Enhanced roll stability indicator for vehicle rollover control
A system and method for providing a vehicle roll stability indicator that dynamically estimates the probability for vehicle rollover. The system determines vehicle kinematics from various vehicle sensors. From these kinematic values, the system estimates a roll angle of the vehicle and a bank angle of the vehicle. The estimated bank angle is used to correct the roll angle. The system determines a roll energy of the vehicle and a roll energy rate of the vehicle from the corrected roll angle. The system also calculates a tire lateral load transfer of the relative forces on the vehicle tires, and the duration that any of the tires have been off of the ground. From the roll energy, the roll energy rate, the tire lateral load transfer and the wheel airborne duration, the system calculates the roll stability indicator.
1. A method for generating a roll stability indicator for indicating the likelihood that a vehicle will tip-up or rollover, said method comprising:
providing a roll rate signal of the roll rate of the vehicle;
providing a yaw rate signal of the yaw rate of the vehicle;
providing a lateral acceleration signal of the lateral acceleration of the vehicle;
providing a speed signal of the speed of the vehicle;
providing a hand-wheel angle signal of the angle of the hand-wheel of the vehicle;
estimating a roll angle signal of the vehicle based on one or more of the roll rate signal, the yaw rate signal, the lateral acceleration signal, the speed signal and the hand-wheel angle signal;
estimating a bank angle signal of the vehicle from one or more of the roll rate signal, the yaw rate signal, the lateral acceleration signal, the vehicle speed signal and the hand-wheel angle signal;
correcting the roll angle signal based on the estimated bank angle signal to provide a corrected roll angle signal;
calculating a roll energy signal based on the corrected roll angle signal;
calculating a roll energy rate signal based on the roll energy signal;
determining a critical energy signal and a critical energy rate signal;
determining a tire lateral load transfer signal between the loads on tires of the vehicle;
determining a duration signal of how long one of the vehicle tires has been off the ground; and
calculating the roll stability indicator based on the roll energy signal, the roll energy rate signal, the critical energy signal, the critical energy rate signal, the tire lateral load transfer signal and the duration signal.
2. The method according to claim 1 wherein calculating the roll stability indicator also includes using speed-dependant constants.
3. The method according to claim 2 wherein the speed-dependent constants are provided in a look-up table for different vehicle speeds.
4. The method according to claim 2 wherein calculating the roll stability indicator includes using the equation:
RSI
=
c
1
E
E
2
WL
+
c
2
E
.
E
.
critical
+
c
3
TLLT
front
+
c
4
TLLT
rear
+
c
5
D
airborne
where RSI is the roll stability indicator, c 1 , c 2 , c 3 , c 4 and c 5 are the speed-dependant constants, E 2WL is the critical energy signal, Ė critical is the critical energy rate signal, E is the roll energy signal, Ė is the roll energy rate signal, TLLT is the tire lateral load transfer signal and D airborne is the duration signal.
5. The method according to claim 1 wherein calculating the roll energy signal includes using the equation:
E
=
T
+
Π
=
1
2
I
1
(
φ
)
φ
.
2
+
Π
susp
(
φ
)
+
MgZ
(
φ
)
where E is the roll energy signal, T is the kinetic energy of the vehicle, Π is the potential energy of the vehicle, I I is the roll moment of inertia, M is the mass of the vehicle, φ is the roll angle, Π susp is the potential energy of a suspension of the vehicle during the roll motion, g is the gravitational constant and Z is the movement of the vehicle center of gravity in a vertical direction.
6. The method according to claim 1 wherein calculating the roll energy rate signal includes using the equation:
Ė={dot over (φ)}Q
where Ė is the roll energy rate signal, {dot over (φ)} is the derivative of the roll angle signal and Q is a generalized force on the vehicle.
7. The method according to claim 1 wherein determining the critical energy signal and the critical energy rate signal includes determining the critical energy signal and the critical energy rate signal experimentally by vehicle testing.
8. The method according to claim 1 wherein estimating a roll angle signal and estimating a bank angle signal includes using a GPS signal.
9. The method according to claim 1 wherein determining the tire lateral load transfer signal includes using tire/wheel vertical force sensors.
10. A method for generating a roll stability indicator for indicating the likelihood that a vehicle will tip-up or roll over, said method comprising:
providing vehicle kinematics signals;
estimating a roll angle signal of the vehicle from the vehicle kinematics signals;
calculating a roll energy signal based on the estimated roll angle signal;
calculating a roll energy rate signal based on the roll energy signal;
determining a tire lateral load transfer signal between the loads on tires of the vehicle;
determining a duration signal of how long one of the vehicle tires has been off the ground; and
calculating the roll stability indicator using the roll energy signal, the roll energy rate signal, the tire lateral load transfer signal and the duration signal.
11. The method according to claim 10 further comprising determining a critical energy signal and a critical energy rate signal, wherein calculating the roll stability indicator includes also using the critical energy signal and the critical energy rate signal.
12. The method according to claim 11 wherein determining the critical energy signal and the critical energy rate signal includes determining the critical energy signal and the critical energy rate signal experimentally by vehicle testing.
13. The method according to claim 11 wherein calculating the roll stability indicator also includes using speed-dependent constants.
14. The method according to claim 13 wherein the speed-dependent constants are provided in a look-up table for different vehicle speeds.
15. The method according to claim 13 wherein calculating the roll stability indicator includes using the equation:
RSI
=
c
1
E
E
2
WL
+
c
2
E
.
E
.
critical
+
c
3
TLLT
front
+
c
4
TLLT
rear
+
c
5
D
airborne
where RSI is the roll stability indicator, c 1 , c 2 , c 3 , c 4 and c 5 are the speed-dependant constants, E 2WL is the critical energy signal, Ė critical is the critical energy rate signal, E is the roll energy signal, Ė is the roll energy rate signal, TLLT is the tire lateral load transfer signal and D airborne is the duration signal.
16. The method according to claim 10 wherein providing vehicle kinematics signals includes providing vehicle kinematic signals from one or more of a roll rate sensor, a yaw rate sensor, a lateral acceleration sensor, a vehicle speed sensor, a vehicle hand-wheel angle sensor and tire force sensors.
17. A system for generating a roll stability indicator that indicates the likelihood that a vehicle will tip-up or roll over, said system comprising:
a plurality of vehicle sensors for providing vehicle kinematics information;
means for estimating a roll angle signal of the vehicle from the vehicle kinematics information;
means for calculating a roll energy signal based on the estimated roll angle signal;
means for calculating a roll energy rate signal based on the roll energy signal;
means for determining a tire lateral load transfer signal;
means for determining a wheel airborne duration signal; and
means for calculating the roll stability indicator using the roll energy signal, the roll energy rate signal, the tire lateral load transfer signal and wheel airborne duration signal.
18. The system according to claim 17 further comprising means for determining a critical energy signal and a critical energy rate signal, wherein the means for calculating the roll stability indicator uses the critical energy signal and the critical energy rate signal.
19. The system according to claim 18 wherein the means for determining the critical energy signal and the critical energy rate signal includes means for determining the critical energy signal and the critical energy rate signal experimentally by vehicle testing.
20. The system according to claim 18 wherein the means for calculating the roll stability indicator uses speed-dependent constants.
21. The system according to claim 20 wherein the speed-dependent constants are provided in a look-up table for different vehicle speeds.
22. The system according to claim 20 wherein the means for calculating the roll stability indicator uses the equation:
RSI
=
c
1
E
E
2
WL
+
c
2
E
.
E
.
critical
+
c
3
TLLT
front
+
c
4
TLLT
rear
+
c
5
D
airborne
where RSI is the roll stability indicator, c 1 , c 2 , c 3 , c 4 and c 5 are the speed-dependant constants, E 2WL is the critical energy signal, Ė critical is the critical energy rate signal, E is the roll energy signal, Ė is the roll energy rate signal, TLLT is the tire lateral load transfer signal and D airborne is the duration signal.
23. The system according to claim 17 wherein the means for calculating a roll energy signal uses the equation:
E
=
T
+
Π
=
1
2
I
1
(
φ
)
φ
.
2
+
Π
susp
(
φ
)
+
MgZ
(
φ
)
where E is the roll energy signal, T is the kinetic energy of the vehicle, Π is the potential energy of the vehicle, I I , is the roll moment of inertia, M is the mass of the vehicle, φ is the roll angle, Π susp is the potential energy of a suspension of the vehicle during the roll motion, g is the gravitational constant and Z is the movement of the vehicle center of gravity in a vertical direction.
24. The system according to claim 17 wherein the means for calculating the roll energy rate signal uses the equation:
Ė={dot over (φ)}Q
where Ė is the roll energy rate signal, {dot over (φ)} is the derivative of the roll angle signal and Q is a generalized force on the vehicle.
25. The system according to claim 17 wherein the means for estimating a roll angle signal includes using a GPS signal.
26. The system according to claim 17 wherein providing vehicle kinematics signals includes providing vehicle kinematic signals from one or more of a roll rate sensor, a yaw rate sensor, a lateral acceleration sensor, a vehicle speed sensor, a vehicle hand-wheel angle sensor and tire/wheel force sensors.