I'm up to 1500 miles and I feel like I'm in control of the vehicle under 40 mph in terms of gas pedal control and what will happen during acceleration and the power use between the ice and battery based upon pedal pressure, but when I'm in highway conditions and want to accelerate to pass from like 55 to 60 the car isn't doing what I am trying to do. The rpms are around 1300-1400 and when I want to accelerate up to 60 the rpms go up to 2200 with electric kicking in. I have soft soled shoes and control the gas pedal with my big toe so its not like I'm flooring it, I'm trying to get rpms up a few hundred to slowly creep up the speed or keep rpms the same and use electric for the speed burst but I can't seem to get it to do that even with light pedal adjustments. It just seems like it is going "crazy" and down shifting and getting into higher rev mode for a more aggressive acceleration than I want or think I need. So, am I thinking in terms of a set geared transmission and throttle control, should I throw out that logic with the cvt and hsd? Since I'm keeping it in the 'sweet spot' range am I over analyzing? Just press the pedal and let the computer do the work and not worry about it? Is this crazy burst the best way to do it, or is a low rpm increase acceleration like in a set geared car a better way to go and I'm not working the pedal right? Any technical insight on what is going on with the computer and what I should do in this scenario would be greatly appreciated. Thanks!
<div class='quotetop'>QUOTE(douglas001001 @ Apr 11 2007, 11:04 PM) [snapback]421855[/snapback]</div> Yes, you are thinking in terms of an ordinary transmission. The HSD always transmits some of the power to the wheels through electricity, so you are always going to use electric. When you ask for a little more power and the ICE revs, it's just the computer running the ICE at its most optimal speed. If you over think, you can find yourself fighting the control system, so just relax, drive, and let the Prius figure out what to do with the engine. Tom
Are you using a tach or CAN-View or Scan Guage to monitor your RPMs? I find it fairly easy to control the ICE rpm when I have the feedback of some sort of monitoring system (I use CAN-View). Certainly the racing when accelerating is not the most efficient range fuel economy wise. But if it's speed/power you're after then it's normal behavior. I like to keep the rpms in the sweet spot of 1700-2300rpm and find that I can usually do that even when passing (if gradual) and taking off from a stop with the help of the displayed RPM.
I have a scan gauge, from a dead stop and in png situations I'm hitting my target rpm without issues, its the slow increases I'm having trouble with at higher speeds and dwl up hills without the rpms doing the aggro increase. A slow increase at the low end of the sweet spot range is what I'm trying to do but keep hitting the rpm at the high end (2200 seems to be the theme) even with what seems like one or two clicks of pressure above my steady state pedal point. Its good that I'm keeping it in the range it sounds like, so not too much to worry about other than learning how the car reacts as I get more miles in and trusting the computer to do its thing.
Power, as requested from the engine, is torque * RPM. Under the throttle management done by the engine computer, torque is relatively constant once you're actually demanding real load from the thing. This is totally backwards from the way you think about traditional engine control, but it is very efficient. Once you've got torque up where you need it to be, how much power [i.e. acceleration ability] is all about RPM. You want more, you get more RPM, period. The electric path simply sorts out what you're trying to do and accomodates it. . http://techno-fandom.org/~hobbit/cars/SAE-bsfc.gif . _H*
My Prius performs very well on the highway. I commute 90 miles a day, and never have problems modulating the speed, either passing, or just cruising. I don't use the CC that often with the LA traffic density, but when I can use it, it works well. Great highway car. Maybe I missed something, but it seems to me that you are over-thinking the driving experience. With a good audiobook, the Prius is my best ever freeway flyer. I have a scan gauge, and it seems to be in about the 2100-2200 RPM level at highway speeds, even less when gliding the hills.
All sounds perfectly normal to me. Like Hobbit said, HSD doesn't work like a normal car. HSD does its best to operate the engine at a wide throttle opening (good for efficiency) and controls power by choking-down engine RPM. Ask for more power, the computers adjust the power flow between the motor-generators to let the engine speed climb. This means that the engine doesn't have to waste so much energy trying to suck air through a nearly closed throttle plate.
One minor point is it takes more energy to go from 55 to 60 mph than the energy required to go from 25 to 30 mph. The kinetic energy is given by: 0.5 * mass * velocity(**2) If we keep the mass the same at two units so 0.5*2=1, and ignore the engineering units, the relative energy changes are the differences in the speeds squared: (30*30)-(25*25) ~= 275 units (60*60)-(55*55) ~= 575 units That change in kinetic energy has to come from the engine. Now there are some tricks: 1. use downgrades to accelerate (let gravity be your friend) 2. avoid rpms greater than 3,200 rpm, when the specific fuel efficiency drops off 3. avoid full throttle that draws significant battery charge that has to be replaced later (*) Bob Wilson * - One interesting speculation is a full-throttle, battery draining, maximum acceleration will, for the acceleration phase, be running the ICE in a relatively inefficient range with the extra power coming from the battery. However, it may be possible to back-off and recharge the battery with the ICE in the sweet-spot. This remains an area for future research. It requires a total energy analysis, which is beyond the scope of this posting.
<div class='quotetop'>QUOTE(Godiva @ Apr 15 2007, 10:27 AM) [snapback]423648[/snapback]</div> My advice is: Don't worry about engine RPM. The HSD is so entirely different from anything else that's ever been in a car before, that all previous assumptions go out the window. The only thing that remains the same is that extremely hard acceleration is less efficient than more moderate acceleration. But the power-splid device (PSD) allows the engine to turn at almost any speed, for almost any vehicle speed (within certain very broad limits set by the PSD geometry and motor-generator limits) so the computer can make the gas engine turn at whatever speed it considers most efficient. With a conventional car, an over-revving engine means you're in too low a gear, and a too-slowly-turning engine means you're in too high a gear. In both cases, the engine alone is turning the wheels. Load on the engine is a function of how hard you press on the gas pedal. But with HSD, engine torque is split 60/40 between the wheels and MG1, and the computer can decide whether MG1 will act as a generator or a motor, in either direction, and to what degree. The battery can absorb unneeded energy, or can supply extra requested energy. MG2 can also be a motor or a generator in either direction, receiving power from the engine, from MG1, or from the battery, or sending it to MG1 or to the battery. With all this going on, you cannot make any assumptions about the load on the engine based only on the speed of the engine. How hard the engine is working cannot be assumed from its speed. So stop worrying about engine rpm. The computer knows what's best. (Now if there was only a way to tell the computer that a big hill is ahead and the battery should be managed accordingly!)
