Thursday, May 31, 2012

Hybrid Technology - A Good Thing?

DUE to high fuel pump prices, there has been a surge of interest in petrol-electric hybrid vehicles.

For instance, hybrid car sales all over the world, dominated by the Toyota Prius, saw a marked increase in the last four year despite a declining new passenger car market.

It has been reported that waiting lists to buy the Prius was stretched to as long as six months in the United States, due to limited supply of batteries for the hybrid car.

Presently, it seems that combining electric drive with the internal combustion engine is the best choice for reducing fuel consumption and emissions.

Hybrid vehicle technology is easily available and it does not require too much engineering.

Inside, the c wins big in three areas - comfort, space and user friendliness.

Of course, there are alternative fuels such as LPG (Liquefied Petroleum Gas), CNG (Compressed Natural Gas), ethanol and hydrogen. Another option is the full electric vehicle.

However, LPG and CNG are non-renewable resources while both ethanol and hydrogen require large amounts of energy to produce.

In the final analysis, one must look at the vast sums of money that have been spent in developing the internal combustion engine to its present technological level. Are we prepared to throw the internal combustion engine away, or can we combine it with something else to obtain the best advantages?

Still, hybrid technology is not new.

In fact, probably the first hybrid car was the Porsche Mixte that was introduced in the early 20th century.

The Mixte used two electric hub motors and a small petrol engine to charge the batteries.

Today, hybrid cars use a similar idea with an electric motor assisting a petrol engine.

Hybrid cars generally come under two broad categories:

(a) Series hybrid: A petrol engine is used to charge the batteries and the vehicle runs purely on electric propulsion.

(b) Parallel hybrid: An electric motor is coupled in parallel with the petrol engine, and is utilised when additional torque is needed. This system can also be configured such that the car starts with the electric motor and the petrol engine is only utilised when additional torque is required, or when the batteries are discharged and the petrol engine charges the batteries while the car is driven.

Parallel hybrids are what almost all automakers are working on.

Variations of parallel hybrids include:

(a) The vehicle starts and runs using the internal combustion engine. The electric motor only comes into play when more torque is required such as during overtaking or hill climbing. As such, one would find that vehicles with this set-up tends to have better fuel consumption when cruising, i.e. when the internal combustion engine is not too stressed.

(b) The vehicle starts using the electric motor. As long as there is sufficient battery charge, the vehicle will continue to run at speeds up to 120 km/h. When the battery charge is low, the internal combustion engine is started and maintains vehicle speed while charging the batteries. Once the batteries are fully charged, the engine shuts down and the vehicle continues in electric mode.

From the description above, it is obvious that (b) appears to be the better method as the use of fossil fuel is kept to a minimum and the emissions when electricity is used are almost zero.

However, this system is not easy to set up for the following reasons:

1. The batteries need to be highly efficient for there to be sufficient charge. Many existing systems use nickel metal hydride batteries (NiMH).

However, if the batteries are replaced with the lithium ion type, it is possible to have a higher capacity with less weight.

2. The power steering, brake servos and air conditioning need electricity, and this puts additional load on the batteries because the engine is not running most of the time. Even the oil pump for the automatic transmission needs power from the batteries.

3. The management of systems such as the internal combustion engine cutting in and out, charging of the batteries as well as load and power control need sophisticated computer technology for the changes to be seamless.

With the advanced technology in the Porsche Cayenne hybrid system, where the motor is running in line with the engine and the transmission uses one way clutches, fuel consumption is reduced from 23 to 36 per cent depending on the test cycle used.

The gains are definitely there but all the additional equipment adds weight. Also, there is some loss of space due to the batteries.

There is also the question - why hybrids? As most vehicle are used in an urban environment with short distances travelled (usually less than 100km per day), would not it be better to design small, light vehicles that run purely on electricity? Some automakers, such as Reva Electric Car Company in India, are already producing such urban vehicles. But that is another story!


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