JP7243047B2 - Auxiliary power supply and electric power steering system - Google Patents

Description

The present invention relates to an auxiliary power supply and an electric power steering system equipped with the auxiliary power supply.

2. Description of the Related Art As an electric device mounted on a vehicle, there is an electric power steering device that assists steering of a driver. An electric power steering device includes a motor for assisting steering. The electric power steering apparatus drives a steering assist motor in accordance with a rotation operation of a steering member such as a steering wheel, and applies power generated by the motor to a steering mechanism to assist steering. .

Further, as seen in Patent Document 1, an electric power steering apparatus has been proposed that includes an auxiliary power supply device having a capacitor. The auxiliary power supply device is provided in a power supply circuit for feeding the assist motor from the vehicle-mounted battery as the main power supply. In an electric power steering apparatus equipped with such an auxiliary power supply, the capacitor of the auxiliary power supply is charged by power supply from the main power supply when the load on the motor is low. When a large steering assist force is required, such as when the vehicle is stopped or when the vehicle is running at a low speed, the motor is driven by the discharge of the capacitor in addition to the power supply from the main power supply.

JP 2015-157519 A

By the way, when the temperature of a capacitor drops below a certain temperature, the internal resistance of the capacitor increases sharply. When the internal resistance increases, the voltage drop at the beginning of the discharge of the capacitor increases, so the output voltage of the auxiliary power supply decreases when the temperature is low.

It is conceivable to apply an auxiliary power supply device that charges a capacitor with power supply from the main power supply and supplies power with discharge of the capacitor to an electric device other than the electric power steering device. Even in such a case, a drop in the output voltage of the auxiliary power supply at low temperatures can similarly occur.

An auxiliary power supply device that solves the above problems is an auxiliary power supply device that is installed in a power supply path from a main power supply to a power supply target, has a capacitor, and charges a charge in the capacitor by power supply from the main power supply. a holding state in which the charge charged in the capacitor is held; and a discharge state in which the charge charged in the capacitor is discharged to the power supply target, wherein the temperature of the capacitor is a predetermined low temperature. A maximum charge voltage is set according to the temperature of the capacitor so that when the temperature of the capacitor is lower than the determination temperature, the voltage becomes higher than when the temperature of the capacitor exceeds the low temperature determination temperature, and when the capacitor is in the charged state, the maximum charging voltage is set. When the charging voltage of the capacitor becomes equal to or higher than the maximum charging voltage, the charging state is switched to the holding state.

In the above configuration, when the charging voltage of the capacitor becomes equal to or higher than the maximum charging voltage while in the charging state, the operating state of the auxiliary power supply is switched from the charging state to the holding state. That is, the capacitor is charged within a range in which the charging voltage does not exceed the maximum charging voltage.

When the temperature of the capacitor is low, the internal resistance increases and the voltage drop at the beginning of discharge increases. In this regard, in the above configuration, when the temperature of the capacitor is low, a higher voltage is set as the maximum charging voltage than when the temperature is high. As a result, when the temperature of the capacitor is low, the capacitor is charged to a higher voltage than when the temperature is high. By charging the capacitor to a higher voltage at a low temperature in this way, even if the voltage drop at the beginning of discharge is large, the drop in the output voltage of the auxiliary power supply can be suppressed.

It is desirable that the auxiliary power supply device include a booster circuit that boosts the voltage of the main power supply in the charged state and applies the boosted voltage to the capacitor. In such a case, by adjusting the boosted voltage of the booster circuit in the charged state, it is possible to change the maximum charging voltage according to the temperature of the capacitor.

Further, in the auxiliary power supply, when the temperature of the capacitor is equal to or higher than the high temperature determination temperature, which is a predetermined temperature higher than the low temperature determination temperature, the temperature of the capacitor exceeds the low temperature determination temperature and is less than the high temperature determination temperature. It is desirable to make the maximum charging voltage lower than in the case of . When the temperature of the capacitor rises, deterioration due to repeated charging and discharging tends to progress, but in such cases, the progress of deterioration can be suppressed by setting the maximum charging voltage low.

Lithium-ion capacitors have a more pronounced increase in internal resistance at low temperatures than other types of capacitors such as electric double layer capacitors. Therefore, the above-described auxiliary power supply device capable of suppressing a decrease in output due to an increase in internal resistance at low temperatures is particularly suitable when employing a lithium ion capacitor.

Note that the above-described auxiliary electrical device can be applied to, for example, an electric power steering device that includes a motor for assisting steering and that uses the motor as a power supply target of an auxiliary power supply device.

ADVANTAGE OF THE INVENTION According to this invention, the fall of the output voltage at the time of low temperature can be suppressed.

1 is a schematic diagram schematically showing the configuration of an electric power steering device according to an embodiment; FIG. FIG. 2 is a circuit diagram showing the configuration of an electric circuit of the electric power steering device; 4 is a table showing operating states of switching elements in respective operating states of the auxiliary power supply device according to the embodiment; 4 is a graph showing the relationship between the temperature and internal resistance of a capacitor provided in the same auxiliary power supply; 4 is a graph showing the relationship between capacitor temperature and maximum charging voltage in the same auxiliary power supply. 4 is a time chart showing changes in capacitor voltage during discharging;

An embodiment of an auxiliary power supply device and an electric power steering device will be described in detail below with reference to FIGS. 1 to 6. FIG.
As shown in FIG. 1, the electric power steering system (hereinafter referred to as EPS 1) of this embodiment includes a steering shaft 4 having a steering wheel 2 fixed to one end and a pinion gear 3 fixed to the other end. . The pinion gear 3 is meshed with a rack gear 6 formed on the rack shaft 5 . The pinion gear 3 and the rack gear 6 constitute a rack and pinion mechanism that converts the rotational motion of the steering shaft 4 into the linear motion of the rack shaft 5 in the longitudinal direction. When the electric power steering device 1 is assembled to a vehicle, the rack shaft 5 is attached to the vehicle body so that its longitudinal direction is aligned with the vehicle width direction. 7 via tie rods 8, respectively.

A torque sensor 9 is attached to the steering shaft 4 to measure the steering torque TR applied to the steering shaft 4 by operating the steering wheel 2 . In this embodiment, as the torque sensor 9, a sensor configured to detect the amount of twisting of a torsion bar forming part of the steering shaft 4 and measure the steering torque TR based on the amount of twisting is employed. there is

A motor for assisting steering (hereinafter referred to as an assist motor 10) is connected to the steering shaft 4 via a speed reducer 11 that reduces the rotation of the assist motor 10 and transmits it to the steering shaft 4. there is In this embodiment, a three-phase brushless motor is used as the assist motor 10 . Further, in this embodiment, a worm gear mechanism is adopted as the speed reducer 11 .

Further, the electric power steering device 1 includes a motor drive circuit 12, an auxiliary power supply device 13, and an electronic control unit 14. The motor drive circuit 12 employs a known circuit having two switching elements for each phase of the assist motor 10 . Further, when the electric power steering device 1 is assembled to the vehicle, the auxiliary power supply device 13 and the electronic control unit 14 are each connected to the vehicle battery 15 as a main power source.

The electronic control unit 14 includes an arithmetic processing circuit 16 that executes arithmetic processing related to control of the electric power steering device 1, and a memory 17 that stores control programs and data. The torque sensor 9 described above is also connected to the electronic control unit 14 . Further, when the electric power steering apparatus 1 is assembled to the vehicle, the electronic control unit 14 is connected to a vehicle speed sensor 18 installed in the vehicle to detect the running speed VS of the vehicle.

The electronic control unit 14 controls the steering assist force applied by the assist motor 10 in the electric power steering device 1 assembled to the vehicle. When controlling the steering assist force, the electronic control unit 14 first determines a target assist force, which is a target value of the steering assist force, based on the steering torque TR and the running speed VS. Then, the electronic control unit 14 controls the operations of the motor drive circuit 12 and the auxiliary power supply 13 in order to generate the steering assist force corresponding to the target assist force.

As shown in FIG. 2 , the auxiliary power supply 13 has an input port 20 and an output port 21 . The input port 20 is connected to the vehicle battery 15 when the electric power steering device 1 is assembled to the vehicle. Also, the output port 21 is connected to the assist motor 10 to which power is supplied through the motor drive circuit 12 when the electric power steering apparatus 1 is assembled.

The auxiliary power supply device 13 is provided with a low-potential line 23 which is wiring connected to the input port 20 via a relay 22 for connecting/disconnecting power supply from the vehicle-mounted battery 15 . In this embodiment, a non-contact relay composed of two MOSFETs is employed as the relay 22 .

In addition, the auxiliary power supply device 13 includes an electric storage device 24 that can be charged and discharged. One end of the capacitor 24 is connected to the low potential line 23, and the other end is connected to the high potential line 26, which will be described later. The capacitor 24 is composed of two capacitors 24A and 24B connected in series. In this embodiment, lithium ion capacitors are used as the capacitors 24A and 24B.

A temperature sensor 27 for detecting the temperature of the capacitors 24A, 24B (hereinafter referred to as capacitor temperature TC) is installed near each capacitor 24A, 24B. The temperature sensor 27 is then connected to the electronic control unit 14 . A thermistor is used as the temperature sensor 27 in this embodiment.

Further, the auxiliary power supply device 13 includes a chopper coil 25 that is a boosting coil. One end of the chopper coil 25 is connected to the low potential line 23, the other end is connected to the ground through a first switching element (hereinafter referred to as FET1), and is connected to a second switching element (hereinafter referred to as FET1). , FET2) to the end of the capacitor 24 opposite to the side connected to the low potential line 23 . The high potential line 26 described above serves as a wiring that connects the FET 2 and the capacitor 24 . The high potential line 26 is connected to the output port 21 via a third switching element (hereinafter referred to as FET3). The low potential line 23 described above is connected to the output port 21 via a fourth switching element (hereinafter referred to as FET4).

In this embodiment, MOSFETs are used as the switching elements (FETs 1 to 4). These FET1 to FET4 and the MOSFETs forming the relay 22 open and close according to the input of drive signals from the electronic control unit 14 to their respective gates. The electronic control unit 14 acquires the voltage of the high potential line 26 as the charging voltage VC of the capacitors 24A and 24B.

Next, the power supply control of the auxiliary power supply device 13 executed by the electronic control unit 14 will be described. After starting the vehicle (ignition is turned on), the electronic control unit 14 performs start-up processing such as failure diagnosis, turns on the relay 22, and then starts power supply control. In power supply control, the electronic control unit 14 calculates a required electric power EPS, which is electric power required for the assist motor 10 to generate a steering assist force corresponding to the target assist force, based on the target assist force. Then, the electronic control unit 14 controls the power (main power supply power PS) supplied from the on-vehicle battery 15 to the auxiliary power supply device 13, the required power EPS, and the charging voltage VC during the charging state, the holding state, and the discharging state. to switch the operating state of the auxiliary power supply 13 with . Note that FIG. 3 shows the driving states of the FETs 1 to 4 in each state.

The electronic control unit 14 sets the operating state of the auxiliary power supply 13 to the charging state when the required power EPS is equal to or less than the main power power PS and the charging voltage VC is less than the maximum charging voltage VMAX, which will be described later. In the charging state, FET3 is turned off (open) and FET4 is turned on (closed). On the other hand, FET1 and FET2 at this time are PWM-driven so as to alternately turn on. At this time as well, current flows from the vehicle-mounted battery 15 to the motor drive circuit 12 through the low potential line 23 . Furthermore, at this time, the FET1, the FET2, the capacitors 24A and 24B of the electric storage device 24, and the chopper coil 25 operate as a booster circuit. As a result, the voltage of the high potential line 26 is boosted, so that the capacitors 24A and 24B are charged.

The electronic control unit 14 maintains the operating state of the auxiliary power supply 13 when the required power EPS is less than or equal to the main power power PS and the charging voltage VC is greater than or equal to the maximum charging voltage VMAX. In the hold state, FET1, FET2, and FET3 are turned off, and FET4 is turned on. At this time, a current flows from the onboard battery 15 to the motor drive circuit 12 through the low potential line 23 . At this time, since both the FET2 and the FET3 are in the OFF state, the charges charged in the capacitors 24A and 24B are held.

On the other hand, when the required power EPS exceeds the main power PS, the electronic control unit 14 sets the operating state of the auxiliary power supply 13 to the discharging state. In the discharging state, FET1, FET2, and FET4 are turned off, and FET3 is turned on. At this time, current flows from the vehicle-mounted battery 15 to the motor drive circuit 12 through the low potential line 23 , the capacitor 24 and the high potential line 26 . Therefore, the auxiliary power supply device 13 at this time boosts the voltage of the vehicle-mounted battery 15 by the charge voltage VC of the capacitors 24A and 24B and outputs the boosted voltage.

As described above, in this embodiment, the capacitors 24A and 24B are charged when the required power EPS is small. Then, when the required electric power EPS becomes large at the time of stationary steering or the like, the amount of electric power supplied to the assist motor 10 is increased without increasing the amount of electric power supplied to the on-vehicle battery 15 by discharging the charged electric charge. I am making it possible. Therefore, it is possible to generate a large steering assist force while suppressing a rapid decrease in the amount of charge of the vehicle-mounted battery 15 and an increase in temperature due to rapid discharge.

As shown in FIG. 4, the capacitors 24A and 24B have temperature characteristics in which the internal resistance increases as the temperature decreases. It is known that the lithium-ion capacitors employed as the capacitors 24A and 24B in this embodiment have a particularly large increase in internal resistance as the temperature drops, compared to other capacitors such as electric double layer capacitors. When the internal resistance increases, the voltage drop at the beginning of discharge increases, and the output voltage of the auxiliary power supply 13 decreases accordingly.

As shown in the figure, the ratio of the change in internal resistance to the change in capacitor temperature TC is as follows: is larger than The low-temperature judgment temperature T1 is extremely low, several tens of degrees below freezing, but the electric power steering apparatus 1 of the present embodiment is assumed to be used in an extremely low temperature environment, so its influence cannot be ignored. It has become. On the other hand, it is known that the capacitors 24A and 24B deteriorate more rapidly in a high temperature range exceeding a certain temperature (hereinafter referred to as a high temperature determination temperature T2) due to repeated charging and discharging. In contrast, in the present embodiment, the value of the maximum charging voltage VMAX is changed according to the capacitor temperature TC, thereby suppressing the decrease in the output voltage in the low temperature range and the progress of deterioration in the high temperature range. ing.

FIG. 5 shows how the maximum charging voltage VMAX is set in this embodiment. As shown in the figure, when the capacitor temperature TC is in the normal temperature range from the low temperature determination temperature T1 to the high temperature determination temperature T2, the predetermined standard voltage V2 is set as the value of the maximum charging voltage VMAX. On the other hand, when the capacitor temperature TC is in the low temperature region equal to or lower than the low temperature determination temperature T1, the low temperature voltage V3 (>V2) higher than the standard voltage V2 is set as the value of the maximum charging voltage VMAX. Further, when the capacitor temperature TC is in a high temperature region equal to or higher than the high temperature determination temperature T2, the high temperature voltage V1 (<V1) lower than the standard voltage V2 is set as the value of the maximum charging voltage VMAX.

FIG. 6 shows transitions of the charging voltage VC when switching from the holding state to the discharging state is performed in the following three situations 1 to 3, respectively. Situation 1 is the case where the capacitor temperature TC is in the normal temperature range in the auxiliary power supply device 13 of the present embodiment, and the transition of the charging voltage VC in that case is indicated by the solid line in FIG. Situation 2 is the case where the capacitor temperature TC is in the low temperature range in the auxiliary power supply device 13 of the present embodiment, and in FIG. Situation 3 is a case in which the maximum charging voltage VMAX is set to the standard voltage V2 in the low temperature range and power supply control of the auxiliary power supply 13 is performed. It is

In any of the situations 1 to 3, a so-called early discharge voltage drop occurs, in which the charging voltage VC sharply decreases immediately after the start of discharge. The voltage drop at the beginning of discharge increases as the internal resistance increases. Therefore, in the low temperature range, the voltage drop at the beginning of discharge is greater than in the normal temperature range. After such a voltage drop in the early stage of discharge, the charging voltage VC gradually drops as the capacitors 24A and 24B discharge.

In the case of situation 3, the capacitors 24A and 24B are charged in the low temperature range by setting the standard voltage V2 to the value of the maximum charging voltage VMAX. Therefore, the charging voltage VC before the start of discharging in this case becomes the standard voltage V2, as in the case of situation 1. On the other hand, in this case, the capacitor temperature TC is low and the internal resistance is high, so the voltage drop at the beginning of discharge is larger than in the case of Situation 1. In addition, in the case of situation 3, the charging voltage VC after the start of discharging is lower than in the case of situation 1 by the amount of the voltage drop. The output voltage of the auxiliary power supply 13 during discharge is the sum of the output voltage of the vehicle battery 15 and the charging voltage VC. lower than

On the other hand, in the present embodiment, in the low temperature range where the voltage drop at the beginning of discharge is large, the maximum charging voltage VMAX is set to the low temperature voltage V3 higher than the standard voltage V2. Therefore, in the case of situation 2, the output voltage of the auxiliary power supply 13 during discharging is higher than in the case of situation 3.

Further, in the present embodiment, in the high temperature range, the maximum charging voltage VMAX is set to the high temperature voltage V1 which is lower than the standard voltage V2. Therefore, in a high temperature range where deterioration tends to progress, the capacitors 24A and 24B are charged and discharged in a lower voltage range than in a normal temperature range, thereby suppressing the progress of deterioration.

According to the present embodiment described above, the following effects can be obtained.
(1) In the low temperature range where the capacitor temperature TC is less than the low temperature determination temperature T1, the maximum charging voltage (low temperature voltage V3) is higher than in the normal temperature range and the high temperature range where the capacitor temperature TC is the low temperature determination temperature T1 or higher. It is set as the value of the voltage VMAX. Therefore, the drop in the output voltage of the auxiliary power supply device 13 at low temperatures can be suppressed.

(2) In the high temperature range where the capacitor temperature TC exceeds the high temperature determination temperature T2, a lower voltage (high temperature voltage V1) than in the normal temperature range is set as the value of the maximum charging voltage VMAX. Therefore, progress of deterioration of the capacitors 24A and 24B at high temperatures can be suppressed.

(3) A lithium-ion capacitor, whose internal resistance increases significantly at low temperatures, is used for the auxiliary power supply 13, because the drop in the output voltage of the auxiliary power supply 13 can be suppressed even at low temperatures when the internal resistance of the capacitors 24A and 24B increases. becomes easier.

It should be noted that the above-described embodiment can be modified as follows.
- A temperature sensor other than a thyristor may be employed as the temperature sensor 27 .
- In the above embodiment, the onboard battery 15 serves as the main power source for supplying power to the auxiliary power supply device 13, but a power source other than the onboard battery, such as a generator, or a combination of the onboard battery and other power sources may be used. You may make it the main power supply.

- A mechanical relay may be employed as the relay 22 .
- A motor other than a three-phase brushless motor may be employed as the assist motor 10 .
- Some or all of the switching elements (FET1 to FET4) may be composed of switching elements other than MOSFETs.

- As the capacitors 24A and 24B of the auxiliary power supply device 13, capacitors other than lithium ion capacitors such as electric double layer capacitors may be employed.
- The number of capacitors constituting the electric storage device 24 of the auxiliary power supply device 13 can be appropriately changed, and the same electric storage device 24 may be configured with a single capacitor or three or more capacitors.

・In the above embodiment, the value of the maximum charging voltage VMAX is switched between three levels in the low temperature range, the normal temperature range, and the high temperature range, but the maximum charging voltage VMAX in the normal temperature range and the high temperature range is the same. As a value, the value of the maximum charging voltage VMAX may be changed only in the low temperature range.

The electric power steering apparatus 1 of the above embodiment is configured as a so-called column-assist type electric power steering apparatus in which the assist motor 10 is connected to the steering shaft 4 via the reduction gear 11 . The electric power steering apparatus 1 may be configured as a rack assist type apparatus in which the assist motor 10 is connected to the rack shaft 5 via the reduction gear 11 .

- The auxiliary power supply device 13 of the above embodiment may be applied to an electric device other than the electric power steering device 1 .

DESCRIPTION OF SYMBOLS 1... Electric power steering apparatus, 2... Steering wheel, 3... Pinion gear, 4... Steering shaft, 5... Rack shaft, 6... Rack gear, 7... Steering wheel, 8... Tie rod, 9... Torque sensor, 10... Assist motor ( Motor for assisting steering), 11... Reducer, 12... Motor drive circuit, 13... Auxiliary power supply, 14... Electronic control unit, 15... Car battery (main power supply), 16... Arithmetic processing circuit, 17... Memory, 18 Vehicle speed sensor 20 Input port 21 Output port 22 Relay 23 Low potential line 24 Battery 24A, 24B Capacitor 25 Chopper coil 26 High potential line 27 Temperature sensor FET1 to FET4 . . . switching elements.

Claims (5)

An auxiliary power supply installed in a power supply path from a main power supply to a power supply target, the auxiliary power supply having a capacitor, a charging state in which the capacitor is charged by power supply from the main power supply, and a charge stored in the capacitor. In an auxiliary power supply device capable of switching between a holding state in which the capacitor is held and a discharge state in which the charge charged in the capacitor is discharged to the power supply target,
setting a maximum charge voltage according to the temperature of the capacitor so that when the temperature of the capacitor is equal to or lower than a predetermined low temperature determination temperature, the voltage becomes higher than when the temperature of the capacitor exceeds the low temperature determination temperature; The capacitor is configured to switch from the charging state to the holding state when the charging voltage of the capacitor becomes equal to or higher than the maximum charging voltage while the capacitor is in the charging state,
In the state of charge, when the required power, which is the power required by the power supply target, is equal to or less than the main power supply power supplied from the main power supply to the auxiliary power supply device, and the charging voltage is less than the maximum charging voltage, a state in which the power supply target and the capacitor are connected in parallel to the main power supply;
The holding state is a state in which the capacitor is electrically disconnected from the main power supply and the power supply target when the required power is equal to or less than the power of the main power supply and the charging voltage is equal to or higher than the maximum charging voltage. ,
The discharge state is a state in which the capacitor is connected in series with the main power supply between the main power supply and the power supply target when the required power exceeds the main power supply power . 2. The auxiliary power supply device according to claim 1, further comprising a booster circuit that boosts the voltage of the main power supply in the charged state and applies the voltage to the capacitor. When the temperature of the capacitor is equal to or higher than the high temperature determination temperature, which is a predetermined temperature higher than the low temperature determination temperature, the maximum 3. The auxiliary power supply device according to claim 1, wherein the charging voltage is lowered. The auxiliary power supply device according to any one of claims 1 to 3, wherein the capacitor is a lithium ion capacitor. An electric power steering apparatus comprising the auxiliary power supply device according to any one of claims 1 to 4 and a motor for assisting steering, wherein the motor is a power supply target of the auxiliary power supply device.

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