Series hybrid or parallel hybrid: which to choose and why?

Parallel and series hybrid are two different architectures for managing the combustion engine and electric motor in a hybrid car. Specifically, the distinction is made based on the way the energy flow is channeled. Although parallel hybrid is a more common system compared to series hybrid.

---

You have decided to do it take big steps: You want to buy your first hybrid car. But you don’t know how to orient yourself and what to choose based on your needs in terms of driving sensation.

They give you suggestions and you even get to try out some vehicles. But you realize that there is no consolidated culture and you want to create one choose the most conscious maybe: you are in the right place.

In this article dedicated to the types of hybrid cars we have seen what the three main categories of hybrid vehicles are based on electrical components and which one to choose based on usage.

We will study some technical aspects and focus differences between the two design paradigms: series hybrid and parallel hybrid, giving special reference to the differences in driving sensation (in contrast, the determining parameter in the purchase choice).

What is meant by parallel hybrid?

In the idea of ​​parallel hybrid systems exists two energy flows who travel, separately, in parallel. Some comes from the chemical energy of the fuel (colored purple) which is converted by the combustion engine into mechanical energy (colored red) and passes through the car’s gearbox.

The gearbox functions as a torque regulator so that the combustion engine can work smoothly rpm range not too wide before broadcast. The second flow comes from electrical energy (colored blue) which is stored in the accumulator which drives the electric motor connected to the wheels.

Therefore, two different energy flows meet at the wheel which can increase. Being able to add two energy streams means being able to add torque (and thus power) from both systems.

This is the classic scheme of Mild Hybrid (MHEV), but is also adopted in many Full Hybrids (FHEV) and so on. Plug-in Hybrid. In Mild Hybrids, the energy flow from the battery is very minimal and the engine is not powerful enough to pull the vehicle on its own.

However, in a Full Hybrid, the presence of the electric current is much sharper and the power (electrical and thermal) of the current is the same. the same order of magnitude and they can work together or be alternatives to each other (only one of the two streams can work). Same thing for Pug-in Hybrids.

Here the accumulator current is greater due to electrical energy comes from an external power grid to the vehicle and the combustion engine intervenes if you are on the road and the battery is low.

Must Read: Electric Cars, What Are They?

Hybrid series, specific definition

In serious hybrids, there is one flow of energy which is transmitted, after a series of transformations, to the wheel. Unlike a parallel hybrid, the engine does not drive the wheels. But it charges, via a generator, the traction battery that provides the energy to move the wheels.

This scheme cannot be applied to mild hybrid vehicles, which do not have electric motors powerful enough to power the entire vehicle on their own. Therefore a design approach only possible for Full Hybrid and Plug-in vehicles and in fact the technology has already been adopted for locomotives.

Advantages and disadvantages of different solutions

If we compare, we can make several considerations. Possibility added strength in parallel hybrids, this allows electrical flow to be realized over a long power range. From a few kW (in Mild hybrids) to several tens of kW in Full and Plug-in Hybrids.

The vehicle can achieve considerable power that can be maintained for short distances, as long as its traction battery can last thermal strength and ordinary electricity.

In contrast, with the same maximum power at the wheels, the hybrid series Of course it has to be sized to regulate the electrical power of generators and engines which are much larger, because only the electric motor determines the maximum power that can be transmitted to the wheels.

This means higher production costs for the electrical part. For parallel hybrids, this is true software management is more complex of all the electronic equipment that must determine, in intervals of hundredths of a second, how much the electrical line contributes and how much the thermal line contributes.

The hybrid series has the peculiarity of not having a gearbox, and can also do without other transmission components such as half-shafts, axles and differentials. And that means having several advantages:

1. Lighter weight due to the absence of various transmission components.
2. More space available.
3. The combustion engine operates only in its ideal operating range.
4. Less complexity and lower maintenance/repair costs.

In addition, the series hybrid, which has a larger electrical share compared to the power of the parallel hybrid, can manage a higher charging power during regenerative braking. Therefore brake maintenance costs are lower and lower lost energy heat on disc brakes.

The driving sensation of both models

But let’s talk about the driving sensation that is the reason for this post. We will not consider mild hybrid cars. Because of the existence of the electrical part almost invisible driving: it is a normal car as we knew it until a few years ago.

We are concerned here with self-propelled car with an electric motor only. Hybrid car manufacturers, although adopting various construction solutions, have chosen to be able to operate the vehicle according to a series or parallel scheme. This depends on the circumstances and driving conditions.

Therefore there is no clear distinction between the two architectures which are always valid and in all situations. The reason is basically one: hybridization makes no sense on long journeys on the highway.

This is because the combustion engine works well at a constant speed typical of smooth roads. Therefore the electrical part is usually hampered in parallel systems. Or, in a series system, it is bypassed by a connecting clutch immediately heats up the engine and wheels, see HONDA hybrid.

Hybrid parts are used on mixed and urban routes to recover energy in braking process. And it is on mixed and city routes that you can appreciate the difference in the driver’s driving sensation between vehicles of series and parallel architecture.

The differences between the two solutions in brief

Vehicles with parallel architecture will provide a driving sensation close to traditional vehicles, with gaps when changing gears, with sound heat engine consistent with the acceleration phase. And maximum power that makes driving exciting for drivers with a sportier sensibility.

Vehicles with series architecture will provide a driving sensation that is close to pure electric vehicles. You have constant torque liquid methodimmediate and proportional response to accelerator commands. But there is also an inconsistency between the power required from the wheels and the noise of the combustion engine.

The feeling of control over the car is lost. The combustion engine can work when the vehicle is stationary and does this not exactly wisdom. To recharge the battery efficiently, the rotation speed and load absorbed by the generator must be high. These factors make it noisy.

Worth reading: electric and hybrid car battery guarantees

Series hybrid or parallel hybrid: which to choose?

Now let’s choose your new hybrid car. If you are used to it driving traditional vehicles and those of you who care about the sensation of controlling a combustion engine should choose a vehicle with parallel architecture.

However, if you are fully projected into the future and like the idea of ​​electric mobility, perhaps having the possibility of charging from the home network, the hybrid series is your way. Do you agree?