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Modifying Your Powertrain to Optimize Performance

May 5, 2016
Vocational vehicles can be digitally customized for speed, PTO operation, permissions, interlocks, auto neutral, and performance

WHETHER it’s a bucket truck, a street sweeper, or a pickup with a snowplow, it has to have the functionality added to the chassis for it to be what the user hopes for it to be.

That requires the chassis to be customized with the body equipment. In the old days, it was done with a hammer and a screwdriver.

“But it’s a changed world—it’s all digital now,” said Joe Johansson of Johansson & Associates LLC ( “As we communicate with the vehicle, we do it using onboard networks.”

In his presentation, “Modifying Your Powertrain to Optimize Performance,” Johansson provided a rundown of what can be digitally customized on a vocational vehicle:


“Low-speed control is often required in some applications—as opposed to high-speed control, which is cruise control, which controls the road speed of the vehicle,” he said. “Low speed controls the engine speed of the PTO governor.

“Most engine manufacturers offer speed-increase capability when operating under low-speed governor control. You can have stepped or ramped speed increases. Ramp is important because there’s some equipment that needs to be engaged and sped up slowly. If you have high-inertia equipment, you don’t want to ramp up too quickly. It could damage the PTOs or drivelines to the equipment. So those ramps are adjustable, customizable. Usually the ramp rate can be changed.”

He said Ford has a PTO mode using Stationary Elevated Idle Control (park or neutral only) with a minimum engine speed of 900 rpm and maximum engine speed of 3000 rpm. It’s SEIC initiated by applying battery voltage to wire tag PTO REQUEST 1. Fixed or variable target speed is obtained by adding a resistor or 5000 Ohm potentiometer to wire tag PTO RPM.

International’s speed control for PTO (MaxxForce7, DT, 9, 10) has stationary PTO applications and preset 6-speed settings, anywhere from low idle to governed RPM. You can pick a ramp rate of 1 to 1500 rpm/sec. Variable: With the cruise “on” switch set, engine speed is increased via the accelerator pedal or the cruise-control switches using programmed ramp rate. There is a Mobile Variable Engine Speed Control that is programmable from 0 to 20 mph.

“PTOs are fundamental to the success of most vocational trucks,” he said. “There’s always something that needs to be powered by the PTO.”

PTO operation.

He said generators have to be engaged carefully because of high inertia. Split-shaft units are mounted in the driveline, and just about every custom fire truck utilizes a split shaft.

“They can be used either for high water pumps about 750,000 gpm and higher or concrete pumps. Concrete pumpers will have long snorkels. Split-shaft PTOs provide high power.

He said PTO operation may need: engagement (“there are parameters which allow and can be set to handle that engagement”); speed control; and torque control (some equipment is susceptible to over-torque, and we need to be able to manage that”); and remote control.

PTOs need to engage at a particular RPM engine speed and a particular RPM driveline speed.

“You have to work backwards because the PTO has a speed ratio. Most PTO manufacturers will tell you that they do not want PTOs to engage above idling. If you have an underdrive PTO, you can engage at higher speeds.

“Allison talks of driveline speed. Cummins talks of road speed. If you talk about driveline speed, you have to work backwards. Allison has an engagement value of 250 rpm of the shaft. If you work backwards, that’s about 7 mph. If you go down the road at 20 mph, and you try to engage the PTO, nothing happens. So what’s wrong? You just left the default value to be low so you have to customize that value and set it for something that works for you.”

Likewise, PTOs need to disengage at a particular rpm engine speed.

PTOs also need to disengage at a particular rpm driveline speed.

“Cummins limits it using a road speed, mph,” he said. “Allison uses rpm of the driveshaft. People complain because the snowplow’s PTO cuts out at 8 mph. ‘What’s going on? What’s wrong?’ Well, the Allison value for operation driveline cutout of the PTO is 300 rpm. Depending on the axle ratio and tire size, that may be somewhere in vicinity of 8 mph. That value has to be adjusted so you can go 30 mph.”


“Permissions is a controller that looks at one or more inputs, and if conditions are met, a circuit is closed,” he said. “It’s sometimes called input/output functions. For example: PTO enable, drive enable, neutral enable, reverse enable. With forward gear/reverse gear: Are engine speeds correct for engagement? Are all switches for auxiliary equipment in their correct state? Is the service brake enabled, if so required by programming? All those conditions are evaluated by the controller, and if they’re all met, it allows drive to be enabled or reverse to be enabled.”


“Interlocks are very important. Some are auxiliary function, dump bed, doors, lift gate, bucket lift, outriggers, range selection, drive, and reverse. All of these are things on the vehicle which you could have an interlock to control that feature.”

He said interlocks prevent fatal mistakes from being made.

“If you’re a fireman and you’re 100 feet in the air and have a high-flow pump up there, imagine what would happen if a shift were to be made—that’s engine rpm change,” he said. “The flow would change, the thrust of pump would change. I would imagine you could be literally thrown up that 100-foot-high ladder. So you have to make sure the interlocks keep the unit in the gear that it’s at, and it doesn’t allow shifts and keeps it at a consistent pump speed.”

Auto neutrals.

Auto neutrals are initiated by the park brake, work brake, or service brake. Drive is re-attained by range reselection (with or without override) and release of the brake and switch.

With Eaton’s UltraShift PLUS & Fuller Advantage Automated, neutral is attained when the parking brake is applied. Auxiliary devices must provide an electrical interface with the transmission. Auto Neutral is integrated via a normally closed pressure switch and J1939 Park Brake status message (on later models).

Shift sequence.

He said that with shift pattern (mask), automated transmissions may skip shift. Allison automatics can start in first or second and be limited in the number of gears that can be attained.


Examples of acceleration control: rate and speed threshold.

“Transmission manufacturers spend vast amounts of money to set up ideal shift points. And shifts for performance are usually made at higher rpms—ideally at peak power. That gives you the power to accelerate the vehicle. For economy, you want the shifts to be made at lower rpm.

“Sometimes an OEM will predefine what they are. If you are the user and want to have them changed, they’re usually changeable.

“Engine, transmission and truck OEMs have a great variety of electronic features which can be used to greatly enhance the vocational capability of your truck. Users and fleet owners should identify the features they need, make sure default values are what they expect, and work with their dealer to customize the values to satisfy their needs. Bodybuilders should work with their customer to identify the features they need, as well as the values, and work with their OEM so that the chassis is delivered to them with as many settings as possible ‘baked into’ the calibration via Vehicle Engineering Programming Stations (VEPS).” ♦