EP4256140B1

EP4256140B1 - Methods for detecting a failure of a speed sensor means of a work vehicle, corresponding control systems and work vehicle comprising such control system

Info

Publication number: EP4256140B1
Application number: EP21836067.5A
Authority: EP
Inventors: Adriano GARRAMONE; Andrea Gravili; Stefano Liberti; Antonio Venezia
Original assignee: CNH Industrial Italia SpA
Current assignee: CNH Industrial Italia SpA
Priority date: 2020-12-07
Filing date: 2021-12-07
Publication date: 2025-09-03
Anticipated expiration: 2041-12-07
Also published as: EP4256140A1; IT202000030083A1; WO2022122761A1

Description

Technical field

The present invention relates generally to a work vehicle, such as for example a compact wheel loader, and particularly to methods for detecting a failure of a speed sensor means of a work vehicle, corresponding control systems and a work vehicle comprising such a control system.

Prior art

Motorized work vehicles are well known for use in material handling that carry an attachment (for example, a bucket) and have a hydraulically operated lifting arm for moving the attachment. Examples of such vehicles are tractors and loaders, such as in documents JP 3 118105 B2 , US 2010/131150 A1 and WO 2014/065963 A1 .
A loader is a heavy equipment machine used in construction to move aside on the ground or load materials such as asphalt, demolition debris, dirt, snow, feed, gravel, logs, raw minerals, recycled material, rock, sand, woodchips, etc. into or onto another type of machinery (such as a dump truck, conveyor belt, feed-hopper, or railroad car). There are many types of loader, which, depending on design and application, are called by various names, including attachment loader, front loader, front-end loader, pay loader, scoop, shovel, skip loader, wheel loader, or skid-steer. In particular, compact wheel loaders are compact vehicles that have road wheels and carry a working attachment, such as an attachment, attached to a lift arm or boom that is hydraulically powered.
Referring to figure 1, a work vehicle 1, such as a compact wheel loader, is shown. However, the invention is not limited to such a kind of work vehicle, but is applicable to any other kind of work vehicle.
A compact wheel loader includes an attachment 2 connected to a frame 3 of the work vehicle for movement relative thereto. As shown, a boom 5 is pivotally connected at one end on opposite sides of frame 3. The attachment 2 is pivotally connected at the opposite end of the boom for tilting movement relative to the frame 3 about a generally horizontal axis. The above-described features form no substantial part of the present invention and are generally well known in the art. An attachment, e.g. a bucket, may be replaced in operation by any other type of attachment, e.g. a blade.
Usually, the movement of the boom 5 and of the attachment 2 is controlled by the operator through a joystick 7 placed inside an operator's cab or cabin 9 of the work vehicle 1.
As can be seen in figure 2, which shows a control diagram of the work vehicle 1, the boom 3 and the attachment 2 are moved by an hydraulic control circuit 10 comprising a first and a second hydraulic actuators 12, 14 which are controlled by an electronic control unit 16 through respective solenoid valves 18, 20 according to the position of the joystick 7 controlled by the operator.
For example, each hydraulic actuator comprises an hydraulic cylinder operatively connected respectively to the boom and the attachment, that uses hydraulic power of a working fluid to facilitate mechanical operation, the working fluid being controlled by means of directional solenoid valves 18, 20, e.g. an open centre valve. As liquids are nearly impossible to compress, a hydraulic actuator can exert a large force. The rate of actuation of the boom and attachment is controlled by the opening degree of the respective directional solenoid valve 18, 20 by means of a driving current thereof as a function of the position of the joystick.
The hydraulic flow rate of the working fluid required to operate the boom and the attachment is produced by a hydraulic pump Pu connected to a fluid reservoir T and driven by an internal combustion engine or an electrical motor M (hereinafter simply referred to as motor) of the vehicle, e.g. by a mechanical linkage. The same motor is also used to drive the wheels as a propulsion means of the work vehicle.
Figure 3 shows an exemplary joystick of a work vehicle. A movement of the joystick in an associated bi-dimensional control area A according to a first direction y causes the actuation of the boom and a movement of the joystick in said bi-dimensional control area A according to a second direction x causes the actuation of the attachment. The intersection of said x and y directions is defined as origin O of the control area A, and corresponds to the neutral position of the joystick.
A neutral region N around the neutral position of the joystick is a region where the boom and attachment are not actuated. A region externally surrounding the neutral region is defined a driving region and indicated D in this figure.
For example, according to the orientation depicted in figure 3, when the joystick is moved up from the origin O of the control area A according to the y direction the boom is lowered with respect to ground and when the joystick is moved down from the origin O according to the y direction the boom is lifted towards ground. Further, when the joystick is moved right from the origin O according to the x direction the attachment, is tilted towards a dumping position, and when the joystick is moved left from the origin O according to the x direction the attachment, is tilted towards a dig or rollback position and beyond.
A combination of movement in both directions x and y of the joystick is allowed in order to move simultaneously the boom and the attachment.
For example, the component of a position P of the joystick 7 along direction y (boom actuation axis) is indicated y_P in figure 3 and is the projection over y axis of a vector representing the position P of the joystick in the control area A. The component of the position P of the joystick 7 along direction x (implement actuation axis) is indicated x_P in figure 3 and is the projection over x axis of the vector representing the position P of the joystick in the control area A. The components y_P, x_P of the position P of the joystick may take on any combination of a "positive" value and a "negative" value on the y axis and x axis, respectively with respect to origin O of the control area A that corresponds to the neutral position of the joystick.
Speed sensor information is very critical in order to have a proper and safe behaviour of the work vehicle with respect to operator commands.
In known work vehicle, the detection of a non-working speed sensor is left to the operator. For example, when the speed sensor indicates a null speed but the work vehicle is moving, the operator can understand that the speed sensor is not working properly. However, during operation, the operator may not notice such situation and it would continue the work operation. This could lead to unsafe situations.

Summary of the invention

The aim of the present invention is to increase the safety and the integrity of the work vehicle when a speed sensor disconnection occurs, without increasing the work vehicle cost.
According to the invention, this aim is achieved by a method for detecting a failure of a speed sensor means of a work vehicle, having the features claimed in claim 1, and by a method for detecting a failure of a speed sensor means of a work vehicle, having the features claimed in claim 2.
Preferred embodiments are defined in the dependent claims, whose content is also to be considered an integral part of the present description. Features of the dependent claims may be combined with the features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.
Further subjects of the invention are control systems according to claims 7 and 8, as well as a work vehicle according to claim 10.
In summary, according to a 1St detection strategy, a control system could detect failures of a speed sensor if all the following conditions are simultaneously meet for a time greater than a predetermined period, e.g. 8 sec:

work vehicle at zero speed;
transmission not in neutral;
Pump Forward or Reverse Command greater than a threshold;
Brake Pedal released; and
Joystick released or hydraulic disabled; and
engine (motor) speed higher than a specific threshold.

This strategy is always able to detect failure but it takes more time than the following second strategy.
In a 2nd detection strategy, a control system could detect failures if within a non-consecutive period of time, e.g 4 sec since KeyOn of the work vehicle, all the following conditions are simultaneously meet:

Transmission not in neutral;
Pump Forward or Reverse Command greater than a threshold;
Brake Pedal released;
Engine (motor) speed higher than a specific threshold; and
Vehicle is at zero speed.

The second strategy is able to detect the disconnection or malfunctioning of the sensor quickly but only if it is already present at keyON.
With keyON it should be understood the moment in which the work vehicle is turned on.

Brief description of the drawings

Further functional and structural characteristics and advantages of the present invention are set out in the detailed description below, provided purely as a non-limiting example, with reference to the attached drawings, in which:

figure 1 shows a prior art exemplary work vehicle, in particular a compact wheel loader;
figure 2 shows a prior art control diagram of a work vehicle;
figure 3 shows a prior art exemplary joystick of a work vehicle;
figure 4 shows an exemplary internal structure of a work vehicle according to the invention.

Detailed description

In the following description, unless otherwise defined, all terms (including technical and scientific terms) are to be interpreted as is customary in the art. It will be further understood that terms in common usage should also be interpreted as is customary in the relevant art and not in an idealized or overly formal sense unless expressly so defined herein. All orientation terms, such as upper and lower, are used in relation to the drawings and should not be interpreted as limiting the invention.
In the following, a first embodiment of a method for detecting a failure of a speed sensor means of a work vehicle is described.
The work vehicle includes a motor arranged to power the work vehicle, a speed sensor means arranged to detect a travel speed of the work vehicle and an hydrostatic transmission.
The hydrostatic transmission comprises a hydraulic pump, a hydraulic motor, a forward line arranged to hydraulically connect an outlet of the hydraulic pump to an inlet of the hydraulic motor, and a backward line arranged to hydraulically connect an outlet of the hydraulic motor to an inlet of the hydraulic pump in such a manner to define a closed hydraulic circuit. In the closed hydraulic circuit flows a work fluid.
Said hydraulic pump of the hydrostatic transmission includes a forward solenoid and a reverse solenoid. The hydraulic pump is arranged to pump the work fluid from the backward line to the forward line when the forward solenoid is powered by a driving current, and to pump the work fluid from the forward line to the backward line when the reverse solenoid is powered by the driving current.
The value of the driving current depends on a rotational speed of the motor arranged to power the work vehicle, i.e. the higher the rotational speed the higher the driving current.
The work vehicle further comprises a command means arranged to allow the decoupling of an hydrostatic circuit of the boom from the hydrostatic transmission by the operator, so that the boom is not movable by the operator, a FNR Forward-Neutral-Reverse switch FNR switchable among a forward position, a neutral position and a reverse position, and arranged to control the operation of the hydrostatic transmission depending on the position of said FNR Forward-Neutral-Reverse switch FNR. In particular, the driving current is provided to the forward solenoid of the pump when the FNR Forward-Neutral-Reverse switch FNR is in the forward position, and the driving current is provided to the reverse solenoid of the pump when the FNR Forward-Neutral-Reverse switch FNR is in the reverse position.
Moreover, the work vehicle includes a brake pedal arranged to activate a control braking means of the work vehicle when pressed by the operator, and a joystick arranged to be controlled by an operator, wherein a movement of the joystick in a predetermined control area, with respect to a neutral position, causes the actuation of a boom or an implement of the work vehicle.
For example, as disclosed above and with further reference to Figure 3, the actuation of the boom may occur by means of a joystick controlled by an operator. In such a case, a movement of the joystick in the predetermined control area according to a preset boom actuation axis causes the actuation of the boom by hydraulic actuating means. The hydraulic actuating means may include an hydraulic cylinder operatively connected the boom, and a directional solenoid valve whose opening degree is adapted to control the flow of a working fluid to the hydraulic cylinder. The rate of actuation of the boom may be controlled by the opening degree of the directional solenoid valve by means of a driving current thereof as a function of a component of the position of the joystick along said preset boom actuation axis in the control area.
In the first embodiment, the method for detecting a failure of a speed sensor means of a work vehicle comprises the step of:

if the following conditions are simultaneously met for a predetermined accumulated amount of time, determining that a failure of the speed sensor means occurred:
1. a) the travel speed of the work vehicle indicated by the speed sensor means is zero;
2. b) the FNR Forward-Neutral-Reverse switch FNR is not in a neutral position;
3. c) the brake pedal is not pressed by the operator;
4. d) the joystick is in the neutral position or the hydrostatic circuit of the boom has been decoupled from the hydrostatic transmission by the operator by means of said command means;
5. e) the driving current provided to the forward solenoid of the pump or to the reverse solenoid of the pump is greater than a predetermined current threshold;
6. f) a rotational speed of the motor arranged to power the work vehicle is higher than a predetermined rotational speed threshold.

In the following, a second embodiment of a method for detecting a failure of a speed sensor means of a work vehicle is described.
The work vehicle includes a motor arranged to power the work vehicle, a speed sensor means arranged to detect a travel speed of the work vehicle and a hydrostatic transmission.
The hydrostatic transmission is equal to the one explained for the first embodiment. Therefore, the explanation of the hydrostatic transmission is not repeated here.
Again, the work vehicle includes a command means arranged to allow the decoupling of an hydrostatic circuit of the boom from the hydrostatic transmission by the operator, so that the boom is not movable by the operator, and a FNR Forward-Neutral-Reverse switch FNR, a brake pedal arranged to activate a control braking means of the work vehicle when pressed by the operator, and a joystick arranged to be controlled by an operator.
Also the command means, the FNR Forward-Neutral-Reverse switch FNR, the brake pedal and the joystick are the same of the first embodiment. Therefore, the explanations of the command means, the FNR Forward-Neutral-Reverse switch FNR, the brake pedal and the joystick are not repeated here.
In the second embodiment, the method for detecting a failure of a speed sensor means of a work vehicle comprises the steps of:

determining the time instant in which the work vehicle is turned-on;
if the following conditions are simultaneously met for a predetermined accumulated amount of time within a predetermined time interval from said time instant, determining that a failure of the speed sensor means occurred:
1. a) the travel speed of the work vehicle indicated by the speed sensor means is zero;
2. b) the FNR Forward-Neutral-Reverse switch is not in a neutral position;
3. c) the brake pedal is not pressed by the operator;
4. d) the driving current provided to the forward solenoid of the pump or to the reverse solenoid of the pump is greater than a predetermined current threshold;
5. e) a rotational speed of the motor arranged to power the work vehicle is higher than a predetermined rotational speed threshold.

The predetermined accumulated amount of time of the second embodiment may be lower than the predetermined accumulated amount of time of the first embodiment. For example, the predetermined accumulated amount of time of the second embodiment may be 4 seconds and the predetermined accumulated amount of time of the first embodiment may be 8 seconds.
For what concerns the second embodiment, said accumulated amount of time may be accumulated in a plurality of non-contiguous sub-intervals of time within a predetermined time interval from said time instant in which the work vehicle is turned-on.
Differently, for what concerns the first and the second embodiments, the accumulated amount of time may also be accumulated in a continuous period.
For what concerns the first and the second embodiments, the method for detecting a failure of a speed sensor means of a work vehicle may further comprise the step of:

when a failure of the speed sensor means is detected, providing an error signal to the operator through a signalling means.

The signalling means may be for example a visual means, e.g. a LED or a display, or a sound means, e.g. a sound generator.
Further, the method for detecting a failure of a speed sensor means of a work vehicle may further comprise the step of:

stop providing the error signal to the operator through the signalling means when, after having determined that a failure of the speed sensor means is occurred, the travel speed of the work vehicle indicated by the speed sensor means is different from zero.

The present invention relates also to control systems for a work vehicle.
In preferred embodiments of the control systems, the control systems include

first input means adapted to receive, from a speed sensor means of the work vehicle, at least a signal or data indicative of the travel speed of the work vehicle;
second input means adapted to receive at least a signal or data indicative of a position of a FNR switch of the work vehicle, wherein said FNR switch is switchable between a forward position, a neutral position and a reverse position;
third input means adapted to receive at least a signal or data indicative of the level of actuation by the operator of a brake pedal of the work vehicle;
fourth input means adapted to receive at least a signal or data indicative of the driving current provided to a forward solenoid and a reverse solenoid of an hydraulic pump of an hydrostatic transmission of the work vehicle;
fifth input means adapted to receive at least a signal or data indicative of the actuation of a command means of the work vehicle, which is arranged to allow the decoupling of an hydrostatic circuit of the boom from the hydrostatic transmission by the operator, so that the boom is not movable by the operator;
sixth input means adapted to receive, at least a signal or data indicative of the position in a predetermined control area of a joystick of the work vehicle, which is controlled by a operator for actuating a boom or an implement of the work vehicle.

In these embodiments, each control system is arranged to carry out one of the methods explained before.
Preferably, the control systems may further comprise first output means adapted to issue at least a signal indicative of the fact that a failure of the speed sensor means has been detected by the control system.
In a further aspect, the invention relates to a work vehicle.
In an embodiment of the work vehicle, in particular compact wheel loader, the work vehicle comprises:

a motor arranged to power the work vehicle;
the speed sensor means arranged to detect a travel speed of the work vehicle;
a hydrostatic transmission comprising
a hydraulic pump, a hydraulic motor, a forward line arranged to hydraulically connect an outlet of the hydraulic pump to an inlet of the hydraulic motor, and a backward line arranged to hydraulically connect an outlet of the hydraulic motor to an inlet of the hydraulic pump in such a manner to define a closed hydraulic circuit in which flows a work fluid, wherein said hydraulic pump of the hydrostatic transmission includes a forward solenoid and a reverse solenoid and the hydraulic pump is arranged to pump the work fluid from the backward line to the forward line when the forward solenoid is powered by a driving current, and to pump the work fluid from the forward line to the backward line when the reverse solenoid is powered by the driving current; the value of the driving current depending on a rotational speed of the motor arranged to power the work vehicle; and
a control system according to one of the embodiments of the control systems described above.

In the present, with "failure of the speed sensor" can be understood both a malfunctioning of the speed sensor and a disconnection of the speed sensor.
The example embodiments are described in sufficient detail to enable those of ordinary skill in the art to implement a control system in a work vehicle arranged to carry out the disclosed control method herein described.
Naturally, the principle of the invention remaining unchanged, the embodiments and the constructional details may vary widely from those described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the invention as defined in the appended claims.

Claims

A method for detecting a failure of a speed sensor means of a work vehicle (1), wherein said work vehicle includes:
- a motor arranged to power the work vehicle (1);

- the speed sensor means arranged to detect a travel speed of the work vehicle (1);

- a hydrostatic transmission comprising
a hydraulic pump (HP), a hydraulic motor (HM, a forward line arranged to hydraulically connect an outlet of the hydraulic pump (HP) to an inlet of the hydraulic motor (HM), and a backward line arranged to hydraulically connect an outlet of the hydraulic motor (HM) to an inlet of the hydraulic pump (HP) in such a manner to define a closed hydraulic circuit in which flows a work fluid, wherein said hydraulic pump (HP) of the hydrostatic transmission includes a forward solenoid and a reverse solenoid, and the hydraulic pump (HP) is arranged to pump the work fluid from the backward line to the forward line when the forward solenoid is powered by a driving current, and to pump the work fluid from the forward line to the backward line when the reverse solenoid is powered by the driving current, the value of the driving current depending on a rotational speed of the motor arranged to power the work vehicle (1);

- a command means arranged to allow the decoupling of an hydrostatic circuit of the boom (5) from the hydrostatic transmission by the operator, so that the boom (5) is not movable by the operator;

- a Forward-Neutral-Reverse switch (FNR) switchable among a forward position, a neutral position and a reverse position, and arranged to control the operation of the hydrostatic transmission depending on the position of said Forward-Neutral-Reverse switch (FNR), wherein the driving current is provided to the forward solenoid of the pump when the Forward-Neutral-Reverse switch (FNR) is in the forward position, the driving current is provided to the reverse solenoid of the pump when the Forward-Neutral-Reverse switch (FNR) is in the reverse position;

- a brake pedal arranged to activate a control braking means of the work vehicle when pressed by the operator;

- a joystick arranged to be controlled by an operator, wherein a movement of the joystick in a predetermined control area (A), with respect to a neutral position, causes the actuation of a boom (5) or an implement of the work vehicle;
the method being characterized in that it comprises the step of:
- if the following conditions are simultaneously met for a predetermined accumulated amount of time, determining that a failure of the speed sensor means occurred:
a) the travel speed of the work vehicle (1) indicated by the speed sensor means is zero;

b) the Forward-Neutral-Reverse switch (FNR) is not in a neutral position;

c) the brake pedal is not pressed by the operator;

d) the joystick is in the neutral position or the hydrostatic circuit of the boom (5) has been decoupled from the hydrostatic transmission by the operator by means of said command means;

e) the driving current provided to the forward solenoid of the pump or to the reverse solenoid of the pump is greater than a predetermined current threshold;

f) a rotational speed of the motor arranged to power the work vehicle (1) is higher than a predetermined rotational speed threshold.
A method for detecting a failure of a speed sensor means of a work vehicle (1), wherein said work vehicle includes:
- a motor arranged to power the work vehicle (1);

- the speed sensor means arranged to detect a travel speed of the work vehicle (1);

- a hydrostatic transmission comprising
a hydraulic pump (HP), a hydraulic motor (HM), a forward line arranged to hydraulically connect an outlet of the hydraulic pump (HM) to an inlet of the hydraulic motor (HM), and a backward line arranged to hydraulically connect an outlet of the hydraulic motor (HM) to an inlet of the hydraulic pump (HP) in such a manner to define a closed hydraulic circuit in which flows a work fluid, wherein said hydraulic pump (HP) of the hydrostatic transmission includes a forward solenoid and a reverse solenoid, and the hydraulic pump (HP) is arranged to pump the work fluid from the backward line to the forward line when the forward solenoid is powered by a driving current, and to pump the work fluid from the forward line to the backward line when the reverse solenoid is powered by the driving current, the value of the driving current depending on a rotational speed of the motor arranged to power the work vehicle (1);

- a command means arranged to allow the decoupling of an hydrostatic circuit of the boom (5) from the hydrostatic transmission by the operator, so that the boom is not movable by the operator;

- a Forward-Neutral-Reverse switch (FNR) switchable among a forward position, a neutral position and a reverse position, and arranged to control the operation of the hydrostatic transmission depending on the position of said Forward-Neutral-Reverse switch (FNR), wherein the driving current is provided to the forward solenoid of the pump when the Forward-Neutral-Reverse switch (FNR) is in the forward position, the driving current is provided to the reverse solenoid of the pump when the Forward-Neutral-Reverse switch (FNR) is in the reverse position;

- a brake pedal arranged to activate a control braking means of the work vehicle when pressed by the operator;

- a joystick arranged to be controlled by an operator, wherein a movement of the joystick in a predetermined control area (A), with respect to a neutral position, causes the actuation of a boom (5) or an implement of the work vehicle;
the method being characterized in that it comprises the steps of:
- determining the time instant in which the work vehicle (1) is turned-on;

- if the following conditions are simultaneously met for a predetermined accumulated amount of time within a predetermined time interval from said time instant, determining that a failure of the speed sensor means occurred:
a) the travel speed of the work vehicle (1) indicated by the speed sensor means is zero;

b) the Forward-Neutral-Reverse switch (FNR) is not in a neutral position;

c) the brake pedal is not pressed by the operator;

d) the driving current provided to the forward solenoid of the pump or to the reverse solenoid of the pump is greater than a predetermined current threshold;

e) a rotational speed of the motor arranged to power the work vehicle (1) is higher than a predetermined rotational speed threshold.
A method according to claim 1 or 2, wherein said accumulated amount of time is accumulated in a continuous period.
A method according to claim 2, wherein said accumulated amount of time is accumulated in a plurality of non-contiguous sub-intervals of time within a predetermined time interval from said time instant.
A method according to any one of the preceding claims, further comprising the step of:
- when a failure of the speed sensor means is detected, providing an error signal to the operator through a signalling means.
A method according to claim 5, further comprising the step of:
- stop providing the error signal to the operator through the signalling means when, after having determined that a failure of the speed sensor means is occurred, the travel speed of the work vehicle (1) indicated by the speed sensor means is different from zero.
A control system for a work vehicle (1), comprising:
- first input means adapted to receive, from a speed sensor means of the work vehicle (1), at least a signal or data indicative of the travel speed of the work vehicle (1);

- second input means adapted to receive at least a signal or data indicative of a position of a Forward-Neutral-Reverse switch (FNR) of the work vehicle, wherein said Forward-Neutral-Reverse switch (FNR) is switchable between a forward position, a neutral position and a reverse position;

- third input means adapted to receive at least a signal or data indicative of the level of actuation by the operator of a brake pedal of the work vehicle;

- fourth input means adapted to receive at least a signal or data indicative of the driving current provided to a forward solenoid and a reverse solenoid of an hydraulic pump of an hydrostatic transmission of the work vehicle (1);

- fifth input means adapted to receive at least a signal or data indicative of the actuation of a command means of the work vehicle (1), which is arranged to allow the decoupling of an hydrostatic circuit of the boom (5) from the hydrostatic transmission by the operator, so that the boom (5) is not movable by the operator;

- sixth input means adapted to receive, at least a signal or data indicative of the position in a predetermined control area of a joystick of the work vehicle (1), which is controlled by a operator for actuating a boom (5) or an implement of the work vehicle (1);
the control system being arranged to carry out a method comprising the step of:
- if the following conditions are simultaneously met for a predetermined accumulated amount of time, determining that a failure of the speed sensor means occurred:
a) the travel speed of the work vehicle (1) indicated by the speed sensor means is zero;

b) the Forward-Neutral-Reverse switch (FNR) is not in a neutral position;

c) the brake pedal is not pressed by the operator;

d) the joystick is in the neutral position or the hydrostatic circuit of the boom (5) has been decoupled from the hydrostatic transmission by the operator by means of said command means;

e) the driving current provided to the forward solenoid of the pump or to the reverse solenoid of the pump is greater than a predetermined current threshold;

f) a rotational speed of the motor arranged to power the work vehicle (1) is higher than a predetermined rotational speed threshold.
A control system for a work vehicle (1), comprising:
- first input means adapted to receive, from a speed sensor means of the work vehicle (1), at least a signal or data indicative of the travel speed of the work vehicle (1);

- second input means adapted to receive at least a signal or data indicative of a position of a Forward-Neutral-Reverse switch (FNR) of the work vehicle, wherein said Forward-Neutral-Reverse switch (FNR) is switchable between a forward position, a neutral position and a reverse position;

- third input means adapted to receive at least a signal or data indicative of the level of actuation by the operator of a brake pedal of the work vehicle;

- fourth input means adapted to receive at least a signal or data indicative of the driving current provided to a forward solenoid and a reverse solenoid of an hydraulic pump of an hydrostatic transmission of the work vehicle (1);

- fifth input means adapted to receive at least a signal or data indicative of the actuation of a command means of the work vehicle (1), which is arranged to allow the decoupling of an hydrostatic circuit of the boom (5) from the hydrostatic transmission by the operator, so that the boom (5) is not movable by the operator;

- sixth input means adapted to receive, at least a signal or data indicative of the position in a predetermined control area of a joystick of the work vehicle (1), which is controlled by a operator for actuating a boom (5) or an implement of the work vehicle (1);
the control system being arranged to carry out a method comprising the step of:
- determining the time instant in which the work vehicle (1) is turned-on;

- if the following conditions are simultaneously met for a predetermined accumulated amount of time within a predetermined time interval from said time instant,

- determining that a failure of the speed sensor means occurred:
a) the travel speed of the work vehicle (1) indicated by the speed sensor means is zero;

b) the Forward-Neutral-Reverse switch (FNR) is not in a neutral position;

c) the brake pedal is not pressed by the operator;

d) the driving current provided to the forward solenoid of the pump or to the reverse solenoid of the pump is greater than a predetermined current threshold;

e) a rotational speed of the motor arranged to power the work vehicle (1) is higher than a predetermined rotational speed threshold.
A control system according to claim 7 or 8, further comprising first output means adapted to issue at least a signal indicative of the fact that a failure of the speed sensor means has been detected by the control system.
A work vehicle (1), in particular compact wheel loader, comprising:
- a motor arranged to power the work vehicle (1);

- the speed sensor means arranged to detect a travel speed of the work vehicle;

- a hydrostatic transmission comprising
a hydraulic pump (HP), a hydraulic motor (HM), a forward line arranged to hydraulically connect an outlet of the hydraulic pump (HP) to an inlet of the hydraulic motor (HM), and a backward line arranged to hydraulically connect an outlet of the hydraulic motor (HM) to an inlet of the hydraulic pump (HP) in such a manner to define a closed hydraulic circuit in which flows a work fluid, wherein said hydraulic pump (HP) of the hydrostatic transmission includes a forward solenoid and a reverse solenoid and the hydraulic pump (HP) is arranged to pump the work fluid from the backward line to the forward line when the forward solenoid is powered by a driving current, and to pump the work fluid from the forward line to the backward line when the reverse solenoid is powered by the driving current; the value of the driving current depending on a rotational speed of the motor arranged to power the work vehicle (1);

- a control system according to claims 7 to 9.