Patent Application
20140221155
The present subject matter relates generally to continuously variable transmissions and, more particularly, to a system and methods for controlling a continuously variable transmission in order to provide for improved shuttle shifting.
Continuously variable transmissions utilizing a hydrostatic power unit, hereinafter sometimes referred to as hydro-mechanical continuously variable transmissions, are well known. A variety of work machines utilize this type of transmission for industries such as agriculture, earth moving, construction, forestry, and mining. In operation, the fluid displacement of the hydrostatic power unit is varied to change the output to input ratio of the transmission, that is, the ratio between the rotating output of the transmission, and the input. This is accomplished by varying the angle in a swash plate of a variable displacement fluid pump or motor of the hydrostatic unit. In a common mode of operation referred to as a shuttle shift, the direction of movement of the machine is changed, often under load, a common example of which being when a tractor loader moves in one direction to pick or scoop up a load, then lifts the load and reverses direction, often involving a turning movement, and unloads the load. This sequence is then reversed, and is often repeated many times. Sometimes, such shuttle shifting operations are performed on slopes or inclines. Such movements tend to subject elements of the transmission to wear and tear, and can raise the temperature of various elements, particularly clutches, and thus raise performance, longevity and reliability concerns. It is also typically desired for shuttle shifts to be completed relatively quickly and seamlessly, with little or no jerking or lurching of the machine.
In one category of the transmissions, the hydrostatic power unit is configured such that to effect movement of the vehicle in one direction, a swash plate of the unit will be tilted in one direction. To effect vehicle movement in the opposite direction, the swash plate is tilted in the opposite direction. When no vehicle movement is sought, e.g., no forward or rearward motion, the swash plate of the unit is moved to a zero tilt angle or near zero angle. Then, to effect movement of the vehicle in one direction or the other, the swash plate is appropriately tilted in the requisite direction to the requisite angle. In this category of transmission, if multiple speed ranges are provided, zero speed for each range will be the zero or near zero position, which presents no problem or limitation for shuttle shifting to move the vehicle in opposite directions.
However, another category of continuously variable transmissions, commonly used in a variety of heavy vehicles such as work machines, including for construction, earth moving, forestry, and agriculture, wherein shuttle shifting is commonly used, employs a hydrostatic power unit configured such that at zero vehicle or machine speed, the swash plate of the hydrostatic power unit is at full displacement or near full displacement, in one direction or the other, depending on the range selected, direction of travel and possibly other factors. Reference as an example in this regard, Weeramantry, U.S. Pat. No. 7,063,638 B2, issued Jun. 20, 2006. When shuttle shifting this type of transmission, the common practice is to reduce the gear ratio to achieve zero vehicle speed, and then shift the transmission to move the machine in the opposite direction. When zero vehicle speed is reached, some time will be required to move the swash plate to its new position, and during this time the operator can apply a brake or engage a combination of opposing clutches to hold the wheels or tracks. However, a shortcoming of this manner of shifting is that a delay can result as the swash plate is moved. As another possible shortcoming, repeatedly performing shuttle shifts in the same manner can raise temperature related performance and reliability issues, particularly if the brake is repeatedly used to decelerate the vehicle or the same clutch is repeatedly used to decelerate and/or accelerate the vehicle during the shifts. Additionally, not all shuttle shifts are performed under the same conditions, and it can be desirable to have alternative manners of performing a shuttle shift for the different conditions.
Thus, what is sought is a manner of overcoming one or more of the disadvantages or shortcomings, and achieving one or more of the desired characteristics, set forth above.
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 method for performing a shuttle shift with a continuously variable transmission of a work machine, wherein the continuously variable transmission includes a hydrostatic power unit. The method may generally include adjusting a swash plate angle of the hydrostatic power unit in a first direction to reduce a travel speed of the work machine in an off-going direction, initiating a directional swap between an off-going directional clutch of the continuously variable transmission and an on-coming directional clutch of the continuously variable transmission while the work machine is traveling in the off-going direction and adjusting the swash plate angle of the hydrostatic unit in a second direction after the initiation of the directional swap to reduce slippage across the on-coming directional clutch, wherein the second direction is opposite the first direction.
In another aspect, the present subject matter is directed to a method for performing a shuttle shift with a continuously variable transmission of a work machine, wherein the continuously variable transmission includes a hydrostatic power unit. The method may generally include adjusting a swash plate angle of the hydrostatic power unit to reduce a travel speed of the work machine in an off-going direction, initiating a directional swap between an off-going directional clutch of the continuously variable transmission and an on-coming directional clutch of the continuously variable transmission while the work machine is traveling in the off-going direction and maintaining the swash plate angle constant after the initiation of the directional swap.
In a further aspect, the present subject matter is directed to a system for shifting a travel direction of a work machine from an off-going direction to an on-coming direction. The system may generally include a continuously variable transmission having an off-going directional clutch for engaging the continuously variable transmission in the off-going direction and an on-coming directional clutch for engaging the continuously variable transmission in the on-coming direction. The continuously variable transmission may further include a hydrostatic power unit having swash plate angle that is adjustable in a first direction and a second direction, wherein the first direction is opposite from the second direction. In addition, the system may include a controller communicatively coupled to the continuously variable transmission. The controller may be configured to adjust the swash plate angle in the first direction to reduce a travel speed of the working machine in the off-going direction. The controller may also be configured to initiate a directional swap between the off-going directional clutch and the on-coming directional clutch while the work machine is traveling in the off-going direction. Further, the controller may be configured to adjust the swash plate angle in the second direction after the initiation of the directional swap to reduce slippage across the on-coming directional clutch.
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 methods for controlling a continuously variable transmission in order to provide fast shuttle shifts with no stopping at zero speed and with reduced amounts of energy dissipated in the directional clutches. In several embodiments, such shuttle shifts may be achieved by simultaneously moving the swash plate of a hydrostatic power unit of the transmission while slipping the on-coming directional clutch of the transmission (i.e., gradually engaging the on-coming directional clutch as the direction of travel of the work machine is reduced/reversed). Such movement of the swash plate may generally allow for the speed differential across the on-coming directional clutch to be reduced, thereby reducing the amount of energy dissipated in such clutch. This may lead to energy savings by reducing the amount of energy required to pump cooling oil to the on-coming directional clutch and may also prevent damage to the clutch due to overheating.
Referring now to the drawings, in
Referring also to
Hydrostatic power unit 12 of transmission 10 includes a fluid pump 16 coupled by fluid conduits 17 in a closed loop to a fluid motor 18. Motor 18 is coupled to power source 4 via an input gear N6 and having an output gear N10. The power to the hydrostatic power unit 12 is provided by a driven gear N4 mounted on the forward shaft and engaged with gear N6. Output gear N10 is connected to ring gear NR of planetary power unit 30 via gears N11 and N12.
Machine 1 includes a processor based controller 100 in connection with an input device 102 located preferably in operator cab 104 of machine 1, via a suitable communications path 108, to adjust the angle of a swash plate of pump 16 (swash plate denoted by a diagonal arrow through pump 16), through a range of positions. As an exemplary embodiment, pump 16 can be an electronically controlled variable displacement hydraulic pump of well known construction.
Planetary power unit 30 includes a primary sun gear NS1 on a planetary input shaft 32 connectable with power source 4 via a forward directional clutch 54 or a reverse directional clutch 52. Power unit 30 is selectively coupled to the load L, coupled to the hydrostatic power unit 12 and selectively coupled to the power source 4, under automatic control of controller 100. For connection to the load L, the hydro-mechanical transmission 10 includes an output shaft 60 coupled to the load L which carries an input gear N18 engaged with an output gear N17 on a range ½ shaft of range gear set 58, and a gear N22 engaged with a gear N19 on a range ¾ shaft. The range ½ shaft can be coupled to planetary power unit 30 via automatic operation of range selectors or clutches R1 and R2 for power flow through gears N13 and N14, or N15 and N16, respectively. The range ¾ shaft can be coupled to unit 30 via range selectors or clutches R3 and R4 for power flow via gears N13 and N20, or N15 and N21. Range ½ shaft and range ¾ shaft can also be simultaneously coupled to power unit 30, to provide dual power flow.
The control of the various clutches will be automatically controlled by controller 100, using actuators 106 connected to controller 100 via suitable conductive paths 108. Transmission 10 also includes appropriate sensors, including pressure sensors 110 for sensing pressure conditions in conduits 17 connecting pump 16 and motor 18, and speed sensors 112 for sensing speeds of load shaft 60, all connected to controller 100 via conductive paths 108. Controller 100 is also connected to engine 4 for receiving speed and other information therefrom.
In operation, the continuously variable hydro-mechanical transmission 10 can be operated to have a combined hydrostatic and mechanical power flow by engaging the reverse clutch 52 to power planetary power unit 30 via gears N1, N3, N5 and N7, or engaging forward clutch 54 to power it via gears N1, N8, and N2. It is also possible to operate transmission 10 for a pure hydrostatic power flow by disengaging both clutches 52 and 54.
As a result, with transmission 10, there is no selection for a work range or road range per se. However, the transmission provides a seamless transition between ranges to provide work/road configurations as desired. Speed change from zero to maximum speed is achieved in a smooth and continuous manner by changing the swash plate angle of the pump 16 under control of controller 100. For each speed range, substantially the full range of travel of the swash plate is used. That is, the swash plate will be at one end of the range of its travel for zero speed within the range, it will be at the other end for maximum speed in that range, and the zero tilt or neutral position of the swash plate will be an intermediate position for the speed range, not the zero speed position as it is for some other transmissions. This presents a challenge for execution of some transmission commands that require a change of state wherein the swash plate will have to be tilted to a position significantly different from the present position, e.g., some shuttle shifts, as some time for the transition or movement to the new position will be required. For other commands, e.g., shuttle shifts at higher speeds, the speed range will need to be changed, but it can be observed that the required ending swash plate position is the same or similar to the beginning position, which presents an opportunity for shifting in a different manner than that for lower speed shifts.
Transmission 10 includes a parking brake 114 in connection with load shaft 60, which is utilized according to the invention for enabling at least one selectable manner of shuttle shifts. Parking brake 114 is connected to controller 100 via a suitable conductive path 108 for automatic operative control thereby, including to proportionally or gradually engage, and release or disengage, under certain conditions. To achieve this latter capability, as a non-limiting example, parking brake 114 can be controlled using a proportional pressure reducing valve operated by an electrical signal from controller 100. For operation when machine 1 is not operating, parking brake 114 can be engaged by a spring or other biasing element or elements, or by mechanical means.
Other conditions wherein parking brake 114 will be automatically controlled by controller 100 to engage, or remain engaged if already engaged, can include, but are not limited to, when power source 4 of machine 1 is turned off, the transmission is disengaged, the operator leaves the operator seat, and if the FNR lever is left in F for a certain period of time without movement. Controller 100 will also control the parking brake to remain engaged when a command is received to disengage the parking brake, until certain conditions are met, as will be explained. Other conditions include when a command is received via an input device 102, e.g., FNR lever or the like, to change the operating state of the transmission. Such commands can include a change to, or in close proximity to, a neutral or zero movement state, or a clutch command.
It should be appreciated that the work machine 1 shown in
Referring also to
Additionally, while the swash plate is being moved from one side to the other, generally the driveline cannot be engaged, since this could result in higher speeds if the clutch is not slipped. There are perhaps two main options to deal with this, one is to four square the transmission (lock the output shaft) by applying both the R1 and R3 clutches, and the second is to use the parking brake. If four squaring is used, it is difficult to control, since the swash plate movement is not completely decoupled, and moving the swash plate tends to move the vehicle in the opposite direction, and this must be compensated for by controlling the pressure in either the R3 or R1 clutches.
As an advantage of the present invention, shuttle shifting shall be allowed from any forward speed to any reverse speed. According to the invention, shuttle shifts will have three phases. During the first, machine 1 is decelerated using the swash plate, with the deceleration limited to a target value. Next, the forward and reverse clutches 54, 52 are swapped. Directional swapping is defined as the part of the shuttle shift from when the off-going directional clutch starts to dump to when the on-going clutch is finished ramping up and is fully engaged. The last phase of a shuttle is when the machine may be accelerated using the swash plate to the final speed in the opposite direction. This is done with the swash plate, range shifting as needed, and limited to the desired transmission acceleration value. It should also be noted that deceleration is controlled in all phases of all types of shuttles, during the ratio changing, deceleration with the parking brake, and deceleration then reacceleration using clutch slipping.
As a consideration, it is advisable to minimize energy dissipated by clutches to prevent damage. It has been found that one of the best ways to do this is to reduce the speed of the vehicle prior to the shift. Directional swapping is always done in the first range. If the speed is higher when the shuttle shift is commanded, the vehicle will be slowed by normal swash plate movement and range shifting. As a result, in the invention, both the speed when the shuttle is commanded (or the current speed) and the final opposite speed will be needed to determine when and how to swap the clutches and move the swash plate.
As another consideration, as evidenced by the distance ROM, shuttle shifting for transmissions, such as transmission 10, is challenging because the swash plate may need to move a considerable distance before the on-coming clutch can be engaged, or the vehicle may go too fast before the swash plate reaches its final position. In this case, it has been found that it is best to apply parking brake 114, to keep the vehicle from rolling while in neutral when the swash plate is being moved. As another consideration, since the time to move the swash plate may vary considerably, and engaging the on-coming clutch while the swash plate is not in position can cause overspeed conditions, controller 100 should fill the on-coming clutch, and then wait until the motor speed (swash plate error) has reached it proper value before engaging the on-coming clutch, to achieve consistent shifts. During shuttle shifts, the desired transmission output acceleration (DTOA) is desirably achieved through all phases, and especially needs to be matched during transitions between phases. The pressure in the on-coming clutch should be carefully controlled to achieve the correct DTOA, both through initialization to the proper pressure and closed loop control. If the parking brake is used for decelerations, it is also controlled in a closed loop fashion to achieve DTOA.
Referring also to
As a first step, the speed is reduced by moving the swash plate, as denoted by distance D1. In
As the vehicle reaches zero speed, the range clutch is dumped, and parking brake 114 is automatically applied to reduce required operator action, e.g., clutching and application of the service brake, to prevent unwanted movements of the vehicle. The applied pressure of the parking brake should be high enough to keep the vehicle from moving in the wrong direction, even on a steep hill. The swash plate will then be moved over distance ROM to reverse tilt. During movement of the swash plate over distance ROM, the on-coming directional clutch is filled. Then, after the swash plate is moved to the correct position and the on-coming directional clutch is filled, the parking brake will be released or disengaged and the vehicle will begin to move. At a selected time, e.g., at the end of the ROM, the directional swap will occur (on-coming directional clutch is engaged and the off-going directional clutch is dumped), and the swash plate is moved in a manner to achieve the selected reverse speed.
Another manner of shuttle shifting according to the invention is illustrated in
Next, when the transmission ratio is at a given point, the directional clutches are swapped and the swash plate is moved to a value for a particular transmission ratio in the opposite direction. The on-coming directional clutch is filled in anticipation of this point. This swap may be initiated such that the swash plate angle either continues change in the same direction slightly, is held constant during the swap, or actually reverses direction during the swap, depending on the relative values of the various parameters. Reversing the direction of the swash plate angle during the swap can result in less energy being dissipated in the clutch, which is desirable, but if the swash plate control is sluggish compared with the time needed for the swap, it may be better to have some movement of the swash plate in the same direction during the swap. Perhaps more importantly, moving the swash plate during the swap creates a reaction torque that affects the deceleration, so consistent decelerations are easier to achieve if the swash plate movement is minimized. However, as will be described below with reference to
Medium speed shuttle shifts are ones where generally there is enough time to move the swash plate into position before the vehicle comes to a stop, although this may not always be the case. The proper time to switch between the shuttle shift strategy using the parking brake to decelerate described here and the shuttle shift using ratio control strategy described above can be determined by which feels better in testing.
As illustrated in
Shuttle shifts may also comprise combinations of the types described above, as illustrated in
If the directional clutches, range clutches or parking brake are too hot, e.g., according to a sensed temperature value or values, or an estimate of the temperature based on the history of clutch pressures and worst case assumptions on the clutches, then controller 100 can inhibit the shuttle logic directional swap, and use ratio changing to bring the vehicle to a stop. If the ratio changing is not effective, there will not be a timeout, the system will continue to wait for the vehicle to slow down, then complete the shuttle.
If the directional swap is in progress and the clutches become too hot (perhaps more typical than starting hot), then a “reverting” logic is used. This includes setting the desired transmission ratio to the current transmission ratio, so the swash plate will be moved to what is needed for re-engaging. Note that the clutches are simply re-engaged and the direction swap is over, regardless of the transmission ratio, or hydrostatic power system ratio. The swash plate will then be moved to reduce the transmission ratio to zero, and then the angle reversed, and then positioned for the target speed in the new direction.
It should be noted that if an operator commands a shuttle shift, and the vehicle does not slow down fast enough, or does not slow at all, such as when pulling a trailer down a hill, it is advisable and normal for the operator to use the service brakes (typically brake pedals on the floor of the operator cab). The service brakes can always be used during shuttle shifts to increase deceleration.
Referring also to
Referring now to
Initially, the shuttle shift may be performed similarly to the shuttle shift shown above in
In addition, while the swash plate angle is being adjusted, the on-coming directional clutch may be filled in anticipation of the directional swap. For instance, in the illustrated embodiment, a forward-to-reverse shuttle shift is being performed and, thus, the reverse directional clutch 52 (
It should be appreciated that, since
It should also be appreciated that a variety of different factors may be used to determine the point 206 at which the directional swap may be initiated. For example, when performing the shuttle shift shown in
Once the TRR reaches point 206, the directional swap is initiated. Specifically, at point 206, the off-going directional clutch (e.g., forward directional clutch 54) may be immediately dumped or disengaged. In addition, the on-coming directional clutch (e.g., reverse directional clutch 52) may be gradually engaged. For instance, the pressure of the hydraulic fluid supplied to the on-coming directional clutch may be gradually increased such that the on-coming directional clutch is partially engaged (i.e., slipping) as the off-going directional clutch is disengaged. As will be described below, the hydraulic pressure within the on-coming directional clutch may continue to be gradually increased as the swash plate angle is adjusted until the on-coming directional clutch is fully engaged (i.e., such that no slippage occurs across the on-coming directional clutch).
It should be appreciated that, as shown in
Additionally, after the directional swap is initiated, the direction in which the swash plate angle is being adjusted may be reversed. Specifically, as shown in
As the slippage across the on-coming directional clutch gets low, the movement of the swash plate may be slowed and subsequently reversed. Specifically, as shown in
It should be appreciated that the predetermined slip threshold may generally be determined based on the actual or expected rate at which the slippage across the on-coming directional clutch may be reduced and/or the actual or expected rate at which the swash plate angle may be adjusted. Specifically, as indicated above, it may be desirable for the movement of the swash plate to be completely reversed by the time the on-coming directional clutch is fully engaged. Thus, the predetermined slip threshold may be selected such that sufficient time is provided for reversing the direction of movement of the swash plate prior to the slippage across the on-coming directional clutch being reduced to zero.
Additionally, as indicated above, although reversing the direction of the swash plate provides for a reduction in the energy dissipated in the on-coming directional clutch, such movement of the swash plate also results in a reaction torque. In particular, moving the swash plate while both the driveline and the on-coming directional clutch are engaged generates a reaction torque that adds to the torque transmitted through the on-coming clutch, which can cause a reduction in the deceleration of the work machine 1. However, in several embodiments, the effect of the reaction torque may be mitigated by carefully regulating the hydraulic pressure within the on-coming directional clutch as the movement of the swash plate reverses direction (e.g., from point 206 to a point at which the swash plate is moving in the second direction 208 at a steady speed). In one embodiment, the pressure within the on-coming directional clutch may be controlled as a function of a rate of change of the transmission ratio (denoted TRR) of the transmission 10. For instance, the rate of change of TRR may be continuously monitored and compared to a target deceleration for the transmission 10. The target deceleration may generally correspond to a control setting for limiting the deceleration rate of the transmission 10 during shuttle shifting and may be controlled by a number of factors including, but not limited to, a user setting for “aggressiveness” (low, medium and high). If the rate of change of TRR varies from the target deceleration, the pressure within the on-coming directional clutch may be adjusted until the target deceleration is achieved.
In addition, the reaction torque may also be counteracted by delaying the movement of the swash plate in the second direction 208 until the pressure in the on-coming directional clutch is increased (e.g., by continuing to adjust to the swash plate angle in the first direction 204 for a period of time after the initiation of the directional swap). Specifically, as shown in
Referring now to
It should be appreciated that the various method elements or steps of the disclosed method 300 may generally be implemented by the controller 100 of the work machine 1. As indicated above, the controller 100 may generally comprise a processor-based device. Thus, in several embodiments, the controller 100 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 100 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 100 to perform various computer-implemented functions.
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.
This application is based upon and claims priority to U.S. Provisional Patent Application No. 61/527,455, filed on Aug. 25, 2011 and entitled “Shuttle Shifting for a Continuously Variable Transmission, the disclosure of which is hereby incorporated by reference herein in its entirety for all purposes.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2012/046413 | 7/12/2012 | WO | 00 | 2/24/2014 |
| Number | Date | Country | |
|---|---|---|---|
| 61527455 | Aug 2011 | US |
