STARTER
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to a starter that starts up, for instance, the engine of a vehicle.
2. Description of the Related Art
[0002] To start an engine using a conventional starter of electromagnetic push-in type, a coil of a starter switch is energized and an internal contact of the starter switch is closed, to supply power from a battery to a motor and generate rotation torque in the armature of the motor. Thereafter, the rotational force of the armature is transmitted to an engine crankshaft via a pinion gear and an engine ring gear that are meshed with each other, and the engine is started as a result.
[0003] Upon closing of the starter switch, the armature is still stationary, and no back electromotive force is generated, accordingly, there flows an inrush current of several hundred to a thousand and several hundred amperes on account of the extremely small internal resistance of the starter. The internal specific resistance of the battery gives then rise to a decrease in terminal voltage, and voltage drop occurs.
[0004] A problem arises as a result since the above-described voltage drop in the battery causes momentary interruptions when other electrical equipment and electronic equipment of the vehicle, for instance audio, navigation systems, electronic control units (ECUs) and the like are used during engine startup. [0005] Such momentary interruptions are not particularly problematic during ordinary engine startup, but there is a concern of discomfort to the driver and passengers, for instance in vehicles provided with an idling stop function, due to the occurrence of momentary interruption during restart after idling stop. Therefore, measures are taken to prevent drops in battery voltage by providing a

standby power supply or by installing a step-up DC/DC converter in order to avoid such momentary interruptions.
[0006] With a view to avoiding momentary interruptions, some known starters are provided with an electromagnetic switch that opens and closes a main contact provided in a motor circuit, a current suppression resistor connected in series to the main contact in the motor circuit, a short-circuiting relay provided so as to be capable of short-circuiting the current suppression resistor, and a timer circuit for delaying the operation of the short-circuiting relay (see for instance Japanese Patent Application Publication No. 2009-287459). [0007] When the main contact of this starter closes, current flows from the battery to the motor via the current suppression resistor. A voltage lower than the total voltage of the battery is applied at this time to the motor, and hence there is reduced a starting current i.e. inrush current to the motor. After a predetermined time has elapsed, an excitation coil of the short-circuiting relay is energized, the current suppressing resistor is short-circuited, and the total voltage of the battery is applied to the motor. This allows starting the engine free of momentary interruptions.
[0008] In order to avoid momentary interruptions, starters are also known that are provided with: a starter switch connected in series between a battery and a motor, a current suppression resistor connected in series to the starter switch, a short-circuiting switch connected in parallel to the current suppression resistor, for short-circuiting the current suppression resistor, and a control circuit that controls opening and closing of the short-circuiting switch (see for instance Japanese Patent Application Publication No. 2011-94555). [0009] When the starter switch of this starter closes, current flows from the battery to the motor via the current suppression resistor. Voltage lower than the total voltage of the battery is applied at this time to the motor, and hence there is reduced the starting current i.e. inrush current to the motor. After a predetermined time has elapsed, the current suppressing resistor is short-

circuited through closing of the short-circuiting switch, and the total voltage of the battery is applied to the motor. This allows starting the engine free of momentary interruptions.
[0010] Also, in order to avoid momentary interruptions, starters are known that are provided with both a permanent magnet and a field coil in a field system portion of the motor (see for instance Japanese Patent Application Publication No. 2016-46906). In this starter, when the contact closes, current flows from the battery to the motor through the field coil, so that the starting current i.e. inrush current to the motor is reduced as a result. The field coil is short-circuited after a predetermined time has elapsed. This allows starting the engine free of momentary interruptions.
[0011] However, the starter disclosed in Japanese Patent Application Publication No. 2009-287459 requires a current suppression resistor and a timer circuit, and hence entails a complex structure and a sizable starter build, all of which is problematic. Moreover, the starter disclosed in Japanese Patent Application Publication No. 2009-287459 utilizes a timer circuit, and therefore a problem arises in that when the friction torque of the engine is high, for instance at low temperatures, the rotational speed of the motor does not rise and a predefined back electromotive force is not exceeded even after a predetermined period of time and the inrush current after short-circuiting of the current suppression resistor is large. The occurrence of momentary interruption becomes therefore a concern.
[0012] In the starter disclosed in Japanese Patent Application Publication No. 2011-94555 the heat capacity of the current suppression resistor is small, and the time for short-circuiting the current suppression resistor is constrained. As a result, there arises the concern of increased inrush current after short-circuiting of the current suppression resistor, and the concern of occurrence of momentary interruption, when a predefined back electromotive force is not exceeded after a predetermined time has elapsed. This is problematic in that,

as a result, the build of the starter is made more sizable in order to secure the heat capacity of the current suppression resistor.
[0013] The starters in both Japanese Patent Application Publication No. 2009-287459 and Japanese Patent Application Publication No. 2011-94555 utilize a current suppression resistor, and hence are problematic in terms of the concern of increased internal resistance of the starter and reduced output of the starter.
[0014] The starter disclosed in Japanese Patent Application Publication No. 2016-46906 requires a field coil current control unit that switches short-circuiting of the field coil through control of the current that flows in the field coil. The structure involved is therefore complex, which is problematic.
SUMMARY OF THE INVENTION
[0015] It is thus an object of the present invention, arrived at in order to solve the above problems, to obtain a starter that allows starting an engine without causing momentary interruption in electrical equipment or electronic equipment, with a simple structure, without a sizable starter build and without reduction of the output of the starter.
[0016] A starter according to the present invention is provided with: an armature of a motor; a battery that supplies power to the armature; a starter switch connected in series between the battery and the armature; a field coil that is connected in series to the armature and generates magnetic flux in the armature; and a short-circuiting switch that is connected in parallel to the field coil and short-circuits the field coil, wherein the short-circuiting switch has a short-circuiting switch contact connected in series between the starter switch and the armature, a driving coil that has one end connected between the field coil and the armature and the other end connected to ground, and that drives a movable contact of the short-circuiting switch contact, and a plunger fixed to the movable contact of the short-circuiting switch contact, the short-circuiting switch being configured such that the plunger is driven and the short-circuiting

switch contact is closed when a voltage applied to the driving coil becomes higher than a voltage set beforehand due to a back electromotive force that is generated as a result of the rotation of the armature upon closing of the starter switch.
[0017] In the starter according to the present invention, the short-circuiting switch that is connected in parallel to the field coil and short-circuits the field coil has: the short-circuiting switch contact connected in series between the starter switch and the armature, the driving coil that has one end connected between the field coil and the armature and the other end connected to ground, and that drives a movable contact of the short-circuiting switch contact, and the plunger fixed to the movable contact of the short-circuiting switch contact, the short-circuiting switch being configured such that the plunger is driven and the short-circuiting switch contact is closed when a voltage applied to the driving coil becomes higher than a voltage set beforehand due to a back electromotive force that is generated as a result of the rotation of the armature upon closing of the starter switch.
As a result, it becomes possible to start an engine without causing momentary interruption in electrical equipment or electronic equipment, with a simple structure without a sizable starter build and without reduction of the output of the starter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a circuit diagram illustrating a starter according to Embodiment 1 of the present invention;
FIG. 2 is a graph illustrating current and voltage waveforms of the starter according to Embodiment 1 of the present invention; and
FIG. 3 is a circuit diagram illustrating another starter according to Embodiment 1 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] Preferred embodiments of the starter according to the present invention will be explained next with reference to accompanying drawings. Identical or corresponding portions in the figures will be denoted by identical reference symbols.
[0020] Embodiment 1
FIG. 1 is a circuit diagram illustrating a starter according to Embodiment 1 of the present invention. In FIG. 1, a starter 10 is provided with an armature la of a motor 1, a battery 2 that supplies power to the armature la, a start switch 3 connected to the battery 2, a starter switch 4 connected in series between the battery 2 and the armature la: a field coil lb being a field system portion and connected in series to the armature la, and a short-circuiting switch 5 that is connected to in parallel to the field coil lb and short-circuits the field coil lb. [0021] The motor 1, which is a motor for starting an engine not shown, has the armature la and the field coil lb described above, and also a field system portion lc that generates magnetic flux as a result of being excited by the battery 2 or by another power source.
[0022] The starter switch 4 is made up of a starter switch contact 4a being a normally-open contact that is connected in series between the battery 2 and the armature la, a driving coil 4b for driving a movable contact of the starter switch contact 4a, a holding coil 4c that holds the movable contact of the starter switch contact 4a at a position of contact with a fixed contact, and a plunger 4d that is fixed to the movable contact of the starter switch contact 4a. One end of the holding coil 4c is connected to the start switch 3, and the other end is connected to ground.
[0023] The short-circuiting switch 5 is made up of a short-circuiting switch contact 5 a being a normally-open contact that is connected in series between the starter switch contact 4a and the armature la, a driving coil 5b for driving a movable contact of the short-circuiting switch contact 5a, and a plunger 5c fixed

to the movable contact of the short-circuiting switch contact 5a. One end of the driving coil 5b is connected between the field coil lb and the armature la, and the other end is connected to ground.
[0024] The operation of the starter 10 having the above configuration will be explained next with reference to FIG. 2. FIG. 2 is a graph illustrating current and voltage waveforms of the starter according to Embodiment 1 of the present invention. In FIG. 2, the vertical axis represents power supply voltage of the battery 2 and the starter current flowing in the armature la, and the horizontal axis represents time.
[0025] In a first step of engine start, the start switch 3 is closed according to an engine start request, at time Tl, whereupon a current la starts flowing from the battery 2 to the armature la, via the start switch 3, the driving coil 4b and the field coil lb. Current flows also herein from the battery 2 to the holding coil 4c via the start switch 3.
[0026] Next, in a second step, the driving coil 4b is energized, as a result of which the plunger 4d is driven and the starter switch contact 4a is closed at time T2. The holding coil 4c as well is energized and hence the plunger 4d is held in position, and the close-circuit in the starter switch contact 4a is preserved.
[0027] Through closing of the starter switch contact 4a, the armature la receives supply of DC power of the battery 2, and generates rotation torque as a result, whereupon a pinion gear coupled to a shaft of the armature la via a one¬way clutch moves towards a ring gear provided on the crankshaft of the engine, and meshes with the ring gear.
[0028] When the starter switch contact 4a is closed, the current la flowing from the battery 2 to the driving coil 4b virtually disappears, and a current lb flows from the battery 2 to the closed starter switch contact 4a, the field coil lb and the armature la. The rotational force of the armature la is transmitted as a result to the engine crankshaft, and engine startup is initiated.
[0029] In a third step, next, the short-circuiting switch contact 5a is closed at

time T3 after a preset lapse of time has passed since the time at which the starter switch contact 4a was closed. Specifically, the plunger 5c is driven and the short-circuiting switch contact 5a is closed when the voltage applied to the driving coil 5b becomes higher than a voltage set beforehand due to the action of a back electromotive force that is generated as a result of the rotation of the armature la and that increases with rising revolutions of the armature la.
[0030] Through closing of the short-circuiting switch contact 5a, current flows from the battery 2 to the armature la via the starter switch contact 4a and the short-circuiting switch contact 5a. Herein the short-circuiting switch contact 5a is closed and the field coil lb is short-circuited, and hence the starter current increases again, as illustrated in FIG. 2.
[0031] Through short-circuiting of the field coil lb, furthermore, the means for generating magnetic flux in the armature la includes now the field system portion lc alone. After starting of the engine has been initiated, engine startup is complete by time T4.
[0032] The short-circuiting switch 5 operates in accordance with the voltage that is applied to one end of the driving coil 5b, due to the action of the back electromotive force, and hence no complex control involving the use of a rotation detection sensor, timer circuit or the like in the motor 1 is required, which makes for a simpler structure. The timing of short-circuiting and the degree of voltage drop at the time of short-circuiting can be adjusted by modifying the voltage at which the short-circuiting switch contact 5a is closed, i.e. the voltage at which the plunger 5c is driven.
[0033] Herein a starter current II denotes the inrush current flowing in the armature la at time T2 at which the starter switch contact 4a is closed. The starter current II is given by Expression (1) below, where V0 denotes the voltage of the battery 2, RB denotes the internal specific resistance of the battery 2, RF denotes the resistance of the field coil lb, RM denotes the internal resistance of the armature la, and RW denotes wiring resistance.

[0034] I1=V0/(RB+RF+RM+RW) ...(1)
[0035] Further, a starter current 12 denotes the current flowing in the armature
la at time T3 at which the short-circuiting switch contact 5a is closed. A back
electromotive force E is generated in the armature la as a result of rotation of
the armature la, given that current flows in the armature la since before time
T3. The starter current 12 is given by Expression (2) using the internal specific
resistance RB of the battery 2, the internal resistance RM of the armature la,
and wiring resistance RW.
[0036] I2=(V0-E)/(RB+RW+RM) ...(2)
[0037] The back electromotive force E is given Expression (3) below, where k
denotes a motor constant, O denotes amount of magnetic flux, and n denotes the
rotational speed of the motor. The starter current 12 flowing in the armature la
can be adjusted by modifying motor specifications.
[0038]E=kxOxn...(3)
[0039] When the voltage at which the short-circuiting switch contact 5a
becomes closed is set high, the field coil lb is not short-circuited until the back
electromotive force E generated in the armature la is high. Given the high
back electromotive force E, specifically, there holds the relationship Il>12
according to Expression (2), and the short-circuiting switch contact 5a becomes
closed at a point where and the motor rotational speed is high, according to
Expression (3). As a result, engine startup takes time on account of the lapse
until the field coil lb is short-circuited, i.e. on account of the lengthened lapse
from time T2 to time T3.
[0040] Accordingly, there is set a voltage at which the short-circuiting switch
contact 5a is closed, in such a manner that the starter current II and the starter
current 12 are equal, as illustrated in FIG. 2, as a result, the lapse of time until
closing of the short-circuiting switch contact 5a and short-circuiting of the field
coil lb is reduced, and it becomes possible to start the engine quickly while

suppressing momentary interruption.
[0041] In consequence, the driving coil 4b of the starter switch 4, the field coil lb and wiring resistance are present in the circuit in the first step, the field coil lb and wiring resistance are present in the second step, and wiring resistance alone is present in the third step. In consequence, electric resistance decreases in three stages, from the first step over to the third step.
[0042] By using herein the field coil lb as a current suppression resistor there is no need for setting separately a current suppression resistor, and it becomes possible to simplify the structure and scale down the build of the starter, and to achieve reductions in weight and cost. Current is suppressed through generation of the back electromotive force, since the armature la is rotating on account of the current la and current lb since before the third step. [0043] Further, the engine can be started quickly and reliably also at times of high load where the friction torque of the engine is large, for instance at low temperatures, since higher torque can be generated than when a current suppression resistor is utilized.
[0044] The current flowing in the field coil lb can be reduced, and the field magnetic flux can be likewise reduced, through short-circuiting of the field coil lb by the short-circuiting switch 5. As a result, the starter characteristic is switched over from torque type to rotation type, and the engine can be started up quickly. This allows reducing the operating time of the starter 10 and increasing quietness. Further, current consumption can be reduced and efficiency enhanced since copper loss derived from the field coil lb is small. [0045] In the starter 10, firstly the field coil lb connected between the battery 2 and the armature la is energized during engine startup, and after a lapse of time that is set beforehand, the current flowing in the field coil lb is reduced by the short-circuiting switch 5. As a result, an initial rush current is reduced and voltage drop is suppressed, and it becomes possible to start the engine efficiently without giving rise to momentary interruptions of electrical

equipment or the like.
[0046] In Embodiment 1, thus, a short-circuiting switch that is connected to in parallel to a field coil and short-circuits the latter has: a short-circuiting switch contact connected in series between the starter switch and the armature, a driving coil that has one end connected between the field coil and the armature and the other end connected to ground and that drives a movable contact of the short-circuiting switch contact, and a plunger fixed to the movable contact of the short-circuiting switch contact, the short-circuiting switch being configured such that the plunger is driven and the short-circuiting switch contact is closed when a voltage applied to the driving coil becomes higher than a voltage set beforehand due to a back electromotive force that is generated as a result of the rotation of the armature upon closing of the starter switch.
Accordingly, it becomes possible to start an engine without causing momentary interruption in electrical equipment or electronic equipment, with a simple structure, without a sizable starter build and without reduction of the output of the starter.
[0047] Instead of the field system portion lc illustrated in FIG. 1 that generates magnetic flux in the armature la in Embodiment 1 a permanent magnet Id may be provided that generates magnetic flux similarly to the field system portion lc, as illustrated in FIG. 3.
[0048] In FIG. 3, for instance the magnetic poles of the field system portion are made up of a plurality of paired up N poles and S poles, where first poles are configured by the field coil lb and second poles configured by the permanent magnet Id. Also a motor 1 having both the field coil lb and the permanent magnet Id elicits the effect of suppressing voltage drops, and allows starting the engine yet more efficiently without giving rise to momentary interruption of electrical equipment or the like.
[0049] Specifically, the strength of the field system during energization of the field coil lb is increased, and motor torque is likewise increased, by virtue of

the feature of having both the field coil lb and the permanent magnet Id. Therefore, the engine can be started reliably also when the friction torque of the engine is large, for instance at low temperatures.
[0050] In a low-load region where load is light and the motor rotational speed is high, the magnetic flux of the field system decreases and high rotation is brought out through shut-off or limitation, by the short-circuiting switch 5, of the current with which the field coil lb is energized. This allows achieving a quick startup. As a result, the operating time of the starter 10 can be shortened and quietness increased. It becomes further possible to suppress excessive increases in motor rotational speed at times of zero load, and to prolong the life of the starter 10.

What Is Claimed Is:
1. A starter, comprising:
an armature (la) of a motor (1);
a battery (2) that supplies power to the armature (la);
a starter switch connected in series between the battery (2) and the armature (la);
a field coil (lb) that is connected in series to the armature (la) and generates magnetic flux in the armature (la); and
a short-circuiting switch (5) that is connected in parallel to the field coil (lb) and short-circuits the field coil (lb),
wherein the short-circuiting switch (5) has a short-circuiting switch contact (5a) connected in series between the starter switch and the armature (la), a driving coil (5b) that has one end connected between the field coil (lb) and the armature (la) and the other end connected to ground, and that drives a movable contact of the short-circuiting switch contact (5a), and a plunger (5c) fixed to the movable contact of the short-circuiting switch contact (5a),
the short-circuiting switch (5) being configured such that the plunger (5c) is driven and the short-circuiting switch contact (5a) is closed when a voltage applied to the driving coil (5b) becomes higher than a voltage set beforehand due to a back electromotive force that is generated as a result of the rotation of the armature (la) upon closing of the starter switch.
2. The starter according to claim 1,
wherein the voltage necessary for operation of the short-circuiting switch (5) is set in such a manner that a starter current that flows in the armature (la) at the time of energization of the armature (la) via the field coi (lb)l is equal to the starter current that flows in the armature (la) at the time of energization of the armature (la) through short-circuiting of the field coil (lb) by the short-circuiting switch (5).

3. The starter according to claim 1 or 2, further comprising, in addition to
the field coil (lb), a permanent magnet that generates magnetic flux in the armature (la).