JP2009154677A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of suppressing power consumption of a relay without impairing the sufficient contact state of a contact. <P>SOLUTION: In the electric power steering device, the contact 9c of the relay 9 is interposed on an electric passage for feeding electric power to a motor 4. A relay coil 9s is excited using a switching element such as FET 12. A control part 1 (relay control part 1R) drives the FET 12 by a pulse width modulation signal, determines a bounce time of the contact 9c by detecting a voltage at a load side of the contact 9c at action of the relay 9, and varies duty of the pulse width modulation signal according to the bounce time. <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 steering torque generated in a steering shaft. Such motor control of the electric power steering apparatus is mainly performed by a CPU and an electronic circuit. However, when a failure occurs in any member related to motor control, a relay contact is inserted in the power supply circuit to the motor in order to reliably stop power supply and ensure safety ( For example, see Patent Document 1.)

  When the electric power steering apparatus is operating normally, the relay is always excited to close the contact, and a current of several hundred milliamperes continues to flow through the relay coil. Therefore, the electric power stored in the battery is consumed.

JP 2006-182166 A (FIG. 1)

The power consumption as described above is desired to be suppressed as much as possible from the viewpoint of energy saving in the recent increase in the number of electrical components of vehicles. In order to suppress power consumption, the excitation voltage may be reduced. However, since the state of the contact surface of the contact varies depending on individual differences of relays, adhesion of foreign matter, deterioration over time, etc., it is not preferable to uniformly reduce the relay excitation voltage in order to maintain a good contact state of the contacts. In some cases.
In view of such a conventional problem, an object of the present invention is to provide an electric power steering device that can suppress power consumption of a relay without impairing a good contact state of the contacts.

  The present invention relates to an electric power steering device that generates a steering assist force by a motor using a battery as a power source, the relay being capable of opening and closing a contact inserted in an electric path for supplying electric power to the motor, and operating the relay The switching element to be driven, the switching element is driven by a pulse width modulation signal, and the bounce time of the contact is obtained by detecting the voltage on the load side of the contact at the time of operation of the relay, and the bounce time is determined according to the obtained bounce time And a control unit for changing the duty of the pulse width modulation signal.

  In the electric power steering apparatus as described above, since the bounce time varies depending on the contact state of the contact, the bounce time is an index indicating the contact state of the contact. Therefore, the control unit changes the duty of the pulse width modulation signal according to the bounce time, and changes the excitation voltage of the relay coil. For example, when the contact state of the contact is good, the duty can be reduced to decrease the excitation voltage, thereby suppressing the power consumption in the relay coil. Conversely, when the contact state of the contact is not good, the duty can be increased to increase the excitation voltage, and the contact pressure necessary for improving the contact state of the contact can be ensured.

In the electric power steering apparatus as described above, the control unit may adjust the duty of the pulse width modulation signal according to the power supply voltage of the battery.
In this case, even if the power supply voltage of the battery fluctuates, the excitation voltage of the relay coil can be kept constant by appropriately adjusting the duty obtained according to the bounce time.

  According to the electric power steering device of the present invention, the control unit changes the excitation voltage of the relay coil according to the bounce time that is an index indicating the contact state of the contact, so that the good contact state of the contact is not impaired. The power consumption of the relay can be suppressed.

  FIG. 1 is a block diagram showing an electric circuit of the electric power steering apparatus according to the first embodiment of the present invention. In the figure, a control unit 1 including a CPU is provided with a motor control unit 1M and a relay control unit 1R in terms of its functions. The motor control unit 1M calculates a drive signal for the motor 4 based on the steering torque signal input from the torque sensor 2 and the vehicle speed signal input from the vehicle speed sensor 3. Further, the motor control unit 1M performs pulse width modulation (PWM) on the drive signal and gives the output signal to the drive circuit 5. The drive circuit 5 constitutes a three-phase inverter, and generates a three-phase AC drive voltage from the DC voltage of the battery 7 using the output signal from the motor control unit 1M as a control signal.

  The motor 4 is a three-phase brushless motor, and is driven by a drive voltage supplied from the drive circuit 5 via the electric circuits U, V, and W. The motor 4 is connected to the steering shaft 13 via a reduction gear (not shown), and applies a steering assist force to the steering shaft 13. A rotation angle sensor 8 is provided in the motor 4, and a rotation angle signal of a rotor (not shown) is sent to the motor control unit 1M.

  The current sensors 10 are provided in the electric circuits V and W, and the current detection circuit 6 detects the current in the electric circuits V and W based on the output of the current sensor 10 and the calculation based on the output of the current sensor 10, and outputs the detected output to the motor control unit. Send to 1M. The motor control unit 1M obtains the coordinate-converted d-axis current and q-axis current using these currents and the rotation angle detected by the rotation angle sensor 8. Control is performed so that these currents are fed back and a drive current corresponding to the drive signal flows.

  A power supply voltage is supplied to the drive circuit 5 from the battery 7 via the contact 9 c of the relay 9. Both ends of the contact 9c are also connected to the relay control unit 1R, and the voltage on the power source side of the contact 9c (same as the power supply voltage of the battery 7) and the voltage on the load side are sent to the relay control unit 1R. The relay coil 9s is connected in series between the drain and source of the FET 12 as an example of a switching element, and the voltage of the battery 7 is applied to this series body. A drive signal is applied to the gate of the FET 12 from the relay control unit 1R. A temperature sensor 14 is provided in the vicinity of the relay coil 9s, and a temperature signal that detects heat generation (power consumption) of the relay coil 9s is sent to the relay control unit 1R. Further, an ON / OFF signal of the ignition key 11 is input to the relay control unit 1R.

  FIG. 2 is a waveform diagram showing excitation of the relay coil 9s and changes in the load side voltage of the contact 9c. When the ignition key 11 is operated from OFF to ON, the relay control unit 1R receiving the ON signal gives a gate voltage to the FET 12 to turn it on. Thereby, the relay coil 9s is excited (time T0). After the operation time has elapsed from the excitation, the contact 9c is closed by electromagnetic adsorption (time T1). Chattering (bounce) occurs between the initial closing and the stable closing of the contact 9c, and the contact 9c repeats contact and separation. If a voltage is applied to the power source side of the contact 9c, a voltage is generated on the load side due to the closing of the contact 9c. Therefore, the contact / separation of the contact 9c can be detected by detecting the voltage as shown in the figure.

  Here, the inventor has experimentally changed the operation time and the time from the time T1 at which the contact voltage is first generated to the time T2 at which the contact voltage is stably generated, that is, the bounce time, varies depending on the contact state of the contact 9c. I found out. That is, when the contact state is good, the operation time and the bounce time are short, and as the contact state gets worse, the operation time and the bounce time become longer. When the contact state is good, the excitation voltage of the relay coil 9s is the operation holding voltage (the lowest voltage for holding the state after operating once, and lower than the minimum operation voltage required when the relay is operated by excitation. ), The electromagnetic attraction of the contact 9c can be maintained. However, if the contact state deteriorates, the excitation voltage cannot be reduced to that extent, and a voltage sufficiently higher than the operation holding voltage is required to improve the contact state. Therefore, it is considered preferable to determine the excitation voltage according to the bounce time or (operation time + bounce time). Here, the contact state is also influenced by the spring force of the contact 9c. For example, if the spring force is strong, the contact state is considered to be improved.

  FIG. 3 is a block diagram showing internal functions (software) of the relay control unit 1R. The relay control unit 1R includes a voltage detection unit 101 that detects a load side voltage of the contact 9c of the relay 9, a bounce time calculation unit 102 that calculates a bounce time based on the detection of the voltage, and a PWM duty according to the bounce time. A duty calculation unit 103 that performs calculation, and a PWM unit 104 that applies a pulse width modulation signal to the gate of the FET 12 based on the duty are provided. Next, an example of a flowchart (FIG. 4) for realizing such a function will be described.

  In FIG. 1, when the ignition key 11 is turned on, the relay control unit 1R turns on the FET 12 to excite the relay coil 9s. At the same time, the process shown in FIG. 4 is started, and the relay control unit 1R stores the time T0 (step S1). Further, the relay control unit 1R performs a process of reading the load side voltage of the contact 9c (step S2). Here, it waits for the load side voltage to be detected (repetition of steps S2 and S3), and when detected, the time T1 is stored (step S4). The elapsed time from time T0 to T1 is the operation time in FIG.

  Next, the relay control unit 1R repeats the process of reading the load side voltage until the voltage is stabilized after the contact 9c is chattered (steps S5 and S6 are repeated). When voltage stability is detected by continuously appearing the voltage for a certain time or longer, the relay control unit 1R stores the time T2 (step S7). Then, the relay control unit 1R obtains a duty corresponding to the bounce time (T2-T1) (step S8). Specifically, assuming that the duty is D and the bounce time is Tb, they have a relationship of D = a · Tb + b as shown in FIG. 5, for example (a and b are constants).

Thereafter, the relay control unit 1R drives the FET 12 with the pulse width modulation signal having the obtained duty. Accordingly, the longer the bounce time, the greater the duty and the longer the on-time ratio of the FET 12 per unit time. As a result, the excitation voltage of the relay coil 9s increases. Conversely, the shorter the bounce time, the smaller the duty and the lower the excitation voltage of the relay coil 9s. However, the maximum value D _{max of the} duty is 1, and the excitation voltage at this time is equal to the power supply voltage of the battery 7. The minimum duty value D _min is set so that the excitation voltage obtained thereby is equal to or higher than the operation holding voltage of the relay 9.

In this way, when the electric power steering apparatus is activated, the relay control unit 1R first obtains the bounce time, performs PWM control of the FET 12 with a duty corresponding to the bounce time, and uses the excitation voltage of the relay coil 9s as the battery 7 It can be made lower than the voltage. When the contact state of the contact 9c is good, the duty can be reduced to reduce the excitation voltage, thereby suppressing the power consumption in the relay coil 9s. Conversely, when the contact state of the contact 9c is not good, the duty can be increased to increase the excitation voltage, and the contact pressure necessary to improve the contact state of the contact 9c can be ensured. However, also in this case, power consumption can be suppressed when an excitation voltage lower than the rated voltage is sufficient.
Note that the gate voltage of the FET 12 when the bounce time is first obtained is given by a PWM signal having a duty of 1.

  Further, in the electric power steering apparatus after startup, the power supply voltage of the battery 7 varies, so it is preferable to adjust the duty according to the variation. Therefore, the relay control unit 1R adjusts the duty according to the power supply voltage of the battery 7 thereafter, using the power supply voltage when the above-described duty is obtained as a reference voltage. That is, when the voltage of the battery 7 is higher than the reference voltage, the same excitation voltage can be obtained even if the duty is made smaller than in the case of the reference voltage, so the initial duty is multiplied by a reduction rate according to the voltage difference, Correct the duty downward. On the contrary, when the voltage of the battery 7 is lower than the reference voltage, it is necessary to obtain the same excitation voltage by increasing the duty as compared with the case of the reference voltage, so the initial duty is multiplied by an increase rate according to the voltage difference, Correct the duty upward. Thus, even if the power supply voltage of the battery 7 fluctuates, the excitation voltage of the relay coil can be kept constant by appropriately adjusting the duty determined in accordance with the bounce time in the initial stage.

  In addition, in the electric power steering apparatus after starting, the temperature of the relay coil 9s can be estimated from the temperature detected by the temperature sensor 14, and the duty can be adjusted according to the temperature. Specifically, when the contact state of the contact 9c is not good, it is considered that heat generation increases due to an increase in contact resistance. Therefore, when the temperature is higher than a predetermined value, the duty is increased from the initial value to increase the excitation voltage, Increase pressure. If the contact resistance decreases due to an increase in contact pressure, heat generation also decreases.

  FIG. 6 is a block diagram showing an electric circuit of the electric power steering apparatus according to the second embodiment of the present invention. The difference from the first embodiment is that the contact 9c of the relay 9 is inserted not in the power supply side of the drive circuit 5 but in an electric circuit (for example, U, V) connecting the drive circuit 5 and the motor 4, and the contact 9c The voltage on both sides (power supply side / load side) is taken into the relay control unit 1R. Others are the same as in the first embodiment. In this case, the relay coil 9s is excited with a predetermined voltage applied to the power supply side of the contact 9c, and the bounce time is obtained by the relay control unit 1R based on the voltage change on the load side of the contact 9c at that time. Similar control can be performed. In the illustrated example, the voltage on both sides of the contact inserted in the electric circuit V is taken. However, the voltage on both sides of the contact inserted in the electric circuit U is also taken, and the longer bounce time is longer. The duty may be obtained based on the above.

  In each of the above embodiments, the duty D is determined based on the bounce time Tb. However, since not only the bounce time but also the operation time is affected by the contact state of the contact 9c, the duty D is expressed as (operation time + bounce time). You may make it obtain | require based on Tb).

It is a block diagram which shows the electric circuit of the electric power steering apparatus by 1st Embodiment of this invention. It is a wave form diagram which shows the excitation of a relay coil, and the change of the load side voltage of the contact. It is a block diagram which shows the internal function (software) of a relay control part. It is a flowchart of the process performed in a relay control part. It is a graph which shows the relationship between bounce time and a duty. It is a block diagram which shows the electric circuit of the electric power steering apparatus by 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control part 1R Relay control part 4 Motor 7 Battery 9 Relay 9c Contact 12 FET (switching element)

Claims (2)

An electric power steering device that uses a battery as a power source to generate a steering assist force by a motor,
A relay capable of opening and closing a contact inserted in an electric path for supplying electric power to the motor;
A switching element for operating the relay;
The switching element is driven by a pulse width modulation signal, and the bounce time of the contact is obtained by detecting the voltage on the load side of the contact at the time of operation of the relay, and the pulse width modulation is performed according to the obtained bounce time. An electric power steering apparatus comprising: a control unit that changes a duty of a signal.   The electric power steering apparatus according to claim 1, wherein the control unit adjusts a duty of the pulse width modulation signal according to a power supply voltage of the battery.

Images