CVT QUESTIONS
After reading the CVT article in the March 2021 issue, I have some questions on three im‐ portant aspects:
1. How does the transmission efficiency (transmission IN to transmission OUT) compare with other types of transmis‐ sions? I understand CVTS are good for optimum engine speed, but transmission effi‐ ciency (low losses) is also im‐ portant. For me, it is difficult to compare due to many factors but I get the impression that acceleration times and fuel consumption of CVTS are not as good as other cars?
2. How reliable (and low maintenance) are CVTS? Manu‐ als are very reliable as are nor‐ mal autos. Our Golf4 AT did nearly 300 000 km in 15+ years without changing the transmis‐ sion oil and I floored the car many times to pass vehicles. DCTS are questionable.
3. How reliable are CVTS in stop/start traffic, including steep incline situations? Nor‐ mal autos capably handle this but DCTS not as well. HERMAN MEYER
Mossel Bay
Transmission efficiency of CVTS is lower than conventional automatic, dual-clutch and manual transmis‐ sions. Continuous development to improve the efficiency of CVTS and ATS makes it difficult to provide pre‐ cise figures but it’s estimated the best ATS are about 3% behind M/TS and the best CVTS a further 3% be‐ hind. CVTS almost match ATS at lower engine speeds but the losses increase with increased engine speed and torque input.
The real efficiency benefit of a CVT is its ability to keep an engine operating within its most efficient range, resulting in typical fuel con‐ sumption improvements in the range of 2% to 5% over both MT and AT.
These figures apply to straightfor‐ ward, normally aspirated engines; variable valve timing/lift, turbochar‐ ging and direct injection all expand the range of engine efficiency and the CVT fuel consumption benefit would be reduced.
Maintenance is not an issue with transmission oil changes typically specified every 30 000 to 40 000 km.
I could find only one recommenda‐ tion for a belt change interval and that was at 160 000 km, less fre‐ quent than a cambelt.
Many CVTS are now fitted with torque convertors which should provide similar durability to conven‐ tional ATS. Others are fitted with electronically controlled wet or dry clutches, similar to DCTS, with dur‐ ability in stop/start traffic, but this is dependent on driving style?