Description:
Gear Down Protection allows you to set an engine rpm limit for the higher gears that ensures cruising speed can only be reached in top gear.
Gear Down Protection has two parameters to specify. The first is the Gear Down Protection Turn On Speed. This is the point, in either mph or km/h, where the RPM limit first takes effect. In the illustration below the Gear Down Protection Turn On Speed is set at 45 MPH. The second parameter is the Gear Down Protection RPM Limit. It is set at 1600 rpm in the illustration.
With some driveline combinations cruising speed can only be reached while in the transmission’s top gear; the Gear Down Protection RPM Limit would not have to be set for these trucks.
It is important to note that although Low/Intermediate Gears parameters are “soft” limits, Gear Down Protection is actually a “hard” limit.
Available:
All electronically controlled on-highway engines covered in this handbook
Range:
Gear Down Protection RPM Limit
Gear Down Protection Turn On Speed
Advantages:
Gear Down Protection helps ensure that the truck is run in the correct (highest possible) gear at cruising speed. Properly setting these parameters will keep the engine in the most fuel efficient rpm range to achieve the best fuel economy at cruising speed.
Disadvantages (possible):
Some driveline combination can allow a driver to reach cruising speed in more than one gear even with this feature properly set. However, gear down protection is still moderately effective in these situations and should be used.
If the Gear Down Protection RPM Limit is set too low, the driver may have to wait too long to downshift when climbing steep grades with heavy loads. This may cause the driver to drop two transmission gears, when one would have been adequate.
Recommendations:
Set the Gear Down Protection RPM Limit such that highway cruising speeds can only be reached in top gear (Use Cat® Design Pro).
Set Gear Down Protection RPM Limit high enough that engine rpm does not drop below peak torque plus 100 rpm during upshift.
Set the Gear Down Protection Turn On Speed well below the cruise speed. As with all electronic shift strategies, do not set “gear-on” speeds on top of shift points.