Category Archives: Electric/Hybrid

Interesting links dealing specifically with electric and hybrid transportation that doesn’t suck.

Hybrid Transmission Architecture, Controls and Mileage

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If you’re a typical car guy, you probably don’t find driving hybrids very interesting. I don’t blame you. But just because the driving experience is usually sterile and unengaging shouldn’t undermine the fact that some serious engineering goes into making them work. This is a breakdown of the 2nd gen Prius transmission by an instructor at Weber State University where they work with Toyota on degree programs specifically having to do with the Hybrid Synergy Drive system.

The transmission is responsible for blending 3 different power input/outputs. The engine provides power to drive the car and to recharge the batteries, but it also requires power input to get started after it’s been turned off at stops. The two permanent magnet AC motors are referred to as Motor-Generators (MG1 and MG2) because they can easily be switched between propulsion and regeneration. MG1 is the smaller of the two electric motors and it acts as a starter, alternator and mainly as a generator fed by the engine power to recharge the battery pack. It’s also responsible for driving the car in reverse since that doesn’t require as much power. MG2 is the larger electric motor that is directly connected to the car’s wheels. It helps propel the car and is also responsible for regenerative braking. The engine and the two electric motors are tied together with a planetary gear set (ring gear, sun gear and planetary gear carrier). The video does an excellent job explaining how that works using the actual parts from the transmission.


The basic hybrid transmission architecture found in the Prius drive train was developed by a Japanese transmission company called Aisin and it is used by both Ford and Toyota. Does that mean that a Ford hybrid and a Toyota hybrid will get the same gas mileage since their hybrid systems have similar components and formats? Nope. Getting the best gas mileage is a complex puzzle of matching the power and torque requirements of the car with the efficiencies and operating points of the gas engine and electric motor. The gas engine is the most efficient at constant rpm and load like on highway driving. The electric motor provides better low end torque but it still has an optimum load and rpm. The planetary gear architecture basically allows an infinitely adjustable blend between the electric motor and the gas engine but you still need to know how to efficiently use it. When is the best time for the generator to use the engine power to recharge the battery pack? How low can the battery charge go before it needs to be recharged? Will using the electric motor’s low speed torque give the best overall gas mileage once the battery pack has been recharged? Should the gasoline be used to charge the battery or will more work be done if the same gas is burned to drive the wheels? It’s up to the software engineers to program the drive train controllers to figure out what the best combination of power input and output is for any situation the car sees. A good portion of the car’s price tag goes into the R&D and data crunching to figure these things out.

Check out Motor Trend’s latest episode of Head 2 Head. They take a look at the Toyota Prius V and the Ford C-Max hybrid. The guys do their usual excellent reviews of the cars, but the interesting part begins when the discussion turns to the gas mileage. Both cars didn’t get what the EPA rated them for and the Prius got the better real world mileage despite the C-Max having the better rating.


Even on a regular gas car, your mileage can vary massively based on where you drive the car (hilly terrain, higher elevations, traffic etc.) and how you drive it (pedal input smoothness, braking early, coasting etc.). The purpose of the EPA testing is not to tell you exactly what kind of mileage you will get, but to give you a standardized comparison between different cars. If you’re shopping for a hybrid, the emphasis really shouldn’t be on flat MPG figures as the Motor Trend guys have demonstrated. Your mileage will be based on how flexible your hybrid drive systems is. The car that will return the better gas mileage is the one that can consistently be the most efficient in a wide spectrum of driving conditions. It’s all in how the controls system (electric motor and gas engine blending) software is tuned.

The Motor Trend guys suspected that the Ford C-Max was tuned to rely on electric power up to a higher speed specifically to do better on the EPA test which ironically made it perform worse in real conditions. This result enforces story a few years ago about Prius drivers who would try to drive slower in an effort to keep the transmission from turning on the gas engine. This technique ended up giving the drivers worse gas mileage because it was completely depleting the battery pack. The system would then have to turn on the gas engine and run it at full recharge through the generator which reduced the overall mileage. The moral of the story is to do your research. What you want to look for is gas mileage consistency. What are other owners getting? Are people in different situations getting similar mileage or do the results vary a lot? My advice would be to put less emphasis on the EPA numbers and high score mileage numbers and try to find the hybrid that returns the least deviation in mileage numbers among a large number of owners. What you need to find is which automaker’s engineers did the best job programming the hybrid system to react to real world driving conditions. It’s a whole new ballgame for evaluating how well cars work. Now you have to look at how well the car is bolted together as well as how refined and effective its software package is.

Sources: Motor Trend and Weber State Automotive on YouTube

How a Lead Acid Battery Works

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A friend of mine asked my advice on using cheap car batteries to put together an electric motorcycle. This video about lead acid batteries is pretty helpful in explaining why car batteries are not ideal for energy storage on electric vehicles:


The important thing to pay attention to is the energy density vs. power density comparison. Your typical car battery is built for outputting a large amount of cold cranking amps (CCA) for a brief duration to start your engine. From there it is immediately recharged by your alternator once the car is running. For that reason, the lead plates are very thin. If you ask a car battery to continually discharge over a long period of time to a very high depth of discharge (DOD), you will permanently damage the plates and the battery’s ability to hold energy.

Lead acid batteries are a good way to build an inexpensive electric vehicle, but it’s pretty important to use a deep cycle battery. Odyssey batteries don’t count, either. They are sold as “deep cycle” batteries, but they are absorbed glass mat (AGM) that are even more susceptible to damage from deep discharging. The way to go is golf cart batteries since they are designed with much thicker lead plates to safely discharge a large percentage of their stored energy. The EV community seems to favor batteries from the Trojan Battery Company. Your best bet will be to try and arrange a batch buy at a local dealer since they’ll be really expensive to ship due to weight. Generally speaking, lead acid batteries will give you a much cheaper battery pack compared to lithium ion, but you only get about half the benefits in terms of weight, discharge performance and longevity. They also need constant maintenance in terms of needing to be watered with steam distilled water about once a month. I would recommend doing a lead acid battery EV on a light truck so you can mount the heavy batteries (somewhere in the neighborhood of 1200 extra pounds) between the frame rails or in the bed and because there will be a lower performance expectation. Another thing to keep in mind is that we’re currently able to recycle lead acid batteries very well simply because they’ve been around for a long time.

Source: Engineer Guy Video on YouTube

Steam Whistle Brewing’s Retro Electro

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The Retro Electro is a 1958 Chevy Apache that was restored and converted to an electric vehicle over about a year and a half by Vancouver based Steam Whistle Brewing Company. Steam Whistle is known for their fleet of vintage vehicles used for their local deliveries. The idea for the Retro Electro was born at one of their employee round table discussions on how to make the company more environmentally responsible. It’s powered by what appears to be Thundersky batteries and an Azure Dynamics AC-90 AC motor and inverter connected directly to a Ford 9 inch rear end. They claim the setup makes 90 horsepower and 456 foot-pounds of torque (this figure is probably at the wheels with the short ring and pinion gearing) in the videos. Steam Whistle also made sure they weren’t simply redistributing their carbon footprint by making sure the power used to charge the truck came from a local windmill farm. Breathing new life into a cool old truck with an electric conversion is just awesome. Check out their 7-part video series detailing the whole project.

Part 1: Birth of the Idea

 

Continue reading →

Tesla Model S – Automobile of the Year

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Automobile Magazine has just announced the Tesla Model S as their 2013 Automobile of the Year. This is big news for the electric vehicle world because the Model S has won out in direct comparison to equivalent gasoline cars. The car is praised for universally recognized strengths and not for being the best of a standard that was lowered for EV’s. Tesla has finally given the world an electric car that is designed and executed well enough for regular customers to consider purchasing it as a daily use car and not because it’s a novelty item. An EV that’s better than a gas car? It can be done.


Automobile’s full written article about the Tesla S can be found here. I also found this bonus footage of the impromptu drag race between the Model S and the BMW M5:


Source: Automobile Magazine on YouTube

2012 Fisker Karma – Car and Driver

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Car and Driver’s contributing editor Csaba Csere takes the 2012 Fisker Karma out for a test drive as well as chatting with Henrik Fisker about the first car from his company. The Karma has always been kind of a oddity in the electric vehicle world because Henrik Fisker comes from a design background. When you listen to Elon Musk talk about Tesla’s cars, the focus is always on technological innovations and engineering. During Fisker’s interview with Csere, they discuss how the Karma has larger wheels and rides lower than other cars in the category. Csaba has to talk about the vehicle architecture, power, range and mileage on his own later in the video. In many ways that demonstrates the things I dislike about the Karma. Yes the car looks great, but is being ugly the main reason EV’s don’t have social acceptability?

The problem is that many of the important engineering aspects of the Karma took a back seat to it’s styling. The car is massively expensive yet weighs as much as a Chevy Tahoe and gets mid 20’s mpg when the Ecotec engine is recharging the batteries on the go. Csere says the drivetrain feels unrefined to boot. That means that beyond making a fashion statement, there is no real incentive for somebody to spend the extra money for the Karma over a regular luxury car that costs far less. That’s why I don’t see Fisker’s customer base extending very far beyond Hollywood movie stars. The worst part about the way Fisker has developed this car is that it reinforces all of the worst stereotypes about electric vehicles being expensive and mediocre technology that taxpayers have footed the bill for.


Source: CAR and DRIVER on YouTube