Electric car range and generator

[Ken Ibold]

This has been driving me crazy. Someone please educate me.

On the market there are hybrids, plug in hybrids, all electric cars. Each has a different kind of strategy for squeezing out mileage, but one strategy I have not seen is something similar to what trains use.

Would this work: You have an all electric car that runs only with electric motors (like the Leaf, only not as dorky, or the Tesla, only not as over the top expensive). Let's say its batteries store enough juice to go 75 miles. You also have an onboard generator that does not link to the drive gear, as on the Volt, only charges the batteries.

The car has two modes: Local and Travel. In local mode, it runs on batteries alone. This gives you your commute to/from work on all electric. However, for those times when you need more range, the Travel mode activates the onboard generator. The generator produces, say, 30kW, which is enough to replace the 45 hp or so it takes to drive the car at 75 mph, plus a small margin for accessories or to keep the house batteries charged up. The batteries handle acceleration etc., so the generator can run at its most efficient speed at all times.

What is the flaw in this notion (which I do not see) that has prevented the automakers from trying this?

 

[Henning]

No worries, it's the way I would do it, however I would have the genset be removable to save the weight when not needed.

 

[MAKG1]

Only inertia. Maybe some critical patent.

There is a lot of sunk cost in transmissions and chassis design that assume a gasoline engine driving a shaft.

But that type of hybrid has been around for many years, and is known to work well. You can design the engine for fixed RPM which dramatically simplifies tuning.

I've also had a thought that, with a decent controller, that could make a low weight (and low CG) AWD. Connect four electric motors directly to the drive wheels. No differentials, no transmissions, but high torque and individual control. The main issue there would be protecting the motors from rock hits, but Unimog has a nice solution for that, too.

 

[Henning]

Only inertia. Maybe some critical patent.

There is a lot of sunk cost in transmissions and chassis design that assume a gasoline engine driving a shaft.

But that type of hybrid has been around for many years, and is known to work well. You can design the engine for fixed RPM which dramatically simplifies tuning.

I've also had a thought that, with a decent controller, that could make a low weight (and low CG) AWD. Connect four electric motors directly to the drive wheels. No differentials, no transmissions, but high torque and individual control. The main issue there would be protecting the motors from rock hits, but Unimog has a nice solution for that, too.

Wheel motors and regenerators are already here. However they are at higher risk of damage rather than lower.

 

[MAKG1]

No worries, it's the way I would do it, however I would have the genset be removable to save the weight when not needed.

I doubt the weight would be significant compared to the battery pack. You can make a pretty light engine, especially if you allow it to run unattended (why not?). VW 1600s weigh barely 80 lbs, and that's 1960s technology. Weight is dominated by the crank and flywheel (which must be steel), and that can go down with V-type or opposed design, smaller high rev pistons (short stroke), etc.

 

[Henning]

I doubt the weight would be significant compared to the battery pack. You can make a pretty light engine, especially if you allow it to run unattended (why not?). VW 1600s weigh barely 80 lbs, and that's 1960s technology. Weight is dominated by the crank and flywheel (which must be steel), and that can go down with V-type or opposed design, smaller high rev pistons (short stroke), etc.

30kw genset a weigh a few hundred pounds. That makes a difference in around town stop and go power consumption on the commute. It would be very easy to rig as a removable pod.

 

[ScottM]

The car has two modes: Local and Travel. In local mode, it runs on batteries alone. This gives you your commute to/from work on all electric. However, for those times when you need more range, the Travel mode activates the onboard generator. The generator produces, say, 30kW, which is enough to replace the 45 hp or so it takes to drive the car at 75 mph, plus a small margin for accessories or to keep the house batteries charged up. The batteries handle acceleration etc., so the generator can run at its most efficient speed at all times.

What is the flaw in this notion (which I do not see) that has prevented the automakers from trying this?

Isn't this exactly what the Chevy volt does?

http://www.chevrolet.com/volt-electric-car.html

With the extended range Volt, you don’t have to choose between electric or gas. You have the option of both. First is the advanced lithium–ion battery that allows you to drive gas-free for an EPA-estimated 38 miles. But Volt doesn’t stop there.
There’s also an onboard gas generator that produces electricity so you can travel a total of 380 miles on a full charge and full tank of gas†. Now that’s long-range savings.

 

[flyingron]

They exist. The Fisker is a pluggable pure series hybrid. The motor when operating only generates electricity for the rest of the system, it is not mechanically connected to the wheels.

And the original poster was right in that the volt can clutch in the gas engine to the drivetrain when it's advantageous to do so. At some speeds the mechanical coupling is less wasteful than an electrical one. The Fisker doesn't have a direct connection, but it does fire up the the engine in "performance" mode to boost the power available even when the batteries are charged.

If you've spent time looking at EV design, you'll find that weight is a big issue and they cut corners on things like rolling resistance of the tires, etc...

That being said, I got the opportunity to drive a Tesla S for about 45 minutes (all while being filmed and interviewed). Pretty darn cool.

 

[MAKG1]

30kw genset a weigh a few hundred pounds. That makes a difference in around town stop and go power consumption on the commute. It would be very easy to rig as a removable pod.

You're asking a "soccer mom" to R/R a few hundred pounds?

You'll need a winch or crane. No one is going to keep that in their garage.

You're going to need to get it below 50 lb to be feasible for end users. And if it's not feasible for end users, what's the point of making it removable?

 

[jhausch]

Isn't this exactly what the Chevy volt does?

http://www.chevrolet.com/volt-electric-car.html

Not exactly. The piston engine has a means of mechanical connection to the drive train. At least that is how it looks to me. As far as I am aware, there are no "series hybrids" like a train or train+batteries.

One would think that a nice small turbo-diesel genset operating a peak efficiency would be a great solution, but you are adding the extra weight and cost of, essentially, two electric motors rather than one (1 on the genset acting as a generator and 1 on the power train acting as the prime mover).

I would suspect many people have invested many hours and dollars evaluating the feasibility and likely acceptance of a car where the motor kicking in would likely only slow the rate of net discharge during a "long" drive. Then, if you do run out of gas, you can't add a couple gallons and go... you would need to add the couple gallons, then wait for the genset to get enough juice in the batteries to get you moving.

Further, on a series-hybrid system, I suspect the motor would kick on randomly and regardless of vehicle speed, and then hum along at full speed when the CPU decides the batteries need topping up. The motor silencing/isolation would need to be really really good because that motor would be likely turning fast and under (for it) heavy load to actually be at peak efficiency.

Only speaking from loose observation here, but I think the Honda and Chevy parallel-hybrid approach uses a big motor/generator attached to the crank (perhaps via clutch); whereas the Toyota (and, via license, Ford) parallel-hybrid approach uses the electric motor to spin the ring gear of a planetary gearbox as more a part of the transmission. Both seem to be capable of using the elec motor for generation, regen, and starting.


-Jim

 

[Ken Ibold]

Isn't this exactly what the Chevy volt does?

http://www.chevrolet.com/volt-electric-car.html

The Volt's generator does charge the batteries, but it also directly couples to the drivetrain during extended highway cruising. That, in my mind, is an added complication (weight, cost, reliability) that should not be necessary.

Trains have been electrically driven with diesel onboard generators for decades. That's the "Travel" mode.

And anybody else notice people who drive Volts seem to love the low end torque. Everyone I see wants to race me away from lights regardless of whether I'm in the Porsche or on the bike.

 

[Ken Ibold]

They exist. The Fisker is a pluggable pure series hybrid. The motor when operating only generates electricity for the rest of the system, it is not mechanically connected to the wheels.

Cool thanks. But it's north of 100K just like the Tesla.

 

[Henning]

You're asking a "soccer mom" to R/R a few hundred pounds?

You'll need a winch or crane. No one is going to keep that in their garage.

You're going to need to get it below 50 lb to be feasible for end users. And if it's not feasible for end users, what's the point of making it removable?

Nope, you can build it as a 'drive in/out pod with legs that slips into the folding floor trunk.

 

[jhausch]

You're asking a "soccer mom" to R/R a few hundred pounds?

You'll need a winch or crane. No one is going to keep that in their garage.

You're going to need to get it below 50 lb to be feasible for end users. And if it's not feasible for end users, what's the point of making it removable?

I could see a set up where the vehicle could drop and retrieve the genset semi automatically and w/o a lot of human lifting.

Picture a front or back of a car hinging in such a way that the bumper/rear "clip" swings up, the car squats to rest the genset module on the ground. The vehicle or the genset is separated (idiot proof self aligning electric and mechanical couplings required...). Voilá...

I would have the fuel tank as part of the genset module, too.

Neat idea to not carry it when not needed, but I concede that what I described would be very difficult to do.


-Jim

 

[Henning]

I could see a set up where the vehicle could drop and retrieve the genset semi automatically and w/o a lot of human lifting.

Picture a front or back of a car hinging in such a way that the bumper/rear "clip" swings up, the car squats to rest the genset module on the ground. The vehicle or the genset is separated (idiot proof self aligning electric and mechanical couplings required...). Voilá...

I would have the fuel tank as part of the genset module, too.

Neat idea to not carry it when not needed, but I concede that what I described would be very difficult to do.


-Jim

Perfectly simple actually.

 

[N747JB]

Ford has 3 types of electric vehicles, the traditional hybrid that will use the battery power when it's available and it's charged from the gas engine. A plug in hybrid, referred to as "energi" models that travel 20-25 miles on the battery alone and then switch to a more traditional gas/electric power. The third is the electric Focus which is total electric and has a range of approximately 75 miles. All have their pluses and minuses, for someone living in town the pure electric makes sense, especially if another vehicle is available for vacations. The plug-ins are supposed to get 90+ eMPG also great for cities. The traditional hybrids are what we have the most demand for, and customers are reporting 40-55 MPG with them.
The biggest issue with these type of vehicles is the cost to design the drivetrains and batteries, not to mention keeping the EPA happy!

 

[jhausch]

Perfectly simple actually.

And extremely complex to engineer well enough to have it work at the simplicity and reliability level expected of modern automobiles.

As I tell customers all the time, "It's easy. All it takes is time and money."


-Jim

 

[jhausch]

A plug in hybrid, referred to as "energi" models that travel 20-25 miles on the battery alone and then switch to a more traditional gas/electric power.

I would like to know more about these.... Interesting.
I wonder if this is a truly unique configuration, or just a variation on parallel-hybrid....




-Jim

 

[MAKG1]

And extremely complex to engineer well enough to have it work at the simplicity and reliability level expected of modern automobiles.

As I tell customers all the time, "It's easy. All it takes is time and money."


-Jim

Yup.

The first reaction I had to the description is, "gee, what could possibly go wrong with that?"

Running over one's genset seems to be the starting point.

It's a clever, but seriously half-baked, idea. That's how ideas get started, but it's by no means obvious that it's feasible. Most clever ideas don't work.

 

[Henning]

And extremely complex to engineer well enough to have it work at the simplicity and reliability level expected of modern automobiles.

As I tell customers all the time, "It's easy. All it takes is time and money."


-Jim

Not really, all the components are commercially available. This isn't rocket science. You build the generator pod in a half egg shape pointy end forward to slip into its slot in the back of the car. That slot has fold down doors to use as a trunk when not occupied by the genset pod. As you back in the floor lifts and the pod slides into it's rails and latches in, then the hydraulic or electric actuated legs retract and off you go. You can have an automatic or manual plug in to the car's electrical system.

 

[Capt. Geoffrey Thorpe]

The Volt's generator does charge the batteries, but it also directly couples to the drivetrain during extended highway cruising. That, in my mind, is an added complication (weight, cost, reliability) that should not be necessary.

Direct mechanical coupling is more efficient than generating electricity then sending it to the electric motor. EPA fuel economy numbers trump purd near everything else.

 

[Capt. Geoffrey Thorpe]

I would like to know more about these.... Interesting.
I wonder if this is a truly unique configuration, or just a variation on parallel-hybrid....

-Jim

http://www.ford.com/cars/fusion/trim/seenergi/

A more capable electric machine, more battery capacity, additional operating mode (charge depletion), sealed fuel tank.

 

[Henning]

Direct mechanical coupling is more efficient than generating electricity then sending it to the electric motor. EPA fuel economy numbers trump purd near everything else.

Yes, but if you have both a generator running and the mechanical coupling, the advantage decreases. An experiment I'm looking to do with my buddy and his Mitsubishi electric is to load up a 1kw portable Honda generator and see how much range we can get out of it.

 

[gismo]

What is the flaw in this notion (which I do not see) that has prevented the automakers from trying this?

AFaIK, the flaw is that the genset/ electric motor combination is less efficient than a transmission and possibly (not so sure on this one) heavier as well. I suspect that a hybrid that got poor gas mileage on trips when the gas engine was used wouldn't be very popular or successful.

If and when someone develops a lightweight, affordable, and rugged in-wheel motor that might change but for now electric cars usually still have a drivetrain so all that's needed to drive the car from a gas engine is a transmission.

I like Henning's idea of a genset "cartridge" so you could leave the extra weight in the garage when the electric range is sufficient. Maybe even include a substitute low power genset for "emergency use" when the main one is left behind and you're running short on juice.

 

[Henning]

What I don't understand is why they don't cover the electric cars with PV cells so it can charge in the parking lot.

 

[Skylane81E]

Sigh, another person who falls for the "volt is a traditional hybrid" propaganda

Volts engine has no mechanical connection to the wheels

 

[flyingron]

What I don't understand is why they don't cover the electric cars with PV cells so it can charge in the parking lot.

Because the charge would be negligable. I had the idea of building a "solar carport" and even covering the carport with cells and angling them to the best advantage, you'd not be able to charge the car in any reasonable amount of time while it was parked there. You'd need to put some sort of storage over a longer duration or grid tie it.

 

[Skylane81E]

What I don't understand is why they don't cover the electric cars with PV cells so it can charge in the parking lot.

Direct sunlight at 100% efficiency is about 1/8 BHP over the surface of a car.

 

[flyingron]

Sigh, another person who falls for the "volt is a traditional hybrid" propaganda

Volts engine has no mechanical connection to the wheels

You are the one who seems to be the victim of propaganda or ignorance. As pointed out by several of us, the Volt will clutch the gasoline motor into the traction system when it is advantageous to do so. It's not like a full parallel drive hybrid, or even as elaborate of a power-split system like the Prius Synergy drive, but it can drive the wheels in conjunction with the electric motor.

You can quibble as to whether the arrangement is as Chevrolet calls it "an extended range electric vehicle" or a "hybrid".

 

[Henning]

Sigh, another person who falls for the "volt is a traditional hybrid" propaganda

Volts engine has no mechanical connection to the wheels

So you're saying the Volt is straight up electromotive traction drive right? That's what I though, but I haven't looked that deeply into them.

 

[Henning]

Direct sunlight at 100% efficiency is about 1/8 BHP over the surface of a car.

Right, but if it's parked outside of work all day it adds xx% to your between charges range.

 

[flyingron]

So you're saying the Volt is straight up electromotive traction drive right? That's what I though, but I haven't looked that deeply into them.

Here's a pretty good description of how it works...
http://translogic.aolautos.com/2010/10/11/gm-comes-clean-on-volt-drivetrain/

 

[Daytonabch04]

http://www.ford.com/cars/fusion/trim/seenergi/

A more capable electric machine, more battery capacity, additional operating mode (charge depletion), sealed fuel tank.

I bought a Fusion Energi last weekend and already put 600 mi on it. I downgraded from a luxury SUV and love it. I can get 21 mi on all electric with no gas. I'm averaging 38-44 mpg. My eMPG is much higher with the electric calculated in.

 

[Henning]

Here's a pretty good description of how it works...
http://translogic.aolautos.com/2010/10/11/gm-comes-clean-on-volt-drivetrain/

Not super clearly written, but it sounds like the engine is driving a generator which will supply electricity to the traction motors to supplement the battery power without going through the battery first while also shunting power to the battery? I don't see where they are saying there is a mechanical link to the transmission. I may be reading it wrong.

 

[jhausch]

Sigh, another person who falls for the "volt is a traditional hybrid" propaganda

Volts engine has no mechanical connection to the wheels

From article

It's the final mode that's come as a bit of a surprise, because it is in this extended range mode where both electric motors and the gasoline engine get connected to drive the wheels. However, GM is still maintaining its stance that there is "no direct mechanical linkage from the engine to the wheels," while explaining that "the Volt is always propelled with electric power delivered by the traction motor."

While there is still likely a semantic argument to be waged here -- whether we call it a plug-in hybrid or an extended-range electric vehicle is a discussion for another day -- the bottom line is that the Volt employs a sophisticated transmission to eke out every efficiency from its drive system.

-Jim

 

[l8evator]

What I don't understand is why the great coaches are doing commentary on TV broadcasts, telling us how the game should be managed and the plays executed. I don't understand why the clever engineers are "out here" instead of in the design studios. I don't understand why the great lawyers are "out here" and not on the bench. I don't understand why the best accident analysts are "out here" not working for the NTSB.

I guess I make more progress in understanding things when I start with something like "I wonder why they did that?" I want to know what trade-offs they made. I like to chase after the reasons behind the trade-offs, whether cost, reliability, liability, political intrigue, marketing, or something I never even imagined. I always assume there are trade-offs and that I probably don't understand them at the outset. I don't always accept the status quo, but I'd like to think even the decisions that turn out to be mistakes were made with at least a modicum of intelligence behind them.

I suppose this approach is easier for me because I'm not a coach, not an engineer nor a lawyer. Perhaps I'm just naive.

Scott

 

[Doggtyred]

While you guys are pondering the economies a gas hybrid that gets maybe 40 to the gallon on a good day, I get 40 mpg with my diesel Jetta.. at 70 mph. closer to 50 mph at 60 mph. Pure electric may be more economical but the 550-600 mile range sure is convenient.

 

[Henning]

While you guys are pondering the economies a gas hybrid that gets maybe 40 to the gallon on a good day, I get 40 mpg with my diesel Jetta.. at 70 mph. closer to 50 mph at 60 mph. Pure electric may be more economical but the 550-600 mile range sure is convenient.

I used to get 52mpg in my 1976 Honda Civic 1200, same with my 72 Datsun 1200 flogging the **** out of them and running 70 down the highway with no overdrive or around town. I used to get 27mpg in a 63 Chevelle with a 283, 2GC carb and a Powerglide, plus I could make it beat emissions requirements for an 83 Chevelle without using a catalytic converter. However we didn't have to deal with alcohol in our gas either.

Diesel used to be a good deal, but now the price premium on the fuel has negated the advantage.

My buddies Mitsubishi electric gets 120eMPG, whatever that is supposed to mean.

 

[Jim Logajan]

On the market there are hybrids, plug in hybrids, all electric cars. Each has a different kind of strategy for squeezing out mileage, but one strategy I have not seen is something similar to what trains use.

Trains ... hmmm ... so I searched for "diesel electric automobile" and suggest you do too. The search yielded these links, showing some existing and one proposed diesel-electric hybrid cars:

http://www.carsdirect.com/green-cars/the-best-diesel-electric-hybrid-car-a-comparison-guide

http://en.wikipedia.org/wiki/Aptera_Motors

 

[Silvaire]

Trains ... hmmm ...

I don't think diesel/electric trains are a good comparison as they are all about torque rather than efficiency. They don't even have an electrical storage medium and even the regenerative braking is blown off as heat through an exchanger into the atmosphere.

Volkswagen designed a car similar to the Volt a few years ago but decided it wasn't economically viable due to the cost of having to have an internal combustion engine, a generator and an electric motor as well as the battery pack. It was a good car, just cost about three times as much as a conventional model.