Patent Publication Number: US-2015061383-A1

Title: Start Control System for Hybrid Driving Mechanism

Description:
TECHNICAL FIELD 
     The present invention relates to a start control system for controlling starting of an engine that a hybrid driving mechanism has. 
     BACKGROUND ART 
     A machine with a hybrid driving mechanism has a generator in addition to an engine. The generator drives a motor, which, in turn, drives parts to be driven. In order to operate the engine, a starter is used, but the use of starter causes increase of costs of machines with a hybrid driving mechanism. Patent Literature 1 discloses a technique to start an engine without resort to a starter. According to the technique of Patent Literature, when a request to start an engine is made while a vehicle is being driven only by a motor, driving force from driving wheels of the vehicle is transmitted to the engine by means of a driving force dividing function to thereby start the engine. 
     PRIOR TECHNIQUE LITERATURES 
     Patent Literature 
     Patent Literature 1: JP2007-55291A 
     SUMMARY OF INVENTION 
     Technical Problem 
     According to the technology disclosed in Patent Literature 1, in order to start the engine, it is necessary for the motor to be rotating. Accordingly, when the motor is not rotating when, for example, it is required to start the entire hybrid driving mechanism, the technology of Patent Literature 1 cannot be used. It may be possible to provide the hybrid driving mechanism with a charge-discharge device, e.g. a battery, and the power provided by the charge-discharge device is supplied to the motor to thereby start the engine by the rotation of the motor. However, if the charge-discharge device has been discharged out when the hybrid driving mechanism as a whole is to be started, the motor cannot rotate and, therefore, the engine cannot be started. 
     An object of the present invention is to provide a hybrid driving mechanism start control system which can start an engine even when a charge-discharge device has been discharged. 
     Solution to Problem 
     A hybrid driving mechanism start control system according to an embodiment of the present invention includes a generator. The generator is coupled to an engine and generates electricity. Also, the generator has a starter function to start the engine. For example, the generator may be one which can be used also as a motor. Further, the generator may be an AC generator. A unit to be driven is driven by the output of the engine. There may be a variety of driven units. In case of hybrid construction machines, the driven unit may be a hydraulic pump which serves as a driving source for a crawler vehicle. In case of hybrid vehicles, driving wheels may be a driven unit. A motor is driven by electric power generated by the generator. As the motor, one which can be used also as a generator may be used. The motor may be an AC motor. In case of hybrid construction machines, the motor may be used to turn, stretch or retract a boom. When the machine is a hybrid vehicle, the motor may be used to drive driving wheels. The electric power generated by the generator is stored in a capacitor. The capacitor is chargeable. A transformer is disposed between the capacitor and the generator. The transformer is used to store the power the generator generates in the capacitor, and may be, for example, one to transform AC power to DC power. Also, the transformer may be used to provide power from the capacitor to the generator to operate the generator as a motor. The transformer may be used with another transformer which is used to supply driving power to the motor. The transformer may form, together with the said another transformer, motor driving means, e.g. a matrix converter. Alternatively, the motor driving means may be, for example, a combination of AC-to-DC converting means and DC-to-AC converting means. Lower-voltage storage means connectable to the capacitor is provided. A battery, for example, may be used as the lower-voltage storage means. The rated voltage of the lower-voltage storage means is lower than the rated voltage of the capacitor. A voltage-booster is disposed between the lower-voltage storage means and the capacitor. Preferably, the voltage-booster can charge the lower-voltage storage means through the transformer and boost the voltage of the lower-voltage storage means for supplying power to the generator through the transformer. 
     If the motor has not been activated and the capacitor has been discharged when the engine is going to be started by means of the hybrid driving mechanism start control system having the above-described arrangement, the voltage of the lower-voltage storage means is boosted by the voltage booster and the boosted voltage is supplied to the motor to thereby rotate the motor. The rotation of the motor causes the engine to start operating. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING 
         FIG. 1  is a block diagram of a hybrid driving mechanism start control system according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A hybrid driving mechanism start control system according to one embodiment of the present invention is practiced in a hybrid construction machine. The hybrid construction machine includes a generator, e.g. a motor-generator  2 . When an engine  4  is operating, the motor-generator  2  is driven as a generator by the engine  4 . The motor-generator  2  is coupled to the engine  4 . The engine  4  is coupled also to a driven unit, e.g. a pump  6 . When the engine  4  is operating, the motor-generator  2  generates electricity and, at the same time, the pump is driven. The pump  6  serves as a driving source for hydraulic actuators of, for example, an arm cylinder, a boom cylinder, a bucket cylinder, and hydraulic travel motors. The motor-generator  2  is operable as a motor, and, when it is operating as a motor with the engine  4  not operating, the motor-generator  2  can be used to start up the engine  4 . 
     The motor-generator  2  is driven by the engine  4  to thereby generate AC power. The AC power is transformed into AC power having a desired frequency and a desired voltage value by motor driving means, e.g. a converter, e.g. 
     a converter  10  of an indirect matrix converter  8 , and an inverter  12  of the indirect matrix converter  8 , and, then, supplied to a motor, e.g. a generator-motor  14 . The generator-motor  14  rotates from the AC power supplied from the indirect matrix converter  8 . In the hybrid construction machine, the generator-motor  14  is coupled to a top rotating carriage of the hybrid construction machine via a rotating system (HRS)  16  in order to rotate the top rotating carriage. 
     The converter  10  and the inverter  12  are controlled by control means, e.g. a control unit  18 . The control unit  18  controls the engine  4 , too. 
     The converter  10  and the inverter  12  of the indirect matrix converter  8  each have a plurality of semiconductor switching devices, e.g. IGBTs or FETs. The IGBTs or FETs are ON-OFF controlled by the control unit  18 . The converter  10  converts the supplied AC voltage to an intermediate DC voltage, and the inverter  12  converts the intermediate DC voltage to an AC voltage having a desired frequency and a desired voltage value. The resulting AC voltage is supplied to the generator-motor  14 . 
     When the motor-generator  2  is rotating as a generator, the intermediate DC voltage, which is the output of the converter  10  of the indirect matrix converter  8 , is supplied to a capacitor  22 , e.g. an EDLC (electric double layer capacitor), through a converter, e.g. a chopper  20 , to thereby charge the capacitor  22 . The chopper  20  is controlled by the control unit  18  so as to make the charging performed. The chopper  20  includes at least one semiconductor switching device, e.g. an IGBT or an FET, which is ON-OFF controlled by the control unit  18 . 
     The charge voltage on the capacitor  22  is supplied to the control unit  18 . When the charge voltage is lower than a predetermined charging START voltage predetermined for the capacitor  22 , which means the capacitor  22  has been considerably discharged, the chopper  20  is controlled by the control unit  18  to charge the capacitor  22 . When the voltage of the capacitor  22  becomes higher than a capacitor charging STOP voltage predetermined for the capacitor  22 , which means that the charge voltage indicates that the capacitor  22  has been sufficiently charged, the chopper  20  is so controlled by the control unit  18  to charge the capacitor  22  no more. The capacitor charging STOP voltage may be equal to the capacitor charging START voltage or may be higher than the capacitor charging START voltage. The regenerated power from the generator-motor  14  is also used to charge the capacitor  22  via the inverter  12  and the chopper  20 . For a hybrid construction machine, relative large regenerated power is generated in the generator-motor  14  in a short time, the capacitor  22  is desirably an EDLC having a short charging time. 
     The power charged in the capacitor  22  may be used, through the chopper  20  and the converter  10 , to drive the motor-generator  2  as a motor. The chopper  20  and the converter  10  serve as bidirectional power passing means or charge-discharge means which can not only charge the capacitor  22  with power generated by the motor-generator  2  but also cause power in the capacitor  22  to be discharged to the motor-generator  2 . The converter  10  and the chopper  20  are controlled by the control unit  18 , and selected ones of the IGBTs or FETs of the converter  10  and the chopper  20  are placed in the ON state, whereby the power in the capacitor  22  can be supplied to the motor-generator  2 . 
     Let it be assumed that both the engine  4  and the motor-generator  2  of the hybrid construction machine are not operating. In order to start up the engine  4 , the power stored in the capacitor  22  is supplied to the motor-generator  2  through the chopper  20  and the converter  10  to thereby rotate the motor-generator  2  as a motor, and, then, the engine  4  is actuated by the rotation of the motor-generator  2 . In other words, the motor-generator  2  operates also as a starter for the engine  4 . 
     Lower-voltage storage means, e.g. a battery  26 , is connected to the junction of the chopper  20  and the capacitor  22  through a voltage-booster, e.g. a chopper  24 . The chopper  24 , too, includes at least one semiconductor switching device, e.g. an IGBT or FET, and also a voltage-boosting inductor or a voltage-transformer. The chopper  24  is ON-OFF controlled by the control unit  18 . 
     The battery  26  has a rated voltage lower than that of the capacitor  22 , and is charged, when the motor-generator  2  is operating as a generator, by the power from the motor-generator  2  through the choppers  20  and  24  and the converter  10 , or charged by the regenerated power from the motor-generator  14  through the inverter  12  and the choppers  20  and  24 . The chopper  24 , too, is controlled by the control unit  18 . For example, the charged voltage on the battery  26  is supplied to the control unit  18 . The converter  10  or the inverter  12  and the choppers  20  and  24  are controlled in such a manner that the battery  26  is charged when the voltage coupled to the control unit  18  is lower than a battery charging START voltage predetermined for the battery  26 , and that the charging of the battery  26  is stopped when the voltage coupled to the control unit  18  is higher than a battery charging STOP voltage predetermined for the battery  26 . The battery charging START voltage is set to a voltage lower than the capacitor charging START voltage for the capacitor  22 . The battery charging STOP voltage may be equal to the battery charging START voltage, or it may be higher than the battery charging START voltage. It should be noted that the battery charging STOP voltage is set to be lower than the capacitor charging START voltage and the capacitor charging STOP voltage. 
     The chopper  24  may boost the voltage of the battery  26  to a voltage equal to the voltage of the capacitor  22  before applying it to the motor-generator  2  through the chopper  20  and the converter  10 . 
     There may be a case where, when it is required for the engine  4  to be actuated while neither the engine  4  nor the motor-generator  2  of this hybrid construction machine is operating, the capacitor  22  has been discharged. There may be a case where, when an EDLC is used as the capacitor  22 , the capacitor  22  has discharged to such an extent that the engine  4  cannot be ignited when an operator tries to start the hybrid construction machine in the morning after it is stopped and left in a construction site in the evening of a previous day, i.e. only one night later. In such cases, the capacitor  22  cannot supply power to the motor-generator  2  through the chopper  20  and the converter  10 . To overcome the problem, the control unit  18  controls the chopper  24  to boost the voltage of the battery  26  up to the voltage of the capacitor  22 , and the boosted voltage is applied to the motor-generator  2  through the chopper  20  and the converter  10 . This makes the motor-generator  2  operate as a motor, causing the engine  4  to rotate. Once the engine  4  is actuated, the motor-generator  2  can be operated as a generator, and the capacitor  22  can be charged, and, furthermore, the generator-motor  14  can be operated as a motor through the indirect matrix converter  8 . Since it is sufficient that the battery  26  can drive the motor-generator  2  as the starter for the engine  4 , the battery  26  can be of a small capacity, so that the charging of the battery  26  does not impede the charging of the capacitor  22 . 
     In the described embodiment, the generator-motor  14  is used to rotate a top rotating carriage, but the invention is not limited to it. The generator-motor  14  may be arranged to drive the hydraulic pump  6 . Further, in the described embodiment, the battery  26  is used as lower-voltage storage means, but a capacitor may be used instead. Although the converter  20  of the indirect matrix converter  8  is used as a converter in the described embodiment, the invention is not limited to it, and an AC-to-DC converter to convert the AC voltage provided by the motor-generator  2  into a DC voltage may be used instead. In this case, in order to drive the generator-motor  14 , a DC-to-AC converter for converting the DC voltage from the AC-to-DC converter to an AC voltage is used.