EP4130494A1

EP4130494A1 - Electric-hydraulic circuit for the actuation of a hydraulic actuator for an electrified work vehicle

Info

Publication number: EP4130494A1
Application number: EP22185770.9A
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: 2021-07-29
Filing date: 2022-07-19
Publication date: 2023-02-08

Abstract

An electro-hydraulic circuit includes a fixed displacement hydraulic pump (P) and an electric motor (M) arranged to drive the hydraulic pump in rotation, a hydraulic actuator (BOOM, BUCKET, AUX) arranged to move an member or work tool and be powered by the hydraulic circuit, a proportional directional solenoid valve (V1, V2, V3) with open center and comprising a rest condition wherein it isolates the hydraulic actuator by connecting the hydraulic pump with the recovery tank, and a processing unit (STK) configured to receive the electrical signals of an input device (joystick) and generate electrical control signals (Spool Command, Rev, Torque) for the valves (V1, V2, V3) and for the engine (M); and programmed to detect the torque of the motor (M) and, when the torque of the motor (M) exceeds a predefined limit value, it commands the execution of at least one power reduction operation by reducing the number of revolutions of the motor (M) and/or bringing the corresponding solenoid valve (V1, V2, V3) to the neutral position with open center.

Description

Field of the invention

The present invention relates to the field of work vehicles, including electrified agricultural vehicles, and in particular of the type comprising an electro-hydraulic circuit for actuating at least one hydraulic member, including an arm and/or a bucket.

State of the art

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.

Summary of the invention

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 a hydraulic circuit for moving a hydraulic work member comprising 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 an embodiment, 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 engine, 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.
The dependent claims describe preferred variants of the invention, forming an integral part of this description.

Brief description of the figures

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:

Figure 1 shows an example of an electro-hydraulic circuit according to the present invention;
Figure 2 shows a work vehicle implementing the present invention; And
Figure 3 shows the diagrams relating to the limit values of the torque generated by the motor based on the selector and the position of the joystick.

The same reference numbers and letters in the figures identify the same elements or components or functions.
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 without however departing from the scope of this application as described below.

Detailed description of exemplary embodiments

Figure 1 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.
Figure 1 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, Pair).
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 engine 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.
Figure 2 shows a work vehicle WL, a mechanical shovel, with an arm B with the hydraulic actuator A1 corresponding to the label "BOOM" in figure 1 and a shovel or bucket T with the relative actuator A2 corresponding to the label "BUCKET" of figure 1.
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 figure 1, 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:

by reducing the number of revolutions: the reduced power with the torque equal to the predefined limit value is less than that which would occur with the maximum torque,
bringing the corresponding solenoid valve to the rest position: the valve is commanded in the rest position when a torque equal to the predefined limit value is detected and therefore in a shorter time than that which would occur with a torque equal to the maximum one.

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 figure 3, 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:

is less, once a mode has been selected, when the joystick is slightly moved from the neutral position compared to when the joystick is far removed from the neutral position,
is less, with the same joystick position, when the selected mode is LOW compared to when the selected mode is MEDIUM or HIGH.

Implementation variants of the described non-limiting example are possible, without however departing from the scope of protection of the present invention, including all the equivalent embodiments for a person skilled in the art, to the content of the claims.
From the above description, the person skilled in the art is able to realize the object of the invention without introducing further construction details.

Claims

Electro-hydraulic circuit comprising
- a fixed displacement hydraulic pump (P) and an electric motor (M) arranged to drive the hydraulic pump in rotation,

- a hydraulic actuator (BOOM, BUCKET, AUX) arranged 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 actuator and comprising a rest condition in which it isolates the hydraulic actuator by hydraulically connecting the hydraulic pump with the recovery tank,

- a processing unit (STK) configured to receive the electrical signals of an input device (joystick) and generate electrical control signals (Spool Command, Rev, Torque) for the valve (V1, V2, V3) and for the motor (M); and programmed to detect the torque of the motor (M) and, when the torque of the motor (M) exceeds a predefined limit value, it commands the execution of at least a power reduction operation by reducing the number of revolutions of the motor (M) and/or bringing the corresponding open center solenoid valve (V1, V2, V3) to the rest position.
Circuit according to claim 1, comprising a pressure relief valve (LP) which establishes the maximum pressure of the hydraulic circuit and wherein the predefined limit value is less than a maximum torque generated by the motor (M), corresponding to the maximum pressure of the hydraulic circuit defined by the pressure relief valve (LP).
Circuit according to any one of the preceding claims, wherein the predefined limit value of the torque generated by the motor is calculated on the basis of a position of the joystick.
Circuit according to any one of the preceding claims, comprising a selector (SEL) for a mode of limiting the electric load of the motor during an actuation operation, wherein the predefined limit value of the torque generated by the motor is calculated based on the mode selected by means of the select.
Circuit according to any one of the preceding claims, wherein the valve (V1, V2, V3) is configured to close the circuit of the corresponding actuator (BOOM, BUCKET, AUX) when in the rest position.
Method of controlling a work vehicle comprising:
- a fixed displacement hydraulic pump (P) and an electric motor (M) arranged to drive the hydraulic pump in rotation,

- a hydraulic actuator (BOOM, BUCKET, AUX) arranged 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 actuator and comprising a rest condition wherein it isolates the hydraulic actuator by hydraulically connecting the hydraulic pump with the recovery tank,

- a processing unit (STK) configured to receive the electrical signals of an input device (joystick) and generate electrical control signals for the valves (V1, V2, V3) and for the motor (M),
And comprising the following steps:
- detect a motor torque (M);

- when the torque of the motor (M) exceeds a predefined limit value, to command through the processing unit (STK) an operation to reduce the power generated by the motor (M) by means of a reduction in the number of revolutions of the motor and/or the actuation of the open center solenoid valve (V1, V2, V3) in the rest position.