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Hybrid Vehicles Hybrid Vehicles - Archived Discussions What type of hybrid should I buy? 
453 messages, Last post on Aug 19, 2005 at 6:05 PM
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Hi Usbseawolf2000: ___An instantaneous change in G’s is the third derivative. This is called “JERK”. It doesn’t matter what the scale is, it matters what the slope is. An instantaneous change is felt like an infinite jerk and is more then likely impossible because of traction and the inability of the Prius to accelerate anything like what is shown. ___Thank you as the graph I remembered seeing was on the same Toyota Prius details web site! Toyota shows the accelerator depression at ~ t = .8 seconds and the vehicle speed begins to respond ~ .25 - .35 seconds later. This is a far cry from 4 ms and could only possibly be explained if the 04 Prius forced the HSD to delay launch below 35 degrees or similar just in case there was snow on the road. I doubt they did this given the poor acceleration response times you would see/feel in winter temperature use. ___There was a mention of this delay in a hands on review somewhere as well but I don’t have that link handy at this time. http://www.toyota.co.jp/en/tech/environment/ths2/system.html ___Good Luck ___Wayne R. Gerdes |
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"An instantaneous change in G’s is the third derivative. This is called “JERK”. It doesn’t matter what the scale is, it matters what the slope is. An instantaneous change is felt like an infinite jerk and is more then likely impossible because of traction and the inability of the Prius to accelerate anything like what is shown" The scale matters here because the max you can accelerate at 30MPH should be no more than 1G(gravity). From that scale, Prius giving instantaneous acceleration of 0.4G is reasonable. So you do not consider clutch-drop acceleration as an instantaneous response? "Thank you as the graph I remembered seeing was on the same Toyota Prius details web site! Toyota shows the accelerator depression at ~ t = .8 seconds and the vehicle speed begins to respond ~ .25 - .35 seconds later. This is a far cry from 4 ms and could only possibly be explained if the 04 Prius forced the HSD to delay launch below 35 degrees or similar just in case there was snow on the road." You are welcome. I am aware of that graph. It is the traction control response time. Dennis |
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Hi Usbseawolf2000: The scale matters here because the max you can accelerate at 30MPH should be no more than 1G(gravity). From that scale, Prius giving instantaneous acceleration of 0.4G is reasonable. So you do not consider clutch-drop acceleration as an instantaneous response? ___Not at all because even dropping the clutch at max throttle w/ a stick does not achieve an instantaneous change in acceleration. There is slip in the clutch plates, gear mesh slop, all kinds of take up in every mechanical drive system between the Pistons and the tires. There is even take up between the tires contact surface and the road. On an even more microscopic scale, I can bet there is take up in the road surface itself! Instantaneous increase in G’s is simply unavailable no matter how small or large the magnitude of the G’s measured but I am not a mechanical engineer so someone else with a better handle on drivetrain jerk will have to either correct my misstatements or concur with them. ___Anyway, the 04 Prius doesn’t jerk like this from an initial throttle position of 0% at t=0 to any other throttle position at t=x seconds after t=0 in my 2 times behind the wheel. If it did, I believe more people would be talking about it. ___As for the traction control, it works under all circumstances thus leaving the lag intact. I wish I had the link handy for the reviewer that noticed it in his time behind the 04 Prius’ windscreen … ___Good Luck ___Wayne R. Gerdes |
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"As for the traction control, it works under all circumstances thus leaving the lag intact" The Y-axis of the graph you were referring to is Speed/Accelerator depression. So, we are talking about deacceleration traction control response time "when the vehicle's driving power changes abruptly, e.g., wheel slippage on icy or other slippery surfaces and wheel locking during braking, a protection control similar to that used in conventional traction control is used to prevent abrupt voltage fluctuation and revolution increase of the planetary gear in the power split device." The acceleration response still give you electric power within 4ms. That is probably why Toyota carefully chose the word Acceleration "Sensation" to avoid nit picking. We, humans can not notice any microscopic delay or slippage. The bottom line is that Prius HSD does give instantaneous acceleration "sensation". Dennis |
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| some magazines will list two 0-60 times...one for the test course and one that they refer to as a "street start", or something similar, that's supposed to more accurately reflect real-world conditions. | |
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