Continuously variable transmission with brake

1. A transmission for a wheeled vehicle, the transmission having a rotary input capable of being driven by a rotary power source, a rotary output capable of driving a vehicle wheel, and a transmission unit coupled between the rotary input and the rotary output to transfer drive between them at a speed ratio which is continuously variable through a range which includes: negative ratios, providing a reversal of rotational direction between the rotary input and the rotary output; positive ratios, in which the rotary input and the rotary output rotate in the same direction; and a ratio at which the rotary output is stationary; the transmission further comprising a brake for braking the rotary output and a control arrangement adapted to automatically apply the brake when the speed ratio is set to the ratio at which the rotatory output is stationary, and to automatically release the brake as the speed ratio is adjusted away from the ratio at which the rotatory output is stationary.

2. A transmission as claimed in claim 1 further comprising a user operable control part which is mechanically coupled to the transmission unit such that the control part's position dictates the speed ratio.

3. A transmission as claimed in claim 2 in which the user operable control part is mechanically coupled to the brake such that when positioned to set the transmission unit to the ratio at which the rotatory output is stationary it automatically causes the brake to be applied.

4. A transmission as claimed in claim 2 in which the brake comprises a cam mechanism coupled to the control part to apply and release the brake.

5. A transmission as claimed in claim 4 in which the cam mechanism comprises a cam part which has a cam surface profiled to provide a predetermined variation of brake force with speed ratio.

6. A transmission as claimed in claim 2 comprising a pre-stressed spring arranged to exert a force to apply the brake, and a mechanism coupled to the user operable control to selectively relieve the spring's force to release the brake.

7. A transmission as claimed in claim 6 comprising a brake lever which has a fulcrum and is arranged to act upon a brake pad and to be acted upon by the pre-stressed spring, the brake pad being closer to the fulcrum than the spring.

8. A transmission as claimed in claim 7 in which the brake is a disc brake.

9. A transmission as claimed in claim 2 in which the user operable control is a lever coupled to the transmission unit through at least one push rod.

10. A transmission as claimed in claim 9 in which the user operable control part is coupled to the brake through at least one push rod.

11. A transmission as claimed in claim 9 in which the user operable control part is coupled to a first push rod which is coupled in turn to a crank, the crank being coupled to the transmission unit through a transmission push rod.

12. A transmission as claimed in claim 11 in which the brake is coupled to the crank through a crank push rod.

13. A transmission as claimed in claim 1 further comprising a user operable parking brake control part movable between a parking brake release position, in which it does not affect the brake's operation, and a parking brake apply position, in which it causes the brake to be applied whether or not the speed ratio is at the ratio at which the rotatory output is stationary.

14. A transmission arrangement comprising two transmission arrangements as claimed in claim 13 whose speed ratios and brakes are independently controllable and whose rotary outputs are for coupling to wheels on opposite sides of a vehicle.

15. A transmission arrangement as claimed in claim 14 in which the user operable parking brake control part is coupled to both brakes and causes both to be applied/released concurrently.

16. A transmission arrangement as claimed in claim 1 in which the transmission unit includes an epicyclic gear and the ratio at which the rotary output is stationary comprises a geared neutral ratio.