In-wheel motor system is a type of EV (electric vehicle) drive system. Electric Motors are directly connected in the wheel where Conventional EVs feature a design and the gasoline engine is substituted with an electric motor.
What is In-wheel motor?
The basic principle behind a vehicle equipped with In-wheel electric motor is simple. The internal combustion engine normally found under the hood is simply not necessary it is replaced with at least two motors located in the hub of the wheels of the vehicle these wheels contain not only the breaking components but also all of the functionality that was formerly performed by the engine, transmission, clutch, suspension and other related parts.
Although the concept is relatively simple in theory and will motors pose a number of questions about performance function and efficiency.
In recent years we have seen some vehicles developers moving towards powertrain configuration where the motor is mounted inside the wheel that is an In-wheel motor system. We must admit there is an impressive amount of new space available when the electric motors are integrated into the wheels and sure these so-called hub motors or In-wheel motors come with certain benefits but they also create some challenges.
In-wheel motor are not new, at the beginning of the 20th century ferdinand porsche’s first hybrid vehicle used hub-mounted electric motors in each wheel. These motors power the wheel directly to the wheel there’s no need for a gearbox or drive shaft. When using a reduction gearbox the speed is reduced and the torque is multiplied. But with an In-wheel motor there is no reduction. In this system wheel speed is equal to motor speed so the required torque and power need to be delivered in a direct drive mode.
In-wheel motors are directly exposed to dust, salt water and other fluids of road and also to vibrations and shocks which shortens their life expectancy. That is one of the main reasons ford eventually decided to ditch the In-wheel motor concepts that they were working on for the new electric f-150 in 2008.
The four In-wheel motors also known as Quad-Motor Drive. These four motors deliver instant power and independently adjust torque at each wheel for precise control in all the conditions and controlling power at the individual level of motors will enables torque vectoring.
What is Torque Vectoring?
Basically torque vectoring is a technology that distributes an engine’s power across the left side and right side of the vehicle. With torque vectoring one side of the wheel on the axle can go faster or slower than other.
Torque vectoring aims to improve steering response and handling through the distribution of the torque between the wheels in vehicle.
How In-Wheel Motor EV is different than other cars?
For traditional IC engine vehicle the drivetrain system consists of conventional mechanical system such as engine, transmission, exhaust, drive shaft, differential.
In a conventional EV the engine is replaced by an electric motor with inverter and a set of batteries installed at the back or at the base of the vehicle.
In the case of EVs that use In-wheel motors all the mechanical subsystems of the powertrain are eliminated and replaced with direct drive and will motors that do not need any driveshaft as they are connected directly to wheels.
Producing a vehicle that uses In-wheel electric motors is a process that is a lot more complex than just tearing out the engine and then cramming electric motors into the unused space inside the wheel. This type of electric motor is designed to work on hybrid vehicles to improve the efficiency of the full battery operated vehicles and even fuel cell powered electric vehicles.
The amount of power generated by these In-wheel motors can vary depending on the manufacturer and the size of the motor to use. The electric motor is installed inside the wheel and provides power to the wheels directly without the need of any transmission.
The idea of installing the motor inside the wheel rim in an EV is a right choice in this way it can be ensured that the full output of power of the motor is available at the wheel without any mechanical transmission losses.
Do these In-wheel electric motors provide enough torque for every application?
Torque plays an important role in any automobile’s response time and its performance. In a vehicle equipped with In-wheel electric motors there is plenty of torque available almost instantly as a matter of fact.
Electric Motors produce a high amount of torque and since that force is transmitted directly to the wheel each wheel can be equipped with the sensors to determine how much torque is required at any given time.
Efficiency of In-wheel motor
In-wheel motor will always suffer move from no load losses and part load losses. because the motors can’t be de-coupled from the wheels. Some companies claim that the efficiency with In-wheel motors is higher because there is no gearbox, although a gearbox does always introduce a bit of inefficiency the one or two speed gearboxes that are typically used for EVs are much more efficient than the complex multi-stage transmissions seen in combustion engine powertrain.
This loss in the efficiency of vehicle is overcompensated by the fact that due to the gearbox. The electric motor can run on its most efficient operating area resulting in an increase in vehicle range when compared to a direct drive system depending on the use case and driving cycle.
Regenerative Breaking Power
Some of the In-wheel motor design offers regenerative breaking as well, that means the system captures some of its own kinetic energy while breaking and sends it back to charge the battery.
Some hybrids such as the toyota prius and tesla roadster already incorporate this regenerative breaking technology which provide the automobiles with a longer driving range. One of the greatest advantages of the In-wheel motors is the fact that the power goes straight from the motor directly to the wheel reducing the distance the power travels increases the efficiency of the motor. For Example- In city driving conditions an internal combustion engine may only run at 20% efficiency meaning that most of its energy is lost or wasted via the mechanical methods employed to get the power to the wheels, but in In-wheel motor in the same environment is said to operate at about 90% efficiency.
Is this the future of Electric Vehicles?
Porsche engineering has developed a torque control system for a four motor electric vehicle drivetrain that lets electric SUVs handle with the ability of a sports car in even the most difficult conditions. Because of the much faster responsiveness of an electric motor as compared to an IC engine EV traction control system can respond much more quickly.
In an electric vehicle the torque is purely electronically controlled which works considerable faster than mechanical clutches. Every millisecond intelligent software distributes the forces in such a way that the vehicle always behaves neutrally but porsche’s solution is not just all-wheel drive it utilizes for separate motors one controlling each wheel in the vehicle.
There are advantages and disadvantages to multiple motors, more motors increase cost and complexity but eliminates the need for a drive-shaft and gives more control. Motors can also increase unsprung weight which can have some negative effects on handling and ride quality.
For Example- It becomes possible to rotate the wheels 90 degrees and drive to the left or the right or even rotate in place instead of just driving forward or backward. This adds another dimension to how the car can move around and makes it easy to navigate tight spaces.
The new rivian r1t features one engine for each wheel this quad motor drivetrain enables the rivian truck to handle like a sports sedan on-road and 4 by 4 off-road with ease this reportedly makes the r1t the fastest truck in the world.
Advantages of In-wheel motor
In-wheel motors are easy to install and replace they add flexibility as they can be used to power rear or front-wheel drive as well as all-wheel drive vehicles without much change in drive-chain they are compact in size as the entire motor is inside the wheel In-wheel motors provides high efficiency due to the lack of mechanical losses from transmission differential and drive shafts and makes the car to run quieter with electronic motor control. This means features such ABS, traction control and even cruise control could be handled more efficiently.
Disadvantages of In-wheel motors
The major challenge in In-wheel motors face is the issue of unsprung weight, unsprung weight is the mass of all components including the frame, motor, passengers and body that are not supported by a vehicle’s suspension. Unsprung weight includes wheels, breaks and it travels up and down over any bumps and potholes and it tries to follow the contours of the road and with hub motors being part of the vehicle’s unsprung weight they will the impact of every pothole bump and high speed turn.
Also they will be exposed to road dirt, mud, dust water and road salt that can be reduce the life of the motors. In-wheel motors are expensive than a single motor mount on rear axle.