I have been thinking about what would happen if the size of the battery in the Camry was increased, and even past that what would happen if the battery could be charged by the power grid and not just the ICE.

In watching how my battery provides power to the car, it is very rare that it indicates less than 2 bars missing. About 90% of my driving is done with only one bar missing from the energy screen. So that leads me to believe a higher capacity pack won't really help anything except add more weight to the car.

Now to charging the pack, I would want the energy level in the pack to be low (but not so low as to hurt the pack's life) so it can recieve a charge from the power grid. Since, I would have to really work at keeping the car in ev mode (when I do work at it, I rarly can get it to go under 1/2 battery before the engine runs considerably) what good would that do me?

So how to the plug-in kits allow you to actually use the extra capacity of the battery and not have the ICE just top it off again?

 

You probably don't run in EV mode too much if your battery is usually between one and two bars of max. The end of my AM and PM commutes consist of a mile or more of low (35 mph and below) speed. By the time I get to my destination I'm usually within 2 - 3 bars from the bottom.

With the current battery capacity you're not going to get more than a couple of miles of EV mode. And the basic design of the PSD requires speeds less than 42 mph for that. So to make a practical plug in hybrid you'd have to change the basic design of the PSD and significantly increase the battery capacity.

 

That is why I question the benifit of the Hymotion type kits. They add a bunch of batteries and poof the vehicle's mileage increases.

I do drive for about 1 - 2 miles at the end of my commute home in EV mode as much as the car will allow. Even then I don't really get down to half battery. I have on occasion been able to get the battery down to two bars, but that is VERY rare. Most of my driving is above 45 MPH (my typical average speed for my 60 mile one way commute is 50 - 55 MPH), but I would love for the motor to give more assist on the hills and keep the engine in it's optimal FE zone. This could be acieved if the battery was larger, and I could charge the battery at night.

Is there anybody out there working on new programing for the ECU in a HSD vehicle? (Not just limited to the TCH, but possible a Prius or a HyHi.) I think if you just reprogramed the motor assist above the 45 threshold you could increase the mileage this car gets (assuming a larger battery pack that is grid chargable). Right now, there are times that the battery is in a high state of charge, and you can feel the motor assist the ICE and the FE shoots way up.

 

Those are all good comments! Based on my recent FE experiments, ag4ever, I agree that increasing the capacity of the battery would not help increase FE. It would only allow a greater range in pure-EV mode. What one needs is some way to prevent the ICE from recharging such a larger battery, so that one can make use of cheaper electricity rates to recharge it overnight from the ac mains. The TCH hybrid control system would need extensive re-coding to allow this. I don't believe that Toyota would provide the needed information to outside parties. Without reliable batteries of much higher capacity, one would have to fill the vehicle with batteries to increase the pure-EV range sufficiently to obviate the need for a gasoline engine as a means of propulsion. The recently-announced GM plan is a series hybrid — the ICE can't drive the wheels mechanically. This must be less efficient than the Toyota system whenever you actually do need the ICE to recharge the battery. Moreover, if it is to be able to recharge the battery at the rate at which the motor is depleting it, so that you can keep on driving, it has to be a substantial ICE too. This GM idea doesn't impress me. Maybe it will never see the light of day in the form announced.

Orcrone, your pure-EV experiences mirror mine.

ag4ever, I think the main reason for limiting the speed in pure-EV mode is to prevent MG1 from over-revving and mechanically damaging itself. The planetary gear ratio makes MG1 spin very fast when the ICE isn't rotating. If this is correct, then re-programming the ECU isn't an option.

Stan

 

The plug-in Prius kits work by faking battery status messages to the cars ECU. They make the car think that the battery SOC is high.

When the SOC (state of charge) is high, the car will easily run in EV mode below 42 MPH. Above 42 MPH the car will use the "extra" battery charge to assist the ICE.

So even if you do a lot of highway driving, you will still get much higher than normal fuel economy. For a few pennies of electricity.

There are a good number of these kits out there (by a few different manufacturers) and they DO WORK.

Unfortunately, with battery prices still high, they are not currently financially efficient.

 

My recollection from reading the various technical documentation is that the battery is limited to a 5kw (?) maximum charge/discharge rate. When run through the motor-generator to provide motion, this translates to a maximum speed of 42 mph on the straight-and-level. This is also why you can only accelerate slowly from a standing stop (on the level) if you work at staying in EV-mode: the discharge cap prevents the battery from providing a higher power level to the electric motor. My recollection (again) is that the charge/discharge rate is a function of the total charge the battery can take, so a deeper battery could have a higher rate (which would require reprogramming the ECU to take advantage of, of course), but that would mean not just higher speed but better acceleration in EV-mode. I don't recall the horsepower of the MG or the wattage equivalent, but I think the MGs could handle in the range of a 50-100% higher discharge rate - 63mph instead of 42. That's why *I* want a bigger battery - not necessarily to run longer, though I do love rolling in EV - but to be able to go faster in EV and run uphill in EV.

 

The only problem is you can't be in EV only mode over about 44 MPH. MG2 will spin too fast and destroy itself. You could have the engine idle, and still use the MG1 and MG2 to provide more propulsion than they would normally and get substancially better FE.

There are a multitude of reasons why I want a bigger battery pack, but better FE is the primary reason.

In the TCH, there is a bunch of wasted space on top of the current battery. It is such an odd size there, that IMPO it is usless as trunk storage space, and could easily be used to double the size of the battery pack. On top of that, if the current battery was replaced with a Lithium pack that was twice the size, the capacity would be about 4-6 time that of the current battery. Then we are talking about some decent range in EV mode and some serious range in motor assit mode getting excelent mileage.

 

I would almost want to question this. I live on a very steep hill and have always had problems with going in reverse since it uses battery only (see this thread reply). I have to push the accelerator almost all the way down before a burst of power comes form the electric motor and I go in reverse. In addition to this, I've played around in parking lots/structures by going into reverse and flooring it - and get a real decent accelerating (on level surfaces) performance response from the car.

Would this be because the 5kw limit is removed for reverse functions or because the limit may not exist at all?

 

I checked toyota.com for the pre-sales info and it lists the battery output as 30kW (40hp).

 

Please be aware that gas-electric hybrid and plug-in hybrid are completely different vehicles.

Prius/Camry Hybrid are designed as a gas-electric hybrid.
The Prius battery history is...
NHW-10 40 modules
NHW-11 38 modules
NHW-20 28 modules
Toyota reduces the battery capacity, but the results are higher performance, better fuel economy and wider trunk space. It is the innovation.

Also, please be aware that using a lot of battery power means you'll see worse mileage.
Have you ever seen the pulse and glide article?
http://hybridcars.about.com/od/owner...seandglide.htm
To see a good mileage number, avoid using battery power.

Prius/Camry Hybrid are not good candidate for plug-in hybrid.
My opinion the plug-in kit for Prius is a joke.
The better platform for the plug-in hybrid is a series hybrid like Chevrolet Volt.

Ken@Japan