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Discussion Starter #1 (Edited)
This question could be really silly as I might be missing something, but why do we need a hold mode if the engine is running at a constant RPM already?

The idea behind hold mode is that if you have, say, 5 miles EV range left in the battery while driving on the highway and you know you will hit traffic once you reach the city, you can switch to hold mode and drive on gas until you reach the city, then switch back to EV mode in traffic.

But doesn't the gas engine run at a constant rpm and is used to replenish the battery, which is used to drive the car ALL the time. Thus the engine efficiency is independent from the speed of the car??

What am I missing here?

[Edit: It turned out to be that the engine doesn't run on a constant RPM, resulting in the engine reving up and down, making the Hold mode relevant. The thread is full of good discussions though, enjoy reading :) ]
 

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The car only runs the engine as much as needed to keep the battery at the target state of charge. At low speeds and low power, the car will run on the battery with the engine off even after the battery is "dead." Hold just lets you choose when you use your battery.
 

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When traveling a mix of city and highway that is longer the battery range, Hold allows you to maximize the distance you can travel by battery.

Highway travel will eat battery range at a greater rate per mile than city driving. Driving at 60 MPH gets you fewer miles on battery than driving at 30 MPH. So the Hold option lets you save the battery for the city driving where it will take you more miles than if you simply used it up on the highway. Without Hold, you can use Mountain Mode to imitate Hold to a limited extent.
 

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Discussion Starter #5
Thank you Henry and Walter,
I must confused the Volt with Via motors' vtrux. Bob Lutz said during his visit to Jay Leno's garage that the ICE in Via trucks runs at a constant rpm, specifically the most economical point of operation. I though this is a very neat engineering idea as the motor doesn't need to rev up or down, avoiding inefficient mode of operation.
What do you think about that guys, should GM run the Volt ICE at a constant RPM to get the best fuel efficiency? It can be engineered so that the ICE shuts down once the battery accumulates enough charge for a specific range, say 1 mile, after that the ICE can re-engage again. Basically the ICE would run in a binary mode ON/OFF with a constant RPM. This would also mean that GM can use a less sophisticated/expensive engine that has a significantly smaller window of operation than a conventional engine that is expected to support a wide ranges of operation, from 1 mph to 120 mph. One can think of more tricks like having the engine run at one of two rpm speeds, a low rpm for traffic driving and one high for highway driving.
 

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I think GM made the right calls, everything they did was very well thought out and vetted.

I very clear GM number one goal was to make the volt feel like a regular car, sure its not the most optimal solution, but the one that would generate the most sales and overall satisfaction.

The Via truck is intended for a fleet, they don't have to worry about what the driver thinks, its all about ROI and as of yet they have zero sales
 

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Discussion Starter #7
Indeed, it seems that GM did a great job designing, testing and executing on the Volt.
I remember reading a while ago that GM's original plan was to custom build an ICE for the Volt but with the restructuring of the firm and the pressure to race to release the Volt they forego that and used the readily available 1.4L ecotec engine.

I found this article from May that discussed this idea for the general range-extended vehicles. They talk specifically about a custom built fixed-RPM ICE for EREV's made by the prestigious German maker Mahle.
http://www.plugincars.com/better-gas-engines-better-plug-ins-way-121773.html

May be GM will change the engine in a future Volt or another voltec car.
If GM has reservations about fixed RPM engines for EREV, I would be really interested in knowing them.
 

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Thank you Henry and Walter,
I must confused the Volt with Via motors' vtrux. Bob Lutz said during his visit to Jay Leno's garage that the ICE in Via trucks runs at a constant rpm, specifically the most economical point of operation. I though this is a very neat engineering idea as the motor doesn't need to rev up or down, avoiding inefficient mode of operation.
What do you think about that guys, should GM run the Volt ICE at a constant RPM to get the best fuel efficiency? It can be engineered so that the ICE shuts down once the battery accumulates enough charge for a specific range, say 1 mile, after that the ICE can re-engage again. Basically the ICE would run in a binary mode ON/OFF with a constant RPM. This would also mean that GM can use a less sophisticated/expensive engine that has a significantly smaller window of operation than a conventional engine that is expected to support a wide ranges of operation, from 1 mph to 120 mph. One can think of more tricks like having the engine run at one of two rpm speeds, a low rpm for traffic driving and one high for highway driving.
Actually, the Volt does some of this. At steady cruise below ~65 mph, the car will cycle the engine on and off (because it never runs slower than 1400 rpm and never at less than WOT, and cruise in that speed range needs less power than that.)

The thing is, there are a bunch of different losses to be balanced here. In your example, where you're storing a bunch of power into the battery - only about 80% of it comes back out to the wheels (lose energy in the generator, and the inverter, then at the battery, at the inverter again, and at the motor again.) So it makes sense to move a little ways off of the most efficient rpms to avoid that.

When the car knows it has to cycle the engine, it adopts a "virtual 6th gear" approach - it stops the main drive motor (MG B), using it only to resist the engine torque, and powers the car entirely off of the engine, while pulling the excess power out with MG A. This means that none of the current motive power for the car goes through generator/inverter losses. By contrast, at higher speeds it goes to a pure HSD approach, running the engine at lower rpms (and thus power outputs, since it's always WOT) continuously - eliminating some of the battery cycle losses in exchange for slightly lower fuel efficiency.

In short, the Volt's economy is a balanced art, and running at a single fixed rpm would almost certainly be less efficient, unless you had some sort of tuned header system that gave you >100% volumetric efficiency (which is possible, with a known operating RPM and CFD,) to make up for the other losses you'd be incurring.
 

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Give us a hold mode please !!

So I went on a 140 mile trip into a big city this weekend - starting on the highway 2 miles from my house. I knew before, his is a perfect scenario for a hold mode - but I didn't know how much. I did the trip in CS mode, which then meant electric for the first 24 miles and ICE after that - at least I had 12 electric miles once I got there. But then I realized if I just want to preserve what is left of the 12 miles once at the destination, putting it into Mountain mode again meant that the engine would run at faster RPM to a) propel my car and ramp the battery back to 12 miles, all I wanted is to keep the remaining 6 electric miles. That's not only loud - but also inefficient.... Just putting it in hold mode and cruising along on the ICE would have done the trick.

So if - of the 2013 model year goodies - we get nothing else but the Hold mode (no additional button needed): PLEASE !

(oh, did I already say how much I love this car ?)
 

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Ray... What you are missing is that it takes different amounts of power to push your car up a hill than push it on a flat road. So if you want to maintain a constant battery level and you are driving aggressively (or up a hill) the engine has to run faster than it does when you are on a flat surface to prevent the battery from draining.

Let's say your Volt has a 50% charge. Now lets say you want to drive 100 miles to your friend's home and demonstrate what it's like to drive in EV mode.

Without HOLD you would deplete the remaining 20 miles on your battery, switch over to gas and arrive at your friends home with no battery power left to demonstrate how your volt runs in EV mode.

WITH HOLD you can drive the 100 miles to your friends house on gas and when you arrive the battery will still have 50% left to demonstrate EV mode to your friend. In HOLD mode the ICE is used to run the car and maintain the battery at the SAME level until you reach your destination. No matter how fast you drive or how many hills you drive over. The engine adjusts to push the car at the desired speed and prevent battery drain.

Hope that helps explain it.
 

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So I went on a 140 mile trip into a big city this weekend - starting on the highway 2 miles from my house. I knew before, his is a perfect scenario for a hold mode - but I didn't know how much. I did the trip in CS mode, which then meant electric for the first 24 miles and ICE after that - at least I had 12 electric miles once I got there. But then I realized if I just want to preserve what is left of the 12 miles once at the destination, putting it into Mountain mode again meant that the engine would run at faster RPM to a) propel my car and ramp the battery back to 12 miles, all I wanted is to keep the remaining 6 electric miles. That's not only loud - but also inefficient.... Just putting it in hold mode and cruising along on the ICE would have done the trick.

So if - of the 2013 model year goodies - we get nothing else but the Hold mode (no additional button needed): PLEASE !

(oh, did I already say how much I love this car ?)
Actually, unless I misunderstand, MM can achieve this. Just put the Volt into MM before the SOC goes below about 15 miles. That way the ICE won't rev. It will act just like CS mode, only the set point will be about 30% SOC instead of 0% SOC. Then, when you are around 12 miles from your destination, flip back to Normal Mode. You will cruise into your destination on battery alone, nice and quiet.

The only difference is that you switch out of MM at 12 miles, instead of switching out of Hold Mode at 6 miles. In both cases you must estimate distance and override your Volt's normal operation.

Note bene: this post is not intended to argue against Hold Mode.
 

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Actually, unless I misunderstand, MM can achieve this. Just put the Volt into MM before the SOC goes below about 15 miles. That way the ICE won't rev. It will act just like CS mode, only the set point will be about 30% SOC instead of 0% SOC. Then, when you are around 12 miles from your destination, flip back to Normal Mode. You will cruise into your destination on battery alone, nice and quiet.

The only difference is that you switch out of MM at 12 miles, instead of switching out of Hold Mode at 6 miles. In both cases you must estimate distance and override your Volt's normal operation.

Note bene: this post is not intended to argue against Hold Mode.
I think his point was that once he switched out of mountain mode to use some electric miles, he either has to use them all right there or push the engine harder to rebuild the 12 mile buffer - he can't use 6 now and the other 6 later. This certainly is a limitation of MM as a quasi HM.
 

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I think his point was that once he switched out of mountain mode to use some electric miles, he either has to use them all right there or push the engine harder to rebuild the 12 mile buffer - he can't use 6 now and the other 6 later. This certainly is a limitation of MM as a quasi HM.
Probably I am misunderstanding, but if I want to use 6 EV miles now and 6 EV miles later (which is common for me), then I switch out of MM at 6 miles from my destination. I then arrive with 6 EV miles waiting and ready to go.

Again, I may be misunderstanding.
 

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Probably I am misunderstanding, but if I want to use 6 EV miles now and 6 EV miles later (which is common for me), then I switch out of MM at 6 miles from my destination. I then arrive with 6 EV miles waiting and ready to go.

Again, I may be misunderstanding.
Yup. But when you start up again, you have two choices. You can stay in normal/sport, and use the other 6 miles immediately, or you can switch to mountain and rebuild the charge with gas. You can't save the other six for some arbitrary point 100 miles later.
 

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Yup. But when you start up again, you have two choices. You can stay in normal/sport, and use the other 6 miles immediately, or you can switch to mountain and rebuild the charge with gas. You can't save the other six for some arbitrary point 100 miles later.
Ah. Completely true. Below 12 miles SOC, MM does force replenishing, even if that's not what you have in mind.
 

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Mountain mode is almost identical to HOLD mode except Mountain mode can only hold the battery when it depletes to about 30% or less. Mountain mode can't hold your battery at 50% or 80%. HOLD can hold your battery at any level.
 

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Thanks for this great thread introducing a soon-to-be Volt owner to the difference between CS and Mountain. You've explained it here more clearly than I've seen anywhere else.

Jordan
 
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Thank You Henry_FL

The Via truck is intended for a fleet, they don't have to worry about what the driver thinks, its all about ROI and as of yet they have zero sales
Thank You Henry_FL for all you add to this space. Thought that I would pass this on to you as I went to the NAIAA this year just to see this truck-

Kinda get the feeling that I had bout early 2009 in comparison to the Volt developement.

Best- Thomas J. Thias

p.s. Be sure to read the last line of the story and bob Lutz's parting comments.........

http://www.pgecurrents.com/2012/03/22/for-pge-adding-via-motors-pickups-to-its-fleet-saves-gas-means-fewer-emissions/
 

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Still seems that there is a much higher likelihood for inefficiency by using hold mode, ie. you get home with EV range left that was produced by using Hold.

Personally would rather just run CS when the battery is dead rather than playing games. What the heck do I care if certain parts of my trip are in EV or CS?
 

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I would prefer my city driving to be in EV mode, where emissions and heat have a higher impact. I also prefer EV mode for the traffic congested portions of my drive.

Why did GM opt to implement a Hold mode for Europe and not for the US?
Because in Europe it saves customers money and allows them to use the car in areas that they would otherwise be denied access to. But GM listened, and 2013 Volts have HM in the US. Now I'm just hoping (without much expectation) for a firmware update. :)

(I'd *really* like HM, but so far not enough to trade my car to get it. If they still haven't done anything next summer, we'll see what interesting innovations the 2014 adds to the pot. :) )
 
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