by Andrew Avarvarii (from topspeed.com)
A vehicle is being called a “hybrid” when to it uses for propulsion two or more sources of power in conjunction. Most common hybrid cars that run today combine traditional internal combustion engines (ICE) and electric motors. They run most of the time using the electric part of the system which is powered by batteries. When the car needs more power (as when going uphill or during quick accelerations) the combustion engine is also switched on. Hybrid cars are focused mostly on fuel efficiency rather then performance, That’s is why they tend to be lighter and more aerodynamic (in terms of reduced drag, not increased down-force). One recent development further increased hybrid cars efficiency. The concept is borrowed from electric locomotives and uses the breaking energy (that is usually wasted) to recharge the car’s batteries.
The main reasons for the increased interest in hybrid-cars seem to be those of environmental concern. As we know combustion engine produce carbon monoxide, carbon dioxide and unburned hydro-carbons that represent the most important sources of pollution of our days. Phenomena such as global warming or the so called “El Nino” effect are blamed mostly on the gasoline and diesel fueled engines. Due to the fact that a sudden change in vehicle power source could not be sustained by the infrastructure (we can’t change overnight all the oil platforms or gas stations in hydrogen plants), car manufacturers found a “transition solution” in the hybrid cars.
Embraced first by “tree hugger” stars and convinced environmentalists due to high prices, the hybrids become more and more popular as their prices dropped due to industrialization. Since the first Toyota Prius where sold in the United States the market has grown over twenty times reaching total sales of over 200,000 units in 2005. This may seem to be impressive, but if we report to the total amount of cars sold last year, that exceeded 17 millions new cars, we see that hybrid cars represent only a bit over 1% of the total sales. The fuel consumption economy of hybrid cars is also diluted due to their poor representation on the streets. If we would assume that every hybrid car would save a gallon of fuel per day, that would make a total economy of 200,000 gallons per day, which represents only 0.05% from the daily fuel consumption. It may not seem much, but it is a start.
The extension of the hybrid power technology will make it cheaper to produce and it is estimated that the hybrid car production will double each year. On an optimistic forecast we could have one million running hybrids in the US by 2007 or 2008. But, we shouldn’t forget that the sales of regular cars will also increase and if there are 200 millions cars now in the US, in less than 20 years there could get to be over 300 millions.
As 2006 models the US market offers 10 different models priced between $19,000 and $53,000. The Honda Civic and Toyota Prius which are considered to be the most popular are available below $30,000. That may not be cheap for a compact sedan, but is not prohibitive either. In the following 5 years the hybrid vehicle offer is expected to reach 50 models that will cover all shapes, sizes and costs.
Another feature that mostly hybrids nowadays share is the regenerative breaking. This feature uses the electric motors for slowing the car down by recovering the kinetic energy the car produces while braking or traveling down a slope. This kinetic energy is converted by the motors (which now act as generators) into electric power and stored in the batteries. The stored energy will be later used when the car will need to accelerate).
The ICE is turned on when the car has to accelerate quickly, to cruise at high speeds or when the batteries are running out. Among other benefits of this system should be mentioned that as the ICE is turned off at a vehicle stop it doesn’t get to cool down the catalytic converter beneath its operating temperature as normal cars do at idle rpm. Usually a gasoline engines run inefficiently with the throttle half opened. Full Hybrid cars overcome that by always running the ICE at high torque rpm range with throttle fully opened.
In the Mild Hybrid vehicles the ICE is running all the time the car is in motion. It is only turned off when the car is at stop to save some fuel. The electrical motor is used to smoothly start the petrol engine and it can also provide assistance to the ICE in traction. This last option makes the difference between several Mild Hybrid technologies.
The Start/Stop system is the simplest one. It only uses the electrical motor to power on smoothly the ICE. All the propelling power is generated by the gasoline engine and the only fuel economy is achieved by turning it off when it would otherwise be idle. This system is used on General Motors trucks. A cheap Start/Stop system is the BAS (Belt Alternator Starter), that due to low price is about to get very popular. This system replaces the usual belt driven alternator with an electric motor/generator. When the ICE is running the electric motor acts as a generator and recharges a separate 36V battery. When the ICE needs to be started the electric motor powers it up via the belt without the need for a regular starter motor. This system uses a larger motor/generator than the usual starters that can quickly and smoothly rev the ICE and therefore make Start/Stop operation possible.
IMA (Integrated Motor Assist) is the last of the Mild Hybrid systems. It is pretty much the same with the ISAD, the only difference being that it uses a larger electric motor than can provide more assistance to the ICE. IMA vehicles also never run “green”, as they keep the petrol engine on all the time they need to maintain propelling.
Another distinction in hybrid systems can be made on the manner in which they combine gasoline and electricity usage. This splits hybrids into Parallel and Series. Parallel Hybrids feed the ICE with fuel, while they power electric motor using the batteries. In parallel systems both motors (fueled and electric) propel the car, usually by means of a CVT (Continuous Variation Transmission). This type of transmission smoothly adjust gear ratios for optimum performance and allows torque to be delivered to the wheels from both engines. Series Hybrids use the ICE to drive a generator producing electric power. This electricity can either directly power the electric motor (that gets to transfer torque to the car’s transmission) or charge the batteries. Therefore the petrol engine is only used to produce electricity, it never gets to directly propel the car. All HEV (Hybrid Electric Vehicles) that are nowadays into production are considered to be parallel. There is an argument only concerning Toyota’s Prius that gets to be somewhere in the middle due to its sophisticated system.
Hybrid vehicles have been criticized for the lack of a plug-in battery recharge feature. This will allow “clean trips” (powered on electricity only) to be further extended. The cars could be recharged by plug-in means during night-time and used for city short trips in the same day without any gas consumption. If the batteries discharge before reaching home the vehicle will still run using the ICE. The hybrid car manufactures seem to have understood the necessity of this feature and it is rumored to became available on most HEVs soon.
It is hard to tell if using a hybrid vehicle is recommendable of not. There are a lot of pros and cons to them, and all the environmental issue surrounding them makes the decision even more subjective. We think it is a matter of individual choice, and each of one should judge their use on its own. It can be said that you save a lot of money form fuel consumption, as the acquisition price is higher that that of an equivalent traditional car. But it can’t be said that they are highly expensive and to worth the price. If you are willing to drive a slightly slower car in order to keep our planet green for a longer period HEVs a re something you should consider.