Steering shaft assembly

A steering shaft assembly is disclosed with an outer shaft operatively connected to a one of a steered member or a steering control. The outer shaft has an open end and a receiving chamber associated with the open end. The steering shaft assembly also includes an inner shaft operatively connected to another of the steered member or the steering control. The inner shaft has an engaging portion axially slideably received in the outer shaft receiving chamber. The inner shaft engaging portion also includes a polymer coating disposed on an outer surface of the inner shaft engaging portion. The coating has an outer surface that slideably engages with a surface of the outer shaft receiving chamber, and which has comprises projections and recesses along the coating outer surface.

BACKGROUND OF THE INVENTION

The invention relates to steering shaft assemblies and, more particularly to a telescopically adjustable steering shaft assembly for a vehicle.

Vehicles are commonly provided with a steering column assembly in which the upper portion, which carries the steering wheel, is arranged for axial adjustment to enable selective telescopic positioning of the steering wheel through a limited range. This arrangement has been found to be exceptionally advantageous in accommodating vehicle operators of varying stature. The telescoping feature can also be utilized to allow collapse of the steering column in the event of a crash.

Telescoping steering shafts can employ multi-tooth splines to rotationally link the inner and outer shafts while providing for telescoping movement in the axial direction. In some configurations, a tubular female sleeve surrounds a splined shaft with a plastic over-molded feature between the inner and outer shafts. Although such over-mold configurations can be reliable and effective, they can be expensive to produce and require a high degree of manufacturing complexity. Additionally, acceptable telescoping loads can be difficult to achieve and maintain.

SUMMARY OF THE INVENTION

In some embodiments of the invention, a steering shaft assembly comprises an outer shaft operatively connected to a one of a steered member or a steering control. The outer shaft comprises an open end and a receiving chamber associated with the open end. The steering shaft assembly also comprises an inner shaft operatively connected to another of the steered member or the steering control. The inner shaft comprising an engaging portion axially slideably received in the outer shaft receiving chamber. The inner shaft engaging portion comprises a polymer coating disposed on an outer surface of the inner shaft engaging portion. The coating comprising an outer surface that slideably engages with a surface of the outer shaft receiving chamber and comprises projections and recesses along said coating outer surface.

In some embodiments of the invention, a method of assembling the above-described steering shaft assembly comprises disposing a lubricant along the engaging portion of the coating outer surface or along a surface of the receiving chamber or along the engaging portion of the coating outer surface and a surface of the receiving chamber. The engaging portion of the inner shaft is inserted into the receiving chamber of the outer shaft to engage the projections of the coating outer surface with the receiving chamber surface and dispose the lubricant into the recesses of the coating outer surface.

In some embodiments of the invention, a method of assembling the above-described steering shaft assembly comprises inserting the engaging portion of the inner shaft into the receiving chamber of the outer shaft. A press fit tolerance is provided between the coating outer surface and the receiving chamber surface by radially-inward compression deformation of the coating outer surface projections. In some embodiments, the radially-inward compression deformation of the coating outer surface projections is accommodated by spaces between the coating outer surface recesses and the receiving chamber surface.

DETAILED DESCRIPTION

Referring now toFIG. 1, a steering shaft assembly10is schematically depicted. As shown inFIG. 1, an inner shaft12comprises an engaging portion14axially slideably received in a receiving chamber of an outer shaft16. As used herein, the term “axis” refer to an axis of rotation of the steering shaft, and the term “axially” refers to a direction parallel to the axis of rotation, extending along the length of the inner and outer shafts12,16. In some embodiments, the steering shaft assembly is integrated with other components into a steering assembly. An example embodiment of a steering assembly with other components is shown inFIG. 1, with the steering inner shaft12connected to a lower mounting assembly for operative connection to an intermediate shaft (not shown) that is connected to a steering mechanism such as a rack and pinion steering assembly (not shown) that is part of a steered member. Outer shaft16is operatively connected to a steering control such as a steering wheel (not shown). As further shown inFIG. 1, rotatable inner and outer shafts12,16are disposed within non-rotating inner jacket18and outer jacket20, which are themselves axially slideably engaged in the region of clamping assembly22. Clamping assembly22can be configured to provide a friction clamping mechanism that alternatively allows or prevents operator-initiated axial sliding movement of the inner and outer jackets18,20(and the inner and outer shafts12,16) with respect to each other.

Engagement between inner shaft12and the outer shaft16is depicted in greater detail inFIG. 2, which is a schematic depiction of a cross-sectional view of the inner and outer shafts12,16in the region of the engagement portion14. In some embodiments, the inner shaft12comprises an outer surface26configures with a plurality of male spline teeth extending axially along the shaft outer surface, as shown inFIG. 2. The male spline teeth are engaged with corresponding female splines on the outer shaft receiving chamber surface28. Engagement of the male and female splines on the surfaces26,28of the inner and outer shafts12,16provides for torsional stiffness along the steering shaft assembly10for transmission of torque from the steering control to the steering member.

As further shown inFIG. 2, a polymer coating30is disposed on the outer surface26of the inner shaft12and is in axially slideable contact with the outer shaft receiving chamber surface28. The polymer coating can be formed from any of a number of polymers. The polymer for the coating can be chosen from any of a number of known polymer resins, including but not limited to polyurethanes, polyesters, epoxy resin coatings, polyacrylates, polyamides (e.g., nylon), polyphenylene sulfide, polyarylether ketones (e.g., polyether ether ketone, i.e., PEEK), poly(p-phenylene), polyphenylene oxide, polyethylene (including crosslinked polyethylene, i.e., PEX), polypropylene, polytetrafluoroethylene, as well as blends and copolymers of any of the above. The coatings can optionally include curing agents that are reactive with functional groups (e.g., active hydrogen groups such as hydroxyl groups or amino groups) on the polymer. Various coating aids and additives, including but not limited to surfactants, flow control agents, antioxidants, stabilizers, etc., can also be optionally included in the coating composition.

The coating can be applied in various forms, including but not limited to a powder, powder slurry, in an aqueous solvent or organic solvent, or as a thermoplastic heated to a fluid state. Powder coatings can be applied by spray application (e.g., electrostatic spray), fluidized bed application, or electrostatic magnetic brush. The powder particles can be initially adhered to the substrate by heating the substrate or by electrostatic attraction. Liquid coating compositions such as powder slurries, aqueous or organic solvent-borne coatings, or fluid thermoplastics can be applied by spray application (e.g., electrostatic spray) or other liquid coating application techniques such as dip coating, roll coating, blade coating, nozzle coating, ink-jet coating, brush coating, sponge coating, etc.

Any of the above types of coatings can be used to provide can be utilized to provide coatings having a target thickness, a varying thickness, or a coating surface comprising projections and recesses. Powder coatings, for example, can be readily adapted to build up thickness during the powder application process, or to provide varying thickness or a surface with recesses and projections. After application of a powder coating, heat is applied to fuse the powder coating, and optionally provide some degree of flow and leveling, while leaving some thickness variation to provide the target recesses and projections at the coating surface.

Powder coating particle sizes can vary widely, for example from a minimum particle size of 1 μm, more specifically 5 μm, more specifically 10 μm, more specifically 25 μm, and even more specifically 50 μm, to a maximum particle size of 250 μm, more specifically 150 μm, more specifically 125 μm, more specifically 100 μm, and even more specifically 75 μm. Average film thickness can also vary widely, from a minimum thickness of 10 μm, more specifically 25 μm, more specifically 50 μm, and more specifically 75 μm, and even more specifically 100 μm, to a maximum thickness of 500 μm, more specifically 400 μm, more specifically 300 μm, more specifically 250 μm, more specifically 225 μm, more specifically 200 μm, more specifically 175 μm, more specifically 160 μm, more specifically 150 μm, more specifically 140 μm, more specifically 130 μm, and even more specifically 120 μm. As used herein, average film thickness means a film thickness that would be achieved for a given mass of applied coating at a uniform thickness. Some of the above thicker coatings may require multiple coating passes to achieve the target thickness. Any of the above minimum and maximum sizes for particles or layer thickness can be independently combined to disclose a number of different ranges, subject to the minimum number being smaller than the maximum number. Particle size and average film thickness can be varied to control the depth and frequency of surface projections and recesses, with larger particle size and thicker coatings favoring a greater variation in layer thickness, and smaller particle size and layer thickness favoring a smaller variation in layer thickness. Surface projections and recesses can also be formed on non-powder coatings by the use of additives, polymer curing mechanisms (e.g., polymer macromolecule displacement effects during cross-linking), shrinkage occurring during solvent evaporation, or by physical processes during application of the coating or before cure is complete (e.g., stippling), or by post-cure processes (e.g., calendering).

As mentioned above, the coating has a surface pattern of projections and recesses, as shown inFIGS. 3 and 4.FIG. 3contains duplicates of a magnified photograph of a surface coating with recesses and protrusions. Selected recesses are identified as32for illustration in the photograph on the right, whereas the photograph on the left is unmarked. The un-numbered horizontal lines shown inFIG. 3are male splines from the underlying inner shaft surface26(FIG. 2). A number of the recesses shown inFIG. 3appear dark in color because of grease or other lubricant42(FIG. 4) disposed in the recesses. An example embodiment of a coating having a pattern of projections and recesses is schematically depicted in a cross-section view inFIG. 4. As shown inFIG. 4, a polymer coating34is disposed on a substrate36. The surface of the coating has a pattern of recesses38and projections40. In some embodiments, the pattern of surface projections and recesses can provide technical effects for the steering shaft assembly. For example, in some embodiments, the recesses38can have a lubricant (e.g., grease)42disposed therein, which provides a series of lubricant reservoirs to provide lubricity for slideable engagement between the inner shaft12and the outer shaft16. Such lubricant reservoirs have reduced susceptibility to ejection (and exhaustion) of lubricant from the space between the inner shaft12and the outer shaft16compared to if the surface were smooth.

In some embodiments, the pattern of recesses and projections can also provide for a press fit tolerance between the inner shaft12and the outer shaft16, with the recesses38providing space to accommodate deformation of the coating surface resulting from radially-inward compression and deformation of the coating outer surface projections40. This can allow for the coating to be applied such the radially-outermost portions of the projections40would provide a slightly tighter than optimal fit against the inner surface28(FIG. 2) of the outer shaft16. Such a tight fit would remain undesirably tight if the coating were smooth because the coating would be essentially non-compressible. The recesses38, however, can provide space to receive coating material from deformation in response to radially-inward compression of the projections40when the inner shaft is inserted into the outer shaft, yielding a desired level of press-fit tolerance.

In some embodiments, the projections and recesses at the coating surface can be characterized by a thickness of the coating that varies in a range with a minimum thickness of 0 mm, more specifically, 0.05 mm, more specifically 0.1 mm, more specifically 0.2 mm, more specifically 0.25 mm, more specifically 0.3 mm, more specifically 0.4 mm, more specifically 0.4 mm, more specifically 0.6 mm, more specifically 0.7 mm, more specifically 0.8 mm, more specifically 0.9 mm, and a maximum of 1 mm, specifically, 0.9 mm, more specifically 0.8 mm, more specifically 0.7 mm, more specifically 0.6 mm, more specifically 0.5 mm, more specifically 0.4 mm, more specifically 0.3 mm, more specifically 0.25 mm, more specifically 0.2 mm, more specifically 0.1 mm. In some embodiments, the projections and recesses can be characterized by a size dimension44of the recesses parallel to the substrate in a range with a minimum dimension of 1 μm, more specifically 10 μm, more specifically 50 μm, more specifically 100 μm, more specifically 200 μm, more specifically 1 mm, more specifically 2 mm, more specifically 3 mm, and a maximum dimension of 5 mm, more specifically 4 mm, more specifically 3 mm, more specifically 2 mm, more specifically 1 mm, more specifically 500 μm, more specifically 400 μm, more specifically 300 μm, more specifically 200 μm. Any of the above thickness or size dimension values can be independently combined to disclose a number of different ranges, subject to the minimum number being smaller than the maximum number.