Controlling Cooling Compactly

Integrated fan and controller reduces underhood space

—by Michael Hillyer, vice president, Advanced Engineering, Johnson Electric

As vehicles become more complex and engine compartments more crowded, one pressing challenge is to package more capability into smaller, lighter assemblies for heating and cooling. All carmakers are looking to refine the cooling systems in their vehicles to improve fuel economy and reduce environmentally harmful emissions. Johnson (Gate), North American subsidiary of Johnson Electric Group based in Hong Kong, has designed a compact cooling fan/control module that provides improved reliability and efficiency, helping to reduce fuel consumption and thus tailpipe pollutants. 

Controlling engine cooling has been a difficult technical challenge since the Model T. As engines became increasingly powerful and engine-driven underhood systems were added to improve safety and comfort, it became necessary to provide a means of preventing overheating. Common practice was to use water jackets around engines to provide cooling, with a radiator as a heat exchange. A cooling fan, driven by the engine, augmented the flow of air passing through the radiator. This standard proved to be adequate for most vehicles until summer traffic jams became epidemic. With vehicles either stopped or crawling at slow speeds, ram air passing through the radiator obviously dropped to a minimum, and fans were too slow at idle speeds to handle the cooling, obviating the need of an electric fan running independently of the motor.

The first electric fan motor ran continuously at one speed, requiring constant consumption of stored energy and a long motor life. At cruising speeds, the ram air forced through the radiator was enough to cool the water, requiring less effort from the fan. A two-speed motor, that lowered the fan’s speed when ram air was adequate, somewhat reduced the drain on electrical energy and the total rpm specifications of the motor. As requirements for engine efficiency to lower fuel consumption and pollutants became more urgent, so, too, did greater finesse in controlling engine block temperatures. A faster engine warm-up cycle — and more precise control over engine temperatures — came through finer control of the water pump and cooling fan speeds, combined with distribution of water flow through an automatic valve control in the water-flow circuits. Still, as underhood environments become more crowded, hotter and subject to hostile conditions (such as spray from highway salt water), optimizing a fan motor and motor controller that can be operated with precision has been a challenge for engineers.

The Johnson radiator-cooling fan module, now in advanced prototype form, provides automakers the opportunity to write algorithms to control engine, radiator and cabin temperatures to a fine degree. One chief advantage over other systems is encasement of the fan motor and control circuit inside a shell to protect the system from harsh underhood conditions in a wide variety of applications.

Automakers, of course, have specific requirements for the duties and performance of cooling systems generally and cooling fans in particular. Depending on the complexity of the total systems, vehicles require one or a pair of electrically driven radiator fans. Sometimes they are mounted on the radiator’s cool side, other times on the hot side. These specifications require that the motor and its control circuit be capable of performing in ambient temperatures ranging from 70-90oC and 110-125oC, respectively. The motor and control circuit have their own electrical resistance heating and must perform flawlessly under all conditions for at least 2,000 hours of rotation.

Speed control requirements vary by vehicle demands. The simplest system requires only that the motor rotate at speeds predicted by performance characteristics related to the average voltages applied through a pulse-width modified input. With this open loop, tolerable small variations in the actual speed would be expected as components wear. To compensate for these changes, where no variation can be tolerated, one can use a feed back system in which the actual velocity of the motor is fed back and small adjustments made to compensate and maintain the desired speed. In more sophisticated systems, temperature sensors, located at points in the vehicle where temperatures need to be controlled more precisely, provide thermal feedback. The motor speed can be adjusted incrementally to maintain those temperatures.
Because the electric motor fan is no longer driven continuously, and the total running life is reduced to approximately 2,000 hours, it is possible to use a brushed motor for this application, which is less costly than brushless systems. However, it has been more common to use electronically commutated devices. The total electronic package to commutate and control through feedback has become larger, and it is preferable to locate the control package close to the motor. In addition, neither the motor nor the control circuit should emit electrical noise that might disturb other electronic components, and they must be hardened so that they experience no deterioration if they are subjected to electrical noise spikes from other sources.

The images show one of Johnson’s most recent designs of a motor/control/fan/shroud package. This package is small, and integrated so that the control circuit is a part of the motor or a small extension of the motor. Besides being protected from hazardous conditions, it benefits from being within the fan’s own airflow, allowing temperatures to be held within a workable range.

The company is designing and producing cooling fans with a wide range of control levels, from series resistance controls to fully integrated feedback systems for advanced cooling systems. While superior control methods will likely first be used in high-end vehicles where the cost is less of a factor, lower cost solutions are being developed for all vehicles.