Patent Description:
The invention is applicable on working machines within the fields of industrial construction machines or construction equipment, in particular wheel loaders. Although the invention will be described with respect to a wheel loader, the invention is not restricted to this particular machine, but may also be used in other working machines such as articulated haulers, excavators and backhoe loaders.

An operator of a working machine such as a wheel loader may control the operation of hydraulic functions by displacing e.g. a joystick. The degree of displacement may be related to the operation speed of the hydraulic function. In order to provide different operation speeds, the hydraulic pressure provided by the hydraulics of the wheel loader is typically varied. For instance, a higher pressure may enable a higher operation speed.

<CIT> describes an example hydraulic drive system for a working machine. The hydraulic drive system described in <CIT> may perform normal operation and precision operation. The precision operation is performed at a smaller manipulation stroke than the normal operation. The hydraulic drive system disclosed by <CIT> is provided with a variable displacement hydraulic pump to provide pressurized oil to a working element. <CIT> discloses a working machine with an electrically powered hydraulic system.

However, working machines such as wheel loaders generally generate relatively high intensities of noise during operation. The noise may be caused by the engines providing propulsion of the wheel loader but also by electric machines controlling the hydraulics system of the wheel loader. The hydraulic system may for example be arranged to control hydraulic functions such as movements of a boom or bucket attached to the wheel loader, a steering hydraulics, or other auxiliary functions.

The noise levels may cause an unsuitable working environment for the crew at the same site as the working machine as well as for the operator of the working machine.

Accordingly, there is a need for less noisy control of hydraulic functions for working machines.

An object of the invention is to provide an electrically powered hydraulic system with improved noise characteristics to thereby alleviate the above mentions problems with prior art.

According to a first aspect of the invention, the object is achieved by a system according to claim <NUM>.

According to the first aspect of the invention, there is provided an electrically powered hydraulic system for a working machine, the electrically powered hydraulic system comprises: an electric motor to power a working hydraulic pump to operate at least one hydraulic function of the working machine, wherein a flow of hydraulic fluid generated by the hydraulic pump is controlled by the operation speed of the electric motor, an electronically controlled control valve for controlling the flow of hydraulic fluid from the pump to the at least one hydraulic function, an operator input device for controlling the at least one hydraulic function, wherein the operator input device is operable in at least two operating ranges, and an electronic control unit configured to: when the operator input device is in a first operating range, maintain the electric motor at a constant rotational speed, and control a variation in flow of hydraulic fluid to the hydraulic function with the control valve, and when the operator input device is in a second operating range, control a variation in flow of hydraulic fluid by varying the electric motor rotational speed and by controlling the control valve, according to displacement of the operator input device.

The present invention is based on the realization that the disturbing noise variations from an electric motor may be reduced by maintaining the electric motor powering the working hydraulic pump at a constant speed. Moreover, it was realized that the operating range for the input device may be divided in several operating ranges, and that the electric motor providing power to the hydraulic pump may be kept at a constant speed in at least one operating range without compromising the functionality of the hydraulic function.

By the provision of a system which comprises an electric motor which is maintained at a constant speed by a control unit when the operator input device is in a first operating range, the advantage of reduced noise variations from the electric motor is provided. Further, in some working conditions, when the operator input device is in a second operating range, the electric motor may vary its rotational speed to provide additional power to the working hydraulic pump only when it is needed. Thereby the overall functionality of the hydraulic system is not compromised.

Moreover, according to the inventive concept, two different control principles for the hydraulic function are advantageously included. The overall generated hydraulic fluid flow by the working hydraulic pump is electronically controlled through the operation speed of the electric motor. The hydraulic fluid flow to the individual hydraulic cylinders for the hydraulic functions may be controlled through an electronically controlled control valve. This so called electro-hydraulic system may be controlled by the electronic control unit.

The operator input device is operable in each of the operating ranges, but may also be operable between the operating ranges, i.e. the operator input device may be transitioned between the ranges by e.g. operator input.

According to one embodiment, the electric motor rotational speed may be higher when the operator input device is in the second operating range, than the constant operation rotational speed of the electric motor when the operator input device is in a first operating range. Hereby, the electric motor may advantageously cause the hydraulic pump to provide higher pressure to the hydraulic function when the operator input device is in the second operating function compared to in the first operating range. Thereby, fast operation of the hydraulic function is enabled when the operating input device is in the second operating range.

In one embodiment, the operator input device is configured to control the operation speed of a wheel loader attachment, or a wheel loader boom. Accordingly, the inventive concept is advantageously applicable to commonly used hydraulic functions for a wheel loader.

According to a further embodiment, the electric motor is a first electric motor, the system further comprising a second electric motor to power the drivetrain of the working machine. Thus, the overall noise from the working machine comprising such the electrically powered hydraulic system is advantageously further reduced by using an electric motor also for providing propulsion.

In addition, there may be a third electric motor for further auxiliary functions, such as for steering.

There is further provided a wheel loader comprising the electrically powered hydraulic system according to the first aspect or embodiments thereof.

According to a second object, there is provided method for controlling an electrically powered hydraulic system for a working machine, the system comprising an electric motor to power a working hydraulic pump to operate at least one hydraulic function of the working machine, wherein a flow of hydraulic flow generated by the hydraulic pump is controlled by the operation speed of the electric motor, and an electronically controlled control valve for controlling the flow of hydraulic fluid from the pump to the at least one hydraulic function, the method is comprising the steps: receiving an input signal from an operator input device to control a speed of a hydraulic function of the working machine, determining that the input signal is related to one of at least two operating ranges of the operator input device, wherein, when the operator input device is determined to be in a first operating range, maintaining the electric motor at a constant rotational speed, and controlling a variation in flow of hydraulic fluid to the hydraulic function with the control valve, and when the operator input device is determined to be in a second operating range, varying the electric motor rotational speed according to input device displacement to thereby, in combination with the control valve control the variation in flow of hydraulic fluid.

According to an embodiment, when the operator input device is determined to be in the second operating range, varying the electric motor rotational speed proportional to input device displacement. Thus, if the operator requests fast operation of the hydraulic function, displacement control of the hydraulic system is used where the electric motor speed will be increased proportionally with the displacement to provide the requested hydraulic fluid flow. Thus, the hydraulic system may provide accelerated operation of the hydraulic function, and operation of the hydraulic function at varying operation speeds, if requested by the operator.

Effects and features of the second aspect of the invention are largely analogous to those described above in connection with the first aspect.

There is further provided a computer program comprising program code means for performing the steps of the method according to the second aspect when said program is run on a computer.

There is further provided a computer readable medium carrying a computer program comprising program code means for performing the steps of the method according to the second aspect when said program product is run on a computer.

There is further provided an electronic control unit for controlling an electrically powered hydraulic system for a working machine, the electronic control unit being configured to perform the steps of the method according to the second aspect.

It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

<FIG> illustrates a working machine in the form of a wheel loader <NUM>. The wheel loader <NUM> comprises an electrically powered hydraulic system <NUM> for controlling at least one hydraulic function. The hydraulic function may relate to controlling the operation speed of a wheel loader attachment such as a bucket <NUM>, or the operation speed of the boom <NUM>. The electrically powered hydraulic system <NUM> of the wheel loader <NUM> comprises an electric motor <NUM> for powering a working hydraulic pump (not shown). The wheel loader <NUM> may optionally further comprise another electric motor <NUM> for providing propulsion for the wheel loader <NUM>. Thus, the wheel loader <NUM> may be an all electric wheel loader <NUM> particularly suitable for indoor operation.

<FIG> is an overview of the electrically powered hydraulic system <NUM>. The system comprises an operator input device which may be in the form of a joystick <NUM> which allows the operator <NUM> to control the operation of a hydraulic function <NUM> via input commands using the joystick <NUM>. Further possible operator input devices may be a drive pedal <NUM>, and a steering wheel <NUM>.

An electric control unit <NUM> is configured to receive input signals form the input device <NUM> (or <NUM>, <NUM>), and to interpret the input signals and control the hydraulic function <NUM> by varying a flow of hydraulic fluid to the hydraulic function <NUM>. For controlling the hydraulic function, the electric control unit <NUM> is configured to control the operation speed of an electric motor <NUM> which is arranged to power a working hydraulic pump <NUM>. The working hydraulic pump <NUM> is arranged to provide a flow of hydraulic fluid (indicated by a dashed line) to an electronically controlled control valve <NUM>.

The electronically controlled control valve <NUM> is configured to distribute the hydraulic fluid (indicated by a dashed line) to the hydraulic functions <NUM> according to instructions provided from the electric control unit <NUM>. For instance, the operator input signals received by the electric control unit <NUM> may indicate that a first hydraulic function and a second hydraulic function desirable to operate. The electric control unit <NUM> provides instruction to the electronically controlled control valve <NUM> to open the respective valve of the electronically controlled control valve <NUM> to the first and second hydraulic functions according to the user input signals. Thus the electronically controlled control valve <NUM> may comprise several valves as will be described in more detail with reference to <FIG>. Generally, the electronically controlled control valve <NUM> is a main control valve (MCV) comprising distinguished valves which may be displaced in order to allow flow of hydraulic fluid to pass through the valve to a respective hydraulic function.

The electronic control unit <NUM> is configured to determine which of at least two operating ranges the operator user input device is presently in. When the operator input device <NUM> is in a first operating range, the electronic control unit <NUM> controls the electric motor <NUM> to maintain at a constant rotational speed. If a variation in flow to the hydraulic function <NUM> is requested from a user input signal in the first range, i.e. by displacement of the input device <NUM> within the first range, then the variation in flow of hydraulic fluid to the hydraulic function is controlled with the electronically controlled control valve <NUM>. Moreover, when the operator input device is in a second operating range, the electronic control unit <NUM> control a variation in flow of hydraulic fluid by varying the electric motor rotational speed and by controlling the control valve, according to displacement of the operator input device <NUM>.

<FIG> conceptually illustrates an operator input device <NUM> and corresponding operating ranges <NUM> and <NUM>. The user input device <NUM> (e.g. a joystick) is here shown centred in the first operating range <NUM>. Thus, if the user input device <NUM> is displaced, it will initiate its displacement in the first operating range <NUM>. The user input device <NUM> may be displaced in any direction indicated by the arrows, or combinations thereof. The further the input user device <NUM> is displaced from the illustrated centre position, the faster operation speed of the hydraulic function is desired by the operator. Accordingly, the further the operator input device <NUM> is displaced from the illustrated centre position, the higher flow of hydraulic fluid is required to the provided to the hydraulic function.

<FIG> is a graph that schematically shows electric motor speed versus operator input device <NUM> displacement. At zero displacement is the operator input device <NUM> at its centre position, i.e. as shown in <FIG>. When the operator input device <NUM> is displaced away from its centre position, i.e. away from displacement equal to zero (or at least nearly equal to zero), the operator input device <NUM> is displaced in the first operating range <NUM>. In the first operating range <NUM> is the electric motor speed maintained at a constant speed <NUM>. When the operator input device <NUM> is displaced further and into the second operating range <NUM>, then the electric motor speed is increased proportionally with the operator input device <NUM> displacement.

<FIG> is a graph that schematically shows electric motor speed versus time (line <NUM>), control valve displacement versus time (line <NUM>) for one hydraulic function, and operator input device displacement versus time (line <NUM>), on a common y-axis. Up to time t1 the user input device has not been displaced and there electric motor speed and the control valve displacement are therefore at or close to zero.

At time t<NUM>, the operator input device is starting to displace within the first operating range <NUM> (see also <FIG>). Thus the electronic control unit controls the electric motor to operate at a constant operating speed <NUM> (see also <FIG>). In the first operating range, the electric motor operates at a speed sufficient to power the hydraulic pump to provide high enough hydraulic fluid flow to the electrically controlled valve to provide all the hydraulic functions with sufficient flow consistent with the first operating range of the operator input device. In other words, the electrically controlled control valve is provided with high enough hydraulic fluid flow to operate all the hydraulic functions connected to the electrically controlled control valve with the highest flow within the first operating range of the operator input device.

In the example graph shown in <FIG>, the operator input device is continuously displaced until time t<NUM>. In this time range, (t<NUM> to t<NUM>), the operator input device is in the first operating range <NUM>. The displacement of the electronically controlled control valve is increased as the operator input device is further displaced, thus requesting higher flow of hydraulic fluid to the hydraulic functions. This is understood from the linear increase in the curve <NUM> representing the control valve displacement versus time at the same time as the increase in curve <NUM> representing operator input device displacement versus time.

At time t<NUM>, the operator input device is displaced into the second operating range <NUM>. Thus, the requested operating speed for the hydraulic function now requires a relatively high flow of hydraulic fluid. Therefore, the electric motor speed also increases as seen in the curve <NUM> after time t<NUM> in order to provide high enough power to the hydraulic pump so that the hydraulic pump can provide sufficient flow of hydraulic fluid flow to the electrically controlled control valve. Additionally, the displacement of the electronically controlled control valve is also affected by the higher fluid flow from the hydraulic pump. After time t<NUM>, the displacement of the electronically controlled control valve does not have to increase at the same rate, in this example. At time t<NUM>, the operator input device is displaced to a maximum displacement whereby the electric motor is at maximum speed and the electronically controlled control valve is displaced to a maximum displacement.

The operator requests an operating speed of a hydraulic function by displacing the input device <NUM>. The electric control unit <NUM> is configured to calculate the hydraulic fluid flow required to satisfy the request by the operator. The electric motor is configured to operate at a speed to be able to supply hydraulic fluid to all functions requiring hydraulic fluid flow given the request by the operator. The electrically controlled control valve <NUM> distributes the hydraulic fluid flow to the hydraulic functions according to the request from the operator.

<FIG> illustrates an example embodiment of an electrically powered hydraulic system <NUM>. The system comprises an electric motor <NUM> to power a working hydraulic pump <NUM>. The working hydraulic pump <NUM> receives hydraulic fluid from a tank <NUM>. The electric motor <NUM> operates at a speed n. The working hydraulic pump <NUM> provides a hydraulic fluid flow Q to the system <NUM> which may be given by Q=Vg*n, where Vg is the hydraulic fluid flow as received from the tank <NUM>. The total fluid flow Q provided to the hydraulic system <NUM> is limited by the maximum operating speed of the electric motor <NUM>, i.e. Qmax=Vg*nmax.

The electrically powered hydraulic system <NUM> further comprises a control pressure unit <NUM> configured to provide a hydraulic fluid pressure to the electrically controlled control valve <NUM> (i.e. the main control valve) in order to displace the individual valves in the electrically controlled control valve <NUM>. An electric signal (indicated by double line) from the control unit <NUM> controls the hydraulic fluid pressure for displacing the respective valve in the electrically controlled control valve <NUM>. There is further a primary shut off valve <NUM> connected to the hydraulic fluid line between the working hydraulic pump <NUM> and the electrically controlled control valve <NUM>. The primary shut off valve <NUM> is configured to redirect overpressure hydraulic fluid from the primary shut off valve <NUM> back to the tank <NUM>. Return line 56a is configured to return the hydraulic fluid used for controlling the displacement of the valves in the electrically controlled control valve <NUM> back to the tank <NUM>.

The electrically controlled control valve <NUM> receives the hydraulic fluid flow Q from the working hydraulic pump <NUM>. The electrically controlled control valve <NUM> further receives control signals (indicated by double line) from an electronic control unit <NUM> indicative of the position or displacement of an operator input device (not shown in <FIG>). The electrically controlled control valve <NUM> is a parallel hydraulic circuit and thus distributes the hydraulic fluid flow Q to multiple hydraulic functions 7a, 7b, and 7c. The total hydraulic fluid flow to the hydraulic functions 7a-c is given by Q'=displacement*Q, where displacement is the displacement of the operator input device in relative terms, e.g. as a percentage of maximum displacement, or a ratio between present displacement and maximum displacement. Secondary shut off units <NUM> (only one is numbered) arranged in the hydraulic fluid flow lines 55a-c between the hydraulic functions 7a-c and the electrically controlled control valve <NUM> are configured to provide overpressure hydraulic fluid back to the tank <NUM>. Return line 56b is configured to return the overpressure hydraulic fluid not used by the electrically controlled control valve <NUM> back to the tank <NUM>.

The electric motor <NUM> receives a control signal from the electronic control unit <NUM>. If the operator input device is in the first operating range, then the electronic control unit <NUM> controls the electric motor <NUM> to operate at a constant operating speed. A variation of hydraulic fluid flow is then controlled by the electrically controlled control valve <NUM> according to operator input device as described above. Thus, the electric motor operates at a fixed speed and the hydraulic fluid flow to the cylinders of the hydraulic functions is regulated by the displacement of the individual valves in the electrically controlled control valve <NUM>. If the operator input device is in the second operating range, then the electronic control unit <NUM> controls the electric motor <NUM> to operate at an operating speed that depends on the operator input device displacement as described with reference to e.g. <FIG>. Furthermore, the electrically controlled control valve <NUM> may still vary the hydraulic fluid flow to the hydraulic functions 7a-c, but when the operator input device is in the second operating range then a variation in the hydraulic fluid flow to the hydraulic functions 7a-c is controlled cooperatively between the electrically controlled control valve <NUM> and the electric motor <NUM> speed variation. Accordingly, If the operator requests fast movements of the hydraulic functions (i.e. in the second operating range), the hydraulic control passes over to a displacement control where the electric motor operation speed will be increased additionally to provide the requested hydraulic fluid flow.

<FIG> is a flow-chart of method steps according to an embodiment of the invention. The method steps are for controlling an electrically powered hydraulic system for a working machine. In step S102 is an input signal received from an operator input device to control a speed of a hydraulic function of the working machine. In step S104 it is determined that the input signal is related to one of at least two operating ranges of the operator input device. If it is determined that the operator input device is a first operating range, the electric motor speed is maintained (S106) at a constant rotational speed, and controlling a variation in flow of hydraulic fluid to the hydraulic function is performed with an electrically controlled control valve. If it is determined that the operator input device is a first operating range, then the electric motor rotational speed is varied (S108) according to input device displacement to thereby, in combination with the control valve control the variation in flow of hydraulic fluid to a hydraulic function.

The hydraulic fluid is preferably hydraulic oil.

The electronic control unit <NUM> may include a microprocessor, microcontroller, programmable digital signal processor or another programmable device. Thus, the electronic control unit comprises electronic circuits and connections (not shown) as well as processing circuitry (not shown) such that the electronic control unit can communicate with different parts of the working machine such as the brakes, suspension, driveline, in particular an electrical engine, an electric machine, a clutch, and a gearbox in order to at least partly operate the working machine. The electronic control unit may comprise modules in either hardware or software, or partially in hardware or software and communicate using known transmission buses such as CAN-bus and/or wireless communication capabilities. The processing circuitry may be a general purpose processor or a specific processor. The electronic control unit comprises a non-transitory memory for storing computer program code and data upon. Thus, the skilled addressee realizes that the electronic control unit may be embodied by many different constructions.

Although the figures may show a sequence the order of the steps may differ from what is depicted. Also two or more steps may be performed concurrently or with partial concurrence. Such variation will depend on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the disclosure. Likewise, software implementations could be accomplished with standard programming techniques with rule based logic and other logic to accomplish the various connection steps, processing steps, comparison steps and decision steps. Additionally, even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art.

Claim 1:
An electrically powered hydraulic system (<NUM>) for a working machine (<NUM>), wherein the electrically powered hydraulic system comprises:
an electric motor (<NUM>) to power a working hydraulic pump (<NUM>) to operate at least one hydraulic function (<NUM>) of the working machine, wherein a flow of hydraulic fluid generated by the hydraulic pump is controlled by the operation rotational speed of the electric motor (<NUM>),
an electronically controlled control valve (<NUM>) for controlling the flow of hydraulic fluid from the pump to the at least one hydraulic function,
an operator input device (<NUM>, <NUM>, <NUM>) for controlling the at least one hydraulic function, wherein the operator input device is operable in at least two operating ranges (<NUM>,<NUM>), and characterized by
an electronic control unit (<NUM>) configured to:
- when the operator input device is in a first operating range (<NUM>) , maintain the electric motor at a constant rotational speed, and control a variation in flow of hydraulic fluid to the hydraulic function with the electronically controlled control valve, and
- when the operator input device is in a second operating range (<NUM>), control a variation in flow of hydraulic fluid by varying the electric motor rotational speed and by controlling the control valve, according to displacement of the operator input device.