You Don’t Do It, I’ll Do It Myself! The Development Journey of the Hondamatic Gearbox

Original: Honda誌, Japanese Car Enthusiast Magazine, 2021-07-22 16:43:25

The history of global automotive technology development spans over 100 years. Have you ever noticed that, in simple terms, the history of automotive technology development is essentially a continuous process of automating cars? However, even to this day, full "automation" has yet to be completely realized. Looking back, every era has seen milestones in automotive automation.

The development of the automatic transmission is one such milestone.

The automatic transmission was born in the late 1920s. It was developed as a gear-shifting assist device based on concepts from British engineer Walter Gordon Wilson and German engineer Hermann Föttinger, under the British Daimler Motor Company. It wasn’t until after 1930, when the fluid flywheel (torque converter) was introduced, that it truly became an automatic pre-selective transmission.

This transmission was initially used in British double-decker buses. It wasn't until the late 1950s and early 1960s that this simplified driving operation transmission was applied to passenger cars, becoming a trend in the United States, where the adoption rate of automatic transmission (AT) vehicles reached nearly 80%.

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In the 1960s, the United States was Honda’s second-largest market outside of Japan. Since automatic transmission was gaining popularity in America, Honda naturally did not want to miss out. In fact, not just Honda—other Japanese brands also did not want to fall behind. However, there was a significant difference between the Japanese and American car markets. Firstly, the U.S. car market was relatively mature, and for consumers, cars were no longer out-of-reach luxury items. But in Japan, it was a different story. The Japanese automobile industry was just starting, and many people couldn't afford cars. How could car manufacturers invest in high-cost vehicle production under such circumstances?

Additionally, Japanese cars were primarily small-displacement models, while early automatic transmissions suffered from significant power loss. Given the lower power of cars at that time, it was almost impossible to implement automatic transmissions. As a result, many Japanese car companies had not even considered mass-producing automatic transmissions.

But times were changing. To compete in the market, car manufacturers had to keep up. So, Honda decided to step into automatic transmission development.

Since Honda had no prior technical experience with automatic transmissions, the development process took longer. However, Honda was forced to take this step. Why was it forced? While Honda had no accumulated technology, BorgWarner had a wealth of expertise in this field, with as many as 40,000 to 50,000 automatic transmission patents, creating a significant barrier to entry. Instead of crashing into this barrier head-on, Honda chose to collaborate to gain initial access to the technology.

Honda reached out to BorgWarner, requesting assistance in developing an automatic transmission that could work with a 500cc engine and accommodate a maximum RPM of 8,000. However, BorgWarner outright rejected the request, stating that such a thing was impossible. But for the persistent Honda, giving up was not an option. Thus, the journey of independent research and development began.

At the beginning of the development process, Honda still chose to acquire existing technology. They purchased BorgWarner's BW35 transmission to use as the foundation for initial development. To streamline the process, Honda based its research on the L700, a car set to launch in October of that year. Since the L700 was still in the prototype stage and had test vehicles readily available, it was the ideal platform for transmission development.

The L700 was a rear-wheel-drive (FR) model. Since rear-wheel-drive cars have more space and are more sensitive to power loss, the L700 was an ideal test vehicle. The key challenge in the early development phase was clear—improving the transmission's efficiency and minimizing power loss.

However, the biggest difficulty lay in the torque converter. The torque converter caused significant power loss, and overcoming this issue was crucial to completing Honda's automatic transmission. The torque converter, analogous to a clutch in a manual transmission, transfers power through a pump impeller, turbine wheel, and stator. Honda's solution was to use a bearing to allow the stator to rotate, creating a sufficient torque difference to transmit hydraulic pressure to the hydraulic control valve and activate the clutch. Compared to traditional designs, this newly developed clutch had a simpler structure and was compatible with smaller displacement engines. This efficiency-improving design eventually became the foundation for Honda's patented technology.

After overcoming the torque converter issue, the automatic transmission prototype was complete. However, this was not yet the final product. The transmission was initially tested using the L700, a rear-wheel-drive model, but Honda mainly produced front-wheel-drive (FF) cars. If they didn’t develop a transmission for FF vehicles, their efforts would be in vain. So, after improving efficiency, the next phase was developing an automatic transmission for FF cars.

For FF vehicles, the primary challenge was transmission size. The engine bay had limited space, as it also needed to accommodate engine peripherals, steering components, and suspension systems. Therefore, managing the transmission's dimensions was critical.

Traditional automatic transmissions used a single planetary gearset for shifting, which resulted in a bulky design—too large to fit in a front-wheel-drive vehicle. To reduce size, Honda needed to rethink the gear arrangement.

Honda’s approach was to design a "parallel-axis system." This system not only reduced size but also differed structurally from planetary gear-based automatic transmissions. Instead of planetary gears, it used a setup similar to, yet distinct from, a manual transmission, utilizing multiple hydraulic clutches for shifting. This new transmission type was not only cheaper to produce but also had lower power transmission losses.

This transmission was eventually named Hondamatic, also known as H2, and was used in the first-generation Civic, first-generation Accord, first-generation Prelude, and even Honda motorcycles.