bam

Since we've had our RX450h from March 2012, we've had the car in Eco mode and the overall mpg is showing 28mpg. That's great although we do notice that whenever we use the A/C, it drops mpg for that particular tank of gas to mid-20's.

Yesterday, I decided to try something different and so I turned off Eco mode and now we're driving in Normal mode. I know there are some differences such as the throttle response and something with the A/C compressor but I'm also hoping that there's a different mapping for the use of the hybrid/traction battery. What I mean by that is, when we originally selected Eco mode, I thought that meant that the car would drive to maximize fuel economy. In my eyes having purchased a hybrid, that meant that it would maximize it's use of the hybrid battery as much as possible since that's where the mpg fuel gains are. I always notice that it seems that the battery indicator never drops below where the "minus/plus" sign is on the battery picture which doesn't make sense to me. I would think that as you're accelerating, the system would use as much battery power as possible and actually let the battery drop to a much lower level before replenshing it. Also, while in Eco mode, I noticed that whenever the battery power does kick in, it doesn't really seem to use the battery power for long bursts while in Eco mode. It seems like it uses it for a couple seconds at a time.

Now after we switched to Normal mode, the battery level still doesn't seem to drop below the "minus/plus" sign on the battery while accelerating but of course, with the different engine mapping, the throttle response is better. Also, it seems that instead of using the hybrid power for a few seconds at a time while accelerating, under Normal mode, the battery power kicks in for a lot longer. In some cases, it'll run in tandem with the gas engine for 15 seconds or so.

Again, I would have thought that the hybrid battery would burn through the energy to a much lower level but I guess that's not how it's designed to work.

Here's an example of how I would have thought the hybrid system would work. So for example, say you're driving a normal route which includes a long uphill and a long downhill. From my observation, the system will currently run on and off while going up hill but will not deplete the battery reserves below the "minus/plus" sign on the battery and then on the downhill, it'll replenish the battery. I woudl have thought that while driving uphill, it would use more battery power and deplete the energy level to almost (if not) empty as this will provide the most help to the engine while driving uphill. Then while driving downhill, the battery will maximize the battery regen therefore maximizing fuel efficiency.

Does anybody have a logical explanation as to why the battery doesn't completely deplete while driving under normal circumstances?

Alpy64

Bam, very interesting analysis and query all drivers are facing when in a hybrid (Lexus) car (others have different hybrid systems. I attempt a response using a hybrid for more than 3 years now (RX 400h black edition and now a 450h model 2010).
When driving in mountains (uphill) I have noticed electrical motors are very active and batteries come to the low levels eventhough we are constantly in a throttle mode (strong accelerations require the support of electrical motor. I have noticed this while driving on "eco mode".
However, the "eco mode" is not active or automatically deactivated during strong accelerations but if you stay at normal range of acceleration (e.g. within a normal driving style) the "eco mode" is optimising use of systems to shut down or reduce their use to decrease consumption. "Eco mode" is also designed to reduce consumption by using oil engine with different parameters than in normal conditions.

The starting point of the batteries use depends on different factors/parameters, such as outside temperature, outside pressure (altitude), pressure when pushing down the pedal (strong throttle), the current level of charge of the batteries themselves.
If your pressure on the pedal is "low" you only use the oil engine is you push down stronger you "add" power from oil engine and electrical motors... and using batteries.

Traveler1

That's because balancing electric energy between MG1 and MG2.
There are 2 motors(generators) on the front wheels. MG2 drives wheels directly. Meanwhile, MG1 works as clutch between ICE and wheels. ECU controls the "clutch" by the volume of electricity generation. If the volume of electricity is zero, clutch is free. And when the volume of electricity is maximized, the clutch is fully works to send power from ICE to wheel. (Planetary gear enables do so.) Estimately 30% of ICE power is for the generation, and 70% is for driving wheels. The generated power (as 30% of ICE) is used for both driving MG2, and/or charging battery.

So... let's enjoy charging on uphill :-P

In addition, MG1 generally works as the clutch (as generator), and sometimes works as revolution assistance (as motor) on high speed, which enables ICE to reduce RPM, to save fuel consumption. Image that clutch itself gets energy to drive wheels faster :-) Meanwhile MG2 generates electricity.

Droid13

I recently got into a 450h after 6+ years driving a Camry Hybrid. It also had an ECO switch and I've found the effects to be relatively the same. The most noticeable difference by far is its effect on the climate system and the willingness of the engine to shut down.

With ECO on and climate system in auto, fan speeds will generally be lower, A/C is less powerful, and engine is much more likely to shut off while waiting at a red light. ECO reduces the electrical load on the vehicle if you typically have your climate system in auto most of the time, as well as puts more emphasis on saving gas at a red light instead of running the engine to provide heat, cooling, or electricity as required.

My 450h is always in ECO, but the Camry had a nasty habit of jumping out of ECO if you used the defogger button. I'd come to a red light and the engine would not shut off, what? oh, not in ECO anymore. Turn it back on, engine shuts off immediately. Same thing happens if you manually turn the fan speed to off.

With ECO off and climate in Auto, climate control system cares about your comfort and will spin up the A/C, fans, and engine as much as possible to make sure you get to your comfortable temp as quickly as possible. Engine will only shut off if the engine is completely warmed up, plenty of juice in the battery, and interior is near your chosen temp setting (climate system is settling back into maintaining temp)

There's also supposed to be that aspect of making the engine less responsive to save gas. I really haven't noticed that much difference here on either the Camry or 450h. Maybe the pedal input is changed somewhat, but if you stomp on it, it'll still give you power. Some people associate the feeling of power (and a sense of satisfaction) with quick acceleration on light throttle settings. To me I don't care if I have to push down 30% or 60% of the pedal to unlock the power, as long as I can "go" when I need to. I think the ECO setting here is just meant to de-tune those people that can't help themselves even though they want to take it easy.

Finally, regarding battery issue. Toyota/Lexus hybrids are NOT designed to exhaust the battery regardless of current driving activity, and has nothing to do with the ECO setting. Heavy cycling of the battery creates heat and wear on the battery, shortening it's service life. These batteries are supposed to last the life of the vehicle so efficient use of the battery is balanced with life of the battery. If you want to exhaust the battery for maximum efficiency, then that's when you buy Plug-In Hybrids instead. These are designed for much greater efficiency by exhausting the battery. It remains to be seen whether the new lithium batteries they are using will last the life of the car. I'm sure the 450h's hybrid programming could be altered to get 50mpg, but you would be replacing the battery every 3 or 4 years to do it.

billy44bo

My wife drive with the ECO on all the time and every time I drive the 45-h I turn it off. When the ECO is on I find myself pushing way to hard on the gas to speed up . Used to driving a v6 Camry and think the 450 should be as fast as the Camry. However when I have the ECO off I can keep the MPG the same if not batter than she can. As far as the AC goes it is on all year long and always on Auto and inside air.

cossie1600

In my 2010 Prius, eco mode used almost as much gas as I had to use a lot more throttle to keep the car going. I saw no noticeable difference in gas consumption. In the Lexus, I noticed a pretty good difference as the car is still okay quick in eco mode and the AC isnt running as much as it does. There is also a lot less engine idling too