WO2019185585A1

WO2019185585A1 - Vehicle equipped with a hydraulic driving assist system, and hydraulic assist system intended for this purpose

Info

Publication number: WO2019185585A1
Application number: PCT/EP2019/057510
Authority: WO
Inventors: Julien Lambey
Original assignee: Poclain Hydraulics Industrie
Priority date: 2018-03-26
Filing date: 2019-03-26
Publication date: 2019-10-03
Also published as: FR3079192A1; FR3079192B1

Abstract

The present invention relates to a vehicle comprising a main drive motor (20) coupled to a pair of driven carrying wheels (10, 12) and an assist system comprising a hydraulic motor (62) coupled to some of the carrying wheels (14, 16), a pump-forming hydraulic machine (60) connected to the hydraulic motor (62) and wheel slip and speed sensors (82), a control module (80) which puts the assistance into operation on the basis of the signals from the sensors (82), the control module (80) exploiting software (90) for limiting the power of the main motor (20) and means for controlling this software adjusting the power of the motor while taking account of the engagement or non-engagement of the assist system, and which adjusts the maximum hydraulic pressure in order to avoid a hydraulic overpressure.

Description

Vehicle equipped with a hydraulic drive assistance system and hydraulic assistance system provided for this purpose

TECHNICAL AREA

The present invention relates to the field of vehicles equipped with a hydraulic drive assistance system. The invention also relates to hydraulic assistance systems as such.

STATE OF THE ART

Many types of hydraulic assist systems have already been proposed for driving vehicles.

Those skilled in the art know indeed different types of hydrostatic transmission used on vehicles to transform 4x2 vehicles, that is to say four-wheeled vehicles with two-wheel drive vehicles, 4x4 vehicles is four-wheel-drive vehicles and four-wheel drive vehicles, temporarily by the use of hydraulic components for transmitting torque of a primary engine of the vehicle, for example a thermal or electric engine, to a carrier train, to turn it into a motor train. The performance of such a type of system is based on the ability to generate pressure in the hydrostatic transmission as a function of the speed differential between the two trains of the vehicle.

FR-3019610 discloses a system comprising a hydraulic driving apparatus having an inlet and a discharge port, a hydraulic driven apparatus having an inlet and a discharge port, the discharge of the apparatus hydraulic drive being connected to the inlet of the hydraulic apparatus driven by a feed line, and the discharge of the hydraulic driven apparatus being connected to the inlet of the hydraulic apparatus leading by a return line, said system characterized in that it further comprises a branch line connected on the one hand to the supply line and on the other hand to the return line, said branch line comprising at least one means configured to automatically provide flow transfer between the feed line and the return line to modulate a rotational speed ratio between the driving hydraulic apparatus and the driven hydraulic apparatus.

Document FR-3019612 describes a method of hydraulic assistance of a vehicle comprising two hydraulic devices connected to each other by a feed line and a return line, a feeding source and a reservoir, the feed source being connected to the supply and return lines via a booster line and taking oil from the tank, a vacuum valve, including an inlet port connected to the supply and return lines, and a port outlet valve connected to the reservoir, the vacuum valve having a first on state and a second blocking state, the method comprising steps of activating the boost source when the vehicle fulfills at least one predetermined condition, the delivery valve with the empty state being in the first on state, and switching from the first state vacuum valve to the second blocking state when the hydraulic assist is required, thereby permitting e in pressure of the supply and return circuits, and thus the feeding of the supply and return circuits and the transmission of torque.

Document FR-3022204 describes a method of activating a hydraulic assistance of a vehicle transmission system, said system comprising a hydraulic pump with variable displacement connected via a high pressure line on the one hand, and a low-pressure line on the other hand, a variable displacement hydraulic motor driving a first axle in rotation, and the method being characterized in that it implements a hydraulic assistance comprising a fixed displacement motor driving in rotation a second axle , an inlet of which is connected to the high pressure line via a first valve, and an outlet of which is connected to the low pressure line via a second valve, and in that it comprises the steps of engaging hydraulic assistance, measuring the pressure difference between the inlet and the outlet of the fixed displacement motor, so as to control a torque supplied by the fixed displacement motor, and according to the torque provided by the fixed displacement motor, modify a torque provided by the variable displacement motor and / or the torque provided by the fixed displacement motor, so as to maintain a total torque supplied by the system generally constant when the assistance is activated.

Document FR 3 033 529 also describes an assistance device comprising a first hydraulic apparatus and a second hydraulic apparatus, the two units being connected by a first line and a second line allowing admission or refoulement of in said apparatus, a booster pump disposed between a reservoir and a booster line, the booster line being in communication with at least one of said lines and capable of feeding said lines by the booster pump, characterized in that that the pump is configured to suck oil in the booster line to allow decompression of said first and second lines.

The known systems described above by way of non-limiting examples are generally referred to as "hydrostatic transmission system" of the "bicycle chain" type, because of the closed circuit connection defined by a high-pressure supply line and a low pressure supply line between the hydraulic pump driving apparatus and the engine driven apparatus.

In all hydraulic assistance systems heretofore proposed, the activation or disengagement of the assistance system is carried out according to skid and speed limit parameters. Slippage is determined on the wheels in a manner known per se.

PROBLEM

A difficulty encountered on almost all known hydraulic assistance systems is that the closed-loop system heats up, which can limit its availability. The person skilled in the art tries so therefore generally use it sparingly and adapted to maintain the availability of the system as long as possible. It can realize it by a bypass valve to limit the power transmitted. But a bypass valve also helps warm up the system. On the other hand, if the system is used to its maximum, and activates pressure relief valves, they also participate in warming the system.

It is indeed well known that in hydraulic assistance systems, it is desirable to provide a high pressure valve or "pressure relief valve" for protecting the hydraulic systems from an overpressure generated by the circuit. For example, on a hydrostatic transmission of the parallel type, the locking of a wheel can create a pressure likely to exceed the recommendations for resistance of the hydraulic components.

In the event of such overpressure, the pressure relief valves protect the system and prevent a risk of damaging the circuit.

However, the pressure limitation through a high pressure safety valve type hydraulic component generally works by rolling the oil through a restriction. Thus, this generates a local heating that can become significant if the amount of circuit oil is low and the opening time of the valve is important.

The pressure relief valves therefore create a heating of the oil.

To generate the transmitted torque, it is also possible to use partial or proportional bypass valves. However, such bypass valves can also create heating of the circuit oil.

The inventors have also found that the effectiveness of the hydraulic assistance systems is disrupted by so-called "ASR" systems.

As part of the application on hydrostatic transmissions of the bicycle chain type, the safety valves are solicited whenever the rate of skating is important. For example in the situation where a vehicle must start on a slope, a carrier train is stopped, the engine can be requested at a speed that can become important depending on the conditions of adhesion. The high rate of slip of the power train can lead to difficult situations of the vehicle with loss of control.

To mitigate this risk, vehicles of the automotive type are generally equipped with so-called ASR systems to temper runaway motor train.

Therefore, unfortunately, the ASR restricts the performance of the hydraulic system by limiting the slippage of the vehicle engine train according to the system characteristics and the setting of the ASR system of the vehicle.

The ASR is a technical term used in the automotive world which corresponds to the abbreviation of the English expression "Anti-Slip Regulation". It is an electronic anti-skid system that regulates acceleration to limit the loss of traction of the drive wheels. This system is most useful during startups and accelerations. Overall an ASR system limits the power of the engine to prevent slippage of the drive wheels, according to a law dependent on the speed of the vehicle. The engine power is all the more limited as the speed of the vehicle is low. The ASR generally limits the power in the start-up situation.

In the context of the invention, the inventors have determined that an ASR system can limit the power / performance of temporary hydraulic assistance at least in certain speed ranges, and also does not avoid the use of pressure relief valves. of the hydraulic system.

BASIS OF THE INVENTION

In this context, the object of the invention is to propose new means making it possible to improve the properties of hydraulic systems for assisting the driving of vehicles. This object is achieved, according to the present invention, by means of a vehicle comprising carrying wheels, a main drive motor, thermal or electrical, coupled to at least one pair of carrying and driving wheels and an assistance system comprising at least a hydraulic motor coupled to at least some of the load wheels, a hydraulic machine forming a pump connected to the hydraulic motor and wheel slip and speed sensors, and a control module which ensures the putting into service of the assistance on the basis of a processing of the signals from the skid and speed sensors, characterized in that the control module uses power limiting software of the main engine and comprises control means of this software which adjusts the power of the engine taking into account the commitment or non-commitment of the assistance system, and if it is engaged that adjusts the maximum hydraulic pressure to avoid do hydraulic overpressure. According to other advantageous features of the invention:

the vehicle comprises speed sensors associated with the various wheels of the vehicle in order to provide the control module with information representative of the difference in speed between the wheels of the various axles.

- The control module uses a characteristic Avitesse / pressure on all speeds of the range of use to control an ASR module to limit slippage to ensure maximum efficiency to the hydrostatic system.

- In a startup phase, the control module requires that the level of slippage required to obtain the maximum pressure of the hydrostatic transmission, does not place the vehicle in a dangerous situation of loss of control.

the vehicle comprises a pressure sensor placed on the circuit, typically on a high pressure line, in order to know the pressure levels in the transmission so that the control module (80) imposes a slip level in adequacy with the performances expected from the system according to the operating range. - The control module uses a specific mapping for a 4x4 hydraulic mode that allows imposing not to exceed a maximum allowed pressure, to draw the best compromise between performance of crossing and optimization of the dynamic behavior of the car in ground skating situation low adhesion.

the control module implements an open regulation loop which comprises the following steps: validation of an assistance activation instruction, limitation of the main motor torque, defined by an ASR software with the aim of limiting the rate of slip and limitation of the difference in speed to reach the maximum torque of the hydraulic transmission for each point.

- The control module implements a closed control loop that exploits the pressure signal from a sensor.

The invention also relates to hydraulic assistance systems as such.

These hydraulic assistance systems comprise at least one hydraulic motor coupled to at least some of the wheels carrying a vehicle, a hydraulic machine forming a pump connected to the hydraulic motor and sensors for wheel slip and speed, as well as a hydraulic module. control (which provides commissioning of the assistance on the basis of a processing of the signals from the skid and speed sensors, in which the control module uses power limiting software of the main motor and comprises means piloting this software that adjusts the power of the engine taking into account the engagement or non-engagement of the assistance system, and if it is engaged that adjusts the maximum hydraulic pressure to avoid a hydraulic overpressure. also relates to a method of assistance.

Such an assistance method for a vehicle comprising carrying wheels, a main drive motor, thermal or electrical, coupled to at least one pair of carrying wheels and motor and an assistance system comprising at least one hydraulic motor coupled to at least some of the load wheels, a hydraulic pump machine connected to the hydraulic motor and wheel slip and speed sensors, and a control module which provides the commissioning of the assistance on the basis of a processing of the signals from the skid and speed sensors, is characterized by the fact that it comprises the exploitation of a power limitation software of the main engine of an ASR module, to adjust the power of the engine taking into account the commitment or non-commitment of the assistance system, and if it is engaged adjust the maximum hydraulic pressure and avoid hydraulic overpressure.

According to other advantageous characteristics of the process of the invention:

the method exploits a speed / pressure characteristic over all the speeds of the range of use in order to drive an ASR module (90) to limit slippage in order to ensure the maximum efficiency of the hydrostatic system.

- In a startup phase, the process requires that the level of slippage required to obtain the maximum pressure of the hydrostatic transmission, does not place the vehicle in a dangerous situation of loss of control.

the method uses a pressure sensor placed on the circuit, typically on a high-pressure line, in order to know the pressure levels in the transmission and to impose a slip level in adequacy with the expected performances of the system according to the range of operation.

the method uses a specific mapping for a 4x4 hydraulic mode which makes it possible not to exceed a maximum permissible pressure, to draw the best compromise between crossing performance and optimization of the dynamic behavior of the car when skating on a low ground. adhesion. the method implements an open regulation loop which comprises the following steps: validation of an assistance activation instruction, limitation of the torque of the thermal or electrical engine, defined by an ASR software with the aim of limiting the rate of slip and limitation of the difference in speed to reach the maximum torque of the hydraulic transmission for each point.

the method implements a closed regulation loop which exploits the pressure signal coming from a sensor.

the method implements the following steps:

. detection of activation of the assistance system,

. monitoring the speed of the vehicle,

. as long as the speed remains below a threshold, controlling the pressure in the circuit to keep it below a threshold,

. on the other hand, when the speed is greater than the threshold, control of the pressure as a function of the speed of the vehicle according to a given map.

QUICK PRESENTATION OF 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 by way of non-limiting examples and in which:

FIG. 1 represents a schematic view of an assistance system according to the state of the art,

FIG. 2 represents a schematic view of an assistance system according to the present invention,

FIG. 3 represents a functional block diagram of a first embodiment according to the invention,

FIG. 4 represents a diagram illustrating the pressure limitation by a high-pressure valve as a function of the speed of the vehicle,

FIG. 5 represents a functional block diagram of a second embodiment according to the invention, and

FIG. 6 represents a functional flowchart of the method according to the present invention. DETAILED DESCRIPTION OF THE STATE OF THE ART

FIG. 1 appended hereto shows the known base of a hydraulic assistance system known per se, comprising four carrying wheels 10, 12, 14 and 16, a main driving motor 20, thermal or electrical, coupled to a first axle 50 via a clutch 30 and a gearbox 40. Each axle 50, 52 is preferably provided with a differential 51, 53.

FIG. 1 also shows a pump 60 coupled to the driven axle 50, by the gearbox 40, and connected by a high pressure line 70 and a low pressure line 72 to a motor 62 coupled to the second axle 52.

The hydraulic circuit comprises a booster circuit 74 known per se, the particular embodiment illustrated in Figure 1 is not limiting.

FIG. 1 diagrammatically shows a control module 80 which ensures the commissioning of the pump 60 on the basis of a processing of the signals coming from sensors 82 for slipping and speed of the drive wheels 10, 12.

FIG. 1 shows schematically an ASR system 90 which controls the main motor 20.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described with reference to FIGS. 2 and following.

The first characteristic of the invention is a pressure limitation by regulating the ASR 90 as a function of the conditions in which the vehicle is located.

Thus, as shown schematically in FIG. 2, the module 80 which drives the pump 60 is coupled to the ASR module 90 so that the control module 80 uses the power limitation software of the thermal engine of the ASR 90 and comprises control means for this software that adjusts the power of the engine taking into account the commitment or non-commitment of the assistance system, and if it is engaged which adjusts the maximum hydraulic pressure on lines 70 and 72 to avoid hydraulic overpressure.

For the rest, Figure 2 is identical to Figure 1. It will not be redescribed. The invention implements a system type "bicycle chain". This system comprises two identical hydraulic machines associated with respective axles and connected by supply and return ducts. As a variant, the system of the invention may comprise a hydraulic machine forming a pump actuated by a main motor and a hydraulic machine forming a motor powered by the pump and connected to the carrying wheels.

Nevertheless, it will be noted from the examination of FIG. 2 that according to the invention, in order to determine sliding or slipping, the module 80 preferably proceeds to measure speed between the various axles, for example between a front axle 50 and the rear axle 52 of the vehicle and for this purpose it is preferably provided a speed sensor 82 on each of the wheels 10, 12, 14 and 16, coupled to the module 80.

In practice the activation of the assistance can be done in different ways, thanks to the booster circuit 74. The activation of the assistance can be operated directly by the commissioning of the booster circuit 74. However preferably the circuit booster 74 is pre-activated (activation of its engine or its clutch), and rapid activation of the assistance is controlled by a bypass valve 75 connected to the power supply line. When the bypass valve 75 is on, it prohibits the increase in pressure of the power supply line assistance and therefore prohibited the commissioning of assistance. On the contrary, when the bypass valve 75 is closed, it allows the pressure rise of the power supply line of the assistance and therefore the commissioning of the assistance.

FIG. 2 diagrammatically shows the booster circuit 74 in the form of an assembly comprising a booster pump proper 740 associated with an electric drive motor 742. The booster circuit 74, in particular the drive motor 742, and the bypass valve 75 are controlled by the control module 80.

According to a first embodiment according to the invention, the system 80 uses the characteristic Avitesse / pression on all the speeds of the range of use. Thus, when the vehicle is positioned in 4x4 position, the ASR 90 is controlled to limit slippage to ensure the maximum efficiency of the hydrostatic system. In the start-up phase, it is required that the slip level necessary to obtain the maximum pressure of the hydrostatic transmission, does not place the vehicle in a dangerous situation of loss of control.

In a second embodiment, a pressure sensor 84 placed on the circuit, typically on the high-pressure line 70, is used in order to know the pressure levels in the transmission so that a satisfactory level of slip is obtained. with the expected performance of the system according to the operating range. Thus, the invention makes it possible to always limit the maximum pressure seen by the system by limiting the slip rate. The invention also makes it possible, on the contrary, to allow more slippage by keeping the vehicle in a safe situation, in order to obtain the best performances.

The invention offers many advantages. It thus makes it possible, either in a first case to limit the opening of the high pressure safety valves in order to limit the heating generated by the rolling of the oil through these or in a second more ambitious case, to eliminate the use high pressure safety valves.

The use of a pressure sensor 84 makes it possible to manage the slip performance over time, taking into account its potential wear and also the dispersion of the systems in the case of mass production of components.

The system 80 in accordance with the invention exploits a specific mapping for the hydraulic 4x4 mode which makes it possible to draw the best compromise between performance of crossing and optimization of the dynamic behavior of the car in situation of slip on ground of weak adhesion. At any moment, it is also possible to limit the maximum difference in speed between the two axles 50 and 52 so as not to exceed the maximum permissible pressure (for example 450 bars).

FIG. 3 shows the general kinematics of the system according to a first embodiment of the invention. This is an open regulatory loop.

The kinematics starts with a step 100 of validation of an assistance activation instruction. Then, the control module 80 according to the invention operates to limit the torque of the main motor 20, thermal or electrical, defined by the ASR software 90 with the aim of limiting the slip rate (step 102 in FIG. ). In step 104 shown in Figure 3 the system 80 leads to a limitation of the speed difference between the two axles 50 and 52, to achieve the maximum torque of the hydraulic transmission for each point (vehicle speed / oil temperature ).

Thus, in an open loop, it is necessary to have a good knowledge of the behavior maps of the system such as that presented in FIG. 4 by way of nonlimiting example, in order to know at each instant what is the difference in speed between the two axles 50 and 52, so as not to exceed the maximum permissible pressure.

In a closed loop, as shown in FIG. 5 on which steps 100, 102 and 104 are found, the pressure reached in the hydraulic circuit is also measured in step 106 using the sensor 84. Thus, it controls the pressure which allows to fine-tune the behavior, in particular according to the aging parameter of the system over time.

Of course, one can couple the two layers, open shown in Figure 3 and closed shown in Figure 5, so as not to make the system completely unavailable in the event of failure of the pressure sensor 84. The invention thus consists in using the software for limiting the power of the vehicle heat engine defined by the ASR module 90. In a known manner, the ASR module 90 limits the power of the main engine 20, thermal or electrical, to avoid the spinning at start-up or loss of vehicle control.

However, the ASR module 90 is provided in itself to limit slippage. Hydraulics are not used as much as they should with a conventional ASR module 90. In order for the hydraulics of the assistance circuit to work well (gives a significant pressure), it is necessary to allow more slippage between wheels, in the scope of the invention, that does not allow a conventional ASR module.

The control of the ASR module 90 so as to adjust a maximum hydraulic pressure according to the invention allows different technical effects and advantages.

A first effect is to avoid using pressure relief valves

High Pressure and Low Pressure and therefore a cost saving.

A second effect is to limit the maximum pressure without rolling the oil in pressure relief valves, which is to spend less power in the hydraulic loop and thus less heat the oil. The oil heats less and the availability of the system is greater.

The invention also makes it possible to avoid point pressure peaks induced by the ASR module 90.

Thus in the context of the invention, the ASR module 90 is used to prevent hydraulic overpressure at startup, and then it is controlled according to the speed of the vehicle on the basis of a speed-dependent law. Thus, the ASR module 90, in the context of the invention is used to obtain the right necessary pressure.

As seen in Figure 6 which illustrates the flow chart of the method according to the invention, the first step 110 is to detect the activation of the assistance system.

When the assistance is activated, the control module monitors the speed of the vehicle (step 112). As long as the speed remains below a threshold, the module 80 controls the pressure in the circuit to keep it below a threshold and avoid overpressure (step 114).

On the contrary, when the speed is greater than the threshold, the control of the pressure is operated according to the speed of the vehicle according to a given map (step 116).

Of course, the present invention is not limited to the particular embodiments that have just been described but extends to all variants in his mind.

In the context of the invention the control module 80 can integrate other parts of the vehicle electronics, in particular the ASR and other functions related to the speed of the wheels and the corresponding sensors.

In the context of the invention, the housing 80 can receive the information relating to the speed of wheels or sliding by other electronic units of the vehicle.

A speed measurement between the front axles 50 and the rear axle 52 of the vehicle has previously been described, using speed sensors 82 fitted to the wheels of the vehicle 10, 12, 14 and 16.

However, the invention is not limited to this provision. The manner of measuring slippage or slip can be subject to many embodiments. In the context of the present invention, any unjustified speed difference (for example, a "justified" difference in speed between two wheels due to a turn) can be taken into account.

It is also provided in the context of the invention, wheel slip control by the individual brake actuators which takes into account the information that the assistance is implemented.

In the context of a particular mode of implementation according to the present invention, in a situation of full power slip, the sliding is measured between the front axles 50 and rear 52, for example by a significant difference in speed between a front wheel 10 or 12 and a rear wheel 14 or 16 (or with respect to all other wheels).

The present invention allows more power to be passed in 4x4 mode than in 4x2 mode, thanks to a higher calibration of the ASR control and the commitment of assistance.

Claims

A vehicle comprising load wheels (10, 12, 14, 16), a main drive motor (20), thermal or electric, coupled to at least one pair of carrying wheels (10, 12) and a driving system support unit comprising at least one hydraulic motor (62) coupled to at least some of the load wheels (14, 16), a pump hydraulic machine (60) connected to the hydraulic motor (62) and slip sensors (82) and wheel speed, as well as a control module (80) which ensures the commissioning of the assistance on the basis of a processing of the signals from the skid and speed sensors (82), characterized by the fact that the control module (80) uses a software (90) for limiting the power of the main engine (20) and comprises means for controlling this software which adjusts the power of the engine taking into account the engagement or non-commitment of the assistance system, and if it is engaged that adjusts the maximum pressure h ydraulic to avoid hydraulic overpressure.

2. Vehicle according to claim 1, characterized in that it comprises speed sensors (82) associated with the various wheels of the vehicle to provide the control module (80) information representative of the difference in speed between the wheels of different axles (50, 52).

Vehicle according to one of claims 1 or 2, characterized in that the control module (80) uses a characteristic

Speed / pressure on all speeds in the operating range to control an ASR module (90) to limit slippage to ensure maximum efficiency of the hydrostatic system.

4. Vehicle according to claim 3, characterized in that in a starting phase, the control module (80) requires that the slip level necessary to obtain the maximum pressure of the hydrostatic transmission, does not place the vehicle in a dangerous situation of loss of control.

5. Vehicle according to one of claims 1 or 2, characterized in that it comprises a pressure sensor (84) placed on the circuit, typically on a high pressure line (70), to know the pressure levels in the transmission so that the control module (80) imposes a slip level in adequacy with the expected performance of the system according to the operating range.

6. Vehicle according to one of claims 1 to 5, characterized in that the control module (80) operates a specific mapping for a 4x4 hydraulic mode that allows imposing not to exceed a maximum allowable pressure, to draw the best compromise between performance of crossing and optimization of the dynamic behavior of the car in situation of slip on ground of weak adhesion.

7. Vehicle according to one of claims 1 to 6, characterized in that the control module (80) implements an open regulation loop which comprises the following steps: validation of an assistance activation instruction ( 100), limitation of the main motor torque (20), defined by ASR software (90) with the aim of limiting the slip rate (102) and limiting the speed difference to reach the maximum torque of the hydraulic transmission for each point (step 104).

8. Vehicle according to one of claims 1 to 6, characterized in that the control module (80) implements a closed control loop which exploits the pressure signal from a sensor (84).

9. Hydraulic assistance system comprising at least one hydraulic motor (62) coupled to at least some of the carrier wheels (14, 16) of a vehicle as defined in one of claims 1 to 8, a hydraulic machine forming a pump (60) connected to the hydraulic motor (62) and sensors (82) for slipping and wheel speed, and a control module (80) for putting the assistance (60) into operation on the base processing of the signals from the skid and velocity sensors (82), in which the control module (80) operates a software (90) for limiting the power of the main engine (20) and comprises means for controlling this software which adjusts the power of the engine taking into account the commitment or non-commitment of the system assistance, and if it is engaged that adjusts the maximum hydraulic pressure to avoid hydraulic overpressure.

A method of assisting a vehicle comprising load wheels (10, 12, 14, 16), a main drive motor (20), thermal or electric, coupled to at least one pair of wheels (10, 12). carriers and an assistance system comprising at least one hydraulic motor (62) coupled to at least some of the carrier wheels (14, 16), a hydraulic pump machine (60) connected to the hydraulic motor (62) and sensors (82) wheel slippage and speed, and a control module (80) which ensures the commissioning of the assistance (60) on the basis of a processing of the signals from the skating sensors (82). and speed, characterized by the fact that it comprises the operation of a software (90) for limiting the power of the main engine (20) of an ASR module (90), to adjust the power of the engine taking into account the commitment or non-commitment of the assistance system, and if it is engaged adjust the maximum pressure h ydraulic and avoid hydraulic overpressure.

11. The method of claim 10, characterized in that it exploits a characteristic Avitesse / pressure on all speeds of the range of use to control an ASR module (90) to limit slippage to ensure the maximum efficiency to the hydrostatic system.

12. A method according to claim 11, characterized in that in a starting phase, it requires that the slip level necessary to obtain the maximum pressure of the hydrostatic transmission, does not place the vehicle in a dangerous situation of loss control.

13. The method of claim 10, characterized in that it implements a pressure sensor (84) placed on the circuit, typically on a high pressure line (70), in order to know the pressure levels in the transmission and impose a slip level in line with the expected performance of the system according to the operating range.

14. Method according to one of claims 10 to 13, characterized in that it exploits a specific mapping for a 4x4 hydraulic mode that allows imposing not to exceed a maximum allowed pressure, to draw the best compromise between performance crossing and optimization of the dynamic behavior of the car in a slip-on situation on a low-traction ground.

15. Method according to one of claims 10 to 14, characterized in that it implements an open regulation loop which comprises the following steps: validation of an assistance activation instruction (100), limitation of the torque of the thermal or electrical engine (20), defined by ASR software (90) with the aim of limiting the slip rate (102) and limitation of the speed difference to reach the maximum torque of the hydraulic transmission for each point ( step 104).

16. Method according to one of claims 10 to 15, characterized in that it implements a closed control loop that exploits the pressure signal from a sensor (84).

17. Method according to one of claims 10 to 16, characterized in that it implements the following steps:

. detecting the activation of the assistance system (110),

. monitoring the speed of the vehicle (112),

. as long as the speed remains below a threshold, controlling the pressure in the circuit to keep it below a threshold (114),

. on the other hand, when the speed is greater than the threshold, control of the pressure as a function of the speed of the vehicle according to a given map (116).