Theory of Operation
Use of LBSC produces fuel economy gains in vehicles with conventional manual transmission by forcing the driver to utilize progressive shifting techniques. The feature functions by monitoring operating conditions and limiting the maximum engine speed while the vehicle is being operated under low or intermediate power requirements. Normal operating conditions such as lightly loaded, bob-tail, or operating on level terrain require low or intermediate power and do not require high engine speeds for acceptable vehicle performance.
If the vehicle is loaded and is climbing a significant grade, the power requirements are high and limiting engine speed will have a negative effect on the driveability of the vehicle. Under these conditions LBSC allows higher engine speeds to extend the operating range and enhance vehicle performance.
The engine break speed is the rpm speed where fueling will temporarily be suspended. This encourages drivers to shift up to the next gear. However full fueling is available if additional performance is required due to heavy vehicle loads, grades exceeding 2%, and when the engine senses an operating condition that warrants additional rpm.
Since LBSC is used in conjunction with Gear Down Protection (GDP) and the Road Speed Governor (RSG), Load Based Speed Control effects all gears up to the last two. The engine break speed point value that is set remains the point where drivers are incentivized to shift into the next gear; however, in the third gear from the top (or two gears down), an additional 100 rpm is provided to the driver. The additional rpm provided to the driver is designed to help the driver transition into the Gear Down Protection electronic feature. An example of a gear split chart can be seen below. Load Based Speed Control is set at 1550 rpm, GDP Light is set at 51 mph, GDP Heavy is set at 62 mph, and the Road Speed Governor is set at 65 mph.