Big changes for Cummins' B series

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

While in many ways, the heart and soul of Cummins Engine Co. has traditionally been heavy-duty, high horsepower diesel engines used in Class 8 trucks and large off-road and industrial equipment, there can be no argument that the engines that have had the greatest impact on the company are its midrange products. Introduced in the early 1980s, the 3.9 and 5.9 L B series and the 8.3 L C series engines quickly became the highest volume engines in the Cummins' lineup. They remain so today - the company estimates it has sold more than 1.7 million B series engines since its introduction - and they have found their way into a dizzying number of applications across a score of automotive, off-highway and marine markets.

Simple logic says you don't mess too much with that kind of success. But with the advances in engine technology and changes in market requirements, you can't stay put either. So just over two years ago, Cummins began work on a new generation of midrange engines, the first of which, the ISB-275, was introduced in March for recreational vehicle applications. (The ISB nomenclature stems from Interact System, which encompasses a range of information products and systems designed to provide customers with increased business management capability).

The full range of ISB engines was formally introduced at the company's annual meeting in Columbus, Ind., on April 1 and the news on a new ISC series engine is expected later this year.

The ISB engines are available in standard ratings of 230 and 250 hp, with a restricted rating of 275 hp for RV and fire equipment markets. Operating speeds range from 2300 to 2500 rpm and torques have gone up from 8 to 35 percent over previous versions, to 660 lb.ft. at 1600 rpm.

"It's a major evolution of our midrange products," said David Koppenhofer, director of marketing strategy for Cummins' automotive group. "At the same time, we worked hard to maintain the base attributes of the B platform, especially from a reliability standpoint."

While many things remain - the bore and stroke, 5.9 L displacement and overall engine dimensions are unchanged - there have been some rather significant changes, particularly in the upper structure of the engine. Among the changes are a new 24-valve head, new electronic fuel injection system, no-adjust overhead assembly and new combustion chamber configuration.

Perhaps the most significant change of all is the addition of the electronic control system. For the most part, engine electronic controls have primarily been a technology associated with larger engines. But a combination of Cummins' accumulated expertise in programming, combined with Motorola's advances in polybend circuit board manufacturing technology, has allowed Cummins to economically bring the technology to its second smallest displacement engine.

The Motorola electronic module, which is extremely compact, is tucked up on the right side of the block and is much more innocuous than the black boxes that commonly house such controls. Yet it has more than enough capacity to control the operation of the Bosch electronic fuel pump and has a 100-pin I/O to support a full array of monitoring, diagnostic and operating options. "From an electronics standpoint, we're using a lot of the hardware that's been proven on heavy-duty," said Jim Trueblood, technical leader of the advanced midrange engine program. "From the standpoint of software, 80 to 85 percent is what we refer to as core, common to other products. The fuel system specific information is unique, as are some of the other control algorithms.

"But there's a lot of commonality. We're not just starting fresh, but building on the previous experience and capability we have with software, sensors, connectors and harnesses."

The electronic system directly controls the operation of the Bosch VP44 fuel pump, which has its own electronic module. The pump is a radial piston, distributor-style unit that is used to deliver fuel at high pressure to the six Bosch pencil-type injectors. Maximum injection pressure is approximately 20,000 psi.

The injectors are vertically positioned at the center of the combustion chamber, a design made possible by the new 24-valve cylinder head. The new head design provides each cylinder with two intake and two exhaust ports and is engineered to provide a 10 percent improvement in airflow, resulting in better low end torque and response, higher power density and improved fuel consumption and emissions performance, the company said.

Interestingly, Trueblood noted that the new head design and injector positioning could potentially allow for the incorporation of a common rail fuel system at a later date. "It really provides us with some flexibility for the future," he said. "The cylinder head is a significant portion of the platform upgrade and it represents a very large investment. There is a new head line going into the Consolidated Diesel (CDC) plant that represents a $200 million investment in this technology."

The centered injector configuration has also led to changes in the piston design. The ISB engines still utilize single-piece aluminum pistons from Mahle and Kolbenschmidt, but the bowl has been centered and the bowl geometry has been changed to accommodate centralized injection. "As we center the bowl, it allows us to do some new things in terms of piston cooling," said Trueblood. "We're also getting improved combustion through better air/fuel mixing. The ring temperatures are more uniform and we've found that to be very beneficial in terms of lowering lube oil consumption.