Patent GB-257986-A (GB)
Title: Improvements in or relating to the driving mechanism of endless track vehicles
IPC: B62D11/08
Filed: 1925-06-05
Abstract: 257,986. Dawson, Sir A. T., and Buckham, Sir G. T. June 5, 1925. Hydraulic transmission. - Comprises driving and steering gear for endless-track vehicles wherein the tracks are driven through separate epicyclic two-speed gears each having a clutch and brake alternately brought into action by a controlling member. The epicyclic gears may be controlled hydraulically by the means shown diagrammatically in Fig. 4, in which the brake band a<3> and clutch fork a<5> are respectively operated by pistons B, B<1> adapted to be put into communication by a hand-operated valve B<4> with a pressure pipe c and an exhaust pipe c<1>. In the position shown the piston B is not under pressure and the brake is "off," the piston B' is under pressure and the clutch is disengaged, the gear therefore being in the neutral position. 'When the valve B<4> is moved downwards neither piston is under pressure and the clutch is engaged by its spring, giving the high gear position; when the valve is moved upwards, both pistons are under pressure and the brake is applied to give the low gear. The valve lever b<5> controls the valves for both epicyclic gears, and means are provided for bringing either gear into the neutral position for steering while leaving the other gear in its set position. Relay or power apparatus.- In the modification shown in Figs. 8 and 10 the clutch and brake are operated from a power-driven shaft F through cams and clutches controlled by handlevers. These clutches are of a known kind and have rollers f disposed between the shaft F and inclined surfaces formed in the cam f<1>. A collar f<2> loosely mounted on the cam is connected thereto by a spring f<4> so that fingers f<3> on the collar tend to push the rollers against the inclined surfaces and clutch the cam to the shaft. A projection f<5> on the collar is normally held stationary by one or other of two arms g, g<1> of a rocker G, the cam not being driven. When the rocker is moved by a slide H to release the stop f<5>. the collar turns relatively to the cam and the rollers move and clutch the cam to the shaft. The cam rotates through half a revolution until the other arm of the rocker stops the projection f<5> and de-clutches the cam from the shaft. One of these clutches acts on the gear brake a<3>, as shown in Fig. 8 and another (not shown) acts on the clutch collar a<5> through suitable mechanism. The two cam clutches for each epicyclic gear are controlled by slides H actuated by rods h, h<1> pivoted to the end of a block H<2> sliding in a curved link H<3> and raised or lowered therein by a bell-crank lever h<2> connected to the gear lever b<5>. The link is pivoted at. its centre and is rocked about its pivot by the steering lever E which also applies the steering brake through an extension of the rod e. The controls are shown in the neutral position, the link H<3> having its centre of curvature in line with the pivots connecting the rods h, h<1> to the slides H. If the steering lever E is moved to. position I the link H<3> is rocked in a clockwise direction, the rod h is not affected but the rod h<1> is,moved to the left, thus causing the gear clutch to be engaged for the high gear. If the gear lever b' is moved to the position shown in broken lines the block H<2> is raised in the link. the rods h, h<1> are both moved to the right causing the gear clutch to disengage and the gear brake to be applied to give the low gear. Movement of the steering lever to position 2 applies the steering brake. In a modification the two links H<3> for the two epicyclic gears may be controlled by a single-hand-wheel instead of by separate levers E.