JP2004282963A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of effectively preventing the nonconformity that excessive voltage from an assist motor by counter electromotive force is applied to a switching element for driving the assist motor. <P>SOLUTION: This electric power steering device 1 for assisting rotation of a steering shaft 3 by driving force of the assist motor 6 includes a boosting circuit 120 for boosting power supply voltage from a motor driving power supply 157 to be converted to motor driving voltage, and a switching driver 18 for controlling rotary drive of the assist motor 6 by switching the motor driving voltage outputted from the boosting circuit 120 and supplying it to the assist motor 6. The booster circuit 120 is provided with a capacitor 124 for holding and smoothing output voltage of the boosting circuit 120, a boosting rectifier section 123 for preventing the capacitor 124 from discharging backward to the input side of the boosting circuit, and a counter electromotive force branching path 126 for allowing a counter electromotive force current of the assist motor 6, which passes the switching driver 18 and flows back to the boosting circuit 120 side, to pass in such a manner that the boosting rectifier section 123 is avoided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electric power steering device for a vehicle.
[0002]
[Prior art]
2. Description of the Related Art In recent years, an electric power steering device (including the concept of an electro-hydraulic power steering device) has been used in a vehicle steering device, particularly a vehicle steering device, in order to achieve low fuel consumption or to simplify and reduce the weight of a steering system. The number of vehicles to be used is increasing. In the electric power steering device, the rotation of the steering shaft is assisted by the driving force of the assist motor, and the assist motor is rotationally controlled so that a steering angle corresponding to the operation angle of the steering handle is obtained. This rotation drive control is often performed by controlling the input of the motor drive voltage (for example, PWM control). In general, since the assist motor has a high output, a vehicle-mounted power supply voltage composed of a battery, a DC-DC converter, and the like is used after being boosted to a motor drive voltage by a booster circuit.
[0003]
[Problems to be solved by the invention]
By the way, the booster circuit for generating the motor drive voltage is supplied to the assist motor via the switching driver in the case of the above-described motor control by switching. When the step-up circuit is constituted by a so-called step-up DC-DC converter, the following problem occurs. In the step-up circuit, a capacitor for holding and smoothing the output voltage, a coil for receiving the power supply voltage on the upper stage side from the rectifying unit for boosting, and a boosting induction by intermittently changing a current passing through the coil. In addition to the step-up switching section for generating the voltage waveform, the step-up rectifying section for preventing the backflow discharge of the capacitor to the input side of the step-up circuit is an essential component. The step-up rectifier configured by a diode or the like allows the passage of current from the booster circuit side to the motor side, but blocks the current flow in the reverse direction, that is, the current passage from the motor side to the booster circuit side.
[0004]
However, in a situation where a large reverse rotation load is applied to the motor from the steering wheel side, such as when operating the steering wheel abruptly or when riding the steering wheel while riding on a large step, the back electromotive force due to the power generation action of the motor increases. In this case, if the step-up rectifying section exists on the side of the step-up circuit and the passage of the back electromotive force current is blocked as described above, the switching element such as an FET incorporated in the switching driver includes the back electromotive force. Excessive voltage is applied, which causes a problem that the element is damaged or the life is shortened. Of course, since this back electromotive force voltage is also applied to the boost rectifying unit, there is a possibility that a similar adverse effect is exerted on elements such as a diode forming the boost rectifying unit.
[0005]
An object of the present invention is to effectively prevent a problem in which an excessive voltage due to a back electromotive force from an assist motor is applied to a switching element for driving the assist motor, thereby extending the life of the switching element. An object of the present invention is to provide an electric power steering device capable of achieving the following.
[0006]
[Means for Solving the Problems and Functions / Effects]
The electric power steering device (including the concept of the electric hydraulic power steering device) of the present invention assists the rotation of the steering shaft by the driving force of the assist motor and obtains a steering angle corresponding to the operation angle of the steering handle. As described above, an electric power steering device configured to rotationally control an assist motor, in order to solve the above-described problem,
A booster circuit that boosts a power supply voltage from a motor drive power supply to generate a motor drive voltage, and inputs a motor drive voltage output from the booster circuit to the assisting motor while switching the motor driving voltage, thereby rotating the assisting motor. Switching driver to perform
A booster circuit, a capacitor for holding and smoothing an output voltage of the booster circuit, a booster rectifier for preventing a backflow of the capacitor from flowing back to the booster circuit input side, and a booster rectifier on the upper side than the booster rectifier. A coil for receiving a power supply voltage; and a booster switching section for generating a booster induced voltage waveform by intermittently changing a current passing through the coil, wherein the booster induced voltage waveform is converted to an input voltage waveform of the power supply voltage. Is configured as a step-up type booster circuit that outputs as a motor drive voltage while smoothing with a capacitor via a boosting rectifier,
A back electromotive force passing branch path is provided for passing the back electromotive force current of the assist motor that flows back to the booster circuit side via the switching driver, bypassing the boosting rectifier.
[0007]
In the above configuration, a booster circuit including a step-up DC-DC converter for supplying a motor drive voltage to the switching driver is provided above the switching driver that drives the assist motor. A step-up rectifier provided in the step-up DC-DC converter blocks a back electromotive force current flowing from the assist motor to the step-up circuit via the switching driver. Further, in the electric power steering apparatus of the present invention, since the back electromotive force passage branch path for passing the back electromotive force current is provided in a form avoiding the boosting rectifier, a large reverse power is provided by the assist motor. Even when an electromotive force is generated, an excessive voltage based on the electromotive force can be effectively prevented from being applied to the switching element in the switching driver, and the life of the switching element can be extended. . In addition, application of a high voltage to the boost rectifier is similarly suppressed, and protection of the boost rectifier can be achieved.
[0008]
Further, in the electric power steering apparatus according to the present invention, it is possible to provide a passing current adjusting means for adjusting the amount of current passing through the branch path for passing back electromotive force in accordance with the voltage on the cathode side of the rectifier for boosting. Since the branch path for passing back electromotive force acts as a discharge path for the capacitor for holding voltage in the booster circuit, from the viewpoint of stabilizing the voltage output of the booster circuit, the branch path for passing back electromotive force passes through the branch path for passing back electromotive force. It is preferable to keep the passage to a minimum necessary when an excessive back electromotive force is generated. Since the voltage on the cathode side of the boosting rectifier increases when the back electromotive force from the assist motor increases, in the above configuration, the amount of current that passes through the back electromotive force passage branch path accordingly. To increase. Thus, in the normal state where the back electromotive force is small, the passing current value of the branch path for passing the back electromotive force is reduced, so that the charged state of the capacitor can be maintained, and the output voltage of the booster circuit can be stabilized. On the other hand, only when the back electromotive force is excessively large, an excessive voltage based on the back electromotive force is applied to the switching element in the switching driver by increasing the passing current value of the branch path for passing the back electromotive force. It is possible to prevent the occurrence of troubles without any problem.
[0009]
More specifically, the passing current adjusting means includes a back electromotive force passing switch for switching the passage of the back electromotive force current in the back electromotive force passing branch path between allowance and cutoff, and a cathode side of the boosting rectification unit. A cathode-side voltage detection unit for detecting a voltage; and a back electromotive force that switches a back electromotive force passing switch unit from a cutoff state to a passage allowable state when a detection voltage of the cathode side voltage detection unit exceeds a predetermined reference voltage. And a power passage switch control means. According to this configuration, only when the voltage rise due to the back electromotive force becomes remarkable, the current passage of the back electromotive force passage branch path is permitted, and otherwise, the current passage is cut off. Discharge of the capacitor can be minimized, and the output voltage of the booster circuit can be maintained stably.
[0010]
Further, a load resistor for consuming the electric energy of the passing back electromotive current can be provided on the back electromotive force passage branch path. As a result, the energy of the back electromotive force current is consumed by the load resistance, and the effect of the load resistance can be effectively prevented or suppressed from affecting other circuit parts via the branch path.
[0011]
Further, the branch path for passing back electromotive force may be a bypass path that bypasses the cathode side and the anode side of the step-up rectifier. According to this configuration, there is an advantage that a part of the back electromotive force can be fed back for boosting. However, it is desirable to provide the above-described load resistance and appropriately lower the voltage before performing feedback so that excessive feedback does not occur. For example, the motor drive power supply includes an AC conversion unit that converts the DC output of a DC vehicle-mounted power supply (for example, a fuel cell) into an AC, a transformer that transforms the AC-converted vehicle-mounted power supply voltage for output, and a secondary side of the transformer. When a DC-DC converter having a rectifier for rectifying an AC output is provided, the provision of the load resistor protects the rectifier in the DC-DC converter when a large back electromotive force occurs. It is effective in doing.
[0012]
On the other hand, when the motor drive power source is an in-vehicle battery, the energy of the back electromotive force is returned to the in-vehicle battery via the bypass path, thereby reducing battery consumption and improving energy efficiency. Can be. In this case, it is not always necessary to provide a load resistor (rather, it may be better to omit the load resistor from the viewpoint of promoting the charging of the battery by the back electromotive force).
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram showing an example of a configuration of an electric power steering device to which the present invention is applied (in the present embodiment, “vehicle” is an automobile, but the application target of the present invention is not limited to this. Is not what is done). In the electric power steering apparatus 1, a steering shaft 3 is coupled to a steering handle 2, and a pinion 10 provided at the tip of the steering shaft 3 and rotating with the steering shaft 3 reciprocates on a rack bar 11 in the axial direction. By moving, the steered angles of the wheels 13, 13 change. Further, the reciprocating movement of the rack bar 11, that is, the rotation of the steering shaft 3 is assisted by the driving force of the assist motor 6. In the present embodiment, the assist motor 6 rotates another pinion 4 that meshes with the rack bar 11.
[0014]
The angular position of the steering shaft 3 and the rotational angle position of the assist motor 6 are detected by a steering shaft angle detecting unit 101 and a motor angular position detecting unit 103, each of which is a well-known angle detecting unit such as a rotary encoder. The steering control unit 110 is constituted by a microcomputer having a CPU 111, a ROM 112, a RAM 113, and an input / output interface 110. The steering control unit 110 executes a control program stored in the ROM 112, and based on the detected angular position of the steering shaft 3 and the angular position of the assist motor 6, detects a steering angle corresponding to the operating angle of the steering handle 2. Thus, the operation of the assist motor 6 is controlled by PWM control via the switching driver 18 so as to obtain.
[0015]
The assist motor 6 is constituted by a brushless motor, in this embodiment a three-phase brushless motor. As shown in FIG. 3, the three-phase brushless motor includes three-phase coils U, V, and W arranged at intervals of 120 °. The angle relationship is detected by a Hall IC serving as an angle sensor provided in the motor. In response to the outputs of these Hall ICs, the switching driver 18 of FIG. 1 switches the energization of the coils U, V, W to W → U (1), U → V (3), V → W (5) is sequentially switched cyclically (in the case of forward rotation: in the case of reverse rotation, the switching is performed in the reverse order described above).
[0016]
The rotation control of the assist motor 6 is performed in such a manner that a duty ratio control sequence based on a PWM signal from the drive control unit 110 is superimposed on the energization switching sequence of each phase of the coils U, V, and W. FIG. 4 shows a circuit example of the switching driver 18. FETs (switching elements) 75 to 80 corresponding to the terminals u, u ', v, v', w, w 'of the coils U, V, W are provided. (Reference numerals 87 to 92 are flywheel diodes that form a bypass path for an induced current accompanying switching of the coils U, V, and W). A logical product signal of the switching signal from the Hall IC (angle sensor) on the assist motor side and the PWM signal from the drive control unit 100 is formed by the AND gates 81 to 86, and the FETs 75 to 80 are switched using this signal. , The coils of the phases involved in the energization can be selectively energized by PWM.
[0017]
Returning to FIG. 1, in the present embodiment, the drive power supply for the assist motor 6 includes a DC vehicle-mounted power supply 150 and a DC-DC converter 157 that converts the output voltage of the DC vehicle-mounted power supply 150 into a motor drive DC voltage. . The DC on-vehicle power supply 150 is, for example, a fuel cell, and its output voltage is set to be as high as 200 to 450 V in consideration of a driving margin of a main power motor (not shown) of an automobile. On the other hand, a DC power source for peripheral electric components having a lower voltage (for example, 30 to 50 V: 42 V in the present embodiment) than the main power system is used for a peripheral electric system in the vehicle including a drive power source for the assist motor 6. The DC-DC converter 157 steps down the input voltage from the DC on-board power supply 150 and outputs it as the peripheral power supply DC power supply voltage.
[0018]
As shown in FIG. 2, the DC-DC converter 157 specifically converts an input DC voltage from the DC vehicle-mounted power supply 150 into an AC, and reduces the AC-converted voltage for output. It has a transformer 163 and a rectifier 164 for rectifying the secondary AC output of the transformer 163. The AC converter 162 is formed by a well-known switching transistor bridge, and switches an input DC voltage at a constant frequency to convert the input DC voltage into a bipolar square wave AC. The common mode choke coil 101 for removing noise is provided on the input side of the AC converter 162. Further, the AC voltage waveform generated by the switching is input to the transformer 163, and the voltage stepped down from the secondary side is output. The rectifying unit 164 is a full-wave rectifying unit composed of a diode bridge, and is ripple-removed by an LC low-pass filter type smoothing unit 165 and output as a DC waveform.
[0019]
Returning to FIG. 1, the booster circuit 120 includes a capacitor 124 for holding and smoothing the output voltage of the booster circuit 120, a boosting rectifying unit 123 for preventing backflow discharge of the capacitor 124 to the input side of the booster circuit, A coil 121 for receiving a power supply voltage at an upper stage side than the step-up rectifying unit 123 includes a step-up switching unit 122 that generates a step-up induced voltage waveform by intermittently changing a current passing through the coil 121. And a step-up DC-DC converter. The boosting induced voltage waveform is superimposed on the input voltage waveform of the power supply voltage, and is output as a motor drive voltage while being smoothed by the capacitor 124 via the boosting rectifier 123.
[0020]
In the present embodiment, a DC output from the DC-DC converter 157 on the vehicle power supply side is input to the booster circuit 120 via the power supply relay 141 and the power supply filter 140. Reference numeral 142 denotes a power switch that is operated in conjunction with the ignition switch. When the power switch 142 is closed, the power relay 141 operates and the voltage input from the DC-DC converter 157 to the booster circuit 120 is reduced. Permissible.
[0021]
On the input path 134 from the DC-DC converter 157, the boosting coil 121 is disposed below the power supply filter 140, and on the switching branch path 135 that branches from the lower stage to the ground side, the boosting coil 121 is provided. A switching unit 122 is provided. On the other hand, the input path 134 is provided with a step-up rectification unit 123 below the branch point of the switching branch path 135, and further provided with a capacitor 124 in a parallel branch.
[0022]
Further, a back electromotive force current of the assist motor 6 flowing backward from the input path 134 to the booster circuit 120 via the switching driver 18 on the cathode side of the booster rectifier 123 bypasses the booster rectifier 123 and passes therethrough. A branch path 126 for passing back electromotive force is provided. In the present embodiment, the back electromotive force passage branch path 126 is a bypass path that bypasses the cathode side and the anode side of the step-up rectification unit 123, but the terminal is grounded without being connected to the anode side. It may be in the form.
[0023]
The back electromotive force passage branch path 126 is provided with a back electromotive force passage switch unit 128 for switching the passage of the back electromotive force current between allowable and cutoff. Further, a cathode-side voltage detection unit composed of voltage dividing resistors 129 and 130 is provided so as to be branched from the voltage measurement point P on the cathode side of the boosting rectification unit 123, and the voltage at the voltage measurement point P is divided and adjusted. The input signal is input to the input / output interface 114 (A / D conversion port) of the steering control unit 110 in the form shown in FIG. The microcomputer constituting the steering control unit 110 (hereinafter also referred to as “microcomputer 110”) switches to the back electromotive force passing switch unit 128 when the detection voltage of the cathode side voltage detection unit exceeds a predetermined reference voltage. A signal SB is sent, and the signal SB is switched from the cutoff state to the passage permitting state (that is, the function of the switch unit control means for back electromotive force passage is realized). On the back electromotive force passage branch path 126, a diode 127 forming a branch path side rectifier for preventing back flow and a load resistor 131 for consuming the electric energy of the back electromotive force current passing through the path are provided. ing. Note that the diode 127 can be omitted.
[0024]
Next, the boosting rectifier 123 is a parasitic diode included in the boosting control FET in FIG. This will be specifically described with reference to FIG. An FET structure having a parasitic diode appears when, for example, a MOSFET is employed. The upper diagram in FIG. 5 is a schematic cross-sectional view of a MOSFET (n-channel type), and the lower diagram is an equivalent circuit diagram. In the thickness direction of the silicon substrate, a semiconductor portion forming a drain and a semiconductor portion forming a depletion layer are adjacent to each other to form a pn junction, and are connected in parallel to an FET structure portion formed in a channel region. Parasitic diodes are occurring.
[0025]
In a power drive circuit such as a motor drive, if a normal silicon diode is used in the rectifier of the step-up booster circuit, the forward current drop of the pn junction and, consequently, the voltage loss on the output side increase because the passing current value is large, May be problematic. In this case, the step-up rectifier 123 is a step-up control FET (hereinafter referred to as “step-up control FET 123”) that is turned on and off in synchronization with the step-up switching part 122 in a synchronized manner. Thereby, the problem can be solved. That is, in FIG. 1, in the ON (closed) cycle of the boosting switching unit 122, the current (electric energy) flowing into the coil 121 increases, and the superimposed voltage waveform for boosting follows a decreasing trend. Next, when the boosting switching unit 122 is turned off (open), the current flowing into the switching branch path 135 is cut off, and the coil 121 emits an induced current. Along with this, the superimposed voltage waveform for boosting turns into an increasing tendency. Therefore, when the boost control FET is turned on in synchronization with the OFF cycle of the boost switching unit 122, in FIG. 5, the current bypasses the parasitic diode portion having a high DC resistance and passes through the FET portion having a low resistance. As a result, the voltage loss can be suppressed. On the other hand, when the boost control FET is turned off in synchronization with the ON cycle of the boost switching unit 122, the channel of the FET portion is closed. When the capacitor 124 side in FIG. 1 has a high potential, the parasitic diode portion in FIG. 5 is in a reverse bias state, and current passage is cut off. That is, it functions as a step-up rectifier.
[0026]
The microcomputer that forms the steering control unit 110 performs synchronous switching control between the boosting switching unit 122 and the boosting control FET 123. In the present embodiment, the boosting switching unit 122 and the back electromotive force passing switch unit 128 are configured by a power MOSFET together with the boosting control FET 123. Since the gate drive voltage of these power MOSFETs is relatively high, the drive command signal from the microcomputer 110 is boosted by the switching booster circuit 115 using the battery voltage, and then the power MOSFETs 122, 123, and 128 are switched via the switching drive circuit 116. Supply to the gate. In the present embodiment, the switching drive circuit 116 monitors the gate voltage and the source voltage of the FETs 122 and 123 when performing the synchronous switching control of the power MOSFETs 122 and 123 forming the boosting switching unit and the boosting control FET. The monitor value is supplied to the microcomputer 110. The microcomputer 110 drives the switching drive circuit 116 such that the gate-source voltage of each of the FETs 122 and 123 is maintained substantially constant (that is, a substantially constant drive voltage is supplied to the assist motor 6). The function as a stabilized power supply is realized by changing the output pattern of the command signal.
[0027]
For example, when switching control is performed on the boosting switching unit 122, the switching pattern can be changed according to the difference from the monitored target value of the gate-source voltage. If the switching duty ratio and the frequency are constant, the voltage level of the superimposed voltage waveform (the value after rectification and smoothing) when the switching is continuously performed is almost the maximum value of the voltage increment due to the step-up. Therefore, if the switching frequency is set so that the maximum value of the voltage increment due to the step-up is larger than the difference between the level of the input gate-source voltage and the target voltage of the DC output to be obtained, By adjusting the time ratio of the stop / continuation of the switching operation, the output voltage can be adjusted to the target voltage.
[0028]
For example, when the difference from the target value of the gate-source voltage is large, the stop / continue time ratio of the switching operation is increased, and when the difference from the target value is small or overshoots (for example, as described later). (When the back electromotive force current is large), control is performed to reduce the time ratio. Instead of adjusting the time ratio of the stop / continuation of the switching operation, a method of changing the switching duty η according to the difference from the monitored target value of the gate-source voltage (that is, the PWM method) is employed. You can also. In this case, the boost control FET 123 performs synchronous switching in a form in which the phase is inverted with the same duty η (that is, the FET 123 is turned off when the FET 122 is on, and the FET 123 is turned on when the FET 122 is off).
[0029]
In the electric power steering device 1 described above, when the steering wheel is operated while turning the steering wheel suddenly or riding on a large step such as a curb, a large back electromotive force is generated in the assist motor 6. When the level of the generated back electromotive force increases, the voltage at the measurement point P in FIG. 1 (the cathode side of the parasitic diode of the power MOSFET 123 forming the boost control FET) increases. The microcomputer 110 monitors the voltage while continuing the switching drive of the FETs 122 and 123 of the booster circuit 120, and when this voltage exceeds a prescribed reference voltage, turns on the back electromotive force passing switch unit 128 to turn on the back electromotive force. The power current is guided to the branch path 126 for passing back electromotive force. The back electromotive force current is consumed by the load resistor 131. Thus, the switching elements (FETs 76 to 80 in FIG. 4) in the switching driver 18 and the rectifier 164 (FIG. 2) of the DC-DC converter 157 on the vehicle power supply side can be protected from excessive back electromotive force voltage application. it can.
[0030]
In addition, the boost control FET 123 can pass the back electromotive force current in the ON cycle, so that there is no fear of breakage or the like. May be done. Therefore, the effect of protecting the boosting control FET 123 can be obtained by conducting the back electromotive force passage branch path 126 to bypass the back electromotive force current.
[0031]
In this case, when the switching of the boosting switching unit 122 is continued, the boosting control FET 123 is in a form inverted from the phase thereof (that is, the FET 123 is turned off when the FET 122 is on, and the FET 123 is turned on when the FET 122 is off. ) Synchronous switching is performed. Further, when the switching operation is stopped, the step-up control FET 123 is kept in a normally closed state to promote current passage on the back electromotive force passage branch path 126 side (this energy is consumed by the load resistor 131). In this state, it is possible to wait for the gate-source voltage to decrease. Further, when the PWM method in which the duty ratio η is changed while continuing the switching at a constant frequency without using the switching stop period is used, the boost control is performed in the cycle in which the back electromotive force passing switch unit 128 is ON. The FET 123 can be controlled so that the OFF period becomes as long as possible (for example, the duty ratio 1-η of the OFF period approaches 1). In any case, increasing the passing current through the load resistor 131 and promoting power consumption when a large back electromotive force current is generated can be achieved by increasing the boost control FET 123 and the rectifying unit 164 of the DC-DC converter 157. This is advantageous from the viewpoint of protection.
[0032]
As shown in FIG. 6, the vehicle-mounted power supply may be a vehicle-mounted battery 57 (detailed description of parts common to FIG. 1 is omitted). In this case, since the rectifying unit is not provided on the vehicle power supply side, the back electromotive force current can be returned to the battery 12. Therefore, it is desirable to omit the load resistance on the branch path 126 for passing back electromotive force. When the back electromotive force passing switch unit 128 is ON, the ON / OFF state of the step-up control FET 123 can be set arbitrarily, but the ON period is set as long as possible (for example, the duty ratio η of the ON period). Is controlled so as to approach 1), the amount of current returned to the battery 57 can be increased.
[0033]
Note that the power MOSFET serving as the boost control FET 123 may easily become insufficient in source-gate voltage when passing a large back electromotive current, and the duty ratio η during the ON period is temporarily set to the maximum value of 1. However, current loss may increase due to an increase in ON resistance. Therefore, from this viewpoint, it is advantageous to provide the back electromotive force passage branch path 126 to increase the current return path to the battery 57.
[0034]
Further, as shown in FIG. 7 (detailed description of portions common to FIG. 1 is omitted), a normal diode 127 may be used instead of the boosting control FET as the boosting rectifier. In this case, since the back electromotive force current cannot pass through the diode 127, the provision of the back electromotive force passage branch path 126 is indispensable for securing a current return path to the battery 57.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a first embodiment of an electric power steering device of the present invention.
FIG. 2 is a circuit diagram illustrating an example of a DC-DC converter included in a vehicle-mounted power supply.
FIG. 3 is an explanatory diagram of an operation of a three-phase brushless motor constituting the assist motor.
FIG. 4 is a circuit diagram showing an example of a switching driver for driving the three-phase brushless motor of FIG.
FIG. 5 is a diagram showing a cross-sectional structure of a MOSFET and its equivalent circuit including a parasitic diode.
FIG. 6 is a circuit diagram showing a second embodiment of the electric power steering device of the present invention.
FIG. 7 is a circuit diagram showing a third embodiment of the electric power steering device of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electric power steering device 2 Steering handle 3 Steering shaft 6 Assist motor 18 Switching driver 57 In-vehicle battery (motor drive power supply)
110 Steering control unit (microcomputer, branch path side switch unit control means 120 Step-up circuit 121 Coil 122 Step-up switching unit 123 Step-up control FET (step-up rectifier)
124 Capacitor 126 Branch path 127 for passing back electromotive force Diode (branch path side rectifier)
129,130 Voltage dividing resistor (cathode side voltage detector)
131 Load resistance 150 DC on-board power supply 157 DC-DC converter 223 Diode (rectifier for boosting)

Claims (8)

In the electric power steering device, the rotation of the steering shaft is assisted by the driving force of the assist motor, and the assist motor is rotationally controlled so as to obtain a steering angle corresponding to the operation angle of the steering handle. ,
A booster circuit that boosts a power supply voltage from a motor drive power supply to generate a motor drive voltage; and switches the motor drive voltage from the booster circuit to the assist motor while switching the motor drive voltage, thereby rotating the assist motor. Switching driver to perform
The booster circuit includes a capacitor for holding and smoothing an output voltage of the booster circuit, a booster rectifier for preventing backflow discharge of the capacitor to the booster circuit input side, and an upper stage than the booster rectifier. A coil that receives the power supply voltage, and a boosting switching unit that generates a boosted induction voltage waveform by intermittently changing a passing current of the coil, A step-up DC-DC converter configured to superimpose on an input voltage waveform and output as the motor drive voltage while smoothing by the capacitor via the boosting rectifying unit;
A back electromotive force passing branch path is provided to pass the back electromotive force current of the assisting motor toward the booster circuit side via the switching driver, bypassing the boosting rectifier. Electric power steering device. 2. The electric power steering apparatus according to claim 1, further comprising a passing current adjusting unit that adjusts an amount of current passing through the branch path for passing back electromotive force in accordance with a voltage on the cathode side of the step-up rectifier. 3. A back electromotive force passing switch unit that switches between passing and blocking of the back electromotive force current through the back electromotive force passing branch path;
A cathode-side voltage detector that detects a cathode-side voltage of the step-up rectifier,
When the detected voltage of the cathode-side voltage detection section exceeds a predetermined reference voltage, the control section has a back electromotive force passing switch section control means for switching the back electromotive force passing switch section from a cut-off state to a passage permitting state. The electric power steering device according to claim 1. The electric power steering apparatus according to any one of claims 1 to 3, wherein a load resistance that consumes energy of the passing back electromotive force current is provided on the back electromotive force passage branch path. The electric power steering apparatus according to any one of claims 1 to 4, wherein the back electromotive force passage branch path is a bypass path that bypasses a cathode side and an anode side of the step-up rectifier. 6. The electric power steering apparatus according to claim 5, wherein the motor drive power source is a vehicle-mounted battery, and the energy of the back electromotive force current is returned to the vehicle-mounted battery via the bypass path. The motor drive power supply includes an AC converter that converts the DC output of the DC vehicle-mounted power supply into an AC, a transformer that transforms the AC-converted vehicle-mounted power supply voltage for output, and a rectifier that rectifies a secondary-side AC output of the transformer. And a DC-DC converter having a
6. The electric power steering device according to claim 5, wherein a load resistor for consuming energy of the passing back electromotive force current is provided on the bypass path. The step-up rectification unit is a parasitic diode of a step-up control FET disposed on a path from an input unit to an output unit of the step-up circuit, and the step-up control FET has a phase inversion with the step-up switching unit. The electric power steering apparatus according to any one of claims 1 to 7, wherein the electric power steering apparatus is turned on and off in synchronization.

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