JP2015206777A - Tread force detection sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the following problem:it is a mainstream conventionally that a tread force sensor and a drive motor are integrated and arranged on the lower part of a crank shaft of a body frame of a bicycle because power assisted bicycles have been disseminated and more refined design and functions are sought after, and the tread force sensor is required to be compact and high in functionality.SOLUTION: In the structure in which a hollow shaft 4 is connected to a crank shaft 2 of a bicycle in a penetration manner and a chain wheel 3 is fixed to the other end of the hollow shaft 4, a secondary coil 6 and a strain gauge 8 are fixed to an outer periphery of the hollow shaft. In addition, a sensor case 5 is arranged in the outside of the hollow shaft 4, and a primary coil 7 is placed in the inside thereof, and both the sensor case and the primary coil are allowed to rotate without contacting with each other, thereby using the hollow shaft 4 as a rotary transformer. The primary coil side is provided with a load resistance 12 in series with the coil, and a power consumption state on the side of the secondary coil 6 can be acquired as a primary coil current also by applying an AC signal 13 to the primary coil 7. When the tread force is applied to the pedal, a strain gauge resistance is changed and the power consumption is changed. This leads to the current change of the primary coil. The voltage at both ends of the load resistance 12 is proportional to the tread force.

Description

  The present invention relates to a sensor used for detecting a pedaling force in an electrically assisted bicycle or the like.

  The power-assisted bicycle has gained recognition in the country, and is now used not only for limited use for the elderly and housewives, but also for youth, sports and business. The assist function has also been refined, and the battery has become lighter and smaller, making it easier to use, and the distance that can be ridden has become longer.

  Due to global energy and resource conservation concerns, the number of sales overseas has increased as well as in Japan, and the market is expected to expand over the long term and over a wide range. For this reason, the future of the business has been found, and many bicycle-related companies and other industries have entered the market one after another.

  The pedal force detection sensor currently installed in electric-assisted bicycles uses a non-contact detection method by converting the pedal force into a vertical force and moving the magnetic core in and out and changing the coil inductance. Converts pedaling force into crankshaft torsion, detects non-contact using the magnetostriction principle, converts pedaling force into displacement of two plates joined by an elastic material, and shifts the phase of magnetic protrusions attached to the plate A typical example is one that detects non-contact.

The following documents listed for reference are pedal force detection means corresponding to the above.
JP 2004-106837 A Japanese Patent No. 3415325 JP 2003-276672 A

  In the invention of the above-described Document 1, the core is moved in the direction perpendicular to the driving direction by the pedal force, and the pedal force is detected by changing the inductance of the coil winding on the outer periphery. In order to smoothly put in and out, a groove with a gap is necessary. For this reason, the change in inductance with respect to the pedal force is not always uniform, and there is a problem in the accuracy of output. Moreover, since the thickness is required in the moving direction of the core and it cannot be made thin, there is also a problem in design on mounting.

  Since the invention in Document 2 has a torque detection mechanism in the crankshaft structure of the bicycle, there is nothing exposed to the outside and the appearance is good, but it is not around the general crankshaft but a dedicated vehicle body Need. In addition, as a mechanism for generating torsion inside the crankshaft, a metal pipe-like hollow member is required which constitutes a spline that meshes with the crankshaft at one end and a screw portion that meshes with the chain wheel at the other end. It is not possible to perform punching by, but requires precision machining with a lathe and the like, and also requires a thin magnetic film and strict gap management, so there is a problem in mass productivity and cost reduction.

  Reference 3 detects the treading force by detecting the displacement between two disks joined by an elastic material as the displacement of the opposing magnetic projections, but it has a simple structure and has no problem with mass productivity. There remains a problem that the pedaling force cannot be detected.

  The present invention solves these problems and provides an easy-to-use smart treading force detection sensor. In the above-mentioned prior documents, a single pedal force sensor is shown. However, the mainstream of the configuration of the electric assist bicycle is a built-in sensor integrated with a drive motor. By integrating the drive motor and the pedal force sensor and placing it in the lower center of the bicycle, you can achieve great benefits in terms of weight balance optimization, unit cost reduction, and wiring reduction.

  The treading force detection sensor according to the present invention relates to a simple system having a different feature in torsion detection in the same structure as that of the above-mentioned prior document [Patent Document 2]. It is assumed that it will be integrated into an integrated structure. The pedaling force detection method in the present plan replaces the twisting state of the shaft with a change in power consumption, and outputs a pedaling force signal in a non-contact manner.

  The detection method of the present invention is not the magnetostrictive type disclosed in [Patent Document 2] and does not require a magnetic film. For this reason, the creation of a magnetic film and the processing of a severe magnetic gap can be omitted, which is advantageous in mass production and cost reduction. Also, by integrating the pedal force detection sensor with the drive motor, batch production at the factory is possible, and wiring between the sensor and the drive unit is eliminated, which is advantageous in improving signal quality.

  Thus, since it can be combined with a driving motor by a simple mechanism that does not require difficult processing or an expensive magnetic film, it is extremely useful practically.

  The outline of the configuration of the present invention will be described below with reference to FIGS. 1 and 3, and the contents and applications of the operation will be described with reference to the drawings.

  First, the configuration will be briefly described with reference to FIG. 1. FIG. 1 is a first configuration diagram of a treading force detection sensor according to the present invention, a crankshaft 2 directly connected to a pedal 1, a hollow shaft 4 penetrating into the crankshaft 2, and its A secondary coil 6 and a strain gauge 8 are fixed to the outer periphery. The hollow shaft 4 needs to be made of a magnetic material.

  One end of the hollow shaft 4 is fixed so as to penetrate into the crankshaft 2, while the other end is fixed to the center portion of the chain wheel 3 on which a chain 11 for driving a rear wheel (not shown) is hung. A sensor case 5 having a function as an outer skin of a treading force detection sensor is provided on the outer side of the hollow shaft 4, and a primary coil 7 is formed by providing a slight gap on the inner side of the hollow shaft 4.

  FIG. 3 is a second block diagram of the pedaling force detection sensor according to the present invention, and the configuration of the parts formed on the outer periphery of the hollow shaft is different from that of FIG. The secondary coil 6 shown in FIG. 3 is widely wound so as to cover the entire surface so as to be affected by the twist received by the hollow shaft. Similarly, an element 9 is arranged instead of the strain gauge of FIG. 1, and this element means, for example, a resistor, a capacitor, a circuit, and the like, and is connected to both ends of the secondary coil 6.

    FIG. 2 shows the electrical circuit in FIG. 1 and corresponds to the machine parts in FIG. 1 by numbers, but the AC signal source 13 and the load resistor 12 are the components in FIGS. Not shown.

  FIG. 4 is a diagram for explaining the change of the secondary coil accompanying the twist of the hollow shaft in FIG. 3, and the secondary coil is wound around the elastic body 15 such as a rubber sheet around the outer periphery of the hollow shaft. It shows that.

  FIG. 5 shows an electric circuit in FIG. 3. An arrow is added to the secondary coil 6 and n2 + Δ at the top indicates that the number of turns of the coil slightly changes. This causes changes in output voltage and inductance.

  FIG. 6 is a circuit diagram in the case where the capacitor 10 is applied to the element 9 shown in FIG. 3, and it is conceivable to form a series resonance circuit with the inductance of the secondary coil.

FIG. 8 shows a circuit diagram in the case where the element 9 in FIG. 3 is composed of a diode, a capacitor, and a Zener diode, but another circuit configuration is also conceivable.
FIG. 7 is a graph of the input / output characteristics of the Zener diode 17 and shows that the Y-axis current (Id) varies greatly with a small change in the X-axis voltage (Vo).
(First embodiment)

  Hereinafter, the first embodiment will be described in more detail with reference to FIGS. 1 and 2. When a pedaling force is applied to the crank 1 of FIG. 1, the force is transmitted from the crankshaft 2 to the hollow shaft 4. 3 is driven to rotate the rear wheel through the chain 11. Due to the relationship between the load on the pedal 1 and the load on the rear wheel applied to the chain wheel 3, a torsional stress is generated at both ends of the hollow shaft 4, and a large strain occurs in the vicinity of the connecting portion with the crankshaft 2. The resistance value of changes.

  As shown in FIG. 2, the secondary coil 6 wound around the outer periphery of the hollow shaft 4 and the primary coil 7 wound in the sensor case 5 are electrically transformers because the hollow shaft 4 is a magnetic material. Is configured. The primary coil 7 and the sensor case 5 are fixed to the bicycle body and do not rotate, but the other elements (2, 3, 4, 6, 8) rotate with the pedal as the pedal 1 rotates. The primary coil 7 and the secondary coil 6 are arranged so as not to mechanically interfere with each other with a small space.

Here, when the load resistance 12 and the AC signal source 13 are connected to the primary coil side as shown in the figure and an AC voltage is applied, a voltage is also induced on the secondary coil side, and the strain gauge 8 consumes power as its load. To do. Since this electric power is the electric power supplied from the primary coil 7, a corresponding current flows through the primary coil, which appears as a voltage at the load resistor 12.

Since this voltage is proportional to the power consumption on the secondary coil side, the resistance change of the strain gauge is seen at both ends of the load resistor 12. That is, the pedaling force applied to the pedal can be measured in a non-contact manner on the fixed side where the primary coil is located. Although only one strain gauge is shown in FIG. 1, it is possible to increase sensitivity related to strain by placing a plurality of strain gauges in an annular shape and connecting them in series.
(Second Embodiment)

  In the structure of FIG. 3, a secondary coil 6 and an element 9 are fixed to the outer periphery of the hollow shaft 4 fixed to the crankshaft 2. The secondary coil 6 is widely wound in the longitudinal direction of the hollow shaft 4, and aims at an effect that the twist of the hollow shaft affects the winding method of the secondary coil.

  FIG. 4 is a diagram for explaining the influence on the secondary coil 6 due to the twist of the hollow shaft 4. In FIG. 3, when the pedal load is applied, if the crankshaft 2 rotates to the right when viewed from the right side of the figure, the left end of the hollow shaft 4 also rotates slightly to the right. The hollow shaft is twisted without rotating the pulled right end.

  Referring to FIG. 4, the C end of the figure rotates clockwise, but the A end does not rotate, so the hollow shaft is twisted and the end of the secondary coil wound around the outer periphery moves from C to B. This means that the number of turns of the secondary coil has increased a little. At the same time, the coil with both ends fixed is wound more in the cylinder, so that the elastic body 15 tightly wound and stuck on the surface is tightened, slightly approaching the hollow shaft magnetic body, and the leakage magnetic flux is reduced. Therefore, the voltage induced in the secondary coil rises overall.

Referring to FIG. 5, when the pedal load is applied, the number of turns of the secondary coil 6 is increased and the magnetic characteristics are also improved. Therefore, more voltage is applied to the resistor 14 which is the load of the secondary coil, and more A lot of power is consumed.
In this way, by applying a large amount of pedal effort, power consumption increases, the primary coil current increases, and the voltage of the load resistor 12 increases. This voltage output is proportional to the treading force and is detected without contact.

  In the configuration of FIG. 3, another embodiment in which the element 9 in FIG. 3 is a capacitor will be described with reference to FIG. For the reasons described above, when the pedal force is applied, the number of turns of the secondary coil slightly changes. Therefore, since the inductance of the secondary coil also changes, if a series resonance circuit is configured with the secondary coil and the capacitor, the current that flows when the resonance state is shifted from the resonance state greatly changes.

  This change in current appears on the load resistor 12 through the primary coil for the same reason as described above. When the circuit resonates, a large current flows, but when the circuit is deviated, the current greatly decreases. Therefore, the magnitude of the pedaling force can be known from the degree of deviation.

  FIG. 8 shows another application example of the configuration shown in FIG. The element 9 shown in FIG. 3 is configured by three elements, and the output characteristic of the Zener diode 17 is used as power consuming means. When a voltage is applied exceeding the Zener voltage of the Zener diode, the current starts to flow gradually as shown in FIG. 7, and a large current change can be obtained with a slight change in the applied voltage.

  Due to the change in the number of turns of the secondary coil, the induced voltage of the secondary coil changes, and the voltage is converted into a direct current by the diode 16 and the capacitor 10 and applied to the Zener diode 17, and a current flows therethrough. The magnitude of this current is reflected on the primary coil side and can be read by the load resistor 12.

  As described above, the voltage proportional to the pedaling force appearing at the load resistor 12 is a voltage that changes as the amplitude of the AC signal source. This signal is converted into a DC signal and read by the CPU and used as a pedaling force proportional signal for assist control. .

  Each electrical element in Fig. 1 and Fig. 3 can use thin chip parts, printed coils, etc. In that case, there are advantages in mounting, workability, durability and reliability. It can be put out.

  As described above, according to the present invention, since the magnitude of the pedal force is converted into the secondary power consumption of the transformer and detected on the primary side, an expensive magnetic film, oblique groove processing, etc. can be performed. Since it does not need to be used, the machining of the members is simplified, and it is possible to obtain a pedaling force proportional signal in a non-contact manner at low cost, which is effective and advantageous.

Schematic showing the overall configuration of the first proposal of the present invention Circuit diagram according to the first proposal of the present invention Schematic showing the overall configuration of the second proposal of the present invention The figure explaining the change of the coil by twist of the hollow shaft Circuit diagram according to the second proposal of the present invention Application circuit diagram 1 according to the second proposal of the present invention Graph showing input / output characteristics of Zener diode Second application circuit diagram of the present invention, part 2

1: pedal 2: crankshaft 3: chain wheel 4: hollow shaft 5: sensor case 6: secondary coil 7: primary coil 8: strain gauge 9: element 10: capacitor 11: chain 12: load resistance 13: AC signal source 14: Resistance 15: Elastic body 16: Diode 17: Zener diode 18: Lead wire

Claims (4)

  In the structure where the hollow shaft is fixedly joined to the outside of the crankshaft where the pedaling force is applied and the chain wheel is fixed to the other end, a secondary coil and a strain gauge are arranged on the outer periphery of the hollow shaft, and both are connected. A primary coil, a hollow shaft, and a secondary coil are used to form a transformer, and an alternating current signal is supplied to the primary coil side by opening the primary coil inside the outer sensor case so that it does not come into contact with the primary coil. The pedal force detection sensor is characterized in that an AC current corresponding to the power consumption on the secondary coil side appears on the primary coil side.   In the structure in which the hollow shaft is fixedly joined to the outside of the crankshaft where the pedaling force is applied and the chain wheel is fixed to the other end, the twist of the hollow shaft on the outer periphery of the hollow shaft is widely secondary in the longitudinal direction as a means of affecting the number of turns. The primary coil, the hollow shaft, and the secondary are wound by winding the coil and connecting the resistors to each other, and then placing the primary coil inside the outer sensor case so as not to contact the hollow shaft. A treading force detection sensor characterized by forming a transformer with a coil and supplying an AC signal to the primary coil side to cause an AC current corresponding to the power consumption on the secondary coil side to appear on the primary coil side. 3. A treading force detection sensor according to claim 2, wherein a series resonance circuit is formed between the secondary coil and the capacitor by placing a capacitor instead of a resistor.   3. A treading force detection sensor according to claim 2, wherein a rectifier circuit and a Zener diode are placed in place of the resistor.

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