WO2018078039A1

WO2018078039A1 - All terrain vehicle drive assistance system

Info

Publication number: WO2018078039A1
Application number: PCT/EP2017/077498
Authority: WO
Inventors: Jean Heren; André PRIGENT; Vincent SOHIER; Cyrille D'hersignerie
Original assignee: Poclain Hydraulics Industrie
Priority date: 2016-10-28
Filing date: 2017-10-26
Publication date: 2018-05-03
Also published as: FR3058101B1; FR3058101A1

Abstract

The present invention relates to a system assisting with the driving of a secondary axle (23, 24) fitted to a vehicle comprising a main axle, comprising a pump (200) driven by a drive such as a combustion engine of the vehicle, a hydraulic machine acting as a motor (130, 140) equipping each driven wheel (23, 24) of the secondary axle, and a control unit (290), characterized in that it comprises control means (290, 292) designed to automatically control the thrust applied by the driven wheels of the secondary axle (23, 24) according to the configuration of the terrain, notably the amplitude and direction of the gradient of the terrain.

Description

Assistance system for training an off-road vehicle

FIELD OF THE INVENTION

The present invention relates to the field of hydrostatic transmissions for engines powered by engines fitted to the wheels or axles.

Such engines are generally referred to as "wheel motors". In particular, such motors may incorporate the bearing function, including bearings and a wheel shaft. The rotor of these engines runs at wheel speed. Such engines may also incorporate static or dynamic brakes. These engines are particularly advantageous for being placed on straddle machines without axle, that is to say with broken axles or independent wheels for hydrostatic traction on steered wheels, or for machines with variable height.

More specifically, the present invention relates to machines of the type illustrated in Figures 1 and 2 attached, comprising at least two motorized axles, a main axle and a secondary axle, and a control unit, for example a central unit formed of a calculator, which drives the motorization of at least one axle.

PRIOR ART

Various types of the type illustrated in FIGS. 1 and 2 are known. Generally, according to the prior art, a main central unit controls the motorization of at least one axle, preferably all the axles, in order to distribute the torque correctly on the axle. set of driving wheels of the machine. Such a main central unit is driven, or driven, for driving the machine, and for this can be interfaced with a driver or robot or an external remote control. The machine is driven or driven in that it receives commands to perform a trajectory at a certain speed.

FIG. 1 schematically illustrates a known machine of the aforementioned type comprising a motorized main axle P and an axle secondary motorized S placed on a common chassis C, powered by a pump Po driven by the ECU.

FIG. 2 schematically illustrates a known machine of the aforementioned type comprising a motorized main axle P placed on a tractor vehicle VT and a motorized second axle S placed on a towed vehicle or trailer R, powered by a pump Po driven by the central unit ECU .

Hydrostatic transmission systems comprising a power source, for example a heat engine or another source of alternating power, at least one pump powered by the power source and at least one wheel or axle motor powered by the pump, are known for the motorization of a machine.

The present invention relates to this type of hydrostatic transmission system.

The combination of a pump powered by a power source, and a wheel or axle motor is a hydrostatic transmission. In a known manner, it is possible to vary the gear ratio of the transmission by varying the displacement of the pump, and possibly motors. The circuit can also be controlled in pressure by the displacement control of the pump. In a usual manner, the hydrostatic transmission machines are controlled in flow or pressure via a displacement control of the pump. For machines equipped with a variable displacement pump, the stoppage of the machine can be obtained by setting the displacement of the pump to zero.

In a manner known per se, the driving of the pump or pumps by the power source, in particular by a heat engine, is carried out directly or indirectly, that is to say that the shaft of the pump can be linked to the shaft of the power source, or through other intercalated bodies.

In a hydrostatic transmission of mobile machinery, the distribution of the torque transmitted to each wheel of the vehicle is proportional to the state of pressure at the motor terminals, and to its active displacement.

When using mobile machinery, the operating conditions may vary greatly. This can be related to the load variation at each wheel, the ground itself, flat or sloping (rise, descent, rears ...), with the consequent risk of slippage of one or more wheels of the wheel. gear.

On certain mobile machines, one can have a part of the machine that has its main transmission, and other parts corresponding to load wheels that have no transmission. For example, one can have carrying axles on a machine, or trailers, or trailed tools. On these machines, we are interested in placing a secondary hydrostatic transmission, or assistance, on these wheels.

As indicated above with reference to FIGS. 1 and 2, some manufacturers propose to the driver to adapt the distribution of the torque to the various driving wheels of the machine, by acting on a selector located at the driving position, at the level of the central unit ECU, and requiring manual control. The driver sets the thrust he wants on the secondary part of the machine that is assisted. On very simple systems, the assisted part provides a constant thrust, and the driver activates or neutralizes the assistance depending on the terrain.

In this type of ergonomics, the intervention of the driver is necessary to anticipate a skating situation and to avoid poor driving conditions for an inexperienced driver and also to adjust the desired torque to the power wheels, in particular according to the machine goes up or down a slope.

The provision of a selector at the driving position, however, creates in practice many problems because the user must drive the vehicle properly, often in difficult conditions, while controlling the selector. (see page 10) It is not necessary to have an ECU electronic entity in the proper sense. In a broader manner according to the state of the art, the part of the machine corresponding to the P and S axles, which are controlled, must simply be managed by the driver. This may be a mechanical transmission, or a hydraulic transmission with mechanical control, or a hydraulic transmission managed by an ECU.

In the remainder of the description and in the claims, the expression "control unit" will be used to designate both a central unit formed of a computer or electronic entity and a control operated by a driver without a central unit, whether it be directly or via a robot, a remote control or any other means.

Attached to FIG. 3 is shown schematically a hydraulic system comprising a hydrostatic transmission thus known to those skilled in the art.

FIG. 3 shows an open-type hydraulic circuit, that is to say in which a hydraulic pump 19 for supplying the circuit draws oil into a reservoir 13 and the oil return at the outlet of the supply circuit is returned to the tank (as opposed to the so-called closed circuits in which generally a booster pump is required to maintain a minimum pressure in the closed circuit, which comprises a forward branch and a return branch between the pump main and hydraulic receiver of the circuit, the closed loop not passing through the tank, while the booster pump taps into the tank to maintain a minimum pressure in the closed loop).

The present invention can also be applied to both an open type hydraulic circuit and a closed type hydraulic circuit.

More precisely still, FIG. 3 appended hereto shows a tractor vehicle referenced schematically 10 and a trailer referenced schematically 20. The tractor vehicle 10 comprises a power source or main motor 12, for example a heat engine, a clutch 14 associated with the engine 12 and a gearbox 16 connected to the output of the clutch and interposed between the clutch 14 and a clutch 14. driving axle 18.

Also shown in Figure 3, a PTO 17 driven directly or indirectly by the main motor 12 and placed for this purpose, either on an output of the motor 12, or at the output of the gearbox 16, and a hydraulic machine pump 19 driven by the PTO 17.

The towing vehicle 10 further comprises a tank 13, a suction pipe 11 which connects the tank 13 to the inlet of the pump 19, a supply pipe 15 connected between the outlet of the pump 19 and a connector 30 intended to to be connected to a complementary connector element 31 provided on the trailer 20 and a return duct 34 placed between a connector 32 intended to be connected to a complementary connector element 33 provided on the trailer 20 and the reservoir 13. The towing vehicle 10 may also comprise a filter 36 placed on the return duct 34.

The trailer 20 comprises a secondary axle 22 comprising two wheels 23, 24 associated with respective hydraulic machines

130, 140 forming engines.

In FIG. 3, the conduits, connected in parallel, for supplying the motors 130, 140 are referenced 131, 141. The return ducts, connected in parallel, of the two motors 130, 140 and 132 are referenced 132, 142 and referenced 133, 143 conduits that lead to the housing of the motors 130, 140.

The links defined between the connectors 31, 33 and the conduits

131, 132, 133, 141, 142, 143 above are controlled by a set of components comprising hydraulic valves grouped in Figure 1 under the reference 50.

As indicated above, a selector 40 with manual control is made available to the user, on the vehicle tractor 10, at the driving station thereof to drive the components 50.

As indicated above, although having rendered great services, the systems of the type illustrated in FIG. 3 have the disadvantage of obliging the driver of the vehicle to keep his attention on both the selector control 40 and the driving of the machine. In practice, these obligations lead to complicated situations for an inexperienced driver. In particular, it is not pleasant, and difficult for an inexperienced driver that the assistance gives effects contrary to driving, in particular that the secondary part of the machine that is assisted pushes the main part of the machine, by example in descents.

PROBLEM POSE TO RESOLVE

In this context, the present invention aims to improve the state of the art by proposing new means that allow automatic control of engine capacity, without requiring the intervention of the driver. In other words, one of the problems to be solved in the context of the invention is, for an assisted secondary axle, which is not the main axle of a vehicle, to automatically control the thrust torque, in particular depending on the slope of the terrain on which the vehicle is moving.

BASIS OF THE INVENTION

This object is achieved in the context of the present invention through a system for assisting the driving of a secondary axle equipping a vehicle also comprising a main axle, which system comprises a pump driven by a drive such as an engine. thermal engine of the vehicle, a hydraulic engine machine equipping each driving wheel of the secondary axle, and a control unit, characterized in that the main axle is a driven drive axle and the secondary axle is a motorized axle follower, and that it includes control means adapted for automatically control and modulate the thrust applied by the driving wheels of the secondary axle according to the configuration of the terrain, including the amplitude and the direction of the slope of the terrain, so that the driving force generated by the thrust applied by the driving wheels of the secondary axle, combined with the driving force induced by the slope of the terrain on which the vehicle is traveling, does not disturb the driving force generated by the driven main engine axle.

In the context of the present invention, the term "does not disturb" that the driving force generated by the thrust applied by the drive wheels of the secondary axle is modulated, taking into account the motor force induced by the slope of the ground. whether a rise or fall, so that the sum of the driving force generated by the thrust applied by the driving wheels of the secondary axle and the driving force induced by the slope of the ground, does not lead to an antagonistic component greater than that of the motor force generated by the main driving axle and driven.

It should be noted that the secondary gear is always follower of the master gear, and that the speed of the wheels is linked only by the ground. The secondary system seeks to define a thrust torque, so that if the wheels of the secondary machine do not touch the ground, their speed may be different from those of the master machine.

According to other advantageous but non-limiting features of the invention:

the system comprises a control unit which controls the main driving axle and a central unit which controls the secondary axle.

the system comprises two central units, one which controls the main driving axle and the other which controls the secondary axle.

- the secondary axle is placed on a towed vehicle or trailer, while the main axle is placed on a towing vehicle,

- the system includes an engagement valve (of clutch) or short-circuit of the motor driving the driving wheels of the secondary axle, - The control means adapted to automatically control and modulate the thrust applied by the driving wheels of the secondary axle according to the terrain configuration are also adapted to operate this control and modulation according to the load on the secondary axle and the configuration of the secondary vehicle element carried by the secondary axle,

- The wheel motors fitted to the secondary axle are wheel-drive engines,

- The wheel motors perform a bearing function of the wheel.

The present invention also relates to a method of assisting the driving of a secondary axle equipping a vehicle also comprising a main axle, with the aid of a system comprising a pump driven by a drive such as a combustion engine. vehicle, a hydraulic engine machine fitted to each driving wheel of the secondary axle, if applicable a (clutch) engagement valve or short-circuit of the engine driving the driving wheels of the secondary axle and a control unit characterized in that the main axle is a driven drive axle and the secondary axle is a follower motorized axle, and comprises steps of automatically controlling and modulating the thrust applied by the drive wheels of the axle depending on the terrain configuration, including the amplitude and direction of the slope of the terrain, so that the driving force generated by the thrust has driven by the driving wheels of the secondary axle, combined with the driving force induced by the slope of the terrain on which the vehicle is traveling, does not disturb the driving force generated by the driven main engine axle.

The present invention also relates to vehicles equipped with the previously defined system and / or implementing the method according to the present invention.

QUICK DESCRIPTION OF THE FIGURES Other features, objects and advantages of the present invention will appear on reading the detailed description which follows, and with reference to the appended drawings, given as non-limiting examples and in which:

FIGS. 1 and 2 previously described schematically represent devices known from the state of the art, comprising a central unit which jointly controls a main axle and a secondary axle,

FIG. 3 previously described represents a hydraulic circuit known from the state of the art,

- Figures 4 and 5 annexed schematically represent gear according to the invention, respectively of the type tractor and towed together for Figure 3, single frame according to Figure 4, comprising a control unit for driving the main axle and a electronic central unit for driving the secondary axle, for example two separate central units for driving respectively the main axle and the secondary axle,

FIG. 6 is a diagrammatic view of an exemplary embodiment of a hydraulic circuit according to the present invention; FIGS. 7, 8, 9 and 10 respectively represent the configurations of the circuit in traction forward on an increasing slope; retained forward on a decreasing slope, held back on an increasing slope in the forward direction and pulled back on an increasing slope in the forward direction,

FIG. 11 schematically represents a summary of the four configurations corresponding to FIGS. 7 to 10,

FIG. 12 represents a view similar to FIG. 11 in the case of taking into account an additional state of braking of the vehicle,

FIGS. 13 and 14 schematically illustrate variants of FIGS. 11 and 12 in the context of a variant of the invention incorporating a proportional piloting function of pressure,

FIG. 15 diagrammatically represents a hysteresis function taken into account in the context of a variant of the invention, FIG. 16 diagrammatically represents the pressure control curve according to a variant of the invention,

FIG. 17 represents a variant of FIG. 14 in the context of pressure steering as a function of the angle of the slope of the terrain on which the vehicle is moving,

FIG. 18 schematically illustrates the transition phase between two pressure configurations according to the present invention, and

- Figure 19 schematically shows a cross-sectional view of a radial piston hydraulic machine preferably used in the context of the present invention.

GENERAL DESCRIPTION

FIGS. 4 and 5 show, in a diagrammatic representation, vehicles according to the present invention, in which a main axle P and a secondary axle S are driven by respective central units ECU1 and ECU2 made up of computers or electronic entities. The central unit ECU 1 which controls the main axle P, receives its orders from a driver or a robot or a remote control. However, it is not necessary in the context of the present invention to have an ECU electronic entity 1 in the proper sense. In a broader manner, the part of the machine corresponding to the P axle, which is controlled, must simply be managed by the driver. This can be a mechanical transmission, or a hydraulic transmission with a mechanical control, or a hydraulic transmission managed by an ECU electronic central unit. In general, it is observed that the part of the machine corresponding to the axle P forms a set driven directly by the driver.

(see page 4) In the remainder of the description and in the claims, the term "control unit" will be used to designate all of the potential control means of the main axle in the context of the present invention. , including in particular both a central unit formed of a calculator or electronic entity and a command operated by a driver without a unit central, whether directly by a driver or driver, or via a robot, a remote control or any other means.

The central unit ECU2 which controls the secondary axle S has its own control based on information specific to the configuration of the terrain, in particular the amplitude and the direction of the slope of the terrain, or even the load on the secondary axle. or the configuration of the element carried by the secondary axle. In the broad sense, the ECU 2 is any means of control to drive the secondary axle S, whatever its form. It can be any form of autopilot, electronic, electrical, or mechanical.

FIG. 4 schematically illustrates a machine comprising a motorized main axle P placed on a tractor vehicle VT powered by a pump Pp driven by a control unit, for example the main central unit ECU 1, and a motorized second axle S placed on a towed vehicle or trailer R, powered by an associated auxiliary pump Po2 driven by the ECU2 subunit. In Figure 4 the possibility of using a control unit to drive the main axle P, not an ECU electronic central unit 1, is shown schematically by the arrow directly connecting the symbol of a driver and the pump Pol.

FIG. 5 schematically illustrates a machine comprising a motorized main axle P and a motorized secondary axle S placed on a common chassis C, the main motorized axle P being fed by a pump Pol driven by the main central unit ECU 1 and the powered secondary axle S being powered by an auxiliary auxiliary pump Po2 driven by the secondary central unit ECU2. In FIG. 5 the possibility of using a control unit to control the main axle P, and not an electronic central unit ECU 1, is also shown schematically by the arrow directly connecting the symbol of a conductor and the pump Pol.

The orders applied respectively to the central units ECU1 and ECU2 are a priori independent and different. The driver controls and modulates the speed of the craft via the main ECU 1 by acting on the main axle P, while the secondary central unit ECU2 can modulate the thrust generated by the secondary axle S without a direct link with the main central unit ECU 1. Typically the secondary central unit ECU2 drives the thrust, following that the craft moves on an upward or downward slope.

In the remainder of the description and in the claims, the term "thrust" will be used to generate both a positive force with respect to the direction of movement of the vehicle corresponding to a traction and a negative force with respect to the direction of movement of the corresponding vehicle. to a restraint.

Thus the main central unit ECU 1 essentially manages the speed of the machine, while the secondary central unit ECU2 essentially manages a torque, via a pressure or a slip speed gap at the wheels. So we can at times have a steering to reduce speed, because the driver wants to slow down on the main part of the machine, while ECU2 pushes the secondary part of the machine, because it is still on a slope rising, and that does not disturb the driving. However, with the same driver's commands, in a downward slope, ECU2 would decide to carry out a restraint so as not to disturb the driving.

Furthermore in the following description and in the claims will be called "vehicle master element" the vehicle part carried by the main axle P and "secondary vehicle element" the vehicle part carried by the secondary axle S. The vehicle master element constitutes a tractor element, while the secondary vehicle element constitutes a towed element, in the case of a two-part vehicle, tractor on the one hand and towed element or trailer on the other hand. On the other hand, the vehicle master element and the vehicle secondary element are combined when the main axle P and the secondary axle S are placed on a common chassis.

EXAMPLE OF CARRYING OUT THE INVENTION Subsequently and for simplification we will essentially describe the invention with respect to a combined type of machine configuration, comprising a towing vehicle and a towed vehicle or trailer. The invention is however not limited to this particular configuration and also applies to machine configurations comprising the main driving and driven axle and the follower secondary axle on a common chassis.

FIG. 6 shows a hydraulic system adapted to be installed on a vehicle trailer, for example the towed element of a tillage implement, such as a plow with hydraulic wheel motors, or such as a towed potato harvester with hydraulic wheel motors.

The system shown in FIG. 6 is adapted to be mechanically driven by the power take-off 17 of the tractor element not shown in FIG. 6.

The hydrostatic transmission shown in FIG. 6 is of the closed circuit type. It could be, if necessary, of open type, as indicated above.

We find in Figure 6:

two bearing wheels 23, 24 of the secondary axle S, in this case the towed element,

- Two engine hydraulic machines 130, 140 connected to the respective shafts of the wheels 23, 24. Where appropriate, the wheels 23, 24 could be connected by a common axle. However, preferably, in the context of the invention, the wheels 23, 24 are placed on a towed trailer type striker without axle, that is to say that the wheels 23, 24 are independent and are not connected by a common axle, although they are coaxial when traveling in a straight line.

supply ducts 131, 141, return ducts 132, 142 and ducts 133, 143 connected to the motor casing.

flow dividers 139, 149 associated respectively with supply lines 131, 141 and return lines 132, 142, brakes 135, 145, for example of the drum brake type,

actuators 136, 146 of the aforementioned brakes 135, 145,

a temperature sensor 134 associated with the flow divider 149, a pressure sensor 144 associated with the flow divider 139.

a flow divider 147 supplied by the line coming from the braking circuit of the tractor, leading to the actuators 136, 146,

a pressure sensor 148 associated with the flow divider 147,

a hydraulic machine 200 forming a pump,

a mechanical switching box 202 interposed between the power take-off 17 and the inlet of the pump 200, making it possible to switch on or off the drive of the pump 200, and possibly having an auxiliary gearbox function,

a booster pump 210 associated with the pump 200,

a pressure limiter 213 associated with the booster pump 210.

an oil tank 220,

a line 212 through which the booster pump 210 pumps into the tank 220 via a filter 214,

a block 230 having a refrigerant function of the oil. The refrigerating block 230 is known per se and does not constitute an essential element of the invention. It will not be described in more detail later.

- A control valve 240. The control valve 240 is according to Figure 6 a three-way valve, three positions. Its structure and operation are known to those skilled in the art and therefore will not be described in more detail later.

a valve 250 of engagement / disengagement or clutch / clutch assistance. The engagement / disengagement valve 250 is a two-way valve, two positions according to Figure 6. Its structure and operation are known to those skilled in the art and will therefore not be described in more detail later.

a feed line, in high pressure in forward direction, referenced 204 which connects the outlet of the pump 200 to the valve of command 240 and a forward or low pressure forward line referenced 206 which connects the control valve 240 to the inlet of the pump 200,

a supply line 242 which connects in advance of the high-pressure supply line 204 to the flow divider 139 and therefore to the supply inlets 131, 141 of the motors 130, 140, via the control valve 240

- A return line 244 connected by the control valve 240 to the return line 206 and which communicates with the flow divider 149 and therefore the outputs 132, 142 of the motors 130, 140.

a pressure-relief assembly 260 placed between the high-pressure lines 204 and the low-pressure lines 206. The structure and operation of such a pressure-limiting assembly 260 are known to those skilled in the art and will therefore not be described more in detail afterwards,

a double-acting cylinder 270 serving to control the pump 200 by controlling the displacement of said pump 200 with variable displacement. Typically and in a manner known per se, the jack 266 controls the position of a plate controlling the variable displacement of the pump 200.

a pressure reducing assembly 275 more precisely comprising two pressure reducers 276, 277 communicating respectively with the two chambers of the double-acting jack 270 to provide proportional pressure control of the jack 270 enabling the displacement of the displacement pump 200 to be controlled; variable.

pressure limiters 278, 279 respectively associated with the proportional pressure reducers 276, 277. The proportional pressure reducers 276, 277 regulate a proportional thrust level at the motors 130, 140,

a switching assembly 280 comprising two on / off switching valves 282, 284 respectively associated with the two chambers of the double-acting jack 270 to switch the system between a traction position and a position retained according to the slope of the ground on which the vehicle,

a central control unit 290, a human / machine interface 292 connected to the central unit 290 and allowing the user to set various operating parameters of the system,

a vehicle speed sensor 294, and

- A tilt sensor 296, or an inclinometer, adapted to measure the slope on which the vehicle moves.

The precise structure of the circuit shown in Figure 6 will not be described in detail later since a number of these components are known to those skilled in the art.

The means 275, 280 and the double-acting cylinder 270 adapted to control the displacement of the variable pump 200 are in particular known to those skilled in the art and described for example in the documents EP 2551524, FR 3011288 and WO2014 / 016304. MEANS AND VARIANTS COMPLYING WITH THE INVENTION

STRUCTURE OF HYDRAULIC MACHINERY

Preferably, the hydraulic machines forming the motors 130, 140 and, if appropriate, the pump 200, are radial piston engines of the type illustrated in the attached FIG.

Preferably, hydraulic machines forming motors 130,

140 are more precisely retractable piston engines.

The structure of such motors 130, 140 is well known in itself to those skilled in the art and will not be described in detail later.

The company POCLAIN HYDRAULICS manufactures and markets many radial piston engines of the type shown schematically in Figure 19.

It should be remembered, however, that, preferably, the radial piston hydraulic motors of the type illustrated in the attached FIG. 19 comprise in a housing 110:

a multi-lobe cam 112 preferably formed on the internal surface of a housing element,

a cylinder block 114 mounted relative rotation in the casing 110,

a shaft 116 connected to rotation with the cylinder block 114, pistons 118 guided in a radial sliding manner in the respective cylinders 117 of the cylinder block and bearing on the lobes of the cam 112, preferably by means of rollers 115.

The radial piston engines of the type illustrated in the attached FIG. 19 also comprise (not shown in FIG. 19) a distributor adapted to successively apply a pressurized fluid in the cylinders 117 and consequently on the pistons 118 in a controlled manner, so that that the successively support of the pistons 118, by means of the rollers 115, on the lobes of the cam 112, causes the relative rotation of the cylinder block 114 and elements which are connected to it relative to the casing 110.

We will now describe various features, optional for some, specific to the control process according to the present invention.

ABSENCE OF POSITIVE PUSH IN DOWNHILL

In the first place, the control means integrated in the central unit 290 according to the present invention are preferably adapted not to apply positive thrust or downward pull on the secondary axle constituted by the wheels 23, 24, that is to say when the vehicle is traveling on a negative or decreasing slope, but instead apply restraint on this secondary axle. In practice such restraint can be operated by applying a high pressure not on the input of the motors 130, 140, but on their output.

DIFFERENT PUSH VALUE BETWEEN FLAT AND SLOPE

For this purpose, the control means 290 are preferably adapted to define a first thrust value when the vehicle is moving on a flat surface and a second thrust value different from the first value when the vehicle is traveling on a slope. TORQUE OR SPEED CONTROL

The thrust defined by the motors 130, 140 is, according to the invention, determined:

- or by a torque control to the wheels 23, 24, that is to say in hydraulic pressure, defined by a pressure control of the pump

200

or by a wheel speed control 23, 24, defined by a control in the displacement position of the pump 200 to which the speed of the secondary wheels 23, 24 is linked, by defining a speed difference, positive or negative, between the wheels 23, 24 of the secondary axle and a speed reference representative of the speed of the vehicle master element, that is to say of the main driving part of the vehicle, for example from a measurement the speed of the main axle or the wheels of the main axle, or of a ground radar, GPS data or speed data measured on a wheel bearing the vehicle master element, or any means equivalent.

PARAMETERS FOR DEFINING THE PUSH

As indicated above, according to the invention, the thrust applied by the drive wheels 23, 24 of the secondary axle is automatically controlled as a function of:

- the load on the secondary axle,

the configuration of the secondary vehicle element carried by this secondary axle, and

- the terrain configuration, including the amplitude and direction of the slope of the terrain on which the vehicle is moving.

The charge represents the state of charge of the secondary vehicle element, that is to say in the case of a towed vehicle, if the machine constituting the towed element is more or less loaded (the load represents by example the filled or empty condition of the trailer or a spray tank). The load value can be entered by the user via the man-machine interface, or given by load sensors, or leveled for liquid loads. The configuration of the machine corresponds to its implementation: for example spray boom deployed or not, special tool in place or not, wheel size.

The configuration of the terrain with respect to the secondary vehicle element corresponds to:

on the one hand at the slope: the configuration can be defined from a map and / or a GPS position of the machine, or by a sensor, in particular a sensor selected from the group comprising an inclination sensor (inclinometer) or a drawbar drawbar or angle sensor, or an inertial control unit or other equivalent means.

- on the other hand to machine data: for example a turn sensor (angle of the steering wheels for example, or angle of the drawbar in a different angle than previously), or by an indication of an inertial unit or by the change of speed, or whether a speed is engaged or not (two different treatments, one can choose to push during the passage of speed or not) or an indication of speed of the master wheels or the tractor to define a target speed of the secondary wheels . It should be noted that the target speed does not make it possible to define the behavior of the secondary part of the machine. To pull or restrain, a positive or negative velocity delta of the wheels of the abutment must be calculated in relation to the target value. This delta speed, or slip, is directly related to the torque exerted by the wheels. A negative slip determines a restraint, a positive slip determines thrust. If the wheels of the abutment were only repeating the target speed, they would not exert any torque, and the machine would coast.

DEPENDENCE OF THE SPEED OF THE VEHICLE

The transmission of the secondary axle can be disengaged by the central unit 290, in particular during operation and from a certain speed. In particular, it is possible to deactivate the motors 130, 140 which are deactivatable cam motors when the vehicle speed exceeds a predetermined threshold.

TAKING INTO ACCOUNT OTHER PARAMETERS THAN THE SLOPE

Preferably, in the context of the present invention, the control operated by the central unit 290 essentially makes a thrust evolution as a function of the slope on which the vehicle moves. Based on the acquisition of slope parameters from the sensor 296, which are compared with a threshold, the central unit 290 defines the thrust of the secondary axle 23, 24, in particular by defining whether to drive in traction or in restraint (traction when the vehicle is moving on flat or uphill, restrained when the vehicle is moving downhill).

The thrust defined by the central unit 290 can also be modulated according to the other parameters (for example and not limited to load, deployment of accessories such as spray bars, turns, etc.).

Thus, in the context of the invention, the thrust value defined by the central unit 290 as a function of the inclination detected by the inclinometer 296 can be modulated by thresholds or proportionally, as a function of the other operating parameters of the vehicle. For example and without limitation the thrust defined by the central unit 290 may be multiplied by a factor as a function of the load or the configuration of the tool equipping the trailer, or for example depending on the amplitude of a turn followed by the vehicle.

DIFFERENT MODES OF REALIZATION

We will maintain different specific embodiments according to the present invention.

FIRST EMBODIMENT

In the context of this first embodiment, the central unit 290 compares the slope on which the vehicle moves with respect to an inclination threshold. The central unit 290 is in this case designed to simply define a positive thrust or traction. This mode is the simplest.

It corresponds to two possible states: a weak traction on the flat and a strong traction uphill.

Initially, it is assumed that the vehicle is moving horizontally on flat.

The central unit 290 drives the pump 200 for the low traction value applied to the flat ground.

The central unit 290 analyzes the acquisition of the inclination obtained from the inclinometer 296.

It compares against a pre-established threshold value.

When the inclination provided by the inclinometer 296 is greater than the threshold, the central unit controls the pump 200 in strong traction defined for a rise.

In this case, the central unit 290 is programmed to aim at two target values of pressure or of difference in speed, for example a first pressure, of low traction, for displacement on a flat ground and a second pressure, of strong traction, during the climb.

SECOND EMBODIMENT

In the context of this second embodiment, the central unit 290 compares the slope on which the vehicle moves with respect to a negative inclination threshold corresponding to a downward slope. In this case, the central unit 290 defines two possible states: traction when the vehicle is traveling on a flat or uphill and a restraint when the vehicle is descending on a negative slope.

As the vehicle moves on flat or uphill, the CPU 290 applies the predefined traction.

When the central unit 290 detects via the inclinometer 296 a negative slope greater than a threshold value, it imposes a restraint on the motors 130, 140. In this case, the central unit 290 is programmed to aim at two target values of pressure or of speed difference, for example a first traction pressure, for moving on a flat or uphill ground and a second retaining pressure, when of a descent.

THIRD EMBODIMENT

According to the third embodiment, the central unit 290 compares with two inclination thresholds which define three states: a low traction on the flat, a strong traction uphill and a downward restraint.

Initially, it is considered that the towed machine is horizontal. The central unit 290 imposes traction which corresponds to driving in flat ground.

The central unit acquires the inclination via the inclinometer 296 and compares with a first threshold value.

When the central unit 290 detects that the inclination measured by the inclinometer 296 is greater than the ascending slope threshold, it controls the pump 200 for the purpose of the traction defined in rise.

When the central unit detects, on the contrary, that the inclination measured by the inclinometer 296 is lower than the second downward slope threshold, which means that the vehicle moves on a negative slope, the central unit 290 imposes a restraint at the motors 130, 140.

This third embodiment is defined by four dials which correspond to the representations illustrated in FIGS. 7, 8, 9 and 10 respectively and summarized in FIG. 11.

FIG. 11 illustrates possible states of constant pressure in situations of forward movement on a downward slope or reverse on an upward slope. As a variant, these states can implement a pressure evolution.

In the third embodiment, the central unit 290 is programmed to target three target values of pressure or deviation of speed: for example a first pressure on the flat, a second upward pressure and a third negative downward pressure.

FOURTH EMBODIMENT

According to this fourth embodiment, the central unit 290 imposes a thrust on the motors 130, 140 proportional to the slope, positive or negative. According to this fourth embodiment, the central unit 290 thus imposes a traction or a restraint proportional to the slope on which the vehicle moves.

Traction and proportional restraint define a pressure or velocity deviation for the secondary transmission formed by the motors 130, 140.

PROPORTIONAL PUSHING AND PILOTAGE AT THE SLOPE

As a preferred example, the control means integrated in the central unit 290 are adapted to apply via the wheels 23, 24 through the motors 130, 140, a thrust proportional to the slope.

FIGS. 13 and 14 and FIG. 17 schematically illustrate piloting proportional to the slope.

It can be seen in these figures 13, 14 and 17 that the regulation curve defining the pressure applied to the motors 130, 140, and driven by the central unit 290, depends on the value of the slope on which the vehicle moves.

TAKING INTO ACCOUNT OF THE BRAKING CONDITION

According to a variant, the central unit 290 is adapted to take into account a braking of the vehicle's main axle.

According to this optional feature of the invention, the central unit 290 defines a specific control of the motors 130, 140 when the vehicle is in braking mode. The parameter "brakes actuated" can be taken into account for controlling the secondary axle composed of the wheels 23, 24, as illustrated in FIGS. 12 and 14.

Compared with the modalities previously described with reference to FIGS. 7 to 10 and FIG. 11, only the control on the flat is modified. In this case, a holding mode with a negative thrust value of restraint is passed.

This arrangement is important insofar as if the tractive machine or the master axle is braked, it may change the traction priorities of the secondary axle placed on the towed or trailer.

If the brake is activated, the support value is changed on the flat by the central unit. Typically in this case, the central unit 290 will choose the selection of the state "0" light retained which will be defined later. The fact that the braking information is used to modify the values of the assistance does not mean that the abutment is directly driven by the driver. The ECU2 always decides whether to apply traction or restraint depending on the terrain configuration. In particular, a braking of the main part of the machine does not generate a repetition of the braking command on the abutment via the ECU 2.

As can be seen in FIGS. 12 and 14, the value of the pressure applied to the motors 130 and 140 can then be kept constant regardless of the speed of the vehicle.

In FIGS. 12 and 14, it has indeed been possible to show possible states of constant pressure in situations of forward travel on a downward slope or reverse on an upward slope, as well as on the flat. As a variant, these states can implement a pressure evolution.

On the other hand if the vehicle is not braked, on the flat the central unit 290 will choose the selection of the state "0" full power.

The same choice is made in reverse.

In a variant when the control means 290, 292 detect a braking mode of the vehicle's master axle, they maintain the previous state, for example traction or restraint, then modifying if necessary the corresponding value of the thrust, traction or restraint, for example to ensure a hill start or ensure a restraint during a descent start.

VALUE OF PUSH OR DIFFERENT RETENTION ACCORDING TO THE SLOPE

The flat hold value may be different from the downhill hold, in the same way that the flat pull may be different from the sloping pull.

TARGET VALUES OF PRESSURE OR SPEED

Preferably in the context of the invention, the central unit 290 is adapted to define 4 pressure target values on the motors 130, 140 or of speed difference between the wheels 23, 24 of the towed element and the wheels of the towing vehicle: for example a first target value of pressure or of difference of speed in traction during a displacement on the flat, a second target value of pressure or of difference of speed in traction during a displacement in uphill , a third target value of negative pressure or holding speed deviation when traveling on a flat accompanied by braking and a fourth target value of negative pressure or holding speed deviation during a displacement downhill.

HYSTERESE

As illustrated in FIG. 15, the central unit 290 can exploit defined slope thresholds with a hysteresis, to avoid jolts on the vehicle. For example, the central unit can control by switching from flat mode to mounted mode from a slope of greater than or equal to 5 °, but only from the mounted mode to the flat mode for a slope less than or equal to 4 °.

As can be seen in FIG. 15, such a hysteresis can be applied to both the upward slope threshold and the downward slope threshold. LOCALIZATION AND CALIBRATION OF THE INCLINOMETER

The inclinometer 296 may be attached to the towing vehicle or the trailer, that is to say the towed element.

In the context of the invention the inclinometer 296 is preferably placed on the towed element, when the secondary axle is placed on a towed element. Thus, it is ensured that the central unit ECU2 receives reliable information on the slope on which the secondary axle moves, even if the towing vehicle is, according to the progress, placed on a different slope.

Preferably according to the invention, there is provided a calibration process of the inclinometer 196 to define which output value of the inclinometer corresponds to a displacement of the vehicle on the flat.

To correct inclinometer mounting and / or crushing of wheels under load and / or angle of hitch and / or tractor height and / or the effect of a tire changing change and / or the mounting of such and such a tool and / or dependence according to the type of tractor used to tow the coupled machine, according to the invention it is preferably also provided a calibration process which consists of: - 1 / Place the machine configured, hitched, equipped and loaded, on a flat ground,

- 2 / Proceed to a step of acquisition of the output value of the inclinometer 296, and

- 3 / Save this value as characteristic value of the flatbed machine.

The man / machine interface 292 is an interface adapted to activate the system, and for a towed tool, such as spray bars, is preferably placed in the cab of the towing vehicle. This human / machine interface 292 is adapted to define the machine parameters, including load, type of tool, desired power, and in particular to initialize the inclinometer and enable assistance. BASIC STRUCTURE OF CYLINDER CONTROL MEANS

As indicated above, the control of the displacement of the pump 200 is controlled by the double-acting cylinder 270 itself controlled by a pressure reducing assembly 275, pressure limiters 278, 279 and a switching assembly 280.

The two switching valves 282, 284 which form the switching assembly 280 and constitute pump solenoid valves regulate the direction of flow.

The two pressure reducers 276, 277 which form the pressure reducing assembly 275, regulate the pressure to be reached and thus operate a pressure control.

All of these means allow to do the four quadrants of traction: front, rear, traction and restraint. DEFINITION OF PUSH OR POWER LIMITING FUNCTION

FIG. 16 illustrates a typical curve used in the context of the present invention by the central unit 296 to define the pressure applied to the motors 130, 140 by the aforementioned means 275, as a function of the speed.

This control curve defines a maximum power applied to the motors 130, 140.

Preferably, the pressure is constant and maximum under a speed threshold, and then is defined by the relation (P denoting the power): P = (600. PWR.n.) / Speed, which is adapted to apply a constant power to the motors 130, 140, and the pressure then drops to reach a zero value when the speed exceeds a maximum threshold.

The corresponding algorithm realizes a power limitation, to preserve the life of the motors 130, 140 as well as to limit the heating of the oil.

As a function of the pressure and the speed, the curved part of the diagram illustrated in FIG. 16 represents a power (P = f (flow, pressure)) constant. Thus the central unit 296 limits the power. In other words, the electronics of the CPU 296 limit the pressure applied to the motors 130, 140 as the vehicle speed increases.

The piloting envelope illustrated in FIG. 16 is therefore defined by:

the maximum pressure given by the pump 200 (maximum u function for the pump 200 or the motors 130, 140) defined by the pump control jack 270 and / or by the software integrated in the central unit 290, the maximum speed for the motors 130, 140, defined by the maximum displacement of the pump 200, and

the curved portion illustrated in FIG. 16 which corresponds to a calculated maximum power (defined by the software integrated in the central unit 290).

The regulation illustrated in FIG. 16 corresponds to a maximum thrust in the context of the application targeted by the present invention.

PLURALITY OF STATES

According to an optional feature of the invention, the central unit 290 offers the driver choice assistance in several states, for example 3-state: a first state without thrust generated by the motors 130, 140, a second state of maximum thrust generated by the motors 130, 140 and a third modulated thrust state.

Specifically, the aforementioned choices may be proposed to the driver, in the context of an application of the invention, in the form of an invitation to choose via the interface 292 between three selections "0", "1" or 2 ».

The selection "0" corresponds to a slight thrust corresponding preferably to a fixed pressure applied to the motors 130, 140 in the case of a pressure control. Alternatively it may be a slight traction or a slight restraint. The pressure applied to the motors 130 and 140 can also be adapted to overcome the inertia and the friction of the motors 130, 140 and then correspond to zero thrust or zero restraint. This selection "0" can correspond in this case to a form of electronic freewheel.

The selection "1" corresponds to a maximum traction of power. This selection "1" corresponds to the control following the maximum power curve illustrated in Figure 16. It is chosen only in case of rise.

The selection "2" corresponds to a modulated thrust depending on the slope. It is chosen downhill only to operate restraint.

Figure 13 illustrates a choice offered to the driver via the interface 292 as follows:

- forward, the driver can choose from the above selections, mode "0" or "1" uphill, mode "0" on the flat mode "2" modulated or mode "0" light retained, or the mode "2" retained modulated downhill.

- In reverse, the driver can choose from the above selections, mode "0" light uphill uphill, mode "1" full power on the flat, mode "1" full power downhill.

According to one variant, the interface 292 may offer the driver only a control in the form of a choice limited to the aforementioned "0" or "2" states. In this context the selection "0" may be a low thrust or freewheel and the selection "2" may be a thrust proportional to the slope, positive or negative (traction or restraint).

MODULATED TRACTION

To achieve the modulated traction, the central unit 290 applies a corrective coefficient connected to the tilt data from the inclinometer 296. Thus the central unit 290 applies a fraction of the maximum available power, which depends on the slope measured. As can be seen in FIG. 17, the central unit defines in this case a 3-dimensional control envelope. The 3 input parameters correspond to torque (or pressure), speed and inclination.

For several inclinations, the central unit 290 defines coefficients a modulating the applied pressure. For example, for a slope at -7 °, the central unit 290 can give a thrust of 70% of the maximum power curve.

In FIG. 17, the curve admitting a pressure of 350 bars is the maximum power curve. The second curve is a corrected coefficient curve and obtained for the moment slope value corresponding to a measured pitch inclination.

TRANSITION

In the case of a transition from the flat or rise corresponding to a pull, to a descent corresponding to a restraint (which restraint can be operated at full power), the central unit 290 preferably uses an algorithm which makes a smooth transition, by making a progression, for example linear, between the state before the change applied for the flat or the rise and the state after the change corresponding to a descent, over a time range t, as illustrated in FIG. Applies in a general way when the inclination data changes abruptly, whether in the flat direction or uphill to a descent or vice versa in the downhill direction to a flat or ascent.

FIG. 18 illustrates the transition applied within the scope of the invention during a rapid passage urged between a traction regime and a restraint regime. Typically the central unit 290 then imposes that the pump 200 rotating at the same speed and in the same direction, proceeds to a transition from a positive pressure to a negative pressure. This transition from one pressure to another with progressivity over a time range t is operated for example over 2 seconds.

The central unit 209 defines a maximum speed of pressure change. This parameter can be entered by the user via the man-machine interface 292. For example by entering the parameter "2 seconds", the driver instructs the system to calculate the displacement change rate of the pump 200 to go from a full positive power to a full negative power in 2 seconds. Thus for a given speed (by the wheels) and a given instantaneous pressure, the central unit 290 defines a rate of change.

ADVANTAGES OF THE INVENTION

The present invention makes it possible to have an assisted secondary axle which does not disturb the pipe required by the driver-controlled master axle.

It allows to drive faster safely in a descent, knowing that the secondary axle retains and does not risk to return the machine.

APPLICATIONS

The present invention applies to all machines, including trailers or towed tools that must be attended.

It applies in general to any drive axle of a machine that one wishes to assist.

As indicated above, the present invention applies in particular to a hydraulic transmission machine comprising a driver-driven axle, which is the master axle, and another secondary axle which is "automatically follower" according to the invention. The master axle can be hydraulically driven, directly driven by the driver.

The invention applies to a machine which has a mechanical transmission on an axle, and an assisted axle, for example a tractor (assisted front axle, mechanical rear axle), a harvester, a truck, a self-propelled machine.

The invention applies to a trailer or wheeled implement, for example a wheeled plow or a potato harvester trailed behind a tractor. Naturally, the present invention is not limited to the embodiments that have just been described, but extends to all variants that conform to its spirit.

In particular, the present invention is not limited to the means described above and illustrated in the accompanying figures for composing the pressure reducing assembly 275, the pressure limiters 278, 279 and the switching assembly 280, but extends to any functionally equivalent means.

The present invention applies preferably, but not exclusively, to the assistance circuits incorporating hydraulic machines, forming a pump or motor, of the radial piston type.

The present invention preferably, but not exclusively, applies to towed vehicles, in particular towed agricultural machinery.

According to other advantageous features of the invention:

the central unit 290 uses the signal coming from a service brake pressure sensor and it controls the system so as not to push the vehicle, in particular the tractor or the towed element, when braking is detected,

the central unit 290 uses the signal coming from an oil temperature sensor and it controls the system to operate a disengagement of the assistance in the event of a temperature above a threshold. In this case preferably information is made available to the driver before reaching the cutoff threshold (for example in the form of a flashing lamp indicating the presence of a fault). This arrangement can be used to directly control the cooling device and if necessary to remove the thermostatic probe at the inlet of the refrigerant module.

the central unit 290 uses the signal coming from a speed sensor in the wheels and it controls the system to authorize the engagements in dynamic whatever the direction of progress. If necessary, the central unit also uses the signal from this wheel speed sensor to prevent the assistance from being engaged at too high a speed. The central unit 290 may for example allow interconnection up to 8km / h (working speed in difficult terrain). It can induce the cut of the assistance in the event of overspeed (number of revolutions with the same wheel whatever the tire mounting). It can also support a speed sensor option to detect the direction of travel relative to a drawbar sensor.

In the context of the invention, it is also conceivable to eliminate the pressure sensor on the high-pressure supply branch in the forward direction because such a sensor makes redundancy with the speed measurement and in this sense is not necessary. essential.

Claims

1. Assistance system for driving a secondary axle (23, 24) fitted to a vehicle also comprising a main axle, which system comprises a pump (200) driven by a drive such as a combustion engine of the vehicle, a hydraulic engine machine (130, 140) fitted to each driving wheel (23, 24) of the secondary axle and a driving unit (290), characterized in that the main axle is a driven driving axle and the secondary axle is a follower motorized axle and comprises control means (290, 292) adapted to automatically control and modulate the thrust applied by the drive wheels of the secondary axle (23, 24) according to the configuration of the terrain, including the amplitude and direction of the terrain slope, so that the driving force generated by the thrust applied by the driving wheels of the secondary axle, combined with the motor force induced by the slope of the terrain on which circulates the vehicle, does not disturb the driving force generated by the driven main drive axle.

2. System according to claim 1, characterized in that it comprises a control unit which controls the main driving axle (P) and a central unit (ECU2) which drives the secondary axle (S).

3. System according to one of claims 1 or 2, characterized in that the secondary axle is placed on a towed vehicle or trailer, while the main axle is placed on a towing vehicle.

4. System according to one of claims 1 to 3, characterized in that the control means adapted to automatically control and modulate the thrust applied by the driving wheels of the secondary axle according to the terrain configuration are also adapted to operate this control and modulation according to the load on the secondary axle and the configuration of the element carried by the secondary axle.

5. System according to one of claims 1 to 4, characterized in that it comprises a man / machine interface (292) connected to a central unit (290) and allowing the user to set various operating parameters of the system.

6. System according to one of claims 1 to 4, characterized in that it comprises a sensor (296) inclination to measure the slope on which the vehicle moves.

7. System according to one of claims 1 to 6, characterized in that the control means (290, 292) are adapted to not apply downward thrust on the secondary axle (23, 24), when the vehicle moves on a negative or decreasing slope.

8. System according to one of claims 1 to 7, characterized in that the control means (290, 292) are adapted to apply restraint on the secondary axle (23, 24), when the vehicle moves on a negative or decreasing slope.

9. System according to one of claims 1 to 8, characterized in that the control means (290, 292) are adapted to define either a torque control on the wheels (23, 24) by a pressure control of the pump (200), a wheel speed control (23, 24), defined by a control in the displacement position of the pump (200) to which the speed of the secondary wheels (23, 24) is connected, in defining a speed difference, positive or negative, between the wheels (23, 24) of the secondary axle and a speed reference representative of the driven machine which corresponds to the master element of the vehicle.

10. System according to one of claims 1 to 9, characterized in that the control means adapted to automatically control and modulate the thrust applied by the drive wheels of the secondary axle according to the terrain configuration are also adapted to effect this control and modulation as a function of the load on the secondary axle and that the load represents the state of charge of the secondary vehicle element, that is to say if the secondary element of vehicle is more or less loaded, for example the filled or empty state of a trailer such as a towed tool.

11. System according to one of claims 1 to 10, characterized in that the control means adapted to automatically control and modulate the thrust applied by the driving wheels of the secondary axle according to the terrain configuration are also adapted to operate this control and modulation according to the configuration of the vehicle sub-element and the configuration of the vehicle sub-element corresponds to:

on the one hand at the slope, according to a parameter chosen for example from the group comprising: a configuration defined from a map and / or a GPS position of the machine, or by a sensor, in particular a selected sensor; in the group comprising an inclination sensor (296) or a drawbar force sensor or an angle sensor or an indication of an inertial unit,

on the other hand to machine data, according to a parameter chosen for example from the group comprising data from a corner sensor, an inertial unit, a gear change, the fact that a speed is engaged or not or a speed indication representative of the speed of the vehicle master element, to define a target speed of the secondary wheels.

12. System according to one of claims 1 to 11, characterized in that the control means (290, 292) are adapted to define a thrust evolution as a function of the slope on which the vehicle moves for example define a first thrust value when the vehicle is traveling on a flat surface and a second thrust value different from the first value when the vehicle is traveling on a slope.

13. System according to one of claims 1 to 12, characterized in that the control means (290, 292) are adapted to define a modulated thrust evolution according to at least one parameter other than the slope, for example the deployment of accessories such as spray bars.

14. System according to one of claims 1 to 13, characterized in that the control means (290, 292) are adapted to compare the slope on which the vehicle moves with respect to a negative inclination threshold corresponding to a downward slope and define two possible states: a pull when the vehicle is moving on flat or uphill and a restraint when the vehicle is descending on a negative slope.

15. System according to one of claims 1 to 14, characterized in that the control means (290, 292) are adapted to compare the slope on which the vehicle moves with respect to two inclination thresholds and define three possible states: low traction on the flat, strong traction uphill and downhill restraint.

16. System according to one of claims 1 to 14, characterized in that the control means (290, 292) are adapted to impose a thrust on the motors (130, 140) proportional to the slope, positive or negative , and thus impose a traction or a restraint proportional to the slope on which the vehicle moves.

17. System according to one of claims 1 to 16, characterized in that the control means (290, 292) are adapted to take into account a braking of the vehicle master axle.

18. System according to claim 17, characterized in that the control means (290, 292) are adapted to impose a holding mode with a constant retaining value when braking of the vehicle master axle is detected.

19. System according to one of claims 1 to 17, characterized in that when the control means (290, 292) detect a braking mode of the master axle of the vehicle, they maintain the previous state, for example traction or restraint, then modifying if necessary the corresponding value of the thrust, traction or restraint, in particular to ensure a hill start or a restraint during a start downhill.

20. System according to one of claims 1 to 19, characterized in that the control means (290, 292) are adapted to define 4 target pressure values on the motors (130, 140) or speed difference between the wheels (23, 24) of the vehicle sub-element and the wheels of the vehicle master element: a first target value of pressure or of difference of speed in traction during a displacement on a flat, a second target value of pressure or of difference of speed in traction during an uphill movement, a third target value of negative pressure or of difference of speed of retention during a displacement on flat accompanied by a braking and a fourth negative pressure target value or a restraint rate deviation when traveling downhill.

21. System according to one of claims 1 to 20, characterized in that the control means (290, 292) are adapted to operate defined slope thresholds with a hysteresis, to avoid jerking on the vehicle.

22. System according to one of claims 1 to 21, characterized in that the control means (290, 292) implement a calibration process of an inclinometer (196) to define which output value of the inclinometer is a movement of the vehicle on the flat.

23. System according to one of claims 1 to 22, characterized in that the control means (290, 292) are adapted to define a constant and maximum pressure on the motors (130, 140) under a speed threshold, a constant power over a speed range, and a pressure that drops to zero when the speed exceeds a maximum threshold.

24. System according to one of claims 1 to 23, characterized in that the control means (290, 292) are adapted to provide the choice of the driver assistance in several states, for example to offer the choice of the driver assistance according to 3 states: a first non-thrust state generated by the motors (130, 140), a second maximum thrust state generated by the motors (130, 140) and a third modulated thrust state.

25. System according to one of claims 1 to 24, characterized in that the control means (290, 292) are adapted to achieve a smooth transition, by making a progression, for example linear, between the state before a change applied for a flat or a rise and the state after the change corresponding to a descent, or vice versa, over a predetermined time range t.

26. A method of assisting the driving of a secondary axle equipping a vehicle comprising a main axle, using a system comprising a pump (200) driven by a drive such as a heat engine of the vehicle, a hydraulic machine (130, 140) forming a motor equipping each driving wheel of the secondary axle, and a driving unit, characterized in that the main axle is a driven driving axle and the secondary axle is a motorized axle follower and that it comprises steps of automatically controlling the thrust applied by the driving wheels of the secondary axle according to the configuration of the terrain, including the amplitude and the direction of the slope of the terrain, so that the driving force generated by the thrust applied by the driving wheels of the secondary axle, combined with the driving force induced by the slope of the terrain on which the vehicle is traveling, does not disturb the driving force driven by the main drive axle.

27. Vehicle equipped with a system according to one of claims 1 to 25 and / or implementing the method according to claim 26.