His title may say marketing, but Mitch Murray is also an engineer. He earned a mechanical engineering degree from Purdue University and joined Allison Transmission in 1984 as an engineer. He is now the company's manager of marketing and development for North America, but Murray relies on his engineering background to describe trends in automatic truck transmissions. One of them is the demise of hydraulics. That means that hydraulically controlled automatics will be phased out over the next 15 months to two years. In their place: electronically controlled models.

"For all practical purposes, hydraulically controlled automatics for commercial trucks have pretty much gone away," says Murray. "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."

Almost all diesel truck engines are now electronically controlled and having transmission systems follow suit will improve communication, says Murray. This electronic shift will also bring more flexibility. Truck fleets can look forward to better integration of devices such as power takeoffs. Moreover, specific control commands between the transmission and the engine can be programmed. "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." says Murray. "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."

Long-term trends may involve even greater transmission capabilities through electronic controls. "We are looking at ways for the transmission itself to monitor transmission oil life," says Murray. "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."

Other trends include increased reliance on synthetic oil and the growing use of automatic transmissions in heavy-duty trucks. According to Murray, half of all automatic truck transmissions will use synthetic oil 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," he says. Meanwhile, the trend towards automatic transmissions in heavy-duty trucks is seen in the growing percentage of Class 8 trucks built and sold with these systems—18% in 2001 from 5% in 1996. "A big factor is the change in the responsiveness of diesel engines as a result of pollution controls," says Murray. "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 continuous power that automatic transmission provides during shifting is an important feature for Class 8 vehicles such as dump trucks, ready-mix concrete trucks and food service delivery tractors, which must operate in stop-and-go environments. This type of power makes drivers more productive and safer since "they can adjust to the flow of traffic more easily if there is no gap in engine power," says Murray. This trend towards automatics will not extend to Class 8 OTR applications, however, since they don't require as much shifting, says Murray.

Source: Transmission Trends
Sean Kilcarr
Fleet Owner, June 1, 2002
http://fleetowner.com/ar/fleet_transmission_trends/index.htm