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File In Section: 07 - Transmission/Transaxle
Bulletin No.: 02-07-30-004A
Date: September, 2002
INFORMATION
Subject:
New Product Information - Grade Brake Feature of Allison(R) 1000 Series Transmission
Models:
2001-03 Chevrolet Silverado Pickup Models
2001-03 GMC Sierra Pickup Models
with Allison(R) LCT1000 Series Automatic Transmission (RPO M74)
This bulletin is being revised to add the 2003 model year and additional information for clarification. Please discard Corporate Bulletin Number 02-07-30-004 (Section 07 - Transmission/Transaxle).
The grade-braking algorithm's primary purpose is to utilize engine braking to slow a heavy vehicle on steep grades in order to reduce wear on the traditional braking system. The method used to slow the vehicle is by overriding the PRNDL position, effectively preselecting the next lower gear range automatically. Because the transmission is electronically controlled and there is no mechanical linkage that needs to be moved for a pre-select downshift, implementation of this algorithm can be done completely in software with no hardware modifications.
This algorithm takes into consideration several factors before commanding a pre-select downshift. These are the primary inputs:
^ Throttle position
^ Brake state (The brake must be applied to activate grade braking)
^ Vehicle acceleration/deceleration
^ Grade/Load
^ Vehicle speed
The determination of the PRNDL position is made by a logic subsystem. Several factors are calculated and weighted and then a sum is calculated. When this calculated sum surpasses a threshold, a PRNDL override is commanded.
Important : The shift speeds for grade-braking are controlled/determined as a result of "Calculated Sum" logic. However, the grade-braking shift point will never be greater than the Pre-Select Shift Point.
Edited by: Mackin
Bulletin No.: 02-07-30-004A
Date: September, 2002
INFORMATION
Subject:
New Product Information - Grade Brake Feature of Allison(R) 1000 Series Transmission
Models:
2001-03 Chevrolet Silverado Pickup Models
2001-03 GMC Sierra Pickup Models
with Allison(R) LCT1000 Series Automatic Transmission (RPO M74)
This bulletin is being revised to add the 2003 model year and additional information for clarification. Please discard Corporate Bulletin Number 02-07-30-004 (Section 07 - Transmission/Transaxle).
The grade-braking algorithm's primary purpose is to utilize engine braking to slow a heavy vehicle on steep grades in order to reduce wear on the traditional braking system. The method used to slow the vehicle is by overriding the PRNDL position, effectively preselecting the next lower gear range automatically. Because the transmission is electronically controlled and there is no mechanical linkage that needs to be moved for a pre-select downshift, implementation of this algorithm can be done completely in software with no hardware modifications.
This algorithm takes into consideration several factors before commanding a pre-select downshift. These are the primary inputs:
^ Throttle position
^ Brake state (The brake must be applied to activate grade braking)
^ Vehicle acceleration/deceleration
^ Grade/Load
^ Vehicle speed
The determination of the PRNDL position is made by a logic subsystem. Several factors are calculated and weighted and then a sum is calculated. When this calculated sum surpasses a threshold, a PRNDL override is commanded.
Important : The shift speeds for grade-braking are controlled/determined as a result of "Calculated Sum" logic. However, the grade-braking shift point will never be greater than the Pre-Select Shift Point.
Edited by: Mackin
