Abstract:
A piston actuated synchronizer system for a split torque transmission where the piston is attached directly to the synchronizer shift collar on the synchronizer centerline to provide the required actuation in a small volume of space and resolve fork and rod deflection issues seen on other synchronizers that use such a system. The piston is pressure applied and spring released. This design also uses a displacement sensor to monitor synchronizer engagement.

Description:
TECHNICAL FIELD 
     This patent disclosure relates generally to multiple range transmissions and, more particularly to a split input continuously variable transmission that provide multiple ratio ranges and uses one or more synchronizers when shifting between ranges. 
     BACKGROUND 
     Because of the limited speed range of most prime mover devices, e.g., engines, motors, etc., such devices are frequently used in conjunction with a transmission to provide a range of transmission input-to-output ratios, e.g., 3-to-1, 1-to-1, or 1.5-to-1 (overdrive). Certain ratios provide lower torque at higher speed, while other ratios provide higher torque for lower speed, i.e., during acceleration or hill climbing. Such discrete ratio transmissions, while useful and ubiquitous, cause discontinuities during operation that may be disconcerting or otherwise disruptive. As such, continuously variable transmissions (CVTs) have been developed to allow smooth acceleration without sharp discontinuities between ranges, and such transmissions are now in widespread use. However, while CVT transmissions do not require shifts between discrete ratios, they do generally require shifts between ratio ranges. For example, a first ratio range may allow transmission ratios from 3-to-1 up to 2-to-1, while a second range may allow transmission ratios from 2-to-1 and 1-to-1. In order to provide ratios from 3-to-1 up to 1-to-1, therefore, a range shift will be needed. 
     While existing systems use fork activated shifting with some success, this type of activation is not optimal for every configuration, due to space constraints. Moreover, fork activated shifting systems impose maintenance and replacement requirements due to the action of spinning transmission components against the shift forks. However, the shift forks also serve to gauge the position of the transmission components and the completion of each shift. Thus, the industry has experienced difficulty in attempting to design a split path CVT shifting system that provides the benefits of fork-activated shifting within a limited volume and without the attendant wear problems caused by the forks. 
     SUMMARY 
     In an aspect of the disclosed principles, a split path CVT is provided for selectively providing multiple transmission ratio ranges between a CVT input and a CVT output. In this aspect, one or more of the ratio ranges are shifted by a piston-actuated synchronizer system. The piston-actuated synchronizer system includes a cylindrical collar connected by a spline to a piston sharing a common rotational axis. The collar is also part of the synchronizer assembly. A cylindrical driven gear has a spline associated with it on a second common rotational axis that is coincident with the first common rotational axis. The gear spline is connected to the synchronizer output ring. The gear is supported on the shaft by a bearing and can rotate independently from the shaft. The cylindrical collar, axially movable along the second common rotational axis, engages the synchronizer hub to the synchronizer output ring to engage the shaft to the gear. 
     A piston is associated with the cylindrical collar. The piston is supported by the hub, which is connected to the shaft, the hub also having one or more fluid inlets formed therein in fluid communication with the cylindrical cavity. The hub is partially enclosed by a manifold. The fluid inlets in the hub coincide with fluid passages in the manifold. The fluid passages in the manifold coincide with fluid passages in the housing. The flow of fluid from the one or more fluid inlets into the cylindrical cavity is regulated by a solenoid valve on the housing to force the piston and the associated cylindrical collar axially toward the synchronizer to engage the synchronizer hub to the synchronizer output ring and therefore to the gear. In an embodiment, a spring is provided for biasing the collar away from the synchronizer engaged position. 
     Further aspects and features of the disclosed principles will be appreciated from the following detailed description and the accompanying drawings, of which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic system diagram showing a split path CVT environment within which the disclosed principles may be implemented; 
         FIG. 2  is a partial cross-sectional side view of a piston-actuated synchronizer system within a split path CVT according to one aspect the disclosed principles, wherein the piston-actuated synchronizer is not engaged; 
         FIG. 3  is a partial cross-sectional side view of a piston-actuated synchronizer system within a split path CVT according to one aspect the disclosed principles, wherein the piston-actuated synchronizer is engaged; and 
         FIG. 4  is a flow chart illustrating a process of range shifting within an embodiment of the disclosed principles. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure relates to machines requiring a transmission to link a power source to the final ground-engaging mechanism, e.g., wheels, tracks, etc., and/or to another powered function or implement. Examples of such machines include machines used for mining, construction, farming, transportation, or any other industry known in the art. For example, the machine may be an earth-moving machine, such as a wheel loader, excavator, dump truck, backhoe, motor grader, material handler or the like. Moreover, one or more implements may be connected to the machine for a variety of tasks, including, for example, loading, compacting, lifting, brushing, and include, for example, buckets, compactors, forked lifting devices, brushes, grapples, cutters, shears, blades, breakers/hammers, augers, and others. 
       FIG. 1  is a diagrammatic illustration showing a transmission architecture  100  within which embodiments of the disclosed principles may be used. The illustrated transmission architecture  100  includes an engine  101 , a variator  103 , and a split path CVT  105 . In addition, a controller  107  is included in order to coordinate the operation of the engine  101 , variator  103 , and split path CVT  105 . A first output shaft  109  provides a first input from the engine  101  to the split path CVT  105 , and a second output  111  provides a second input from the variator  103  to the split path CVT  105 . A third output  113  from the split path CVT  105  is provided for linkage to a final drive train or other power transfer system, not shown. The third output  113  provides a weighted combination of the inputs to the split path CVT  105 . More precisely, at a given engine speed, the effective transmission ratio of the split path CVT  105  will depend upon the speed and direction of the variator  103  as well as upon a range setting of the split path CVT  105 . 
     The engine  101  is an example of a primary mover, but it will be appreciated that other primary mover systems may be used additionally or alternatively without departing from the scope of the described principles. Similarly, the variator  103  is simply an example of a secondary mover, and it will be appreciated that other types of secondary movers may be used additionally or alternatively without departing from the scope of the disclosed principles of operation. 
     The operation of the engine  101  is controlled based on one or more inputs, including, for example, an input from a user interface (not shown), e.g., a pedal or lever, as well as an input from the controller  107 , e.g., for purposes of torque control, traction control, etc. The operation of the variator  103  is controlled by the controller  107  based on the current and desired state of the split path CVT  105 . Finally, the split path CVT  105  is managed by the controller  107  based on a number of parameters including, for example, available engine power and torque, as well as vehicle speed. 
     The controller  107  may be any computing device capable of sensing one or more conditions of the split path CVT  105 , engine  101  and/or variator  103  and providing control outputs to one or more of the split path CVT  105 , engine  101  and/or variator  103 . By way of example but not limitation, the controller  107  may be integrated with an engine or machine control module, or may be a separate device. The controller  105  operates by reading computer-readable instructions from a computer-readable medium and executing the read instructions. The computer-readable medium may be a tangible medium such as a hard drive, optical disc, jump drive, thumb drive, flash memory, ROM, PROM, RAM, etc., or may be an intangible medium such as an electrical or optical wave form traveling in air, vacuum, or wire. 
     Although shift forks have traditionally served to execute accurate shift timing in split path CVT architectures, the use of these forks is not without consequence. The forks are non-rotating members that must forcefully interface with rapidly rotating transmission parts to execute a shift. Because rapid shifts are required, high shift loads may be applied, causing substantial wear to the forks and/or the mating transmission surfaces. Such wear necessitates maintenance and repair, both of which can be costly. Typically, the forks and the other associated parts of the system also require a fair amount of spatial volume to accommodate their bulk and range of motion. 
     In an embodiment of the disclosed principles, a piston-actuated shift mechanism is introduced to execute one or more range shifts in the split path CVT  105 . Although various configurations may be used without departing from the scope of the disclosed principles, one exemplary configuration is shown in cross-sectional side view in  FIG. 2  and  FIG. 4 . The illustrated piston-actuated shift mechanism  200  includes a cylindrical driven gear  201  and a cylindrical collar  205  that may selectively couple or uncouple the gear  201  to the shaft  225  via the synchronizer  203 . The collar  205  surrounds and is keyed to a substantially annular piston  213 . The piston  213  is axially slidable on a hub  209 , to selectively engage or disengage the driven gear  201  via a spline  207 . 
     A cylindrical compression spring  206  is located between the piston  213  and the synchronizer  203  to bias the assembly including the force collar  205  away from the spline  207 . A distal end of the collar  205  furthest from the spline  207  is formed into or joined with the cylindrical piston  213 , which fits closely on the hub  209 , forming a cylindrical cavity  215  there between. The hub  209  is attached to the shaft  225  by bolt  221 . The cylindrical cavity  215  is filled and drained of pressurized hydraulic fluid via one or more fluid inlets  219 . The hydraulic fluid is supplied through passages in the manifold  239  and in the housing  217 . 
     A solenoid valve  237  on the housing  217  is controlled via the controller  107  to regulate the flow of fluid from the one or more fluid inlets  219  into the cavity  215  The solenoid valve  237  may be proportional or binary (switching) and is electronically controlled by a solenoid control signal in an embodiment. However, other types of solenoid control may be used instead, including mechanical or hydraulic control for example. It will be appreciated that as pressurized fluid is introduced into the cavity  215  via the one or more fluid inlets  219 , the piston  213  is forced forward, compressing the return spring  206  as in  FIG. 3 . 
     The collar  205  has an annular step  242  thereon to engage a flange  241  of the piston  213 . Thus, the action of displacing the piston  213  also axially displaces the collar  205  towards the spline  207 . If sufficient fluid is introduced into the cavity  215 , the displacement of the collar  205  will be such that the collar  205  causes the synchronizer  203  to reduce the relative speed difference of the shaft  225  and the gear  201  to zero. This allows the collar  205  to move axially to engage the spline  207  of the synchronizer output ring which is engaged to the gear  201  through spline  227 . 
     In an embodiment of the disclosed principles, the engagement of the collar  205  with the spline  207  is used as a threshold precondition to further accelerate the shaft  225 . This is because any acceleration prior to the engagement of the driven collar  205  with the spline  207  will delay synchronization and will cause excessive wear to the synchronizer friction material. 
     To this end, a displacement sensor  229  is adapted to detect the axial position of the collar  205  and to convey a signal indicative of the axial position of the collar  205  to the transmission controller  107  via a sensor output  231 . The displacement sensor  229  may be of any suitable type and configuration, but in an embodiment of the disclosed principles, the displacement sensor  229  comprises a magnetic sensor. In an alternative embodiment, the displacement sensor  229  comprises a two-state switch. The displacement sensor  229  detects the axial location of the sensor target  233  that is contained in the sensor target keyway  235  in the piston  213 . The sensor target  233  is prevented from rotating by the displacement sensor  229 . 
       FIG. 4  is a flow chart illustrating a process of range shifting within an embodiment of the disclosed principles. The illustrated process  400  begins at stage  401 , wherein the controller  107  receives or generates an acceleration command to accelerate the split path CVT output. The Controller  107  causes the split path CVT output to accelerate via the variator  103  and/or engine  101  at stage  403 . The Controller continues to accelerate the split path CVT output at stage  405 . In stage  407 , the controller  107  determines whether a shift point has been attained. If such a point has been reached, the Controller  107  first reduces the torque output by the engine  101  and variator  103  at stage  409 , and then activates the solenoid valve  237  at stage  409  to fill the chamber  215  with pressurized hydraulic fluid, driving the piston  235  forward. 
     At stage  413 , the controller determines whether the driven collar  205  has engaged the spline  207 . This can be determined based on a reading of the signal from the displacement sensor  229 . Once it is determined that he driven collar  205  has engaged the spline  207 , the controller  107  increases the torque applied by the engine  101  and variator  103  at stage  415  to resume the prior rate of acceleration. 
     INDUSTRIAL APPLICABILITY 
     The described principles are applicable to machines requiring a transmission to link a power source to the final ground-engaging mechanism, e.g., wheels, tracks, etc., and/or to another powered function or implement. Examples of such machines include machines used for mining, construction, farming, transportation, or any other industry known in the art. For example, the machine may be an earth-moving machine, such as a wheel loader, excavator, dump truck, backhoe, motor grader, material handler or the like. Exemplary implements include, without limitation, buckets, compactors, forked lifting devices, brushes, grapples, cutters, shears, blades, breakers/hammers, augers, and others. 
     In this context, the disclosed principles allow rapid shifts in a split path CVT without the replacement and maintenance requirements imposed by the exclusive use of fork shifters. It will be appreciated, however, that a split path CVT generally involves multiple sets of gears that mesh and unmesh to shift the range of the transmission. Moreover, it is contemplated that certain range shifts can still be executed via fork shifters, such that the CVT includes a combination of one or more piston-actuated shift mechanisms as described herein and one or more traditional fork shift mechanisms. 
     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 the disclosure or examples thereof 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 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 disclosure 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.