But there are a few features that have been made possible by the development of hybrid technology. Some of these features are new, while others have been around for a while but have become more relevant with the advent of hybrid cars.
Regenerative braking
The big breakthrough
Normal friction brakes convert a car’s kinetic energy into heat that is wasted in the atmosphere. Regenerative braking recovers some of the energy used to move the car and bring it up to speed. The electric motor of the hybrid drive turns into a generator during braking or deceleration. This causes friction which slows the car down, and the electricity thus generated is fed back to the battery. This system is also used in electric vehicles, plug-in hybrids and mild hybrids.
The main benefit of regenerative braking is of course greater fuel efficiency. The friction brakes also last longer because they are used less. In the long run, this more efficient use of energy requires less work from the gas engine, meaning it will last longer than a gas-only propulsion.
Automatic engine stop/start
Improvement of existing technology
Automatic stop/start technology can be used in normal ICE cars, but this works much better with a hybrid drive. The engine switches off when the car is stationary and restarts automatically when the driver takes his foot off the brake pedal.
While a petrol car must use the starter motor to restart the ICE, a hybrid can use its electric motor during stop/go driving, with the engine only starting when more power is needed. Operation in a hybrid is much smoother and functions such as the air conditioning can continue to work while the engine is off.
Advanced battery technology and management
Also used in EVs and battery storage
The arrival of the hybrid drive led to significant improvements in battery technology and the way in which they are monitored, controlled and optimized. This opened the door not only to better hybrid vehicles, but also to electric vehicles and other uses. New battery chemistries were developed, starting with a focus on lithium-ion. The way these batteries were made improved, giving them better performance and reliability. This technology was then adapted for other uses, including battery storage and devices such as cell phones.
Parallel to making better batteries came the way these batteries are managed, with software that protects the battery from operating outside safe limits, monitors the battery’s health and manages its life cycle.
Power electronics and engine controls
Making a complicated system work
Hybrid drivetrains have led to the development of power electronics and motor control systems to manage the electrical energy between the battery and the electric motor. These include DC-AC converters that convert DC power from the battery into AC power for the motor, and DC/DC converters that regulate the voltage for various systems.
During regenerative braking, the process is reversed and the motor’s alternating current is converted into direct current to charge the battery. Various sensors collect input based on driving conditions and regulate the speed and torque of the electric motor.
Intelligent energy management
Linking engine, engine, driver and driving conditions
A hybrid car uses both an ICE and an electric system, sometimes separately, but usually together. Intelligent energy management enables the optimal operation of these systems for maximum fuel efficiency and battery operation.
As the title suggests, this requires advanced computing, including machine learning, rule-based strategies, and fuzzy logic controllers. It can make real-time decisions by analyzing driving behavior, road conditions and traffic flow around the car.
The Atkinson Cycle
Giving new life to old technology
A normal ICE operates on the Otto cycle, which is the operation of each cylinder through its four strokes. The Atkinson Cycle uses the same engine, but the variable valve technology changes the way it works. There is also the Miller cycle which does the same thing, but with a turbocharger or supercharger.
The Atkinson was developed in the late 19th century as a kind of steampunk device. The current Atkinson cycle uses electronic valve control, making it more reliable and resulting in less power but greater fuel efficiency. This lower power is compensated by the battery in a hybrid drive. Toyota and other automakers now make Atkinson/Otto cycle combination gas engines, with the former used for daily driving, while valve timing can be electronically adjusted to the Otto cycle when more power is needed.
Making mechanical functions electric
Essential for hybrids, better in ICE
Before hybrids came along, systems like power steering worked with mechanical connections, often belts. Hybrids had to run on electricity so that these systems could function when the engine was off. Much of the power for these power functions used to be taken directly from the engine, affecting both power and efficiency.
Replacing mechanical functions with electrical ones resulted in fewer moving parts, smoother operation and less weight. Many newer ICE cars have switched to using electric power for steering, braking and other functions that used to be performed mechanically.
Four-wheel drive on request
All benefits, no punishment
All-wheel drive provides better traction on slippery roads, but reduces the vehicle’s fuel consumption. Some ICE vehicles had on-demand AWD, which allowed efficient front-wheel drive during normal driving, but with the AWD kicking in when the front wheels began to slip. This required a complex, heavy and expensive mechanical/electronic system with a drive shaft and differential.
Toyota introduced AWD upon request in its hybrids, where the car would usually have two-wheel drive, with the non-driven wheels equipped with an electric motor on the axle. When the drive wheels lose traction, battery power is immediately sent to the other set of wheels. The system is light, cheap and can be switched on or off very quickly.
Sources: Toyota, Midtronics.com
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