Shaft bearing seal

A seal (2) for a bearing (6) that rotatably supports a shaft (14) extending through a housing opening (8) of a housing element (10) that limits, at least partially, a lubricant-receiving chamber (4), includes a sealing ring (26) retainable between the housing element (10) and the shaft (14) and forming together with a limiting element (28) an annular gap (30), and having aeration recesses (34) which connect the annular gap (30) with the grease-containing chamber (4).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a seal for a bearing that rotatably supports a shaft. The shaft extends through a housing opening of a housing element that limits, at least partially, a chamber containing a lubricant in form of a lubricating grease or oil. Between the lubricant-containing chamber and the bearing, there is provided a sealing ring that surrounds the shaft and is retained between the shaft and the housing element for protecting the bearing from the lubricant. The sealing ring forms, together with a limiting element, an annular gap.

2. Description of the Prior Art

The seals of the type descried above, are provided, e.g., on lubricant-receiving chambers or receptacles for gear units of, e.g., hand-held power tools. The sealing ring prevents the lubricant, which is provided in the associated gear housing, from directly contacting the bearing and from flowing through the bearing from the gear housing outwardly, e.g., into a motor housing.

European Patent EP 0 202 702 B1 discloses a seal for a shaft bearing and which includes a swivel ring connected with the shaft for a joint rotation therewith. The swivel ring forms a hub which extends radially outwardly and forms, together with a hub fixedly connected with the housing and extending from the housing opening radially inwardly, an annular gap. This annular gap has a labyrinth-shaped cross-section.

U.S. Pat. No. 5,876,126 discloses a shaft bearing seal that has a sealing disc retained on an outer ring of the bearing which is fixedly secured to the housing. The sealing disc forms, together with a shaft and a bearing inner ring press-fitted on the shaft, a labyrinth-shaped annular gap.

The drawback of the known shaft bearing seals consists in that despite the labyrinth-shaped annular gap, in particular at a vertical orientation of the shaft, the lubricant reaches the bearing and can leave the lubricant-receiving chamber through the bearing.

Such seals are not suitable for hand-held power tools which, e.g., are often used in overhead works and have the shaft oriented vertically for an extended time period in an operational or shut-down condition of the power tool when no lubricant should flow through the shaft bearing.

Accordingly, an object of the present invention is to provide a shaft bearing seal suitable for hand-held power tools and in which the above-mentioned drawback of the known shaft bearing seals is eliminated, and the bearing is better protected from the lubricant such as grease.

SUMMARY OF THE INVENTION

This and other objects of the present invention, which will become apparent hereinafter, are achieved according to the present invention by providing a shaft bearing seal of the type discussed above and in which the sealing ring has aeration recesses which connect the annular gap with the lubricant containing chamber. The aeration recesses permit to remove the lubricant, which penetrated in the annular gap during the operation or shut-down of the power tool as a result of a vertical orientation of the bearing, from the annular gap. To this end, a dynamic effect is used which is produced by a rotation of the sealing ring that limits the annular gap on one side, relative to another limitation that limits the annular gap on the second side. The sealing ring can be fixedly connected, e.g., with the shaft for joint rotation therewith, and the limiting element can be fixedly secured to the housing element or vice versa. The aeration recesses aerate the annular gap. The aeration of the annular gap during operation prevents development of underpressure in the annular gap that can cause an aspiration of lubricant in the annular gap or its retention there.

According to a particular advantageous embodiment of the present invention, the sealing ring is formed by an impeller-like disc connectable with the shaft for a joint rotation therewith, and the limiting element is fixedly connected with the housing element. During an operation, the sealing ring rotates together with the shaft, accelerating the lubricant accumulated on the sealing ring. Thereby, in particular with a suitable shape of the sealing ring, the lubricant can be particularly effectively forced out of the annular gap.

Advantageously, the annular gap is formed between a radially outer rotational surface of the sealing ring and the limiting element. This insures a maximum acceleration of the lubricant that accumulated on the sealing ring during operation. This further optimizes removal of the lubricant from the annular gap.

Advantageously, the aeration recesses open into the rotational surface of the sealing ring, which insures a particularly good aeration of the annular gap and, thus, an unobstructed delivery of the lubricant out of the annular gap.

Preferably, the aeration recesses are substantially identical and are spaced from each other by a same angular distance. This insures a uniform removal of the lubricant over the sealing ring circumference.

Advantageously, there are provided at least three aeration recesses. This permits to achieve a particularly high delivery output of the sealing ring with respect to the lubricant in the annular gap.

Preferably, the aeration recesses extend from a lubricant containing chamber side end surface of the sealing ring to a bearing-side end surface of the sealing ring. Thereby, the aeration of the annular gap takes place over the entire width of the rotational surface. In addition, thereby, even the region of the annular gap, which is limited by the bearing-side end surface of the sealing ring remote from the lubricant-containing chamber, is aerated.

It is further particular advantageous when the aeration recesses extend radially inwardly up to a virtual cylinder a diameter (dZ) of which is smaller than an outer diameter of an inner ring of the bearing. Thereby, the side of the bearing adjacent to the lubricant-containing chamber can be completely aerated in the region between the shaft-side inner ring of the bearing and the outer ring of the bearing fixed to the housing. In this region, because of the insufficient sealing, the lubricant exits from the lubricant exits from the lubricant-containing chamber. Complement aeration prevents underpressure in this region. Therefore, with a suitable shape of the sealing ring, in this region also, a substantially complete removal of the lubricant is possible.

Advantageously, the aeration recesses extend over from 70% to 95% of a sealing ring circumference, and an acceleration element is formed between each two adjacent aeration recesses. With this propeller-shaped design of the sealing ring a particularly high delivery output with respect to the annular gap is achieved.

It is advantageous when the acceleration element has a side surface adjacent to a rotational direction and inclined toward a bearing axis at an angle. This likewise increases the delivery output.

Advantageously, the acceleration element alternatively or in addition is inclined toward the bearing axis at the rotational surface of the sealing element, at an angle. In this way, the sealing ring forms, during an operation, a conical rotational body, and an improved lubricant delivery takes place over the circumference of the sealing ring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a shaft bearing seal2which is provided on a grease-containing chamber4of a gear housing, not shown in detail, of a hand-held power tool, e.g., in form of a hammer drill or a screw driving tool. The shaft bearing seal2is provided on a bearing6that is retained in the housing opening8of a wall-shaped housing element10. The housing element10separates the grease-containing chamber4from an outer chamber12of a motor housing, not shown in detail.

The bearing6serves for supporting a shaft14for rotation about an axis A. The shaft14projects from the outer chamber12into the grease-receiving chamber4. The bearing6has an inner ring16which, e.g., is press fit-mounted on the shaft14for joint rotation therewith. The inner ring16is rotated relative an outer ring20of the bearing6by a ball-shaped bearing body18. The outer-ring20is held fixedly in the housing element10and is axially secured with a circlip22. Between the inner ring16and the outer ring20, there are provided sealing elements24.

On the shaft14, there is further provided a sealing disc26in form of an impeller-like disc that, e.g., is connected with shaft14by a press fit for joint rotation therewith. The sealing disc26is held, with respect to the axis A, at an axial height of a limiting element28that is formed by a collar section of the housing element10, which projects radially inwardly in the housing opening8. A circumferential rotational surface32, which is defined by radially outer surfaces of the sealing disc26, and the limiting element28form an annular gap30.

As shown inFIGS. 2-3, the sealing disc26has three acceleration elements33which are separated from each other by aeration recesses34. The aeration recesses34extend over more than 90° of the rotational surface32. The acceleration elements33form radially outer circumferential surfaces35which define the rotational surface32.

Alternatively, the aeration recesses34can be formed by a multiplicity of smaller grooves which can be formed on the circumference of the sealing disc26(not shown). In each case, the rotational surface32is formed by the radially outer surfaces36of the sealing disc26which upon rotation of the sealing disc26in a direction D, form an outer cylindrical surface of the corresponding rotational body.

The aeration recesses34and thus, the acceleration elements33extend, as shown inFIG. 1, over an entire width of the sealing disc26from a chamber-side end surface36adjacent to the grease-receiving chamber4to a bearing-side end surface28adjacent to the bearing6.

As shown inFIG. 1, the aeration recesses34extend radially inwardly up to a common virtual cylinder Z having a diameter dZ. The diameter dZ is smaller than the outer diameter dR of the inner ring16of the bearing6.

When the respective hand-held power tool is operated or is shut down and the shaft14is so aligned that it extends, as shown inFIG. 4, vertically, the grease can flow from the grease-receiving chamber4into the annular gap30between the sealing disc26and the limiting element28and through the annular gap30into an intermediate chamber40between the sealing disc26and the bearing6. As a result, the grease directly contacts the sealing elements24.

As soon as the shaft14begins to rotate about the axis A, the grease would be accelerated in the annular gap30and in the intermediate chamber40by the sealing disc26and would be transported from the annular gap30.

The aeration recesses34, which connect the grease-receiving chamber4with the annular gap30and the intermediate chamber40, insure that both the annular recess30and at least a region of the intermediate chamber40that extends over the sealing elements24, is adequately aerated. In this way, the built-up of an underpressure is prevented, and almost complete removal of grease, which accumulated on the sealing elements, is insured. At that, a grease cone42is formed that permanently adjoins the annular gap30but cannot penetrate thereinto as long as the sealing disc rotates.

FIGS. 4 through 7show alternative embodiments of the sealing disc26, with the elements, which perform the same functions, all having the same reference numerals as inFIGS. 1-3.

In the embodiment shown inFIGS. 4-5, the acceleration elements33form, with respect to the axis A, an angle (α) on both side surfaces44aligned in the rotational direction D.

In the embodiment ofFIGS. 6 and 7, additionally, the radially outer circumferential surface35of the acceleration elements33forms, with respect to axis “A” an inclination angle (β), so that the sealing disc26forms, upon rotation in the rotational direction D, a conical rotational body, as shown with dash-dot lines.