Patent EP-0054500-A1 (EP)
Inventor: FOUQUET JEAN-CLAUDE
IPC: B60K17/356
Filed: 1981-12-16
Abstract: 1. Hydraulic device for driving a semi-trailer coupled to a road tractor vehicle or vehicle for site work, which device is adapted to be controlled from the gear box (2) and a declutchable power take off (3) of a combustion engine (1) of the tractor in order to transmit the mechanical torque of the engine (1) to at least one axle of the semi-trailer, comprising a closed hydrostatic system (13, 14, 15) which ensures the mechanical transmission between the power take off (3) of the tractor and the corresponding axle (9) of the semi-trailer, this hydrostatic system being capable of reproducing the movements controlled from the gear box (2) of the tractor, and comprising a hydraulic pump (13) of variable flowrate, connected to the power take off (3), and a hydraulic motor (14) mounted of the semi-trailer, supplied by the hydraulic pump (13) and connected to a transfer box (7) coupled to an axle assembly (9) of the semi-trailer, it being possible for the hydraulic pump (13) to be locked to one or the other of two separate displacements corresponding in one direction to the forward movement of the vehicle and in the other to the reverse movement of the vehicle, characterized in that there are provided means to synchronize the gears of the tractor and of the semi-trailer over at least one gear of forward movement and at least one gear of reverse movement, and this synchronization is effected by determining the displacement X of the hydraulic pump of variable flowrate and the displacement Y of the hydraulic motor, according to the following formulae : X=Y . DP . R1/Z . BTC . V . R2 Y=X . Z . BTC . V . R2/DP . R1 in which : D=constant demultiplication of the declutchable reducing transfer box (7) mounted on the semi-trailer, P=constant demultiplication of the axle assembly (9) mounted on the semi-trailer, R1=rolling circumference of the tyres provided on the axle assembly (5) of the tractor, R2=rolling circumference of the tyres provided on the axle assembly (9) of the semi-trailer, V= volumetric efficiency of the pump (13) and of the hydraulic motor (14), Z=constant ratio of demultiplication of the power take off (3) with respect to the engine (1) of the tractor, B=constant ratio of the gear box (2) of the tractor in which synchronization is effected, T=constant ratio of the transfer box which is capable of being mounted between the gear bos and the axle assembly, C=constant, total reduction of the axle assembly (5) mounted on the tractor, and the hydraulic motor (14) has two separate displacements, proportional to the two corresponding gearing ratios used in the  gear box (2) in forward movement, namely : - Y(AV1) for the value B corresponding to the demultiplication of the first gear of forward movement of the gear box (2) of the tractor, - Y(AV2) for the value B corresponding to the demultiplication of the second gear of forward movement of the gear box (2) of the tractor, the device provided, moreover, with means for automatically controlling the hydrostatic system (13, 14, 15, 16) from the gear box (2) of the tractor, in particular for declutching, clutching, for the first forward movement gear, for the first reverse movement gear and for the second forward movement gear.