Patent Description:
In the field of work and agricultural vehicles, the operation of members, such as arms and related tools, is carried out by means of a hydraulic circuit.

The hydraulic circuit is powered by a hydraulic pump driven in rotation by a prime mover, very often an internal combustion engine as shown in <CIT>. However, the progressive technological development of battery power systems makes it possible to design work vehicles with electric propulsion and/or with hydraulic systems operated by electric motors, such as a hydraulic circuit for the actuation of at least one hydraulic actuator enslaved to the movement of a work hydraulic organ.

With "work hydraulic organ" we mean one of those components such as arms, buckets, etc. distinct and separated from those inherent to the movement of the work vehicle, such as for example transmissions, braking systems, etc. Hereinafter, for convenience, reference is made to a "hydraulic organ" meaning a "work hydraulic organ".

In work machines the most known and implemented members are the arms equipped with bucket or forks or other devices.

The lifting and lowering of the arm is carried out by means of at least one double-acting linear hydraulic actuator. It includes a pair of opposing chambers that fill and empty alternately to raise or lower the arm.

There are different types of valves for controlling hydraulic actuators. Those that are most implemented are the open center directional ones. These valves, in relation to the position of the relative movable spool, divide the hydraulic oil fluid pumped by the hydraulic pump into a first flow destined for one of the hydraulic actuator chambers, while the second, remaining flow is sent to a collection tank, where the hydraulic pump draws to recirculate the hydraulic oil.

In particular, when the spool is in the rest position, all the pump flow is sent to the tank, during the adjustment phase, the flow of the hydraulic pump is divided between the actuator and the tank. When the spool is in the maximum opening position, all the pumped flow is sent to the actuator.

The position of the movable spool is generally controlled by the operator using a joystick placed in the vehicle's cockpit.

The electrical signal generated by the joystick is acquired by a processing unit, which processes it to control the directional control valve. The control direction valve is obviously of the electro-hydraulic type.

Wear of the hydraulic pump or a malfunction in the hydraulic circuit can lead to unexpected behavior of the actuator or the inability to lift a load.

If not specifically excluded in the detailed description that follows, what is described in this chapter is to be considered as an integral part of the detailed description.

The purpose of the present invention is to indicate a method and system for monitoring a hydraulic circuit of a work vehicle in particular to monitor the volumetric efficiency of the relating hydraulic pump. The monitoring method and control system of the invention comprise the features set forth in claims <NUM> and <NUM>.

The basic idea of the present invention is to calculate the effective flow rate of the hydraulic pump based on the displacement of the hydraulic actuator in a predetermined time interval and to correlate this effective flow rate to the nominal flow rate of the pump itself.

However, since the hydraulic circuit is controlled by an open center directional valve, the calculation is performed only when the valve spool is in the fully open condition. Therefore, the extraction or retraction over time of the actuator powered by the hydraulic circuit represents the effective port of the hydraulic pump.

To avoid calculation errors, the extraction or retraction of the hydraulic actuator over time is monitored away from the limit switches.

According to a preferred variant of the invention, the electro-hydraulic system is powered by a fixed displacement hydraulic pump driven in rotation by an electric motor, powered by a battery pack. According to this embodiment, the operation of the electric motor is coordinated with the movement of the movable spool of the directional valve as a function of a position of the joystick. More specifically, when the so-called dead band or guard band, adjacent to the release position of the joystick lever, is exceeded, the movable spool of the open-center directional valve is automatically brought to the "maximum opening" position of the valve, while the flow of hydraulic oil generated by the fixed displacement hydraulic pump is achieved directly or indirectly controlling the pump rotation speed, based on the position of the joystick lever.

According to this hydraulic circuit control scheme, it is always possible to measure the effective flow rate of the hydraulic pump in the conditions of extraction or retraction over time of the hydraulic actuator, in the positions far from the ends of stroke.

Preferably, according to the present invention, only one hydraulic pump feeds the hydraulic supply circuit of the hydraulic actuator of the hydraulic organ.

Preferably, when the same hydraulic circuit is arranged to operate several hydraulic actuators, the aforementioned monitoring is inhibited when more than one actuator are activated at a time. More preferably, the monitoring is performed exclusively on the actuator that controls the arm of the work vehicle, such as for example a mechanical shovel or an excavator.

Further objects and advantages of the present invention will become clear from the following detailed description of an example of its embodiment (and its variants) and from the annexed drawings given purely for explanatory and non-limiting purposes, in which:.

It should be noted that the terms "first", "second", "third", "upper", "lower" and the like can be used here to distinguish various elements. These terms do not imply a spatial, sequential or hierarchical order for the modified elements unless specifically indicated or inferred from the text.

<FIG> shows an example of an electro-hydraulic circuit for powering an A1 hydraulic actuator.

The circuit is powered by a fixed displacement hydraulic pump P, driven in rotation by a prime mover E, which can be an internal combustion engine or an electric motor powered by battery or fuel cells.

The pump draws oil from an accumulation tank T and sends it to an open center directional valve V.

The valve is arranged to feed the hydraulic actuator A1, therefore it is connected through two ports to the two opposing chambers of the double action hydraulic actuator. In relation to the chamber fed by the directional valve, the actuator extracts or retracts its shaft allowing the relative working member to move in two opposite directions. For example, the arm B of a compact wheel loader CWL raises or lowers.

A position sensor S is associated with the actuator shaft. The JOYSTICK lever, preferably arranged in the cockpit of the work vehicle CWL, in relation to the deflection imposed by an operator, is capable of generating an electrical signal, detected by a CONTROL UNIT.

The control unit, based on this electrical signal, is configured to generate a control signal for the electro-hydraulic directional valve V.

At the same time, the processing unit is able to acquire, through the S sensor, a position of the actuator shaft.

In <FIG>, it can be seen that the vehicle is equipped with an arm B and with a tool TO evidently controlled by a relative hydraulic actuator A2. The actuator A2 can be powered by the same hydraulic pump P or by a distinct and separated electro-hydraulic circuit.

According to the present invention, when only the actuator A1 is activated to move the related work member, specifically the arm B, it is possible to calculate the effective flow rate Qr of the hydraulic oil generated by the hydraulic pump P according to the relationship: <MAT>.

Where |X1 - X2| represents the variation of the shaft position of the actuator A1, while W represents the time interval between the acquisition of the two positions X1 and X2.

The method object of the present invention can be summarized with the following steps performed in cyclic succession, in accordance with <FIG>:.

By "predetermined time interval" it is meant a time interval of predetermined width.

Obviously, knowing the geometric characteristics of the chambers of the hydraulic actuator A1, it is possible to calculate the effective flow rate quite accurately.

The nominal flow rate Qn is instead equal to V * RPM, where V represents the pump displacement and RPM the average value of the rotation speed of the same pump in the time interval W.

The ratio η = Qr / Qn represents the efficiency of the hydraulic pump P.

In relation to the calculated efficiency value, the following actions can be performed.

Since the directional valve V is of the open center type, the efficiency calculation is performed only when the valve spool is in a maximum opening position, where the hydraulic oil is fully sent to the hydraulic actuator. No fraction of hydraulic oil is sent to the recovery tank T.

This check is indicated in <FIG> with the block V = max ?.

Optionally, another check can be performed, immediately following the previous one and indicated with "CHKS?": When the same hydraulic pump supplies more than one hydraulic actuator and therefore there are more control directional valves of the corresponding actuators, then the calculation of the efficiency is subject to CHKS verification? that is only one actuator is powered at a time. Although it is possible to add up the effective flow rates of hydraulic oil addressed to all the actuators, it is believed that this solution can lead to inaccurate calculations and in particular to a greater probability that one of the members reaches an end-of-stroke position.

In fact, a further check is performed to avoid calculating the effective flow rate of oil Qr at the end strokes of S1 and S2 of the actuator. This check is performed through block S1<X1, X2<S2?.

After calculating the efficiency η of the hydraulic pump, various operations can be performed.

According to a preferred embodiment of the invention, an average value of a predetermined number of consecutive calculated volumetric efficiency values is calculated and when this average value is lower than a predetermined threshold the operator is warned by means of an optical and/or acoustic signal AL or this average value is sent to a remote server, preferably together with other information including the oil temperature, a vehicle identification, etc..

The average value is calculated by means of a sliding average for example on the last <NUM> - <NUM> efficiency values calculated.

The electrification of a work vehicle involves the elimination of the internal combustion engine in favor of at least one electric motor.

For example, it is possible to provide a first electric motor used exclusively to drive the hydraulic pump for feeding at least one hydraulic working member in rotation. A second electric motor can be provided which is used to move the vehicle and therefore to move a vehicle wheel.

There are many differences between internal combustion engines and electric motors. In addition to the substantial different source of energy, the internal combustion engine, when active, has a minimum rotation speed, which is essential for its operation, while an electric motor starts rotating as soon as it is electrically powered.

All of this has repercussions on the operation of the hydraulic pump driven by the first electric motor.

A minimum rotation speed of the electric motor implies a consumption of electricity not necessary for the intrinsic operation of the same.

Saving electricity is essential to allow the spread of electrified vehicles, replacing traditional work vehicles equipped with internal combustion engines.

According to a preferred variant of the invention, the hydraulic circuit HC is operatively connected to a fixed displacement hydraulic pump P and an electric motor is arranged to drive the hydraulic pump in rotation. The hydraulic actuator A1 is arranged to be powered by the hydraulic circuit through an open center directional solenoid valve and the control lever JOYSTICK is arranged to control an opening of the solenoid valve. The lever can assume a release position corresponding to a position of zero opening of the solenoid valve, in which all the flow of the pump is sent to a hydraulic tank T, and a position of maximum deviation corresponding to a position of maximum opening of the solenoid valve, where the entire pump flow is sent to the hydraulic actuator. The processing unit is configured to perform the following steps:.

<FIG> shows the corresponding flow diagram.

Obviously, when the lever is released, the spool is brought back into closure.

The control of the hydraulic oil flow is achieved by controlling the rotation speed of the electric motor E.

When the present invention and the control scheme according to <FIG> is implemented, the check "V = max?" is always satisfied, therefore, if the circuit HC supplies a single actuator, or if the operator commands the operation of a single member for the time necessary (W) to perform the calculation of the efficiency, then the efficiency is calculated as described above.

The processing unit is preferably configured to keep the electric motor off or at a speed below a predetermined threshold as long as the deviation of the control lever does not exceed said predetermined guard threshold.

<FIG> shows both the opening control law STK of the mobile spool (solid line) of the open center directional solenoid valve, but also the flow of hydraulic oil generated by the fixed displacement hydraulic pump (dotted line).

It should be noted that when the lever deviation threshold DB1 is exceeded, with respect to a relative release position, the valve spool rapidly passes to the "maximum opening" position DB2.

In other words, the signal generated by the control lever causes the solenoid valve to function as an ON/OFF valve. At the same time, however, the extent of the deviation of the control lever linearly regulates the flow of hydraulic oil generated by the fixed displacement pump by adjusting the number of revolutions of the pump or of the electric motor M that drives it in rotation.

In fact, the dotted line that relates the hydraulic oil flow to the deviation of the control lever JOYSTICK is approximately linear.

In other words, thanks to the present invention, even if an open center directional solenoid valve is implemented, the hydraulic oil directed to the recovery tank is zero in all lever positions that exceed the guard band. This means that the pumping energy not useful for operating the hydraulic actuator is minimized and at the same time repeated measurements of the hydraulic pump efficiency can be carried out for efficient control of the same.

The present invention can be advantageously carried out by a processing unit, which comprises instructions for carrying out one or more steps of the method, when this program is executed on a computer. Therefore, it is intended that the scope of protection extends to said computer program and further to computer readable means comprising a recorded message, said computer readable means comprising program coding means for carrying out one or more steps of the method, when said program is run on a computer.

Implementation variants of the described non-limiting example are possible, without however departing from the scope of protection of the present invention as defined by the appended claims.

Claim 1:
Monitoring method of a hydraulic circuit of a work vehicle, the vehicle including
- a hydraulic circuit (HC) operatively connected to a fixed displacement hydraulic pump (P) and a prime mover arranged to drive the hydraulic pump in rotation,
- a hydraulic actuator (A1) arranged to be powered by the hydraulic circuit through an open center directional solenoid valve (V), wherein the actuator includes a movable shaft, and
- a control lever (JOYSTICK) arranged to control an opening of the directional solenoid valve, the lever comprising a release position corresponding to a zero opening position of the directional solenoid valve in which the entire pump flow is sent to a hydraulic tank (T), and a position of maximum deviation corresponding to a position of maximum opening of the directional solenoid valve in which all the flow generated by the hydraulic pump is sent to the hydraulic actuator (A1), the method including the following steps:
- (a) Monitoring of a position of a movable spool of the directional solenoid valve, when it is detected that the movable spool is in the condition of maximum opening, then
- (b) Acquisition of two positions (X1, X2) of the movable shaft in two distinct instants identifying a predetermined time interval (W),
- (c) Calculation of an effective flow rate (Qr) of the hydraulic pump as a value proportional to a ratio of a distance between said two positions (Dist (X1, X2)) and said time interval (W),
- (d) Calculation of a nominal flow rate (Qn) of the hydraulic pump as the product of a value of the displacement of the hydraulic pump for an average value of the rotation speed of the hydraulic pump in the time interval (W) and
(e) Calculation of an efficiency (η) of the hydraulic pump as a ratio between the effective flow rate and the nominal flow rate.