The present invention relates to gear selector assemblies of automatic transmissions and in particular to a means for controlling the engagement of the guide shaft with the gear selector positioning means of an automatic transmission. The invention has particular application as a vehicle anti-theft mechanism. DISCLOSURE OF THE INVENTION: According to the invention there is provided a gear selector assembly of an automatic transmission comprising, a guide shaft connected to a gear stick, a gear selector positioning means connected to the working gears of the automatic transmission, a gear selector control shaft connected to the said guide shaft and adapted to engage the said gear selector positioning means, and a means for controlling the engagement of the said gear selector control shaft with the said gear selector positioning means, whereby, when the said gear selector control shaft is engaged with the said gear selector positioning means, manipulation of the said guide shaft will operate the said gear selector positioning means in the conventional manner.

BRIEF DESCRIPTION OF THE DRAWINGS:

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which:- Fig 1 is a partly broken away perspective view of a gear selector assembly of an automatic transmission according to one embodiment of the invention in its non-engaged position, and Fig 2 is a perspective view of the gear selector assembly of Fig 1 in its engaged position.

DESCRIPTION OF PREFERRED EMBODIMENT:

Referring to Fig 1, the gear selector assembly 10 includes an electronically operable solenoid 11 that has an operating shaft 12 connected to a drive arm 13. A spring 14 connects between the solenoid 11 and the drive arm 13. The drive arm 13 has a forked projection 15 at its other end (partly shown) that fits into a recess (not shown) of a hollow gear selector control shaft 16.

Passing through the bore of the gear selector control shaft 16 is a guide shaft 17 which is rotatabie about axis 18 through operation of the transmission gear stick (not shown) . The guide shaft 17 has a projecting pin 19 that passes through an aperture 20 of the gear selector control shaft 16. The gear selector control shaft 16 may slide along the guide shaft 17 under the action of the solenoid operating shaft 12, but only to an extent determined by the longitudinal length

of the aperture 20.

The gear selector control shaft 16 has a male part 21 that can engage a female part 22 of a gear selector positioning cam 23 under the action of the solenoid operating shaft 12. When so engaged, rotation of the guide shaft 17 will cause the positioning cam 23 to rotate. When the male part 21 is not engaged in the female part 22, the gear selector control shaft 16 is in the non-engaged position shown in Fig 1 by the action of the spring 14, and rotation of the guide shaft 17 will not cause the positioning cam 23 to rotate. The positioning cam 23 is connected to a shift valve and park arm of the working gears (not shown) of the automatic transmission in the conventional manner.

Referring to Fig 2, in order to operate the working gears (not shown) , the operator first sends the appropriate electrical signal through the wiring 24 to the solenoid 11. The signal causes the operating shaft 12 to retract, bringing the drive arm 13 with it in the direction of arrow A. By virtue of the engagement of the drive arm 13 with the gear selector control shaft 16, the control shaft 16 slides along the guide shaft 17 until the projecting pin 19 abuts against the trailing end of the aperture 20. At that stage, the male part 21 of the shaft 16 is mated with the female part 22 of the positioning cam 23. Rotation of the guide shaft 17 (shown by arrow B), through operation of the gear stick (no shown) , will now cause the positioning cam 23 to rotate in the conventional

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manner so allowing for the operation of the working gears of the automatic transmission during the period that the gear selector control shaft 16 is engaged with the positioning cam 23. In order to isolate the positioning cam 23 from the operation of the guide shaft 17, the appropriate signal is sent to inactivate the solenoid 11. The solenoid 11 will no longer maintain the gear selector control shaft 16 in its engaged position with the positioning cam 23 and the gear selector control shaft 16 will slide in the direction opposite to arrow A by the action of the spring 14, so disconnecting the linkage between the guide shaft 17 and the positioning cam 23.

It is apparent from the above embodiment that the present invention has particular application as a vehicle an -theft mechanism- Various modifications can be made in details of design and construction without departing from the scope or ambit of the invention. For instance, the engagement of the gear selector control shaft with the gear selector positioning means may be controlled by any one of pneumatic, hydraulic, mechanical or electrical means. Also, the gear selector control shaft 16 may have a terminal female part that can mate with a male part of the positioning cam 23.