SPLINED SLIDER HAVING A PLURALITY OF ELONGATED SPLINES INCLUDING A PEAK

CLAIM OF PRIORITY

[0001] This application claims priority to U.S. Provisional Application No. 63/047,726, filed July 2, 2020, the entire disclosure of which is incorporated by reference herein.

FIELD OF THE INVENTION

[0002] The present invention relates generally to disc brake assemblies. More particularly, the present invention relates to designs and assembly methods of electric screw actuated disc brake assemblies.

BACKGROUND OF THE INVENTION

[0003] The application being disclosed is a screw activated disc brake system which would replace the direct acting piston systems commonly utilized today. The current application is able to apply approximately 8000N of force in one direction (outward - extension) and adjust as a function of a control system and force sensor. The force in a traditional brake system is applied, but there is limited control to undo that action other than removal of pressure from the piston and the runout of a wheel disc to push the brake back.

[0004] The present invention recognizes and addresses considerations of prior art constructions and methods. SUMMARY OF THE INVENTION

[0005] One embodiment of the present disclosure provides a splined slider having a shaft including a plurality of elongated splines extending axially along an outer surface thereof, each spline including a peak, and an outer housing having a plurality of elongated splines extending axially along an inner surface thereof, each spline including a peak, wherein the shaft is disposed concentrically within the outer housing so that each spline of the shaft is disposed at least partially between a pair of splines of the outer housing, the peak of each spline of the shaft extending radially-outwardly beyond the peaks of the pair of splines of the outer housing between which the spline of the shaft is disposed.

[0006] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS [0007] A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended drawings, in which;

[0008] Figure 1A is a perspective view of a splined slider in accordance with an embodiment of the present disclosure;

[0009] Figure IB is a partial cross-sectional view of the splined slider shown in Figure

1A, taken along line IB -IB;

[0010] Figures 2A and 2B are perspective views of prior art lead screw assemblies;

[0011] Figure 3 is a partial cross-sectional view of a formed lead screw assembly in accordance with an embodiment of the present disclosure; [0012] Figure 4 is a perspective view of a hollow formed lead screw in accordance with an embodiment of the present disclosure;

[0013] Figure 5 is a view of a rounded thread form;

[0014] Figure 6 is a view of an ACME thread form;

[0015] Figure 7 is a view of an asymmetric thread form;

[0016] Figure 8 is a series of views of drawn cups at various stages;

[0017] Figure 9 is a cross-sectional view of an alternate embodiment of a lead screw assembly in accordance with the present disclosure;

[0018] Figures 10 through 12 are perspective views of caged blanks formed by hydro forming processes;

[0019] Figure 13 is a cross-sectional view of a lead screw assembly in accordance with an embodiment of the present disclosure; and

[0020] Figure 14 is a cross-sectional view of an inner diameter/outer diameter screw and nut combination in accordance with an embodiment of the present disclosure.

[0021] Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention according to the disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0022] Reference will now be made in detail to presently preferred embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation, not limitation, of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope and spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0023] Referring now to Figures 1A and IB, the first development of the present disclosure is to employ two technologies, one of which is the ability to form drive splines 100 to a final shape. For example, drive splines 100 formed on solid round stock such as those used within a steering column required to collapse during crash or expand for adjustment. These splines 100 also move during typical car motions. A three-roll forming machine may be used to put the splines 100 onto the shaft 102, whereas an outer mating part 104, or housing, may be made by a forming machine or rotary swaging machine.

[0024] In prior art, both of these parts would have clearance with each other, but were filled with elastomeric/plastic molded material part 106 between the shaft 102 and outer housing 104 that minimized backlash as well as filled imperfections of the metal forms. One of the design aspects utilizes a layout in which the metal part of the inner splines 100 overlaps the outer splines 108 outer housing 104 in such a way that safe operation still results even if the plastic molding (not shown in Figure IB) fails. This is different than previously available lead screws where metal to metal interference does not exist. Formed screws 110 (Figures 2A and 2B) do exist with elastomeric/plastic nuts and even spring pre-loaded preload nuts, but these do not have the metal to metal overlap interference described with regard to the embodiments of a splined linear actuator 101 shown in Figures 1A and IB. The formed screws 110 shown in Figures 2A and 2B are also not overformed over the exact lead screw 110 for which its use is intended. These prior art lead screws 110 and nuts 112 are not made as matched screw 110 and nuts 112, therefore these assemblies may have clearance concerns and other concerns about match precision. [0025] Another aspect of the present disclosure is a Teflon coating 120, separation agent

122, and elastomeric/plastic material 124 and its allowances for imprecisions in forming or metal components. A metrology challenge of prior art splined sliders used in steering systems is unique due to the forgiveness of unintentional characteristics in the forming. Known spline rolling operations could almost miss an entire tooth, or create a wider tooth than intended, but the final splined slider product could function due to the overmolding outer part as long as the character of the molded area matched that of the rest of the spline. Basically the spline needs to be an axial extrusion like shape copied closely in shape along the length of the shaft. Even if a lead or thread type twist occurred the product would function as long as it was consistent up and down the length of the splined shaft.

[0026] The metrology of the situation was difficult at best as the “master nominal profile” for each long spline was the shape next to it in the area of over molding. Even the best of metrology machines at the time could have issues and no hard gage methods could be produced. The main operation of the slider required consistency of profile and not necessarily precision of the designed profile.

[0027] As shown in Figure 3, the design of the present disclosure includes a formed lead screw 130 with an overformed/molded nut 132 that effectively does the same as the splined slider. As with the splined slider, full function can be achieved even with imprecise tooth forms, root or top tooth forms, or even severe errors of lead dimensions. As long as the forms remain consistent up and down the spline the full function will occur. Even if a consistent major lead error of ±1% exist (10 pm over 1 mm), as long as sufficient thread material is molded onto the thread, a working drive screw results. Almost like self-tapping screws where the ‘nut’ thread is formed to the individual screw as first used. The present application should not have issues due to it being uni-direction (mainly) as well as force controlled. Similar to why Coordinate Measurement Machine drive screws can be low precision as long a smooth and somewhat consistent in speed.

[0028] Another advantage may be achieved with strategic molding of the separation layer, as shown in Figure 3, prior to the bearing elastomeric/plastic mold operation. For example, if the lead screw 130 form of each tooth 136 is valid in important areas (i.e., tooth flank sides 138) but not consistent in the root 140 or peak 142 form of the lead teeth, then a thick separation coating, such as a solid wax fill 124, or solid grease, can be put onto the root 140 and top peaks 142, but kept thin in flank sides 138 (Figures 3 and 9). The thick separation coating could be made of a formed material that would be washed, melted, or brushed out, or a solid grease that was to be maintained in application as the primary and permanent lubricant.

[0029] The above noted developments can be utilized on solid screws as well as on forms other than solid. The lead screw and nut can be formed by similar techniques even if hollow (Figure 4). The thread forms can be a rounded thread form 150 (Figure 5), an ACME thread form 152 (Figure 6), or even anti- symmetric thread form 154 (Figure 7, saw-toothed threads for biased one-way lift). These thread forms may be put onto seamless tubing in a throughfeed method and then cut and joined to the application, seamless tubing that has been cut first then formed. As well, these thread forms could be put onto drawn cup type shapes (Figure 8). If made from drawn cup type shapes, the infeed stock could be flat strip stock 160 and within current usage of current capital equipment. As well, drawn cups (Figure 8) could be hydroformed by a process used to form cage blanks 162 from tube, as shown in Figures 10, 11, and 12. Shapes large and severe enough can be formed by hydroforming to be utilized for thread forming and even non-symmetric threaded shapes can be made. [0030] Another development is a concept of a single formed or machined inner diameter/outer diameter (ID/OD) screw 170 and nut 172 combination. This is realized conceptually in the situation where perhaps not enough force generation or durability can be obtained within one thread lead only. They also could conceptually be utilized as a pre-load generation device with two leads countering each other in pre-load.

[0031] This concept involves using threads of similar dimensional lead on both the OD

174 and ID 176 of a tube-like member 178 at the same time as shown in Figure 14. What is shown is a thin cross section ‘screw’ member 178 and two thick cross sections ‘nuts’ 180. [0032] One aspect of the ID/OD screw concept is the ability to fully realize a shape matching that is compliant to form errors if the screw is formed. If the main central thread on the ID has a form error then the OD will probably have the mirror of that form error, but this will be accommodated within the operations as all contact between any two metal parts is done by the molded polymer that is to run on metal or on Teflon coated metal, i.e., unlike a machining operation where the OD pitch might be long by a small amount and the ID pitch might be different, but with a formed operation where the OD and ID threads are made via the same process as the same time there can be no such pitch differential. As long as the pitch error of the ID and OD are identical and the molded components match then the screw will not bind against itself i.e., if the OD screw has a 1% too long of pitch the ID nut will have a 1% too long of pitch, but both the matching components will match to them due to the molding of the polymer.

[0033] Another aspect of the ID/OD screw concept is for more load capacity. Load capacities in range of 5000 lbf rated load capacity are possible. As the ID/OD screw has two leads the load rating can be nearly doubled. With a formed design it will be natural for the ID thread shape to have a decrease of area by maybe 30%, thus yielding a load capacity increase to 170% over what a single thread might get.

[0034] Another aspect of the disclosure is to utilize in the design of either a single thread or dual thread designs is a concept of equivalent stiffness. Traditional thread design of bolted joints utilizes only the first few thread forms to derive strength. A bolted joint thread failure will exist in the first few threads if a bolt (internal compliant member) is put into a solid block type nut (external stiff member). This is due to the expansion or contraction of the length of the bolt due to linear forces as additional threads beyond the first few attempt to take up a load and yet the length of the stiffer nut member does not allow its threads to accommodate and equalize the forces on the threads.

[0035] An analogy would be to put a series of glue dots along a rubber band placed flat onto a thick piece of steel. As one pulls on the band, one would only need to break one glue dot at a time to get failures. If the rubber band was instead secured by the same glue dots to another rubber band then there are two equally compliant members being joined. As the bands are pulled all joints will attempt to support load. Both members receive the same deformations and stress. [0036] Even ball screws suffer from a maximum effective thread engagement length that is the same issue. As the first revolutions of threads and balls take up load the shaft expands or contracts behind the first few members so that subsequent revolutions full of balls receive less and less loading. Almost similar to spindle design that cannot automatically be doubled in strength or load rating simply by putting on twice the bearings.

[0037] For the present design, there is little need for extreme stiffness as there is fast actuation and a load sensor is utilized within the design. It is believed that the compliances mentioned here about two members acting to preserve their threads are still orders of magnitude stiffer than requirements. The compliance mentioned is for design so that all surfaces down the length of a screw are in contact and sustaining compression. This increases load capacity of the polymer system beyond that usually stated.

[0038] As such, both strength and lightweighting implications are achievable as when load sharing is properly done throughout the thread sections the loads will be equalized yielded strong screw utilizations as well as favorable failure modes. The utilization of the screws being fully stressed throughout length will lead the lightest weights desirable for manufacture material costs as well as final weight.

[0039] While one or more preferred embodiments of the invention are described above, it should be appreciated by those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope and spirit thereof. It is intended that the present invention cover such modifications and variations as come within the scope and spirit of the appended claims and their equivalents.