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World-first ASC Transmission Technology for Hybrid Vehicles


Hybrid cars have great fuel economy, but at the cost of sluggish transmission and lack of responsiveness. The Hyundai Motor Group developed the world’s first technology that dramatically improves this shortcoming.

The greatest strength of hybrid electric vehicles (HEV) are that their electric motors provide fuel efficiency far exceeding combustion-engine vehicles. The driving motor largely supports what the engine does, saving a lot of fuel use. That strength is maximized by the entire HEV’s design focused on fuel economy. Aerodynamic design is one such design consideration. 

Conventional hybrid transmission systems had to compromise for transmission and driving pleasure

Hybrid models tend to seek fuel-efficiency over powertrain performance. This is most obvious in the transmission system. Conventional automatic transmissions us a torque converter (transmits engine torque via fluid) to mitigate shift shock. Torque converters help mitigate shock and are relatively fast in transmitting power. 

A torque converter (large component to the left) attached to the front of the auto automatic transmission reduces shift shock, but at the cost of lost power

Torque converters are not without their disadvantages. Torque converters convey power through a fluid inside the converter, so there is energy loss. Furthermore, torque converters are heavy components and disadvantageous to fuel economy. This means that torque converters are counterproductive to fuel-efficiency seeking HEVs.

That is why most HEVs no longer have torque converters now, decreasing power loss and heft. 

However, this is not an ideal solution, because shift shock can damage the transmission. One solution to mitigate shift shock and allow smooth transmission shifting is artificially extended transmission time. This allows sufficient time for the hydraulics to absorb shift shock. It allows for smoother shifting, but the downsides include sluggish or inconsistent transmission. 

This was why stepping on the gas in conventional HEVs felt sluggish, the acceleration kicking in with a delay.

Do you remember the uncanny feeling from first driving an HEV? The sluggish acceleration, feeling like the pedal had not been pushed in far enough, was because of that transmission system. It was a necessary tradeoff for the improved fuel economy, the main advantage of HEVs. That tradeoff is no longer necessary. Hyundai presents Active Shift Control(ASC) a world-first solution for HEV precision transmission.

ASC uses precision transmission technology using the drive motor

ASC overcomes all the shortcomings and necessary compromises in HEVs discussed above. The sluggish and uneven shifting is gone, the transmission occurs much faster in a responsive manner, and with greater durability.

All of this was made possible by utilizing the drive motor present in all HEVs, in an innovative way. Hyundai applied its proprietary transmission logic, using the drive motor. This eliminated the issue of added weight and excessively complex structures, resolving the HEV transmission downfalls. 

Basic understanding of ASC principles requires an understanding HEV powertrain structure

Conventional combustion-engine vehicles have the engine, automatic transmission, and wheels in series, where the power from the engine is transmitted directly to the wheels. The role of the automatic transmission in that case is to control engine power to the wheels depending on travel speed, vehicle weight, and road conditions. It is easy to grasp if you think about automatic transmissions selecting lower gears for starting from a standstill and higher gears for less power-demanding situations such as high-speed constant speed operation. 

In the case of HEVs, a hybrid drive motor is positioned between the engine and the automatic transmission, engaging in power transmission. In other words, the power of the engine and the power of the driving motor generate combined power, transmitted to the wheels through the transmission. As the electric motor the engine’s power, fuel economy is boosted and positively impacts acceleration. 

Overcoming the shortcomings of conventional HEV transmission, using only control logic to improve shift smoothness, performance, durability, and fuel economy

The HCU logic controls the drive motor, and the motor makes 500 precision transmission adjustments per second

The ASC was possible due to a new interpretation of what an electric motor can do in HEVs. Specifically, the proprietary transmission control logic algorithm was applied to the HCU, which controls an HEV’s overall power output. 

The algorithm affects the hybrid drive motor, its internal sensors adjusting up to 500 times per second, the speed of the engine input into the box to the output of the box, rapidly synchronizing the transmission rotation speeds to the engine’s. Simply put, the box synchronizes engine-transmission using the drive motor, and not the hydraulics as was seen in conventional HEVs. 

In the past, transmission speeds were static, as it could not account for real-time road conditions, transmission box oil temperatures, and other variables. For example, with a static value, driving up a steep hill would raise the temperature inside the transmission box, creating bubbles in the automatic transmission fluid (ATF), which can hinder smooth transmission. This results in sluggish transmission and lowered driving performance.

The ASC prevents any of that from happening. In fact, it prevents such events from happening in the first place. The sensor inside the driving motor makes calculated estimations of road conditions, oil temperature change within the transmission box, and provides optimized transmission control. 

Average shift time

Transmissions with ASC are about 30% faster than their non-ASC counterparts

ASC can reduce shifting time by about 30% over conventional systems. Accounting for external conditions for quick responses improves shifting consistency (deviation in shifting time) by up to 50%.

ASC creates consistent shifting times by real-time responsiveness to internal and external conditions

Rapid and consistent transmission improves acceleration performance, fuel economy, while minimizing friction to improve durability. 

ASC is paradigm-changing transmission control technology for HEVs

ASC technology is registered for 20 patents around the world, including 6 in the United States, as well as several more in the EU and in China. Starting from the ASC technology featured in the Sonata Hybrid, it will continue to be implemented in other hybrids, and even in SUVs.

ASC technology is a breakthrough technology that brings precision motor control for hybrid multi-speed shifting. Hyundai continues to research and implement innovative solutions that boost HEV positioning in the global market.