Question about top speed

That video is just freaky. I've seen it before...the battery just wipes out and the car just sounds really unhappy. I can't imagine what kind of wear/strain it's under.

 

I've had mine at 82 mph 49.4 mpg

 

I've had mine to 100 mph. It gets to speed relatively quickly. The engine is at high rpm and is responsive. MPG is irrelevant. Pretty solid, a bit buzzy, but I've been faster in worse.

 

Thats 98.1 mph for 158 kph.

 

C&D calculated it. Maximum hp is achieved at 4800rpm and the gear ratio for the CVT is 3.19. So for 195/55x15 or 195/50x16 tires the tire diameter in 1.95 feet and 6.15 feet per revolution. So 4800 rpm divided by 3.19 and multiplied by 6.15 feet is 9257 feet per minute or 1.75 mpm, or 105 mph. Wonder what happens if you upgrade the cam and valve springs to yaris specs ? It gets max hp at 6000 rpm (its final drive has a 3.73 gear so its top speed isn't noticeably faster; but a prissy with 6000 rpm and 3.19 gear ratio ... Enough to do 124 mph ? Don't think so, the aero drag is too much but 110 maybe.

 

Only problem is that our cars don't have 195s on them.

 

I don't think it is correct to use engine RPM for this calculation. Our engine is not directly driving the wheels, it is via PSD (Power Split Device). We should be looking at MG2 instead since it is connected to the Ring gear via the Motor Speed Reduction Planetary Gear Unit.

The no. of teeth of the Motor Speed Reduction Planetary Gear Unit are as follows:

Motor Speed Reduction Sun Gear: 22
Motor Speed Reduction Pinion Gear: 18
Motor Speed Reduction Ring Gear: 58

MG2 speed reduction Ratio (Sun to Ring Gear) = 58/18 * 18/22 = 58/22 = 2.636

The PSD's Ring gear is driving the Counter gear and Final gear to drive the wheels.

Counter Gear Drive Gear Teeth: 48
Counter Gear Driven Gear Teeth: 49
Final Gear Drive Gear Teeth: 24
Final Gear Driven Gear Teeth: 75

Final Drive Ratio = Final Gear ratio (75/24) X Counter Gear ratio (49/48) = 3.19

MG2 has 13000 RPM max.So,

MG2 to wheel speed = 13000 / (58/22 * 75/24 * 49/48) = 1545.73 rpm

185/60-R15 has 849.54 rev. per mile, so

Max. speed = 1545.73 / 849.54 * 60 = 109 mph

Vincent

 

Interesting: where did you get the data ?
In any case I believe you have to use the rpm of the engine as it is cetainly the power to the wheels; the motor has pretty well tapped out.
I found the ratio of the transmission ratio at 3.19: 1 which is 'close' to your 3.19:1 which led to the 1504.7 revs per mile of the wheels/tires. As the circumference of the 195/55x15 tires is 6.15 feet thats 9253.9 feet per minute, or 1.75 miles per minute or 105.15 mph. While most cars will get a few more rpm than the rpm at max power the common hybrids aren't among them so using the 4800 rpm at max power is altogether realistic. Using your 1545 revs/ min wheel speed I get 107.9 mph and is far more likely than what you'd get with heavy 185/60x15 tires.
So I dont see where you got your power speed of 13,000 rpm as the engine will be the power source and 4800 rpm is likely its limit to maximum power to overcome aero forces, hence max speed. Then there's the difference between 185/60x15 tires (where from ? Ours start with 175/65x15) compared to 195.55x15 tires, 23.7" diameter vs 23.44" diameter; that's really the difference between our calculations. But the Prissy doesn't run 185/60x15 tires but does run 195/55x15's. I like your calculation but have reservations about the 13,000 rpm input maximum to the CVT. Oh, and thanks for the data.
And yes I am aware that tire revs per mile from the tire manufacturer is easy to get at tirerack, we make our top speed runs at higher pressures so the calculated revs per mile is closer to reality.
I'll stick with 105 mph.
cheers. Besides we have track data as backup.

 

The engine does not drive the wheels, but MG2 does. In reality the engine never drives the wheels directly, the Prius is an electrically powered car. Top speed of the car is directly related to the maximum speed that MG2 may run at.

 

The gear info. can be found in the NCF. You can subscribe to TIS and download from there.

The max. MG2 RPM can be found in the 2012 Prius c Technical Presentation.

You can play the Power Split Device simulator and get a feel of how it works. It is for the earlier Gen 1 but everything is the same except it doesn't have the Motor Speed Reduction Planetary Gear Unit so MG2 need to be multiply by 2.636 for our c. You can try to move the various slider and see the changes in speed. You should find that speed is not dependent on engine rpm. For e.g., you can have 0 engine rpm while vehicle speed is 40 mph or max. engine speed and vehicle speed is 0.

Vincent

 

The 73 hp engine drives the wheels thru a CVT with the assistance of a net 26 hp electric motor in series ; and the max input of the MG2 may be 13,000 rpm but that doesn't mean the MG2 will actually generate the power to drive the wheels thru the CVT if there's not that much input power, and where does a 4800 rpm engine and 4000 rpm motor get 13,000 rpm ?. The combined power of the two power sources is the spec 99 hp but since the engine is reaching max power at 4800 and the motor at 4000 rpm which achieves that max power together as a result of 2 different 'gear ratios' that match, the 4800 rpm of the engine must be the controlling one so 4800/3.19 * 6.15/5280 * 60 = 105 mph is the most accurate measure of top speed..

 

There is no CVT, there is a planetary gearset and software to emulate a CVT.

M/G2's RPM is linear with the tires RPM (single speed transmission with no clutch) when MG/2 hits redline, you are done accelerating. The RPM of the engine are almost unrelated to the tires, it can't get to redline below about 45 MPH (varies by Prius model, I am not sure when a c allows it) and at a similar speed it must be at least idling. Other than those constraints, engine RPM is unrelated to vehicle speed.

Here is a dyno test of a Gen 3, what you notice is that the engine is able to provide max Horsepower just around 45 MPH and that Horsepower after that only varies as the HV Battery runs low on SoC.


A Prius c has both a smaller engine and a smaller HV Battery, so I would expect the chart to be 30 HP lower and have more drop off on longer runs. (higher speeds)

 

Very interesting. My spec sheets and drawings state clearly its a CVT transmission. Nevertheless if there is only 99 hp input I have doubts about 109 mph. Are you saying the motor variable speed is the driving force behind varying the vehicle speed. If so, what's the 3.19 gear doing ? And just what is MG2 ?

 

And how about an engine rpm curve with vehicle speed.

 

Honest to goodness engine RPM and vehicle speed are almost completely unrelated.

In Gen 1 and 2, you can go about 45 MPH without the engine spinning at all, and you can't hit redline in the engine much below 65 MPH.

In Gen 3, PiP, v and c. these constraints were made more lax, and I think you can do 62 MPH before the engine must start in the PiP, and you can achieve redline in the engine nearer to 45 MPH.

 

Toyota often describes it as an eCVT. Think of the e as emulated. M/G2 is directly geared to the tires, yes, I suspect that on the c 3.19 is the final drive ratio.

This is the correct video for the Gen3, v, and c.

This is the simpler design in the Gen 1 and 2 Prius, if he confuses you, watch the simpler video

(in you tube, you will see videos on REAL CVTs, which have cones and pulleys)

 

It's not, though it achieves a similar effect.

Motor Generator 2. The Prius c has two MGs often referred to as MG1 and MG2.

 

Duplicate post

 

My tires are 175... I can take a picture if you'd like.

 

Not true, I took mine up to 80 something to evaluate its ability to pass a truck on interstate 5 on my test drive before buying it.