Kawabata, who test-drove a number of prototypes at Honda Meeting 2012, was most surprised by the sheer speed at which Honda develop three new hybrid systems—complete with new engines, transmissions, and other components—after the IMA hybrid system, which had taken over a decade to develop. She says she could sense Honda's determination not only to push efficiency to the limit in order to win the race for best fuel economy but also to realize a sporty driving feel at the same time. In this conversation, the engineers disclose for the first time their experiences developing the three new Honda SPORT HYBRID systems.
Kawabata From here I would like to ask questions about specific technologies in the Earth Dreams Technology suite. First, the one-motor hybrid system that will replace IMA. Honda has already announced that this hybrid system will be used in small-sized vehicles. It was very refreshing to drive. There was a purity to it that made me like it the most. Frankly speaking, it felt very different from all of the previous Fit models. Of course the Fit was already a fun car, but it was taken to a whole new level with this model. I was particularly surprised by the direct mechanical sensation of the dual clutch transmission (DCT), which felt like a sports car transmission. At the same time, it still kept the satisfying thrust provided by the electric motor—kind of like a super charger—that the original IMA had. The whole system felt very much like something Honda would create.
What I wanted to find out most today was your reason for choosing the new packaging: an Atkinson engine, seven-speed DCT, and motor mounted in the transmission, not near the engine like usual.
Hasegawa There was a time when I researched every kind of hybrid system I could find. A lot of variations had already been considered, such as decoupling the engine at the clutch so only the motor propels the car, or designing the transmission to be as close as possible to a manual transmission to maximize efficiency, or using the Atkinson cycle to maximize engine efficiency. When we put all those decisions together, this is the packaging we came up with.
Wakamatsu There was a good deal of hesitation especially around changing from a continuously variable transmission (CVT), which moves smoothly between an infinite number of gear ratios, to a manual transmission. But in a contest over fuel economy and which type wastes the least amount energy, with current technology, manual transmission beats CVT. Even with a manual transmission, we figured we could recreate the feeling of a CVT by compensating for the jump in torque between gears with the motor, so we decided to go for it. Making such a big decision didn't make our jobs easier [laughing]. But the fuel economy potential is very high. We're determined to come up with something successful.
Kawabata When driving the prototype at Honda Meeting 2012, I was pleasantly surprised to find that such a fuel-efficient car could be so fun to drive.
Wakamatsu The dual clutch transmission technology is still in its infancy, so we're still conducting research to determine whether it can be used in all vehicles, including by measure of durability and reliability. In a hybrid, though, you can use the motor to accelerate from a stop without decoupling the clutch, so there is no need to control slipping that occurs when the clutch isn't fully engaged. In other words, a hybrid system and a dual clutch transmission are a good match for each other since they are easy on the clutch.
Kawabata I've always thought it a shame that people tend to complain about gear noise and whatnot when transmissions break but they don't really appreciate it when they're working properly.
Wakamatsu Exactly! You know how I feel, then [laughing]. I've said this to my colleagues before, but the difficulty with transmissions is that once they make their presence known, it's over. They can't have shift shock. They can't make a sound. The best transmission is an invisible one. So if we slack off our transmissions will be noticeable and that immediately brings down the value of the car.
Kawabata The new one-motor hybrid system gave me an impression of luxury. Based on what you just said I think now I understand—the right balance between responsiveness and seamlessness of the transmission was what led to a sense of luxury. Next, as for engines, what made you decide to use an Atkinson cycle engine this time?
Otsu Engines have only one area where fuel economy is best. We want to make that area as high and wide as we can, but if you increase it it narrows, and if you decrease it it gets wider. In other words, if you improve fuel economy at that one area you end up narrowing the range of engines speeds where that economy is achieved; if you widen that area, maximum fuel economy declines.
But in a hybrid, even if you shorten that range in order to increase maximum fuel economy, the motor can help compensate for the lack of width. So when we considered engine specifications based on this concept, we came to the conclusion that the Atkinson cycle can make the most efficient engine.
Of course we're also developing the next technology, but at this point in time the best combination is a hybrid system. However, in the world of engines, there are still many things we don't know until we make a prototype and run it, or put the prototype in a car and drive it. That's why there's a development process we have to follow, and when you multiply that by the number of engines that are currently under development, the result is an enormous amount of work. It's not easy even when development is going according to schedule [smiling].
Kawabata I'd like to pose this question to Mr. Ishibashi since he's involved in product planning. Honda has stated publicly that its goal is to have the best fuel economy in the next three years. Will Honda's next small-sized car be number one?
Ishibashi Of course! But when you say number one, the words and figures tend to take on too much meaning. The point of this car is for people to drive it and think, "That was fun. And it's also the most fuel efficient!" That's why it bears the name Earth Dreams Technology.
It will be number one in environmental performance, but that's not all. It's packed with all of our dreams. The next small-sized Honda car will definitely live up to its name.
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