Fuel Consumption Optimization For A Hybrid Electric Vehicle

Although Ferdinand Porsche developed the Lohner-Porsche in 1901, hybrid electric vehicles, a type of vehicle powered by electricity and fossil fuel, did not become widely available until the release of the Toyota Prius in Japan in 1997, followed by the Honda Insight in 1999. While initially perceived as unnecessary due to the low cost of gasoline, nowadays, environmental pollution and petroleum problems have become more and more serious, which pushes the advancement of vehicle technology towards energy conservation and environment protection. With a large potential to save fuel consumption and to reduce pollutant emission, the hybrid electric vehicle becomes more and more popular in the international vehicle market.

As of January 2017, over 12 million hybrid electric vehicles have been sold worldwide since their inception in 1997. As of April 2016, Japan ranked as the market leader with more than 5 million hybrids sold, followed by the United States with cumulative sales of over 4 million units since 1999, and Europe with about 1.5 million hybrids delivered since 2000. Japan also has the world’s highest hybrid market penetration. In 2016, the hybrid market share accounted for 38% of new standard passenger car sales, and 25.7% of new passenger vehicle sales included Kei cars. Norway ranks second with a hybrid market share of 6.9% of new car sales in 2014, followed by the Netherlands with 3.7%, France and Sweden, both with 2.3%.

Global sales are led by the Toyota Motor Company with more than 10 million Lexus and Toyota hybrids sold as of January 2017, followed by Honda Motor Co., Ltd. with cumulative global sales of more than 1.35 million hybrids as of June 2014; Ford Motor Corporation with over 424,000 hybrids sold in the United States through June 2015; the Hyundai Group with cumulative global sales of 200,000 hybrids as of March 2014, including both Hyundai Motor Company and Kia Motors hybrid models. As of January 2017, worldwide hybrid sales are led by the Toyota Prius liftback, with cumulative sales of almost 4 million units. The Prius nameplate had sold more than 6 million hybrids up to January 2017. Global Lexus hybrid sales achieved the 1 million unit milestone in March 2016. As of January 2017, the conventional Prius is the all-time best-selling hybrid car in both Japan and the U.S., with sales of over 1.8 million in Japan and 1.75 million in the United States.

Modern hybrid electric vehicles make use of efficiency-improving technologies such as regenerative brakes, which converts the vehicle’s kinetic energy into electric energy to charge the battery, rather than wasting it as heat energy as conventional brakes do. Generally, it is driven by more than one power source and usually refers to a combination of internal combustion engine and electric motor. Some varieties of hybrid electric vehicles use their internal combustion engine to generate electricity by spinning an electrical generator (this combination is known as a motor–generator) to either recharge their batteries or to directly power the electric drive motors. Many hybrid electric vehicles reduce idle emissions by shutting down the internal combustion engine at idle and restarting it when needed; this is known as a start-stop system. A hybrid-electric produces less emissions from its internal combustion engine than a comparably sized gasoline car since a hybrid electric vehicle’s gasoline engine is usually smaller than a comparably sized pure gasoline-burning vehicle (natural gas and propane fuels produce lower emissions) and if not used to directly drive the car, can be geared to run at maximum efficiency which further improves fuel economy.

In an effort to reduce the production of greenhouse gasses of which emission standards are becoming increasingly strict, control strategies for the hybrid electric vehicle are put in place in order to optimize battery and fuel consumption. The usage of electric energy should be maximized and the usage of chemical energy burned from the gasoline should be minimized. To achieve this goal, the gasoline and electric usage should be controlled.

There are several aspects that affect the energy consumption of the hybrid electric vehicle. The first one is the mass of the car. With the increasing of the total mass, the friction between the wheel and the ground would increase. In order to overcome this increasing friction, more power should be supplied from the engine. In addition, the front surface area is also a key factor as bigger front surface area would lead to a higher air resistance and consume more energy. Additionally, the torque demand is the most important factor. An engine produces power by providing a rotating shaft which can exert a given amount of torque. When the car is climbing a hill or running with acceleration, more power should be supplied from the engine for overcoming the external force and keeping the car running with an optimal speed. However, due to the relatively low supplied torque limit, the electric motor cannot supply enough torque that the car needed and in this way, internal combustion engine would increase the burning of gasoline for the demanding of output power. As estimated by EPA, quick acceleration and heavy braking can reduce fuel economy by up to 33% on the highway and 5% around town.

For the same car, the mass and surface area cannot be changed for optimizing fuel consumption. Therefore, we can only manipulate the supplied torque from the internal engine. The feature of the road and driver’s behaviors’ are not easily altered, therefore in order to decrease the fuel consumption, what we can do is maximize the usage of electric motor when the demand of power is within the electric motor’s power limit. Based on this criteria, two system are developed. The first system comprises a feedback control loop. The torque sensor located in the electric motor measures the rotating speed of the shaft. When the number reaches the upper rotating limit of the electric motor, information would be delivered to the engine controller. Finally, the controller makes the internal combustion engine start combusting gasoline and satisfies the needs for the car to move forward. If the rotating speed is within the limit, the controller would only let the electric motor work. The second system is also a feedback loop to control the electric quantity in the battery. The sensor connects to the battery and measures the amount electric energy stored in the battery. An engine controller connects the sensor and the air supply valve connected to the internal combustion engine. When the electricity in the battery drops below 5%, the controller would stop the electric power working and make the internal combustion engine start working. Then, it starts combusting the gasoline and provides enough power for the car’s energy demands. However, there are some other factors known as disturbance variables which may disturb the control system. In these two feedback loops, disturbances are giant heat loss from the combustion of fossil fuels. We know that the typical efficiency for the internal combustion engine is around 30%, which means that only 30% of the heat combusted from the gasoline is able to be converted to the mechanical energy to power the vehicle. The other 70% heat would be discharged to the outside environment with waste gasses. It is worthwhile to collect the other 70% energy and converting it to electricity by spinning an electrical generator (this combination is known as a motor–generator, a currently matured technology) to either recharge their batteries or to directly power the electric drive motors.

Another disturbance variable is the road situation that the car traveled.  Driving in the blocked road makes the vehicle frequently accelerate and decelerate, which would dramatically increase the amount of demanding torque. This disturbance could be alleviated by adding a navigation system to the vehicle for a smooth and uncongested road for keeping the car moving at a relatively constant speed and decreasing the amount of demanding torque. In addition, the traveled distance would also affect the total demanding torque. The distance cannot be manipulated but we can maximize the torque supplied from the electric motor in this distance.

With the help of these two feedback loops system, the usage of the electric power is able to be maximized and the fuel consumption can be controlled. With the improvement of the technology in the realm of material science, more powerful and suitable battery will be developed for the hybrid electric vehicle and people will definitely benefit from the fuel economy and low emissions brought from the hybrid electric vehicle.

(Article by Junwei Xiang, Xiaoyu Xu, Sean Hu)


 Work Cited

Brouk, S., Buey, M., Ly, S., Pedron, M., & Burgalat, S. (2015). Control Strategies for Hybrid Vehicles in Mountainous Areas. Procedia Computer Science, 60, 284-291.

Crolla, D. Cao, The impact of hybrid and electric powertrains on vehicle dynamics, control systems and energy regeneration, Veh. Syst. Dyn. 50 (2012) 95–109.

History of Hybrid Vehicles. (n.d.). Retrieved March 10, 2017, from https://web.archive.org/web/20090208230718/http://www.hybridcars.com/history/history-of-hybrid-vehicles.html

Li, L., Wang, X., & Song, J. (2017). Fuel consumption optimization for smart hybrid electric vehicle during a car-following process. Mechanical Systems and Signal Processing, 87, 17-29.

Montazeri-Gh, M., & Mahmoodi-K, M. (2016). Optimized predictive energy management of plug-in hybrid electric vehicle based on traffic condition. Journal of Cleaner Production, 139, 935-948.

Roger Schreffler  WardsAuto. (n.d.). Toyota Remains Unchallenged Global Hybrid Leader. Retrieved March 10, 2017, from http://wardsauto.com/industry/toyota-remains-unchallenged-global-hybrid-leader

Transportation, I. C. (n.d.). FROM THE BLOGS. Retrieved March 10, 2017, from http://www.theicct.org/blogs/staff/hybrids-break-through-japan-auto-market

Worldwide Sales of Toyota Hybrids Surpass 10 Million Units. (n.d.). Retrieved March 10, 2017, from http://newsroom.toyota.eu/global-sales-of-toyota-hybrids-reach-10-million







  1. I think this was very informative. It’s very good that the focus is on clean energy, which is very good for the environment. I believe this application makes sense, because not only does is save energy, minimizing usage of the car’s engine would significantly increase the engine’s lifespan.
    I think it would be nice to explore how performance of a vehicle is affected with a change I power source- would the car get noisier/quieter, would the total horsepower increase/decrease, would the handling of the vehicle be impacted in anyway? These things may not be directly related to the control scheme, but are all factors that affect the consumer, and influence their decision to purchase or not.
    I think the control scheme is practical, but I do wonder if selecting a cutoff point for battery of 5% is reasonable enough. It is likely that vehicle performance would have fallen significantly once battery power passes a certain threshold, which may be higher than 5%, so waiting until then would worsen the driving experience. Maybe implement the witch earlier, or implement some manner of dual power system during which time both the engine and the battery are functioning, before the battery goes offline fully.
    With respect to the disturbance variables, you mentioned that you would implement a navigation system for finding a clear road. However, congested roads are where hybrids excel most, as the low speed that cars travel during road congestion assures that only the cars electric motor will be running, due the lower power requirement. So then there is some kind of trade-off there.
    Still I think you guys have a good idea in mind, and I like how you addressed what to do with the 70% energy loss from the engine use. Nice work

  2. The arguments in this blog post were coherent, concise and contemporary. I think it was especially important to note the timelines of the invention since hybrid cars first arose at a time when the cost of oil did not warrant an alternative fuel source. The use of the written statistics was a bit overwhelming, but the information was useful in illustrating the up and coming industry and establishment of hybrid vehicles in society. I do, however, think a visual schematic could have portrayed that particular form of information better.
    As someone who considers herself to be an advocate of the environment, I especially appreciated the breakdown on how exactly the car uses electricity to reduce its emissions. I can certainly see myself making use of this technology and bragging to my friends on how exactly I am making the world a better, more inhabitable place. The comparison of the gasoline engines is a useful tool in making the application both accessible and relatable. The reasoning behind the need to control the type of energy being utilized is apparent and the means by which to control it very clear. I will argue that the mass of the car may change depending on the load being carried. This can vary according to the number of passengers or the amount of luggage, though I don’t know if this fluctuation in mass is marginal or not. I’m also wondering if there is any way to use the 70% energy loss as heat to potentially heat the car during winter months. This may already be true of automotive vehicles, but perhaps the heat lost by the combustion engine could go towards heating the air, windshield or seats of the vehicle to make colder months more comfortable for those operating the vehicle. I am also wondering how much fuel is consumed to generate the electricity in comparison to directly driving the car.
    The use of a navigation system is brilliant. I would imagine that for someone looking to reduce his or her carbon emissions, a longer (but cheaper) commute to and from work is not a problem. The hills or elevation involved in navigation will require a higher energy output and maintenance of the car’s engine and tire pressure is a must. I would imagine with modern accessories such as the radio, navigation, lights etc. that the 5% battery indicator may have to be adjusted and increased to account for those uses. Otherwise, I think the above process does actually provide a means to control the amount of fuel being used and therefore lower the environmental burden of cars all together.
    Well done Junwei, Xiaoyu, and Sean, thanks for the great read.

  3. When I was in fifth grade, my science teacher confronted me with the question as to what I think would be the future of alternative power vehicles? Without knowing whether my idea would actually be feasible, I suggested her a car that can run without gasoline. The creative idea that popped into my mind at that moment was perceived from the episode of the futuristic cartoon, ‘The Jetsons’. However, little did I know that the world of technology would advance in such a fast pace, that one day a hybrid electric vehicle will be launched in the market making it possible to combine the conventional gasoline engine with the electric motor. In addition to the twin powered engine, hybrid electric cars also have other advantages over the traditional cars in that they run cleaner (reduce carbon footprint) and have better gas mileage which makes them environmentally friendly. Also, each time a person applies brake while driving, hybrid vehicle helps to recharge the battery a little. The combination of the power of traditional gas, and use of the battery to harness all of the energy that a normal vehicle normally wastes makes hybrids undeniably an attractive option.

    However all this technology comes at a price: a hybrid car is complex and expensive. It has two motors and all the ancillary systems to manage plus a heavy battery and a regeneration system used to produce electricity during breaking. All of these systems must work together, adding complexity. The hybrid version of car will usually be heavier than the traditional version (because of the electric motor and battery), and therefore may not handle as smoothly or accelerate as fast as the average economy car. If you are a conservative driver, the handling probably will not be an issue. With that being said, if you are looking for a car that offers high performance, then the hybrid may not be for you. While cars and, just as importantly, the computers that control them, have become more reliable, they still suffer from failures. So owners of hybrids can expect more time in the shop and larger repair bills.

    Overall, the control scheme mentioned makes sense, with the aim to control the gasoline and electric usage in order to maximize the use of electric energy and minimize the use of chemical energy. The disturbance variable that effects the energy consumption for the hybrid car- mass of the car and the manipulated variable needed to control the controlled variable- supplied torque from the internal engine are explained in a nice detailed fashion. The use of navigation system as a solution to counteract the disturbance variable does not work for congested roads as mentioned because the car accelerate and decelerate continuously. So if hybrid is operated in a city (where most people work and live), the energy consumption will be negatively affected as the supplied torque would increase. This is one thing to consider when buying the vehicle. One more thing, how exactly is the 70% heat that is discharged to the environment be collected in order to convert into electricity? This suggests that the disturbance variables really influence and do have a large impact on the functioning of the feedback loops and overall control system.

    The third paragraph that deals with the statistical data of the sales of hybrid vehicles is largely unnecessary. It does give a background on the popularity of hybrids in this decade, but it doesn’t make me want to read the article further.

    I think hybrid electric vehicles are probably a transition technology. Hydrogen or methane fuel cell powered cars are probably the cars of the future. As for the environment, there are many ways to reduce emissions – using public transport, carpooling, riding a bicycle and even walking. Even just buying a smaller, fuel efficient car makes a big difference. One should think about what they are really trying to accomplish before buying a hybrid and should not just blindly throw hard earned dollars at new technology for its own sake because it may be fashionably “green”. Lastly, the purchase of the hybrid car really depends on the person’s financial situation, environmental priorities and daily driving habits

  4. I thought it was a great idea to give some background on how hybrid electric vehicles originated. I had no idea the concept was developed in 1901! This article is very relevant to what today’s society is struggling with in terms of cost of fuel and what the environmental implications are when burning fossil fuels. I think that this idea is definitely applicable to today’s world and that it would be popular in the market for people who already own hybrid electric vehicles. It was nice to include some of the statistics on the percentages in different countries and different manufacturers, but I feel as though the background information outweighs the process control scheme. I would like to know more about the car itself: do you plug it into the wall to recharge the battery or would the 70% energy being converted to electricity by a motor-generator be enough to power the battery? How practical is it for long trips if the gas tank is smaller than a normal car?
    I like your explanation of the two feedback loops. They make sense! For the disturbance variables, I’m not sure if I would consider the heat loss a disturbance variable. I may call it a disturbance variable if it not a constant heat loss, but if it is always 70% heat lost, wouldn’t that just be built into the system? I agree that the road conditions would be a disturbance variable, though I am not sure a GPS system would always be able to handle this. I could see it being a problem in a town where every intersection has a stop sign or in a city where there are many traffic lights. Maybe there a way to use this technology while only on the highway. I’m just not sure if I understand, would it still be able to work when there are high demands of torque, just less efficiently? Maybe this is something that you can explain more clearly in your presentation. I really like the idea and the systematic way that your group decided on manipulating the supplied torque from the engine, I just think there need to be a few more details provided. Thanks for choosing a topic that is so relevant!

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