Shaft assembly for a drive unit of an electric bicycle and method for determining a force transmitted between two shafts

Abstract

The proposed solution relates to a shaft assembly for a drive unit of an electric bicycle, comprising two shafts rotatably mounted about a common axis of rotation. One shaft is designed as a hollow shaft, and the other shaft is arranged inside the hollow shaft, creating a gap between the shafts along a circumferential direction around the axis of rotation. Several clamping elements are arranged in the gap and are adjustable between a first and a second state. In the first state, the clamping elements clamp the shafts together, allowing a force to be transmitted between them. In the second state, the clamping elements allow movement of the shafts relative to each other. The shafts can be clamped together in the first state such that the transmitted force influences the radial height of the gap.In addition, a measuring assembly is provided to determine the transmitted force, which is designed to measure a change in the circumference of one of the shafts resulting from a change in the height of the gap.

Description

[0001] The proposed solution relates to a shaft assembly according to claim 1, a method for determining a transmitted force according to claim 12, a drive unit according to claim 13, an electric bicycle according to claim 14 and a computer program product according to claim 15.

[0002] An electric bicycle typically has a drive unit that provides additional electric motor torque for propulsion, supplementing the torque applied by the rider. This allows the rider to achieve faster speeds with less effort.

[0003] The drive unit includes an electronic control unit to regulate the amount of drive torque. For a comfortable driving experience, the electronic control unit typically regulates the drive unit based on the torque applied by the driver. For precise control, it can be advantageous to determine the torque as accurately as possible using a measuring device. The more precisely the torque is known to the electronic control unit, the better the additional drive torque can be determined based on the driver's torque.

[0004] Torque can be measured on a shaft assembly of the drive unit. This assembly can incorporate at least one measuring element, such as a strain gauge. This single measuring element can measure the shear stress caused by the torque applied by the driver to a shaft within the assembly. Magnetorestric, ultrasound-based, or optical methods are also known to be used. These solutions are relatively expensive. Strain gauges, in particular, can be affected by other forces acting on the shaft, such as local surface pressure and / or bending moments, making precise torque measurement difficult. Furthermore, the manufacturing and application of strain gauges present both financial and technical challenges.

[0005] The proposed solution is based on the task of providing a shaft assembly with a measuring assembly that enables cost-effective and robust measurement of the torque.

[0006] According to a first aspect of the proposed solution, the problem is solved by a shaft assembly for an electric bicycle drive unit, comprising two shafts rotatably mounted about a common axis of rotation. One shaft is designed as a hollow shaft, and the other shaft is arranged inside the hollow shaft, creating a gap between the shafts along a circumferential direction around the axis of rotation. This gap provides a clearance in the radial direction to the axis of rotation. The gap can extend 360° around the axis of rotation. The axial extent of the gap can encompass up to 100% of the length of at least one of the shafts.

[0007] The shaft assembly also has several clamping elements arranged in the gap and adjustable between a first state and a second state, wherein in the first state the clamping elements clamp the shafts together so that a force can be transmitted between the shafts via the clamping elements, and wherein in the second state the clamping elements allow movement of the shafts relative to each other.

[0008] The shafts can be clamped together in the first state via the clamping elements in such a way that the transmitted force influences the radial height of the gap. A measuring assembly is provided to determine the transmitted force; this assembly is designed to measure the change in circumference of one of the shafts resulting from a change in the height of the gap.

[0009] A fundamental principle underlying the proposed solution is that the use of clamping elements allows for a change in circumference depending on whether a force is transmitted between the shafts and, if so, how large that force is. Such clamping elements are used, for example, as part of a clamping element freewheel. This freewheel can be designed and configured so that the shafts are freely rotatable relative to each other along a first direction of rotation, and a force can be transmitted via the clamping elements along a second direction of rotation. For example, one of the shafts can be a drive shaft through which the torque is applied by the driver, and the other shaft can be an output shaft through which an output torque, including the driver's torque, can be delivered (e.g., to a power transmission element).

[0010] The change in circumference can, for example, take the form of an expansion or contraction of the hollow shaft's circumference. Alternatively, the change in circumference can also be measured as a reduction or expansion of the circumference of the other shaft located inside the hollow shaft (inner shaft). Such a measurement of the change in circumference allows for a simple determination of the force (e.g., torque) transmitted between the shafts. In particular, a force in the form of torque applied by the driver to the inner shaft can be transmitted between the shafts. This type of measurement is particularly robust against disturbances such as local surface pressures on the shaft assembly.

[0011] When the shaft assembly is used as intended in a drive unit, a gear, for example, can be mounted on the hollow shaft to engage a power transmission device such as a chain or belt. In the intended use of the drive unit on an e-bike, the hollow shaft can be connected to the rear wheel of the bike via this power transmission device. The rider can then apply torque to the inner shaft, which transmits this torque to the hollow shaft. The torque is measured by the change in the hollow shaft's circumference. Additionally, an electric motor in the drive unit can apply motor torque to the hollow shaft, allowing the rider's torque, in combination with the motor torque, to be further transmitted from the hollow shaft (e.g., to the power transmission device or via the gear).In particular, measuring the change in circumference allows the driver torque (as the transmitted force) to be measured separately from the engine torque, which is transmitted separately to the hollow shaft that carries out the power transmission. Conversely, the hollow shaft can be used to apply a force provided by a driver, and the inner shaft to apply a force generated by an electric motor. The power transmission can then occur from the hollow shaft to the inner shaft, from where it can be transmitted to a power transmission device.

[0012] The first state of the clamping elements can differ from the second state in that, in the first state, the clamping elements create a force-fit connection between the shafts. In the first state, the clamping elements can, for example, connect the shafts via static friction. In the second state, the clamping elements can connect the shafts loosely via sliding friction, so that no force transmission occurs. The clamping elements can be pre-tensioned in the first state by a spring element such as a ring spring. When transitioning from the second to the first state, the clamping elements can, for example, align themselves radially between the shafts, thus clamping the shafts together.

[0013] The degree of binding can be proportional to the force transmitted between the shafts. This transmitted force can drive the clamping elements into the binding. For example, high torque applied by the driver can cause the clamping elements to bind more tightly between the shafts. The driver's torque can, for instance, create a circumferential force on the clamping elements, which in turn generates a proportional radial force on the shafts. This radial force can be more than ten times greater than the circumferential force. For example, the transmission ratio between the forces can be 1:14. The greater the transmitted force, the further the shafts can be driven apart along a radial direction by the clamping elements (due to the radial force). The circumference of the hollow shaft can increase, while the circumference of the inner shaft can decrease.The respective change in circumference can increase with the transmitted force.

[0014] In particular, the clamping elements can be arranged such that the gap height changes uniformly around the circumference when the transmitted force changes. For this purpose, the clamping elements can be distributed equidistantly around the axis of rotation. It is conceivable and possible to provide more than twelve clamping elements to achieve uniform support between the shafts.

[0015] In one embodiment, the clamping elements between the first and second states are adjustable by changing the direction of rotation of the shafts relative to each other. For example, a first shaft can transmit a force to a second shaft along a first direction of rotation and be freely rotatable relative to the second shaft along a second direction of rotation. The second shaft can be freely rotatable relative to the first shaft along the first direction of rotation and transmit a force to the first shaft along the second direction of rotation. The clamping elements can therefore be designed and configured such that a direction of rotation along which the first shaft can transmit a force to the second shaft is opposite to a direction of rotation along which the second shaft can transmit a force to the first shaft.

[0016] In general, the first state can encompass a multitude of clamping element positions. These positions can differ in the degree of contact force between the clamping elements and the shafts. Furthermore, the higher the transmitted force, the stronger the restoring force can be, caused, among other things, by changes in the gap height (because the gap height can change elastically). This restoring force can cause the gap height to continuously adjust to the transmitted force, thus providing a reliable measure of the transmitted force. By changing the direction of rotation in the first state, the clamping elements can be released from the first state and transferred to the second state.

[0017] In one embodiment, the clamping elements are tilted in the first state about a tilting axis relative to the second state, which extends parallel to the axis of rotation. For example, in the first state, the clamping elements can form a smaller angle radial to the axis of rotation than in the second state. In particular, the angle in the first state can be less than 4°. The clamping elements can be longer along the radial direction than their width along the circumferential direction. For example, the clamping elements can have contact surfaces on their shaft-side sections, which rest against the shafts. The contact surfaces can be curved. This allows the clamping elements to be easily moved from the second state to the first state. The curved contact surfaces also enable a continuous change in the contact force (static friction) without sudden jumps when the transmitted force changes (e.g.,The contact force can be proportional to the transmitted force).

[0018] In one embodiment, the measuring assembly is designed and configured to measure the change in circumference of one of the shafts by measuring the change in the electrical resistance of at least one measuring element arranged on the shaft. The measuring assembly can, in principle, comprise a plurality of measuring elements. These measuring elements can, for example, be arranged at different locations on one shaft. Alternatively, the measuring elements can be arranged at different locations on both shafts. The measurements of the measuring elements can complement each other, allowing for a more robust determination of the transmitted force. Furthermore, the measuring elements can be designed and configured to employ different measurement methods for measuring the change in circumference.

[0019] In one embodiment, the hollow shaft has a radial projection on its outer surface, against which the at least one measuring element for measuring the change in the circumference of the hollow shaft engages. For this purpose, the at least one measuring element can be arranged on a radially outer surface of the radial projection. The radial projection can, for example, have an axial length of more than 5 mm, in particular 8 to 12 mm, and in particular 10 mm. The projection can be designed to form a receiving space on the hollow shaft for the clamping elements. For this purpose, the projection can form an additional cavity on the hollow shaft towards the inner shaft. The receiving space can extend around the axis of rotation. By arranging the at least one measuring element on the projection, a dual use of the projection can be achieved (receiving the clamping elements and arranging the at least one measuring element).

[0020] In one embodiment, the at least one measuring element comprises a strain gauge or a measuring wire. The strain gauge can measure the change in circumference, for example, via a deformation of several parallel conductor tracks, which is measurable by a change in resistance. The conductor tracks are thinner than 10 µm. For example, the conductor tracks can be applied to a flexible substrate (e.g., by lithography). The strain gauge can be arranged on the shaft to be measured such that the conductor tracks extend along the circumferential direction. For the arrangement of the strain gauge, it can be advantageous to provide an additional projection (e.g., in the form of a shaft shoulder).The strain gauge can be arranged, in particular, along an axial direction (at half or at least within the second third of the length) between the clamping bodies and a point where the driver torque is applied to the hollow shaft (i.e., in the middle of the force flow of the transmitted force).

[0021] The measuring wire can have a thickness of over 20 µm, particularly 40 µm or more. Changes in circumference can be measured by deformation of the measuring wire. The measuring wire can be arranged along the circumference of the shaft being measured. A change in circumference can thus cause, in particular, the measuring wire to stretch. Specifically, the change in circumference can alter the length of the measuring wire and / or its cross-section (e.g., diameter). This can cause the electrical resistance of the measuring wire to increase or decrease. The measuring wire can be metallic. In particular, the measuring wire can consist of an alloy. The alloy can contain copper and / or nickel. Such an alloy can exhibit an approximately constant specific electrical resistance over wide temperature ranges. For this purpose, the alloy can, in particular, contain more than 50% copper.An example of a suitable alloy is an alloy with 55% copper, 44% nickel and 1% manganese (constantan).

[0022] In one embodiment, the measuring wire is wound at least once around the shaft whose change in circumference is to be measured. The measuring wire can therefore have at least one winding. In principle, the measuring wire can be wound around the shaft multiple times. For example, the measuring wire can have three or more such windings. Manufacturing such a measuring element in the form of a measuring wire can involve winding the measuring wire onto the shaft to be measured. The measuring wire can be glued to the shaft in the desired position for securing it. For example, the measuring wire can be glued to the shaft and / or secured from the outside with an adhesive film. In particular, the use of a measuring wire enables cost-effective production of the shaft to be measured because no special surface quality requirements are placed on the shaft for such a measurement (unlike with strain gauges).Furthermore, the shaft being measured can be optimized more freely with regard to strength and weight, because no additional projection (besides the radial projection already present for the clamping elements) is required for strain gauges. In addition, the cost of a measuring element in the form of a measuring wire is lower than that of a strain gauge. Measuring the transmitted force via the gap height can also have the advantage of allowing more flexible use of axial installation space on the shaft assembly (the arrangement of at least one measuring element is arbitrary), leading to greater design freedom.

[0023] In one embodiment, the measuring assembly includes an electrical circuit with a quarter-bridge and / or an amplifier for amplifying a measurement signal. Regardless of the design of the electrical circuit, the at least one measuring element can be connected to the circuit via at least one electrical interface. This interface can, for example, be a solder point. For a measuring element with a strain gauge, up to three interfaces can be provided. For a measuring element with a measuring wire, interfaces can advantageously be reduced because only each end of the wire needs to be connected to the electrical circuit. Therefore, only two interfaces are required in this case.

[0024] The quarter bridge can have two arms, each with two resistors, one of which is formed by the at least one measuring element. On the arm where the at least one measuring element is located, an additional measuring resistor can be provided, the resistance of which is identical to that of the at least one measuring element when no force is transmitted between the shafts. On the other arm, two bridge resistors can be provided, the resistance of which is identical to each other. The measurement of the change in circumference can then be carried out by measuring the voltage between the two pairs of resistors on the respective arm.

[0025] The amplifier can amplify the measurement signal (for example, the measured voltage between the arms of the quarter bridge). This allows even a weak measurement signal to be detected. A weak measurement signal can result, for example, from a slight deformation of at least one of the measuring wires.

[0026] In one embodiment, the circuit is designed and configured to shift a measured voltage by a predetermined value for voltage compensation. The predetermined value can be chosen, for example, to compensate for tolerances in the components of the shaft assembly, such as the two shafts. Furthermore, it can be used to correct shifts in the measurement signal caused by other influencing factors.

[0027] In one embodiment, the shaft assembly includes a signal processing unit designed and configured to modify a measurement signal from the measuring unit based on the shaft assembly's temperature, to perform zero-point compensation on the measurement signal, to linearize the measurement signal, and / or to apply a low-pass filter to the measurement signal. The signal processing unit allows for the optimization of the measurement signal.

[0028] For example, a temperature change in the shaft assembly can cause a change in the circumference of the shaft being measured and / or a change in the specific resistance of the sensing element. For instance, the hollow shaft might expand as the temperature rises. The shaft assembly could, for example, include a thermometer unit that measures the temperature and sends this data to the assembly for signal processing. The measurement signal can then be adjusted based on this temperature reading.

[0029] Alternatively or additionally, zero-point adjustment can be performed on the measurement signal. Zero-point adjustment can be carried out, for example, after the measurement signal has been changed based on temperature. Zero-point adjustment may be particularly necessary if the measurement signal drifts. For zero-point adjustment, a specific drift value can be assumed, corresponding to the slope of the measurement signal (e.g., in the case of a maximum expected drift). By integrating the drift value, a correction value can be determined by which the measurement signal can be reduced. If the reduction results in a measurement signal with a value less than zero, it can be corrected again by adding a compensation value. This compensation value can, for example, be determined based on a zero value.The zero value can be determined because the transmitted force is zero at periodic intervals during normal use of the shaft assembly on an e-bike drive unit (when the crank is in a vertical position, the rider cannot exert any torque, so this is zero and the transmitted force can therefore be zero). Furthermore, the transmitted force can have a local minimum at this zero value. Thus, it is possible to calibrate the compensation value with each crank revolution. Basically, for zero-point compensation, at least one local minimum of the measurement signal can be determined in a first step. In a second step, it can be determined whether this at least one local minimum is negative. If so, in a third step, the difference between this at least one local minimum and a zero value of the measurement signal (e.g., 0 V or 0 Nm) can be determined.In a fourth step, the measurement signal can be shifted by the difference towards the zero value. This allows the zero point adjustment to be performed based on the local minima of the measurement signal that occur periodically during the intended use of the shaft assembly with an e-bike.

[0030] Linearization of the measurement signal can be performed in the signal processing module using a linearization unit. A filter unit can be provided to apply a low-pass filter to the measurement signal, thereby smoothing it.

[0031] In one embodiment, the measuring assembly is designed and configured to measure the change in circumference of one of the shafts resulting from a change in the height of the gap at a first and a second location on the shaft, wherein the resulting change at the first location is greater than at the second location. The first and second locations can be axially spaced apart. The first location can, in particular, be arranged axially at the same height as the clamping elements, because the resulting change in circumference of one of the shafts is greatest there. The second location can be arranged at one end of the shaft. The clamping elements can cause a change in the circumference of the shafts that appears conical in cross-section along the axial direction. The change can therefore be smallest (in particular zero) at the ends of the shafts. The measuring assembly can measure a measurement signal at the first location and a reference signal at the second location.The electrical circuit can correct the measurement signal using the reference signal. This eliminates disturbances in the measurement signal (such as temperature-dependent fluctuations in the resistance of measuring wires and / or magnetic interference fields, which can be caused, for example, by the electric motor), that are independent of the change in circumference.

[0032] In a further embodiment, the measuring assembly comprises an electrical circuit with a half-bridge having a first arm comprising a first measuring element and a second measuring element in series, and a second arm parallel to the first arm comprising two bridge resistors in series, wherein the first measuring element is provided at the first position and the second measuring element at the second position, and the measuring assembly is configured and provided to tap a voltage between the first and second measuring elements and the bridge resistors in order to measure the change in the electrical resistance of the first measuring element and, via this, the change in circumference at the first position.

[0033] One way to correct the measurement signal (measured at the first position) with the reference signal (measured at the second position) is to use a half-bridge circuit. The first arm of the circuit contains at least one sensor for the measurement signal and another sensor for the reference signal, while the second arm contains two bridge resistors (with identical resistance). This allows for the simple elimination of changes in the measurement signal caused by disturbances occurring in both sensors during the measurement process itself.

[0034] According to a second aspect of the proposed solution, the problem is solved by a method for determining the force transmitted between two shafts of a shaft assembly for a drive unit of an electric bicycle. The method comprises the following steps: - Providing two shafts rotatably mounted about a common axis of rotation, one of which is designed as a hollow shaft and the other shaft is arranged inside the hollow shaft, so that a gap is formed between the shafts along a circumferential direction around the axis of rotation, - Providing several clamping elements in the gap and adjusting the clamping elements into a first of two states in which the clamping elements clamp the shafts together so that a force can be transmitted between the shafts via the clamping elements, wherein in the second state the clamping elements allow movement of the shafts relative to each other, - Driving one of the waves with a force, - Transmission of force to the other shaft via the multiple clamping elements, - Measuring a change in the circumference of one of the waves resulting from a change in the height of the gap and - Determination of the transmitted force from the change in circumference.

[0035] The transmitted force can, for example, include a transmitted torque, in particular a rider torque applied by a rider of the electric bicycle.

[0036] The process can exhibit advantages and features of the shaft assembly that were described in connection with the first aspect.

[0037] The proposed solution also concerns a drive unit for an electric bicycle with a shaft assembly according to the first aspect and an electric bicycle with such a drive unit and / or a shaft assembly according to the first aspect.

[0038] Furthermore, the proposed solution relates to a computer program product comprising instructions which, when executed by at least one processor of an electronic control unit for a drive unit of an electric bicycle, cause the at least one processor to execute a method according to the second aspect.

[0039] The attached figures illustrate possible implementation variants of the proposed solution.

[0040] This shows: Fig. 1 a schematic view of an electric bicycle in which embodiments of the proposed solution are used; Fig. 2 a sectional view through a shaft assembly with a measuring assembly; Fig. 3 a sectional view through a gap with clamping elements arranged therein between a hollow shaft and an inner shaft of a shaft assembly; Fig. 4 a view of a design variant of a measuring assembly; Fig. 5. An electrical circuit diagram of an electrical circuit with a measuring wire; Fig. 6. A diagrammatic view of a signal processing unit; Fig. 7 a graphical representation of the course of a drifting measurement signal compared to the measurement signal after zero point adjustment; Fig. 8 a detail excerpt from Fig. 7; and Fig. 9 Schematic view of a drive unit with a shaft assembly and an electronic control unit.

[0041] Fig. Figure 1 shows a schematic view of an electric bicycle 1. The electric bicycle 1 has a front wheel 11 and a rear wheel 12, which are connected to each other via a frame 10. The rear wheel 12 can be driven by a drive unit A via a power transmission element 13. An electronic control unit 8 is provided to specify parameters to the drive unit A and to collect and process measurement data relating to the drive unit A (e.g., via measurement signals). The electronic control unit 8 can also be controlled by a rider via a control unit 2, which is located on the handlebars of the electric bicycle 1. The control can, for example, include a selection of different riding modes. The rider can apply a rider torque to the drive unit A to propel the electric bicycle 1 via pedal cranks T.

[0042] Fig. Figure 2 shows a sectional view through a shaft assembly that is part of the drive unit A of the electric bicycle 1. Fig. Figure 1 can be represented. The shaft assembly has two shafts 3, 4 which are rotatably mounted about an axis of rotation D. One of the shafts is designed as a hollow shaft 3. The other shaft is arranged as an inner shaft 4 inside the hollow shaft 3. A gap S is formed between the shafts 3, 4. The gap S extends along a circumferential direction around the axis of rotation D. A clamping element freewheel unit 5 with several clamping elements 51 is arranged in the gap S.

[0043] The clamping element freewheel unit 5 enables power transmission between the inner shaft 4 and the hollow shaft 3 only in one of two opposing directions of rotation D1, D2 about the axis of rotation D. To enable power transmission, the clamping elements 51 can be in a first state. If they do not enable power transmission, the clamping elements 51 can be in a second state. Power transmission is enabled by the clamping elements 51 clamping the shafts 3 and 4 together. The higher the transmitted force, the more tightly the shafts 3 and 4 are clamped together. This is achieved by raising the clamping elements 51 along a radial direction to the axis of rotation D. Raising the clamping elements 51 increases the gap S between the shafts 3 and 4. The increase in the gap S results in an increase in the circumference of the hollow shaft 3.The increase in circumference is measured by a measuring assembly 6, which is arranged on the hollow shaft 3.

[0044] In principle, the measuring assembly 6 can measure the change in circumference of the hollow shaft 3 and / or the inner shaft 4. For this purpose, the measuring assembly 6 can have at least one measuring element 61. The measuring element 61 can be arranged at any point on the shafts 3 and 4. Advantageously, the measuring element 61 can be arranged axially at the same level as the clamping elements 51 (as shown here) or at least in close proximity to them (e.g., within an axial distance of less than a quarter of the length of the hollow shaft 3). Such an arrangement can be advantageous because the change in circumference due to the transmitted force is greatest axially at the same level as the clamping elements 51. In principle, a plurality of measuring elements 61 can be used to measure the change in circumference of the shafts 3 and 4.

[0045] An additional measuring element 61' is provided as an optional reference element to help eliminate disturbances in the measured resistance of measuring element 61. This additional measuring element 61' is arranged axially spaced from measuring element 61 on the same shaft (here, the hollow shaft 3). The additional measuring element 61' is thus exposed to, for example, the same temperature and magnetic fields as measuring element 61. The arrangement of the additional measuring element 61' is chosen such that it is not (or hardly) affected by a change in the circumference of the hollow shaft 3. For example, the additional measuring element 61' can be arranged on a radially relatively rigid section of the hollow shaft 3, as illustrated here. In principle, the additional measuring element 61' can be arranged at a distance from the at least one measuring element 61.The clamping unit 5 can cause a local change in the circumference of the shafts 3, 4, such that the degree of change decreases with increasing axial distance from the clamping unit 5. This distance can be more than one-tenth, and in particular more than one-fifth, of the axial length of the hollow shaft 3. For example, the additional measuring element 61' can be arranged at one end of the hollow shaft 3.

[0046] In the illustrated embodiment, the inner shaft 4 and the hollow shaft 3 each have a radial projection 31, 41, which extends along a radial direction. An inner projection 41 of the inner shaft 4 projects into an outer projection 31 of the hollow shaft 3. Clamping elements 51 are arranged between the projections 31, 41 on an axial section of the gap S between the hollow shaft 3 and the inner shaft 4. Specifically, the clamping elements 51 are arranged in a receiving space on the hollow shaft 3. The radial force exerted by the clamping elements 51, which in the second state causes an increase in the height of the gap S, is greatest at the radial projections 31, 41. Therefore, the measuring element 61 of the measuring assembly 6 is arranged on an outer surface of the outer projection 31 of the hollow shaft 3.By arranging the measuring element 61 on the outer projection 31, it is used twice (forming the receiving space for the clamping bodies 51 and arranging the measuring element 61), thus saving installation space.

[0047] The measuring element 61 consists of a measuring wire wound five times around the hollow shaft 3. The five (or more, generally multiple) windings allow the change in circumference to be determined more precisely by measuring the change in the electrical resistance of the measuring wire than with a single winding. Furthermore, the use of multiple windings can produce readily measurable changes in resistance when the circumference changes (without requiring the measuring wire to be too thin). In principle, any number of windings can be provided. For example, more than five windings can be used. The windings can span, for instance, up to 5 mm along the axial direction of the hollow shaft 3. It can be advantageous for the measuring wires to be close together, adjacent to one another. In particular, an axial segment of up to 1 mm on one of the shafts 3, 4 can be spanned by a plurality of windings.

[0048] The measuring assembly 6 has a communication interface in the form of a wireless interface 63, which allows the measured signal from the (rotating) shafts 3 and 4 to be transmitted to a stationary part of the shaft assembly where the shafts 3 and 4 are mounted. In this way, the measurement signal can be transmitted, for example, to a signal processing assembly 7. The wireless interface 63 can, for example, use RFID technology for wireless communication. The measuring assembly 6 can also be supplied with electrical power for operation via the wireless interface 63.

[0049] Fig. Figure 3 shows a sectional view transverse to the axis of rotation D through the gap S between shafts 3 and 4. Clamping elements 51 are arranged in the gap S. When the inner shaft 4 rotates about the axis of rotation D along a first direction of rotation D1, the inner shaft 4 slides under the clamping elements 51. When the hollow shaft 3 rotates along a second direction of rotation D2, it slides over the clamping elements 51. In both cases, no power transmission between shafts 3 and 4 is possible. In these directions of rotation D1 and D2, the clamping elements 51 are in a second state in which they allow the shafts 3 and 4 to rotate relative to each other. The clamping elements 51 are pre-tensioned into the first state by a ring spring 52.

[0050] When the inner shaft 4 rotates about the axis of rotation D along the second direction of rotation D2, the rotation causes the clamping elements 51 to move from the second to a first state. The clamping elements are simply carried along by the inner shaft 4 via internal contact surfaces. During this movement, the clamping elements 51 tilt about a tilting axis K, aligning themselves parallel to the axis of rotation D. This results in a frictional engagement with the shafts 3 and 4, mediated by static friction. The greater the torque applied to the inner shaft 4, the further the clamping elements 51 are driven into the first state. Due to the curved shape of the contact surfaces of the clamping elements 51 facing the shafts 3 and 4, an increase in the transmitted force causes an increase in the gap S, which is illustrated by radially outward-pointing arrows.

[0051] The contact surfaces are advantageously concave. The contact surfaces are designed such that the distance between a point on a contact surface facing the hollow shaft 3 and a point on a contact surface facing the inner shaft 4, measured parallel to the radial direction to the axis of rotation D, is smaller when the clamping elements 51 are in the second state than when they are in the first state.

[0052] Enlarging the gap S, in turn, causes an increase in the circumference of the hollow shaft 3, as illustrated by a double arrow. This increase in circumference is relatively easy to measure and can be used to determine the change in the gap height and, consequently, the transmitted force.

[0053] Adjusting the clamping elements 51 generates a restoring force, causing the clamping elements 51 to shift around the tilting axis K from the first state towards the second state. Therefore, when the transmitted force decreases, the circumference of the hollow shaft 3 also returns to its original position, allowing the circumference to be used to determine the transmitted force even when it decreases.

[0054] Fig. Figure 4 shows a view of an embodiment of a measuring assembly 6 with a measuring wire having five windings. This embodiment can be used, for example, in the embodiment of the Fig. 3. The measuring wire has two ends that are connected to an electrical circuit, for example, via interfaces in the form of solder points. The electrical circuit 62 can be used to measure a measurement signal that represents a change in the resistance of the measuring wire. For example, the measurement signal can be measured as a voltage. By using a measuring wire, the number of interfaces to the measuring element 61 can be particularly small. In addition, the measuring wire can be arranged at any point on the hollow shaft 3 (or the inner shaft 4) with any number of windings.

[0055] Fig. Figure 5 shows an electrical circuit diagram of an electrical circuit 62. The electrical circuit 62 has a quarter bridge, which can be used to measure a change in a measuring element 61. The quarter bridge is particularly suitable for measuring small changes. For this purpose, it has two arms. The measuring element 61 (e.g., the measuring wire) is assigned to one of the arms, to which a measuring resistor 621 is also arranged. The resistance of this resistor is identical to the resistance of the measuring element 61 when no force is transmitted between the shafts 3 and 4. If another measuring element 61' (e.g., a reference element) is provided, the measuring resistor 621 can be replaced by it. The other arm has two bridge resistors 622, whose resistances are identical to each other. A current flows across the arms at a potential V. dd The current is divided, flows through the arms, and is brought back together by the grounding system.

[0056] The voltage v is measured between the resistors on each arm. tap The voltage is measured. A change in this voltage represents a change in the resistance of the measuring element 61. In a variant where another measuring element 61' is used instead of the measuring resistor 621 (half-bridge), the measured voltage v changes. tap not if disturbances such as a temperature change lead to a change in resistance at both measuring elements 61, 61'. If the further measuring element 61' is arranged at a point on the shaft 3, 4 whose circumference changes little or not at all depending on the transmitted force, the tapped voltage v tap primarily due to a change in the resistance of the measuring element 61 caused by the change in circumference. Thus, by using a half-bridge and two axially spaced measuring elements 61, 61', a more robust measurement of the transmitted force can be achieved.

[0057] The tapped voltage is amplified by an optional amplifier 623. Since the resistance of the measuring element 61 may only change slightly, even small changes in resistance can be made more easily measurable by the amplification.

[0058] A first input of amplifier 623 (positive) is connected to the arm of the quarter bridge on which the measuring element 61 is located. A second input of amplifier 623 (negative) is connected to the other arm of the quarter bridge. An optional balancing voltage v is also applied to this input. dac supplied via a balancing resistor 625. A tapped voltage v is obtained using the balancing voltage. tapThe signal is shifted by a predetermined value. The compensating voltage can be selected to compensate for tolerances in the components of the shaft assembly, such as the two shafts 3 and 4. Furthermore, the compensating voltage can be used to correct shifts in the measurement signal caused by other influencing factors.

[0059] A measuring voltage v is applied to one output of the amplifier 623. out measured, which is based on the tapped voltage v tap and the equalization voltage v dac based on. Basically, the measuring voltage v out Alternatively, measurements can be taken directly between the arms (without an amplifier).

[0060] The second input of amplifier 623 is negatively fed to the output via a gain resistor 624. The gain resistor 624 can be used to set the gain. The gain can be determined by the ratio of a resistance of the gain resistor 624 to a resistance that is less than any resistance of the bridge resistors 622, the gain resistor 624, and / or the balancing resistor 625. Specifically, this resistance can be the inverse of the sum of the individual quotients of one of the bridge resistors 622 (the one on the side of V). dd ), of the amplification resistor 624 and the balancing resistor 625, because these are connected in parallel with respect to the second input of the amplifier 623.

[0061] Fig. Figure 6 shows a diagrammatic view of a signal processing assembly. Figure 7 is based on a real, transmitted force F. realfrom, which is supplied to the signal processing assembly 7. In the proposed solution, the transmitted force is measured by a change in the circumference of one of the shafts 3, 4. A measured value of the transmitted force is subject to various influences. These can include: temperature, drift, and / or a mechanical change in components of the shaft assembly, for example, due to wear. The transmitted force F measured by the measuring assembly 6 roh The measured transmitted force can therefore deviate from the actual force generated. To compensate for the influences that change the value of the measured transmitted force, the measurement signal is fed from the measuring module 6 to the signal processing module 7.

[0062] The signal processing assembly 7 includes a temperature compensation unit 71. The temperature compensation unit 71 can, for example, perform signal processing using an analytical model or empirical data. Processing with the temperature compensation unit 71 can compensate for the influence of the shaft assembly's temperature on the measurement signal. The temperature compensation unit 71 can, for example, be coupled to a thermometer unit with which the shaft assembly's temperature can be determined. After processing by the temperature compensation unit 71, a temperature-compensated measurement signal F can be output by this unit. temp will be made available.

[0063] In a further step, the (optionally) temperature-compensated measurement signal is corrected by an offset using a zero-point compensation unit 72. The offset can be determined from the measurement signal (here F). tempThe offset can be subtracted or added. Adding the offset can be used for zero-point adjustment. The zero-point adjustment unit 72 has a limiting unit 721, which is designed and intended to ensure that zero-point adjustment is only performed when the measurement signal has negative values.

[0064] Furthermore, the zero-point compensation unit 72 has an optional gain adjustment unit 722, which is set up and intended to specify a strength and / or dynamics of the zero-point compensation.

[0065] Furthermore, the zero-point compensation unit 72 includes a pitch adjustment unit 723, which can subtract an offset from the measurement signal. The pitch adjustment unit 723 can utilize a maximum assumed drift. For this purpose, this unit can, for example, access an electronic storage unit of the signal processing assembly or the electronic control unit, in which the maximum assumed drift is stored. Based on this maximum assumed drift, the pitch adjustment unit 723 can estimate a specific drift value that corresponds to the slope of the measurement signal at maximum drift. The maximum drift can, for example, depend on other parameters such as the temperature of the shaft assembly, so that the maximum assumed drift can, for example, be recorded in tabular form. The measurement signal (here F) tempThe drift value can be reduced by an offset in the form of a correction value to compensate for drift. To determine the correction value, the drift value can, for example, be integrated using a unit of integration 724 (the integration corresponds to calculating the drift value from the slope).

[0066] When the measurement signal is reduced by the correction value, a value less than zero may result. Such a value can be corrected by adding a smoothing factor to the drift value (before integration).

[0067] Generally, it can be assumed that the transmitted force is zero at periodic intervals because, during the intended use of the shaft assembly with the signal processing assembly 7 and a drive unit A of an electric bicycle 1, the rider exerts a torque that fluctuates between local maxima and local minima. This is because the rider is provided with pedals T when operating the shaft assembly. In a horizontal position, maximum rider torque can be applied, while in a vertical position, applying rider torque is very difficult, so that in this position the rider torque is usually zero. Negative values ​​cannot occur, so zero-point compensation is performed if negative values ​​are present.

[0068] The signal processing module 7 can therefore be designed and configured to determine a zero value of the measurement signal based on the assumption of a periodic curve of the transmitted force and the local minima of the measurement signal. From the distance of the zero value to the x-axis, the offset by which the measurement signal must be corrected so that the zero value is at zero can be determined. For example, the compensation value used to correct the drift value can be determined in this way.

[0069] The zero-point compensation unit 72 can thus, together with the limiting unit 721, the gain adjustment unit 722 and / or the slope adjustment unit 723, correct the measurement signal by a correction value and, if necessary, an additional compensation value, in order to obtain the corrected measurement signal F. offs to obtain.

[0070] Furthermore, the signal processing assembly can include a linearization unit 73. The corrected measurement signal can be linearized using the linearization unit 73. The linearized signal is then fed to the zero-point compensation unit 72 for checking for negative values.

[0071] The linearized measurement signal is then filtered by a unit 74 to F filt filtered.

[0072] Fig. Figure 7 shows a graphical representation of an exemplary curve of a drifting measurement signal M1 for the torque M in Newton meters and a measurement signal after zero-point compensation M2, each over time in seconds. The drift causes a shift of the measurement signal into the negative range. Zero-point compensation shifts the local minima of the respective measurement signal to the x-axis (here to 0 Nm). This results in a corrected measurement signal that reproduces the curve of an ideal measurement signal M3 of a real transmitted force much more accurately than the drifting measurement signal M1. This is also shown in the detailed section of the graphical representation. Fig. 7 in Fig. 8. In particular, the following are Fig. 7 and Fig. 8. The periodically occurring local minima are also recognizable, on the basis of which a zero value is determined within the framework of zero point adjustment.

[0073] Fig.Figure 9 shows a schematic view of a drive unit A with a shaft assembly and an electronic control unit 8. The shaft assembly comprises a hollow shaft 3 and an inner shaft 4 arranged therein. A radial gap S is formed between the hollow shaft 3 and the inner shaft 4. The gap S extends along the circumferential direction around a rotational axis D about which the shafts 3 and 4 are rotatably mounted. A measuring assembly 6 is arranged on the hollow shaft 3, with which a change in the circumference of the hollow shaft 3 can be measured. The measuring assembly 6 is designed and configured to communicate wirelessly with a signal processing unit 7, which is statically arranged relative to the shafts 3 and 4. A wireless interface 63 can be provided for this purpose. Additionally, the measuring assembly 6 can be supplied with electrical energy for operation via the wireless interface 63.The signal processing unit 7 processes a measurement signal representing the height of the gap S. This measurement signal can be measured by at least one measuring element 61 of the measuring unit 6. Additionally, a further measuring element 61' can measure a reference signal (at a different section of the hollow shaft 3 where the height of the gap S is constant relative to the measurement point of the at least one measuring element 61). The electrical circuit 62 can be configured and designed to correct the measurement signal with the reference signal in order to isolate a resistance change resulting from a change in the height of the gap S from interference that would cause an undesired change in resistance. This is because interference affects both the at least one measuring element 61 and the further measuring element 61', whereas the height of the gap S only affects the at least one measuring element 61.

[0074] An electronic control unit 8 controls at least one parameter of an electric motor E of the drive unit A, such as its motor power, based on the processed measurement signal. The electric motor E applies a motor torque to the hollow shaft 3 based on this at least one parameter, so that the drive unit A can generate drive power based on the rider torque and the motor torque to propel an electric bicycle 1. Reference symbol list 1 electric bicycle 10 frames 11 Front wheel 12 rear wheel 13 Power transmission element 2 Control unit 3 Hollow shaft 31 Outside lead 4 inner shaft 41 Inside projection 5 Clamping element freewheel unit 51 clamping bodies 52 ring springs 6 Measuring assembly 61, 61' Measuring element 62 electrical circuit 621 Measuring resistor 622 bridge resistors 623 amplifiers 624 Gain resistor 625 Balancing resistor 63 Wireless interface 7 Signal processing module 71 Unit for temperature compensation 72 units for zero-point adjustment 721 Limiting unit 722 Unit for gain adjustment 723 Unit for gradient adjustment 724 Unit for integration 73 Unit for linearization 74 units for filtering 8 electronic control unit A drive unit D axis of rotation D1, D2 Direction of rotation E electric motor K tilting axle M1, M2, M3 signals S gap T crank

Claims

[1] Shaft assembly for a drive unit (A) of an electric bicycle (1), with - two shafts (3, 4) rotatably mounted about a common axis of rotation (D), one of which is designed as a hollow shaft (3) and the other shaft (4) is arranged inside the shaft designed as a hollow shaft (3), such that a gap (S) is formed between the shafts (3, 4) along a circumferential direction about the axis of rotation (D), and with - several clamping elements (51) arranged in the gap (S) and adjustable between a first state and a second state, wherein in the first state the clamping elements (51) clamp the shafts (3, 4) together so that a force can be transmitted between the shafts (3, 4) via the clamping elements (51), and wherein in the second state the clamping elements (51) allow movement of the shafts (3, 4) relative to each other, characterized by, that the shafts can be clamped together in the first state via the clamping elements (51) in such a way that the transmitted force influences a radial height of the gap (S), and that a measuring assembly (6) is provided to determine the transmitted force, which is designed to measure a change in the circumference of one of the shafts (3, 4) resulting from a change in the height of the gap (S). [2] Shaft assembly according to claim 1, characterized by , that the clamping elements (51) can be adjusted between the first and second states by changing a direction of rotation (D1, D2) of the shafts (3, 4) relative to each other. [3] Shaft assembly according to one of claims 1 and 2, characterized by , that the clamping bodies (51) in the first state are each tilted about a tilting axis (K) relative to the second state, which extends parallel to the axis of rotation (D). [4] Shaft assembly according to any one of claims 1 to 3, characterized by, that the measuring assembly (6) is designed and configured to measure the change in circumference of one of the shafts (3, 4) by means of a change in the electrical resistance of at least one measuring element (61) arranged on the shaft (3, 4). [5] Shaft assembly according to claim 4, characterized by , that the hollow shaft (3) has a radial projection on an outer side, on which the at least one measuring element (61) for measuring the change in the circumference of the hollow shaft (3) engages. [6] Shaft assembly according to one of claims 4 or 5, characterized by , that the at least one measuring element (61) comprises a strain gauge or a measuring wire. [7] Shaft assembly according to claim 6, characterized by , that the measuring wire is wound at least once around the shaft (3, 4) where the change in circumference is to be measured. [8] Shaft assembly according to any of the preceding claims, characterized by, that the measuring assembly (6) has an electrical circuit (62) with a quarter bridge and / or an amplifier (623) for amplifying a measuring signal. [9] Shaft assembly according to any of the preceding claims, characterized by a signal processing assembly (7) which is designed and configured to modify a measurement signal from the measurement assembly (6) based on a temperature of the shaft assembly, to perform zero-point compensation on the measurement signal, to linearize the measurement signal and / or to apply a low-pass filter to the measurement signal. [10] Shaft assembly according to any of the preceding claims, characterized by, that the measuring assembly (6) is designed and configured to measure the change in circumference of one of the shafts (3, 4) resulting from the change in the height of the gap (S) at a first and at a second location on one of the shafts (3, 4), wherein the resulting change at the first location is greater than at the second location. [11] Shaft assembly according to claim 10, characterized by, that the measuring assembly (6) comprises an electrical circuit (62) with a half-bridge having a first arm comprising a first measuring element (61) and a second measuring element (61') in series, and with a second arm in parallel to the first arm comprising two bridge resistors (622) in series, wherein the first measuring element (61) is provided at the first position and the second measuring element at the second position, and the measuring assembly (6) is configured and provided to tap a voltage between the first and second measuring elements (61, 61') and the bridge resistors (622) in order to measure the change in electrical resistance of the first measuring element (61) and, via this, the change in circumference at the first position. [12] Method for determining a force transmitted between two shafts (3, 4) of a shaft assembly for a drive unit (A) of an electric bicycle (1), comprising the following steps: - Providing two shafts (3, 4) rotatably mounted about a common axis of rotation (D), one of which is designed as a hollow shaft (3) and the other shaft (4) is arranged inside the shaft designed as a hollow shaft (3), such that a gap (S) is formed between the shafts (3, 4) along a circumferential direction about the axis of rotation (D), - Providing several clamping elements (51) in the gap (S) and adjusting the clamping elements (51) into a first of two states in which the clamping elements (51) clamp the shafts (3, 4) together so that a force can be transmitted between the shafts via the clamping elements (51), wherein in the second state the clamping elements (51) allow movement of the shafts relative to each other, - Driving one of the shafts (3, 4) with a force, - Transmission of force to the other shaft (3, 4) via the multiple clamping elements (51), - Measuring a change in the circumference of one of the waves (3, 4) resulting from a change in the height of the gap (S) and - Determination of the transmitted force from the change in circumference. [13] Drive unit (A) for an electric bicycle (1) with a shaft assembly according to one of claims 1 to 11. [14] Electric bicycle (1) with a drive unit (A) according to claim 13 and / or a shaft assembly according to claims 1 to 11. [15] Computer program product comprising instructions which, when executed by at least one processor of an electronic control unit (8) for a drive unit (A) of an electric bicycle (1), cause the at least one processor to execute a method according to claim 12.

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