The difference between the propulsion mechanisms of electric vehicles (EVs) and gasoline cars is best demonstrated by two things: their fuels and transmissions. Since the gas vs battery discussion – including the myths – is well documented at this point, let’s focus on transmissions.
When driving an EV for the first time, one of the first things you’ll most likely notice is the smooth acceleration. Step on the “gas” pedal, and the electric car gains speed without stepping in and out of different gears. That is because most EVs run on a single-speed transmission, negating the need to switch between gears. The level of power does not vary by transmission type, but the way that it is delivered is unique.
The gear ratios in a traditional transmission exist as a torque multiplier. This is just like the gears on a bicycle. Because an EV has so much torque, a single gear ratio can be used – or single speed – that covers everything from accelerating from a standstill to reaching a predetermined top speed.
But first, what the heck is power transmission and why does it matter anyway?
The Essentials of Power Transmission
People often mistake transmission as the vehicle part that allows for shifting gears, as in manual transmission vs automatic transmission. It’s not far from the truth, though, just that it’s a little more complicated.
Simply put, power transmission refers to the way a vehicle distributes power from the fuel source throughout the different parts of the car. Every car transmits kinetic energy – through an internal combustion engine (ICE) in the case of gasoline cars or electric motors in the case of EVs. The energy powers the differentials, which are the parts rotating the wheels or gears, and parts controlling speed, and electrical components.
Internal combustion engines require gears because they generate energy with different levels of efficiency at different RPMs. To understand what that implies, first, you need to grasp the concepts of RPM and torque.
Revolutions per minute, or RPM, refers to the speed that motors are spinning at, while torque refers to the rate at which a motor’s speed is transferred to the wheels.
The trick for any vehicle is transferring the right energy in the right way to match different speeds and terrains. ICE cars use gear ratios to accomplish that efficiently.
Manufacturers carefully calculate gear ratios based on the engine's power output to find the right balance between acceleration, top speed, and fuel consumption.
What people call transmission is the gear alternation unit. With manual transmission, you need to press on the clutch to release a gear so you can switch to another one, while automatic transmission disengages gears automatically.
How Does EV Power Transmission Work?
In the case of electric cars, the electric motor is used as the power source, which eliminates most of the need for multi-speed transmission. That means most electric cars have one gear and one gear ratio. There isn’t any switch. Think of it like having an ICE car that can take off at lights and get to 85 miles per hour on the freeway all in 3rd gear.
Unless an EV has a motor at each hub, then typically the energy passes from the motor, through the gearbox (which is very basic because it's a single gear) and then through to the differential which splits the power to the two wheels that it is driving.
Keep in mind: vehicles typically have an open differential, which allows it to send 100% of the power to just one wheel. This is how things like electronic stability control work so if a vehicle detects slipping on one wheel, it can then determine how much power to send to the other wheel.
EVs are far more energy-efficient than their gasoline counterparts. On average, electric vehicles transfer 70% to 98% of the power from batteries to the wheels, whereas gasoline engines convert only about 12% to 30% of their fuel. The rest escapes as heat. Acceleration occurs smoothly and quietly in EVs because there’s no friction from the transmission unit. Plus, fewer moving parts means less wear and tear and less maintenance needs.
But, Do EVs Have Gears Or Not?
The short answer is yes. EVs with a single speed transmission still require a gear to transmit energy from the motor to the wheels.
Some manufacturers offer EV models with multiple gears. Multiple gears are a great way to maximize acceleration and top speed, as they are the two competing elements. A gear ratio that gives very fast acceleration will lower the top speed and vice versa.
Here are some examples:
- The 2008 Tesla Roadster offered a two-speed transmission, though it was changed to a one-speed transmission in subsequent releases.
- One modern EV with multi-speed transmission is the latest Porsche Taycan. It uses a two-speed transmission on the rear wheels, with the front wheels still using a single-speed transmission. This multi-transmission combination allows for robust take-off and mid-speed transmissions.
- Audi e-tron also has multi-speed transmission geared towards increased torque.
- The forthcoming Jeep Magneto promises manual transmission, like to accommodate it’s off-road lifestyle.
- EV trucks, especially heavy-duty models, are expected to have multi-speed transmission. Trucks and cars used for towing other vehicles require much more torque than speed, hence gears are needed for more efficient power transmission. Tesla’s upcoming Semi will have double-speed transmission.
Other Alternative EV Transmissions
Continuous variable transmission is a version of automatic transmission used in some ICE and hybrid engines. It uses pulleys rather than gears to enable a smoother speed transition because pulleys allow for more torque. Essentially, CVT strikes a better balance between speed and torque. As such, it allows for greater energy efficiency, and that in turn improves mileage, which is a key consideration for buyers. And given their torque advantage, CVT systems are now being considered for heavier EVs.
Multiple motors are also used in some EVs to increase torque. Rather than using multiple gears, multiple motors are combined with different gear ratios to better regulate torque, with electronic components modulating the charges of each motor. And unlike gears in a gasoline engine, the multiple motors in an EV can be engaged both simultaneously and separately, allowing for even more reliable speed and torque.
Lucid Air models feature either dual or tri-motor transmissions. Many Tesla models also feature multiple motors. The Rivian electric pickup truck has a motor dedicated to each wheel, enabling the truck to perform “tank turns”.
The power transmission modules of EVs are wildly different from those of gasoline cars. EVs do away with many of the limitations of ICE, allowing for a smoother ride. EVs can provide the same amount of torque consistently throughout a journey, compared to the fits and bursts of ICE. With fewer moving parts and more efficient energy transmission, acceleration and deceleration is much easier and smoother.
EVs generate maximum power instantly on ignition and transmit rotational energy directly to the wheels. And because energy isn’t transferred through a complex transmission unit, energy transmission is far much more efficient in EVs.
As such, EVs can do away with the expenses and extra weight of a multi-speed transmission system, minimizing the production cost as well as the cost of maintenance for the car owners. EVs still have gears of sorts, but nowhere near as complex as those of ICE.