CAT integrates the Humvee

"We knew that because they were Caterpillar, they were used to operating in the same extremes in temperature, moisture, and vibration regularly encountered by the military," says Jeff Dowell, AM General Corp's director of product assurance and engine engineering. He worked with Caterpillar Inc. (Peoria, IL) and developed an entirely new electrical system for the new A3 model of High Mobility Multipurpose Wheeled Vehicle (HMMWV, also know as the Humvee) developed by AM General.

Dowell explains that the challenge of designing the A3 Humvee included integrating new electronic components with existing systems. "We inherited hardware from General Motors and electronics from Delphi," says Dowell. He adds that the electrical, exhaust, and fuel systems were originally engineered in the early 1990s.

Unlike previous versions of the Humvee, the A3 requires a new mass airflow sensor and a new exhaust gas recirculation valve to meet current EPA standards. "When we started developing the next generation of Humvee, we realized we needed a new controller with more inputs and outputs for the new sensor and valve," says Dowell.

Dowell turned to Caterpillar for development of an integrated electronics system and heavy-duty components that withstand extremes in temperature, vibration, and moisture. "Systems integration on the Humvee started with taking a fresh look at the entire electrical system," says Amy Moore-McKee, an electrical engineer and the technical manager of commercial electronics at Caterpillar. "First, we broke the systems down into their components and then defined the interfaces between them."

Caterpillar defined the electrical and electronic requirements for both the military and consumer version of the Humvee. "We didn't want a different electrical and electronic system for each version, so we designed a common wiring harness and set up for controller I/O, says Moore-McKee. "Only software changes for the different applications."

The A3 fuel system has a fuel injection pump, an angular speed timing encoder, engine shut-off, an actuator, a pump-mounted driver, and fuel valves. Caterpillar's advanced diesel engine management (ADEM) controller provides information about fuel temperature, valve injection timing, and injection duration. Caterpillar developed software algorithms for integrating the new sensor and valve with existing General Motors transmission control module.

The new electronic control module calculates the fuel rate to provide the desired air-to-fuel ratio using the mass airflow sensor. The mass airflow sensor information also is used to determine the desired position of the exhaust gas recirculation valve, which controls the amount of exhaust gas recirculated back through the intake.

The totally sealed ADEM controller is microprocessor based and provides I/O circuit protection. The controller adapts to different applications when Caterpillar changes the software.

"There were no changes in order for the electronic control module to be used in the AM General vehicle," says Moore-McKee. "All we had to do for the hardware itself was to validate it against AM General's environmental requirements." Moore-McKee adds that tests of the controller's reliability and durability include rigorous conditions found all over the world in places where Caterpillar equipment operates.

For this application, AM General uses GM protocol for communication with the vehicle's transmission. "Caterpillar's data link can be configured to communicate at different baud rates", says Moore-McKee. "GM protocol is supported at 500k." The controller communicates with various vehicle service tools.

There are 140 pins available for I/O. "We are monitoring more than 100 different sensed and calculated parameters running on a J1939 CANbus system," says Moore-McKee.

Caterpillar designed and developed all software for the engine controller. The company also integrated the process of installing the software (that drives the new components) into the engine.

"Proof of the Humvee's unsurpassable off-road capabilities was demonstrated in Operation Desert Storm, Bosnia peacekeeping missions, and today as a major factor in the war against terrorism," says Patricia Grashik, System Acquisition Manager, HMMWV Production/Sustainment from the U.S. Army. The smarter A3 will soon provide better environmental performance, too.