Patent GB-959690-A (GB)
Title: A hydraulic transmission
IPC: F16H61/46
Filed: 1961-07-18
Abstract: 959,690. Hydrostatic transmissions. SOC. ANON. DES ANCIENS ETABLISSEMENTS PANHARD & LEVASSOR. July 18, 1961 [July 19, 1960], No. 26036/61. Heading F2C. [Also in Division F1] In an hydraulic transmission comprising a pump with a homokinetic delivery and a motor connected in a closed hydraulic circuit, the pump has two cam-operated piston-cylinder groups, in which the delivery periods are slightly longer than the suction periods, and a further compensating piston - cylinder group permanently in communication with the pump suction and with its piston arranged to move in synchronism with the pistons in the other groups by mechanical means such that the volume of hydraulic fluid swept out or sucked in per second by this piston is at all times equal to the excess or deficit of the volume of hydraulic fluid sucked in per second by the other piston-cylinder groups, in comparison to the volume of hydraulic fluid discharged per second under homokinetic conditions from the motor. A shaft 5, Figs. 1 and 3, driven by an I.C. engine (not shown), drives the pump cam-shaft 9 arranged with cams 7 and 8, each of which operates on a roller 47, fixed to a guiding member 47a, to operate rockers 10 and 11, Fig. 2, and thereby cause the pistons 3 and 4 to reciprocate in their cylinders 1 and 2. The cams 7 and 8 have the same profile but are arranged 180 degrees out of phase on the shaft 9. An oscillating lever 34 fixed to the shaft 9 by an obliquely mounted ring 35 causes a slide-valve 22 to operate in synchronism with the pistons 3 and 4. In the position shown in Fig. 2, the slide-valve 22 allows the piston 4 to deliver to a motor 14 through ports 28, chamber 24, port 30, chamber 42 and conduit 16. The piston 3 receives from the motor 14 through conduit 15, chamber 43, chamber 25 and ports 27. When the valve 22 has moved to the left, piston 3 will be on delivery and piston 4 on suction. A slide-valve 40 may be positioned as by manual control 46 either to the right (as shown) or to the left to allow the suction and delivery conduits 15, 16 to be interchanged and thereby reverse the motor 14. The cams 7 and 8 are profiled to provide delivery periods exceed ing 180 degrees duration (say, 210 degrees) and thereby provide an overlap of the respective delivery periods to produce a constant total delivery to the motor 14, which eventually returns the constant flow to the pistons 3 and 4. However, since the suction periods of the pistons 3 and 4 are less than the delivery periods, compensation means must be provided to partially store the returned flow until required by one of pistons 3 or 4. The compensating means comprises a piston 18 operated by a cam 19, arranged on the shaft 9, and a rocker 20. The piston 18 is operated in synchronism with the pistons 3 and 4 to deliver to the latter in accordance with their suction characteristics. The delivery from the cylinders 3 and 4 and the corresponding compensation produced by piston 18 is varied, without altering the position of the T.D.C. of the pistons, by adjusting the position Z about which the rockers 10, 11 and 20 rotate along a line joining the axis X passing through the position of the piston cranks when the pistons are at T.D.C., and an axis Y, passing through the centre of the rollers 47; the axes QQ and PP being parallel. The adjustment of the position Z is achieved by adjusting the position of rocker pivots 52, which support ribs 48 of the rockers on needle rollers. The position of pivots 52 preferably adjusted by an hydraulic control comprising cylinders 58 and 59 which are each caused to slide over a fixed piston, such as 60, under the action of oil admitted at will to the left-hand or right-hand side of the piston 60 by piping 61. The rocker pivot supporting bushes 49-51 are connected so as to move in unison, for example by a transverse shaft 55 carrying teeth 56 which engage rack teeth 57. The piston-rods 12, 13 and 21 each have segments 53 provided with a spigot 54 which engages an opening in the rocker rib 48 to prevent longitudinal relative movement. The compensating piston 18 with a positive drive enables the engine, coupled to the shaft 5, to be started-up by acting on the output shaft of the motor 14.