Electrohydraulic system

Abstract

A work machine electrohydraulic system including: pilot hydraulic circuit 20 with pilot pump 22, joystick manual pilot control valves 24, and pilot pressure sensors 28 downstream of the pilot valves;

Description

FIELD The present disclosure relates to an electrohydraulic system, a controller, a working vehicle and a method. BACKGROUND It is known to provide one or more user inputs (e.g., joysticks or levers) to control hydraulic actuators in a hydraulic system of a working vehicle. For example, a joystick or lever may be moved in a first direction to extend a hydraulic cylinder and in a second direction to retract the hydraulic cylinder. Similarly, a joystick or lever may be moved in first and second directions to rotate a hydraulic motor in opposite directions. One type of user input for controlling a hydraulic actuator is a hydraulic joystick or lever. Such a hydraulic joystick or lever directly controls the position of a pilot control valve in a pilot hydraulic circuit, so that movement of the joystick or lever results in a change of pressure in pilot pressure lines acting on opposite ends of a directional control valve of the hydraulic system. For example, moving the joystick or lever in one direction actuates the pilot control valve to increase pressure in the pilot pressure line acting on the first side of the directional control valve, which urges the directional control valve towards a first state (causing the corresponding hydraulic actuator to move in a first direction). Moving the joystick or lever in an opposite direction actuates the pilot control valve to cause the corresponding hydraulic actuator to move in an opposite direction. Such a hydraulic joystick / lever configuration has been widely used in hydraulic systems of working vehicles because it is reliable, simple and low cost in comparison to alternatives. Another type of user input for controlling a hydraulic actuator is an electric joystick or lever. Such an electric joystick or lever has one or more position sensors which detect a position of the joystick / lever. A controller determines how the corresponding directional control valve should be moved based on input signals from the position sensor(s), and sends output signals to solenoids which move the corresponding directional control valve to the desired state. This causes the hydraulic actuator to move accordingly. Such a configuration is known as an electrohydraulic system because it combines electric control with hydraulic actuation. Such an electrohydraulic system has been used in working vehicles because it provides more flexibility (e.g., making it easier to override or modify signals from the joystick depending on other inputs or operating conditions of the working vehicle). It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY The present teachings provide an electrohydraulic system, a controller, a working vehicle and a method according to the appended claims. An aspect of the teachings provides an electrohydraulic system for a working machine, the electrohydraulic system comprising: a pilot hydraulic circuit comprising a pilot pump, one or more user-operable pilot control valves, and one or more pilot pressure sensors selectively coupled to the pilot pump via the one or more user-operable pilot control valves; a main hydraulic circuit comprising a main hydraulic pump, a main control valve, and a hydraulic actuator selectively coupled to the main hydraulic pump via the main control valve; and a control system comprising a controller configured to: receive one or more input signals from the one or more pilot pressure sensors; and send one or more electric output signals to actuate the main control valve depending on the one or more input signals received from the one or more pilot pressure sensors. The electrohydraulic system may include a combination of hydraulic pilot pressure control and electric control (hereinafter referred to as "electrohydraulic control") to actuate the hydraulic actuator. Such an electrohydraulic control configuration allows a hydraulic joystick or lever to be used to control the hydraulic actuator (avoiding the need for electric position sensors on the joystick and associated complexity / cost), whilst providing the flexibility of electric control (e.g., by the controller modifying the relationship between position of the user-operable pilot control valve and position of the main control valve, when desired). This may be particularly beneficial in systems where there is a need for more flexible control of one hydraulic actuator (e.g., a hydraulic slew motor), but not for another hydraulic actuator (e.g., a working arm hydraulic cylinder). In particular, the electrohydraulic control configuration allows a single hydraulic user input device (e.g., hydraulic joystick) to be used to provide both electrohydraulic control (for the hydraulic actuator requiring more flexible control) and standard hydraulic control (for the other hydraulic actuator). For example, a hydraulic joystick could be moved: left / right to actuate a first hydraulic actuator using electrohydraulic control; and forward / backward to actuate a different hydraulic actuator via standard hydraulic pilot control. In this context, the term "user-operable pilot control valve" will be understood to be a valve which is directly controlled by a user (e.g., via a mechanical connection between the valve and a mechanical user input such as a joystick, lever, button, pedal, or switch), rather than a valve which is only indirectly controlled by a user (e.g., by an electric user input). The hydraulic actuator may be a hydraulic slew motor configured to slew a superstructure of a working vehicle relative to an undercarriage of said working vehicle. It may be desirable to have more flexible control of a hydraulic slew motor than other hydraulic actuators (e.g., to dampen transient slewing movements, and / or e-fence the allowable rotary positions of the superstructure). Therefore, by having an electrohydraulic control in which the direct hydraulic connection between user input device (e.g., joystick) and hydraulic slew motor is broken, this allows more flexible control strategies to be implemented. The controller may be configured to vary the one or more output signals at a slower rate of change than the one or more input signals. The controller may be configured so that the hydraulic slew motor reacts more slowly than the one or more user-operable pilot control valves. Put another way, the controller is configured to dampen transient changes in slewing speed. This may be particularly beneficial for reduced tail swing excavators (i.e., excavators in which a rear end of the superstructure does not overhang a rear of the undercarriage), since the dampening of transient changes in slewing speed allows the reduced tail swing excavator to mimic the greater inertia associated with the larger rear end of a conventional excavator superstructure, providing an operator "feel" that is more familiar for those trained on conventional excavators. The controller may be configured to filter the one or more input signals and to use the filtered one or more input signals to determine the one or more output signals; optionally, wherein the controller may be configured to apply a low-pass filter to the one or more input signals. Such a filtering of the one or more input signals provides a simple means for slowing transient changes in slewing speed. The controller may be configured to receive a position input signal indicative of a rotary position of the superstructure relative to the undercarriage of said working vehicle, and to set the one or more output signals to restrict slewing of the superstructure beyond a predetermined range of rotational orientations. The controller may be configured to e-fence the allowable rotary positions of the superstructure. This may be beneficial when working in close proximity to obstructions or obstacles, since the e-fencing can be set up to restrict movement into positions which could lead to a collision. The control system may comprise one or more user inputs for setting the predetermined range of rotational orientations. For example, a touchscreen, buttons, or other inputs may be used to manually set the predetermined range of rotational orientations. Alternatively, a user may actuate the hydraulic slew motor to move the superstructure to a given rotational position and then set a boundary of the predetermined range of rotational positions at the given rotational position (e.g., by pressing a button). The controller may be configured to send the one or more output signals to one or more solenoids to actuate the main control valve; optionally, wherein the one or more solenoids are proportional solenoids. Such solenoids allow electric output signal(s) from the controller to be converted into mechanical movement of valves in the electrohydraulic system. Proportional solenoids allow movement of the associated valve(s) to intermediate positions which allows variability in the speed of actuation of the hydraulic actuator. This may be particularly beneficial in cases where it is desirable for the controller to dampen transient changes in speed of the hydraulic actuator, since the output signal(s) sent to the solenoid(s) can be gradually varied to gradually change the speed of actuation of the hydraulic actuator. The main control valve may be a pilot-operated valve having one or more pressure ports on one or more sides of the main control valve. The pilot hydraulic circuit may comprise one or more solenoid pilot control valves comprising the one or more solenoids, wherein the one or more pressure ports are selectively coupled to the pilot pump via the one or more solenoid pilot control valves, and wherein the controller is configured to send the one or more output signals to the one or more solenoids of the one or more solenoid pilot control valves to control pressure at the one or more pressure ports of the main control valve. Such a configuration is particularly beneficial in configurations where the electrohydraulic control of the hydraulic actuator is being combined with direct hydraulic control of further actuators, since it allows standard pilot-operated main control valves to be used in the main hydraulic circuit, with the added flexibility of electrohydraulic control by adding the one or more solenoid pilot control valves to the pilot hydraulic circuit. Alternatively, the main control valve may be a solenoid valve comprising the one or more solenoids. The pilot hydraulic circuit may comprise one or more feedback pressure sensors between the one or more solenoid pilot control valves and the first and second pressure ports, and wherein the controller may be configured to receive one or more feedback signals from the one or more feedback pressure sensors and to implement feedback control to determine the one or more output signals. In other words, the controller is configured to set the one or more output signals using closed-loop control. This allows more accurate control of the speed of actuation of the hydraulic actuator. The electrohydraulic system may comprise a joystick for actuating the one or more user-operable pilot control valves. The joystick may be deflectable from a neutral position in a first plane to actuate the one or more user-operable pilot control valves and thereby control the hydraulic actuator. The joystick may be deflectable from the neutral position in a second plane different to the first plane to control a further hydraulic actuator. It will be understood that, because one or more pressure sensors in the pilot hydraulic circuit are used to generate electric input signals (rather than by detecting using electric position sensors on the joystick), such a joystick can be used to provide standard hydraulic pilot control of the further hydraulic actuator (i.e., when deflected in the second plane) whilst simultaneously being used for electrohydraulic control of the hydraulic actuator. In other words, the joystick can be considered as a hybrid hydraulic / electric joystick. The hydraulic actuator may comprise a hydraulic slew motor configured to slew a superstructure of a working vehicle relative to an undercarriage of said working vehicle. The further hydraulic actuator may comprise a working arm hydraulic cylinder. There may be less need for flexible control of working arm hydraulic cylinders than hydraulic slew motors. Therefore, it will be understood that the joystick may be used to electrohydraulically control the hydraulic slew motor (and provide associated flexibility of slew control), whilst maintaining a simpler full-hydraulic control of the working arm hydraulic cylinder. The main hydraulic circuit may be a closed-loop circuit, wherein the main hydraulic pump is a uni-directional pump, and wherein the main control valve is a directional control valve comprising a first state configured to direct hydraulic fluid from the main hydraulic pump in a first direction around the closed-loop circuit, and a second state configured to direct hydraulic fluid from the main hydraulic pump in a second direction around the closed-loop circuit. Such a configuration allows a closed-loop circuit to be used (and associated benefits of increased efficiency) whilst maintaining flexibility of control by sending output signals from the controller to actuate the directional control valve. The present teachings may comprises a controller for a slew motor of an excavator, wherein the controller is configured to: receive an input signal in response to actuation of a user input device; filter the input signal to smooth out changes in the input signal; determine an output signal based on the filtered input signal; and send the output signal to actuate the slew motor. In other words, the controller is configured so that the slew motor reacts more slowly than the user input device. Put another way, the controller is configured to dampen transient changes in slewing speed. This may be particularly beneficial for reduced tail swing excavators, since the dampened transient changes in slewing speed allows the reduced tail swing excavator to mimic the greater inertia associated with the projecting rear end of a conventional excavator superstructure. This provides an operator "feel" that is more familiar for those trained on conventional excavators. In this context, the term "reduced tail swing excavator" will be understood to mean an excavator with a rear end of the superstructure which: a) does not overhang a rear end of the undercarriage (known as "zero tail swing excavator"); or b) overhangs a rear end of the undercarriage to a lesser extent than on a conventional excavator. Optionally, the controller is configured to vary the output signal at a slower rate of change than the input signal. Optionally, the controller is configured to apply a low-pass filter to the input signal. Such a low-pass filter provides a simple means for slowing transient changes in slewing speed. Optionally, the controller is configured to receive a position input signal indicative of a rotary position of a superstructure relative to an undercarriage of said reduced tail swing excavator, and to set the output signal to restrict slewing of the superstructure beyond a predetermined range of rotational orientations. In other words, the controller is configured to e-fence the allowable rotary positions of the superstructure. This may be beneficial when working in close proximity to obstructions or obstacles, since the e-fencing can be set up to restrict movement into positions which could lead to a collision. Optionally, the control system comprises one or more user inputs for setting the predetermined range of rotational orientations. For example, a touchscreen, buttons, or other inputs may be used to manually set the predetermined range of rotational orientations. Alternatively, a user may actuate the hydraulic slew motor to move the superstructure to a given rotational position and then set a boundary of the predetermined range of rotational positions at the given rotational position (e.g., by pressing a button). Optionally, the slew motor is a hydraulic slew motor and the controller is configured to send the output signal to one or more solenoids to actuate the hydraulic slew motor; optionally, wherein the one or more solenoids are proportional solenoids. Such solenoids allow an electric output signal from the controller to be converted into mechanical movement of a valve(s) in a electrohydraulic system. Proportional solenoids allow movement of the associated valve(s) to intermediate positions which allows variability in the speed of actuation of the hydraulic slew motor. This may be particularly beneficial in cases where it is desirable for the controller to dampen transient changes in speed of the hydraulic slew motor, since the output signal(s) sent to the solenoid(s) can be gradually varied to gradually change the speed of actuation of the hydraulic slew motor. Optionally, the controller is configured to receive one or more feedback signals from one or more feedback pressure sensors and to implement feedback control to determine the output signal. In other words, the controller is configured to set the output signal using closed-loop control. This allows more accurate control of the speed of actuation of the slew motor. In a further aspect, the present teachings may comprise a controller for a hydraulic actuator of a working vehicle, wherein the controller is configured to: detect pressure in a pilot hydraulic circuit downstream of one or more user-operable pilot control valves; determine one or more electric output signals based on the detected pressure; and send the one or more electric output signals to actuate a main control valve and thereby control the hydraulic actuator. In other words, the controller is configured to receive pressure signals from a hydraulic system and convert into an electric output signal to actuate a control valve of a hydraulic circuit. Such a control configuration allows a hydraulic joystick or lever to be used to control the hydraulic actuator (avoiding the need for electric position sensors on the joystick and associated complexity / cost), whilst providing the flexibility of electric control (e.g., by the controller modifying the relationship between position of the user-operable pilot control valve and position of the main control valve, when desired). This may be particularly beneficial in systems where there is a need for more flexible control of one hydraulic actuator (e.g., a hydraulic slew motor), but not for another hydraulic actuator (e.g., a boom hydraulic cylinder). In particular, the control configuration allows a single hydraulic user input device (e.g., hydraulic joystick) to be used to provide both electrohydraulic control (for the hydraulic actuator requiring more flexible control) and standard hydraulic control (for the other hydraulic actuator). For example, a hydraulic joystick could be moved: left / right to actuate a first hydraulic actuator using electrohydraulic control; and forward / backward to actuate a different hydraulic actuator via standard hydraulic pilot control. In this context, the term "user-operable pilot control valve" will be understood to be a valve which is directly controlled by a user (e.g., via a mechanical connection between the valve and a mechanical user input such as a joystick, lever, button, pedal, or switch), rather than a valve which is only indirectly controlled by a user (e.g., by an electric user input). Optionally, the controller is configured to vary the one or more electric output signals at a slower rate of change than the detected pressure. In other words, the controller is configured so that the hydraulic actuator reacts more slowly than the user-operable pilot control valves. This may be particularly beneficial when the hydraulic actuator is a hydraulic slew motor for a reduced tail swing excavator, since it mimics the greater inertia associated with the larger rear end of the superstructure on conventional excavators. Optionally, the controller is configured filter the detected pressure to smooth out changes in the detected pressure; optionally, wherein the controller is configured to apply a low-pass filter to the detected pressure. Such a filtering of the detected pressure provides a simple means for slowing transient changes in slewing speed. Optionally, the hydraulic actuator is a hydraulic slew motor and the controller is configured to receive a position input signal indicative of a rotary position of a superstructure relative to an undercarriage of said working vehicle, and to set the one or more electric output signals to restrict slewing of the superstructure beyond a predetermined range of rotational orientations. In other words, the controller is configured to e-fence the allowable rotary positions of the superstructure. This may be beneficial when working in close proximity to obstructions or obstacles, since the e-fencing can be set up to restrict movement into positions which could lead to a collision. Optionally, the controller is part of a control system comprising one or more user inputs for setting the predetermined range of rotational orientations. For example, a touchscreen, buttons, or other inputs may be used to manually set the predetermined range of rotational orientations. Alternatively, a user may actuate the hydraulic slew motor to move the superstructure to a given rotational position and then set a boundary of the predetermined range of rotational positions at the given rotational position (e.g., by pressing a button). Optionally, the controller is configured to send the one or more electric output signals to one or more solenoids to actuate the hydraulic slew motor; optionally, wherein the one or more solenoids are proportional solenoids. Such solenoids allow the electric output signal(s) from the controller to be converted into mechanical movement of valves in a electrohydraulic system. Proportional solenoids allow movement of the associated valve(s) to intermediate positions which allows variability in the speed of actuation of the hydraulic actuator. This may be particularly beneficial in cases where it is desirable for the controller to dampen transient changes in speed of the hydraulic actuator, since the output signal(s) sent to the solenoid(s) can be gradually varied to gradually change the speed of actuation of the hydraulic actuator. Optionally, the controller is configured to receive one or more feedback signals from one or more feedback pressure sensors and to implement feedback control to determine the one or more electric output signals. In other words, the controller is configured to set the one or more electric output signals using closed-loop control. This allows more accurate control of the speed of actuation of the hydraulic actuator. A further aspect of the teachings comprises a control system comprising a controller as disclosed herein. The present teachings may provide a working vehicle comprising the electrohydraulic system described herein and / or a control system comprising a controller described herein. Such a working vehicle may benefit from the advantages of the electrohydraulic system and or controller(s) disclosed herein. The working vehicle may comprise an undercarriage, a superstructure which is rotatable relative to the undercarriage, and a slew motor configured to slew the superstructure relative to the undercarriage. The working vehicle may comprise a working arm, wherein the working arm is actuated by one or more working arm actuators. The working vehicle may be an excavator. The superstructure may be sized such that, when the superstructure is slewed relative to the undercarriage so that the working arm extends perpendicular to a front end of the undercarriage, a rear end of the superstructure does not overhang a rear end of the undercarriage. In other words, the excavator is a "reduced tail swing excavator". The electrohydraulic system and / or control system(s) disclosed herein may be particularly beneficial for this type of working vehicle (e.g., to dampen transient changes in slewing speed to mimic the greater inertia of a conventional excavator). The present teachings may provide a method of controlling a hydraulic actuator, the method comprising: detecting pressure in a pilot hydraulic circuit downstream of one or more user-operable pilot control valves; determining one or more electric output signals based on the detected pressure; and sending the one or more electric output signals to actuate a main control valve and thereby control the hydraulic actuator. In other words, the method is configured to receive pressure signals from a hydraulic system and send electric output signals to actuate a control valve of a hydraulic circuit. Such a method allows a hydraulic joystick or lever to be used to control the hydraulic actuator (avoiding the need for electric position sensors on the joystick and associated complexity / cost), whilst providing the flexibility of electric control (e.g., by modifying the relationship between position of the user-operable pilot control valve and position of the main control valve, when desired). This may be particularly beneficial in systems where there is a need for more flexible control of one hydraulic actuator (e.g., a hydraulic slew motor), but not for another hydraulic actuator (e.g., a boom hydraulic cylinder). In particular, the method allows a single hydraulic user input device (e.g., hydraulic joystick) to be used to provide both electrohydraulic control (for the hydraulic actuator requiring more flexible control) and standard hydraulic control (for the other hydraulic actuator). For example, a hydraulic joystick could be moved: left / right to actuate a first hydraulic actuator using electrohydraulic control; and forward / backward to actuate a different hydraulic actuator via standard hydraulic pilot control. In this context, the term "user-operable pilot control valve" will be understood to be a valve which is directly controlled by a user (e.g., via a mechanical connection between the valve and a mechanical user input such as a joystick, lever, button, pedal, or switch), rather than a valve which is only indirectly controlled by a user (e.g., by an electric user input). The method may comprise varying the one or more electric output signals at a slower rate of change than the detected pressure; optionally, wherein the method comprises filtering the detected pressure; optionally, wherein the method comprises applying a low-pass filter to the detected pressure. In other words, the method ensures that the hydraulic actuator reacts more slowly than the user-operable pilot control valves. This may be particularly beneficial when the hydraulic actuator is a hydraulic slew motor for a reduced tail swing excavator, since it mimics the greater inertia associated with the larger rear end of the superstructure on conventional excavators. Such a filtering of the detected pressure provides a simple means for slowing transient changes in slewing speed. The hydraulic actuator may be a hydraulic slew motor of a working vehicle, wherein the method comprises detecting a rotary position of a superstructure relative to an undercarriage of the working vehicle, and setting the one or more electric output signals to restrict slewing of the superstructure beyond a predetermined range of rotational orientations; optionally, wherein the method comprises receiving one or more user inputs for setting the predetermined range of rotational orientations. In other words, the method e-fences the allowable rotary positions of the superstructure. This may be beneficial when working in close proximity to obstructions or obstacles, since the e-fencing can be set up to restrict movement into positions which could lead to a collision. The method may comprise sending the one or more electric output signals to one or more solenoids to actuate the main control valve. Such solenoids allow the electric output signal(s) from the controller to be converted into mechanical movement of valves in a electrohydraulic system. The method may comprise receiving one or more feedback signals from one or more feedback pressure sensors and implementing feedback control to determine the one or more electric output signals. In other words, the method involves setting the one or more electric output signals using closed-loop control. This allows more accurate control of the speed of actuation of the hydraulic actuator. In a further aspect, the present disclosure may comprise a method of controlling a slew motor of an excavator, the method comprising: receiving an input signal in response to actuation of a user input device; filtering the input signal to smooth out changes in the input signal; determining an output signal based on the filtered input signal; and sending the output signal to actuate the slew motor. In other words, the method ensures that the slew motor reacts more slowly than the user input device. Put another way, the controller is configured to dampen transient changes in slewing speed. This may be particularly beneficial for reduced tail swing excavators (i.e., excavators in which a rear end of the superstructure does not overhang a rear of the undercarriage), since the dampened transient changes in slewing speed allows the reduced tail swing excavator to mimic the greater inertia associated with the larger rear end of a conventional excavator superstructure, providing an operator "feel" that is more familiar for those trained on conventional excavators. BRIEF DESCRIPTION OF DRAWINGS Embodiments will now be described by way of example only with reference to the accompanying figures, in which: Figure 1A shows a schematic side view of an excavator, according to an embodiment; Figure IB shows a schematic side view of a reduced tail swing excavator, according to an embodiment; Figure 2 shows a prior art hydraulic system for a working vehicle; Figure 3 shows a prior art electrohydraulic system for a working vehicle; Figure 4 shows an electrohydraulic system according to an embodiment; Figure 5 shows a more detailed diagram of the user-operable valves, shuttle valve block and pressure sensors of the electrohydraulic system of Figure 4; Figure 6 shows a more detailed diagram of the solenoid valves of the electrohydraulic system of Figure 4; Figure 7 shows a schematic diagram of the controller of the electrohydraulic system of Figure 4; Figure 8 shows a graph illustrating change in output signal from the controller of Figure 7 in response to a change in input signal, according to an embodiment; Figure 9 shows a plan view of a reduced tail swing excavator according to an embodiment, in different rotational orientations; Figure 10 shows a flow chart of a method of controlling a hydraulic actuator according to an embodiment; and Figure 11 shows a flow chart of a method of controlling a slew motor of an excavator according to an embodiment. DETAILED DESCRIPTION In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of various embodiments and the teachings. However, those skilled in the art will understand that: the present teachings may be practiced without these specific details or with known equivalents of these specific details; that the present teachings are not limited to the described embodiments; and, that the present teachings may be practiced in a variety of alternative embodiments. It will also be appreciated that well known methods, procedures, components, and systems may not have been described in detail. References to vertical and horizontal in the present disclosure should be understood to be in relation to the machine when stood on horizontal ground in a non-working condition. The term axial is generally used in relation to the longitudinal axis of the machine. The term width is generally used in relation to the longitudinal length, that is, transverse to the length. With reference to Figure 1A, a working vehicle is indicated at 100. The working vehicle 100 has an undercarriage 102 which includes left and right tracks 104. In other embodiments, the undercarriage 102 may include one or more wheels or other means of propulsion instead of the tracks 104. The working vehicle 100 also has a superstructure 106 which is rotatable relative to the undercarriage 102. A slew motor 56 is provided to slew the superstructure 106 relative to the undercarriage 102. In other words, the slew motor 56 is configured to rotate the superstructure 106 relative to the undercarriage 102 about a vertical axis. In the illustrated embodiment, the slew motor 56 is a hydraulic slew motor. The working vehicle 100 also has a working arm 108. The working arm 108 is pivotally connected to the superstructure 106 but is fixed laterally and longitudinally relative to the superstructure 106. In particular, the working arm 108 extends from a front end 120 of the superstructure, so that as the superstructure 106 is slewed by the hydraulic slew motor 56, the working arm 108 slews with it. In this embodiment, the working arm 108 includes: a boom 110 which is pivotally connected to the superstructure 106; a dipper arm 112 which is pivotally connected to the boom 110; and a bucket 114 which is pivotally connected to the dipper arm 112. The working arm is actuated by one or more working arm actuators 62, 64, 66. In particular, there is: a boom actuator 62 for pivoting the boom 110 relative to the superstructure 106; a dipper arm actuator for pivoting the dipper arm 112 relative to the boom 110; and a bucket actuator for pivoting the bucket 114 relative to the dipper arm 112. In this embodiment, the working arm actuators 62, 64, 66 are hydraulic cylinders. In the illustrated embodiment, the working vehicle 100 is an excavator. In other embodiments, the working vehicle 100 may be another type of working vehicle (e.g., a backhoe loader, a telescopic handler, a rotary telescopic handler, a loader, or any other type of working vehicle having one or more hydraulic actuators or other actuators). In the illustrated orientation, the superstructure 106 of the excavator is slewed relative to the undercarriage so that the working arm 108 extends perpendicular to a front end 116 of the undercarriage 102. In other words, the front end 120 of the superstructure 106 and the front end 116 of the undercarriage 102 are approximately parallel. In this orientation, a rear end 122 of the superstructure 106 overhangs a rear end 118 of the undercarriage 102. Such a configuration will be referred to as a "conventional excavator". Figure IB shows an alternative excavator 100 known as a "reduced tail swing excavator". The reduced tail swing excavator 100 of Figure IB is similar to the conventional excavator 100 of Figure 1A, but in this embodiment the rear end 122 of the superstructure 106 does not overhang the rear end 118 of the undercarriage 102. This may be known as a "zero tail swing excavator". In other embodiments, the rear end 122 of the superstructure 106 of the reduced tail swing excavator 100 may still overhang the rear end 118 of the undercarriage 102, but to a lesser extent than in a conventional excavator. Although not illustrated in these figures, the excavators 100 of Figures 1A and IB include an electrohydraulic system 10 and / or control system 78 and / or controller 80 as described below with reference to Figures 4 to 11. Figure 2 shows a prior art hydraulic system that may be used in working vehicles 100 of the kind illustrated in Figures 1A and IB. In this example, there is a main hydraulic circuit 50 which includes a main hydraulic pump 52, a main control valve 54 and a hydraulic actuator 56. In this example, the hydraulic actuator 56 is a hydraulic slew motor having an output shaft 58 which is rotated by the hydraulic slew motor 56. The hydraulic slew motor 56 is selectively coupled to the main hydraulic pump 52 via the main control valve 54. In particular, the main hydraulic circuit 50 includes: a pump outlet line 68 which connects an outlet of the main hydraulic pump 52 to the main control valve 54; a pump return line 70 which connects the main control valve 54 to an inlet of the main hydraulic pump 52; and first and second motor driving lines 72A, 72B which connect the hydraulic slew motor 56 to the main control valve 54. The main control valve 54 has a first state 54A which causes the hydraulic slew motor 56 to move in a first direction (i.e., to rotate the output shaft 58 clockwise). The first state 54A of the main control valve 54 connects the pump outlet line 68 to the first motor driving line 72A, and the second motor driving line 72B to the pump return line 70. In this way, hydraulic fluid flows from the main hydraulic pump 52, along the pump outlet line 68, to the first motor driving line 72A, and then back to the main hydraulic pump 52 along the second motor driving line 72B and pump return line 70. The main control valve 54 also has a second state 54B which causes the hydraulic slew motor 56 to move in a second direction (i.e., to rotate the output shaft 58 anti-clockwise). The second state 54B of the main control valve 54 connects the pump outlet line 68 to the second motor driving line 72B, and the first motor driving line 72A to the pump return line 70. In this way, hydraulic fluid flows from the main hydraulic pump 52, along the pump outlet line 68, to the second motor driving line 72B, and then back to the main hydraulic pump 52 along the first motor driving line 72A and pump return line 70. The main control valve 54 also has a neutral state 54C in which the pump outlet line 68 and pump return line 70 are isolated from the motor driving lines 72A, 72B. There is a biasing force (in this example provided by springs on opposite ends of the main control valve 54) which biases the main control valve 54 towards the neutral state 54C. First and second pressure ports 60A, 60B are provided on opposite ends of the main control valve 54 to facilitate movement of the main control valve 54 out of the neutral state 54C. In particular, when a pressure applied to the first pressure port 60A is greater than a pressure applied to the second pressure port 60B, the main control valve 54 will transition to the first state 54A. Conversely, when a pressure applied to the second pressure port 60B is greater than a pressure applied to the first pressure port 60A, the main control valve 54 will transition to the second state 54B. The main hydraulic circuit 50 described above is a closed-loop circuit 50, because the inlet side of the main hydraulic pump 52 is connected to the outlet side of the hydraulic slew motor 56, rather than to a tank (as in an open-loop system). It will be understood that, although not shown in the simplified diagram of Figure 2, various other hydraulic lines and components may be present as part of the closed-loop circuit. For example, one or more charge pumps and associated valves and hydraulic lines may be provided to maintain the closed-loop circuit 50 at an elevated pressure. In alternative configurations, the main hydraulic circuit 50 may be an open-loop circuit. In such configurations, the return line 70 is connected to a hydraulic fluid reservoir (i.e., tank) and the inlet side of the main hydraulic pump 52 is connected to the hydraulic fluid reservoir. In the illustrated configuration, a pilot hydraulic circuit 20 is provided to supply pressure to the first and second pressure ports 60A, 60B and thereby control the main control valve 54 and associated hydraulic slew motor 56. In particular, the pilot hydraulic circuit 20 includes a pilot hydraulic pump 22 and one or more user-operable pilot control valves 24 for directing pressure generated by the pilot hydraulic pump 22 to the first and second pressure ports 60A, 60B. The one or more user-operable pilot control valves 24 are operated by a joystick 12. There is a mechanical connection between the joystick 12 and the one or more user-operable valves, so that the one or more user-operable valves 24 are actuated directly when the joystick 12 is moved. The one or more user-operable valves 24 may be provided as part of a valve block, or as individual valves. The joystick 12 is deflectable from a neutral position in a first plane in order to actuate the one or more user-operable valves 24. For example, when the joystick is moved in a first direction in the first plane (e.g., left) from the neutral position, the one or more user-operable valves 24 are moved so that a pump pressure line 40 is connected to a first pilot pressure line 40A which is connected to the first pressure port 60A of the main control valve 54. In this way, pressure generated by the pilot pump 22 is applied to the first pressure port 60A. At the same time, a second pilot pressure line 40B which is connected to the second pressure port 60B of the main control valve 54 is connected by the one or more user-operable valves to a hydraulic reservoir (i.e., tank) 16, which de-pressurises the second pressure port 60B. This causes the hydraulic slew motor 56 to move in a first direction. Conversely, when the joystick is moved in a second direction in the first plane (e.g., right) from the neutral position, the one or more user-operable valves 24 are moved so that the pump pressure line 40 is connected to a second pilot pressure line 40B connected to the second pressure port 60B of the main control valve 54. In this way, pressure generated by the pilot pump 22 is applied to the second pressure port 60B. At the same time, the first pilot pressure line 40A is connected by the one or more user-operable valves to the hydraulic reservoir 16, which de-pressurises the first pressure port 60A. This causes the hydraulic slew motor 56 to move in a second direction opposite to the first direction. It will be understood that, although not shown in the simplified diagram of Figure 2, the pilot hydraulic circuit 20 may include various other hydraulic lines and components as are known in the art. For example, one or more pressure relief valves, filters, flow restrictors, further valves etc. may be provided. Although the illustrated main hydraulic circuit 50 only includes a single hydraulic actuator 56, it will be understood that the main hydraulic circuit 50 may include one or more further hydraulic actuators. For example, considering the excavators of Figures 1A and IB, the boom actuator 62, dipper arm actuator 64, bucket actuator 66 and / or hydraulic track motors for tracks 104 may be part of the main hydraulic circuit 50. It will be understood that in such a configuration, each further hydraulic actuator 62, 64, 66 would have a dedicated main control valve 54 which selectively couples the respective further hydraulic actuator 62, 64, 66 to a respective main hydraulic pump (e.g., the illustrated main hydraulic pump 52, or a further main hydraulic pump 52). In such configurations, the pilot hydraulic circuit 20 would also be adapted so that there are further pressure lines extending to pressure ports 60A, 60B on the main control valve(s) 54 of the further hydraulic actuator(s) 62, 64, 66. For example, the joystick 12 may be deflectable from the neutral position in a second plane, different to the first plane in order to control a further hydraulic actuator 62, 64, 66. Alternatively or additionally, a further joystick 12 may be provided for controlling one or more further hydraulic actuators 62, 64, 66. Figure 3 shows a prior art electrohydraulic system that may be used in working vehicles 100 of the kind illustrated in Figures 1A and IB. In this context, the term "electrohydraulic system" will be understood to mean a system which combines both hydraulic circuits and electric control. The electrohydraulic system of Figure 3 is similar to the hydraulic system of Figure 2, and so only differences will be discussed below. In this configuration, instead of pressure ports 60A, 60B there are first and second solenoids 32A, 32B at opposite ends of the main control valve 54. The pilot hydraulic circuit 20 is replaced by an electric control system which includes one or more joystick position sensors 14 which send one or more joystick position input signals 82 to a controller 80. Based on the one or more position input signals 82, the controller determines one or more output signals 84A, 84B which are sent to the respective solenoids 32A, 32B to move the main control valve 54. In particular, a first output signal 84A may be sent to the first solenoid 32A to move the main control valve 54 to the first state 54A, and a second output signal 84B may be sent to the second solenoid 32B to move the main control valve 54 to the second state 54B. In alternative electrohydraulic systems, the pilot hydraulic circuit 20 and pressure ports 60A, 60B of Figure 2 may still be used, but one or more solenoid valves are controlled by solenoids using one or more output signals from the controller 80, rather than via a mechanical connection to the joystick 12. Referring now to Figures 4 to 6, an electrohydraulic system according to an embodiment is indicated at 10. The electrohydraulic system 10 may be used to control the hydraulic slew motor 56 and / or other hydraulic actuators 62, 64, 66 of either of the working vehicles 100 of Figures 1A and IB described above. The main hydraulic circuit 50 of the electrohydraulic system 10 is the same as in the hydraulic system of Figure 2, and so will not be described again in detail. The electrohydraulic system 10 includes a pilot hydraulic circuit 20. Components of the pilot hydraulic circuit 20 which are common to the pilot hydraulic circuit 20 of Figure 2 have been given the same reference numerals, and only differences will be discussed in detail. In this embodiment, the pilot hydraulic circuit 20 includes one or more pilot pressure sensors 28A, 28B which are selectively coupled to the pilot pump 22 via the one or more user-operable pilot control valves 24. In other words, instead of the one or more user- operable valves 24 being connected downstream to the pressure ports 60A, 60B on the main control valve 54, the one or more user-operable valves 24 are connected downstream to the one or more pilot pressure sensors 28A, 28B. The electrohydraulic system 10 has a control system 78 which includes a controller 80. The controller 80 may comprise: control circuitry; and / or processor circuitry; and / or at least one application specific integrated circuit (ASIC); and / or at least one field programmable gate array (FPGA); and / or single or multi-processor architectures; and / or sequential / parallel architectures; and / or at least one programmable logic controllers (PLCs); and / or at least one microprocessor; and / or at least one microcontroller; and / or a central processing unit (CPU), to perform the described methods. The controller may include an associated memory or the memory may be located locally to the controller or remotely. The memory may be a non-volatile flash memory. The controller 80 is configured to: receive one or more input signals 82A, 82B from the one or more pilot pressure sensors 28A, 28B; and send one or more electric output signals 84A, 84B to actuate the main control valve 54 depending on the one or more input signals 82A, 82B received from the one or more pilot pressure sensors 28A, 28B. In other words, the electrohydraulic system 10 includes a combination of hydraulic pilot pressure control and electric control to actuate the hydraulic slew motor 56. Such a control configuration allows a hydraulic joystick 12 of the kind illustrated in Figure 2 to be used to control the hydraulic slew motor 56 (avoiding the need for electric position sensors 14 such as those illustrated in Figure 3), whilst providing the flexibility of electric control (e.g., by the controller 80 modifying the relationship between position of the user-operable pilot control valve(s) 24 and position of the main control valve 54, when desired). This allows the same hydraulic joystick 12 to be used to provide both electrohydraulic control (for the hydraulic slew motor 56) and standard hydraulic control (for a further hydraulic actuator 62, 64, 66). For example, the hydraulic joystick 12 could be moved: left / right to actuate the hydraulic slew motor 56 using electrohydraulic control; and forward / backward to actuate a further hydraulic actuator 62, 64, 66 via standard hydraulic pilot control (as illustrated in Figure 2). With reference to Figures 4 and 5, the controller 80 is configured to detect pressure in the pilot hydraulic circuit 20 downstream of the one or more user-operable pilot control valves 24A, 24B. The pilot hydraulic circuit 20 includes a first pilot pressure sensor 28A which is selectively coupled to the pilot pump 22 via a first user-operable pilot control valve 24A. In particular, the first pilot pressure sensor 28A is connected to the first user-operable pilot control valve 24A by a first sensing pilot line 38A. Similarly, the pilot hydraulic circuit 20 includes a second pilot pressure sensor 28B which is selectively coupled to the pilot pump 22 via a second user-operable pilot control valve 24B. In particular, the second pilot pressure sensor 28B is connected to the second user-operable pilot control valve 24B by a second sensing pilot line 38B. The first pilot pressure sensor 28A and first user-operable pilot control valve 24A are associated with the left swing direction of the hydraulic slew motor 56, and the second pilot pressure sensor 28B and second user-operable pilot control valve 24B are associated with the right swing direction of the hydraulic slew motor 56. When the joystick 12 is moved by a user to indicate a desire to slew the superstructure 106 left relative to the undercarriage 102, the first user-operable pilot control valve 24A is actuated so that the pilot pump 22 is connected to the first sensing pilot line 38A. At the same time, the second user-operable pilot control valve 24B is actuated so that the second sensing pilot line 38B is connected to the hydraulic fluid reservoir 16 via a return line 44. As a result, pressure detected by the first pilot pressure sensor 28A is greater than pressure detected by the second pilot pressure sensor 28B. The controller 80 is therefore able to determine that the user wishes to slew the superstructure 106 left because the first input signal 82A is greater than the second input signal 82B. Conversely, when the joystick 12 is moved by a user to indicate a desire to slew the superstructure 106 right relative to the undercarriage 102, the second user-operable pilot control valve 24B is actuated so that the pilot pump 22 is connected to the second sensing pilot line 38B. At the same time, the first user-operable pilot control valve 24A is actuated so that the first sensing pilot line 38A is connected to the hydraulic fluid reservoir 16 via a return line 44. As a result, pressure detected by the second pilot pressure sensor 28B is greater than pressure detected by the second pilot pressure sensor 28A. The controller 80 is therefore able to determine that the user wishes to slew the superstructure 106 right because the first input signal 82A is lower than the second input signal 82B. It will be understood that, based on these changes in the input signals 82A, 82B, the controller 80 is configured to determine the one or more electric output signals 84A, 84B based on the detected pressure. In Figures 4 and 5, the first and second user-operable valves 24A, 24B for actuating the hydraulic slew motor 56 are part of the same valve block 24. In addition, the valve block 24 includes third and fourth user-operable valves 26A, 26B for actuating a further hydraulic actuator (e.g., the dipper arm actuator 64 of the excavator 100). The valve block 24 has output ports 42A, 42B for connecting the third and fourth user-operable valves 26A, 26B to pressure ports on a main control valve for the further actuator (e.g., via actuating pilot lines as in the configuration of Figure 2). In some embodiments, the same joystick 12 is deflectable from a neutral position in a first plane to actuate the first and second user-operable pilot control valves 24A, 24B for the hydraulic slew motor 56, and is deflectable from the neutral position in a second plane different to the first plane to actuate the third and fourth user-operable pilot control valves for the further hydraulic actuator. In other embodiments, different joysticks 12 are used for the different actuators. In Figures 4 and 5, the first and second sensing pilot lines 38A, 38B are connected to the respective pressure sensors 82A, 82B via a shuttle valve block 36. Such a shuttle valve block 36 is often used in hydraulic pilot circuits of the kind illustrated in Figure 2, to allow hydraulic inputs to be connected to ports 37 on the shuttle valve block 36 to override the hydraulic signals output from the one or more user-operable valves 24A, 24B (e.g., when a swing brake or swing lock function is activated). In the illustrated configuration, the first and second input signals 82A, 82B can be overridden in the controller 80 when needed, and so no hydraulic inputs are connected to the ports 37. However, the shuttle valve block 36 has been retained to allow packaging and hydraulic line routing of a standard hydraulic system (of the kind illustrated in Figure 2) to be re-used in the electrohydraulic system 10. In other embodiments, the shuttle valve block 36 may be omitted. With reference to Figures 4 and 6, the controller 80 is configured to send the one or more output signals 84A, 84B to one or more solenoids 32A, 32B to actuate the main control valve 54. In the illustrated embodiment, because the main control valve 54 is a pilot-operated valve having pressure ports 60A, 60B on opposite sides (as described above with reference to Figure 2), the one or more solenoids 32A, 32B are used to control one or more solenoid pilot control valves 30A, 30B in the pilot hydraulic circuit 20. The pressure ports 60A, 60B are selectively coupled to the pilot pump 22 via the one or more solenoid pilot control valves 30A, 30B. In this way, the controller 80 can selectively pressurise the first or second swing actuating pilot lines 40A, 40B. In alternative embodiments, the main control valve 54 may be a solenoid valve (e.g., of the kind illustrated in Figure 3) including the one or more solenoids 32A, 32B. In the configuration of Figure 6, there is a first solenoid pilot control valve 30A and a second solenoid pilot control valve 30B. The first solenoid pilot control valve 30A has a first solenoid 32A which is actuated by a first electric output signal 84A sent from the controller 80. Similarly, the second solenoid pilot control valve 30B has a second solenoid 32B which is actuated by a second electric output signal 84B from the controller 80. In the illustrated configuration, the first and second solenoid pilot control valves 30A, 30B are provided as part of a solenoid valve block 30. In other configurations, the first and second solenoid pilot control valves 30A, 30B may be separate valve blocks. The first pressure port 60A of the main control valve 54 is selectively coupled to the pilot pump 22 by the first solenoid pilot control valve 30A. In particular, the first solenoid pilot control valve 30A is biased (e.g., by a spring) towards a de-activated state in which the first pressure port 60A is coupled to the hydraulic reservoir 16 via a return line 44. When the first solenoid 32A is activated by the first electric output signal 84A, the first solenoid pilot control valve 30A is moved against the biasing force to an activated state in which the first pressure port 60A is connected to the pilot pump 22 and is thereby pressurised. Similarly, the second pressure port 60B of the main control valve 54 is selectively coupled to the pilot pump 22 by the second solenoid pilot control valve 30B. In particular, the second solenoid pilot control valve 30B is biased (e.g., by a spring) towards a de-activated state in which the second pressure port 60B is coupled to the hydraulic reservoir 16 via the return line 44. When the second solenoid 32B is activated by the second electric output signal 84B, the second solenoid pilot control valve 30B moves towards an activated state in which the second pressure port 60B is connected to the pilot pump 22 and is thereby pressurised. In alternative embodiments, the one or more solenoid valves 30A, 30B may have a different configuration (e.g., a single directional control valve instead of two separated valves). In the illustrated embodiment, the one or more solenoids 32A, 32B are proportional solenoids. This allows movement of the associated one or more solenoid pilot control valves 30A, 30B to intermediate positions which allows variability in the speed of actuation of the hydraulic slew motor 56. In the configuration of Figure 6, the pilot hydraulic circuit 20 includes one or more feedback pressure sensors 34A, 34B, 34C between the one or more solenoid pilot control valves 30A, 30B and the first and second pressure ports 60A, 60B. In other words, the one or more feedback pressure sensors 34A, 34B, 34C are positioned to detect pressure in the swing actuating pilot lines 40A, 40B. The controller 80 controller is configured to receive one or more feedback signals 90A, 90B, 90C from the one or more feedback pressure sensors 34A, 34B, 34C and to implement feedback control to determine the one or more output signals 84A, 84B. In other words, the controller is configured to set the one or more output signals 84A, 84B using closed-loop control. In the illustrated configuration, there is a first feedback pressure sensor 34A configured to sense pressure of the first swing actuating pilot line 40A, and a second feedback pressure sensor 34B configured to sense pressure of the second swing actuating pilot line 40B. The first and second feedback pressure sensors 34A, 34B send respective first and second feedback signals 90A, 90B to the controller 80. In this way, actual pressure applied to the pressure ports 60A, 60B of the main control valve 54 can be monitored and used by the controller 80 to adjust the position of the proportional solenoids 32A, 32B accordingly. A third feedback pressure sensor 34C is connected to the first and second swing actuating pilot lines 40A, 40B via a shuttle valve 35 which, in this embodiment, is part of the solenoid valve block 30. In this way, the third feedback pressure sensor 34C is configured to sense pressure in whichever of the first and second swing actuating pilot lines 40A, 40B has the greatest pressure. The third feedback pressure sensor 34C sends a third feedback signal 90C to the controller 80. The third feedback signal 90C can be used to verify the first and second feedback signals 90A, 90B to provide more accurate control and identify malfunctioning of the first or second feedback sensors 34A, 34B. In other embodiments, the feedback pressure sensors 34A, 34B, 34C may have a different configuration. For example, the third feedback pressure sensor 34C and associated shuttle valve 35 may be omitted. Alternatively, all of the feedback pressure sensors 34A, 34B, 34C may be omitted entirely and the controller 80 may instead use open-loop control. As mentioned above, the electrohydraulic system 10 of Figures 4 to 6 is used to control the hydraulic slew motor 56. The added flexibility of this electrohydraulic system 10 may be particularly beneficial for such a hydraulic slew motor 56. For example, it may be desirable to have more flexible control of the hydraulic slew motor 56 than other hydraulic actuators 62, 64, 66 (e.g., to dampen transient slewing movements, and / or e-fence the allowable rotary positions of the superstructure 106). However, in other embodiments, the same configuration of the electrohydraulic system 10 may be used to control any other type of hydraulic actuator (e.g., one of the boom actuator 62, dipper arm actuator 64, bucket actuator 66 or a hydraulic motor for driving the left or right tracks 104 of an excavator 100). In some embodiments, the controller 80 is configured to vary the one or more electric output signals 84A, 84B at a slower rate of change than the one or more input signals 82A, 82B. In other words, the controller 80 may be configured so that the hydraulic slew motor 56 reacts more slowly than the one or more user-operable pilot control valves 24. Put another way, the controller 80 may be configured to dampen transient changes in slewing speed. Such behaviour is illustrated in Figure 8, in which a sudden change in input signal (dashed line) leads to a more gradual change in output signal (solid line). It will be understood that this more gradual change in output signal would result in more gradual change in the associated movement of the main control valve 54 and hydraulic slew motor 56 relative to the input signal. This may be particularly beneficial for reduced tail swing excavators 100 of the kind illustrated in Figure IB, since the dampening of transient changes in slewing speed allows the reduced tail swing excavator 100 to mimic the greater inertia associated with the larger rear end 122 of a conventional excavator superstructure 106 (e.g., of the kind illustrated in Figure 1A). This provides an operator "feel" that is more familiar for those trained on conventional excavators 100. In other embodiments, the controller 80 may be configured to vary the one or more electric output signals 84A, 84B at a slower rate of change than the one or more input signals 82A, 82B on a conventional excavator 100, which may be beneficial for other reasons. The controller 80 may be configured to filter the one or more input signals 82A, 82B and to use the filtered one or more input signals 82A, 82B to determine the one or more output signals 84A, 84B. For example, the controller may be configured to apply a low-pass filter to the one or more input signals 82A, 82B. Such a filtering of the one or more input signals 82A, 82B provides a simple means for slowing transient changes in slewing speed. In some embodiments, the controller 80 is configured to receive a position input signal 86 indicative of a rotary position of the superstructure 106 relative to the undercarriage 102 of the working vehicle 100, and to set the one or more output signals 84A, 84B to restrict slewing of the superstructure 106 beyond a predetermined range of rotational orientations. For example, Figure 9 illustrates a schematic plan view of a working vehicle 100 with left and right boundaries 94A, 94B of the predetermined range of rotational positions indicated in dashed lines. In other words, the controller 80 is configured to e-fence the allowable rotary positions of the superstructure 106. This may be beneficial when working in close proximity to obstructions or obstacles, since the e-fencing can be set up to restrict movement into positions which could lead to a collision. The position input signal 86 may be provided by any suitable rotary position sensor 85, as indicated schematically on Figure 7 (e.g., an encoder, potentiometer, or other sensor). In some embodiments, the control system 78 includes one or more user inputs 91 for setting the predetermined range of rotational orientations. In other words, the controller 80 may be configured to receive a rotational orientation limit signal 92 from the one or more user inputs 91 (as illustrated schematically on Figure 7). For example, a touchscreen, buttons, or other inputs may be used to manually set the predetermined range of rotational orientations and left and right boundaries 94A, 94B. Alternatively, a user may actuate the hydraulic slew motor 56 to move the superstructure 106 to a given rotational position and then set the respective boundary 94A, 94B of the predetermined range of rotational positions at the given rotational position (e.g., by pressing a button). It will be understood that, although the description above relates to a hydraulic slew motor 56 and associated control, in other embodiments the slew motor 56 may be a non-hydraulic actuator. In such embodiments, there may still be a controller 80 configured to: receive an input signal in response to actuation of a user input device (e.g., from an electric joystick); filter the input signal to smooth out changes in the input signal; determine an output signal based on the filtered input signal; and send the output signal to actuate the slew motor 56. In other words, the controller 80 may be configured so that the slew motor 56 reacts more slowly than the user input device. Put another way, the controller 80 may be configured to dampen transient changes in slewing speed. It will be understood that the benefits associated with dampening transient changes in slewing speed outlined above may be equally applicable to non-hydraulic slew motors. In particular, such a controller 80 may be particularly beneficial for reduced tail swing excavators 100 of the kind illustrated in Figure IB, since the dampened transient changes in slewing speed allows the reduced tail swing excavator 100 to mimic the greater inertia associated with the projecting rear end 122 of a conventional excavator superstructure 106 (as illustrated in Figure 1A). This provides an operator "feel" that is more familiar for those trained on conventional excavators. In such embodiments, the controller 80 may be configured to: vary the output signal at a slower rate of change than the input signal; and / or apply a low-pass filter to the input signal; and / or receive a position input signal indicative of a rotary position of a superstructure relative to an undercarriage of said reduced tail swing excavator, and to set the output signal to restrict slewing of the superstructure beyond a predetermined range of rotational orientations; and / or receive one or more feedback signals from one or more feedback sensors and to implement feedback control to determine the output signal. Referring now to Figure 10, a method of controlling a hydraulic actuator 56 of a working vehicle 100 is illustrated as a flow chart. The method comprises the following steps: detecting pressure in a pilot hydraulic circuit 20 downstream of one or more user-operable pilot control valves 24A, 24B; determining one or more electric output signals 84A, 84B based on the detected pressure; and sending the one or more electric output signals 84A, 84B to actuate a main control valve 54 and thereby control the hydraulic actuator 56. The method may comprise varying the one or more electric output signals 84A, 84B at a slower rate of change than the detected pressure. For example, the method may comprise filtering the detected pressure (e.g. using a low-pass filter). The hydraulic actuator 56 may be a hydraulic slew motor and the method may comprise detecting a rotary position of a superstructure 106 relative to an undercarriage 102 of the working vehicle 100, and setting the one or more electric output signals 84A, 84B to restrict slewing of the superstructure 106 beyond a predetermined range of rotational orientations. Such a method may further comprise receiving one or more user inputs 92 for setting the predetermined range of rotational orientations. The method may comprise sending the one or more electric output signals 84A, 84B to one or more solenoids 32A, 32B to actuate the main control valve 54. The method may comprise receiving one or more feedback signals 90A, 90B, 90C from one or more feedback pressure sensors 34A, 34B, 34C and implementing feedback control to determine the one or more electric output signals 84A, 84C. Referring now to Figure 11, a method of controlling a slew motor 56 of an excavator 100 is illustrated as a flow chart. The method comprises the following steps: receiving an input signal 82A, 82B in response to actuation of a user input device 12; filtering the input signal 82A, 82B to smooth out changes in the input signal 82A, 82B; determining an output signal 84A, 84B based on the filtered input signal 82A, 82B; and sending the output signal 84A, 84B to actuate the slew motor 56. The one or more embodiments are described above by way of example only and it will be appreciated that the variations are possible without departing from the scope of protection afforded by the appended claims. It should also be noted that whilst the appended claims set out particular combinations of features described above, the scope of the present disclosure is not limited to the particular combinations hereafter claimed, but instead extends to encompass any combination of features herein disclosed.

Claims

1. An electrohydraulic system for a working machine, the electrohydraulic system comprising:a pilot hydraulic circuit comprising a pilot pump, one or more user-operable pilot control valves, and one or more pilot pressure sensors selectively coupled to the pilot pump via the one or more user-operable pilot control valves;a main hydraulic circuit comprising a main hydraulic pump, a main control valve, and a hydraulic actuator selectively coupled to the main hydraulic pump via the main control valve; anda control system comprising a controller configured to:receive one or more input signals from the one or more pilot pressure sensors; and send one or more electric output signals to actuate the main control valve depending on the one or more input signals received from the one or more pilot pressure sensors.

2. The electrohydraulic system of claim 1, wherein the hydraulic actuator is a hydraulic slew motor configured to slew a superstructure of a working vehicle relative to an undercarriage of said working vehicle.

3. The electrohydraulic system of claim 2, wherein the controller is configured to vary the one or more output signals at a slower rate of change than the one or more input signals.

4. The electrohydraulic system of claim 3, wherein the controller is configured to filter the one or more input signals and to use the filtered one or more input signals to determine the one or more output signals; optionally, wherein the controller is configured to apply a low-pass filter to the one or more input signals.

5. The electrohydraulic system of any of claims 2 to 4, wherein the controller is configured to receive a position input signal indicative of a rotary position of the superstructure relative to the undercarriage of said working vehicle, and to set the one or more output signals to restrict slewing of the superstructure beyond a predetermined range of rotational orientations.

6. The electrohydraulic system of claim 5, wherein the control system comprises one or more user inputs for setting the predetermined range of rotational orientations.

7. The electrohydraulic system of any preceding claim, wherein the controller is configured to send the one or more output signals to one or more solenoids to actuate the main control valve; optionally, wherein the one or more solenoids are proportional solenoids.

8. The electrohydraulic system of claim 7, wherein the main control valve is a pilot-operated valve having one or more pressure ports on one or more sides of the main control valve, wherein the pilot hydraulic circuit comprises one or more solenoid pilot control valves comprising the one or more solenoids, wherein the one or more pressure ports are selectively coupled to the pilot pump via the one or more solenoid pilot control valves, and wherein the controller is configured to send the one or more output signals to the one or more solenoids of the one or more solenoid pilot control valves to control pressure at the one or more pressure ports of the main control valve.

9. The electrohydraulic system of claim 8, wherein the pilot hydraulic circuit comprises one or more feedback pressure sensors between the one or more solenoid pilot control valves and the first and second pressure ports, and wherein the controller is configured to receive one or more feedback signals from the one or more feedback pressure sensors and to implement feedback control to determine the one or more output signals.

10. The electrohydraulic system of any preceding claim, further comprising a joystick for actuating the one or more user-operable pilot control valves, wherein the joystick is deflectable from a neutral position in a first plane to actuate the one or more user-operable pilot control valves and thereby control the hydraulic actuator, and wherein the joystick is deflectable from the neutral position in a second plane different to the first plane to control a further hydraulic actuator.

11. The electrohydraulic system of claim 10, wherein the hydraulic actuator comprises a hydraulic slew motor configured to slew a superstructure of a working vehicle relative to an undercarriage of said working vehicle, and wherein the further hydraulic actuator comprises a working arm hydraulic cylinder.

12. The electrohydraulic system of any preceding claim, wherein the main hydraulic circuit is a closed-loop circuit, wherein the main hydraulic pump is a uni-directional pump, and wherein the main control valve is a directional control valve comprising a first state configured to direct hydraulic fluid from the main hydraulic pump in a first direction aroundthe closed-loop circuit, and a second state configured to direct hydraulic fluid from the main hydraulic pump in a second direction around the closed-loop circuit.

13. A controller for a slew motor of an excavator, wherein the controller is configured to:receive an input signal in response to actuation of a user input device;filter the input signal to smooth out changes in the input signal; determine an output signal based on the filtered input signal; and send the output signal to actuate the slew motor.

14. A controller for a hydraulic actuator of a working vehicle, wherein the controller is configured to:detect pressure in a pilot hydraulic circuit downstream of one or more user-operable pilot control valves;determine one or more electric output signals based on the detected pressure; and send the one or more electric output signals to actuate a main control valve and thereby control the hydraulic actuator.

15. A working vehicle comprising the electrohydraulic system of any of claims 1 to 12 and / or a control system comprising the controller of claim 13 and / or the controller of claim 14.

16. The working vehicle of claim 15, wherein the working vehicle comprises an undercarriage, a superstructure which is rotatable relative to the undercarriage, and a slew motor configured to slew the superstructure relative to the undercarriage.

17. The working vehicle of claim 16, wherein the working vehicle comprises a working arm, wherein the working arm is actuated by one or more working arm actuators.

18. The working vehicle of claim 17, wherein the working vehicle is an excavator.

19. The working vehicle of claim 18, wherein the superstructure is sized such that, when the superstructure is slewed relative to the undercarriage so that the working arm extends perpendicular to a front end of the undercarriage, a rear end of the superstructure does not overhang a rear end of the undercarriage.

20. A method of controlling a hydraulic actuator, the method comprising:detecting pressure in a pilot hydraulic circuit downstream of one or more user-operable pilot control valves;determining one or more electric output signals based on the detected pressure; andsending the one or more electric output signals to actuate a main control valve and thereby control the hydraulic actuator.

21. The method of claim 20, wherein the method comprises varying the one or more electric output signals at a slower rate of change than the detected pressure; optionally, wherein the method comprises filtering the detected pressure; optionally, wherein the method comprises applying a low-pass filter to the detected pressure.

22. The method of claim 20 or 21, wherein the hydraulic actuator is a hydraulic slew motor of a working vehicle, wherein the method comprises detecting a rotary position of a superstructure relative to an undercarriage of the working vehicle, and setting the one or more electric output signals to restrict slewing of the superstructure beyond a predetermined range of rotational orientations; optionally, wherein the method comprises receiving one or more user inputs for setting the predetermined range of rotational orientations.

23. The method of any of claims 20 to 22, wherein the method comprises sending the one or more electric output signals to one or more solenoids to actuate the main control valve.

24. The method of any of claims 20 to 23, wherein the method comprises receiving one or more feedback signals from one or more feedback pressure sensors and implementing feedback control to determine the one or more electric output signals.

25. A method of controlling a slew motor of an excavator, the method comprising: receiving an input signal in response to actuation of a user input device; filtering the input signal to smooth out changes in the input signal; determining an output signal based on the filtered input signal; and sending the output signal to actuate the slew motor.s

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