EV and Alt Fuel Vehicles, Part 8
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BB
Flashlight Enthusiast
Darell,
You are correct... This is a multi-variable problem. There are the energy losses (drag, friction, conversion losses-what gear you are in, fixed losses, etc.), losses that are variable (temperature related, altitude, weather, etc.), and efficiencies of fuel to work conversions (the engine's temp, rpm, moisture, type of fuel, torque vs rpm, parasitic loads--alt, pumps, etc.) that all go to create multiple local minimums and maximums (peaks and valleys in the fuel economy graph), and external traffic conditions (stop and go, speed limits, driving styles)--to solve this using engineering and math (or fully simulate in a computer) is not easy. Experimentation is what most of the rest of us will have to do (like you did).
Want to through something else into the economy mix... Wages for the driver, costs of capital, repairs, breaks, etc.--alll of those are also important too... (example, driving faster uses more fuel, but less wages and can transport more cargo for the same time, or for farther distances before manidtory breaks)... Hence folks willing to pay for airplane flights instead of taking the bus, and paying for next day air shippment for their packages.
-Bill
You are correct... This is a multi-variable problem. There are the energy losses (drag, friction, conversion losses-what gear you are in, fixed losses, etc.), losses that are variable (temperature related, altitude, weather, etc.), and efficiencies of fuel to work conversions (the engine's temp, rpm, moisture, type of fuel, torque vs rpm, parasitic loads--alt, pumps, etc.) that all go to create multiple local minimums and maximums (peaks and valleys in the fuel economy graph), and external traffic conditions (stop and go, speed limits, driving styles)--to solve this using engineering and math (or fully simulate in a computer) is not easy. Experimentation is what most of the rest of us will have to do (like you did).
Want to through something else into the economy mix... Wages for the driver, costs of capital, repairs, breaks, etc.--alll of those are also important too... (example, driving faster uses more fuel, but less wages and can transport more cargo for the same time, or for farther distances before manidtory breaks)... Hence folks willing to pay for airplane flights instead of taking the bus, and paying for next day air shippment for their packages.
-Bill
Darell
Flashaholic
Quite true. This is the "trucker paradox" as I call it. It is obviously more expensive for them to drive faster (higher fuel cost, more tire wear, more maintenance), but it nets them more money in the end.BB said:
DUMB BLONDE MOMENT...
So, you put the egg between your foot and petal, not the petal and floor?????
That makes more sense now.
Yeah, we had an example about using linear equations to guestimate stuff and fuel economy was one of them. Cars have a sweep spot between the power band of the engine, gearing and aerodynamics. Mostly larger trucks need to go slower, smaller cars, faster.
THat is interesting about the gun and run technique for the prius. Its my understanding the ice and electric motor work together with a mixer gearing, where the other hybrids use it as a helper motor.
Yeah, the electric car is still on the back burner. I need to find out abut charging and make some money once I pay off the debt from getting my license before I can swing that. Thinking of getting an electric ford ranger online and buying a new set of batteries, having both shipped to work, putting it together there, charging it for a few days before driving.
So, you put the egg between your foot and petal, not the petal and floor?????
That makes more sense now.
Yeah, we had an example about using linear equations to guestimate stuff and fuel economy was one of them. Cars have a sweep spot between the power band of the engine, gearing and aerodynamics. Mostly larger trucks need to go slower, smaller cars, faster.
THat is interesting about the gun and run technique for the prius. Its my understanding the ice and electric motor work together with a mixer gearing, where the other hybrids use it as a helper motor.
Yeah, the electric car is still on the back burner. I need to find out abut charging and make some money once I pay off the debt from getting my license before I can swing that. Thinking of getting an electric ford ranger online and buying a new set of batteries, having both shipped to work, putting it together there, charging it for a few days before driving.
PlayboyJoeShmoe
Flashaholic
Funny Darell! My RAM (if you take all hills etc. into consideration) likes 63 or so the best too. But if the road is flat and traffic will bear it, 35 works pretty good too!
This is a great thread!
This is a great thread!
winny
Flashlight Enthusiast
Darell,
Yes, you are indeed correct but I would just like to add that fuel efficiency is not the only reason why you have a gearbox. Unless you have a massive amount of torque (read electric engine), you need a gearbox to impedance match the engine against the load (friction to air, road and such). Our old Audi A4 had just about the same efficiency whether I did go in 4:th or 5:th gear in 70 km/h but the amount of power I had to play with at that speed almost doubled at 4:th gear. In 110 km/h, there was another issue where 5:th gear would save me 40% or so fuel.
Hmm, back to the impedance matching. Although I haven't read that comment here, I'd like to take the opportunity to straighten out the issue with electric cars and gearboxes once and for all. It's often said that due to the flat torque-rotation speed frequency curve of most electric engines they don't need gearboxes and that they will accelerate just as good without one. Not true, at least if we disregard the weight added by the gearbox itself. They will accelerate very good but they would have done better with a gearbox in most cases.
If we would have a fixed value of say x Nm or torque all over the rotation speed frequency range, the power will increase linear from standstill to max speed (blue curve) and as the power needed is increasing with speed to the power of three, the acceleration will be slower and slower. That's it.
If you on the other hand would have a gearbox, you would be able to use peak power at n times during that acceleration (red curve), where n is the number or gears.
I'll draw a picture for you:
I have neglected any loss in the gearbox here and chosen a four-speed gearbox. It's only schematic.
Just in case anyone wonder...
Yes, you are indeed correct but I would just like to add that fuel efficiency is not the only reason why you have a gearbox. Unless you have a massive amount of torque (read electric engine), you need a gearbox to impedance match the engine against the load (friction to air, road and such). Our old Audi A4 had just about the same efficiency whether I did go in 4:th or 5:th gear in 70 km/h but the amount of power I had to play with at that speed almost doubled at 4:th gear. In 110 km/h, there was another issue where 5:th gear would save me 40% or so fuel.
Hmm, back to the impedance matching. Although I haven't read that comment here, I'd like to take the opportunity to straighten out the issue with electric cars and gearboxes once and for all. It's often said that due to the flat torque-rotation speed frequency curve of most electric engines they don't need gearboxes and that they will accelerate just as good without one. Not true, at least if we disregard the weight added by the gearbox itself. They will accelerate very good but they would have done better with a gearbox in most cases.
If we would have a fixed value of say x Nm or torque all over the rotation speed frequency range, the power will increase linear from standstill to max speed (blue curve) and as the power needed is increasing with speed to the power of three, the acceleration will be slower and slower. That's it.
If you on the other hand would have a gearbox, you would be able to use peak power at n times during that acceleration (red curve), where n is the number or gears.
I'll draw a picture for you:
I have neglected any loss in the gearbox here and chosen a four-speed gearbox. It's only schematic.
Just in case anyone wonder...
idleprocess
Flashaholic
Ah, but the acceleration of electrics doesn't seem to suffer enough with a single gear to merit them ... unlike an internal combusion engine which cannot mange a car with a single gear. With an electric, you have the option of sacraficing efficiency by allowing the motor to draw absurd currents since motors have most torque when stalled.
Taking a look at the tZero brochure and FAQ it looks like it has a pack with 28 lead-acid batteries and can dump up to 580 amps into the motor. On the surface, that sounds like 28 x 12V x 580A, or just under 195kW. The tZero has a 4.6s 0-60 time. The Wrightspeed Xa manages a 3.0s 0-60 time; power consumption is unknown, but it has a 8.35:1 gear ratio.
I've seen ~1200W direct-drive vacuum motors bend and break stout screwdriver shafts or catch fire trying to (when they weren't popping breakers; don't remember many parallel circuits we ultimately had to use for that test) during locked-rotor tests. Scale that up by a factor of 30 or so with a reduction gear and a load that the motor can actually move and you'll get zippy acceleration. I suspect that a multiple-speed gearbox would be diminishing returns at best.
Taking a look at the tZero brochure and FAQ it looks like it has a pack with 28 lead-acid batteries and can dump up to 580 amps into the motor. On the surface, that sounds like 28 x 12V x 580A, or just under 195kW. The tZero has a 4.6s 0-60 time. The Wrightspeed Xa manages a 3.0s 0-60 time; power consumption is unknown, but it has a 8.35:1 gear ratio.
I've seen ~1200W direct-drive vacuum motors bend and break stout screwdriver shafts or catch fire trying to (when they weren't popping breakers; don't remember many parallel circuits we ultimately had to use for that test) during locked-rotor tests. Scale that up by a factor of 30 or so with a reduction gear and a load that the motor can actually move and you'll get zippy acceleration. I suspect that a multiple-speed gearbox would be diminishing returns at best.
winny
Flashlight Enthusiast
idleprocess,
Yes, but if you would have combined that overdrive with a gearbox, you could have been accelerating even faster if you could change gears in zero time.
The power consumption of the Wrightspeed should be about the same as the t-zero as they use the same propulsion system unless the li-ions can't deliver that power.
Yes, but if you would have combined that overdrive with a gearbox, you could have been accelerating even faster if you could change gears in zero time.
The power consumption of the Wrightspeed should be about the same as the t-zero as they use the same propulsion system unless the li-ions can't deliver that power.
idleprocess
Flashaholic
I believe that the X1 weighs signifigantly less than the tZero, so it shouldn't need to deliver as much power although the motor horsepower ratings are the same.
Some sort of CVT might make sense for high-performance electrics; I'd think that a discrete multispeed gearbox would just introduce shifting delay. A 3.0 second 0-60 time is mightly close to what the best motorcycles can do. I can see an electric with 2 or 3 speeds if you're not happy with the ~112MPH top speed of the X1, but not for faster acceleration; you'll shift into 2nd as you near the motor redline long after you've traveled that first quarter mile.
Some sort of CVT might make sense for high-performance electrics; I'd think that a discrete multispeed gearbox would just introduce shifting delay. A 3.0 second 0-60 time is mightly close to what the best motorcycles can do. I can see an electric with 2 or 3 speeds if you're not happy with the ~112MPH top speed of the X1, but not for faster acceleration; you'll shift into 2nd as you near the motor redline long after you've traveled that first quarter mile.
winny
Flashlight Enthusiast
I agree. With the high wind resistance of the Ariel Atom/Wrightspeed, you don't need that much higher top speed and a 0.4 sec gear change would kill off any time saved by higher power to the wheels during acceleration.
However, if I would have had a normal four seated electric car, I would like to have at least some gears to keep the noise down during normal cruising (although very little from an electric motor, lower frequencies are more pleasant) and the performance up when climbing hills at low speed or pulling a trailer from standstill.
However, if I would have had a normal four seated electric car, I would like to have at least some gears to keep the noise down during normal cruising (although very little from an electric motor, lower frequencies are more pleasant) and the performance up when climbing hills at low speed or pulling a trailer from standstill.
Darell
Flashaholic
You'll certainly get no argument from me on that! I was only discussing the situation where fuel economy from an ICE vehicle with a gearbox is NOT going to necessarily correspond with speed in a logical way. Didn't mean to imply that the gearbox was there ONLY to screw with that graph.winny said:
And you'll get no argument from me on this either (I must be getting soft, or you're making sense.
)It is the added drag, complexity, weight and expense that makes gearboxes on EVs a losing proposition (as Mr. Idle points out so well above). If a cheap, lightweight, lossless VARIABLE transmission were incorporated, EVs could have BETTER acceleration (up to the limits of traction!) and more efficient cruising all from the same battery/motor combination. Finding parity with these factors has not yet happened, and EV builders (even the guys who WANT to build EVs) typically skip the transmission. One important thing to note: Dr. Andy Frank at UCD, and made a 99%+ efficient constantly variable transmission that he's using on his plug-in hybrids to achieve astonishing torque gains from the E traction motors. If this thing gets into production we may see something spectacular. He says efficiency is so good that they typically safely ignore the transmission loss in their calculations. For my money, the constantly variable trans is the answer - not the antique "gear box" of yester year.
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gadget_lover
Flashaholic
Regarding the "punch it and coast" technique in the Prius....
Many have reported great results with this technique, yet I find it difficult to do consistantly. It has a downside in that people behind you are not always happy when you coast below the speed limit. I do find myself coaxing the car into turning off the ICE (by letting off the gas for a second) if I know I'm approaching a downhill incline of a fraction of a degree. That's in city driving. Inertia, gravity and the electric motor maintain my speed.
As for hills and the Prius? I find that simply driving normally with cruise on works quite well. No speed changes as you aproach nor as you climb the hill. The gas consumtion increases as you climb (like any car) but it levels off pretty quick and the ICE stays off as you go down the other side. I guess if the hill were only a hundred feet high you might see an advantage to speeding up on approach then coasting... Not a lot of those in my area. I'm thinking of hills as 600 foot climb in a mile or two.
On gears and electics:
The use of gearing allows some benefits with the electric motor. It can reduce the "cogging" effect. It can make accelleration even faster, or it can reduce the motor's RPM to a range that ensures long life.
On speed and ICE efficiency:
Is it a coincidence that 100 kph is the limit in many countries and that Darell's Civic is most fuel efficient at 62 MPH? 100kph = 62 mph. I think not. That was one of the arguements against the national 55MPH speed limit. People argued that cars were designed to go 65 and therfore most efficient at that speed. Cars built in the 70's and 80s were designed to be most efficient at 55.
Daniel
Many have reported great results with this technique, yet I find it difficult to do consistantly. It has a downside in that people behind you are not always happy when you coast below the speed limit. I do find myself coaxing the car into turning off the ICE (by letting off the gas for a second) if I know I'm approaching a downhill incline of a fraction of a degree. That's in city driving. Inertia, gravity and the electric motor maintain my speed.
As for hills and the Prius? I find that simply driving normally with cruise on works quite well. No speed changes as you aproach nor as you climb the hill. The gas consumtion increases as you climb (like any car) but it levels off pretty quick and the ICE stays off as you go down the other side. I guess if the hill were only a hundred feet high you might see an advantage to speeding up on approach then coasting... Not a lot of those in my area. I'm thinking of hills as 600 foot climb in a mile or two.
On gears and electics:
The use of gearing allows some benefits with the electric motor. It can reduce the "cogging" effect. It can make accelleration even faster, or it can reduce the motor's RPM to a range that ensures long life.
On speed and ICE efficiency:
Is it a coincidence that 100 kph is the limit in many countries and that Darell's Civic is most fuel efficient at 62 MPH? 100kph = 62 mph. I think not. That was one of the arguements against the national 55MPH speed limit. People argued that cars were designed to go 65 and therfore most efficient at that speed. Cars built in the 70's and 80s were designed to be most efficient at 55.
Daniel
Darell
Flashaholic
Ah. I can tell from these comments that you have not yet had the pleasure of driving an EV???winny said:
The EV1 was a special case where you could hear the gears. The Rav4, for example is quieter than my bicycle - at any speed (ignoring wind noise at speed). There is NO sound from the motor or the grears that makes it into the passenger area. IF noise is your reason for gearing - forget it!
Climbing hills is better in even an under-powered EV than in a comperable ICE. Pulling a trailer? No problem for the same reason. Do the comparison at altitude, and the EV shines even brighter. A car like the E1 with only a ~100kW motor could smoke the tires from a standstill (no clutch, folks, just "roll-on" power) and will comfortably drive 80mph in that same gear. No, a gearbox is most definitely NOT needed. Yes, it has the potential of making the whole system more efficient, and could allow for the use of a smaller motor, and will allow for even MORE tire smoke... But again - not "needed" for any of the scenarios you mention.
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Excuse me guys, but all EVs have gears. They have around a 10 to one reduction in the final drive. Its my understanding any gearing takes at least 10% from the power in frictional losses.
Ive used wheelchairs with worm, parallel gearing and direct drive brushless motors. Needless to say, the brushless motors were nothing but problems, over heat quicklyand did not give the performance vs efficiency they were suppsoed to. The worm reduction units gave great torque, but poor economy. THe best was the parallel gearing, both were at about 20-28 to one gearing.
Further, when sucking the last bit out of a pack, over doing it can cause you to fall flat on your face. I recall in rehab the ramp to the dinning room was right at specs for ada, 12 degree grade. I could go all over the place at full throttle, but that ramp I had to limp up it or zap, it would suck my batteries down too low and had to just sit and wait for them to recharge or get a push up, then I was fine to run around the whole place.
So, yeah, I would want gearing too, maybe a 2 or 3 speed box or some CV thing. Unless they make a dual or tripple winding motor or that brushless thing improves.
Man, if I win the lottery, I am giving this my undivded attention.
Ive used wheelchairs with worm, parallel gearing and direct drive brushless motors. Needless to say, the brushless motors were nothing but problems, over heat quicklyand did not give the performance vs efficiency they were suppsoed to. The worm reduction units gave great torque, but poor economy. THe best was the parallel gearing, both were at about 20-28 to one gearing.
Further, when sucking the last bit out of a pack, over doing it can cause you to fall flat on your face. I recall in rehab the ramp to the dinning room was right at specs for ada, 12 degree grade. I could go all over the place at full throttle, but that ramp I had to limp up it or zap, it would suck my batteries down too low and had to just sit and wait for them to recharge or get a push up, then I was fine to run around the whole place.
So, yeah, I would want gearing too, maybe a 2 or 3 speed box or some CV thing. Unless they make a dual or tripple winding motor or that brushless thing improves.
Man, if I win the lottery, I am giving this my undivded attention.
Darell
Flashaholic
No question that it has limited practicality in the real world. Was just pointing how how different driving techniques in different cars can give wildly different results. And it surprises most folks that the "pulse and glide" can work on just about ANY ICE to increase mileage if there were no real-world practical limits to doing so. It is just easier in the Prius since you can "turn it off" by just using your right foot.gadget_lover said:
I have found that there are many times when it is actually useful in the real world, however. When stop signs are spaced just right you can zip up to speed with the ICE, and let it "glide" to the next stop. Gives about twice the average mileage than accelerating gently with the ICE on the whole time.
In the EV I find myself using very little gasoline power at all.
It can, yes. But that's a really poor use of it. The cogging can be totally eliminated through electronics, and the gearing can then be chosen for practicality, not the brute-force method of eliminating cogging.
Ha. Only up to the limits of traction
The X1 would accelerate no faster with more torque. It reaches the tire limits WAY before it runs out of torque. It would have better quarter mile time if it had a taller gear though. It reaches the 112 mph limiter well before the quater mile. This one isn't even in the running. Electric motors last for freaking ever. I have yet to hear of a single failed AC motor in the production cars (at least not a failure caused simply by usage). The EV1 motors were tested well beyond 1,000,000 miles of sythesized driving. I wouldn't spend an extra penny in an attempt to prolong electric motor life. No return on that investment when they already outlast any resonable vehicle in which they'd be used.
Right on the money as far as I understand it.
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Darell
Flashaholic
I'm pretty sure that we were all talking about a changeable "gearbox" known as a traditional transmission. Certainly most EVs need to gear the output shaft to keep the motor in a prescribed safe RPM range. But this is fixed gearing - different than a standard/variable transmission.cobb said:
Certainly not. In smaller applications like circular saws, and maybe even wheel chairs, this might be the case. And that's probably pretty close to what happens in a traditional/variable transmission. Not the case for a well-designed full-size EV with single-ratio gearing, however. There are losses in the gearing, of course, but nothing like 10%.
?? You realize that all the production EVs have brushless AC motors, yes? Super efficient and drop-dead reliable. That they're expensive is really the only draw-back.
Attention is cheap! I sure haven't won the lotter, and this stuff is about all *I* think about (maybe that was obvious?)
gadget_lover
Flashaholic
I was probably not clear. It's possible for spinning parts to be over stressed when they spin too fast. Windings de-laminate, bearings overheat, etc. Gearing allows parts to spin faster or slower than the motor.
Daniel
Darell
Flashaholic
Ah! In that case then gearing is of course MANDATORY!gadget_lover said:
For whatever reasons, the EV1 motor spun almost twice the RPM as the Rav4 motor. The high-rev EV1 motor definitely made for a louder situation. But I liked it - was like driving a space-ship. You could always tell by the pitch of the gear whine how fast you were going, and all small speed changes were audible.
Man, if I'd known we could have had some new, interesting discussion by just starting a new thread, I would have done it months ago! I think it is still wise to keep them down to just a few hundred posts each. Many folks are scared to peek in when the thing gets so long that it would take a year just to catch up!
Sorry Darell, I was referring to brush and gear less. In the wheelchair world, if a motor was brushless it was also gearless, dont know why, maybe it was designed for lower rpm operation?
"Opinion 1: Horsepower loss through drive train is a constant percentage based on the type of transmission you have. A manual transmission loses around 15%-17% of engine horsepower and an automatic transmission loses between 20%-25%. " http://www.superstang.com/horsepower.htm
Yes, you are on my list to hire if I do win the lottery. You, a few other guys here and the suck amps guy.
I am glad we like the gun and run method, I find it makes driving way easier and lessens my slippage problem or torque convert inconviently locking and unlocking. Shame I cant rig up a way to cut out the engine and put it in nutral at the same time to coast to the next stop light. at 35mph in the city I seem to roll on forever, going 45 or more, it seems to slow to 35 in a few seconds, then rolls. I have 6 lights in the 5 miles trip to go through and for the most part miss them all as I coast from one to the other only loosing or gaining 10mph between the two.
"Opinion 1: Horsepower loss through drive train is a constant percentage based on the type of transmission you have. A manual transmission loses around 15%-17% of engine horsepower and an automatic transmission loses between 20%-25%. " http://www.superstang.com/horsepower.htm
Yes, you are on my list to hire if I do win the lottery. You, a few other guys here and the suck amps guy.
I am glad we like the gun and run method, I find it makes driving way easier and lessens my slippage problem or torque convert inconviently locking and unlocking. Shame I cant rig up a way to cut out the engine and put it in nutral at the same time to coast to the next stop light. at 35mph in the city I seem to roll on forever, going 45 or more, it seems to slow to 35 in a few seconds, then rolls. I have 6 lights in the 5 miles trip to go through and for the most part miss them all as I coast from one to the other only loosing or gaining 10mph between the two.
winny
Flashlight Enthusiast
Darell,
Please forgive my lack of experience with EV here. I only wanted to straighten out the issue with what makes a car move forward and power. Although I'm confident what I said is correct in theory, you would need an underpowered EV to actualy see it in practice, just like you said.
Anywho, I'm building a 0.5 kW electric bike with a friend of mine which should be ready within the next weeks. Would anyone be interested to see it?
Please forgive my lack of experience with EV here. I only wanted to straighten out the issue with what makes a car move forward and power. Although I'm confident what I said is correct in theory, you would need an underpowered EV to actualy see it in practice, just like you said.
There are not buts to more tire smoke...Darell said:
Anywho, I'm building a 0.5 kW electric bike with a friend of mine which should be ready within the next weeks. Would anyone be interested to see it?
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