---
title: "CVT and dual clutch transmission"
subject: "Automotive Technology"
chapter: 5
key: "semester_5/automotive_technology:cvt-dct-short-notes"
source: https://www.bctengineer.com/q/semester_5/automotive_technology/cvt-dct-short-notes
site: BCT Engineering
---

# CVT and dual clutch transmission

Automotive Technology · Chapter 5: Transmission Systems

- Asked in: year not given, 4+4 marks
- Video: [Manual vs Dual Clutch - What's The Best Transmission?](https://www.youtube.com/watch?v=oQQ3nfIf6EE) — Engineering Explained
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/automotive_technology/cvt-dct-short-notes
- Whole chapter: https://www.bctengineer.com/md/semester_5/automotive_technology/chapter-5

## Question

Write short notes on (a) the continuously variable transmission (CVT) and (b) the dual clutch transmission (DCT). State one advantage and one limitation of each.

## Short answer

CVT uses variable-diameter pulleys and a steel belt for infinite ratios, giving smooth shifts and better economy, but has limited torque capacity and belt wear. DCT uses two clutches for odd and even gears, pre-selecting the next gear for fast seamless shifts and good efficiency, but can be jerky at low speeds and complex.

## Answer

#### (a) Continuously variable transmission (CVT)

A CVT provides an infinite number of ratios between two limits, without fixed gear steps.

```text
 Engine -> [Primary pulley]==steel belt==[Secondary pulley] -> wheels
            (moves apart/close)           (moves close/apart)
 Low speed: primary small radius, secondary large radius
 High speed: primary large radius, secondary small radius
```

- Two **conical (V) pulleys**, each with one movable half, are connected by a steel push-belt or chain.
- Hydraulic pressure (controlled by the ECU) changes the width of the pulley grooves. When the primary pulley closes, the belt rides at a larger radius on the primary and a smaller radius on the secondary, so the ratio decreases (higher road speed).
- The engine can therefore stay near its most efficient speed.
- **Advantage:** smooth, no shift shock, better economy.
- **Limitation:** belt slip and wear limit the torque capacity; the "rubber-band" feel with engine drone; costly to repair.

#### (b) Dual clutch transmission (DCT)

A DCT has two clutches, one for the odd gears (1, 3, 5) and one for the even gears (2, 4, 6, R), each with its own input shaft (a hollow shaft over a solid shaft).

```text
 Engine -> [Clutch A: odd gears 1,3,5 ]
        -> [Clutch B: even gears 2,4,6 ]
 One gear engaged, next gear pre-selected
```

- While one gear carries the power, the next gear is already selected on the other shaft. At the shift, clutch A opens as clutch B closes, so there is almost no interruption of power (shift time under 100 ms).
- It is actuated electro-hydraulically by the transmission control unit (TCU); wet clutches are used for high torque and dry clutches for light cars.
- **Advantage:** fast shifts and good efficiency, like a manual with automatic convenience.
- **Limitation:** jerky at low speed and clutch overheating in traffic; complex and costly.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How does a CVT obtain variable ratios?
   A. Fixed gear steps
   B. Two conical pulleys with movable halves and a steel belt changing running radius
   C. A planetary gearset
   D. Torque converter only
   Answer: B. Hydraulic pressure changes groove widths, so belt radius on each pulley varies, giving infinite ratios between limits. (Key point: CVT principle)

2. At high vehicle speed the CVT primary pulley radius is?
   A. Small
   B. Large, with the secondary small
   C. Equal to secondary
   D. Zero
   Answer: B. Large primary radius and small secondary radius gives a lower ratio, i.e. higher speed. (Key point: CVT high speed)

3. How does a DCT avoid power interruption?
   A. Two clutches, odd and even gears; the next gear is pre-selected and clutches swap
   B. Only one clutch
   C. Hydraulic coupling
   D. Slipping lock-up
   Answer: A. One clutch opens as the other closes, so shift time is under 100 ms. (Key point: DCT principle)

4. Which is a stated limitation of DCT?
   A. Slow shifts
   B. Low-speed jerk and clutch overheating in traffic
   C. Infinite ratios
   D. Belt slip
   Answer: B. DCT is complex and costly, with low-speed jerk and overheating; belt slip is a CVT limit. (Key point: Limitations)

## Related in Automotive Technology

- [Automatic transmission and torque converter](https://www.bctengineer.com/question.md?key=semester_5%2Fautomotive_technology%3Aautomatic-transmission-torque-converter) — Automotive Technology, chapter 5
- [Carburettor vs injection; TBI, MPFI, GDI](https://www.bctengineer.com/question.md?key=semester_5%2Fautomotive_technology%3Acarburettor-vs-fuel-injection-systems) — Automotive Technology, chapter 2

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