JP2009078742A - Control device of steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of a steering device capable of discharging large power over a comparatively prolonged period of time, and responding to a request of instantaneously large current. <P>SOLUTION: The control device of a steering device is equipped with a main power source 4 which supplies the power to a motor 1m of a steering device 1s of a vehicle, an electric double-layer capacitor 9a and a secondary battery 9b capable of supplying the power to the motor 1m, and a control circuit 15 which is constituted so as to use the electric double-layer capacitor 9a when the power required for a steering assist of the steering device 1s is larger than a second threshold value, and use the secondary battery 9b when the power is not larger than the second threshold value and larger than the first threshold value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for a steering device. More specifically, the present invention relates to a control device in a steering device that uses the driving force of an electric motor.

An electric power steering device mounted on a vehicle such as an automobile needs to pass a larger current through the motor as the required steering assist force is larger. Therefore, power is usually supplied to the motor from the in-vehicle battery, which is the main power source. However, when the terminal voltage of the main power source decreases due to an increase in load such as when entering the garage or parking, the auxiliary power previously stored is stored. A configuration has been proposed in which power is supplied from a power source to reduce the burden on the main power source (see, for example, Patent Document 1).
Patent Document 1 describes that a secondary battery such as a lithium ion battery or a nickel cadmium battery, a capacitor, or an electric double layer capacitor can be used as an auxiliary power source.

JP 2003-320942 A

  By the way, among the auxiliary power sources described above, secondary batteries such as lithium ion batteries and nickel cadmium batteries have a high energy density and can pass a current for a relatively long time, but are required for current electric power steering devices. Therefore, if a required output current is obtained, the capacity becomes very large. On the other hand, an electric double layer capacitor can pass a large current because of no chemical change as in a secondary battery, but its energy density is very small compared to a secondary battery (for example, approximately the same as a lithium ion battery). High output cannot be sustained. For this reason, if a predetermined output is to be obtained continuously, a large capacity is required.

  The present invention has been made in view of such circumstances, and is a steering device that can discharge a large output over a relatively long period of time and can meet an instantaneous large current demand. The object is to provide a control device.

A control device for a steering device according to a first aspect of the present invention (hereinafter also simply referred to as a “control device”) includes a main power source that supplies power to a motor of a steering device of a vehicle,
An electric double layer capacitor and a secondary battery capable of supplying electric power to the motor;
An electric double layer capacitor is used when the power required for steering assist of the steering device is greater than a second threshold, and a secondary battery is used when the power is less than or equal to the second threshold and greater than the first threshold. And a control circuit configured as described above (claim 1).

  The control device according to the first aspect of the present invention includes an electric double layer capacitor and a secondary battery having different characteristics as an auxiliary power source, and uses both according to the required characteristics of the electric power steering apparatus. . That is, the electric double layer capacitor is used when the power required for steering assist of the steering device is larger than the second threshold, and the secondary battery is used when the power is equal to or lower than the second threshold and larger than the first threshold. Thus, the assist duration time can be ensured and the instantaneous large current discharge can be dealt with. In order to achieve the assist duration and instantaneous high current discharge with either a double layer capacitor or a secondary battery, a very large capacity is required, which is not preferable from the viewpoint of space saving and cost saving. By separately using the double layer capacitor and the secondary battery according to the required current (electric power) of the electric power steering device, it is possible to save space and cost of the auxiliary power supply.

A control device for a steering device according to a second aspect of the present invention includes a main power source that supplies power to a motor of a steering device for a vehicle,
An electric double layer capacitor and a secondary battery capable of supplying electric power to the motor;
An electric double layer capacitor and a secondary battery are used together when the power required for steering assist of the steering device is greater than a second threshold, and secondary when the power is less than or equal to the second threshold and greater than the first threshold. And a control circuit configured to use a battery (claim 2).

  Similarly to the control device according to the first aspect, the control device according to the second aspect of the present invention includes an electric double layer capacitor and a secondary battery, and both of them are matched to the required characteristics of the electric power steering device. I use it. That is, the electric double layer capacitor and the secondary battery are used together when the power required for steering assist of the steering device is larger than the second threshold, and when the power is less than the second threshold and larger than the first threshold, Since the secondary battery is used, the assist duration can be ensured and the instantaneous large current discharge can be dealt with. Further, like the control device according to the first aspect, space saving and cost saving of the auxiliary power source can be achieved.

  The secondary battery is preferably a lithium ion battery. In this case, a larger current can be passed as compared to other secondary batteries such as a nickel cadmium battery.

  According to the control device for a steering device of the present invention, it is possible to discharge a large output for a relatively long time, and it is also possible to cope with an instantaneous large current demand.

Hereinafter, embodiments of a control device of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a circuit diagram of a control device 2 of an electric power steering device 1 according to an embodiment of the present invention. In the figure, a steering assist force is applied to a vehicle steering device 1s by a motor 1m. More specifically, the motor 1m is driven and controlled according to the output (steering torque) of a torque sensor such as a torsion bar type attached to a steering shaft (not shown) of the steering device 1s, and the steering shaft or steering gear (rack) Assist to pinion, rack shaft, etc. The motor drive circuit 3 supplies power to the motor 1m.

  The main power supply 4 is composed of an in-vehicle battery 4b and an alternator 4a, and a diode 6 is provided in the middle of a non-grounded electric circuit 5 that guides the main power supply 4 to the motor drive circuit 3. . A smoothing electrolytic capacitor 8 is provided between the cathode of the diode 6 and the ground side electric circuit 7.

  On the other hand, the auxiliary power source 9 is composed of two auxiliary power sources 9a and 9b connected in parallel to each other. One auxiliary power source 9a is composed of an electric double layer capacitor (capacitor), and the other auxiliary power source 9b is It is composed of a lithium ion battery (secondary battery). The auxiliary power supplies 9a and 9b are connected in series to the main power supply 4, respectively. The power supply circuit (high potential side circuit) 10 of the auxiliary power supplies 9 a and 9 b is connected to the motor drive circuit 3 via the discharge control circuit 11. The discharge control circuit 11 includes a MOS-FET 11a and a PWM voltage source 11b. The discharge current can be controlled by PWM controlling the gate voltage. The anode of the diode 13 is connected to the low potential side of the auxiliary power supplies 9a and 9b via the reactor 12, and the cathode of the diode 13 is connected to the power supply circuit 10 of the auxiliary power supplies 9a and 9b. In addition, a MOS-FET 14 is provided between the anode of the diode 13 and the ground-side electric circuit 7. The protective diode 14d is connected in parallel to or built in the MOS-FET 14. The gate of the MOS-FET 14 is driven by the gate drive circuit 20.

Switching means 30a and 30b are respectively arranged between the auxiliary power supplies 9a and 9b and the non-grounded electric circuit 5, and these switching means 30a and 30b are opened and closed independently from each other by a control circuit described later. Be controlled. The switch means 30a and 30b are normally set to “closed” (when the auxiliary power supply is not used).
A current detector 31 for detecting a discharge current from the auxiliary power supplies 9a and 9b is disposed in the power feeding circuit 10. In addition, voltage detectors 32a and 32b for detecting the voltage between the terminals of the auxiliary power supplies 9a and 9b are provided. Each signal from the current detector 31 and the voltage detectors 32 a and 32 b is transmitted to the control circuit 15.

  The motor drive circuit 3, the discharge control circuit 11 and the gate drive circuit 20 operate in response to a command signal from the control circuit 15. The control circuit 15 is adapted to receive information on the steering torque of the steering wheel by the driver and the vehicle speed, and the control circuit 15 generates appropriate steering assist force in accordance with the information. The motor 1m is driven.

  When the MOS-FET 14 is in the on state, current flows from the alternator 4a through the reactor 12 and the MOS-FET 14, but when the MOS-FET 14 turns off, a high voltage is applied to the reactor so as to prevent magnetic flux change due to current interruption. Thus, the auxiliary power supply 9 is charged with a voltage obtained by boosting the output of the alternator 4a. In this way, the auxiliary power supply 9 can be charged by repeatedly turning on and off the MOS-FET 14.

  In the above configuration, when the required steering assist force is relatively small, the control circuit 15 turns off the discharge control circuit 11. Therefore, the voltage of the main power supply 4 is smoothed by the smoothing capacitor 8 and then supplied to the motor drive circuit 3. The motor drive circuit 3 drives the motor 1 m based on the control signal from the control circuit 15. On the other hand, the voltage of the auxiliary power supply 9 is not supplied to the motor drive circuit 3.

  Further, when the required steering assist force is relatively large and cannot be covered by the main power supply 4 alone, the control circuit 15 turns on the discharge control circuit 11. As a result, the current defined by the discharge control circuit 11 is supplied to the motor drive circuit 3 based on the voltage of the main power supply 4 and the auxiliary power supply 9 in series with each other.

  In the present embodiment, an auxiliary power source 9a composed of an electric double layer capacitor having different characteristics and an auxiliary power source 9b composed of a secondary battery are used as the auxiliary power source 9. The electric double layer capacitor can pass a large current as much as the secondary battery is not accompanied by a chemical change. However, the energy density is very small compared to the secondary battery, and a large output cannot be maintained. On the other hand, since the secondary battery has a high energy density, it can flow a current for a relatively long time, but cannot flow a large current required for the current electric power steering device.

  Therefore, in the present embodiment, attention is paid to the characteristics of the electric double layer capacitor and the secondary battery, and both are used in accordance with the required characteristics of the electric power steering device. Specifically, two threshold values are set for the electric power for steering assistance, and an electric double layer capacitor is used when the electric power required for the steering assistance of the steering device is larger than the second threshold value. A secondary battery is used when it is below the threshold and greater than the first threshold.

FIG. 2 shows the relationship between time and power consumption when a certain steering operation is performed in the electric power steering apparatus. When the power consumption is equal to or less than the first threshold Th1, as described above, the control circuit 15 turns off the discharge control circuit 11, and only the main power supply 4 supplies power to the motor drive circuit 3. When the power consumption is greater than the first threshold Th1 and less than or equal to the second threshold Th2, the control circuit 15 turns on the discharge control circuit 11 and “opens” the switch means 30a. Thereby, electric power is supplied to the motor drive circuit 3 from the main power supply 4 and the auxiliary power supply (lithium ion battery) 9b. Further, when the power consumption is greater than the second threshold Th2, the control circuit 15 turns on the discharge control circuit 11, and “closes” the switch means 30a and “opens” the switch means 30b. Thereby, electric power is supplied to the motor drive circuit 3 from the main power supply 4 and the auxiliary power supply (electric double layer capacitor) 9a.
As a result, it is possible to secure the assist duration and to deal with an instantaneous large current discharge (portion shown by double hatching in FIG. 2).

  In the above embodiment, when the power consumption is larger than the second threshold Th2, the switch means 30a is “closed” and the switch means 30b is “open”, so that the main power supply 4 and the auxiliary power supply (electric double layer capacitor) 9a. Although the power is supplied to the motor drive circuit 3 from the main power supply 4 and the auxiliary power supplies 9a and 9b, the power can be supplied to the motor drive circuit 3 by closing both the switch means 30a and 30b. .

  In the present embodiment, the voltage detectors 32a and 32b detect the voltages between the terminals of the auxiliary power supplies 9a and 9b, and a failure of the auxiliary power supplies 9a and 9b is detected by an abnormality (abrupt decrease, etc.) of this voltage. It is configured to be able to. And it is comprised so that electric power may be supplied from the auxiliary power supply except the auxiliary power supply by which the failure was detected by the voltage detector which is a failure detection means. Thereby, the output fall at the time of failure can be suppressed to the minimum. The detection of the failure can be performed, for example, by sequentially closing only one of the switch means 30a and 30b by the control circuit 15.

  As the secondary battery, a nickel cadmium battery can be used instead of the lithium ion battery. However, it is preferable to use a lithium ion battery from the viewpoint that a large current can flow.

It is a circuit diagram of one embodiment of a control device of the present invention. It is a figure which shows the relationship between time and power consumption at the time of performing a certain steering in an electric power steering device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 1s Steering apparatus 1m Motor 2 Control apparatus 3 Motor drive circuit 4 Main power supply 4a Alternator 4b In-vehicle battery 9a Auxiliary power supply (electric double layer capacitor)
9b Auxiliary power supply (lithium ion battery)
15 Control circuit 30 Switch means 31 Current detector 32 Voltage detector

Claims (3)

A main power source for supplying electric power to a motor of a vehicle steering device;
An electric double layer capacitor and a secondary battery capable of supplying electric power to the motor;
An electric double layer capacitor is used when the power required for steering assist of the steering device is greater than a second threshold, and a secondary battery is used when the power is less than or equal to the second threshold and greater than the first threshold. A control device for a steering device, comprising: a control circuit configured as described above. A main power source for supplying electric power to a motor of a vehicle steering device;
An electric double layer capacitor and a secondary battery capable of supplying electric power to the motor;
An electric double layer capacitor and a secondary battery are used together when the power required for steering assist of the steering device is greater than a second threshold, and secondary when the power is less than or equal to the second threshold and greater than the first threshold. A control device for a steering device, comprising: a control circuit configured to use a battery.   The control device for a steering apparatus according to claim 1, wherein the secondary battery is a lithium ion battery.

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