Gearbox assembly for a vehicle

Abstract

The present invention relates to a gearbox assembly, comprising: a housing; an output shaft; a worm wheel fixed to the output shaft; an input shaft; a torsion bar connecting the input shaft to the output shaft; an electric motor; a worm rotatably fixed to a rotor and engaging the worm wheel to transfer torque from the motor to the output shaft; and a key lock assembly including an adapter, a locking collar, and a key lock, the adapter having an annular inner portion, an annular outer portion, and a connecting plate, the inner portion being fixed to the output shaft on a side of the worm wheel opposite to the input shaft, the outer portion having a diameter larger than that of the inner portion, and the connecting plate connecting the inner portion to the outer portion; the locking collar being supported by the outer portion of the adapter; the key lock being fixed to the housing and movable between an extended position where a portion of the key lock engages the locking collar and a retracted position where this portion is separated from the locking collar, and wherein a sealing assembly is provided to isolate the locking collar from the worm wheel.

Description

Technical Field

[0001] The present invention relates to improvements in gearbox assemblies, and more particularly to a gearbox assembly for an electric power steering assembly for a vehicle. Background Art

[0002] There is known a gearbox assembly of a housing type that positions and protects a worm gear assembly. The worm gear assembly includes a first shaft assembly and a second shaft assembly. The first shaft assembly includes a worm in the form of a screw extending along the length of the shaft, and the worm is supported relative to the housing by at least one annular support assembly; the second shaft assembly carries a worm gear, which is also supported relative to the housing by at least one support assembly. These two shafts are axially offset and arranged perpendicular to each other such that the teeth on the periphery of the worm gear engage with the helical teeth of the worm. Rotation of the worm gear will cause rotation of the worm, and vice versa. This allows torque to be transmitted between the two shafts. One shaft can define the input of the gearbox assembly and the other shaft can define the output of the gearbox assembly.

[0003] Worm gear assemblies are particularly suitable for applications that require a simple and compact mechanism with a high transmission ratio. By appropriately selecting the design of the transmission gear teeth, a worm gear assembly can provide small backlash and low friction in both transmission directions. These are important characteristics of an electric power steering assembly in which a motor applies an auxiliary torque through a gearbox to a steering mechanism to assist a driver in turning a steering wheel. Any backlash will give an undesirable feeling to the driver through the steering wheel. The 90-degree offset between the input and the output allows the drive motor to be conveniently positioned next to the steering shaft.

[0004] The worm gear of the gearbox assembly can be provided on a part of a hollow shaft that is connected in line between the input shaft of the support handwheel of the steering assembly and a flexible joint to a steering rack. In some arrangements, the worm gear can be fixed to a hollow output shaft that is located within the gearbox and is connected to the flexible joint. A torsion bar can be provided within this hollow shaft, and the torsion bar interconnects the input shaft and the output shaft. The function of the torsion bar is to allow a relatively large angular displacement between the input shaft and the output shaft when the driver applies a torque to the handwheel. This can be measured to determine the value of the torque, and a controller can then generate a drive signal for the motor based on the measured torque. Generally, the higher the measured torque, the higher the motor assist force required to assist the driver in turning the handwheel.

[0005] To prevent vehicle theft, in many countries / regions, it is required to install a key lock that engages with a part of the steering assembly when locked and prevents the handwheel from rotating. The key lock typically acts on a locking ring fixed to the input shaft. Summary of the Invention

[0006] The present applicant has recognized that it may be desirable to provide a key lock that is integrated with the gearbox rather than acting on the input shaft.

[0007] According to a first aspect of the present invention, there is provided a gearbox assembly comprising:

[0008] a housing;

[0009] an output shaft,

[0010] a worm wheel fixed to the output shaft,

[0011] an input shaft,

[0012] a torsion bar connecting the input shaft to the output shaft,

[0013] an electric motor,

[0014] a worm rotatably fixed to the rotor and engaging the worm wheel to transmit torque from the motor to the output shaft,

[0015] and a key lock assembly comprising:

[0016] an adapter having an annular inner portion, an annular outer portion, and a connecting plate, the inner portion being fixed to the output shaft on a side of the worm wheel facing away from the input shaft, the outer portion having a diameter larger than that of the inner portion, and the connecting plate connecting the inner portion to the outer portion;

[0017] a locking collar supported by the outer portion of the adapter; and

[0018] a key lock fixed to the housing and movable between an extended position and a retracted position, in the extended position, a part of the key lock engages the locking collar, and in the retracted position, the part is separated from the locking collar,

[0019] and wherein a sealing assembly is provided to isolate the locking collar from the worm wheel.

[0020] The sealing assembly may include a radially extending collar that extends radially outward from the adapter such that an outer edge of the collar overlaps an inwardly protective shoulder formed on an inner side of the housing to form a seal between the key lock ring and the worm wheel.

[0021] The shoulder that overlaps the outer edge of the radially extending collar (baffle) may be formed as a step between an enlarged inner portion and a diameter-reduced inner portion of the housing.

[0022] The collar and the shoulder together provide a tortuous path between the locking collar and the worm wheel.

[0023] The collar can be fixed to the outer part of the adapter by welding or any other suitable means. The collar can be fixed to the connecting plate of the adapter or to the inner part of the adapter.

[0024] Alternatively, the collar can be fixed to the transfer ring (if any). The transfer ring can include a radial flange at one end of the transfer ring. This allows the collar and the ring to be formed from a single piece of material.

[0025] The shoulder that overlaps the edge of the baffle can be formed as a stepped diameter change between the enlarged inner part and the diameter-reduced inner part of the housing. When viewed in cross-section, this defines the inner and outer corners of the shoulder.

[0026] The outer edge of the baffle can be spaced from the axis of the outer shaft by a distance greater than the distance between the outer corner of the shoulder and the axis, such that as the baffle rotates, the baffle always overlaps the shoulder. The outer edge can have a constant radius, and so can the shoulder, but the outer edge does not have to be a perfect circle as long as the overlap is maintained for all orientations of the baffle.

[0027] The stepped diameter that forms the shoulder is positioned such that the adapter and the collar can be pushed onto the output shaft towards the worm wheel until the edge of the collar is close to but does not touch the shoulder. This forms a simple labyrinth seal.

[0028] The baffle and the connecting plate of the adapter can together form a continuous barrier to prevent oil or grease from transferring from the worm wheel to the key lock ring.

[0029] The collar can include a solid baffle formed from a thin disk of material, which is welded to the adapter at the inner diameter.

[0030] The baffle can be located in the housing such that the baffle does not touch the housing.

[0031] As an alternative to the baffle forming a non-contact labyrinth seal, a contact seal can be provided between the adapter and the housing, which isolates the locking collar from the worm wheel, although this will introduce some friction in the assembly, which may be undesirable.

[0032] The contact seal can be fixed to the adapter and slide on the housing, or can be fixed to the housing and slide on the adapter.

[0033] In a preferred arrangement, the collar can form part of a tolerance ring that fixes the locking collar to the adapter.

[0034] The adapter may have an inner portion provided with a set of splines that extend radially inwardly towards the center of the inner portion, and these splines engage corresponding outwardly extending splines on the output shaft. The splines may be an interference fit.

[0035] The worm gear may be fixed to the output shaft by splines on the inner diameter of the worm gear, and these splines engage corresponding splines on the output shaft.

[0036] The outer diameter of the splines supporting the worm gear may be greater than the outer diameter of the splines supporting the adapter. The outer diameter of the splines supporting the adapter may be less than the inner diameter of the splines of the worm gear. This allows the worm gear to be pressed into place through the splines of the supporting adapter without any interference, and then the adapter is pressed into place.

[0037] The adapter may be provided with at least one hole that is radially offset from the inner diameter of the transfer ring, which allows a locking tool to be placed in the hole to prevent the tolerance ring from rotating when torque is applied to the worm gear. This allows the performance of the locking mechanism to be tested during assembly.

[0038] The locking collar may include a set of teeth circumferentially spaced around the outer portion of the adapter, and recesses are defined between adjacent teeth, which receive a part of the key lock when the key lock is in the extended position.

[0039] The locking collar and the adapter may be formed as a single part.

[0040] In an alternative, a torque transfer ring or a tolerance ring may be located between the adapter and the locking collar, and this torque transfer ring or tolerance ring prevents relative rotation between the locking collar and the transfer ring until a defined torque load limit is reached, after which rotation occurs. This arrangement prevents excessive torque from damaging the assembly while still making it impossible to freely maneuver the vehicle.

[0041] The torque transfer ring may include an annular support and a plurality of raised contact portions. The support is concentrically fitted around the outer portion of the adapter, and these raised contact portions extend radially outwardly from the support to engage the annular inner face of the locking collar. These raised portions may be in a diamond shape.

[0042] The outer portion of the adapter may include a cylinder, and the connecting plate of the adapter may include an annular end wall of the cylinder. The inner portion of the adapter may further include a cylinder that is fixed at one end of the end wall and is concentrically located inside the outer cylinder.

[0043] The assembly may be arranged such that the assembly can be assembled in the following order:

[0044] - Insert the input shaft and the output shaft as a single assembly into the housing from one side;

[0045] - Press the worm gear onto the output shaft from opposite sides of the housing;

[0046] - Press the adapter onto the output shaft.

[0047] The assembly method may include fixing a locking ring and a transfer ring to the adapter before fixing the adapter to the output shaft.

[0048] The method may include testing the pre-assembled locking ring, transfer ring, and adapter before assembly to ensure compliance with anti-theft standards specified by the country or manufacturer by applying torque across the entire assembly. Description of the Drawings

[0049] An embodiment of the present invention will now be described, by way of example only, with reference to the drawings and as shown in the drawings, in which:

[0050] Figure 1 is a cross-sectional view of an embodiment of a gearbox assembly according to the present invention;

[0051] Figure 2 is Figure 1 an enlarged cross-sectional view of a part of the gearbox assembly;

[0052] Figure 3 shows the torsional load path through the gearbox assembly when the key lock is engaged;

[0053] Figure 4 (a), Figure 4 (b), and Figure 4 (c) show the steps of assembling a locking collar onto an adapter to form a testable sub-assembly;

[0054] Figure 5 is a detailed view of the output shaft, with all other parts removed for clarity;

[0055] Figure 6 (a) and Figure 6 (b) show how the worm gear and adapter are pressed onto the output shaft in sequence; and

[0056] Figure 7 is a perspective view of the locking assembly as seen from the open end of the gearbox housing at the adapter and output shaft. Detailed Description

[0057] As Figures 1 to 7As shown in, the gearbox assembly 10 includes a housing 20 having three open ports, two of which, ports 30 and 40, are axially aligned at opposite ends of the gearbox housing 20, and one port 50 is offset from and orthogonal to the axis connecting the two aligned openings. One of the ports, port 30, receives an end portion of an input shaft 60 which has a set of splines at its opposite ends for receiving the hub of a steering wheel. This shaft can be telescopic and is supported within a steering column shroud (also not shown) by bearings (not shown) such that the shaft can rotate as the steering wheel rotates.

[0058] The other aligned port 40 receives an end portion of an output shaft 70. The two opposite ends of the input shaft 60 and the output shaft 70 that are located within the gearbox housing are connected by a torsion bar 80. The function of this bar is to allow relative angular movement between the input shaft and the output shaft when torque is applied to the torsion bar.

[0059] The third open port 50 of the housing receives the output shaft of an electric motor 90. The body of the motor is fixed to the housing 20. The rotor carries a worm 100.

[0060] As Figure 2 best seen in, the output shaft 70 carries a worm wheel 110 and the worm 100 meshes with the worm wheel 110. In use, when torque is applied, the twist of the torsion bar 80 is detected by a torque sensor (not shown) and the output of the torque sensor is fed to a controller. The controller generates a drive signal which causes the motor 100 to apply a desired assist torque to the output shaft 70 via the worm and worm wheel. This assist torque helps the driver to turn the steering wheel by providing a degree of assistance.

[0061] The worm wheel 110 is provided with a set of internal splines 130 which mesh with a corresponding set of circumferentially spaced splines 120 on the output shaft.

[0062] The output shaft 70 also carries a second set of circumferentially spaced splines 140. These splines are located between the worm wheel 110 and the end of the output shaft that projects from the gearbox housing 20. Figure 5 Two sets of splines on the output shaft are shown and as Figure 6 (a) and Figure 6 (b) best seen, the diameter D1 of the splines supporting the worm wheel is larger than the diameter D2 of the splines supporting the adapter. This allows the worm wheel to pass easily through the second set of splines without any interference during assembly.

[0063] The second set of splines meshes with corresponding splines on an adapter 150. The adapter has a cylindrical inner portion 160 which is provided with splines that mesh with the second set of splines 140 on the output shaft.

[0064] The adapter 150 also has a cylindrical outer portion 170 with a diameter larger than that of the inner portion, and a connecting plate 175 that connects the inner portion to the outer portion. The inner portion 160, the connecting plate 175, and the outer portion 170 can be formed by pressing a single metal sheet, or can be molded or cast into a single piece using additive manufacturing techniques.

[0065] The outer portion 170 of the adapter 150 supports a locking collar 180. The locking collar includes a circle of teeth circumferentially spaced around a support ring. This is best visible in Figure 4 which.

[0066] A fourth opening in the gearbox housing is provided in a region facing the locking collar 180, and a key lock 190 is fixed to the housing such that a movable locking portion 200 faces the locking collar 180. The key lock is movable between an extended position and a retracted position. In the extended position, the locking portion of the key lock engages the locking collar, and in the retracted position, the locking portion is separated from the locking collar. When engaged, the movable portion enters the space formed between adjacent teeth of the locking collar. As shown, this movement is in a radial direction relative to the axis of rotation of the output shaft.

[0067] In the example shown, the inner diameter of the locking collar 180 is larger than the outer diameter of the outer portion of the adapter, and an optional tolerance ring 210 is disposed in the gap formed between the outer portion of the adapter and the locking collar. The three parts - the outer portion, the tolerance ring, and the locking collar - are thus concentrically arranged. The tolerance ring includes an annular band that has a plurality of diamond-shaped raised contact elements 235 on its outer face that engage the locking collar. These can be seen in Figure 4 which. In use, the tolerance ring prevents relative rotational movement between the adapter and the locking collar until a predetermined torque limit is reached, after which the tolerance ring will allow slip. This feature allows the steering input shaft to be forced to rotate if a large enough torque is applied, even when the key lock is engaged, without causing any permanent damage.

[0068] Figure 2 and Figure 4 also best visible in which, a baffle or collar 220 is provided. The baffle or collar includes a disc-shaped member formed by a lip at the end of the tolerance ring. This baffle 220 has an outer edge that extends outwardly to overlap a shoulder 230 formed on the inner side of the housing. The shoulder faces the open end through which the output shaft of the gearbox housing protrudes. The baffle 210 and the connecting plate 175 of the adapter 140 provide a continuous wall that eliminates any direct path for oil or grease to move from the worm gear to the surface of the locking collar. The only path is an indirect path around the shoulder and the edge of the baffle.

[0069] The gearbox assembly 10 shown is easy to assemble and also enables pre - assembly and testing of the adapter, tolerance ring, and locking collar to see if the gearbox assembly provides correct and repeatable performance under torsional loads.

[0070] A suitable assembly sequence is as follows.

[0071] Step 1: Insert the input shaft and torsion bar into the gearbox housing.

[0072] Step 2: Press the output shaft onto the torsion bar until the output shaft reaches its limit stop position. Then the output shaft can be slightly pulled out by inserting a release tool into the threaded hole in the free end of the output shaft until correct axial alignment of the input shaft and output shaft is achieved.

[0073] Step 3: Assemble the adapter 150, tolerance ring 210, and locking collar 180. This is shown in Figure 4 and they can also be tested at this stage.

[0074] Step 4: Press the worm gear onto the first set of splines on the output shaft. This is shown in Figure 6

[0075] Step 5: Press the adapter onto the second set of splines until it reaches the end stop position where the edge of the baffle overlaps but does not contact the shoulder in the housing. This is also shown in Figure 6

[0076] Step 6: Fix the key lock to the gearbox housing and set the motor and worm.

[0077] Once assembled, further testing of the assembled anti - theft performance can be carried out. To assist with this testing, the adapter has three holes 241, 242, 243 in the connecting plate 170 that can receive the locking pins 250 of a locking tool, which prevent the connecting plate from rotating or allow the connecting plate to rotate while other parts of the assembly (such as the input shaft, worm, or key lock) are held in place. Of course, there can be only one hole or any other number of holes, and in addition to holes, some other engagement feature can be provided that allows the adapter to be held without rotation.

[0078] The assembly method can include fixing the locking ring and transfer ring to the adapter before fixing the adapter to the output shaft.

[0079] The method can include testing the pre - assembled locking ring, transfer ring, and adapter before assembly to ensure compliance with national or manufacturer - specified anti - theft standards by applying torque across the entire assembly. Figure 3 ​​The key load path through the steering shaft and key lock to the gearbox housing is shown by box arrows, and the load is then transferred to the fixed part of the vehicle.

Claims

1. A gearbox assembly, comprising: a housing having three open ports, wherein the first and second ports (30, 40) are axially aligned at opposite ends of the housing, and the third port (50) is offset from and orthogonal to the axis connecting the first and second ports; an output shaft, the second port (40) receiving an end portion of the output shaft (70); a worm wheel fixed to the output shaft; an input shaft, the first port (30) receiving an end portion of the input shaft (60); a torsion bar connecting the input shaft to the output shaft; an electric motor, the body of the electric motor being fixed to the housing, the third port (50) receiving the output shaft of the electric motor; a worm rotatably fixed to the rotor of the electric motor and engaging the worm wheel to transfer torque from the electric motor to the output shaft of the gearbox assembly; and a key lock assembly, the key lock assembly comprising: - an adapter having an annular inner portion, an annular outer portion, and a connecting plate, the inner portion being fixed to the output shaft on a side of the worm wheel facing away from the input shaft, the outer portion having a diameter larger than that of the inner portion, the connecting plate connecting the inner portion to the outer portion, the second port receiving the adapter; - a locking collar supported by the outer portion of the adapter; and - a key lock fixed to the housing and movable between an extended position and a retracted position, in the extended position, a part of the key lock engages the locking collar, and in the retracted position, the part is separated from the locking collar; wherein the output shaft of the gearbox assembly has a first set of splines (120) supporting the worm wheel and a second set of splines (140) located between the worm wheel and the end of the output shaft protruding from the housing, supporting the adapter, the diameter (D1) of the first set of splines being larger than the diameter (D2) of the second set of splines, such that the worm wheel is assembled onto the first set of splines through the second set of splines; and wherein a sealing assembly is provided to isolate the locking collar from the worm wheel.

2. The gearbox assembly according to claim 1, wherein, the sealing assembly includes a radially extending collar that extends radially outward from the adapter such that the outer edge of the radially extending collar overlaps an inwardly protective shoulder formed on the inner side of the housing to form a seal between the key lock ring and the worm wheel.

3. The gearbox assembly according to claim 2, wherein, the shoulder overlapping the outer edge of the radially extending collar is formed as a step between an enlarged inner portion and a reduced-diameter inner portion of the housing.

4. The gearbox assembly according to claim 2 or 3, wherein, the radially extending collar forms part of a tolerance ring that fixes the locking collar to the adapter.

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