Method and apparatus for estimating steering behavior for integrated chassis control
View Patent ↗A method and apparatus for providing integrated chassis control of a vehicle over the entire range of the vehicle dynamic state, including steady state and non-steady state steering conditions and linear and non-linear tire behavior, based on the general steer equation by using an estimated understeer and oversteer steering behavior indicator. The method and apparatus are particularly adapted to provide a yaw control apparatus and method. The steering behavior indicator may be calculated as a function of certain vehicle dynamic state inputs. A weighting factor for the calculation of the steering behavior indicator is determined as a function of certain vehicle dynamic state indication parameters.
1. A method of controlling a vehicle, comprising:
providing a plurality of dynamic state inputs to a controller in a vehicle that is adapted to execute a plurality of control loops, each dynamic state input indicative of a dynamic state of the vehicle;
calculating an estimated oversteer-understeer coefficient corresponding to a general steering equation using the controller and the dynamic state inputs during each of the plurality of control loops; wherein the estimated oversteer-understeer coefficient is adapted to provide an indication of the oversteer-understeer behavior of the vehicle during the dynamic state;
storing information related to the dynamic state inputs and the calculation of the estimated oversteer-understeer coefficient for a portion of the plurality of control loops; and
controlling the vehicle in response to the estimated oversteer-understeer coefficient.
2. The method of claim 1 , wherein said calculating an estimated steering coefficient for a control loop comprises updating an estimated steering coefficient of a prior control loop using a dynamic state correction term that is a function of the dynamic state of the vehicle.
3. The method of claim 2 , wherein the dynamic state correction term is a function of a weighting factor that varies as a function of the vehicle dynamic state.
4. The method of claim 3 , further comprising:
determining the weighting factor as a function of a predetermined dynamic state indication parameter.
5. The method of claim 4 , wherein the predetermined dynamic state indication parameter comprises a lateral velocity rate, a steering angle rate and a prior control loop covariance related to the calculation of the prior control loop estimated oversteer-understeer coefficient.
6. The method of claim 5 , wherein said controlling the vehicle comprises providing an output from the controller to a yaw control system.
7. The method of claim 6 , wherein the yaw control system is selected from a group consisting of a propulsion subsystem, a steering subsystem, a braking subsystem, and a suspension subsystem.
8. A method of controlling a vehicle, comprising:
sensing a plurality of dynamic state parameters of a vehicle; providing a plurality of dynamic state inputs which are representative of the dynamic state parameters to a controller in the vehicle that is adapted to execute a plurality of control loops, each dynamic state input indicative of a dynamic state of the vehicle;
calculating an estimated oversteer-understeer coefficient corresponding to a general steering equation ({circumflex over (K)} μ ) using the controller and the dynamic state inputs during each of the plurality of control loops; wherein the estimated oversteer-understeer coefficient is adapted to provide an indication of the oversteer-understeer behavior of the vehicle during the dynamic state;
storing information related to the dynamic state inputs and the calculation of the estimated oversteer-understeer coefficient for a portion of the plurality of control loops; and
controlling the vehicle using the controller in response to the estimated steering coefficient.
9. The method of claim 8 , wherein calculating said estimated steering coefficient for a control loop (k 0 ) comprises updating an estimated oversteer-understeer coefficient of a prior control loop ({circumflex over (K)}μ(k −1 )) using a dynamic state correction term (C(k 0 )) that is a function of the dynamic state of the vehicle according to the relationship:
{circumflex over (K)} μ ( k 0 )= {circumflex over (K)} μ( k −1 )+ C ( k 0 ).
10. The method of claim 9 , wherein the dynamic state correction term comprises an estimation error related to the calculation of the estimated oversteer-understeer coefficient for the control loop.
11. The method of claim 10 , wherein the estimation error is factored by an estimation error correction factor that is adapted to correct the estimation error as a function of the vehicle dynamic state.
12. The method of claim 11 , wherein the estimation error correction factor is a function of a weighting factor that varies as a function of the vehicle dynamic state.
13. The method of claim 12 , wherein the dynamic state inputs comprise a vehicle speed, a yaw rate, a steering angle and a lateral acceleration.
14. The method of claim 13 , wherein calculating the estimated oversteer-understeer coefficient {circumflex over (K)} μ (k 0 ) is performed according to the relationship comprising:
{circumflex over (K)} μ ( k 0 )={circumflex over (K)} μ ( k −1 ) + F ε(k 0 )ε( k 0 )
wherein:
ε( k 0 )=γ( k 0 )−ξ( k −1 ) {circumflex over (K)} μ ( k −1 ),
γ(k 0 )=δ f ( k 0 ) V x ( k 0 ) − L {dot over (ψ)}( k 0 ),
ξ( k 0 )= a y ( k 0 ) V x ( k 0 ),
P
(
k
-
1
)
=
1
α
(
k
-
1
)
[
P
(
k
-
2
)
-
P
2
(
k
-
2
)
ξ
2
(
k
-
1
)
α
(
k
-
1
)
+
ξ
2
(
k
-
1
)
P
(
k
-
2
)
]
F
ɛ
(
k
0
)
=
P
(
k
-
2
)
ξ
(
k
-
1
)
α
(
k
-
1
)
+
ξ
2
(
k
-
1
)
P
(
k
-
2
)
,
and:
k 0 is one of the plurality of control Loops,
k 1 is a first prior control loop, wherein k 1 precedes k 0,
k 2 is a second prior control loop, wherein k 2 precedes k 1,
L comprises a wheelbase of the vehicle,
P(k 1 ) is a covariance term calculated for the first prior control loop,
P(k 2 ) is a covariance term calculated for the second prior control loop,
α(k 1 ) is a weighting factor determined for the first prior control loop,
α(k 2 ) is a weighting factor determined for the second prior control loop.
15. The method of claim 14 , further comprising determining the weighting factors as a function of a predetermined dynamic state indication parameter.
16. The method of claim 15 , wherein the predetermined dynamic state indication parameter comprises a lateral velocity rate, a steering angle rate and a prior control loop covariance related to the calculation of the prior control loop estimated oversteer-understeer coefficient.
17. The method of claim 16 , further comprising: determining the lateral velocity rate during the control loop; determining the steering angle rate (SAR(k 0 )) during the control loop; and determining the prior loop covariance.
18. The method of claim 17 , wherein determining a steering angle rate comprises calculating an estimated steering angle rate (SAR est (k 0 )).
19. The method of claim 18 , wherein calculating the estimated steering angle rate is performed according to the relationship comprising:
SAR est ( k 0 )= SAR est ( k −1 )+ T k 0 ( g 2 ) (δ f ( k 0 )− SA est ( k 0 ))
where:
SA est ( k 0 )=(1 −T k ( g 1 )) ( SA est ( k −1 ))+ T k 0 ( g 1 )(δ f ( k 0 ))+ T k ( SAR est ( k −1 )),
g 1 =2(ζ)(2π( fn )),
g 2 =(2π( fn )) 2
and:
fn is a frequency coefficient,
ζis a damping coefficient,
T k 0 is a sampling time interval of the control loop (k 0 ),
SA est (k 0 ) is a steering angle estimate for the control loop (k 0 ),
SA est (k −1 ) is a steering angle estimate for the control loop (k −1 ),
SAR est (k −1 ) is a steering angle rate estimate for a control loop (k −1 ).
20. The method of claim 17 , wherein a weighting factor α(k 0 )for the control loop k 0 has a value which is determined by:
selecting a covariance threshold (P TH ), a lateral velocity rate threshold
(
V
.
yd
TH
)
,
a first steering angle rate threshold
(
SAR
TH
1
)
,
a second steering angle rate threshold
(
SAR
TH
2
)
,
a first timer count threshold
(
t
1
TH
)
and a second timer count threshold
(
t
2
TH
)
;
initializing a first timer to a first timer initial value and a second timer to a second timer initial value,
setting the value of the weighting factor α(k 0 ) to a first value α 1 (k 0 );
determining a first condition, wherein the first condition is satisfied if
SAR
(
k
0
)
≤
SAR
TH
1
,
and if the first condition is satisfied, incrementing the first timer while the first condition is satisfied to determine a first timer count (t 1 (k 0 )), and if the first condition is or becomes not satisfied, returning to initializing the first timer and the second timer;
determining a second condition while the first condition is satisfied, wherein the second condition is satisfied if
t
1
(
k
0
)
≥
t
1
TH
;
determining a third condition, wherein the third condition is satisfied if the second condition is satisfied, or P(k −1 )>P TH , or
V
.
y
d
(
k
0
)
>
V
.
y
d
TH
;
if the third condition is satisfied, calculating a second value α 2 (k 0 ) for the weighting factor α(k 0 ) as a function of the estimation error, the lateral acceleration and the vehicle speed;
if the third condition is not satisfied, determining a fourth condition, wherein if |SAR est (k 0 )|<SAR TH 2 , the fourth condition is satisfied, and if the fourth condition is satisfied, incrementing the second timer while the fourth condition is satisfied to determine a second timer count (t 2 (k 0 )), and if the fourth condition is or becomes not satisfied, the second timer is reset to the second timer initial value;
if the fourth condition is satisfied, determining a fifth condition while the fourth condition is satisfied, wherein the fifth condition is satisfied if (t 2 (k 0 )≧t 2 TH , and wherein if the fifth condition is satisfied, setting the value of the weighting factor α (k 0 ) to a third value α 3 (k 0 ), where α 3 (k 0 )(α 1 (k 0 ), and wherein if the fifth condition is not satisfied, setting the value of the weighting factor α(k 0 ) to a fourth value α 4 (k 0 ).
21. The method of claim 20 , wherein calculating a second value α 2 (k 0 ) for the weighting factor α(k 0 ) is performed according to the relationship comprising:
α
2
(
k
0
)
=
1
-
α
′
[
ɛ
2
(
k
0
)
1
+
ξ
2
(
k
-
1
)
P
(
k
-
2
)
]
,
and: α′ is a vehicle weighting factor.
22. The method of claim 21 , wherein α 1 (k 0 )=1.
23. The method of claim 20 , wherein said step of controlling the vehicle comprises providing an output from the controller to a yaw control system.
24. The method of claim 23 , wherein the yaw control system is selected from a group consisting of a propulsion subsystem, a steering subsystem, a braking subsystem, and a suspension subsystem.
25. An integrated chassis control system for a vehicle, comprising:
a controller which is adapted to execute a plurality of control loops, and receive a plurality of dynamic state inputs that are indicative of a dynamic state of a vehicle during its operation and determine an oversteer-understeer coefficient corresponding to a general steering equation from the dynamic state inputs that is adapted to provide an indication of the oversteer-understeer behavior of the vehicle during the dynamic state of the vehicle; and
a control system that is adapted to communicate with said controller and provide control of the dynamic state of the vehicle in response to the oversteer-understeer coefficient.
26. The system of claim 25 , wherein the dynamic state inputs comprise a speed input, a yaw rate input, a steering angle input and a lateral acceleration input.
27. The system of claim 26 , wherein the estimated steering be coefficient for a control loop is determined by updating an estimated oversteer-understeer coefficient of a prior control loop using a dynamic state correction term that is a function of the dynamic state of the vehicle.
28. The system of claim 27 , wherein the dynamic state correction term is a function of a weighting factor that varies as a function of a dynamic state indication parameter.
29. The system of claim 28 , wherein the predetermined dynamic state indication parameter comprises a lateral velocity rate, a steering angle rate and a prior control loop covariance related to the calculation of the prior control loop estimated oversteer-understeer coefficient.
30. The system of claim 29 , wherein the control system comprises a yaw control system.
31. The method of claim 30 , wherein the yaw control system is selected from a group consisting of a propulsion subsystem, a steering subsystem, a braking subsystem, and a suspension subsystem.