Development Story 03
We pursued even lower fuel consumption than our conventional machines as we attempted to increase productivity. In addition, we maintained the durability associated with the Model 10 SK Series, creating a new value for hybrid excavators.
Currently, the reduction of greenhouse gases and Nox (nitrogen oxide) causing global warming, air pollution or health damage is major concern of the overall international community under the call of ecology and a sustainable society.
Excavators used at various construction sites for land leveling, digging and demolition urgently require energy-saving and environmental load reduction solutions. The current trend is the hybrid electric vehicle which has both the engine and motor as a power source.
In response to this situation, KOBELCO developed the SK200H-10, 20-ton class hybrid excavator which features the company's own hybrid technology.
Koji Yamashita, the leader of this development project had this to say.
First of all, KOBELCO has a track record as the pioneer of hybrid excavators. From 1999, the company joined hands with the Technology Development Division of Kobe Steel, Ltd. to begin the research and development of hybrid technology. In the Spring of 2006, KOBELCO introduced the SK70H, its first hybrid excavator at Intermat, the international exhibition for construction machinery held in Paris. In September 2009, the company launched the sales of SK80H. This unit went beyond our expectations of a 25% decrease in fuel consumption, actually achieving a reduction of 40%.
In 2012, we released the 20-ton class SK200H-9 with an overwhelming low fuel consumption performance that secured KOBELCO’s reputation for low fuel consumption.
For the SK200H-10, we wanted to succeed the high durability characteristic of the SK Series Model 10 while further lowering its fuel consumption. Also, the unit would feature a performance capability that would overcome any of the negative comments such as the work speed being inferior to those of conventional machines. The three keys to accomplish those goals were "upsizing the generator motor", "full motorization for revolving" and "adopting a lithium ion battery".
At the time when the development for the SK200H-10 started, adopting the use of a lithium ion battery had several hurdles to cross in terms of safety, resulting in the common view that "practical use was premature". However, KOBELCO not only responded to the “United Nations Recommendations on the Transport of Dangerous Goods” but also conducted tests that assumed construction sites under severe conditions that included vibration, impact, ambient temperature and surrounding dust. After fully verifying the safety, we decided on adopting a lithium ion battery.
At the same time, we were looking at upsizing the generator motor to increase productivity. Kazushige Koiwai, who was in charge of system development, remembers the following.
The biggest theme was how to release the heat. For that purpose, we took into consideration air flow and created a simple internal structure. By doing so, we reduced the risk of malfunction and made maintenance operations easier.
Seiji Saeki, who was in charge of production design, he proudly proclaimed the following.
After repeated designing, analyzing and testing to improve product precision, we upgraded the output of the SK200H-10's generator motor to the top level for this class, with keeping the compact design to fit in the same engine space as the conventional machine's.
For the SK200H-10, each and every component was developed by KOBELCO to heighten the compatibility with the product concept. This included the controller for the hybrid excavator which is typically produced by a specialized manufacturer for the conventional machines. So, KOBELCO sent its development engineer, Sho Fujiwara, to a control manufacturer.
First and foremost, we had to start by sharing each of the requirements sought for excavator and the development thoughts that went into the SK200H-10 with the other party's engineers. From there, we began our efforts to develop the optimum controller for this machine.
Later, development moved to the next phase, the tuning of the operability and usability of the hybrid machine. At this stage, we conducted a mutual adjustment of various fields that pursued the best methods to bring out the best system. To put it simply, our theme was "partial optimization to overall optimization".
For overall optimization, we needed to construct a dedicated bench test environment in the factory. This was not just for evaluating the performance of a hybrid machine unit, but also for evaluating the performance of a combined system. Repeated examinations were conducted, adding conditions such as temperature and load changes to fully test the machine’s power, reliability and safety.
Furthermore, with the support of our customers throughout Japan, from Hokkaido to Kyushu, we carried out monitored operations with a prototype. Installing sensors at each point of the machine, we collected data and took the on-site suggestions for improvement from our customers and provided the feedback to our development group.
This machine was equipped with electric motor for turning. We were able to smoothly tune the unit by repeated tests and taking in the opinions of our monitors. In addition, the engine is assisted by a large generator motor that helps maintain the necessary power even if the engine's rotation speed is lowered. At the same time, we also succeeded in improving the work environment of the operator due to reducing the noise by the engine's rotation cutting.
I believe that the mobility and acceleration which instantly produce torque are more than those of our current machines. In fact, an operator will strongly experience the improvement when attempting a complex movement such as operating the attachment while turning.
During the monitoring stage, we had customers who were interested in purchasing the prototype for immediate use. Also, customers who were surprised by the unit's thorough energy-saving characteristics mentioned that they thought the fuel meter was broken. (Laughs)
In this manner, the unit passed a substantial number of quality confirmations that lead to the completion of the SK200H-10.
If you operate the machine for real, your former concept to a hybrid excavator must completely change.
We want people to try out this machine, including those who gave hybrid machines a wide berth due to doubts concerning operability and power, as well as those who were unsatisfied with the performance of other hybrid machines. That's the message from our confident engineers.
Realized the top-level motor output for a 20-ton class which secured an operational capability that was equal to conventional non-hybrid machines.
Installed an electric motor for turning and utilized the energy used for turning so far for operations such as digging, to improve the machine's productivity. We also focused on tuning to allow a turning operability that was equal to that of standard machines.
Because it can continually retain stored electricity, the retained energy can be used to hold down the engine output, depending on the load range.
* The contents described above is based on the information at the time of issuing (October, 2016).