Hydraulic assistance system

The invention relates to a vehicle hydraulic assistance method comprising: two hydraulic devices connected therebetween by a supply line, a return line, a power boost source, and a tank, the power boost source being connected to the supply line and return line via a power boost line and taking the oil from the tank; and a vacuum valve including an input port, connected to the supply line and return line, and an output port connected to the tank. The vacuum valve has a first passing state and a second blocking state. The method includes the steps of: (E1) activating the power boost source when the vehicle fulfills at least one predetermined requirement, the vacuum valve being in the first passing state; and (E2) switching the vacuum valve from the first passing state to the second blocking state when hydraulic assistance is required, thus making it possible to boost power to the supply system and return system.

GENERAL TECHNICAL FIELD

The invention relates to the field of hydraulic assistance circuits used in particular for vehicles. In particular, the invention relates to the optimization of the activation time of hydraulic assistance motors.

PRIOR ART

Hydraulic assistance systems for vehicles are known which can be selectively engaged depending on the operating conditions of the vehicle or on command by a user.

Such systems thus complement a main high-speed vehicle transmission, usually mechanical, electrical or even hydrostatic.

In all of the present text, a hydraulic device is designated as a device capable of operating both as a motor and as a hydraulic pump. A hydraulic device conventionally comprises a plurality of pistons positioned in recesses, in a cylinder block, and carrying out reciprocal movements in contact with a multilobe cam in the case of a hydraulic device with radial pistons.

A particular structure of an assistance system is presented in patent application EP2013/069519 filed on 19 Sep. 2013 on behalf of the applicant.

This structure consists of mounting a first hydraulic device, which is designated as driving, on a shaft of the vehicle driven in rotation by the main transmission of the vehicle, and one or more hydraulic devices, which are designated as driven, on one of the other shafts of the vehicle, not driven by the main transmission, the driving and driven hydraulic devices being connected by a hydraulic circuit. The hydraulic devices each have an intake port and a discharge port. The discharge ports are each connected to an intake port by supply and return lines.

In operating without assistance, the two hydraulic devices are in a free wheel configuration; these are typically hydraulic devices with radial pistons, the pistons not being functional in the free wheel mode.

More precisely, for hydraulic devices with retractable pistons, a free wheel configuration is defined, i.e. a configuration in which the hydraulic device operates without fluid pressure and more particularly where the pistons are not in contact with the associated cam. For hydraulic devices with cylinder block de-coupling, i.e. when the cylinder block is no longer engaged on the shaft, a free wheel configuration is defined in the same manner, in which the shaft do not drives the cylinder block (or conversely).

In both cases, the pistons do not carry out reciprocating movements in contact with the multilobe cam. Such configurations are advantageous, for example, on devices having mixed operating conditions.

The opposite of this free wheel configuration is the operating condition, in which the hydraulic device operates with fluid pressure and the pistons carry out reciprocating movements in contact with the multilobe cam.

Transition from the free wheel configuration to the service configuration is called placement into service of the hydraulic device.

During engagement of the hydraulic assistance, the different hydraulic devices must be put into service. To that end, patent application FR 1351245, filed on 13 Jan. 2013 on behalf of the applicant, presents a booster system comprising in particular a booster source delivering a flow rate adapted to be selectively engaged, said booster source being connected to the supply line and to the discharge line via a booster line. As soon as slippage is observed on a rear axle of the vehicle, the booster source is activated to then deliver a flow rate to the driving hydraulic device, thus allowing the assistance system to be put into service.

However, such a booster system can have a rather extended reaction time (on the order of a second), which corresponds to the time required to raise the supply lines and discharge lines to boost pressure. Moreover, the hydraulic assistance system is generally engaged on demand by the driver, who can activate it in situations which do not necessarily require it.

Coupled with the starting reaction time, it happens that the hydraulic assistance system is activated when that is not necessary, which causes avoidable wear to the system.

PRESENTATION OF THE INVENTION

To correct the foregoing disadvantages, the invention proposes a hydraulic assistance method for a vehicle including:two hydraulic devices interconnected by a supply line and a return line,a booster source and a reservoir, the booster source being connected to the supply and return lines via a booster line and taking oil from the reservoir,a vacuum valve, comprising an input port connected to the supply and return lines, and an output port connected to the reservoir, the vacuum valve having a first, passing, state and a second, blocking, state;

the method comprising the steps of:E1: Activation of the booster source when the vehicle satisfies at least one predetermined condition, the vacuum valve being in the first, passing, state;E2: Switching of the vacuum valve from the first, passing, state to the second, blocking, state when hydraulic assistance is required, thus allowing boosting of the supply and return circuits.

Such a method makes it possible to improve the reaction time for putting the system into service and thus limiting the use of hydraulic assistance to necessary cases.

Advantageously, the invention has the following features, taken alone or in combination:The method comprises a third step E3: switching of the vacuum valve from the second, blocking, state to the first, passing, state when hydraulic assistance is no longer required, the booster source remaining activated,step E2 is always carried out when the booster source is activated,The method further comprises a fourth step E4: deactivation of the booster source when the vehicle no longer satisfies one of the predetermined conditions,the booster source is an electro-pump unit (GEP) comprising an electric motor and a pump, wherein the activation of the booster source consists of supplying electric power to the electric motor of said unit,the vacuum valve is a solenoid valve, controlled electronically by a control unit,one of the predetermined conditions is a speed of the vehicle lower than a threshold speed, such as 30 km/h,one of the predetermined conditions results from the analysis of the itinerary and/or the trajectory of the vehicle,information relative to the predetermined condition resulting from said analysis is provided by a global positioning system,the hydraulic machines are fixed displacement machines, having radial pistons and multilobe cam that can be disengaged,the booster circuit comprises non-return valves and pressure limiters between the booster source and the supply and return lines,a circuit selector is interposed between the supply and return lines and the vacuum valve.

The invention also proposes a hydraulic assistance system including:two hydraulic devices interconnected by a supply line and a return line,a booster source and a reservoir, the booster source being connected to the supply and return lines via a booster line and taking oil from the reservoir,a vacuum valve, comprising an input port connected to the supply and return lines, and an output port connected to the reservoir, the vacuum valve having a first, passing, state and a second, blocking, state;

characterized in that the hydraulic system includes:means for detecting a predetermined condition for triggering the activation of the booster source,means of determining the need for hydraulic assistance,means for controlling the states of the vacuum valve;the valve being put in the first, passing, state by the means for controlling the states of the valve when the detection means detect one of the predetermined conditions, andthe valve being put in the second, blocking, state by the means for controlling the states of the valve when the determination means determine a need for hydraulic assistance, thus allowing boosting of the supply and return circuits.

The invention also proposes a vehicle equipped with a hydraulic assistance system previously described and adapted to implement the methods previously described.

DETAILED DESCRIPTION

With reference toFIGS. 1a, 1b(from document EP2013/069519) and2, a schematic of the hydraulic system will be described.

The hydraulic assistance system is mounted on a vehicle V.

The system shown comprises a driving hydraulic device1, mounted on a front axle AV of the vehicle V and a driven hydraulic device2, mounted on a rear axle AR of the vehicle V. The hydraulic devices1,2typically have radial pistons, a multilobe cam and are fixed displacement devices, the radial pistons being mounted in a cylinder block. In particular, the multilobe cam can be disengaged, particularly by decoupling the cylinder block and the shaft of the axle.

So as to illustrate the operation of the system, its intake and discharge are labelled for each of these hydraulic devices, respectively intake11and discharge12of the driving hydraulic device1, and intake21and discharge22of the driven hydraulic device2.

The discharge12of the driving hydraulic device1is connected to the intake21of the driven hydraulic device2by a supply line4, and the discharge22of the driven hydraulic device2being connected to the intake11of the driving hydraulic device1by a return line5.

The hydraulic devices1and2are each associated with a rotating shaft, respectively13and23, typically a vehicle axle V. For example, the hydraulic devices1,2rotate at the speed of the shaft of the axle, or at the mean speed of the two wheels comprised on the axle (in the case of a differential).

A primary motor M is typically a thermal or electric engine.

The primary motor M can be coupled to a booster source3via a clutch33, allowing the engagement or disengagement of this booster source3with the primary motor M (seeFIGS. 1b, 2b).

This primary motor M is for example connected to a main transmission of the vehicle V allowing its wheels to be driven, the different structures of the main transmission and the wheels being well-known to a person skilled in the art and not being shown in the figures.

According to another variant, the primary motor M is an independent motor with respect to the main transmission of the vehicle V or the device considered. The primary motor M and the booster source3can then for example form an electro-pump unit (GEP). Typically, the electro-pump unit (GEP) comprises the primary motor M, when this is an electric motor, and a pump.

According to the embodiments shown, the booster source3comprises a booster pump31, and/or a hydraulic accumulator (not shown in the figures), and/or a filter34(seeFIGS. 1a, 2a).

The booster source3takes oil from a reservoir R, typically at ambient pressure. What is meant by reservoir is also the drive lines leading to the reservoir R and which can serve for storing oil.

The booster source3is connected to the supply4and return5lines via a booster line32.

In particular, the booster line32is connected to the return line5by a non-return valve61in the forward direction (booster source3toward the return line5) and by a pressure limiter62in the return direction (return line5toward the booster source3). The booster line32is connected to the supply line4by a non-return valve63in the forward direction and by a pressure limiter64in the return direction (seeFIGS. 1a, 2a).

The driving1and driven2hydraulic devices thus form a closed hydraulic circuit, the booster source3whereof provides a booster in pressure through the non-return valves61,63and pressure limiters62,64so as to compensate for losses and leaks in the circuit.

A vacuum valve7connects the return5and supply4lines to the reservoir R.

According to a first embodiment (seeFIGS. 1a, 2a), the vacuum valve7comprises an input port and an output port (two ports, two positions). The return and supply lines are connected to two inputs of a circuit selector8(seeFIGS. 1a, 2a), the output of the selector being connected to a port of the vacuum valve, the output port of the vacuum valve7being connected to the reservoir R. Alternatively, the circuit selector8can be replaced by a simple node (seeFIGS. 2a, 2b). The line extending from the supply4and return5lines is then connected to the input port of the vacuum valve7.

According to a first state, the valve7is passing and according to a second state, the valve is blocking.

According to a second embodiment (seeFIGS. 2a, 2b), the vacuum valve7comprises two input ports and one output port (three ports and two positions). The supply4and return5lines are each connected to an input port, the output port of the vacuum valve7being always connected to the reservoir R.

According to a first state, the valve7is passing, i.e. the two input ports communicate with the output port; according to a second state, the valve is blocking.

The vacuum valve7is controlled by an actuator71which can switch it from the first to the second state. A restoring element72, such as a spring, holds said valve7in the first state by default. The valve7is for example a solenoid valve and the actuator71is controlled by a control unit U.

At present, a method for using the booster circuit will be described with reference toFIG. 3.

The hydraulic assistance system is provided to be activated only when the vehicle V verifies at least one predetermined condition. As soon as at least one of the predetermined conditions is satisfied, the vehicle V is said to be in a standby state. For example, this standby state can be defined by speeds of the vehicle V lower than a threshold speed, typically 30 km/h. To that end, the hydraulic system or the vehicle has means for detecting said predetermined conditions.

When the standby state is in effect, the service configuration can be put into service during slippage of the rear axle AR or when a driver of the vehicle V desires it. To be put into service, it is necessary that the supply4and return5lines are boosted, so that the pressurization of said lines is possible to allow the torque transfer between the driving device1and the driven device2.

The slippage of the rear axle AR can be detected in particular by measuring the speed of the wheels of the vehicle V by means of sensors.

The shaft13applies an input torque to the driving hydraulic device1; the latter being passed in service configuration, it then delivers a flow rate through the intake21of the driven hydraulic device2, which causes its entry into service.

In a first step E1 (seeFIGS. 1a, 1b), if the vehicle V is in the standby state, the booster source3is activated, bringing oil from the reservoir R into the supply4and return5lines, and the vacuum valve7is in its first state (i.e. passing). Typically, the booster source3is the electro-pump unit (GEP).

The vacuum valve7is then passing, the oil injected by the booster source3into the supply4and return5lines will return to the reservoir R through the vacuum valve7(and/or the circuit selector8), thus opening the booster circuit of the supply5and return4lines. The system is therefore still in free wheel configuration.

In a second step E2 (seeFIGS. 2a, 2b), if the vehicle V needs hydraulic assistance, i.e. a slippage is observed, the control unit U commands the actuator71which causes the switching of valve7from the first into the second state (blocking state), thus closing the booster circuit of the supply and return lines. The booster source3remains activated. The supply4and return5circuits are then boosted by the booster source3and will allow torque transfer between the driving device1and the driven device2, as was explained previously. Once placement into service is carried out, the hydraulic devices1,2are in service configuration (seeFIG. 3): torque taken from the front axle AV is transferred to the rear axle AR.

As soon as hydraulic assistance is no longer demanded, in a third step E3, the actuator71puts the valve7into its first, i.e. passing, state, and the booster circuit is again open, which causes the pressure in the supply4and return5lines to drop. The hydraulic system thus transitions into the free wheel configuration.

As long as the vehicle V remains in the standby state, the booster source3remains activated. The booster source3is thus rotating “unloaded.” Finally, in a fourth step E4, if the vehicle V leaves the standby state, i.e. none of the predetermined conditions is satisfied, the booster source3is deactivated.

So as to be able to initialize this method, it is possible to provide a preliminary step E0, in which it is verified that none of the predetermined conditions is satisfied and that the booster source3is deactivated. In use, step E0 will follow step E4, allowing the method to be repeated.

Thanks to this method, the torque transfer from the driving device1to the driven device2occurs more rapidly because it is not necessary to wait for the activation time of the booster source3, nor to wait for the driver to activate hydraulic assistance. In addition, the hydraulic devices1,2are put into service only in a slipping situation of the vehicle V, which makes it possible to reduce the number of cycles carried out by the devices1,2and makes it possible to avoid noise nuisances.

The booster source3is dimensioned so that it is always capable of supplying a quantity of oil under a certain pressure, the vacuum valve7being capable of causing head losses.

The standby state can also be caused by analyses of the itinerary and/or the trajectory executed by the vehicle V, so as to anticipate a need for hydraulic assistance. In this manner, the predetermined condition can typically take into account the speed of the vehicle V and the characteristics of the trajectory (slope, road, etc.)

For example, it is possible to couple a global positioning system9, such as a GPS, to the hydraulic assistance system (seeFIG. 5) so that said global positioning system9supplies information relating to the predetermined condition.

The vehicle V needing to travel from a point A to a point B, the global positioning system detects the position91of the vehicle V and makes it possible to anticipate the presence of a rise92and of ground difficult to travel93(obstacles, mud, etc.) which require a torque on the rear axle AR of the vehicle V.

Thus, as soon as the vehicle reaches the beginning of the rise92and of the ground93, a predetermined condition is thus verified, which triggers the standby state of the vehicle V.