What do I have to expect if I choose a hybrid car? (Parallel/series)

Fiat Multipla Ibrida

The last post about cars with hybrid engine will focus on one of my projects, but never place on the market, when I worked at the Fiat planning department.

The only vehicle with a parallel/series hybrid propulsion, produced and tested on the road, was the Fiat Multipla Hybrid.

Produced in ten copies, and destined for the City of Naples in the context of the Atena Project (The Telematic Traffic Environment of Naples), it gave us the possibility of a field test about the functionality and environmental impact of our project.

A parallel/series hybrid car, as you can easily guess, uses the typical technologies of both parallel hybrid and series hybrid power supplies.

The electric components, for the hybrid transformation of the car, are basically the same as in the hybrid parallel vehicles with the addition of the generator with the connection to the thermal engine and some peculiarities depending on the solution.

In more detail, compared to a Multipla with only a thermal engine, there are in addition:

  • Electric motor (three-phase asynchronous) with alternating electricity that has a maximum power of 30 kW (15 kW on-going) and a maximum torque of 130 Nm (13.02 kgm);
  • The inverter, a converter that converts the direct power of the batteries into three-phase alternating electricity;
  • The same batteries, 15 innovative nickel-metal hydrides elements that together provide energy of 19 kWh;
  • The DC-DC converter, which transforms the direct power of the traction batteries from 220 V to 12 V;
  • The on-board charger to recharge the batteries;
  • The robotized transmission of the Selespeed brand, which manages the selection and engagement of the gears in a totally automatic way, with great advantages in the consumption reduction and the improvement of comfort.

I’ll describe below, with schematic pictures, the three ways of functioning of the Hybrid Multipla.

Fiat Multipla Ibrida_schema

OPERATION IN ELECTRIC ONLY

The Multipla Hybrid can also travel with the electric motor thrust only, operating like a ZEV (Zero Emission Vehicle); with a top speed of 80 km/h and an autonomy of over 80 km.

The electric motor transmits torque and power to the wheels through a connection with gear wheels according to a certain ratio to the gearbox primary.
[Note: The gearbox primary is the gear axis that is driven by the heat engine.
There is even the secondary, linked through gears to the primary one, which connects, through the insertion of a synchronizer, the engine to the wheels according to its relationship.]

A mechanical system keeps the clutch of the heat engine gear open.

Normally the car starts in second gear because it exceeds the starting specifications but it is also possible to insert the first gear in case of particular conditions; for example with gradients over 25% or if you need to transport excessive weights.

Fiat Multipla Ibrida_schema funzionamento solo elettrico

(Click on the picture to see the details)

An automatic system warns the driver when the state of charge of the traction batteries drops below 40%, and automatically starts the generation as soon as it falls below 20% of autonomy.

PARALLEL HYBRID OPERATION

When the car travels long distances at a constant and sustained speed, such as suburban roads and motorway, the propulsion is ensured by the joint work of the thermal engine and the electric one, similar to the parallel hybrid that we have already seen in detail.

The performances (but with much lower emissions) are similar to those of a traditional car.

Indeed we have been able to test a top speed of over 155 km / h, with an autonomy of 600 km.

More in detail, on this Hybrid Multipla, the car starts with the electric engine, with the clutch of the heat engine gearbox not connected to the traction; at 20km / h it turns on the thermic and at about 30 km / h it connects the thermal to the traction.

From this moment on, the electric engine provides torque in acceleration, recovering energy in slowing down and braking.

In the slowdown phase, as soon as it goes down to 10km/h, the thermal engine goes off and the electric motor takes over.
Fiat Multipla Ibrida_schema funzionamento ibido parallelo

(Click on the picture to see the details)

The gear changes, both increasing and climbing, are made by the fixed speed robotic system and the electromagnetic clutch of the electric one acts in the same way as the thermal in the gear change.

HYBRID SERIES OPERATION

In this mode, the Hybrid Multiple is moved by the electric motor, while the thermal engine, also in operation, runs at a stationary speed to operate the generator that provides energy both for the traction and for recharging the batteries.

The thermal engine works, in this case, at “fixed point“; that is to say, at constant load and speed.
T?£Normally 3 to 5 or more generation points are used, which are chosen according to the values of some parameters, such as the vehicle speed, the state of charge of the traction batteries, etc.

Our Multipla Hybrid used the hybrid series mode when it was necessary to increase the autonomy of the vehicle in electric ONLY mode and we didn’t have the opportunity, immediately, to connect to the electricity network.

The performances were similar to the ones obtained with the electric mode.

In the hybrid series mode the clutch of the thermal engine is opened and, based on the state of charge of the traction batteries, the system decides whether to start the generation.

Fiat Multipla Ibrida_schema funzionamento ibido serie
(Click on the picture to see the details)

The production starts when the residual energy is below 60% – to not damage the batteries.

At the starting of the thermal, the clutch, placed between the thermal and the generator, is closed, the generator ends its delivery and the thermal reaches the defined number of turns for maximum efficiency of the generator.

At this point the generation begins, which is sent to both the traction motor and the batteries. In the case of a slowdown, with energy recovery, the generation is instantly interrupted and resumes as soon as it accelerates.

If the batteries charge reaches 80%, the thermal engine stops and then resumes as soon as it falls below 60%; the autonomy almost reached 1000 km.

 hybrid

PROBLEMS OF THIS SOLUTION

Considering the components are much greater in number than the hybrid series or the parallel hybrid, it is very difficult to find the spaces in a car of any segment and to be able to pass all the tests of safety, reliability, handling, etc. without occupying spaces for people or luggage.

I was abele to overcome these problems, on the Multipla, thanks to the high platform and the engine compartment quite high.

Fiat Multipla Ibrida_emissioni

(Click on the picture to see the details)

ADVANTAGES

  1. It is the best solution in terms of consumption, emissions and autonomy.
  2. It is suitable for cars with 8 seats, or small commercial vehicles.
  3. It groups the advantages of the parallel and series hybrid.
  4. In case of problems on the electric traction part, a recovery allows operations with reduced performance with the thermal engine in order to reach the service point.

DISADVANTAGES

  1. High cost, about twice than the one of a parallel hybrid car.
  2. Weight increase of about 350 / 400kg if compared to the version with only thermal engine.
  3. You need to set up your own support network, as you need to train specific staff.

*****

My personal opinion is that the series/parallel hybrid car, while offering the best compromise consumption/emissions, is not convenient to the private customer for the complications arising out its daily management.

Indeed the Hybrid Multipla was in great demand by state agencies, local governments, companies but had not arisen any interest in the private user.

*****

  1. What do I have to expect if I choose a CNG car?
  2. What do I have to expect if I choose a LPG car?
  3. What do I have to expect if I choose a hybrid car? (Parallel hybrid)
  4. What do I have to expect if I choose a hybrid car? (Hybrid series)
  5. What do I have to expect if I choose a hybrid car? (Parallel/series)
  6. What do I have to expect if I choose an electric car?
  7. What do I have to expect if I choose a hydrogen-powered car?

Translated by Federica Izzo

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