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Discussion Starter · #1 · (Edited)
Smartstream IVT

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In internal combustion engine vehicles (ICEVs), the transmission serves an important role of situationally adjusting the engine RPM to allow controlled application of power. Appropriate shifting of gears can let the engine to continuously function at the desired range of high-efficiency, improving both performance and fuel economy. Recently, auto consumers have developed divergent preferences for vehicles with distinct acceleration performance and shifting ‘feel,’ and a variety of transmissions have emerged in the market to meet their needs. Hyundai Motor Group’s continuously variable transmission Smartstream IVT is one such entrant to the market.

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Continuously variable transmissions (CVTs) have the structure in which two pulleys connected to the engine output shaft and the driveshaft are linked via a belt. The belt contracts and expands to alter the diameter of the pulleys, thus varying the gear ratio. Because they can continuously vary the gear speed, even from the lowest gear to the highest gear, CVTs is capable of setting the optimal engine RPM for maximal power output and efficiency.

In fact, thanks to this structure (as distinguished from standard 8-speed ATs), CVTs can theoretically set the optimum gear ratio down to the decimal point within the available range. As a result, they boast a 20 to 30% improvement in fuel economy over regular transmissions, not to mention allowing for a smooth ride without clunking from the shifting. This smoothness, though, is often misinterpreted by some drivers as “low in power,” and some even go further to state that it lacks of “driving fun that comes from shifting.” What’s more, there were some mechanical difficulties in the early versions as well: the belt could not withstand the engine’s power output for too long, causing durability issues. In other instances, the pulleys and the belt often slipped against each other, causing unwanted noise and worsened fuel economy.

Hyundai Motor Group’s Smartstream IVT is the next generation of CVT that has maximized its advantages and addressed the durability and ‘feel’ issues that plagued the original. It approximates the shifting feel of regular ATs by creating virtual shifting patterns that respond to the driver’s intent. In essence, the IVT is the CVT with virtual gear speeds—and it is an answer to those who found the CVT uninteresting to drive.

Moreover, the IVT uses not the typical metallic belt but a chain belt, the first of its kind on a similar transmission, that can better and longer withstand the power output from the engine. The chain belt, in addition, uses the belt’s tension to adjust the diameter of the pulley, a mechanism that eliminates the slippage that had been the cause of the noise and the fuel economy loss.

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As an engineer, I applaud the genius design of the CVT. Definitely a new generation of technology with tremendous potential. But as a driver, I hate them. They suck all the fun out of driving. Give me a manual four-speed any day.
 

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As an engineer, I applaud the genius design of the CVT. Definitely a new generation of technology with tremendous potential. But as a driver, I hate them. They suck all the fun out of driving. Give me a manual four-speed any day.
I think, as long as there is a torque converter between the engine and transmission the fun factor and direct connected feel cannot be duplicated compared to a clutch. The Hyundai chain design is a step up though. It narrows to go deeper into the pulley and widens to climb higher up the pulley giving a wider gear ratio, when compared to the segmented V belt used in other CVT designs.
 

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Good programming matters with these transmissions. Normal mode down shift ratio changes are too sluggish, particularly when graded roads are driven. It forces the driver to search for a lower gear with the throttle to increase rpm. The result in some cases is an over correction in rpm. Put simply, it is wonky in its ratio changes on graded road conditions.
Sport mode by contrast is excellent at lower speeds with its throttle pattern, but only gives you 5 ratio changes and cannot be used at high speeds because of fuel economy.
The best of both worlds is what is needed imo. That would be a sport mode programming that will have all 8 ratio changes available.
The mechanics of these transmissions are amazing, but the ivt is at the mercy of the programming and more work is needed. No way is my venue maximizing fuel consumption when it is either bogged down at 1700 rpm trying to go up an incline, or over correcting at 3500 rpm.
Just my .02 ✌🏼
 
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