GM: Volt reaches 2 million miles, 1.3 million of them gas-free

Sorry for my imprecise use of the word "boondoggle", but austingreen and sagebrush above have the right of it as far as the answer to your question. (btw, I am a Volt owner)

 

Prius PHV power in that graph does not match with the dyno PencilGeek did (below). Both the cordless and PHV have 134hp peak in spec so the graph should be similar but they are not. Perhaps MT graph only show the 98hp gas engine power?

It is also interesting to see Volt's gas engine power does not peak until the top speed.

 

It isn't a graph of bench horsepower. The engine likely peaks earlier, and the peak in the graph is just the result of more and more engine power going to the wheels as speed increases.

As to the Prius, MT had a pre-production plug-in. Perhaps its actual specs don't match paper or the battery may have been depleted.

 

Why do you think so? We can't really tell from comparing the blue and red lines.

It is possible the battery provides less power since it is "depleted" and the gas engine makes up for it. If that were true, why then would the total power peak at 100 mph? The battery power should fade just like the blue line indicates.

I think the clutch engaged and ICE output direct mechanical power between 60 and 70 mph. Due to the lack of conversion loss, the hp at the wheel got a bit of the boost. ICE RPM is now tied to the wheel speed therefore you see that straight incline line from 70 to 100 mph.

If I am right, Volt can't go past 100 mph due to mechanical limitation - not limited electronically.

 

But you're only assuming the peak is at at 100 mph because of the graph which stops at 100 mph because of the electronic limit that won't allow testing beyond that. I suspect you are right and there is a mechanical limit, but we have no way of knowing if it is at 100, 105 or 110.

I can tell you I have hit 100 mph and a message appears on the screen saying the speed is limited to 101 mph. So there is at least some software recognition of the limit, it doesn't just mechanically peter out.

 

It is electronically limited.

 

I'm also going on reports of the ICE operating in narrow rpm ranges, at least when decoupled from the drive train. The Volt, in theory, could run the engine at peak power as soon as CS mode engages regardless of vehicle speed.

Even in traditional cars, you can't infer the engine's peak power from readings at the wheel because of the transmission in between. You can reach peak ICE power in a manual car while still in 1st gear.The engine's power in linked to its rpm, not vehicle speed.

To flip the question around, why do you think we can know the engine's peak power from a measurement that has it blended with a motor?

 

Because we have a baseline. The blue line indicates what the battery is capable of. The red line indicates the combined output. Just look at the area between the two lines. That suggests the gas engine output. The big assumption is the battery is used as hard (and able to match the output) in CS mode than in EV mode.

Looking at both MT and PencilGeek graphs again, Volt in EV mode puts out about the same hp at the wheel as a cordless Prius above 80 mph.

 

A very polite way to say that I am wrong.

Any engineering references to back it up?

 

It's not tied to the wheel speed directly because it's a planetary drivetrain. Doesn't the Prius behave the same way?

MT also posted an ICE RPM chart somewhere but it was time compressed and difficult to read. We would really need to see the MG2 RPM to understand what's going on.

 

I would say: what the electric motor is capable of. The battery is indifferent to the car speed.

 

You know I strive for politeness.

Well, it clearly stops accelerating and displays "speed limited to 101" at 101mph, so I'm a first person reference I guess. It's still accelerating at 101 even in CD mode. More strongly (for what it is) in CS mode.

I think what you're wondering is "is the electronic limit in place for mechanical reasons?" I have no data to say one way or the other.

The battery cares about discharge rate. I've been curious how long the car will let you run 101mph in CD mode. Until it switches to CS? Or will it shut down the fun sooner as things heat up?

 

We could use the area between the lines to speculate on the ICE, but that's all it is. Hybrids are simply too complicated (remember, GM lied about the Volt's simplicity ) to do more.

Here's some more speculation: while it can happen sooner, the Volt's ICE doesn't directly drive the wheels until 70mph. It's probably safe to assume that is how worked during MT's test.

Also, the power output for both modes follow the same curve up to 60mph. This likely because it is just the motor supplying power to the wheels. The differences between the lines is just do to the energy source. Conversion inefficiencies allow the battery to edge out the ICE/generator in power at lower speeds, but the genset can provide more electrons overall and boosts the motor's maximum power.

Power levels out for both modes level out until 60 mph, then the slopes deviate. EV mode drops off, and CS climbs. Why is just guesswork going off the lone chart. Maybe the ICE is now coupled to the drive train, or perhaps the battery is now putting in energy.

Even when we know the ICE is engaged to the drive train, we can't tell what it's exact contribution is to the wheel horsepower do to the nature of the transmission and software. It very well have reached its peak power back at 40 mph, and the system is just juggling how much is going to the motor, wheels, and battery. Not likely, but we can't tell from the graph.

At 100 mph, the only thing I can tell about the car's total power from the graph is it may not have peaked because the slope is still climbing.

 

Battery putting energy to where? Why it is not doing it in EV mode?

 

During CS mode the Volt can use the battery like the Prius, as a boost of on demand extra power. Electricity from both the generator and battery can go to the motor. There's no reason to assume the Volt can't make use of the battery's charge outside EV mode. Mountain mode alters the CS start point to allow for a larger reserve of power in the battery for anticipated extra need.

 

This is all obvious, you still did not answer my question.
In EV mode the power curve drops off above 60 mph, I assume its the capability of the traction motor at high speed that causing it, not the battery capability. Do you have any other explanation to this drop?
If it is the motor, then the climbing power above 60 in CS mode can only be attributed to the ICE being mechanically connected to the wheels (and at the same time reducing, or limiting, the motor speed as the ring gear is no more anchored to the case).
Where am I wrong?

 

Your are assuming the EV curve reflects the motor's total capabilities. The drop is do to the nature of electric motors. However, the source of the motor's power has an effect. We see that in the two curves up sixty. They are similar but slightly different. We know the ICE will couple at seventy. It can happen before that speed. I think the curve would be different it happened here, though.

It very well might be coupling at sixty, but there is the possibility of the motor being powered by both the genset and battery, and this is what is seen in the curve.