Patent Application
20190211891
The disclosure relates to a clamping freewheel, in particular a clamping freewheel with a ring element, in particular an inner ring or outer ring, that has at least one clamping ramp for clamping a clamping element, and one clamping element for each clamping ramp that bears on the at least one clamping ramp.
A freewheel, or a clamping freewheel, respectively, is a directionally shifted coupling, and normally has an inner ring, an outer ring, and a cage with clamping rollers and springs. The clamping freewheel can disengage a portion of the drive train from a rotational movement if the load ratios change.
Freewheels are typically used as return stops or overrunning clutches.
With a starting freewheel used as an overrunning clutch, springs and clamping rollers or clamping elements are normally used, which are pressed into pockets or onto clamping profiles or clamping ramps of an inner or outer ring. Because the clamping elements are in receiving spaces that are delimited in part by the clamping profiles or the clamping ramps that taper away from the springs, a torque that is transferred from the inner ring to the outer ring increases, for example, as the two rings are rotated in relation to one another.
With an appropriate selection of the angle of incidence, or clamping, of the clamping profile, the freewheel is prevented from slipping, because it is in the so-called self-inhibiting state. The clamping angle is selected such that it is less than or equal to the arc tangent of the slippage friction coefficient μ of the two materials rubbing against one another. If the clamping angle is greater than the arc tangent of μ, the freewheel slips, and cannot transfer forces.
A starting freewheel is used in particular in internal combustion engines for motorcycles with electric starters. A starter pinion equipped with a freewheel is driven by an electric motor to start the internal combustion engine. The starter pinion is normally connected to the inner ring of the freewheel, while the outer ring is normally connected to the alternator.
The freewheel transfers forces to the alternator via the outer ring until the internal combustion engine ignites. As soon as the engine ignites, the crankshaft connected to the alternator is accelerated to a higher rotational rate than that for starting the engine.
The freewheel then disengages the running engine, or its crankshaft, from the electric starter, such that the engine does not damage or destroy the starter with an excessive rotational rate.
A problem of overload forces being introduced in a freewheel is known from the prior art, in which the clamping elements are pressed back and quickly into the clamping profile or against the clamping ramps such that these are deflected, which can result in an immediate total breakdown of the freewheel.
It is therefore an object of the disclosure to produce a freewheel or clamping freewheel, respectively, and a freewheel assembly, which provides effective protection against overload forces introduced into the freewheel, or a rotational rate limit, wherein such a freewheel, or such a freewheel assembly, may ensure a high level of functionality, and can be produced inexpensively and in a material-saving manner.
This object is achieved according to embodiments disclosed below.
According to an embodiment, a clamping freewheel, in particular a clamping roller freewheel, comprises a ring element in a first aspect, in particular an inner ring or an outer ring, that has at least one clamping ramp or one clamping profile for clamping a clamping element.
The clamping freewheel may also comprise a clamping element or a clamping roller for each clamping ramp, which bears on the at least one clamping ramp.
The at least one clamping ramp may have at least one first and one second subsection, wherein the second subsection may be configured as a power transfer region, such that a relative movement between the clamping element and the ring element can be suppressed. In this manner, the clamping freewheel can transfer a force or torque from an inner ring to an outer ring, or vice versa. As a result, an internal combustion engine, for example, can be started.
The first subsection may be configured as an overload region, in which a relative movement between the clamping element and the ring element can be obtained. As a result, it is possible to prevent a transfer of force from the first ring element to the at least one clamping element.
In other words, it is beneficial when, if a high torque is quickly or suddenly applied to the clamping freewheel, the clamping elements move from the power transmission region to the overload region. This overload region may prevent damage to the overall freewheel, or clamping freewheel. If overload forces are applied to a freewheel, the clamping elements are quickly pressed backward, into the clamping profile, or against the clamping ramps such that these are pushed out, which in turn can lead to a total breakdown of the freewheel.
Moreover, when the ring element is rotated to transmit forces in the first subsection, the second subsection may follow, such that if there is an overload, the clamping element moves from the second subsection to the first section. As a result, the transmission of force between the first subsection and the at least one clamping ramp, or between the ring element and the clamping element, respectively, can be interrupted. Because of this interruption, the freewheel can be protected against an overload that can damage the freewheel.
The at least one clamping ramp may extend along the circumference. Because the ring elements are normally rotationally symmetrical, they extend radially and axially, wherein the ring elements may have the at least one clamping ramp on their circumference, as well as the associated clamping elements.
The first subsection may be allowed to move between the clamping element and ring element. As a result, no forces or torques can be transferred that can damage the freewheel.
The first subsection may allow for relative movement between the clamping element and the ring element, in that the tangent of the angle between a force that is to be transmitted and a perpendicular to the first subsection at the bearing point between the clamping element and the clamping ramp is greater than or equal to the frictional coefficient of the material of the frictional pair comprising the ring element and clamping element.
Simply put, the first subsection of the clamping ramp may implement the relationship tan α≥μ, via which a clamping between the clamping ramp and the ring element is released, or via which a clamping element slips on the clamping ramp. This in turn results in the freewheel limiting the torque/force applied to the ring element, thus resulting in an overload safeguard.
The second subsection may prevent relative movement between the clamping element and ring element. Forces or torques can be transferred as a result.
The second subsection may prevent relative movement between the clamping element and the ring element, in that the tangent of the angle at the bearing point between the clamping element and clamping ramp, formed between a force that is to be transferred and a perpendicular to the second subsection at the bearing point, is less than the frictional coefficient for the material of the frictional pair comprising the ring element and the clamping element.
In other words, the second subsection of the clamping ramp may implement the relationship tan α<μ, whereby a clamping is obtained between the clamping ramp and the ring element, or whereby a clamping element is clamped to the clamping ramp. As a result, the freewheel transfers the torque/force applied to the ring element.
The angle for the first subsection may be greater than 15°, wherein the angle at the second subsection may be 3° to 4.5°. The angular ranges result in slippage when tan α≥μ, or clamping when tan α<μ. In other words, with an angle of greater than 15°, slippage can be easily obtained between the clamping element and clamping ramp or ring element, while in contrast, with an angle between 3° and 4.5°, the clamping element is clamped to the clamping ramp or ring element.
Moreover, the ring element is thin-walled. This results in material savings, and thus cost savings.
The ring element may be thin-walled, such that the hollow cylindrical ring element has a wall thickness outside a clamping ramp comprising a fraction of the thickness of a clamping element, e.g., less than half the thickness of the clamping element, more particularly less than 0.3 times the thickness of the clamping element. The circumferential wall thickness at the thickest or thinnest part of the first ring element may be a fraction of the thickness of a clamping element. The aforementioned relationship results in a particularly simple and material-saving production possibility.
A second embodiment of the present disclosure comprises a freewheel assembly with a clamping freewheel, a first ring element, in particular in the form of an inner ring or outer ring, that has at least one clamping ramp for clamping a clamping element, and a second ring element, in particular an outer or inner ring, respectively.
It is expressly noted that the features of the clamping freewheel specified under the aspect of the present description can be used individually or in combinations thereof for the freewheel assembly.
In other words, the features specified above under the first embodiment relating to the clamping freewheel, can also be combined with other features herein under the second embodiment.
Advantageously, the first ring element may include a clamping element for each clamping ramp, which bears on the at least one clamping ramp.
The at least one clamping ramp may have at least one first and one second subsection.
The first subsection may be designed as an overload region, such that the clamping element moves in relation to at least one clamping ramp, whereby a transfer of forces from the first ring element via the clamping element to the second ring element can be prevented. As a result, transfer of forces from the first ring element to the second ring element, or in the other direction, can be prevented. In other words, the clamping element can move from the force transferring region to the overload region if a high torque is suddenly or quickly applied to the clamping freewheel. This overload region preferably protects the freewheel, or clamping freewheel, from damage. If excessive forces are applied to a freewheel, the clamping element is pressed backward and quickly into the clamping profile, or against the clamping ramp, such that it would be deflected, which could then result in a total breakdown of the freewheel.
The second subsection may be designed as a force transferring region, such that the at least one clamping ramp and the clamping element clamp together. The clamping ramp and the clamping element may fulfill the condition tan α<μ, whereby it can be ensured that forces are transferred from the first ring element via the clamping element to the second ring element.
The first subsection may be designed as an overload region, such that the at least one clamping ramp and the clamping element can slip. The clamping ramp and clamping element advantageously fulfill the slippage condition tan α≥μ, whereby it is possible to prevent a transfer of force from the first ring element via the clamping element to the second ring element.
The first ring element and the second ring element may be concentric. Such a configuration ensures low mechanical losses and a simple construction, resulting in savings in costs.
The clamping element may bear on the at least one clamping ramp of the first ring element and on a surface of the second ring element. The clamping element thus connects the first and second ring elements to one another directly, such that forces can be transferred from the first ring element to the second, or in the other direction.
The at least one clamping ramp is oriented spatially in the first ring element such that the spacing between the at least one clamping ramp of the first ring element and the surface of the second ring element is increased, e.g. continuously, along the course thereof in the direction of rotation for the first ring element, in which a force can be transferred from the first ring element to the second ring element. Forces can thus be transferred from the first ring element to the second, or in the other direction.
The spacing may relate to a path that runs in the extension through a rotational center of the first and/or second ring elements. The spacing is therefor the shortest distance between the first and second ring elements, or between the clamping ramp and ring element.
The surface of the first subsection of the at least one clamping ramp on the first ring element may form an angle with a tangent at the bearing point between the clamping element and the surface of the second ring element that is greater than 30° when the freewheel assembly is at a standstill.
The surface of the second subsection of the at least one clamping ramp on the first ring element may form an angle with a tangent at the bearing point between the clamping element and the surface of the second ring element that is between 6° and 9° when the freewheel assembly is at a standstill.
The aforementioned angular ranges result in slippage when tan α≥μ, and clamping when tan α<μ. In other words, with an angle of greater than 30°, slippage between the clamping element and the clamping ramp, or between the clamping element and ring element can be obtained, while in contrast, with an angle between 3° and 4.5°, clamping of the clamping element and clamping ramp, or the clamping element and ring element can be ensured.
The first ring element may form an outer ring and the second ring element forms an inner ring.
Alternatively, it is also possible for the first ring element to form an inner ring and the second ring element to form an outer ring.
The concepts of the disclosure given above may be expressed differently below.
These concepts may be based on—in a simplified version—different types of freewheels used as electric starter freewheels for motorcycles. These include clamping element freewheels and roller freewheels.
Most of the freewheels have a torque capacity that is many times greater than the nominal load. The reason for this oversizing is a “worst case” scenario that may result from misfiring, in which a large torque or force is quickly applied to the freewheel.
If the freewheel is not robust enough, or the environment is not stable enough, the starter suffers a total breakdown.
For this reason an object is to equip current freewheel designs with an overload protection—a torque limiting function.
Clamping freewheels are normally constructed with a clamping ramp/ramp/clamping angle α1 of 3° to 4.5°, in order to obtain the greatest degree of starting safety.
The formula tan α<μ may be applied thereby. Perpendicular forces act on the outer ring/housing of the freewheel when clamping, and expand them. The clamping rollers beneficially move along the ramp geometry, or the clamping ramp.
A freewheel according to the disclosure may have a further, significantly steeper ramp section, in which the contact points between the clamping rollers or clamping elements and the outer ring or ring element are displaced when a predetermined torque has been reached, whereby the clamping condition becomes unbalanced. As a result, the clamping elements slip in the further ramp section, limiting the torque that is to be transferred, or the load.
In other words, the clamping ramp in a freewheel may be provided with a second, significantly steeper section at a targeted position. The clamping condition tan α<μ may then no longer be satisfied, and the clamping rollers or clamping elements begin to slip on the clamping ramp or the ring element.
The disclosure shall be explained in greater detail below based on exemplary embodiments in conjunction with associated drawings. Therein:
The same reference symbols are used for identical objects in the following description.
The freewheel assembly 10 has a clamping freewheel 1 with a first ring element 2 that comprises numerous clamping ramps 3 and numerous clamping elements 4, wherein each clamping ramp 3 clamps a clamping element 4. The first ring element 2 is an outer ring therein.
The first ring element 2 is pressed into an outer ring element 22 for a form fitting and force fitting connection. In this manner, the first ring element 2 can be thin walled and used in various configurations inside an outer ring element 22.
The first ring element 2 is made of sheet metal in order to obtain the thin walled construction.
In the present case, the ring element 2 is thin walled such that the hollow cylindrical ring element 2 has a wall thickness H outside the clamping ramp 3, or at the thickest point of the first ring element 2 along the circumference U, that comprises a fraction of the thickness of a clamping element 4.
According to the exemplary embodiment in
Furthermore, the freewheel assembly 10 comprises a second ring element 11, which in the present exemplary embodiment is an inner ring.
The first ring element 2, or the outer ring, has one clamping element 4 for each clamping ramp—as indicated above—wherein the clamping element 4 bears on the respective clamping ramp 3, or the clamping element 4 is in contact with the clamping ramp 3, respectively.
Moreover, each of the clamping elements 4 shown therein bears on the associated clamping ramp 3 of the first ring element 2 and on a surface O of the second ring element 11. In this manner, a force can be transferred from the first ring element 2 to the second ring element 11 via the clamping element, or vice versa.
Each clamping ramp 3 has at least a first subsection 5 and a second subsection 6.
When the clamping freewheel 1 or the freewheel assembly 10 is in operation, the first ring element, rotating in the direction of rotation D, transfers a force to the second ring element 11 via the clamping elements 4.
The clamping elements 4 move along the tapered ramp geometry of the clamping ramps 3 when the first ring element 2 moves in the rotational direction D.
The clamping elements are clamped between the clamping ramp 3, or the first ring element 2, and the second ring element 11 inside the second clamping region 6 of the clamping ramp 3.
If, however, a large force or torque is applied to the clamping freewheel 1 in a short time interval, the clamping elements 4 move from the second subsection 6 of the clamping ramp 3 to the first subsection 5.
This second subsection prevents the overall clamping freewheel 1, or the overall clamping freewheel assembly 10, from becoming damaged. This is because if excessive forces are applied to a freewheel, the clamping elements 4 are pressed back quickly into the clamping profile, or against the clamping ramp 3, such that it becomes damaged, which in turn can lead to a total breakdown of the freewheel.
Consequently, the first subsection 5 in the exemplary embodiment in
In other words, the first subsection 5 forms an overload region, such that a clamping element 4 slips on the respective clamping ramp 3.
Specifically, the first subsections 5 of each clamping ramp 3 and an associated clamping element 4 fulfill the slippage condition tan α≥μ, via which a transfer of force from the first ring element 2 to the second ring element 11 via the clamping element 4 can be suppressed, or is prevented.
In contrast, the second subsection 6 is a force transfer region, designed such that a clamping element 4 clamps to the respective clamping ramp 3. The second subsection 6 of each clamping ramp 3 and an associated clamping element 4 fulfill the clamping condition tan α<μ thereby, via which a transfer of force from the first ring element 2 to the second ring element 11 via the clamping element 4 can be ensured, or can take place.
Moreover,
The outer ring element in the present exemplary embodiment shown in
As specified above, the drive direction, or the rotational direction D for transferring forces from the first ring element 2, or the outer ring element 22, to the second ring element 11, is indicated in
The freewheel assembly 10 according to
In addition to the clamping elements 4, one spring element 20 for each clamping element 4 is shown between the first ring element 2 and the second ring element. The spring elements 20 are compression springs that press against the associated clamping element 4 counter to the direction of rotation D.
While a clamping element 4 bears on one end of a spring element 20, the spring element 20 bears on a web 21 at the other end. This web 21 is connected to the first ring element 2.
Each clamping ramp 3 is oriented spatially in the first ring element 2 such that it enlarges the spacing X between the clamping ramp 3 of the first ring element 2 and the surface O of the second ring element 11 along its course in the rotational direction D of the first ring element 2. The enlargement is continuous, at least in the second subsection 6 of the clamping ramp 3.
It should be noted with regard to
Therein, the ring element 2 is an outer ring in the clamping freewheel 1, or the clamping roller freewheel 1, that has various clamping ramps 3, each of which clamps the clamping elements 4.
The clamping freewheel 1 also comprises—as explained above—one clamping element 4 for each clamping ramp 3, bearing on the respective clamping ramp 3.
Each clamping ramp 3 has at least one first subsection 5 and one second subsection 6, and extends in the circumferential direction U.
The first subsection 6 forms a force transferring region, such that a relative movement between the clamping element 4 and the ring element 2 can be prevented.
The first subsection 5 forms an overload region that allows for relative movement between the clamping element and ring element 2, by means of which a transfer of force from the first ring element 2 to the at least one clamping element 4 can be prevented.
When the ring element 2 is rotated for transferring force, or when the ring element 2 rotates in the rotational direction D, the first subsection 5 follows the second subsection 6. As a result, if there is an overload, the clamping element 4 moves from the second subsection 6 to the first subsection 5 in order to interrupt the transfer of force between the first subsection 5, each clamping ramp 3, and the respective associated clamping elements 4.
In the state shown in
In this state, the second subsection 6 prevents relative movement between each clamping element 4 and ring element 2.
This is obtained in that the tangent of the angle α at the bearing point between the clamping element 4 and the clamping ramp 3, which is formed between a force F that is to be transferred and a perpendicular N2 to the second subsection 6 at the bearing point A, is less than the frictional coefficient μ for the material of the frictional pair formed by the ring element 2 and the clamping element 4.
The angle α is between 3° and 4.5° in the second subsection 6. The perpendicular N2 is perpendicular to the plane of the second subsection 6 of the clamping ramp 3.
Simply put, this means that each clamping ramp 3 and each associated clamping element 4 are clamped, or clamped to one another, such that the clamping condition tan α<μ is satisfied. As a result, forces can be transferred from the first ring element 2 to the second ring element 11 via the clamping element 4.
In the state shown in
This is obtained in that the tangent of the angle α at the bearing point A between each clamping element 4 and each clamping ramp 3, which is formed between a force F that is to be transferred and a perpendicular N1 to the first subsection 5 at the bearing point A, is greater than or equal to the frictional coefficient μ for the materials of the frictional pair formed by the ring element 2 and the clamping element 4.
The angle α is greater than 15° for the first subsection 5. The perpendicular N1 is perpendicular to the plane of the first subsection 5 of the clamping ramp 3.
Simply put, in reference to
It should also be noted that in a comparison of
When stationary, the surface of the first subsection 5 forms an angle α1 with each clamping ramp 3 of the first ring element 2 with a tangent at the bearing point B between the clamping element 4 and the surface O of the second ring element. This angle α1 is greater than 30°.
Furthermore, when the freewheel assembly 10 is at a standstill, the surface of the second subsection 6 in each clamping ramp 3 of the first ring element 2 forms an angle α2 with a tangent at the bearing point B between the clamping element 4 and the surface O of the second ring element 11. This angle is between 6° and 9°.
Firstly, angles α1 and α2 are again indicated therein, as described above in reference to
Moreover, it can be clearly seen in
Thus, spacing X2 is greater than spacing X1, as shown in
These spacings X1 and X2 are distances that extend through the rotational center, or center M, of the ring element 2. In this manner, the spacings indicate the shortest distance between the first ring element 2 and the second ring element 11, or between the clamping ramp 3 and the surface O of the ring element 11.
In the present example according to
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 218 929.8 | Sep 2016 | DE | national |
This application is the U.S. National Phase of PCT/DE2017/100793 filed Sep. 18, 2017, which claims priority to DE 102016218929.8 filed Sep. 29, 2016, the entire disclosures of which are incorporated by reference herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2017/100793 | 9/18/2017 | WO | 00 |
