An Improved Regenerative Braking System EDGSN 100 Penn State December 16, 2014 Nick Dermo Burook Affa Will Maloney Naman Kabra
Executive Summary In the Delphi design project, MAD-K Inc. worked to come up with ideas of how to improve the regenerative braking system that is implemented in many hybrid vehicles today. After much thought and discussion about the topic, the group agreed that one way to improve the system would be to harness the heat given off by the traditional frictional braking system. This type of braking is used when the vehicle needs more braking power, such as braking at high speeds. Capturing the heat energy would increase the overall efficiency of the regenerative braking system. The group had four concepts that were evaluated using a concept matrix screening. Concept 4 was a combinations of the first three concepts, utilizing the original regenerative braking system, a thermoelectric system, and ultracapacitors to maximize system efficiency. This design has potential to be implemented into electric cars today, making these vehicles even more energy efficient and environmentally friendly. Introduction and Problem Statement The automobile industry envisions a future vehicle that is able to capture all of the energy that is lost through braking and put all of that energy back into the system, leaving no waste energy due to braking. Improving the efficiency of the system is the goal for the industry, and researchers are looking for new ways to make this a possibility. Currently, some vehicles are equipped with a regenerative braking system that is able to take some of the energy lost by braking and put it back into the system. A regenerative braking system captures the energy that would be lost by traditional brakes by instead using a system that uses the motor as an electric generator. The braking systems used today only work on drive wheels, do not provide enough braking force under panic stop condition, and are forced to use supplemental dynamic braking that does not store the reclaimed kinetic energy. In addition, the efficiency of regenerative braking systems today are limited by factors like the capacity of the energy storage system and the output of the electric motor. This project will investigate ways to improve the efficiency of a regenerative braking system by harnessing thermoelectric elements in the frictional braking system and coupling it with the regenerative braking system. This will allow the vehicle to recover the kinetic and heat energy lost during the process of braking. A system like this will improve the efficiency of the regenerative braking system and improve the overall quality and performance of the vehicle.
Research With regenerative brakes, the system that drives the vehicle does the majority of the braking. When the driver steps on the brake pedal of an electric or hybrid vehicle, these types of brakes put the vehicle's electric motor into reverse mode, causing it to run backwards, thus slowing the car's wheels. While running backwards, the motor also acts as an electric generator, producing electricity that's then fed into the vehicle's batteries. Figure 1 is a graph that shows the use of frictional and regenerative brakes over time when braking. It shows that regenerative brakes are used at the beginning of the braking process, but frictional brakes are used to make the vehicle come to a complete stop. Figure 1: Shows the relationship between vehicle speeds, deceleration, power, and time during the braking process in a vehicle with a regenerative braking system Figure 2 on the following page shows the thermoelectric effect, or the Seebeck effect. In this effect, a thermoelectric device creates a voltage when there is a different temperature on each side. This can be used within the wheel of a vehicle. In a tr aditional braking system, brake pads produce friction with the brake rotors to slow or stop the vehicle. Additional friction is produced between the slowed wheels and the surface of the road. This friction is what turns the car's kinetic energy into heat. The heat produced during braking using a regenerative system, but in certain situations, the frictional brakes are still used and produce heat. The heat can be captured using the thermoelectric effect and the energy can be put back into the system.
Figure 2: Shows the Seebeck effect Customer Needs Table 1 shows the thoughts and questions that the customer would impose if they were considering purchasing a vehicle with our product or implementing our product into their vehicle. The topics such as energy saving, efficiency, price, and others are discussed in the customer needs assessment. Table 1: Customer needs assessment
Conception Generation Concept 1 Concept 1 will include the traditional regenerative braking system. This system will able to capture the energy lost while braking and put it back into the system. This system generally is able to capture able 25% of the energy lost while braking, therefore is not exactly as efficient as the consumer would like to be. The system works alongside the traditional braking system because the regenerative braking system is not powerful enough to stop the vehicle at high speeds. This concept is basic and does not include any other features that increase the efficiency of the system. Concept 2 Concept 2 will have the thermoelectric generator to capture the frictional energy from the brake disks that are usually lost as heat by capturing the heat in the metal and using the seebeck effect to directly convert it to electricity. Concept 3 Concept 3 will incorporate features from Concepts 1 and 2. Hence it will include the traditional regenerative braking system and use the thermoelectric generator to capture the excess heat (friction) energy from the brake discs during the braking process. These two systems work together to increase the overall efficiency of the system. The regenerative braking system recovers the lost energy and transfers it back to the car battery. In addition, the thermoelectric generator uses the heat generated due to friction and uses that to transfer voltage to the battery, due to the seebeck effect. However, the problem with this concept is that there is no storage for the excess energy that is recovered and results in wastage of the excess energy. Concept 4 Concept 4 will be a combination of concepts 1,2, and 3. In addition, this concept will include the ultracapacitors. It will take care of the excess energy that isn t used by the thermoelectric system and the regenerative braking system. This will ensure that the car saves a lot more energy while being much more efficient than the other 3 concepts.
Concept Selection A concept scoring matrix, Table 2, was used in the selection of the final concept, and concept with the highest score was Concept 4. The team weighed each category according to how important each one was, and then ranked the concepts in each category on a 1 to 5 scale. Adding up the total in each category with the weight factored in, Concept 4 had the highest score, and proved to be the best concept for a modified regenerative braking system. Weight Concept 1 Concept 2 Concept 3 Concept 4 Efficiency 30% 3 3 4 5 Cost 10% 3 3 2 1 Maintenance and Durability 10% 3 3 3 3 Emissions 10% 5 5 5 5 Ease of maintenance Weight of system Ease of manufacturing 5% 4 4 3 3 10% 4 4 3 3 5% 4 3 3 3 Reliability 20% 2 3 4 5 Total 100% 3.2 3.35 3.6 4.0 Table 2: Concept Screening Matrix
Final Description The final product consists of the regenerative braking system enhanced by ultracapacitors and the thermoelectric elements in the brake disk. The regenerative braking system will be a standard one but the efficiency of the system is improved by adding ultracapacitors that will redirect the flow of electricity and cause an increase in the speed the energy can go back into the system. The second part, the thermoelectric generator, is a completely original concept. by harnessing thermoelectric elements we can make the brake disk into a heat to electricity converter. The amount of energy recovered from this system is only limited by the types of metals used and the way the driver uses the car. An alloy of some sort will need to be used to balance heat capacity and strength. Hopefully style can be maintained and a sporty look would be nice to show off the color differences in the two types of metals. The final design is basically the combination of all our good ideas and a great solution to some of the flaws of a normal braking system. Figure 3: Shows a model of the final product made on Sketch up
Systems Diagram Figure 4: Shows the system diagram of the final product Scenarios Scenario 1 : Slow Braking at 25mph Based on the way the car is driven or based on the scenario the regen and thermoelectric systems work together but in varying magnitudes. When a car is going a slower steady pace of 25 mph and begins to brake slowly the system primarily relies on regenerative braking to bring the car to a halt. The car uses regen braking to slow up until the last second where the torque of the regen cannot slow it down any further and the frictional brake finishes the job with a halting action. The thermoelectric elements are barely activated in this scenario because there is little to no heat generated by the frictional brake. Scenario 2: Highway Braking In the event of highway braking both systems are used to slow the car. In highway braking regenerative braking is used to slow the car in small amounts. At high speeds if harder braking is required regenerative braking becomes less efficient and traditional brakes are required. When frictional brakes are triggered a significant amount of heat is generated and the thermoelectric elements are activated and begin to return energy to the battery. Somewhere between highway braking and slow braking is where the systems efficiency reaches its full potential balancing thermoelectric elements and the uses of regenerative braking. Scenario 3: Emergency stopping In the case of emergency braking the use of regenerative braking is almost completely neutralized. Frictional brakes engage and significant amounts of heat are generated by contact between the brake pads and the brake disks. Thermoelectric elements in the
brake disks are activated and the temperature difference generates energy using the seebeck effect and energy the energy generated is routed back into the central battery. Total Cost Analysis Table 3: Shows the cost analysis of the product compared to a traditional braking system Life Cycle Analysis Various metals are mined and taken to a factory. Factory purifies and casts metal parts. Electronic parts are added. Finished regen and thermoelectric elements are installed in vehicle. Car is used for about 10-15 years before being scrapped Parts are recycled to be used in other cars as repairs or smelted down to be used in other things with metallic components. Sometime down the road when enough systems have been used a part recycler can be used where manufacturers can reuse parts of regen and thermoelectric elements without use of extra manufacturing energy. And the cycle continues Conclusions Therefore, in conclusion, the success of this upgrade in the current system is evident through all the facts listed above in this report. This improved system meets the criteria that we as a group envisioned. Using the current regenerative braking system with the concept of thermoelectric effect, it is possible to say that a lot more of the energy that is wasted whilst braking can be put back into the system to provide energy to the battery of the car. It is not very complicated to install this system, hence most customers will be willing to incorporate some extra components in their car if they will benefit by saving energy. Even though this upgrade in the system will increase some costs for the car-owners, with the energy savings in the long-term the customers will benefit from saving a lot of money from all that recovered energy by the system.
References http://auto.howstuffworks.com/auto-parts/brakes/brake-types/regenerative-braking.h tm http://www.explainthatstuff.com/how-regenerative-brakes-work.html http://www.thermoelectrics.caltech.edu/thermoelectrics/index.html