阅读说明：本技术 用于优化车辆的制动和加速的经由主动悬架进行的滑移控制 (Slip control via active suspension for optimizing braking and acceleration of a vehicle ) 是由 阿迪蒂亚·钱德拉谢卡尔·切蒂 艾伦·纯-浩·陈 于 2020-01-03 设计创作，主要内容包括：用于通过增大车辆车轮的轮胎与路面之间的摩擦力的大小来提高制动效率的系统和方法。制动效率可以基于车轮的滑移率通过使用主动悬架致动器控制施加在车轮上的法向力来提高。(Systems and methods for improving braking efficiency by increasing the amount of friction between a tire of a vehicle wheel and a road surface. Braking efficiency may be improved by controlling the normal force exerted on the wheel using active suspension actuators based on the slip rate of the wheel.)

1. A method for controlling an active suspension system of a vehicle, wherein the active suspension system comprises an actuator, and wherein the vehicle comprises a wheel, the method comprising:

(a) determining (e.g., by a controller, by a set of one or more controllers) (e.g., during a braking event) a slip rate (e.g., during a braking event) of a wheel of the vehicle;

(b) determining (e.g., by a controller, by the set of one or more controllers) a command (e.g., command force, command pressure, command voltage, command current) based at least in part on the determined slip rate;

(c) outputting the command (e.g., from the controller, from the set of one or more controllers) to the actuator of the active suspension system.

2. The method of claim 1, further comprising:

(d) generating an output force by the actuator of the active suspension system in response to the command received by the actuator.

3. The method of claim 2, wherein generating the output force by the actuator comprises:

applying, by the actuator, the output force (e.g., during a braking event) to a first portion of the vehicle (e.g., wherein the first portion of the vehicle is one of a wheel assembly including the wheel, a portion of a body (e.g., a corner)).

4. The method of claim 2, wherein (a) comprises:

detecting an angular velocity of the wheel of the vehicle (e.g., using a wheel velocity sensor);

estimating an operating speed of the vehicle (e.g., using one or more of a positioning sensor (e.g., global positioning system), an inertial measurement device, a wheel speed sensor);

determining the slip rate of the wheel of the vehicle based at least in part on the sensed angular velocity and the sensed operating speed of the vehicle.

5. The method of any of the preceding claims, wherein the determined command is based at least in part on a product of the determined slip rate multiplied by a slip gain.

6. The method of claim 5, further comprising:

measuring one or more vehicle parameters (e.g., wherein the one or more vehicle parameters include at least one, at least two, or at least three of a fluid pressure of a brake cylinder of the vehicle or a rate of change of a fluid pressure of a brake cylinder of the vehicle, a position of an accelerator pedal or a rate of change of a position of the accelerator pedal, and/or a position of a brake pedal or a rate of change of a position of the brake pedal);

determining a value of the slip gain based at least in part on the one or more vehicle parameters.

7. The method of claim 6, wherein determining the value of the slip gain based at least in part on a set of vehicle parameters comprises: a lookup table is accessed that specifies a plurality of values of the slip gain as a function of a vehicle parameter (e.g., where the vehicle parameter belongs to a set of one or more vehicle parameters).

8. The method of any preceding claim, further comprising: an aspect of vertical motion of a second portion of the vehicle (e.g., a second corner of the vehicle) is measured, and wherein the command is determined based at least in part on the aspect of vertical motion.

9. The method of claim 8, wherein the aspect of the vertical motion is an acceleration of the second portion of the vehicle (e.g., in a vertical direction).

10. The method of claim 8, wherein the aspect of motion is a speed of the second portion of the vehicle (e.g., in a vertical direction).

11. The method of any of claims 8 to 10, wherein the first portion is the same as the second portion.

12. The method of any of claims 8 to 10, wherein the command is determined based at least in part on a product of an aspect of the motion multiplied by a second gain.

13. The method of claim 12, further comprising:

measuring one or more vehicle parameters (e.g., wherein the one or more vehicle parameters include at least one, at least two, or at least three of a fluid pressure of a brake cylinder of the vehicle or a rate of change of a fluid pressure of a brake cylinder of the vehicle, a position of an accelerator pedal or a rate of change of a position of the accelerator pedal, and/or a position of a brake pedal or a rate of change of a position of the brake pedal);

determining a value of the second gain based at least in part on the one or more vehicle parameters.

14. The method of claim 13, wherein determining the value of the second gain based at least in part on a set of vehicle parameters comprises: a lookup table is accessed that specifies a plurality of values of the second gain as a function of a vehicle parameter (e.g., where the vehicle parameter belongs to a set of one or more vehicle parameters).

15. A method according to any preceding claim, wherein application of the output force (e.g. to a first and/or second part of the vehicle) results in a reduction in the slip rate of the wheel.

16. A method for controlling an active suspension system of a vehicle having wheels, the method comprising:

applying a force to a portion of the vehicle (e.g., to a wheel assembly including the wheel, to a portion of a body (e.g., a corner)) via an actuator of the active suspension system associated with the wheel, wherein the applied force is determined (e.g., via a controller, via a set of controllers) based at least in part on an observed slip rate of the wheel.

17. A method for controlling an actuator of an active suspension system of a vehicle, the method comprising:

estimating a slip rate of a wheel of the vehicle at a given time;

comparing the estimated slip rate to a threshold slip rate;

applying a force to the wheel of the vehicle by an actuator of the active suspension system to increase a normal load applied to the wheel upon determining that the estimated slip rate exceeds the threshold slip rate.

18. The method of claim 17, wherein the threshold slip ratio exceeds a critical slip ratio.

19. The method of claim 17, wherein the threshold slip ratio is approximately equal to a critical slip ratio.

20. The method of claim 17, wherein applying the force to the wheel of the vehicle comprises extending the actuator.

21. The method of claim 17, wherein the force is applied to the wheel of the vehicle to reduce the slip rate of the wheel.

22. A method for controlling an active suspension system in a vehicle, the method comprising:

(a) applying a braking force to a wheel of a vehicle to retard rotation of the wheel while the vehicle is running, resulting in an increase in a slip rate of the wheel;

(b) subsequently applying a second force to a portion of the vehicle through an actuator of the active suspension system, wherein the application of the second force causes the slip rate of the wheel to decrease.

23. The method of claim 22, wherein applying the second force increases a normal load applied to the wheel.

24. The method of claim 22, further comprising:

(c) determining that the slip rate of the wheel of the vehicle exceeds a threshold, wherein (c) occurs after (a), and wherein (b) occurs in response to (c).

25. The method of claim 22, further comprising:

determining (e.g., by a controller, by a set of controllers) a slip rate of the wheel;

determining (e.g., by the controller, by the set of controllers) a command for the actuator based at least in part on the determined slip rate;

outputting the command (e.g., from the controller, the set of controllers) to the actuator;

in response to the command received by the actuator: applying the second force to a portion of the vehicle through the actuator.

26. A method for controlling an active suspension system of a vehicle having wheels, the method comprising:

(a) measuring (e.g., using an accelerometer) an aspect (e.g., acceleration, velocity, amplitude) of motion (e.g., vertical motion) of a first portion of the vehicle (e.g., a corner of a body of the vehicle);

(b) measuring one or more vehicle parameters (e.g., wherein the one or more vehicle parameters include at least one, at least two, at least three, or at least four of a rate of change of a fluid pressure of a brake cylinder of the vehicle or a brake cylinder of the vehicle, a rate of change of a position of an accelerator pedal or a position of the accelerator pedal, a rate of change of a position of a brake pedal or a position of the brake pedal, and/or a rate of change of a position of a steering wheel or a position of the steering wheel);

(c) determining a value of the gain based at least in part on a set of one or more vehicle parameters;

(d) determining (e.g., by one or more controllers) a command based at least in part on a product of the aspect of the motion times the gain;

(e) outputting the command (e.g., from one or more controllers) to an actuator of the active suspension system;

(f) in response to the command received by the actuator: applying, by the actuator of the active suspension system, an output force to a first portion of the vehicle (e.g., a wheel assembly including the wheel, a portion (e.g., a corner) of the body).

27. The method of claim 26, wherein determining the value of the gain based at least in part on a set of vehicle parameters comprises: accessing a lookup table that specifies a plurality of values of the gain as a function of the one or more vehicle parameters.

28. A vehicle, comprising:

a vehicle body;

a plurality of wheels including a first wheel associated with a first corner of the body and a second wheel associated with a second corner of the body;

an active suspension system, wherein the active suspension system comprises:

a first actuator configured to apply a first force to the first wheel in response to a first command from a first controller; and

a second actuator configured to apply a second force to the second wheel in response to a second command from a second controller;

a set of one or more controllers, wherein the set of one or more controllers includes the first controller, and wherein the set of one or more controllers is configured to:

determining a first slip rate of the first wheel of the vehicle;

determining a first command force based at least in part on the first slip ratio;

commanding the first actuator to apply the first command force to the first wheel.

29. The vehicle of claim 28, wherein the set of one or more controllers includes the second controller, and wherein the set of one or more controllers is further configured to:

determining a second slip rate of the second wheel of the vehicle;

determining a second command force based at least in part on the second slip rate;

commanding the second actuator to apply the second command force to the second wheel.

30. The vehicle of claim 28, wherein the set of one or more controllers is further configured to:

determining a vertical motion (e.g., bump/rebound) of the first corner of the body relative to the first wheel;

determining the first command force based at least in part on the determined vertical motion.

31. The vehicle of any of claims 28-30, wherein the first controller is the same as the second controller.

32. The vehicle of any of claims 28-30, wherein the first controller is different from the second controller.

Background

Braking of a moving vehicle typically relies on the frictional forces that exist between the road surface and one or more tires of the vehicle. The magnitude of these frictional forces, and therefore the distance and/or time required for a moving vehicle to stop, may be affected by the dynamic slip rate of each wheel of the vehicle. Advanced vehicle functions, such as, for example, anti-lock braking systems, have been utilized to optimally control slip rate during braking, thereby minimizing the distance and/or time required for a moving vehicle to stop.

Disclosure of Invention

Various systems and methods for controlling an active suspension system of a vehicle are disclosed. In one aspect, a method for controlling an active suspension system of a vehicle is disclosed, wherein the active suspension system comprises an actuator, and wherein the vehicle comprises a wheel. In certain embodiments, the method comprises: (a) determining (e.g., by a controller, by a set of one or more controllers) a slip rate of a wheel of a vehicle (e.g., during a braking event); (b) determining (e.g., by a controller, by a set of one or more controllers) a command (e.g., command force, command pressure, command voltage, command current) based at least in part on the determined slip rate; and (c) outputting commands to actuators of the active suspension system (e.g., from a controller, from a set of one or more controllers). In certain embodiments, the method further comprises: (d) an output force is generated by an actuator of the active suspension system in response to a command received by the actuator. In some embodiments, generating the output force by the actuator includes applying the output force (e.g., during a braking event) to a first portion of the vehicle by the actuator. In certain embodiments, the first portion of the vehicle may be a wheel assembly that includes a wheel and/or a portion of the body (e.g., a corner).

In some embodiments, determining the slip rate of the wheel comprises: detecting (e.g., using a wheel speed sensor) an angular speed of a wheel of the vehicle; estimating an operating speed of the vehicle (e.g., using one or more of a positioning sensor (e.g., global positioning system), an Inertial Measurement Unit (IMU), a wheel speed sensor); and determining a slip rate of a wheel of the vehicle based at least in part on the sensed angular velocity and the sensed operating speed of the vehicle. In some implementations, the command is ultimately determined based in part on a product of an observed slip rate multiplied by a slip gain. In some embodiments, the slip gain may be dynamically set based at least in part on one or more vehicle parameters (e.g., wherein the one or more vehicle parameters include at least one, at least two, or at least three of a fluid pressure of a brake cylinder of the vehicle or a rate of change of a fluid pressure of a brake cylinder of the vehicle, a position of an accelerator pedal or a rate of change of a position of an accelerator pedal, and/or a position of a brake pedal or a rate of change of a position of a brake pedal). In some embodiments, the slip gain may be determined by accessing a lookup table that specifies a plurality of values of the slip gain as a function of a vehicle parameter (e.g., where the vehicle parameter belongs to a set of one or more vehicle parameters).

In certain embodiments, the method includes measuring an aspect of vertical motion of a second portion of the vehicle (e.g., a second corner of the vehicle), and determining the command based at least in part on the aspect of vertical motion. In some embodiments, the aspect of vertical motion is an acceleration of the second portion of the vehicle (e.g., in a vertical direction), while in other embodiments, the aspect of motion is a velocity of the second portion of the vehicle (e.g., in a vertical direction). In some embodiments, the first portion and the second portion are the same, while in some embodiments, the first portion and the second portion are different portions of the vehicle.

In some embodiments, the command is also determined based at least in part on a product of the aspect of the motion multiplied by a second gain. In some embodiments, the second gain may be dynamically set based on one or more vehicle parameters. In these embodiments, the method includes measuring one or more vehicle parameters (e.g., wherein the one or more vehicle parameters include at least one, at least two, or at least three of a rate of change of a fluid pressure of a brake cylinder of the vehicle or a brake cylinder of the vehicle, a rate of change of a position of an accelerator pedal or a position of the accelerator pedal, and/or a rate of change of a position of a brake pedal or a position of the brake pedal); and determining a value of the second gain based at least in part on one or more vehicle parameters. In some embodiments, the value of the second gain may be determined by accessing a lookup table that specifies a plurality of values of the second gain as a function of a vehicle parameter (e.g., where the vehicle parameter belongs to a set of one or more vehicle parameters). In certain embodiments, application of the output force (e.g., to the first portion and/or the second portion of the vehicle) results in a reduction in the slip rate of the wheel.

In another aspect, a method for controlling an active suspension system of a vehicle is disclosed, wherein the vehicle has wheels. In some embodiments, the method includes applying a force to a portion of the vehicle (e.g., to a wheel assembly including the wheel, a portion of the vehicle body (e.g., a corner) via an actuator of an active suspension system associated with the wheel, wherein the applied force is determined based at least in part on an observed slip rate of the wheel (e.g., via a controller, via a set of controllers). The threshold slip rate exceeds the critical slip rate. In other embodiments, the threshold slip rate is approximately equal to the critical slip rate. In some embodiments, applying the force to the wheel of the vehicle includes extending the actuator. In some embodiments, a force is applied to a wheel of the vehicle, thereby at least temporarily reducing the slip rate of the wheel.

In yet another aspect, a method for controlling an active suspension system in a vehicle is disclosed, the method comprising: (a) applying a braking force to a wheel of the vehicle to retard rotation of the wheel while the vehicle is running, resulting in an increase in a slip rate of the wheel; and (b) subsequently applying a second force to a portion of the vehicle through an actuator of the active suspension system, wherein the application of the second force results in a reduction in a slip rate of the wheel. In some embodiments, applying the second force results in an increase in a normal load applied to the wheel. In certain embodiments, the method further comprises: determining (e.g., by a controller, by a set of controllers) a slip rate of the wheels; determining (e.g., by a controller, by a set of controllers) a command for an actuator based at least in part on the determined slip rate; output commands to actuators (e.g., slave controller, slave set of controllers); and applying, by the actuator, a second force to a portion of the vehicle in response to the command received by the actuator.

In yet another aspect, a method for controlling an active suspension system of a vehicle having wheels is disclosed, the method comprising: (a) measuring (e.g., using an accelerometer) an aspect (e.g., acceleration, velocity, amplitude) of motion (e.g., vertical motion) of a first portion of a vehicle (e.g., a corner of a body of the vehicle); (b) measuring one or more vehicle parameters (e.g., wherein the one or more vehicle parameters include at least one, at least two, at least three, or at least four of a rate of change of a fluid pressure of a brake cylinder of the vehicle or a brake cylinder of the vehicle, a rate of change of a position of an accelerator pedal or a position of an accelerator pedal, a rate of change of a position of a brake pedal or a position of a brake pedal, and/or a rate of change of a position of a steering wheel or a position of a steering wheel); (c) determining a value of the gain based at least in part on a set of one or more vehicle parameters; (d) determining (e.g., by one or more controllers) a command based at least in part on the aspect of motion multiplied by the product of the gain; (e) outputting commands to actuators of the active suspension system (e.g., from one or more controllers); (f) in response to a command received by the actuator, an output force is applied by the actuator of the active suspension system to a first portion of the vehicle (e.g., a wheel assembly including a wheel, a portion of a body (e.g., a corner)). In certain embodiments, determining the value of the gain based at least in part on a set of vehicle parameters includes accessing a lookup table that specifies a plurality of values of the gain as a function of one or more vehicle parameters.

In yet another aspect, a vehicle is disclosed, comprising: a wheel; an active suspension system including an actuator associated with a wheel (e.g., an actuator arranged to apply a force to a wheel assembly including the wheel); and a set of one or more controllers. In certain embodiments, a set of one or more controllers and actuators may be configured to perform any of the methods disclosed herein. In some embodiments, the vehicle may include a set of sensors in communication with the controller.

In certain embodiments, a vehicle is disclosed, comprising: a vehicle body; a plurality of wheels including a first wheel associated with a first corner of a vehicle body and a second wheel associated with a second corner of the vehicle body; an active suspension system including a first actuator configured to apply a first force to a first wheel in response to a first command from a first controller and a second actuator configured to apply a second force to a second wheel in response to a second command from a second controller; and a set of one or more controllers, wherein the set of one or more controllers comprises a first controller, and wherein the set of one or more controllers is configured to: (a) determining a first slip rate of a first wheel of a vehicle; (b) determining a first command force based at least in part on the first slip rate; and (c) commanding the first actuator to apply a first command force to the first wheel. In certain embodiments, the set of one or more controllers includes a second controller, and the set of controllers is further configured to: (a) determining a second slip rate of a second wheel of the vehicle; (b) determining a second command force based at least in part on the second slip rate; (c) a second actuator is commanded to apply a second command force to the second wheel. Alternatively or additionally, the set of one or more controllers may also be configured to determine vertical motion (e.g., pitch/rebound) of a first corner of the vehicle body relative to the first wheel; and determining a first command force based at least in part on the determined vertical motion. In some embodiments, the first controller and the second controller may be the same, or the first controller and the second controller may share some common hardware. In some embodiments, the first controller and the second controller may be different controllers.

Drawings

FIG. 1 illustrates an embodiment of a vehicle having a suspension system.

FIG. 2 illustrates a graph depicting an exemplary relationship between a coefficient of friction and a slip rate of a wheel of a vehicle.

FIG. 3 illustrates a method for determining a command force in an active suspension system.

FIG. 4 illustrates a method for determining a command force in an active suspension system.

FIG. 5 illustrates a method for determining a command force in an active suspension system.

FIG. 6 illustrates a method for determining a command force in an active suspension system.

Detailed Description

Braking of a moving vehicle uses the friction between the tires of the vehicle and the road surface to decelerate the vehicle. Optimization of braking may be achieved by increasing the amount of friction that exists between the tires of the vehicle and the road surface on which the vehicle is traveling. The magnitude of the friction force, sometimes referred to as traction, is the product of the coefficient of friction (μ) times the normal load (N) acting on the wheel. The coefficient of friction itself may depend on a variety of factors, including the slip rate of the corresponding wheel, which in turn may depend on the normal force applied to the wheel.

When the slip rate of a given wheel is relatively low (e.g., generally below a critical slip rate), the wheel may rotate substantially synchronously with the forward motion of the vehicle, and the frictional force between the corresponding tire and the road surface may be of a relatively low magnitude due primarily to the rolling resistance of the tire. As the slip ratio of the wheel increases, the magnitude of the frictional force may also increase and reach a maximum at the critical slip ratio. When the slip increases beyond a critical slip rate, the wheels of the vehicle may lock, resulting in a reduction in the magnitude of the friction when the locked wheels slip on the road surface. Thus, in some embodiments, to minimize braking time and/or distance, the slip rate of each wheel may be controlled to remain close to, but preferably below, a critical level, thereby maximizing frictional (i.e., decelerating) forces.

The slip rate of the wheel itself depends on a number of factors including, for example, the braking force applied to the wheel and the normal force applied to the wheel. For example, many vehicles employ anti-lock braking systems designed to maintain slip at near critical levels through pulsed braking forces to prevent excessive slip (or locking) of the wheels during a braking event.

The inventors have recognized that in a vehicle having an active suspension system, in some embodiments, by controlling the magnitude of the normal load acting on one or more wheels of the vehicle, the slip rate of the wheels may be varied in a controllable manner during a braking event. This control of the normal load acting on the wheels may be used alone or in combination with a conventional anti-lock braking system to achieve improved braking distance and/or time. In an exemplary use case, the slip rate of each wheel of the vehicle may be monitored during a braking event, and the active suspension system may be controlled based on the slip rate of each wheel. For example, if it is determined that a given wheel is experiencing deep slip (i.e., the slip rate exceeds a given threshold), the active suspension system may be actuated to increase the normal load acting on the given wheel (e.g., the actuators of the active suspension system may be extended, thereby exerting a downward force on at least the particular wheel). By increasing the normal load acting on a given wheel, the slip rate of the wheel may be reduced in order to bring the wheel close to the critical slip rate. Additionally, active suspension systems may be used to reduce variations in the normal load experienced by one or more wheels during a braking event, which can help increase the available traction at the contact pads of the tire. Further, increasing the normal load acting on a given wheel may increase the amount of friction between the corresponding tire and the road surface. Specifically, by controlling the distribution of the normal load between each wheel, the frictional or deceleration force between each corresponding tire and the road surface can be controlled.

Additionally, due to vehicle dynamics, rapid braking of the vehicle can result in vertical motion of the body (e.g., pitch or roll vibration), which in turn can affect the distribution of normal loads at each wheel of the vehicle. In some embodiments, the active suspension system may be controlled based on the observed vertical motion of the vehicle body in addition to responding to the measured slip rate of each wheel. For example, an accelerometer may be placed near each corner of the body to measure vertical motion of the body, and the active suspension system may be controlled based on the measured motion. Alternatively, instead of using accelerometers located near each corner, accelerometers located at two or three corners of the body or near the front or rear of the body may be used to determine movement of the body. Alternatively or additionally, vertical movement of the body or each corner may be predicted based on vehicle handling or commands, such as braking and/or steering commands. For example, the sensor may measure the position of the brake pedal. In some embodiments, when a rapid change in the position of the brake pedal is observed or when an increase in brake pressure is observed, it may be predicted that the vehicle may decelerate rapidly and a corresponding tilting motion may be expected. In some embodiments, control of the active suspension system, and the vertical force at one or more wheels, can therefore be based on the slip rate measured at each wheel of the vehicle, and the observed or expected vertical motion of the body.

Turning now to the drawings, several non-limiting embodiments of various vehicles, suspension systems, and suspension system components are now described in detail. It should be understood that the various systems, components, features, and methods described with respect to these embodiments may be used either individually and/or in any suitable combination, as the present disclosure is not limited to only the specific embodiments described herein.

Fig. 1 illustrates an exemplary vehicle having four wheels 103 a-103 d, each associated with a respective corner of the vehicle (e.g., front left 103a, rear left 103b, front right 103c, and rear right 103 d). Each wheel may also include a tire that contacts the road surface. The vehicle also includes a body 105. The body 105 may be coupled to the wheels 103 a-103 d of the vehicle via a suspension system that includes springs 107 a-107 d (e.g., coil springs, air springs) and force-generating devices 109 a-109 d interposed between each wheel of the vehicle and a corresponding corner of the body. In the illustrated embodiment, each spring is shown as being coaxially arranged with respect to its corresponding force-generating device. However, it should be understood that any suitable arrangement may be used. The weight of the vehicle body may cause a normal force to be exerted on each of the four wheels. The relative magnitude of each normal force at each corresponding wheel may be determined by the weight distribution of the vehicle when the vehicle is stationary. When the vehicle is undergoing various operations such as braking, acceleration, or steering, vehicle dynamics can result in a corresponding change in the vertical (i.e., out-of-plane) motion of the body (e.g., pitch, roll, heave) and the distribution of the normal load of one or more wheels. For example, when rapid braking of the vehicle occurs, the left and right front corner portions of the vehicle may be lowered (thereby compressing the corresponding suspension springs), while the left and right rear corner portions of the vehicle may be raised (thereby extending the corresponding suspension springs). In this case, the normal force applied to the front two wheels may be increased (i.e., the front wheels may be "loaded"), while the normal force applied to the rear two wheels may be decreased (i.e., the rear wheels may be "unloaded"). In a passive or semi-active suspension system, the force generating device may be a passive or semi-active damper as known in the art, configured to resist vertical movement of the vehicle body, for example, by increasing damping.

In an active suspension system, each force-generating device 109 a-109 d may be an actuator. Various types of actuators may be used as known in the art, including, but not limited to, hydraulic actuators, electromagnetic actuators, mechanical actuators, and/or electro-hydraulic actuators may be used. In the first mode of operation, the actuator may be configured to resist vertical movement of the vehicle body that occurs during braking, acceleration, or steering operations (i.e., the actuator functions like a damper of a passive or semi-active suspension system). Additionally, in the second mode of operation, the actuator may be actively extended or compressed independent of the dynamic forces exerted on the vehicle body. Active extension or compression of the actuator may be actively controlled by, for example, an actuator controller and/or a central controller that may include one or more microprocessors.

The inventors have recognized that active suspension systems may be used to control the magnitude and/or time dependence of the normal load at one or more wheels in order to optimize the available traction at each wheel. For example, extension of one actuator of an active suspension system may cause upward acceleration of an associated corner of the body and a corresponding downward force on an associated wheel, thereby at least temporarily increasing the normal load acting on the wheel. Additionally or alternatively, depending on the center of gravity of the vehicle body, the weight distribution in the individual wheels of the vehicle may be statically changed, for example by a twisting operation, so that the load on one or more wheels may be increased or decreased.

During operation of the vehicle, the wheels of the vehicle may rotate as the vehicle moves forward. To brake the vehicle (i.e., intentionally slow the vehicle), a braking force may be applied to one or more wheels of the vehicle to retard rotation of those wheels. For example, in most conventional vehicles, a non-rotating brake pad may press against a rotating brake disc, thereby creating friction between the pad and the disc that resists rotation of the wheel. Alternatively or additionally, various regenerative braking systems are also known. In an exemplary regenerative braking system, wheels of a vehicle may drive a generator, and a counter-electromotive force generated by rotation of the generator may impede rotation of the wheels.

In any case, the braking force applied to the wheel may impede the free rotation of the wheel, causing the wheel to be in a slipping condition. The degree of slip experienced by a wheel may be referred to as the "slip rate" of the wheel-when the slip rate is zero, the wheel may be considered to be rotating freely. When the slip ratio is 100, the wheel may be considered to be "fully locked" such that any rotation of the wheel is prevented (i.e., the fully locked wheel slips substantially along the road surface without rotating when the vehicle body is moving).

Each wheel typically comprises a tyre which is in contact with the road surface by means of contact pads. As shown in fig. 2, the coefficient of friction between a given tire and the road surface may vary as a function of the slip ratio of the corresponding wheel. Fig. 2 illustrates the coefficient of friction (in μ) between a tire and a road surface on the y-axis as a function of the associated slip ratio of the wheel on the x-axis. When there is no slip, the slip ratio can be said to be zero and the coefficient of friction is approximately equal to the rolling coefficient of friction of the tire (zero slip regime can be approached, but cannot generally be fully achieved due to factors such as tire hysteresis characteristics). The phrase "approximately equal" as used herein is understood to mean within +/-10% of the value. As the braking force increases, the slip ratio may increase until a critical slip ratio 201 is reached. The critical slip ratio is understood to mean the slip ratio of the wheel corresponding to when the coefficient of friction between the tire and the road surface is at a maximum, and may depend on many factors including the road surface and the tire characteristics. Further increasing the slip ratio beyond the critical slip ratio 201 results in a decrease in the coefficient of friction and a corresponding decrease in available traction, as the wheels may begin to enter a deep slip regime. It should be understood that the graph depicted in fig. 2 is an example of a single wheel, and that actual behavior may vary based on various conditions including road surface type, tire characteristics, vehicle load, and the like.

The inventors have recognized that in order to optimize the braking time and/or distance (i.e., the time required to bring the vehicle to a full stop and/or the distance required to bring the vehicle to a full stop), it may be desirable to control the slip rate of one or more wheels during a braking event. The phrase "braking event" as used herein should be understood to refer to an event in which a braking system of a vehicle is activated by, for example, depressing a brake pedal or otherwise applying a braking force to one or more wheels of the vehicle. The slip rate of a given wheel may also be a function of the normal load acting on the given wheel during a braking event. The inventors have recognized that slip rate during a braking event may be controlled by using the active suspension system of the vehicle to adjust the normal load acting on one or more wheels. Similarly, an acceleration event may also increase the likelihood that deep slip will occur at the wheels, and the acceleration time and/or distance (i.e., the time required to accelerate the vehicle to a given speed and/or the distance required to accelerate the vehicle to a given speed) may be optimized by controlling the slip rate of each wheel during the acceleration event in order to increase the traction between the tires of the vehicle and the road surface during rapid acceleration. The phrase "acceleration event" as used herein should be understood to refer to an event that causes the vehicle to increase speed in a forward direction using the vehicle's propulsion system.

In an exemplary embodiment, the slip rate of each wheel of the vehicle may be monitored during a braking event and/or an acceleration event. As one of ordinary skill in the art will recognize, slip ratio generally refers to the difference between the observed wheel angular velocity and the expected angular velocity based on vehicle speed, if there is pure rolling motion. Slip ratio may be expressed as a ratio or percentage. An exemplary definition of slip rate is given in SAE J670, but those skilled in the art will recognize that other definitions exist and the disclosure is not limited thereto. Various methods of monitoring the slip rate of a wheel are known in the art. In one example method, the slip rate of a given wheel may be determined by collecting information from (a) a wheel speed sensor configured to determine an angular velocity of the given wheel, and; (b) a vehicle speed sensor configured to determine an operating speed of the vehicle. Based on geometric considerations (e.g., the rolling radius of the wheel), the slip rate of the wheel at a given time may be determined according to methods known in the art. It should be understood that there are other methods for calculating slip rate, as the present disclosure is not so limited.

In an exemplary embodiment, when an observed slip rate of a wheel exceeds a threshold, an actuator of an active suspension associated with the wheel may be extended to adjust a normal force at the wheel. In some embodiments, the threshold value may be approximately equal to the critical slip ratio. In other embodiments, the threshold may exceed the critical slip rate. It should be understood that the threshold slip may have any suitable value between 0 and 100, as the present disclosure is not limited thereto. Extension of the actuator may result in an upward force being applied to a corresponding corner of the body and an associated downward force being applied to a corresponding wheel, thereby at least temporarily increasing the normal load applied to the wheel. As the normal load applied to the wheel increases, a decrease in the slip rate of the wheel may occur (e.g., thereby bringing the slip rate of the wheel closer to the critical slip rate). Thus, by controlling each actuator of the active suspension system based at least in part on the observed slip rate of the respective wheel of the vehicle, the slip rate of one or more wheels can be controlled such that braking distance and/or time can be optimized.

FIG. 3 illustrates a flow chart of an exemplary method of controlling an actuator of an active suspension system of a vehicle based at least in part on a slip rate of a wheel of the vehicle. In certain embodiments, the controller 301 receives inputs corresponding to the vehicle speed and the rotational speed of the wheels. The controller 301 may include a microprocessor (e.g., a general purpose processor or an application specific integrated circuit). In a first step 303, an approximate slip rate of a wheel of the vehicle may be determined, for example, based on the vehicle speed and the rotational speed of the wheel. In a second step 305, the controller may determine a commanded force based at least in part on the determined slip rate. The command force may additionally be determined based on other parameters including, for example, any measured vertical movement of the vehicle body. In a subsequent step 307, the command force may then be output to an actuator of the active suspension system. The actuators may be arranged to exert forces on the wheels, and the corresponding actuators may exert a commanded force on the wheels in response to a received command. In certain embodiments, the force may be applied by extending or retracting the length of the actuator, as is known in the art for linear actuators.

FIG. 4 illustrates a second exemplary method of controlling an actuator of an active suspension system based at least in part on a slip rate of a wheel of a vehicle. In the illustrated method, the controller 301 receives input from a first set of one or more sensors 403. In some embodiments, the first set of one or more sensors 403 may include: a wheel speed sensor configured to determine an angular speed of a wheel of the vehicle; and a vehicle speed sensor configured to determine an operating speed of the vehicle. In certain embodiments, the vehicle speed sensors may be based on data from one or more individual sensors including, for example, a positioning system (e.g., a global positioning system), an inertial measurement device, and one or more wheel speed sensors, as is known in the art. Based on the input from the first set of one or more sensors, an approximate slip rate of the wheels of the vehicle at a given time may be estimated. In some implementations, the controller may determine the commanded force based at least in part on a product of the determined slip rate times a slip gain. In some controller configurations, a higher gain value indicates that the system is responding faster and/or more aggressively to potential state changes, and a lower gain value indicates that the system is responding slower and/or less aggressively to potential state changes. That is, the value of the slip gain may represent the sensitivity of the active suspension system to observed changes in the slip rate of the wheels of the vehicle. The inventors have recognized that it may be desirable to control an active suspension system such that: in the case associated with an increased likelihood of deep wheel slip, the active suspension system may be tuned to be more sensitive to changes in observed slip rate. In some embodiments, the controller may dynamically change the slip gain based on the likelihood that one or more wheels of the vehicle are experiencing a deep slip or lock-up condition. For example, when rapid braking or rapid acceleration of the vehicle is commanded, the likelihood of one of the wheels experiencing a deep slip condition (e.g., due to locking or burning) increases, and the slip gain of the control system may increase in response to such an increase in likelihood.

Thus, in some embodiments, the controller 301 may receive input from the second set of one or more sensors 405. In some embodiments, the second set of sensors 405 may monitor one or more vehicle parameters corresponding to rapid braking or rapid acceleration operation. In various embodiments, these one or more vehicle parameters may include: the pressure of the master brake cylinder; the rate of change of other pressures in or of the brake system; a position of an accelerator pedal or a rate of change of position of the accelerator pedal; and/or the position of the brake pedal or the rate of change of the position of the brake pedal. In these embodiments, the controller 301 may receive input from a second set of one or more sensors 405, wherein the set of one or more sensors includes at least one, at least two, or three of: a pressure sensor configured to detect a pressure of the master brake cylinder or other pressure in the brake system; a sensor configured to detect a position of an accelerator pedal or a change in the accelerator pedal, and a sensor configured to detect a position of an accelerator pedal or a change in the accelerator pedal. The controller 301 may then determine a value for the slip gain based at least in part on the input from the set of sensors. In this way, the controller may dynamically change the value of the slip gain based on the set of one or more vehicle parameters. In some embodiments, the controller may have access to a look-up table that specifies a plurality of values of the slip gain as a function of the set of one or more vehicle parameters. In certain embodiments, the lookup table may be stored in a computer-readable memory (e.g., a non-transitory computer-readable memory) that is accessible by the controller. In some implementations, the estimated slip rate may be multiplied by the determined slip gain to determine the commanded force output to the actuator.

In some embodiments, the controller may receive input from a plurality of wheel speed sensors (e.g., from four wheel speed sensors), wherein each wheel speed sensor is configured to determine an angular velocity of a different wheel of the vehicle. In these embodiments, the controller may determine an approximate slip rate for each wheel of the vehicle, and may determine command forces based at least in part on the approximate slip rates, wherein each command force is associated with an actuator of the active suspension system. In various embodiments, as one of ordinary skill in the art will recognize, the functionality ascribed herein to a single controller may be distributed among multiple controllers.

FIG. 5 illustrates another exemplary method of controlling an actuator of an active suspension system based at least in part on a slip rate of a wheel of a vehicle. In the illustrated embodiment, in a first step 503, the slip rate of the wheel is estimated as known in the art (e.g., based on the vehicle speed and the rotational speed of the wheel). In certain embodiments, in a subsequent step 505, the estimated slip ratio may be compared to a threshold slip ratio. In various embodiments, the threshold slip rate may be approximately equal to the critical slip rate, or the threshold slip rate may exceed the critical slip rate. In certain embodiments, in step 507, when it is determined that slip rate of at least one wheel of the vehicle is observed to exceed a threshold slip rate, the controller may command the corresponding actuator to apply a command force that results in an increase in the normal load applied to the wheel in step 507. In some embodiments, the command force may be applied by an actuator that extends a length at an appropriate rate. By increasing the normal load, the slip rate of the wheel may be reduced such that it approaches the critical slip rate, thereby increasing the available traction at the wheel.

During a braking event, the body may be tilted forward due to vehicle dynamics as understood in the art. It may be desirable to use one or more actuators of the active suspension system to impede, mitigate or eliminate such tilting motion and/or mitigate any vibratory tilting motion of the vehicle body during a braking event. FIG. 6 illustrates an embodiment of active suspension control in which the commanded force is based at least in part on both: (i) measured slip rate of the wheel (as described above), and (ii) observed vertical movement of the associated corner of the body relative to the wheel, referred to herein as either jounce or rebound. The illustrated embodiment of fig. 6 is similar to the embodiment of fig. 4 in that a first set of one or more sensors 403 may be used to estimate the slip rate of the wheels of the vehicle, and a second set of one or more sensors 405 may be used to determine the optimal slip gain. Additionally, in some embodiments, the controller 301 may receive input from a set of one or more motion sensors 603. The set of one or more motion sensors 603 may include an accelerometer and/or a suspension position sensor configured to measure the pitch or rebound of a corner of the body associated with the wheel. Based on the input from the set of motion sensors 603, the controller can determine the magnitude of the bump or rebound that the corner of the vehicle body is experiencing. In some embodiments, the input from the set of one or more motion sensors and/or the determined magnitude of the jerking or bouncing as a function of time may be filtered (e.g., low pass filtered or band pass filtered) to, for example, remove noise and/or drift from the signal. In certain embodiments, the commanded force output to the actuator may be based at least in part on both an observed slip rate of the wheel and on an observed relative vertical movement (e.g., jounce/rebound) of an associated corner of the body. In particular, in certain embodiments, the commanded force may be based at least in part on both a product of slip rate times slip gain and a product of a bump or rebound amplitude times bump or rebound gain. It should be understood that in various embodiments, the commanded force may be based on other parameters (e.g., vehicle load, operating speed, road surface characteristics, driving mode, operator input, vehicle occupant input, etc.) in addition to those described herein.

Similar to the previous discussion of the slip gain, the value of the pitch or rebound gain may represent the sensitivity of the active suspension system to observed motion of the corners of the vehicle body. For example, a larger value of the jounce gain may mean that the active suspension system will respond faster and/or more aggressively to the observed jounce/rebound than if a smaller value of the jounce/rebound gain was used. The inventors have recognized that it may be desirable to control an active suspension system such that: such that the active suspension system is tuned to be more sensitive to jounce or rebound in the likely event of such a vehicle corner bump or rebound. Thus, in certain embodiments, the controller may dynamically vary the pitch or rebound gain as a function of the likelihood that one or more corners of the vehicle body experience pitch or rebound greater than a threshold value. For example, when a vehicle is commanded to brake quickly or accelerate quickly, there is an increased likelihood that one or more corners of the vehicle will experience jounce or rebound, and in response to the increased likelihood, it may be desirable to increase the jounce or rebound gain used by the control system of the active suspension system.

Thus, in some embodiments, the controller 301 may receive input from the second set of one or more sensors 405. In some embodiments, the second set of sensors 405 may monitor one or more vehicle parameters corresponding to rapid braking or rapid acceleration operation. In various embodiments, these one or more vehicle parameters may include: a pressure of the master brake cylinder or a rate of change of the pressure of the master brake cylinder, a position of the accelerator pedal or a rate of change of the position of the accelerator pedal, and/or a position of the brake pedal or a rate of change of the position of the brake pedal. In these embodiments, the controller may receive input from a set of one or more sensors, wherein the set of one or more sensors includes at least one, at least two, or three of: a pressure sensor configured to detect a pressure of the master brake cylinder, a change in the pressure of the master brake cylinder, and a rate of change of the pressure of the master brake cylinder; a sensor configured to detect a position of an accelerator pedal, a change in the position of the accelerator pedal, or a rate of change of the position of the accelerator pedal; and a sensor configured to detect a position of the accelerator pedal, a change in the position of the accelerator pedal, or a rate of change of the position of the accelerator pedal. The controller may then determine a value for the pitch or bounce gain based at least in part on the input from the set of motion sensors. In this way, the controller may dynamically change the value of the pitch or bounce gain based on one or more vehicle parameters. In some embodiments, the controller may have access to a look-up table that specifies values of the pitch or bounce gain as a function of the set of one or more vehicle parameters. In certain embodiments, the lookup table may be stored in a computer-readable memory (e.g., a non-transitory computer-readable memory) that is accessible by the controller. In some embodiments, the product of the observed pitch/rebound amplitude multiplied by the determined pitch/rebound gain may be added to the product of the estimated slip ratio of the wheels multiplied by the determined slip gain to determine the commanded force output to the actuator 605.

In various embodiments, as will be appreciated by one of ordinary skill in the art, the functionality attributed herein to a single controller may be distributed among multiple controllers. For example, in certain embodiments, multiple controllers may be used, wherein each controller is associated with a different corner of the body, a different actuator of the active suspension system, and/or a different wheel of the vehicle. In these embodiments, each controller may receive input from a single associated wheel speed sensor and body accelerometer, and each controller may determine a single commanded force associated with one actuator of the active suspension system. Alternatively, a central controller may be used and may receive signals from a plurality of accelerometers (e.g., each accelerometer associated with one corner of the body) and a plurality of wheel speed sensors (e.g., each wheel speed sensor associated with one wheel of the body). The central controller may then determine a plurality of command forces, each command force associated with one actuator of the active suspension system, and the central controller may command each actuator to apply a respective command force. Alternatively, the slip rate of the wheels and/or other vehicle parameters may be determined by a vehicle controller shared between multiple vehicle systems (e.g., ABS, stability control, etc.) and may be communicated to a second controller specific to the active suspension system.