Technical Field

The present invention relates to a method and device for determining shim thickness. More particularly the present invention relates to a method and device for determining the desired thickness of a shim for preloading pinion bearings of a rear drive module in a vehicle. Background

All wheel drive (AWD) cars, i.e. cars having an option to switch between two wheel drive mode and four wheel drive mode, are traditionally provided with a driven front axle, an intermediate axle, an AWD coupling, and a final drive for driving also the rear axle.

While the final drive comprises a pinion axle having a pinion gear being in gear engagement with a crown gear journaled for rotation transversely to the pinion axle, the AWD coupling includes a disc package axially controlled by a hydraulic piston for optionally transmitting torque from an ingoing axle to the pinion axle as well as a disc drum or similar means for rotatably connecting the disc package to the pinion axle.

When a car is to be provided with an AWD coupling, the AWD coupling and the final drive (including the differential) are normally supplied from different sources. However, these vehicle components may be integrated to form a rear drive module (RDM).

The journaling of the pinion axle in the RDM is rather intricate as e.g. discussed in US20130042453. This is due to the fact that a certain pre-load has to be provided. The pinion axle is typically journaled by two conical roller bearings or angular contact bearings, which are pre-loaded by a locking ring providing the correct pre-load value.

The outer race of the pinion bearing is typically supported by a radial step formed in a surrounding RDM housing and the locking ring, snapping into a radial groove of the pinion axle, is applying a pre-load to the inner race of the pinion bearing. A shim is arranged between the inner race and the locking ring in order to compensate for an axial gap between the inner race and the locking ring.

In order to maintain an accurate per-load it is important to determine a suitable shim. Summary

The object of the present invention is therefore to provide an improved method for determining a suitable shim thickness.

According to a first aspect, a method for determining a suitable shim thickness is provided. The method comprises rotatably supporting a pinion axle by means of at least one bearing, applying a preload to said bearing by pressing a contact surface of a preload member against the bearing, arranging at least one measurement surface at a well defined axial distance from a radial groove of the pinion axle, and measuring the axial distance between the at least one

measurement surface and a reference surface of the preload member, wherein the measured axial distance corresponds to a desired shim thickness.

In one embodiment, the reference surface is arranged at the preload member at a well-defined axial distance from the contact surface.

In one embodiment, arranging at least one measurement surface is performed by arranging an engagement portion of at least one arm in the radial groove of the pinion axle, wherein the at least one measurement surface is arranged at a well defined axial distance from the engagement portion.

The method may further comprise supporting the pinion axle by means of a rotatable counterhold.

In an embodiment, measuring the axial distance between the at least one measurement surface and the reference surface is performed during rotation of the pinion axle.

The engagement portions of a plurality of arms may be arranged circumferentially in the axial groove of the pinion axle.

In an embodiment, the axial distance between the engagement portion and the measurement surface of one arm is different from the axial distance between the engagement portion and the measurement surface of at least one other arm.

The axial distances between the engagement portion and the

measurement surface of the arms may be all different.

In an embodiment the contact surface of the preload member is pressed against an inner race of the bearing.

Measuring the axial distance between the at least one measurement surface and the reference surface may be performed by a non-contact sensor, such as an optical sensor.

According to a second aspect a device for determining a thickness of a shim for pre-loading a bearing of a pinion axle is provided. The device comprises a preload member having a contact surface and a reference surface being arranged at a well defined axial distance from the contact surface, means for applying a force to the preload member, at least one member having an engagement portion configured to fit in a radial groove of the pinion axle and a measurement surface being arranged at a well defined axial distance from the engagement portion, and a sensor configured to measure the axial distance between the at least one measurement surface and the reference surface, wherein the measured axial distance corresponds to a desired shim thickness.

In an embodiment the device further comprises a counterhold for supporting the pinion axle, and means for rotating the counterhold.

The device may comprise a plurality of members, wherein each member is formed by an arm, said arms being arranged circumferentially wherein the engagement portion of each arm is directed radially inwards.

The plurality of arms may be arranged at an equal angular distance from each other.

In an embodiment the axial distance between the engagement portion and the measurement surface of one arm is different from the axial distance between the engagement portion and the measurement surface of at least one other arm.

The pre-load member may form a sleeve into which the pinion axle may be inserted.

Brief Description of Drawings

The invention will be described in more detail below under reference to the accompanying drawings, in which:

Fig. 1 is a cross-sectional view of a rear drive module;

Figs. 2a-b are cross-sectional views of a device for determining shim thickness according to an embodiment; and

Fig. 3 is a schematic view of a method according to an embodiment. Detailed Description

An example of a RDM in a road vehicle - a car - is schematically shown in Fig 1.

In one embodiment, a disc package 2 comprising a number of discs is arranged in a coupling housing 1. These discs are alternatingly connected on one hand to a rotatably journaled ingoing axle 3 and on the other hand to a rotatably journaled outgoing axle 4 in the form of a pinion axle 4. The connection to the outgoing axle 4 is performed via a disc drum 2A. The disc drum 2A is in splines engagement with the pinion axle 4 and thus axially movable in relation thereto.

In this embodiment, the disc package 2 is controlled by hydraulic pressure applied on a hydraulic piston 5 in the housing 1. The magnitude of the force from the hydraulic piston 5 will control the clamping force on and thus the torque transmitted by the disc package 2 from the ingoing axle 3 to the outgoing axle 4. The force from the piston 5 is transmitted to the disc package 2 and back into the housing 1 by means of axial bearings 6, preferably needle bearings. A pinion gear 10 operatively engaged with the pinion axle 4 is rotatably journaled in a RDM housing 11, which may be connected to the coupling housing 1 or formed integral therewith. The RDM comprises the pinion gear 10 and a crown gear 12 to form a bevel gear set, normally a hypoid gear set. A differential housing 13 is engaged with the crown gear 12 and may contain a conventional differential mechanism, from which two drive shafts 14 extend out to driving wheels of the vehicle. The arrangement may be journaled in the RDM housing 11 by combined axial and radial bearings 15.

The journaling of the pinion axle 4 comprises two bearings, a head bearing 16 and a tail bearing 17. These two bearings 16, 17 are preferably capable of taking up the radial and axial forces from the gear engagement in the hypoid gear set. They also have the capability of handling forces in both axial directions, because the force direction changes for example between driving the vehicle in the forward and the reverse direction. The bearings 16, 17 may in some embodiments be conical roller bearings or angular contact ball bearings thus having an inner race and an outer race.

For the proper functioning of the rear drive module, it is of great importance to prevent play from occurring in the journaling of the pinion axle 4. This is accomplished by applying an axial pre-load on the journaling by means of a locking ring 18, which is snap fitted in a radial groove of the pinion axle 4 and thus applies an axial force on the inner race of the head bearing 16 via a shim 19. The magnitude of the pre-load is so chosen that the deformation due to loads and temperature expansion does not result in any play. For this purpose the shim 19 is arranged between the locking ring 18 and the inner race of the head bearing 16 in order to ensure that the locking ring 18 applies the desired pre-load to the bearing 16.

Due to manufacturing standards and tolerances the axial distance between the locking ring groove and the inner race of the bearing 16 may vary slightly, why it is important to select a correct thickness of the shim. Such shim thickness determination may be performed using a device as is shown in Figs. 2a and Fig. 2b.

The device 100 is designed to determine a suitable shim thickness for pre-loading a bearing 16 of a pinion axle 4. According to an embodiment the device 100 comprises a supporting counterhold 102 having at least one means

104, such as pin or similar, for engagement with the pinion gear 10 when the pinion axle 4 is journaled in the rear drive module housing 11. The counterhold

102 is driven by a motor 106 for rotating the pinion axle 4.

The device 100 further comprises a sleeve 110 into which the pinion axle 4 fits; the sleeve 110 is mounted onto the pinion axle 4 from the free end, i.e. the end being opposite the pinion gear 10. The sleeve 110, having a cylindrical shape for receiving the pinion axle 4, has a contact surface 112 at its end. The contact surface 112 has a radius being selected such that it will come into contact with the inner race of the forward bearing 16 to be pre-loaded.

The sleeve 110 is driven in its axial direction by means of controllable pressure source 120 such that the sleeve 110 may be controlled to apply a predetermined pre-load to the bearings 16, 17.

The upper end of the sleeve 110, i.e. the end being opposite the contact surface 112, forms a reference surface 114. The reference surface 114 may have a radial extension outwards, and the axial distance between the reference surface

114 and the contact surface 112 is well defined. Preferably, the sleeve 110 may be carefully machined and measured in a coordinate measuring machine for this purpose.

The device 100 further comprises a plurality of arms 130 being arranged circumferentially around the sleeve 110. Each arm 130 has a limited thickness such that they will be able to pass through axial slits (not shown) in the sleeve 110.

The lower end of each arm 130 is provided with an engagement portion 132 forming a protrusion extending radially inwards towards the pinion axle 4. The upper end of each arm 130 is provided with a measurement surface 134.

Similarly to the reference surface 114 of the sleeve 110, the measurement surface 134 may have a radial extension outwards, and the axial distance between the reference surface 134 and the contact surface 132 is well defined. Preferably, each arms 130 are carefully machined and measured in a coordinate measuring machine for this purpose.

The arms 130 are pivotally supported by a frame structure 140 of the device 100 (see Fig. 2b), such that the engagement portion 132 may move radially inwards and outwards. Preferably, the engagement portions 132 are spring biased such that they will strive to move radially inwards to snap into the radial groove of the pinion axle 4.

A driving cylinder 150 is further provided for moving the arms 130 upwards and downwards and a sensor 160, preferably a non-contact sensor such as a laser displacement sensor, an optical sensor, an ultrasonic sensor, etc, is arranged to measure the distance between the reference surface 114 of the sleeve 110 and the measurement surfaces 134 of the arms 130. As is readily understood, the measured axial distance corresponds to the desired thickness of the shim.

The above described device 100 is thus capable of performing a measurement method able to measure the axial distance between a pre-loaded bearing inner race and a lock ring groove of the pinion axle 4. The method is performed in order to assign a suitable shim and lock ring that keeps the preload force within narrow accuracy. This should be done during rotating pinion, in order to apply a force on the bearing according to manufacturer's

recommendations.

Hence, the device 100 creates two surfaces whereby the axial distance between those surfaces is possible to measure with a non-contact sensor 160 during rotating of the pinion axle 4.

When operating the device 100, the internal cylinder 150 is actuated for moving the measuring arms 130 such that they are at their lower position. The measuring arms 130 are thereafter opened, by pivoting, to allow the pinion axle 4 to be inserted. The rear drive module housing 11 with its associated pinion axle 4 and bearings 16, 17 is mounted on the counterhold 102 and being guided by a centering pin 104.

The counterhold 102 thereafter starts to rotate the pinion axle 4. A preset force is applied on the inner race of the bearing 16 by means of the sleeve 110. The internal cylinder 150 then releases the spring loaded measuring arms 130 that align with the pinion axle 4 while the internal cylinder 150 moves upwards forcing the engagement portions 134 of the measuring arms 130 into the lock ring groove and finally locking them in the desired position.

The sensor 160 makes several measurements between the sleeve reference surface 114 and the plurality of measurement surfaces 134 of the measurement arms 130 during rotating of the pinion axle 4. The number of measurement values, required for evaluation, may vary. These values are used to establish the difference between the sleeve reference surface 114 and the measurement surfaces 134. In one specific embodiment, the number of measurement surfaces is three.

Each one of the plurality of measurement arms 130 is preferably designed with different axial length making it possible to identify which arm 130 that needs to be taken into consideration when evaluating the measurement result.

In Fig. 3 a method 200 for determining a shim thickness is schematically shown. In 202, a pinion axle 4 is rotatably supported in a rear drive module housing 11 by means of at least one bearing 16. In 204, a pre-load is applied to the bearing 16 by pressing a contact surface 112 of a sleeve 110 against the bearing 16. As described above, the sleeve 110 has a reference surface 114 being arranged at a well defined axial distance from the contact surface 112.

In 206, an engagement portion 132 of at least one arm 130 is fitted in an axial groove of the pinion axle 4. Each arm 130 has a measurement surface 134 being arranged at a well defined axial distance from the engagement portion 132. In 208, the axial distance between the at least one measurement surface 134 and the reference surface 114 is measured, wherein the measured axial distance corresponds to a desired shim thickness.

204, as well as the subsequent steps, may preferably be performed during rotation of the pinion axle 4. For this, the counterhold 102 is rotated whereby the arms 130 as well as the sleeve 110 are rotating with the pinion axle 4.

The invention has mainly been described with reference to a few embodiments. However, as is readily understood by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended claims.