Clutch Volume Indexes

An important function of the TCM is to monitor Clutch Volume Indexes (CVI). CVIs represent the volume of fluid needed to compress a clutch pack.
The TCM monitors gear ratio changes by monitoring the Input and Output Speed Sensors. The Input, or Turbine Speed Sensor sends an electrical signal to the TCM that represents input shaft rpm. The Output Speed Sensor provides the TCM with output shaft speed information.
By comparing the two inputs, the TCM can determine transmission gear position. This is important to the CVI calculation because the TCM determines

Fig. 28:

CVIs by monitoring how long it takes for a gear change to occur (Fig. 28).
Gear ratios can be determined by using the DRB Scan Tool and reading the Input/Output Speed Sensor values in the "Monitors" display. Gear ratio can be obtained by dividing the Input Speed Sensor value by the Output Speed Sensor value.
For example, if the input shaft is rotating at 1000 rpm and the output shaft is rotating at 500 rpm , then the TCM can determine that the gear ratio is 2:1. In direct drive (3rd gear), the gear ratio changes to 1:1. The gear ratio changes as clutches are applied and released. By monitoring the length of time it takes for the gear ratio to change following a shift request, the TCM can determine the volume of fluid used to apply or release a friction element.
The volume of transmission fluid needed to apply the friction elements are continuously updated for adaptive controls. As friction material wears, the volume of fluid need to apply the element increases.

Clutch Volume Index Chart:

Certain mechanical problems within the input clutch assembly (broken return springs, out of position snap rings, excessive clutch pack clearance, improper assembly, etc.) can cause inadequate or out-of-range element volumes. Also, defective Input/Output Speed Sensors and wiring can cause these conditions. The Clutch Volume Index Chart identifies the appropriate clutch volumes and when they are monitored/ updated:

SHIFT SCHEDULES

Shift Schedule Chart:

As mentioned earlier, the TCM has programming that allows it to select a variety of shift schedules. Shift schedule selection is dependent on the following:
- Shift lever position
- Throttle position
- Engine load
- Fluid temperature
- Software level
As driving conditions change, the TCM appropriately adjusts the shift schedule. Refer to the Shift Schedule chart to determine the appropriate operation expected, depending on driving conditions.