Device for controlling the pressure in a vehicle tyre

A device for providing air to a tyre which is mounted on a rim which itself is free to rotate about a fixed, that is, non-rotatable axle, the device comprising:—

• a) a pump which in use rotates with the tyre and which is configured to provide, when activated, air under pressure to the tyre:—
• b) a pump drive system for activating the pump upon a loss of air pressure in the tyre, the pump drive system comprising:—
• b1) a first part that is rotationally connected to the tyre;
• b2) a second part which includes a first clutch plate and which rotates with the first part whilst the pump is not activated, the pump being activated by inhibiting the second part from rotating with the first part, relative rotation between the first and second parts driving the pump to provide air under pressure to the tyre;
• c) a second clutch plate which is configured so that it can be attached to said fixed axle so that it itself is fixed, that is, non-rotatable, the first and second clutch plates normally being spaced apart;
• d) a clutch piston, moved by pressure in the tyre, for engaging the clutch by urging the first clutch plate against the second clutch plate, upon the pressure in the tyre dropping below a predetermined value, whereby rotation of said second part with respect to the first part is inhibited and the pump is activated.