Patent Publication Number: US-2022234436-A1

Title: Vehicle

Description:
TECHNICAL FIELD 
     The present invention relates to a vehicle including a high voltage battery and a low voltage battery. 
     BACKGROUND ART 
     JP2013-95246A discloses a vehicle that includes a high voltage battery including a lithium-ion battery and a low voltage battery including a lead-acid battery. 
     SUMMARY OF INVENTION 
     As a request for a vehicle having a function, such as automatic driving, a high reliability of a low voltage system power supply is requested. Therefore, a low voltage battery is possibly constituted by a highly reliable lithium-ion battery instead of a lead-acid battery. 
     However, a lithium-ion battery has a property that its output decreases at a low temperature. In view of this, for example, at a very low temperature (such as −20° C. to −30° C.), the output of the lithium-ion battery decreases, which possibly causes an insufficient output of a motor that starts an engine. 
     The present invention has been made in view of such technical problem, and it is an object of the present invention to allow an engine to be reliably started at a very low temperature even when a low voltage battery is constituted by a lithium-ion battery. 
     According to one aspect of the present invention, a vehicle includes: an engine; a low voltage battery constituted by a lithium-ion battery, the low voltage battery supplying an electric power to an electric component mounted to the vehicle; a high voltage battery constituted by a lithium-ion battery, the high voltage battery having an output voltage higher than an output voltage of the low voltage battery; a first rotating electrical machine that operates by an electric power supplied from the high voltage battery, the first rotating electrical machine generating a torque for driving the vehicle; and a second rotating electrical machine for starting the engine. The second rotating electrical machine operates by an electric power supplied from the high voltage battery. 
     According to the above-described aspect, the engine is allowed to be reliably started at a very low temperature even when the low voltage battery is constituted by a lithium-ion battery. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic configuration diagram of a vehicle according to an embodiment. 
         FIG. 2  is a flowchart illustrating a flow of a charge control according to the embodiment. 
         FIG. 3  is a schematic configuration diagram of a modification of the vehicle according to the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes the embodiment of the present invention with reference to attached drawings. 
       FIG. 1  is a schematic configuration of a vehicle  100  according to the embodiment of the present invention. The vehicle  100  includes: a low voltage battery  1  as a first battery; a high voltage battery  2  as a second battery; an engine  3  as a driving source for running; a starter motor  5  (hereinafter referred to as “SM  5 .”) as a second rotating electrical machine used for start of the engine  3 ; a starter generator  6  (hereinafter referred to as “SG  6 .”) as a first rotating electrical machine used for electric generation and assist and start of the engine  3 ; a DC-DC converter  7 ; an inverter  8 ; a mechanical oil pump  9  and an electric oil pump  10  as sources of generation of a hydraulic pressure; a torque converter  11 , a forward/reverse switching mechanism  12 , a continuously variable transmission  13  (hereinafter referred to as “CVT  13 .”), and a differential mechanism  14  that constitute a power train; drive wheels  18 ; and a controller  20 . 
     The low voltage battery  1  is a lithium-ion battery having a nominal voltage of 12 V DC. The low voltage battery  1  supplies an electric power to, for example, electric components  15  (such as an automatic driving camera  15   a,  a sensor  15   b,  a navigation system  15   c,  an audio  15   d,  and an air conditioner blower  15   e ) that are mounted to the vehicle  100  and operate at 12 V DC, and the electric oil pump  10 . The low voltage battery  1  is connected to a low voltage circuit  16  together with the electric component  15 . 
     The high voltage battery  2  is a lithium-ion battery having a nominal voltage (or output voltage) of 48 V DC higher than that of the low voltage battery  1 . The nominal voltage of the high voltage battery  2  may be lower or higher than this and may be, for example, 30 V DC and 100 V DC. The high voltage battery  2  is connected to a high voltage circuit  17  together with, for example, the SM  5 , the SG  6 , and the inverter  8 . 
     The DC-DC converter  7  is disposed on an electric circuit that connects the low voltage battery  1  to the high voltage battery  2 . Accordingly, the low voltage circuit  16  and the high voltage circuit  17  are connected via the DC-DC converter  7 . The DC-DC converter  7  converts an input voltage and outputs it. Specifically, the DC-DC converter  7  has: a step-up function that steps up 12 V DC of the low voltage circuit 16 to 48 V DC and outputs 48 V C to the high voltage circuit  17 ; and a step-down function that steps down 48 V DC of the high voltage circuit  17  to 12 V DC and outputs 12 V DC to the low voltage circuit  16 . The DC-DC converter  7  can output the voltage of 12 V DC to the low voltage circuit  16  regardless of during driving or stop of the engine  3 . In addition, when the remaining capacity of the high voltage battery  2  becomes low, 12 V DC of the low voltage circuit  16  can be stepped up to 48 V DC to be output to the high voltage circuit  17 , thus allowing charging the high voltage battery  2 . 
     The engine  3  is an internal combustion engine that uses, for example, gasoline and light oil as a fuel, and has, for example, a rotation speed and a torque to be controlled on the basis of a command from the controller  20 . 
     The torque converter  11  is disposed on a power transmission path between the engine  3  and the forward/reverse switching mechanism  12  and transmits power via fluid. In addition, when the vehicle  100  runs at a predetermined lock-up vehicle speed or more, engaging a lock-up clutch  11   a  allows the torque converter  11  to enhance a power transmission efficiency of driving power from the engine  3 . 
     The forward/reverse switching mechanism  12  is disposed on a power transmission path between the torque converter  11  and the CVT  13 . The forward/reverse switching mechanism  12  includes a planetary gear mechanism  12   a,  a forward clutch  12   b,  and a reverse brake  12   c.  When the forward clutch  12   b  is engaged, and the reverse brake  12   c  is disengaged, rotation of the engine  3  input to the forward/reverse switching mechanism  12  via the torque converter  11  is output from the forward/reverse switching mechanism  12  to the CVT  13  with its rotation direction maintained. Conversely, when the forward clutch  12   b  is disengaged, and the reverse brake  12   c  is engaged, the rotation of the engine  3  input to the forward/reverse switching mechanism  12  via the torque converter  11  is decelerated and reversed to be output from the forward/reverse switching mechanism  12  to the CVT  13 . 
     The CVT  13  is arranged on a power transmission path between the forward/reverse switching mechanism  12  and the differential mechanism  14  and steplessly changes a speed ratio corresponding to, for example, a vehicle speed and an accelerator position as an operation amount of an accelerator pedal. The CVT  13  includes a primary pulley  13   a,  a secondary pulley  13   b,  and a belt  13   c  wound around both the pulleys. The CVT  13  changes groove widths of the primary pulley  13   a  and the secondary pulley  13   b  by the hydraulic pressure to change contact radiuses of the pulleys  13   a,    13   b,  and the belt  13   c,  which can steplessly change the speed ratio. A hydraulic pressure circuit (not illustrated) generates the hydraulic pressure required for the CVT  13  by using the hydraulic pressure generated by the mechanical oil pump  9  or the electric oil pump  10  as a source pressure. 
     The SM  5  is arranged such that a pinion gear  5   a  can be meshed with an outer peripheral gear  3   b  of a flywheel  3   a  of the engine  3 . When the engine  3  starts from a cold state for the first time (hereinafter referred to as “initial start.”), the electric power is supplied from the high voltage battery  2  to the SM  5 , the pinion gear  5   a  is meshed with the outer peripheral gear  3   b,  and the flywheel  3   a  and further, a crankshaft are rotated. 
     It should be noted that the torque and the output required for starting the engine  3  are the largest at the initial start and are smaller at a start from a warm-up state, that is, a restart than those at the initial start. This is because while a temperature of an engine oil is low at the initial start, and a viscous resistance of the engine oil is large, after the initial activation, the temperature of the engine oil has risen, and the viscous resistance of the engine oil has been decreased. Since the SG  6  described later is driven via the belt, a large torque cannot be transmitted. In view of this, at the initial start, the engine  3  is driven by using the SM  5 . 
     The SG  6  is connected to the crankshaft of the engine  3  via a V belt  22  and functions as an electric generator when receiving rotational energy from the engine  3 . The electric power thus generated charges the high voltage battery  2  via the inverter  8 . The SG  6  operates as an electric motor that is rotatably driven by receiving the supply of the electric power from the high voltage battery  2  and generates a torque for assisting the driving of the engine  3 . Furthermore, the SG  6  is used for restarting the engine  3  by rotatably driving the crankshaft of the engine  3  when the engine  3  is restarted from an idling stop state. Since the SG  6  is connected to the crankshaft of the engine  3  by the V belt  22 , when the engine  3  is started, a quiet and smooth start can be performed without a mesh sound of the gears. In view of this, at the restart, the engine  3  is driven by using the SG  6 . 
     The mechanical oil pump  9  is an oil pump that operates by the rotation of the engine  3  transmitted via a chain  23 . The mechanical oil pump  9  suctions a hydraulic oil stored in an oil pan to supply the oil to the lock-up clutch  11   a,  the forward/reverse switching mechanism  12 , and the CVT  13  via a hydraulic pressure circuit (not illustrated). 
     The electric oil pump  10  is an oil pump that operates by the electric power supplied from the low voltage battery  1 . The electric oil pump  10  operates when the engine  3  stops, and the mechanical oil pump  9  cannot be driven by the engine  3 , such as in the idling stop state. Similarly to the mechanical oil pump  9 , the electric oil pump  10  suctions a hydraulic oil stored in an oil pan to supply the oil to the lock-up clutch  11   a,  the forward/reverse switching mechanism  12 , and the CVT  13  via a hydraulic pressure circuit (not illustrated). In particular, the ensured hydraulic pressure required for the CVT  13  suppresses slipperiness of the belt  13   c.  The electric oil pump  10  may be an oil pump that operates by the electric power supplied from the high voltage battery  2 . 
     The controller  20  includes one or a plurality of microcomputers including a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input/output interface (I/O interface). The controller  20  corresponds to control means and executes a program stored in the ROM or the RAM by the CPU to integrally control, for example, the engine  3 , the inverter  8  (the SG  6  and the electric oil pump  10 ), the DC-DC converter  7 , the SM  5 , the lock-up clutch  11   a,  the forward/reverse switching mechanism  12 , and the CVT  13 . 
     In addition, the controller  20  performs a charge control of the low voltage battery  1  and the high voltage battery  2  and an electric generation control of the SG  6  on the basis of a remaining capacity SOC 1  of the low voltage battery  1  detected by a first remaining capacity detector  31  and a remaining capacity SOC 2  of the high voltage battery  2  detected by a second remaining capacity detector  32 . It should be noted that, in this embodiment, the first remaining capacity detector  31  corresponds to battery remaining capacity detecting means. 
     As described above, in this embodiment, the low voltage battery  1  and the high voltage battery  2  are constituted by a lithium-ion battery. 
     Typically, in a vehicle including a low voltage battery and a high voltage battery, during running, a low voltage system is ensured by using a dual system where the low voltage battery and a DC-DC converter are used. Then, conventionally, as such a low voltage battery, a lead-acid battery has been used. 
     For example, when automatic driving is performed, a high reliability is required for the low voltage system. However, a lead-acid battery is more difficult to grasp its deterioration and capacity than those of a lithium-ion battery, and has a reliability lower than that of the lithium-ion battery. In view of this, conventionally, when a lead-acid battery is used as the low voltage battery  1 , since allocation of a reliability of the DC-DC converter  7  is needed to be increased, a high-performance DC-DC converter  7  is required. This increases the cost. 
     Therefore, in the vehicle  100  of this embodiment, the low voltage battery  1  is constituted by a lithium-ion battery. This allows the allocation of the reliability of the DC-DC converter  7  to be decreased, and thus the high-performance DC-DC converter  7  is not required. This can suppress the increase in cost. 
     However, under a very low temperature (such as a temperature of −20° C. to −30° C.) environment, a performance of a lithium-ion battery is inferior to that of a lead-acid battery. In view of this, when the low voltage battery  1  is used as a power supply of the SM  5 , an output at the very low temperature is insufficient, and the engine  3  is not possibly started. Therefore, in this embodiment, the high voltage battery  2  is used as the power supply of the SM  5 . Accordingly, at the very low temperature, an electric power required for the start of the engine  3  can be ensured. 
     Thus, the low voltage battery  1  is constituted by a lithium-ion battery, and furthermore, the high voltage battery  2  is used as the power supply of the SM  5 . The present invention is thereby applicable to a vehicle where a reliability of a power supply system is required, and the engine  3  can be reliably started at the very low temperature. 
     Incidentally, since the electric power of the low voltage battery  1  is used for a backup of the electric component  15  (such as a timepiece) also when an ignition is OFF (for example, in parking), the remaining capacity SOC 1  of the low voltage battery  1  decreases with passage of time. In view of this, in the vehicle  100  in the embodiment, when the remaining capacity SOC 1  of the low voltage battery  1  decreases when the ignition is OFF, the controller  20  performs the charge control that charges the low voltage battery  1  by using the high voltage battery  2 . The following specifically describes this charge control with reference to the flowchart illustrated in  FIG. 2 . 
     At Step S 1 , the controller  20  determines whether the ignition is OFF or not. When the ignition is OFF, the process proceeds to Step S 2 . When the ignition is ON, the process proceeds to Step S 8 , and an ordinary charge control is performed. 
     At Step S 2 , the controller  20  determines whether the remaining capacity SOC 1  is equal to or less than a predetermined value E 1  or not. The controller  20  determines whether the remaining capacity SOC 1  of the low voltage battery  1  detected by the first remaining capacity detector  31  is equal to or less than the predetermined value E 1  or not. When the remaining capacity SOC 1  is equal to or less than the predetermined value E 1 , the process proceeds to Step S 3 . When the remaining capacity SOC 1  is larger than the predetermined value E 1 , the process proceeds to END. 
     At Step S 3 , the controller  20  activates the DC-DC converter  7 . Since the DC-DC converter  7  is stopped when the ignition is OFF, the DC-DC converter  7  is activated. 
     At Step S 4 , the controller  20  starts the charge. Specifically, the controller  20  controls the DC-DC converter  7  to start the charge of the low voltage battery  1  using the high voltage battery  2 . The DC-DC converter  7  converts the voltage input from the high voltage battery  2  via the high voltage circuit  17  into 12 V DC and outputs the converted voltage to the low voltage circuit  16 . Accordingly, the low voltage battery  1  can be charged. 
     At Step S 5 , the controller  20  determines whether the remaining capacity SOC 2  is equal to or less than a predetermined value E 2  or not. The controller  20  determines whether the remaining capacity SOC 2  of the high voltage battery  2  detected by the second remaining capacity detector  32  is equal to or less than the predetermined value E 2  or not. When the remaining capacity SOC 2  is equal to or less than the predetermined value E 2 , the charge control is canceled, and the process proceeds to Step S 7 . When the remaining capacity SOC 2  is larger than the predetermined value E 2 , the process proceeds to Step S 6 . 
     At Step S 6 , the controller  20  determines whether the charge has been completed or not. Specifically, the controller  20  determines whether the remaining capacity SOC 1  of the low voltage battery  1  detected by the first remaining capacity detector  31  is equal to or more than a predetermined value E 3  or not. When the remaining capacity SOC 1  of the low voltage battery  1  is equal to or more than the predetermined value E 3 , the process proceeds to Step S 7 . When the remaining capacity SOC 1  of the low voltage battery  1  is less than the predetermined value E 3 , the process returns to Step S 5 . 
     At Step S 7 , the controller  20  stops the DC-DC converter  7 . This ends the charge control. 
     Thus, in this embodiment, even when the ignition is OFF, the controller  20  monitors the remaining capacity SOC 1  of the low voltage battery  1 . Then, when the remaining capacity SOC 1  of the low voltage battery  1  is detected to fall below the predetermined value E 1  when the ignition is OFF, the controller  20  activates the DC-DC converter  7 , and the low voltage battery  1  is charged by the electric power of the high voltage battery  2 . Accordingly, in, for example, parking for a long period, the backup of the electric component  15 , and the like can be continuously performed. 
     It should be noted that, the controller  20  does not need to always monitor the remaining capacity SOC 1  of the low voltage battery  1  when the ignition is OFF and may detect the remaining capacity SOC 1  of the low voltage battery  1  at regular intervals. 
     The lithium-ion battery includes a relay for cutting off a circuit for just in case, such as overdischarge. Since use of a latching relay as this relay eliminates the need for always energizing the relay, an electric power consumption of the low voltage battery  1  can be suppressed when the ignition is OFF. 
     While the above-described embodiment has been described that the low voltage battery  1  is charged by the electric power of the high voltage battery  2  when the remaining capacity SOC 1  of the low voltage battery  1  is detected to fall below the predetermined value E 1 , the high voltage battery  2  may be configured to be charged by the electric power of the low voltage battery  1  when the remaining capacity SOC 2  of the high voltage battery  2  is detected to fall below the predetermined value E 2 . In this case, the DC-DC converter  7  converts the voltage input from the low voltage battery  1  via the low voltage circuit  16  into 48 V DC and outputs the converted voltage to the high voltage circuit  17 . Accordingly, the high voltage battery  2  can be charged. 
     Thus, according to this embodiment, the low voltage battery  1  is constituted by a lithium-ion battery, and furthermore, the high voltage battery  2  is used as the power supply of the SM  5 . The present invention is thereby applicable to a vehicle where a reliability of a power supply system is required, and the engine  3  can be reliably started at the very low temperature. 
     In addition, in this embodiment, since the batteries (the low voltage battery  1  and the high voltage battery  2 ) are constituted by only a lithium-ion battery, the reliability of the power supply system is improved. 
     Furthermore, since the low voltage battery  1  can be charged by the high voltage battery  2  even when the ignition is OFF, in, for example, parking for a long period, the backup of the electric component  15 , and the like can be continuously performed. 
     Here, with reference to  FIG. 3 , a modification of this embodiment is described. 
     It should be noted that the following mainly describes the matters different from the configuration illustrated in  FIG. 1 , same reference numerals are given to the configurations same as the configuration illustrated in  FIG. 1 , and their descriptions are omitted as necessary. 
     The vehicle  100  illustrated in  FIG. 3  further includes a motor-generator  4  (hereinafter referred to as “MG  4 .”) as a driving source for running. 
     The MG  4  is a synchronous rotating electrical machine in which a permanent magnet is embedded in a rotor, and a stator coil is wound around a stator. The MG  4  is connected to a shaft of the primary pulley  13   a  via a chain  21  wound between a sprocket disposed on a shaft of the MG  4  and a sprocket disposed on the shaft of the primary pulley  13   a.  The MG  4  is controlled by applying a three-phase alternating current generated by the inverter  8  on the basis of a command from the controller  20 . 
     The MG  4  operates as an electric motor that receives the electric power supplied from the high voltage battery  2  to rotatably drive, thus generating a torque for driving the vehicle  100 . In addition, the MG  4  functions as an electric generator that generates an electromotive force on both ends of the stator coil when the rotor receives the rotational energy from the engine  3  and the drive wheels  18 , thus allowing the high voltage battery  2  to be charged. It should be noted that the MG  4  corresponds to the first rotating electrical machine. 
     The sprocket disposed on the shaft of the MG  4  and the sprocket disposed on the shaft of the primary pulley  13   a  are configured such that the latter has more teeth (for example, the number of teeth=1:3), and an output rotation of the MG  4  is decelerated and transmitted to the primary pulley  13   a.  Accordingly, the torque required for the MG  4  is decreased to downsize the MG  4 , and a degree of a flexible arrangement of the MG  4  is improved. It should be noted that a gear train may be used instead of the chain  21 . 
     Subsequently, actions and effects of the above-described embodiment are collectively described. 
     The vehicle  100  of this embodiment includes the engine  3 , the first battery (low voltage battery  1 ), the second battery (high voltage battery  2 ), the first rotating electrical machine (SG  6 , MG  4 ), and the second rotating electrical machine (SM  5 ) for starting the engine  3 . The first battery (low voltage battery  1 ) is constituted by a lithium-ion battery and supplies an electric power to the electric component  15  mounted to the vehicle  100 . The second battery (high voltage battery  2 ) is constituted by a lithium-ion battery and has an output voltage higher than an output voltage of the first battery (low voltage battery  1 ). The first rotating electrical machine (SG  6 , MG  4 ) operates by an electric power supplied from the second battery (high voltage battery  2 ) and generates a torque for driving the vehicle  100 . The second rotating electrical machine (SM  5 ) operates by an electric power supplied from the second battery (high voltage battery  2 ). 
     According to this configuration, even when the first battery (low voltage battery  1 ) is constituted by a lithium-ion battery, since the second rotating electrical machine (SM  5 ) for starting the engine  3  is connected to the second battery (high voltage battery  2 ) having the output voltage higher than the output voltage of the first battery (low voltage battery  1 ), the engine  3  can be reliably started also at the very low temperature. 
     Furthermore, since the first battery (low voltage battery  1 ) and the second battery (high voltage battery  2 ) are constituted by a lithium-ion battery, the reliability of the power supply system can be improved. 
     In addition, the vehicle  100  includes the SG  6  as the first rotating electrical machine. The SG  6  generates a torque for starting the engine  3  or assisting driving of the engine  3  when an electric power is supplied from the high voltage battery  2 . The SG  6  is allowed to generate an electric power for charging the low voltage battery  1  and the high voltage battery  2  when receiving a rotational energy from the engine  3 . 
     Since the SG  6  does not generate the mesh sound of the gears, driving the engine  3  by using the SG  6  at the restart can perform a quiet and smooth start. 
     The vehicle  100  includes the MG  4  as the first rotating electrical machine. The MG  4  generates a torque for driving the drive wheels  18  when an electric power is supplied from the high voltage battery  2 . The MG  4  is allowed to generate an electric power for charging the low voltage battery  1  and the high voltage battery  2  when an input from the drive wheels  18  or the engine  3  is present. 
     Since the vehicle  100  including the MG  4  is, what is called, a strong hybrid vehicle and is equipped with the high voltage battery  2 , a battery can be shared by the MG  4  and the SM  5 . 
     The vehicle  100  further includes the DC-DC converter  7 , the first remaining capacity detector  31  (battery remaining capacity detecting means), and the controller  20  (control means). The DC-DC converter  7  is disposed on an electric circuit connecting the low voltage battery  1  to the high voltage battery  2 , converts an input voltage, and outputs the converted voltage. The first remaining capacity detector  31  detects the remaining capacity SOC 1  of the low voltage battery  1 . The controller  20  performs a charge control of the low voltage battery  1  and the high voltage battery  2 . 
     The controller  20  activates the DC-DC converter  7  to charge the low voltage battery  1  by the electric power of the high voltage battery  2  when the remaining capacity SOC 1  of the low voltage battery  1  is detected to fall below the predetermined value E 1  when the ignition is OFF. The remaining capacity SOC 1  is detected by the first remaining capacity detector  31 . 
     Since the electric power of the low voltage battery  1  is used for a backup of the electric component  15  (such as a timepiece) also when an ignition is OFF (for example, in parking), the remaining capacity SOC 1  of the low voltage battery  1  decreases. In view of this, when the remaining capacity SOC 1  of the low voltage battery  1  decreases when the ignition is OFF, the controller  20  charges the low voltage battery  1  by using the high voltage battery  2 . Accordingly, in, for example, parking for a long period, the backup of the electric component  15 , and the like can be continuously performed. 
     The embodiment of the present invention is described above. However, the above embodiment does not intend to limit the technical scope of the present invention to the specific configurations of the above embodiment but only indicates part of application examples of the present invention. 
     This application claims priority based on Japanese Patent Application No. 2019-115813 filed with the Japan Patent Office on Jun. 21, 2019, the entire contents of which are incorporated into this specification.