Electronic controls for diesel engines.

ABOUT 30 years ago, one big argument in favor of the new-fangled diesel tractor was that the power plant didn't need an elelctrical system to keep running.

That argument helped sell a lot of machinery, and was part of the reason that diesels provide the power for more than 90 per cent of all farm machinery these days.

For other reasons, like fuel economy, diesels are showing up in riding lawn mowers, passenger cars, pickup trucks and most every machine powered by a reciprocating internal combustion engine.

Now that they've won the battle for dominance on the farm and respectability in other applications, the diesel engine industry is turning full circle and planning to put electrical systems back on engines--but this time to operate the fuel injection system, not to create an ignition spark.

Elelctronic control of diesel fuel injection has become a hot topic, and many within the diesel industry predict it will show up on vehicles, from tractors to cars, by the 1985 or 1986 model year.

Engine manufacturers are currently testing elelctronic injection systems developed by Stanadyne and Robert Bosch, two of the world's largest injection pump builders, and research into such systems is going on in companies and universities on this continent, in Europe and Japan.

Like so many new technological developments of recent years, electronic injection control is an idea that has become possible because of the small computer, on microprocessor, which can survive the harsh environment aboard a mobile vehicle.

Stanadyne, which is working with Motorola on an "electronic full-authority diesel fuel injection system," says the microprocessor would "look" at engine functions like top dead center, start of injection, water temperature, altitude and intake manifold pressure, to determine the precise fuel delivery rate and timing for peak performance of an engine.

By contrast, the standard mechanical governor looks at one performance reading, engine speed, and adjusts fuel flow and timing to speed up or slow down the engine to match the setting of the governor. Speed and efficiency

In addition to the electronic controls in its system, Stanadyne incorporates a new fuel pump concept, called the "PCF" pump, with an internal mechanism that allows the pump plunger stroke to be varied while the pump is operating. The design is said to allow improved fuel control levels and timing accuracy compared to previous designs.

One industry source familiar with the Stanadyne and Robert Bosch projects in electronic injection control explained that the high accuracy of fuel volume and timing in the new systems will likely be needed to meet federal emission standards for diesel-powered cars and trucks, and this government pressure is a big incentive for development of the new systems, which could be quickly adapted to agricultural equipment to improve performance.

"The most visible pollution in a diesel is the black cloud you get when you accelerate and the injector dumps in extra fuel before the turbocharger gets up to speed," he said.

"With electronic control, your computer can read intake manifold pressure and set an injection rate that's matched to the amount of air entering the cylinder, so the fuel charge gets burned completely," he explained. "You take that a step further, and let the processor know the temperature of the incoming air and the engine cooling system, and you get even better combustion control. And the computer does it on the run, in the field. You don't have to go back to the shop, or stop work to adjust the system."

Besides controlling visible smoke emissions, electronic systems have been shown to control other pollutants, such as nitrous oxides and noise.

While emission control may be the motivating force for developing electronic injection for on-highway vehicles, the source said there should be direct spin-offs into agricultural machinery, where power output and response to load are more critical parameters than pollution.

"In principle, once you work out the details of making a system work, you can change engine characteristics by changing the programming in the computer," he said. "The same engine could be retuned simply by changing a computer cartridge, like a video game." Refining the details

As presently configured, the Stanadyne electronic system retains conventional "poppet" type fuel injection nozzles, which use a spring-loaded valve that opens only after the fuel from the pump reaches a certain pressure. The PCF pump controls the timing of injection and the volume of fuel delivered.

But British researchers at Loughborough University reported development of an electronically-controlled fuel injection nozzle that worked out successfully in an indirect-injection (IDI) diesel engine.

Their research was reported in SAE Paper 830576, "Microprocessor Controlled Fuel Injection for Automotive Diesel Engines," by G.G. Lucas, D. McLean and P. Adcock.

The injector used a solenoid to open the injector, with a spring to close it. The next step, they say, is development of an injector with two solenoids, one for opening and one for closing the injection valve, which they say would "allow the possibility of closed loop control of cylinder pressure."

Among potential benefits seen by the British researchers for the electronic injection system:

* Providing a versatile tool for adjusting fuel injection parameters in accordance with operator's demands.

* suitability for complex engine management systems for controlling emissions, fuel consumption, noise, maximum cylinder pressure and other operating characteristics.

* Great potential for diagnostic work because each cylinder can be controlled independently, allowing balance between cylinders to be determined.

"In the short term," they concluded, "the device offers flexibility in determining the best operating conditions for the engine, and in the long term, with the necessary work on control algorithms having been done, will help in operating the engine at a closer-to-optimum point."

It should be pointed out that their research dealt with an IDI engine, where fuel is injected into the intake air before entering the cylinder. This requires considerably less fuel pressure than a direct injection (DI) engine, in which fuel is injected into the compressed air in the engine cylinder.

Typically, large diesel engines require fuel pressure of 15,000 pounds per square inch to overcome the force of compressed air in the cylinder. The British test system used a pump supplying 3,700 psi to the IDI injection nozzle.

"We can see the benefits of electronic control." Our problem is finding a solenoid that can lift a valve against the fuel pressure needed for direct injection. A solenoid that strong takes an awful lot of current and produces a lot of heat, so there is some reliability question.

"The nozzle is a refinement we need to make in the electronic system, and we may end up with some type of lever arrangement, or something radically different from the conventional injection nozzle. But for right now, it looks like we'll stick with conventional nozzles and work primarily on the pump, the processor and the sensors, to make the product commercially practical." Keeping it safe

Another element of commercial practicality, making the electronic injection system fail-safe, has been dealt with by two Robert Bosch engineers, in SAE Paper 830527, "Strategy for a Fail-Safe Electronic Diesel Control System for Passenger Cars."

The authors, Gerhard Stumpp and Herman Kull, outlined a design strategy that should avoid safety failures and engine damage if the fuel control system suffers a failure in the sensors, the digital processor or actuators.

"A careful distinction must be made between reliability and fail-safety," they say. "A fail-safe system can fail frequently and thus be unreliable. However, each such failure must lead to a safe condition."

The Bosch electronic diesel control (EDC) system controls fuel delivery, start of injection and exhaust gas recirculation through actuators. Sensors on the engine read water temperature and angular position of the crankshaft, and a third sensor mounted on an injector detects the opening of the injector, thus confirming whether the system is functioning correctly.

A microprocessor accepts signals from the sensors and sends commands to the actuators, to regulate the engine.

Signals from the injection sensor and crankshaft sensor are evaluated to determine when the next injection cycle should start, and this can be varied as a function of engine speed and temperature.

The pulse frequency from the start-of-injection sensor can also provide a redundant speed signal. If injection starts too early or too late, the fuel supply can be cut by means of a solenoid valve in the fuel inlet line, to protect the engine.

The quantity of fuel injected is dependent on throttle movement and engine speed, and can be varied from zero to maximum delivery. When the controller is de-energized, springs reduce fuel delivery to zero.

Failures in the system could occur at any sensor or actuator, the connecting cables, the processor, or in the electrical power supply to the entire system or a single element.

Countermeasures to failures in individual parts of the system should be such that the vehicle can be operated on an emergency basis, with engine shut-down occurring only if such measures cannot be applied, the Bosch engineers said. Aiming for reliability

Two research papers coming out of the Cummins Engine Co. address the issue of reliability of electronic systems, setting goals for component suppliers and going back to the old issue of diesels being more reliable than gas engines because they didn't have electrical ignition systems.

In SAE Paper 820905, "Electronic Diesel Fuel Controls," Eric Day of Cummins and Howard L. Frank, of Motorola, Inc., say that system reliability must come up to about 10,000 hours for Class 8 trucks, equivalent to four years of use at 100,000 miles per year.

Among obstacles to achieving that reliability goal, they note, are:

* Vibration, causing fatigue of soldered and crimped wire connections, causing wiring insulation to wear through, making pin-type connector bores wear out, and shaking apart printed circuit boards and press-fit actuator assemblies.

* Sealing moisture out of components is more critical than on conventional electrical systems, such as starting and lighting circuits, because the micro-computers and related components use very low currents, often less than one milli-amp. Problems include oxide build-up on pin connectors and short-circuiting between adjacent connectors in a plug due to moisture "wicking" down wire insulation and into the plug. Steam cleaning can create these kinds of problems.

* Electromagnetic interference can disrupt the on-board computers, coming from sources like CB radios and overhead power lines. This requires additional filter capacitors on circuit boards and more expensive shielded cables in some wiring circuits.

* Voltage deprivation can occur, as when an engine is cranked in cold weather, requiring a special bypass circuit that would let the engine start even when the computer didn't have enough power for normal computer control logic to take hold.

A second paper, from J.W. Austin of Cummins, sets up 20 test criteria for electronic components and notes the need for setting SAE standards and test procedures where none now exist.

In SAE Paper 830101, "Sensor and Actuator Requirements for Heavy Duty Diesels," Austin notes that military standards already exist for some test areas, such as certain vibration, humidity, mechanical and thermal shock and exposure to salt, fog, sand and dust.

"More work needs to be done to define test methods and correlate them to real world environment," Austin concludes. "This is especially true of vibration, electromagnetic interference, pressure washing and mechanical shock. A recommended practice covering the truck environment is being developed at present by the SAE. This should help clarify and standardize this area further." Worth the bother

While development work must obviously be done to meet the demands of reliability in the truck and tractor market, electronic diesel control seems likely to become a standard offering in the near future, and may bring about some changes in the internal design of diesel engines.

In late 1982, Isuzu Motors Ltd., of Japan, a General Motors affiliate that built the Chevy LUV trucks and now markets under its own name in the U.S., started offering passenger cars with an adapted version of the Bosch electronic diesel control system. (Isuzu engines are also found in some smaller agricultural tractors.)

Advantages of the system are said to include better fuel economy, less noise at idle, better cold startability and higher output performance. The Isuzu engines have a new combustion chamber design, called the Commet IV, developed specifically for use with electronic injection control.

The new combustion chamber has a larger area ratio than conventional swirl-chamber engines, providing better fuel economy, less idle noise and more power, but was inferior in cold starting and produced more smoke at low speeds.

These drawbacks were overcome by the electronic system, particularly by electronic timing of injection, according to three Isuzu engineers, Ryoji Kihara, Yasuo Mikami and Hirohide Kanao, in SAE Paper 830528, "The Performance Advantages of Electronic Control Diesel Engine for Passenger Cars."

The Isuzu system incorporates six sensors to measure fuel temperature, coolant temperature, engine speed, accelerator position, injected fuel quantity and vehicle speed.

Additional benefits Isuzu reports from adoption of the new injection control system on diesel cars include: good acceleration response; steady idle speed control to compensate for engine temperature and parasitic loads like the charging and air conditioning systems; capability for cruise control, and a built-in self-diagnostic system.