Electric vehicles are becoming a popular alternative to traditional internal combustion powered vehicles. From savings money on fuel, to reducing one’s carbon footprint, there are many reasons why today’s consumers are demanding electric cars. But how much do you really know about the powertrain assembly of Electric Vehicles (EVs)?
With the expected rise in electric vehicle production it makes sense for engineers, managers, marketers, and consumers to gain a better understanding of the source fueling the battery electric car. This course offers a detailed technical explanation with design considerations of the EV powertrain components, how they work together, and how they compare to the internal combustion engine in value.
- Electric vehicle power train and its similarities with IC Engine
- How can we select the electric power train of any existing ICE vehicle by its own performance parameters?
- Components in an electric power train system?
- Calculations of the electric power transmission system of any vehicle.
a. Gradient Resistance
b. Rolling Resistance
c. Aerodynamic Resistance
d. Drag Resistance
e. Angular velocity
5. Range calculation of an electric vehicle.
6. How to select the battery, motor, controllers with respect vehicle load?
TRENDING TOPICS ELECTRIC VEHICLES IN INDIA:
- What is the main difference of make in India motor than china motor?
- How low powered electric china vehicles (scooters and bikes) are giving top speed as like as high powered electric motor vehicles?a. How it is possible? If possible what is the necessity of high powered motors? If not, how those vehicles are reaching top speeds?
FUNDAMENTALS OF ELECTRIC VEHICLE (EV) POWERTRAINS
Although most Electric Cars look similar on the outside to their Gas-Powered cousins, underneath the hood things are very different. See below for a schematic comparison of the two.
Figure 1: EV’s vs. Traditional ICE powered cars
The functional elements of the electric vehicle may look conceptually similar to that of a traditional car, but the implementation is very different. Let’s take a closer look at some of the differences up close.
ENERGY STORAGE: BATTERIES VS. GASOLINE
We often take it for granted how valuable petroleum products are in terms of energy density. A kilogram of Gasoline contains about 46 MJ of energy, while a Lithium Ion Battery (the most common type used in EVs) has a maximum of a measly 0.875MJ. This means that for a given weight, gas contains more than 50X the amount of energy! That raises the question: why bother with electricity at all?
There are many compelling reasons why we should move away from a gas-powered vehicle. A strong reason that is often widely discussed is the green-energy argument: burning gasoline is polluting and harmful to our health, the environment, and the earth as a whole. There are also strong economic arguments as well, and these will only get stronger as fossil-fuel reserves are further depleted, and alternative green-energy becomes less and less expensive. From an end user perspective there is also a huge cost savings as explored the Union of Concerned Scientists.
There is also a benefit from an engineering perspective. As most readers will be familiar: cars with an Internal Combustion Engine (ICE) often reported worse efficiencies when driving in the city, than on the highway. The electric car flips this concept on its head and exhibit longer ranges during city driving than highway. As EV’s can harvest energy from braking, most of the kinetic energy spent to accelerate you when the light turns green is recaptured at the next block’s red-light. With an ICE, energy recapture is impossible; we don’t have the technology to create gasoline with the energy from braking and instead it escapes as waste-heat.
On the highway, EV’s are actually less efficient. Aerodynamic drag is the biggest energy hog. Any cyclist will be familiar with this phenomenon: riding quickly into a headwind can be exhausting. Car’s with ICE’s are simply less-inefficient, wasting energy through braking.
ENERGY CONVERSION: ELECTRONICS AND MOTORS VS. INTERNAL COMBUSTION ENGINES
Energy conversion from electricity is a much more efficient process than from gasoline. Electric motors can have efficiencies of more than 90%, compared to that of an ICE which usually is about 25-50% efficient. In-fact, no matter how well we engineer them, there’s fundamental limitations in how efficient an engine can run. No matter how hard we try, we will never be able to be as efficient as a simple electric motor.
Another big problem for ICE’s is their limited operation range, limited to about 1500 to 6000 RPM. We must attach complicated, expensive and heavy multi-ratio gearboxes to allow them to produce usable power over the operation range of the car; from a standstill all the way to its max speed.
Figure 2: ICE power Curve (Ehsan, Gao, & Gay, 2003)
Figure 3: Electric Motor Power Curve (Ehsan, Gao, & Gay, 2003)
As you can see, Electric motors don’t necessarily require expensive multi-ratio transmission components, which simplifies the vehicle design significantly.
CHALLENGES IN ELECTRIC VEHICLE POWERTRAIN DESIGN AND ASSEMBLY
Battery technology has moved forward leaps and bounds in the last 20 years. We are reaching the point where it is economically sensible for the average person to invest in an Electric Car, considering the costs, range and re-charge times. There are still challenges however. Battery design is a big challenge, OEMs will be investing significant design-to-cost efforts into this major component in the years ahead.
With the exception of the Nissan Leaf, most electric vehicles require sophisticated liquid cooling circuits to keep their batteries operating properly. This adds to the battery complexity significantly. As of today, EV batteries involve a lot of manual work to produce, assemble and test. There’s a lot of design work that needs to go into developing solutions that can be automated.
Automotive OEMs are masters at not re-inventing the wheel. They have optimized their car frame designs over decodes of research and development to squeeze every penny possible out of the cost to produce these designs. The issue: these designs have been optimized for ICEs, transmissions, exhaust systems etc. EV’s require an entirely new approach to the design. Expect to see EV costs continue to fall over the coming years as OEMs develop better, more efficient means of producing them.
As EVs become more ubiquitous, innovative solutions will be required to produce them, and their powertrain components efficiently. Partners like Innovative Automation can help OEM’s by bringing a depth of automation experience to the table. Design for automation is a big consideration in EV powertrain components, and it’s a trend that we expect to see grow over the next decade.
The electric vehicle transmission systems consist of a motor, inverter and battery and these play a major role in the overall working mechanism:
- When a 3 phase input is given to stator it creates a rotating magnetic field and hence induces a current in rotor and it starts rotating. The speed of induction motor depends on the frequency of AC supply, by changing the frequency of power supply, the speed of drive can be changed.
- The IC engine requires speed varying transmission whereas electric vehicle can work on any speed, it does not require a speed varying transmission.
- The power generated in the electric vehicle motor is transferred to a drive wheel via gearbox. The EV uses single-speed transmission because the motor is efficient in wide range of condition.
- The output speed of motor is reduced in two steps that is speed reduction and torque multiplication.
- Open differential can control torque rather than slip differential, the arrangement of differential is another important feature of electric vehicle.
- The traction control of differential can be overcome by two methods that is selective braking and cutting the power supply
- EV can be run by first pedal, it saves huge kinetic energy in the form of electrical as soon as acceleration pedal is applied and hence regenerative braking is introduced in electric vehicle. During regenerative braking, motor acts as generator so wheels drive the motor
- Motor rotor speed less than rmf speed
- Generator rotor speed greater than rmf speed
- The generated electric energy can be stored in battery after conversion.
- Opposing electromagnetic field acts on the rotor, so drive wheel and car will slow down so that vehicle stopped can be controlled using single pedal
- Electric vehicle has planetary gear set and torque converter instead of clutch pack
As mentioned above, the EVs have only one driving gear (a step-down transmission) because an electric induction motor is efficient from 0 RPM all the way up to around 6,000 RPM (a speed which a car will perhaps never need to run at!). The opposite of ICEs, induction motors generate the vast majority of their torque, which is needed for acceleration, at 0 RPM, and are most efficient at power generation at high RPM, which is needed for cruising. In a frictionless world, it would be helpful – but still not necessary – for an EV to have multiple gears, as fuller advantage could be taken of the motor’s peak efficiency. But for the foreseeable future, adding gears would only complicate a simple, reliable system.
In reality, there is no logical reason for a clutch to exist in an electric car. An electric motor can’t stall, which is why a clutch is needed in a traditional internal combustion engine in the first place, so adding a clutch to an electric car doesn’t make rational sense.
RESEARCH WORKS CITED
- Ehsan, M., Gao, Y., & Gay, S. (2003). Characterization of electric motor drives for traction applications. in Proc. Industrial Electronics Society, IECON’03, 891-896.
- Dynamic modeling and control of hybrid electric vehicle powertrain systems. Published in: IEEE Control Systems Magazine ( Volume: 18 , Issue: 5 , Oct. 1998 )
- A comprehensive overview of hybrid electric vehicle: Powertrain configurations, powertrain control techniques and electronic control units, KÇ Bayindir, MA Gözüküçük, A Teke – Energy conversion and …, 2011 – Elsevier
- Hybrid electric powertrain including a two-mode electrically variable transmission, AG Holmes, MR Schmidt – US Patent 6,478,705
- Electric and hybrid electric powertrain for motor vehicles. B Roethler, M Berhan – US Patent 7,238,139, 2007
- Electric continuously variable transmission. TC Bowen – US Patent 6,371,878, 2002
- Torque fill-in for an automated shift manual transmission in a parallel hybrid electric vehicle. RC Baraszu, SR Cikanek – Proceedings of the 2002
- Design and Assessment of Battery Electric Vehicle Powertrain, with Respect to Performance, Energy Consumption and Electric Motor Thermal Capability
|introduction and explanation of parameters of EV transmission system|
|Explanation and theoretical calculations of EV at different conditions(slope and parallel road conditions)|
|Different variants and its calculations of EV transmission system|
|Selection of Battery , Range Calculation & C Rating|
|New Folder 3rd day Shoot|
|battery system p1 (002)||00:00:00|
|Battery System p2 0003||00:00:00|
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