Method and apparatus for determining a desired yaw rate for a vehicle
Methods and systems are provided for determining a desired yaw rate for a vehicle. The vehicle has a plurality of handling states and comprises a yaw rate sensor for determining an actual yaw rate. The method comprises selecting one of the plurality of handling states, determining the desired yaw rate for the vehicle based on the road wheel angle, the velocity, and the selected one of the plurality of handling states, and activating one or more vehicle stability control measures if the difference between the desired yaw rate and the actual yaw rate for the vehicle exceeds a predetermined threshold.
1. A method for determining a desired yaw rate for a vehicle, the vehicle having a plurality of handling states and comprising a yaw rate sensor for determining an actual yaw rate, the method comprising:
selecting one of the plurality of handling states via a processor;
determining the desired yaw rate for the vehicle based on the road wheel angle, the velocity, and the selected one of the plurality of handling states via the processor, wherein the step of determining the desired yaw rate of the vehicle further comprises:
determining a desired steady state yaw rate for the vehicle based on the road wheel angle and the velocity; and
applying a filter to the desired steady state yaw rate, wherein the value of the filter is dependent on the selected one of the plurality of handling states, wherein the step of applying the filter to the desired steady state yaw rate further comprises:
determining the value of at least one filter coefficient that is dependent on the selected one of the plurality of handling states; and
applying the filter to the desired steady state yaw rate, wherein the value of the filter is based on the at least one filter coefficient, wherein the step of applying the filter to the desired steady state yaw rate further comprises applying the filter to the desired steady state yaw rate according to the equation:
Y_des
=
(
1
-
2
ζω
+
ω
2
s
2
-
s
2
ζω
+
ω
2
)
(
τ
s
(
τ
-
1
)
+
1
)
(
Y_ss
)
where:
Y_des is the desired yaw rate;
s is the Laplace transform variable;
ζ, ω, and τ are each filter coefficients; and
Y_ss is the desired steady state yaw rate; and
activating one or more vehicle stability control measures for the vehicle if the difference between the desired yaw rate and the actual yaw rate for the vehicle exceeds a predetermined threshold.
2. The method of claim 1 , wherein the step of determining the desired steady state yaw rate further comprises determining the desired steady state yaw rate for the vehicle as given by the equation:
Y_ss
=
(
δ
V
L
+
K_us
V
2
)
where:
Y_ss is the desired steady state yaw rate for the vehicle;
δ is the road wheel angle for the vehicle;
V is the velocity for the vehicle;
K_is an understeer gradient for the vehicle; and
L is the wheel base for the vehicle.
3. The method of claim 1 , wherein the step of determining the desired steady state yaw rate further comprises identifying the desired steady state yaw rate that corresponds to the road wheel angle and the velocity in a lookup table.
4. The method of claim 1 , wherein the step of determining the value of the at least one filter coefficient further comprises:
identifying a lookup table that corresponds to the selected one of the plurality of handling states, the lookup table associating the velocity of the vehicle with a corresponding value for the at least one filter coefficient; and
identifying the value for the at least one filter coefficient that corresponds to the velocity of the vehicle.
5. The method of claim 1 , wherein the vehicle comprises a suspension system having a plurality of operational modes and the step of selecting one of the plurality of handling states of the vehicle further comprises selecting one of the plurality of handling states based on a selected one of the plurality of operational modes of the suspension system.
6. The method of claim 1 , wherein the vehicle comprises a plurality of wheels and the step of selecting one of the plurality of handling states of the vehicle further comprises selecting one of the plurality of handling states based on the tire pressure for at least one of the plurality of wheels of the vehicle.
7. The method of claim 1 , wherein the step of selecting one of the plurality of handling states of the vehicle further comprises selecting one of the plurality of handling states based on one or more operational faults of the vehicle.
8. A system for determining a desired yaw rate for a vehicle having a plurality of handling states, the system comprising:
a steering angle sensor for providing output signals indicative of a steering angle of the vehicle;
at least one wheel speed sensor for providing output signals indicative of a velocity of the vehicle; and
a processor, coupled to the steering angle sensor and to the at least one wheel speed sensor, the processor configured to:
select one of the plurality of handling states for the vehicle;
determine a road wheel angle based on the steering angle;
determine a desired steady state yaw rate for the vehicle based on the road wheel angle and the velocity; and
apply a filter to the desired steady state yaw rate, wherein the value of the filter is dependent on the selected one of the plurality of handling states and on at least one filter coefficient, wherein the processor is further configured to:
determine the value of the at least one filter coefficient based on the velocity of the vehicle and the selected one of the plurality of handling states,
identify a lookup table that corresponds to the selected one of the plurality of handling states of the vehicle, wherein the lookup table associates the velocity of the vehicle with a corresponding value for the at least one filter coefficient; and
identify the value for the at least one filter coefficient that corresponds to the desired steady state yaw rate;
wherein the value of the filter is determined according to the equation:
Y_Des
=
(
1
-
2
ζω
+
ω
2
s
2
-
s
2
ζω
+
ω
2
)
(
τ
s
(
τ
-
1
)
+
1
)
(
Y_ss
)
where:
Y_Des is the desired yaw rate;
s is the Laplace transform variable;
ζ, ω, and τ are each filter coefficients; and
Y_ss is the desired yaw rate.
9. The system of claim 8 , wherein the desired steady state yaw rate for the vehicle is determined according to the equation:
Y_ss
=
(
δ
V
L
+
K_us
V
2
)
where:
Y_ss is the desired steady state yaw rate for the vehicle;
δ is the road wheel angle for the vehicle;
V is the velocity of the vehicle;
K_us is an understeer gradient for the vehicle; and
L is the wheel base for the vehicle.
10. The system of claim 8 , wherein the processor identifies the desired steady state yaw rate that corresponds to the road wheel angle and the velocity of the vehicle in a lookup table.
11. The system of claim 8 , further comprising a suspension system coupled to the processor and having a plurality of operational modes and wherein the processor selects one of the plurality of handling states of the vehicle based on a selected one of the plurality of operational modes of the suspension system.
12. A method for determining a desired yaw rate for a vehicle having a plurality of handling states, the method comprising:
selecting one of the plurality of handling states via a processor;
determining a desired steady state yaw rate for the vehicle based on the road wheel angle and the velocity of the vehicle via the processor; and
applying a filter to the desired steady state yaw rate for the vehicle, wherein the value of the filter is dependent on a selected one of the plurality of handling states and on at least one filter coefficient, and wherein the step of applying the filter to the desired steady state yaw rate further comprises:
determining the value of the at least one filter coefficient based on the velocity of the vehicle and the selected one of the plurality of handling states; and
applying the filter to the desired steady state yaw rate according to the equation:
Y_des
=
(
1
-
2
ζω
+
ω
2
s
2
-
s
2
ζω
+
ω
2
)
(
τ
s
(
τ
-
1
)
+
1
)
(
Y_ss
)
where:
Y_is the desired yaw rate;
s is the Laplace transform variable;
ζ, ω, and τ are each filter coefficients; and
Y_ss is the desired steady state yaw rate.