Automatic Shifting

Automatic shifting chooses the gear in Drive and Sport. It can also add automatic up shifts, down shifts and kickdown to Manual mode, for example to shift up at the rev limit or down before the engine lugs.

There are three ways to tell the TCM when to shift:

• Speed - Simple: one up shift table and one down shift table give the speed to shift at.
• Speed - Per Gear: a separate table for every up shift and down shift.
• Gear Request: the table holds the gear to be in.

Whichever is used, every automatic shift still has to pass the same checks as a manual shift (input shaft speed limits, Takeup, time since the last shift and so on, see When an Automatic Shift Is Blocked).

Enabling

Turn on Enable in Automatic Shift > Auto Shift Setup. The rest of the settings and the Drive Mode, Sport Mode, Manual Mode and Hill Control folders appear once it is on.

Speed Reference

In the Speed modes, the up shift and down shift tables hold a speed, in the units of the Speed Reference:

With an RPM reference (engine or input shaft), the same number can suit every gear, for example “shift up at 6500 RPM at full pedal”. With a road-speed reference (vehicle, drive or output shaft speed), every gear needs its own shift points: use Speed - Per Gear, or put Gear on an axis of the Simple tables.

Skip shifts are worked out from the gear ratios, so they need an Engine Speed or Input Shaft Speed reference. With a road-speed reference each automatic shift moves one gear, see Skip Shifts.

Table Modes

Every mode also uses:

• Drive Mode Up Shift Enable and Drive Mode Down Shift Enable (and the Sport versions), see Shift Enable Tables.
• Drive Mode Shift Trigger Delay (and Sport Mode Shift Trigger Delay), see Shift Trigger Delay.

The table axes can be any channel. Typical choices are Pedal Position or Throttle Position against Gear, a speed, or Transmission Fluid Temperature.

Speed Modes

How a Shift Is Triggered

In Drive and Sport, every control cycle:

• Up shift when the Speed Reference is at or above the up shift speed, the Up Shift Enable table is on, and both have been true for longer than the Shift Trigger Delay.
• Down shift when the Speed Reference is at or below the down shift speed, the Down Shift Enable table is on, and both have been true for longer than the Shift Trigger Delay.

Up shifts are checked first. A shift speed of 0 means no shift in that direction.

In Speed - Simple mode with Gear on an axis, the column for a gear holds the shift point from that gear. In the up shift table, the gear 3 column is the 3 to 4 shift point. In the down shift table, it is the 3 to 2 shift point. Set the top gear’s up shift column to 0.

Up and Down Shift Speeds

Leave a gap between the up shift and down shift points, or the transmission will shift back and forth. With an RPM reference, check the speed after each shift:

• After an up shift the RPM drops by the ratio step. On a ZF 8HP, 6500 RPM in 2nd becomes about 4400 RPM in 3rd. The 3rd gear down shift speed must be well below that.
• After a down shift the RPM rises by the ratio step. The up shift speed for the lower gear must be well above that.

With a road-speed reference the speed doesn’t change through the shift, so simply keep each gear’s down shift speed below the speed it was up shifted at.

Typical shapes:

• Up shift speed rising with pedal: early, economical up shifts at light pedal, and full use of the engine’s speed range at full pedal.
• Down shift speed rising with pedal: pressing the pedal further down shifts sooner. This is the Drive mode kickdown.

Shift Enable Tables

The Up Shift Enable and Down Shift Enable tables switch automatic shifting in each direction on (1) or off (0), based on any channels. For example:

• Transmission Fluid Temperature: hold lower gears while the fluid warms up.
• Lateral acceleration: no up shifts mid-corner in Sport.
• A User Function or switch: a “hold gear” button.

Any value above 0 counts as on. Between an on cell and an off cell, the shift stays enabled right up to the off cell.

Shift Trigger Delay

The Shift Trigger Delay tables (ms) set how long a shift condition must hold before the shift is requested. This stops a speed that briefly crosses a shift point, or a quick pedal movement, from causing a shift. Putting Pedal Position on an axis lets kickdowns at high pedal be quick while light-pedal shifts wait longer.

The delay starts again after every shift, so each shift needs its own shift condition to hold for the delay.

The delay is also what allows skip shifts, see Skip Shifts.

Skip Shifts

Up Shift Stacking Limit and Down Shift Stacking Limit (Shift Setup > Up Shift > Up Shift Setup and Shift Setup > Down Shift > Down Shift Setup) set the most gears one automatic shift can move. 0 and 1 both mean one gear at a time for automatic shifts.

Above 1, the TCM keeps going to the next gear while the speed that gear would give is still past the shift point, for example dropping from 6th straight to 3rd when the pedal is floored. This needs an Engine Speed or Input Shaft Speed (or Input Shaft Speed (Calculated)) Speed Reference. A road speed doesn’t change when the gear changes, so with a Vehicle, Drive or Output Shaft Speed reference the stacking limits are not used and each automatic shift moves one gear. A skip shift never goes past the top gear or below the gear in the Initial Gear table. It is shortened to keep Input Shaft Speed between Input Shaft Speed Min and Input Shaft Speed Max. On a dual-clutch transmission a skip shift has to change to the other clutch, so the TCM may shorten it by a gear.

The number of gears is worked out when the Shift Trigger Delay runs out. A skip shift needs a Shift Trigger Delay above 0. With a delay of 0, the shift is requested the moment the shift point is crossed, when the speed is only just past it, so only one gear is ever justified and the transmission shifts one gear at a time whatever the stacking limit. The delay gives the speed, or a shift point that moves with the pedal, time to get further past, and that is what lets the TCM skip gears. For skip-shifting kickdowns, keep the delay short at high pedal, but not 0.

Gear Request Mode

In Gear Request mode, the Drive Mode Gear Request and Sport Mode Gear Request tables hold the gear to be in (1 to 12). The axes can be anything, typically Vehicle Speed against Pedal Position.

The table is interpolated, so between a 3 cell and a 4 cell its value moves smoothly from 3.0 to 4.0. The Auto Shift Gear Table channel shows the value.

Hysteresis

Gear Request Table Hysteresis (0-100%) sets how far past the halfway point between two gears the table value must go before the TCM shifts:

At 100% the shift points are exactly where the cells are: up to 4th when the table reaches the 4 cell, back to 3rd only when it reaches the 3 cell. The spacing between neighbouring cells is then the hysteresis. 0% gives no hysteresis and isn’t recommended.

Holding the Gear

A cell of 0 means “hold the current gear”. Any table value below 1 holds.

To hold the gear under particular conditions (a hold switch, cold fluid, cornering), the Up Shift Enable and Down Shift Enable tables are usually easier: they hold the gear without interpolating against the gear cells.

Limits

The table can ask for any gear, but each shift is limited:

• It moves no more than the stacking limit (see Skip Shifts). As in the Speed modes, a skip shift needs a Shift Trigger Delay above 0, so the table value has time to move more than one gear.
• It never goes above the top gear or below the gear in the Initial Gear table.
• An up shift is shortened to the highest gear that keeps Input Shaft Speed above Input Shaft Speed Min. A down shift is shortened to the lowest gear that keeps it below Input Shaft Speed Max.
• The Up/Down Shift Enable and Shift Trigger Delay tables still apply.

Speed Reference, Shift Lead Time Compensation and Hill Control are not used by Gear Request mode. Shift Lead Time Compensation still applies to the Manual mode Auto Up Shift and Auto Down Shift.

Sport Mode

With Sport Tables on, Sport uses every table in the Sport Mode folder: the shift speed or gear request tables, the enable tables and the trigger delay. With it off, Sport behaves like Drive. See Drive Modes for how Sport is selected.

Shift Lead Time Compensation

A shift takes time to complete. While the speed is rising quickly, the engine is already past the up shift point by the time the shift finishes. With Shift Lead Time Compensation on, the TCM looks at how fast the Speed Reference is changing and starts the shift early by the amount it will change during the shift. Up shifts under hard acceleration then finish close to the table’s up shift speed. Down shifts while slowing down are started early in the same way.

The shift time is taken from the clutch fill time, plus the up shift transfer time for up shifts (see Multi-Clutch Shifting). The Shift Trigger Delay is allowed for as well: the shift point is moved early by the change over the shift time plus the delay, so the delay still filters out a speed that only briefly crosses the shift point, and the shift still finishes near the table’s speed.

Compensation never brings an up shift point forward by more than half of its table value, so a very low up shift speed under hard acceleration still gives a sensible shift.

It only acts while both are true:

• Engine Speed is at or above Shift Lead Time Engine Speed Min.
• Pedal position (or throttle position if there is no pedal) is at or above Shift Lead Time Pedal/Throttle Min.

It also applies to the Manual mode Auto Up Shift and Auto Down Shift.

Hill Control

Hill Control (Speed modes only) changes the down shift points on steep grades, using Pitch Angle (X) from the TCM’s IMU (positive nose up). The IMU must be mounted and calibrated. Hill Control is off while the IMU is calibrating or has a hardware error.

Hill Ascent

With Hill Ascent Control on, Hill Ascent becomes active when Pitch Angle (X) stays above Hill Ascent Pitch Threshold for Hill Ascent Delay. It ends once the pitch has been below the threshold minus Hill Ascent Pitch Hysteresis for the same delay, so a bump in the road doesn’t end it.

While it is active, the Hill Ascent Down Shift Speed table (in Speed Reference units) is used as the down shift speed when it is higher than the normal one, and the up shift speed is raised by the same amount. The transmission down shifts sooner on the climb and holds the lower gear instead of shifting up and down.

Hill Descent

With Hill Descent Control on, Hill Descent becomes active when Pitch Angle (X) stays below Hill Descent Pitch Threshold (a negative angle, nose down) for Hill Descent Delay. It ends once the pitch has been above the threshold plus Hill Descent Pitch Hysteresis for the same delay.

While it is active, the Hill Descent Down Shift Speed table works the same way, to hold a lower gear for engine braking.

Hill Ascent Control and Hill Descent Control show ON while each is active and its table is above 0.

Manual Mode

Manual mode normally only shifts when the driver asks. Automatic Shift > Manual Mode > Manual Mode Auto Shift Setup adds optional automatic shifts. They need automatic shifting Enable on, and also work while Manual has been selected by Manual Override.

Auto Up Shift and Auto Down Shift

• Auto Up Shift: shifts up one gear as soon as the Speed Reference reaches Manual Mode Up Shift Speed. Typically used to shift at the rev limit if the driver doesn’t.
• Auto Down Shift: shifts down one gear as soon as the Speed Reference falls to Manual Mode Down Shift Speed. Typically used to stop the engine lugging or stalling. It doesn’t shift below the Initial Gear.

These shifts only wait for a very short fixed delay, enough to ignore a single bad speed reading. A value of 0 in either table means no shift.

Kickdown

With Kickdown on, the TCM down shifts when the Speed Reference has been below Kickdown Speed for Kickdown Shift Trigger Delay (ms). With Pedal Position on an axis of the Kickdown Speed table (0 at light pedal, a speed at full pedal), flooring the pedal at low RPM in a high gear kicks down.

The Kickdown Setup page sets:

• Kickdown Minimum Gear: kickdown only acts above this gear and never shifts below it.
• Kickdown Stacking Limit: the most gears one kickdown can drop. Above 1, it drops as many gears as needed to bring the Speed Reference above Kickdown Speed, but never below the Initial Gear and never so far that Input Shaft Speed would go above Input Shaft Speed Max. 0 and 1 both mean one gear. As with Skip Shifts, dropping more than one gear needs an Engine Speed or Input Shaft Speed reference, and a Kickdown Shift Trigger Delay above 0.

While a kickdown is being requested, Auto Up Shift and Auto Down Shift are ignored.

Coming to a Stop

In Drive and Sport, if the car stops in a gear above the Initial Gear, the TCM shifts down towards the Initial Gear even when the shift tables don’t ask for it. This covers a 0 cell in a down shift table, a Gear Request hold cell, or braking harder than the down shifts can keep up with. Each shift moves as many gears as Down Shift Stacking Limit allows.

The car counts as stopped when all of these are true:

• Output Shaft Speed is low enough that even the Initial Gear would put the input shaft at or below Input Shaft Speed Min.
• The speed of the shaft the engaged gear is on (Input Shaft Speed, or on a dual-clutch transmission the active clutch’s shaft) is at or below Input Shaft Speed Min.
• Vehicle Speed and Drive Speed read 0, if they are set up.

The Down Shift Enable table must be on, and the stop must last for the Shift Trigger Delay. Because every speed source has to agree, one failed speed sensor reading 0 can’t cause a down shift while driving. With Input Shaft Speed Min at 0, only a complete stop counts.

This is a backstop. Tune the down shift tables so the transmission is normally already in the Initial Gear by the time the car stops.

When an Automatic Shift Is Blocked

An automatic shift is not made while any of these apply. Auto Shift Status shows what automatic shifting is doing (Auto Shift Status), and Shift Request Status shows why a requested shift was refused (Shift Request Status).

Input Shaft Speed Min and Max are the main protection against lugging and over-revving. Set them before tuning the shift tables.

When Drive is selected from Neutral, the TCM engages the gear in the Initial Gear table. If the car is already moving, it picks the highest gear that keeps Input Shaft Speed above Input Shaft Speed Min.

Up / Down Shift Switches in Drive and Sport

Up / Down Shift Switch Behaviour sets what an Up Shift or Down Shift switch press does in Drive or Sport:

Holding Down Shift in 1st to select Neutral, and holding Up Shift in Neutral to select Drive, work with either setting (see Drive Modes).

Monitoring

The automatic shift channels read 0 (Auto Shift Status: Off) in Park, Reverse and Neutral.

Auto Shift Status

Tuning Procedure

1. Basics first. Check the gear ratios, Number of Forward Gears, Initial Gear, Input Shaft Speed Min and Input Shaft Speed Max, and Next Up Shift Delay / Next Down Shift Delay. Get the shifts themselves working well with the switches in Manual (see Multi-Clutch Shifting).
2. Choose the mode. Pick a Table Mode and, for the Speed modes, a Speed Reference. Input Shaft Speed with Speed - Simple is the quickest start. Gear Request suits a road-speed based shift map.
3. Start simple. Set both stacking limits to 1, and leave Sport Tables, Shift Lead Time Compensation and Hill Control off. Set the enable tables to 1 everywhere and the trigger delays to a few hundred milliseconds.
4. Up shifts. Fill the up shift tables: early at light pedal, near the top of the engine’s useful speed range at full pedal.
5. Down shifts. Fill the down shift tables, leaving a clear gap below the speed each up shift lands at, and make sure each gear down shifts before the car slows to a stop.
6. Drive and log. Look for hunting (repeated up and down shifts), shifts that come too late at full pedal, and lugging at light pedal. Adjust the tables and trigger delays. When an expected shift doesn’t happen, Auto Shift Status and Shift Request Status show why.
7. Refine. Add enable table conditions (fluid temperature, cornering), Sport tables, skip shifts and Shift Lead Time Compensation, one at a time.
8. Hill Control and Manual mode. Set these up last, on a known grade and with Manual selected.

Channels worth logging while tuning:

• Auto Shift Status
• Gear
• Requested Gear
• Transmission Drive Mode
• Auto Up Shift Speed
• Auto Down Shift Speed
• Auto Shift Gear Table (Gear Request mode)
• Shift Request Status
• Your Speed Reference
• Pedal Position or Throttle Position
• Input Shaft Speed
• Your table axes