A hydrostatic bridge comprising an overall casing, two hydraulic motors having two distinct operating cylinder capacities, and a device for simultaneously selecting the cylinder capacities of said motors, each motor comprising:
- a cylinder block which is mounted to rotate about an axis of rotation relative to a reaction member secured to the overall casing against rotation about said axis, and including a plurality of radial cylinders suitable for being fed with fluid under pressure, the cylinder block being provided with a communication face perpendicular to the axis of rotation;
- and
- an internal fluid distributor secured to the overall casing against rotation and having a distribution face perpendicular to the axis of rotation, and a connection face, said distributor including distribution ducts which open out into said distribution face to be put into communication with the cylinders, said distribution face being suitable for being pressed against the communication face of the cylinder block;
- the axis of rotation being common to the two motors;
- the connection faces of the distributors of the two motors being situated facing each other, and the distribution faces of said distributors being urged axially against the respective communication faces of the cylinder blocks of the two motors;
- the motors including "main" ducts both of a first type and of a second type, said ducts being found in the overall casing, co-operating with the device for selecting the cylinder capacity of the motors, and being suitable for communicating with the distribution ducts, the main ducts of the first type belonging to one of two groups constituted by cylinder feed ducts and ducts for exhausting fluid from the cylinders, and the main ducts of the second type belonging to the other of said two groups;
- the bridge including four main ducts of the first type and two main ducts of the second type:
- the first and second main ducts of the first type being connected via respective first and second grooves to respective first and second groups of distribution ducts of the first motor;
- the third and fourth main ducts of the first type being connected via respective third and fourth grooves to respective first and second groups of distribution ducts of the second motor;
- the first main duct of the second type being connected via a fifth groove to a third group of distribution ducts of the first motor and to a third group of distribution ducts of the second motor, the ducts of the third group of distribution ducts of the first and second motors being hydraulically connected via the connection faces of the distributors of said motors;
- and
- the second main duct of the second type being connected via a sixth groove to a fourth group of distribution ducts of the first motor and to a fourth group of distribution ducts of the second motor, the ducts of the fourth groups of distribution ducts of the first and second motors being hydraulically connected via the connection faces of the distributors of said motors;
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- wherein the overall casing includes first, second, and third upstream ducts suitable for being connected to a main fluid source via a fluid circuit, the cylinder capacity selection device having a "large cylinder capacity" first position in which the first, second, and third upstream ducts are connected respectively to the first and second main ducts of the first type, to the third and fourth main ducts of the first type, and to the first and second main ducts of the second type, and a "small cylinder capacity" second position in which the first, second, and third upstream ducts are connected respectively to the first main duct of the first type, to the third main duct of the first type, and to the first main duct of the second type, the second and fourth main ducts of the second type communicating, in said second position, with each other and with the second main duct of the second type;
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- wherein the bridge includes an anti-spin device which comprises means for measuring the speed of rotation of each motor and for transmitting correction signals as soon as the speed of rotation of one of the motors becomes excessive, a first anti-spin valve suitable for reducing the fluid flow rate in the first upstream duct as a function of the correction signal relating to the first motor, and a second anti-spin valve suitable for reducing the fluid flow rate in the second upstream duct as a function of a correction signal relating to the second motor.