Lifting device and control method

Abstract

A lifting device and a method for controlling it are provided. The lifting device comprises an electric motor coupled to a traction unit and a traction battery. A hydraulic circuit includes a pump with a motor and a valve. When the voltage exceeds a threshold while the electric motor generates braking torque and supplies electrical energy to the battery, the pump flow rate increases, and the valve is controlled to reduce its opening and increase the pressure in the pressure line, thereby decreasing the electrical energy supplied to the traction battery. Thus, the pump flow rate and valve position are controlled when the braking power exceeds a threshold to dissipate that power in the hydraulic circuit and charge the traction battery with the remaining braking power.

Description

Lifting device and control method CROSS REFERENCE TO RELATED APPLICATIONS TECHNICAL FIELD Various embodiments refer to a lifting device or work vehicle with an electric drive train and a hydraulic function manifold. BACKGROUND A hoist with an electric drive line can use regenerative braking from a traction motor to recharge a traction battery. A motor controller manages the traction motor and communicates with the traction battery. During braking, the motor controller and / or battery voltage may rise above a certain threshold. Typically, a hoist can be equipped with a motor controller with a higher voltage threshold than that of the associated traction battery and / or an oversized traction battery that does not experience a significant voltage change at high charging rates; however, these components can add cost and weight to the hoist.Alternatively, the device may be equipped with a resistive heater connected to the traction battery via a switch. This heater operates when the voltage is high to discharge the battery and reduce the voltage. If the motor controller and / or battery voltage approaches or reaches the associated limit, the motor torque output is reduced; however, this comes at the expense of braking torque, which may cause the vehicle speed to increase above the commanded speed, or may cause the parking brake to engage abruptly. SUMMARY The invention is defined in the claims. In an embodiment not part of the invention, a lifting device is provided with a chassis, a plurality of traction devices for supporting the chassis on an underlying surface, an electric motor coupled by transmission to at least one of the plurality of traction devices, a motor controller in electrical communication with the electric motor, and a traction battery in electrical communication with the electric motor via the motor controller. A hydraulic circuit has a pump, a pressure gallery, a return line, and a valve that controls the pressure in the pressure gallery and fluidly connects the pressure gallery to the return line. A pump motor is connected by transmission to the pump and in electrical communication with the traction battery. A user input is provided for controlling the speed of the lifting device.A controller is configured to, in response to a voltage being above a threshold voltage while the electric motor is emitting braking torque and supplying electrical power to the battery, increase a pump flow and control the valve to reduce a valve opening size and increase the pressure in the pressure gallery, thereby reducing the electrical power to the traction battery. In an embodiment not part of the invention, a method for controlling a lifting device is provided. The lifting device is powered by at least one electric motor connected to a wheel, with the at least one electric motor electrically connected to a traction battery via a motor controller. A hydraulic circuit is provided with a pump that supplies flow to a pressure gallery, a valve that fluidly connects the pressure gallery to a return line, and an actuator fluidly connected to the pressure gallery and the return line. The pump is driven by a pump motor electrically connected to the traction battery. A braking power output is determined for the at least one electric motor to control the vehicle at a commanded speed based on the actual speed of the lifting device and the load on the electric motors.A pump flow is increased and the valve is controlled to reduce the size of a valve opening in response to the braking power output being greater than a threshold to dissipate a braking power output above the threshold in a hydraulic circuit and charge the traction battery with the remaining braking power output. In an embodiment not part of the invention, a propulsion device is provided with an electric motor adapted for transmission coupling to at least one wheel, a motor controller in electrical communication with the electric motor, and a traction battery in electrical communication with the electric motor via the motor controller. A hydraulic circuit has a pump, a pressure gallery, a return line, and a valve that controls the pressure in the pressure gallery and fluidly connects the pressure gallery to the return line. A pump motor is transmission-driven to the pump and in electrical communication with the traction battery. A user input controls the speed of the lifting device.A controller is configured to, in response to a voltage being above a threshold voltage while the electric motor is emitting braking torque and supplying electrical power to the battery, increase a pump flow and / or control the valve to reduce a valve opening size and increase the pressure in the pressure gallery, thereby reducing the electrical power to the traction battery. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 illustrates a perspective view of a lifting device according to a first embodiment; FIGURE 2 illustrates a perspective view of a lifting device according to a second embodiment; FIGURE 3 illustrates a schematic for the lifting device of Figure 1 or Figure 2; FIGURE 4 illustrates a hydraulic schematic for the lifting device of Figure 1 or Figure 2; FIGURE 5 illustrates a flowchart for a method according to an embodiment not part of the invention, and for use with the lifting device of Figures 1 or 2. DETAILED DESCRIPTION As required, detailed embodiments of the present invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely illustrative of the invention, which can be implemented in various ways. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, the specific structural and functional details disclosed herein should not be construed as limiting, but merely as a representative basis for teaching a person skilled in the art how to employ the present invention in various ways. Figure 1 illustrates a lifting device 10 or work vehicle 10 according to a first embodiment and for use with this disclosure. Lifting devices or work vehicles are used in a commercial or industrial setting and may include lifting equipment, including a portable material lift, an aerial work platform, a telescopic handler, a scissor lift, a telescopic rough terrain loader, and a telescopic articulated boom. In Figure 1, the lifting device 10 is illustrated as a telescopic articulated boom according to a non-limiting example. The lifting device 10 has an electric propulsion system that propels the vehicle, as described below with reference to Figure 3. The lifting device 10 also has an electrically powered or hybrid hydraulic system that operates the working function, such as a lifting platform, of the lifting device as well as other vehicle systems such as the steering, and is described below with reference to Figure 4. The lifting device 10 has a base 12 or chassis 12 that is supported above the underlying ground by a plurality of traction devices 14, such as four wheels 14. The lifting device 10 is configured to lift a load, such as a person, tools, cargo, and the like, with respect to a supporting surface 16 or the underlying ground, such as paved or unpaved ground, a road, a paved surface such as a sidewalk or parking lot, an interior or exterior floor of a structure, or other surfaces. The lifting device 10 includes a vehicle lifting component 18, such as a platform, base, or chassis 12, and a support assembly 20 that couples the platform 18 and the base 12. The base 12 is supported on the support surface 16 by traction devices 14, such as wheels. The traction devices 14 may include tires and / or tracks. The vehicle 10 has a first axle 24 with two wheels 14 and a second axle 26 with another two wheels 14. Axle 24 may be a front axle, and axle 26 may be a rear axle. In other embodiments, the vehicle 10 may have more than two axles. In other embodiments, the traction devices 14 may be aligned with each other along a lateral axis of the vehicle, but do not have axles 24 and 26 extending between them. The support assembly 20 may include one or more hydraulic actuators, as described below, along with other structural members, to provide a lifting mechanism for platform 18. The base 12 has opposite sides or ends, first and second 30, 32, which correspond to the front and rear ends of the base and the vehicle, respectively. The vehicle 10 is configured to move in both a forward and a backward direction, for example, in any direction along a longitudinal vehicle axis 40, depending on the direction in which the wheels 22 are rotating. The operator of the lifting device 10 inputs commands into the lifting device via an operator input or user input 50, for example, on a control panel. The operator input 50 may include a joystick for inputting speed and direction commands for the lifting device 10. For example, moving the joystick forward from its neutral center position provides a forward speed command for the vehicle; for example, the vehicle moves in a forward direction, or to the left in Figure 1, at a selected speed. Moving the joystick backward from its neutral center position provides a reverse speed command for the vehicle; for example, the vehicle moves in a reverse direction, or to the right in Figure 1, at a selected speed.The magnitude of the speed command is based on the distance between the actual joystick position and the neutral center position. The control panel 50 may additionally have an operator input for selecting a speed mode for the device 10. In one example, the lifting device 10 has three speed modes, each with a different maximum speed. The first speed mode has the highest maximum speed and is used when the lifting platform is retracted; the second speed mode has a lower maximum speed and is also used when the lifting platform is retracted; and the third speed mode has the lowest maximum speed and is used when the lifting platform is extended from the retracted position. The joystick can be recalibrated based on the selected mode, so that the fully forward position of the joystick provides the maximum permissible speed for that mode, and the same applies to the fully rearward position. In one example, the first speed mode allows vehicle speeds ranging from zero to twenty miles per hour in either direction, the second speed mode allows vehicle speeds ranging from zero to five miles per hour in either direction, and the third speed mode allows vehicle speeds ranging from zero to two miles per hour in either direction. In another example, the first speed mode allows vehicle speeds ranging from zero to four miles per hour in either direction, the second speed mode allows vehicle speeds ranging from zero to two miles per hour in either direction, and the third speed mode allows vehicle speeds ranging from zero to less than one mile per hour in either direction. The system controller can additionally select the speed mode for the device based on the operating conditions, and can override the operator's selection via input 50. The control panel 50 also provides other operator inputs, such as controlling the position of the lifting component 18 relative to the base 12. In addition, the control panel 50 may include a display screen, indicator lights, and the like to provide information to the operator regarding the lifting device 10. Figure 2 illustrates a lifting device 10 according to another embodiment and for use with this disclosure. Elements that are the same as or similar to those described above with respect to Figure 1 are given the same reference number for simplicity. In Figure 2, the lifting device 10 is illustrated as a scissor lift according to another non-limiting example. Figure 3 illustrates a schematic of lifting device 10 from Figure 1 or Figure 2, or another lifting device such as a forklift, or similar. For simplicity, items that are the same as or similar to those described above with respect to Figure 1 are given the same reference number. The lifting device 10 has a plurality of traction devices 14. In one example, the traction devices 14 are provided by means of wheels, and the lifting device 10 has four wheels as shown above with reference to Figures 1 and 2. In other examples, the lifting device 10 may have more than four wheels. The lifting device 10 has an electric propulsion system 60. The electric propulsion system 60 includes one or more electric motors 62 that are connected by transmission to at least one of the plurality of traction devices 14 to propel the lifting device over the underlying ground. In one example, the electric motors 62 are provided as hub motors for two or more of the wheels 14. In a further example, as shown, the electric propulsion system 60 has four electric motors 62 that are provided as hub motors for all four wheels 14. In other examples, the electric motors 62 may be connected to more than one wheel, for example, by means of a differential in a driveline. Alternatively, only some of the wheels 14 provide traction for the vehicle, for example, as a two-wheel drive. Each electric motor 62 is connected to a traction battery 64 via an associated motor controller 66. The motor controller 66 controls the speed and torque of each electric motor 62, and the motors 62 can be controlled independently. The motor controller 66 is shown as a single integrated unit but can be provided as a separate unit for each motor 62. The voltage of the motor controller 66 can be equivalent to the voltage of the traction battery 64. The motor controller 66 has an associated voltage limit. Each motor controller 66 communicates with a system controller 68. The control panel 50 and operator inputs, such as the joystick, also communicate with the system controller 68. The traction battery 64 may consist of one or more cells, may be a wet cell or a dry cell, and may be made with lead-acid, lithium-based, or other chemistry. The traction battery 64 may have an associated voltage limit, current limit, state-of-charge limit, or temperature limit. As a non-limiting example, the motor controller 66 has a voltage limit. In another example, with a lithium-ion battery, the battery 64 may have voltage and current limits, as well as operating temperature limitations. For example, the battery 64 may have a limited charge when it is outside a certain temperature range, such as after a cold start in cold ambient temperatures, and the motor controller 66 and / or system controller 68 may limit the battery's charge under these conditions.System controller 68 communicates with the various propulsion and hydraulic components and sensors to control device 10. Controller 68 may provide or be part of a vehicle systems controller (VSC), and may include any number of controllers. It may be integrated into a single controller or consist of multiple modules. Some or all of the controllers may be connected via a controller area network (CAN) or other system. The controller may also be connected to a random access memory or other data storage system. The motor controller 66 can control the electric motor 62 in a speed control feedback loop based on a speed input from the operator. For example, the operator can input a selected speed using the joystick 50, and the motor controller 66 can control or modulate the torque of the electric motor 62 to provide the desired speed output based on the operator's request. Thus, to reduce the speed of the traction motor 62, the motor controller 66 can command the traction motor to output a reduced torque or a torque in the opposite direction to the motor's rotation, for example, as a braking torque. The traction motors 62 can be provided as four-quadrant motors that can be controlled between forward braking, forward drive, reverse drive, and reverse braking. Additionally, the 64 traction battery can be charged externally, for example, by means of an electrical input from an external power source such as a charging station. Each electric motor 62 can be controlled to rotate in a first and second direction, and additionally has controlled speed and torque outputs. The electric motor 62 can therefore propel the vehicle across the underlying terrain with a positive torque output. The electric motors 62 can also act as a generator to provide a negative torque output for braking or slowing the vehicle, and to supply electrical power to the traction battery 64. In the example shown, the lifting device 10 is provided without a service braking system. As such, the electric motors 62 are the only devices that apply a braking force to the wheels 14 to control the vehicle's speed while driving. A service braking system is conventionally provided by drum brakes, disc brakes, or similar devices that provide an operator-controlled braking input, for example, to slow the vehicle to a lower speed. In the example shown, the lifting device 10 has a parking brake system. Within the parking brake system, a parking brake 70 is provided on each wheel 14. In a non-limiting example, the parking brake 70 is integrated into the drive assembly of the traction motor 62 and the wheel 14, and may be provided as a spring-applied coil-release brake, for example, a disc brake. The controller 68 or the operator can engage the parking brakes 70 to stop the lifting device 10, or release the parking brakes 70 to allow the lifting device 10 to move relative to the underlying ground. When the parking brakes 70 are engaged or activated while the device 10 is in motion, the wheels 14 do not rotate, and the lifting device 10 skids to a stop. In the electrically propelled lifting device 10, as described above with reference to Figures 1-3, the traction motors 62 can provide both propulsion and braking torque in both forward and reverse directions. When these motors 62 are moving the device forward using positive torque, the traction battery 64 is discharged to provide electrical power. When these traction motors 62 are slowing the vehicle by braking, the direction of the battery current is reversed, and the braking power charges the battery 64, for example, by means of regenerative braking. Charging, for example, by means of regenerative braking, results in an increase in the voltage of the traction battery 64. Depending on the size and chemistry of the battery 64, as well as the braking power applied, the voltage of the battery 64 can increase significantly. Although this voltage increase may be temporary, the motor controller 66, the traction battery 64, and / or other onboard power electronics devices may have associated voltage or current limits. For example, a three-phase motor controller 66 may have an associated voltage threshold, and the torque of the motor 62 under braking may be limited when this threshold is reached.This, in turn, can limit the ability of the traction motor 62 to brake and control the speed of the vehicle 10, for example, on an incline, which can result in unintended downhill acceleration for the device 10 and / or a speed of the lifting device exceeding the commanded speed. The method described below with reference to Figure 5 provides control of the lifting device 10 during such a scenario. Figure 4 illustrates a hydraulic schematic for the lifting device of Figure 1 or Figure 2. The hydraulic system 80 can be a closed-loop or open-loop hydraulic circuit. In the example shown, the hydraulic system has two pumps 82, 84, with the second pump 84 superimposed on the first pump 82. Alternatively, a single pump housing can be provided, with the housing sectioned to provide two pump volumes 82, 84. The first and second pumps 82, 84 are driven by a pump motor 86, which is an electric motor electrically coupled to the traction battery 64 described above with reference to Figure 3 by means of a pump motor controller 88. The speed of the pump motor 86 can be controlled to regulate the flow from pumps 82, 84.As used herein, the flow from pumps 82, 84 can be controlled by controlling a pump speed and / or a displacement from the pumps or by means of pump valves 90, 92. In alternative examples, the hydraulic system may have a single pump, such as pump 82, which is driven by the pump motor. Pumps 82, 84 can be provided as variable displacement pumps. Alternatively, and as shown, each pump 82, 84 can have an associated pump valve 90, 92 that seamlessly connects the associated pump to the pressure gallery 100 or the return line 102 and to the tank 104. The displacement or flow to the pressure gallery 100 can therefore be controlled by selectively controlling the first and / or second pump valves 90, 92 to provide flow to the pressure gallery 100. The displacement or flow to the pressure gallery 100 can be further controlled within a range provided by the pump valves 90, 92 in selected positions by selectively controlling the speed of the pump motor 86. In several examples, and as shown, the hydraulic system 80 additionally has an internal combustion engine 110, such as a diesel or gasoline engine, which is coupled to the pump motor 86 by means of a freewheel clutch 112. The pump motor 86 is therefore located between the engine 110 and the pumps 82, 84. The engine 110 and / or the pump motor 86 can be operated to drive the pumps 82, 84. The freewheel clutch 112 engages to mechanically couple the engine 110 and the pump motor 86 when the rotational speed of the engine 110 output shaft is equal to or less than the rotational speed of the pump motor 86 shaft. Therefore, the freewheel clutch 112 disengages, and the pump motor 86 operates independently of the engine 110 when the pump motor speed is greater than the engine speed.In other examples, the hydraulic system 80 may be electrically powered only, so there is no motor or freewheel clutch, and only the pump motor 86 turns the pump(s). The motor 110, the pump motor controller 88 and the selected valves are also in communication with the vehicle controller 68. The first and second pumps 82, 84 provide pressurized fluid flow to a pressure gallery 100. The hydraulic functions 120 for the lifting device 10 are connected to the pressure gallery 100 to receive pressurized fluid from it, for example, via valves 122. For example, hydraulic actuators 124 for the lifting platform support assembly, wheel steering, axle control, and other device functions are fluidly connected to the pressure gallery 100. The hydraulic actuators 124 are also coupled to a return line 102, which is downstream of the pressure gallery 100 and the actuators 124. The return line 102 provides a fluid path to the reservoir 104 and the pumps 82, 84 from the pressure gallery 100 and the actuators 124.Although only two hydraulic actuators 124 are shown, any number of hydraulic actuators are contemplated for use with the hydraulic system 80. A valve 130, such as a relief valve, is located between the pressure gallery 100 and the return line 102 to seamlessly connect the pressure gallery directly to the return line. The valve 130 may be a variable-position valve, for example, a proportional relief valve or a reverse proportional relief valve. In examples not part of the invention, the valve 130 may be a fixed relief valve. The position of the valve 130 may be controlled by a solenoid in communication with the system controller 68. The position of the valve 130 may be controlled to regulate the pressure within the pressure gallery 100. When the valve 130 is open, flow from pumps 82, 84, and the pressure gallery 100 flows to the return line 102, bypassing the actuators 124, and the pressure in the pressure gallery 100 is minimized.When valve 130 is closed, all flow is directed from pumps 82, 84 to pressure gallery 100, to maximize the pressure in pressure gallery 100. The position of valve 130 can be controlled or modulated between open and closed positions, and partially open positions, to control the pressure within pressure gallery 100. The hydraulic system 80 may have other components not shown, including other valves, actuators, filters, and the like. The hydraulic system 80 can be used to draw electrical power from the battery 64 while the lifting device 10 is braking by means of the electric motors 62 and when the voltage or other limits associated with the motor controller 66 or the traction battery 64 are approaching their thresholds or limits as described in this disclosure. As the flow from pumps 82, 84 and / or the pressure in system 80 increases, the electrical power consumption by the hydraulic system 80 also increases. For example, when a high-pressure fluid is metered through the relief valve 130, energy is dissipated as heat in the fluid.Since the present disclosure provides control over the speed and / or displacement of pumps 82, 84, as well as control over the position of valve 130, the amount of electrical energy dissipated by the hydraulic system 80 can be controlled as described below with reference to Figure 5 to keep the operation of the lifting device 10 within its electrical limits and charge the traction battery 64 to the extent that it can be charged. Figure 5 illustrates a method, not part of the invention 200, for controlling a lifting device, such as the lifting device 10 shown above with respect to Figures 1-4. In various instances, the steps in method 200 may be performed in a different order, performed in parallel or in series, and / or added or omitted. Various embodiments of method 200 have associated, but not limited to, advantages. For example, method 200 and device 10 control vehicle speed by releasing or transferring energy to the hydraulic system 80 when a parameter associated with regenerative braking by the traction motors 62 is above a threshold to avoid or delay engagement of the parking brake 70 and abrupt stopping of the device 10, especially at higher speeds. As described above, during braking by the traction motors 62, and especially during braking while descending a slope, the electric traction motors 62 act as generators, converting wheel torque and speed into electrical energy. At higher speeds, steeper slopes, and rapid decelerations for the lifting device 10, the braking power generated by the traction motors 62 can exceed a threshold or limit associated with the battery 64, the motor controller 66, or another electrical component. This threshold can be reached more easily during braking when the traction battery 64 is nearly or fully charged and / or cold. When braking power is applied to the traction battery 64 by means of regenerative braking, the voltage of the traction battery 64 can rise rapidly.The motor controller 66 may limit regenerative braking when the traction battery voltage 64 is close to a threshold to protect the battery 64 and / or the motor controller 66. Therefore, braking by means of the electric motors 62 may be limited under certain circumstances for the lifting device 10. Similarly, when the device 10 has a lithium-chemistry traction battery 64, the battery may have associated current and / or voltage thresholds. Since the lifting device 10 is without service braking, the controller 68 would need to engage the parking brake 70, resulting in a sudden stop of the device and impacting its drivability.The hydraulic system 80 is used as described herein to dissipate excess braking power generated by the traction motors 62, and to allow extended regenerative braking when the device 10 is approaching the electrical thresholds for the motor controller 66, the traction battery 64, and other power electronics components. In steps 202 and 204, method 200 determines whether the lifting device 10 is operating, and if so, whether the electric motors 62 are generating braking torque and supplying electrical power to the traction battery 64. For example, the electric motors 62 may be generating braking torque based on an operator request to reduce the vehicle's speed, or to maintain the vehicle's speed while descending a slope or incline. The controller 68 may be configured to command the electric motor 62 to emit braking torque in response to receiving a signal from the user input to reduce the speed of the lifting device 10, or to maintain the speed of the lifting device 10 on a downhill slope or incline, or similar. In stage 206, system controller 68 compares the voltage to a first threshold voltage. For example, system controller 68 can compare the voltage at the motor controller to this first threshold voltage. The first threshold voltage can be set below a voltage limit associated with motor controller 66. In a non-limiting example, the voltage limit of motor controller 66 is 63 volts, the first threshold voltage is set to 55 volts, and the nominal voltage is 48 volts. In other examples, different threshold voltages can be set, or system controller 68 can monitor the voltage of another power electronics device in device 10. For example, when braking or torque output occurs, and when the battery is partially or almost fully charged, the voltage at the motor controller 62 and battery 64 increases. The control system 68 detects the voltage increase and sets the pressure in the pressure gallery 100 to a nominal value and turns on pumps 82 and 84 to a nominal flow setting in preparation for reacting to braking, for example, if the hydraulic system 80 is no longer operating. Therefore, for a hydraulic system 80 without an internal combustion engine 110, the pump speed 82, 84 can be set to a low value within its operating range. In stage 208, if the lifting device 10 is equipped with an internal combustion engine 110 in the hydraulic system 80, the controller 68 is further configured to, in response to the voltage at the motor controller 66 exceeding the first threshold voltage, control the pump motor speed 86 to be greater than the speed of the motor 110 when the engine is running and the electric motor 62 is delivering the braking torque. This keeps the freewheel clutch 112 in an open or disengaged position and prevents the engine 110 from placing a load on or slowing down the pump motor 86. Therefore, for a hydraulic system 80 with an internal combustion engine 110, and when the engine is running, the speed of the pump 82, 84 or the pump motor 86 is set to a value that is higher than the speed of the engine 110 so that the freewheel clutch allows the pump motor to spin faster than the engine 110, and it begins to discharge the battery 64 instead of charging the battery. In stage 210, if the voltage exceeds the first threshold, system controller 68 increases the flow of pumps 82 and 84 in hydraulic system 80. As the flow of pumps 82 and 84 increases, pump motor 86 draws electrical power from traction battery 64, which in turn reduces the electrical power supplied to traction battery 64 from traction motors 62. The voltage will therefore decrease. Controller 68 can also be configured to increase the flow of pumps 82 and 84 if the flow falls below a predetermined threshold, and continue to do so until the flow reaches that threshold. In stage 212, the system controller compares the voltage to the first threshold voltage, and if the voltage still exceeds the first threshold, it proceeds to stage 214, where the system controller 68 controls the relief valve 130 to reduce the valve opening size and increase the pressure in the pressure gallery 100. This also reduces the electrical power to the traction battery 64, since providing the higher pressure in the pressure gallery 100 and the dissipation of energy as heat through the relief valve 130 also consumes electrical power from the traction battery 64, which in turn reduces the electrical power to the traction battery 64 from the traction motors 62. Note that, in one example, steps 210 and 214 are performed sequentially as shown in the flow diagram, and controller 68 is configured to control valve 130 to reduce the valve opening size in response to the flow from pumps 82 and 84 reaching the predetermined threshold. Controller 68, therefore, controls pumps 82 and 84 to their flow threshold before controlling valve 130 to the pressure threshold. In another example, steps 210 and 214 are performed in different orders. For instance, controller 68 is further configured to increase the flow of pumps 82 and 84 if the flow falls below a predetermined flow threshold, while simultaneously controlling valve 130 to reduce the valve opening size and increase the pressure in pressure gallery 100 if the pressure falls below a predetermined pressure threshold to discharge battery 64. The flow of pumps 82 and 84 and the position of valve 130 can therefore be controlled simultaneously as long as both are below their respective thresholds. In another example, controller 68 is further configured to control valve 130 to reduce the valve opening size and increase the pressure in pressure gallery 100 until the pressure reaches a predetermined pressure threshold to discharge battery 64, and to increase the flow of pumps 82, 84 in response to the pressure in pressure gallery 100 reaching the predetermined pressure threshold to discharge battery 64. Controller 68, therefore, controls valve 130 to the pressure threshold before controlling pumps 82, 84 to the flow threshold. Controller 68 can control the flow of pumps 82 and 84 to be dependent on, or a function of, the voltage at motor controller 66 and the first threshold voltage. In one example, controller 68 controls the flow of pumps 82 and 84 to be proportional to the difference between the voltage at motor controller 66 and the first threshold voltage when the voltage is greater than the first threshold. As the voltage becomes increasingly greater than the first threshold, the flow output of pumps 82 and 84 increases accordingly, thereby consuming more electrical or braking power to attempt to bring the voltage at motor controller 66 back down to the first threshold. Controller 68 can control the size of the valve opening 130 to be dependent on, or a function of, the voltage at motor controller 66 and the first threshold voltage. In one example, controller 68 controls the size of the valve opening 130 to be proportional to the difference between the voltage at motor controller 66 and the first threshold when the voltage is greater than the first threshold. As the voltage becomes increasingly greater than the first threshold, the size of the valve opening 130 is reduced accordingly, thereby consuming more electrical or braking power to attempt to bring the voltage at motor controller 66 back down to the first threshold. Alternatively or additionally, steps 210 and 214 may be performed in response to the controller determining in step 206 that the temperature of traction battery 64 is outside a predetermined range and / or in response to the voltage of traction battery 64 being above a predetermined battery threshold. Note that, during steps 210 and 214, traction battery 64 may be charged by means of electrical power from motor controller 66 as long as the voltage at motor controller 66 is above the threshold voltage and the electric motor 62 is delivering braking torque to the extent that battery 64 is below a maximum state of charge. Furthermore, and for a hydraulic system 80 with more than one pump, the controller 68 can control the flow output of one or both of the pumps 82, 84.In one example, controller 68 is further configured to increase the flow from pumps 82, 84 by: closing the first pump valve 90 and opening the second pump valve 92 in response to the device speed being below a first speed, opening the first pump valve 90 and closing the second pump valve 92 in response to the device speed being above the first speed and below a second speed, closing the first and second pump valves 90, 92 so that the flow from the first and second pumps 82, 84 is directed to the pressure gallery 100 in response to the speed being above the second speed, and increasing the speed of the pump motor 86 if the first and second pump valves 90, 92 are open and if the speed is below a predetermined pump speed to discharge the battery 64. Therefore, the hydraulic system 80 operates in parallel with the traction motor control and the regenerative braking system. When the system controller 68 detects voltage or current above the first threshold, it initiates a discharge from the traction battery 64 using the battery-powered pump motor 86 to pump hydraulic fluid through the relief valve 130 at a high flow rate, proportional to the excess voltage or current measured by the controller 66. This creates a power draw or discharge from the traction battery 64, allowing the traction motors 62 and motor controllers 66 to continue generating braking torque and replace the current being discharged to the hydraulic system 80. The system controller 68 can apply proportional-integral (PI) feedback control loops to set the flow rate of pumps 82 and 84 and / or the opening position of valve 130. In one example, the feedback variable is the measured voltage of battery 64. The measured voltage is compared to the first threshold. A measured voltage of battery 64 above the first threshold results in an error equal to the measured voltage of battery 64 minus the voltage threshold. The feedback loop then uses this positive error to increase the flow rate of pumps 82 and 84 (e.g., pump motor speed and / or displacement 86) and / or the position of relief valve 130. The control feedback loop can use inputs including the drive speed of the lifting device 10 and the voltage of battery 64.The control feedback loop can provide control outputs that include: valve positions for pump valves 1 and 2 (90, 92), pump motor speed (86), and relief valve position (130). Pump valves 90, 92, and relief valve 130 can be controlled by controlling a current to a coil or solenoid associated with each valve. The lifting device 10, therefore, operates with two linked PI controls for flow and valve position. In the example shown, flow control is prioritized, with pressure control held fixed until flow is maximized. In other examples, pressure control may be prioritized, or the two controls may be implemented concurrently or simultaneously. As the difference between the voltage of battery 64 and the first threshold increases, controller 68 applies the control feedback loop to increase the speed and / or displacement of pump motor 86 using PI control so that pump motor 86 accelerates rapidly with the increasing voltage. This increase in speed and hydraulic flow proportionally increases the energy dissipated by relief valve 130. If the difference between the voltage of battery 64 and the first threshold drives the speed of pump motor 86 up to the flow threshold, controller 68 maintains the speed of pump motor 86 at the flow threshold and implements a second PI control loop that increases the pressure in the hydraulic system's pressure gallery 100 according to the voltage error, by controlling the size of the relief valve 130 opening.As the cross-sectional area of ​​relief valve 130 decreases, the pressure in pressure gallery 100 increases. The pressure can be increased up to a pressure threshold permitted by relief valve 130. The operation of the hydraulic system 80 in this way requires a discharge from the battery 64. This discharge compensates for the charge produced by the braking motors 62 during regenerative braking, so that, in effect, the braking power is converted into heat in the hydraulic fluid. Since the charging current is offset by the discharging current, the voltage of the battery 64 is brought back below the first threshold, allowing the motors 62 to continue braking until the maximum torque output of the traction motor is reached. Since only a portion of the braking power is dissipated in the hydraulic system 80 as needed to limit stress, the remaining braking power can be used to charge the battery 64. A similar control feedback loop can be applied by the system controller 68 to control excess current, or to limit the charging current based on a battery temperature 64, for example, for a cold lithium chemistry battery. In other examples, other feedback loops can be used to control the hydraulic system 80. In additional examples not part of the invention, the controller 68 can alternatively control the flow of pumps 82, 84 and / or the position of relief valve 130 to be dependent on or a function of a speed input from the lifting device 10. In one example, the system controller 68 implements a PI feedback loop that uses the difference between a speed commanded for the lifting device by joystick 50 and the actual speed. When the actual speed of the vehicle or lifting device exceeds the user-commanded speed, hydraulic power is increased by increasing the flow of hydraulic pumps 82, 84 and increasing the pressure in pressure gallery 100, either simultaneously or sequentially as described above. The amount of the hydraulic power increase is controlled by PI gains. If the voltage remains above the first threshold after steps 210 and 214, the method proceeds to step 216 and compares the voltage to a second threshold. The second threshold voltage is greater than the first threshold voltage, and in various non-limiting examples, it is 60 volts, or the same as the voltage limit, for example, 63 volts as described above. In stage 218, controller 68 is further configured to reduce the braking torque output of electric motor 62 in response to the voltage at motor controller 66 exceeding the second threshold voltage. System controller 68 can implement a voltage control feedback loop for motor controller 66 when the voltage exceeds the second threshold. For example, the feedback loop might input a battery voltage 64, determine an overvoltage number based on how much the battery voltage 64 exceeds the second threshold, and reduce the motor 62 output torque based on that overvoltage number. In stage 222, the controller is set to command the parking brake 70 to engage to stop the lifting device in response to the voltage in the motor controller 66 being above the second threshold value in stage 220 and if the speed of the lifting device 10 is increasing. Therefore, Method 200 determines a braking power output for the electric motor 62 to control the vehicle at a commanded speed based on an actual speed of the lifting device 10 and a load on the electric motors 62. Method 200 then increases a flow from pumps 82 and 84 and controls valve 130 to reduce the size of a valve opening in response to the braking power output exceeding a threshold. This dissipates the braking power output above the threshold in a hydraulic circuit 80 and charges the traction battery 64 with the remaining braking power output. The threshold may be associated with a traction battery 64 and / or the motor controller 66, and in one example is a voltage threshold or current threshold as described above. This disclosure, therefore, allows for varying both the flow of pumps 82 and 84 and the pressure of relief valve 130 to provide a wide range of discharge power to enable continuous regenerative braking near the electrical limits of the lifting device 10. Note that hydraulic power is a function of pressure and flow. Since both flow and pressure are controlled in the hydraulic system 80, hydraulic power can be controlled and set based on the power output of motor 62 and the voltage of motor controller 66 and / or the current of battery 64, regardless of vehicle speed 10 or grade. A portion of the braking power may still be charging the traction battery 64 for later use.

Claims

1. Lifting device (10) comprising: a chassis (12); a plurality of traction devices (14) for supporting the chassis (12) on an underlying surface; an electric motor (62) coupled by transmission to at least one of the plurality of traction devices (14); a motor controller (66) in electrical communication with the electric motor (62); a traction battery (64) in electrical communication with the electric motor (62) by means of the motor controller (66); and a hydraulic circuit (80) with a pump (82), a pressure gallery (100),a return line (102) and a valve (130) that controls the pressure in the pressure gallery (100) and seamlessly connects the pressure gallery (100) to the return line (102); a pump motor (86) connected by transmission to the pump (82) and in electrical communication with the traction battery (64); a user input (50) for controlling a speed of the hoisting device (10); and a controller (68) configured to, in response to a voltage being above a threshold voltage while the electric motor (62) is emitting a braking torque and supplying electrical power to the battery (64),increasing a pump flow (82) and controlling the valve (130) to reduce the valve opening size and / or increase the pressure in the pressure gallery (100), thereby reducing the electrical power to the traction battery (64); wherein the controller (68) is further configured to: i) increase the pump flow (82) if the flow is below a predetermined threshold, and control the valve (130) to reduce the valve opening size and increase the pressure in the pressure gallery (100) to discharge the battery (64) in response to the pump flow (82) reaching the predetermined threshold, ii) increase the pump flow (82) if the flow is below a predetermined flow threshold while controlling the valve (130) to reduce the valve opening size and increase the pressure in the pressure gallery (100) if the pressure is below a predetermined pressure threshold to discharge the battery (64),or iii) controlling the valve (130) to reduce the size of the valve opening and increase the pressure in the pressure gallery (100) until the pressure reaches a predetermined pressure threshold for discharging the battery (64), and increasing the flow of the pump (82) in response to the pressure in the pressure gallery (100) reaching the predetermined pressure threshold for discharging the battery (64).

2. Lifting device (10) of claim 1 further comprising a lifting mechanism (20) supporting a lifting platform (18) relative to the chassis (12); and wherein the hydraulic circuit (80) has an actuator (124) positioned to smoothly connect the pressure gallery (100) and the return line (102), the actuator (124) being coupled to the lifting mechanism (20).

3. Lifting device (10) of claim 1 further comprising a control lever communicating with the controller,providing the joystick with user input 50 to the lifting device (10) for speed control of the plurality of traction devices (14); wherein the controller (68) is further configured to command the electric motor (62) to emit braking torque in response to receiving a signal from the joystick to reduce the speed of the lifting device (10).

4. Lifting device (10) of claim 1, wherein the flow of the pump (82) is voltage-dependent and the threshold voltage-dependent; and wherein the controller (68) is further configured to control the flow of the pump (82) proportionally to a difference between the voltage at the motor controller (66) and the threshold voltage-dependent.

5. Lifting device (10) of claim 1, wherein the controller (68) is further configured to: i) control the size of the valve opening (130) voltage-dependent and the threshold voltage-dependent,or ii) controlling the size of the valve opening proportionally to a difference between the voltage at the motor controller (66) and the threshold voltage.

6. Lifting device (10) of claim 1, wherein the threshold voltage is a first threshold voltage; and wherein the controller (66) is further configured to reduce the braking torque output of the electric motor (62) in response to the voltage being above a second threshold voltage,the second threshold voltage being greater than the first threshold voltage.

7. Lifting device (10) of claim 6 further comprising a parking brake (70) associated with at least one of the plurality of traction devices (14); wherein the controller (68) is configured to command the parking brake (70) to engage to stop the lifting device (10) in response to the voltage being above the second threshold voltage and if the speed of the lifting device (10) is increasing.

8. Lifting device (10) of claim 1 further comprising an internal combustion engine (110) connected by transmission to the pump motor (86) by means of a one-way clutch (112); wherein the controller (68) is further configured to, in response to the voltage being above the threshold voltage,Controlling the pump motor speed (86) to be greater than the motor speed (110) when the motor (110) is running, and the electric motor (62) is emitting braking torque.

9. Lifting device (10) of claim 1, wherein the controller (68) is further configured to: i) in response to a traction battery (64) temperature being outside a predetermined range, limit the charging of the battery (64) by increasing the pump flow (82) and / or controlling the valve (130) to reduce the valve opening size, or ii) in response to a traction battery (64) voltage being above a predetermined battery threshold, limit the charging of the battery (64) by increasing the pump flow and / or controlling the valve (130) to reduce the valve opening size.

10. Lifting device (10) of claim 1,wherein the traction battery (64) is charged by means of electrical energy from the motor controller (66) while the voltage is above the threshold voltage and the electric motor (62) is emitting the braking torque.

11. Lifting device (10) of claim 1, wherein the hydraulic circuit (80) has a second pump (84), a first pump valve (90) fluidly connecting the first pump (82) to the pressure gallery (100), and a second pump valve (92) fluidly connecting the second pump (84) to the pressure gallery (100), wherein the pump motor (86) is connected by transmission to the second pump (84); and wherein the controller (68) is further configured to, in response to the voltage being above the threshold voltage while the electric motor (62) is emitting the braking torque and supplying electrical energy to the battery (64),11. The lifting device (10) of claim 11, wherein the controller (68) is further configured to increase the flow from at least one of the first pump (82) and the second pump (84) by: closing the first pump valve (90) and opening the second pump valve (92) in response to the speed being below a first speed, opening the first pump valve (90) and closing the second pump valve (92) in response to the speed being above the first speed and below a second speed, and closing the first and second pump valves (90, 92) so that the flow from the first and second pumps (82, 94) is increased by: closing the first pump valve (90) and closing the second pump valve (92) in response to the speed being above the first speed and below a second speed, and closing the first and second pump valves (90, 92) so that the flow from the first and second pumps (82, 94) is increased by:84) direct to the pressure gallery (100) in response to the speed being above the second speed, and increasing the pump motor (86) if the first and second pump valves (90, 92) are open and if the speed is below a predetermined pump speed to discharge the battery (64).

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