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| Illustration 1 | g00926721 |
Service brake and retarder pressure switch | |
Some input signals to the Electronic Programmable Transmission Control (EPTC II) during a shift can cause a hunting condition of the transmission. A hunting condition is a series of rapid, unwanted transmission upshifts and rapid, unwanted transmission downshifts. A hunting condition is caused by ground speed changes near a transmission shift point.
The EPTC II is designed to prevent a hunting condition. After two seconds, the EPTC II will allow one shift back to the original gear.
In normal operating conditions, a rapid shift may be necessary. An example of a normal operating condition is stopping the machine. If a rapid downshift is not made in this example, the engine will stop. When the service brake or the retarder is used, the service brake and retarder pressure switch (1) will signal the EPTC II that rapid shifts are necessary.
Service brake and retarder switch (1) will signal the EPTC II when a higher engine rpm is necessary for an upshift or for a downshift. Service brake and retarder switch (1) also signals the EPTC II to allow rapid shifts.
When the service brakes or the retarder are not used, the EPTC II receives a ground through the service brake and retarder pressure switch (1). The EPTC II will use normal engine rpm for upshifts or for downshifts. The EPTC II allows only one shift back to the previous gear to occur for every two seconds.
When the service brake or the retarder is used, the EPTC II will allow rapid upshifts and rapid downshifts in order for the machine to stop quickly. The downshift point will also be raised. This will maintain a higher engine rpm during downshifting. This function maximizes the amount of cooling oil that flows to the brakes during braking. Service brake and retarder switch (1) is open when either the service brakes are used or the retarder is used.