KOMATSU
Making Inroads in Hybrid Technology to Power the Future
In May 2008, Komatsu announced the world's first commercially available hybrid construction equipment, the PC200-8 Hybrid hydraulic excavator. We spoke with Mr. Hikosaburo Hiraki, who was centrally involved from the outset with the development of the Komatsu Hybrid System, which contributes to reductions in CO2 emissions and fuel consumption.

Views: Can hybrid systems be effective in hydraulic excavators?

Mr. Hiraki: Actually, hybrid systems are more effective in hydraulic excavators than passenger cars. When a car travels on an ordinary road, the driver will typically apply the brakes (decelerate) about once every 5 to 10 minutes. In contrast, the upper structure of a hydraulic excavator turns at a rate of once every seven seconds when loading, generating energy each time it slows down. Since the structure turns and reduces speed at a high frequency by efficiently storing energy, it makes the hybrid system a perfect fit.

Views: How is the hybrid system of a passenger car different from that of the PC200-8?

Mr. Hiraki: It may seem surprising, but the kinetic energy of the PC200-8 hydraulic excavator is about the same as that of a standard passenger car. Kinetic energy is proportional to the multiplication of the mass and the square of velocity. As such, there is little difference in the kinetic energy of a passenger car that is light and moves quickly and that of the PC200-8, which is heavy and moves slowly, but the upper structure turns quickly. We therefore believed it was possible to take certain aspects of the hybrid system of a passenger car and apply them to the PC200-8 hybrid system. With this in mind, we pursued further research into the hybrid system of the passenger car, confident that we could utilize it in construction equipment. However, because the upper structure of hybrid excavators are required to turn frequently, it was imperative to identify how to efficiently store in a small device the instantaneous energy generated while turning in order to make hybrid construction equipment a reality. Eventually, we developed a capacitor that could store and discharge electric energy instantaneously. In the PC200-8 hybrid system, the electricity discharged from the capacitor is used to assist the engine when it is accelerating, which is the major difference from the hybrid system of a passenger car.


Views: It seems that some of the people who viewed the PC200-8 Hybrid for the first time were disappointed that it looked almost the same as conventional models. Is there a reason the exteriors look the same?

Mr. Hiraki: We commenced development based on the idea that as long as conventional and hybrid systems existed together, the appearance should be similar. The reason for this is to make it possible to mass produce this machine on standard factory production lines rather than equipment solely for research purposes. Originally, however, the shape and size were such that it looked nothing like conventional construction equipment. In the end, I am proud we found a way to make it look the same, which is what we do at Komatsu.

Our basic policy is to make all core components in-house. We have always manufactured engines and hydraulic devices internally, but electric motors were a whole different realm. Komatsu always seeks to challenge unfamiliar territory, however, which is our policy and part of our corporate characteristics. Through in-house production, we can make refinements according to our needs and provide outstanding products to customers.

Views: What other areas were particularly difficult during development?

Mr. Hiraki: Since the voltage used by hybrid systems is higher than conventional construction equipment, we had to be vigilant in ensuring a safe design. Simply switching off the power doesn't necessarily make construction equipment safe, and we needed to consider every possible scenario for how the machine would be used. This meant we had to think of each and every possible safety measure. We visited the factory on numerous occasions to seek advice and considered various scenarios before deciding on the safest possible design. In addition to guaranteeing human safety, we also enhanced monitoring to ensure the proper operating condition of the construction equipment itself, or in other words, improved fault diagnostics. We extensively conducted logic checks as well as preliminary tests using actual equipment. It took a long time, for example, to resolve unexpected variations in voltage that occurred when the environmental temperature was -30°C (-22°F).

Views: What has been the result at customers' sites?

Mr. Hiraki: Some customers have achieved a 30% or 40% reduction in fuel consumption, surpassing the 25% reduction our test results showed.

Outline of the Komatsu Hybrid System

The proprietary Komatsu Hybrid System converts energy generated when the upper structure of a hydraulic excavator reduces its speed while turning, stores the energy in the capacitor and uses it to assist the power of the engine via the power generation motor when the engine accelerates.

While standard equipment normally uses a hydraulic motor to turn the upper structure, we have developed an electric motor exclusively for the Hybrid. Through the use of this new motor, which recovers energy generated when the upper structure's turns slow down, we have achieved a hybrid hydraulic excavator.

Compared with the standard PC200-8, we have achieved an average reduction in fuel consumption of 25% via test results. Furthermore, in field tests with our customers, we confirmed a maximum reduction of 41% at a job site where the machine's upper structure turns more frequently.