Micro vs Mild vs Full Hybrid & Regenerative Braking
Micro vs. Mild vs. Full Hybrid
As we have already discussed on Micro, Mild and Full Hybrids last week, lets briefly go through the simplest definition of Micro, Mild and Full hybrid
Micro Hybrids are the vehicles wherein the electric motor doesn't add thrust to the combustion engine or where it doesn't provide power assistance to the combustion engine.
Mild Hybrids are the vehicles wherein the electric motor adds thrust to the combustion engine or provides power assistance to the combustion engine; however it doesn't allows purely electric driving.
Full Hybrids are the vehicles wherein the electric motor not only adds thrust to the combustion engine or does power assistance to the combustion engine but also allows purely electric driving.
We will see some pictures to visualize the features and differences between these systems.
Source: PWC automotive Institute & Internet
Let's put the differences in tabular form so you can remember easily.
| MICRO HYBRID | MILD HYBRID | FULL HYBRID | |
| Start Stop | Yes | Yes | Yes |
| Power Assist | No | Yes | Yes |
| Electric Engine output | 0kW | 5-15kW | 50-70kW |
| Electric drive | No | No | Yes |
| Regenerative Braking | No* | Yes | Yes |
| Engine Downsizing possible1 | No | Yes | Yes |
| Fuel economy gains | Very Low (5-8%) | Low (10-18%) | Medium (20-30%) |
| Cost | Low | Medium | High |
*Some text may say Regenerative braking can also be present in Micro Hybrids.
** Fuel gains are approximate and for gasoline hybrid vehicle; actuals will vary in diesel vehicles. Also it can differ with Hybridization factor and other factors.
1Engine downsizing
This power assist ability reduces the demands on the gasoline engine, allowing for the use of a smaller, more efficient gasoline engine while maintaining the same performance as a vehicle with a larger engine. This engine "downsizing" may be achieved by using physically smaller engines with less cylinders or smaller displacements, or may be achieved using more efficient combustion cycles.
Regenerative Braking system
Introduction
About half of the vehicular energy is consumed in the form of heat generated from braking in the urban driving cycle. If this part of energy can be recycled, fuel consumption will be greatly reduced. This reduction would significantly improve vehicle fuel economy and emissions performance. The traditional vehicle poses difficulties to achieve this function, while the mild hybrid and full Hybrid systems with greater power motors and large-capacity battery can convert extra kinetic energy into electrical energy for storage.
In hybrid vehicles (such as mild and full hybrid) the kinetic energy of the drive wheels can converted into electrical energy by the electric motor (which is operated as a generator for this purpose). In this way some of the energy which is normally lost as frictional heat during braking is fed in the form of electric energy to the battery and then utilized. At the same time the generator operation of the electric motor brings about a vehicle-braking effect. This process is known as regenerative or recuperative braking.
System with a regenerative braking system
Source: Autoshop101.com
A typical regenerative braking system is shown in the fig above.
Braking Force from regenerative braking
In regenerative braking the braking may not be sufficient to provide the full required brake force so generally service brakes are combined with regenerative braking system to provide the required braking force. So in regenerative braking the vehicle is not only braked by the generator braking torque of the electric motor but also it may combines the service brake's friction torque depending on the brake force requirements.
The actual regenerative braking force is varied with desired braking deceleration and vehicle speed, and it is calculated based on an analysis of the required deceleration, maximum braking force of ISG, engine braking force and state of charge (SOC) of battery.
Distribution of braking force
A braking force distribution strategy is required to find the optimal distribution ratio of the regenerative braking torque and the friction braking torque so that the regenerated energy can be maximized.
Actual regenerative braking force of an ISG motor is achieved based on the relationship among vehicle braking efficiency, braking force of the electromotor and engine, and charging power of the battery during the regenerative braking process.
When the vehicle with regenerative braking brakes, the ISG motor runs into the generation model to recover kinetic energy under certain conditions. In the process of regenerative braking, the engine and ISG motor will synchronize their rotary speed, the driven engine will produce engine braking force and the driven motor will produce electricity while regenerating braking force. The braking force of the system, including friction braking force and regenerative braking force, is equal to the required braking force less the engine braking force. The braking force of the system will come from the regenerative brake completely if the regenerative braking force is bigger than the system braking force. On the contrary, if the regenerative braking force is smaller than the system braking force, the rest of the braking force will be provided by friction braking. The regenerative braking force is restricted by both the ISG motor efficiency and battery charge performance. To obtain the actual regenerative braking force of a mild HEV or full HEV brake system, it is necessary to research relationships among required braking force, engine braking force, ISG motor regenerative braking force, and battery charge efficiency.
Disclaimer
The article doesn't include any confidential information. Nor does it include any references from the sources which doesn't allow taking excerpts from articles. The images have been taken from internet not necessarily from direct source. The article is only for your reference; please do not forward without permission.
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