Abstract:
A method of operating a driveline including a powersplit transmission is provided. The driveline may be operated in a hydrostatic power transmission mode and a blended hydrostatic/mechanical power transmission mode. The method comprises the steps of providing a hydrostatic circuit, detecting a rapid deceleration of the vehicle, and adjusting a threshold of at least one pressure relief valve forming a portion of the hydrostatic circuit in response to the sudden deceleration. The at least one pressure relief valve facilitates quickly changing the driveline from the blended hydrostatic/mechanical power transmission mode to the hydrostatic power transmission mode.

Description:
CLAIM OF PRIORITY 
       [0001]    The present application claims priority to and incorporates by reference U.S. Provisional Application No. 61/589,987 filed Jan. 24, 2012, entitled “FREEWHEEL DEVICE FOR HYDROSTATIC GROUP IN A POWERSPLIT TRANSMISSION.” 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Certain powersplit transmissions suffer from their associated power sources, such as an internal combustion engine, stalling when the vehicle encounters a load, such as when the vehicle enters a pile of aggregate material. The vehicle may be, by way of example, a wheel loader. In most cases, the stall condition occurs when the transmission is in a driving gear configuration used for higher speeds. 
         [0003]    Typically, the stall occurs because the output of the transmission maintains driving engagement with the power source and the overall transmission ratio set cannot follow the fast deceleration (speed gradient) that the vehicle is subjected to when entering a pile. At a certain point, the power source is unable to deliver the requested drive torque, which results in an engine stall. 
         [0004]    In a wheel loader equipped with a conventional powersplit transmission, this rapid changing ratio set is in the first instance accomplished by the torque converter. When the wheel loader is entering a pile (typically in a driving gear configuration used for higher speeds) the speed ratio of the torque converter changes from a high value (for example approximately 0.8 to approximately 0.9, which is typically associated with a driving mode) to a rather low value, or even zero (stall condition). 
         [0005]    Another advantage of the torque converter is that the torque received from the engine is increased during the stall condition with a factor (typically a factor of 2 to 3 in these applications), enhancing the push power of the machine. To even further increase the push power of the machine, a downshift may be made from the second driving gear to the first driving gear to obtain a maximum push power available from the vehicle. This downshift typically occurs with an interruption in the torque delivered by the vehicle. 
         [0006]    In order to overcome the above-mentioned deficiency, the transmission may be put into neutral. The vehicle thus comes to a full stop, such as during pile entry. Re-initialization of the drive train is then required prior to resuming the actual operation. This solution significantly compromises the performance of the wheel loader to a negative extent and therefore is unacceptable for modern vehicles. Generally, transmissions convert power from the power source, for example a diesel engine, to the drive axles of the vehicle. Some transmissions have a powersplit configuration. This means that power can be transferred by using a hydraulic branch, a mechanical branch or a combination of both branches used together. 
         [0007]    Powersplit transmissions can be operated in different modes. In a first drive range, the transmission is operated in the hydrostatic mode, where only a hydrostatic motor drives an output of the vehicle. In a second or a third drive range, the transmission is operated in the powersplit mode, where a combination of the hydraulic branch and the mechanical branch of the transmission are used to drive the output of the vehicle. 
         [0008]    It would be advantageous to develop a method of operating a driveline including a power split transmission that militates against a torque interruption from occurring during a shifting procedure and militates against a stall condition from occurring. 
       SUMMARY OF THE INVENTION 
       [0009]    Presently provided by the invention, a method of operating a driveline including a power split transmission that militates against a torque interruption from occurring during a shifting procedure and militates against a stall condition from occurring, has surprisingly been discovered. 
         [0010]    In one embodiment, the present invention is directed to a method of operating a driveline including a powersplit transmission. The driveline may be operated in a hydrostatic power transmission mode and a blended hydrostatic/mechanical power transmission mode. The method comprises the steps of providing a hydrostatic circuit, detecting a rapid deceleration of the vehicle, and adjusting a threshold of at least one pressure relief valve forming a portion of the hydrostatic circuit in response to the sudden deceleration. The at least one pressure relief valve facilitates quickly changing the driveline from the blended hydrostatic/mechanical power transmission mode to the hydrostatic power transmission mode. 
         [0011]    Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention will become readily apparent to those skilled in the art from the following detailed description when considered in the light of the accompanying drawings in which: 
           [0013]      FIG. 1  is a schematic depiction of a powersplit transmission according to an embodiment of the present invention; 
           [0014]      FIG. 2  is a schematic depiction of a powersplit transmission according to another embodiment of the present invention; 
           [0015]      FIG. 3  is a schematic depiction of a powersplit transmission according to another embodiment of the present invention; and 
           [0016]      FIG. 4  is a table indicating an engagement status of each of a plurality of components of the power split transmission in each of the operating modes a vehicle driveline including the powersplit transmission may be placed in. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions, directions or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise. 
         [0018]      FIG. 1  illustrates a vehicle driveline  100 . The vehicle driveline  100  comprises a power source  102 , a powersplit transmission  104 , a freewheel device  106 , a controller  108 , and a vehicle output  110 . The power source  102  is drivingly engaged with the powersplit transmission  104 . The powersplit transmission  104  is drivingly engaged with the vehicle output  110 . The freewheel device  106  is in fluid communication with a portion of the powersplit transmission  104 . It is understood that the powersplit transmission  104  illustrated in  FIG. 1  is merely exemplary in nature, and that the freewheel device  106  and the controller  108  may be used with any powersplit transmission. 
         [0019]    The power source  102  is an internal combustion engine as is known in the art. However, it is understood the power source  102  may be another type of power source such as an electric motor, for example. The power source  102  rotates a transmission input  112 . A transmission (not shown) or a clutching device (not shown) may be disposed between the power source  102  and the transmission input  112  to permit selective engagement of the power source  102  with the transmission input  112 . Further, the transmission or the clutching device may be used to modify a characteristic of a power transferred from the power source  102  to the powersplit transmission  104 . 
         [0020]    The powersplit transmission  104  comprises a hydrostatic circuit  114  and a mechanical portion  116 . A variable displacement pump  118  and a variable displacement motor  120  of the hydrostatic circuit  114  are drivingly engaged with the mechanical portion  116 . 
         [0021]    The hydrostatic circuit  114  comprises the variable displacement pump  118 , a variable displacement motor  120 , a pair of safety valves  122 , a pair of pressure transducers  124 , a first plurality of drive fluid conduits  126 , and a second plurality of drive fluid conduits  128 . 
         [0022]    The variable displacement pump  118  is a hydraulic axial piston pump having a movable swashplate (not shown). However, it is understood the variable displacement pump  118  may be any other type of variable displacement pump. A position of the movable swashplate is determined in response to a signal received by the variable displacement pump  118  from the controller  108 , which the variable displacement pump  118  is in communication with. The variable displacement pump  118  is drivingly engaged with the power source  102  through the transmission input  112 . A first fluid port  130  of the variable displacement pump  118  is in fluid communication with the first plurality of drive fluid conduits  126 . A second fluid port  132  of the variable displacement pump  118  is in fluid communication with the second plurality of drive fluid conduits  128 . 
         [0023]    The variable displacement motor  120  is a hydraulic axial piston pump having a movable swashplate (not shown). However, it is understood the variable displacement motor  120  may be any other type of variable displacement motor. A position of the movable swashplate is determined in response to a signal received by the variable displacement pump  118  from the controller.  108 , which the variable displacement pump  118  is in communication with. The variable displacement motor  120  is drivingly engaged with a drive range selector  134  of the mechanical portion  116 . A first fluid port  136  of the variable displacement motor  120  is in fluid communication with the first plurality of drive fluid conduits  126 . A second fluid port  138  of the variable displacement motor  120  is in fluid communication with the second plurality of drive fluid conduits  128 . 
         [0024]    The pair of safety valves  122  is in fluid communication with the first plurality of drive fluid conduits  126  and the second plurality of drive fluid conduits  128 . One of the pair of safety valves  122  is configured to sense a fluid pressure within the first plurality of drive fluid conduits  126  and the remaining one of the pair of safety valves  122  is configured to sense a fluid pressure within the second plurality of drive fluid conduits  128 . The pair of safety valves  122  is configured to facilitate fluid communication between the first plurality of drive fluid conduits  126  and the second plurality of drive fluid conduits  128  when a fluid pressure within one of the first plurality of drive fluid conduits  126  and the second plurality of drive fluid conduits  128  is above a safety threshold. It is understood that the pair of safety valves  122  shown in  FIG. 1  is merely exemplary in nature and that the pair of safety valves  122  may be replaced with any fluid power safety device, which are commonly known in the art. 
         [0025]    The pair of pressure transducers  124  is in communication with the controller  108 . The pair of pressure transducers  124  is configured to sense a fluid pressure within the first plurality of drive fluid conduits  126  and the second plurality of drive fluid conduits  128  and relay the fluid pressure within the drive fluid conduits  126 ,  128  using a signal. It is understood that the arrangement of pressure transducers  124  shown in  FIG. 1  and the communication between the pressure transducers  124  and the controller  108  described hereinabove is merely exemplary in nature and that the pressure transducers  124  may be arranged or operated in any conventional manner. 
         [0026]    The first plurality of drive fluid conduits  126  are conduits used in hydraulic power systems as is known in the art. The first plurality of drive fluid conduits  126  may comprise flexible conduits, rigid conduits, or conduits formed within other components of the powersplit transmission  104 . The first plurality of drive fluid conduits  126  is in fluid communication with the variable displacement pump  118  through the first fluid port  130  and the variable displacement motor  120  through the first fluid port  136 . 
         [0027]    The second plurality of drive fluid conduits  128  are conduits used in hydraulic power systems as is known in the art. The second plurality of drive fluid conduits  128  may comprise flexible conduits, rigid conduits, or conduits formed within other components of the powersplit transmission  104 . The second plurality of drive fluid conduits  128  is in fluid communication with the variable displacement pump  118  through the second fluid port  132  and the variable displacement motor  120  through the second fluid port thereof  138 . 
         [0028]    The mechanical portion  116  comprises a transmission input  112 , a directional selector  140 , the drive range selector  134 , a planetary gearset  142 , and a transmission output  144 . The transmission input  112  is a geared shaft drivingly engaged with the variable displacement pump  118  and the drive range selector  140 . The drive range selector  140  is also drivingly engaged with the planetary gearset  142  through an intermediate shaft  146 . The planetary gearset  142  is also drivingly engaged with the drive range selector  134  and the transmission output  144 . The transmission output  144  is a gear which is also drivingly engaged with the vehicle output  110 . 
         [0029]    The directional selector  140  comprises a forward clutch  148  and a reverse clutch  150 . The forward clutch  148  and the reverse clutch  150  are each drivingly engaged with the transmission input  112  and the intermediate shaft  146 . The forward clutch  148  and the reverse clutch  150  are in communication with the controller  108 . 
         [0030]    The forward clutch  148  is a clutching device which may be variably engaged in response to a signal received from the controller  108 . When the forward clutch  148  is in an engaged position, torque applied to the transmission input  112  is applied to the intermediate shaft  146  through the forward clutch  148 . The forward clutch  148  may be a plate clutch, a cone clutch, or any other type of clutch that may be variably engaged. The forward clutch  148  is a hydraulically operated clutch; however, it is understood that the forward clutch  148  may be operated in any other manner. 
         [0031]    The reverse clutch  150  is a clutching device which may be variably engaged in response to a signal received from the controller  108 . When the reverse clutch  150  is in an engaged position, torque applied to the transmission input  112  is applied to the intermediate shaft  146  through the reverse clutch  150 . The reverse clutch  150  reverses a rotational direction of the intermediate shaft  146  when compared to the forward clutch  148 . The reverse clutch  150  may be a plate clutch, a cone clutch, or any other type of clutch that may be variably engaged. The reverse clutch  150  is a hydraulically operated clutch; however, it is understood that the reverse clutch  150  may be operated in any other manner. 
         [0032]    The drive range selector  134  comprises a primary range clutch  152  and a secondary range clutch  154 . The primary range clutch  148  and the secondary range clutch  152  are each drivingly engaged with the variable displacement motor  120  and the planetary gearset  142 . The primary range clutch′  148  and the secondary range clutch  152  are in communication with the controller  108 . 
         [0033]    The primary range clutch  152  is a clutching device which may be variably engaged in response to a signal received from the controller  108 . When the primary range clutch  152  is in an engaged position, torque applied by an output of the variable displacement motor  120  is applied to a carrier  156  of the planetary gearset  142  through the primary range clutch  152 . The primary range clutch  152  may be a plate clutch, a cone clutch, or any other type of clutch that may be variably engaged. The primary range clutch  152  is a hydraulically operated clutch; however, it is understood that the primary range clutch  152  may be operated in any other manner. 
         [0034]    The secondary range clutch  154  is a clutching device which may be variably engaged in response to a signal received from the controller  108 . When the secondary range clutch  154  is in an engaged position, torque applied by an output of the variable displacement motor  120  is applied to a ring gear  158  of the planetary gearset  142  through the secondary range clutch  154 . The secondary range clutch  154  may be a plate clutch, a cone clutch, or any other type of clutch that may be variably engaged. The secondary range clutch  154  is a hydraulically operated clutch; however, it is understood that the secondary range clutch  154  may be operated in any other manner. 
         [0035]    The planetary gearset  142  comprises a sun gear  160 , a carrier  156  including a plurality of planet gears  162  rotatably disposed thereon, and a ring gear  158 . The sun gear  160 , the carrier  156  including the plurality of planet gears  162  rotatably disposed thereon, and the ring gear  158  form an epicyclic gearset which is common and known in the art. The sun gear  160  is drivingly engaged with the intermediate shaft  146 . The carrier  156  is drivingly engaged with a portion of the primary range clutch  152  and the transmission output  144 . The ring gear  158  is drivingly engaged with a portion of the secondary range clutch  154 . 
         [0036]    The freewheel device  106  illustrated in  FIG. 1  comprises a first pressure relief valve  164  and a second pressure relief valve  166 . 
         [0037]    The first pressure relief valve  164  is in fluid communication with the first plurality of drive fluid conduits  126  and the second plurality of drive fluid conduits  128 . The first pressure relief valve  164  is also in communication with the controller  108 , and the first pressure relief valve  164  is configured to be operated in a proportional manner by the controller  108  in response to a fluid pressure of the first plurality of drive fluid conduits  126 . When the first pressure relief valve  164  is placed in an open or a partially open position, fluid communication between the first plurality of drive fluid conduits  126  and the second plurality of drive fluid conduits  128  is afforded. 
         [0038]    The second pressure relief valve  166  is in fluid communication with the first plurality of drive fluid conduits  126  and the second plurality of drive fluid conduits  128 . The second pressure relief valve  166  is also in communication with the controller  108 , and the second pressure relief valve  164  is configured to be operated in a proportional manner by the controller  108  in response to a fluid pressure of the second plurality of drive fluid conduits  128 . When the second pressure relief valve  166  is placed in an open or a partially open position, fluid communication between the first plurality of drive fluid conduits  126  and the second plurality of drive fluid conduits  128  is afforded. 
         [0039]    The controller  108  is in communication with the variable displacement pump  118 , the variable displacement motor  120 , the pair of pressure transducers  124 , the forward clutch  148 , the reverse clutch  150 , the primary range clutch  152 , the secondary range clutch  154 , the first pressure relief valve  164 , and the second pressure relief valve  166 . The controller  108  may be in one of an electrical, a hydraulic, a pneumatic, and a wireless communication with the variable displacement pump  118 , the variable displacement motor  120 , each of the pressure transducers  124 , the forward clutch  148 , the reverse clutch  150 , the primary range clutch  152 , the secondary range clutch  154 , the first pressure relief valve  164 , and the second pressure relief valve  166 . 
         [0040]    The controller  108  receives a signal from the pair of pressure transducers  124  in response to the fluid pressure within the drive fluid conduits  126 ,  128 . The variable displacement pump  118 , the variable displacement motor  120 , the forward clutch  148 , the reverse clutch  150 , the primary range clutch  152 , the secondary range clutch  154  each receive a signal from the controller  108  to control a position of the moveable swashplate or an engagement thereof. The first pressure relief valve  164  and the second pressure relief valve  166  each receive a signal from the controller  108  to control an engagement thereof in a proportional manner. The controller  108  includes at least one of a predetermined set of instructions and conditions that are used to determine a signal sent to each of the each of the variable displacement pump  118 , the variable displacement motor  120 , the pressure transducers  124 , the forward clutch  148 , the reverse clutch  150 , the primary range clutch  152 , the secondary range clutch  154 , the first pressure relief valve  164 , and the second pressure relief valve  166  in response to at least the signal the controller  108  receives from each of the pressure transducers  124 . 
         [0041]    The vehicle output  110  is in driving engagement with the transmission output  144 . A shown in  FIG. 1 , the vehicle output  110  comprises an axle and wheel assembly; however, it is understood that the vehicle output  110  may be any other conventionally used drive assembly. 
         [0042]      FIG. 2  illustrates an alternative embodiment of the vehicle driveline  100 . Similar structural features of the hydrostatic driveline  100  are similarly referenced, with the exception of the below identified features. 
         [0043]    A vehicle driveline  200  shown in  FIG. 2  includes comprises a power source  202 , a powersplit transmission  204 , a freewheel device  170 , a controller  172 , and a vehicle output  210 . The power source  202  is drivingly engaged with the powersplit transmission  204 . The powersplit transmission  204  is drivingly engaged with the vehicle output  210 . The freewheel device  170  is in fluid communication with a portion of the powersplit transmission  204 . It is understood that the powersplit transmission  204  illustrated in  FIG. 2  is merely exemplary in nature, and that the freewheel device  170  and the controller  172  may be used with any powersplit transmission. 
         [0044]    The freewheel device  170  illustrated in  FIG. 2  comprises a pressure relief valve  174 . 
         [0045]    The pressure relief valve  174  is in fluid communication with a first plurality of drive fluid conduits  226  and a second plurality of drive fluid conduits  228 . The pressure relief valve  174  is also in communication with the controller  172 , and the pressure relief valve  174  is configured to be operated in a proportional manner by the controller  172  in response to a fluid pressure of the first plurality of drive fluid conduits  226  and the second plurality of fluid drive conduits  228 . When the pressure relief valve  174  is placed in an open or a partially open position, fluid communication between the first plurality of drive fluid conduits  226  and the second plurality of drive fluid conduits  228  is afforded. 
         [0046]    The controller  172  is in communication with a variable displacement pump  218 , a variable displacement motor  220 , a pair of pressure transducers  224 , a forward clutch  248 , a reverse clutch  250 , a primary range clutch  252 , a secondary range clutch  254 , and the pressure relief valve  174 . The controller  172  may be in one of an electrical, a hydraulic, a pneumatic, and a wireless communication with the variable displacement pump  218 , the variable displacement motor  220 , each of the pressure transducers  224 , the forward clutch  248 , the reverse clutch  250 , the primary range clutch  252 , the secondary range clutch  254 , and the pressure relief valve  174 . 
         [0047]    The controller  172  receives a signal from the pair of pressure transducers  224  in response to the fluid pressure within the drive fluid conduits  226 ,  228 . The variable displacement pump  218 , the variable displacement motor  220 , the forward clutch  248 , the reverse clutch  250 , the primary range clutch  252 , the secondary range clutch  254  each receive a signal from the controller  172  to control a position of the moveable swashplate or an engagement thereof. The pressure relief valve  174  receives a signal from the controller  172  to control an engagement thereof in a proportional manner. The controller  172  includes at least one of a predetermined set of instructions and conditions that are used to determine a signal sent to each of the each of the variable displacement pump  218 , the variable displacement motor  220 , the pressure transducers  224 , the forward clutch  248 , the reverse clutch  250 , the primary range clutch  252 , the secondary range clutch  254 , and the pressure relief valve  174  in response to at least the signal the controller  172  receives from each of the pressure transducers  224 . 
         [0048]    A vehicle driveline  200  shown in  FIG. 2  includes comprises a power source  202 , a powersplit transmission  204 , a freewheel device  170 , a controller  172 , and a vehicle output  210 . The power source  202  is drivingly engaged with the powersplit transmission  204 . The powersplit transmission  204  is drivingly engaged with the vehicle output  210 . The freewheel device  170  is in fluid communication with a portion of the powersplit transmission  204 . It is understood that the powersplit transmission  204  illustrated in  FIG. 2  is merely exemplary in nature, and that the freewheel device  170  and the controller  172  may be used with any powersplit transmission. 
         [0049]      FIG. 3  illustrates an alternative embodiment of the vehicle driveline  100 . Similar structural features of the hydrostatic driveline  100  are similarly referenced, with the exception of the below identified features. 
         [0050]    A vehicle driveline  300  shown in  FIG. 3  includes comprises a power source  302 , a powersplit transmission  304 , a freewheel device  180 , a controller  182 , and a vehicle output  310 . The power source  302  is drivingly engaged with the powersplit transmission  304 . The powersplit transmission  304  is drivingly engaged with the vehicle output  310 . The freewheel device  180  is in fluid communication with a portion of the powersplit transmission  304 . It is understood that the powersplit transmission  304  illustrated in  FIG. 3  is merely exemplary in nature, and that the freewheel device  180  and the controller  182  may be used with any powersplit transmission. 
         [0051]    The freewheel device  180  illustrated in  FIG. 3  comprises a shuttle valve  184 , a pressure relief valve  186 , and a pair of check valves  188 . The shuttle valve  184  is conventional and well known in the art and is in fluid communication with a first plurality of drive fluid conduits  326  and a second plurality of drive fluid conduits  328 . The pair of check valves  188  is in fluid communication with the first plurality of drive fluid conduits  326  and the second plurality of drive fluid conduits  328 . As shown in  FIG. 3 , the pair of check valves  188  is disposed on a bridging conduit  190  in opposing orientations to prevent fluid from each of the first plurality of drive fluid conduits  326  and the second plurality of drive fluid conduits  328  to a portion of the bridging conduit  190  between the pair of check valves  188 . 
         [0052]    The pressure relief valve  186  is in fluid communication with the shuttle valve  184  and the portion of the bridging conduit  190  between the pair of check valves  188 . The pressure relief valve  186  is also in communication with the controller  182 , and the pressure relief valve  186  is configured to be operated in a proportional manner by the controller  182  in response to a fluid pressure of the first plurality of drive fluid conduits  326  and the second plurality of fluid drive conduits  328 . When the pressure relief valve  186  is placed in an open or a partially open position, fluid communication between one of the first plurality of drive fluid conduits  226  and the second plurality of drive fluid conduits  228 , depending on whichever of the conduits  226 ,  228  has a greater pressure, and a remaining one of the first plurality of drive fluid conduits  226  and the second plurality of drive fluid conduits  228 , through one of the pair of check valves  188 , is afforded. 
         [0053]    The controller  182  is in communication with a variable displacement pump  318 , a variable displacement motor  320 , a pair of pressure transducers  324 , a forward clutch  348 , a reverse clutch  350 , a primary range clutch  352 , a secondary range clutch  354 , and the pressure relief valve  186 . The controller  182  may be in one of an electrical, a hydraulic, a pneumatic, and a wireless communication with the variable displacement pump  318 , the variable displacement motor  320 , each of the pressure transducers  324 , the forward clutch  348 , the reverse clutch  350 , the primary range clutch  352 , the secondary range clutch  354 , and the pressure relief valve  186 . 
         [0054]    The controller  182  receives a signal from the pair of pressure transducers  324  in response to the fluid pressure within the drive fluid conduits  326 ,  328 . The variable displacement pump  318 , the variable displacement motor  320 , the forward clutch  348 , the reverse clutch  350 , the primary range clutch  352 , the secondary range clutch  354  each receive a signal from the controller  182  to control a position of the moveable swashplate or an engagement thereof. The pressure relief valve  186  receives a signal from the controller  182  to control an engagement thereof in a proportional manner. The controller  182  includes at least one of a predetermined set of instructions and conditions that are used to determine a signal sent to each of the each of the variable displacement pump  318 , the variable displacement motor  320 , the pressure transducers  324 , the forward clutch  348 , the reverse clutch  350 , the primary range clutch  352 , the secondary range clutch  354 , and the pressure relief valve  186  in response to at least the signal the controller  182  receives from each of the pressure transducers  324 . 
         [0055]      FIGS. 1-3  each contain transformation devices  90 , such as valves, for transforming an electrical signal to a hydraulic signal, or vice versa. The devices  90  may be located anywhere between controllers  108 ,  172  and/or  182  and they devices they are controlling (e.g., motors, pumps, relief valves, etc.). Therefore, the location of the devices  90  in the figures is intended for illustrative purposes and should not considered to be limiting. 
         [0056]    Regardless of whether these devices are located between a controller and a motor, pump or valve, they effectively work in the same way to convert signals between the controller and the motor, pump or valve. The devices may vary in their construction, location or size with respect to one another depending on the load they are subject to, the physical space allotted to them, the environmental conditions they experience, or other factors, but they all function in essentially the same way. With the understanding that the devices essentially function in the same way, they have all been designated with reference number  90  even though they may have variations between them. 
         [0057]    In use, the vehicle driveline  100 ,  200 ,  300  may be operated in a hydrostatic mode or in a powersplit mode. In the hydrostatic mode, the power source  102 ,  202 ,  302 , through the hydrostatic circuit  114 ,  214 ,  314 , solely drives the vehicle output  110 ,  210 ,  310 . In the powersplit mode, the power source  102 ,  202 ,  302 , through both the hydrostatic circuit  114 ,  214 ,  314  and the mechanical portion  116 ,  216 ,  316 , drive the vehicle output  110 ,  210 ,  310 . 
         [0058]    In the powersplit mode, when the forward clutch  148 ,  248 ,  348  is engaged and the reverse clutch  150 ,  250 ,  350  is disengaged, the mechanical portion  116 ,  216 ,  316  can be considered to have a positive ratio. Conversely, when the reverse clutch  150 ,  250 ,  350  is engaged and the forward clutch  148 ,  248 ,  348  is disengaged, the mechanical portion  116 ,  216 ,  316  can be considered to have a negative ratio. 
         [0059]    In the powersplit mode, the intermediate shaft  146 ,  246 ,  346 , through one of the forward clutch  148 ,  248 ,  348  and the reverse clutch  150 ,  250 ,  350 , drives the sun gear  160 ,  260 ,  360  of the planetary gearset  142 ,  242 ,  342 . The variable displacement motor  120 ,  220 ,  320 , through the secondary range clutch  154 ,  254 ,  354 , drives the ring gear  158 ,  258 ,  358  of the planetary gearset  142 ,  242 ,  342 . As the sun gear  160 ,  260 ,  360  and the ring gear  158 ,  258 ,  358  are driven, the carrier  156 ,  256 ,  356 , through the planet gears  162 ,  262 ,  362 , transfers power to the transmission output  144 ,  244 ,  344 . The output speed of the powersplit transmission  104 ,  204 ,  304  can be controlled by varying the speed of the variable displacement motor  120 ,  220 ,  320 , in accordance with the planetary gearset  142 ,  242 ,  342 . 
         [0060]    In the hydrostatic mode, the primary range clutch  152 ,  252 ,  352 , and the secondary range clutch  154 ,  254 ,  354  are both engaged while the forward clutch  148 ,  248 ,  348  and the reverse clutch  150 ,  250 ,  350  are both disengaged. Such an operating condition causes the intermediate shaft  146 ,  246 ,  346  to be backdriven. The vehicle driveline  100 ,  200 ,  300  is switched from the hydrostatic mode to the powersplit mode when the differential speed between the forward clutch  148 ,  248 ,  348  and the reverse clutch  150 ,  250 ,  350  and the intermediate shaft  146 ,  246 ,  346  is substantially equal to zero. 
         [0061]      FIG. 4  is a table indicating an engagement status of each of the forward clutch  148 ,  248 ,  348 , the reverse clutch  150 ,  250 ,  350 , the primary range clutch  152 ,  252 ,  352 , the secondary range clutch  154 ,  254 ,  354  and a rotation of the variable displacement motor  120 ,  220 ,  320  in each of the operating modes the vehicle driveline  100 ,  200 ,  300  may be placed in. 
         [0062]    A vehicle driveline similar to the vehicle driveline  100 ,  200 ,  300 , but not including the freewheel device  106 ,  170 ,  180  or the controller  108 ,  172 ,  182  cannot handle rapid decelerations of the vehicle driveline. Such rapid decelerations may occur when a portion of the vehicle enters a pile of aggregate material, for example. Consequently, a power source of the vehicle driveline may stall during the rapid deceleration, which is undesirable. The rapid deceleration does not allow for sufficient time for the vehicle driveline to switch from the powersplit mode to the hydrostatic mode, which includes adjusting a position of the moveable swashplates of the variable displacement pump and the variable displacement motor and changing an engagement status of the clutches of the drive range selector and the directional selector. 
         [0063]    The vehicle driveline  100 ,  200 ,  300  according the embodiments of the invention, include the freewheel device  106 ,  170 ,  180  and the controller  108 ,  172 ,  182 , which allow the vehicle driveline  100 ,  200 ,  300  to encounter a rapid deceleration. 
         [0064]    When a vehicle the vehicle driveline  100 ,  200 ,  300  is incorporated in undergoes the rapid deceleration from the hydrostatic mode, the power source  102 ,  202 ,  302  becomes loaded. As it is unlikely that the vehicle output  110 ,  210 ,  310  will slip against an operating surface (such as a stone substrate, for example), the loaded condition of the power source  102 ,  202 ,  302  and the rapid deceleration of the vehicle driveline  100 ,  200 ,  300 , causes a fluid pressure within one of the first plurality of drive fluid conduits  126 ,  226 ,  326  and the second plurality of drive fluid conduits  128 ,  228 ,  328  to increase significantly. Upon the increase in the fluid pressure within one of the first plurality of drive fluid conduits  126 ,  226 ,  326  and the second plurality of drive fluid conduits  128 ,  228 ,  328 , increased fluid pressure is detected by the controller  108 ,  172 ,  182  through the pressure transducers  124 ,  224 ,  324 . If the fluid pressure detected by the controller is above a threshold value programmed in the controller  108 ,  172 ,  182 , the controller  108 ,  172 ,  182  will activate the freewheel device  106 ,  170 ,  180 . 
         [0065]    The controller  108 ,  172 ,  182  activates the freewheel device  106 ,  170 ,  180  by lowering a set point of the pressure relieve valves  164 ,  166 ,  174 ,  186  to a level that militates against the power source  102 ,  202 ,  302  stalling. The set point of the pressure relieve valves  164 ,  166 ,  174 ,  186  may be determined by a maximum torque available or a maximum power available of the power source  102 ,  202 ,  302  based on a throttle setting of the power source  102 ,  202 ,  302 . 
         [0066]    Upon activation of the freewheel device  106 ,  170 ,  180 , the vehicle driveline  100 ,  200 ,  300  is placed into a freewheel mode. In the freewheel mode, a rotational speed of the vehicle output  110 ,  210 ,  310  is determined by a rotational speed of the sun gear  160 ,  260 ,  360  and a rotational speed of the carrier  156 ,  256 ,  356 , which define a rotational speed of the ring gear  158 ,  258 ,  358 . 
         [0067]    When the vehicle driveline  100 ,  200 ,  300  placed in the powersplit mode undergoes the rapid deceleration, the power source  102 ,  202 ,  302  may become loaded. The controller  108 ,  172 ,  182  detects the loaded condition of the power source  102 ,  202 ,  302 . In response, the controller  108 ,  172 ,  182  maintains a near constant level of load on the power source  102 ,  202 ,  302  by activating the freewheel device  106 ,  170 ,  180 . By maintaining the near constant level of load on the power source  102 ,  202 ,  302 , the fluid pressure within one of the first plurality of drive fluid conduits  126 ,  226 ,  326  and the second plurality of drive fluid conduits  128 ,  228 ,  328  is maintained at a near constant level, which results in a similarly near constant application of torque to the vehicle output  110 ,  210 , 310 . 
         [0068]    During the rapid deceleration, a rotational speed of the sun gear  160 ,  260 ,  360  remains at a substantially constant value, as the sun gear  160 ,  260 ,  360  is drivingly engaged with the power source  102 ,  202 ,  302 . A rotational speed of the carrier  156 ,  256 ,  356  decreases to zero during the rapid deceleration, where the rapid deceleration causes the vehicle output  110 ,  210 ,  310  to come to a stop. As such, a rotational speed of the ring gear  158 ,  258 ,  358  must increase; however, in an opposing rotational direction. In the event that a rotational direction of the ring gear  158 ,  258 ,  358  is the same as a rotational direction of the sun gear  160 ,  260 ,  360 , during the rapid deceleration, a rotational speed of the ring gear  158 ,  258 ,  358  will decrease and reverse as the vehicle driveline  100 ,  200 ,  300  is placed into the freewheel mode. 
         [0069]    It is understood that at a greatest value (such as a high speed of the vehicle) of the rotational speed of the sun gear  160 ,  260 ,  360  the rotational speed of the ring gear  158 ,  258 ,  358  may exceed a maximum rotational speed of the variable displacement motor  120 ,  220 ,  320  during the rapid deceleration. In response to the high rotational speed of the sun gear  160 ,  260 ,  360 , the controller  108 ,  172 ,  182  decreases a rotational speed of the power source  102 ,  202 ,  302  to militate against damage that may occur to the variable displacement motor  120 , 220 , 320 . 
         [0070]    Upon activation of the freewheel device  106 ,  170 ,  180 , the controller  108 ,  172 ,  182  also performs other tasks. The controller  108 ,  172 ,  182  adjusts a position of the moveable swashplate of the variable displacement pump  118 ,  218 ,  318  and the variable displacement motor  120 ,  220 ,  320  to a new operating point, begins a filling process for engaging the primary range clutch  152 ,  252 ,  352 , and reduce a pressure on one of the forward clutch  148 ,  248 ,  348  and the reverse clutch  150 ,  250 ,  350 . 
         [0071]    When the vehicle driveline  100 ,  200 ,  300  is placed in the hydrostatic mode and is desired to be operated at speeds close to zero, the movable swashplate of the variable displacement pump  118 ,  218 ,  318  is set to a small swivel angle to deliver a small amount of hydraulic fluid. At the same time, in order to maximize a tractive effort at such low speeds, the movable swashplate of the variable displacement motor  120 ,  220 ,  320  is set to a large swivel angle. 
         [0072]    Prior to the rapid deceleration that the vehicle driveline  100 ,  200 ,  300  may be subjected to, the movable swashplates of the variable displacement pump  118 ,  218 ,  318  and the variable displacement motor  120 ,  220 ,  320  are determined based on a requested speed of the vehicle at that moment. During the rapid deceleration, the powersplit transmission  104 ,  204 ,  304  will be operated in the freewheel mode and an amount of torque will be applied to the vehicle output  110 ,  210 ,  310  as the vehicle driveline  100 ,  200 ,  300  comes to a complete stop. As a speed of the vehicle approaches zero, the movable swashplates of the variable displacement pump  118 ,  218 ,  318  and the variable displacement motor  120 ,  220 ,  320  are moved to a new swivel angle. 
         [0073]    Within most of the operating range of the vehicle driveline  100 ,  200 ,  300 , the variable displacement motor  120 ,  220 ,  320  will already have a correct swivel angle setting, which is the large swivel angle. The large swivel angle facilitates a maximum torque loading (and thus a maximized tractive effort) of the planetary gearset  142 ,  242 ,  342  during the freewheel mode. Within most of the operating range of the vehicle driveline  100 ,  200 ,  300 , the variable displacement pump  118 ,  218 ,  318  will require a correction in the swivel angle setting. When the swivel angle set of the variable displacement pump  118 ,  218 ,  318  is set to a positive value (such as during higher vehicle speeds), the swivel angle setting will require inversion. 
         [0074]    Upon activation of the freewheel device  106 ,  170 ,  180  the controller  108 ,  172 ,  182  also begins a filling process for engaging the primary range clutch  152 ,  252 ,  352 . The filling process of the primary range clutch  152 ,  252 ,  352  includes the steps of moving a clutch piston from an end stop position to a position where it starts applying a force onto a clutch pack while minimizing or preventing any torque from being transferred through the primary range clutch  152 ,  252 ,  352 . 
         [0075]    The last process that has to take place upon activation of the freewheel device  106 ,  170 ,  180 , prior to be able to change from the powersplit mode to the hydrostatic mode is reducing the hydraulic pressure on one of the forward clutch  148 ,  248 ,  348  and the reverse clutch  150 ,  250 ,  350  to a level (with a certain safety margin) that the forward clutch  148 ,  248 ,  348  or the reverse clutch  150 ,  250 ,  350  is still capable of transferring all of the torque applied thereto. Such a pressure level can be determined based on the setting of the pressure relief valves  164 ,  166 ,  174 ,  186  and based upon a specific design of the forward clutch  148 ,  248 ,  348  or the reverse clutch  150 ,  250 ,  350 . When reducing the hydraulic pressure on one of the forward clutch  148 ,  248 ,  348  and the reverse clutch  150 ,  250 ,  350 , a slipping of the forward clutch  148 ,  248 ,  348  or the reverse clutch  150 ,  250 ,  350  must be prevented, which is caused by reducing the hydraulic pressure too much. The controller  108 ,  172 ,  182  is configured to monitor the status of the forward clutch  148 ,  248 ,  348  or the reverse clutch  150 ,  250 ,  350  based on speed measurements thereof and the controller  108 ,  172 ,  182  will increase the hydraulic pressure in the event that a slipping of the forward clutch  148 ,  248 ,  348  or the reverse clutch  150 ,  250 ,  350  is detected. 
         [0076]    After the Controller  108 ,  172 ,  182  adjusts a position of the moveable swashplate of the variable displacement pump  118 ,  218 ,  318  and the variable displacement motor  120 ,  220 ,  320  to a new operating point, completes the filling process for engaging the primary range clutch  152 ,  252 ,  352 , and reduces a pressure on one of the forward clutch  148 ,  248 ,  348  and the reverse clutch  150 ,  250 ,  350 , the powersplit transmission  104 ,  204 ,  304  is ready to be shifted from the powersplit mode into the hydrostatic mode. 
         [0077]    A shift sequence from the powersplit mode into the hydrostatic mode comprises a plurality of steps. The first step is to begin a controlled slipping of one of the forward clutch  148 ,  248 ,  348  and the reverse clutch  150 ,  250 ,  350  (whichever is an engaged position). The controlled slipping reduces a hydraulic pressure to below a threshold value, which maintains a static condition. To perform the controlled slipping, the controller  108 ,  172 ,  182  monitors one of the forward clutch  148 ,  248 ,  348  and the reverse clutch  150 ,  250 ,  350  to determine if the forward clutch  148 ,  248 ,  348  or the reverse clutch  150 ,  250 ,  350  is in an engaged or a slipping condition based on a speed measurement of the forward clutch  148 ,  248 ,  348  or the reverse clutch  150 ,  250 ,  350 . 
         [0078]    Once the forward clutch  148 ,  248 ,  348  or the reverse clutch  150 ,  250 ,  350  is in a slipping condition, the primary range clutch  152 ,  252 ,  352  can be closed using a fixed gradient pressure slope while the load on the power source  102 ,  202 ,  302  is maintained at a substantially a constant value by simultaneously decreasing the pressure on the forward clutch  148 ,  248 ,  348  or the reverse clutch  150 ,  250 ,  350 . The fixed gradient pressure slope is performed with respect to a maximum peak power a material the forward clutch  148 ,  248 ,  348  or the reverse clutch  150 ,  250 ,  350  can handle without being damaged. When the controller  108 ,  172 ,  182  detects no differential speed between the components of the primary range clutch  152 ,  252 ,  352 , the fixed gradient pressure slope engagement is aborted and the primary range clutch  152 ,  252 ,  352  is pressurized to a required value for transferring torque in the hydrostatic mode. 
         [0079]    At the same the primary range clutch  152 ,  252 ,  352  is energized, the forward clutch  148 ,  248 ,  348  or the reverse clutch  150 ,  250 ,  350  (whichever was in an engaged position) is fully disengaged, and a clutch piston thereof retracts to an end stop. To apply full hydraulic pressure in the hydrostatic mode (which is required for maximum tractive effort) the next step is to deactivate the freewheel device  106 ,  170 ,  180 . The freewheel device  106 ,  170 ,  180  is deactivated by increasing the set point of the relief valves  164 ,  166  or valve  174 ,  186  to a maximum setting (so that full hydraulic pressure can be applied to the first plurality of drive fluid conduits  126 ,  226 ,  326  and the second plurality of drive fluid conduits  128 ,  228 ,  328  without activating the valves  164 ,  166  or valve  174 ,  186  again). It is necessary to perform this step in a gradual way to have a gradual pressure (and thus tractive effort) increase while transitioning into the hydrostatic mode. As in the process of limiting a rotational speed of the variable displacement motor  120 ,  220 ,  320  by reducing a rotational speed of the power source  102 ,  202 ,  302 , the process of increasing the set point of the relief valves  164 ,  166  or valve  174 ,  186  to the maximum setting should also be gradually performed. Upon completion of this step, the shift sequence is completed. The vehicle driveline  100 ,  200 ,  300  is now operating in the hydrostatic mode, and the vehicle driveline  100 ,  200 ,  300  may continue the rapid deceleration while maintaining a maximum push power. 
         [0080]    Further, it is understood that by incorporating the pressure transducers  124   224 ,  324 , an algorithm may be developed to determine an operating point at which the pressure relief valves  164 ,  166  or valve  174 ,  186  are always above (a fixed value, for example, such as 20 bar) an actual load (a certain average load will be needed) required in hydrostatic mode. Additionally, when shock loading of the vehicle drivetrain  100 ,  200 ,  300  occurs, which the pressure relief valves  164 ,  166  or valve  174 ,  186  may be opened to limit the peak pressure within the first plurality of drive fluid conduits  126 ,  226 ,  326  or the second plurality of drive fluid conduits  128 ,  228 ,  328 . By limiting the peak pressures the components of the vehicle drivetrain  100 ,  200 ,  300  are exposed to, a service life of the components can be extended and the vehicle drivetrain  100 ,  200 ,  300  can be operated in a more desirable manner. 
         [0081]    In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiments. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.