Engine power modulation in a vehicle

1. A method of operating a vehicle having an internal combustion engine coupled through a drivetrain to drive wheels which propel the vehicle, the method comprising:

a) when the vehicle is traveling at a target velocity which is being maintained by control of engine fueling in accordance with a torque/speed map for the engine to control power to the drive wheels, initiating an acceleration phase by increasing the quantity of fuel being introduced into the engine to cause the engine to accelerate into a zone of the map in which fuel efficiency is greater than fuel efficiency when the engine is traveling at the target velocity, thereby causing the vehicle to accelerate by increasing power flow from the engine through a power flow path to the drive wheels;

b) when acceleration of the vehicle has caused vehicle velocity to become greater than an upper velocity limit, terminating the acceleration phase and initiating a deceleration phase by reducing the quantity of fuel being introduced into the engine sufficiently to cause the engine to decelerate into a zone of the map in which fuel efficiency is less than fuel efficiency when the vehicle is traveling at the upper velocity limit and by also interrupting the power flow path to prevent the drive wheels from back-driving the engine, thereby allowing the vehicle to decelerate; and

c) when the vehicle has decelerated to a vehicle velocity which no longer exceeds the target velocity, terminating the deceleration phase by restoring the power flow path and initiating the acceleration phase.

2. The method as set forth in claim 1 in which terminating the deceleration phase by restoring the power flow path and initiating the acceleration phase commences when the vehicle has decelerated to a lower velocity limit which is less than the target velocity.

3. The method as set forth in claim 2 in which difference between the target velocity and the upper velocity limit is equal to difference between the target velocity and the lower velocity limit.

4. The method as set forth in claim 1 in which interrupting the power flow path to prevent the drive wheels from back-driving the engine is caused by unlocking a mechanism in the drivetrain.

5. The method as set forth in claim 1 in which interrupting the power flow path to prevent the drive wheels from back-driving the engine is caused by unlocking an overrun clutch in the drivetrain.

6. The method as set forth in claim 1 in which the acceleration phase causes the engine to accelerate into a zone of the map and operate with a defined BSFC.

7. The method as set forth in claim 6 in which defined BSFC is defined by a best fit line in the zone of the map best fitted to scattered points having the same BSFC value.

8. A vehicle comprising:

an internal combustion engine coupled through a drivetrain to drive wheels which propel the vehicle, a fueling system for introducing fuel into the engine, a mechanism in the drivetrain for coupling and uncoupling the engine to and from the drive wheels, and at least one controller for controlling operation of the engine and the vehicle;

the at least one controller being operable:

a) to control engine fueling in accordance with a torque/speed map for the engine to control power to the drive wheels which maintains a target velocity for the vehicle with the mechanism coupling the engine to the drive wheels;

b) with the mechanism coupling the engine to the drive wheels, to perform an acceleration phase by increasing the quantity of fuel being introduced into the engine to cause the engine to accelerate into a zone of the map in which fuel efficiency is greater than fuel efficiency when the engine is traveling at the target velocity and thereby cause the vehicle to accelerate by increasing power flow from the engine through the drivetrain to the drive wheels;

c) to terminate the acceleration phase when acceleration of the vehicle has caused vehicle velocity to become greater than an upper velocity limit, and initiate a deceleration phase by reducing the quantity of fuel being introduced into the engine sufficiently to cause the engine to decelerate into a zone of the map in which fuel efficiency is less than fuel efficiency when the vehicle is traveling at the upper velocity limit and by also causing the mechanism to uncouple the engine from the drive wheels, thereby allowing the vehicle to decelerate; and

d) when the vehicle has decelerated to a vehicle velocity which no longer exceeds the target velocity, to terminate the deceleration phase by causing the mechanism to re-couple the engine to the drive wheels and to initiate the acceleration phase.

9. The vehicle as set forth in claim 8 in which the at least one controller is operable to terminate the deceleration phase and initiate the acceleration phase when the vehicle has decelerated to a lower velocity limit which is less than the target velocity.

10. The vehicle as set forth in claim 9 in which difference between the target velocity and the upper velocity limit is equal to difference between the target velocity and the lower velocity limit.

11. The vehicle as set forth in claim 8 in which the mechanism comprises an overrun clutch.

12. The vehicle as set forth in claim 11 in which the overrun clutch is disposed in the drivetrain between a drive shaft and a transmission.

13. The vehicle as set forth in claim 11 in which the overrun clutch is disposed in the drivetrain between a transmission and a drive clutch.

14. The vehicle as set forth in claim 6 in which the at least one controller is operable during the acceleration phase to cause the engine to accelerate into a zone of the map and operate with a defined BSFC.

15. The vehicle as set forth in claim 14 in which defined BSFC is defined by a best fit line in the zone of the map best fitted to scattered points having the same BSFC value.