JP2009120086A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric steering device, in which short-time steering assist is possible even after a battery has failed. <P>SOLUTION: A backup power 11 is connected in parallel with the battery 7, and an auxiliary power source 12 is serially connected to these to compose a three power source constitution. When failure of the battery 7 is detected based on voltage detected by a voltage detector 27, power is fed to a motor 4 from the backup power source 11 and the auxiliary power source 12 which are serially connected to each other, and control power voltage Vcc is fed from the backup power source 11 to a control circuit 23. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that generates a steering assist force by a motor, and more particularly to a configuration of an electric circuit thereof.

  The electric power steering device is a device that generates a steering assist force by a motor in accordance with a driver's steering torque. In recent years, the demand for electric power steering devices for large vehicles has increased rapidly, and the steering assist force required for such large vehicles has also increased. Therefore, more power must be supplied to the motor. However, there are cases where such a large amount of power cannot be adequately provided by using only the battery as the main power source. Therefore, an auxiliary power source for secondary batteries is provided separately from the battery. Usually, only the battery can be used. When a larger amount of power is required, the battery and auxiliary power source are connected in series to supply power from both power sources. Has been proposed (see, for example, Patent Document 1).

Japanese Patent Laying-Open No. 2005-287222 (FIG. 1)

In the conventional electric power steering apparatus as described above, when the battery fails (fails), power is insufficient with only the auxiliary power source, and sufficient steering assistance cannot be performed. If the steering assistance cannot be performed, the steering wheel operation becomes heavy, and it is not easy to retract the vehicle to a safe place.
In view of such a conventional problem, an object of the present invention is to provide an electric power steering device capable of assisting steering for a short time even if a battery fails.

  The present invention relates to an electric power steering device that generates a steering assist force by a motor, a battery that supplies electric power to the motor as a main power source, a backup power source connected in parallel with the battery, the battery and the backup power source An auxiliary power source connected in series to the parallel body of the power source and capable of supplying power to the motor, a detector for detecting the output of the battery, and charging the auxiliary power source based on the battery A first output state in which power is supplied to the motor by the output voltage of the battery; and a first output state in which power is supplied to the motor by an output voltage in a state where the auxiliary power source is connected in series to the battery or backup power source. A charge / discharge circuit that selectively configures two output states, and an output state of the charge / discharge circuit according to a required steering assist force And when the failure of the battery is detected based on the detection result of the detector, the second output state is selected, and the auxiliary power source is connected in series to the backup power source. A control circuit for supplying electric power to the motor with the output voltage, and a control power supply circuit for supplying a control power supply voltage to each of the control circuits from both the battery and the backup power supply.

  In the electric power steering apparatus configured as described above, the control circuit connects the backup power supply and the auxiliary power supply in series by selecting the second output state of the charge / discharge circuit when detecting a failure of the battery. Power is supplied to the motor from the power supply. Therefore, even if the battery breaks down, it is possible to maintain the operation of the electric power steering by generating the necessary steering assist force by the backup power source and the auxiliary power source for a short time. Even if the battery voltage is lost, the control power supply voltage is supplied from the backup power supply.

Further, the electric power steering apparatus can be designed to be 2000 to 4000 joules when the energy of the auxiliary power source is added to the energy of the backup power source.
In this case, even when the battery breaks down, it is possible to generate the steering assist force necessary for retracting the vehicle to a safe place. Further, by using the backup power source and the auxiliary power source at the same time, it is not necessary for the backup power source to have this energy alone. That is, as compared with the case where the backup power supply has this energy alone, the energy burden of the backup power supply becomes lighter, resulting in lower costs.

In the electric power steering apparatus, the + side circuit of the battery and the + side circuit of the backup power source are connected to each other via a switch that can be opened and closed, and the control circuit switches the switch when the battery fails. You may comprise so that it may open.
In this case, the control power supply voltage can be supplied from the backup power supply by opening the switch when the battery fails, thereby eliminating the influence of the failed battery.

  According to the electric power steering apparatus of the present invention, even if the battery breaks down, it is possible to maintain the operation of the electric power steering by generating the necessary steering assist force by the backup power source and the auxiliary power source for a short time. it can. Further, by using the backup power source and the auxiliary power source at the same time, the energy that each power source should have can be suppressed. On the other hand, even if the voltage of the battery is lost, the control power supply voltage can be supplied from the backup power supply, and the operation of the control circuit is also guaranteed.

  FIG. 1 is a circuit diagram illustrating a configuration mainly including an electric circuit of an electric power steering apparatus 1 according to an embodiment of the present invention. In the figure, a steering device 2 is driven by a driver's steering torque applied to a steering wheel (handle) 3 and a steering assist force generated by a motor 4. A reduction gear (not shown) is used for power transmission from the rotor 4 r of the motor 4 to the steering device 2. The motor 4 is a three-phase brushless motor and is driven by a motor drive circuit 5. The motor drive circuit 5 is formed by connecting MOS-FETs 51 to 56 constituting a three-phase bridge circuit and a resistor 57 as shown in the figure. The MOS-FETs 51 to 56 are switched by a gate drive circuit (FET driver) 6.

  The battery 7 supplies power to the motor drive circuit 5 as a main power source. A reactor 26 is connected in series to the battery 7, and a voltage detector 27 is connected to the reactor 26 in parallel. Reactor 26 is provided as a low-resistance element that causes a voltage drop proportional to the current flowing through battery 7. However, the resistance value is very small. Therefore, the voltage drop as seen from the normal voltage of the battery 7 is negligibly small. The reactor 26 and the voltage detector 27 constitute a detector 28 that detects the output (current) of the battery 7.

  The voltage from the battery 7 through the reactor 26 is guided to the motor drive circuit 5 and the motor 4 through electric paths L1 and L3 in which the relay contact 8, the MOS-FET 9 and the reactor 10 are inserted. The MOS-FET 9 is an N channel, and is connected so that the source is on the battery 7 side and the drain is on the motor drive circuit 5 side. Further, the parasitic diode 9d is configured such that a current flows in the forward direction when power is supplied from the battery 7 to the motor 4.

The backup power source 11 is composed of an electric double layer capacitor or a lithium ion battery, and is in a state where it can be connected in parallel with the battery 7. Strictly speaking, it is not “in parallel with the battery 7” but “in parallel with the battery 7 and the reactor 26 connected in series with each other”, but as described above, the voltage drop in the reactor 26 is Since it is small, it can be understood that the backup power supply 11 is substantially connected in parallel with the battery 7.
Further, the + side electric circuit LB of the battery 7 and the + side electric circuit (electric circuit L1) of the backup power source 11 are connected to each other via a relay contact 8 as a switch that can be opened and closed.

  The auxiliary power source 12 is composed of an electric double layer capacitor or a lithium ion battery, and is connected in series with a parallel body of the battery 7 and the backup power source 11. The high potential side electric circuit L2 of the auxiliary power source 12 is connected to a connection point between the drain of the MOS-FET 9 and the reactor 10 through the MOS-FET 13. The output voltage (voltage of the electric circuit L2) in a state where the battery 7 and the auxiliary power supply 12 are connected in series with each other passes through the electric circuits L2 and L3 in which the MOS-FET 13 and the reactor 10 are inserted, and then the motor drive circuit 5 and the motor 4 Led to. The MOS-FET 13 is an N channel, and is connected so that the source is on the motor drive circuit 5 side and the drain is on the auxiliary power supply 12 side. Further, the parasitic diode 13d is in a direction opposite to the direction in which current flows when power is supplied from the battery 7 and the auxiliary power supply 12 to the motor 4.

  A booster circuit (bootstrap circuit) 14 is connected to the electric circuit L1 to which the voltage from the battery 7 is applied, and the output voltage is applied to the gate drive circuits 6 and 15. The gate drive circuit 15 drives the MOS-FETs 9 and 13 so that they are alternately turned on. A smoothing electrolytic capacitor 16 is connected to the motor drive circuit 5 in parallel.

  On the other hand, the anode of the diode 18 is connected to the electric circuit L <b> 1 through the reactor 17. The cathode of the diode 18 is connected to the high potential side electric circuit L <b> 2 of the auxiliary power source 12. A P-channel MOS-FET 19 is provided between the anode of the diode 18 and the ground-side electric circuit LG. The MOS-FET 19 is driven by the gate drive circuit 20. The charging circuit 100 of the auxiliary power source 12 is configured by these elements (17 to 20).

  In addition, the discharge circuit 200 including the MOS-FETs 9 and 13 constitutes a charge / discharge circuit 300 together with the charging circuit 100 described above. The charging / discharging circuit 300 charges the auxiliary power supply 12 based on the battery 7, and supplies the power to the motor 4 by the output voltage of the battery 7, and the auxiliary power supply 12 to the battery 7 or the backup power supply 11. The second output state in which electric power is supplied to the motor 4 by the output voltage in a state where the two are connected in series is selectively configured.

  The voltage from the battery 7 becomes the control power supply Vcc via the diode 21. Further, the voltage of the backup power supply 11 also becomes the control power supply Vcc via the diode 22. In this way, the control power supply circuit 400 having two power supplies is configured. When the relay contact 8 is closed, the battery 7 and the backup power supply 11 are parallel to each other, and both contribute to the provision of the control power supply Vcc, but when the relay contact 8 is open, the battery 7 And the backup power supply 11 can provide the control power supply Vcc independently of each other.

  The motor drive circuit 5, the gate drive circuits 6, 15, 20, and the relay contact 8 operate in response to a command signal from a control circuit 23 including a microcomputer. The control circuit 23 receives an output signal from a torque sensor 24 that detects a steering torque applied to the steering wheel 3. An output signal from the vehicle speed sensor 25 that detects the vehicle speed is input to the control circuit 23. The motor 4 is provided with an angle sensor 31 that detects the rotational angle position of the rotor 4 r, and an output signal thereof is input to the control circuit 23.

A voltage detector 27 connected in parallel to the reactor 26 detects a voltage V _B proportional to the current flowing through the battery 7 and inputs the output signal (battery current detection signal) to the control circuit 23. Since the sign of the voltage V _B is reversed between when the current flows out from the battery 7 and when it flows in, the direction can be detected together with the magnitude of the current.
On the other hand, a voltage detector 29 is connected to the backup power source 11 and a voltage detector 30 is connected to the auxiliary power source 12 in parallel. The voltage detector 29 connected in parallel to the backup power supply 11 detects the voltage V1 of the parallel power supply of the battery 7 and the backup power supply 11 and inputs the output signal to the control circuit 23. The voltage detector 30 connected in parallel to the auxiliary power source 12 detects the voltage (inter-terminal voltage) V <b> 2 of the auxiliary power source 12 and inputs the output signal to the control circuit 23.

Based on the steering torque signal sent from the torque sensor 24, the vehicle speed signal sent from the vehicle speed sensor 25, and the rotor angular position signal sent from the angle sensor 31, the control circuit 23 performs appropriate steering assistance. In order to generate a force, the motor drive circuit 5 is operated through the gate drive circuit 6 to drive the motor 4.
The relay contact 8 is normally turned on (closed) by a command signal from the control circuit 23. Therefore, the voltage from the battery 7 is applied to the electric circuit L1, and the backup power supply 11 can be always charged.

  On the other hand, when the MOS-FET 19 is in the ON state, a current flows from the battery 7 through the reactor 17 and the MOS-FET 19. When the MOS-FET 19 is turned off from this state, a reverse high voltage is generated in the reactor 17 so as to prevent the magnetic flux change due to the current interruption, whereby the diode 18 is a voltage obtained by boosting the output voltage of the battery 7. The auxiliary power supply 12 is charged via Therefore, the auxiliary power supply 12 can be charged by repeatedly turning on and off the MOS-FET 19. The control circuit 23 monitors the voltage V <b> 2 of the auxiliary power supply 12, and when it does not reach a certain voltage, the MOS-FET 19 is turned on / off via the gate drive circuit 20 to charge the auxiliary power supply 12. This charging is performed, for example, when the torque sensor 24 does not detect the steering torque.

  Further, the control circuit 23 estimates a required power for obtaining a required steering assist force based on the steering torque and the vehicle speed, and compares this with a reference value. When the required power is below the reference value, the control circuit 23 turns on the MOS-FET 9 and turns off the MOS-FET 13 (first output state of the charge / discharge circuit 300). Accordingly, the voltage from the battery 7 is smoothed by the smoothing capacitor 16 and supplied to the motor drive circuit 5. The motor drive circuit 5 drives the motor 4 based on the control signal from the control circuit 23. In this case, the power of the auxiliary power supply 12 is not supplied to the motor drive circuit 5. The on-resistance of the N-channel MOS-FET 9 is much smaller than the forward resistance of the parasitic diode 9d (for example, about 1 mΩ), so that most of the current flowing from the battery 7 to the motor drive circuit 5 is from the source to the drain. The current flowing through the parasitic diode 9d is small.

  On the other hand, when the required power exceeds the reference value, that is, when the required power cannot be covered by the battery 7 alone, the control circuit 23 turns off the MOS-FET 9 and turns on the MOS-FET 13 (charge / discharge circuit). 300 second output state). As a result, the output voltage is supplied to the motor drive circuit 5 with the battery 7 and the auxiliary power supply 12 connected in series with each other. As a result, a large amount of power exceeding the power that can be output from only the battery 7 can be supplied to the motor drive circuit 5. At this time, since the cathode of the parasitic diode 9d of the MOS-FET 9 is at a higher potential than the anode, that is, a reverse voltage, current from the auxiliary power supply 12 to the battery 7 is prevented.

In this way, control is performed to select either the battery 7 alone or the battery 7 + auxiliary power supply 12 according to the required power.
Note that power can be supplied to the motor 4 also from the backup power supply 11 in parallel with the battery 7, but since the discharged charge is immediately replenished from the battery 7, as long as the battery 7 is normal. Eventually, the battery 7 bears.

Next, failure determination of the battery 7 will be described with reference to the flowchart of FIG. This flowchart shows an example of a process for determining whether or not the battery 7 has failed, and the control circuit 23 repeatedly executes this process. First, in step S1, the control circuit 23 obtains the rotational speed ω [rad / sec] of the motor 4 (rotor 4r) by differentiating the angular position signal input from the angle sensor 31 with respect to time, and this is measured in advance. The counter electromotive force V _G is calculated by multiplying the counter electromotive voltage constant Ke obtained as described above. That is, V _G = Ke · ω.

After the calculation, the control circuit 23 determines whether or not the back electromotive force V _G is equal to or less than a predetermined value (step S2). When the motor 4 is rotating at high speed, the counter electromotive force exceeds the voltage of the battery 7 and the current due to the counter electromotive force may flow (reverse) into the battery 7, but this is not abnormal. Therefore, in such a case, it is necessary to set an appropriate predetermined value lower than the voltage of the battery 7 so that the failure determination is not performed. Therefore, the control circuit 23, when the counter electromotive force V _G exceeds the predetermined value terminates the determination process (to cancel), on the other hand, if it is less than a predetermined value is output from the voltage detector 27 The voltage V _B is read (step S3).

Next, the control circuit 23 determines whether or not a backflow current exceeding a predetermined value (regardless of the predetermined value in step S2) flows through the battery 7 from the magnitude and sign of the voltage V _B (step S4). . This predetermined value is set by estimating or actually measuring a current value when a current flows from outside the battery due to a failure of the battery 7. If the magnitude of the backflow current is equal to or less than the predetermined value, the determination process ends. If the magnitude of the reverse current exceeds the predetermined value, the control circuit 23 determines that the battery 7 has failed and performs the process when the battery fails. (Step S5).

  Specifically, the control circuit 23 turns off the relay contact 8 (open). At this time, the control power supply voltage Vcc is not supplied from the failed battery 7 but is supplied from the backup power supply 11 to be provided to the control circuit 23 and other circuit elements that require the control power supply voltage Vcc. Control power supply voltage Vcc is maintained.

  If the relay contact 8 remains closed when the battery 7 fails, the potential of the electric circuit LB whose voltage has dropped affects the control power supply voltage Vcc, and the backflow from the backup power supply 11 to the battery 7 occurs. Current continues to flow. However, by opening the relay contact 8 when the battery 7 fails, the influence of the failed battery 7 can be quickly eliminated and the control power supply voltage Vcc can be reliably supplied from the backup power supply 11.

  Further, the control circuit 23 turns off the MOS-FET 9 and turns on the MOS-FET 13 (second output state of the charge / discharge circuit 300) upon detection of a battery failure. As a result, electric power is supplied to the motor 4 by the output voltage when the auxiliary power supply 12 is connected in series to the backup power supply 11. Thereby, even if the battery 7 loses voltage, if it is a short time, electric power required for the motor 4 can be supplied. Therefore, even when the battery 7 breaks down, it is possible to generate the steering assist force necessary to retract the vehicle to a safe place.

  As described above, according to the electric power steering apparatus 1 according to the present embodiment, the control circuit 23 selects the second output state of the charging / discharging circuit 300 when detecting a failure of the battery 7, thereby performing backup. Electric power is supplied to the motor 4 by the output voltage in a state where the auxiliary power source 12 is connected in series with the power source 11. Therefore, even if the battery 7 fails, the operation of the electric power steering 1 can be maintained by generating a necessary steering assist force by the backup power source 11 and the auxiliary power source 12 for a short time. Further, by using the backup power supply 11 and the auxiliary power supply 12 at the same time, the energy that each power supply should have can be suppressed. On the other hand, even if the voltage of the battery 7 is lost, the control power supply voltage Vcc can be supplied from the backup power supply 11, and the operation of the control circuit 23 is also guaranteed.

  Further, since the backup power source 11 and the auxiliary power source 12 are used at the same time, it is sufficient that these two power sources have energy necessary for steering assistance. In other words, the backup power source 11 does not need to have this energy alone, and may be provided in combination with the energy of the auxiliary power source 12. Therefore, as compared with the case where the backup power supply 11 is provided with this energy alone, the energy burden of the backup power supply 11 is reduced, and as a result, the cost is reduced.

  Specifically, when the energy of the auxiliary power supply 12 is added to the energy of the backup power supply 11, the capacity is selected so as to be 2000 to 4000 joules, so that the vehicle is safe even if the voltage of the battery 7 is lost. A steering assist force necessary for retreating to a place can be generated. The numerical value of energy to be selected within this range varies depending on the vehicle. For example, if the energy that generates the steering assist force necessary to retreat a vehicle to a safe place is 3000 joules, the energy of the backup power supply 11 is 2000 joules, and the energy of the auxiliary power supply 12 is 1000 joules. A configuration can be selected. Therefore, as compared with the case where the backup power supply 11 alone bears the total energy, the energy burden of the backup power supply 11 is greatly reduced, resulting in lower costs.

  In the control power supply circuit 400 of the above-described embodiment, the relay contact 8 is used as a switch that can be controlled to open and close, but instead, a semiconductor switching element such as a MOS-FET can be used.

  In the above embodiment, when determining whether or not to use the auxiliary power supply 12 to supply power to the motor 4, the control circuit 23 estimates the required power for obtaining the required steering assist force, Is compared with the reference value, but other ways of determination are possible. For example, the current supplied to the motor drive circuit 5 changes according to the steering assist force required by the assist control by the control circuit 23, the gate drive circuit 6 and the motor drive circuit 5. Therefore, when the voltage of the battery 7 and the current supplied to the motor drive circuit 5 are actually detected and multiplied to obtain the current value of the power, the current value is supplied from the battery 7 alone. Power may be supplied only from the battery 7 if the power is below the maximum power, and power may be supplied from a series power supply of the battery 7 and the auxiliary power supply 12 if the maximum power is exceeded.

1 is a circuit diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a flowchart which shows the failure determination process of a battery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 4 Motor 7 Battery 8 Relay contact 11 Backup power supply 12 Auxiliary power supply 23 Control circuit 28 Fault detector 300 Charging / discharging circuit (charging circuit 100, discharging circuit 200)
400 Control power circuit

Claims (3)

An electric power steering device that generates a steering assist force by a motor,
A battery for supplying power to the motor as a main power source;
A backup power source connected in parallel with the battery;
An auxiliary power source connected in series to the parallel body of the battery and the backup power source and capable of supplying power to the motor;
A detector for detecting the output of the battery;
A first output state in which the auxiliary power source is charged based on the battery and power is supplied to the motor by the output voltage of the battery, and the auxiliary power source is connected in series to the battery or backup power source A charge / discharge circuit that selectively configures a second output state for supplying power to the motor by an output voltage at
While selecting the output state of the charge / discharge circuit according to the necessary steering assist force, and when detecting a failure of the battery based on the detection result of the detector, select the second output state, A control circuit for supplying electric power to the motor by an output voltage in a state where the auxiliary power supply is connected in series to the backup power supply;
A control power supply circuit that supplies a control power supply voltage to each of the control circuits from both the battery and the backup power supply.   2. The electric power steering apparatus according to claim 1, wherein the energy of the auxiliary power source is added to the energy of the backup power source to be 2000 to 4000 joules. 3.   The positive side circuit of the battery and the positive side circuit of the backup power supply are connected to each other via a switch that can be controlled to open and close, and the control circuit opens the switch when the battery fails. Electric power steering device.

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