Patent Description:
In the field of work and agricultural vehicles, the operation of users, 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.

The progressive technological development of battery power systems makes it possible to design work vehicles with electric traction 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 hydraulic work member.

By "work hydraulic unit" it is meant one of those components distinct and separate 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 member" meaning a "working hydraulic member".

The electrification of a work vehicle involves the elimination of the internal combustion engine in favour 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 for moving the vehicle.

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 rotation 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 diffusion of electrified vehicles, replacing traditional work vehicles equipped with internal combustion engines.

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 propose a method and system for saving electricity in an electrified work vehicle. In particular, for those work vehicles completely without an internal combustion engine.

The object of the present invention is to provide an electro-hydraulic circuit as defined in claim <NUM> and a method of controlling a work vehicle as defined in claim <NUM>. An electro-hydraulic circuit for moving a hydraulic work member comprises a fixed displacement hydraulic pump and an open center directional control solenoid valve controlled by the user by means of a joystick or other control device, preferably lever, wherein the solenoid valve and the motor are controlled to save energy, in particular energy stored in the batteries, in a hydraulic stall condition or when a hydraulic actuator reaches its end-of-stroke.

The basic idea is to provide that, in the hydraulic circuit indicated above, the torque generated by the motor is monitored and, when a torque limit value is reached, the processing unit commands an operation to reduce the power generated by the motor (M) by reducing the number of revolutions of the motor (M) and/or by activating the solenoid valve in the neutral position with open center.

In this way, the pump flow rate is either reduced and/or the pump delivery pressure is reduced and this reduces the electric power consumption of the motor.

According to the invention, the limit value of the torque generated by the motor, which is proportional to the pump delivery pressure, is always less than the torque generated by the motor when the pump delivery pressure is equal to the calibration value of a pressure relief valve of the hydraulic system, this allows to work at a pressure, and therefore at a torque generated by the motor, which is always less than the maximum of the system, thus reducing the electric energy consumption of the engine.

According to an embodiment, wherein the circuit comprises a selector for a motor load limiting mode during an actuation operation and the limit value of the torque generated by the motor is calculated based on a position of the joystick and/or based on the mode selected by the user using the selector. The selector can be either analogic, e.g. a knob, push button or lever, or digital, e.g. the user can select the desired threshold via a touch screen programmed to present one or more thresholds that can be selected by the user.

In this way, energy savings are adapted to the conditions of use of the cylinder controlled by the user.

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 also be noted that the terms "first", "second", "third", "upper", "lower" and the like can be used as labels 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.

The elements and features illustrated in the various preferred embodiments, including the drawings, can be combined with each other as long as not departing from the scope of the invention, which is defined by the appended claims.

<FIG> shows an example of an electro-hydraulic circuit comprising hydraulic actuators of hydraulic working parts and are indicated with "BOOM", BUCKET "and" AUX ", i.e. labels taken from the Anglo-Saxon terminology that indicates a "Boom" arm of work or agriculture vehicle and a relative bucket "Bucket". "AUX" refers to any other hydraulic actuator for controlling vehicle implements but not for propulsion, such as an angle sweeper.

The electro-hydraulic circuit also includes a fixed displacement pump P and an electric motor M.

<FIG> shows three proportional directional control solenoid valves with open center V1, V2 and V3 which have in the rest position a corresponding center closed towards the actuator and open towards pump P to connect the latter to a storage tank T for oil collection. The circuit also comprises a pressure relief valve LP arranged along a supply branch FB arranged in parallel to the open center branch OB with respect to the pump P. When the valves V1, V2, V3 are in the rest/neutral position, the pump P is connected to the collection tank T via branch OB and the supply branch FB is closed by the limiting valve LP. When at least one of the valves regulates, the actuator corresponding to the actuated valve is connected to the pump P via the power supply branch FB. The maximum pressure on this branch is controlled by the pressure relief valve LP and is equal to the calibration value of the latter.

The electro-hydraulic circuit also comprises a processing unit STK configured to receive the electrical signals of a joystick or other preferably lever control device and generate electrical control signals for the valves V1, V2, V3 and for the motor M (Rev, Torque).

A manual selector SEL is also connected to the processing unit, for example a knob or other user interface, including electronic, arranged in the passenger compartment, so that the user can select a mode for limiting the motor load during actuation of hydraulic tools, for example identified in at least two load thresholds one lower and one higher, preferably three i.e. low (LOW), medium (MEDIUM), high (HIGH). Each actuation mode substantially involves a more or less high limit value of the torque generated by the motor.

<FIG> shows a work vehicle WL, a mechanical shovel, with an arm B with the hydraulic actuator A1 corresponding to the label "BOOM" in <FIG> and a shovel or bucket T with the relative actuator A2 corresponding to the label "BUCKET" of <FIG>.

The vehicle WL is equipped with a battery pack BAT and an electric motor M with at least one hydraulic circuit similar to that of <FIG>, fixed to a relative frame F.

Each of the illustrated actuators is of the double-acting type, i.e. it has two opposing chambers which serve for example to raise and lower an arm. Each chamber includes a port through which the hydraulic oil is forced to enter or exit.

The hydraulic oil is forced out of the port of a first chamber when the hydraulic oil is pumped into the second chamber, opposite the first, of the same actuator.

The open center directional solenoid valve is configured to keep the port of both opposing chambers closed when the joystick is in the rest (neutral) position, in order to keep said hydraulic member still. In such conditions, the movable spool is in a central position in the valve body, inhibiting the passage of oil towards both chambers of the actuator and directing all the oil to the collection tank T.

Each valve is represented with three drawers, in a per se known manner. Recalling that it is a proportional valve, that is able to reach intermediate positions between the position of complete closure and complete opening towards one or the other chamber of the actuator.

According to an embodiment, wherein the circuit comprises a selector for a motor load limiting mode during an actuator operation and the limit value of the torque generated by the motor is calculated based on a position of the joystick and/or based on the mode selected by the user using the selector.

Under normal operating conditions, without engine load limitation, a stall condition, e.g. defined by a load that the hydraulic circuit is not designed to lift, or a stroke end condition of the actuators causes the opening of the pressure relief valve LP and the maximum pressurization of the actuator without the stem moving. On the other hand, when one of the thresholds is selected, the STK processing unit is programmed to detect the load conditions of the motor M and, when the torque generated by the motor exceeds a predefined limit value based on the threshold, it commands the execution of at least one power reduction operation by reducing the number of revolutions of the engine M and/or bringing the corresponding solenoid valve to the rest position. Power is saved when the valve is commanded in the rest position because the pump delivery pressure is the minimum of the circuit (i.e. lObar). Based on the previous description, of the valves, the actuator circuit is closed in the central position so that, unless there is leakage, the position of the stem remains blocked since the hydraulic fluid cannot flow out.

Furthermore, the predefined limit value of the torque generated by the motor is variable on the basis of input parameters and chosen in such a way that it is always less than the maximum torque generated by the motor, corresponding to the calibration value of the pressure relief valve LP, i.e. the maximum pressure of the system, this involves a further energy saving because when the power reduction is commanded:.

Furthermore, the limit value of the torque generated by the motor M is preferably defined by means of a mathematical function based on the position of the joystick and/or of the mode selected by the selector SEL as indicated in <FIG>, which refers to the X axis of the joystick (Joystick X axis) which operates valve V2.

In particular, once the mode (LOW, MEDIUM, HIGH) has been selected using the selector SEL, the torque limit value (Torque limit) increases with the increase of a distance of the joystick from a neutral position of the joystick itself, while for the same joystick position the torque limit value increases or decreases according to the selected mode.

This means, for example, that the pressure of the electro-hydraulic circuit at which the power reduction operation is performed:.

Implementation variants of the described non-limiting example are possible, as long as not departing from the scope of protection of the present invention as defined by the appended claims, including all the equivalent embodiments for a person skilled in the art, to the content of the claims.

Claim 1:
Electro-hydraulic circuit comprising
- a fixed displacement hydraulic pump (P) and an electric motor (M) configured to drive the fixed displacement hydraulic pump in rotation;
- a hydraulic actuator (BOOM, BUCKET, AUX) configured to move an member or work tool and be powered by the hydraulic circuit;
- a recovery tank (T) arranged to collect hydraulic oil;
- an open center proportional directional solenoid valve (V1, V2, V3) interposed between said fixed displacement hydraulic pump and said hydraulic actuator and comprising a rest position in which it is configured to isolate the hydraulic actuator by hydraulically connecting the fixed displacement hydraulic pump with the recovery tank via an open center branch (OB);
- an operator input device (joystick);
- a processing unit (STK) configured to receive electrical signals of the operator input device (joystick) and generate electrical control signals (Spool Command, Rev, Torque) for the open center proportional directional solenoid valve (V1, V2, V3) and for the electric motor (M) and configured to detect the torque of the electric motor (M) and, when the detected torque of the electric motor (M) exceeds a predefined limit value, the processing unit is configured to command the execution of at least a power reduction operation by reducing the number of revolutions of the electric motor (M) and/or bringing the corresponding open center proportional directional solenoid valve (V1, V2, V3) to the rest position; said electro-hydraulic circuit is characterized in that it further comprises a pressure relief valve (LP) arranged along a supply branch (FB) which connects the pump (P) to the recovery tank (T), the supply branch (FB) being arranged in parallel to the open center branch (OB), the pressure relief valve (LP) establishing the maximum pressure of the electro-hydraulic circuit and wherein the predefined limit value is less than a maximum torque generated by the electric motor (M), corresponding to the maximum pressure of the electro-hydraulic circuit defined by the pressure relief valve (LP).