Hydraulic Fan Drives for Internal Combustion Engines

By Mike Carney, CFPS

In a typical internal combustion engine application, much of the energy released from the fuel is wasted and appears within the system as heat. One way to combat this wasted heat energy is to incorporate an engine fan, but these contribute to the overall machine noise level and use additional horsepower to provide cooling. An engine driven fan cools at a fixed rate and must be sized for the maximum cooling requirement.

Hydraulic fan drives can deliver greater efficiency in a wide range of machines and applications. Temperature activated, electronically controlled hydraulic fan drive systems can offer finer control which allows for reducing the fan speed during time of low cooling demand and therefore the fan drive system uses less horsepower. Hydraulic fan drives also allow the cooling package to be located remotely from the engine, which saves space, makes placement more convenient, and improves noise insulation. Normally any hydraulic fan drive system is designed to “fail high”, meaning that if electric power is lost, the fan provides full cooling.

Hydraulic fan drives can also provide reversing. This is used for “blow off” of the cooler. In environments where there is airborne debris that can clog the cooler, reversing the fan is critical to insure proper cooling.

Hydraulic fan drives can be on/off or of the modulating type. On/off fan speed control uses a venting relief valve to turn the fan on and off. It is the simplest and most cost effective system. But efficiency and noise control are not as good as can be achieved with variable speed fan drives. With on/off types, system pump volume and relief valve setting determine the maximum fan speed. A temperature switch in the engine coolant tells the hydraulic fan drive when to cycle on or off. This type of system saves energy in times of low cooling demand.

Variable speed fan drive systems provide the highest efficiency and most noise reduction. An engine coolant temperature sensor sends a signal to the electronic controller to vary the signal to the proportional relief valve. The sensor reads engine temperature, and through the proportional relief valve, it modulates the fan speed to provide the correct cooling. The variable speed system reduces horsepower (and therefore energy) loss by using only the hydraulic power needed to maintain a consistent engine temperature. This results in power savings, lower noise and reduced fuel consumption. A variable system will also prevent abrupt fan speed changes, reducing hydraulic shock as well as system fatigue.