JP2019157694A - Power control device for vehicle - Google Patents

Abstract

To provide a power control device capable of compatibly attaining appropriate restart of an engine and appropriate power supply to an electric load.SOLUTION: The power control device includes a power generator 4 to be driven by the engine to generate power, a storage battery 9 capable of storing power generated by the power generator 4, a driving force imparting device 4 capable of imparting driving force to the engine 2 using the power of the storage battery 9, and a step-down device 10 laid between an electric load 13 and the storage battery 9 for stepping down the voltage of the storage battery 9 to supply the power to the electric load 13. At the automatic stop of the engine 2, output voltage of the step-down device 10 is set lower when a piston position determination distance as a distance between the position of a piston 2d of a cylinder 2c in a compression stroke and the position of a compression top dead center is long than when it is short.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power control device provided in a vehicle capable of automatically stopping and restarting an engine.

  Conventionally, for the purpose of improving fuel economy performance, in a vehicle, a generator is driven by an engine when decelerating to generate power, or a so-called idle stop that automatically stops the engine during idle operation of the engine and the accelerator pedal The engine is restarted in response to depression.

  For example, Patent Document 1 discloses a vehicle including a motor generator that is connected to an engine and functions as an electric motor and a generator, and a capacitor that supplies electric power to the motor generator and stores electric power generated by the motor generator. Has been. In this vehicle, at the time of deceleration, a motor generator is driven by an engine to generate electric power, and the generated electric power is stored in a capacitor. When the engine is restarted after the idle stop, the motor generator is driven by the power of the capacitor to forcibly rotate the engine.

  In the vehicle of Patent Document 1, a lead storage battery is provided in addition to the capacitor. A part of the electric power stored in the capacitor or the electric power generated by the motor generator is stepped down by a DC-DC converter and applied to the lead storage battery and various electric loads.

JP-A-2006-118126

  In the configuration of Patent Document 1, the converter interposed between the capacitor and the electrical load is configured to have only a function of stepping down voltage without boosting voltage. Therefore, the cost can be kept low. However, in this configuration, there is a possibility that the electric load supplied with power from the capacitor via the DC-DC converter does not operate properly.

  Specifically, when the voltage of the capacitor is significantly reduced as the motor generator is driven when the engine is restarted, the input voltage of the converter may be lower than the output voltage of the converter. Thus, when the input voltage of the converter falls below the output voltage of the converter, the converter cannot step down the input voltage, and power supply from the capacitor through the converter to various electric loads is stopped. As a result, the electric power source of these electric loads is switched to a lead storage battery having a voltage lower than that of the capacitor, and the voltage applied to the electric load is suddenly lowered, and the electric load may not operate properly.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a power control apparatus that can achieve both appropriate engine restart and power supply to an appropriate electric load.

  In order to solve the above-described problems, the present invention provides a power control device for a vehicle provided in a vehicle capable of automatically stopping and restarting the engine, wherein the power generation device is driven by the engine to generate electric power, Between a storage battery capable of storing the electric power generated by the power generation device during deceleration, a driving force application device capable of applying a driving force to the engine using the electric power of the storage battery, an electric load provided in a vehicle, and the storage battery And a step-down device for stepping down the voltage of the storage battery to supply electric power to the electric load, and the step-down device can be controlled so that the output voltage of the step-down device is changed. A control device that controls the driving force application device so that a driving force for restarting the engine is applied from the driving force application device to the engine when there is a request to start the engine; The control device, when the engine is automatically stopped, than when the piston position determination distance, which is the distance between the piston position of the cylinder in the compression stroke and the compression top dead center position, is smaller, An output voltage of the step-down device is lowered, and a vehicle power control device is provided (claim 1).

  According to this configuration, energy efficiency can be increased by causing the storage battery to store energy as power when the vehicle is decelerated. Moreover, the engine can be restarted appropriately by driving the driving force applying device with the electric power stored in the storage battery when the engine is restarted to apply the driving force to the engine.

  Here, when the engine is restarted, when the piston position determination distance, which is the distance between the position of the piston of the cylinder in the compression stroke and the position of the compression top dead center, is large, than when the piston position determination distance is small. However, it is necessary to increase the driving force of the driving force applying device because the distance that the piston must be forced up is long. However, when this driving force is increased, the voltage drop amount of the storage battery increases, and the voltage of the storage battery may fall below the output voltage of the step-down device. On the other hand, in this configuration, when the engine is automatically stopped, the output voltage of the step-down device is made lower when the piston position determination distance is larger than when it is smaller. Therefore, even when the piston position determination distance is large, when the engine is restarted, the driving force of the driving force applying device is increased so that the piston is more reliably pushed up to the compression top dead center while the voltage of the storage battery is reduced. Therefore, it is possible to maintain an appropriate power supply to the electric load. When the piston position determination distance is small, it is possible to prevent the output voltage of the step-down device from being excessively lowered, and to secure many opportunities to stably supply a high voltage to the electric load. As a result, the electric load can be appropriately operated while the engine is appropriately restarted.

  In the above configuration, the control device performs output voltage reduction control that gradually decreases the output voltage of the step-down device toward an adjustment voltage lower than the voltage before the engine is automatically stopped when the engine is automatically stopped, and the piston position It is preferable to set the adjustment voltage to a lower value when the determination distance is large than when the determination distance is small.

  According to this configuration, when the engine is restarted, the output voltage of the step-down device can be reliably made lower than the voltage of the storage battery. Therefore, it is possible to maintain the power supply from the storage battery to the electric load and prevent the voltage applied to the electric load from changing suddenly. In addition, since the adjustment voltage is changed according to the piston position determination distance, it is possible to secure many opportunities to stably supply a high voltage to the electric load while obtaining the above effect. In addition, in this configuration, since the output voltage of the step-down device is gradually reduced toward the adjustment voltage, the output voltage of the step-down device and therefore the voltage applied to the electric load change suddenly when the output voltage is reduced to the adjustment voltage. Can also be prevented.

  In the above configuration, when the piston position determination distance is less than a predetermined first determination distance, the control device performs the output voltage reduction control when the internal resistance of the storage battery is equal to or greater than a preset first reference resistance value. When the internal resistance of the storage battery is less than the first reference resistance value, the output voltage reduction control is prohibited. When the piston position determination distance is equal to or greater than the predetermined first determination distance, the internal resistance of the storage battery is The output voltage drop control is performed when the second reference resistance value is smaller than the first reference resistance value, and the output voltage drop control is prohibited when the internal resistance of the storage battery is less than the second reference resistance value. (Claim 3).

  According to this configuration, output voltage reduction control is performed only when the internal resistance of the storage battery is equal to or greater than a predetermined resistance value (first reference resistance value or second reference resistance value). That is, output voltage reduction control is performed only when the internal resistance of the storage battery is high and the voltage drop of the storage battery is large when the driving force application device is driven. In addition, in this configuration, when the piston position determination distance is greater than or equal to a predetermined distance, the predetermined resistance value for determining whether to perform output voltage reduction control is smaller than when the piston position determination distance is less than the predetermined distance. Value. Therefore, while avoiding that the output voltage of the step-down device becomes higher than the voltage of the storage battery at the time of restarting the engine, it is possible to reduce the opportunity to perform the output voltage reduction control and to increase the voltage from the storage battery to the electric load via the step-down device. Many opportunities for stable supply.

  The said structure WHEREIN: It is preferable that the said control apparatus estimates the internal resistance of the said storage battery based on the deterioration state of the said storage battery, and the temperature of the said storage battery (Claim 4).

  In this way, the internal resistance of the storage battery can be estimated more accurately.

  In the above configuration, the vehicle includes a pair of side sills that extend in the vehicle front-rear direction along both sides of the vehicle compartment in the vehicle width direction, and a floor tunnel that is provided below the floor of the vehicle compartment and extends in the vehicle front-rear direction. The storage battery includes a plurality of batteries arranged in a row, and the batteries are arranged below the floor of the passenger compartment and between the floor tunnel and one of the side sills in the vehicle front-rear direction. It is preferable that they are arranged (claim 5).

  If it does in this way, the comparatively big storage battery containing a some battery can be mounted in a vehicle using the space between a floor tunnel and a side sill. However, when a plurality of batteries are arranged in a row as described above, that is, when a plurality of batteries are arranged in series, the internal resistance of the storage battery becomes large, and the driving force applying device is required when the engine is restarted. The voltage drop of the storage battery when driven is likely to increase. In contrast, in the present invention, as described above, the output voltage of the step-down device can be maintained at a voltage lower than the voltage of the storage battery even if the storage battery drops when the engine is restarted. Therefore, the operation of the electric load can be stably brought into an appropriate state while laying out the storage battery as described above.

  In the above configuration, the battery further includes a secondary storage battery capable of storing the power output from the step-down device and having a maximum output voltage lower than that of the storage battery, and the electric load is supplied from the secondary storage battery in addition to the step-down device. They are preferably connected to these so that they can also receive power (claim 6).

  If it does in this way, even if the voltage of a storage battery becomes lower than the output voltage of a pressure | voltage fall apparatus, electric power can be supplied to an electrical load with a secondary storage battery, and the action | operation of an electrical load can be maintained. Moreover, the electric power generated by the generator and not stored in the storage battery can be stored in the secondary storage battery, and the energy efficiency can be improved.

  The said structure WHEREIN: It is preferable that the said driving force provision apparatus is driven only with the electric power of the said storage battery among the said storage battery and the said secondary storage battery at least at the time of restart of an engine.

  If it does in this way, degradation of a secondary storage battery can be suppressed by suppressing the power consumption opportunity of a secondary storage battery few.

  As described above, according to the power control apparatus of the present invention, both appropriate engine restart and power supply to an appropriate electric load can be achieved.

1 is a diagram schematically showing a configuration of a vehicle equipped with a power control apparatus according to an embodiment of the present invention. 1 is a plan view schematically showing a part of a vehicle. It is the schematic for demonstrating the structure of a DC-DC converter. It is a block diagram which shows the control system of an engine. It is a figure for demonstrating the relationship between the position of a piston, and a target range, (a) is a figure when the position of a piston is in a target range, (b) is when the position of a piston is outside a target range. FIG. It is the flowchart which showed the flow of stop position control. It is the figure which showed the time change of each parameter at the time of vehicle travel which concerns on a comparative example. It is the flowchart which showed the first half part of the engine automatic stop control. It is the flowchart which showed the second half part of the engine automatic stop control. It is the figure which showed the target output map. It is the figure which showed the relationship between the temperature of Li battery, internal resistance, and the progress of deterioration. It is the figure which showed the relationship between target drop voltage and voltage drop speed. It is the figure which showed the time change of each parameter at the time of vehicle travel. It is the figure which showed the other example of the map of the target output voltage of a DC-DC converter.

  Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each figure, the same numerals are given to the same element, and explanation is omitted suitably.

(1) Overall Configuration of Vehicle FIG. 1 is a diagram schematically showing a configuration of a vehicle on which an engine stop control device is mounted.

  The vehicle 1 is, for example, a four-wheeled vehicle. The engine 2 is provided in the engine room of the vehicle 1. The driving force of the engine 2 is transmitted from the crankshaft 2a to the wheels 1a via a transmission, a final reduction gear, a drive shaft, and the like, thereby causing the vehicle 1 to travel.

  As shown in FIG. 1, the vehicle 1 includes an engine 2, a starter 3, a motor generator 4, a Li battery (lithium battery) 9, a DC-DC converter 10, a lead battery 12, and various electric devices as a vehicle drive source. Equipment is installed. As will be described later, the motor generator 4 is a so-called ISG (Integrated Starter-Generator) having a function as an electric motor and a function as a generator. Hereinafter, this is referred to as an ISG 4.

  The Li battery 9 corresponds to the “storage battery” in the claims, the lead battery 12 corresponds to the “secondary storage battery” in the claims, and the DC-DC converter 10 corresponds to the “step-down device” in the claims. The ISG 4 corresponds to a “power generation device” and a “driving force applying device” in the claims. That is, in this embodiment, the power generation device and the driving force applying device are integrated into a single device.

  In the example of FIG. 1, the engine 2 is an in-line four-cylinder engine having four cylinders 2c arranged in a row. The engine 2 is a reciprocating engine and includes a piston 2d (see FIG. 5A) that reciprocates in the cylinder 2c. In the present embodiment, the engine 2 is an engine driven by fuel including gasoline. The engine 2 includes an injector 30 (see FIG. 4) that injects fuel into each cylinder 2c, and an ignition plug 31 (see FIG. 4) that ignites an air-fuel mixture (air / fuel mixture) in each cylinder 2c. I have. One injector 30 and one spark plug 31 are provided for each cylinder 2c.

(High voltage circuit)
The Li battery 9 is electrically connected to the ISG 4, the seat heater 5, and the PTC heater 6 through the high voltage line L 1, and these constitute a high voltage circuit 14.

  The ISG 4 is a device that can operate as a generator and an electric motor. The ISG 4 is connected to the crankshaft 2a of the engine 2 via a belt 4a.

  When the ISG 4 operates as a generator, the ISG 4 generates power by rotating a rotor that rotates in conjunction with the crankshaft 2a of the engine 2 in a magnetic field. The ISG 4 can adjust the generated voltage within a range up to several tens of volts in accordance with the increase or decrease of the current supplied to the field coil that generates the magnetic field. The ISG 4 incorporates a rectifier (not shown) that converts the generated AC power into DC power. The electric power generated by the ISG 4 is converted into direct current by this rectifier, then output to the high voltage line L1, and stored in the Li battery 9 via the high voltage line L1.

  In the present embodiment, the ISG 4 is controlled to operate as a generator when the vehicle is decelerated, and converts the rotational energy of the engine 2 into electricity. That is, in the present embodiment, the ISG 4 is configured to perform so-called deceleration regenerative power generation.

  When the ISG 4 operates as an electric motor, the ISG 4 is driven by power supplied from the Li battery 9 and transmits the driving force to the crankshaft 2a of the engine 2 via the belt 4a to apply the driving force to the engine 2. .

  Thus, in the present embodiment, the ISG 4 functions as a power generation device that generates power by being driven by the engine 2 and a driving force application device that can apply a driving force to the engine 2 using the power of the Li battery. Further, the Li battery functions as a storage battery capable of storing the electric power generated by the ISG 4 when the vehicle is decelerated.

  The ISG 4 operates as an electric motor to start the engine 2 at the start of the engine except during the cold start (forcibly rotates the engine 2). In the present embodiment, the vehicle 1 is configured so that the engine 2 can be automatically stopped, and the engine 2 is restarted by the ISG 4 even when the engine 2 is restarted after the engine 2 is automatically stopped. Specifically, the engine 2 is started / stopped by the passenger operating an ignition switch provided in the vehicle 1. Further, the engine 2 is automatically stopped when a condition such as the vehicle speed is equal to or less than a predetermined value and the engine is in an idle state, and then the engine 2 is automatically restarted when a condition such as the accelerator pedal is depressed. Is done.

  Further, the ISG 4 is controlled so as to operate as an electric motor when the engine load is low, etc., and applies driving force to the engine 2. That is, in this embodiment, the ISG 4 is also configured to perform so-called torque assist.

  The Li battery 9 is a battery that contains lithium in the positive electrode and is charged and discharged by movement of lithium ions between the positive electrode and the negative electrode. The Li battery 9 can be charged / discharged at a faster speed than the lead battery 12, and deterioration due to charge / discharge is less likely to proceed than the lead battery 12. In the present embodiment, since the electric power generated by the ISG 4 is configured to be stored in the Li battery 9, the deceleration energy of the engine 2 can be efficiently stored in the vehicle 1 as electric power. The nominal voltage of the Li battery 9 is higher than the negotiated voltage of the lead battery 12 so that more electric power generated by the ISG 4 can be stored. In this embodiment, the nominal voltage of the Li battery 9 is DC 24V. Here, there is a capacitor as a device capable of storing a large amount of electric power with a high charge / discharge speed, but the Li battery 9 can have a larger capacity than a capacitor of the same size. Therefore, in this embodiment, miniaturization of the device for storing electric power is also realized.

  FIG. 2 is a plan view schematically illustrating a part of the vehicle 1 for explaining the arrangement of the Li battery 9. In the example of FIG. 2, the engine room 1 is formed in the front part of the vehicle 1, and the vehicle interior 80 is formed in the back.

  The vehicle 1 is provided at a lower portion of a panel 81 provided above the floor panel and constituting a floor surface of the passenger compartment, and openings (door portions) formed on both sides in the vehicle width direction of the vehicle. And a pair of side sills 82 extending in the vehicle front-rear direction along both sides in the vehicle width direction. The vehicle 1 includes a floor tunnel 83 provided below the panel 81 so as to communicate with the engine room 1 and through which a duct for discharging exhaust gas of the engine 2 to the outside of the vehicle 1 passes. The floor tunnel 83 is formed by the center portion of the floor panel 81 in the vehicle width direction bulging upward. The Li battery 9 is disposed below the panel 81 and between the floor tunnel 83 and one side sill 82 (right side sill 82 in the example of FIG. 2). In the example of FIG. 2, the Li battery 9 is disposed below the front portion of the panel 81 and below the driver seat or the passenger seat.

  By being arranged in this way, in this embodiment, the distance between the ISG 4 and the Li battery 9 and, in turn, the electric wire connecting them is kept short.

  Here, the distance in the vehicle width direction between the floor tunnel 83 and the side sill 82 is short. In contrast, in the present embodiment, a plurality of Li storage battery cells (batteries) 9a constituting the Li battery 9 are arranged in a line and connected in series, and the Li battery 9 is predetermined in plan view. The shape extends long in the direction. And the Li battery 9 is arrange | positioned so that the longitudinal direction, ie, the sequence direction of the cell 9a, may follow a vehicle front-back direction. Thereby, the Li battery 9 can be disposed at a position where the distance from the ISG 4 can be kept short as described above.

  The seat heater 5 (an example of a high-voltage electric device, an example of a passenger compartment heater) is a heater for heating the seat of the vehicle 1. The PTC heater 6 (an example of a high-voltage electric device, an example of a vehicle compartment heater) is a heater for heating the interior of the vehicle 1. The catalyst heater 7 is a heater for heating a catalyst that purifies exhaust gas. The seat heater 5, the PTC heater 6, and the catalyst heater 7 are disposed on the high voltage line L1 side in order to operate stably even at several tens of volts DC.

(Low voltage circuit)
The lead battery 12 is electrically connected to the starter 3 and the low-voltage electric device 13 through the low-voltage line L 2, and these constitute a low-voltage circuit 15. The low-voltage electric device 13 corresponds to an “electric load” in the claims.

  In the present embodiment, the lead battery 12 includes a 6-cell lead storage battery connected in series. With this configuration, the nominal voltage of the lead battery 12 is DC 12V.

  The starter 3 is a device for starting the engine 2. The starter 3 is a gear drive type device, and has a pinion gear 3 a connected to the ring gear 2 b of the engine 2. The driving force of the starter 3 is transmitted to the crankshaft 2a of the engine 2 through the pinion gear 3a and the ring gear 2b. The starter 3 is driven only at the time of cold start (when the engine 2 is started in accordance with the operation of the passenger's ignition switch at the time of cold) to start the engine 2.

  The low-voltage electric device 13 is an electric device that operates at a voltage equal to or lower than the nominal voltage of the lead battery 12 (DC 12 V in this embodiment). The low voltage electrical device 13 includes, for example, an electric power steering mechanism (EAPS), an air conditioner, an audio device, and various lighting devices.

(DC-DC converter)
The DC-DC converter 10 is provided between the high voltage circuit 14 and the low voltage circuit 15, and connects the circuits 14 and 15.

  The DC-DC converter 10 is a device for stepping down the voltage of power supplied from the high voltage line L1 to the low voltage line L2 (that is, from the left side to the right side in FIG. 1). The output power from the Li battery 9 and the power generated by the ISG 4 are stepped down by the DC-DC converter 10 and supplied to the low-voltage electrical device 13. Moreover, the surplus part of the electric power generated by the ISG 4 is supplied to the lead battery 12, and the lead battery 12 is charged.

  The DC-DC converter 10 does not have other functions, for example, a function of allowing power supply in the opposite direction (that is, from the right side to the left side in FIG. 1) or boosting the voltage. Instead, only the voltage is stepped down. With this configuration, in this embodiment, the structure of the converter for connecting the high voltage line L1 and the low voltage line L2 can be simplified and the cost can be significantly reduced.

  FIG. 3 is a schematic diagram for explaining the configuration of the DC-DC converter 10. The DC-DC converter 10 incorporates switching elements 10a and 10b (Hi-FET 10a and Low-FET 10b) made of FETs, and changes and outputs an input voltage by on / off switching of these switching elements 10a and 10b. In the DC-DC converter 10, the output voltage can be changed by changing the on / off times of the switching elements 10a and 10b. The on / off time of the switching elements 10a and 10b is changed by the ECU 100, which will be described later. The ECU 100 sets a target value of the output voltage as will be described later, and the switching element that realizes the target value. The on / off times of 10a and 10b are calculated, and a command signal is output to the DC-DC converter 10 so that the on / off times are realized.

  Here, the output voltage of the DC-DC converter 10 is basically such that power is stably supplied from the high voltage line L1 side to the low voltage line L2 side, that is, to the lead battery 12 and the low voltage electrical device 13. The basic output voltage is sufficiently higher than the nominal voltage of the lead battery 12 and the operating voltage of the low-voltage electrical device 13. That is, the target output voltage, which is the target value of the output voltage of the DC-DC converter 10, is used as the basic output voltage, and the ECU 100 performs the DC-DC converter 10 (the FET 10a built in the DC-DC converter 10) so that this is realized. 10b) is controlled. In this embodiment, the basic voltage of the lead battery 12 is set to 14.4V while the nominal voltage of the lead battery 12 is 12V. The basic output voltage may be changed according to the liquid temperature of the Li battery 9 or the like.

(2) Control System FIG. 3 is a block diagram schematically showing the electrical configuration of the control system of the vehicle 1 shown in FIG. The ECU 100 shown in FIG. 3 is a microprocessor for comprehensively controlling the engine, and includes a known CPU, ROM, RAM, and the like.

  ECU 100 receives detection information from various sensors and operation signals of various switches.

  Specifically, the vehicle 1 includes a crank angle sensor SN20, a water temperature sensor SN21, an outside air temperature sensor SN22, an accelerator sensor SN23, a brake sensor SN24, a vehicle speed sensor SN25, a Li battery voltage sensor SN26, a Li battery current sensor SN27, and an ignition switch SW28. , A PTC heater switch SW29, a seat heater switch SW30, and the like are provided.

  The crank angle sensor SN20 detects the rotational speed of the crankshaft 2a and thus the engine speed. The water temperature sensor SN21 detects the temperature of engine cooling water for cooling the engine 2. The outside air temperature sensor SN22 detects the outside air temperature, that is, the air temperature around the vehicle 1. The accelerator sensor SN23 detects the amount of depression of an accelerator pedal provided in the vehicle 1. The brake sensor SN24 detects the depression amount of the foot brake pedal. The vehicle speed sensor SN25 detects the vehicle speed. The Li battery voltage sensor SN26 and the Li battery current sensor SN27 detect the input / output voltage and the input / output current of the Li battery 9, respectively. The ignition SW (ignition switch) 20 is a switch for the occupant to start / stop the engine 2 as described above. The PTC heater SW 28 is a switch for an occupant to drive / stop the PTC heater 6. The seat heater SW29 is a switch for the occupant to drive / stop the seat heater 5.

  The ECU 100 controls each device provided in the vehicle 1 while performing various determinations and calculations based on input information of each sensor and each switch. The ECU 100 is electrically connected to the injector 30, spark plug 31, starter 3, ISG 4, seat heater 5, PTC heater 6, DC-DC converter 10, low-voltage electrical equipment 13, etc. Based on this, a control signal is output to each of these devices. The ECU 100 corresponds to a “control device” in the claims.

  For example, when the ignition SW 20 is operated when the temperature of the engine coolant detected by the water temperature sensor SN21 is lower than a predetermined temperature, the ECU 100 determines that it is during a cold start and drives the starter 3. The ECU 100 drives the seat heater 5, the PTC heater 6, the low-voltage electric device 13, and the like according to the operation of the switches such as the PTC heater SW 28 and the seat heater SW 29.

  In addition, the ECU 100 drives the ISG 4 as a generator when the vehicle speed detected by the vehicle speed sensor SN25 is decreasing, etc., and causes the ISG 4 to perform deceleration regenerative power generation as described above. The ECU 100 calculates the engine load based on the amount of depression of the accelerator pedal, the engine speed detected by the crank angle sensor SN20, and the like, and when the engine load is less than a predetermined value, the ISG 4 is driven as an electric motor from the ISG 4 to the engine. Torque is applied to 2.

  Further, the ECU 100 indicates that the temperature of the engine coolant is equal to or higher than a predetermined temperature, the accelerator pedal is in an off state (the accelerator opening is zero), and the foot brake pedal is depressed more than 0 (the foot brake pedal is depressed). The engine 2 is automatically stopped, including the condition that the engine speed is equal to or lower than the predetermined engine speed. Further, after that, when the conditions such as the brake pedal not being depressed and the accelerator pedal being depressed are satisfied, the ISG 4 is driven as an electric motor, and the engine 2 is restarted.

  In addition, the ECU 100 performs stop position control for adjusting the position of the piston 2d when the engine 2 is automatically stopped, and performs output voltage adjustment control for adjusting the output voltage of the DC-DC converter 10 in accordance with operating conditions. carry out. These controls will be described next. Hereinafter, the automatic engine stop is simply referred to as idle stop.

(Stop position control)
5A and 5B are schematic cross-sectional views of the engine body for explaining the position of the piston 2d.

  The stop position control is a control for adjusting the position of the piston 2d so as to keep the driving force of the ISG 4 smaller when the engine is restarted.

  Specifically, when the engine is restarted, fuel is first injected into the cylinder 2c in the compression stroke and ignition is performed, and combustion is first started in the cylinder 2c. Combustion starts when fuel is injected into the cylinder 2c and ignition is performed. However, if ignition is performed with the position of the piston 2d close to the bottom dead center as shown in FIG. 5B, the piston 2d is lowered by the combustion energy, and the engine 2 rotates in reverse. Therefore, in order to appropriately rotate the engine, it is necessary to perform ignition in a state where the piston 2d is located near the compression top dead center. Therefore, if the position of the piston 2d of the cylinder in the compression stroke before the engine restart is far from the compression top dead center, the amount that the piston 2d has to be pushed up only by the ISG 4 to the vicinity of the compression top dead center when the engine is restarted. As the number increases, the driving force of the ISG 4 increases. Therefore, in the present embodiment, the position of the piston 2d of the cylinder 2c in which the stroke at the time of restarting the engine becomes the compression stroke at the time when the idling stop is performed in order to keep the driving force of the ISG 4 small is shown in FIG. As shown in Fig. 4, adjust so that it is close to the compression top dead center.

  Stop position control will be described with reference to the flowchart of FIG.

  First, ECU 100 determines in step S1 whether or not a transition to the idle stop state is in progress. Specifically, as described above, after the stop of the fuel injection of the injector 30 is started in accordance with the establishment of the idle stop permission condition and when the engine speed is not 0, the idle stop state It is determined that the transition is in progress.

  If the determination in step S1 is NO and the transition to the idle stop state is not in progress, the process proceeds to step S6. In step S6, the ISG 4 is stopped (without driving), and the process is terminated.

  On the other hand, when the determination in step S1 is YES and the shift to the idle stop state is in progress, the process proceeds to step S2. In step S2, the ECU 100 predicts the piston arrival position when the engine 2 stops. Specifically, the ECU 100 determines the position of the piston 2d of each cylinder 2c when the engine speed is reduced to 0 based on the current engine speed (when step S2 is performed) and the speed at which the engine speed is reduced. Predict each one. Then, the ECU 100 predicts the cylinder 2c whose stroke when the engine speed is reduced to 0 from the position of the piston 2d of each cylinder 2c, and the position of the piston 2d of the cylinder 2c It is estimated as the position of the piston 2d of the cylinder 2c where the stroke at the start becomes the compression stroke (hereinafter, referred to as a determination piston position as appropriate).

  After step S2, the process proceeds to step S3. In step S3, it is determined whether or not the determination piston position estimated in step S2 is outside a preset target range. In this embodiment, as shown in FIG. 5A, if the position of the piston 2d is in the range from the compression top dead center (TDC) to 90 ° CA before compression top dead center (BTDC 90 ° CA), the determination piston When it is determined that the position is within the target range, and the determination piston position is in the range from 90 ° CA before compression top dead center to intake bottom dead center (BDC), it is determined that this position is outside the target range. . That is, the piston position determination distance that is the separation distance between the determination piston position and the compression top dead center is less than the first determination distance that is the separation distance between the compression top dead center and the piston position at 90 ° CA before the compression top dead center. Is determined to be within the target range, and when the piston position determination distance is equal to or greater than the first determination distance, it is determined that the determination piston position is outside the target range.

  If the determination in step S3 is NO and the determination piston position is within the target range, the process proceeds to step S6, the ISG 4 is stopped (without driving), and the process is terminated.

  On the other hand, when the determination in step S3 is YES and the determination piston position is outside the target range, the process proceeds to step S4.

  In step S4, the ECU 100 drives and drives the ISG 4 necessary for shifting the position of the piston 2d of the cylinder 2c in which the stroke at the time of restarting the engine is the compression stroke (predicted) to the target range. Calculate time.

  After step S4, the process proceeds to step S5. In step S5, the ECU 100 drives the ISG 4 so that the driving torque of the ISG 4 becomes the driving torque calculated in step S4, and drives the ISG 4 for the driving time calculated in step S4.

  After step S5, the process proceeds to step S6, and the ISG 4 is stopped.

(Output voltage adjustment control)
As described above, if the DC-DC converter 10 having a step-down function is used as the converter that connects the high voltage circuit 14 and the low voltage circuit 15, the cost can be kept extremely small. However, with this configuration, there is a possibility that the voltage applied to the low-voltage electrical device 13 connected to the low-voltage circuit 15 at the time of restarting the engine 2 may suddenly decrease.

  This will be specifically described with reference to FIG. FIG. 7 is a diagram schematically showing a time change of each parameter of the vehicle when the output voltage drop control described later is not performed. FIG. 7 shows the vehicle speed, the engine speed, the voltage of the Li battery 9, the output voltage of the DC-DC converter 10, and the voltage input to the low-voltage electric device in order from the top.

  When the vehicle starts decelerating at time t11, the voltage of the Li battery 9 rises as the ISG 4 is driven as a generator to generate power. However, when the engine 2 is automatically stopped at the time t12 when the engine speed has decreased to the idle speed, the voltage of the Li battery 9 gradually decreases. Thereafter, when there is a request to restart the engine at time t13, the ISG 4 is driven as an electric motor to forcibly rotate the engine 2. At this time, very large electric power is released from the Li battery 9 toward the ISG 4, and the voltage of the Li battery 9 suddenly drops. If this amount of voltage drop is large, the voltage of the Li battery 9 will be lower than the output voltage of the DC-DC converter 10 indicated by the broken line. When the voltage of the Li battery 9 is lower than the output voltage of the DC-DC converter 10, the DC-DC converter 10 has only a step-down function, so that power is transferred from the Li battery 9 to the low voltage circuit 15 side. The voltage supplied to the low-voltage electrical device 13 is suddenly lowered because the supply is stopped.

  In the present embodiment, since the lead battery 12 is provided in the low voltage circuit 15, each low voltage provided in the low voltage circuit 15 by the lead battery 12 even if power is not output from the DC-DC converter 10. The power supply to the electric device 13 can be continued. However, as described above, the output voltage of the DC-DC converter 10 is basically set to a value sufficiently higher than the nominal voltage of the lead battery 12. Therefore, when power is not output from the DC-DC converter 10 and the power supply source to each low-voltage electrical device 13 is switched to the lead battery 12, the voltage supplied to these low-voltage electrical devices 13 suddenly decreases, The operating state of the low-voltage electrical device 13 changes. For example, when a light is operating as the low voltage electrical device 13, the light may flicker. Further, when the audio is operating as the low-voltage electrical device 13, the audio volume may change. These make the passenger feel uncomfortable.

  Therefore, in the present embodiment, output voltage reduction control is performed to prevent such a voltage supplied to the low-voltage electrical device 13 from suddenly dropping when the engine is automatically stopped.

(Automatic stop control)
The engine automatic stop control including the output voltage drop control will be described with reference to the flowcharts of FIGS.

  In step S11, ECU 100 reads various types of vehicle information including detection values of the sensors. After step S11, the process proceeds to step S12.

  In step S12, the ECU 100 determines whether an idle stop permission condition is satisfied.

  When the determination in step S12 is NO and the idle stop permission condition is not satisfied, the ECU 100 ends the process (returns to step S11).

  On the other hand, when the determination in step S12 is YES and the idle stop permission condition is satisfied, the process proceeds to step S13. In step S13, the ECU 100 idles the engine. Specifically, ECU 100 stops fuel injection by injector 30 and stops ignition by the spark plug. In step S13, the stop position control is performed.

  After step S13, the process proceeds to step S14. In step S14, the ECU 100 determines whether or not the vehicle speed is equal to or lower than a predetermined determination vehicle speed. The determination vehicle speed is set to 0 km / h. In step S14, it is determined whether or not the vehicle is stopped. That is, in the present embodiment, the idle stop is performed even when the vehicle is not stopped. Hereinafter, the idling stop made in a state where the vehicle is not stopped as described above is referred to as a vehicle speed idling stop. An idle stop made while the vehicle is stopped is called a stopped idle stop. In the vehicle speed idle stop, since the vehicle is not stopped, the connection between the engine 2 and the transmission is released when the idle stop is performed.

  When the determination in step S14 is YES and the stop idling stop is performed, the process proceeds to step S15. In step S15, the ECU 100 determines whether or not the determination piston position is within the target range. That is, the ECU 100 determines whether or not the position of the piston 2d of the cylinder 2c, which is predicted to be the compression stroke when the engine is restarted, is actually within the target range with the engine 2 actually stopped. To do. ECU 100 makes this determination based on the detected value of crank angle sensor SN20.

  When the determination in step S15 is YES, that is, when the determination in step S14 is YES and the vehicle is idle stopped, and the determination piston position is within the target range, the process proceeds to step S16. In step S16, the ECU 100 sets the first resistance value R1 set in advance as the determination resistance value, and sets the first map as the target output map.

  The first resistance value R1 is set to 13 mΩ, for example. The target output map is a map of the target output voltage that is the target value of the output voltage of the DC-DC converter 10 with respect to the internal resistance of the Li battery 9. Hereinafter, the target output voltage of the DC-DC converter 10 is simply referred to as a target output voltage as appropriate.

  The first map is set as indicated by the solid line (thick line) in FIG. Specifically, in the first map, when the internal resistance of the Li battery 9 is less than the first resistance value R1, the target output voltage is set to the basic output voltage regardless of the internal resistance, and the internal resistance of the Li battery 9 is the first resistance. In the resistance value R1 or more, the map is set so that the target output voltage is lower when the internal resistance is larger than when the internal resistance is small. In the example of FIG. 10, the first map shows that the target output voltage decreases in proportion to the increase of the internal resistance of the Li battery 9 in the range where the internal resistance of the Li battery 9 is larger than the first resistance value R1. Is set to After step S16, the process proceeds to step S21.

  On the other hand, when the determination in step S15 is NO and the stop idling stop is made, and the determination piston position is not within the target range, the process proceeds to step S17. In step S17, the ECU 100 sets the second resistance value R2 set to a value smaller than the first resistance value R1 as a determination resistance value, and sets the second map as a target output map.

  The second resistance value R2 is set to 11 mΩ, for example. The second map is set as indicated by a solid line (thin line) in FIG. Specifically, in the second map, when the internal resistance of the Li battery 9 is less than the second resistance value R2, the target output voltage is set to the basic output voltage regardless of the internal resistance, and the internal resistance of the Li battery 9 is the second resistance. In the resistance value R2 or more, the map is set so that the target output voltage is smaller than the target output voltage of the first map. Further, in the second map, in the range where the internal resistance of the Li battery 9 is equal to or greater than the second resistance value R2, the target output voltage is set to be smaller than when the internal resistance of the Li battery 9 is small. ing. In the example of FIG. 10, in the second map, the target output voltage decreases in proportion to the internal resistance of the Li battery 9 in the range of the internal resistance second resistance value R2 or more of the Li battery 9 as the internal resistance of the Li battery 9 increases. Is set.

  As described above, even when the vehicle is idled and stopped in the same manner, when the internal resistance of the Li battery 9 is equal to or higher than the second resistance value R2, the target output voltage is determined to be outside the target range. It is set to a lower value than when the hour is within the target range.

  After step S17, the process proceeds to step S21.

  Returning to step S14, if the determination in step S14 is NO and the vehicle speed idle stop is performed, the process proceeds to step S18.

  In step S18, the same determination as in step S15 is performed. That is, in step S18, the ECU 100 determines whether or not the determination piston position is within the target range.

  When the determination in step S18 is YES, that is, when the determination in step S14 is NO and the vehicle speed idle stop is made, and the piston position is within the target range, the process proceeds to step S19. In step S19, the ECU 100 sets a third resistance value R3 set in advance as a determination resistance value, and sets the third map as a target output map.

  In the present embodiment, the third resistance value R3 is set to the same value (for example, 13 mΩ) as the first resistance value R1. The third map is set as indicated by a broken line (thick line) in FIG. Specifically, in the third map, when the internal resistance of the Li battery 9 is less than the third resistance value R3, the target output voltage is set to the basic output voltage regardless of the internal resistance, and the internal resistance of the Li battery 9 is the third resistance. Above the resistance value R3, the map is set such that the target output voltage of the DC-DC converter 10 is lower when the internal resistance is larger than when the resistance is small. In the example of FIG. 10, the third map is such that the target output voltage decreases in proportion to the increase in the internal resistance of the Li battery 9 in the range where the internal resistance of the Li battery 9 is equal to or greater than the third resistance value R3. Is set. After step S19, the process proceeds to step S21.

  On the other hand, if the determination in step S18 is NO and the vehicle speed idle stop is made and the piston position is not within the target range, the process proceeds to step S20. In step S20, the ECU 100 sets the fourth resistance value R4 set to a value smaller than the third resistance value R3 as the determination resistance value.

  In the present embodiment, the fourth resistance value R4 is set to a value smaller than any of the first to third resistance values R1 to R3. For example, the fourth resistance value R4 is set to about 11.5 mΩ. The fourth map is set as indicated by a broken line (thin line) in FIG. Specifically, in the fourth map, when the internal resistance of the Li battery 9 is less than the fourth resistance value R4, the target output voltage is set to the basic output voltage regardless of the internal resistance, and the internal resistance of the Li battery 9 is the fourth resistance. In the resistance value R4 or more, the map is set so that the target output voltage is lower than the value of the third map. In the fourth map, in the range where the internal resistance of the Li battery 9 is equal to or greater than the fourth resistance value R4, the target output voltage is set to be lower when the internal resistance is larger than when the internal resistance is small. In the example of FIG. 10, the fourth map is such that the target output voltage decreases in proportion to the increase in the internal resistance of the Li battery 9 in the range where the internal resistance of the Li battery 9 is greater than the fourth resistance value R4. Is set.

  Thus, even when the vehicle speed idle stop is made in the same manner, when the internal resistance of the Li battery 9 is equal to or greater than the fourth resistance value R4, the target output voltage of the DC-DC converter 10 is determined by the determination piston. It is set to a lower value when the position is outside the target range than when it is within the target range.

  In addition, as shown in FIG. 10, even when the determination piston position is within the target range, the target output voltage is lower at the vehicle speed idle stop than at the stop idle stop. Further, as shown in FIG. 10, even when the determination piston position is out of the target range, the target output voltage is lower at the vehicle speed idle stop than at the stop idle stop.

  Here, when the stop idling stop is performed, the first resistance value R1 and the second resistance value R2 correspond to the “first reference resistance value” and the “second reference resistance value” in the claims, respectively. . On the other hand, when the vehicle speed idle stop is performed, the third resistance value R3 and the fourth resistance value R4 correspond to the “first reference resistance value” and the “second reference resistance value” in the claims, respectively. .

  After step S20, the process proceeds to step S21.

  In step S21, the ECU 100 determines whether or not the internal resistance of the Li battery 9 is less than the determination resistance value set in any of steps S16, S17, S19, and S20.

  The internal resistance of the Li battery 9 is estimated by the temperature of the Li battery 9 and the progress of deterioration of the Li battery 9.

    Specifically, ECU 100 determines the amount of heat generated by charging / discharging of Li battery 9 based on the input / output voltage and input / output current of Li battery 9 detected by Li battery voltage sensor SN26 and Li battery current sensor SN27. While estimating at any time, the temperature rise amount of the Li battery 9 accompanying this heat generation is estimated at any time based on the estimated heat generation amount. Further, the ECU 100 estimates the temperature of the Li battery 9 as needed based on the temperature increase amount and the outside air temperature.

  The ECU 100 also detects the current and voltage released from the Li battery 9 when the ISG 4 is driven as the engine is restarted (current and voltage detected by the Li battery voltage sensor SN26 and the Li battery current sensor SN27). Based on the above, the progress of deterioration of the Li battery 9 is estimated. Specifically, the ECU 100 estimates that the deterioration of the Li battery 9 progresses as the current discharged from the Li battery 9 decreases and the discharged voltage decreases. In the present embodiment, a parameter that is a larger value as the current is smaller and the voltage is lower and the progress of degradation of the Li battery 9 is quantified (hereinafter referred to as a degradation parameter as appropriate) is set. The ECU 100 calculates the value of the deterioration parameter based on the current and voltage. The ECU 100 calculates, updates, and stores the value of the deterioration parameter every time the ISG 4 is driven as the engine is restarted.

  In the present embodiment, the ECU 100 stores a map shown in FIG. In this map, the horizontal axis represents the temperature of the Li battery 9 and the vertical axis represents the internal resistance of the Li battery 9. In addition, the plurality of lines shown in this map are lines having different deterioration parameter values (degradation progress of the Li battery 9). From this map, the ECU 100 determines the temperature of the Li battery 9 corresponding to the estimated value of the temperature of the Li battery 9 at the current time (step S7 execution time) and the deterioration parameter value stored at the current time (step S7 execution time). The internal resistance is extracted, and this is estimated as the internal resistance of the Li battery 9 at the present time (when step S7 is performed). As shown in FIG. 11, the internal resistance of the Li battery 9 is estimated to be higher as the temperature of the Li battery 9 is lower and the deterioration parameter value is larger and the progress of deterioration of the Li battery 9 is larger.

  Returning to FIG. 9, when the determination in step S21 is NO and the internal resistance of the Li battery 9 is less than the determination resistance value, the process proceeds to step S30. In step S30, ECU 100 maintains the target output voltage at the basic output voltage and ends the process (returns to step S1).

  Thus, when the internal resistance of the Li battery 9 is less than the determination resistance value, the output voltage drop control is not performed, and the target output voltage is maintained at the basic output voltage.

  On the other hand, if the determination in step S21 is YES and the internal resistance of the Li battery 9 is greater than or equal to the determination resistance value, the process proceeds to step S22.

  In step S22, the ECU 100 extracts a value corresponding to the estimated internal resistance of the Li battery 9 from the target output map set in any of steps S16, S17, S19, and S20, and sets this value as the target output voltage. To do.

  Step S22 is a step that proceeds when the determination in step S21 is YES and the internal resistance of the Li battery 9 is greater than or equal to the determination resistance value. Accordingly, the target output voltage set in step S22 is set to a voltage lower than the basic output voltage regardless of which target output map is used. Therefore, in step S22, the target output voltage is reduced from the basic output voltage, which is the target output voltage at the normal time, to a lower voltage. The target output voltage set in step S22 and lower than the basic output voltage is the “regulated voltage” in the claims.

  Further, when the stop idling stop is performed and the piston position is not within the target range, the second resistance value R2 is set as the determination resistance value, and the second map is set as the target output map. As described above, the second map is set so that the target output voltage is smaller than the target output voltage of the first map in the range where the internal resistance of the Li battery is not less than the second resistance value R2. ing. Therefore, even if the internal resistance of the Li battery 9 is the same, when the stop idle stop is performed and the piston position is outside the target range, the stop idle stop is performed and the piston position is within the target range. The target output voltage is made lower than when it is within. Similarly, even if the internal resistance of the Li battery 9 is the same, when the vehicle speed idle stop is performed and the piston position is outside the target range, the vehicle speed idle stop is performed and The target output voltage is set lower than when the piston position is within the target range.

  After step S22, the process proceeds to step S23. In step S23, the ECU 100 decreases the output voltage of the Li battery based on the difference between the current output voltage (current output voltage) of the Li battery (current output voltage) and the target output voltage determined in step S22. Determine the voltage drop rate. In this embodiment, the command value of the output voltage set by the ECU 100 is used as the current output voltage.

  FIG. 12 is a diagram showing the relationship between the target output voltage subtracted from the actual output voltage and the target value of the output voltage decrease amount (hereinafter referred to as the target decrease voltage) and the voltage decrease rate. As shown in FIG. 12, in this embodiment, the voltage drop rate is increased when the target drop voltage is large than when it is small. In the example of FIG. 12, the voltage drop rate is kept constant when the target drop voltage is equal to or greater than the predetermined value dV0, and the voltage drop rate increases as the target drop voltage increases in proportion to the target drop voltage when the target drop voltage is less than the predetermined value dV0. It is made smaller. For example, the target voltage drop is set to about 0.5 V / sec to 2 V / ses.

  After step S23, the process proceeds to step S24. In step S24, the ECU 100 decreases the output voltage of the DC-DC converter 10. Specifically, as described above, the ECU 100 changes the on / off time of the switching elements 10a and 10b built in the DC-DC converter 10 to lower the output voltage. At this time, the ECU 100 sets the on / off times of the switching elements 10a and 10b built in the DC-DC converter 10 so that the output voltage of the DC-DC converter 10 decreases at the voltage decrease rate set in step S10. adjust. Thereby, the output voltage of the DC-DC converter 10 is gradually decreased toward the target output voltage.

  After step S24, the process proceeds to step S25. In step S25, it is determined whether or not the current output voltage of the DC-DC converter 10 is equal to or lower than the target output voltage. If this determination is NO and the current output voltage of the DC-DC converter 10 has not yet decreased to the target output voltage, the process returns to step S24. On the other hand, if this determination is YES and the current output voltage of the DC-DC converter 10 decreases to the target output voltage, the process proceeds to step S26. In step S26, the output voltage drop control of the DC-DC converter 10 is stopped.

  As described above, in the present embodiment, when the internal resistance of the Li battery 9 is equal to or higher than the determination resistance value during the idle stop, the output voltage of the DC-DC converter 10 is gradually reduced.

  Similarly, even when the vehicle is stopped idle and stopped, if the determination piston position is outside the target range, the determination resistance value (second resistance value R2) is set to be within the target range. Lower than the current value (first resistance value R1). Accordingly, when the internal resistance of the Li battery 9 when the stop idling stop is performed is equal to or greater than the second resistance value R2 and less than the first resistance value R1, the DC-DC converter only when the determination piston position is outside the target range. When the target output voltage of 10 is reduced and the determination piston position is within the target range, reduction control of the target output voltage of the DC-DC converter 10 is prohibited.

  Further, when the internal resistance of the Li battery 9 when the stop idling stop is performed is equal to or greater than the second resistance value R2, the determination piston position is outside the target range and the determination piston position is within the target range. Rather, the target output voltage of the DC-DC converter 10 is set to a lower value.

  Similarly, even when the vehicle speed idle stop is performed, when the determination piston position is out of the target range, the determination resistance value (fourth resistance value R4) is determined and the determination piston position is within the target range. It is made lower than the value at that time (third resistance value R3). Accordingly, when the internal resistance of the Li battery 9 when the vehicle speed idle stop is performed is equal to or greater than the fourth resistance value R4 and less than the third resistance value R3, only when the determination piston position is outside the target range, DC-DC When the target output voltage of the converter 10 is reduced and the determination piston position is within the target range, reduction control of the target output voltage of the DC-DC converter 10 is prohibited.

  Further, when the internal resistance of the Li battery 9 when the vehicle speed idle stop is performed is equal to or greater than the third resistance value R3, the determination piston position is within the target range when the determination piston position is outside the target range. The target output voltage of the DC-DC converter 10 is set to a lower value than sometimes.

(3) Operation, etc. FIG. 13 is a diagram schematically showing a time change of each parameter when the engine automatic stop control including the output voltage reduction control is performed during vehicle travel. FIG. 13 is a diagram when the internal resistance of the Li battery 9 is within a range that is less than the first resistance value R1 and higher than the fourth resistance value R4. In FIG. 13, in order from the top, the vehicle speed, the idle stop permission flag, the engine speed, the determination piston position (the position of the piston 2d of the cylinder that becomes the compression stroke at the time of idle stop and engine restart), the voltage of the Li battery 9, The output voltage of the DC-DC converter 10 and the voltage input to the low-voltage electrical device 13 are shown. The idle stop permission flag is 1 when the idle stop permission condition is satisfied, and is 0 at other times.

  When the vehicle starts decelerating at time t1, ISG 4 starts generating power. Accordingly, after time t1, the voltage of the Li battery 9 gradually increases. When the idle stop permission condition is satisfied at time t2 (the idle stop permission flag is changed from 0 to 1), the idle stop is performed and the engine 2 is stopped (the engine speed is 0).

  At time t2, the determination piston position is a position on the advance side of 90 ° CA before compression top dead center and is out of the target range. At time t2, the vehicle speed is 0 km / h and the vehicle is stopped. As described above, the internal resistance of the Li battery 9 is higher than the second resistance value R2. Therefore, output voltage drop control is started at time t2. Further, the value of the second map is set to the target output voltage V1 of the DC-DC converter 10, and the output voltage of the DC-DC converter 10 is gradually decreased toward the target output voltage V1. Along with this, after time t2, the input voltage of the low-voltage electrical equipment 13 gradually decreases. When a predetermined time elapses from time t2 and the output voltage of the DC-DC converter 10 reaches the target output voltage V1, the reduction control of the output voltage of the DC-DC converter 10 is stopped.

  After the timing slightly before time t2, the supply of power from the ISG 4 to the Li battery 9 is stopped as the engine 2 is idling and the engine 2 is stopped. Therefore, the voltage of the Li battery 9 gradually decreases after time t2.

  When the idle stop permission condition is not satisfied at time t3 and the condition for restarting the engine is satisfied, the voltage of the Li battery 9 is suddenly decreased by driving the ISG 4 as an electric motor. However, in the present embodiment, since the output voltage of the DC-DC converter 10 is set to the voltage V1 lower than the basic output voltage, the voltage of the Li battery 9 is higher than the output voltage of the DC-DC converter 10. Maintained. Therefore, at time t3, the input voltage of the low-voltage electrical device 13 does not rapidly decrease, and the necessary voltage is stably supplied to the low-voltage electrical device 13.

  As the engine is restarted at time t3, the output voltage of the DC-DC converter 10 is returned to the basic output voltage V0. In the example of FIG. 13, at this time, the output voltage of the DC-DC converter 10 is gradually increased toward the basic output voltage V0.

  Thereafter, when the vehicle starts to decelerate again at time t4 after the vehicle is accelerated and travels steady, the voltage of the Li battery 9 increases again. Further, when the idle stop permission condition is satisfied at time t5, the idle stop is performed again. At time t5, idle stop is performed in a state where the vehicle has not yet stopped. Even at time t5, the determination piston position is out of the target range, and the internal resistance of the Li battery 9 is higher than the fourth resistance value 4, so that the output voltage of the DC-DC converter 10 is higher than the basic output voltage V0. Is gradually reduced to a lower voltage V2. However, at this time, the value of the fourth map is set to the target output voltage V2 of the DC-DC converter 10, and the output voltage of the DC-DC converter 10 is gradually decreased toward the target output voltage V2. Accordingly, after time t5, the input voltage of the low-voltage electrical device 13 gradually decreases. When a predetermined time elapses from time t5 and the output voltage of the DC-DC converter 10 reaches the target output voltage V2, the reduction control of the output voltage of the DC-DC converter 10 is stopped.

  As described above, the voltage of the Li battery 9 gradually decreases from around time t5, and when the engine is restarted at time t6, the voltage of the Li battery 9 rapidly decreases. However, since the output voltage of the DC-DC converter 10 is set to a sufficiently low voltage V2 at time t6, a sudden change in the input voltage of the low-voltage electrical device 13 is prevented.

  On the other hand, at time t8, after the vehicle is decelerated from time t7, idle stop is performed with the vehicle stopped. At this time, the determination piston position is compressed from 90 ° CA before compression top dead center. It is in the target range to the dead point. Further, as described above, the internal resistance of the Li battery 9 is lower than the first resistance value R1. Therefore, at time t8, the output voltage of the DC-DC converter 10 is not reduced, and this output voltage is maintained at the basic target output V0.

  Thus, according to the present embodiment, the energy efficiency of the entire vehicle can be increased by storing the energy at the time of deceleration of the vehicle in the Li battery 9 as electric power, and the Li battery 9 is restarted when the engine 2 is restarted. The ISG 4 can be driven by the electric power stored in the engine 2 to apply driving force to the engine 2 and the engine 2 can be restarted appropriately.

  Moreover, in the present embodiment, as shown in FIG. 10, when the internal resistance of the Li battery 9 is the second resistance value R2 or more (at the time of vehicle speed idle stop) or the fourth resistance value R4 or more (at the time of stop idling stop). When the determination piston position, which is the position of the piston 2d in the compression stroke at the time of automatic engine stop and engine restart, is outside the target range, the DC is more effective than when the determination piston position is within the target range. -The output voltage of the DC converter 10 is lowered. That is, the output voltage of the DC-DC converter 10 is made lower than when the determination piston position is closer to the compression top dead center.

  Therefore, while maintaining the power supply from the Li battery 9 to the low voltage electrical device 13 and operating the low voltage electrical device 13 appropriately, the engine can be reliably restarted, and a high voltage is stabilized in the electrical load. Many opportunities to be supplied.

  Specifically, when the determination piston position is far from the compression top dead center and the distance between the determination piston position and the compression top dead center is large, the determination piston position is close to the compression top dead center and the piston position determination is performed. It is necessary to increase the driving force of the ISG 4 when the engine is restarted because the distance that the piston must be forced up is longer than when the distance is small. However, when this driving force is increased, the amount of voltage drop of the Li battery 9 increases. On the other hand, as described above, when the engine is automatically stopped, the determination piston position is closer than when the distance from the compression top dead center is closer (than when the piston position determination distance is larger). If the output voltage of the DC-DC converter 10 is lowered, the voltage of the storage battery is prevented from falling below the output voltage of the step-down device even if the driving force of the ISG 4 is increased as the piston position determination distance is longer. can do. In addition, when the piston position determination distance is small, it is possible to prevent the output voltage of the step-down device from being excessively lowered, and it is possible to secure many opportunities to stably supply a high voltage to the electric load.

  In the present embodiment, if the determination piston position is within the target range when the engine is automatically stopped, the internal resistance of the Li battery 9 is the first resistance value R1 (when the vehicle is idling stopped) or the third resistance value R3 (existing). When the vehicle speed is idling, the output voltage drop control is performed to gradually reduce the output voltage of the DC-DC converter 10 toward a voltage lower than the voltage before the engine is automatically stopped. On the other hand, if the determination piston position is outside the target range when the engine is automatically stopped, the internal resistance of the Li battery 9 is the third resistance value R3 (during stop idling) or the fourth resistance value R4 (during vehicle speed idling stop). At the above time, the output voltage drop control is performed. The third resistance value R3 and the fourth resistance value R4 are set to values smaller than the first resistance value R1 and the third resistance value R3. Therefore, as the distance between the determination piston position and the compression top dead center is long, and the internal resistance of the Li battery 9 is large, the voltage of the Li battery 9 is changed to a DC-DC converter when the engine is restarted. The output voltage of the DC-DC converter 10 and thus the voltage applied to the low-voltage electric machine 13 is automatically stopped while reliably preventing the output voltage from dropping below the output voltage of 10 and suppressing the opportunity for execution of the output voltage drop control. The opportunity to be maintained at the previous high value (basic output voltage) can be increased.

  Further, in the output voltage reduction control, the output voltage of the DC-DC converter 10 is gradually reduced, so that it is possible to prevent the voltage applied to the low-voltage electrical device 13 from changing suddenly due to the reduction of the output voltage. The low voltage electrical device 13 can be operated stably and appropriately.

  Moreover, at the time of vehicle speed idle stop, there is a possibility that the engine is restarted after the vehicle is not stopped. When the engine is restarted in such a state where the vehicle is not stopped, the engine must be increased to a high speed corresponding to the vehicle speed when the engine is restarted, and the engine is automatically stopped while the vehicle is stopped. The driving force of ISG4 must be higher than when Therefore, in this case, the amount of voltage drop of the Li battery 9 when the engine is restarted increases.

  On the other hand, in the present embodiment, even when the determination piston position is similarly within the target range, the determination resistance value is lower at the time of vehicle speed idle stop than at the time of stop idling. At the same time, the output voltage of the DC-DC converter 10 is lowered. Even when the determination piston position is out of the target range, the determination resistance value is set to a lower value at the vehicle speed idle stop than at the stop idle stop, and the output voltage of the DC-DC converter 10 is increased. Lowered. Therefore, in both the vehicle speed idle stop and the stop idle stop, the voltage of the Li battery 9 is reliably prevented from dropping below the output voltage of the DC-DC converter 10 when the engine is restarted. It is possible to prevent the output voltage of the DC-DC converter 10 from being excessively lowered during the stop.

  In addition, according to the present embodiment, the Li battery 9 in which a plurality of Li storage battery cells are arranged in a line is used, and this is disposed below the floor panel 81 and between the floor tunnel 83 and the side sill 82. It is arranged in the space. Therefore, using this space, the Li battery 9 can be appropriately arranged at a position closer to the ISG 4. The distance between the ISG 4 and the Li battery 9, and thus the wire connecting them can be kept short.

  However, when a plurality of batteries are arranged in a row in this way and the plurality of batteries are connected in series, the internal resistance of the Li battery 9 tends to increase. If the internal resistance of the Li battery 9 is large, the voltage of the Li battery 9 is likely to be greatly reduced when the engine is restarted. On the other hand, in the present embodiment, as described above, the output voltage of the DC-DC converter 10 is maintained at a lower voltage than the voltage of the Li battery 9 even when the voltage of the Li battery 9 decreases when the engine is restarted. Is done. Therefore, it is possible to maintain the power supply from the Li battery 9 to the low voltage electrical device 13 and to stabilize the operation while realizing the layout.

(4) Modifications In the above description, a case has been described in which the output voltage of the DC-DC converter 10 is switched between when the determination piston position is within the target range and when the determination piston position is outside the target range. However, instead of this, as shown in FIG. 14, the target output voltage (output voltage) of the DC-DC converter 10 is determined so that the determination piston position is more advanced than the compression top dead center (determination piston position and You may set so that it may become a large value (as the separation distance from a compression top dead center is large). Moreover, you may make it control the switch elements 10a and 10b of the DC-DC converter 10 so that it may become this target output voltage irrespective of the internal resistance of Li battery.

  In the above description, the case where the output voltage reduction control is performed when the internal resistance of the Li battery 9 is high even when the determination piston position is within the target range has been described. However, the determination piston position is within the target range. In some cases, output voltage drop control may be prohibited.

  In the embodiment, when the engine 2 is automatically stopped, the output voltage reduction control is performed when the internal resistance of the Li battery 9 is equal to or higher than the determination resistance value, and the output is output when the internal resistance of the Li battery 9 is less than the determination resistance value. Although the case where the voltage drop control is not performed has been described, the output voltage drop control may always be performed regardless of the internal resistance of the Li battery 9.

  Further, the determination of whether or not the output voltage reduction control is to be performed may be performed using parameters other than the internal resistance of the Li battery 9. For example, the output voltage drop control is performed when the deterioration of the Li battery 9 has progressed from a predetermined state, and the output voltage drop control is prohibited when the deterioration of the Li battery 9 has not advanced to the predetermined state. May be. Alternatively, the output voltage reduction control may be performed when the temperature of the Li battery 9 is lower than a predetermined temperature, and the output voltage reduction control may be prohibited when the temperature of the Li battery 9 is equal to or higher than the predetermined temperature.

  Further, the determination of whether or not to perform the output voltage reduction control may be performed based on the SOC of the Li battery 9. For example, the output voltage drop control may be performed when the SOC of the Li battery 9 is less than a predetermined value, and the output voltage drop control may be prohibited when the SOC of the Li battery 9 is greater than or equal to a predetermined value. Further, by combining the SOC of the Li battery 9 and the internal resistance of the Li battery 9, the output voltage drop control is performed when the SOC of the Li battery 9 is less than a predetermined value and the internal resistance of the Li battery 9 is equal to or higher than the predetermined value. The output voltage reduction control may be prohibited when the SOC of the Li battery 9 is equal to or greater than a predetermined value, or when the internal resistance of the Li battery 9 is less than the predetermined value.

  Moreover, although the said embodiment demonstrated the case where Li battery 9 was used as a storage battery which accumulate | stores the electric power generated by ISG4, this storage battery is not restricted to Li battery 9. FIG.

  Further, the stop position control can be omitted.

2 Engine 4 ISG (Power generation device, Driving force application device)
9 Li battery (storage battery)
10 DC-DC converter (step-down device)
12 Lead battery (secondary battery)
13 Low-voltage electrical equipment (electric load)
14 High voltage circuit 15 Low voltage circuit 100 ECU (control device)

Claims (7)

A power control device for a vehicle provided in a vehicle capable of automatically stopping and restarting an engine,
A power generation device driven by an engine to generate electricity;
A storage battery capable of storing the electric power generated by the power generator when the vehicle decelerates;
A driving force applying device capable of applying a driving force to the engine using the power of the storage battery;
A step-down device that is interposed between an electric load provided in a vehicle and the storage battery, and reduces the voltage of the storage battery to supply electric power to the electric load;
The step-down device can be controlled so that the output voltage of the step-down device is changed, and when there is a request to restart the engine, a driving force for restarting the engine is transmitted from the driving force applying device to the engine. A control device for controlling the driving force applying device to be applied to,
When the engine is automatically stopped, the control device reduces the step-down pressure when the piston position determination distance, which is the distance between the piston position of the cylinder in the compression stroke and the compression top dead center position, is larger. A power control apparatus for a vehicle, characterized in that the output voltage of the apparatus is lowered. The power control apparatus for a vehicle according to claim 1,
The control device performs output voltage reduction control for gradually decreasing the output voltage of the step-down device toward an adjustment voltage lower than the voltage before the engine is automatically stopped when the engine is automatically stopped, and the piston position determination distance is large. A power control apparatus for a vehicle, wherein the adjustment voltage is set to a lower value than when the time is smaller. The power control apparatus for a vehicle according to claim 2,
The control device includes:
When the piston position determination distance is less than a predetermined first determination distance, the output voltage reduction control is performed when the internal resistance of the storage battery is equal to or greater than a preset first reference resistance value, and the internal resistance of the storage battery is Prohibiting the output voltage drop control when less than the first reference resistance value;
When the piston position determination distance is equal to or greater than the predetermined first determination distance, the output voltage reduction control is performed when the internal resistance of the storage battery is equal to or greater than a second reference resistance value that is smaller than the first reference resistance value, The power control apparatus for a vehicle, wherein the output voltage drop control is prohibited when an internal resistance of the storage battery is less than the second reference resistance value. The power control apparatus for a vehicle according to claim 3,
The control device estimates an internal resistance of the storage battery based on a deterioration state of the storage battery and a temperature of the storage battery. In the vehicle power control apparatus according to any one of claims 1 to 4,
The vehicle includes a pair of side sills that extend in the vehicle front-rear direction along both sides in the vehicle width direction of the passenger compartment, and a floor tunnel that is provided below the floor surface of the passenger compartment and extends in the vehicle front-rear direction.
The storage battery includes a plurality of batteries arranged in a row, and the batteries are arranged in a posture below the floor of a passenger compartment and between the floor tunnel and one of the side sills in the vehicle front-rear direction. A power control apparatus for a vehicle, characterized in that In the vehicle power control apparatus according to any one of claims 1 to 5,
A secondary storage battery capable of storing the power output from the step-down device and having a maximum output voltage lower than that of the storage battery;
The electric load is connected to the electric load so as to be able to receive the electric power from the secondary storage battery in addition to the step-down device. The power control apparatus for a vehicle according to claim 6,
The power control device for a vehicle, wherein the driving force applying device is driven only by the electric power of the storage battery among the storage battery and the secondary storage battery at least when the engine is restarted.