Cruise control system and method of operation for downshifting in descent following a repeated or prolonged activation of the driver

1. A method of operating a cruise control system of a vehicle, said system having a driver input to command a reduction in vehicle speed, and an output for causing a downshift of a vehicle transmission, the method comprising:

detecting at least one of repeated activations of said driver input and prolonged activation of said driver input, and in response

causing a downshift of the vehicle transmission.

2. The method of claim 1 , wherein said repeated activations are at a rate greater than 2 Hz.

3. The method of claim 2 , wherein a number of said repeated activations meets or exceeds a threshold of four.

4. The method of claim 1 , wherein said prolonged activation occurs for at least two seconds.

5. The method of claim 1 , wherein said system has a vehicle speed input, and the method is enabled by

detecting an increase in vehicle speed above a pre-set cruise speed.

6. The method of claim 5 , wherein said system has an engine fueling input indicative of instant fueling of a vehicle engine, and the method is enabled by

detecting that fueling of the vehicle engine has substantially ceased.

7. The method of claim 6 , comprising at least temporarily disabling causing when detecting fueling of said vehicle engine.

8. The method of claim 5 , comprising at least temporarily disabling the causing when detecting a vehicle speed at or below the pre-set cruise speed.

9. The method of claim 1 , wherein said system includes a gradient input indicative of instant road gradient, and the method being enabled by

detecting a negative road gradient.

10. The method of claim 9 , comprising at least temporarily disabling the causing when detecting a non-negative road gradient.

11. The method of claim 1 , wherein said output causes a downshift of two or more sequential speed ratios.

12. The method of claim 1 , wherein said system has an indicator of vehicle engine speed, and the method comprises:

continually determining for a plurality of potential downshift ratios, an available amount of engine braking at an instant engine speed;

determining which one of the downshift ratios best achieves a desired vehicle deceleration rate; and

commanding downshift to said one of the downshift ratios.

13. The method of claim 12 , comprising:

continually determining for a plurality of potential upshift ratios, an available amount of engine braking at the instant engine speed;

detecting that vehicle speed is substantially equal to a cruise speed;

determining which one of the upshift ratios best maintains cruise speed; and

commanding an upshift to said one of the upshift ratios.

14. The method of claim 1 , comprising automatically controlling a vehicle engine to attempt to cause vehicle speed to maintain a pre-set cruise speed, wherein at least the causing the downshift of the vehicle transmission is performed during the automatically controlling the vehicle engine.

15. A cruise control system of a motor vehicle, said system comprising:

a driver input to command a cruise speed to be reduced, and

a system output to cause a downshift of a vehicle transmission in response to operation of said driver input by at least one of repeated activations and prolonged activation.

16. A cruise control system according to claim 15 , including a gradient input indicative of road gradient.

17. A cruise control system according to claim 15 , including an engine speed input indicative of instant vehicle engine speed.

18. A cruise control system according to claim 15 , including an engine fueling input indicative of instant fueling of a vehicle engine.

19. An engine and transmission of a motor vehicle incorporating a cruise control system according to claim 15 .

20. A motor vehicle incorporating the engine and transmission of claim 19 .