Ask Joe Mechanic: Alternative Energy Vehicles, Part 2

            In this second part of my article about alternative energy vehicles, I will describe the different types of gas/electric hybrids and what makes them distinctive. There are a variety of hybrid powertrain configurations.

            The first type is the parallel hybrid. The best example of this type was the first generation Honda Insight, which was the first hybrid vehicle to go on market outside Japan. In a parallel hybrid vehicle, the single electric motor and the internal combustion engine are installed such that they can power the vehicle either individually or together. In contrast to the power split configuration typically only one electric motor is installed. Most commonly the internal combustion engine, the electric motor and gearbox are coupled by automatically controlled clutches. For electric driving the clutch between the internal combustion engine is open while the clutch to the gearbox is engaged. While in combustion mode the engine and motor run at the same speed.

            The mild parallel hybrid is a configuration used by many manufacturers. Some examples include Honda Civic Hybrid, Honda Insight 2nd generation, Honda CR-Z, Honda Accord Hybrid, Mercedes Benz S400 BlueHYBRID, BMW 7-Series hybrids, General Motors BAS Hybrids, and Smart fortwo with micro hybrid drive. These types use a generally compact electric motor (usually <20 kW) to provide auto-stop/start features and to provide extra power assist during the acceleration and to generate on the deceleration phase (aka regenerative braking).

The power-split or series parallel hybrid is the highest production version of hybrid vehicle currently on the market. Many of the examples are household names including; Toyota Prius, Ford Escape and Fusion, as well as Lexus RX400h, RX450h, GS450h, LS600h, and CT200h. In a power-split hybrid electric drive train there are two motors: an electric motor and an internal combustion engine. The power from these two motors can be shared to drive the wheels via a power splitter, which is a simple planetary gear set. The ratio can be from 0–100% for the combustion engine, or 0–100% for the electric motor, or anything in between, such as 40% for the electric motor and 60% for the combustion engine. The combustion engine can act as a generator charging the batteries. Modern versions such as the Toyota Hybrid Synergy Drive have a second electric motor/generator on the output shaft (connected to the wheels). In cooperation with the "primary" motor/generator and the mechanical power-split this provides a continuously variable transmission.

On the open road, the primary power source is the internal combustion engine. When maximum power is required, for example to overtake, the electric motor is used to assist. This increases the available power for a short period, giving the effect of having a larger engine than actually installed. In most applications, the engine is switched off when the car is slow or stationary, reducing curbside emissions. A series or series-parallel hybrid has also been referred to as an extended range electric vehicle or range-extended electric vehicle (EREV/REEV).  However, range extension can be accomplished with either series or parallel hybrid layouts. This type configuration has not been used until recently in passenger car applications, but has been popular in heavier duty type usage.

Series-hybrid vehicles are driven by the electric motor with no mechanical connection to the engine. Instead there is an engine tuned for running a generator when the battery pack energy supply isn't sufficient for demands.  This arrangement is not new, as it is common in diesel-electric locomotives and ships. Ferdinand Porsche used this setup during the early 20th century in racing cars, effectively inventing the series-hybrid arrangement. Porsche named the arrangement "System Mixt". A wheel hub motor arrangement, with a motor in each of the two front wheels was used, setting speed records. This configuration was sometimes referred to as an electric transmission, because the electric generator and driving motor replaced a mechanical transmission. The vehicle could not move unless the internal combustion engine was running. The setup has never proved to be suitable for production cars, however several manufacturers are currently revisiting it.

In 1997, Toyota released the first series-hybrid bus sold in Japan. GM introduced the Chevy Volt series plug-in hybrid in 2010, aiming for an all-electric range of 40 mi (64 km), and a price tag of approximately $40,000 USD. AFS Trinity has used supercapacitors combined with a lithium ion battery bank in a converted Saturn Vue SUV vehicle. Using supercapacitors they claim up to 150 mpg in a series-hybrid arrangement.

A final subtype of hybrid vehicles is the plug-in hybrid electric vehicle (PHEV). The plug-in hybrid is usually a general fuel-electric (parallel or serial) hybrid with increased energy storage capacity, usually through a li-ion battery.  Which allows the vehicle to drive on all-electric mode a distance that depends on the battery size and its mechanical layout (series or parallel). To avoid using the on-board internal combustion engine for charging, it may be connected to a main electricity supply at the end of the journey. This concept is attractive to those seeking to minimize on-road emissions by avoiding – or at least minimizing – the use of ICE during daily driving.  As with pure electric vehicles, the total emissions saving, for example in CO₂ terms, is dependent upon the energy source of the electricity generating company.

For some users, this type of vehicle may also be financially attractive so long as the electrical energy being used is cheaper than the petrol or diesel that they would have otherwise used. Current tax systems in many European countries use mineral oil taxation as a major income source. This is generally not the case for electricity, which is taxed uniformly for the domestic customer, however that person uses it. Some electricity suppliers also offer price benefits for off-peak night users, which may further increase the attractiveness of the plug-in option for commuters and urban motorists. Examples of this type are the Toyota Prius Plug in Hybrid and the Ford Fusion Energi.

Next week, we will take a look at the environmental and cost factors of alternative energy vehicles.

This weeks recalls:
139,917 2013 Escape equipped with 1.6L engines.
The affected vehicles may experience localized overheating of the engine cylinder head, which may cause cracks that could cause an oil leak. Leaking engine oil may come into contact with a hot engine surface potentially resulting in an engine compartment fire.

If you own one of these vehicles, contact your local dealer for further instructions on what to do.