Patent GB-1184694-A (GB)
Title: Improvements in or Relating to Fluid Pressure Transmission Systems
IPC: B60K17/10
Filed: 1967-06-26
Abstract: 1,184,694. Hydrostatic transmission. SIMIT S.p.A. 26 June, 1967 [27 June, 1966], No. 29328/67. Heading F2D. An hydrostatic transmission for motor vehicles providing six forward ratios and reverse, comprises a constant-delivery engine driven pump supplying two sets of motors 1 and 2, 3 and 4 driving, in a three-axle vehicle, output shafts carrying wheels 7, 10, 14 and 17, the shafts on each side of the vehicle being interconnected by chains 11 and 18, or in a twoaxle vehicle each set of motors 1 and 2, 3 and 4 driving a respective output shaft carrying wheels (7<SP>1</SP>), (14<SP>1</SP>), Figs. 3-8 (not shown), and a distributer valve 21 for varying the transmission ratio by selectively connecting the sets of motors to the pump in series or in parallel. The control includes two further valves 19, 20, one for each set of motors. Each valve has three positions: a first for supplying one motor 1 and 4 of each set; a second supplying the other motors 2 and 3 of each set; and a third supplying both motors, in parallel, of each set. Motors 1 and 4 are identical, as are motors 2 and 3, but the motors 1 and 4 differ from motors 2 and 3 by effective stroke, cylinder sweep or gear ratio of their connection to the vehicle wheels, such that motor 2 and 3 provided the higher output speed. Operation.-First gear is obtained by supplying motors 1 and 2, and 3 and 4 in parallel, whilst second gear is obtained by operating only motors 1 and 4 in parallel. Operating motors 1 and 2, and 3 and 4 in series provides third gear, and fourth gear is provided by operating motors 2 and 3 in parallel. By operating motors 1 and 4 in series, or motors 2 and 3 in series, fifth and sixth gears respectively are provided. Distributer valve 21, Fig. 9 (not shown), consists of a pedal-operated control spool (21a) having two positions; (a) to connect the valves 19, 20, and hence the sets of motors, in parallel, in which position pressure is supplied from line 22 to both of lines 43, 45 to the valves 19, 20 and hence to the operative motors or motor of each set, and is returned in lines 44, 46, and (b) to connect the valves 19, 20 and hence each set of motors, in series, in which position pressure is supplied from line 22 to line 43 and hence valve 19 only, the return line 44 being now connected to line 45 to supply valve 20, The valve 21 also includes a further two spools (57), (58) operated by a hand lever (59) for forward, reverse, and a third position blocking supply to valves 19, 20 to lock the vehicle wheels. Differential action during steering.-To prevent skidding of the driving wheels when the motor sets are in series and the vehicle turns, a by-pass valve 42 is opened by compressed air from a reservoir 37 to connect lines 45, 46 to isolate motors 3 and 4. When the motor sets are in parallel, a valve 40 in the compressed air circuit is opened by the spool 21a of valve 21 so that, on turning the steerable wheels 24, 25, a slide 33 connected to the tie bar 31 of the wheels and carrying a cam surface 33a opens a valve 35 by means of a roller 34 abutting the cam surface, to open the valve 42 and isolate motors 3 and 4.