EV & HV miles doubling up

Yes, both energy sources are driving the car giving you very good gas mpg. However, high speed driving in EV is not the best way to use your EV miles. If you are going on a trip of considerably more than the EV range its best to drop into HV for those high speeds on the highway and save the EV miles for around town.

 

We've come to call that EV-BOOST mode.

The engine starts up at faster speeds, but the system continues to draw plug-supplied electricity from the battery-pack. So, the RPM is very low... which results in very high MPG.

Here's a video which shows that:

MG1 is the larger electric-motor, the one primarily used for propulsion. It's also used for regenerating when braking.

MG2 is the smaller electric-motor, the one primarily used for generating electricity. It's also used for starting the engine.

 

Actually once the vehicle exceeds 62 mph, full EV mode is no longer possible, because the maximum RPM of the MG electric motors has been reached. The gasoline engine has to kick in to prevent over-speed of certain parts of the transaxle.

The reason both EV and HV miles are accumulating is due to the fact that the car continues to benefit from the EV charge, even though it also needs to run in HV mode to protect the transaxle. A more accurate display might be "HV-EV hybrid mode" but that would probably cause endless confusion.

 

Use the HV/EV button near the "gear" shift. There is an indicator above the mph display that shows "EV mode" if you are in EV. The car always starts in in EV when you turn on the car unless the battery is so low there are no EV miles available. You can Always switch from EV to HV, a good thing to do on longer trips as soon as you move up to highway speeds. If you are operating in HV on the highway and want to switch to EV in town simply push the button when you reach the slower speed (say 40 mph). If there are EV miles available (enough battery charge) it will switch to EV.

 

Also, MG2 is used in a unique way to control the gearing ratio in a variable-speed transmission. Both the gasoline engine and the MG2 are connected to the wheels through a planetary power-differential at all times (there is no clutch). Since the gasoline motor must either be stopped, or running within a fairly narrow range of rpm while the car is traveling at various speeds, the MG2 takes up all the slack, adjusting to whichever speed is needed to satisfy all the right conditions.

It has the effect of starting the gasoline engine when it slows down in relation to the wheels, and it generates power when needed to charge the battery. Interesting to note; when you are idling the car in park during warm-up, the MG2 has to run in reverse to prevent the car from rolling away due to the running gasoline engine.

 

That's a very common misconception, based in part on outdated information. The design has been improved over the years. That is clearly not the case anymore, as the videos confirm.

MG2 has a maximum RPM of 13,500. You can see the spinning doesn't come close to that, even when cruising at 60 mph in EV.

The actual reason for the blending is to not sacrifice efficiency. Rather than wasting electricity to spin the motor extremely fast, especially since power fades as RPM increases, the system takes advantage of having an engine available. Running it at low RPM is a much better for overall efficiency. It uses very little gas that way, while also better using the electricity.

 

If it's indeed not a motor-safety issue, I wish they had designed the system to simply "beep" for the first few seconds of over-speed driving in EV, allowing one to back off to keep the ICE from starting. On my 10-mile commute, part of which is on an Interstate, I often come up to just below the over-speed point, and it's distracting to keep watch over the display as I try to keep my trip in EV only. Once the ICE starts, it has to run until the CAT comes up to temperature (as I understand the reason), so I waste fuel.

 

Notice the RPM during warm up? The engine is kept from exceeding 1500, a very efficient speed for warming. So, there really isn't much gas actually being consumed as it would seem.

This video from my commute 2 days ago features EV-BOOST mode, where you can easily see the RPM being held during initial warm-up.

Note: Since I recharge at work, I don't take advantage of the HV/EV button to save electricity for use later.

 

The MG rotational speed may not be the issue, but other components in the planetary array may be spinning faster than that. In any case the top speed in EV mode has been explained as a limitation created to protect the drive-train from over-speed.

 

What? A sales guy that doesn't know how the car works. How unusual (NOT).

 

And it has been pointed out that the explanation is outdated, no longer applicable. The design has changed.

 

The upper speed limit changed from 40 mph to 62 mph with the Gen III. Is this the change to which you are referring?

 

Greg, it kinda seems like all you do on this site lately is get in arguments.

 

Nope. And if you want more info, let's discuss elsewhere rather than clutter this topic. There are threads which address this already. It's also a bit of a red-herring, since the engine can spin without actually consuming any gas.

 

MG1 would be around 9,500 rpm at 62 mph. MG2 is rated 12,500 rpm so MG1 should be able to go that high as well. Though, I have not seen the actual rating.

Look at it this way. Volt's second motor kicks in to slow down the first motor, in order to gain some EV efficiency.

PiP starts the ICE to slow down MG1 (and eliminate inefficient EV operation) and that speed is also when ICE can achieve max efficiency.

 

I've been experimenting whenever I can, given that the roads are quieter during my commute in August, and I'm as convinced as I can be without a scan gauge that (as previously reported) the European model doesn't provide EV-BOOST. If the ICE is warming up we get the same effect until it does, and from the sound it is clear that rpm is being kept down. But once in HV automatically, at above 53 or so real, 58 nominal, with a warm ICE and the EV light off, EV range doesn't drop. EV will kick back in (and ICE cut out) below about 53 nominal, say 48 real.

However, what happens in the US model when HV is selected but with EV mileage left, if speed and acceleration drops? The further I am below the halfway line on the power bar, the higher the speed at which the EV light will come on and the ICE will cut out - between about 40 - 45 mph. Crucially, this WILL reduce EV range, and it WON'T be recovered except by regeneration - the ICE doesn't run faster to recover it as it eventually would if EV range was zero.

This seems to contradict what I understood the US model to do, which was to recover the EV mileage when deliberately in HV mode, or have I misunderstood?

Incidentally I have compared the US and the UK manual describing the modes, and they are almost identical, and identically uninformative, not giving mph figures at which transitions take place etc. However, the EU PiP is rated for emissions just below 50 g/km traveled, which affects things like eligibility for zero car tax, rebates etc. that may be the reason for different - what? Software, firmware?

 

EV-BOOST is simply when the engine spins while still in EV mode. In other words, you don't press the HV/EV button... which the European model does not have. So, we look for a similar outcome using the gauges available.

What you'll see is MPG fully illuminated on the instant readout. That sustained 100+ wouldn't be possible without plug-supplied electricity while driving at highway speeds.

HV cannot deliver continuous efficiency at that level. You'll see it when going downhill, but not when traveling flat highway at 65 mph. EV-BOOST can and does.

As for EV recovery in HV mode via generating using the engine, that only happens enough to add back the electricity consumed for warm-up. You can generate more via re-generating using the brakes though.