Subaru Impreza STi Manual Transmission Documents

Subaru Impreza STi Manual Transmission Material


Vehicle specs

  • Year: 2000
  • Model: GDB
  • Engine model: EJ207
  • Transmission model: TY85

table of contents

Overview of 6-speed manual transmission and operating system

In order to improve driving performance by transmitting and controlling the torque of the STi specification DOHC high power turbo engine (maximum output 206kW-maximum torque 373Nm), a full-time 4WD 6-speed manual transmission has been adopted to improve the operation system. There is. As an operation system, in order to cope with the high power of the engine, the starting performance is improved by increasing the clutch capacity and improving the clutch oil pressure gauge.

Main features of full-time 4WD 6-speed manual transmission
  • A double cone synchromesh mechanism is used for 1st, 3rd and reverse, and a triple cone synchromesh mechanism is used for 2nd speed to improve durability and operability.
  • The main case is a split type to improve rigidity.
  • The reverse gear always uses a meshing method.
  • The oil pump is located in the main case.
  • The front differential is equipped with a torque-sensitive cam type LSD, and the center differential is equipped with a driver’s control type or viscous coupling type.
  • The gear shift system uses a floor shift parallel link type and slider type reverse erroneous operation prevention mechanism.

Figure 1: Inside the transmission

Clutch and operating system

The clutch capacity of the clutch disc has been increased from the conventional outer diameter x inner diameter: 230 mm x 150 mm to 240 mm x 160 mm. The clutch operation system is a hydraulic pull type, and an orifice is provided in the hydraulic circuit to prevent sudden clutch engagement.


Figure 2: Hydraulic clutch control system

Hydraulic clutch control system

The clutch master cylinder is a compensatory type, and a clutch orifice is added to the hydraulic circuit between the clutch master cylinder and the clutch operating cylinder to reduce the shock torque when the clutch is connected, and inside the orifice. A compression spring made of a shape memory alloy is provided in the hydraulic circuit to ensure that the clutch operation delay due to the orifice does not occur at low temperatures.

  • Operates at room temperature

The clutch orifice is integrated into the clutch operating cylinder and consists of an orifice retainer, an orifice valve and a compression spring. The orifice valve is usually pressed against the body with compression spring No1.


Figure 3: Clutch orifice operates at room temperature

  • Operates at low temperatures

At low temperatures, the shape memory alloy compression spring No. 1 contracts to eliminate the spring action, and the compression spring No. 2 presses against the orifice retainer to ensure a sufficiently wide oil passage.


Figure 4: Clutch orifice operating at low temperatures

About 6-speed transmission

Specification drawing

Figure 5: Transmission specification diagram

Speed ​​change mechanism

The transmission mechanism has two main transmission gears with a main shaft and a drive pinion shaft arranged in parallel, with 6 forward and 1 reverse gears that are always engaged, and the reverse reverses the direction of rotation via the reverse idle gear. It is a method to make.

Helical gears are used for all gears, and the gear specifications and tooth width have been reviewed and the distance between the centers of the main transmission gears has been expanded to 85 mm to improve gear strength.

  • Synchromesh mechanism

The synchromesh mechanism adopts multi-cone synchro for 1st to 3rd speed and reverse to reduce the shift operation force. The reverse synchro is located in the reverse idle gear section.

In addition, asymmetric gear dogs are used for 2nd to 6th gears to improve operability.


Figure 6: Transmission gear and cone types


Figure 7: Inside the synchromesh mechanism

  • Reverse gear

As the reverse gear is constantly engaged, a scissors gear is installed in the reverse idler gear No. 1 to improve quietness.

The reverse idle gear consists of a reverse idle gear N01, a scissors gear, a spring friction plate and a snap ring.

By sandwiching the drive side gear between the scissors gear and the idler gear that have received the spring force, the backlash of the gear is set to 0 and rattling due to the meshing of the gear is prevented.


Figure 8: Reverse gear

Shift and select mechanism

The shift pattern is a floor shift system with 6 forward steps and 1 backward step, and friction is achieved by adopting slide ball bearings for each rod support and mounting a ball built-in plunger on the shift detent mechanism. Has been reduced and operability has been improved.


Figure 9: Shift fork

The select mechanism unit realizes a short select stroke as a parallel link method. The interlock (double meshing prevention) mechanism adopts a slider pull-up type as a reverse check (reverse malfunction prevention) mechanism as a block type.

  • Shift dedent mechanism and rod support structure

The shift dedent mechanism uses a check ball to prevent the gear from coming off. A small ball is embedded in the back of the check ball part.

Slide ball bearings are used for each rod support.


Figure 10: Shift dedent mechanism (prevention of gear disengagement)

  • Select / return mechanism

The select / return mechanism consists of a shifter arm shaft, selector arms (No. 1 and 2), a striking rod and a set spring (neutral).


Figure 11: Select return mechanism

The select / return force corresponds to the movement of the selector arm, and the set spring (neutral) is expanded by the fulcrum on the selector arm, and is generated by the return force of the spring.


Figure 12: Selector arm movement

  • Interlock mechanism
The interlock mechanism is a block type, and the reverse is arranged independently on the layout.

Figure 13: Interlock mechanism

    • Normal selection
Except for the selected arm, the interlock block engages and is locked.

Figure 14: Normal selection

    • During an intermediate shift (during double engagement)
At the position where the two shifter arms are selected, all shifter arms are locked by the interlock block.

Figure 15: During an intermediate shift

  • Reverse check mechanism
The reverse check mechanism in the transmission is operated via the reverse check cable by pulling up the slider on the shift lever, and the reverse check mechanism is located in the extension case of the transmission.

Figure 16: Reverse check mechanism

    • When shifting to 5th or 6th gear

When selected to the 5th or 6th speed side, the selector arm comes into contact with the plunger. Since the plunger is interlocked by the pins, the rotation of the selector arm is restricted.


Figure 17: 5th or 6th gear shift

    • At the time of reverse shift
By pulling up the slider (shift lever) to reverse, the reverse check mechanism on the transmission side is unlocked via the reverse check cable, so the selector arm rotates while pushing up the plunger, enabling selection to reverse. Become.

Figure 18: During reverse shift

4WD transfer device (center differential)

The 4WD transfer device is installed behind the transmission and has a compact center differential LSD between the drive pinion shaft that drives the front wheels and the transfer gear that drives the rear wheels. There are two types of this LSD, the viscous coupling method and the driver’s center differential. Here, the driver’s center differential will be explained.
Driver’s Control Center Differential
The basic structure is a planetary gear system for the center differential, the operation limiting device is an electromagnetic crimp variable control multi-plate clutch, and the front-rear drive distribution is 45:55. In addition, the overall length has been shortened to support 6-speed gears, and the outer diameter of planetary gears and multi-plate clutches has been reduced.

Figure 19: Driver’s Control Center Differential

  1. When an electric current flows through the electromagnetic coil, a magnetic field is generated between the electromagnet, the differential case, the pilot clutch, and the armature.
  2. The pilot clutch and armature are attracted to the electromagnet by the next induction action, and the rotational torque (pilot torque) of the differential case rotates the cam NO2.
  3. When the cam NO2 rotates, the rotation is different from that of the cam NO1, so the ball rolls and a thrust force is generated, and the planetary gear that can move in the axial direction is slid to press the main clutch to generate the differential limiting torque.
  4. Since the strength of the magnetic field increases in proportion to the amount of current flowing, the differential limiting torque also increases in proportion to the amount of current. In addition, the amount of current can be changed in 5 stages by the driver operating the control switch.

Figure 20: Driver’s Control Center Differential operation

Front differential

The front differential uses a large hypoid gear (R180) for high output. In addition, a torque-sensitive cam-type LSD is set as a manufacturer option for the front differential.
Torque sensitive cam type LSD
The structure is the same as the torque-sensitive cam type LSD used for the rear differential, and it has the feature that the torque bias ratio can be selected widely.
Since no relative rotation occurs between the left and right face cams while traveling straight, the input torque from the drive gear is transmitted to the face cam from the side surface of the cam follower.
When relative rotation occurs in the face / upper notch due to turning or slipping, the cam follower reciprocates left and right while transmitting torque to the face cam.

Figure 21: Torque-sensitive cam LSD

Transmission / lubrication system

An oil pump is installed at the rear of the main case and pumped to the lubrication passages such as the main shaft, drive pinion shaft, and transfer to forcibly lubricate each part, and an oil chamber is provided to reduce stirring resistance. We are trying to improve efficiency.
The oil pump is a thin trochoid type, driven via a gear integrated with the center differential case, and has a regulator valve and a relief valve on the discharge side.

Figure 22: Transmission lubrication system

Citation sources / references / websites

Some of the texts on this site are quoted from the following books, publications, and websites.
・ “Vehicle motion performance and chassis mechanism” Takaaki Uno (Author) Grand Prix Publishing
・ Maintenance Chief Training Material (Technology) Automotive Maintenance New Technology Department Training General Incorporated Association Japan Automobile Maintenance Promotion Association (Author) * Publication year unknown

Leave a Reply

Your email address will not be published. Required fields are marked *