Gearbox assembly for a vehicle

Abstract

A gearbox assembly includes a housing, an output shaft, a wheel gear, an input shaft, a torsion bar, an electric motor, a worm gear and a key lock. The wheel gear may be fixed to the output shaft for engagement with a wheel gear. The torsion bar may connect the input shaft to the output shaft. The worm gear may be rotationally fixed to the rotor and engages the wheel gear to transfer torque from the motor to the output shaft. The key lock may include an adapter, an annular outer part, a web, and a locking collar. The key lock may be fixed to the housing and is movable between an extended position in which a part of the key lock engages the locking collar and a retracted position in which the part is held clear of the locking collar.

Claims

1. A gearbox assembly comprising: a housing; an output shaft; a wheel gear that is fixed to the output shaft for engagement with a worm gear; an input shaft; a torsion bar that connects the input shaft to the output shaft; an electric motor; a worm gear that is rotationally fixed to the rotor and engages the wheel gear to transfer torque from the motor to the output shaft; and a key lock assembly further comprising: an adapter having an annular inner part that is secured to the output shaft on the side of the wheel gear facing away from the input shaft; an annular outer part, the outer part having a larger diameter than the inner part; a web that connects the inner part to the outer part; a locking collar supported by the outer part of the adapter; and a key lock that is fixed to the housing and is configured to engage and disengage with the locking collar.

2. The gearbox assembly according to claim 1 wherein the adapter has an inner part that is provided with a set of splines that extend radially inwards towards the center of the inner part that engage corresponding outwardly extending splines on the output shaft.

3. The gearbox assembly according to claim 2 wherein the wheel gear is fixed to the output shaft by splines on an inner diameter of the wheel gear that engage with corresponding splines on the output shaft.

4. The gearbox assembly according to claim 3 wherein the inner diameter of the splines of the wheel gear is larger than the outer diameter of the splines on the output shaft that support the adapter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) There will now be described, by way of example only, one embodiment of the present disclosure with reference to and as illustrated in the accompanying drawings of which:

(2) FIG. 1 is a cross sectional view of an embodiment of a gearbox assembly in accordance with the present disclosure;

(3) FIG. 2 is an enlarged cross-sectional view of a part of the gearbox assembly of FIG. 1;

(4) FIG. 3 shows the torsional load path through the gearbox assembly when the key lock is engaged;

(5) FIG. 4(a) shows the outer part, tolerance ring and locking collar assembled together;

(6) FIG. 4(b) shows the tolerance ring and locking collar assembled together;

(7) FIG. 4(c) shows the tolerance ring before the locking collar is assembled onto the tolerance ring;

(8) FIG. 5 is a detailed view of the output shaft with all other parts removed for clarity;

(9) FIG. 6 (a) shows the wheel gear and adapter prior to being assembled onto the output shaft;

(10) FIG. 6(b) shows the wheel gear and adapter being pressed onto the output shaft; and

(11) FIG. 7 is a perspective view of the assembly looking in through an open end of the gearbox housing at the adapter and output shaft.

DETAILED DESCRIPTION

(12) As shown in FIGS. 1 to 7, a gearbox assembly 10 comprises a housing 20 having three open ports, two ports 30, 40 of which are in axially in line on opposing ends of the gearbox housing 20 and one port 50 is offset from and orthogonal to the axis connecting the two inline openings. One of the ports 30 receives an end portion of an input shaft 60 that has a set of splines at its opposite end for receiving a hub of a steering wheel. This shaft may be telescopic and is supported inside a steering column shroud (not shown) by bearings (also not shown) so that it can rotate as the steering wheel is rotated.

(13) The other inline port 40 receives an end portion of an output shaft 70. The two facing ends of the input shaft 60 and output shaft 70 that are located within the gearbox housing 20 are connected by a torsion bar 80. The function of the bar is to allow angular movement between the input and output shaft 70 when a torque is applied across the torsion bar.

(14) The third open port 50 of the housing 20 receives an output shaft 70 of an electric motor 90. The body of the motor 90 is secured to the housing 20. The rotor carries a worm gear 100.

(15) As best seen in FIG. 2, the output shaft 70 carries a wheel gear 110 and the worm gear 100 meshes with the wheel gear 110. In use, the twisting of the torsion bar 80 when a torque is applied is detected by a torque sensor (not shown) and the output of the torque sensor is fed to a controller. This generates a drive signal that causes the motor 90 to apply a demanded assistance toque to the output shaft 70 through the worm and wheel gear. This assistance torque helps the driver to turn the steering wheel by providing a degree of assistance. The wheel gear 100 is provided with a set of internal splines 120 that mesh with a corresponding set of circumferentially spaced splines 130 on the output shaft 70.

(16) The output shaft 70 also carries a second set of circumferentially spaced splines 140. These splines are located between the wheel gear 110 and the end of the output shaft 70 that protrudes from the gearbox housing 20.

(17) FIG. 5 shows the two sets of splines on the output shaft 70 and as best seen in FIGS. 6(a) and (b) the diameter of the splines that support the gearwheel is D1 which is larger than the diameter D2 of the splines that support the adapter. This allows the gear wheel to easily be threaded over the second set of splines without any interference during assembly. The second set of splines mesh with corresponding splines on an adapter 150. The adapter 150 has a cylindrical inner part 160 that is provided with splines that mesh with the second set of splines 140 on the output shaft 70.

(18) The adapter 150 also has a cylindrical outer part 170, of larger diameter than the inner part 160, and a web 175 that connects the inner part 160 to the outer part 170. The inner part 160, web 175 and outer part 170 may be formed by pressing a single sheet of metal or may be molded or cast of formed using an additive manufacturing technique as a single piece. The outer part 170 of the adapter 150 supports a locking collar 180. The locking collar 180 comprises a ring of teeth 181 that are spaced circumferentially around a support ring 183. This is best seen in FIG. 4.

(19) Therefore, the key lock assembly 151 may include an adapter 150, an annular outer part 170, a web 175, a locking collar 180 and a key lock 190. The adapter 150 includes the annular inner part 160 that is secured to the output shaft 70 on the side of the wheel gear 110 facing away from the input shaft 60. The annular outer part 170 has an outer part 170 having a larger diameter than the inner part 160. The web 175 may connect the inner part 160 to the outer part 170. The locking collar 180 supported by the outer part 170 of the adapter 150. The key lock 190 may be fixed to the housing 20 and may be movable between an extended position in which a part of the key lock 190 engages the locking collar 180 and a retracted position in which the part is held clear of the locking collar 180.

(20) A fourth opening in the gearbox housing 20 is provided in a region that faces the locking collar 180 and a key lock 190 is fixed to the housing 20 so that a movable locking part 200 faces the locking collar 180. The key lock 190 is movable between an extended position in which the locking part of the key lock 190 engages the locking collar 180 and a retracted position in which the part is held clear of the locking collar 180. When engaged the movable part enters a space formed between adjacent teeth of the locking collar 180. As shown this movement is in a radial direction relative to the axis of rotation of the output shaft 70.

(21) In the example shown the inner diameter of the locking collar 180 is larger than the outer diameter of the outer part 170 of the adapter 150 and an optional tolerance ring 210 is provided in the gap formed between the adapter outer part 170 and the locking collar 180. The three parts-outer part 170, tolerance ring 210 and locking collar 180 are therefore arranged concentrically. The tolerance ring 210 comprises an annular band 211 that has a plurality of lozenge shaped raised contact elements 235 on an outer face that engage the locking collar 180. These can be seen in FIG. 4. The tolerance ring 210 in use prevents relative rotational movement of the adapter 150 and locking collar 180 up to a predetermined torque limit, whereafter it will allow slip. This feature enables the steering input shaft 60 to be forced around if sufficient torque is applied without causing any permanent damage even when the key lock 190 is engaged.

(22) Also best seen in FIG. 2 and FIG. 4 a baffle or collar 220 is provided that comprises a disk shaped member that is formed by a lip on an end of the tolerance ring 210. This baffle 220 has an outer rim that extends outwards to overlap a shoulder 230 formed on the inside of the housing 20. The shoulder faces the open end of the gearbox housing 20 that the output shaft 70 protrudes through. The baffle 220 and the web 175 of the adapter 150 provides a continuous wall that eliminates any direct path for oil or grease to move from the wheel gear onto the surface of the locking collar 180. The only path is the indirect path around the shoulder and rim of the baffle.

(23) The gearbox assembly 10 shown is simple to assemble and also enables the adapter 150, tolerance ring 210 and locking collar to be preassembled and to be tested to see if it provides a correct and repeatable performance when under torsional loads.

(24) A suitable assembly sequence is as follows.

(25) Step 1: The input shaft 60 and torsion bar is inserted into the gearbox housing 20

(26) Step 2: The output shaft 70 is pressed onto the torsion bar until it reaches a limit stop. It may then be withdrawn slightly by inserted a release tool into a threaded bore in the free end of the output shaft 70 until the correct axial alignment of the input and output shafts is achieved.

(27) Step 3: The adapter 150, tolerance ring 210 and locking collar 180 are assembled. This is shown in FIG. 4. They may also be tested at this stage.

(28) Step 4: The wheel gear is pressed onto the first set of splines on the output shaft 70. This is shown in FIG. 6.

(29) Step 5: The adapter 150 is pressed onto the second set of splines until an end stop is reached which sets the rim of the baffle overlapping but not contacting the shoulder in the housing 20. This is also shown in FIG. 6.

(30) Step 6: The key lock 190 is fixed to the gearbox housing 20 and the motor 90 and worm gear and located.

(31) Once assembled further testing may be performed on the anti-theft performance of the assembly. To assist this testing the adapter 150 is provided with three holes 241, 242, 243 in the web 175 that may receive locking pins 250 of a lock tool which prevent the web 175 from rotating or allow the web 175 to force around whilst other parts of the assembly, such as the input shaft, wheel gear or key lock 190, are fixed in place. Of course, there may be as few as one hole or any other number, and rather than holes some other engagement feature may be provided that allows the adapter 150 to be held so it cannot rotate. The method of assembly may comprise securing the locking ring and the transfer ring onto the adapter 150 prior to fixing the adapter 150 to the output shaft 70.

(32) The method may include testing the preassembled locking ring, transfer ring and adapter 150 prior to fitment to ensure it complies with a national or manufacturer specified theft resistance standard by applying torque across the assembly. FIG. 3 shows with block arrows the key load path 80 through the steering shaft 82 and key lock 190 onto the gearbox housing 20 where it is then transferred to a fix part of the vehicle.