Motor vehicles – Power – Including traction motor of kind driven by noncompressible...
Reexamination Certificate
1999-10-12
2002-04-09
Hurley, Kevin (Department: 3619)
Motor vehicles
Power
Including traction motor of kind driven by noncompressible...
C180S243000
Reexamination Certificate
active
06367572
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a drive assistance apparatus for a vehicle having a mechanical main transmission for driving displacement members of the vehicle, the apparatus comprising a main source of fluid under pressure suitable for being driven by first drive means to deliver fluid under pressure, and at least one hydraulic motor suitable for being fed with fluid under pressure by the main source of fluid to drive at least one displacement member of the vehicle, said motor having a stator and a rotor suitable for rotating relative to the stator about an axis of rotation, the motor comprising a cylinder block which belongs to a first one of the two elements constituted by the stator and the rotor, which is disposed inside a case, and which presents a plurality of cylinder-and-piston assemblies disposed radially relative to the axis of rotation, together with a reaction member for the pistons which belongs to the second one of said two elements, the motor also having a main fluid feed duct and a main fluid exhaust duct suitable for being put into communication with the cylinders, and an auxiliary duct connected to an internal space provided inside the case around the cylinder block and suitable for being put into communication with a fluid return tank, the motor being suitable for adopting a “working” configuration in which the pistons co-operate with the reaction member and are suitable for generating outlet torque under the effect of the fluid delivered by the main fluid source, and also a “free-wheel” configuration in which the pistons are maintained in the retracted position inside their cylinders so that the rotor is free to rotate relative to the stator without generating any outlet torque.
BACKGROUND OF THE INVENTION
French patent No. 1 425 800 discloses an assistance hydraulic motor and relates more particularly to maintaining said motor in its free-wheel configuration. It thus proposes using the leak return duct of the motor, which corresponds to the above-mentioned auxiliary duct, to connect it temporarily to a source of fluid under pressure which, by causing a relatively high pressure to exist inside the case, enables the pistons to be urged in such a manner as to cause them to be retracted radially into the cylinder block. That document also states that to pass from the free-wheel configuration to the working configuration, it is necessary to disconnect the leak return duct from said source of fluid under pressure and to connect it to a fluid return tank.
French patents Nos. 2 426 812 and 2 504 987 propose using resilient return springs to hold the pistons in their retracted positions inside their respective cylinders, while the motor is in its free-wheel configuration. For passing to the working configuration, those documents state merely that in operation the cylinders are fed with fluid under pressure, thereby causing the wheels carried at the free ends of the pistons to come into contact with the cam against the resilient return force exerted by the springs.
Conventionally, a vehicle fitted with drive assistance apparatus of the above-specified type is normally driven solely by the first drive means, e.g. the wheels of a first axle themselves driven by a main transmission that is mechanical. It is only when the travel conditions of the vehicle require additional drive force over and above that provided by the mechanical main transmission (e.g. going uphill) or additional braking force (e.g. going downhill) that the assistance hydraulic motor is used. This can apply, for example, under difficult conditions, e.g. on a worksite or on slippery ground. Conventionally, the assistance hydraulic motor is designed to drive other vehicle drive members, for example the wheels on a second axle.
With existing apparatuses, starting from a situation in which the vehicle is driven solely by the mechanical main transmission, it is necessary to slow the vehicle down considerably, or even to stop it completely, prior to causing the assistance hydraulic motor to change over from its free-wheel configuration to its working configuration.
When the vehicle is being driven solely by its mechanical main transmission, the drive members that are coupled to the assistance hydraulic motor cause the rotor of said motor to rotate, which motor is then in its free-wheel configuration. When the pistons are caused to move out from their cylinders so as to place their free ends (possibly fitted with wheels) in contact with the cam, this contact takes place suddenly, giving rise to shocks between the pistons and the cam, which runs the risk of prematurely damaging the cam and the free ends of the pistons (the wheels), and also to successive banging noises which are disagreeable and which give the driver of the vehicle the impression that the equipment is of poor quality.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention seeks to propose an apparatus to which changeover from the free-wheel configuration to the working configuration takes place under better conditions, thus making it possible to perform said changeover while the vehicle is traveling at a relatively high speed and while avoiding or greatly limiting any risk of premature wear of motor components and/or disagreeable banging noises.
This object is achieved by the fact that the apparatus comprises means for performing the successive stages of a sequence for causing the motor to pass from its free-wheel configuration into its working configuration, said sequence comprising an initialization stage in which the auxiliary duct is isolated from the fluid return tank and is connected to a “service” duct which is fed with fluid under pressure such that a “service” fluid pressure exists inside the internal space of the case, and in which the main feed and exhaust ducts are placed at a common “filling” pressure which is less than the service pressure but greater than the pressure of the fluid return tank, the sequence further comprising, after the initialization stage, a clutch engagement stage during which the auxiliary duct is put into communication with the fluid return tank and during which the main feed and exhaust ducts are isolated from each other.
In the free-wheel configuration, the pistons can be held retracted inside the cylinders either by fluid pressure inside the case, or by return means such as resilient springs.
In the first case, the piston deactivation pressure can be equal to or substantially equal to the service pressure and it can be obtained by the leak return duct being connected to the service pressure source. In the free-wheel configuration, the main feed and exhaust ducts are conventionally connected to the fluid return duct.
Thus, in this first case, when it is decided to change over from the free-wheel configuration to the working configuration, the first condition for obtaining the initialization stage, i.e. obtaining the service pressure inside the case, is already acquired, and the initialization stage is implemented by placing the main feed and exhaust ducts at the filling pressure which is higher than the pressure of the fluid return tank.
When resilient return means such as springs are used for deactivating the pistons, the main ducts and the fluid return ducts are normally connected to the fluid return tank in the free-wheel configuration. Consequently, when it is decided to pass from said configuration to the working configuration, it is necessary firstly to connect the leak return duct to the service duct so as to cause the service pressure to exist therein, and secondly to place the main feed and exhaust ducts at the filling pressure.
Such resilient return means enable the hydraulic motor to be deactivated without requiring deactivation pressure to be permanently maintained in the circuit.
In any event, at the end of the initialization stage, the main feed and exhaust ducts are at the filling pressure while the space inside the case is at the service pressure which is slightly higher than the filling pressure. In this situation, when the auxiliary duct is put into communi
Maletschek Karl-Günther
Rouillard Jean-Marie
Hurley Kevin
Poclain Hydraulics Industrie
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