Fork top bridges for connecting steer tubes of a motorcycle or bicycle

According to the invention, a fork crown for connecting fork tubes of a motorbike or bicycle includes clamping collars with at least two clamping tongues which extend from a collar base in opposite peripheral directions.

This application is the U.S. national phase of International Application No. PCT/EP2014/002803 filed 16 Oct. 2014, which designated the U.S. and claims priority to DE Patent Application No. 10 2013 018 337.5 filed 31 Oct. 2013, the entire contents of each of which are hereby incorporated by reference.

The invention relates to a fork top bridge for connecting steer tubes of a motorcycle or bicycle as defined by the preamble to claim1.

Fork top bridges of this type typically have clamping collars in the end areas opposite one another, into which clamping collars the two steer tubes of a front wheel fork of a motorcycle or bicycle are introduced and firmly clamped. Besides one-piece clamping collars, which have only a single clamping tongue, two-piece clamping collars are also known, in which two clamping tongues are located one above the other in the axial direction and can be clamped shut by means of separate clamping screws. As a result, the clamping collars can be clamped shut equally in the upper and lower peripheral area and thus over their entire height. The clamping tongues extend, beginning at the collar base, in the same direction in the circumferential direction; the flange bases through which the clamping screw extends are located one above the other.

In the known clamping collars, it is disadvantageous that whenever a torsional moment acts on the clamped-in steer tube and the steer tube rotates about its longitudinal axis, are self-inhibiting in only one direction of rotation, that is, they pull shut only in one direction of rotation. If a torque acts on the steer tube in the opposite circumferential direction, a frictional force acts on the clamping tongue or clamping tongues, which force seeks to move the clamping tongue or clamping tongues in the opening direction. Such rotary forces thus have the tendency of loosening the fixed clamping seat between the clamping collar and the steer tube.

The attempt is made to counteract this unwanted effect by clamping the collars shut with a suitably high force. However, the steer tube may become deformed as a result. Such a deformation, however, worsens the function of the fork, which is typically embodied as a telescoping fork, since the inner tube then no longer slides easily, as desired, in the outer tube.

The object of the invention is to create a fork top bridge of the type mentioned at the outset with a clamping collar which securely and reliably holds the clamped-in steer tube with the least possible clamping forces and in so doing reduces the deformation of the steer tube.

This object is attained according to the invention by a fork top bridge having the features of claim1. Advantageous embodiments of the invention are described in the further claims.

The fork top bridge of the invention has at least one clamping collar with a first clamping tongue and a second clamping tongue, and the first clamping tongue extends outward from the collar base in a first circumferential direction, while the second clamping tongue extends outward from the collar base in a second circumferential direction, which is the opposite of the first circumferential direction.

Because the two clamping tongues extend in opposite circumferential directions, the clamping collar always has one clamping tongue which pulls closed if the steer tube makes a rotary motion about its longitudinal axis, regardless of rotational direction of this rotary motion. The clamping-shut forces of the clamping collar can therefore be reduced without impairing the reliable retention of the steer tube in the collar. These slight clamping-shut forces result in reduced deformation of the steer tube. In addition, the free ends of the two clamping tongues that move the most as the clamping collar is clamped shut are also offset in the circumferential direction. As a result, the steer tube likewise is uniformly stressed when the clamping collar is being clamped shut and the deformation of the steer tube is reduced. The highly reduced deformation of the steer tube ensures a smoothly moving, very precise function of the telescoping fork.

Advantageously, the clamping tongues each extend over a circumferential area of 100° to 260°, in particular 170° to 190°, along the circumference of the clamping collar. It is especially advantageous if the clamping tongues extend over a circumferential area of approximately 180° along the circumference of the clamping collar. As a result, because of the flexibility of the clamping tongues, the clamping forces can be transmitted especially effectively and uniformly to the steer tube, and at the same time the clamping-shut devices of the two clamping tongues are offset from one another in the circumferential direction so much that the free ends of the clamping tongues, which move the most, are located relatively far apart.

Advantageously, the clamping collar has a slot, which has an upper axial slot segment, a lower axial slot segment which is offset from the upper axial slot segment in the circumferential direction by 170° to 190°, in particular 180°, and a slot segment extending in the circumferential direction, which segment connects the upper and lower axial slot segments and divides the first clamping tongue from the second clamping tongue. As a result, the clamping collar can be produced relatively simply from a single, tubular part.

Advantageously, the collar base and clamping tongues are embodied in one piece with the bridge body. As a result, an especially stable, rigidly connected arrangement is obtained. Under lesser stresses, for instance in the bicycle field, however, it is also conceivable to produce the clamping collar separately from the bridge body and to secure it afterward to the bridge body by means of suitable connecting means.

One exemplary embodiment of the invention will be described as an example in further detail below in conjunction with the drawings.

The invention will be described below in terms of a fork top bridge arrangement or fork top bridge which is used in motorcycle forks. However, its use in bicycles is equally possible.

InFIG. 1, a fork top bridge arrangement having a lower fork top bridge1and an upper fork top bridge2, which are joined to one another by means of a central steering head shaft3, can be seen.

In the lower end area of the steering head shaft3, a lower bearing ring4is provided, which, together with an upper bearing ring not shown, forms a bearing arrangement with which the fork top bridge arrangement and thus the entire fork of the motorcycle is supported rotatably in a steering tube, not shown, of a motorcycle frame.

Each fork top bridge1,2has two clamping collars5,5′, which are located on the opposite ends of the fork top bridges1,2. The clamping collars5,5′ are each embodied essentially cylindrically or in tubular fashion and enclose receptacle chambers6, through which the steer tubes that are to be clamped extend. The longitudinal axis of the upper clamping collar5is aligned with the longitudinal axis of the lower clamping collar5, while the longitudinal of the upper clamping collar5′ is aligned with the longitudinal axis of the lower clamping collar5′. The steer tubes retained by the fork top bridge arrangement therefore extend parallel to one another.

Below, the construction of the lower fork top bridge1will be described in further detail in terms ofFIGS. 2 through 4. The upper fork top bridge2is constructed identically or quite similarly with regard to the parts that are essential to the invention.

As can be seen fromFIG. 2, the two clamping collars5,5′ of the fork top bridge1are integrally formed onto a bridge body7, which is located between them and is embodied in as stable and rigidly connecting a way as possible. An opening8is provided centrally in the bridge body7; it serves to receive and secure the lower end area of the steering head shaft3.

The two clamping collars5,5′ are embodied in one piece with the bridge body7and comprise the same material. Expediently, this material is a high-strength aluminum alloy, or some other metal, such as steel. The material is selected such that on the one hand, the fork top bridge has the desired great strength and stability, and on the other, the clamping collars5,5′ have a certain flexibility, so that they can be clamped shut and opened.

Both clamping collars5,5′ are located symmetrically to the vertical center plane of the fork top bridge1and moreover are embodied identically. The clamping collars5,5′ have a dimensionally stable collar base9in the transition area to the bridge body7. This collar base9extends, in the exemplary embodiment shown, over approximately 180° of the total circumference of the clamping collars5,5′. The surface of the collar base9that demarcates the receptacle chamber6is thus semicircular, in the plan view shown inFIG. 4; it extends over the entire axial length of the clamping collar5,5′.

Since the two clamping collars5,5′ have the same construction, only the clamping collar5will be described in further detail below. This description applies accordingly to the clamping collar5′.

As can be seen fromFIG. 2, the collar base9has a radially outward-protruding first flange base10, which is located in the upper half of the clamping collar5and in a first circumferential end area16of the collar base9, and a radially outward-protruding second flange base11, which is located in the lower half of the collar base9and in an opposite, second circumferential end area22of the collar base9. Both flange bases10,11each have a respective threaded bore12, which serves to screw in a clamping screw, not shown.

Each clamping collar5furthermore has a clamping tongue assembly with a first, upper clamping tongue13and a lower, second clamping tongue14that is movable separately from the first. The first clamping tongue13extends from a third circumferential end area19of the collar base9in semicircular fashion in a first circumferential direction15into the vicinity of the opposed first circumferential end area16of the collar base9, that is, into the vicinity of the first flange base10.

On the free end area of the first clamping tongue13, a radially outward-protruding third flange base17is provided, having a bore18that is aligned with the threaded bore12and that serves to allow the passage through it of the clamping screw, not shown. The second clamping tongue14extends in a second circumferential direction21, which is the opposite of the first circumferential direction15, from a third circumferential end area20of the collar base9, which area is located below the first circumferential end area16, to the vicinity of the second circumferential end area22of the collar base9, which area is located below the third circumferential end area19and has the second flange base11. Moreover, in the free circumferential end area of the second clamping tongue14, a radially outward-projecting fourth flange base24is provided, having a bore25that is aligned with the threaded bore12and serves to allow the passage through it of a second clamping screw, not shown, with which the free end of the second clamping tongue14can be pulled against the collar base9in order to firmly clamp the steer tube. The two flange bases10,17thus together with a clamping screw form a first clamping-shut device, with which the first clamping tongue13can be pulled in the first circumferential direction15in order to firmly clamp a steer tube, while the flange bases11,24, together with a clamping screw, form a second clamping-shut device, with which the second clamping tongue14can be pulled in the second circumferential direction21, which is the opposite of the first circumferential direction15, in order to firmly clamp the steer tube in the immediate axial vicinity of the first clamping tongue13.

The first clamping tongue13is divided from the second clamping tongue14by a slot26, which has a slot segment27extending in the circumferential direction of the clamping collar5, an upper axial slot segment28extending in the axial direction of the clamping collar5, and a lower axial slot segment29, extending in the axial direction of the clamping collar5, which is located in the opposite circumferential area of the clamping collar5. Thus the slot has an S-shaped course.

Within the scope of the invention, many variations are possible. For instance, it is possible for the clamping collars5,5′ to have more than two clamping tongues13,14, for instance three or four clamping tongues. In that case, it is advantageous if one clamping tongue each extends in the opposite direction from the adjacent clamping tongue. It is furthermore possible that the vertical slot segments28,29are not offset from one another by 180°, but by a different angular amount, such as 100° to 260°, in particular 170° to 190°. Expediently, both clamping collars5,5′ are embodied identically. However, different embodiments are fundamentally also possible.