Transmission trends

Don't let Mitch Murray's title fool you. Though he's Allison Transmission's manager of marketing and development for North America, Murray not only has a degree in mechanical engineering from Purdue University, but joined Allison as an engineer in 1984. While he's not quite sure how he ended up in the marketing department, Murray says his engineering background has proved vital in communicating the

Don't let Mitch Murray's title fool you. Though he's Allison Transmission's manager of marketing and development for North America, Murray not only has a degree in mechanical engineering from Purdue University, but joined Allison as an engineer in 1984. While he's not quite sure how he ended up in the marketing department, Murray says his engineering background has proved vital in communicating the kinds of change automatic truck transmissions are headed for in the near future.

In the short term, that means phasing out hydraulically controlled automatics over the next 15 months to two years in favor of electronically controlled models.

“For all practical purposes, hydraulically controlled automatics for commercial trucks have pretty much gone away,” Murray says. “With hydraulic controls, you are at the mercy of a lot of physics, from the internal temperature of the hydraulic fluid to the external temperature's affect on the system's mechanisms. With electronic or digital controls, you don't have that; the shifting tolerances are greatly improved, too, so you can get a more precise shift at the optimum horsepower and torque point than ever before.”

Murray adds that almost all diesel truck engines are now electronically controlled, so having the same system in place on the transmission means improved communication pathways. They also allow for more flexibility, so truck fleets can better integrate devices such as power takeoffs, or program in specific control commands between the engine and transmission.”

“Take refuse trucks, for example. We can program the transmission to automatically shift into neutral when the vehicle stops for a certain length of time, based on engine speed, etc.,” he explains. “Overall, electronic controls enable us to provide a transmission with a lower installed cost, as well as higher quality shifting and a wider range of options based on truck application needs.”

In the long term, however, Murray believes new levels of capability can be brought to truck transmissions via electronic controls. “We are looking at ways for the transmission itself to monitor transmission oil life,” he says. “The primary factor in gauging oil life is time at temperature, or how long the oil is exposed to high operating heat. Viscosity and contamination of the oil are also factors, but time at temperature is the real determinant. It would take some sophisticated technology to do it, but having the transmission accurately gauge when its oil needs to be changed could save fleets a lot of money.”

Murray says the use of synthetic oil is likely to rise dramatically, with 50% of all automatic truck transmissions using itl within the next five years. “The interest in synthetics is going through the roof because fleets are getting four to six times longer oil change intervals with synthetic vs. mineral oils.”

Another trend is the use of automatic transmissions in heavy-duty trucks. Last year, 18% of all Class 8 trucks built and sold were equipped with automatic transmissions, up from 5% in 1996. “A big factor is the change in the responsiveness of diesel engines as a result of pollution controls,” he explains. “Despite all the electronics on today's engines, there can be up to three seconds of low or no torque between shifts when you use manual or automated mechanical transmissions.”

The kind of power during the shift that automatic transmissions can offer is especially important for fleets using Class 8 vehicles in heavy stop-and-go environments, such as dump trucks, ready-mix concrete trucks, and food service delivery tractors. “Having that power through the shift not only makes drivers more productive,” says Murray, “it makes them safer; they can adjust to the flow of traffic more easily if there is no gap in engine power.

For Class 8 OTR applications, however, automatics will likely remain on the outside looking in. “Pure linehaul drivers simply don't shift as much during highway driving,” Murray says. “So we're not going after that part of the Class 8 market, at least for now.”




Each month this column looks at emerging truck technology issues through the eyes of a leading engineer.

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