ZF GETRIEBE N.V. SINT-TRUIDEN - Description Automatic Gearbox VT1F

ZF GETRIEBE N.V. SINT-TRUIDEN

Description
Automatic Gearbox
VT1F
Davy Geuns
June 2003

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Table of contents
I.
General Description VT1F 4
1. Introduction 4
2. Conventional Autom. Transmission vs. Continuously Var. Transmission 6
3. Basic Principles of Continuously Variable Transmission 7
4. Shift Positions 8
5. Functionality in Park and Neutral 9
6. Normal Operation 9
7. Transmission Communication 10
8. Related Car Components 10
8.1 Centre Controle LEDs 10
8.2 Instument Cluster Display 10
8.3 Selector Lever Mechanics 10
8.4 Torsional Damper 11
9. Towing of the Vehicle 11
10. Drain and Refill 11
II.
Transmission Layout 12
1. Group One – Mechanical Torque Flow 13
1.1 Planetary Gear Set 13
1.2 Multiplate clutches 14
1.3 Pulley and Steel Belt 15
1.4 Pinion Shaft 16
1.5 Differential 16
1.6 Mechanical Operation 17
1.6.1 Selector Lever in the Park or Neutral Position 17
1.6.2 Selector Lever in the Drive Position 18
1.6.3 Selector Lever in the Reverse Position 19
2. Group Two – Control System 20
2.1 Oil Pump 20
2.2 Valves 21
2.3 Pitot system 21
2.4 Sensing Shoe 22
2.5 Oil Temperature Sensor 22
3. Group Three – External Connections 23
3.1 Park / Neutral Switch 23
3.2 Oil Cooler Locations 24
3.3 Transmission Secondary Speed Sensor 25
3.4 Selector Shaft 26
3.5 Connector 26
III.
Strategies 27
1. Behaviour in Specific Situations 27
1.1 Idle when Drive is Selected 27

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1.2 Take Off / Pulling Away 27
1.3 Light Throttle Acceleration in Drive or Sport 27
1.4 Kick Down in Drive or Sport 28

1.5 Emergency Stop 28
1.6 Reverse Running 28
1.7 Fault Mode 28
2. CVT Software 29
3. Transmission Reset and Reference 30
IV.
Adaptation Procedures 31

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Description Transmission VT1F
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Automatic Gearbox – VT1F
Fig. 1: Gearbox and selector mechanism
I. General description VT1F
1. Introduction
The stepless shifting pattern of the transmission provides a very comfortable drive, as well as
having full vehicle performance, available at any time.

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Description Transmission VT1F
Page 5 of 31
The advantages of using an automatic transmission of this type are:
- Low engine revolutions at constant speeds.
- Improved emission control/fuel consumption.
- Low noise, vibration and harshness levels.
- Smooth acceleration.
- Flexible driving on mountain roads.
Fig. 2:
CVT box
Fig. 3:
Bell Housing

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Description Transmission VT1F
Page 6 of 31
2. Conventional Automatic Transmission vs. Continuously Variable Transmission.
In the figure below the variograms of a hand shifted or normal automatic transmission and the
CVT are compared with each other. With the conventional automatic transmission, maximum
6 ratio’s (gears) are available, but mostly even less. When the transmission upshifts, it has to
follow the bold or dotted lines of the first image depending of the amount of throttle. With the
CVT, the whole range of ratios between the Low and the Overdrive lines is available for
shifting as shown in the second image.
The shift point of both transmissions is related to the amount of throttle. As more throttle is
applied, the transmission upshifts at a higher engine speed. With the conventional
transmission it is clear that the engine speed drops back when shifting to a higher gear. This is
not the case with the CVT. The CVT will upshift at a constant engine speed, by moving the
pulleys as explained in the next part. However, alternative shifting strategies are also possible.
This can help to create a quicker acceptance by new CVT drivers.
Fig. 4: Variogram 4 step automatic transmission and CVT Transmission.

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Description Transmission VT1F
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3. Basic Principles of Continuously Variable Transmission
1 Input from the engine
2 Output to the wheels
3 Drive pulley at minimum
diameter (Low)
4 Driven pulley at maximum
diameter (Low)
Fig. 5:
Pulleys in low position
1 Input from the engine
2 Output to the wheels
3 Drive pulley at maximum
diameter (overdrive)
4 Driven pulley at minimum
diameter (overdrive)
Fig. 6:
Pulley positions in high ratio (overdrive)
Unlike conventional planetary automatic transmissions that provide a limited number of gear
ratios, usually four, five or six, the CVT, as its name suggests, continuously varies the gear
ratio. A low gear (low ratio) makes it easier to pull away from a rest position, the drive pulley
diameter being relatively small, while the driven pulley diameter is large by comparison. The
drive belt is used to transmit power and torque. As acceleration takes place it becomes
possible to select a higher ratio by increasing the diameter of the drive pulley while, at the
same time, decreasing the diameter of the driven pulley. This degree of change can be
controlled to ensure that the most suitable ratio is provided.
The CVT uses a primary pulley and a secondary pulley. Both pulleys have one fixed half and
one mobile half, controlled by hydraulic pressure. The position of the drive belt on the pulleys
will determine the ratio. If the mobile half of the pulley is close to its opposite half then the
drive belt is forced to travel around the outer circumference. When the pulley is open wide
then this circumference is reduced. The primary and secondary pulley mobile halves are

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Description Transmission VT1F
Page 8 of 31
diagonally opposed so when the drive belt diameter is reduced on the primary pulley, it
increases on the secondary pulley.
To pull away, a low ratio is required. To provide this, the primary pulley is open, allowing the
drive belt to sit down into the pulley and forcing it to run around the outer of the closed
secondary pulley. As vehicle speed increases, a higher gear ratio is required. To do this, the
primary pulley gradually moves towards its fixed partner, increasing the pulley
circumference. At the same time the secondary pulley is forced apart reducing pulley
diameter, therefore creating a higher gear ratio. An overdrive ratio is obtained when the
primary pulley is fully closed and the secondary pulley is fully open. The secondary pulley is
now forced to rotate approximately two and a half time for every turn of the primary pulley.
4. Shift Positions.
Possible shift positions for the VT1F are Park, Reverse, Neutral, Drive and Sport/Manual
position (other shifter lay outs are also possible of course, for instance with an L position).
In the Drive position, the car will move forwards in standard CVT mode. The engine speed
will be limited to approximately 4500 rpm unless kick down is used by fully depressing the
throttle pedal when the engine speed will rise to approximately 5500 rpm. Of course other
calibrations are also possible.
In the Manual/Sport position, the car will move forwards in CVT sport mode. The engine
speed will be limited to approximately 5000 rpm unless kick down is used by fully depressing
the throttle pedal when the engine speed will rise to approximately 5500 rpm. Again, other
calibrations are also possible.

1. Illuminated gear position
2. Gear selector lever
Fig. 7:
VT1F gear lever & M+ /-
In Sport position the transmission will be tuned in a different way than in Drive mode. The
transmission will upshift at a higher engine speed, providing more sportive driving. The Sport
driving calibration is designed to be more responsive to driver command, but will be less
refined than the D position.

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Description Transmission VT1F
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If the gear shift lever is moved into the ‘Plus’ or ‘Minus’ position from Manual/Sport, the
system will change into Manual mode. The transmission then works with 6 (or more) “gear”
ratios. The system will select a gear appropriate to road and driving conditions. To change up
a gear, the driver must move the gear lever to the ‘Plus’ position. To change down, the driver
must move the gear lever to the ‘Minus’ position.
If the CVT software decides that a shift might cause damage to the transmission, such as
attempting to shift to 1st gear at 100 km/h, the gear change will be prevented. If the driver
does not shift up, the next gear will be automatically selected when the engine revolutions
reach approximately 6000 rpm. Equally, if the driver does not shift down when reducing
vehicle speed, the system performs the down-change automatically thus ensuring the
transmission is in the appropriate gear.
5. Functionality in Park and Neutral
The engine can only be started in Neutral or Park, as with any automatic transmission.
A spring and cone operated pawl mechanically locks the secondary pulley when the selector
lever is moved to the Park position. If the lever is set in the Park position when the vehicle
has a higher speed, the pawl will rattle without engaging Park. It will not engage until the
vehicle speed drops below approximately 5 km/h.
1. Parking pawl
2. Secondary pulley
Fig. 8:
Parking lock
6. Normal Operation
The operation of the transmission, during driving, has no comparison with that of a
conventional automatic transmission. All kinds of tunings are possible. A possible tuning is
that if the accelerator pedal is depressed sharply, the engine rpm will rise considerably more
than in relation to the speed of the vehicle. This functionality is normal for a CVT but may
surprise drivers not familiar with this type of transmission. Other tunings / variograms are
also possible, for example tunings that are closer to that of a conventional automatic
transmission.

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Description Transmission VT1F
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7. Transmission Communication
The VT1F has electronic components to control the gear ratios, the clamping force on the belt
and the clutch pressure. The location of the components that form the steptronic transmission
vary depending upon vehicle installation.
There are different options for the position of electronic components in the transmission. For
example, the control methods associated with the transmission can be run as part of the
software in the ECU. The CVT software in the ECU receives inputs from the main sensors of
this system, communicates with the gearbox interface unit (GIU) to control the transmission,
accepts driver inputs and provides information to the driver via the instrument cluster. With
this example the software is located in the ECU, while the drivers are in the Gearbox Interface
Unit (GIU). It is also possible to put both the software and the drivers in a TCU.
8. Related Car Components
8.1
Centre Console LEDs
The configuration of which controle LEDs are to be used depends on customer.
8.2
Instrument Cluster Display
The same is valid for this part. The Instrument Cluster Display is also defined by the
customer.
8.3
Selector Lever Mechanics
Park, Reverse, Neutral and Drive Switches
The configuration of the selector lever is customer specific. A shift lock (as in the picture
below) must be integrated in the mechanism, to provide an idiot start protection.
1. Gear selector lever
2. Gear selector lever detent
3. Shift lock
4. Gear change selector rod
Fig. 9:
VT1F selector lever mechanism

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