Transmission system with traction motor driven hydraulic circuit and its control method

Abstract

This invention relates to a transmission system with a traction motor-driven hydraulic circuit and a control method thereof. The transmission system includes a drive assembly with a clutch that transmits power from an input shaft to an output shaft at multiple gear ratios. While a controller controls the operation of the drive assembly and the traction motor, the traction motor drives the input shaft and propels a work vehicle. The hydraulic circuit, in response to commands from the controller, controls the actuation of the clutch. The hydraulic circuit includes: a hydraulic pump driven by the traction motor; an accumulator connected to the hydraulic pump and maintaining hydraulic fluid in the accumulator under pressure; and an unloading valve positioned in an auxiliary flow path extending from the outlet of the hydraulic pump to a reservoir. The unloading valve operates in a closed state to direct hydraulic fluid from the hydraulic pump to the accumulator, and operates in an open state to direct hydraulic fluid from the hydraulic pump to the reservoir.

Description

Technical Field

[0001] This disclosure generally relates to the transmission of a work vehicle, and more specifically, to a hydraulic circuit for controlling the actuation of a clutch in the transmission. Background Technology

[0002] In many types of work vehicles, conventional transmissions utilize hydraulic systems or circuits, specifically designed to control multiple torque-transmission devices, such as clutches and brakes. A hydraulic system may include a pump that supplies pressurized hydraulic fluid to multiple actuators, including valves and / or solenoids, which operate to direct the pressurized hydraulic fluid through a hydraulic fluid circuit to the clutches and brakes in the transmission. The hydraulic pump can be directly driven via an input shaft that rotates through the vehicle's engine, thus always rotating and generating a pressurized hydraulic fluid flow whenever the engine is running. Therefore, the hydraulic pump is able to deliver control pressure for the transmission during the operation of the work vehicle, allowing the clutches and brakes to engage or disengage to achieve different gear ratios. Summary of the Invention

[0003] A transmission system for a work vehicle is disclosed. The transmission system includes a transmission assembly having an input shaft, an output shaft, and a plurality of clutches operable to transmit power from the input shaft to the output shaft at multiple gear ratios. The transmission system further includes: a traction motor that drives the input shaft and operates a drive assembly to propel the work vehicle; a controller including a processor and memory architecture that controls the operation of the transmission assembly and the traction motor; and a hydraulic circuit configured to control the actuation of the plurality of clutches in response to commands from the controller. The hydraulic circuit sequentially includes: a hydraulic pump driven by a traction motor to draw hydraulic fluid from a reservoir and circulate it through the hydraulic circuit; an accumulator connected to the hydraulic pump via a high-pressure fluid path and configured to maintain the hydraulic fluid therein under pressure to actuate the plurality of clutches; and an unloading valve positioned in an auxiliary flow path extending from the outlet of the hydraulic pump to the reservoir. The unloading valve is operable in a closed state to direct the hydraulic fluid flow from the hydraulic pump to the high-pressure fluid path, and is operable in an open state to direct the hydraulic fluid flow from the hydraulic pump to the reservoir.

[0004] A controller implementation method for operating a transmission system of a work vehicle is disclosed. The method includes the following steps: providing a transmission assembly having an input shaft, an output shaft, and a plurality of clutches operable to transmit power from the input shaft to the output shaft at a plurality of gear ratios; and providing a traction motor configured to drive the input shaft of the transmission assembly and propel the work vehicle via a drive assembly of the work vehicle. The method further includes the following steps: operating the traction motor via the controller to drive a hydraulic pump, thereby drawing hydraulic fluid from a reservoir and circulating the hydraulic fluid through a hydraulic circuit; selectively charging an accumulator fluidly connected to the hydraulic pump via the controller using the hydraulic fluid to actuate the plurality of clutches; and operating an unloading valve via the controller, the unloading valve being positioned in an auxiliary flow path extending from the outlet of the hydraulic pump to the reservoir to guide the flow of hydraulic fluid from the hydraulic pump within the hydraulic circuit. The steps of operating the unloading valve are as follows: operating the unloading valve in the closed state to guide the hydraulic fluid flow from the hydraulic pump to the accumulator, and operating the unloading valve in the open state to guide the hydraulic fluid flow from the hydraulic pump directly to the reservoir.

[0005] Furthermore, a powertrain for a work vehicle is disclosed. This powertrain includes: a transmission having multiple clutches configured to selectively engage in multiple gears to operate the work vehicle; a traction motor providing power to drive the input side of the transmission and propel the work vehicle; and a controller provided to control the operation of the transmission. A hydraulic circuit operates the transmission and actuates the multiple clutches in the transmission, and the hydraulic circuit includes: a hydraulic pump driven by the traction motor to circulate hydraulic fluid in the hydraulic circuit from a reservoir along a high-pressure flow path; an accumulator connected to the high-pressure flow path and configured to maintain the hydraulic fluid therein under pressure to provide actuation of the multiple clutches when pressurized; and an unloading valve positioned in an auxiliary flow path extending from the outlet of the hydraulic pump to the reservoir. The unloading valve can operate in the closed state to direct the hydraulic fluid flow from the hydraulic pump to the high-pressure flow path, and can operate in the open state to direct the hydraulic fluid flow from the hydraulic pump to the reservoir.

[0006] Details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will become apparent from the description, the drawings, and the claims. Attached Figure Description

[0007] Figure 1It may include a side perspective view of an example work vehicle that may include a transmission system according to an embodiment;

[0008] Figure 2 yes Figure 1 A schematic diagram of the powertrain of the work vehicle, including the transmission system and associated hydraulic circuits;

[0009] Figure 3 This is a simplified schematic diagram of a hydraulic circuit; and

[0010] Figure 4 The example used for control Figure 3 The flowchart of the method for constructing a hydraulic circuit.

[0011] The same reference numerals in the various figures indicate the same elements. For simplicity and clarity, descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the exemplary and non-limiting embodiments of the invention described in the following detailed description. It should also be understood that, unless otherwise stated, features or elements appearing in the figures are not necessarily drawn to scale. Detailed Implementation

[0012] The following describes one or more exemplary embodiments of the disclosed drive system as illustrated in the accompanying drawings, which are briefly described above. Various modifications to the exemplary embodiments will be conceived by those skilled in the art without departing from the scope of the invention as set forth in the appended claims.

[0013] Overview

[0014] As previously mentioned, conventional transmissions typically utilize a hydraulic circuit with a pump driven from the input side of the transmission, and this hydraulic pump is directly connected to the vehicle's engine to generate a pressurized hydraulic fluid flow when the engine is running. Therefore, the hydraulic pump can deliver control pressure for the transmission, enabling the transmission to actuate its torque transmission components (including clutches and brakes).

[0015] The difference between an electro- or hydrostatic drive transmission and a conventional transmission is that the input side of the transmission is not always powered under normal conditions. Instead, in an electro- or hydrostatic drive transmission, the input side only rotates as the vehicle is in motion because the selective operation of the electric or hydrostatic motor driving the input side is coordinated with the operation used for vehicle movement. This means that a typical hydraulic circuit cannot be used because the hydraulic pump that generates control pressure in the circuit cannot generate flow during periods when the work vehicle is stationary. To solve this problem, a dedicated electric motor is typically used to drive a transmission control circuit pump that is separate from the main transmission. The advantage of this type of circuit is that it can be driven "on demand" and only, and therefore consumes power as needed. However, including and using a dedicated electric motor for driving the hydraulic pump on demand increases the cost and complexity of the circuit because additional electricity needs to be generated and / or converted to drive the pump and provide associated mechanical installations and connections.

[0016] To address the limitations and drawbacks of existing hydraulic circuits used in electro- and hydrostatic drive systems, this paper presents a drive system with a traction motor-driven hydraulic circuit, and an associated control method for this drive system. The pump in this hydraulic circuit is driven by a traction motor that also propels the vehicle's powertrain, thus eliminating the need for a separate dedicated electric motor to drive the pump. When powered by the traction motor, the pump circulates hydraulic fluid through the hydraulic circuit. An accumulator in the hydraulic circuit can be pressurized by the pump to maintain the hydraulic fluid in the accumulator under pressure, enabling the accumulator to supply pressurized hydraulic fluid to actuate the torque drive in the drive system when the work vehicle is not moving (or moving slowly) and the pump is not powered by the traction motor.

[0017] According to the implementation, the controller monitors the state of charge of the accumulator to maintain the control pressure in the hydraulic circuit and ensure that the hydraulic circuit can provide sufficient pressure for executing clutch shift events. Based on the accumulator's state of charge, the controller selectively operates the pump and associated unloading valve in the hydraulic circuit to recharge the accumulator as needed. When the controller determines that the accumulator's state of charge is not at a sufficient level, the controller causes the traction motor to drive the pump and operates the unloading valve in the closed state to direct the hydraulic fluid flow from the pump to the accumulator. When the controller determines that the accumulator's state of charge is at a sufficient level, the controller operates the unloading valve in the open state so that any hydraulic fluid flow from the pump returns directly to the low-pressure sump in the hydraulic circuit, thereby minimizing parasitic losses in the hydraulic circuit.

[0018] In some implementations, when the accumulator is not under sufficient pressure, the controller identifies the operating mode of the work vehicle and accordingly controls the traction motor and transmission to provide pressurization to the accumulator. Specifically, when the work vehicle is in a starting sequence, while the transmission is in neutral, the controller operates the traction motor and rotates the input side of the transmission to drive the hydraulic pump. This pumps hydraulic fluid through the hydraulic circuit and to the accumulator to provide pressurization. The operation of the traction motor and the neutral transmission are maintained until the accumulator is sufficiently pressurized. Conversely, when the work vehicle is in normal operating mode, the controller restricts the transmission to its current operating mode or gear. The traction motor drives the hydraulic pump to pump hydraulic fluid to the accumulator to repressurize it, and the transmission is restricted to its current operating mode until the accumulator has been sufficiently pressurized.

[0019] Therefore, a transmission system and its control method are provided, which allow a pump in a hydraulic circuit to be driven from the input side of the transmission via a traction motor and generate only high pressure, thereby consuming high power as needed.

[0020] Now, will be combined Figures 1 to 4 This document describes exemplary embodiments of work vehicles having a drive system with a hydraulic circuit driven by a traction motor and an associated control method for that drive system. As a non-limiting example, a drive system incorporated into a backhoe loader with an electro-hydraulic drive is described below. Although the following example is provided, this drive system can be incorporated into other types of work vehicles or machines, including hydraulic circuits for operating electro- or hydrostatic drive systems therein. Therefore, it should be understood that aspects of the invention are not intended to be limited to the specific embodiments described below. As will become apparent from the discussion herein, the drive system and associated control scheme can be advantageously used in a variety of contexts and with a variety of machines.

[0021] Example implementation of a work vehicle with a transmission system having a traction motor-driven hydraulic circuit

[0022] initial reference Figure 1The example work vehicle 10 of this disclosure is depicted as a backhoe loader. Although the work vehicle 10 is illustrated and described below as "backhoe loader 10", the work vehicle may include a motor grader, tractor, bulldozer, feller buncher, crawler, excavator, skidder, forwarder, or other utility vehicle. The backhoe loader 10 includes a chassis 12 and a ground engagement mechanism or ground drive component 14. The ground engagement mechanism 14 is capable of supporting the chassis 12 and advancing the chassis 12 across the ground. Although the illustrated backhoe loader 10 includes wheels as the ground engagement mechanism 14, the backhoe loader 10 may include other ground engagement mechanisms, such as steel tracks, rubber tracks, or other suitable ground engagement components.

[0023] The backhoe loader 10 also includes a loader assembly 16 and a backhoe assembly 22. For example... Figure 1 As illustrated, the loader assembly 16 includes a loader boom 18 and a work tool 20 in the form of a bucket. The work tool 20 is capable of moving, excavating, plowing, or performing other material handling functions on loads such as sludge or other materials. Other suitable work tools include, for example, shovels, forks, bale lifts, screw conveyors, harvesters, tillers, mowers, and grab buckets. The loader boom 18 is configured to move relative to the chassis 12 to move and operate the work tool 20. The backhoe assembly 22 of the backhoe loader 10 includes a backhoe boom 24 and a tool such as a backhoe bucket 26 having the features of a telehandler. The backhoe boom 24 is attached to the chassis 12 via a swing frame and is pivotable relative to the chassis 12. The backhoe bucket 26 can be pivotally mounted to the backhoe boom 24 and can extend from the backhoe boom 24 via an extendable bucket dipperstick, giving the backhoe bucket 26 further freedom of movement during operation.

[0024] The operator controls the functions of the backhoe loader 10, including the ground engagement mechanism 14, the loader assembly 16, and the backhoe assembly 22, from the operator's console 27 in the backhoe loader 10. Although Figure 1Although not shown, it should be understood that operator console 27 may include a human-machine interface (HMI) and various controls within that HMI, configured to receive input commands from the operator to, for example, control various electrical or hydraulic systems associated with the actuation and control of the loader assembly 16 and the backhoe assembly 22. The HMI can be configured in various ways and may include one or more joysticks, various switches or levers, one or more buttons, a touchscreen interface that may be overlaid on a display, a keyboard, a speaker, a microphone associated with a voice recognition system, or various other HMI devices.

[0025] The chassis 12 also supports the powertrain 28, which provides, generates, and distributes mechanical and electrical power to the various components of the backhoe loader 10. Now refer to... Figure 2 This describes various components that may be included in an example powertrain 28 on a backhoe loader 10. The powertrain 28 is generally characterized as including: a primary power source 30 and an associated power converter 32, and a drivetrain 33 including a traction motor 34 and a transmission assembly 36, along with associated control components described further below. In operation of the drivetrain 33, output power from the traction motor 34 can be provided to the input shaft 37 of the transmission assembly 36, and the transmission assembly 36 selectively transmits power from the input shaft 37 to the output shaft 38 of the transmission assembly at multiple gear ratios. The output shaft 38 provides power to the final drive unit 40 (drive shaft, gear reduction, etc.) and the ground engagement mechanism 14 to propel the backhoe loader 10.

[0026] In an example implementation, the powertrain 28 can be configured as a hybrid-electric powertrain or a battery-electric powertrain. In either configuration, the power source 30 of the powertrain 28 includes an energy storage device 42. The energy storage device 42 is configured as a high-voltage or high-power energy storage device and may be, for example, a battery, flywheel system, fuel cell, supercapacitor, or a combination of supercapacitor, fuel cell, and / or battery. The energy storage device 42 is configured to provide power for operating the traction motor 34 and also to receive energy during operation of the backhoe loader 10 for recharging.

[0027] like Figure 2As shown in the dashed diagram, power source 30 may further include an engine 44 configured to generate power for the backhoe loader 10 and to supply power to components and attachments on the backhoe loader. Engine 44 may be configured, for example, as a diesel engine or other internal combustion engine. In the case where power source 30 includes engine 44, a generator 45 (also shown in the dashed diagram) is additionally provided to convert the mechanical energy from engine 44 into electrical energy. Generator 45 may therefore include an alternator and rectifier combination (not shown) that generates an alternating current voltage from engine 44, and then rectifies the alternating current voltage to generate low DC voltage power, which is supplied to power source 30 for storage.

[0028] Power converter 32 receives power from energy storage device 42, such as via a DC bus. Power converter 32 can be configured as a traction boost converter, sometimes referred to as a bidirectional DC-DC converter or a bidirectional boost / buck converter. In motor-driven operation mode, power converter 32 receives a low DC voltage power input from energy storage device 42 and “boosts” that low DC voltage to generate a high DC voltage power output. The high DC voltage power output can then be regulated (e.g., reversed) by power converter 32 before being supplied to traction motor 34. In regenerative operation mode, power converter 32 receives the high DC voltage power generated from traction motor 34 during operation and “bucks” that high DC voltage to a low DC voltage power output, which is then provided back to energy storage device 42.

[0029] The traction motor 34 can be configured to convert electrical energy into mechanical energy (“motor drive mode”) or mechanical energy into electrical energy (“regenerative mode”). In motor drive mode, the traction motor 34 can operate to receive electrical energy from the power converter 32 and convert it into mechanical energy to drive the input of the drivetrain 36 and power the final drive unit 40 and the ground engagement mechanism 14. In regenerative mode, the traction motor 34 can operate to convert mechanical energy back into electrical energy to supply electrical energy back to the power converter 32, thereby braking (i.e., slowing down) the rotational speed of the traction motor 34 and thus braking the speed of the backhoe loader 10. According to embodiments, the traction motor 34 can take the form of a permanent magnet AC motor, a DC motor, or another suitable motor, such as a switched reluctance motor or an induction motor (which can operate at variable speed).

[0030] Although the power converter 32 and traction motor 34 are described above as a DC-DC converter and a motor, they can alternatively take the form of a hydrostatic press that receives mechanical input power (e.g., from engine 44, where the energy storage device 42 and generator have been removed from power source 30) and converts that power into hydraulic power to drive input shaft 37. Therefore, according to an embodiment, the power converter 32 and traction motor 34 can be configured as a hydraulic pump and a hydraulic motor that provide power to output shaft 38.

[0031] Still refer to Figure 2 The transmission assembly 36 can be configured as an electro- or hydrostatically driven transmission, which includes various selectable transmission components, including a clutch 46 with appropriate configurations (wet clutch, dry clutch, dog collar clutch, etc.) and a brake 48 (such as...). Figure 2 (shown), and synchronizers (not shown) or other similar devices. Clutch 46 and brake 48 may have engaged and disengaged positions, selectively transmitting power between the power input and power output sides of the transmission assembly 36 or preventing power transmission. Furthermore, in some implementations, the transmission assembly 36 may be configured as an infinitely variable transmission (IVT) or a continuously variable transmission (CVT), which selectively allows power from multiple types of power sources to be supplied to the output shaft 38 and to the final drive unit 40 and the ground engagement mechanism 14. In this embodiment, the arrangement of the clutches 46 and brakes 48 in the transmission assembly 36, along with the additional gear sets and shafts (not shown), enables the IVT / CVT to supply power to the output shaft 38 in multiple combinations, allowing the transmission assembly 36 to operate, for example, in direct drive mode, split path mode, and series operation mode.

[0032] The transmission assembly 36 includes a plurality of actuators 50 for switching the clutch 46 and brake 48 between an engaged and disengaged position. The actuators 50 may be configured, for example, as electro-hydraulically controlled proportional valves and operated via a hydraulic circuit 52 to actuate the clutch 46 and brake 48. The hydraulic circuit 52 may be configured as a closed-loop hydrostatic system that operates via a pressurized hydraulic fluid (i.e., hydraulic oil) flow to provide control of the actuators 50 for engaging and disengaging the clutch 46 and brake 48 according to desired operation.

[0033] The powertrain 28 also includes a controller 54 that can electrically (or otherwise) communicate with various devices of the backhoe loader 10 to control various aspects of the backhoe loader's operation. Specifically, the controller 54 can communicate with the hydraulic circuit 52 and the traction motor 34 to generally control the operation of the drivetrain 36 and the powertrain 28. The controller 54 can be configured as a computing device with one or more associated processors 54a and memory architectures 54b, and can be configured as a hydraulic, electrical, or electro-hydraulic controller, or others. Similarly, the controller 54 can be configured to perform various computational and control functions relating to the hydraulic circuit 52 and the traction motor 34, and can be electronically or hydraulically connected to those systems / devices. In various embodiments, the controller 54 can communicate with actuators, sensors, valves, and other devices associated with the hydraulic circuit 52 and the traction motor 34.

[0034] Now refer to Figure 3 The hydraulic circuit 52 of the powertrain is illustrated in further detail. The hydraulic circuit 52 typically includes a pump 56, an accumulator 58, a reservoir 60, and an actuator 50 for operating a clutch 46. The hydraulic circuit 52 is operable to selectively engage the clutch 46 by selectively communicating hydraulic fluid from the reservoir 60 to the actuator 50, which, in this illustrated embodiment, is an electro-hydraulic proportional valve operable to engage the plurality of clutches 46. Hydraulic fluid is communicated under pressure from the reservoir 60 to the actuator 50 via the operation of the pump 56 and the accumulator 58.

[0035] The sump 60 is a tank or reservoir into which hydraulic fluid returns from the various components and areas of the transmission assembly 36 and is collected. For example... Figure 3As shown, hydraulic fluid flows from reservoir 60 via pump 56, which is driven by traction motor 34 of powertrain 28. Pump 56 can be a stationary positive displacement pump that generates a pressurized hydraulic fluid flow, such as a gear pump, vane pump, or cycloidal pump. Pump 56 includes inlet 62 and outlet 64. Inlet 62 communicates with reservoir 60 via suction passage 66. Outlet 64 connects the pressurized hydraulic fluid to high-pressure flow path 68. High-pressure flow path 68 may include various optional features, such as a pressure-side filter 70 and a filter bypass 72.

[0036] High-pressure flow path 68 is connected to accumulator 58 and positions check valve 74 on high-pressure flow path 68. Check valve 74 can be opened by hydraulic pressure from pump 56 and locked in the opposite direction. Accumulator 58 is an energy storage device in which incompressible hydraulic fluid is maintained under pressure by an external source. Although Figure 3 Not shown, but it should be understood that accumulator 58 may include a piston having a seal that slides along the bore of the accumulator housing. Hydraulic fluid is present on one side of the piston, while one or more springs or pressurized gases (e.g., nitrogen) are present on the other side. Accumulator 58 uses the springs or pressurized gas to generate a force on one side of the piston, which reacts with the hydraulic fluid pressure on the opposite side of the piston. When accumulator 58 is pressurized with hydraulic fluid and at a pressure higher than that of high-pressure flow path 68, it supplies pressurized hydraulic fluid to actuator 50 to actuate clutch 46. Return line 76 (discharge line) is then led from actuator 50 back to reservoir 60 to allow hydraulic fluid to return to reservoir 60 at low pressure.

[0037] The hydraulic circuit 52 also includes an unloading valve 78 positioned along an auxiliary flow path 80 between the outlet 64 of the pump 56 and the reservoir 60. The unloading valve 78 may be an electro-hydraulic control valve (i.e., an "EH (electro-hydraulically) unloading valve") that is selectively opened and closed to allow and prevent hydraulic fluid from being pumped into the reservoir 60. When the unloading valve 78 is in the open position, the hydraulic fluid flow from the pump 56 is directly discharged into the reservoir 60 through the auxiliary flow path 80. When the unloading valve 78 is in the closed position, the hydraulic fluid flow from the pump 56 is directed into the high-pressure flow path 68 and subsequently into the accumulator 58.

[0038] Controller 54 is operationally connected to and operates in conjunction with hydraulic circuit 52 to control the flow of hydraulic fluid through the system. Controller 54 receives operating data about powertrain 28 to selectively control the operation of components within that powertrain, including clutch 46, unloading valve 78, accumulator 58, and traction motor 34. Controller 54 receives input from one or more sensors in hydraulic circuit 52 in the form of operator commands and operating data, and Figure 3 An accumulator load sensor 82 (e.g., a linear position sensor) is shown to sense the load state of the accumulator 58, as well as a pressure sensor 84 and a temperature sensor 86 to read the pressure and temperature of the hydraulic fluid in the system, and these sensors provide this data to the controller 54 in real time. An additional sensor 88 can monitor the operation of the traction motor 34 and provide this data to the controller 54.

[0039] Via controller 54, pump 56 in hydraulic circuit 52 can be selectively driven by traction motor 34 to generate high pressure only as needed, or when the backhoe loader 10 is not moving or moving slowly and pump 56 cannot generate the required flow, high pressure is generated when accumulator 58 is used to provide the flow pressure of hydraulic fluid. Controller 54 monitors the load pressure status of accumulator 58 and controls unloading valve 78 to either return pump flow directly to reservoir 60 or direct pump flow to repressurize accumulator 58 to maintain control pressure and sufficient margin in hydraulic circuit 52.

[0040] Still referencing Figure 4 And continue to refer to Figure 2 and Figure 3 The flowchart illustrates a method or control scheme 90 implemented by controller 54 according to this disclosure. Typically, method 90 is implemented at startup and during typical operation of the backhoe loader 10 (e.g., during forward and reverse propulsion) to enable the vehicle to shift gears between different gears.

[0041] The method begins at step 92: determining the accumulator load state required to perform the desired operation in hydraulic circuit 52. As an example, controller 54 may calculate the accumulator load state required to actuate one or more clutches 46 of transmission assembly 36 to allow the backhoe loader 10 to shift gears. According to embodiments, the load state required to perform the desired operation in hydraulic circuit 52 can be based on a variable or value of the requested operation to be performed, i.e., the load state required to perform a specific operation such as gear shifting, or alternatively, it can be a constant fixed amount or value independent of the specific requested operation. Therefore, according to embodiments, the load state required to perform the desired operation in hydraulic circuit 52 can be set as a load threshold, which can be a fixed threshold or a threshold that changes based on the requested operation to be performed.

[0042] When calculating the required accumulator load state, at step 94, it is determined whether the current accumulator load state is sufficient to meet the requirement, i.e., whether the load state meets the calculated load threshold. This determination can be made by the controller 54 based at least on the accumulator load reading obtained by the sensor 82. If it is determined at step 94 that the accumulator load state is sufficient to meet the determined requirement, method 90 continues to step 96 and actuates the unloading valve 78 to the open state. With the unloading valve 78 in the open state, the pump 56 operates in a low-power, low-pressure state, and the output flow from the pump 56 is returned directly to the reservoir 60, thereby minimizing parasitic losses in the hydraulic circuit 52. Therefore, with the accumulator load state sufficient to meet the desired operational requirements and with the unloading valve 78 in the open state, at step 98, normal operation of the backhoe loader 10 is allowed to proceed unimpeded, and shifting between different gears / operating modes via the use of the transmission assembly 36 is not restricted.

[0043] If it is determined at step 94 that the accumulator load condition is insufficient to meet the determined demand, method 90 proceeds to step 100, where the current state of the backhoe loader 10 is subsequently determined. Specifically, at step 100, it is determined whether the backhoe loader 10 is currently in a startup sequence in which the traction motor 34 will not generate sufficient power to drive the pump 56 to generate the high-pressure flow required to pressurize the accumulator 58 and / or operate the drivetrain 36. If it is determined at step 100 that the backhoe loader 10 is currently in a startup sequence, method 90 continues to step 102, where the unloading valve 78 is actuated to a closed state. With the unloading valve 78 closed, method 90 proceeds to steps 104 and 106, where the drivetrain 36 operates (and remains) in neutral mode, and the traction motor 34 is operated at the desired speed (i.e., the input side of the drivetrain 36 is rotated). With the drivetrain 36 in neutral mode, the operation of the traction motor 34 at the desired speed allows it to drive the pump 56, thereby generating a high-pressure hydraulic fluid flow that is directed to the high-pressure flow path 68 and then to the accumulator 58, without any actuation of the clutch 46 in the drivetrain 36 and / or power supplied from the traction motor 34 to the output shaft 38 of the drivetrain 36. In this way, hydraulic fluid is supplied to the accumulator 58, increasing the load on the accumulator 58.

[0044] Then, at step 108, based on the operation of the traction motor 34 at the desired speed, another determination is made regarding whether the accumulator load condition is now sufficient to meet the determined demand. If the accumulator load condition is still insufficient, method 90 returns to steps 104 and 106, wherein the drive assembly 36 is kept in neutral and the traction motor 34 continues to operate the pump 56 to generate hydraulic fluid flow. When it is determined at step 108 that the accumulator load condition is sufficient to meet the determined demand, then, at step 110, method 90 proceeds to actuate the unloading valve 78 to the open state. With the unloading valve 78 in the open state, the pump 56 operates in a low-power, low-pressure mode, and the output flow from the pump 56 is returned directly to the reservoir 60, thereby minimizing parasitic losses within the hydraulic circuit 52. Therefore, when the accumulator load is sufficient to meet the requirements of the desired operation and the unloading valve 78 is in the open state, at step 112, the normal operation of the backhoe loader 10 is allowed to proceed without hindrance, and there is no restriction on shifting between different gears / operating modes via the use of the transmission assembly 36.

[0045] Returning to step 100 and determining the current state of the backhoe loader 10, if it is determined at step 100 that the backhoe loader 10 is not currently in a startup sequence but in a normal operating mode (e.g., normal forward propulsion mode), then method 90 continues to step 114, and the unloading valve 78 is actuated to its closed state. With the unloading valve 78 actuated to its closed state, a high-pressure output flow is generated by pump 56 and directed to high-pressure flow path 68 and then to accumulator 58. If the backhoe loader 10 is in normal operating mode but the accumulator 58 is not under sufficient load pressure, the operating pump 56 operates to pressurize the accumulator 58. Simultaneously, method 90 proceeds to step 116, where the transmission assembly 36 is maintained in its current gear, and during this time, no actuation of clutch 46 is permitted. In this way, hydraulic fluid is supplied to the accumulator 58, and the load pressure of the accumulator 58 is increased.

[0046] With the backhoe loader 10 maintained in its current gear, method 90 continues to step 118, where another determination is made as to whether the accumulator load pressure is sufficient to meet the desired operation (e.g., gear shifting) of the drivetrain 36.

[0047] If the accumulator load is still insufficient, the method returns to step 116, where the drive assembly 36 is maintained in its current gear, and the traction motor 34 continues to operate the pump 56 to generate a high-pressure hydraulic fluid flow. When it is determined at step 118 that the accumulator load is sufficient to meet the determined requirements, method 90 then proceeds to step 120 to actuate the unloading valve 78 to the open state. With the unloading valve 78 in the open state, the pump 56 operates in a low-power, low-pressure mode, and the output flow from the pump 56 is returned directly to the reservoir 60, thereby minimizing parasitic losses within the hydraulic circuit 52. Therefore, with the accumulator load sufficient to meet the desired operational requirements and with the unloading valve 78 in the open state, at step 122, normal operation of the backhoe loader 10 is allowed to proceed unimpeded, and shifting between different gears / operating modes via the use of the drive assembly 36 is not restricted.

[0048] Upon completion of any of steps 98, 112, or 122, method 90 returns to step 92 and continues to monitor the accumulator load condition and its suitability for the desired operation of the drive assembly 36, wherein additional iterations of method 90 are performed to allow the accumulator 58 to operate under the required load condition.

[0049] Therefore, this hydraulic circuit 52 provides an efficient method for actuating the clutch 46 in the drivetrain 36 using power derived solely from the traction motor 34 of the backhoe loader 10. A method or control scheme 90 is implemented in which the pump 56 (driven by the traction motor 34) selectively operates in a high-pressure mode to pressurize the hydraulic circuit 52 and the accumulator 58, and in a low-pressure mode in which hydraulic fluid is pumped directly into the reservoir 60, while the accumulator 58 provides the pressurized hydraulic fluid flow required to operate the clutch 46. These aspects of the hydraulic circuit 52 eliminate the need for a separate dedicated electric motor, which would be used to drive the pump 56 of the hydraulic circuit 52 in an electro- or hydrostatically driven transmission.

[0050] Listed examples

[0051] The following examples are provided and numbered for easy reference.

[0052] 1. A transmission system for a work vehicle, the transmission system comprising: a transmission assembly having an input shaft, an output shaft, and a plurality of clutches operable to transmit power from the input shaft to the output shaft at a plurality of gear ratios. The transmission system further comprises: a traction motor driving the input shaft and operating a drive assembly to propel the work vehicle; a controller including a processor and a memory architecture, the controller controlling the operation of the transmission assembly and the traction motor; and a hydraulic circuit configured to control the actuation of the plurality of clutches in response to a command from the controller. The hydraulic circuit sequentially comprises: a hydraulic pump driven by the traction motor to draw hydraulic fluid from a reservoir and circulate the hydraulic fluid through the hydraulic circuit; an accumulator connected to the hydraulic pump via a high-pressure flow path and configured to maintain the hydraulic fluid therein under pressure to provide actuation of the plurality of clutches; and an unloading valve positioned in an auxiliary flow path extending from the outlet of the hydraulic pump to the reservoir. The unloading valve can operate in the closed state to direct the hydraulic fluid flow from the hydraulic pump to the high-pressure flow path, and can operate in the open state to direct the hydraulic fluid flow from the hydraulic pump to the reservoir.

[0053] 2. The drive system according to Example 1, wherein the controller is programmed to determine the load state of the accumulator; and to selectively operate the unloading valve based on the load state of the accumulator.

[0054] 3. According to the drive system of Example 2, wherein, in determining the load state of the accumulator, the controller is programmed to: identify the required load state of the accumulator needed to perform a requested operation of the drive assembly; and determine whether the current load state of the accumulator satisfies the required load state.

[0055] 4. According to the transmission system of Example 3, wherein when the current load pressure state meets the required load pressure state, the controller is programmed to operate the unloading valve in the open state so that hydraulic fluid is pumped directly from the hydraulic pump to the reservoir.

[0056] 5. The transmission system according to Example 4, wherein when the current load condition satisfies the required load condition, the controller is programmed to allow the plurality of clutches to be actuated to drive the output shaft at any of the plurality of gear ratios.

[0057] 6. According to the transmission system of Example 3, wherein when the current load pressure state does not meet the required load pressure state, the controller is programmed to operate the unloading valve in the closed state to pump hydraulic fluid from the hydraulic pump to the high-pressure flow path and to pressurize the accumulator.

[0058] 7. The transmission system according to Example 6, wherein when the unloading valve is operated in the closed state, the controller is programmed to determine the current operating state of the work vehicle, the current operating state including one of a start-up sequence and a normal operating mode.

[0059] 8. The transmission system according to Example 7, wherein when the work vehicle is in the starting sequence, the controller is programmed to operate the transmission assembly in neutral; operate the traction motor to drive the hydraulic pump, thereby pumping hydraulic fluid from the hydraulic pump to the high-pressure flow path and pressurizing the accumulator; and maintain the operation of the transmission assembly in neutral and maintain the operation of the traction motor to drive the hydraulic pump until the accumulator has been pressurized to such that the current load pressure state meets the required load pressure state.

[0060] 9. The transmission system according to Example 7, wherein when the work vehicle is in the normal operating mode, the controller is programmed to prevent the actuation of the plurality of clutches to restrict the operation of the transmission assembly to the current operating mode of the transmission assembly, and the traction motor drives the hydraulic pump to pump hydraulic fluid from the hydraulic pump to the high-pressure flow path and to pressurize the accumulator; and to maintain the operation of the transmission assembly in the current operating mode of the transmission assembly until the accumulator has been pressurized to such that the current load pressure state meets the required load pressure state.

[0061] 10. The transmission system according to Example 3, wherein the demand load state for performing the requested operation of the transmission assembly includes: a clutch pressure sufficient to actuate one or more of the plurality of clutches during a shift event.

[0062] 11. A controller implementation method for a transmission system for operating a work vehicle, the method comprising the steps of: providing a transmission assembly having an input shaft, an output shaft, and a plurality of clutches operable to transmit power from the input shaft to the output shaft at a plurality of gear ratios; and providing a traction motor configured to drive the input shaft of the transmission assembly and to propel the work vehicle via a drive assembly of the work vehicle. The method further comprises the steps of: operating the traction motor via the controller to drive a hydraulic pump, thereby drawing hydraulic fluid from a reservoir and circulating the hydraulic fluid through a hydraulic circuit; selectively pressurizing an accumulator fluidly connected to the hydraulic pump via the controller to actuate the plurality of clutches; and operating an unloading valve via the controller, the unloading valve being positioned in an auxiliary flow path extending from the outlet of the hydraulic pump to the reservoir to guide a flow of hydraulic fluid from the hydraulic pump within the hydraulic circuit. The steps of operating the unloading valve are as follows: operating the unloading valve in the closed state to guide the hydraulic fluid flow from the hydraulic pump to the accumulator, and operating the unloading valve in the open state to directly guide the hydraulic fluid flow from the hydraulic pump to the reservoir.

[0063] 12. According to the method of Example 11, the method further includes the steps of: identifying the load state of the accumulator via the controller; and selectively operating the unloading valve via the controller based on whether the load state of the accumulator meets a threshold load level, wherein the unloading valve is operated in a closed state when the load state does not meet the threshold load level, and in an open state when the load state meets the threshold load level.

[0064] 13. The method according to Example 12, wherein when the unloading valve is operated in the closed state, the method further includes the step of: determining the current operating state of the work vehicle via the controller, the current operating state including one of a start-up sequence and a normal operating mode.

[0065] 14. The method according to Example 13, wherein when the work vehicle is in the starting sequence, the method further comprises the steps of: operating the transmission assembly in neutral; operating the traction motor to drive the hydraulic pump, thereby pumping hydraulic fluid from the hydraulic pump to pressurize the accumulator; and maintaining the operation of the transmission assembly in neutral and maintaining the operation of the traction motor to drive the hydraulic pump until the accumulator has been pressurized to such that the load pressure state meets the threshold load pressure level.

[0066] 15. The method according to Example 13, wherein when the work vehicle is in the normal operating mode, the method further comprises the steps of: preventing actuation of the plurality of clutches to restrict the operation of the transmission assembly to the current operating mode of the transmission assembly, wherein the traction motor drives the hydraulic pump to pump hydraulic fluid from the hydraulic pump to pressurize the accumulator; and maintaining the operation of the transmission assembly in the current operating mode of the transmission assembly until the accumulator has been pressurized to such that the load pressure state meets the threshold load pressure level.

[0067] in conclusion

[0068] Therefore, the foregoing provides a transmission system for a work vehicle, characterized by: a transmission assembly having an input shaft, an output shaft, and multiple clutches operable to transmit power from the input shaft to the output shaft at multiple gear ratios; a traction motor driving the input shaft and operating a drive assembly to propel the work vehicle; and a controller controlling the operation of the transmission assembly and the traction motor. A hydraulic circuit, responding to commands from the controller, controls the actuation of the multiple clutches, wherein the hydraulic circuit includes a hydraulic pump driven by the traction motor to draw hydraulic fluid from a reservoir and circulate the hydraulic fluid through the hydraulic circuit; an accumulator connected to the hydraulic pump via a high-pressure flow path and configured to maintain the hydraulic fluid in the accumulator under pressure to provide actuation of the multiple clutches; and an unloading valve positioned in an auxiliary flow path extending from the outlet of the hydraulic pump to the reservoir. The unloading valve can operate in the closed state to direct the hydraulic fluid flow from the hydraulic pump to the high-pressure flow path, and can operate in the open state to direct the hydraulic fluid flow from the hydraulic pump to the reservoir.

[0069] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, unless the context clearly indicates otherwise, the singular form of the description is intended to include the plural form. It should also be understood that the terms "comprise" and / or "comprising" in any use in this specification specify the presence of a defined feature, element, step, operation, element, and / or component, and do not exclude the presence or addition of one or more other features, elements, steps, operations, elements, components, and / or combinations thereof.

[0070] The description of this disclosure has been presented for purposes of illustration and description, but is not intended to be exclusive or to limit the disclosure to its disclosed form. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of this disclosure. The embodiments expressly referenced herein were chosen and described in order to best explain the principles of this disclosure and its practical application, and to enable those skilled in the art to understand this disclosure and recognize many alternatives, modifications, and variations to the described examples. Therefore, various other implementations are within the scope of the appended claims.

Claims

1. A drivetrain (33) for a work vehicle (10), the drivetrain (33) comprising: a transmission assembly (36) having an input shaft (37), an output shaft (38), and a plurality of clutches (46) operable to transmit power from the input shaft (37) to the output shaft (38) at a plurality of drive ratios; a traction motor (34) driving the input shaft (37) and operating a drive assembly (40) to propel the work vehicle (10); a controller (54) including a processor (54a) and a memory architecture (54b), the controller (54) controlling operation of the transmission assembly (36) and the traction motor (34); and a hydraulic circuit (52) configured to control actuation of the plurality of clutches (46) in response to commands from the controller (54), the hydraulic circuit (52) including: a hydraulic pump (56) driven by the traction motor (34) to draw hydraulic fluid from a sump (60) and circulate the hydraulic fluid through the hydraulic circuit (52); an accumulator (58) connected to the hydraulic pump (56) via a high pressure flow path (68), and the accumulator configured to maintain hydraulic fluid in the accumulator at a pressure to provide actuation of the plurality of clutches (46); and a relief valve (78) positioned in an auxiliary flow path (80) extending from an outlet (64) of the hydraulic pump (56) to the sump (60); wherein the relief valve (78) is operable in a closed state to direct hydraulic fluid flow from the hydraulic pump (56) to the high pressure flow path (68), and in an open state to direct hydraulic fluid flow from the hydraulic pump (56) to the sump (60), wherein the controller (54) is programmed to: determine a state of charge of the accumulator (58); and selectively operate the relief valve (78) based on the state of charge of the accumulator (58), wherein in determining the state of charge of the accumulator (58), the controller (54) is programmed to: identify a required state of charge of the accumulator (58) needed to perform a requested operation of the transmission assembly (36); and determine whether a current state of charge of the accumulator (58) satisfies the required state of charge.

2. The transmission system (33) according to claim 1, wherein, when the current state of charge satisfies the required state of charge, the controller (54) is programmed to operate the relief valve (78) in an open state to pump hydraulic fluid directly from the hydraulic pump (56) to the sump (60).

3. The transmission system (33) according to claim 2, wherein, when the current state of charge satisfies the required state of charge, the controller (54) is programmed to allow actuation of the plurality of clutches (46) to drive the output shaft (38) at any of the plurality of drive ratios.

4. The transmission system (33) according to claim 1, wherein, when the current charge pressure condition does not satisfy the demand charge pressure condition, the controller (54) is programmed to operate the unloading valve (78) in a closed condition to pump hydraulic fluid from the hydraulic pump (56) to the high pressure flow path (68) and to charge the accumulator (58).

5. The transmission system (33) according to claim 4, wherein, when operating the unloading valve (78) in the closed condition, the controller (54) is programmed to determine a current operating condition of the work vehicle (10), the current operating condition including one of a start-up sequence and a normal operating mode.

6. The transmission system (33) according to claim 5, wherein, when the work vehicle (10) is in the start-up sequence, the controller (54) is programmed to: operate the transmission assembly (36) in neutral; operate the traction motor (34) to drive the hydraulic pump (56) to pump hydraulic fluid from the hydraulic pump (56) to the high pressure flow path (68) and to charge the accumulator (58); and maintain operation of the transmission assembly (36) in neutral and maintain operation of the traction motor (34) to drive the hydraulic pump (56) until the accumulator (58) has been charged such that the current charge pressure condition satisfies the demand charge pressure condition.

7. The transmission system (33) according to claim 5, wherein, when the work vehicle (10) is in the normal operating mode, the controller (54) is programmed to: prevent actuation of the plurality of clutches (46) to limit operation of the transmission assembly (36) to a current operating mode of the transmission assembly and the traction motor (34) drives the hydraulic pump (56) to pump hydraulic fluid from the hydraulic pump (56) to the high pressure flow path (68) and to charge the accumulator (58); and maintain operation of the transmission assembly (36) in the current operating mode of the transmission assembly until the accumulator (58) has been charged such that the current charge pressure condition satisfies the demand charge pressure condition.

8. The transmission system (33) according to claim 1, wherein, the demand charge pressure condition for performing a requested operation of the transmission assembly (36) includes a clutch pressure sufficient to actuate one or more of the plurality of clutches (46) during a shift event.

9. A controller-implemented method (90) for operating a drivetrain (33) of a work vehicle (10), the method (90) comprising the steps of: providing a transmission assembly (36) having an input shaft (37), an output shaft (38), and a plurality of clutches (46) operable to transmit power from the input shaft (37) to the output shaft (38) at a plurality of gear ratios; providing a traction motor (34) configured to drive the input shaft (37) of the transmission assembly (36) and propel the work vehicle (10) via a drive assembly (40) of the work vehicle (10); operating the traction motor (34) via a controller (54) to drive a hydraulic pump (56) to draw hydraulic fluid from a reservoir (60) and circulate the hydraulic fluid through a hydraulic circuit (52); selectively pressurizing, via the controller (54), an accumulator (58) fluidly coupled to the hydraulic pump (56) with the hydraulic fluid to provide actuation of the plurality of clutches (46); and operating, via the controller (54), a unloader valve (78) positioned in an auxiliary flow path (80) extending from an outlet (64) of the hydraulic pump (56) to the sump (60) to direct hydraulic fluid flow from the hydraulic pump (56) within the hydraulic circuit (52); wherein operating the unloader valve (78) includes: operating the unloader valve (78) in a closed state to direct hydraulic fluid flow from the hydraulic pump (56) to the accumulator (58); and operating the unloader valve (78) in an open state to direct hydraulic fluid flow from the hydraulic pump (56) directly to the sump (60), the method (90) further including the steps of: identifying, via the controller (54), a required pressurization state of the accumulator (58) needed to perform a requested operation of the driveline assembly (36); determining, via the controller (54), whether the pressurization state of the accumulator (58) satisfies the required pressurization state; and selectively operating, via the controller (54), the unloader valve (78) based on whether the pressurization state of the accumulator (58) satisfies the required pressurization state, wherein the unloader valve (78) is operated in the closed state when the pressurization state does not satisfy the required pressurization state and the unloader valve (78) is operated in the open state when the pressurization state satisfies the required pressurization state.

10. The method (90) of claim 9, wherein, when operating the unloader valve (78) in the closed state, the method (90) further including the step of determining, via the controller (54), a current operating state of the work vehicle (10), the current operating state including one of a start-up sequence and a normal operating mode.

11. The method (90) of claim 10, wherein, when the work vehicle (10) is in the start-up sequence, the method (90) further including the steps of: operating the driveline assembly (36) in neutral; operating the traction motor (34) to drive the hydraulic pump (56) to pump hydraulic fluid from the hydraulic pump (56) to pressurize the accumulator (58); and maintaining operation of the driveline assembly (36) in neutral and maintaining operation of the traction motor (34) to drive the hydraulic pump (56) until the accumulator (58) has been pressurized such that the pressurization state satisfies the required pressurization state.

12. The method (90) of claim 10, wherein, when the work vehicle (10) is in the normal operating mode, the method further including the steps of: preventing actuation of the plurality of clutches (46) to limit operation of the driveline assembly (36) to a current operating mode of the driveline assembly, wherein the traction motor (34) drives the hydraulic pump (56) to pump hydraulic fluid from the hydraulic pump (56) to pressurize the accumulator (58); and maintaining operation of the transmission assembly (36) in a current mode of operation of the transmission assembly until the accumulator (58) has been pressurized such that the charge state satisfies the demand charge state.

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