[omnimoeish]

So I got an email from GM about the Volt's generator producing 53kW of power.

Here's what it said in my email

Chevy Volt is an extended-range EV, an electric vehicle that generates its own electricity. It will use a 53-kilowatt gas-powered generator (the Range Extender) to provide electricity once the battery charge is nearly depleted. Unlike a traditional hybrid or future plug-in hybrid, the gas engine simply generates electricity to power the electric motor. A large generator you would buy for your house would be somewhere in the neighborhood of 5kW! 53kW could power half your street! Obviously moving a vehicle this size is going to quite a bit of juice.

Does the Volt really need that much power or is it just convenient to use the 1.4L engine because that's the smallest engine they make? The reason I ask is because I'm curious how much excess power will be getting dumped into the battery. I would think you could recharge your battery (especially when driving around town because you would be stopping at lights and stuff which would not let the electric motor drain any power) within an hour or so.

 

[RobertSullivan]

Please read: http://gm-volt.com/2008/09/27/how-charging-of-the-battery-works-in-the-chevy-volt/

 

[misslexi]

I just read the link and find it confusing, to wit:

[my comments in square braces]

"The electricity, at around 50 kw, serves primarily to propel the car [we are using petroleum to travel, no?]. As the driver drives, there may be times when more electricity is made than the motor needs. Guess where that goes? The battery of course. GM doesn’t want to waste energy or unnecessarily use petroleum. As well the regenerative brakes opportunistically may put charge back into the battery.

The generator does not fully recharge the battery. It doesn’t make any sense to, for then you would be using petroleum to travel [huh?].

 

[omnimoeish]

I understand how it works, it just seems like there would be a lot of excess power, maybe not.

 

[G35X]

Omnimoeish,
The answer to your question is not simple, I think.

1) The Volt has a 111kW electric drive unit.
2) The ICE/generator has 53kW of max power
3) The battery pack’s capacity is 16kWh, 8kWh of which is usable.
4) Part of the balance of 8kWh is available for short burst demands.
5) Cruising on a flat highway requires about 15 to 20kW.
6) All the 111kW (about 150HP) is needed to accelerate going up a steep grade.
7) Duration of this max power must be limited because once the battery is depleted the available supply power is 53kW and also (possibly) too long operation at the max power overheats the electric drive unit.

Judging from the above conditions, I think the Volt is quite capable of going around the town even on the float-charging mode with depleted battery with occasional “withdrawals” of the reserve energy from the battery. But, do you have to drive on the truck lane when going uphill on the Interstate? I do not know. (Actually this question is the reason why I joined the forum.) I have seen the first generation Honda Insight slowing down in Ashland, OR on I-5. I have experienced driving a Datsun Sunny, a sub-100HP car, driving up a grade with its speed getting slower and slower even shifting down the gears. Since the terminal speed is determined by the maximum power I think on the Interstate you need more than 100HP to keep up with the traffic.

If the field tests being conducted by GM prove that the Volt is as capable as regular cars with an ICE of about 100HP on the Interstate or off, it will change the rule of the game entirely. The industry just can forget about 150, 200 or even 300HP ICE cars and start using the serial drive design with much smaller capacity battery pack (say, 5kWh) with the ICE/generator (of various sizes but smaller than ICE only application) always running (keep the idling-stop feature, please). The serial design premium can be compensated, if not entirely, by smaller narrow rpm range ICE, absence or simplicity of transmission and cheaper cat converter. This design will certainly improve gas mileage (read: reduction of CO2 emission).

 

[IamIan]

I understand how it works, it just seems like there would be a lot of excess power, maybe not.

Of course there will be excess power... but I think that is intentional... most drivers like haveing more power they they use ... they like knowing they can accelerate up a hill against the wind on a cold rainy day starting at 70MPH and still accelerate 'fast enough' for them to be happy for passing... and for pulling out from a stop going up a hill and being able to pull out faster than the other cars when they feel like 'droppping the hammer'.

They are playing to what the masses want... not what they will actually use.... but you have to play to what they want if you want them to buy your product.

 

[fishmahn]

I understand how it works, it just seems like there would be a lot of excess power, maybe not.

In addition to what G35X said, the ICE will have a few (3? 5?) 'set-points' for generating power. Hypothetically, let's say one will produce 20kw, one 35kw and one full power (53kw) Cruising around in town after battery depletion (approx 30% battery charge) will generally run at the lower-power set point. Extra power will go to the battery, eventually charging it to let's say (hypothetically) 40%, then the ICE shuts down for a few minutes until the battery is depleted to 30% again. The same thing will happen at highway speeds - I presume it will use whichever set-point generates the closest to current power draw with excess going to the battery.

If you start going up a grade the ICE would first switch to maximum power (53kw) if needed and if even more power is required, the battery will provide extra power as needed until the battery is truly depleted (probably not to 0%, more like 5 or 10%), then it will start slowing the car because there's only 53kw available. When you top the hill and don't need full power any more, the ICE will stay at high power until the battery is recharged to 30% then reduce power. That 20% or so of battery charge 'buffer' (about 3-4kwh I'm assuming) should give you over 4 min of 'full draw' power. Normally you shouldn't need all 111kw (150hp) - I would think generally 100hp is enough, so you're only drawing about 1/3 of the max from the battery (under 20kW) which means (I would think) you should get more like 12-15 min of steep hill time. I can't see that being a problem 99% of the time unless you like climbing those hills at 100mph or towing a boat/trailer (in which case you probably shouldn't take the Volt)

I remember reading this here on the site, but I don't recall where. I'm sure I pieced my picture of how it works from several posts of interviews with GM - I'm pretty sure it was on one of Lyle's front-page blog posts from a few months ago. I'm making an assumption about how it uses set-points - but the fact that it would have 'a few' set generation levels was reported from GM. They also reported that it would have enough reserve power to cover over 95% of grades in the US for reasonable drivers (or some such similar wording),

Hopefully this answers your question too, G35X - You should have plenty of power to cruise at 70+ mph up steep grades for several minutes, which should cover 95% of roads in the US. You may run into a situation when a 'perfect storm' of issues - heavily loaded vehicle, steepest, longest grade in the States, and driver with a lead foot - happens, in which case you will end up slowing down after a bit and using the truck lane to get to the top.

Fishmahn

 

[omnimoeish]

Good post Fishmahn. That was the kind of detail I was after I too would think with 30% of the battery power left, which ordinarily should provide about 25 miles of all electric power (extrapolation from the fact that 50% gives it 40 miles) without the gas engine supplementing, you could take some pretty serious hills. There are few elevation gains around Oregon that might give the Volt a run for its money going over the Siskiyou Summit on the Oregon/California Border and Santiam Pass, heading over the Cascade mountain range, but I only drive over them about once every 2 years or so, and even those are too steep.

 

[MrBogey]

A large generator you would buy for your house would be somewhere in the neighborhood of 5kW!

A 5kW genset is actually quite small for a house. To run a whole house you need 15-25kW generators.

 

[FrayAdjacent]

Keeping a heavy car like the Volt moving at 65mph on a highway would probably take ~30kW of energy. Accelerating to 65mph (at least faster than 15 minutes) would take considerably more energy.

It sounds like a lot of energy when you compare it to a lightbulb. Moving a 3000+lb car takes orders of magnitude more energy.

The generator is capable of a peak of 53kW, which would be about half of the energy the motor can take when accelerating with the accelerator floored. The other half of the energy has to come from the battery.

Once cruising speed is achieved, the energy from the battery needs to be replaced, so the output of the generator would have to be higher than the amount of energy needed to maintain a cruise. Otherwise, there would be a loss of performance. Imagine in stop-and-go traffic if the battery kept depleting and depleting. You'd eventually only have the generator to power the vehicle, thus you would be operating with only 50% of the power you had before.

 

[omnimoeish]

Interesting. Although stop and go traffic should even out since there would be regenerated electricity from the brakes (notice I didn't say breaks this time )

Also, it will probably be more efficient at lower speeds when the air resistance is much lower, also, remember that while you're stopped, the generator is still running as efficient as ever, it's not just needlessly wasting the gas its burning.

 

[FrayAdjacent]

Well, stop and go traffic evening out would not be likely. There would be some regeneration, but you can never get back all the energy you put into moving.

At lower speeds, it should be more efficient. If the generator runs at it's most efficient output, some of that energy would go back into the battery. The good thing is, when the engine/generator is running, the energy would not be wasted. It's either making the car move or charging the battery.

I'd suspect in stop and go traffic, if the battery is 'depleted', the generator would turn on and divert energy to the battery when not moving the car, up to a certain point, then it would turn off again.

How exactly it behaves is yet to be seen.

 

[Shaft]

Just a test

Just a test1

 

[omnimoeish]

That was kind of my logic at first, but the current Prius gets better mpgs in town than on the highway simply due to low air resistance and regenerative brakes. I would expect the Prius to get better highway mpg than the Volt all things being equal since the Prius has a transmission that can adjust the gear ratio for faster speeds. I don't know, we'll see.

 

[misslexi]

I get much better mileage on the highway with my Prius. I think mostly because my city driving is all done on a cold or just warmed up ICE. Absolute best MPG is freeway to warmed up, then bumper to bumper crawl all under 40 mph.

The short city trips are a MPG killer.

 

[omnimoeish]

I just got my info from the EPA.

http://www.fueleconomy.gov/feg/hybrid_sbs.shtml

I would think what you're saying to be true though.

The EPA needs to somehow get actual real world drivers to submit their mpg, especially for top 25 best selling vehicles or something so that people can make better educated decisions than one test they ran.

 

[FrayAdjacent]

That was kind of my logic at first, but the current Prius gets better mpgs in town than on the highway simply due to low air resistance and regenerative brakes. I would expect the Prius to get better highway mpg than the Volt all things being equal since the Prius has a transmission that can adjust the gear ratio for faster speeds. I don't know, we'll see.

It does not get better gas mileage simply due to less drag and more regen. With those as the only considerations, there is still a net loss.

It gets good economy in city driving due to the ability to offload a lot of the work to the electrical system - Under low throttle, the ICE doesn't turn on until over 30mph. Offloading acceleration to the electric motor saves a bunch of fuel.


Of course, the situation depends. If enough city driving is done, the battery eventually becomes depleted (again, net loss overall), and then the car relies on the gas engine.

 

[FrayAdjacent]

I get much better mileage on the highway with my Prius. I think mostly because my city driving is all done on a cold or just warmed up ICE. Absolute best MPG is freeway to warmed up, then bumper to bumper crawl all under 40 mph.

The short city trips are a MPG killer.

If the Prius could be hacked to not need to run the ICE until it reaches op temp, it may be more efficient overall.

I've thought about how the Prius would work in my situation: I live in a housing development that feeds directly to a highway. I drive that highway into the city (about 21 miles) then go through downtown to get to my office (about 4-5 miles).

Going TO work would be pretty efficient. The long highway trek would get the engine up to speed and replenish the battery giving me juice to use over the short distance of downtown driving.

On the way home, though, if I go through downtown again, it's slow speeds and lots of lights with a cold engine. Economy would suffer.

(although, I can get on another freeway right from the office, then cut through the city to get back on the original highway to the house)

I'd be curious. If I knew someone that would let me borrow a Prius for a week, I'd test it out.

Right now, I'm seriously considering trying to trade or sell my car in another year to buy a Honda Insight. I bet I'd average 50+mpg.

 

[misslexi]

I've never installed it but I probably will one of these days. It's an EV-only mode modification that allow the Prius to be forced into pure EV mode, the Japanese Prius supposedly has it installed as a standard feature.

EV mode will only be maintained up to 30-35 MPH regardless of this device.

It is only supposed to be used for VERY short trips, like to move the vehicle from from the street to the garage. I've heard that the stock battery will carry the Prius about 1 mile before it's SOC drops below threshold.

Interestingly, consensus says the way to get the best mileage out of a Prius is to NOT try to stay in EV mode; using the ICE to convert gasoline back to stored electrical energy is not efficient. Rather, it's to get the ICE operating at it's most efficient speed.

In theory I think, the electric drive part of the system tries to allow the ICE to remain at an efficient speed as much as possible, and to provide a much needed torque boost for short bursts, something the ICE is not good at.

Some folks who understand the system way better than I do are able to exploit it to gain remarkably good fuel economy. I'm satisfied with the economy just driving like I would any car, finding the extra effort to hypermile fiddly and distracting. Although I will confess I gave it more thought when gas was $4.30/gallon.

 

[Andy0x1]

Combustion coupling

I'm a bit confused.

Why wouldn't GM couple the combustion engine directly to the drive-train rather then add the extra weight of a dedicated generator?

Coupling the combustion engine to the drive wheels via an input sprag, would allow the combustion engine to de-couple when in EV mode.

Implementing that capability alone, could add 50% more peak power for acceleration, as well as improve the extended range economy

Once charge was depleted below threshold (i.e. 35%) the Gas engine could start, and rev to optimum speed, with the electric motors providing a computer controlled balancing act of regenerative braking / thrust assist depending on acceleration / maintain / deceleration demands.