Abstract:
A method of controlling a machine drive having a driveline PTO establishes a driveline torque perturbation via conversion of internal inertia through two transmission neutral conditions. In an example, when a request is received, e.g., from an operator, to shift the driveline PTO from a first mode to a second mode, the transmission is automatically modulated between its first neutral condition and its second neutral condition while the driveline PTO is shifted from the first mode to the second mode, thus minimizing torque lock and facilitating mode changes.

Description:
TECHNICAL FIELD 
     This patent disclosure relates generally to drive line PTO transmissions, and, more particularly to a system and method for minimizing input torque to a drive line PTO transmission to facilitate mode shifts. 
     BACKGROUND 
     Many powered machines use a single power source for multiple uses. For example, a riding lawn mower may use its engine for both locomotion of the machine as well as driving an implement such as a mulcher, mower, or tiller. On a larger scale, a fire response machine may use its engine for locomotion as well as to power an auxiliary device such as a water pump. Such machines typically employ a power takeoff, or PTO, to selectively direct the engine power to the machine wheels for locomotion or to the implement, e.g., the pump. In some cases the PTO is configured to select either the locomotion function or the auxiliary device, but not both. For example, with respect to a fire response machine, the locomotion function is not needed while pumping water, e.g., when fighting a fire, and the water pumping feature is not needed while moving, e.g., while traveling to the scene of a fire. 
     One such PTO is referred to a driveline PTO (DPTO) or a split-shaft PTO. An example of a DPTO is shown in US Published Application 2007/0006572 to Yu et al., entitled “System and Method for Controlling an Engine Having a Power Take Off Output Device.” In general, a DPTO allows a machine transmission to deliver power to a PTO load through the machine&#39;s transmission output shaft (i.e., “pump mode”) instead of delivering power to the machine wheels (i.e., “road mode”). In the DPTO system, one output yoke of the DPTO is linked to the machine axles and another output yoke is linked to the water pump. An input yoke of the DPTO receives power from the machine engine via the machine&#39;s transmission output shaft. This type of PTO provides certain benefits over other types of PTO such as side-drive PTO&#39;s, which typically provide less power than the DPTO, and front and rear engine PTO&#39;s, which often do not fit well within the physical layout of a typical fire response machine. 
     Most DPTOs include a split shaft sliding collar to selectively shift between road mode and pump mode. However, essentially all planetary transmissions provide some amount of incidental or windage generated torque at the output shaft even when in neutral. Thus, the sliding collar may be “torque locked” if too much torque is present when trying to slide the collar to change modes. Moreover, when shifting from pump mode to drive mode, if the windage generated torque at the output shaft is sufficient at engine idle to spin the pump, the operator may experience gear “grinding” as the rotating collar is forced against the stationary machine drive shaft. Although it is possible to use a clutched input to the DPTO to alleviate certain of these problems, this solution is costly and introduces additional mechanical complications and failure points into the system. 
     The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the disclosure, and thus should not be taken to indicate that any particular element of a prior system is unsuitable for use within the disclosed examples, nor is it intended to indicate any element, including solving the motivating problem, to be essential in implementing the examples described herein. The full scope of the implementations and application of the examples described herein are defined by the appended claims. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     In one aspect, a method is provided for controlling a machine drive having an engine linked to a driveline PTO via a transmission. The transmission supports at least two neutral conditions, and the driveline PTO supports a first mode, e.g., wherein the transmission output is linked to one or more wheels of the machine to move the machine, and a second mode, e.g., wherein the transmission output is linked to an auxiliary device rather than to the machine wheels. More generally, the disclosure applies to PTO shifts between any two modes as will be appreciated by those of skill in the art. When a request is received, e.g., from an operator, to shift the driveline PTO from a first mode to a second mode, the transmission is automatically modulated between its first neutral condition and its second neutral condition while the driveline PTO is shifted from the first mode to the second mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a transmission system including a DPTO; 
         FIG. 2  is a schematic diagram of a DPTO in an example wherein the DPTO is in pump mode; 
         FIG. 3  is a schematic diagram of a DPTO in an example wherein the DPTO is in road mode; 
         FIG. 4  is a clutch diagram showing the logical structure of an exemplary machine planetary gear transmission in a clutch  5  neutral state; 
         FIG. 5  is a clutch diagram showing the logical structure of an exemplary machine planetary gear transmission in a clutch  2  neutral state; 
         FIG. 6  is a timing diagram showing torque perturbations or disturbances according to an aspect of the disclosed system; 
         FIG. 7  is a clutch diagram showing the logical structure of an exemplary machine planetary gear transmission in a clutch  5  neutral state braked by clutch  4 ; and 
         FIG. 8  is a flow chart illustrating a process for transmission control according to an illustrative example. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure describes a system for facilitating mode changes in a DPTO by overcoming torque locking that often make mode changes difficult.  FIG. 1  is a schematic diagram of a machine power system  100  including a DPTO usable in conjunction with examples described herein. The power system  100  comprises primarily a power source such as an engine  101 , a transmission  102 , and a DPTO  103 . The transmission  102  includes an output shaft  104  that is linked to an input of the DPTO  103 . The DPTO  103  includes two outputs, one of which is connected to the machine drive shaft  105 , which operates the machine wheels  106 . The other output of the DPTO  103  is connected to an auxiliary device, e.g., a water pump  107 . Finally, the power system  100  also comprises a controller  108 , linked to the engine  101 , transmission  102 , and DPTO  103  via sensors and or actuators to control the operation of the system  100 . 
     Referring again to  FIG. 1 , the controller  108  may include one or more engine operation sensor inputs  109  and/or engine control outputs  110 , one or more transmission operation sensor inputs  111  and/or transmission control outputs  112 , and one or more DPTO operation sensor inputs  113  and/or DPTO control outputs  114 . The controller  108  is actuated via an included processor adapted to execute the steps and calculations described herein. The controller, through the processor may operate by executing computer-executable code, i.e., instructions, stored on a computer-readable medium such as ROM, RAM, flash, and other types of media, whether optical, magnetic, or electronic. 
     As discussed above, the DPTO  103  is shiftable between two modes, for example a “road mode” and a “pump mode.” In the illustrated example, the engine  101  drives the wheels  106  of the machine in road mode (a first mode), and drives the water pump  107  in pump mode (a second mode). The illustration of  FIG. 2  shows a detailed schematic diagram of the DPTO  103  when the DPTO  103  is configured in pump mode. The DPTO  103  comprises an input shaft  200  for receiving rotary power from the transmission output shaft. The input shaft  200  is fixed to an input gear  201  such that the input shaft  200  and the input gear  201  rotate as a unit. 
     The DPTO  103  in the illustrated example further includes a shift collar  202  that is slidable to link the input gear  201  to either an output gear  203  of an output shaft  204  or to a pump input gear  205  via a drive gear  206 . The input shaft  200  is maintained concentrically with the pump input gear  205  via a bearing or bushing  207 . The shift collar bears internal lands and grooves configured to mate with the teeth of input gear  201  while it mates with output gear  203  or drive gear  206  so as to selectably fix the input gear  201  to output gear  203  or drive gear  206  depending upon the mode of the DPTO  103 . In the illustrated example, the shift collar  202  is in a position to fix the input gear  201  to the drive gear  206 . In this configuration, the rotation of the input shaft  200  is transferred via the shift collar  202  to the drive gear  206  and the pump input gear  205 , thus driving the pump  208  via gear  209 . It will be appreciated that other gearing arrangements are possible within the disclosed principles. 
     When the shift collar  202  is slid out of engagement with drive gear  206  and into engagement with output gear  203 , the DPTO  103  is considered to be in road mode, in that the motion of input shaft  200  is transferred via shift collar  202  to the output shaft  204 .  FIG. 3  is a schematic diagram of the DPTO  103  when in road mode. It can be seen that shift collar  202  links the input shaft  200  to the output shaft  204 . At the same time, in this mode the pump drive gear  206  is not connected to the vehicle transmission and is free to coast. This mode is useful, for example, when the machine housing the DPTO  103  is traveling rather than performing auxiliary functions such as pumping. 
     In general, the engine  101  of the machine  100  is idling at such time as the user or operator requests a shift from one DPTO mode to the other. Indeed, it is desirable to minimize the engine speed in many cases to avoid component strain when shifting, and so an interlock may be used to assure that a DPTO shift is not executed when the engine speed and/or torque are excessive. However, even with the engine  101  at idle and the transmission  102  in a neutral gear, there is generally a certain amount of torque transmitted through the transmission  102 . Indeed, essentially all planetary transmissions provide some amount of incidental or windage generated torque at the transmission output shaft (i.e., the input shaft  200 ) even when in neutral. The windage torque can be significant, and has been measured to be as high as 30 Nm. 
     This incidental torque causes a number of problems, one of which is known as “torque lock.” Torque lock occurs when the shift collar  202  cannot be slidably disengaged from its present arrangement to change modes because too much torque is present between the shift collar  202  and a mating element. The friction between the mating surfaces of the shift collar  202  and a driven surface is essentially proportional to the force between the surfaces, which is proportional to the applied torque. Thus, in any mode, when excess torque is present, excess sliding friction with respect to the shift collar  202  is also present, increasing the difficulty of, or even preventing, shifting between modes. 
     Moreover, in an example when shifting from pump mode to drive mode, if the windage generated torque at the transmission output shaft  200  is sufficient at engine idle to spin the pump  208 , the operator may experience gear “grinding” as the rotating collar  202  is forced against the stationary machine output gear  203 . This phenomenon can be both damaging to the machine  100  and disconcerting to the operator. 
     In an embodiment, the windage torque of the transmission  102  is overcome to allow mode shifts without first shifting to a non-neutral transmission state such as reverse. In particular, a calculated train of torque pulses is applied during a mode shift by way of a deliberate series of shifts between multiple neutral states. The shifts between neutral states periodically build and release internal inertial forces within transmission  102  due to the differences in rotating and stationary elements in each state. The disturbance thus created at the shift collar releases the friction of engagement and allows the shift collar  202  to be moved into engagement with an alternative mating element, thus executing a mode shift. 
     Although an operator may rapidly alternate between first gear and reverse to allow a DPTO shift, this will pose a risk of unintended vehicle motion. The illustrated example substantially eliminates this risk, since it entails using internal inertia to generate torque disturbances, and does not, in the preferred embodiment, actually place the transmission in a drive gear to create a torque disturbance. 
     To understand the affect of using multiple neutral states, the logical structure of an exemplary five clutch planetary gear transmission  400  is shown in the clutch diagram of  FIG. 4 . In the illustrated example, the transmission  400  is engaged in a clutch  5  neutral state, causing certain elements to rotate and others to stay stationary. In the illustrated example, the elements along the dotted path  401  are stationary in the clutch  5  neutral state. 
       FIG. 5  is a schematic diagram of the logical structure of an example five clutch planetary gear transmission  400 , wherein the transmission  400  is engaged in a clutch  2  neutral state. In the illustrated example, the elements along the dotted path  401  are now rotating rather than stationary. The rotating elements along path  401  have angular momentum that is released when the transmission  102  is shifted from the clutch  2  neutral state to the clutch  5  neutral state. In other words, a change in torque is required to change angular momentum. Increasing the momentum of link  401  results in a positive torque impulse at the output shaft  104  (engaging clutch  2 ). Reducing the momentum of link  401  results in a negative torque impulse at the output shaft  104  (engaging clutch  5 ). 
     Thus, shifting back and forth between two differently clutched neutral states provides an alternating positive/negative torque at the transmission output shaft  104 .  FIG. 6  is a timing diagram  600  illustrating the torque pulse train created by alternating between the clutch  2  neutral state and the clutch  5  neutral state. The vertical axis denotes transmission output torque in Nm, while the horizontal axis represents elapsed time in seconds. It can be seen that the positive torque pulses rise to a magnitude of approximately 200 Nm and decay gradually within approximately 3 seconds, while the negative torque pulses rise to similar magnitude but decay sharply within approximately 1.5 seconds. 
     As noted above, the axial friction experienced by the shift collar  202  is proportional to the torque at the DPTO input shaft  200  (i.e., transmission output shaft  104  in the illustrated example). Thus, the axial friction experienced by the shift collar  202  during the torque pulse train is of the same shape as the timing diagram  600 . This periodic disruption of the axial torque allows the shift collar  202  to begin moving with less effort and to then continue moving once the static axial friction of the shift collar  202  is overcome. 
     In an embodiment, one or more clutches of the transmission  102  are used to brake the transmission output  402  (shaft  104 ) when shifting the DPTO  103  from pump mode to road mode. In particular, the windage torque of the transmission  102  is often sufficient to turn the pump, especially when the pump is dry, raising the possibility of gear grinding when shifting the DPTO  103  back to road mode. 
     Thus, in a further embodiment, an additional clutch is activated to brake the transmission output  402  (shaft  104 ) just prior to a shift of the DPTO  103  from pump mode to road mode. In the illustrated example, the number four clutch, when activated during a clutch  5  neutral state, causes the output  402  (shaft  104 ) to cease rotating. In particular, once two elements of a planetary train are stationary (e.g., along paths  401  and  403 ), the third element (e.g., along path  404 ), which in this case includes the output  402 , must also be stationary. 
     The principles described above may be applied in a wide variety of shift sequences and processes. An exemplary DPTO shift process  800  is illustrated via the flowchart of  FIG. 8 . Initially at stage  801 , the process receives an operator indication, such as via user interface  115  to shift the mode of the DPTO  103 . The process checks the transmission state at stage  802  to verify that requirements for the mode change are met. For example, the transmission should preferably be in a neutral gear, and the speed of any rotating components associated with the DPTO should less than a certain amount, e.g., 175 RPM. This prevents excessive component stress, e.g., clutch wear or damage during shifts. 
     At stage  802   a , the process determines whether the requested shift is from pump mode to road mode. If so, the process flows to stage  803 , wherein it applies a brake such as a transmission brake to stop the rotation of components associated with the DPTO  103 . For example, if the DPTO  103  input shaft  200  and pump  208  are rotating, it is desirable to stop these elements prior to the mode change. A suitable transmission brake system is discussed above with respect to  FIG. 7 , but other suitable braking devices or processes may be used instead. 
     The process verifies at stage  804  that the components associated with the DPTO  103  have ceased rotation. If the components have not ceased rotation, the process may loop back to stage  803  to continue braking. Optionally, after a predetermined number of loops, e.g., 3, between stages  804  and  803 , the process may signal a mode change failure at stage  808  and exit. Once effective braking has been confirmed at stage  804 , the process flows to stage  804   a  and slides the shift collar from its current position to the alternate position and exits. 
     If at stage  802   a  it is instead determined that the requested shift is from road mode to pump mode, the process flows to stage  805  and begins to periodically modulate the transmission  102  gear between its current neutral state and a second neutral state to create a torque disturbance while sliding the shift collar  202  from its current position to the opposite position. At stage  806 , the process verifies that the collar  202  has been shifted. Stage  806  may be repeated a predetermined number of times, e.g., 3 times, and if the collar  202  still has not been successfully shifted, the process may signal a mode change failure at stage  808  and exit. 
     Otherwise, at stage  807 , the process ceases the modulation of the transmission  103  between neutral states, signals via the user interface  115  that the mode shift is complete, and unlocks the transmission  103 , i.e., allows the operator to shift to transmission gears other than neutral. 
     Industrial Applicability 
     The industrial applicability of the DPTO shift control system described herein will be readily appreciated from the foregoing discussion. The present disclosure is applicable to machines having a driveline and having associated therewith a Driveline PTO (DPTO), examples of such machines are certain machines such as fire response machines that provide both locomotion and auxiliary services such as the pumping of water, operation of a tool or implement, etc. The described system and technique allows for easier shifting between a road mode, wherein the machine driveline is used for propulsion, and another mode, e.g., a pump mode, where the machine driveline is instead used to power the auxiliary function. For example, a fire response machine that employs a DPTO to power a water pump may benefit from application of the teachings herein. In such machines, application of the foregoing teachings can provide increased drive train and DPTO longevity and ease of operation by minimizing the torque lock encountered when shifting between road mode and pump mode. The described system allows the operator of such a machine to automatically overcome torque locking without shifting the machine transmission to determine a setting wherein the torque locking is alleviated or minimized. Thus, for example, when a fire response machine arrives at a fire incident scene, it will arrive in road mode. However, once stationary, the machine will be able to quickly shift via the DPTO into pump mode and supply water to one or more hoses and nozzles to be directed toward the fire. Similarly, when the fire response machine has completed its task at the fire scene, it is able to quickly revert back to road mode and begin movement to another incident or back to a firehouse or other storage facility. 
     It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to examples herein are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure or claims more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the claims entirely unless otherwise indicated. 
     Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. 
     Accordingly, this disclosure contemplates the inclusion of all modifications and equivalents of the subject matter recited in the appended claims as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is contemplated unless otherwise indicated herein or otherwise clearly contradicted by context.