| Author |
Message |
steve (130.245.220.188)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 23, 2003 - 1:05 am: | |
I was riding CoachUSA route 27 to princeton NJ yesterday. I noticed that the Allison gear indicator changed from 6 to 2 whenever the engine brake engaged. Anyone know why that is? The bus was doing at least 60 so if the trans. shifted into second gear there would be problems. Anyone idea why 2 was displayed? |
Jason Windecker (198.81.26.108)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 23, 2003 - 1:18 am: | |
its probably the rate of retard that the trans is in, on alot of the allison trans there is a staged retarder and is usually controlled by a lever next to the shifter, if it was a 102DL3 thats probably the case, it was simply tellign the driver the retarder setting,
Jason |
DrEd (65.134.242.200)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 23, 2003 - 6:24 am: | |
::Steve, Allison provided the manufacture of the Bus/Motorhome/etc with the ability to program a lower gear for the transmission when operating the Jake Brake in order to better take advantage of the engine's compression to slow the vehicle down. On the World Transmission which has 6 gears (two overdrives) to down shift automatically when the Jake comes, typically 4th gear is used for this purpose but any gear can be programmed into the WTECM. If the bus you were riding in was one of the world transmissions with 6 gears than 4th should have been selected. However, on a 4 speed (I don't know what transmission this would be) transmission then 3rd or 2nd would probably have been selected. But if your CoachUSA was relatively new (since 96) then it probably has the 6 speed WT. I would think that 4th gear should have been used. Another however, is that the world transmission will not downshift into a lower range than permitted by Allison design engineers, so 2nd gear would not be activated until the coach had slowed down to a speed which would allow the shift to occur but it would down shift into 4th and used 4th until the coach slowed down enough for the 3rd and 2nd gear down shift. There is a lot more to the theory involved here but maybe this will help some in the understanding.Thanks DrEd. |
Buswarrior (Buswarrior) (64.229.209.184)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 01, 2003 - 2:38 pm: | |
There are two styles of display out there for the Allison World.
One has a lighter green colour, smaller display, and indicates both the range selected and the actual gear that the transmission is in
The other, newer one has a larger single digit, red coloured display and will indicate the range selected, or target gear, not the gear that the transmission is currently in.
The computer can be programmed to leave choices up to the driver, or set to do whatever the fleet manager wants.
In the original example, the computer has been programmed to seek the lowest possible gear for the road speed all the way down to 2 gear. NJT has set it this agressively to extend brake life in their stop, go, go like hell, style of operation.
Dr Ed's example is a much more typical setting for the computer, where the computer is programmed to only seek the lowest possible gear until 4 engages.
My personal preference is to leave the computer out of it and properly train the driver to use the combination of gears and jake/retarder that best suits the road conditions and passenger comfort. But, where do you find those good drivers to train, or the trainers to fascilitate the understanding and appreciation of conserving the fleet's brake money? oh well....
FYI, with a retarder or jake brake equipped Series 60 and Allison World set-up, to assist the braking, typically 4th will engage somewhere between 55 and 60 mph, 3rd 45 to 50mph. I personally would not want to use the shift to 2, as it is a little rough on the passengers.
4th is 1:1, with 5th around .7 and 6th about .62 or so. A coach governed to civilized speeds will achieve full governed speed in both 5 and 6.
Lots more flexibility to keep the steam up on the interstate!
happy coaching!
buswarrior |
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