Performance Comparison of Different Transmission Types

I. Functional Positioning and Core Role of the Transmission

As a core component of the automotive powertrain, the transmission's core function is to dynamically match engine power with driving conditions. From a power transmission perspective, the transmission connects the engine crankshaft via an input shaft at one end and the drive axle via an output shaft at the other. By varying the gear ratio, the transmission converts engine speed and torque into the power parameters required by the vehicle.

Technically, the engine's effective operating range is limited by its speed range (typically 1000-6000 rpm), while vehicle speeds must cover a range of 0-120 km/h and above. Torque requirements vary significantly during starting, acceleration, and hill climbing. The transmission achieves a balance between power and fuel efficiency by meshing multiple gears. A high gear ratio is used during starting to maximize torque (ensure starting power), while a low gear ratio is used during high-speed cruising to reduce engine speed (improve fuel efficiency).

II. Transmission Technology Classification and Performance Characteristics

Based on their structural form and shift control method, current automotive transmissions are primarily categorized into three main types: manual transmission (MT), automatic transmission (AT), and continuously variable transmission (CVT). These transmissions exhibit significant differences in their technical characteristics and applicable scenarios.

(I) Manual Transmission (MT): The Basic Form of Mechanical Transmission

Manual transmissions utilize a fixed-axis gear transmission structure. The driver operates the clutch pedal to cut power, and then uses the shift lever to adjust the gear meshing pair to achieve gear ratio adjustment. Their core advantages lie in their high mechanical efficiency (transmission efficiency can reach over 95%), simple structure (primarily consisting of a gear train, clutch, and shift mechanism), high reliability (no risk of electronic control unit failure), and low maintenance costs (regular maintenance intervals can reach 60,000-80,000 kilometers).

From an application perspective, manual transmissions are suitable for applications requiring high control precision (such as racing and off-road vehicles). However, due to the limitations of manual shifting, they can easily lead to driver fatigue in congested urban areas and require high driving skills. Currently, their penetration rate in the passenger car market has dropped below 5%, primarily concentrated in low-end models and commercial vehicles.

(II) Automatic Transmission (AT): The Mainstream Passenger Car Transmission Solution

Automatic transmissions, based on automatic shift control technology, eliminate the need for the driver to manually operate the clutch. They automatically shift gears based on parameters such as vehicle speed and throttle opening. They are primarily categorized into torque converter ATs and dual-clutch ATs (DCTs).

Torque converter ATs utilize a hydraulic transmission mechanism (torque converter) instead of a mechanical clutch, transmitting power through hydraulic fluid for uninterrupted power transmission. Their core advantages include smooth starting (shock ≤ 5 m/s³) and strong shock resistance (ability to withstand transient torque fluctuations). They are suitable for vehicles with high comfort requirements, such as family passenger cars and mid- to high-end sedans. However, due to the limitations of hydraulic transmission, transmission efficiency is relatively low (approximately 85-90%), and fuel economy is slightly inferior to other transmission types.

Dual-clutch automatic transmission (DCT): Utilizing two parallel-shaft clutches, one controls odd-numbered gears (1st, 3rd, 5th, and 7th) and the other even-numbered gears (2nd, 4th, and 6th). Shift timing is synchronized via an electronic control unit, reducing shift intervals to less than 0.2 seconds. Its core advantages lie in its high transmission efficiency (approximately comparable to manual transmissions, reaching 92-94%) and fast shift response, making it suitable for sports sedans and new energy vehicles (especially plug-in hybrids).

However, at low speeds (below 20 km/h), shift jerks are prone to occur due to the lack of clutch semi-clutch control precision. Furthermore, DCT places high demands on the cooling system (requiring an independent cooling circuit), resulting in higher maintenance costs than torque converter automatic transmissions.

(III) Continuously Variable Transmission (CVT): A Highly Efficient and Energy-Saving Transmission Technology

The CVT utilizes a belt/chain transmission structure. The drive radius is altered by movable cones on the driving and driven pulleys, achieving a continuously variable transmission ratio (typically ranging from 2.5 to 7.0). Its technical advantage lies in its continuously adjustable transmission ratio, which allows the engine to consistently operate within the optimal fuel economy range (effectively reducing fuel consumption by 5-10%), without shift shock, and providing excellent ride smoothness.

In terms of application limitations, the torque carrying capacity of a CVT is limited by the strength of the belt/chain (current mainstream products have a maximum torque capacity of approximately 350 N·m), making it unsuitable for high-performance vehicles. Furthermore, prolonged high-load operation (such as continuous hill climbing and rapid acceleration) can easily lead to belt wear, necessitating regular transmission oil changes (maintenance intervals of approximately 40,000-60,000 kilometers). Its service life is slightly shorter than that of an automatic transmission, primarily suitable for family passenger cars with a displacement of 1.0-2.0L.

III. Transmission Technology Innovation in the New Energy Vehicle Era

With the transition to electrification, transmission technology is trending toward simplification and integration, primarily within pure electric and hybrid vehicle technologies.

(I) Pure Electric Vehicles: Single-Speed ​​Transmissions Are the Mainstream

Pure electric vehicles (PEVs) have a wide speed range (typically 0-15,000 rpm), covering all operating conditions from starting to high speeds. Therefore, single-speed transmissions (with a fixed gear ratio, typically 8-12) are commonly used. Their advantages include a simple structure (consisting solely of an input shaft, an output shaft, and a set of fixed gears), high transmission efficiency (reaching over 96%), strong reliability, and a smooth ride without shifting. Currently, mainstream PEVs such as the Tesla Model 3 and BYD Dolphin all utilize single-speed transmissions.

(II) Hybrid Vehicles: Multi-Gear DHT Transmissions Becoming a Trend

Hybrid vehicles (including plug-in hybrid electric vehicles (PHEVs) and gasoline-electric hybrid electric vehicles (HEVs)) require coordinated power output from the engine and electric motor, and therefore often utilize a multi-gear DHT (Dedicated Hybrid Transmission) transmission. For example, the BYD DM-i Super Hybrid and the Great Wall DHT utilize a two- to three-gear design. Low-speed driving (≤40 km/h) is driven solely by the electric motor, while medium- and high-speed driving (≥60 km/h) involves the transmission shifting to a higher gear, enabling direct engine drive. This effectively reduces motor speed at high speeds and improves fuel economy (fuel consumption can be reduced to less than 4L/100km).

In addition, intelligent shift control technology has become a key development focus. By integrating road condition information (such as slope and curvature), driving habits (such as the rate of change in throttle opening), and battery status (such as the SOC value), it optimizes adaptive shift strategies, further improving power response and fuel economy.