Gearboxes are a key part of any traditional vehicle—they’re responsible for transferring the engine’s energy to the wheels in the most efficient way possible. But with direct drive, EVs have the option of omitting that piece. So what is the difference between Direct Drive and Transmission?
Transmission uses a gearbox to transfer power from the motor to the wheels. EV direct drive connects directly to the wheels. Transmission allows for higher torque at low speeds and higher top speeds. Direct drive requires less maintenance and is more efficient
In this article, I will break down the advantages of each system and how to choose between direct drive and transmission. Each one has its own advantages, but as you’ll see, one is much more efficient than the other.
Direct Drive vs. Transmission
In direct-drive EVs, the electric motor is directly connected to the vehicle’s wheels. This means fewer moving parts, reduced maintenance costs, and a longer life for the engine. It also means there is no need for a transmission.
On the other hand, transmission EVs use an electric motor to turn an input shaft of a transmission. The output shaft of the transmission turns the wheels of the vehicle.
While transmissions offer better control of the vehicle’s torque to the wheels in different driving conditions, they require more complex manufacturing, add extra weight and complexity to the vehicle’s drivetrain, and may cause more maintenance issues over time because of their additional moving parts.
Direct drive systems like Tesla’s have no transmission. Still, most EV makers use a transmission to control gear ratios.
Having a direct drive in an electric car means there is no gearbox between the motor and the wheels. A gearbox transfers power from the engine to the wheels and changes the motor’s rotational speed to suit different driving conditions. It contains several gear ratios that the car can switch between, allowing it to go faster or slower as needed.
On the other hand, a direct drive system does not have a gearbox but rather a single gear ratio, which may not be ideal for all driving conditions. In some cases, an electric motor attached directly to the wheel will produce enough torque, but in others, it will require too much energy from the battery pack.
If you’d like to know if electric cars have Catalytic Converters, check out this helpful and related article that I wrote: Do Electric Cars Have Catalytic Converters. I also discuss Hybrids.
The lack of a gearbox also means that many of the components inside an electric vehicle—such as the batteries, motors, and controllers—must be larger than they would be in a transmission-equipped car. This increases weight and raises costs.
Direct drive systems are more common in large vehicles with relatively low top speeds, such as buses or delivery trucks. Their low maintenance costs and reduced complexity make them more economical than vehicles with a conventional transmission.
Both direct-drive and transmission systems have their own unique advantages. Let’s look at them in more detail.
The Pros and Cons of Direct Drive
- Energy efficient. Direct drive systems are designed to increase energy efficiency and reduce maintenance costs. This type of EV consists of only one moving part—the wheel—, which increases its durability.
- Easier to operate. If you select an EV with direct drive, you won’t have to worry about changing gears or using a clutch while driving. This helps make these vehicles easier to operate—they don’t require any driver input other than accelerating or braking.
- Smooth acceleration. A direct drive system, because it has no gears, allows for smooth acceleration. The reason is that there are no gear shifts that would be otherwise felt by the driver. There’s a reason gear shifts are also known as ‘kickdowns’. Smooth acceleration makes for safer driving and allows for better control over the vehicle.
- Low maintenance costs. As there are no gears in a direct drive system, drivers don’t have to worry about changing their gearbox oil or replacing the clutch plate periodically. This leads to lower maintenance costs over time and less hassle for drivers. It also results in less wear and tear on the car itself.
The downside —if you want to call it that— of a direct drive is that the motor needs to be big enough to provide maximum torque at all times.
This is why most direct-drive cars have been tiny urban runabouts like Smart cars, BMW’s i3 city runabout, and Renault’s Twizy electric quadricycle. But even in one of those, an electric motor has to be relatively large and powerful.
Other problems include:
- Lack of power
- Noise pollution
- Higher costs
Watch this video by Lesics about how an electric direct drive works:
The Pros and Cons of Having Transmission in an Electric Vehicle
- Transmissions can optimize the torque in each gear. In a traditional car, the engine produces less torque at higher speeds and more torque at lower speeds. However, an EV’s torque curve is relatively flat. A transmission helps optimize the amount of torque for each gear ratio, which leads to better acceleration performance.
- A transmission improves the top speed at the expense of acceleration performance. However, in an EV, there’s no need to compromise on acceleration performance. There’s no noise or emissions penalty to be paid for greater motor speeds—and so much higher top speeds.
Transmissions have moving parts, which add weight and cost to the vehicle they’re in. They also have friction, which causes them to lose efficiency. These losses drain power from the engine and slow the car down.
Transmission adds complexity, cost, and weight to the vehicle. This ends up being their biggest con.
Like with internal combustion engines, transmissions need maintenance and can break down. In the best case, this may be annoying and expensive.
If your transmission breaks down, you might have to have your car towed to the repair shop. But if it breaks down while driving, it could potentially cause serious harm to your vehicle’s moving parts.
Transmissions are complex and need maintenance or replacement after a specific time. After all, the more moving parts something has, the more things can go wrong with it.
In electric vehicles, this is particularly problematic because transmissions are connected to the motor through a drive shaft. To fix a problem, you need to remove that drive shaft and open up the transmission casing.
I also wrote a related article about Teslas and Transmissions. I’ve done extensive research and compiled detailed info. Check it out!
|Smooth Acceleration||Lack of Power||Optimized Torque||Complexity|
|Low Maintenance Cost||Noise Pollution||Achieves Higher Speeds Easier||Maintenance Cost|
|No Need To Change Gear||Higher Costs||Can Control Torque Depending on Need||Weight|
|Easy To Drive||Difficulty Operating at Highway Speeds||Easy To Use in City and Highway|
In the end, this discussion comes down to efficiency. And transmission, although complex, is still more efficient than direct drive.
This means less energy is wasted on overcoming rolling resistance and drag while cruising at highway speeds, which improves the driving range of an EV.
Also, by having more gears, an EV can take advantage of different-sized motors for different situations. A small motor will help improve efficiency during city driving when full power isn’t needed, but a larger motor will be better for highway driving.
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