Slip control via active suspension for optimization of braking and accelerating of a vehicle
System and method for improving braking efficiency by increasing the magnitude of a frictional force between a tire of a vehicle wheel and a road surface. Braking efficiency may be improved by controlling the normal force applied on the wheel, with an active suspension actuator, based on the wheel's slip ratio.
1. A method for controlling an active suspension system of a vehicle, wherein the active suspension system includes a first actuator associated with a first wheel of the vehicle, the method comprising:
(a) determining a slip ratio of the first wheel of the vehicle;
(b) based at least in part on the determined slip ratio, determining a command; and
(c) outputting the command to the first actuator of the active suspension system to increase the vertical force applied on the first wheel by the first actuator.
2. The method of claim 1 , wherein step (a) comprises:
detecting an angular velocity of the first wheel of the vehicle;
estimating an operating speed of the vehicle; and
based at least in part on the detected angular velocity of the first wheel of the vehicle and the estimated operating speed of the vehicle, determining the slip ratio of the first wheel of the vehicle.
3. The method of claim 1 , wherein the determined command is based at least in part on a product of the determined slip ratio and a slip gain.
4. The method of claim 3 , further comprising:
measuring one or more vehicle parameters, wherein the one or more vehicle parameters includes at least one of a fluidic pressure of a brake cylinder of the vehicle or a rate of change thereof, a position of the acceleration pedal or a rate of change thereof, and/or a position of a brake pedal or a rate of change thereof; and
determining a value of the slip gain based at least in part the one or more vehicle parameters.
5. The method of claim 4 , wherein determining the value of the slip gain based at least in part on the set of vehicle parameters comprises: accessing a look-up table that specifies a plurality of values of the slip gain as a function of a vehicle parameter.
6. The method of claim 1 , further comprising: measuring an aspect of vertical motion of a second portion of the vehicle, and wherein the command is determined based at least in part on the aspect of vertical motion.
7. The method of claim 6 , wherein the aspect of vertical motion is an acceleration of the second portion of the vehicle.
8. The method of claim 6 , wherein the aspect of motion is a velocity of the second portion of the vehicle.
9. The method of claim 6 , wherein the first portion is the same as the second portion.
10. The method of claim 6 , wherein the command is determined based at least in part on a product of the aspect of movement and a second gain.
11. The method of claim 10 , further comprising:
measuring one or more vehicle parameters, wherein the one or more vehicle parameters includes at least one of a fluidic pressure of a brake cylinder of the vehicle or a rate of change thereof, a position of the acceleration pedal or a rate of change thereof, and/or a position of a brake pedal or a rate of change thereof; and
determining a value of the second gain based at least in part on the one or more vehicle parameters.
12. The method of claim 11 , wherein determining the value of the second gain based at least in part on the set of vehicle parameters comprises accessing a look-up table that specifies a plurality of values of the second gain as a function of a vehicle parameter.
13. The method of claim 1 , wherein application of the output force results in a decrease in the slip ratio of the wheel.
14. A method for controlling an actuator of an active suspension system of a vehicle, the method comprising:
estimating a slip ratio of a wheel of the vehicle at a given time;
comparing the estimated slip ratio with a threshold slip ratio; and
upon determining that the estimated slip ratio exceeds the threshold slip ratio:
applying, with an actuator of the active suspension system, a force to the wheel of the vehicle to increase a total normal force applied to the wheel.
15. The method of claim 14 , wherein the threshold slip ratio exceeds a critical slip ratio.
16. The method of claim 14 , wherein the threshold slip ratio is substantially equal to the critical slip ratio.
17. A method for controlling an active suspension system of a vehicle having a wheel, the method comprising:
measuring an aspect of motion of a first portion of the vehicle;
measuring one or more vehicle parameters, wherein the one or more vehicle parameters includes at least one of a fluidic pressure of a brake cylinder of the vehicle or a rate of change thereof, a position of the acceleration pedal or a rate of change thereof, a position of a brake pedal or a rate of change thereof, and/or a position of a steering wheel or a rate of change thereof;
determining, based at least in part on a set of one or more vehicle parameters, a value of a gain;
determining a command based at least in part on a product of the aspect of motion times the gain;
outputting the command to an actuator of the active suspension system; and
in response to the actuator receiving the command: applying, with the actuator of the active suspension system, an output force to a first portion of the vehicle.
18. The method of claim 17 , wherein determining the value of the gain based at least in part on the set of vehicle parameters comprises: accessing a look-up table that specifies a plurality of values of the gain as a function of the one or more vehicle parameters.