Different off-road machines can work in very different RPM ranges. Forestry machinery engines, for example, run most of their time at steady 1500 RPM while tractors with CVT transmission work at higher revolutions. This is why it makes sense to customize engines to give their best performance and fuel economy in the most used RPM range – horses for courses, as they say.
At AGCO Power, we pride ourselves on our ability to tailor our engines to customer needs for optimal fuel economy and usability. In the previous articles in the CORE Insights series, we have discussed the importance of optimizing the cooling system (parts one and two), as well as reducing unnecessary idling. Now it is time to talk about the optimal RPM range for each use. While a tractor, CTL forestry machine and combine harvester may share the same basic engine, its properties are always fine-tuned to suit the special needs of the application at hand.
“Calibrating the engine for the needed RPM range has two major benefits”, says Tapani Katila, Sales Manager at AGCO Power. “Firstly, optimizing the fuel economy for the most used RPM range leads to significant savings in the long run. And secondly, tailoring the torque curve for the application makes sure the engine responds well and does not stall under peak loads.”
Of course, the optimal working RPM is always a compromise.
“If we optimize a certain RPM range, we compromise another,” Katila says. “By discussing with the customer, we can find a perfect torque map for the intended engine use.”
Less RPM is more
When a machine manufacturer wishes to reduce fuel consumption or noise level, there is another effective solution: to reduce the overall engine RPM.
“As a rule, lowering the engine RPM alone enables bigger savings in fuel efficiency,” Tapani Katila says. “This can be further improved by calibrating the engine properties for the desired RPM range as described earlier.”
Lower RPM has many benefits. It reduces many kinds of losses, such as mechanical losses caused by friction, while also reducing the engine wear.
“Every engine has so-called pumping losses caused by air pumping through the engine”, Tapani Katila says. “If the amount of air is reduced from, let’s say 1000 kg to 800 kg per hour, much less work is required to pump it and less energy lost.”
”Historically, machines have resorted to higher RPMs to prevent stalling during takeoff or sudden loads, such as a patch of harder soil in field work” Katila reminds. “This is familiar to everyday car drivers with a manual transmission: too little revs and your car will stall on traffic lights, or when you drive slowly, and a curb or other obstacle appears. But from our point of view, it’s better to customize the torque curve so that the highest torque is available already in the low RPM area and the engine is designed to respond well to throttle.”
A great example of the lower RPM benefits is the successful Fendt 700 Vario tractor, which features the award-winning CORE75 engine by AGCO Power.
“More and more manufacturers are discovering the benefits of low-RPM design, which means that also hydraulic pumps and other ancillaries are increasingly made to operate on lower revs,” Tapani Katila sums it up. “When designing a whole new machine, it is a good idea to give it a thought.”
System optimization for best results
Besides torque, each engine type has a certain RPM range for the highest power output. Optimizing the shape and location of the output power curve for each machine type can be crucial for the drivetrain lifetime.
“If the power output is too big on upper RPMs, outside typical use, it can put too much stress on the transmission, for example,” Katila says. “Also, having too much power on low RPMs can cause wear by exposing the power train to excessive torque.”
Calibrating the maximal power to the correct RPM according to machine, transmission type and other factors pays off by increasing the machine lifetime.
“All and all, while optimizing the engine is good, optimizing the whole system is better and leads to best savings,” says Tapani Katila. “At AGCO Power, our customer-centric approach is to focus on the desired outcome and find the means to achieve it, together with the customer.”
See also the previous articles of our CORE insights series:
CORE insights: How cooling system optimization improves fuel-efficiency (part 1)
CORE insights: Improve fuel-efficiency with cooling system optimization (part 2)
CORE insights: How to reduce unnecessary engine idling