Patent GB-1337714-A (GB)
Title: Combined hydraulic and mechanical drive for multiaxle vehicles
IPC: F04B1/107
Filed: 1972-05-01
Abstract: 1337714 Vehicle drive system C K GREENE 1 May 1972 20117/72 Heading B7H [Also in Divisions F1 and F2] A drive system for a vehicle having driven wheels on two axles includes a differential pump having an input shaft coupled to the power plant, a high pressure fluid outlet, a fluid inlet, a pump output shaft and mechanical reacting means for driving the output shaft at a speed which varies, in relation to the speed of the input shaft, inversely with the quantity of fluid flowing through said inlet and outlet, the output shaft driving the wheels on a first axle and the fluid outlet and inlet being connected to at least one hydraulic motor for driving the wheels on a second axle. As described the differential pump 24 (Fig. 2) includes a housing 41, 42 in which are journalled an input shaft 23 and an output shaft 26. Fixed to the input shaft 23 is an assembly consisting of a swash plate 45, a skirt 50 and a valve plate 51. The output shaft 26 carries a pump block 52 formed with axial bores 53 having ports 56 and which contain pistons 57 having shoes 59 in contact with the swash plate 45. The valve plate 51 is formed with two semicircular grooves (not shown) which communicate with the cylinder ports 56. One of the semicircular grooves is connected by a duct (not shown) to an annular groove 64 which communicates with the pump outlet 68 and the other semicircular groove is connected by a duct (not shown) to an annular groove 65 which communicates with the pump inlet 69. In use the speed of the output shaft 26 varies inversely with the volume of fluid flowing through the pump. In a first embodiment (Fig. 1) the vehicle has tandem rear axles 18, 19. The input shaft 23 of the pump 24 is connected by reversing gear 25 to an I.C. engine and the pump output shaft 26 is connected via gear-box 28 and differential 27 to the wheels 14, 15 on axle 18. The wheels 16, 17 on axle 19 are driven by fixed displacement hydraulic motors 29, 20 via reduction gearing 31, 32. The motors 29, 30 are connected by ducts 34 and 35 to the pump outlet 33 and inlet 36. A by-pass duct 37 having a fluid control valve 38 is connected across the pump 24. The valve 38 can be operated by the driver by a cable 135, the valve being closed to start the vehicle. The valve 38 can also be opened by a solenoid 142 when changing gear, the solenoid being energized by switches 143 or 143a associated with the gear lever of the boxes 25 and 28 respectively. In this embodiment the differential pump 24 acts as a differential between the axles 18 and 19. In a second embodiment (Fig. 7) the vehicle, e.g. a passenger vehicle or racing car, has a fourwheel drive, the front wheels 70, 71 being connected to the differential pump 83 output shaft 84 via differential 75 and axle 73 and the rear wheels 76, 77 being connected to variable displacement motor 87 via shafts 86, 85, differential 78 and axle 79. The motor 87 is connected by ducts 89, 90 to the pump outlet 91 and inlet 92 and again a by-pass duct 93 with control valve 94 is provided. When starting the vehicle or accelerating the motor 87 is set at maximum displacement to provide a four-wheel drive. As the vehicle gains speed the displacement of the motor 87 can be progressively reduced until, at zero displacement, the pump input shaft 82 and output shaft 84 lock to provide front wheel drive only. A suitable construction of variable displacement motor is shown in Fig. 9, and includes a rotor 105 having radial bores 106 and pistons 109, the bores 106 communicating with ports 107, 108 in a fixed shaft. The pistons 109 carry rollers 110 which engage a cam ring which can be moved by screw 117 to vary the displacement of the motor. In a modification (not shown) of the second embodiment the assembly of the single motor 87 shafts 86, 85 and differential 78 is replaced by a pair of variable displacement motors, each of which is connected to a rear wheel through reduction gearing.