Patent Grant
9217505
The present subject matter relates generally to continuously variable transmissions (CVTs) utilized within work vehicles and, more particularly, to a system and method for enhancing the operation of a work vehicle CVT.
Transmissions with hydraulically operated clutches (e.g., continuously variable transmissions (CVTs)) are well known in the art. When operating such transmissions, it is important to accurately control clutch engagement in order to provide the desired vehicle performance. However, due to tolerances within the clutch valve and errors associated with the controller's ability to command the correct current, the pressure needed to move the clutch's actuator (e.g., a hydraulically actuated piston) to the point at which the clutch plates touch and the clutch begins to transmit torque can vary significantly. As a result, it is often necessary to calibrate transmission clutches to ensure that the proper clutch pressures are being supplied for engaging each clutch.
When performing a clutch calibration, the accuracy of the calibration process may often be impacted by imperfections, inconsistencies and/or other mechanical and relates issues within the transmission. For example, air bubbles/pockets trapped within the hydraulic system can cause a clutch to calibrate to a different current value than the value that will be required once the trapped air has been removed. Similarly, mechanical issues, such as friction between one or more of the clutch components, shifting of one or more of the clutch components at start-up, the lack of or excessive seal wear, burrs on metal components and/or the like, may also result in inaccuracies within clutch calibration values.
Accordingly, a system and method that enhances the operation of a CVT, such as by allowing more accurate clutch calibrations to be performed, would be welcomed in the technology.
Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
In one aspect, the present subject matter is directed to a computer-implemented method for enhancing the performance of a continuously variable transmission of a work vehicle. The method may generally include engaging a range clutch of the continuously variable transmission, cycling a directional clutch of the continuously variable transmission between an engaged state and a disengaged state while the range clutch is engaged and controlling a position of a swash plate of the continuously variable transmission such that a ground speed of the work vehicle is maintained substantially at zero while the directional clutch is cycled between the engaged and disengaged states.
In another aspect, the present subject matter is directed to a computer-implemented method for enhancing the performance of a continuously variable transmission of a work vehicle. The method may generally include engaging a directional clutch of the continuously variable transmission, cycling a range clutch of the continuously variable transmission between an engaged state and a disengaged state while the directional clutch is engaged and controlling a position of a swash plate of the continuously variable transmission such that a ground speed of the work vehicle is maintained substantially at zero while the range clutch is cycled between the engaged and disengaged states.
In a further aspect, the present subject matter is directed to a system for enhancing the performance of a work vehicle. The system may include a continuously variable transmission having a first directional clutch, a second directional clutch and a plurality of range clutches. The transmission may also include a hydrostatic power unit having a pump in fluid communication with a motor. The pump may include a swash plate. The system may also include a controller communicatively coupled to the first directional clutch, the second directional clutch, the plurality of range clutches and the hydrostatic power unit. The controller may be configured to engage one of the plurality of range clutches, cycle the first directional clutch between an engaged state and a disengaged state while the range clutch is engaged and control a position of the swash plate such that a ground speed of the work vehicle is maintained substantially at zero while the first directional clutch is cycled between the engaged and disengaged states.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
In general, the present subject matter is directed to a system and method for enhancing the operation of a continuously variable transmission (CVT) of a work vehicle. Specifically, in several embodiments, the disclosed system and method may provide a means for automatically and repeatedly cycling one or more clutches of the CVT between engaged and disengaged states, which may allow for the CVT to be broken-in and/or warmed-up prior to operation of the work vehicle and/or prior to the performance of a maintenance operation on the CVT. For instance, for both new and old work vehicles, various system inconsistencies, imperfections and/or other issues may be present due to non-use, wear, manufacturing tolerances and/or the like. Such issues may, for example, include, but are not limited to, air bubbles/pockets trapped in the fluid lines and/or other components of the hydraulic system, friction between one or more of the clutch components, shifting of one or more of the clutch components at start-up, the lack of or excessive seal wear, burrs on metal components and/or the like. By cycling one or more of the transmission clutches in accordance with aspects of the present subject matter, such issues may be eliminated or, at the very least, their impact on the overall performance of the transmission may be reduced.
For example, clutch calibrations are often performed on brand new vehicles at the manufacturing plant by plant technicians. When performing such a calibration on a newly manufactured vehicle, it is often the case that small bubbles or pockets of air may be trapped within one or more of the components of the hydraulic system (e.g., within the valve, fluid lines and/or the clutch actuator), which leads to inaccuracies in the resulting clutch calibration values. For instance, while the air is trapped within the system, it may be determined during the calibration that a specific current command is needed to properly engage a given clutch. However, when the air is no longer within the system (e.g., after several hours of operation), the current command resulting from the calibration may no longer be adequate to achieve the required clutch torque. Similarly, for work vehicles that have been operating in the field for an extended period of time, mechanical issues and/or imperfections (e.g., friction, metal burrs, shifting components, uneven seal wear, etc.) may be present that can lead to similar inaccuracies in subsequent clutch calibrations performed by service technicians. Thus, in accordance with aspects of the present subject matter, one or more of the clutches of a CVT may be cycled immediately prior to the performance of a clutch calibration to flush out any trapped air and/or to eliminate any mechanical or other issues. As a result, the accuracy of the subsequent clutch calibration may be significantly improved, thereby allow for the overall operation of the CVT to be enhanced.
Referring now to the drawings,
As shown in
Moreover, the work vehicle 10 may include an engine 23 and a transmission 24 mounted on the chassis 16. The transmission 24 may be operably coupled to the engine 23 and may provide variably adjusted gear ratios for transferring engine power to the wheels 14 via an axle/differential 26. The engine 23, transmission 24, and axle/differential 26 may collectively define a drivetrain 28 of the work vehicle 10.
It should be appreciated that the configuration of the work vehicle 10 described above and shown in
Referring now to
The hydrostatic power unit 30 of the transmission 10 may generally include a fluid pump 36 coupled by fluid conduits 38 in a closed loop to a fluid motor 40. The motor 40 may be coupled to the engine 23 via an input gear N6. Specifically, as shown in
In general, the pump 36 may comprise any suitable electronically controlled pump known in the art, such as an electronically controlled variable displacement hydraulic pump. As such, operation of the pump 36 may be automatically controlled using an electronic controller 44 of the work machine 10. For example, as shown in
It should be appreciated the controller 44 may generally comprise any suitable processor-based device known in the art. Thus, in several embodiments, the controller 44 may include one or more processor(s) and associated memory device(s) configured to perform a variety of computer-implemented functions. As used herein, the term “processor” refers not only to integrated circuits referred to in the art as being included in a computer, but also refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits. Additionally, the memory device(s) of the controller 44 may generally comprise memory element(s) including, but are not limited to, computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and/or other suitable memory elements. Such memory device(s) may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s), configure the controller 44 to perform various computer-implemented functions, such as the method 600 described below with reference to
Referring still to
The controller 44 may also be communicatively coupled to a swash plate actuator 64 for automatically controlling the position or angle of the swash plate 48 of the pump 36. For example, the actuator 64 may be configured to move the swash plate 48 across a range of angles in response to control signals (e.g., current commands) received from the controller 44. In addition, the controller 44 may be coupled to any number of sensors for monitoring the various operating parameters of the transmission 24 including, but not limited to, pressure transducers or sensors 66 for sensing the pressure within the conduits 38 connecting the pump 36 to the motor 40 and/or for sensing the pressure of the hydraulic fluid within the various clutches of the transmission 24, speed sensors 68 for sensing speeds of the various shafts of the transmission 24 (e.g., by sensing the motor speed of the fluid motor 40), temperature sensors for sensing the temperature of one or more fluids within the transmission 24 and/or any other suitable sensors. Similarly, the controller 44 may also be connected to the engine 23 (e.g., a speed governor of the engine 23) for receiving engine speed data and other information therefrom.
Additionally, as shown in
During operation, the transmission 24 may be operated to have a combined hydrostatic and mechanical power flow by engaging the reverse directional clutch 54 to the power planetary power unit 32 via gears N1, N3, N5 and N7, or engaging the forward directional clutch 52 to power the power planetary power unit 32 via gears N1, N8, and N2. Alternatively, the transmission 44 may be operated to have a pure hydrostatic power flow by disengaging both of the directional clutches 52, 54. Regardless, the transmission 24 may provide a seamless transition between ranges to provide work/road configurations as desired. In particular, speed changes from zero to the maximum speed within each speed range of the transmission 24 may be achieved in a smooth and continuous manner by automatically changing the swash plate angle of the pump 36 via control signals transmitted from the controller 44. For each speed range, substantially the full range of travel of the swash plate may be used. For example, in several embodiments, the swash plate may be at one end of its range of travel for zero speed within a specific speed range, may be at the other end of its range of travel for the maximum speed of that speed range and may be at a zero tilt or neutral position within its range of travel for an intermediate speed of that same speed range.
Referring still to
In addition, for operation when the controller 44 is not powered or is not properly functioning, the parking brake 70 may also be configured to be engaged using a separate means. For instance, the parking brake 70 may be spring applied or may include any other suitable biasing means configured to bias the parking brake 70 into engagement. Alternatively, the parking brake 70 may include a suitable mechanical means for engaging the brake 70 when the controller 44 is not powered or is not properly functioning. Moreover, a means may be provided to store pressurized hydraulic fluid in the event the engine 23 stalls so that the parking brake 70 may remain released and/or may be applied and released several times if needed to control the vehicle 10 until the engine 23 can be restarted. Additionally, other means (e.g., a hand pump) may be provided to disengage the parking brake 70 if there is a fault and no stored pressurized hydraulic fluid is left within the system.
It should be appreciated that the configuration of the transmission 24 shown in
Referring now to
As shown, the hydraulically operated clutch may include an enclosure or can 72 that contains one or more clutch plates 74 coupled to an output shaft 76 and one or more clutch plates 78 coupled to an input shaft 80. In addition, the clutch may include both a clutch spring(s) 82 configured to hold the clutch plates 74, 78 apart and a fluid operated actuator (e.g., actuator 62 described above with reference to
Moreover, as shown in
Referring now to
Referring now to
In general, the method 600 may allow for the operation of a CVT 24 to be enhanced by reducing the amount of time required to break-in and/or warm-up the transmission. Specifically, as will be described below, the disclosed method 600 allows for a computer-implemented clutch cycling routine to be performed in which one or more of the clutches of a CVT 24 are automatically and quickly cycled on and off (i.e., between engaged and disengaged states) to remove, reduce and/or eliminate any system inconsistencies, imperfections and/or other potential issues that may impact the overall performance and/or maintenance of the CVT 24, such as air trapped within the hydraulic system, friction within the clutch springs, plates, piston or valve, shifting of the clutch springs and/or other clutch components (e.g., due to initial wear on the clutch seals), burrs on metal components and/or any other potential issues. For instance, prior to performing a clutch calibration on a CVT 24, the disclosed method 600 may be performed to flush out any air bubbles/pockets contained within the hydraulic system and/or to address any mechanical issues within the transmission 24, which may improve the overall accuracy of the resulting clutch calibration. Accordingly, aspects of the present subject matter may be advantageously utilized, for example, by plant workers prior to performing the initial clutch calibration on a CVT 24 and/or by service technicians prior to performing a routine clutch calibration.
As shown in
Additionally, at (604), the method 600 includes receiving a signal associated with selecting a forward travel direction or a reverse travel direction for the work vehicle. Specifically, in several embodiments, the operator of the work vehicle 10 may select which directional clutch 52, 54 is to be cycled by selecting the corresponding forward or reverse travel direction via the FRNP lever 20. For example, if it is desired for the forward directional clutch 52 to be cycled, the operator may be required to select forward using the FNRP lever 20, which, in turn, causes the forward directional clutch 52 to be engaged within the transmission 24.
It should be appreciated that, in several embodiments of the present subject matter, the forward or reverse travel direction may selected before or after instructing the controller 44 to enter into the clutch cycling mode. For instance, when the clutch cycling mode is initiated, a message window may, in one embodiment, be displayed (e.g., via the display panel 22) that prompts the operator to select forward or reverse by moving the FNRP lever 20 to the appropriate position. It should also be appreciated, that in alternative embodiments, any other suitable input device may be utilized by an operator to select the forward or reverse travel direction, such as push buttons, a control panel or any other suitable input device.
Referring still to
Additionally, at (608), the method 600 includes engaging a range clutch of the CVT 24 (e.g., range clutch R1, R2, R3 or R4). Specifically, in several embodiments, the disclosed clutch cycling routine may be configured to be performed in a “powered zero” operating mode in which the drivetrain 28 is engaged while the ground speed of the work vehicle 10 is maintained at or substantially at zero. In the “powered zero” mode, both a directional clutch 52, 54 and a range clutch R1-R4 must be engaged. Thus, when the FRNP lever 20 is moved to the forward or reverse position and the corresponding directional clutch 52, 54 is engaged within the transmission 24, one of the range clutches R1-R4 may also be engaged to constrain the planetary gear unit 32. For instance, given the configuration of the CVT 24 described above with reference to
Referring still to
As used herein, the term “engaged state” refers to a clutch operating state in which at least some amount of torque is transmitted through the clutch. Thus, to cycle one of the directional clutches 52, 54 to the engaged state, the hydraulic pressure within the clutch may be increased to the appropriate pressure (e.g., the engagement pressure of
When cycling each directional clutch 52, 54 between the engaged and disengaged states, a slight delay period may be provided to ensure that the clutch is fully engaged or fully disengaged prior to subsequently decreasing or increasing the clutch pressure. For instance, if the hydraulic pressure is being reduced down to zero pressure in order to cycle the clutch to the disengaged state, the controller 44 may be configured to wait a short time period (e.g., time period 90 shown in
When performing the disclosed clutch cycling routine, the controller 44 may, in several embodiments, be configured to continuously cycle the selected clutch between the engaged and disengaged states until the routine is cancelled. For instance, the operator may provide a suitable user input (e.g., via a button, touch screen or other suitable user input device) to terminate the clutch cycling. Similarly, the clutch cycling routine may also be cancelled if the operator commands movement of the work vehicle 10. For instance, if the operator pushes the speed lever (not shown) forward to increase the speed of the vehicle 10, the clutch cycling routine may be cancelled and the appropriate directional clutch engaged to allow the vehicle 10 to move in the selected direction.
Additionally, the operator may also be allowed to switch from cycling one directional clutch 52, 54 to the other while in the clutch cycling mode. For instance, if the forward directional clutch 52 is currently being cycled, the operator may select the reverse travel direction for the work vehicle (e.g., by moving the FRNP lever 20 to the reverse position) to initiate cycling of the reverse directional clutch 54. In doing so, the forward directional clutch 52 may be immediately disengaged. Thereafter, the reverse directional clutch 54 may be engaged and subsequently cycled between the engaged and disengaged states.
Referring still to
It should be appreciated that, in several embodiments, the ground speed of a work vehicle 10 is maintained “substantially at zero” if the ground speed is less than a predetermined speed threshold. For instance, in one embodiment, the speed threshold may correspond to a ground speed of less than 2 kilometers per hour (KPH), such as less than 1.5 KPH or less than 1 KPH. Additionally, a time component may also be combined with the speed threshold to determine whether the ground speed of the work vehicle is maintained “substantially at zero.” For instance, in several embodiments, the ground speed is maintained “substantially at zero” as long as the ground speed does not exceed the predetermined speed threshold for a predetermined time period, such as by exceeding 1.5 KPH for 0.1 seconds or by exceeding 0.8 KPH for 0.2 seconds.
It should also be appreciated that any suitable sensor feedback may be provided to the controller 44 to ensure that the angle of the swash plate 48 is properly adjusted in order to maintain the ground speed of the work vehicle 10 at or substantially at zero. For instance, the controller 44 may be configured to correlate the current commands transmitted to the swash plate actuator 64 to a corresponding output speed of the fluid motor 40 (e.g., by monitoring the motor speed via a speed sensor(s) 68). The swash plate angle may then be controlled to ensure that the appropriate motor speed is achieved for maintaining the ground speed at or substantially at zero.
Additionally, it should be appreciated that, although the method 600 was described above with reference to cycling one or both of the directional clutches 52, 54, a similar methodology may also be utilized to cycle one or more of the range clutches R1-R4 of the transmission 24. For instance, when the operator selects the forward or reverse travel direction and the corresponding directional clutch 52, 54 is engaged, one of the range clutches R1-R4 may be cycled between engaged and disengaged states while the directional clutch 52, 54 is maintained in engagement and the swash plate angle is controlled in a manner that provides for a ground speed that is at or substantially at zero. For instance, referring to the CVT configuration shown in
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
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| Number | Date | Country |
|---|---|---|
| WO 2013029056 | Feb 2013 | WO |
| WO 2013029058 | Feb 2013 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20150112558 A1 | Apr 2015 | US |
| Number | Date | Country | |
|---|---|---|---|
| 61893313 | Oct 2013 | US |
