Toyota Power Split device

In discussing Prius Transmission, we mentioned Toyota Power Split Device but never explained it in any detail. So I did more research and here is what I learned about the Toyota Power Split Device.

What is a Power split device?

Toyota Prius is a hybrid electric vehicle model developed by Toyota in the year 1997. It is one of the pioneer models in Hybrid technology and has evolved to the needs of the modern consumer requirements. The hybrid vehicles have become the need of the hour with conventional petrol and diesel cars causing environmental pollution issues. The hybrid vehicles will combine the power for Internal combustion engines and electric motors and can work on power from both sources separately too. Toyota Prius is one of the top hybrid models that caught the attention of people and is expected to be a big market player in hybrid vehicles segment.

Toyota Prius is rated as one of the cleanest cars by the United States Environmental Protection Agency (EPA) due to their lesser smog emissions. In this article, we are going to know in depth about how power transmission takes place in hybrid vehicles and how the power from different sources are effectively managed and transmitted across the wheels.

The Power split device is one of the integral parts of the hybrid vehicles and in fact, they are termed as the heart of the Hybrid car models. The power split device is specially designed gearbox that integrates the power from the Internal Combustion engines (IC Engines) and the electric motor drive together.

The power split device can operate the vehicle with electric motor power and the IC Engine separately or can also combine the power from both sources. It also acts as a Continuously Variable Transmission (CVT) and eliminates the need for any manual or automatic transmission. The power split device is also called as PSD or power-splitter. It provides an extremely smooth operation and provides rapid response.

Here is a video explanation about Toyota Power split device

https://www.youtube.com/watch?v=3xeyqGcfb8M

Know Your Toyota Mechanical: Power Split Device (https://www.youtube.com/watch?v=3xeyqGcfb8M)

Power Split device – Construction

The power split device is a planetary gear set design.

The planetary gearbox set is made of three different sets of gear types named sun gears, planet gears, and a ring gear.

Let us look at the different gear connections in the transmission system of the hybrid cars.

Ring gear – connects the main electric motor to the driving wheels through the output axle.

Planetary Gears – A gear carrier consists of four planetary gears and these gears are connected to the IC Engine and the ring gears.

Sun Gear – The sun gear connects the generator with the planetary gears. It is used to start the vehicle without the need for the starter motor.

In a planetary gear set design, the input and the output shafts are aligned in a straight line.

The power split device has an IC Engine and two electric motors in the assembly. The Primary Electric motor (MG2) which is a power source is connected across the ring gear. The other electric motor (MG1) is connected across the IC engine and the planetary gear carrier. This electric motor acts as the generator and helps start the vehicle without a starter motor.

Power Split device – Functions

Now, let us look at the different functions of the power split device in our vehicles and how they are useful to the operation of our vehicles.

The Power split devices help to operate our vehicle in both parallel hybrid and series hybrid transmissions.

Parallel hybrid – The power is transferred to the wheels from either the electric motor or the IC engine or a combination of both the electric motor and the IC engine.

Series hybrid – In this case, the wheels are powered by the Electric motor through the power split device and the IC engine runs separately and charges the battery.

During high acceleration phases, the power split device makes the IC engine to take control of power transmission to the wheels due to additional power requirement. This can happen while we overtake other vehicles while driving on a highway.
We don`t need a separate automatic or manual power transmission system in our vehicles. The power split device takes control and acts as a Continuously Variable Transmission system (CVT) but with a fixed gear ratio.
It also eliminates the need for a starter motor to power starts the vehicles. The power split device allows the generator to start the vehicle that is connected across its planetary gear system.

Power Split device – Operation

We have now looked at the construction, different gears set up in the power split device and their functions to help in our vehicle`s operation. Let`s look at how the PSD operates during different phases of the vehicle and how the power transmission takes place.

Starting the car – First, let us consider starting the car from a stationary state where our engine is in an idle state. The electric motor connected to the sun gear and first powers the generator. The generator then starts the engine and is allowed to charge the batteries when the vehicle is stationary. The ring gear does not move and it is the gear that transmits power to the vehicle. Now our car has started but is yet to move and is in a stationary state.

Moving the car – Now while moving our car the power from the electric motor is used to move our car in lower speeds in the range of 40-60 kmph. The sun gear is connected across the planetary gears and which in turn rotates the ring gear. The ring gear is connected across the wheel axle and the motion of ring gear moves our vehicle forward. The planetary gear carrier will not rotate as the IC engine is disconnected from the power transmission to the wheels.

Accelerating the car – Let’s consider, we are accelerating the car over 60 kmph speed and our transmission system needs more power to be produced. The generator starts to run a higher speed and in turn turns on the IC engine. The electric motor power will be cut off now and the IC engine powers our vehicle. The planetary gear carrier rotates the ring gear and the planetary gears will stop rotating. When the car is IC engine powered the entire power comes from the generator. The generator varies the speed of the gears as per the output speed with the electric motor.

Power Split device – Advantages

Advantages of using the power split device in our vehicles are as follows:

Low emissions
Fuel efficiency
Driving comfort

Low emissions

Hybrid vehicles aim to be environmental friendly with lower emissions of pollutants and smog from the vehicles. In fact, they produce 70% lower emissions than normal vehicles and make our vehicles environment cleanly vehicles.

Fuel Efficiency

Hybrid vehicles combine the power from the IC engine and batteries seamlessly and help in the fuel efficiency to a greater extent. They save the power from the engine while braking, stalling at signal lights, and stopping of vehicles in the batteries.

Driving Comfort

These cars produce good driving experience by interchanging the power to torque ratio based upon the requirements. Hybrid cars are energetic and fun to ride without compromising on fuel efficiency. These vehicles operate with a quiet IC engine and are very smooth to ride. They automatically allot power in the most efficient way and give us the best possible comfort in our ride.

Power Split device – Hybrid vehicles

Listed below are different hybrid vehicles that use the power split device transmission system:

Frequently Asked Questions and answers

Do we need to charge the batteries externally? No, the batteries will be charged by the power split device. It uses the power from the IC engine, to charge the battery. It also uses power from regenerative braking, vehicle stalling conditions, etc to power up the batteries in the vehicle.
Does Toyota provide warranty for the power split device? Yes, Toyota provides a standard 10-year/100,000-mile warranty. But the warranty period may vary across different dealers and locations as per the Toyota guidelines.
What kind of batteries do they use? Toyota Prius uses NiMH type (Nickel Metal Hydride battery) or Li-Ion type (Lithium-Ion) batteries.

https://www.youtube.com/watch?v=ZmHpSyTsfm0

2004 – 2009 Prius P112 Hybrid Transaxle (eCVT) Operation (https://www.youtube.com/watch?v=ZmHpSyTsfm0)

For details about Toyota Hybrid synergy drive, start here