The present invention relates to a motor vehicle gearbox comprising an input shaft, two intermediate shafts which are drivable alternately via gear wheels on the input shaft and respective intermediate shafts, at least one of said gear wheels of each cooperating pair of gear wheels being releasable, and an output shaft which presents a gear wheel engaging a fixed gear wheel on each of said intermediate shafts.

In most cars with manual gearboxes, mechanical chatter is present during idling and driving at low engine revolutions. The noise arises as the teeth of the gear wheels impact each other at a certain frequency when an acceleration is imparted to the gear wheels in the gearbox due to uneven running of the motor at low revs. This unevenness is transmitted via the clutch and input shaft and is dependent on the engine as well as lag in the gearbox. The engine's flywheel has larger angular acceleration and amplitude of oscillation at low revs, so that the idling noise in most cases increases with reduced revs. A low idling speed is however generally desirable since it results in better fuel economy.

Several different methods for damping or totally eliminating idling chatter in gearboxes are nown. For example, clutches with particular rigidity and damping can be used, the moment of inertia of the flywheel can be increased or the tooth clearance reduced. In addition, friction brakes can be used in the gearbox, though these tend to adversely affect the gear change quality. In most cases these measures are insufficient to dampen the chatter or are expensive since they require relatively comprehensive modification to existing components. As regards reduction of the tooth clearance, from a functional

and production/technical aspect it is impossible to obtain such a small clearance that effective damping is achieved.

Several of the above-mentioned disadvantages are eliminated by means of an arrangement in which one gear wheel of a pair of meshing gear wheels has a hub portion on which a gear wheel in the form of a thin disc with the same tooth pattern as the actual gear wheel is rotatably carried. Resilient elements are located between the gear wheel and the disc and are pretensioned in the gear wheel's engagement position. Such an arrangement entails low production costs and high efficiency and, thanks to its damping properties, is uninfluenced by the natural frequency of the transmission components.

This arrangement does however have certain limits. On the one hand, the tooth clearance is eliminated only between the gear wheel pair which has a gear wheel with a pretensioned disc and, on the other hand, due to production techniques, such a gear disc cannot be positioned on the side of the gear wheel which is provided with teeth for engagement with a clutch sleeve. This can of course in certain circumstances restrict its use in gearboxes.

The object of the present invention is to provide a gearbox of the type according to the preamble of claim 1 with a simple pretensioning arrangement which can eliminate tooth clearance between several sets of gear wheels on three shafts.

This is achieved in accordance with the present invention by the provision of a releasable gear wheel on the input shaft which engages with two equal-sized gear wheels, each of which is non-releasably arranged on its respective intermediate shaft, with at least one of said non-releasable gear wheels comprising a hub portion and a gear ring, with the hub portion being fixed to the intermediate shaft whilst the gear ring is restrictively rotatable with respect to the hub portion, and the pretensioned spring means being operative between the gear ring and the hub portion.

In such a gearbox, a take-up force is applied by just one pretensioned gear wheel to all shafts in the gearbox in all gears and in neutral.

The invention has been developed particularly, though not exclusively, for five-speed gearboxes, with these gearboxes having sufficient "spare" room on the one intermediate shaft which is used only for torque transmission in fifth and reverse gear. Advantageously, a pretensioned gear wheel can be arranged in engagement with the releasable gear wheel on the input shaft which engages with the gear wheel for third gear on the other intermediate shaft.

The invention will be described in greater detail by way of example and with reference to the annexed drawings, in which:

Fig. 1 is a sectional view through a gearbox according to the present invention;

Fig. 2 is an elevational view of a component in Fig. 1;

Figs. 3 and 4 are cross sections through parts making up the component of Fig. 2, and

Fig. 5 is a plan view of the part shown in Fig. 3

In the drawings, reference numeral 1 denotes the housing of a five-speed motor vehicle gearbox which has an input shaft 2, a first intermediate shaft 3, a second intermediate shaft 4 and an output shaft 5.

The input shaft 2 cooperates with a clutch, only a part 6 of which is shown. The input shaft is provided with first and second fixed gear wheels 7, 8 resp., a gear ring 9 milled directly on the shaft, and a rotatably carried gear wheel 10 which is lockable to the shaft via a clutch and synchromesh arrangement, generally denoted by numeral 11, comprising an axially displaceable clutch sleeve 12. With the aid of the

clutch, arrangement 11, the input shaft 2 and the output shaft 5 can be locked up as a single unit for direct drive.

Each of the intermediate shafts 3, 4 presents a fixed gear wheel 13, 14 resp. which meshes with a fixed gear wheel 15 of equal size on the output shaft 5. In addition, the first intermediate shaft 3 presents a fixed gear wheel 16 which meshes with the rotatably carried gear wheel 10 on the input shaft 2.

The gear wheel 7 on the input shaft 2 meshes with a freely rotatable gear wheel 17 on the second intermediate shaft 4. The gear wheel 17 is lockable to the intermediate shaft 4 via a clutch arrangement, generally denoted by 18, which includes an axially displaceable clutch sleeve 19. The gear wheels 8 and 9 on the input shaft 2 respectively engage with gear wheels 20, 21 which are freely rotatable on the first intermediate shaft 3. The gear wheels 20, 21 are alternately lockable on the shaft 3 via a clutch arrangement, generally denoted by 22, which includes an axially displaceable clutch sleeve 23. The gear wheel 21 is combined with a gear wheel 24 which meshes with a gear wheel 25 (in practice the shafts 2, 3 and 4 are .oriented in a V-shape) which in turn is freely rotatably carried on and lockable to the shaft 4 via the clutch arrangement 18.

The torque transmission paths in the various gears are as follows:

First gear: gear wheels 9, 21, 13 and 15

Second gear: gear wheels 8, 20, 13 and 15

Third gear: gear wheels 10, 16, 13 and 15

Fourth gear: direct, shaft 2 to shaft 5

Fifth gear: gear wheels 7, 17, 14 and 15

Reverse: gear wheels 9, 21, 24, 25, 14 and 15

According to the invention, the second intermediate shaft 4 carries a gear wheel, generally denoted by 30, which is of the same diameter as the gear wheel 16 and similarly meshes with

the gear wheel 10 on the input shaft. The gear wheel 30 is shown in greater detail in Figs. 2 to 5 and consists of a hub portion 31 with splines for non-rotatable attachment of the hub portion to the shaft 4, a circumferential gear ring 32 and three helical springs 33 therebetween. Each spring 33 is accommodated in an arc-shaped curved recess or slot 34 in the inner circumferential surface of the gear ring 32. The hub portion 31 is formed with three equally spaced projections or dogs 35, each of which extends into a slot 34 and forms a stop for the one end of the spring 33 in the slot. The other end of the spring abuts an end surface 37 in the slot 34.

In one of its opposed sidewalls 38 (Fig. 5) , each slot 34 presents an opening 39, the shape of which is adapted to the shape of the projection 35. The three openings are distributed in accordance with that of the projections 35 on the hub portion 31 so that the hub portion can be axially inserted into the gear ring 32 with the projections placed straight in front of the openings 39 and then rotated like a bayonet connection.

When rotating the hub portion 31 clockwise (see Fig. 2) in relation to the gear ring 32, the springs 33 are tensioned. With tensioned springs, the hub portion 31 is slid along the splines of the intermediate shaft 4 at the same time that the gear ring 32 is brought to engage with the gear wheel 10 on the input shaft 2. In this manner, a take-up effect is achieved in all gears, and in neutral. In Fig. 1, P, denotes the transmission path of the take-up force. The force transmission path in third gear is illustrated by way of example by P ₂ . By means of the take-up force, the impact of the teeth flanks against each other due to irregular torsional forces is prevented.

It is to be understood that the expression "fixed gear wheel" means that the gear wheel is fixed to its shaft so as not to be rotatable with respect to the shaft. The expression "releasable gear wheel" means that the gear wheel can optionally be locked

to the shaft to thereby rotate therewith, or can be disengaged from the shaft to freely rotate thereon.