Automobile starter electromagnetic switch and automobile starter

Abstract

The utility model discloses a kind of automobile starter electromagnetic switch, including suction coil, holding coil, return spring, moving iron core, moving contact piece, static contact, yoke and electronic control circuit. By setting the number of turns of suction coil is less than the number of turns of holding coil, and introducing the electronic control circuit composed of field effect transistor, voltage divider resistance and diode, after starting end, automatically cut off coil loop, avoid moving static contact repeatedly on-off, effectively solve the existing soft engagement starter electromagnetic switch easy burnout, holding force is insufficient, the problem of poor reliability. The utility model is suitable for various automobile starter, with the advantages of simple structure, high reliability, wide applicability.

Description

Technical Field

[0001] This utility model belongs to the field of automotive starter technology, specifically relating to an automotive starter electromagnetic switch and an automotive starter. Background Technology

[0002] Currently, automotive starters are mainly divided into two types: forced engagement and soft engagement. The structure and electrical principles of soft engagement starters are basically the same as those of forced engagement starters. The difference lies in the fact that the electromagnetic switch of a soft engagement starter appropriately reduces the number of turns in the suction coil and holding coil, and increases the wire diameter of the suction coil (i.e., increases the cross-sectional area of ​​the suction coil wire) to achieve the soft-start function. Soft engagement starters are widely used due to their smooth starting and high engagement power. Here, we will use a planetary reduction soft engagement starter with a working voltage of 24V and a power of 7.5KW as an example to illustrate its working process and existing problems.

[0003] I. Working principle of soft-engagement starter

[0004] like Figure 1 The diagram shown is a simplified mechanical structure and electrical schematic of a planetary reduction soft-meshing starter with an operating voltage of 24V and a power of 7.5KW. Its relevant technical data is as follows:

[0005] Attraction coil: wire diameter φ2.0mm, number of turns n=110 turns, instantaneous working current I=140A, according to the magnetomotive force formula: F=In, where: F-electromagnetic force, I-current, n-number of coil turns;

[0006] Then the magnetomotive force F = 140 × 110 = 15400 (ampere-turns)

[0007] The instantaneous soft engagement speed provided by the suction coil is n=1700r / min (actual measurement).

[0008] Heat generated per unit time:

[0009] According to the formula for the heating effect of electric current: Q = 0.24IVt; Q - heat energy, I - current, V - voltage, t - working time;

[0010] The heat is Q = 0.24 × 140 × 24 t = 806.4 t (joules).

[0011] Holding coil: wire diameter φ0.64mm, effective number of turns n=110 turns, operating current I=18A;

[0012] The generated magnetomotive force is similar: F = 18 × 110 = 1980 (ampere-turns).

[0013] Similarly, the heat generated per unit time is: Q = 0.24 × 18 × 24 t = 103.68 (joules).

[0014] Return spring: Elastic tension: F = 200 Newtons (actual measurement)

[0015] Its working process is as follows:

[0016] When the start switch 2 is closed, the current flows through the positive terminal of the battery 1 and the start switch 2 to the start terminal O of the electromagnetic switch 10. One path is grounded through the holding coil 7 to form a circuit; the other path is input through the suction coil 6 and point H on the stationary contact 4 to the stator winding coils 12 and 13, the insulating brushes 14 and 15, the rotor commutator 18, and the grounding brushes 16 and 17 to form a circuit. Under the action of these two currents, the following mechanical action will occur: the moving iron core 8, under the electromagnetic resultant force of the suction coil 6 and the holding coil 7, overcomes the elastic tension of the return spring 9 and moves to the left, causing the drive gear 20 to move axially to the right through the lever force of the shift fork 11; at the same time, the suction coil 6, through a current of 140A, passes through the fixed winding coils 12 and 13, the insulating brushes 14 and 15, the steering gear 18, and the grounding brushes 16 and 17 to ground, generating a rotating magnetic field in the DC motor, driving the rotor 19 and the drive gear 20 to rotate at a soft meshing speed of 1700r / min. In this way, the drive gear 20 moves axially to the right and has the opportunity to slowly seek meshing with the flywheel ring gear 21. When the tooth hits the ground, the drive gear 20 compresses the buffer spring 22 and retracts axially to reduce the impact force with the flywheel ring gear 21. When the drive gear 20 rotates to offset the position of the tooth hit (finding the tooth groove aligned), the buffer spring 22 releases its elastic force, causing the drive gear 20 to mesh into the flywheel ring gear 21. Thirdly, the moving iron core 8 drives the moving contact 5 to contact and close with the stationary contacts 3 and 4, and the starter starts with full voltage operation. At this time, because the potential of the starting terminal O of the suction coil 6 is equal to that of the output terminal H, no current flows. Only the electromagnetic force generated by the coil 7 can maintain the meshing state of the drive gear 20 and the flywheel ring gear 21 and the reliable power supply of the moving contact 5 and the stationary contacts 3 and 4 of the main power supply circuit, and maintain the entire starting process.

[0017] Therefore, it can be seen that during the starting process, the suction coil 6 and the holding coil 7 operate in parallel. After the engine starts, the starter switch 2 is disconnected, and the starting terminal O of the solenoid switch 10 is de-energized. At this moment, the suction coil 6 and the holding coil 7 instantly switch to a series circuit. Due to the slow mechanical movement of the moving iron core 8, the moving contact 5 cannot disconnect from the stationary contacts 3 and 4 in a timely and synchronous manner. Therefore, the output terminal H of the suction coil 6 receives power from the stationary contacts 3 and 4 in the reverse direction. The current forms a circuit through the suction coil 6 and the holding coil 7 to ground. At this time, since the two coils have the same number of turns and the current directions are opposite, the electromagnetic forces generated cancel each other out, and the resultant force is zero. Under the combined action of the reverse spring force of the return spring 9 and the overrunning force of the one-way drive gear, the moving iron core 8 disconnects the moving contact 5 from the stationary contacts 3 and 4. The drive gear 20 is disengaged under the action of the shift fork lever force, completing the starting process. Therefore, if the number of turns of the suction coil and the holding coil are not equal, an electromagnetic force difference will be generated in the above process. As a result, the contacts of the main power supply circuit cannot be disconnected, the drive gear cannot be disengaged, and the starter will run continuously with the engine.

[0018] II. Performance differences between forced engagement starter solenoid switches and soft engagement starter solenoid switches

[0019] 1. Forced engagement starter solenoid switch

[0020] The biggest drawback of forced engagement starter solenoid switches is that they lack soft-start characteristics, leading to frequent maintenance and replacement of the starter and flywheel ring gears due to the constant "gear-mounting," "gear-milling," and "idling." However, the rationality of the electrical and mechanical design data of the forced engagement starter solenoid switch's suction coil, holding coil, and return spring, as well as its operational stability and reliability, have been tested and proven by a century of automotive industry history, and are worthy of reference and consideration.

[0021] 2. Soft-engagement starter solenoid switch

[0022] The soft-engagement starter solenoid switch achieves a soft-start function by significantly increasing the wire diameter of the suction coil and appropriately reducing the number of turns in both the suction and holding coils. This overcomes the shortcomings of the forced-engagement starter and represents a major technological upgrade for automotive starters. However, its drawbacks include a high failure rate, susceptibility to burnout, and significant copper wire consumption. The technical differences between the soft-engagement starter solenoid switch and the forced-engagement starter solenoid switch are as follows:

[0023] A. The electromagnetic force generated by the electromagnetic switch suction coil of the soft-engagement starter is twice that of the electromagnetic switch suction coil of the forced-engagement starter.

[0024] B. The heat energy generated per unit time by the electromagnetic switch suction coil of a soft-engagement starter is 3 times that of the electromagnetic switch suction coil of a forced-engagement starter.

[0025] C. The electromagnetic force generated by the holding coil of the solenoid switch in a soft-engagement starter is basically equivalent to the electromagnetic force generated by the holding coil of the solenoid switch in a forced-engagement starter.

[0026] D. Because the soft-engagement starter solenoid switch has fewer turns in the holding coil, it has a larger operating current and generates 1.5 times more heat per unit time than the holding coil of the forced-engagement starter solenoid switch.

[0027] E. The elastic tension of the return spring of the soft-engagement starter solenoid switch is twice that of the return spring of the forced-engagement starter solenoid switch.

[0028] III. Disadvantages and Causes of Soft-Meshing Starters

[0029] Based on the above comparison, there are significant differences between the technical data of the soft-engagement starter solenoid switch and the forced-engagement starter solenoid switch. If the technical data of the forced-engagement starter solenoid switch is used as a reference standard, we can analyze the problems that the soft-engagement starter solenoid switch may encounter during operation.

[0030] During starter motor operation, the suction coil only operates momentarily, as no current flows because the input and output terminals are at the same potential. The holding coil, however, operates throughout the entire starting process. Its characteristics include a longer operating time, and it plays a crucial role in overcoming the strong elastic tension of the return spring, ensuring reliable power supply to the moving and stationary contacts of the main power supply circuit, and ensuring reliable meshing of the drive gear and flywheel ring gear. Therefore, the relevant technical data of the holding coil are important technical indicators.

[0031] Because the elastic tension of the return spring in a soft-engagement starter solenoid switch is twice that of a forced-engagement starter solenoid switch, and the electromagnetic force of the holding coil in a soft-engagement starter solenoid switch is roughly equivalent to that in a forced-engagement starter solenoid switch, it can be concluded that the holding force of the holding coil in a soft-engagement starter solenoid switch is half that of a forced-engagement starter solenoid switch. This data is one of the important reasons for the failure of soft-engagement starter solenoid switches and starters. Furthermore, because the holding coil of a soft-engagement starter solenoid switch has fewer turns and a larger operating current, the Joule heat generated per unit time is 1.5 times that of the holding coil in a forced-engagement starter solenoid switch. This increases the probability of burnout, which is another important reason for the failure of soft-engagement starters.

[0032] In the frigid winter conditions of northern my country, vehicle batteries experience slow chemical reactions and reduced capacity, while engine lubricating oil viscosity increases, leading to greater resistance torque. Low-temperature fuel is also difficult to ignite, making engine cylinder detonation challenging. These factors, along with the long starting time and sometimes the need for multiple attempts, pose a significant challenge to starter motors.

[0033] When a vehicle is started in a low-temperature environment, in addition to the objective factor that the battery capacity decreases due to the low ambient temperature, the battery terminal voltage and output current will continue to decrease due to the longer starting time of a single start or the increase in the number of starts. The starter and its solenoid switch will also have their temperature rise due to the current heating effect as the starting time increases or the number of starts increases. This not only reduces the power of the starter, but also increases the resistance of the solenoid switch holding coil due to the temperature rise, reduces the current, and further reduces the electromagnetic force.

[0034] Furthermore, the irreconcilable contradiction between the electromagnetic force of the starter solenoid switch holding coil and the strong elastic tension of the return spring further exacerbates the already halved holding electromagnetic force. As a result, during the starting process, the holding force of the holding coil will be less than the combined force of the elastic tension of the return spring and the axial overrun force of the drive gear. Under the action of this combined force, the moving contact will retract, instantly disconnecting the main power supply circuit (because the retraction stroke is small (1mm-3mm), it will not affect the meshing of the drive gear and the flywheel ring gear). At this moment, a large current (140A) instantaneously flows through the potential difference between the two ends of the suction coil, generating a strong electromagnetic force that connects the moving and stationary contacts of the main power supply circuit. Then, because the input and output ends of the suction coil are at the same potential, no current flows, and the electromagnetic force disappears. Afterward, the return spring disconnects the moving iron core from the moving and stationary contacts again. Thus, the suction coil and the moving and stationary contacts are repeatedly energized and de-energized. The large operating current of the suction coil causes severe burnout in a short time, which is one reason. Secondly, a starting current of 500A-700A will flow between the moving and stationary contacts. During the repeated opening and closing of the moving and stationary contacts, a strong electric arc is generated, causing the moving and stationary contacts to stick together, leading to starter motor failure and burnout as the engine continues to run. Thirdly, a strong electric arc is generated between the brushes and the rotor commutator. Due to the extremely high temperature, the brush leads detach, the commutator segments melt, and a blowout fault occurs. Fourthly, regarding the coil itself, due to the large operating current, it generates a large amount of heat per unit time, and the high temperature easily causes short circuits or open circuit faults. Utility Model Content

[0035] The purpose of this invention is to solve the above-mentioned technical problems and provide an automotive starter electromagnetic switch and automotive starter that can overcome the limitation of the number of coil turns, reduce the operating current of the holding coil and heat generation.

[0036] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows:

[0037] An automotive starter electromagnetic switch includes a battery, a starter switch, a first stationary contact, a second stationary contact, a moving contact, a return spring, an electromagnetic switch, a shift fork, a commutator, a rotor, a drive gear, a flywheel ring gear, a buffer spring, a planetary reducer, and a one-way clutch. The positive terminal of the battery is connected to one end of the starter switch and the first stationary contact, and the negative terminal of the battery is grounded. The other end of the starter switch is connected to the starter terminal O of the electromagnetic switch 10. The electromagnetic switch includes a suction coil, a holding coil, and a moving iron core. The suction coil and the holding coil are wound in the same direction on the moving iron core, which is installed in the inner cavity of a sleeve frame. The input ends of the suction coil and the holding coil are both connected to the starter terminal O, and the output end of the suction coil is connected to the second stationary contact. The first and second stationary contacts are mounted on a bakelite cover. The moving contact is located at the left end of the moving iron core and... Near the first and second stationary contacts, the upper end of the shift fork is movably connected to the right end extension of the moving iron core. The return spring is located between the right end of the moving iron core and the upper end of the shift fork. The lower end of the shift fork is movably connected to the guide cylinder of the one-way clutch. The shift fork is hinged and fixed to form a lever structure. Insulating brushes are connected to both ends of the commutator. The other ends of the insulating brushes are connected to the stator windings. The other ends of the stator windings are connected to the second stationary contact. The commutator is also connected to one end of the ground brush. The other ends of the ground brushes are grounded. The rotor and the commutator are integrally formed. The end of the rotor is connected to the planetary reducer via a key. The one-way clutch is mounted on the planetary reducer shaft and engaged with a helical key. The right end of the output shaft of the one-way clutch is connected to the drive gear via a key. The buffer spring is placed on the straight key shaft on the left side of the drive gear and is freely engaged.

[0038] The number of turns of the holding coil is greater than the number of turns of the suction coil. It also includes resistors R1 and R2 and a field-effect transistor (FET). One end of resistor R1 is connected to the start terminal O of the electromagnetic switch, and the other end is connected to one end of resistor R2. The other end of resistor R2 is connected to the source S of the FET, which is grounded. The drain D of the FET is connected to the output terminal of the holding coil. The gate G of the FET is connected to the junction between resistors R1 and R2. The voltage V provided by the series voltage divider of resistors R1 and R2 is the operating voltage V for the gate G of the FET. GS For 4V≤V GS ≤6V.

[0039] Furthermore, a diode is connected to the connecting wire between the start terminal O of the electromagnetic switch and the resistor R1. The positive terminal of the diode is grounded, and the negative terminal is connected to the resistor R1.

[0040] Furthermore, the number of turns of the holding coil is 1.5-3 times the number of turns of the suction coil.

[0041] Furthermore, the field-effect transistor is an N-channel field-effect transistor.

[0042] An automobile starter motor includes an electromagnetic switch as described.

[0043] Compared with the prior art, the beneficial effects of this utility model are:

[0044] 1. This utility model solves the bottleneck that the number of turns of the starter electromagnetic switch's suction coil and holding coil must be equal by the coordinated design of the resistor-field-effect transistor control circuit and the differentiated coil turns;

[0045] 2. This utility model reduces the electromagnetic force generated by the suction coil and decreases the elastic tension of the return spring by reducing the number of turns of the suction coil and increasing the number of turns of the holding coil, thereby relatively increasing the holding force of the holding coil.

[0046] 3. This utility model increases the number of turns of the holding coil and reduces the operating current of the holding coil, thereby reducing the Joule heat generated per unit time and significantly improving the stability and reliability of the holding coil.

[0047] 4. This utility model reduces the wire diameter of the suction coil, reduces the number of turns of the suction coil, saves copper wire consumables, and effectively solves the problem of the suction coil burning out due to the repeated opening and closing of the moving and stationary contacts of the battery under low voltage conditions in cold winter.

[0048] 5. This utility model can be used for both soft-engagement and forced-engagement starters without modifying the original electromagnetic switch parts to achieve the soft-start function. Attached Figure Description

[0049] Figure 1 A schematic diagram of the mechanical structure and electrical principle of an existing planetary reduction soft-meshing starter;

[0050] Figure 2 This is a schematic diagram of the mechanical structure and electrical principle of this utility model;

[0051] Figure 2 In the diagram: 1-Battery; 2-Start switch; 3-First stationary contact; 4-Second stationary contact; 5-Moving contact; 6-Attraction coil; 7-Holding coil; 8-Moving iron core; 9-Return spring; 10-Electromagnetic switch; 11-Shift fork; 12 / 13-Stator winding; 14 / 15-Insulating brush; 16 / 17-Ground brush; 18-Commutator; 19-Rotor; 20-Drive gear; 21-Flywheel ring gear; 22-Buffer spring; 23-Planetary reducer; 24-One-way clutch; 25-Diode D; 26-Resistor R1; 27-Resistor R2; 28-N-channel MOSFET. Detailed Implementation

[0052] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0053] Example 1

[0054] Taking a 24V, 7.5KW planetary reduction soft-mesh starter as an example, we will analyze and explain its working principle and superior performance. The specific working parameters of each component are as follows:

[0055] Suction coil: wire diameter φ1.5mm, number of turns n=70 turns, instantaneous working current I=140A;

[0056] According to the formula: F=I*n

[0057] The magnetomotive force is: f = 140 × 70 = 9800 (Amperes·turns);

[0058] The Joule heat generated per unit time is expressed by the formula: Q = 0.24I * Vt;

[0059] The Joule heat is: Q = 0.24 × 140 × 24t = 806.4t (joules);

[0060] Holding coil: wire diameter φ0.64mm, number of turns n=180 turns, operating current I=10A;

[0061] According to the formula: F=I*n

[0062] The magnetomotive force is: F = 10 × 180 = 1800 (Amperes·turns);

[0063] The Joule heat generated per unit time is expressed by the formula: Q = 0.24I * Vt;

[0064] The Joule heat is: Q = 0.24 × 10 × 24 t = 57.6 (joules);

[0065] Return spring: elastic tension set to 120N;

[0066] Electronic components: Field-effect transistor: IRFP250N, current: 30A, voltage: 200V; Diode: 1N5408, current: 3A, voltage: 1000V; Resistor R1: 16KΩ; Resistor R2: 10KΩ.

[0067] like Figure 2As shown, an automotive starter solenoid switch includes a battery 1, a starter switch 2, a first stationary contact 3, a second stationary contact 4, a moving contact 5, a return spring 9, a solenoid switch 10, a shift fork 11, a commutator 18, a rotor 19, a drive gear 20, a flywheel ring gear 21, a buffer spring 22, a planetary reducer 23, and a one-way clutch 24. The positive terminal of the battery 1 is connected to one end of the starter switch 2 and the first stationary contact 3, respectively. The negative terminal of the battery 1 is grounded. The other end of the starter switch 2 is connected to the starter terminal O of the solenoid switch 10. The electromagnetic switch 10 includes a suction coil 6, a holding coil 7, and a moving iron core 8. The suction coil 6 and the holding coil 7 are wound in the same direction on the moving iron core 8, and the number of turns of the holding coil 7 is greater than the number of turns of the suction coil 6. The moving iron core 8 is installed in the inner cavity of the sleeve frame. The input ends of the suction coil 6 and the holding coil 7 are both connected to the start terminal O. The output end of the suction coil 6 is connected to the second stationary contact 4. The first stationary contact 3 and the second stationary contact 4 are installed on the bakelite cover. The moving contact piece 5 is located at the left end of the moving iron core 8 and... Near the first stationary contact 3 and the second stationary contact 4, the upper end of the shift fork 11 is movably connected to the right end extension of the moving iron core 8. The return spring 9 is disposed between the right end of the moving iron core 8 and the upper end of the shift fork 11. The lower end of the shift fork 11 is movably connected to the guide cylinder of the one-way clutch 24. The shift fork 11 is hinged and fixed, forming a lever structure. Insulating brushes 14 / 15 are connected to both ends of the commutator 18, and the other ends of the insulating brushes 14 / 15 are connected to the stator windings 12 / 13, respectively. The other ends of the stator windings 12 / 13 are also connected to... The second stationary contact 4 is connected, and the commutator 18 is also connected to one end of the ground brush 16 / 17 respectively. The other end of the ground brush 16 / 17 is grounded. The rotor 19 is integrally set with the commutator 18. The end of the rotor 19 is connected to the planetary reducer 23 by a key. The one-way clutch 24 is mounted on the shaft of the planetary reducer 23 and is engaged with a helical key. The right end of the output shaft of the one-way clutch 24 is connected to the drive gear 20 by a key. The buffer spring 22 is placed on the straight key shaft on the left side of the drive gear 20 and is freely engaged.

[0068] The number of turns of the holding coil 7 is 2.6 times that of the suction coil 6. It also includes resistors R1-26 and R2-27, and a field-effect transistor 28. The field-effect transistor 28 is an N-channel MOSFET. One end of resistor R1-26 is connected to the start terminal O of the electromagnetic switch 10. A diode 25 is connected between the start terminal O of the electromagnetic switch 10 and resistor R1-26. The positive terminal of diode 25 is grounded, and the negative terminal is connected to resistor R1-26. The other end of resistor R1-26 is connected to one end of resistor R2-27. The other end of resistor R2-27 is connected to the source S of the field-effect transistor 28, which is grounded. The drain D of the field-effect transistor 28 is connected to the output terminal of the holding coil 7. The gate G of the field-effect transistor 28 is connected to the junction point between resistors R1-26 and R2-27. The series voltage divider provided by resistors R1-26 and R2-27 supplies the operating voltage V to the gate G of the field-effect transistor 28. GS This makes the drain (D) and source (S) of the field-effect transistor 28 conduct.

[0069] An automobile starter motor, including the electromagnetic switch described above.

[0070] Resistor selection calculation: For a 24V system, V O =24V, choose 4V≤V GS If the voltage is ≤6V, then R1=16KΩ and R2=10KΩ are selected. The voltage drop ∆V generated after the current passes through resistors R1-26 and R2-27 is 5.54V. ∆V is the operating voltage of MOSFET 28, which meets the requirements. MOSFET 28 can work stably.

[0071] The number of turns of the holding coil 7 can also be any value between 1.5 and 3 times the number of turns of the suction coil 6. A ratio lower than 1.5 times may not be able to effectively offset the potential and turn off the field-effect transistor 28; a ratio higher than 3 times may result in an excessively large coil volume, increased cost, and insufficient electromagnetic force.

[0072] Experimental data:

[0073] Through comparative experiments, this embodiment has the following improvements compared to the traditional scheme (with the same number of coil turns):

[0074] The coil operating current was reduced from 18A to 10A, a decrease of 44.4%.

[0075] The coil heat output was reduced from 103.68J to 57.6J, a decrease of 55.6%.

[0076] The success rate of low-temperature startup has increased from 76% to 95%.

[0077] The lifespan of the electromagnetic switch has been increased from 50,000 cycles to 120,000 cycles.

[0078] Example 2

[0079] For small and medium power starters with a working voltage of 12V, power of 1.0KW-3.0KW, drive gear teeth ≤11, and module ≤3, the current of the holding coil 7 should not exceed 10A; the soft engagement speed provided by the suction coil 6 is 800r / min-1000r / min.

[0080] Component parameters: Field-effect transistor: IRFP150N, current: 40A, voltage: 100V, resistor 26-R1 is 12K, resistor 27-R2 is 5K;

[0081] V O =12V, choose 4V≤V GS ≤6V. Calculation shows that the voltage drop ∆V generated after the current passes through resistors R1-26 and R2-27 is 4.94V. ∆V is the operating voltage of MOSFET 28, which meets the requirements. MOSFET 28 can work stably.

[0082] Example 3

[0083] For high-power starters with a working voltage of 24V, a power of 6.5KW-9.0KW, a drive gear with ≥11 teeth and a module of ≥3.5, the current of coil 7 should not exceed 12A; the soft engagement speed provided by suction coil 6 is 1200r / min-1800r / min, resistor 26-R1 is 16K and resistor 27-R2 is 10K.

[0084] The working process of this utility model:

[0085] When the start switch 2 is closed, the current flows through the positive terminal of the battery 1, the start switch 2, and the start terminal O of the electromagnetic switch 10. Then, one path flows through the suction coil 6, through point H on the stationary contact 4, into the stator windings 12 / 13, through the insulating brushes 14 / 15, the commutator 18, and the ground brushes 16 / 17 to form a circuit. The other path is divided by resistors 26-R1 and 27-R2 in series, generating a working voltage at the gate G of the field-effect transistor 28 that is 1-2V higher than the turn-on voltage of the field-effect transistor 28, making the drain D and source S of the field-effect transistor 28 conduct. At this time, the current at the start terminal O flows through the holding coil 7, the drain D and source S of the field-effect transistor 28 to form a circuit.

[0086] Under the combined electromagnetic force generated by the currents in the suction coil 6 and the holding coil 7, the following mechanical action is produced:

[0087] First, the moving iron core 8 overcomes the elastic tension of the return spring 9 and moves to the left, driving the upper end of the shift fork 11 to move to the left. Through the lever action, the lower end of the shift fork 11 moves to the right, causing the drive gear 20 to move axially to the right. At the same time, the suction coil 6, through a current of 140A, forms a circuit via the stator windings 12 / 13, the insulating brushes 14 / 15, the commutator 18, and the ground brushes 16 / 17. The DC motor generates a rotating magnetic field, driving the rotor 19 to rotate. The drive gear 20 rotates at a slow speed of 1700r / min. In this way, the drive gear 20 moves axially to the right and has the opportunity to slowly find the meshing opportunity with the flywheel ring gear 21. When the top tooth appears, the drive gear 20 compresses the buffer spring 22 and retracts axially to reduce the impact force with the flywheel ring gear 21. When the drive gear 20 rotates to offset the position of the top tooth (finding the tooth groove to be aligned), the buffer spring 22 releases its elastic force, and the drive gear 20 meshes with the flywheel ring gear 21.

[0088] Secondly, the moving iron core 8 drives the moving contact piece 5 to contact and close with the first stationary contact 3 and the second stationary contact 4, and the starter motor starts operating at full voltage. At this time, because the potential of the starting terminal O of the suction coil 6 is equal to that of the output terminal H, no current flows. Only the electromagnetic force generated by the coil 7 maintains the meshing state of the drive gear 20 and the flywheel ring gear 21 and ensures reliable power supply to the moving contact piece 5 of the main power supply circuit and the first stationary contact 3 and the second stationary contact 4, thus maintaining the entire starting process.

[0089] When the engine is started and the start switch 2 is disconnected, the suction coil 6 and the holding coil 7 instantly change from a parallel connection to a series connection. Although the moving contact 5 is not disconnected from the first stationary contact 3 and the second stationary contact 4, and power can be obtained from point H, the suction coil 6 has 70 turns, while the holding coil 7 has 180 turns. The number of turns in the holding coil 7 is 2.6 times that of the suction coil 6. Furthermore, the current directions in the holding coil 7 and the suction coil 6 are opposite. Therefore, at the instant the start switch 2 is disconnected, the self-induced electromotive force generated by the holding coil 7 is 2.6 times that of the suction coil 6, and the potential directions are opposite. This higher self-induced electromotive force in the holding coil 7 instantly counteracts the self-induced electromotive force of the suction coil 6 and the potential of the original supply voltage, causing the original supply voltage to drop instantaneously. This lower voltage, after being divided by the series resistors 26-R1 and 27-R2, does not reach the turn-on voltage of the gate G of the field-effect transistor 28. Under the pull-down action of the turn-off resistor 27-R2, the gate potential of MOSFET 28 is pulled down to zero, the drain (D) and source (S) of MOSFET 28 are turned off, and no current flows through the entire series circuit of the suction coil 6 and the holding coil 7, thus the magnetic field disappears. Under the combined action of the return spring 9 and the overrunning force of the unidirectional drive gear, the moving iron core 8 disconnects the moving contact 5 from the first stationary contact 3 and the second stationary contact 4, simultaneously causing the upper end of the shift fork 11 to move to the right; the drive gear 20 moves to the left under the lever force of the shift fork 11, completing the start-up. Diode 25 acts as a freewheeling diode, absorbing reverse voltage spikes in the circuit and protecting MOSFET 28.

Claims

1. An electromagnetic switch for an automobile starter, comprising a battery (1), a starter switch (2), a first stationary contact (3), a second stationary contact (4), a moving contact (5), a return spring (9), an electromagnetic switch (10), a shift fork (11), a commutator (18), a rotor (19), a drive gear (20), a flywheel ring gear (21), a buffer spring (22), a planetary reducer (23), and a one-way clutch (24); The positive terminal of the battery (1) is connected to one end of the start switch (2) and the first stationary contact (3), respectively. The negative terminal of the battery (1) is grounded. The other end of the start switch (2) is connected to the start terminal O of the electromagnetic switch (10). The electromagnetic switch (10) includes a suction coil (6), a holding coil (7), and a moving iron core (8). The suction coil (6) and the holding coil (7) are wound in the same direction on the moving iron core (8). The moving iron core (8) is installed in the inner cavity of the sleeve frame. The suction coil (6) The input ends of the holding coil (7) and the suction coil (6) are both connected to the starting terminal O. The output end of the suction coil (6) is connected to the second stationary contact (4). The first stationary contact (3) and the second stationary contact (4) are mounted on the bakelite cover. The moving contact piece (5) is located on the left end of the moving iron core (8) and close to the first stationary contact (3) and the second stationary contact (4). The upper end of the shift fork (11) is movably connected to the right end extension of the moving iron core (8). The return spring (9) is located on the right end of the moving iron core (8) and connected to the shift fork (11). Between the upper ends, the lower end of the shift fork (11) is movably connected to the guide cylinder of the one-way clutch (24). The shift fork (11) is hinged and fixed to form a lever structure. Insulating brushes (14 / 15) are connected to both ends of the commutator (18). The other ends of the insulating brushes (14 / 15) are connected to the stator windings (12 / 13). The other ends of the stator windings (12 / 13) are connected to the second stationary contact (4). The commutator (18) is also connected to ground brushes (16 / 17). One end of the ground brush (16 / 17) is grounded, the rotor (19) and the commutator (18) are integrated, the end of the rotor (19) is connected to the planetary reducer (23) by a key, the one-way clutch (24) is mounted on the shaft of the planetary reducer (23) and is engaged with a spiral key, the right end of the output shaft of the one-way clutch (24) is connected to the drive gear (20) by a key, and the buffer spring (22) is placed on the straight key shaft on the left side of the drive gear (20) and is freely engaged; characterized in that The number of turns of the holding coil (7) is greater than the number of turns of the suction coil (6), and it also includes resistors R1 (26), R2 (27), and a field-effect transistor (28). One end of resistor R1 (26) is connected to the start terminal O of the electromagnetic switch (10), and the other end is connected to one end of resistor R2 (27). The other end of resistor R2 (27) is connected to the source S of the field-effect transistor (28), and the source S is grounded. The drain D of the field-effect transistor (28) is connected to the output terminal of the holding coil (7). The gate G of the field-effect transistor (28) is connected to the connection point between resistors R1 (26) and R2 (27). The resistors R1 (26) and R2 (27) are connected in series to divide the voltage and provide the working voltage V to the gate of the field-effect transistor (28). GS For 4V≤V GS ≤6V.

2. An electromagnetic switch for a starter motor of an automobile according to claim 1, wherein A diode (25) is also connected between the current input point O of the electromagnetic switch (10) and the resistor R1 (26). The positive terminal of the diode (25) is grounded, and the negative terminal is connected to the resistor R1 (26).

3. An electromagnetic switch for a starter motor of an automobile according to claim 1, wherein The number of turns of the holding coil (7) is 1.5-3 times the number of turns of the suction coil (6).

4. The electromagnetic switch according to claim 1, wherein The field-effect transistor (28) is an N-channel field-effect transistor.

5. An automotive starter characterized by comprising: Including the electromagnetic switch as described in any one of claims 1 to 4.

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