Real-time anticipatory speed control
An anticipatory speed-control system and method for generating a speed profile in real time by iteratively calculating proposed reduced speeds associated with an electronically identified target curve until the proposed speed is compliant with a lateral-acceleration-based comfort metric and a steering-angle-based safety metric and implementing the speed profile in accordance with a longitudinal comfort metric and providing a user with override options.
1. An anticipatory speed-control system for a vehicle with front and rear axles, the anticipatory speed-control system comprising:
a vehicular speed-profile generator configured to generate a speed profile in accordance with predicted lateral acceleration of a target curve identified at least partly from map data; and
a speed controller configured to actuate vehicle deceleration in accordance with the speed profile,
wherein the predicted lateral acceleration is calculated in accordance with
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wherein {dot over (v)} y is the predicted lateral acceleration, g is a gravitational acceleration constant, a and b are distances between a vehicle center of gravity and the front axle and the rear axle, respectively, δ pred is a predicted steering angle, {dot over (w)} and w are predicted vehicle motion variables, v y is a vehicle lateral speed, v x is a vehicle longitudinal speed, m is a vehicle mass, I is a vehicle inertia, C f and C r are a vehicle front and a vehicle rear cornering stiffness, respectively, and θ bank is a bank angle.
2. The anticipatory speed-control system of claim 1 , wherein the vehicular speed-profile generator is further configured to generate the speed profile in accordance with predicted lateral acceleration at the target curve.
3. The anticipatory speed-control system of claim 2 , wherein the vehicular speed-profile generator is further configured to generate the speed profile in accordance with a change in steering angle.
4. The anticipatory speed-control system of claim 1 , wherein the vehicular speed-profile generator is further configured to model a travel path as a Vehicle Centered Path (VCP) in accordance with a 5th order polynomial equation.
5. The anticipatory speed-control system of claim 2 , wherein the speed-profile generator is further configured to calculate a deceleration location “s curve ” in accordance with “s curve ”=(v x,pred 2 −v x,current 2 )/2a x,lim , wherein “s curve ” is a distance spanning a current vehicle location and the target curve, “a x,lim ” is a longitudinal deceleration limit, “v x,pred ” is a predicted longitudinal velocity, and “v x,current 2 ” is a current longitudinal velocity.
6. The anticipatory speed-control system of claim 1 , wherein the speed-profile generator includes a position-tracking unit that includes a Global Positioning System (GPS) receiver.
7. The anticipatory speed-control system of claim 5 , wherein the position: tracking unit is configured to track the vehicle position in accordance with a dead reckoning algorithm responsively to a loss of a GPS signal, the dead reckoning algorithm including Kalman filtering.
8. The anticipatory speed-control system of claim 1 , further comprising a Human Machine Interface (HMI) configured to inform a driver of a planned deceleration.
9. The anticipatory speed-control system of claim 8 , wherein the HMI is further configured to prompt the driver to override the planned deceleration.
10. A method for anticipatory speed-control for a vehicle with front and rear axles, the method comprising:
providing a vehicular speed-profile generator including a processor configured to generate a speed profile in accordance with predicted lateral acceleration of a target curve identified at least partly from map data; and
providing a speed controller in communication with the vehicular speed-profile generator and configured to responsively decelerate the vehicle in accordance with the speed profile generated by the vehicular speed-profile generator,
wherein the predicted lateral acceleration is calculated in accordance with
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wherein {dot over (v)} y is the predicted lateral acceleration, g is a gravitational acceleration constant, a and b are distances between a vehicle center of gravity and the front axle and the rear axle, respectively, δ pred is a predicted steering angle, {dot over (w)} and w are predicted vehicle motion variables, v y is a vehicle lateral speed, v x is a vehicle longitudinal speed, m is a vehicle mass, I is a vehicle inertia, C f and C r are a vehicle front and a vehicle rear cornering stiffness, respectively, and θ bank is a bank angle.
11. The method of claim 10 , wherein the speed-profile generator is further configured to calculate a deceleration location “s curve ” in accordance with “s curve ”=(v x,pred 2 −v x,current 2 )/2a x,lim , wherein “s curve ” is a distance spanning a current vehicle location and the target curve and “a x,lim ” is a longitudinal deceleration limit, “v x,pred ” is a predicted longitudinal velocity, and “v x,current 2 ” is a current longitudinal velocity.
12. The method of claim 11 , wherein the longitudinal deceleration limit “a x,lim ” is implemented at a value less than or equal to 0.15 g.
13. The method of claim 10 , wherein the vehicular speed-profile generator is further configured to generate the speed profile in accordance with predicted steering angle associated with the target curve.
14. The method of claim 13 , wherein the vehicular speed-profile generator is further configured to generate the speed profile in accordance with a predicted change in the steering angle associated with the target curve.
15. The method of claim 14 , wherein the speed-profile generator includes a position-tracking unit configured to track vehicle position.
16. The method of claim 15 , wherein the position-tracking unit includes a Global Positioning System (GPS) receiver.
17. The method of claim 15 , wherein the position-tracking unit is configured to track the vehicle position in accordance with a dead reckoning algorithm responsively to a loss of a GPS signal, the dead reckoning algorithm including Kalman filtering.
18. The method of claim 10 , further comprising informing a driver of a proposed deceleration.
19. The method of claim 10 , further comprising providing a prompt requesting driver override of the proposed deceleration.
20. The method of claim 18 , further comprising providing a prompt requesting driver override of the proposed deceleration.