Realizing the World’s Highest Fuel Efficiency^*1
Fuel Economy of 35 km/L^*2, and Behind the Scenes

In 1996, development of the first-generation Insight began.
The goal given to the development team was to “create the world's most fuel-efficient car.” The specific target was to achieve 35 km/L, which no other mass-produced car had achieved.
Prior to the development of the Insight, advanced development of the power unit was already underway. Among the many hybrid systems available, Honda first began work on a system that would later be called IMA (Integrated Motor Assist). This system, in which the motor assists the engine when necessary, such as during acceleration or starting, while the engine is the main power source, made full use of the fuel-efficient engine technology that had been pursued up to that point, and was lightweight and compact, using only one motor and a relatively small-capacity battery. The production cost could also be kept low. Moreover, motor-assisted acceleration provided turbo-like powerful acceleration, making it possible to achieve both low fuel consumption and an exhilarating ride. However, relying solely on IMA was not enough to achieve the goal.
The Insight project was driven by the extremely demanding requirement that if it did not achieve the goal of world’s best fuel economy, it would have no purpose to exist. If there was any element that could lead to even a slight improvement in fuel economy, it was incorporated without hesitation.
The body design was based on the idea that aerodynamics must come first, and the drag coefficient (Cd) was pursued to an unprecedented level for a mass-produced vehicle. For weight reduction, the “new lightweight aluminum body frame” was developed by further evolving the aluminum body technology that had already been realized in the NSX. Furthermore, the vehicle weight of 820 kg, which was set in anticipation of fuel efficiency standards in Europe and the United States, was a figure that had to be met, so all components were considered for weight reduction.

“New lightweight aluminum body frame” to minimize drag coefficient.

Insight’s IMA uses the parallel system
The Prius uses the series-parallel system

In the midst of development, Honda’s biggest miscalculation occurred in 1997. Toyota Motor Corporation announced its mass-produced hybrid car, the Prius. The development team felt beaten. Even Honda executives at that time regretted being beaten to market, saying, “Honda should have been the first to launch a hybrid car like that.”
The Prius hybrid system was motor-driven when starting off and at low speeds, and used both the engine and motor when speed increased, and was a system that took advantage of engine and motor characteristics. However, it differed to the Insight’s hybrid system, and once the development team realized they could be confident of their unique technology, development accelerated. They believed that they could win on fuel economy.
In November 1999, the first-generation Insight, equipped with Honda’s unique IMA hybrid system, was launched. It featured the world’s highest fuel economy of 35 km/L, outstanding aerodynamic performance, and a vehicle weight of 820 kg^*3 thanks to its aluminum frame. Honda’s unique hybrid car caught the world’s attention. In order to speed up the development of its hybrid cars, Honda began development with compact cars, and ensuring the system could be installed in existing models, completed IMA, an engine-motor parallel system that was lightweight, compact, and highly compatible with engines. This was, however, only one answer.
Honda R&D was looking ahead to the near future, and was studying the next evolution of the ideal hybrid system, which could be used in a variety of models and serve as the base technology for electrification.

• As of 1999. Honda research.
• Fuel consumption: 35.0 km/L (10-15 Mode) / 5-speed manual transmission
• 5-speed manual transmission model

First-generation Insight

IMA (ECA)

Insight (1st generation) in Action

2-Motor Hybrid is Ideal
But Electrification Technology Lags Behind

Qualitatively best hybrid car driving characteristics
achieved

As a result of repeated discussions on what the ideal driving characteristics would be for the evolution of a hybrid car, the conclusion was that a system that could freely switch between motor-only driving, motor driving while generating electricity with the engine, and engine driving, would theoretically be the most efficient. The initial goal of the next phase of hybrid system development was to come up with a system that could achieve this.
Manabu Niki (then Senior Researcher, Honda R&D’s Automobile R&D Center), who has been involved in the development of hybrid cars for many years, said, “We already had a qualitative image of the ideal driving characteristics when we were developing the Insight.”
There are many possible combinations of elements that make up a hybrid system. The question was what combination of the elements, including the number of motors, engine displacement, transmission type, and battery capacity, could achieve the world’s highest fuel efficiency and still provide a good driving experience. The initial choice was a series-parallel system combining an engine, continuously variable transmission (CVT), motor for power generation, and motor for driving.
”With this system, the car can run on EV (electric power only), it can run on a motor while generating electricity with the engine, or it can run efficiently on the engine alone. In 1999, we built a prototype using the LOGO, a small model. Since the mode can be freely selected, we achieved very good fuel efficiency and the car ran very well," said Niki.
At this stage, however, it was not a viable package. The entire system had to be made compact while further increasing efficiency of the motor’s power generation.

“Take It All Out”
Breakthrough to World’s Highest Efficiency^*4

IMA was praised worldwide after the launch of Insight, winning numerous awards. 2001 saw the launch of the Civic Hybrid, which had IMA installed in existing Civic models. In 2005 the Civic was fully revamped, with a hybrid model being launched at the same time. In 2004 the Accord (U.S. model) was launched with IMA combined with a V6 engine. Other, mainly small models, equipped with IMA followed.
At the same time, the development team had been struggling to make the two-motor system more compact. In principle, a two-motor system, one for power generation and the other for driving, is more efficient as a power unit for a hybrid car. Increasing the size of the motor increases its output, but makes it more difficult to install. The key to achieving low fuel consumption with two motors while downsizing the entire system was to thoroughly improve the efficiency of the individual motors and inverters in order to increase the efficiency of electrical transmission from the power generation motor to the drive motor.
In 2005, the preliminary study of the two-motor system was officially launched. This led to a review of the team structure, which had been a concern. There was a strong sense of crisis at the development site that it would be difficult to achieve goals with an organization divided into electrical and mechanical teams. The teams were therefore integrated as AHR (Advanced Hybrid Research).
The research structure of the hybrid team was established by breaking down the organizational barriers that had separated the engine, transmission, and motor. The team members recognized that they had to create the world’s best system if they were going to do it at all. The goal was set at 85% electrical transmission efficiency, which would enable the hybrid system to beat other manufacturers’ hybrid systems at the time in terms of fuel efficiency. Both the electrical and mechanical teams brought together their results, and combined them. This process continued day after day.
Yet, it did not work. The biggest challenge was to make the system more compact, apart from increasing the efficiency of the motors: mounting two motors in the transmission case where the CVT fits was a difficult task. A breakthrough came as a result of a series of technical studies and discussions aimed at solving this problem.
“Take everything but the motors out.”
This meant eliminating the CVT and simplifying the structure to only two motors, driven by a direct clutch when the engine is running.
Honda's unique series-parallel system switches to engine mode during high-speed cruise driving. This is because it is more fuel-efficient to use the engine output directly for driving rather than for electricity generation. If a gear corresponding to the top gear of a manual transmission and a clutch directly connected to the engine are installed instead of a pulley and belt as in a CVT, the engine output can be efficiently transmitted to the tires.

Breakthrough occurred by reviewing the
series-parallel system and removing the CVT

“Why didn't we think of this from the beginning? It was because of preconceived notions about series hybrids, such as the inefficient transmission of electricity, which would make it difficult to achieve good fuel economy, and the large size of the motor, which would be difficult to install and would have only a limited use. It was necessary to take a fresh look at the structure.” (Niki)
In March 2009, the two-motor hybrid system moved from the research phase to the mass-production development phase. The development goal was set at “the world’s highest efficiency.” By making this declaration to management and setting high goals, each team member was further motivated.
“I don't think we would have achieved the results that we did without the AHR team. It would have been absolutely impossible for us to achieve our goals if we had not all removed departmental barriers to share the same work, hardware, and realities, and tackled problems with the same passion. This is the result of respecting and trusting each individual and continuing our research.” (Niki)

• Goal to achieve world’s highest powertrain (PT) efficiency: PT efficiency (%) = Vehicle drive energy (Wh) + fuel energy consumption (Wh)

Accord Achieves 30 km/L^*5 Fuel Efficiency
With 2-Motor i-MMD

Honda's hybrid car strategy was to be able to offer a wide range of models for all classes. IMA-equipped cars had been well received as hybrid cars that customers can drive without any change from their previous engine-powered cars, and by October 2012, the cumulative sales had reached 1 million units in approximately 50 countries worldwide. However, it was necessary to establish a more fuel-efficient system.
Hiroo Shimada (then Senior Researcher, Honda R&D’s Automobile R&D Center), who was in charge of two-motor system development at the time, said:
“Honda promoted hybrids with the IMA. It has played an important role as a one-motor hybrid that can be achieved with a simple system configuration and low cost. We wanted to leverage this experience to maintain our superiority in the future, and to break through as a hybrid, we arrived at this two-motor system.”
The development goal was to use this system with the installation in the 2013 Accord. Engineers competed for high efficiency in their areas of development.
“With a two-motor system, when running on electricity, the efficiency of the motor for power generation and its inverter, and the efficiency of the motor for driving and its inverter, are multiplied together. For example, even if the efficiency of each of these is very high, around 93%, when they are multiplied together, the efficiency quickly drops to the 70% range. That is why it was necessary to set the efficiency target for each of them to the limit.” (Masashi Murata, in charge of Technology Development office at Honda R&D’s Automobile R&D Center at the time)
“The motivation to achieve the world’s highest efficiency raised the performance of every member of the team.” (Niki)
After a long period of hard work, the i-MMD hybrid system, which could be installed in the Accord, was complete. It was a motor-driven system that thoroughly improved the electric components’ efficiency, including power generation, charge-discharge, motor, and regenerative efficiencies, and when combined with the newly developed 2.0L Atkinson-cycle DOHC i-VTEC engine, achieved 30km/L, an extremely low fuel consumption for an upper-middle sized sedan, yet with a smooth, powerful driving feel.
Niki reflected on the strengths of the team that made it possible.
“We were always saying to each other what was good was good, and what was not wasn’t, regardless of our position. Members clashed with the other, but they were all working toward the same goal. Each of us would come up with ideas and listen to different ones. Even if one person alone cannot demonstrate their strengths, united we could maximize our abilities as a team.”

Accord with i-MMD

i-MMD two-motor hybrid system

i-MMD 2-motor hybrid system structure

e:HEV - Three Hybrid Systems into One 2-Motor System
Based on Further Evolved i-MMD

In 2012, when the Accord's development on track, Honda announced three types of hybrid systems, the result of its ongoing research and development efforts to explore the possibilities of hybrid systems in addition to the two-motor system.
These were the lightweight and compact SPORT HYBRID i-DCD (Intelligent Dual Clutch Drive), a one-motor system that is ideal for compact cars, the two-motor SPORT HYBRID i-MMD (Intelligent Multi Mode Drive), ideal for midsize cars and was featured on the Accord, and the SPORT HYBRID SH-AWD (Super Handling All-Wheel Drive), ideal for large cars combining a V6 engine and three motors.

SPORT HYBRID i-DCD

SPORT HYBRID i-MMD

SPORT HYBRID SH-AWD’s
twin-motor unit and
7-speed DCT with
high-output motor

It was a lineup of hybrid systems unique to Honda, that tackled fuel-efficiency and decarbonization technologies from various angles, and increased the number of choices by incorporating them into models with various displacements, offering hybrid cars that fit the customer’s lifestyle.
In 2013, the Accord with i-MMD was launched. The development team, however, was not being complacent. Although it could be used on the Accord’s platform, the motor needed to be more compact in order to be applied to other medium-sized models.
The i-MMD motor introduced with the Accord used distributed winding, which uses common round copper wire for the coil. To make the motor smaller, segment conductor winding, in which square cross-section copper wire is processed and assembled, could be adopted to increase volumetric efficiency. The development team called this next evolutionary motor the “HAW (Honda Advanced Winding) motor,” a motor to attain the world’s highest efficiency.

Comparison of distributed winding using round
copper wire and segment conductor winding made by
processing and assembling copper wire with square cross section

HAW Mortor

At the end of 2011, while the HAW motor was being developed, another surprise came from Toyota. The Aqua was launched with a motor that was the same as the HAW motor concept, and the team was astonished at the similarity. Although verification proved that the HAW motor was superior to the Aqua in both size and specifications, the fact that the HAW motor had been developed earlier caused the team headaches heading into the mass-production stage.
Since the structure was similar, so was the manufacturing process. Although there were patents issues to consider, this was overcome by the teamwork of Honda R&D at the time, and Honda Engineering Co., Ltd. (EG). It was truly a team effort that overcame the obstacle through sheer hard-earned wisdom and teamwork.
Masaaki Kaizuka (then at the Technology Development Office at Honda R&D’s Automobile R&D Center), who was in charge of the development, said:
“What was important was to aim to be the world’s first, a high goal. And communication was also important. Honda is all about communication. If you have a good discussion, people will cooperate with you a lot. For example, if there was a problem with Hamamatsu, we would talk with them about it thoroughly. They would reconsider our conditions. That kind of flexible communication is important.”
Through many innovations and developing new methods in manufacturing, mass production of HAW motors was made possible. The second-generation i-MMD, which was 23% smaller and lighter than the previous i-MMD, achieved higher output and torque, and was applied to the 2016 Odyssey. Since then, the system was also used in the Step Wagon in 2017, and the Clarity PHEV and CR-V in 2018. That year, the Insight was equipped with motors free of heavy rare earth material, contributing to the further reduction of environmental impact and stable production.
In October 2019, Honda combined its hybrid systems into a two-motor system that could be installed in compact cars, and renamed it from i-MMD to e:HEV. The e:HEV was launched with the Step Wagon in January 2020, followed by the Fit and Accord.

Continuing to Aim for the World’s Best as a Team,
For the Future

As the automotive industry is said to be in the midst of a once-in-a-century transition, cars will be increasingly electrified in the future. Power and fuel economy, which have been discussed in terms of engines, will be replaced by the efficiency of electric power units. The “world's highest efficiency” that Honda aimed for in hybrid systems, without a doubt, leads the company into the future. The technologies developed along this path and the engineers’ passion will live on as the foundation of future Honda vehicles.
Shimada said:
“I think that for an engineer, the meaning of being the best in the world is not only the satisfaction. We can offer the best value at that point in time to our customers. The Accord Hybrid was a class-leader. By becoming the industry leader in this way, others will work hard to catch up with and surpass the Accord Hybrid. As a result, in terms of CO₂ reduction for example, the effect would be greater than Honda’s sales volume. In other words, by becoming a world-class company, we can do greater things. We became engineers because we wanted to do work that would contribute to the environment and to the world. When I think about it, we cannot afford to slow down our evolution in the future.”
Niki, who had finally succeeded in creating the “ideal hybrid,” does not believe that his work is finished:
“The ‘world's best’ is not something that is achieved in a day. It is the result of the combined efforts of each team member. It may be frustrating when things don’t go well, but every step the team takes becomes the team’s strength. When you finally see it take shape, you realize that there is still more to come.”
The hybrid system technologies the engineers accumulated have been handed on to the efforts for electric vehicles such as EVs and FCVs, which are expected to be widely used in the future. And, Honda continues to take on new challenges to realize the carbon-neutral society it aims for.