Power supply device for vehicle

Abstract

A power supply device 10 for a vehicle includes: a motor 11 (low-voltage motor) that can operate at a voltage within an operation voltage range that is lower than a minimum output voltage of an on-vehicle battery 92; a backup power supply 20 serving as a spare for the on-vehicle battery 92; a motor drive unit 12 that supplies, to the motor 11, a voltage supplied from the on-vehicle battery 92 or the backup power supply 20, and drives the motor 11; and an adjustment unit 25 that adjusts the voltage supplied from the motor drive unit 12 to the motor 11 to a voltage within the operation voltage range when the voltage is supplied from the on-vehicle battery 92 to the motor drive unit 12.

Description

Vehicle power supply device

[0001] The present invention relates to a vehicle power supply device.

[0002] Patent Document 1 discloses a door latch device that supplies power from a backup power source to a motor in an emergency of a vehicle. The motor can operate at an automotive standard voltage of, for example, 8V to 16V. The backup power source is formed by connecting two supercapacitors in series. The backup power source can be charged up to about 5V at maximum, but this voltage is lower than the operating voltage range of the motor. Therefore, when using the backup power source, a boost circuit is used to boost the voltage and supply power to the motor.

[0003] Japanese Patent Translation of PCT International Publication No. 2016-503135

[0004] Here, it may be considered that if a low-voltage motor with a lower operating voltage range is used, the backup power source can be used as the power source for the motor without a boost circuit. However, normally, power is supplied from the in-vehicle battery to the motor, and the nominal voltage of the in-vehicle battery (12V) is higher than the operating voltage range of the low-voltage motor. If the voltage of the in-vehicle battery is directly supplied to the low-voltage motor, it may interfere with the operation of the low-voltage motor, such as the low-voltage motor not operating properly or malfunctioning.

[0005] An object of the present invention is to provide a vehicle power supply device that can stably operate a low-voltage motor with an in-vehicle battery.

[0006] One aspect of the present invention provides a vehicle power supply device including: a low-voltage motor operable at a voltage within an operating voltage range lower than the minimum output voltage of an in-vehicle battery; a backup power source as a backup for the in-vehicle battery; a motor drive unit that supplies a voltage supplied from the in-vehicle battery or the backup power source to the low-voltage motor to drive the low-voltage motor; and an adjustment unit that adjusts the voltage supplied from the motor drive unit to the low-voltage motor to a voltage within the operating voltage range when a voltage is supplied from the in-vehicle battery to the motor drive unit.

[0007] With the above configuration, the motor can be operated without a boost circuit even if the output of the backup power supply is low. The power supply unit configuration is simplified, and the manufacturing cost of the power supply unit is reduced. On the other hand, even if the output voltage of the vehicle battery is high, the adjustment unit can adjust the voltage supplied from the motor drive unit to the low-voltage motor to a voltage within the operating voltage range. Therefore, the low-voltage motor can be stably operated with the vehicle battery.

[0008] According to the present invention, it is possible to provide a vehicle power supply device that can stably operate a low-voltage motor using an on-board battery.

[0009] A block diagram showing a vehicle power supply device and a vehicle door latch device equipped therewith according to the first embodiment. A flowchart showing the processing performed by the control unit in Figure 1. A flowchart showing the non-PWM type motor drive processing in Figure 2. A flowchart showing the voltage adjustment processing in Figure 2. A flowchart showing the PWM type motor drive processing in Figure 2. A graph showing the relationship between the output voltage of the vehicle battery and the duty cycle. A graph showing the relationship between ambient temperature and the duty cycle. A graph showing the relationship between the motor current and the duty cycle. A block diagram showing a vehicle power supply device and a vehicle door latch device equipped therewith according to the second embodiment. A flowchart showing the processing performed by the control unit in Figure 9. A flowchart showing the voltage adjustment processing in Figure 10. A flowchart showing the non-PWM type motor drive processing in Figure 10.

[0010] Embodiments will be described below with reference to the drawings. The same or corresponding elements are denoted by the same reference numerals throughout the drawings, and redundant detailed descriptions will be omitted.

[0011] (First Embodiment) Referring to Figure 1, the vehicle door latch device 1 according to the first embodiment comprises a vehicle power supply device 10 and a latch mechanism 2. The power supply device 10 is mounted on the vehicle and serves as a power source for the on-board electric equipment. The on-board electric equipment is equipment or a mechanism mounted on the vehicle and driven by a motor. The latch mechanism 2 is an example of on-board electric equipment.

[0012] The latch mechanism 2 is driven by the motor 11 of the power supply unit 10. The latch mechanism 2 is attached to a vehicle door (not shown). The latch mechanism 2 switches between a latched state, which holds the striker 91 attached to the vehicle, and a released state, which allows the striker 91 to detach. For example, the motor 11 can be used to perform a release operation, which switches the latch mechanism 2 from the latched state to the released state. The latch mechanism 2 has a fork 3 and a claw 4, and the motor 11 rotates the claw 4.

[0013] The power supply unit 10 is connected to the vehicle battery 92. The power supply unit 10 can drive the motor 11 using the power from the vehicle battery 92.

[0014] The on-board battery 92 stores the power necessary for the operation of the vehicle and supplies power to the prime mover and electrical components as needed. When the charge level of the on-board battery 92 decreases, the on-board battery 92 is recharged, for example, by a generator driven by the prime mover or by regenerative braking. The on-board battery 92 is, for example, a lead-acid battery mounted on the vehicle, and generally has a nominal voltage of 12V. The output voltage of the on-board battery 92 can vary, for example, within a range of 8V to 16V.

[0015] Motor 11 is a DC motor capable of forward and reverse rotation. Motor 11 can operate at voltages within its operating voltage range. Motor 11 is a so-called low-voltage motor, and its operating voltage range is lower than the minimum output voltage of the onboard battery 92. For example, the minimum output voltage of the onboard battery 92 is 8V, and the operating voltage range of motor 11 is 3V to 8V.

[0016] The power supply unit 10 includes, in addition to the motor 11, a backup power supply 20, a motor drive unit 12, a switching unit 13, a charging unit 14, a discharge unit 15, a voltage stabilization unit 16, a pre-driver 19, and a control unit 30.

[0017] The backup power supply 20 is provided in the power supply unit 10 as a backup power source for the onboard battery 92. In this embodiment, as will be described later, the onboard battery 92 is basically used to power the motor 11 when the vehicle is not in an accident state, while the backup power supply 20 is basically used to power the motor 11 when the vehicle is in an accident state.

[0018] The backup power supply 20 is composed of, for example, capacitors. As shown in the figure, the backup power supply 20 is composed of two capacitors 21 and 22 connected in series. Each capacitor 21 and 22 is, for example, an electric double-layer capacitor. The voltage across each capacitor 21 and 22 drops due to discharge. For example, when fully charged, the voltage across each capacitor 21 and 22 is in the range of 2.5V to 3V, and the voltage of the backup power supply 20 is in the range of 5V to 6V.

[0019] The motor drive unit 12 supplies voltage from the onboard battery 92 or backup power supply 20 to the motor 11. The motor drive unit 12 is controlled by the control unit 30 and drives the motor 11 by supplying power to the motor 11 to rotate it in the forward or reverse direction.

[0020] The motor drive unit 12 is connected to the vehicle battery 92 via the main power supply line 51. The motor drive unit 12 is grounded via the ground line 52. The backup power supply 20 (capacitor 21) is connected to the main power supply line 51 via the auxiliary power supply line 53, and thus to the motor drive unit 12. The backup power supply 20 (capacitor 22) is connected to the ground line 52.

[0021] The switching unit 13 has a main switch element 13a that opens and closes the main power supply line 51, and a sub-switch element 13b that opens and closes the sub-power supply line 53. The main switch element 13a is interposed on the main power supply line 51 on the vehicle battery 92 side with respect to the connection point with the sub-power supply line 53. The operation of the switching unit 13, that is, the opening and closing of the main switch element 13a and the opening and closing of the sub-switch element 13b, is controlled by the control unit 30.

[0022] If the main switch element 13a is closed and the sub-switch element 13b is open, the motor drive unit 12 is powered by the vehicle battery 92. If the main switch element 13a is open and the sub-switch element 13b is closed, the motor drive unit 12 is powered by the backup power supply 20.

[0023] The charging unit 14 charges the backup power supply 20 using the on-board battery 92. The backup power supply 20 is connected to the on-board battery 92 via a charging line 54. The charging unit 14 can be implemented by a switch that opens and closes the charging line 54. The operation of the charging unit 14, i.e., the opening and closing of the switch, is controlled by the control unit 30. When the switch is closed, the backup power supply 20 is charged with the power of the on-board battery 92. When the switch is open, the power supply from the on-board battery 92 to the backup power supply 20 is cut off. The backup power supply 20 becomes dischargeable.

[0024] The charging line 54 may be connected to the main power supply line 51 on the vehicle battery 92 side with respect to the main switch element 13a, and the portion from the vehicle battery 92 to the connection point may be shared with the main power supply line 51. The charging line 54 may be connected to the auxiliary power supply line 53 on the backup power supply 20 side with respect to the auxiliary switch element 13b, and the portion from the backup power supply 20 to the connection point may be shared with the auxiliary power supply line 53.

[0025] The discharge unit 15 discharges the backup power supply 20 by making the voltages of the two capacitors 21 and 22 equal. For example, the discharge unit 15 is realized by two discharge control lines 55a and 55b, and an equalization circuit or cell balancing circuit that includes elements such as resistors and switches. The discharge control lines 55a and 55b are connected to the control unit 30 and the backup power supply 20.

[0026] The operation of the discharge unit 15, that is, the operation of the switch in the equalization circuit, is controlled by the control unit 30. The control unit 30 can detect the potential of each discharge control line 55a, 55b. The discharge unit 15 also serves as a backup voltage detection unit 49 for detecting the output voltage of the backup power supply 20 and the voltages of each capacitor 21, 22 that constitute the backup power supply 20.

[0027] The voltage stabilization unit 16 adjusts the voltage supplied from the on-board battery 92 to a voltage (for example, 5V) that allows the control unit 30 to operate stably. The control unit 30 is connected to the on-board battery 92 via the main control power line 56. The voltage stabilization unit 16 is interposed on the main control power line 56. The control unit 30 uses the on-board battery 92 as its power source and is supplied with the voltage adjusted by the voltage stabilization unit 16.

[0028] The pre-driver 19 is interposed between the control unit 30 and the motor drive unit 12. The pre-driver 19 functions as a PWM adjustment unit 26 that controls the motor drive unit 12 using PWM and adjusts the voltage supplied from the motor drive unit 12 to the motor 11 to within the operating voltage range of the motor 11.

[0029] The output voltage of the backup power supply 20 tends to fluctuate within the operating voltage range of the motor 11. In contrast, the output voltage of the onboard battery 92 exceeds the operating voltage range of the motor 11. Therefore, voltage adjustment by PWM control is performed when the onboard battery 92 is selected as the power source for the motor 11.

[0030] The pre-driver 19, acting as a PWM adjustment unit 26, is an example of an adjustment unit 25 that adjusts the voltage supplied from the motor drive unit 12 to the motor 11 to a voltage within the operating voltage range when voltage is supplied from the vehicle battery 92 to the motor drive unit 12. By having the pre-driver 19 (PWM adjustment unit 26) perform this role as an adjustment unit 25, the motor 11 can be operated stably even if a low-voltage motor is used for the motor 11, or even if the vehicle battery 92 is selected as the power source for the motor 11.

[0031] The control unit 30 commands the pre-driver 19 to set the duty cycle for PWM control. The pre-driver 19 performs PWM control on the motor drive unit 12 according to the command from the control unit 30. The motor drive unit 12 is controlled by the pre-driver 19, and subsequently by the control unit 30, to drive the motor 11.

[0032] The duty cycle is approximately equal to the ratio of the voltage supplied from the motor drive unit 12 to the motor 11 (hereinafter also simply referred to as the "effective voltage") to the input voltage to the motor drive unit 12. For example, if the output voltage of the vehicle battery 92, i.e., the input voltage to the motor drive unit 12, is 12V, then controlling the motor drive unit 12 with a 40% duty cycle using PWM will result in an effective voltage of approximately 4.8V. Even if the input voltage to the motor drive unit 12 exceeds the operating voltage range, the effective voltage will remain within the operating voltage range.

[0033] The pre-driver 19 is connected to the vehicle battery 92 via the main drive line 57 and also to the ground line 52. This allows the pre-driver 19 to operate using the vehicle battery 92 as its power source.

[0034] As shown in the figure, the main control power line 56 may be connected to the charging line 54 on the vehicle battery 92 side of the charging unit 14, and the portion from the vehicle battery 92 to the connection point may be shared with the charging line 54. The same applies to the main drive line 57.

[0035] The control unit 30 and the pre-driver 19 can also operate using the backup power supply 20 as their power source. The voltage stabilization unit 16 is also connected to the backup power supply 20 via a sub-control power supply line 58, which is independent of the main control power supply line 56. The voltage stabilization unit 16 can adjust the voltage supplied from the on-board battery 92 to a voltage at which the control unit 30 can operate stably. The voltage stabilization unit 16 is also connected to the pre-driver 19 via a sub-drive line 59. The voltage stabilization unit 16 can adjust the voltage supplied from the on-board battery 92 to a voltage at which the pre-driver 19 can operate stably.

[0036] As shown in the figure, the sub-control power line 58 is connected to the sub-supply line 53 on the backup power supply 20 side with respect to the sub-switch element 13b, and the portion from the backup power supply 20 to the connection point may be shared with the sub-supply line 53. The sub-drive line 59 branches off from the main control power line 56 on the control unit 30 side with respect to the voltage stabilization unit 16 and is connected to the main drive line 57.

[0037] On the auxiliary drive line 59, a diode 61 is provided that allows current to flow only in the direction from the backup power supply 20 to the pre-driver 19. On the main drive line 57, a diode 62 is provided on the vehicle battery 92 side of the connection point with the auxiliary drive line 59 that allows current to flow in the direction from the vehicle battery 92 to the pre-driver 19.

[0038] The control unit 30 may include, for example, a CPU (Central Processing Unit) or MPU (Micro Processing Unit) that works in cooperation with software to realize a predetermined function. The control unit 30 may consist of hardware circuits such as dedicated electronic circuits or reconfigurable electronic circuits designed to realize a predetermined function, or it may consist of various semiconductor integrated circuits. Examples of various semiconductor integrated circuits include, in addition to CPUs and MPUs, microcomputers, DSPs (Digital Signal Processors), FPGAs (Field Programmable Gate Arrays), and ASICs (Application Specific Integrated Circuits). The control unit 30 may also include storage devices such as RAM (Random Access Memory), ROM (Read Only Memory), and EEPROM (Electrically Erasable Programmable Read-Only Memory).

[0039] The control unit 30 is connected to the motor drive unit 12, the switching unit 13, the charging unit 14, the discharging unit 15, the voltage stabilization unit 16, and the pre-driver 19, and controls their operation. Through this control, the power supply for the motor 11 is selected, the voltage supplied to the motor 11 is adjusted when the onboard battery 92 is selected, and the operation of the motor 11 is controlled.

[0040] The memory device of the control unit 30 temporarily or permanently stores a program for selecting the power supply for the motor 11 when performing a release operation, a program for adjusting the voltage supplied to the motor 11 when the onboard battery 92 is selected, and information used to execute these programs.

[0041] The control unit 30 is realized by, for example, an input / output interface and has an acquisition unit that receives or acquires information. The acquisition unit of the control unit 30 is connected to a release command output unit 41, a latch mechanism state detection unit 42, a temperature detection unit 43, an in-vehicle battery voltage detection unit 44, a current detection unit 45, an accident signal output unit 46, and a backup voltage detection unit 49 (discharge unit 15), and receives signals or information output from these units. The release command output unit 41, the latch mechanism state detection unit 42, the temperature detection unit 43, the in-vehicle battery voltage detection unit 44, the current detection unit 45, the accident signal output unit 46, and the backup voltage detection unit 49 are provided in the power supply device 10, or in the door latch device 1 including this, or in the vehicle including this.

[0042] The accident signal output unit 46 outputs an accident signal indicating that the vehicle is in an accident state, for example, that a collision accident has occurred. The control unit 30 can determine whether the vehicle is in an accident state according to the presence or absence of the output of the accident signal.

[0043] The accident signal output unit 46 may be, for example, an ECU of the vehicle. In that case, the ECU determines whether the vehicle is in an accident state based on a detection signal from a collision sensor composed of, for example, an in-vehicle acceleration sensor or a millimeter wave radar. When the ECU determines that the vehicle is in an accident state, it outputs an accident signal indicating that. However, the collision sensor may be the accident signal output unit 46 itself, or the control unit 30 may be directly connected to the collision sensor as the accident signal output unit 46.

[0044] If the vehicle is in an accident state, it becomes difficult or impossible to use the in-vehicle battery 92 as the power source for the motor 11, such as a failure or disconnection of the in-vehicle battery 92. As described later, when a command to operate the motor 11 is input under such a situation, the control unit 30 connects the backup power supply 20 to the motor drive unit 12 (see FIG. 2).

[0045] The release command output unit 41 outputs a release command which is a command to electrically execute the release operation. A typical example of the release command output unit 41 is a handle sensor provided on a vehicle door handle. When a user touches the door handle, the handle sensor detects this and outputs a release command. However, the release command output unit 41 can also be realized by devices other than the handle sensor. Note that the release command output unit 41 can operate using the backup power supply 20 as a power source. As will be described later, when the control unit 30 acquires the release command, the control unit 30 causes the motor 11 to execute the release operation (see FIG. 2).

[0046] The latch mechanism state detection unit 42 is constituted by, for example, a push switch attached to the fork 3, the claw 4, or a member connected thereto, and detects the state of the latch mechanism 2. The latch mechanism state detection unit 42 outputs a detection signal indicating the state of the latch mechanism 2. The latch mechanism state detection unit 42 can detect whether or not the latch mechanism 2 has been switched to the release state during the execution of the release operation. Alternatively, the control unit 30 can determine whether or not the latch mechanism 2 has been switched to the release state by monitoring the detection signal from the latch mechanism state detection unit 42 during the execution of the release operation.

[0047] The temperature detection unit 43 is constituted by, for example, a thermistor, detects the ambient temperature around the power supply device 10, and outputs ambient temperature information indicating the detection result. Examples of the ambient temperature include the ambient air temperature around the backup power supply 20 and the surface temperature of the backup power supply 20. As will be described later, the control unit 30 adjusts the voltage supplied to the motor 11 according to the acquired ambient temperature information (see FIG. 4).

[0048] The vehicle-mounted battery voltage detection unit 44 detects the output voltage of the vehicle-mounted battery 92 and outputs the detection result. As will be described later, the control unit 30 adjusts the voltage supplied to the motor 11 according to the acquired voltage information (see FIG. 4).

[0049] The current detection unit 45 detects the amount of current flowing through the motor 11 while it is operating and outputs the detection result. As described later, the control unit 30 adjusts the voltage supplied to the motor 11 while it is operating according to the acquired current amount information (see Figure 5).

[0050] As described above, the control unit 30 works in cooperation with the backup voltage detection unit 49 to detect the output voltage of the backup power supply 20 and the voltages of each capacitor 21 and 22. The acquisition unit of the control unit 30 is connected to the discharge control lines 55a and 55b.

[0051] Although detailed illustrations are omitted, the acquisition unit of the control unit 30 may be connected to the ignition signal output unit. The ignition signal output unit outputs an ignition signal indicating whether the vehicle's ignition switch (not shown) is on or off. For example, the ignition signal output unit may be an ECU (electronic control unit) mounted on the vehicle. The control unit 30 may change the charge / discharge mode of the backup power supply 20 according to the acquired ignition signal.

[0052] The control performed in the power supply unit 10 configured as described above will be explained below with reference to Figures 2 to 8. The main processing flow in Figure 2 is executed repeatedly.

[0053] As shown in Figure 2, the control unit 30 determines whether or not it has received a release command from the release command output unit 41 (step S1). If it has not received a release command (S1: NO), the process ends. If it has received a release command (S1: YES), the control unit 30 determines whether or not the vehicle is in an accident state based on the presence or absence of an accident signal from the accident signal output unit 46 (step S2).

[0054] If the vehicle is in an accident state when the release command is received (S2: NO), the control unit 30 controls the switching unit 13 so that the onboard battery 92 is not connected to the motor drive unit 12, and the backup power supply 20 is connected to the motor drive unit 12 (step S3). Next, the control unit 30 executes a non-PWM type motor drive process S4 (see Figure 3). The non-PWM type motor drive process S4 is a process that drives the motor 11 by non-PWM control (i.e., without using PWM control).

[0055] As shown in Figure 3, in the non-PWM type motor drive process S4, the motor drive unit 12 operates the motor 11 with the input voltage to the motor drive unit 12 (i.e., the output voltage of the power supply), causing the motor 11 to perform a release operation (step S41). In other words, the duty cycle for the motor drive unit 12 is fixed at 100%.

[0056] The control unit 30 monitors the detection signal from the latch mechanism state detection unit 42 and determines whether the latch mechanism 2 has switched to the release state (step S42). The control unit 30 continues to operate the motor 11 until the latch mechanism 2 switches to the release state (S42: NO → S41). When it switches to the release state (S42: YES), the motor 11 stops and the process ends.

[0057] Returning to Figure 2, if the vehicle is not in an accident state when the release command is received (S2: YES), the control unit 30 controls the switching unit 13 and does not connect the backup power supply 20 to the motor drive unit 12, but connects the on-board battery 92 to the motor drive unit 12 (step S5). Next, the control unit 30 sequentially executes a voltage adjustment process S6 (see Figure 4) to adjust the effective voltage, and a PWM type motor drive process S7 (see Figure 5). The PWM type motor drive process S7 is a process that drives the motor 11 using PWM control.

[0058] As shown in Figure 4, in the voltage adjustment process S6, the control unit 30 sets the duty cycle command value output from the control unit 30 to the adjustment unit 25 (PWM adjustment unit 26) in the PWM motor drive process S7. As will be described later, if the duty cycle is adjusted in the PWM motor drive process S7, the control unit 30 sets the initial value of the duty cycle command value for PWM control in the voltage adjustment process S6.

[0059] In this embodiment, first, the control unit 30 sets the duty cycle for PWM control such that the effective voltage is within the operating voltage range of the motor 11 (step S61).

[0060] Furthermore, the control unit 30 acquires the output voltage of the onboard battery 92 detected by the onboard battery voltage detection unit 44 (step S62). The control unit 30 sets the duty cycle for PWM control according to the detected output voltage of the onboard battery 92 (step S63).

[0061] Furthermore, the control unit 30 acquires the ambient temperature detected by the temperature detection unit 43 (step S64). The control unit 30 sets the duty cycle for PWM control according to the detected ambient temperature (step S65).

[0062] Here, "setting the duty cycle" also includes correcting the duty cycle set in a previous setting process during the current setting process. The correction may be performed by multiplication by a correction rate, or by addition or subtraction of correction values.

[0063] For example, in the voltage adjustment process S6 illustrated in Figure 4, the basic value of the duty cycle may be set in the setting process of step S61. The basic value is a fixed value pre-stored in the memory of the control unit 30, and is, for example, 40%.

[0064] In the setting process of step S63, the duty cycle (basic value) set in the setting process of step S61 may be corrected according to the output voltage, and a correction value for the duty cycle may be set.

[0065] In the setting process of step S65, the duty cycle (correction value) set in the setting process of step S63 may be corrected according to the ambient temperature, and a recorrected duty cycle value may be set. Since there are no further setting processes, this recorrected value may be set as the command value output to the PWM adjustment unit 26.

[0066] Regarding the settings according to the output voltage, even if the nominal voltage of the vehicle battery 92 is 12V, the output voltage of the vehicle battery 92 can fluctuate within a range of approximately 8V to approximately 16V. If the duty cycle is constant, when the output voltage is near the upper limit of the fluctuation range, the effective voltage may exceed the operating voltage range, potentially causing the motor 11 to fail. Also, when the output voltage is near the lower limit of the fluctuation range, the effective voltage may fall below the operating voltage range, potentially preventing the motor 11 from operating properly. If the duty cycle is constant, it is difficult to avoid both of these problems.

[0067] Referring to Figure 6, in step S63, the duty cycle is set so that the higher the output voltage, the lower the duty cycle. When the base value is corrected according to the output voltage, the duty cycle is corrected so that the correction rate multiplied by the base value decreases as the output voltage increases. This makes it possible to adjust the effective voltage to a voltage within the operating voltage range regardless of fluctuations in the output voltage.

[0068] Regarding settings according to ambient temperature, the torque generated by the motor 11 (generated torque) changes with ambient temperature, even if the voltage or effective voltage is the same. The higher the ambient temperature, and the lower the ambient temperature, the lower the generated torque. Therefore, even if the motor 11 can generate the torque necessary to operate the latch mechanism 2 (required torque) in the normal temperature range when the effective voltage is at a certain value, the generated torque may fall short of the required torque in the high-temperature or low-temperature range.

[0069] Referring to Figure 7, in step S65, the duty cycle is set to increase as the ambient temperature is higher than the reference temperature. Also, the duty cycle is set to increase as the ambient temperature is lower than the reference temperature. When correcting the base value or correction value according to the ambient temperature, the duty cycle is corrected so that the correction rate multiplied by the base value or correction value increases as the ambient temperature deviates from the reference temperature. As a result, the motor 11 can generate the required torque regardless of the ambient temperature. The reference temperature is, for example, 20°C.

[0070] Once the command value for the duty cycle of the PWM control is set in this way, the process returns to the main flow shown in Figure 2. The process then proceeds to the PWM motor drive process S7 shown in Figure 5.

[0071] Referring to Figure 5, in the PWM motor drive process S7, the control unit 30 acquires the amount of current flowing to the motor 11 detected by the current detection unit 45 (step S71). The control unit 30 drives the motor 11 while adjusting the duty cycle of the PWM control according to the detected amount of current, and causes the motor 11 to perform a release operation (step S72).

[0072] Referring to Figure 8, in step S63, the command value set in voltage adjustment process S6 is corrected so that the duty cycle increases as the current increases. The duty cycle is corrected so that the correction rate multiplied by the command value increases as the current increases. As a result, if the operating speed is high, the operating speed can be reduced. If the operating speed is low, the operating speed can be increased. Therefore, the operating speed of the motor 11 during release operation becomes appropriate.

[0073] Through such corrections or adjustments, the duty cycle of the PWM control can be set, for example, within a range of 30% to 65%.

[0074] The control unit 30 monitors the detection signal from the latch mechanism state detection unit 42 and determines whether the latch mechanism 2 has switched to the release state (step S73). The control unit 30 continues to operate the motor 11 while adjusting the duty cycle until the latch mechanism 2 switches to the release state. When it switches to the release state (S73: YES), the motor 11 stops and the process ends.

[0075] As described above, the vehicle power supply device 10 according to this embodiment includes a motor 11 (low-voltage motor) that can operate at a voltage within an operating voltage range lower than the minimum output voltage of the onboard battery 92, a backup power supply 20 as a backup for the onboard battery 92, a motor drive unit 12 that supplies voltage supplied from the onboard battery 92 or the backup power supply 20 to the motor 11 and drives the motor 11, and an adjustment unit 25 that adjusts the voltage supplied from the motor drive unit 12 to the motor 11 to a voltage within the operating voltage range when voltage is supplied from the onboard battery 92 to the motor drive unit 12.

[0076] This allows the motor 11 to operate without a boost circuit, even if the output of the backup power supply 20 is low. The configuration of the power supply unit 10 is simplified, and the manufacturing cost of the power supply unit 10 is reduced. On the other hand, even if the output voltage of the onboard battery 92 is high, the adjustment unit 25 can adjust the voltage supplied from the motor drive unit 12 to the motor 11 to a voltage within the operating voltage range. Therefore, a low-voltage motor can be stably operated with the onboard battery 92.

[0077] The adjustment unit 25 is a PWM adjustment unit 26 that controls the motor drive unit 12 using PWM and adjusts the voltage supplied to the motor 11 to a voltage within the operating voltage range. By controlling the motor drive unit 12 using PWM, the voltage (effective voltage) supplied from the motor drive unit 12 to the low-voltage motor can be easily adjusted to a voltage within the operating voltage range.

[0078] The power supply unit 10 further includes an on-board battery voltage detection unit 44 that detects the output voltage of the on-board battery 92. The PWM adjustment unit 26 sets the duty cycle of the PWM control according to the output voltage of the on-board battery 92 detected by the on-board battery voltage detection unit 44, and adjusts the voltage supplied to the motor 11 to a voltage within the operating voltage range. As a result, even if the output voltage of the on-board battery 92 fluctuates from the nominal voltage, the voltage supplied from the motor drive unit 12 to the low-voltage motor can be accurately adjusted to a voltage within the operating voltage range according to the output voltage at that time.

[0079] The power supply unit 10 further includes a temperature detection unit 43 for detecting ambient temperature. The PWM adjustment unit 26 sets the duty cycle for PWM control according to the ambient temperature detected by the temperature detection unit 43 and adjusts the voltage supplied to the low-voltage motor to a voltage within the operating voltage range. This allows the low-voltage motor to be operated to generate the required torque according to the ambient temperature at that time, even if the torque generated by the low-voltage motor decreases due to the influence of ambient temperature.

[0080] The power supply unit 10 further includes a current detection unit 45 that detects the amount of current flowing to the motor 11. The PWM adjustment unit 26 sets the duty cycle of the PWM control according to the amount of current detected by the current detection unit 45 when the motor drive unit 12 is driving the motor 11. This makes it possible to operate the low-voltage motor at an appropriate speed.

[0081] (Second Embodiment) Next, with reference to Figures 9 to 12, the second embodiment will be described, focusing on the differences from the first embodiment.

[0082] As shown in Figure 9, in the power supply device 10 according to this embodiment, the adjustment unit 25 is a step-down unit 27 that steps down the voltage supplied from the onboard battery 92 to the motor drive unit 12 to a voltage within the operating voltage range. When the onboard battery 92 is connected to the motor drive unit 12, the output voltage of the step-down unit 27, rather than the output voltage of the onboard battery 92, becomes the input voltage to the motor drive unit 12.

[0083] The step-down unit 27 is composed of, for example, a DC / DC converter or a regulator. The step-down unit 27 is interposed on the main power supply line 51 on the vehicle battery 92 side relative to the switching unit 13. The step-down unit 27 is configured to be able to change the output voltage. The operation of the step-down unit 27, that is, the output voltage of the step-down unit 27, is controlled by the control unit 30.

[0084] Referring to Figure 10, similar to the first embodiment, if the vehicle is in an accident state when the release command is acquired (S1: YES, S2: NO), the backup power supply 20 is connected to the motor drive unit 12 (step S3), and the non-PWM type motor drive process S4A is executed. Referring to Figure 12, the non-PWM type motor drive process S4A also proceeds in the same manner as the first embodiment (steps S41, S42). When the latch mechanism 2 switches to the release state (S42: YES), the process ends.

[0085] Returning to Figure 10, similar to the first embodiment, if the vehicle is not in an accident state when the release command is received (S1: YES, S2: YES), the on-board battery 92 is connected to the motor drive unit 12 (step S5).

[0086] In this embodiment, unlike the first embodiment, a voltage adjustment process S8 (see Figure 11) is performed before the connection process (step S5). Also, after the connection process (step S5), a non-PWM type motor drive process S4A (see Figure 12) is performed instead of a PWM type motor drive process.

[0087] Referring to Figure 11, in the voltage adjustment process S8 according to this embodiment, the control unit 30 sets the output voltage of the step-down unit 27 to a voltage within the operating voltage range of the motor 11 (step S81).

[0088] Furthermore, the control unit 30 acquires the ambient temperature detected by the temperature detection unit 43 (step S82). The control unit 30 sets the output voltage of the step-down unit 27 according to the detected ambient temperature (step S83).

[0089] Here, "setting the output voltage" also includes correcting the output voltage that was set in a previous setting process. The correction may be performed by multiplication by a correction rate, or by addition or subtraction of a correction value.

[0090] For example, in the voltage adjustment process S8 illustrated in Figure 11, the basic value of the output voltage may be set in the setting process of step S81. The basic value is a fixed value pre-stored in the memory of the control unit 30, and is, for example, 5V. The basic value is lower than the minimum output voltage of the onboard battery 92, and therefore can be set regardless of the output voltage of the onboard battery 92.

[0091] In the setting process of step S83, the output voltage (basic value) set in the setting process of step S81 may be corrected according to the ambient temperature, and a correction value for the output voltage of the step-down unit 27 may be set. In this embodiment as well, the more the ambient temperature deviates from the reference temperature, the higher the output voltage is set to. This makes it possible to generate the required torque in the motor 11 regardless of the ambient temperature.

[0092] Once the output voltage of the step-down unit 27 is set in this way, the control unit 30 operates the step-down unit 27 so that its output voltage becomes this set value (step S84). The process returns to the main flow in Figure 2, and the onboard battery 92 is connected to the motor drive unit 12 via the step-down unit 27. The process then proceeds to the non-PWM type motor drive process S4A in Figure 12.

[0093] Referring to Figure 12, in the non-PWM type motor drive process S4A according to this embodiment, the control unit 30 determines whether or not the backup power supply 20 is connected to the motor drive unit 12 (step S40). If the backup power supply 20 is connected (S40: YES), the process proceeds as described above, in the same manner as in the first embodiment.

[0094] If the vehicle battery is connected after the voltage adjustment process S8 described above (S40: NO), the control unit 30 acquires the amount of current flowing to the motor 11 detected by the current detection unit 45 (step S43). The control unit 30 drives the motor 11 while adjusting the output voltage of the step-down unit 27 according to the detected amount of current, causing the motor 11 to perform a release operation (step S44). In this embodiment as well, the output voltage of the step-down unit 27 is adjusted so that the output voltage of the step-down unit 27 increases as the amount of current increases. This ensures that the operating speed of the motor 11 during the release operation is appropriate.

[0095] Through such correction or adjustment, the output voltage of the step-down unit 27, i.e., the input voltage to the motor drive unit 12, is set to, for example, within the range of 4V to 6V.

[0096] The control unit 30 monitors the detection signal from the latch mechanism state detection unit 42 and determines whether the latch mechanism 2 has switched to the release state (step S45). The control unit 30 continues to operate the motor 11 while adjusting the output voltage of the step-down unit 27 until the latch mechanism 2 switches to the release state. When it switches to the release state (S45: YES), the motor 11 stops and the process ends.

[0097] As described above, in the vehicle power supply device 10 according to this embodiment, the adjustment unit 25 is a step-down unit 27 that steps down the voltage supplied from the on-board battery 92 to the motor drive unit 12 to a voltage within the operating voltage range.

[0098] This allows the voltage supplied to the motor 11 to be kept within the operating voltage range without reducing the effective voltage through PWM control. Therefore, the pre-driver 19 does not need to function as an adjustment unit 25, and the power supply unit 10 can be configured simply. In this embodiment, while simplifying the power supply unit 10, the motor 11 can be operated stably without using PWM control even when the onboard battery 92 is selected as the power source.

[0099] (Variations) Although embodiments have been described so far, the above configuration is merely an example and can be modified as appropriate within the scope of the spirit of the present invention.

[0100] In the voltage adjustment process S6 according to the first embodiment, the duty cycle is set in the following order: setting a basic value (step S61), correction according to the output voltage of the onboard battery 92 (step S63), and correction according to the ambient temperature (step S65). This is merely one example. If there are three setting processes, the correction according to the output voltage of the onboard battery 92 and the correction according to the ambient temperature may be performed in the reverse order.

[0101] Steps S63 and S65 may be omitted, and the command value for the duty cycle may always be set to a constant value. Either step S63 or step S65 may be omitted. If step S63 is omitted, step S62 is also omitted. If step S65 is omitted, step S64 is also omitted.

[0102] Step S61 may be omitted. In this case, the duty cycle corresponding to the correction value in the first embodiment may be directly derived according to the output voltage. Subsequently, the duty cycle may be corrected according to the ambient temperature as needed. Alternatively, the duty cycle obtained by multiplying the base value in the first embodiment by a correction rate according to the ambient temperature may be directly derived according to the ambient temperature. Subsequently, the duty cycle may be corrected according to the output voltage of the onboard battery 92 as needed.

[0103] In the PWM motor drive process S7 according to the first embodiment, the duty cycle is adjusted according to the amount of current. This adjustment is optional.

[0104] In the voltage adjustment process S8 according to the second embodiment, the output voltage of the step-down unit 27 is set in the order of setting a basic value (step S81) and correcting according to the ambient temperature (step S83). This is merely an example. Step S83 may be omitted. When step S83 is omitted, step S82 is also omitted. Step S81 may also be omitted. In this case, the output voltage corresponding to the correction value in the second embodiment is directly derived according to the ambient temperature.

[0105] In the non-PWM type motor drive process S4A according to the second embodiment, when the onboard battery 92 is connected to the motor drive unit 12, the output voltage of the step-down unit 27 is adjusted according to the amount of current. This adjustment is optional.

[0106] In the above embodiment, the backup power supply 20 is configured with a capacitor. This is just one example. The backup power supply 20 may be other secondary batteries, such as a lithium-ion battery.

[0107] In the above embodiment, the power supply unit 10 is applied to the door latch device 1. This is just one example. The power supply unit 10 can also be applied to other devices such as electric tailgates, electric sliding doors, electric fuel lids, electric side mirrors, or power windows.

[0108] 1 Door latch device 2 Latch mechanism 3 Fork 4 Claw 10 Power supply unit 11 Motor (low voltage motor) 12 Motor drive unit 13 Switching unit 13a Main switch element 13b Sub-switch element 14 Charging unit 15 Discharging unit 16 Voltage stabilization unit 19 Pre-driver 20 Backup power supply 21, 22 Capacitors 25 Adjustment unit 26 PWM adjustment unit 27 Step-down unit 30 Control unit 41 Release command output unit 42 Latch mechanism state detection unit 43 Temperature detection unit 44 Onboard battery voltage detection unit 45 Current detection unit 46 Fault signal output unit 49 Backup voltage detection unit 51 Main power supply line 52 Ground line 53 Sub-power supply line 54 Charging line 55a, 55b Discharge control line 56 Main control power supply line 57 Main drive line 58 Sub-control power line 59 Sub-drive lines 61, 62 Diode 91 Striker 92 Onboard battery S4, S4A Non-PWM motor drive processing S6, S8 Voltage adjustment processing S7 PWM motor drive processing

Claims

1. A vehicle power supply device comprising: a low-voltage motor capable of operating at a voltage within an operating voltage range lower than the minimum output voltage of the vehicle battery; a backup power supply as a backup for the vehicle battery; a motor drive unit that supplies voltage from the vehicle battery or the backup power supply to the low-voltage motor and drives the low-voltage motor; and an adjustment unit that adjusts the voltage supplied from the motor drive unit to the low-voltage motor to a voltage within the operating voltage range when voltage is supplied from the vehicle battery to the motor drive unit.

2. The vehicle power supply device according to claim 1, wherein the adjustment unit is a PWM adjustment unit that controls the motor drive unit and adjusts the voltage supplied to the low-voltage motor to a voltage within the operating voltage range.

3. The vehicle power supply device according to claim 2, further comprising an on-board battery voltage detection unit for detecting the output voltage of the on-board battery, wherein the PWM adjustment unit sets the duty cycle of the PWM control according to the output voltage of the on-board battery detected by the on-board battery voltage detection unit, and adjusts the voltage supplied to the low-voltage motor to a voltage within the operating voltage range.

4. The vehicle power supply device according to claim 2, further comprising a temperature detection unit for detecting ambient temperature, wherein the PWM adjustment unit sets the duty cycle of the PWM control according to the ambient temperature detected by the temperature detection unit and adjusts the voltage supplied to the low-voltage motor to a voltage within the operating voltage range.

5. A vehicle power supply device according to any one of claims 2 to 4, further comprising a current detection unit for detecting the amount of current flowing through the low-voltage motor, wherein the PWM adjustment unit sets the duty cycle of the PWM control according to the amount of current detected by the current detection unit when the motor drive unit is driving the low-voltage motor.

6. The vehicle power supply device according to claim 1, wherein the adjustment unit is a step-down unit that steps down the voltage supplied from the vehicle battery to the motor drive unit to a voltage within the operating voltage range.

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