Eccentric bearing

Abstract

Eccentric bearing for converting a rotary motion into a linear motion, comprising a rotatably driven shaft (2), a bearing ring (3) enclosing the shaft (2), and rolling elements (5) arranged around the shaft (2) in a gap (4) between the shaft (2) and the bearing ring (3), characterized in that the bearing ring (3) is eccentric to the shaft (2), that the rolling elements (5) have different diameters corresponding to a different gap width between the shaft (2) and the bearing ring (3), and that the rolling elements (5) are enclosed by an annular loop (7) which acts on the rolling elements (5) against a circumference of the shaft (2).

Description

State of the art

[0001] The invention relates to an eccentric bearing with the features of the preamble of claim 1. The eccentric bearing according to the invention is intended in particular for an electro-hydraulic piston pump unit of a hydraulic brake system of a motor vehicle. Such pump units are used to generate hydraulic brake pressure for brake actuation in slip-controlled and / or externally powered brake systems.

[0002] Common eccentric bearings feature an eccentric shaft that is rigidly and eccentrically mounted, either as a single piece or in some other manner, to the motor shaft of an electric motor or to the output shaft of a gearbox driven by the electric motor. A rolling bearing is mounted on the eccentric shaft, comprising a bearing ring that concentrically surrounds the shaft and rolling elements arranged in a gap between the eccentric shaft and the bearing ring around the shaft, usually, but not necessarily, at equidistant intervals. The rolling elements are typically rollers or needles, but other rolling elements, such as balls, are also possible. The bearing ring can be considered an outer ring; an inner ring may be present, for example, pressed onto the eccentric shaft. However, an inner ring is not always necessary; the rolling elements can also roll directly on the eccentric shaft.On the outside of the bearing ring, one or more pump pistons of the pump piston assembly rest against the bearing ring with their ends. The pump pistons are pressed against the bearing ring from the outside, for example by springs.

[0003] In a rotary drive, the eccentric shaft, due to its eccentricity, moves along a circular path and rotates on its own axis. Because of the eccentric shaft's circular movement, the bearing ring also moves along the same circular path, thereby driving the pump pistons located on its outer surface into the desired stroke. This stroke is used to pump brake fluid or other fluids by alternating suction and displacement, as is known from piston pumps. Due to its rolling bearing arrangement, the bearing ring does not rotate with the eccentric shaft.

[0004] In electro-hydraulic piston pump units for hydraulic brake systems of motor vehicles, the eccentric bearings convert a rotary movement of an electric motor or an output shaft of a gearbox into a reciprocating movement to drive the pump pistons.

[0005] Patent application JP S61-215 480 A discloses a screw compressor with an eccentric bearing for converting rotary motion into circular motion. The eccentric bearing has a stub shaft around which cylindrical rollers are arranged as rolling elements. The cylindrical rollers are rotatably mounted in a cylindrical roller cage, which maintains the circumferential spacing between the cylindrical rollers. The roller cage is pressed into a cylindrical blind hole in the head of a shaft that is rotatable about its axis and is arranged parallel to and eccentric to the stub shaft. Due to the eccentricity, an annular gap surrounding the stub shaft in the blind hole of the head shaft has a gap width that varies around the circumference. The cylindrical rollers have different diameters corresponding to the gap width at their respective circumferential locations. A rotary drive of the head shaft moves the stub shaft in a circular path. Disclosure of the invention

[0006] The eccentric bearing according to the invention, with the features of claim 1, comprises a rotatably driven shaft on which a rolling bearing is mounted, the bearing having a bearing ring surrounding the shaft and rolling elements arranged around the shaft in a gap between the shaft and the bearing ring. The rolling elements may, but need not, be arranged equidistantly. In contrast to known eccentric bearings, the shaft of the eccentric bearing according to the invention is concentric to its axis of rotation, although it is conceivable, and not excluded by the invention, that the shaft may be eccentric to its axis of rotation. Instead of, or possibly in addition to, an eccentricity of the shaft, the bearing ring is eccentric to the shaft, and the rolling elements have different diameters corresponding to a different gap width between the shaft and the bearing ring due to the eccentricity of the bearing ring to the shaft.The rolling elements have diameters that are as large as the width of the gap between the bearing ring and the shaft at the circumferential point where the respective rolling element is located.

[0007] The rolling elements of the eccentric bearing according to the invention are enclosed by an annular loop that presses the rolling elements against the circumference of the shaft. The loop causes the rolling elements to bear against the shaft and, when the shaft rotates, to roll on it and thus rotate around it. The loop of the eccentric bearing according to the invention ensures that the rolling elements rotate around the rotating shaft even if there is play between the bearing ring and the rolling elements. This ensures the circular motion of the bearing ring around the axis of the shaft when the shaft is driven by rotation. As described, the circular motion of the bearing ring causes the stroke motion of the pump piston(s) located on the outside of the bearing ring.

[0008] In a rotary drive, the rolling elements roll on the shaft and in the bearing ring, rotating around the shaft as is typical for rolling bearings. The larger-diameter rolling elements push the bearing ring away from the shaft, while on the opposite side, where the smaller-diameter rolling elements are located, the bearing ring moves closer to the shaft. In effect, the varying gap width, along with the rolling elements, rotates around the driven shaft; that is, the widest, the narrowest, and every other gap width rotate with the rolling elements. The bearing ring moves in a circular path around the shaft with an eccentricity relative to the shaft. The rotary motion of the shaft is converted into a reciprocating motion of one or more pump pistons located on the outside of the bearing ring.Assuming a bearing ring that does not rotate with the shaft, the rolling elements rotate at half the rotational speed of the shaft, and the speed at which the bearing ring moves on its circular path is also halved. The eccentric bearing according to the invention features a speed reduction; the rotational speed of the bearing ring's eccentricity is halved relative to the shaft's rotational speed when the bearing ring is fixed. This speed reduction has the advantage of enabling a higher drive speed, which, for the same power output, allows the use of a smaller and lighter electric motor.

[0009] Another advantage of the eccentric bearing according to the invention is its simple and cost-effective design.

[0010] The eccentric bearing according to the invention is intended in particular for use as described in an electro-hydraulic piston pump unit for generating brake pressure in a hydraulic brake system of a motor vehicle, where it converts the rotary motion of an electric motor into a reciprocating motion for driving pump pistons. However, the invention is not limited to this use but also relates to the eccentric bearing itself.

[0011] The dependent claims relate to advantageous embodiments and further developments of the invention specified in claim 1.

[0012] A preferred embodiment of the invention according to claim 2 provides that the loop is elastic and exerts an inward preload on the rolling elements against the circumference of the shaft. The loop can be tension-elastic. Alternatively, the loop can be rigid, i.e., inelastic in the tensile direction and flexible. In this case, the loop is shorter than a circumference around the rolling elements bearing against the circumference of the shaft and longer than a ring enclosing the rolling elements, bearing against them, and running straight and tangentially between adjacent rolling elements. Between adjacent rolling elements, such a loop is elastically deformed, thereby reducing its curvature. The elastic deformation of the loop in the bending direction causes the rolling elements to be elastically pressed inwards, i.e., with preload against the circumference of the shaft. A suitable material for the loop is, for example, steel or another metal.The loop must be made of a material that can withstand the stress exerted on it by the rolling elements when they roll in the bearing ring, because the loop is located between the bearing ring and the rolling elements, meaning the rolling elements roll on the loop.

[0013] One possibility is a loop, or several loops arranged parallel to one another at a distance, which are narrow in relation to the width of the bearing ring or the length of the rolling elements in the axial direction. Such loops can be arranged in circumferential grooves of the rolling elements and / or on the inside of the bearing ring, so that the rolling elements roll directly on the inside of the bearing ring instead of on the loop arranged within the bearing ring. Claim 4 provides a band-shaped loop that is approximately as wide as the bearing ring or as wide as the length of the rolling elements in the axial direction. The loop is located between the rolling elements and the bearing ring, and the rolling elements roll on the loop. Brief description of the drawing

[0014] The invention is explained in more detail below with reference to an embodiment illustrated in the drawing. The single figure shows an eccentric bearing according to the invention in a close-up view. embodiment of the invention

[0015] The eccentric bearing 1 according to the invention, as shown in the drawing, has a shaft 2 enclosed by a bearing ring 3. Rollers 5 are arranged around the shaft 2 in a gap 4 between the bearing ring 3 and the shaft 2, acting as rolling elements. The bearing ring 3 and the rollers 5 can optionally be considered a rolling bearing together with the shaft 2. The shaft 2 can be driven by an electric motor (not visible in the drawing because it is located behind the plane of the drawing) to rotate about its axis 6, which is also its axis of rotation. The shaft 2 has no eccentricity. It can, for example, be the end of a motor shaft of the electric motor.

[0016] The bearing ring 3 is eccentric to the shaft 2; the width of the gap 4 between the bearing ring 3 and the shaft 2 varies circumferentially. Starting from a maximum gap width, which is at the top right in the drawing, the gap width decreases in both circumferential directions to a minimum gap width, which is located opposite the maximum gap width, i.e., at the bottom left in the drawing.

[0017] The rollers 5, which form the rolling elements, have different diameters corresponding to the different gap widths. The diameters of the rollers 5 are each as large as the gap 4 between the bearing ring 3 and the shaft 2 at the point where the respective roller 5 is located.

[0018] When the shaft 2 is driven by a rotating drive, the rollers 5 roll around a circumference of the shaft 2, rotating at half the speed of the shaft 2. The largest gap width of the gap 4 between the bearing ring 3 and the shaft 2 is driven by the two rollers 5 with the largest diameters. Similarly, the smallest gap width of the gap 4 between the bearing ring 3 and the shaft 2 is driven by the two rollers 5 with the smallest diameters, rotating around the shaft 2 at half the speed of the shaft 2. In other words, when the shaft 2 is driven by a rotating drive, an eccentric component of the bearing ring 3 rotates around the shaft 2, with the rotational speed of the eccentric component being half the rotational speed of the shaft 2 when the bearing ring 3 is not rotating.The bearing ring 3 moves on a circular path around the axis 6 of the shaft 2, which is also its axis of rotation, whereby the speed of the circular motion of the bearing ring 3 is half as large as the rotational speed of the shaft 2, thus a speed reduction takes place.

[0019] The rollers 5 are enclosed by a band 7, which is as wide as the rollers 5 are long in the axial direction. The band 7 can also generally be considered an annular loop. The band 7 is located between the rollers 5, which form the rolling elements of the eccentric bearing 1, and its bearing ring 3. When the shaft 2 is driven by a rotary drive, the rollers 5 roll on the band 7, which is located on the inside of the bearing ring 3.

[0020] The strip 7, for example, is made of steel. The strip 7 can be considered rigid in tension, i.e., inelastic in the tensile direction, and elastic in bending. It is shorter than an imaginary circumference enclosing the rollers 5 and longer than an imaginary line enclosing the rollers 5, running straight and tangentially between adjacent rollers 5. The strip 7 enclosing the rollers 5 is elastically bent; in the sections where it rests against the rollers 5, its curvature is increased to the radii of the rollers 5, and in the sections between the rollers 5, the curvature of the strip 7 is decreased. Due to its elastic deformation, the strip 7 exerts a radial inward force on the rollers 5 against the circumference of the shaft 2. The strip 7 causes the rolling elements 5 to roll on and around the shaft 2 when the shaft 2 is driven by rotation.The rollers 5, which form the rolling elements of the eccentric bearing 1, roll on the rotating shaft 2 thanks to the band 7 surrounding them, even if there is play between the bearing ring 3 and the rollers 5. The rollers 5 are free of play on the shaft 2 due to their elastic radial inward bearing by the band 7.

[0021] The rollers 5 are rotatably mounted in rectangular recesses, so-called pockets, of a roller cage 8. Such roller cages 8 are known from rolling bearings. The roller cage 8, which can also generally be considered a rolling element cage, holds the rollers 5, which form the rolling elements of the eccentric bearing 1, at their circumferential distance from one another.

[0022] Band 7 is not held in a rotationally fixed position in bearing ring 3; it is fundamentally rotatable relative to bearing ring 3.

[0023] The ends of the pump pistons 9 rest against the outer surface of the bearing ring 3. The pump pistons 9, of which only their ends are shown in the drawing, are arranged radially to the shaft 2 and are pressed against the bearing ring 3 from the outside by piston springs (not shown). The pump pistons 9 are axially displaceable within pump bores 10 of a pump housing 11, i.e., radially displaceable to the shaft 2. The eccentric bearing 1 is located in a cylindrical eccentric chamber 12 of the pump housing 11 between the two pump pistons 9, which in this embodiment are arranged opposite each other, i.e., in a boxer configuration. When the shaft 2 is rotated, the bearing ring 3 moves, without rotating with the shaft 2, at half the rotational speed of the shaft 2 in a circular path around the axis 6, which is also the axis of rotation of the shaft 2. The circular motion of the bearing ring 3 drives the pump pistons 9 into a stroke.The eccentric bearing 1 thus converts a rotary motion of the shaft 2 into a reciprocating motion to drive the pump pistons 9. The pump housing 11 is part of a so-called hydraulic block, in which, in addition to the pump pistons 9, further hydraulic components (not shown), such as solenoid valves of a slip control device for a hydraulic braking system of a motor vehicle, are arranged and hydraulically interconnected. Such hydraulic blocks are known per se and will not be explained further here.

Claims

[1] Eccentric bearing for converting a rotary motion into a linear motion, comprising a rotatably driven shaft (2), a bearing ring (3) surrounding the shaft (2), and rolling elements (5) arranged around the shaft (2) in a gap (4) between the shaft (2) and the bearing ring (3), characterized by , that the bearing ring (3) is eccentric to the shaft (2), that the rolling elements (5) have different diameters corresponding to a different gap width between the shaft (2) and the bearing ring (3), and that the rolling elements (5) are enclosed by an annular loop (7) which acts on the rolling elements (5) against a circumference of the shaft (2). [2] Eccentric bearing according to claim 1, characterized by , that the loop (7) is elastic. [3] Eccentric bearing according to claim 1, characterized by , that the loop (7) is thin. [4] Eccentric bearing according to claim 1, characterized by , that the loop (7) is a band. [5] Eccentric bearing according to claim 1, characterized by , that the bearing ring (3) is rotatable relative to the loop (7). [6] Eccentric bearing according to claim 1, characterized by , that the eccentric bearing (1) has a rolling element cage (8).

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