Abstract:
A command assembly for controlling a splitter in a transmission allows shifting between first and reverse-low gears while the splitter is engaged without requiring the splitter to cycle during the shift. The command assembly creates a signal path for a split enable signal that keeps the transmission in the split mode as long as the transmission engages a low rail of a main drive box. By creating a separate signal path for the split enable signal when the transmission is operating in split mode, the splitter does not need to be cycled when the driver shifts between first and reverse-low gears.

Description:
TECHNICAL FIELD 
   The invention relates to manual transmission controls, and more particularly to a control circuit that controls the operation of gears in an auxiliary drive box. 
   BACKGROUND OF THE INVENTION 
   Many vehicles with manual transmission have gears in a main drive box with synchronizers and/or splitters in an auxiliary drive box. As is known in the art, most driving is conducted using gears in the main drive box, with a higher gear range, a low gear range, and/or an extra-low mode determined by the state of the auxiliary drive box. The extra-low gear is used to drive in conditions requiring high torque or low speed. In all cases, shifting between forward and reverse directions is performed in the main drive box, even if the vehicle is operating with the extra-low gear in the auxiliary drive box. 
   To operate the extra-low range gear, the driver can engage a splitter, operating the transmission in a split mode. However, if the driver wishes to go from forward to reverse while operating in the extra-low range gear, the transmission will naturally disengage the splitter and shift from forward to reverse. The driver would then re-engage the splitter to resume driving in the extra-low gear. This splitter cycling tends to cause premature wear of the splitter because splitters are not designed to withstand constant use. Although it is possible to make splitters more robust, doing so would increase the cost of manual transmissions due to the additional durability testing that would be required for such a modification. 
   There is a desire for a system and method that prevents excessive cycling of the splitter during shifting without requiring modification of the splitter itself. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a transmission system having a splitter switch that allows shifting to occur between gears that can be operated in a split mode (e.g., first-low and reverse-low gears) without causing cycling of a splitter in an auxiliary drive box. The latching circuit receives a feedback signal via a switch in a main drive box of the transmission. The feedback signal allows shifting to occur between first and reverse-low gears without causing the splitter to cycle. 
   In one embodiment, the transmission system includes a splitter select switch that is closed when the driver chooses to operate in a split mode. Closing the splitter select switch creates a feedback path that maintains an uninterrupted, self-feeding split enable signal to a solenoid assembly that maintains the transmission in the split mode. By creating a separate signal path for the split enable signal when the transmission is operating in the split mode, the splitter does not disengage when the driver shifts between forward and reverse gears. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram illustrating components in a transmission system incorporating one embodiment of the present invention; and 
       FIG. 2  is a schematic illustrating the system of  FIG. 1  in greater detail. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
     FIG. 1  is a block diagram illustrating a transmission system  100  incorporating one embodiment of the present invention. The transmission system  100  includes a command assembly  102  with user-operable switches, including a range select switch  106  and a splitter select switch  108 . The range select switch  106  and the splitter select switch  108  allow a user to select operation modes for the transmission system  100 . Operation of the switches in the command assembly  102  will be described in greater detail below with respect to  FIG. 2 . In one embodiment, the range select switch  106  switches the transmission system  100  between high and low gear ranges, and the splitter select switch  108  switches the transmission system  100  between direct and split modes. A shift lever harness  109  and a transmission wiring harness  110  act as interfaces between the command assembly  102  and other components in the transmission system  100  by receiving user-defined inputs from the range select switch  106  and the splitter select switch  108 . 
   Control of the range select switch  106  switches the transmission system  100  operation between high and low range gears by connecting and disconnecting signal paths to a high solenoid assembly  120 , which causes the synchronizer in the auxiliary drive box (not shown) in the transmission to shift to the high range, and a low solenoid assembly  122 , which causes the transmission to shift to the low range. Switching the splitter select switch  108  energizes and de-energizes a direct solenoid assembly  124 , which causes a splitter  125  located in the auxiliary drive box to operate in a direct mode or a split mode, respectively. The split mode is possible only when the transmission system  100  is in first or reverse-low gears and when the splitter select switch  108  is set to a “split” position. A splitter switch  126  closes when the transmission has engaged a low rail (not shown) in the main drive box. The low rail is engaged when the main drive box is in its lowest gear plane, which includes first gear, reverse-low gear, and other gears specific to the transmission model. The closed splitter switch  126  forms a signal path as long as a split condition exists in the transmission. 
   Other components in the transmission system  100  include an optional cruise assembly  104 , a vehicle harness  132  for communicating with other vehicle systems, and a neutral/in gear indicator switch  134 . The optional cruise assembly  104  includes a set select switch  140 , a resume select switch  142 , and a pause select switch  144  that are operable by the user in a currently known manner. Similar to the range select switch  106  and the splitter select switch  108  in the command assembly  102 , the other components in the transmission system  100  receive user-defined inputs from the set select switch  140 , the resume select switch  142 , and the pause select switch  144  in the cruise assembly  104  via the shift lever harness  109 . 
   As is known in the art, the transmission system  100  can operate in the split mode only when the low rail in the main drive box is engaged. Referring to  FIG. 2 , the range select switch  106  can be moved between high and low independently of the splitter select switch  108 . More particularly, power only reaches the splitter select switch  108  to enable the split mode when the transmission main drive box has closed the splitter switch  126  by engaging the low rail. As can be seen in  FIG. 2 , moving the splitter select switch  108  to the direct mode position connects the low solenoid assembly  122 , the high solenoid assembly  120 , and the direct solenoid assembly  124  into the overall transmission system  100 , allowing power to reach the direct solenoid assembly  124  and either the low solenoid assembly  122  or the high solenoid assembly  120 . Also, when the splitter select switch  108  is in the direct mode position, the splitter switch  126  is open, causing the direct solenoid assembly  124  to switch to a direct mode (i.e., be energized), effectively disconnecting the splitter  125  from the transmission system  100 . 
   If the splitter select switch  108  is moved to the split mode position and the transmission has engaged the low rail in the main drive box (i.e., first gear or reverse-low gear), the splitter switch  126  closes. The direct solenoid assembly  124  connects the splitter  125  into the transmission system  100 . Typically, any deviation from these conditions (i.e., between first gear and reverse-low gear) discontinues the split mode of the transmission system  100  and the splitter  125  switches the transmission system  100  to the direct mode. The inventive system briefly prevents the splitter  125  from changing to the direct mode when the main drive box is still engaged with the low rail (i.e., between first gear and reverse-low gear). In one embodiment, the command assembly  102  may be designed to physically prevent the user to switch the range select switch  106  to the high gear mode to prevent accidental direct mode operation. 
   Shifting into first gear or reverse-low gear effectively closes the splitter switch  126 , providing a dedicated signal path for a split enable signal to reach the command assembly  102 . As shown in  FIG. 2 , the split enable signal travels from the command assembly  102  through the shift lever harness  109  and the transmission wiring harness  110  to the low solenoid assembly  122 , causing the transmission to operate in low range. The split enable signal also travels to the splitter switch  126 , through the signal path formed by the closed splitter switch  126  through the splitter  125 , back to the command assembly  102 , thus maintaining the split mode. 
   As long as the splitter select switch  108  remains in the split position and the main drive box engages the low rail, the closed splitter switch  126  ensures that the split enable signal remains uninterrupted, keeping the splitter  125  engaged even when the user switches between first and reverse-low gears. If the user switches between first and reverse-low in the split mode, the user can simply conduct the shift without having to first interrupt the split enable signal, which would disengage the splitter  125 , before shifting. 
   Without the splitter switch  126  providing a continuous, constant signal path for the split enable signal in the split mode, the transmission system  100  would have to switch out of the split mode, switch between first and reverse-low, and then switch back to the split mode. In other words, the splitter switch  126  allows the transmission system  100  to stay in the split mode while shifting between first and reverse-low. As is known in the art, shifting between forward and reverse occurs in the main drive box. The split enable signal that is supplied when the splitter switch  126  is closed allows the main drive box to virtually ignore the state of the splitter in the auxiliary drive box when shifting. The transmission system  100  can shift between first and reverse-low without ever leaving the split mode. 
   By incorporating a splitter switch  126  in the transmission system  100 , the invention allows switching between forward (first) and reverse (reverse-low) gears without disengaging and re-engaging the splitter  125  to conduct the shift. Instead, the splitter switch  126  ensures that there is an uninterrupted signal path for the split enable signal so that the splitter  125  can remain engaged as shifts occur between first and reverse-low during the split mode. As a result, the invention prevents excessive cycling of the splitter  125 , reducing wear on the splitter without requiring potentially costly changes to the splitter  125  structure itself. 
   It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby.