INTRODUCTON - MANUAL GEARBOX WITH DIFFERENTIAL

1.9 JTD 8v, 1.9 JTD 16v

SPECIFICATIONS

Transverse five/six speed gearbox with two shafts supported by roller bearings and additional shaft for reverse with double idler gears and synchromesh.

The external controls have a twin cable.

The structure of the gearbox consists of:

- a "closed end" gearbox casing configuration, the rear cover having been eliminated. This contains and supports the main and lay shafts, the gear engagement forks and rods and the gear selector/engagement device;

- clutch bell housing which contains the clutch and associated coaxial control device (CSC).

Gears are splash lubricated and also lubricated by means of ducts inside the following components:

- clutch casing and gearbox casing;

- 3rd and 4th speed control rod;

- main shaft.

The excellent lubrication of the ducts makes it possible to:

- improve the efficiency of the lubrication;

- reduce the amount of oil used thanks to the lubrication aimed at the main couplings.

1. Main shaft

2. 5th speed drive gear

3. 4th speed drive gear

4. 3rd speed drive gear

5. 2nd speed drive gear

6. 1st speed drive gear

7. Reverse drive gear

8. Layshaft

9. Satellite gears

10. Planet gears

11. Toothed ring gear

12. Gearbox casing

13. Clutch casing

14. Differential support casing

15. "CSC" clutch release co-axial hydraulic actuator

DESCRIPTION OF COMPONENTS

Main shaft

The main shaft is supported by two high precision taper bearings.

The main shaft rear bearing (1) has a Viton ring device (2), which compensates for axial thermal expansion of the gearbox casing and the main shaft.

This ring makes it possible to:

- reduce synchroniser wear;

- improve the matching of the gears;

- reduce noise from the bearings;

- improve the manoeuvrability of the gearbox.

The main shaft consists of:

- 1st speed, reverse and 2nd speed gears formed out of one piece;

- gears for 3rd, 4th and 5th/6th speeds, fitted on needle bearings with synchronisers.

Layshaft

The layshaft consists of:

- gears for 1st and 2nd speeds, fitted on needle bearings with synchronisers;

- 3rd, 4th and 5th/6th speed gears fitted on the shaft.

The layshaft is supported by two high precision taper bearings.

Gears

All the gears are designed with high contact factor teeth, i.e. when one of the teeth in the coupling is in contact, the next one has already begun meshing. This has the advantage of:

- reducing transmission irregularities;

- reducing operating noise.

The gears for 2nd and 5th/6th speeds and the final drive gears have undergone a "super-finish" treatment on the teeth after the thermal treatment.

The gears are the following type:

- helical toothed for the forward gears;

- straight toothed for reverse gear.

Synchronisers

The synchronisers for all the gears are Borg Warner, with the following brass baulk rings:

- triple cone (1) for 1st and 2nd speeds;

- single cone (2) for the 3rd, 4th and 5th/6th speeds.

Multiple cone synchronisers make it possible to:

- distribute the lever engagement load over several cones;

- facilitate the engagement of the gears.

GEAR ENGAGEMENT/SELECTION SYSTEM

The gear engagement/selection system has four selection planes with the gear positioner fitted with a bearing.

The system ensures that it is impossible to engage reverse gear accidentally because it is on a separate plane.

Bushes with a Permaglide (6) facing are used to reduce wear on:

- the couplings between the gear engagement/selector control shaft and the gearbox casing;

- the couplings between the fork rods and the gearbox casing.

The bushes make it possible to:

- achieve improved sliding;

- produce more accurate gear engagement.

1. Selector pawl

2. 1st - 2nd speed engagement/selector fork

3. 3rd - 4th speed engagement/selector fork

4. 5th - 6th speed engagement/selector fork

5. Reverse gear engagement/selector fork

6. Permaglide bushes

7. Gear engagement lever

1.4 16v TJet

CONSTRUCTION SPECIFICATIONS

The M20 manual gearbox is designed to be installed in front wheel drive systems with the engine tranversely mounted.

1. Gearbox casing

2. Clutch casing

3. Differential casing

4. Differential internal casing

5. Differential ring gear

6. Main shaft (A)

7. Clutch control coaxial actuator

8. Upper layshaft (B)

9. Second lower layshaft (C)

The specific features are:

- manual gearbox with fixed idler with six transmission ratios plus reverse;

- all gears with synchromesh (including reverse);

- toothed wheels with helical teeth;

- three shafts, one input plus two secondary (upper and lower);

- differential integrated in the gearbox casing;

- dry weight 46.7 kg;

- activation by hydraulic clutch;

- designed for matching with twin mass flywheel;

- body divided into three sections to facilitate maintenance operations.

COMPOSITION OF THE GEARBOX

Inside the gearbox each transmission ratio is produced by means of a pair of gears that mesh constantly with one freewheeling on the respective shaft. Reverse gear is an exception and is produced by means of a train with three gears to reverse the direction of power.

The main shaft receives the drive directly from the crankshaft; when a gear is selected, the torque is transferred, via the pair of gears for the speed selected, to the layshaft and, from there, to the fixed idler, connected to the differential.

First and second speed engagement diagram

First speed engagement

Second speed engagement

In first speed the power enters the gearbox via the main shaft and is transmitted, through the fixed drive gear, to the driven gear for the first speed fitted in neutral on the lower layshaft.

The activation of the synchronizer (for first and second speed) makes the toothed wheel form one piece with the layshaft and, by means of the fixed idler wheel, with the differential.

By moving the synchronizer in the opposite direction, the driven gear for the second speed forms one piece with the layshaft; the second speed is produced in this way.

Third and fourth speed

Third speed engagement

Fifth speed engagement

The power enters the gearbox via the main shaft and, by means of the fixed drive gear, is transferred to the driven gear, fitted on the upper layshaft; the activation of the synchronizer (for third and fourth speed) makes it possible to transfer the power to the toothed wheel for the fixed idler, also forming one piece with the differential ring gear, like the one on the lower shaft.

Moving the synchronizer in the opposite direction produces the engagement of fourth speed.

Fifth and sixth speed

Fifth speed engagement

Sixth speed engagement

The power enters the gearbox via the main shaft and, by means of the fixed drive gear, is transferred to the driven gear, fitted on the lower layshaft; the activation of the synchronizer (for fifth and sixth speed) makes it possible to transfer the power to the toothed wheel for the fixed idler, also forming one piece with the differential ring gear.

To engage sixth speed, the same synchronizer is activated in the opposite direction to previously.

Reverse gear

Reverse gear engagement

The power entering the gearbox is transferred from the main shaft to the gear for first speed fitted on the lower layshaft; this gear acts as a free wheel because it transfers the power to the toothed wheel for reverse gear fitted on the upper layshaft with which it meshes; at the same time, this allows the reversal of the power. The synchronizer for reverse gear makes the wheel form one piece with the upper layshaft, transferring the power to the differential.

Toothed wheels

MATERIALS AND MACHINING: the toothed wheels are subjected to variable loads over a period of time which produce stresses and fatigue; for these reasons nickel chrome steel alloys are used which afford good mechanical resistance; after machining the toothed wheels firstly undergo a finishing process (grinding) and afterwards a heat treatment that improves their resistance properties to fatigue and wear (binding and tempering).

SPECIFICATIONS: the toothed wheels used have helical teeth. The adoption of toothed wheels with helical teeth allows the transmission of higher torques compared with those of the same size with straight teeth; in addition, toothed wheels with helical teeth afford smoother and quieter operation; another important feature of the gears in the gearbox in question is the teeth with a high covering factor; several teeth (and not just one) are always meshed, with the advantage of smooth transmission.

Shafts

Main shaft (a)

1. Front bearing

2. Rear bearing

3. 1st speed gear

4. 2nd speed gear

5. 3rd-5th speed gear

6. Spacer

7. 4th speed gear

8. 6th speed gear

9. Needle bearing

SPECIFICATIONS: the gearbox input shaft has all the toothed wheels forming one piece: in particular the toothed wheels for first and second are directly on the part, i.e. they physically form part of the shaft as they are produced through mechanical machining processes, whilst the others for third and fifth speeds and fourth and sixth are fitted by means of splining in the actual shaft and are an interference with on the shaft itself.

The gearbox main shaft is supported by two conical roller bearings.

Upper layshaft (b)

1. Pinion

2. Front bearing

3. Rear bearing

4. Reverse gear

5. Reverse single cone synchronizer

6. Spacer

7. 3rd speed gear

8. 3rd-4th speed double cone synchronizer

9. 4th speed gear

SPECIFICATIONS: the upper layshaft supports the wheels that produce third and fourth forward speeds and reverse; these wheels are all fitted in neutral on roller bearings.

There are two synchronizers: one, triple cone synchronizer, designated to form one piece between the wheels for third or fourth speed with the shaft, the other single cone synchronizer, for reverse.

There is a toothed wheel on the shaft that transfers the power to the differential ring gear.

The shaft is supported by two conical roller bearings.

Second lower layshaft (c)

1. Pinion

2. Front bearing

3. Rear bearing

4. 1st speed gear

5. 1st-2nd speed triple cone synchronizer

6. 2nd speed gear

7. 5th speed gear

8. 5th-6th speed single cone synchronizer

9. 6th speed gear

The wheels that produce first, second, fifth and sixth forward speeds are fitted on this shaft; the toothed wheel for first speed is also involved in producing reverse.

The shaft is supported by two conical roller bearings.

Synchronisers

The diagram shows the exploded view of the synchronizer for first and second speeds. It is the triple cone type to ensure optimum continuity and smooth transfer of torque between the shafts.

1. On the synchronizer for first and second speeds, two of the three cones contain a carbon friction ring

2. The synchronizer for first and second speeds also has this friction ring on all three cones.

3. The synchronizers for fifth and sixth speeds and reverse are the single cone type (they do not have the first two cones).

In the case of the synchronizer for fifth and sixth speeds and reverse, given the lesser torque produced by the actual gearbox, a single cone synchronizer is used.

In the case of the synchronizer for third and fourth speeds, a double cone synchronizer is used.

Gear selector and engagement assembly

The gear selector and engagement assembly comprises a kinematic arrangement connected, by means of cables, to the control lever in the passenger compartment.

The kinematic arrangement has two possible movements: vertical travel designed to select the synchronizer; movement in a rotary direction is designed to activate the fork for the synchronizer.

1. Gear engagement lever

2. Gear selection lever