WO2017081162A1

WO2017081162A1 - Hydraulic assist engagement method

Info

Publication number: WO2017081162A1
Application number: PCT/EP2016/077283
Authority: WO
Inventors: Rana-Omer NAEEM
Original assignee: Poclain Hydraulics Industrie
Priority date: 2015-11-10
Filing date: 2016-11-10
Publication date: 2017-05-18
Also published as: FR3043371B1; FR3043371A1

Abstract

The invention relates to a hydraulic assist engagement method comprising steps of: measurement of the rotation speed of at least two different wheels (12, 13, 22, 23); engagement of the hydraulic assist upon fulfillment of an engagement condition, taking account of the measured rotation speeds and the set angle (c_angle).

Description

Method of engaging hydraulic assistance

GENERAL TECHNICAL FIELD The present invention relates to the field of vehicles comprising hydraulic assistance, typically vehicles that can go from a two-wheel drive configuration to an integral transmission.

STATE OF THE ART

Vehicles with hydraulic assistance which can be engaged selectively according to the desired driving conditions for carrying out all or part of the wheels are known. When engaged, the hydraulic assistance consumes a significant power and generates a heating. That is why it is desirable to engage it only when necessary and to disengage it as soon as it ceases to be necessary. In the current state of the art, the hydraulic assistance is generally activated manually by the driver.

Other hydraulic assistance systems are configured to be engaged below a certain speed threshold.

It can also be provided further that the hydraulic assist system is engaged above a certain speed threshold. Such a condition of engagement of the hydraulic assistance does not make it possible to optimize the engagement of the assistance according to the real need at the level of the connection with the ground of the vehicle. PRESENTATION OF THE INVENTION

The present invention thus aims to provide a parameterizable engagement method hydraulic assistance directly related to the actual wheel slip and does not require the intervention of the driver. To this end, the invention proposes a method of engaging the hydraulic assistance in a vehicle comprising a chassis, at least one mechanical axle linked to mechanical wheels and at least one carrying axle linked to load wheels and a primary motor driving in rotation the mechanical axle, said vehicle further comprising at least two hydraulic devices configured to selectively perform a hydraulic assist for driving the wheels, and a steering control defining an angle setpoint,

the method of engaging the hydraulic assistance comprising steps of:

measuring the rotational speed of at least two different wheels;

measuring the average speed of the vehicle;

- commitment of the hydraulic assistance when the absolute value of the difference between the two rotational speeds measured exceeds a commitment threshold value,

the method of engaging the hydraulic assistance being characterized in that:

for an angle set point lower than a low angle setpoint threshold, the engagement threshold value depends solely on the average speed of the vehicle;

for an angle setpoint between the low angle setpoint threshold and a high angle set point threshold, the engagement threshold value depends on the vehicle average speed Vmoy and the angle setpoint;

for an angle set point greater than a high angle set point threshold, the engagement threshold value depends solely on the average vehicle speed (Vmoy),

the commitment threshold value being defined on the basis of four points (A, B, C, D) in a reference having the abscissa the angle reference (c_angle), and for the ordinate axis the threshold value of commitment (v_seuil_engagement), the coordinates of the four points (A, B, C, D) being configurable,

the first and second points (A, B) corresponding to the commitment threshold value (v_seuil_engagement) for a high average vehicle speed (Vmoy) and the third and fourth points (C, D) corresponding to the threshold value d commitment (v_seuil_engagement) for a low average vehicle speed (Vmoy), the first and third points (A, C) having abscissas corresponding to the low angle set point, and the second and fourth points (B, D) having abscissas corresponding to the high angle setpoint. The first and third points (A, C) have the same abscissa corresponding to the low angle set point, and the second and fourth points (B, D) having the same abscissa corresponding to the high angle set point threshold.

For an angle setpoint (c_angle) lower than a low angle setpoint threshold, the engagement threshold value (v_seuil_engagement) is proportional to the average vehicle speed (Vmoy);

for an angle setpoint (c_angle) between the low angle set point threshold and a high angle set point threshold, the engagement threshold value (v_seuil_engagement) is proportional to the average vehicle speed Vmoy (Vmoy) and at the angle setpoint (c_angle); for an angle set point greater than a high angle set point threshold, the engagement threshold value (v_seuil_engagement) is proportional to the average vehicle speed (Vmoy). The rotational speeds of at least one carrier wheel (22, 23) and at least one mechanical wheel (12, 13) are measured, the engagement condition taking into account the difference between the rotational speed of the carrier wheel (22). 23) and that of the mechanical wheel (12, 13). The rotational speeds of two load wheels carried by different carrying axles are measured, the engagement condition taking into account the difference between the speeds of rotation of the two carrying wheels carried by different carrying axles. The rotational speeds of two load wheels carried by the same carrier axle are measured; the engagement condition taking into account the difference between the speeds of rotation of the two carrying wheels carried by the same carrier axle. The engagement method according to the invention allows to engage the hydraulic assistance when a situation of slippage of at least one wheel is detected. The engagement method according to the invention makes it possible not to trigger the hydraulic assistance without reason during a turn. Indeed, a turn induces a difference in rotational speed between two axles that could be misinterpreted as a skating situation.

The engagement method according to the invention is parameterizable, that is to say that it can be adapted to any type of vehicle by choosing values adapted to the constants parameterizable.

The method of engaging the hydraulic assistance further comprises a step of disengaging the hydraulic assistance when the absolute value of the difference between the two rotational speeds measured is less than a threshold value of disengagement, in which

for an angle setpoint lower than the low angle setpoint threshold, the threshold value of disengagement depends solely on the average speed of the vehicle;

for an angle setpoint between the low angle setpoint and the high angle setpoint, the disengagement threshold value depends on the average vehicle speed and the angle setpoint;

for an angle setpoint higher than the high angle setpoint threshold, the threshold value of disengagement depends solely on the average speed of the vehicle,

the threshold value of disengagement being defined on the basis of four secondary points A ', B', C, D 'in a coordinate system having the abscissa of the angle setpoint, and for the ordinate axis the threshold value of the disengagement, the coordinates of the four secondary points A, B ', C, D' being configurable, the first and second secondary points A, B 'corresponding to the threshold value of disengagement for a high average vehicle speed and the third and fourth points C , D 'corresponding to the threshold value of disengagement for a low average speed of the vehicle,

the first and third points A ', C having abscissae corresponding to the low angle set point, and the second and fourth points B', D 'having abscissae corresponding to the high angle set point threshold. For an angle set point lower than a low angle set point threshold, the disengagement threshold value is proportional to the average speed of the vehicle;

for an angle set point between the low angle setpoint threshold and a high angle set point threshold, the disengagement threshold value is proportional to the average vehicle speed and the angle setpoint; for an angle setpoint greater than a high angle set point threshold, the disengagement threshold value is proportional to the average speed of the vehicle.

The engagement method according to the invention also allows to disengage the hydraulic assistance as soon as it is no longer necessary, which reduces the consumption and warming generated by the hydraulic assistance.

The invention also proposes a system for engaging the hydraulic assistance in a vehicle comprising a chassis, at least one mechanical axle linked to mechanical wheels and at least one carrying axle linked to carrying wheels, and a primary engine driving in rotating the mechanical axle, said vehicle further comprising at least two hydraulic devices configured to selectively perform a hydraulic assist for driving the wheels,

the hydraulic assistance engagement system comprising:

a sensor adapted to measure the speed of rotation of one of the wheels; a sensor adapted to measure the speed of rotation of another wheel;

means for determining the average speed (Vmoy) of the vehicle; a calculator comprising a memory in which the coordinates of four points are stored in a coordinate system having the angle setpoint (c_angle) as the abscissa axis, and the engagement threshold value (v_seuil_engagement) as the ordinate axis,

means for entering the coordinates of these four points,

the first and second points A, B corresponding to the commitment threshold value (v_seuil_engagement) for a high average vehicle speed and the third and fourth points C, D corresponding to the commitment threshold value for a mean speed of the vehicle; weak vehicle, the first and third points A, C having abscissas corresponding to the low angle setpoint, and the second and fourth points B, D having abscissas corresponding to the high angle setpoint;

the computer being configured to engage the hydraulic assistance, when the absolute value of the difference between the two rotational speeds measured exceeds an engagement threshold value;

for an angle set point lower than a low angle set point threshold, the engagement threshold value depending solely on the average speed of the vehicle;

for an angle set point between the low angle setpoint threshold and a high angle setpoint threshold, the engagement threshold value depending on the average vehicle speed and the angle setpoint; for an angle setpoint greater than a high angle set point threshold, the engagement threshold value depending solely on the average speed of the vehicle.

The invention also proposes a vehicle comprising a chassis, at least one mechanical axle linked to mechanical wheels and at least one carrying axle linked to carrying wheels and a primary motor rotating the mechanical axle, said vehicle further comprising at least two hydraulic apparatuses configured to selectively provide a hydraulic assist for driving the wheels, the vehicle further comprising a steering control defining an angle setpoint, and a speed control, such as a pedal, defining an acceleration instruction, and a system for engaging the hydraulic assistance as described above.

The invention also proposes a parameterization method for the implementation of a method of engaging the hydraulic assistance in a vehicle as described above and or for a system as described above, characterized by the it comprises a step of entering the coordinates of the four points A, B, C, D defining the engagement threshold, in a reference having the abscissa axis the angle setpoint, and for the ordinate axis the threshold value. engagement,

the first and second points A, B corresponding to the commitment threshold value for a high average vehicle speed and the third and the fourth point C, D corresponding to the commitment threshold value for a low average vehicle speed,

the first and third points A, C having abscissas corresponding to the low angle set point, and the second and fourth points B, D having abscissas corresponding to the high angle set point threshold.

PRESENTATION OF FIGURES

Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the appended drawings, in which:

FIG. 1 schematically shows an example of a hydraulic assistance circuit equipped with an engagement system according to one aspect of the invention,

FIG. 2 schematically shows another example of a hydraulic assistance circuit equipped with an engagement system according to one aspect of the invention,

FIG. 3 represents the engagement threshold of the hydraulic assistance according to one aspect of the invention,

Figure 4 shows the disengagement threshold of the hydraulic assistance according to one aspect of the invention.

DETAILED DESCRIPTION Figure 1 schematically shows an example of a driver circuit.

This figure shows schematically a vehicle structure comprising a chassis, a mechanical axle 14 and a carrier axle 24, each of the axles carrying two wheels, respectively 12, 13, 22 and 23.

The mechanical axle 14 is connected to a primary motor M, typically a heat engine, via a clutch 2 and a gearbox 3 thus ensuring its drive. A transmission shaft line connects the gearbox to the wheels. The mechanical axle is therefore a mechanical transmission axle. The axle carrier is not mechanically connected to the engine M. It essentially constitutes a wheeled axle carriers when assistance is not engaged.

In the embodiment shown in FIG. 1, each of the mechanical axles 14 and the carrier 24 comprise a differential, respectively 1 1 and 21, making it possible to turn the wheels of one and the same axle at different speeds of rotation, particularly in the case of cornering or loss of grip of one of the wheels.

In the embodiment shown, each of the axles comprises a hydraulic apparatus. The mechanical axle 14 comprises a hydraulic apparatus 20 operating essentially as a pump connected on the one hand to the chassis, and on the other hand to the mechanical axle 14, and the carrying axle 24 comprises a hydraulic apparatus 20 operating essentially as a linked engine on the one hand to the chassis, and on the other hand to the carrier axle 24.

An equivalent vehicle can be created by not using a differential on the carrying axle 24, but by assigning each wheel 22 23 a hydraulic motor 20. The combination of two hydraulic devices 10, 20 can take traction torque on a mechanical axle 14 and to transfer it to a carrier axle 24, which makes it possible to transform a two-wheel drive vehicle into a four-wheel drive vehicle.

These two hydraulic devices 14 and 24 are typically reversible hydraulic devices of radial piston type well known to those skilled in the art, which can alternate between a freewheel configuration and a service configuration, for example by retracting the pistons in their respective housings, or by disengaging the cylinder block so as to have a zero displacement.

The hydraulic devices may have a pump or motor operation, depending on the nature of their supply, that is to say according to the direction of fluid flow, and depending on the pressures that are established in the lines.

An example of a structure of such a hydraulic apparatus p is given in WO 2014048841 for example. The operation of such a circuit is for example described in the patent application WO 2014048841. The vehicle structure thus presented allows for hydraulic assistance, by taking a torque on a mechanical axle of a vehicle and transmitting this torque on another axle on which is performed the hydraulic assistance.

The vehicle structure shown in FIG. 1 corresponds, for example, to that described in application WO 2014048841. It is also possible to apply the invention to a different circuit, as illustrated in FIG. 2.

Figure 2 shows a conventional six-wheel truck structure distributed over three axles:

- A mechanical axle 14 comprising a differential 1 1 rotated by a gearbox 3 coupled to a primary motor M via a clutch 2,

a steering front axle 24 comprising two carrying wheels 22 and 23, a rear axle 64 comprising a differential 61 and two wheels 62 and 63.

The vehicle further comprises a hydraulic apparatus 10 driven directly or indirectly by the heat engine M, and sending assistance torque hydraulically to the wheels of an assisted axle equipped with hydraulic apparatus 20 operating in engine mode. The assisted axle can be manager or not. The assisted axle may be the steering front axle 24 or the rear axle 64. The axle 24 and the axle 64 may also be present at the same time. In general, the pump must be rotated by a movement taken from the mechanical transmission chain between the heat engine M and a mechanically driven wheel.

The hydraulic apparatus 10 operates as a pump is driven by the engine. However, it can also be caused by a force related to the gearbox. In this case, the hydraulic apparatus 10 may be connected to a rotating shaft in proportion to the speed of the engine, or to a shaft rotating in proportion to the speed of the wheels. A clutch may be provided to mechanically disengage the hydraulic apparatus 10. The hydraulic apparatus 10 may be of fixed or variable displacement. This architecture is for example used for commercial vehicles, buses or trucks, or towed trailers.

Such devices are used in particular in assistance on a vehicle, to allow in case of need to operate the hydraulic motor as a booster or assistance engine, in difficult vehicle traveling conditions such as a slippery floor, a steep slope etc. The hydraulic motor 20 is generally arranged on an axle of the vehicle whose wheels are not driving in the normal mode of advance of the vehicle; also, when the hydraulic transmission device is activated, the vehicle has additional drive wheels.

The operation of such a hydraulic apparatus is described in particular in application WO 2014048842. Advantageously, the hydraulic units are of the radial piston and multilobe cam type and are placed so as to rotate at the speed of the wheels. However, one can also consider similar systems with a single engine linked to the speed of the cage of a differential that rotates at the average speed of the two wheels of the same carrier axle. It is also conceivable, although this is not the preferred solution for multilobe cam motors, to have a reduction or multiplication stage between the wheels and the engines.

The two hydraulic devices 10 are typically reversible radial piston type hydraulic devices well known to those skilled in the art, which can alternate between a freewheel configuration and a service configuration, for example by retracting the pistons in their housing. respective, or by disengaging the cylinder block so as to have zero displacement

Hydraulic motors 20 having a free wheel configuration, that is, a configuration in which the hydraulic apparatus operates without fluid pressure and the pistons are not in contact with the cam. This freewheeling configuration is opposed to the work configuration, in which the pistons are in contact with the cam, and the hydraulic apparatus operates with fluid pressure.

The hydraulic motors 20 are in freewheel configuration when the additional hydraulic transmission is not requested, and goes into working configuration when it is requested.

This passage from the freewheel configuration to the working configuration is achieved by an output of the pistons, which are in contact with the cam, or more precisely their free ends are placed in contact with the cam. This transition from the freewheel configuration to the working configuration is commonly called interconnection.

The use of hydraulic devices that can be put into service or disengaged by engagement or disengagement of the cylinder block is also possible.

The vehicle further comprises a steering control 4, such as a steering wheel, defining a c-angle angle setpoint, a speed control 5, such as an acceleration pedal, defining an acceleration setpoint, and a control brake 5, such as a brake pedal, defining a brake setpoint.

Hydraulic assistance commitment

The vehicle comprises a hydraulic assistance engagement system comprising a computer 9. The computer 9 is connected to the steering wheel 4 and receives the corner angle setpoint. The computer 9 is furthermore connected to the acceleration pedal 5 and receives the acceleration command and is connected to the brake pedal 6 and receives the braking instruction. Rotation speed sensors 17 (respectively 27) are placed on the wheels whose speed is measured. These wheel rotation speed sensors may especially be those of the anti-lock wheel system (ABS).

When one (or more) of the wheels of the mechanical axle 14 begins to spin because the engine torque of the engine that is coupled to it is excessive given the grip of the wheel on the ground, the speed of the skating wheel increases compared to those wheels that do not slip. Indeed, a wheel that is only carrier (that is to say associated with a carrier axle) can not slip due to a pulling torque generated by the mechanical transmission. It can therefore be used as a reference for a wheel speed representative of the progress of the vehicle, without being significantly disturbed by slippage. It is therefore possible to detect a slip situation by the speed difference between a mechanically driven wheel (that is to say associated with a mechanical axle), which can slip substantially according to the traction force, and a wheel bearing which does not skate noticeably. If the slip of a wheel is defined by the difference in speed between the actual speed of rotation of the wheel that is slipping, and the theoretical speed of rotation of this wheel if it does not slip, we can estimate the slip by the measurement of the speed difference between a mechanically driven wheel and a carrier wheel.

We can therefore decide to engage the assistance from a certain sliding threshold, which we consider admissible. However, this threshold can be set by the user according to the characteristics of the vehicle, such as for example the vehicle geometry, the speed, and the radius of gyration, which is related to the steering wheel angle.

Indeed, if a vehicle rolls slowly, we can tolerate a difference in speed between a carrier wheel and a mechanically driven wheel greater than if it rolls quickly .. Also, a small slip can be characteristic of slippage if the vehicle goes into straight line, while cornering, the outer wheels will travel more than the inner wheels, and one axle will travel more than another. It will therefore be necessary to modulate the threshold which defines a sensitive slip as a function of the overall speed of the vehicle, and the angle of gyration. These parameters will also vary from one vehicle to another depending on its geometric dimensions, and the threshold valid for a vehicle will be different from the threshold valid for a vehicle of different dimensions. For example, the criteria for an articulated vehicle will not be the same as for a vehicle without articulation. The criterion will also depend on the number of axles considered and the modularity of the axles.

The invention consists in taking into account a certain number of parameters, so as to define a condition of engagement, these parameters including at least the speed of rotation of two different wheels, and the angle setpoint. The constructor can specify other parameters at a later time.

In a particular embodiment, the engagement condition can take into account, in particular, the speed of rotation of the mechanical axle 14, and the speed of rotation of the carrier axle 24. For this purpose, rotational speed sensors 17 are placed on the wheels 22, 23 of the mechanical axle 14, and sensors 27 on the wheels 12 and 13 of the carrier axle 24.

In particular, the rotational speed of the mechanical axle 14 can be defined as the average between the rotational speeds of the two wheels of the mechanical axle 14. Similarly, the speed of rotation of the axle 24 can be defined as the average between the rotational speeds of the two wheels of the carrier axle 24.

In the case of a vehicle with several carrying axles 24, 64, some of which are equipped with a hydraulic assistance 10, and at least one other is not, as illustrated in Figure 2, the commitment condition may take in account the speed difference between the mechanical axle 14 and the axle 64 not equipped with hydraulic assistance. For this purpose, the rotational speed sensors 17, 27 are placed on the wheels of two different carrying axles 24, 64, namely an axle 24 equipped with hydraulic assistance and an axle 64 not equipped with hydraulic assistance.

In another particular embodiment, the engagement condition takes into account the rotational speeds of two wheels 12, 13 carried by the same mechanical axle 14. For this purpose, the rotational speed sensors 17, 27 are placed on the wheels 12, 13 of the same mechanical axle 14. If the vehicle is fairly simple, for example with a single differential, it is possible that only one of the wheels carried by the same mechanical axle slips. The difference in rotational speed between the two wheels 12, 13 carried by the same mechanical axle 14 then makes it possible to detect slippage. In the case of a vehicle with several axles and several mechanical axles, we can simplify by measuring only one axle, representative of a group of axles. The speeds of the two carrying axles are correlated with each other or compared to define a speed of movement of the vehicle as accurate as possible, and estimate the slip of each axle. In the case of several carrying axles, only one of which is assisted, the engagement condition takes into account, on the one hand, the difference between the rotational speed of the unassisted carrier axle 64, and that of the mechanical axle 17, and secondly, the difference between the rotational speed of the unassisted carrier axle 64 and that of the assisted axle 24.

In the case of a lift axle vehicle, the measurement on certain axles may or may not be taken into account.

The computer 9 is configured to:

measure the rotational speed of at least two different wheels;

detecting a slip situation the absolute value of the difference d between the rotational speeds measured is greater than a certain engagement threshold value v_seuil_engagement.

The threshold value v_seuil_engagement is set according to the c_angle angle setpoint and the average vehicle speed Vmoy.

The system comprises for this purpose means 37 for determining the average speed of the vehicle. The average speed Vmoy of the vehicle can be measured by a speed sensor on board the vehicle or deducted from the acceleration and braking instructions. An average speed of movement of the vehicle can be determined by various means, for example by a ground radar, or GPS information.

The threshold value v_seuil_engagement is typically proportional to the average speed Vmoy of the vehicle.

In FIG. 3, the value v_seuil_engagement is represented as a function of the angular angle set c_angle, for an average speed Vmoy of the vehicle Vmoy weak, on the one hand, and for an average speed Vmoy of the high vehicle Vmoy, on the other hand . For a low c angle angle set point, lower than a low angle setpoint threshold c_angle inf, the value v_seuil_engagement does not depend on the corner angle setpoint c_angle but only the average speed Vmoy of the vehicle. In particular, the value v_seuil_engagement can be proportional to the average speed Vmoy of the vehicle. We then v_seuil_engagement = k1 ^* Vave, with adjustable constant k1.

For an angle setpoint c_ mean angle, between the low angle setpoint threshold and a high angle setpoint threshold c_angle_sup, the value v_seuil_engagement depends on the c_angle angle setpoint and the average vehicle speed Vmoy. In particular, the value v_seuil_engagement can be proportional to the average speed Vmoy of the vehicle and the c_angle angle setpoint.

We then v_seuil_engagement = k2 ^* ^* Vmoy c_angle with adjustable constant k2.

For a large angle setpoint, between the low angle set point c_angle inf and the upper angle set point c_angle_sup, the value v_seuil_engagement does not depend on the angle set point c_angle but only the average speed Vmoy of the vehicle. In particular, the value v_seuil_engagement can be only proportional to the average speed Vmoy of the vehicle.

We then have v_seuil_engagement = k3 ^* Vmoy, with k3 parameterizable constant.

The low angle set point c_angle inf and the high angle setpoint threshold are configurable and will be chosen by the manufacturer depending on the vehicle to be equipped.

By way of example, the low angle setpoint threshold c_gle parameterizable is typically equal to 50 °, and the high angle setpoint threshold is typically equal to 400 °.

By way of example, the average c_angle angle setpoint range, between the low angle set point threshold and a high angle setpoint threshold c_supervalue, is typically equal to more than 2/3 of the setpoint range. angle setpoint total angle. The fact that the value v_seuil_engagement depends on the c_angle angle setpoint for an average angle c_ angle setpoint makes it possible to take into account the fact that a bend induces a difference in speed of rotation between two axles which could be misinterpreted as a skating situation.

Thus, the engagement method allows to engage the hydraulic assistance when a wheel slip situation of at least one wheel is detected while ensuring not to trigger the hydraulic assistance without reason during a turn.

The commitment threshold value is defined on the basis of four points A, B, C, D in a coordinate system having the abscissa of the angle setpoint c_angle, and for the ordinate axis the engagement threshold value v_seuil_engagement, the coordinates of the four points A, B, C, D being configurable.

The commitment threshold value is defined by a constant in the coordinate system having the angle setpoint c_angle as the abscissa axis, and the engagement threshold value v_seuil_engagement as the ordinate axis, for a low c_angle angle setpoint, and for a high angle angle setpoint.

The commitment threshold value is defined by an affine line in the coordinate system having the angle setpoint c_angle as the abscissa axis, and the engagement threshold value v_seuil_engagement as the ordinate axis, for an average c_angle angle setpoint. The slope of this affine line depends on the value of the average speed of the vehicle. The higher the average speed of the vehicle, the higher the slope.

The points A, B, correspond to the engagement threshold for an average vehicle speed Vmoy high, and the points C, D, correspond to the commitment threshold for an average speed Vmoy of the weak vehicle.

The abscissas of the points A and C correspond to the lower angle c_angle set point below which the value v_seuil_engagement does not depend on the corner angle setpoint but only on the average speed Vmoy of the vehicle. The abscissas of the points B and D correspond to the threshold of_point of angle c_ upper angle above which the value v_seuil_engagement does not depend on the angle set c_angle but only the average speed Vmoy of the vehicle.

For a c_angle angle setpoint between the abscissa of the points A and C corresponding to the low angle set point, and the abscissa of the points B and D corresponding to the upper setpoint, the value v_seuil_engagement depends on the setpoint angle of angle c_angle and the average speed Vmoy of the vehicle.

The engagement method can be parameterized, to be adapted to any type of vehicle, by choosing values adapted for the abscissa and the ordinate of points A, B, C, D on a diagram having as ordinate the value v_seuil_engagement , and on the abscissa the corner angle setpoint.

The engagement method is parameterizable, that is to say that it can be adapted to any type of vehicle by choosing suitable values for the constants, which are the coordinates of the points A, B, C , D.

The abscissas of the points A and C, on the one hand, and B and D, on the other hand, being identical, the parameterizable constants are 6 in number.

To determine the commitment threshold at each instant, the calculator 9:

acquires the average speed of the vehicle Vmoy and the setpoint angle c_angle;

determines an engagement threshold value for an average speed Vmoy of the weak vehicle, as a function of the c-angle angle setpoint;

determines an engagement threshold value for an average vehicle speed Vmoy high, as a function of the c_angle angle setpoint;

- determines the commitment threshold by extrapolation of the commitment threshold values calculated for a low and high average speed Vmoy. The engagement threshold is typically determined by proportionality from, on the one hand, the commitment threshold value calculated for a mean speed Vmoy low, and the commitment threshold value calculated for a high average speed Vmoy , and other by the average speed of the measured Vmoy vehicle.

The computer 9 includes a memory in which are stored the configurable constants defined by the vehicle manufacturer, namely the coordinates of the points A, B, C, D.

The engagement system comprises means 30 for entering the coordinates of the four points A, B, C, D. These input means 30 are typically a human machine interface. The system is parameterized by a parameterization method which comprises a data entry step. coordinates of the four points A, B, C, D defining the engagement threshold.

The computer 9 implementing an algorithm having as parameters, at least the rotational speeds measured, the angle setpoint and the speed control, and parameters entered by the manufacturer. In this way, the same computer containing the algorithm can equip various vehicles. The user or the manufacturer of the vehicle can further define other parameters, depending on the geometry of the vehicle, its use, and the type of reaction of the vehicle he wishes to obtain. The parameters are sufficient to engage and disengage the assistance in a satisfactory manner, that is to say early enough, but not inadvertently, whether the vehicle is traveling in a straight line or not. In a manner known per se, the parameters are acquired by the sensors and analyzed by the computer periodically.

The input means 30 may further comprise a command to enable or disable the assistance, the algorithm triggering the assistance if the commitment condition is fulfilled only if the assistance is activated. The gripping means 30 may further include a command for forcing the engagement of the assistance even when the engagement condition is fulfilled. This mode is called "permanent assistance". The computer 9 is configured to engage the hydraulic assistance when the condition of engagement of the hydraulic assistance is verified.

For this purpose, the computer 9 controls the commissioning of the two hydraulic devices 10 and 20, typically by output of the pistons of their housing in the case of retractable radial piston hydraulic devices.

In the embodiment illustrated in FIG. 1, the first hydraulic apparatus 10 is then driven by the mechanical axle 14, and more particularly by the differential case 11 of the mechanical axle 14 and operates as a hydraulic pump, to deliver a flow which feeds the second hydraulic apparatus 20 which then functions as a hydraulic motor, and thereby causes the differential housing 21 of the carrier axle 24 to rotate.

An integral transmission is thus obtained on the vehicle by taking a torque from the mechanical axle 14 and transmitting this torque onto the carrying axle 24 via the hydraulic devices 10 and 20.

In the embodiment illustrated in FIG. 2, the hydraulic pump 10 driven by the heat engine M sends hydraulic assistance torque to the carrier wheels 22, 23 equipped with hydraulic motors 20.

The engagement system may further be programmed to disengage assistance when a maximum average speed threshold is reached. Indeed, for each vehicle equipped with hydrostatic assistance, depending in particular on the motors, the pump and the diameter of the wheels chosen, it is possible to determine a maximum average speed value from which it is not desirable to keep the assistance in a committed state. Indeed, some components of the assistance, such as hydraulic motors, or pumps, have an operating limit when an average speed threshold is reached. For example, pumps and motors must not operate above a maximum flow, the PTO must not operate above a maximum power. It is therefore useful to provide a speed threshold value maximum average not to be exceeded for assistance, from which it must be disengaged. This threshold value may consist of an additional configurable constant to be entered by the vehicle manufacturer, which defines the parameterization of the control electronics.

The condition of engagement of the assistance can further take into account the temperature of the hydraulic system, which is then another parameter of the algorithm.

The engagement system 1 then comprises at least one temperature sensor 8 adapted to measure the temperature of the hydraulic system. For example, if you drive in "continuous assistance" mode, but the hydraulic system becomes too hot, the algorithm switches to the normal operating mode "slip calculation" to avoid unnecessary heating of the hydraulic system. On the other hand, in very cold weather, one can choose the mode "permanent assistance" as long as the hydraulic system has not reached a sufficient temperature. The engagement system 1 can switch from one mode of operation to another, depending on the hydraulic temperature, while the vehicle is traveling.

A simplified equivalent system can be achieved by using the outside temperature information in place of the hydraulic temperature.

It is possible to define a plurality of configurable constant systems corresponding to different modes: For example a "sporty" mode, in which the threshold for triggering the assistance is lower and therefore the assistance is more easily engaged, and a mode " Economic 4x4 "in which the trigger of assistance is higher and therefore assistance will be less easily engaged.

Disengage hydraulic assistance

In a first embodiment of the disengagement process, the computer 9 is configured to disengage the hydraulic assistance, when a disengagement condition is verified.

The disengagement condition takes into account the same parameters as the engagement condition, namely, at least the rotational speeds of two different wheels, as well as the c-angle angle setpoint. In particular, the disengagement condition advantageously takes into account, as parameters, the speed of an unassisted carrier axle, which would probably be the best reference for knowing the effective speed of the vehicle, and the speed of the mechanical axle, or that of the assisted axle, to check that there is no slippage at all.

The computer 9 is configured to disengage the assistance when the absolute value of the difference d between the rotational speeds measured is less than a second threshold value of disengagement v_seuil_de commitment.

The threshold value v_seuil_dengagement is set according to the c_angle angle setpoint and the average vehicle speed Vmoy. The threshold value v_seuil_dengagement is typically proportional to the average speed Vmoy of the vehicle.

Like the engagement method, the disengagement process is parameterizable, that is to say that it can be adapted to any type of vehicle by choosing values adapted to the parameterizable constants.

The parameterizable constants can also be defined as the abscissa and the ordinate of points A ', B', C, D 'on a diagram having as ordinate the value v_seuil_deengagement, and on the abscissa the angle setpoint c_angle, as illustrated by FIG. 3.

The disengagement process can be parameterized, to be adapted to any type of vehicle, by choosing values adapted for the abscissa and the ordinate of points A ', B', C, D 'on a diagram having as ordinate the value v_seuil_dengagement, and abscissa the angle set c_angle.

The points A ', B' correspond to the disengagement threshold for an average vehicle speed Vmoy high, and the points C, D 'correspond to the disengagement threshold for an average speed Vmoy of the weak vehicle. The abscissas of the points A 'and C correspond to the lower angle set point c_angle below which the v_seuil_de commitment value does not depend not of the angle set c_angle but only of the average speed Vmoy of the vehicle.

The abscissas of the points B 'and D' correspond to the upper corner angle set point above which the value v_seuil_dengagement does not depend on the corner angle setpoint but only on the average speed Vmoy of the vehicle.

The abscissae of the points A ', B', C and D 'are typically the same as those of the points A, B, C and D. In other words, the thresholds of the lower and upper angle angle set are identical for the process of commitment and disengagement.

The threshold value of the v_seuil_dengagement disengagement is always lower than the commitment threshold value v_seuil_engagement.

The second threshold value v_seuil_dengagement can also be equal to a percentage of the first threshold value v_seuil_engagement at the time of the engagement of the hydraulic assistance. The second threshold value v_seuil_dengagement is typically equal to 20% of the first threshold value v_seuil_engagement at the time of engagement of the hydraulic assistance. For this purpose the hydraulic assistance engagement system comprises a memory configured to store the value of the first threshold value v_seuil_engagement at the moment of engagement of the hydraulic assistance The threshold value of disengagement v_seuil_engagement can also be equal to the commitment threshold value v_seuil_engagement to which a fixed value is deducted.

In a second embodiment of the disengagement process, the computer 9 is configured to disengage the hydraulic assistance, after a predetermined time interval has elapsed since the engagement of the hydraulic assistance. This time interval is typically of the order of 2 seconds.

To disengage the hydraulic assistance, the computer 9 controls the tilting of the hydraulic devices 10 and 20 in freewheel configuration, for example by retracting their pistons in the respective housing of their cylinder blocks.

In addition, during braking, a negative torque is applied to the mechanical axle 14. The operation of the hydraulic devices is then reversed; the hydraulic apparatus 10 of the axle 14 has a motor operation, while the hydraulic apparatus 20 of the axle 24 has a pump operation, which allows a synchronization of the axles when braking, by transfer of the braking torque All predefined thresholds and predefined time intervals are parameterizable constants of the algorithm that can be defined by the vehicle manufacturer to adapt the skating detection system algorithm to the vehicle that it equips.

Claims

1. A method of engaging the hydraulic assistance in a vehicle comprising a chassis, at least one mechanical axle (14) connected to mechanical wheels (12, 13) and at least one carrier axle (24) connected to load wheels (22). 23), and a primary motor (M) driving the mechanical axle (14) in rotation, said vehicle further comprising at least two hydraulic apparatuses (10, 20) configured to selectively provide a hydraulic power assist driving the carrier wheels (22, 23), and a steering control (4) defining an angle setpoint (c_angle),

the method of engaging the hydraulic assistance comprising steps of:

measuring the rotational speed of at least two different wheels (12, 13, 22, 23);

measuring the average speed (Vmoy) of the vehicle;

- engagement of the hydraulic assistance when the absolute value of the difference (d) between the two rotational speeds measured exceeds a commitment threshold value (v_seuil_engagement),

the method of engaging the hydraulic assistance being characterized in that:

for an angle setpoint (c_angle) lower than a low angle setpoint threshold the engagement threshold value (v_seuil_engagement) depends solely on the average vehicle speed (Vmoy);

for an angle setpoint (c_angle) between the low angle setpoint threshold and a high angle set point threshold, the engagement threshold value (v_seuil_engagement) depends on the average vehicle speed Vmoy (Vmoy) and the angle setpoint (c_angle);

for an angle set point greater than a high angle set point threshold, the engagement threshold value (v_seuil_engagement) depends solely on the average vehicle speed (Vmoy),

the commitment threshold value being defined on the basis of four points (A, B, C, D) in a reference having the abscissa the angle reference (c_angle), and for the ordinate axis the threshold value of commitment (v_seuil_engagement), the coordinates of the four points (A, B, C, D) being configurable, the first and second points (A, B) corresponding to the commitment threshold value (v_seuil_engagement) for a high average vehicle speed (Vmoy) and the third and fourth points (C, D) corresponding to the threshold value d commitment (v_seuil_engagement) for a low average vehicle speed (Vmoy),

the first and third points (A, C) having abscissas corresponding to the low angle set point, and the second and fourth points (B, D) having abscissas corresponding to the high angle setpoint.

2. A method of engaging the hydraulic assistance according to the preceding claim, the first and third points (A, C) having the same abscissa corresponding to the low angle set point, and the second and fourth points (B, D ) having the same abscissa corresponding to the high angle setpoint.

3. A method of engaging the hydraulic assistance according to one of the preceding claims, wherein:

for an angle setpoint (c_angle) lower than a low angle set point threshold, the engagement threshold value (v_seuil_engagement) is proportional to the average vehicle speed (Vmoy);

for an angle setpoint (c_angle) between the low angle set point threshold and a high angle set point threshold, the engagement threshold value (v_seuil_engagement) is proportional to the average vehicle speed Vmoy (Vmoy) and at the angle setpoint (c_angle); for an angle setpoint greater than a high angle set point threshold, the engagement threshold value (v_seuil_engagement) is proportional to the average vehicle speed (Vmoy).

Hydraulic assistance engagement method according to one of the preceding claims, wherein the rotational speeds of at least one carrier wheel (22, 23) and at least one mechanical wheel (12, 13) are measured, the engagement condition taking into account the difference between the speed of rotation of the carrier wheel (22, 23) and that of the mechanical wheel (12, 13).

Method of engaging the hydraulic assistance according to one of claims 1 to 3, wherein the rotational speeds of two carrying wheels (22, 23, 62, 63) carried by carrying axles (24, 64) are measured. different, the engagement condition taking into account the difference between the rotational speeds of the two carrying wheels (22, 23, 62, 63) carried by different carrying axles (24, 64).

6. A method of engaging the hydraulic assistance according to one of claims 1 to 3, wherein are measured the rotational speeds of two carrier wheels (22, 23) carried by the same carrier axle (24); the engagement condition taking into account the difference between the rotational speeds of the two carrying wheels (22, 23) carried by the same carrier axle (24).

7. A method of engaging the hydraulic assistance according to one of the preceding claims, the method of engaging the hydraulic assistance further comprising a step of disengaging the hydraulic assistance when the absolute value of the difference (d ) between the two rotational speeds measured is lower than a threshold value of disengagement (v_seuil_decommitment)

in which

for an angle setpoint (c_angle) lower than the low angle setpoint threshold, the threshold value of disengagement (v_seuil_de commitment) depends solely on the average speed of the vehicle (Vmoy);

for an angle setpoint (c_angle) between the low angle setpoint threshold and the high angle setpoint threshold, the disengagement threshold value (v_seuil_deengagement) depends on the average vehicle speed Vmoy (Vmoy) and the angle setpoint (c_angle);

for an angle setpoint higher than the high angle setpoint threshold, the threshold value for disengagement (v_session_offset) depends solely on the average speed of the vehicle (Vmoy),

the threshold value of disengagement being defined on the basis of four secondary points (Α ', Β', C, D ') in a reference having the abscissa axis the angle reference (c_angle), and for the ordinate axis the value disengagement threshold (v_seuil_dengagement), the coordinates of the four secondary points (Α ', Β', C, D ') being configurable, the first and second secondary points (Α ', Β') corresponding to the threshold value of disengagement (v_seuil_déengagement) for a mean vehicle speed (Vmoy) high and the third and fourth points (C, D ') corresponding to the threshold value of disengagement (v_seuil_disengagement) for a low average vehicle speed (Vmoy),

the first and third points (Α ', C) having abscissas corresponding to the low angle set point, and the second and fourth points (Β', D ') having abscissas corresponding to the high angle setpoint.

8. A method of engaging the hydraulic assistance according to the preceding claim, wherein:

for an angle setpoint (c_angle) lower than a low angle setpoint threshold, the threshold value of disengagement (v_seuil_dengagement) is proportional to the average speed of the vehicle (Vmoy);

for an angle set point (c_angle) between the low angle setpoint threshold and a high angle setpoint threshold, the disengagement threshold value (v_seuil_disengagement) is proportional to the average vehicle speed Vmoy (Vmoy) and at the angle setpoint (c_angle); for an angle setpoint greater than a high angle setpoint threshold, the threshold value of disengagement (v_seuil_disengagement) is proportional to the average speed of the vehicle (Vmoy).

9. System for engaging hydraulic assistance in a vehicle comprising a chassis, at least one mechanical axle (14) connected to mechanical wheels (12, 13) and at least one carrying axle (24) connected to load wheels (22, 23), and a primary motor (M) rotating the mechanical axle (14), said vehicle further comprising at least two hydraulic apparatuses (10, 20) configured to selectively provide assistance hydraulic system for driving load wheels (22, 23),

the hydraulic assistance engagement system comprising:

a sensor (17) adapted to measure the speed of rotation of one of the wheels (12, 13, 22, 23);

a sensor (27) adapted to measure the speed of rotation of another wheel (12, 13, 22, 23); means (37) for determining the average speed (Vmoy) of the vehicle;

a calculator (3) comprising a memory in which are stored the coordinates of four points (A, B, C, D) in a reference having the abscissa the angle setpoint (c_angle), and the ordinate axis the value commitment threshold (v_seuil_engagement),

- input means (30) of the coordinates of these four points (A, B, C, D),

the first and second points (A, B) corresponding to the commitment threshold value (v_seuil_engagement) for a high average vehicle speed (Vmoy) and the third and fourth points (C, D) corresponding to the threshold value d commitment (v_seuil_engagement) for a low average vehicle speed (Vmoy),

the first and third points (A, C) having abscissas corresponding to the low angle setpoint, and the second and fourth points (B, D) having abscissas corresponding to the high angle setpoint;

- The computer (3) being configured to engage the hydraulic assistance, when the absolute value of the difference (d) between the two rotational speeds measured exceeds a commitment threshold value (v_seuil_engagement).

for an angle setpoint (c_angle) lower than a low angle setpoint threshold, the engagement threshold value (v_seuil_engagement) depends solely on the average vehicle speed (Vmoy);

for an angle setpoint (c_angle) between the low angle set point threshold and a high angle set point threshold, the engagement threshold value (v_seuil_engagement) depending on the vehicle average speed Vmoy (Vmoy) and the angle setpoint (c_angle);

for an angle set point greater than a high angle setpoint threshold, the engagement threshold value (v_seuil_engagement) depends solely on the average vehicle speed (Vmoy).

10. Vehicle comprising a chassis, at least one mechanical axle (14) connected to mechanical wheels (12, 13) and at least one carrier axle (24) connected to load wheels (22, 23), and a primary motor ( M) driving the mechanical axle (14) in rotation, said vehicle further comprising at least two hydraulic apparatus (10, 20) configured to selectively provide a hydraulic assist for driving the carrier wheels (22, 23), the vehicle further comprising a steering control (4) defining an angle setpoint ( c_angle), and a speed control (5), such as a pedal, defining an acceleration set point, and a hydraulic assist engagement system according to claim 9.

1 1. Parametrization method for the implementation of a method of engaging the hydraulic assistance in a vehicle according to one of claims 1 to 8 and or for a system according to claim 9, characterized in that it comprises a step of entering the coordinates of the four points (A, B, C, D) defining the engagement threshold, in a reference having the abscissa axis the angle setpoint (c_angle), and for ordinate axis the threshold value of commitment

(V_seuil_engagement)