Slow vs Fast Acceleration and the Eco light

I typically accelerate to the right hand side of the Power band. I do this first to keep up with normal traffic flow. Plus I found out that I actually get better mpg around town since I can get up to speed quicker and then can coast or glide sooner.

 

Personally i believe the answer is fast accelearation (PWR band) into the 40's, then come down a little to get the ECO light on and stay at the top of the ECO bar until you reach desired speed. I could be wrong!

 

I never practiced fast accel. in Prius (if there is such a thing!) as it takes lots of energy to accelerate. I just think smooth.

 

If there is nobody behing me and there is no incline in the road in front of me i will try to keep the eco light on, and the other 95% of the time i am always at least 50% into the red power area, I try not to piss off other drivers.

 

if you do fast accelerate you should shift at peak torque rpm as any farther than that the efficiency of the combustion engine goes down. peak torque is where combustion engines are the most efficient as it is where the maximum percentage of the fuel is being converted from energy to mechanical motion.

 

I always drive in ECO mode and stay in the ECO zone of the bar. Other than that I just go with the flow of the traffic and accelerate enough to keep up and leave some space in front for me to coast if I can.

 

This is the only response so far based on fact rather than opinion. Does anyone have any numbers to justify this response?

 

I have also no number for you dkelly, but I made an "experiment" the other day driving the same route, at the same time of day (e.g. same average traffic) but instead of using ECO, using Normal mode, i.e. accelerating more aggressively to truly keep up with traffic and overall driving "normally" or at least as I used to before getting the Prius.

For me, on that route, with that traffic, I essentially needed 1L/100km more as usual. And got to the office stressed - but that is just me.
But like you, I would like to know number-wise, the differences between different types of acceleration types.

 

Err, not applicable, Prius is Automatic, so you can't choose when to shift.

In Normal mode, I accelerate in the top end of the second half of the display, just below the pwr section, keeping the Eco indicator on, up to my desired speed, then cruise in the lower half of the display as long as I can. If it looses speed then I repeat this, traffic permitting.
If I need a swift overtake, I put it in PWR mode and give it pedal to the metal.

 

You can do the same in ECO - assuming that ECO does not also change the meaning of the bar (ie. a certain length of bar in ECO means a different request of power from the HSD compared to Normal mode; which would mean that the eco light turns off in Normal, later, that is with more power request from the HSD, than in ECO).

 

If you accelerate at the right side of the PWR region from a stop up to your given speed you will consume 4.5% more fuel for the duration of the acceleration than if you stayed at the optimum 3/4 position on the HSI. The Prius consumes 220g/kWh in it optimum range and 230g/kWh at the right side of the PWR region. (The fuel flow rate may be twice as high, but for about half the amount of time, so that's why it's not double the amount of fuel, it's only 4.5% more) So how will this impact your overall fuel consumption, well if 10% of you overall fuel consumption is used for acceleration from a stop up to your average speed and the rest of you fuel is used maintaining your speed plus or minus, then the faster acceleration should increase your overall fuel consumption (i.e. reduce mpg) by 10% of 4.5% which is 0.45% that's right 0.45% impact on your overall fuel consumption. There are probably a dozen things that will affect your fuel consumption far more. 1. unecessary braking, 2. not using pulse and glide, 3. high speed, 4. A/C, 5. tire pressure, 6. too much operation in the EV region, 7,........... So I can see how people that accelerate the Prius faster when there is open road ahead and then practice all the other techniques properly will get very close mpg figures to those that accelerate slowly and not give Prius drivers a bad name (in terms of pissing off other drivers).

Now if acceleration from a stop consists of 50% of your fuel consumption then I would say going to the upper PWR region will increase your fuel consumption by 2.25% instead of the 0.45% figure I mentioned, but then I would recommend that you may not be choosing the optimum route (as in a route with far too many stops).

 

I don't have instrumentation (SGII or sth like this) to check or prove that but I feel two things:
1) Going over visible PWR zone uses battery power to support the engine. Later engine will work harder to refill the battery which is less efficient than accelerating using engine itself in optimum (or even 220g/kWh range)
2) In ECO mode system uses battery power to keep engine in optimum range and recharges battery slower (which may be more effective) - this is thing I would like to check - combined with accelerometer readings to match pakitt feeling of different HSI mapping in ECO and Normal modes.

 

If I'm not mistaken, I believe battery assist only comes into play when one exceeds the PWR region.

As one approaches the right tip of the PWR region, the engine is running at about 3000 rpm and just at the edge of the 220 g/kWh contour and still well within the 230 g/kWh contour in the attached chart (Gen III on the right). In fact when accelerating and you are at the to 55 kW (73 hp) power level, you are then just at the edge of the 230 g/kWh region in the chart (The 55 kW contour will touch the upper right of this contour. For reference 55 kW (73 hp) will get a 3200 lb car up to 60 mph in about 15 seconds. So in the "bang for the buck" analysis of getting highest overall mpg, not going into the PWR region (when accelerating from 10 mph to 50 mph) maybe is number 10 on the mpg priority list, but this is not always communicated as such. One should concentrate their mpg improvement efforts in proportion to their return on investment (of concentration, of time, safety (taking eyes off road))
Now I'm whining......

 

You can't shift the Prius as its transmission is a CVT.

 

In a short energy burst almost all the energy is use to get to the desired speed and the energy needed to maintain a speed and keep gravity, friction, and wind resistant at bay is reduced (because we are looking a shorter time frame) So to overcome iertia to get to a given speed - accelerating faster does requires a higher power levels ( power = energy/time) but in theory the amount of energy (energy = power * time) should be approximately the same because time varies. The reason Pulse and Glide(P&G) is more energy efficient is because once the Prius goes into glide mode and decelerate after the acceleration - part of the kinetic energy used in the acceleration is used to over come rolling resistance and aerodynamic drag - no more energy is being put into the Prius. In a long energy burst to accelerate the Prius, additional energy is needed to keep the forces of rolling resistance and aerodynamic drag over this extra time from causing the Prius to decelerate. In addition when accelerating uphill, gravitational forces will extert more force over time.

Think of it this way:
Given a 10 pound box (or a bowling ball)

For the first energy test: As fast as you can lift up this 10 pound box up 3 feet high from the ground (e.g. lift in 01 seconds) and then gently lower it down back to the ground over the next 2 minutes.
For the second energy test: Now slowly and gently lift the 10 pound box up 3 feet high from the ground (e.g. lift in 60 seconds) and keep it at that height for 2 minute before dropping the box to the floor.

Repeat the above tests with a 20 pound box (something twice as heavy).

Question: Which took more energy to do?

 

In 0-60 acceleration, the car's acceleration rate would vary from about 12 mph/sec going from 0 mph down to about 3 mph/sec by the time your reach 60 mph with the accelerator pushed to the floor. Constant power is not constant acceleration (That is 100 wheel hp, for example, pushes you back into the seat about several times more at 0 mph, than at 60 mph at Prius continuously varying transmission ratios) see the Accel. (g) last column in this spreadsheet Prius EstimatedAcceleration data sheet. Note if the Prius delivered 100 hp to the wheel at 0 mph you would have nearly 5g acceleration wheels would spin at 0.5g so of course the system limits hp to about 12 hp (9 kW) at 0 mph at full throttle, kind of like every other car with any type of convential transmission out there. Otherwise the Prius would have sub 7 second 0 to 60 mph times with 100 wheel hp. The initial 133 hp is reduced by the drivetrain inefficiencies that nearly all vehicles suffer except pure EVs which have other inefficiencies at high power.

 

My mpg is a lot lower with fast acceleration and gliding "longer" than just slow acceleration. This seems a clear distinction when in EV mode too. With the former, I also see gas pips "burn off" a lot more quickly too for traversing the same distances and routes. Gliding doesn't particularly help since there aren't really many stretches of my routes that are suitable and I still lose speed pretty quickly (although I suspect the tire pressure is standard or lower for the past month we've had it).

I noticed the same behavior with 2 regular Priuses and a c that were both rentals, so I admit I may not have mastered this "accelerate and glide" technique. However, the 2 major trends I've noticed are that mileage is much better at lower speeds than higher ("in-town" vs. freeway), and much better with lower acceleration in general. And it makes sense to me that fuel consumption is a function whose predominant factor is acceleration, a second derivative of position.

 

I've been driving my Prius in Eco Mode since I bought it. For this tank however, I decided to drive it like I would a normal car (no more Eco Mode, Power Mode, or EV Mode). For the previous tanks I averaged about 48 mpg. So far, in normal, I averaged 60 mpg. Granted, it has been cold here in Queens/Long Island and yesterday was a 70+ degree weather, I'm no longer going to care for hyper-miling. The trade-off doesn't seem worth it for me and the kind of driving I do.

 

I didn't vote as you didn't have a choice for the very top of ECO, right below the power, where I accelerate most of the time (if possible). Most people understands slow as mid HSI.

Now this is for city and suburban driving only. For any decent hwy driving one has to forget HSI and go with flow of traffic.

Now, this is not for hybrid but still relevant:

Driving Tips to Save Gas - Save Gas This Summer - Popular Mechanics