Velocity detection device in eddy current type instruments

Abstract

We provide a highly accurate and reliable mounting structure for retrofit speed detection devices without requiring large manufacturing facilities. [Solution] Multiple omnipolar Hall ICs, which detect changes in the magnetic flux of the magnetic rotor of an eddy current instrument, are installed at locations shifted by 90 degrees in phase with the magnet. A speed detection device is constructed by mounting these omnipolar Hall ICs to a metal holding member made by bending a metal plate. This speed detection device is temporarily assembled to the frame of the eddy current instrument, the distance between the omnipolar Hall ICs and the rotor is adjusted, and then the external housing is placed over it and fixed in place. This realizes a highly reliable and accurate retrofit eddy current instrument with a speed detection device without the need for large-scale production equipment.

Description

Technical Field

[0001] The present invention relates to a speed detection device that is retrofitted to an eddy current type instrument.

Background Art

[0002] An eddy current type instrument is configured such that rotational motion of a wheel or a drive shaft mounted on a vehicle via a flexible cable is transmitted to a magnet rotor provided on a rotating shaft inside the instrument, the instrument includes an induction rotor disposed in the magnetic circuit of the magnet rotor and biased to the zero point by a spiral spring, and speed is displayed by a pointer coupled to the induction rotor that is rotationally displaced by the eddy current effect generated by the rotation of the magnet. As described in Patent Document 1, a conventional rotation detection device for an eddy current type speedometer is known to be equipped with a magnetic detection element. This instrument is provided with a speed detection device that detects a magnetic field change caused by the rotation of the magnet using a magnetoelectric conversion element such as a Hall element, and activates an alarm when the speed of the vehicle reaches or exceeds a predetermined value. Further, a retaining device is disposed on the mounting screw of this detection device to improve reliability.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0004] The conventional eddy current type instruments described in Patent Documents 1 and 2 have only one speed detection device built into the instrument, using a small Hall element. However, there is only one sensor per magnet, and even if an add-on speed detection device is added, there are limits to how much the resolution per revolution can be increased. With a single-pole pair magnet rotor and a reed switch, it is only possible to obtain two pulses per revolution. To increase the resolution and expand the control range, a major modification is required, such as adding a joint to the cable that transmits the rotation of the vehicle's wheels or output shaft to the eddy current type instrument, and interposing a separate high-resolution sensor with a waterproof and dustproof mechanism at that joint.

[0005] Meanwhile, recent advancements in semiconductor technology have made it possible to create Hall ICs that integrate Hall elements and signal processing circuits. Omnipolar bipolar sensing Hall ICs, which can extract signals from both S and N poles, are switching elements that turn ON when the S and N poles are close together and OFF when they are in the middle. When this is attached as a sensor to an eddy current type instrument with a single-pole pair of magnetic rotors, it is possible to extract two pulses of signal per rotation, enabling the same number of switches as a reed switch.

[0006] On the other hand, aftermarket speed detection devices require a signal of 4 pulses or more per revolution to control the output signal using a signal processing device equipped with a frequency divider, or to improve the resolution of the trip meter. To achieve this, a signal of 4 pulses per revolution can be realized by placing bipolar magnetic detection elements at positions shifted by 90° in magnetic pole phase. As a conventional technique, as shown in Patent Document 4, there is a method of noise reduction in which a reed switch, which is a bipolar magnetic detection element, is placed at a 90° shift. The specific mounting structure is not shown here. It is structurally very difficult to retrofit multiple such reed switches into an existing speedometer. Therefore, it is conceivable to install a Hall IC, which is smaller than a reed switch. In this case, it is possible from a design perspective to have the Hall IC protrude inward from the outer casing, but with this method, adjusting the distance from the rotating body after the entire assembly is completed would require some kind of adjustment structure from outside the closed casing, increasing the number of parts and making the adjustment process complicated. [Means for solving the problem]

[0007] In this invention, a speed detection device is provided that detects rotation by adding a plurality of additional magnetic detection elements within the rotating magnetic field generated by the magnet rotor of an eddy current type instrument equipped with a magnet rotor that rotates together with the main shaft. The device comprises two circuit boards to which magnetic detection elements made of omnipolar Hall ICs are connected, and these plurality of circuit boards are fixed to a metal support member formed by sheet metal bending with a magnetic phase of 90 degrees. The metal support member is attached in a structure that is additionally sandwiched between the eddy current type instrument mechanism, which is held in place by the frame, and the outer housing. The attachment of the support member to the frame has a positioning structure that is uniquely determined. The metal support member, formed by sheet metal bending, maintains a three-dimensional rib structure by soldering the edges of the bent parts at an angle to each other.

[0008] The metal retaining member is designed to reduce the rigidity of the magnetic circuit in the air gap direction between the magnetic detection element and the rotor, allowing for plastic deformation. The structure allows for adjustment of the air gap while the metal retaining member is placed on the frame and the housing is temporarily fastened without covering it. After that, the housing is placed on and the final tightening is performed, allowing for assembly with the correct air gap. [Effects of the Invention]

[0009] According to the present invention, even with an eddy current type instrument C2 of a single-pole pair magnetic rotor 22, a retrofitted speed detection device W2 can obtain a signal of 4 pulses per revolution. Furthermore, because it is constructed with a support member 29 made of metal plate material, it is easily plastically deformable, and the distance between the magnetic detection element 27 and the induction rotor 23 can be measured and adjusted when it is temporarily assembled to the frame. The adjustment will not be affected even if the housing 26o is placed over it and assembled after the adjustment is complete. This reduces the number of parts and the adjustment man-hours. Even in small-scale production, if the solderable metal plate material is made of a soft metal such as copper or brass, the processing work can be done with metal shears, punches, knives, etc., and it can also be bent by hand, eliminating the need for large equipment or molds for manufacturing. In terms of the mounting structure, the part of the metal holding member that is sandwiched between the frame and housing is a thin plate structure, so there is no significant change in dimensions, and no processing is required when mounting it on a vehicle after assembly. [Brief explanation of the drawing]

[0010] [Figure 1] Longitudinal section view in the embodiment [Figure 2] Cross-sectional view in an embodiment [Figure 3] Developed view of the sensor support member in the embodiment [Figure 4] Internal block diagram of a typical Hall IC [Figure 5] Characteristic diagram of an omnipolar (active, high) Hall IC. [Figure 6] This diagram shows the operation of a Hall IC with 1 magnetic pole pair and 2 units installed, where the characteristics are omnipolar (active, high). [Figure 7] This diagram shows the operation of a Hall IC with 1 magnetic pole pair and 2 units installed, where the characteristics are omnipolar (active, low). [Figure 8] Characteristic diagram of an omnipolar (active, low) Hall IC. [Figure 9] Overview of a variable frequency divider for vehicle speed signals [Figure 10] Schematic diagram of an electric power steering system equipped with a variable frequency divider for the vehicle speed signal. [Figure 11a]Electric power steering assist operation characteristics at 4 pulses per revolution [Figure 11b] Reference electric power steering assist operation characteristics at 2 pulses per revolution [Figure 11c] Electric power steering assist operation characteristics equipped with a vehicle speed signal variable frequency divider at 1 pulse per revolution [Figure 11d] Electric power steering assist operation characteristics equipped with a vehicle speed signal variable frequency divider at 1 / 2 pulse per revolution [Mode for Carrying Out the Invention]

[0011] Next, embodiments of the speed detection device in the eddy current type meter according to the present invention will be specifically described with reference to the attached FIG. 1, FIG. 2 and FIG. 3.

[0012] The eddy current type meter C2 of the present embodiment is composed of a main shaft 21, a magnet rotor 22, an induction rotor 23, a pointer 24, a pointer shaft 25, a frame body 26, and an external housing 26o. The speed detection device W2 is composed of a circuit board 28 on which a magnetic detection element 27 is mounted, and a metal support member 29. The circuit board 28 is integrally joined by connecting, adhering and soldering the circuit board 28a on which the magnetic detection element 27 is surface-mounted to the circuit board 28b. This adopts a two-stage structure due to the fine pitch of the connection wiring of the surface-mounted Hall IC 27 and the assembly efficiency of the boards. Naturally, it is also possible to implement this with a single printed circuit board. The circuit board 28b is fastened and fixed to the support member 29 by screws 29i and nuts 29j. The screws 29i are soldered 28d after being tightened. The nuts 29j are soldered 29d to the support member 29 to be integrated therewith. The circuit board 28 is soldered 28c to the metal support member 29. The speed detection device W2 has a structure in which the metal support member 29 is clamped and fixed between the frame body 26 and the external housing 26o by screws 210.

[0013] The metal support member 29 is made of a copper plate in the unfolded shape shown in Figure 3, and has a three-dimensional structure with bent edges. The bent edges are soldered 26h to the tangents of adjacent edges to give the structure rigidity. The central hole of the support member 29 is designed to fit snugly into the part that supports the main shaft at the center of the frame 26, and is centered with respect to the main shaft. In addition, the angle of the support member 29 is uniquely determined in relation to the frame 26 by the positions of the two mounting screw holes 210.

[0014] The main shaft 21 transmits the rotation of the vehicle's wheels and drive shafts, which are transmitted via a flexible cable (not shown), to the magnet rotor 22. The main shaft 21 is rotatably supported on the frame 26.

[0015] The magnetic rotor 22 consists of a magnet 22a and a soft magnetic holder 22b for the magnet 22a. The magnetic rotor 22 is fixed to the end of the main shaft 21.

[0016] The induction rotor 23 is a cup-shaped conductor. It is positioned with a small gap between it and the magnet 22a of the magnet rotor 22. The induction rotor 23 rotates due to the eddy current action generated by the rotation of the magnet rotor 22, and generates rotational torque proportional to the rotational speed of the magnet rotor 22. A pointer shaft 25 for mounting the pointer 24 is provided at the center of the induction rotor 23.

[0017] The pointer 24 is press-fitted and fixed to the end of the pointer shaft 25, and rotates together with the pointer shaft 25 mounted on the induction rotor 23 to display the vehicle's speed.

[0018] A plate 26c is mounted on the frame 26 and secured with screws. The pointer shaft 25 is supported by a bearing 213 on this plate and a lower bearing 21c located at the center of the upper end of the main shaft 21. The inner end of the whisker spring 211 is fixed to the pointer shaft 25, and its outer end is fixed to the plate 26c.

[0019] The frame 26 is made of a metal material such as aluminum, and a plate 6c is attached to its upper end. The frame 26 holds the various components such as the main shaft 21, the magnet rotor 22, and the induction rotor 23.

[0020] In this embodiment, the magnetic detection element 27 is positioned opposite the side surface of the induction rotor 23 and is fixed to a circuit board 28, which is fixed to a support member 29, so as to detect the magnetic flux of the magnet 22 that has leaked out after penetrating the induction rotor 23. Two sets of this combination are installed with a 90-degree phase difference. The magnetic detection element 27 detects changes in the magnetic field associated with the rotation of the magnet rotor 22, converts these changes in the magnetic field into an electrical signal, and outputs this electrical signal to various control devices mounted on the vehicle.

[0021] Furthermore, electronic components such as resistors and capacitors (not shown) that protect the magnetic detection element 27 from external noise may be mounted. The control equipment is connected via electrical wiring (not shown). The circuit board 28 is fixed to the support member 29 by screws 29i. In this case, the ground wire is connected to the external housing 26o through the screw portion and the support member 29, and power is supplied to the vehicle body. This not only eliminates the need for a ground wire within the narrow meter space but also enables highly reliable power supply.

[0022] Figure 4 shows an internal block diagram of a typical Hall IC. In this type, the drain of the final stage FET is open for output. It is known that the Hall plate that obtains the Hall effect in the magnetic detection section of a Hall IC is generally very small and therefore has almost no effect on the original magnetic circuit.

[0023] As shown in Figure 5, this is the case for omnipolar (active high) characteristics. When the magnetic flux changes from 0 to S (or N), the output resistance of the Hall IC becomes high and the output voltage increases.

[0024] This embodiment describes the operation of two sensors with a pole-to-pole ratio of 1. Figure 5 shows a detection device with two omnipolar Hall ICs (active high) from Figure 5, installed 90 degrees apart. The output of these ICs is a pulled-up FET transistor circuit, which switches OFF (resistance increases) when it approaches a magnetic pole (S, N), causing the output voltage to rise. As the S pole approaches the upper Hall IC Q1, it switches OFF (resistance increases) and the voltage rises. At this time, Q2, which is 90 degrees behind in phase, is still switched ON (resistance zero) and the voltage is zero. After the S pole passes in front of Q1, Q1 switches ON (resistance zero) and the output voltage becomes zero. Then, when the S pole comes in front of Q2, Q2 switches OFF (resistance increases) and the output voltage rises. After the S pole passes in front of Q2, Q2 switches ON (resistance zero) and the output voltage becomes zero. The same operation is repeated for the N pole, and voltage characteristics like those shown in the chart appear in each output circuit. By suppressing reverse current with a diode, the summed voltage waveform is obtained at the output. Therefore, a single-pole magnetic rotor can produce 4 pulses of signal per rotation.

[0025] Next, we will explain the operation of two sensors with 1 pole pair and different electrical characteristics of omnipolar sensors. Figure 8 shows the characteristics of an omnipolar Hall IC (active low). When this IC approaches a magnetic pole (S, N), the output switches ON, the internal resistance decreases, and the output voltage drops. When the magnetic flux density is near zero, the switch turns OFF and the voltage rises.

[0026] Figure 7 shows two omnipolar Hall ICs (active low) placed 90 degrees apart. As the south pole approaches the upper Hall IC Q1, it switches ON (resistance drops). At this time, Q2, which is 90 degrees behind, is still switched OFF. After the south pole passes in front of Q1, Q1 switches OFF and the voltage rises. Then, when the south pole approaches Q2, Q2 switches ON (resistance drops). After the south pole passes in front of Q2, Q2 switches OFF and the voltage rises. The same operation repeats for the north pole, and the voltage characteristics shown in the chart appear in each output circuit. Originally, the resistance drops and current flows only when the pull-up is ON, so even if the two switching elements are placed in parallel, there is no interference in operation. As a result, the circuit can be built with fewer components such as diodes.

[0027] In the past, when cable-driven eddy current type instruments were common, it was standard practice to use a vehicle speed signal of 2 pulses per revolution of the speedometer cable for engine, transmission, and power steering control. This was because the magnetic detection element was a reed switch, requiring a large span of the reed switch for magnetic detection. To achieve this span, it was necessary to use a single pole pair (S and N) at the end of the magnetic rotor to ensure reliable operation of the reed switch. Also, one revolution of the speedometer cable allows the vehicle to move approximately 1.3m to 1.5m. Therefore, since one pulse corresponds to about 70cm, one pulse was sufficient accuracy for controlling the target. Now, with the ability to control with 4 pulses per revolution, the distance per pulse becomes approximately 30cm, significantly improving the accuracy of trip meter readings for automobile rallies where reliability is paramount, and greatly improving driving accuracy at low speeds.

[0028] It is also possible to install an additional speed detection device on an existing eddy current type instrument that already has a rotation detection device that generates vehicle speed pulses. In this case, while sending a new vehicle speed signal to aftermarket trip meters, car navigation systems, power steering systems, etc., the original rotation detection device can continue to send conventional signals to the electronic controls of the engine, transmission, etc., so it can be added without affecting them or compromising reliability.

[0029] We previously explained that the number of pulses per revolution can be varied by changing the type and number of semiconductors attached to the speedometer. Next, we will show a system that switches the number of generated pulses by electrical circuit processing. Figure 10 shows the signal processing device 30. The input signal is input to the 1 / 2 frequency divider 31 through the buffer 32. The frequency divider 31 is composed of flip-flop circuits. It has a total of three stages and can extract four types of signals. If a signal with 4 pulses per revolution is input, four types of signals can be obtained per revolution: 4, 2, 1, and 1 / 2. A final stage 34 is provided at the output of a switch 33 that can select each of these signals. As mentioned above, if the signal from a typical vehicle speed sensor is 2 pulses per revolution, it will be converted to 2 times, 1 / 2 times, and 1 / 4 times. The signal can also be selected by the switch 33.

[0030] As shown in Figure 4 of Patent Document 3, in electric power steering, the amount of power steering assist changes depending on the vehicle speed. Therefore, by setting a relatively large number of pulses from the vehicle speed sensor and switching the number of pulses generated by the signal processing device 30, the amount of power steering assist can be switched and made variable.

[0031] Figure 10 shows a configuration in which the signal processing device 30 is incorporated into a typical electric power steering system. In electric power steering, the ignition signal indicates whether the ignition is ON, the engine signal indicates whether the vehicle is in operation, the steering torque is obtained from a torque detector, and the vehicle speed is obtained from a vehicle speed sensor.

[0032] The Calculation Control Unit (ECU) calculates the amount of assist from torque and vehicle speed using the map shown in Figure 11b (2 pulses / REV) and drives the motor. If the toggle switch is set to 4 pulses per revolution and the vehicle speed signal is provided to the ECM, twice the number of pulses are provided to the ECM as needed. As shown in Figure 11a, the steering is light when turning, but once the vehicle starts moving, it becomes heavier with less assist and a more direct feel. Conversely, setting it to 1 pulse / REV in Figure 11c or 1 / 2 pulse / REV in Figure 11d provides light torque performance across the entire range. The weight of the power steering can be varied according to the driver's preference.

[0033] As described above, this aftermarket vehicle speed signal generator does not require large production facilities, enhances the mechanical reliability of the assembly, absorbs product variations in the elements, and can achieve an output signal that is optimal for the control system being used. [Explanation of symbols]

[0034] 21 Spindle 22 Magnet Rotor 23 Induction rotor 24 Guidelines 25 Pointer axis 26 Frame 27 Magnetic detection element 28 Circuit boards 29 Support member 210 volts C2 Eddy current type instrument W2 Speed ​​Detection Device

Claims

1. A rotation detection device comprising an eddy current instrument having a magnetic rotor on a rotating shaft, an induction rotor that generates eddy currents due to the rotational magnetic flux of the magnetic rotor and generates rotational torque proportional to the rotational speed of the rotating shaft, and a pointer shaft driven by the rotation of the induction rotor, wherein a plurality of magnetic detection elements are attached to the eddy current instrument to measure the rotational magnetic flux, and a plurality of bipolar magnetic detection elements with S poles and N poles are arranged at intervals of a phase angle of 90° of the magnetic poles relative to the polarity of the rotating magnet.

2. A rotation detection device according to claim 1, wherein the magnetic detection element that detects both the north and south poles is an omnipolar Hall IC that incorporates a processing circuit including a Hall element.

3. A rotation detection device according to claim 1, wherein the number of magnetic pole pairs of the magnetic rotor is 1 and the two magnetic detection elements are configured to be arranged geometrically at a 90° angle around the axis.

4. The rotation detection device according to claim 3, wherein the eddy current instrument has a frame structure formed by cross-shaped arms, an external housing is placed on the outside thereof, the metal holding member of the rotation detection device is made of a metal plate, and this metal plate is configured to be bent to maintain the three-dimensional structure of the metal holding member, and the metal holding member is fixed so as to be sandwiched between the frame and the housing, and mounting points made by bending the metal plate of the metal holding member are provided between the cross-shaped arms, and a bipolar magnetic detection element with S and N poles is directly or indirectly placed at these mounting points.

Images