Power test unveils new Transit Chassis Dynamometers - Test Equipment

Diesel Progress North American Edition, Oct, 2002 by Mike Brezonick

In yet another significant expansion of its engine and vehicle testing system product line, Power Test, Inc., has developed a new chassis dynamometer system designed specifically to meet the needs of the transit bus and coach market. The CF2lM Transit Chassis Dynamometer is targeted at bus manufacturers and fleet owners and is the latest in the company's product line of chassis and engine dynamometers and controls.

"This is a hybrid machine that's designed for assisting in preventive maintenance and safety assessments for transit fleets," said Alan Petelinsek, president of the Menomonee Falls, Wis., manufacturer. "In the transit industry, they test the brakes, the transmission, the running gear and the engine all as part of a preventive maintenance schedule.

"We took this project onto fill a void in the market. There had been a company, Maxwell Dynamometer, that existed for about 25 years and bad produced a machine for the transit industry That company is now defunct and what we've done is fill the void using modern technology."

The CF21M chassis dyno combines dual electric motors with Power Test's well-known waterbrake dynamometer technology This design eliminates clifferential assemblies and provides independent wheel loading, which allows for a wide variety of test capabilities while maintaining cost effectiveness, according to Petelinsek. "To drive the rolls and perform the tests that are required by spinning rollers, you need less power than you do in absorbing the power through the drivetrain," he explained. "We've been able to put in smaller motors and drives to perform the motorized roll application than what would be required when using the motors as absorbers as in a typical dynamometer application. The waterbrake allows us to load to high capacity economically."

The chassis dyno features a heavy structural steel frame to support oversized bearings and axle shafts, which are needed to accommodate the heavy axle weights of transit coaches. The dynamically balanced 20 in. diameter roll sets offer increased tire traction while minimizing tire heat for extended testing. Independent load absorbers handle up to 800 hp total absorption and allow full torque and automated testing through the full engine speed range. This feature ensures that the engine power curve is documented and the transmission loaded to its full potential. Full load testing can also be used to measure cooling system performance.

Heavy-duty roll brakes lock the cradle roll assemblies to allow drive on- and off-vehicle positioning. "Customers will be able to place the front axle of the coach on the dyno and by having independent motors, measure the amount of force that it takes to drive the left and right wheels, check vibration and verify alignment. The brakes can be applied to determine brake bias and braking force. Most of the same tests can be performed when the rear axle of the coach is on the dyno as well.

"Additionally, brake savers and retarders may be checked. Drivetrain losses can be measured to more accurately assess efficiency When used as a conventional chassis dynamometer, transmission shift points and function, as well as engine power verification and cooling tests may be performed."

With continuous independent motoring capabilities to 150 hp, these brake tests, drivetrain parasitic loss tests and vehicle alignment verification tests may be performed at a variety of road speeds. Independent wheel power absorption and motoring reduces wear and tear on the vehicle's drivetrain and gives a true indication of vehicle condition, the company said. All of these tests axe performed using a hand-held operator and display device.

All of the potential uses of the transit chassis dynamometer are brought together through the use of Power Test's PowerNet data acquisition and automated control system. PowerNet consists of a standard Windows desktop computer connected by a local area network to the controller system and to the remote hand-held operator interface and display station.

A series of tests may be preconfigured on the Commander desktop computer, complete with prompted steps for the technician to follow. These tests may be saved by name for recall from the handheld display. The Commander set-up is used to define the tests to be performed, the sensors to be viewed, and set alarm limits for conditions that are beyond normal ranges. The PowerNet system includes sensors to be connected to various pressure and temperature inputs. An ECM interface is supplied to connect to the vehicles diagnostic port for monitoring and recording engine sensor information and faults.

The operator may perform automated tests or enter test points as necessary into the hand-held control. During testing, the hand-held displays all of the selected dynamometer and vehicle sensor information. Once vehicle tests are prepared on the Commander system, the hand-held touch screen is taken into the cab of the vehicle and used to select the tests required. While the vehicle is on the dyno, customary ECM service tools may be used to perform cylinder cutouts, reset cruise limits and other engine specific tests.