This is known as corner weight. F N To be related to weight F W Equal and opposite normal forces. In this paper, the normal force is also referred to as the contact force between the wheel and the ground.

[0071] Figure 2B The y-axis represents the traction force F. T And the x-axis is a curve of the applied torque Tq. Figure 2B The solid line diagram illustrates that, for a given normal force F... N1 traction force F T The torque Tq is increased proportionally until the usable traction limit is reached. Above this limit, further increases in torque Tq will provide less additional traction F as the wheels begin to slip. T As torque increases, and consequently wheel slippage rate increases, traction force F... T It will begin to descend because the kinetic friction is less than the static friction.

[0072] However, if the normal force decreases to FN2 (Dashed line) indicates a reduction in the available traction limit. This can lead to premature wheel slippage and loss of traction. This relationship between normal force and wheel slippage can be used to obtain information about the relative traction level. For example, in the event of a loss of traction during driving, if the vehicle weight can be temporarily redistributed to other wheels, the normal force passing through the wheels can be temporarily reduced. The resulting change in wheel slippage of the unloaded (weight-reduced) wheels can be measured, and then unloading and measuring can be performed on different wheels. The wheels that slip more due to unloading are those with the lowest traction. Therefore, the relative traction levels of the wheels can be ranked from worst to best. This indication of the relative traction level can be sent to other vehicle subsystems to help vehicle 100 maintain traction or disengage from a jam.

[0073] The suspension of vehicle 100 is an active suspension system, which can temporarily change the normal force F passing through each wheel of vehicle 100. N This changes the traction at these wheels. The active suspension system 104 is such a system that can be configured in the control system 300, for example... Figure 3 Energy is supplied under the control of the control system shown to alter the normal force at the vehicle's wheels. By increasing the energy to increase the actuator force at one corner of the vehicle 100 relative to other corners (the force used to increase the distance between the wheel and the vehicle body), the weight balance of the vehicle 100 is shifted so that more of the vehicle 100's weight is supported by some wheels other than the others. This allows different wheels of the vehicle 100 to be unloaded, making it possible to measure slippage.

[0074] First, the example active suspension system 104 and control system 300 will be described.

[0075] Figure 3 The control system 300 includes a controller 301. In other examples, the control system 300 may include multiple controllers located on and / or outside the vehicle 100. In some examples, the control system 300 or controller 301 may be provided as part of the active suspension system 104.

[0076] Figure 3The controller 301 includes: at least one processor 304; and at least one memory device 306 electrically connected to the electronic processor 304 and having instructions 308 (e.g., a computer program) stored therein, the at least one memory device 306 and the instructions 308 configured to perform any one or more of the methods described herein via the at least one processor 304. The processor 304 may have an interface 302, such as electrical input / output (I / O) or an electrical input for receiving information and interacting with external components, such as the active suspension system 104.

[0077] Figure 4 The illustration shows a non-transitory computer-readable storage medium 400 including instruction 308 (computer software).

[0078] Figure 5 The illustration shows an example implementation of the active suspension system 104.

[0079] The active suspension system 104 includes a left front active suspension 106 for the left front wheel FL, a right front active suspension 116 for the right front wheel FR, a left rear active suspension 108 for the left rear wheel RL, and a right rear active suspension 118 for the right rear wheel RR. The active suspension for each wheel of the vehicle 100 (e.g., sidewall wheels / corner wheels) can be individually controllable.

[0080] Figure 5 Also shown is a torque source 103, such as an internal combustion engine or an electric motor, for driving at least some of the vehicle's wheels. In some examples, vehicle 100 is an all-wheel-drive vehicle. In one implementation, all wheels are coupled to a single torque source, such as an internal combustion engine. In another implementation, the vehicle is a "hybrid vehicle for on-road use," configured to provide torque from a first torque source (e.g., an internal combustion engine) to one axle (e.g., two front wheels or two rear wheels) and from a second torque source (e.g., an electric motor) to a second axle (e.g., two rear wheels or two front wheels). Alternatively, the first and second torque sources are of the same type. In yet another implementation, the vehicle includes a torque source (typically an electric motor) for each wheel, such as a hub motor. Possible vehicle architectures are not limited to the examples described above.

[0081] The active suspension for each corner of vehicle 100 includes actuator 502.

[0082] Actuator 502 may be a hydraulic actuator, such as a hydraulically filled chamber that houses a piston. One end of actuator 502 is connected to a vehicle wheel, and the other end is connected to the vehicle body 102. Spring 504 (e.g., a coil spring or a pneumatic spring) may be in a balanced state and may act in parallel with actuator 502.

[0083] When the vehicle suspension is undisturbed, the piston of the hydraulic actuator 502 is in a specific neutral position in the chamber.

[0084] The piston can move in either direction within the chamber, for example, due to road disturbances that compress actuator 502. The piston can remove fluid from the chamber to enter a hydraulic circuit (not shown). The fluid exerts a restoring force against the piston's movement. Energy can be added to and / or extracted from actuator 502 by pumping fluid and / or controlling valves to regulate the fluid pressure on either side of the piston.

[0085] Therefore, the control system 300 can dynamically control the restoring force resisting the displacement piston. This force is equivalent to the spring force (spring stiffness) of a coil spring resisting displacement. Dynamic control allows the force-displacement relationship to be changed to adapt to the driving scenario. Energy can be added or removed rapidly, for example, within tens of milliseconds. To control the spring force, the control system 300 can output a force request that depends on the sensed wheel travel (displacement / articulation of the wheel to the vehicle body).

[0086] The damping rate of actuator 502 can be modified by controlling a fluid valve at the contraction point, which regulates the rate at which fluid is transferred into and removed from actuator 502 by the movement of the piston. In some examples, the impact damping rate and the rebound damping rate can be controlled independently.

[0087] Furthermore, energy can be added to or removed from actuator 502 to alter the normal force applied to the tire contact surface associated with actuator 505. This change in force may cause actuator 502 to extend or retract. Figure 5 This allows the distance from the wheels to the vehicle body to vary independently at different ends and / or different corners of the vehicle 100.

[0088] The above example relates to a hydraulic actuator 502, and in other embodiments, the actuator may be an electromagnetic actuator or a pneumatic actuator, etc.

[0089] exist Figure 5In, but not necessarily in all, examples, spring 504 includes an active spring, such as a pneumatic spring, capable of controlling ride height. Control system 300 can be configured to pump gas (e.g., air) into or out of pneumatic spring 504 to control ride height. The air conditioning function of control system 300 attempts to maintain a set ride height regardless of vehicle load, and achieves this by changing the air volume and thus the air pressure.

[0090] Energy can be added to or removed from the pneumatic spring 504 to increase or decrease its volume. Increasing the volume can lift the vehicle body 102 along the z-axis. Figure 5 This allows the distance from the wheels to the vehicle body to vary independently at different ends and / or different corners of the vehicle 100.

[0091] Alternatively or alternatively, spring 504 may include a passive spring (e.g., a coil spring) or may be omitted entirely.

[0092] Control of the active suspension system 104 relies on one or more sensors. For example, wheel travel can be sensed by a wheel-to-body displacement sensor 514 (a sensor based on suspension displacement). The wheel-to-body displacement sensor 514 is positioned somewhere on the active suspension and can sense the position of the wheel along an arc defined by the suspension geometry. An example of the wheel-to-body displacement sensor 514 is a rotary potentiometer attached to a lever, wherein one end of the lever is connected to the vehicle body 102 and the other end is connected to a suspension link.

[0093] In some examples, the control system 300 determines wheel travel and / or its associated derivatives more accurately by fusing information from wheel-to-body displacement sensors 514 with information from wheel hub accelerometers.

[0094] The pressure in the pneumatic spring 504 can be sensed to indicate the weight on the wheel.

[0095] In at least some examples, the control system 300 is configured to control the active suspension system 104 by sending force requests to the active suspension or its lower-level controller. The force request can be an arbitrated force request based on requests from various requesters and information from various sensors.

[0096] Figure 5 The illustration shows additional optional features that can interact with the control system 300 to request influence calculations. These additional optional features include one or more of the following:

[0097] - Wheel speed sensor 512 for each wheel. In the example implementation, wheel speed sensor 512 is part of the anti-lock braking system (ABS).

[0098] - An accelerometer 516 mounted on the hub for each wheel, which is connected to the unsprung mass of the vehicle 100.

[0099] Human-Machine Interface (HMI) 520. The HMI 520 refers to any of the various input devices and input / output devices available to the driver, such as touch screens, displays, hardware switches / sliders / selectors, etc.

[0100] - At least one vehicle body accelerometer 522, said at least one vehicle body accelerometer 522 being coupled to the vehicle body 102 (sprung mass). Specific examples include a 3DOF inertial measurement unit (IMU) or a 6DOF inertial measurement unit (IMU). The unit may include an accelerometer or a set of multi-axis accelerometers.

[0101] - Tire pressure monitoring system (TPMS) 524, which includes a tire pressure monitor for each wheel.

[0102] Figures 6A to 8 The diagram illustrates an example implementation for traction force estimation:

[0103] - Figures 6A to 7E The illustration shows an example of an estimation function that determines relative traction levels—for example, which wheel (corner / contact surface) has the greatest grip (traction). The estimation function controls the active suspension system to change the normal force (e.g., pulsation / oscillation) and measures the effect of that change on traction indicators, such as wheel speed (spinning).

[0104] - Figure 8 The example control method is illustrated.

[0105] First, the estimation function is described with reference to various implementation methods. Figures 6A to 7E An example of an estimation function is provided, which obtains information indicating relative traction levels by modifying the weight balance of vehicle 100, enabling the identification of one or more wheels with the highest traction. This estimation function includes:

[0106] - Control the active suspension system 104 to change the normal force through one or more wheels of the first subgroup (e.g., oscillator extension and retraction).

[0107] - Determine the traction-related variables (e.g., wheel speed or a derived variable of wheel speed) at each wheel in the first subgroup of wheels when a known torque (e.g., a measured constant torque request or variable torque request) is applied while the normal force is changed.

[0108] - Controlling the active suspension system 104 to alter the normal force through one or more wheels of the second subgroup (e.g., oscillator extension and retraction); and

[0109] - Determine the traction-related variables (e.g., wheel speed or a derivative of wheel speed) at each wheel in the second subgroup of wheels when a known torque (e.g., a measured constant torque request or variable torque request) is applied while the normal force is changed.

[0110] The control system 300 can then assess the effect of a known change in normal force (a known actuator force request / torque request) on wheel speed or a derived variable of wheel speed. If the change in normal force causes the wheel to slip at a different speed, or causes a change in wheel acceleration, or causes a transition between slippage and non-slippage (disruption of traction or regain of traction), the wheel speed will change relative to the speeds of other wheels in a manner that indicates the available traction of that wheel.

[0111] If the vehicle 100 includes an active differential, the control system 300 can at least partially unlock the active differential during the measurement of traction-related variables, and then return the active differential to its previous relatively locked state.

[0112] If the vehicle 100 includes hub motors in which a single motor drives each wheel, the control system 300 can apply a constant torque to each motor during the measurement of traction-related variables.

[0113] Knowing the exact traction force is not always necessary if the relative traction force levels of different wheels are determinable. For example, control system 300 can rank wheel traction force levels between best and worst based on the degree to which traction-related variables are affected. Methods include, but are not limited to, comparing the average wheel speed, maximum wheel speed, or rate of change of maximum wheel speed for each wheel. The parameter of interest can indicate the speed difference on each axle.

[0114] There are multiple ways to modify the normal force to estimate the relative traction force. These modifications can include:

[0115] - The steady state is reduced by lifting the wheels toward the vehicle body 102;

[0116] - Increase stability by pushing the wheels away from the vehicle body 102; or

[0117] - Oscillates (pulses) between decreasing and increasing, such as Figures 6A to 7E As shown in the figure, it will now be described.

[0118] Figures 6A to 6C The illustration shows a first example of actuator-based traction force estimation. Figure 6A , Figure 6B These are schematic diagrams of the vehicle wheels FL, FR, RL, RR and the vehicle body 102 at different times.

[0119] In this example, actuator 502 is controlled to cause the wheels of the first subgroup (first pair) at opposite corners on the first diagonal of vehicle 100 to pulsate vertically in a first phase, and to cause the wheels of the second subgroup (second pair) at opposite corners on the second diagonal of vehicle 100 to pulsate vertically in a second phase, in which case the second phase is approximately 180 degrees out of phase. Thus, one wheel is lifted / pulled (weight reduction / unloading), while the other wheel is pushed (weight increase / loading).

[0120] When vertical pulsation occurs, traction-related variables are measured while a known torque is applied. The "known torque" is known to the control system 300. The known torque can be based on a torque requested by the driver or a torque requested automatically. The torque can be expressed as a torque request, force request, pedal position, etc. If the torque is variable, the control system 300 can receive an indication of a torque request to ensure that the estimation of traction-related parameters compensates for any differences in the torque request when estimating the traction-related variables for each wheel. If the torque is fixed during the estimation period, the control system itself can request a predetermined or arbitrary value for the torque request, known to be maintained at that predetermined or arbitrary value throughout the estimation period.

[0121] Figure 6A The diagram illustrates the state of the wheels at the first moment t1, where the right front wheel FR and the left rear wheel FL are pulled upward as a diagonal pair, while the left front wheel FL and the right rear wheel RR are pushed downward as a diagonal pair.

[0122] Figure 6B The diagram illustrates the state of the wheels at time t2, where the right front wheel FR and the left rear wheel FL are pushed downwards as a diagonal pair, while the left front wheel FL and the right rear wheel RR are pulled upwards as a diagonal pair.

[0123] In some, but not necessarily all, examples, the smoothness of the pattern approximates a sine wave, such as... Figure 6C The amplitude (A) versus time (t) curve is shown in the figure. In other examples, the waveforms are different or are discontinuous pulse sequences.

[0124] In some examples, the pattern has a predetermined frequency. Figure 6C The diagram shows that one diagonal pair of wheels FR, RL pulses at a first frequency f(FR, RL), and the other diagonal pair of wheels pulses at approximately the same frequency f(FL, RR). However, it should be understood that these frequencies do not necessarily need to match.

[0125] Figure 6C It is also shown that the waveforms are 180 degrees out of phase, so one pair of wheels is under maximum load / load while the other pair is under maximum unload / reduction. It should be understood that although the force is altered by actuator 502, it is still desirable to maintain tire contact with the ground at all corners in many situations. Therefore, the displacement change from wheel to vehicle body can be relatively small, which is advantageous because it tends not to cause uncomfortable disturbances during vehicle movement or damage to the ground surface on which the vehicle travels.

[0126] In the example, the frequency during the estimation period (the first frequency) is at least about 0.25 Hz. This frequency may not exceed about 15 Hz.

[0127] Appropriate oscillation amplitude is another parameter that can be controlled. At least if the vehicle 100 is moving, the frequency and amplitude can be controlled outside the range that would cause wheel hopping. Therefore, the wheels maintain continuous contact with the ground.

[0128] The selection of diagonal pairs, together with a 180-degree phase offset, helps to keep the vehicle body stable during estimation, thereby minimizing the roll or pitch of the vehicle body.

[0129] The estimation may include measuring wheel slippage (based on relative wheel speed) to determine which diagonal pair has the greatest overall traction. The estimation may also include measuring the relative wheel speed within each diagonal pair to identify the wheel with optimal traction. The estimation may identify the wheel or subgroup of wheels with optimal traction.

[0130] This estimation can be repeated for each oscillation / pulse cycle. More than one pulsation increases the confidence level, for example, increasing the confidence level of average wheel slip / average peak wheel slip. The pulsation ends after the desired number of pulsation cycles.

[0131] Figures 6A to 6C An alternative implementation is to push the wheels of the first diagonal pair downwards without pulling the other pair upwards, and then push the other pair of wheels downwards without pushing the first pair upwards. In other words, the estimation is performed sequentially, not simultaneously.

[0132] In another embodiment, the lateral wheels FL and FR at opposite lateral sides of vehicle 100 pulsate sequentially or simultaneously in a 180-degree out-of-phase manner, while the wheels RL and RR at the other longitudinal end of vehicle 100 do not pulsate. In another embodiment, for example, if vehicle 100 is configured for rear-wheel drive, the rear wheels RL and RR pulsate, while the front wheels FL and FR do not. The opposite applies to a front-wheel drive arrangement. In this two-wheel drive arrangement, the speed of the non-driven wheels of vehicle 100 can be measured to provide an accurate indication of the vehicle's speed on the ground. In another embodiment, vehicle 100 rolls left or right or pitches up or down by changing the normal force at the wheels simultaneously or in an out-of-phase oscillation / pulsation mode. The illustrated diagonal pattern is most advantageous for vehicle body stability.

[0133] Figures 7A to 7E The illustration shows another estimated implementation in which the individual wheels pulsate around the vehicle clockwise or counterclockwise in a universal joint pattern or sequentially.

[0134] exist Figure 7A At time t1, the first wheel FR pulses in the first phase, wherein the first wheel is located at the first lateral side (right side) of the vehicle 100 and at the first longitudinal end (front) of the vehicle 100.

[0135] exist Figure 7B At time t2, the second wheel FL pulses at a second phase that is behind the first phase, wherein the second wheel is located at the second lateral side (left side) of the vehicle 100 and at the first longitudinal end (front).

[0136] exist Figure 7C At time t3, the third wheel RL pulses at a third phase that is behind the second phase, wherein the third wheel is located at the second lateral side (left side) and the second longitudinal end (rear) of the vehicle 100.

[0137] exist Figure 7D At time t4, the fourth wheel RR pulses at a fourth phase that is behind the third phase, wherein the fourth wheel is located at the first lateral side (right side) and at the second longitudinal end (rear).

[0138] like Figure 7E As shown, the first to fourth phases can lag behind each other by approximately 90 degrees to provide a uniformly rotating variation of the contact surface force around the vehicle. The frequencies f(FR), f(FL), f(RL), and f(RR) can be one or more frequencies that are approximately the same as each other.

[0139] Universal joint motion helps maintain the stability of the vehicle body, ensuring that the vehicle body movement is neither purely roll nor purely pitch.

[0140] In an alternative implementation, the wheels pulse / displace sequentially, rather than simultaneously in out-of-phase manner. That is, the next wheel can pulse / displace after the previous wheel has returned to its normal target position or target normal force.

[0141] The universal joint mode enables wheel slip estimation for each pulsating wheel and obtains the relative traction level.

[0142] Once the estimation is complete, the implementation phase begins, in which the control system 300 triggers mitigation actions to help the vehicle 100 maintain traction or disengage from the jam. (See below for further details.) Figure 8 Operation 912 provides an example of the implementation phase.

[0143] Figure 8 This is a flowchart illustrating an example control method 900 for traction force estimation implemented by control system 300.

[0144] Method 900 begins at operation 902, in which method 900 is enabled. Enabling method 900 may optionally require disabling one or more suppression conditions based on one or more of the following:

[0145] - Vehicle speed. For example, method 900 may not be enabled when vehicle 100 is traveling faster than a threshold speed, which has a value between approximately 5 m / s and approximately 15 m / s. In some examples, method 900 may be available during an attempt to pull the vehicle away from a stationary state.

[0146] - Vehicle stability system intervention and suppression conditions.

[0147] - Enable / disable settings that can be manually configured via HMI 520.

[0148] - Fault signals or suppression signals from the controller of the active suspension system 104, such as those indicating fault conditions or excessive temperature.

[0149] - The following is the ground information.

[0150] The hybrid function associated with the speed-based suppression condition allows the magnitude of the force request to the active suspension system 104 to increase as vehicle speed decreases and decrease as vehicle speed increases, thus avoiding obvious bi-state behavior. The hybrid function can have a threshold speed as an upper limit and can also have a lower limit speed below which method 900 is fully enabled. In the example, the lower limit is 1 to 10 meters per second slower than the upper limit.

[0151] The ground information data block is checked 904 based on an example suppression condition based on ground information. Ground information may include a selected terrain mode and / or information from one or more sensors in data block 910. Terrain modes are defined at the end of the specification. In the example, method 900 may determine whether vehicle 100 is in a first terrain mode or a second terrain mode. If vehicle 100 is in the first terrain mode, method 900 does not proceed. If vehicle 100 is in the second terrain mode, method 900 continues. In one implementation, the first terrain mode is a road mode, and the second terrain mode is an off-road mode.

[0152] At operation 906, a trigger condition is met to initiate the estimation phase. In this example, the trigger condition is based on receiving an indication of traction loss from vehicle 100, such as wheel slippage exceeding a threshold and / or vehicle speed deviating from a setpoint. The traction loss may be global or may be limited to one or more individual wheels.

[0153] Alternatively or concurrently, the triggering condition may require determining the deviation of the vehicle's forward movement from the expected forward movement. Determining the deviation from the expected forward movement may include receiving feedback indicating the expected forward movement. If the vehicle is being manually driven, this feedback may indicate the magnitude and / or rate of change of the driver-requested braking relative to a threshold, and / or the magnitude and / or rate of change of the driver-requested torque relative to a threshold. This is because excessive use of the brakes / accelerator by the driver can indicate dissatisfaction with the current rate of forward movement. If the vehicle is being driven autonomously, this feedback may indicate the deviation of the vehicle speed from the speed setpoint.

[0154] The above example is reactive. In some examples, a pre-emptive check can be performed in addition to or instead of a reactive trigger. Example pre-emptive checks involve evaluating ground information from one or more sensors configured to detect deformable / granular ground, such as radar sensors, lidar sensors, ultrasonic sensors, or visible light cameras.

[0155] In some examples, the triggering of the estimation phase depends on the driver's intention. Triggering conditions may also require indications of anticipated vehicle motion (e.g., a torque request exceeding a threshold and / or an appropriate speed setpoint).

[0156] At operation 908, an estimation phase is performed, for example by estimating the relative traction level while changing the normal force passing through the wheel. In the example implementation, the control system 300 starts with an initial approximation based on wheel slippage estimation, and then proceeds as per... Figures 6A to 7E The wheel is pulsed as described to provide additional confidence.

[0157] At operation 908, the characteristics (amplitude / frequency) of the pulsation pattern used for the estimation stage are first determined.

[0158] In the example, global and local characteristics of the pulsation pattern are determined. The global characteristics govern the common amplitude and frequency targets for all wheels. The local characteristics modify the force request for individual corners to compensate for differences in suspension characteristics.

[0159] When calculating the local features used for each corner, various differences between these corners can be taken into account. The suspension at each corner has a natural frequency, which depends on the stiffness of deformable elements such as actuator 502, springs, and tires, and also on the sprung mass on the wheels, which varies between these corners. While the differences from left to right may be small, there may be differences from front to rear. The rear suspension can have a higher frequency than the front suspension to improve vehicle stability at speeds.

[0160] Therefore, the force request for each corner may need to be a force request frequency that does not necessarily match the inherent frequency of each corner, in order to ensure that the pulsation frequency generated from the perspective of the wheel is the same at different corners of the vehicle 100.

[0161] Therefore, one or more variables can be taken into account when determining the force request for each corner (each actuator 502).

[0162] First, the sprung mass at a given corner can be estimated. One method for estimating the sprung mass is to measure the steady-state pneumatic / hydraulic pressure in the actuator 502 or spring 504, which is a function of weight.

[0163] Secondly, since wheel speed can be affected by ride height, ride height-related parameters can be taken into account. In this example, ride height-related parameters include the requested ride height or the measured ride height (e.g., measured by the wheel-to-vehicle displacement sensor 514).

[0164] Third, tire pressure monitoring data from the TMPS 524 can be used to account for any deflation of the tires and the resulting reduction in their inherent frequency. This is useful when the driver has already released some air from their tires to aid driving. Tire pressure indications for each tire can be received by the control system 300. The tire pressure acquisition function can compensate for differences in tire pressure between different tires to ensure that the resulting waveform is as... Figure 6C or Figure 7E As shown in the image.

[0165] Once the estimation phase is complete, the implementation phase is performed at operation 912 based on traction-related variables. In this example, step 912 involves control of the vehicle subsystem based on the relative traction level. Estimation and implementation may not occur simultaneously.

[0166] The implementation phase may include controlling at least one of the following parameters as a mitigation action: controlling the torque supplied to the wheels; controlling the friction braking supplied to the wheels; controlling the active suspension spring stiffness; controlling the active suspension damping rate; controlling the regenerative braking setting; controlling the steering of the steerable wheels; or controlling the selection of the terrain mode.

[0167] Knowing the relative traction level has the advantage that mitigation actions can include localized control of parameters, that is, individual control of parameters for one or more wheels in each subgroup. An example is provided below.

[0168] It should be understood that some mitigation actions may include global control of parameters, including routine parameter changes for all wheels. Global mitigation actions may depend on global traction-related parameters calculated based on variables related to the traction of each wheel. Global traction-related parameters may include, for example, the slip index. Some mitigation actions may control both global and local parameters.

[0169] Pulsating / Slowed Wheel Rotation: In some examples, controlling the local or global mitigation of torque supplied to the wheels may include controlling at least one torque source 103 to rotate at least one wheel of the vehicle at a predetermined speed and / or a predetermined rate of change based on parameters related to the relative traction level and / or global traction. If the vehicle 100 has multiple torque sources coupled to different wheels and / or has an active differential, the wheel speed / rate can be controlled individually. An example implementation is to pulsate and / or slow down the wheel rotation. Slowing down the rotation compacts loose material under the wheel, rather than dispersing it in front of or behind the wheel. The wheel speed can be maintained within a target recovery speed range, such as vehicle speeds corresponding to ≤ 1 km / h or ≤ 5 km / h. This pulsating / slowed wheel rotation may be performed for a specific surface, such as sand (e.g., a sand terrain pattern) rather than other surfaces—e.g., depending on surface information.

[0170] Torque redistribution: In some examples, the local mitigation action controlling the torque supplied to the wheels can be individually controlled based on the relative traction levels to alter the torque distribution to the individual subgroups of wheels. The mitigation action can reduce the torque supplied to one or more wheels estimated to have low traction, or increase the torque supplied to one or more other wheels estimated to have high traction, or in combination, simultaneously reduce the torque supplied to one or more wheels estimated to have low traction and increase the torque supplied to one or more other other wheels estimated to have high traction. Torque redistribution can be achieved if vehicle 100 has multiple torque sources coupled to different wheels and / or has an active differential. Otherwise, friction brakes can be controlled to provide the same effect (described later).

[0171] Global torque variation: In some examples, the global mitigation action that controls the torque supplied to all driven wheels may include reducing the net torque request applied to all driven wheels based on parameters related to global traction, in order to reduce wheel slippage on all driven wheels.

[0172] Throttle mapping: In some examples, controlling the global mitigation action of the torque supplied to all driven wheels may include controlling throttle mapping (throttle position mapping) based on parameters related to global traction. Controlling throttle mapping may include changing a function that associates the position of the accelerator (e.g., accelerator pedal) with the output driver torque request. This change can aid traction by requiring additional accelerator travel within a range of accelerator position values ​​to achieve the same output driver torque request. This gives the driver more control.

[0173] Throttle Response: In some examples, controlling the global mitigation of torque supplied to all driven wheels may include controlling the throttle response (accelerator response) based on parameters related to global traction. Controlling the throttle response may include changing the value of a torque rate limiter. If the rate of change of torque request exceeds a predetermined rate limit, the torque rate limiter may reduce the value of the torque request to reduce or eliminate the exceedance of the predetermined rate limit. This change can aid traction by reducing throttle responsiveness, for example, by reducing the value of the predetermined rate limit.

[0174] Gear shifting: In some examples, controlling the global mitigation action of torque supplied to all driven wheels may include controlling gear shifting based on parameters related to global traction. Controlling gear shifting may include changing the shift mapping. The shift mapping determines one or more shift points for changing gears in the transmission based on vehicle speed and torque supplied to the wheels. Changing the shift mapping may include raising / lowering one or more shift points to aid traction. In some examples, the shift point may be modified to hold a higher gear (lower gear reduction from the torque source to the wheels) for a longer period to reduce wheel torque. In some examples, the shift point may be modified to hold the current gear for a longer period to maintain continuous torque delivery, such as preventing downward tilting during gear shifting. Requesting a gear change may include requesting a transmission gear that provides lower gear reduction from the torque source to the wheels.

[0175] Friction braking: In some examples, controlling the local or global relief of friction braking may include controlling friction braking at one or more wheels via a set of friction brakes (e.g., disc brakes). This method of controlling friction braking can provide the effects of pulsating / slowed wheel rotation as described above and / or torque redistribution as described above. Friction braking and the torque supplied to the wheels can be controlled simultaneously, or friction braking can be controlled instead of controlling the torque supplied to the wheels.

[0176] In some examples, anti-lock braking system parameters can be modified for wheels with low traction relative to wheels with high traction.

[0177] In some examples, a wheel with traction below a threshold can be fully braked and prevented from rotating, allowing maximum torque to be transferred via the differential to the other wheel with high traction.

[0178] Regenerative braking: Alternatively or alternatively, regenerative braking settings, such as the regenerative braking amplitude, can be controlled to at least partially achieve the same objective as controlling friction braking.

[0179] Spring stiffness: In some examples, local or global relief actions controlling the spring stiffness of the active suspension may include controlling the actuator 502 and / or spring 504 of the active suspension system 104 to modify the spring stiffness. Regarding the actuator 502, the relief action may, for example, alter the relationship between the sensed wheel travel and the force request of the active suspension system by changing the gain parameter.

[0180] Localized Spring Stiffness Changes: Spring stiffness can be changed in different ways for different wheels. For example, relief actions can be based on the relative traction level by increasing / decreasing the spring stiffness at one or more wheels in a subgroup of wheels estimated to have low traction, or by decreasing / increasing the spring stiffness at one or more wheels in a subgroup of wheels estimated to have high traction, or by simultaneously increasing / decreasing the spring stiffness at one or more wheels in a subgroup of wheels estimated to have low traction and decreasing / increasing the spring stiffness at one or more wheels in a subgroup of wheels estimated to have high traction, all in combination. Traction feedback (e.g., measured wheel slippage) can indicate whether increasing or decreasing spring stiffness improves traction.

[0181] Changes in global spring stiffness: In some examples, the relief action of controlling the spring stiffness of the active suspension may include: the spring stiffness is changed globally based on parameters related to global traction, that is, it is changed together for all wheels.

[0182] Damping ratio: In some examples, local or global mitigation actions controlling the damping ratio of the active suspension may include controlling the actuator 502 of the active suspension system 104 to modify the damping ratio. Mitigation actions may, for example, alter the relationship between the sensed wheel speed and the force request of the active suspension system 104 by setting gain parameters.

[0183] Changes in local damping ratio: The damping ratio can be changed in different ways for different wheels. For example, mitigation actions can be based on the relative traction level by increasing / decreasing the damping ratio at one or more wheels in a subgroup of wheels estimated to have low traction, or by decreasing / increasing the damping ratio at one or more wheels in a subgroup of wheels estimated to have high traction, or by simultaneously increasing / decreasing the damping ratio at one or more wheels in a subgroup of wheels estimated to have low traction and decreasing / increasing the damping ratio at one or more wheels in a subgroup of wheels estimated to have high traction, all based on the relative traction level. Traction feedback (e.g., measured wheel slippage) can indicate whether increasing or decreasing the damping ratio helps traction.

[0184] Changes in global damping ratio: In some examples, the mitigation action of controlling the damping ratio of an active suspension may include: the damping ratio being changed globally based on parameters related to global traction, i.e., changed together for all wheels.

[0185] Steering: In some examples, global mitigation actions controlling steering may include changing the steering angle at one or more steerable wheels based on parameters related to global traction. This applies when vehicle 100 is moving forward, where the front wheels are steerable wheels, or if the vehicle is equipped with all-wheel steering where each wheel is steerable, this applies when the vehicle is moving in either direction. Changing the steering angle may include sawing the steering angle from left to right to help the wheels find traction. Electronic power steering systems (EPAS) have associated actuators for performing this operation.

[0186] For specific terrain surfaces, such as non-grass surfaces—for example, depending on ground information—steering angle changes can be enabled. Steering angle changes can be disabled in terrain modes optimized for grass (such as Grass-Gravel-Snow mode, GGS), where such sawing of the steering wheels can lead to excessive interference with the primary ground surface, resulting in unwanted path erosion and ultimately reduced grip for subsequent vehicle traffic.

[0187] Local terrain mode selection: In some examples, controlling local mitigation actions for terrain modes may include selecting a terrain mode individually for one or more wheels in each individual subgroup. Each subgroup of wheels can then receive its own set of parameters (e.g., torque / braking / suspension / steering).

[0188] Global Terrain Mode Selection: In some examples, controlling the global mitigation action of the terrain mode may include selecting a terrain mode that is more suitable for heterogeneous terrain compared to the currently selected terrain mode. Heterogeneous terrain refers to terrain with significantly different ground friction under each wheel. Certain types of terrain modes may be better suited to heterogeneous surfaces, even if these terrain modes are not labeled as the correct terrain modes for the actual terrain. For example, the torque / braking / suspension / steering parameters of some terrain modes may be suitable for heterogeneous surfaces.

[0189] The implementation phase described in the example above can continue until the exit condition is met. The example exit condition can be based on the same sensed information as the trigger condition: no longer receiving an indication of traction loss from vehicle 100 or the indication falling below a threshold. As long as vehicle 100 continues moving forward in the predetermined direction, another estimation phase is not required.

[0190] In some examples, the exit condition may include determining that the vehicle has stopped or is being braked.

[0191] When the exit condition is met, method 900 can loop back to before operation 906.

[0192] For the purposes of this disclosure, it should be understood that the one or more controllers described herein may each include a control unit or computing device having one or more electronic processors. A vehicle and / or its systems may include a single control unit or electronic controller, or alternatively, different functions of one or more controllers may be implemented in or hosted in different control units or controllers. A set of instructions may be provided that, when executed, cause the one or more controllers or one or more control units to implement the control techniques (including the described methods) described herein. This set of instructions may be embedded in one or more electronic processors, or alternatively, the set of instructions may be provided as software to be executed by one or more electronic processors. For example, a first controller may be implemented as software running on one or more electronic processors, and one or more other controllers may also be implemented as software running on one or more electronic processors, optionally the same one or more processors as the first controller. However, it will be understood that other arrangements are also useful, and therefore, this disclosure is not intended to be limited to any particular arrangement. In any case, the aforementioned set of instructions can be embedded in a computer-readable storage medium (e.g., a non-transitory computer-readable storage medium), which may include any mechanism for storing information in a form readable by a machine or electronic processor / computing device, including but not limited to: magnetic storage media (e.g., floppy disks); optical storage media (e.g., CD-ROMs); magneto-optical storage media; read-only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROMs and EEPROMs); flash memory; or electrical media or other types of media for storing such information / instructions.

[0193] Terrain modes are defined. Different terrain modes control one or more vehicle subsystems based on different configuration sets. A terrain mode typically refers to a vehicle mode optimized for driving on a specific driving surface. An example of a terrain mode is an off-road terrain mode configured to optimize vehicle 100 for driving on off-road terrain, such as areas traversing grass, gravel, sand, mud, or even climbing rocks. Another example of a terrain mode is a ground vehicle optimization mode configured to optimize vehicle 100 for driving on low-friction surfaces, such as snow or ice-covered surfaces—whether on or off roads. Vehicle 100 may include a basic road mode and / or a basic ground vehicle optimization mode for regular surfaces, and may include multiple terrain modes for various surfaces and / or terrains.

[0194] Terrain modes and / or detection of specific terrain types can configure one or more ground traction-related settings, such as differential locking settings and / or traction control settings. Additionally or alternatively, other settings can be adjusted, such as: suspension settings; ride height settings; suspension damper settings; throttle response settings; shift point settings; locking / lockable differential settings; vehicle braking settings or traction control settings; torque distribution settings; torque shaping settings; or steering weight settings. These configurations can be preset or reconfigurable.

[0195] Manual user selection may include using a human-machine interface input device 520. In some examples, the terrain mode may be automatically changeable.

[0196] An example HMI 520 is a terrain pattern selector. In some implementations, the terrain pattern selector can be configured to allow a user to provide ground information by selecting one terrain pattern from a plurality of terrain patterns, said plurality of terrain patterns including at least some of the following: sand pattern; climbing pattern; grass-gravel-snow pattern; mud and ruts pattern; and normal pattern (basic pattern).

[0197] In some implementations, the terrain mode selector may be configured to allow a user to select an "automatic" mode or an "automatic" mode, in which the vehicle 100, for example at the control system 300, determines the most suitable terrain mode at a given time. This is achieved by obtaining ground information from one or more sensors, which includes at least some of the following: rolling resistance; terrain roughness; inclination; wheel slippage; wheel articulation; vehicle yaw. Suitable sensors include IMU / accelerometers 522, 516, wheel speed sensors 512, etc.

[0198] It will be understood that various changes and modifications can be made to the invention without departing from the scope of this application.

[0199] Figure 8 The boxes in the illustrations may represent steps in the method and / or code segments in computer program 308. The illustration of a specific order of boxes does not necessarily imply a required or preferred order for the boxes, and the order and arrangement of the boxes may be changed. Furthermore, some steps may be omitted.

[0200] Although embodiments of the invention have been described with reference to various examples in the preceding paragraphs, it should be understood that modifications may be made to the given examples without departing from the scope of the claimed invention.

[0201] The features described above may be used in combinations other than those explicitly described.

[0202] Although the functions have been described with reference to certain features, those functions can be performed by other features regardless of whether they are described or not.

[0203] Although the features have been described with reference to certain embodiments, those features may exist in other embodiments, whether or not they are described.

[0204] Although the foregoing description has been dedicated to focusing on those features of the invention that are considered particularly important, it should be understood that the applicant reserves the right to claim protection for any patentable features or combinations of features referenced herein and / or illustrated in the accompanying drawings, whether or not they have been specifically emphasized.

Claims

1. A control system for controlling an active suspension system of a vehicle to determine a relative traction level, the control system comprising one or more controllers, wherein, The control system is configured to: The active suspension system is controlled to change the normal force passing through one or more wheels of the first subgroup; Determine the variables related to traction force at each wheel in the first subgroup of wheels to which a known torque is applied; The active suspension system is controlled to change the normal force passing through one or more wheels of the second subgroup; as well as Determine the variables related to the traction force at each wheel of the second subgroup of wheels to which a known torque is applied. The change includes reducing the normal force passing through the wheels. The traction-related variables include wheel speed and / or derived wheel speed variables, which indicate wheel slippage caused by a decrease in normal force. The traction-related variables also indicate the relative traction levels between best and worst. Specifically, within the first subgroup and the second subgroup, the subgroup with wheels exhibiting more slippage in response to the decrease in normal force was identified as having a worse traction level and thus was identified as having lower traction. The control system is configured to obtain an initial approximation of the relative traction level based on wheel speed measurements of the wheels of the first subgroup and the second subgroup before changing the normal force passing through the wheels of the first subgroup and the second subgroup. The traction force-related variables determined during the change of normal force improve the initial approximation.

2. The control system according to claim 1, wherein, The first subgroup of wheels includes a first pair of wheels located at opposite corners on a first diagonal of the vehicle, and the second subgroup of wheels includes a second pair of wheels located at opposite corners on a second diagonal of the vehicle.

3. The control system of claim 2, wherein the control system is configured to determine the traction-related variables when the normal force of the wheels passing through the first subgroup is repeatedly pulsed in a first phase and the normal force of the wheels passing through the second subgroup is repeatedly pulsed in a second phase.

4. The control system according to claim 3, wherein, The second phase is offset by 180 degrees relative to the first phase.

5. The control system according to claim 1, wherein, The first subgroup is the first wheel at the first corner of the vehicle, and the second subgroup is the second wheel at the adjacent second corner of the vehicle.

6. The control system according to claim 5, wherein, The first corner is located at the first lateral side of the vehicle and at the first longitudinal end of the vehicle, and the second corner is located at the second lateral side of the vehicle and at the first longitudinal end of the vehicle.

7. The control system according to claim 6, wherein the control system is configured to: The active suspension system is controlled to change the normal force passing through a third wheel located at the second lateral side of the vehicle and at the second longitudinal end. Determine the variables related to the traction force at the third wheel to which a known torque is applied; The active suspension system is controlled to alter the normal force passing through the fourth wheel, wherein the fourth wheel is located at the first lateral side and at the second longitudinal end; and Determine the variables related to the traction force at the fourth wheel where a known torque is applied. The traction-related variables at the first wheel, second wheel, third wheel, and fourth wheel indicate the relative traction levels among the first wheel, second wheel, third wheel, and fourth wheel.

8. The control system of claim 7, wherein the control system is configured to determine the traction-related variables when the normal force through the first wheel is repeatedly pulsed in a first phase, the normal force through the second wheel is repeatedly pulsed in a second phase, the normal force through the third wheel is repeatedly pulsed in a third phase, and the normal force through the fourth wheel is repeatedly pulsed in a fourth phase.

9. The control system according to claim 8, wherein, The second phase lags behind the first phase by 90 degrees, wherein the third phase lags behind the second phase by 90 degrees, and wherein the fourth phase lags behind the third phase by 90 degrees.

10. The control system according to any one of claims 1 to 9, which, based on the relative traction level, causes at least one of the following to occur: Control the torque supplied to the wheels; Control the friction braking at the wheels; Controlling the spring stiffness of the active suspension; Control the damping rate of the active suspension; Control regenerative braking settings; Control the steering at the steerable wheels; or Control the selection of terrain patterns.

11. An active suspension system comprising a control system according to any one of claims 1 to 10.

12. A vehicle comprising a control system according to any one of claims 1 to 10 or an active suspension system according to claim 11.

13. A method for controlling an active suspension system of a vehicle to determine a relative traction level, the method comprising: The active suspension system is controlled to change the normal force passing through one or more wheels of the first subgroup; Determine the variables related to traction force at each wheel in the first subgroup of wheels to which a known torque is applied; The active suspension system is controlled to change the normal force passing through one or more wheels of the second subgroup; as well as Determine the variables related to the traction force at each wheel of the second subgroup of wheels to which a known torque is applied. The change includes reducing the normal force passing through the wheels. The traction-related variables include wheel speed and / or derived wheel speed variables, which indicate wheel slippage caused by a decrease in normal force. The traction-related variables also indicate the relative traction levels between best and worst. Specifically, within the first subgroup and the second subgroup, the subgroup with wheels exhibiting more slippage in response to the decrease in normal force was identified as having a worse traction level and thus was identified as having lower traction. The method includes obtaining an initial approximation of the relative traction level based on wheel speed measurements of the wheels of the first subgroup and the second subgroup before changing the normal force passing through the wheels of the first subgroup and the second subgroup. The traction force-related variables determined during the change of normal force improve the initial approximation.

14. A non-transitory computer-readable medium comprising computer-readable instructions configured, when executed by a processor, to perform the method of claim 13.

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