Mechanical transmissions for heavy-duty vehicles up until recently could be classified into one of two categories differentiated by the shifting effort required. In one category, the shifting effort is predominantly physical and the force applied to the shift lever is used to synchronize the gears to be engaged, thereby reducing the mental effort required to make a gear change. Transmissions of this type are well known as synchromesh transmissions which employ heavy-duty synchronizers. In the other case, the shifting effort is predominantly mental in that by correct control of the engine speed and clutch brake on the part of the driver, relatively low forces were required to be applied to the shift lever to change gears. Transmissions of this type are well known as non-synchronized or constant mesh transmissions.
The arrival of electronics on heavy-duty vehicles has recently opened up a whole new category of transmissions, a category in which shifting effort is truly reduced. Those who earlier supported the synchromesh technology recognize that electronically controlled transmissions provide the means to reduce physical effort while retaining a low mental effort advantage. Similarly, those who earlier supported the constant mesh transmission technology recognize that electronically controlled transmissions provide the means to reduce the mental effort while retaining a low physical effort advantage.
This paper outlines a family of advanced transmissions which bridge the gap from conventional technology to a sophisticated, fully automatic transmission for heavy-duty vehicles. These advanced transmission systems can be proven to improve the over-the-road performance of the vehicle, particularly under difficult operating conditions.