Mechanics
Due to a series of hybrid omits a mechanical relationship between the combustion engine and wheels, the engine can run at a constant speed and efficient even when the vehicle speed changes. Vehicle speed and engine speed are not necessarily in sync. The engine can thus maintain an efficiency closer to the theoretical limit of 37% more than the current average of 20%. At low speeds or joint can lead to ~ 50% increase in overall efficiency (19% vs. 29%). However, General Motors has designed the Chevrolet Volt engine / generator to operate between 1,200 and 4,000 revolutions per minute. The company has introduced a Lotus motor / generator design that works at two speeds, providing 15 kW of electrical power and 35 kW at 1,500 rpm to 3,500 rpm through the integrated electric generator.
Whereas the requirements for the engine are not directly linked to vehicle speed, this gives you a greater margin for designs more efficient engines or alternative, such as microturbines, Atkinson cycle engine or a rotary combustion engine linear.
There are stages of operation of the combustion engine to power the electric motor generator and then, depending on the design, can also be run through the generator and electric motor to the battery after further reducing efficiency (see illustration). Each transformation through each stage causes a loss of energy. However, in normal vehicle operating conditions of the buffer energy battery bank, which stores braking energy recovered and the optimal operation of the combustion engine can increase the overall efficiency of operation, although each stage be a waste of energy. Engine mechanical efficiency in an automatic transmission shift is approximately 70-80%. Conventional mechanical clutch transmission has an engine to the transmission efficiency of 98%. In a series hybrid vehicle, during long distance highway driving at high speed, the combustion engine must provide the most energy, in this case a series of hybrids may be a 20 - 30% less efficient than a parallel hybrid.
Bi-vehicle: liquefied petroleum gas and natural gas are very different from petroleum or diesel and can not be used in the same tanks, so it would be impossible to build (LPG or NG) flexible fuel system. Instead, the vehicles are built with two parallel, fuel systems feeding one engine. While the duplicated tanks cost space and some applications, increased choice and flexibility, where (LPG or NG) infrastructure is inadequate, may be significantly more advantageous to buy.
Some vehicles have been modified to use another fuel source if it is available, such as cars modified to run on the car (LPG) and diesel engines modified to run on waste vegetable oil, biodiesel is not treated.
Power-assist mechanisms for bicycles and other human-powered vehicles are also included (See Motorized bicycles).