Newest MCI coach integrates versatile cooling system

Diesel Progress North American Edition, Feb, 1997 by Mike Brezonick

It was with those conditions in mind that Motor Coach Industries (MCI) developed the cooling system for its newest product, the E-series coach. Christened the Renaissance, the E-series vehicle was introduced at the American Bus Association's meeting in Hawaii late last year.

Scheduled for customer delivery in mid-1997, the E-series coach is a 45 ft. bus designed to accommodate as many as 56 passengers. It is one of the most innovative products ever manufactured by MCI and it was the result of a new design and manufacturing process that incorporated 70 people working in dedicated groups - including driver and passenger teams, axle and system teams, a structures team and power-train team - that took the project from ideas to production in just over 30 months. "We needed a dramatically new vehicle and we needed it extremely quickly," said Mark Sealy, new coach program leader for MCI. "We took those 70 people from different areas of the company and had them do nothing but eat, sleep and breathe the new coach."

The E-series coach is powered by a 12.7 L, turbocharged and intercooled Detroit Diesel series 60 engine rated 370 to 430 hp. Cummins M11 and Caterpillar C10 and C12 diesels will also be available. The engine package includes Nelson air cleaner, and Delco Remy America starter and alternator.

The engine drives an Allison B500R automatic transmission with integral hydraulic retarder. The rest of the powertrain consists of ZF gear power steering systems with Luk steering pumps, air suspension systems, Rockwell axles in the front and rear, respectively, and Lucas disc brakes, with an MGM spring-applied parking brake. In its 56-passenger configuration, the E-series coach has a gvwr of 49,900 lb.

The cooling package received some special attention during the design phase, partly because of the nature of the application and partly because MCI sought to do things a little differently for this vehicle. As usual, the engine, transmission and cooling system was placed at the rear of the bus, but in this case, the cooling system components were positioned below floor level. "MCI, throughout its history, has always had above-floor cooling," noted Sealy. "Putting it below the floor was a major change for us.

"Then there were the usual challenges. In coaches, there is no ram air, so they can't enjoy the same kind of cooling that a truck gets. They have to have systems that will pull in the dirty air at the rear of the bus and survive. The other thing that makes coaches difficult is that they have a lot of idle time, where they're running air-conditioning systems, etc." The other important maintenance requirement is easy power wash cleaning, which requires an open fin spacing. The cooling package also swings out for more significant repair activities.

Finally, there was the issue of cost of manufacture. Despite the different operating venues and different engine options, MCI wanted a single system that could accommodate all of the variations of engines and conditions. "Our vehicles operate all across North America," said Greg Hannah, purchasing manager for new coaches. "We go from one extreme to another and it's difficult to do that with one cooling package. But we needed to do it with one package, because you can't develop and manufacture a lot of different systems economically."

The cooling package MCI ended up with utilizes a large, remote-mounted Modine parallel flow combination radiator/charge-air cooler with 34 in. Kysor Cadillac fan, Hub City fan drive gearbox and Horton multi speed fan clutch.

The operation of the fan clutch is particularly important to the effective function of the system. Linked electronically to the DDEC III electronic engine controller, it has three engagement modes designed to more precisely tailor the amount of air drawn through the radiator/charge-air cooler. "We challenged Horton in a number of ways," said Sealy. "Most of their products go on the front of an engine in the front of a truck. We wanted a shaft drive output on a belt driven unit mounted away from the engine.

"We also have a very demanding duty cycle. The transmission retarder is water-cooled and when it cuts in, there is a very abrupt requirement for additional cooling. Finally, we had to have a system that was very light, yet would be able to survive being mounted next to a series 60 engine."

Horton originally supplied MCI with its MSC2, two-speed clutch, an air-actuated system that offers low and high rpm operating ranges. "Later in the program, we saw we needed to have an off/no rpm mode," said Sealy. "We were overcooling and getting white smoke in very, very cold ambients."

So the result was the Horton MSC 3 clutch, which features three operating modes: completely off; a "slow" mode that allowed the fan to turn at a constant low rpm independent of engine speed; and a lockup mode to provide direct ratio to rpm and maximum cooling. The off and high rpm modes are air actuated. In the low rpm or "slow" mode, a series of magnets in the clutch are used to spin the fan without any mechanical connection.