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Auto downshifting while in the Manual mode!

6429 Views 4 Replies 5 Participants Last post by  SpottsVee
One of the things I've noticed when driving my IS-F in the "M" Manual mode is that at times the car will downshift prior to my actually manually activating the downshift lever. This usually happens when driving casually as opposed to when I am really "driving" the car hard and trying to stay in the power band.

So while at the Toyota Long Beach Grand Prix a couple of weeks back, I had the chance to enter into a discussion with the Lexus Technical guru's about this. Here is there written technical explanation I just received from Lexus Headquarters for this happening:

"In order to preserve the advantages of a completely direct power-path when the IS F is driven in full-manual ("M") mode, we completely lock-up the torque converter.
This means that if you slow down without commanding any downshifts, the vehicle can slow below the engine's idle speed. In order to prevent the engine from stalling in these cases, downshifts will occur automatically as shown below.

Here's a detailed technical description of how the gear hold control holds the IS F transmission in the gear selected by the driver when in M mode.

In M position, it is possible to make use of the highest engine speeds by holding the vehicle in a gear. Gear hold control means that gear shifts will not be performed as long as the paddle switches or shift lever are not operated in either the“+” (UP), or “-” (DOWN) direction.

• If the vehicle speed drops below any of the designated points shown in the following table, a downshift will be performed from the current gear. When the temperature of the ATF or engine coolant is low, shifts will be performed based on the shift points for low fluid temperature.
Vehicle speed for each required automatic downshift when throttle opening angle = 0%
in km/h and [mph]
M2→M1 10 to 15 [6 to 9]
M3→M2 15 to 20 (9 to 12]
M4→M3 35 to 41 [22 to 25]
M5→M4 42 to 48 (26 to 30]
M6→M5 53 to 59 [33 to 37]
M7→M5 56 to 62 [35 to 39]
M8→M7 67 to 74 [42 to 46]

• When the vehicle comes to a stop, 1st gear (M1) will be automatically selected.

Complete lock-up control is used during both acceleration and deceleration when in 2nd gear and higher, without using the torque converter function. This enables changes in engine output to be transmitted directly to the transmission just as would occur with a manual transmission.

However, even for 2nd gear and higher, if engine speed is too low to allow lock-up, the torque converter function will be used.
• For 1st gear, to make use of the torque increasing action of the torque converter, lock-up is not operated."

For us older manual tranny lovers, this means that when we would downshift while using a real manual tranny and either go into netural or play with the clutch/gas relationship while downshifting to prevent a stall by keeping the Rev's high, the IS-F senses the impeding downshift and downshifts for us so the car does not hit it's stall point. When driving the car hard, we would normally stay higher in the RPM range then when casually driving so the cars actions are now understandable and predictable IMHO...

Hope this makes sense for all you readers?

I really apprecaite Lexus for getting back to me with this technical explanation and is just another example of thier complete openess about the IS-F and their wanting to communicate their design thought that went into our cars.
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That definitely makes sense. I would have first thought that if I experienced it firsthand. :)

Thanks for the technical explanation!
That definitely makes sense. I would have first thought that if I experienced it firsthand. :)

Thanks for the technical explanation!

Thanks for posting, Dean.

1 - 5 of 5 Posts
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