Hybrid vehicle charging control device

Abstract

To provide a charging control device of a hybrid vehicle that can restore a battery that is insufficiently charged, when actual engine torque of an engine is insufficient.SOLUTION: When a residual charge amount SOC of a battery 54 falls below a predetermined value, an engine torque-decrease control part 94 decreases torque of an engine 12 so that an operation point of the engine 12 is kept within a preset engine torque stable region TS. In a state where the operation point of the engine 12 is kept within the engine torque stable region TS, a charging control part 96 controls torque of an electric motor MG so that an actual amount of charging by the electric motor MG is equal to a preset target charge amount. This can restore the battery 54 that is charged insufficiently.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a charging control device for a hybrid vehicle that includes an electric motor provided between an engine and drive wheels, and a battery that is charged with electric power generated by the electric motor. [Background technology]

[0002] There is known a control device for a hybrid vehicle that includes an electric motor (motor generator) provided between the engine and the drive wheels and a battery that is charged with the electric power generated by the electric motor. For example, a charge control device for a hybrid vehicle is described in Patent Document 1. In Patent Document 1, when generating electricity by rotating the electric motor using the engine's idle speed, the engine's idle speed and the torque consumption of the electric motor are changed according to the charge level of the battery. When the battery's charge level is low, the engine's idle speed is increased and the torque consumption of the electric motor is reduced, thereby reducing the load on the high-power system, such as the electric motor and inverter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-029319 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the battery is charged while maintaining the rotational speed of the electric motor by balancing the positive torque of the engine and the negative torque of the electric motor. However, when the engine is in a low rotational speed range, such as idling, high engine intake air temperature, engine knocking, engine misfire, or resonance of power transmission components can hinder accurate engine torque control. This can result in a torque discrepancy, which causes the actual engine torque to be insufficient compared to the required engine torque, resulting in a decrease in the rotational speed of the electric motor. In such cases, the rotational speed of the electric motor can be increased by reducing the negative torque of the electric motor, but this can result in an insufficient charge on the battery. Furthermore, if the torque discrepancy significantly reduces the engine torque, the negative torque of the electric motor will stick to the upper limit of the negative torque (the limit value of the electric motor) for rotational speed matching, causing a decrease in rotational speed. This can result in insufficient torque being obtained from the low-rotation engine, further resulting in an insufficient charge on the battery. The hybrid vehicle control device described in Patent Document 1 does not at all consider the issue of the actual engine torque being insufficient compared to the required engine torque.

[0005] The present invention has been made against the background of the above circumstances, and its purpose is to provide a charging control device for a hybrid vehicle that can recover a battery from insufficient charging when the actual engine torque of the engine is insufficient.

[0006] The present inventors have conducted various studies in light of the above circumstances and have found that when charging a battery due to a low remaining battery charge, if the actual engine torque is insufficient relative to the required engine torque, the engine torque can be reduced to obtain accurate engine torque control, and then the engine torque can be controlled so that the battery charge amount becomes a target charge amount, thereby enabling optimal battery charging. The present invention was made based on this finding. [Means for solving the problem]

[0007] That is, the gist of the first invention is a vehicle comprising: (a) an electric motor provided between an engine and a driving wheel; and a battery that is charged with electric power generated by the electric motor that is driven by the engine. The battery is charged while maintaining the rotational speed of the electric motor by controlling the torque of the electric motor so that the positive torque of the engine and the negative torque of the electric motor are balanced. A control device for a hybrid vehicle, comprising: (b) The hybrid vehicle stops and the engine speed drops to a predetermined value or less, and an engine torque reduction control unit that reduces the torque of the engine so that the operating point of the engine is within a predetermined engine torque stable region when the remaining charge amount of the battery drops below a predetermined value; and (c) in a state where the operating point of the engine is within the engine torque stable region by the engine torque reduction control unit, the control unit reduces the torque of the electric motor so that the actual charge amount by the electric motor becomes a predetermined target charge amount. torque a charging control unit that controls the (d) the engine torque stability region is a region within a two-dimensional coordinate system of the engine speed and the engine torque, excluding a region where the engine torque accuracy is insufficient and the engine torque becomes unstable; (e) the charging control unit executes rotation speed feedback control of the electric motor so that the actual rotation speed becomes a preset target lower limit rotation speed when the hybrid vehicle is stopped; and (f) the target lower limit rotation speed is a value on the boundary between an engine torque unstable region within a two-dimensional coordinate system of the engine speed and the engine torque, where the engine torque accuracy is insufficient and the engine torque becomes unstable, and an engine torque stable region where the engine torque is stable and the torque accuracy is high. The reason is that [Effects of the Invention]

[0008] According to the first aspect of the present invention, when the remaining charge of the battery falls below a predetermined value, the engine torque reduction control unit reduces the torque of the engine so that the operating point of the engine is within a predetermined engine torque stable region. Then, with the operating point of the engine within the engine torque stable region, the charge control unit controls the torque of the electric motor so that the actual charge rate of the electric motor is equal to a predetermined target charge rate. This allows the battery to recover from an insufficient charge state. In addition, since the engine torque is controlled so that the actual charge amount by the electric motor matches the predetermined target charge amount in the region where the engine torque control accuracy is easily achieved, excluding the region where the engine torque is unstable, the battery can be easily recovered from a state where the charge amount is insufficient.

[0010] Preferably, in the first aspect of the present invention, if the engine rotation speed continues to decrease even after reducing the engine torque, the engine torque reduction control unit stops charging the battery and causes the engine to operate autonomously, thereby putting the engine into an idling state with no load.

[0011] Preferably, the first aspect of the present invention further includes an idle speed learning control unit that learns an engine torque for maintaining a target idle speed of the engine when the engine is autonomously operated by the engine torque reduction control unit, thereby eliminating deviation in the engine torque for maintaining the target idle speed of the engine. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram illustrating a hybrid vehicle and an electronic control device to which the present invention is applied, and is also a diagram illustrating the main control functions of the control device. [Figure 2] 1 is a diagram illustrating an example of a boundary line between an area where engine torque accuracy is unstable and an area where engine torque accuracy is stable in a two-dimensional coordinate system of engine rotation speed and engine torque; [Figure 3] FIG. 10 is a diagram illustrating a direction in which the engine speed is increased during battery charging after the engine operating point is moved into a region where the engine torque accuracy is stable and the deviation of the actual torque from the required engine torque is reduced in a two-dimensional coordinate system of the engine speed and the engine torque. [Figure 4] 2 is a flowchart illustrating the main control functions of the electronic control device of FIG. 1. [Figure 5] 2 is a time chart illustrating the main control operations of the electronic control device of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Example]

[0016] Fig. 1 is a diagram illustrating the schematic configuration of a hybrid vehicle (hereinafter referred to as vehicle) 10 to which the present invention is applied, and also illustrates the main parts of the control functions and control systems for various controls in the vehicle 10. In Fig. 1, the vehicle 10 is equipped with an engine 12 and an electric motor MG that function as power sources. The vehicle 10 also has the electric motor MG in a power transmission path 16 between the engine 12 and drive wheels 14.

[0017] The engine 12 has a rotation speed Ne (rpm) and an engine torque Te (Nm) controlled by an engine control device 50 controlled by an electronic control device 90 (described later).

[0018] The electric motor MG is a rotating electric machine that functions as a motor and as a generator that generates electric power, and is a so-called motor generator. The electric motor MG is connected to a battery 54 via an inverter 52. The battery 54 is an electricity storage device that supplies and receives electric power to the electric motor MG. The inverter 52 is controlled by an electronic control device 90, whereby the output torque Tm, which is the positive torque of the electric motor MG, and the generating (regenerative) torque -Tm, which is the negative torque, are controlled.

[0019] The power transmission path 16 includes a K0 clutch 20 provided within a case 18 between the engine 12 and the electric motor MG, a pulsation absorbing damper 21 that absorbs torque pulsations while transmitting power, a torque converter 22 with an LU clutch 40, and an automatic transmission 24.

[0020] The power transmission path 16 includes, outside the case 18, a propeller shaft 28 connected to a transmission output shaft 26, which is the output rotating member of the automatic transmission 24, a differential gear 30 connected to the propeller shaft 28, and a pair of drive shafts 32 connected to the differential gear 30.

[0021] The automatic transmission 24 is a known planetary gear automatic transmission equipped with, for example, one or more planetary gear devices (not shown) and engagement devices CB. The engagement devices CB include, for example, a plurality of known hydraulic friction engagement devices. The automatic transmission 24 is a stepped transmission in which one of a plurality of gear stages (also referred to as gear stages) with different speed ratios (also referred to as gear ratios) γat (=AT input rotation speed Ni / AT output rotation speed No) is formed by engaging one of the engagement devices CB. The gear stages of the automatic transmission 24 are switched by an electronic control device 90 (described later) in response to the accelerator operation by the driver, vehicle speed V, etc. The MG rotation speed Nm is equal to the rotation speed Ne of the engine 12 when the K0 clutch 20 is engaged, and is equal to the input rotation speed of the torque converter 22 and the AT input rotation speed Ni when the LU clutch 40 is engaged.

[0022] The vehicle 10 is equipped with an electronic control unit 90. The electronic control unit 90 is configured to include a so-called microcomputer equipped with, for example, a CPU, RAM, ROM, an input / output interface, etc., and the CPU executes various controls of the vehicle 10 by performing signal processing in accordance with programs stored in the ROM in advance while utilizing the temporary storage function of the RAM. The electronic control unit 90 is configured to include computers for engine control, electric motor control, clutch control, transmission control, etc. as necessary.

[0023] The electronic control device 90 is supplied with various signals based on the detected values ​​from various sensors provided on the vehicle 10 (e.g., engine rotation speed sensor 70, turbine rotation speed sensor 72, output rotation speed sensor 74, MG rotation speed sensor 76, accelerator opening sensor 78, throttle valve opening sensor 80, brake switch 82, battery sensor 84, oil temperature sensor 86, water temperature sensor 88, etc.). For example, the following signals are supplied: engine rotation speed Ne, which is the rotation speed of engine 12; turbine rotation speed Nt, which is the same value as AT input rotation speed Ni; AT output rotation speed No, which corresponds to vehicle speed V; MG rotation speed Nm, which is the rotation speed of electric motor MG; accelerator opening θacc, which is the driver's accelerator operation amount indicating the magnitude of the driver's acceleration operation; throttle valve opening θth, which is the opening of the electronic throttle valve; brake-on signal Bon, which is a signal indicating the state in which the brake pedal for operating the wheel brakes is being operated by the driver; battery temperature THbat, battery charge / discharge current Ibat, and battery voltage Vbat of battery 54; hydraulic oil temperature THoil, which is the temperature of the hydraulic oil in hydraulic control circuit 56; and coolant temperature THwe of engine 12.

[0024] The electronic control device 90 outputs various command signals to each device (for example, the engine control device 50, the inverter 52, the hydraulic control circuit 56, etc.) provided in the vehicle 10. For example, an engine control command signal Se for controlling the engine 12, an MG control command signal Sm for controlling the electric motor MG, a CB hydraulic control command signal Scb for controlling the engagement device CB, a K0 hydraulic control command signal Sko for controlling the K0 clutch 20, an LU hydraulic control command signal Slu for controlling the LU clutch 40, etc. are output.

[0025] The electronic control device 90 includes an engine control unit 92 a, an electric motor control unit 92 b, an engine torque reduction control unit 94, and an insufficient charge power generation control unit 98 including a charge control unit 96 in order to realize various controls in the vehicle 10.

[0026] The electronic control device 90 functions as a hybrid control unit that performs hybrid drive control using the engine 12 and the electric motor MG, through the functions of an engine control unit 92a and an electric motor control unit 92b that controls the operation of the electric motor MG via the inverter 52. The hybrid drive control mainly controls the drive of the vehicle 10 so as to obtain sufficient acceleration performance with the lowest possible fuel consumption.

[0027] The electronic control unit 90 calculates the amount of driving demanded by the driver for the vehicle 10, for example, by applying the accelerator opening θacc and the vehicle speed V to a driving demand map. The amount of driving demand is, for example, the required driving torque Trdem [Nm] at the drive wheels 14. The required driving torque Trdem [Nm] is the required driving power Prdem [W] at the vehicle speed V at that time. To achieve the required driving power Prdem, the engine control unit 92a outputs an engine control command signal Se to control the engine 12, and the electric motor control unit 92b outputs an MG control command signal Sm to control the electric motor MG. When the accelerator opening θacc is zero, the engine control unit 92a performs idle rotation control to autonomously rotate the engine 12 to achieve a target idle rotation speed. The target idle rotation speed has a target lower limit rotation speed as a basic value, i.e., a lower limit value, and is increased depending on the warm-up state of the engine 12, etc.

[0028] When the required drive torque Trdem can be satisfied by the output of the electric motor MG alone, the electronic control unit 90 establishes the motor drive mode, i.e., the BEV drive mode, as the drive mode for driving the vehicle 10. On the other hand, when the required drive torque Trdem cannot be satisfied without using at least the output of the engine 12, the electronic control unit 90 establishes the engine drive mode, i.e., the HEV drive mode, as the drive mode. The HEV drive mode is a hybrid drive mode that enables engine driving, i.e., hybrid driving (=HEV driving), using at least the engine 12 as the power source SP when the K0 clutch 20 is engaged. On the other hand, even when the required drive torque Trdem can be satisfied by the output of the electric motor MG alone, the electronic control unit 90 establishes the HEV drive mode as the drive mode when, for example, the battery 54 needs to be charged, the engine 12 needs to be warmed up, or the hydraulic oil temperature THoil is extremely low.

[0029] When charging of the battery 54 is required, the K0 clutch 20 is engaged, the engine 12 drives the electric motor MG to rotate, and the output current (negative torque) of the electric motor MG is controlled to obtain a target charge amount based on the power generated by the electric motor MG, thereby charging the battery 54. That is, in such a charging state, the rotation of the electric motor MG is maintained by balancing the positive torque of the engine 12 and the negative torque of the electric motor MG, thereby charging the battery 54. However, when the vehicle 10 is stopped or coasting at a low speed, for example, the accelerator opening θacc is zero and the engine 12 is idling, i.e., in a relatively low rotation speed range of 950 rpm or less, the torque of the engine 12 may become unstable due to high intake air temperature of the engine 12, knocking of the engine 12, misfire of the engine 12, vibration of the pulsation absorbing damper 21, etc., as shown in FIG. 2 , and the actual torque of the engine 12 may become insufficient for the required engine torque, causing the electric motor MG to slow down in rotation. In such a case, the rotation of the electric motor MG can be increased by reducing the negative torque of the electric motor, but this causes a problem of insufficient charge in the battery 54. On the other hand, if an attempt is made to increase the negative torque of the electric motor MG in order to ensure sufficient charge in the battery 54, the rotation of the engine 12 connected to the electric motor MG decreases, and sufficient torque cannot be obtained from the low-speed engine 12, which also causes a problem of insufficient charge in the battery 54.

[0030] 2, in the low rotation speed range of the engine 12 of 950 rpm or less, a two-dimensional coordinate system with the horizontal axis representing the engine rotation speed Ne and the vertical axis representing the engine torque Te shows the following regions of engine torque decrease due to the idle rotation of the engine 12, where low rotation speeds result in weak combustion in the engine 12 and the optimal ignition timing MBT torque becoming flat and the adaptive value easily deviating; a region of engine torque decrease due to a decrease in the accuracy of the optimal ignition timing MBT resulting from knocking of the engine 12; a region of engine torque decrease due to misfires in the engine 12; and a region of engine torque decrease due to rotation fluctuations caused by resonance of the pulsation absorbing damper 21. These regions are regions where the torque accuracy of the engine 12 cannot be obtained relative to the required engine torque (required output), and the actual torque of the engine 12 is likely to be insufficient. Line L in FIG. 2 is a characteristic line in which the rotation speed of the engine 12 rises from around 650 rpm and the engine torque Te increases as the rotation speed Ne of the engine 12 increases. Line L indicates the boundary between an unstable engine torque region TU, in which the torque of the engine 12 is unstable and has low torque accuracy, and an engine torque stable region TS, in which the torque of the engine 12 is stable and has high torque accuracy. In this embodiment, line L indicates the target lower limit rotation speed NeTs-α of the engine 12 after the operating point of the engine 12 is moved into the stable engine torque region TS. α is a value between 0 and several tens of rpm and is a margin value. In other words, the target lower limit rotation speed NeTs of the engine 12 is a value on line L or a value along line L.

[0031] In contrast to this, in this embodiment, when the rotation speed Ne of the engine 12 is in a low rotation range, for example, below 950 rpm, and the remaining charge SOC of the battery 54 becomes low due to insufficient torque of the engine 12, an insufficient charge power generation control unit 98 is provided which reduces the torque Te of the engine 12, as shown by arrows A1 and A2 in Figure 2, to bring the operating point of the engine 12 into the stable engine torque region TS where the torque of the engine 12 is stable, while maintaining the target charge amount of the battery 54.

[0032] When the vehicle 10 stops, the engine 12 speed drops to a low level of 950 rpm or less, and the state of charge (SOC) of the battery 54 drops below a predetermined value, such as a first determination value SOC1 for determining whether the SOC has dropped below the normal operating range and to the extent that torque is considered insufficient, the engine torque reduction control unit 94 of the insufficient-charge power generation control unit 98 inhibits the energy management priority process that had been executed up until that point and temporarily reduces the torque of the engine 12 by a predetermined value from the target torque Tit that had been used up until that point to a target reduced torque Tit1, as shown by arrow A1 in FIG. 2, so that the operating point of the engine 12 moves from the unstable engine torque region TU to a predetermined position within the stable engine torque region TS in FIG. 2. At the same time, the target charge rate of the battery 54 is reduced, thereby reducing the actual charge rate of the battery 54. The predetermined value is a value that causes the operating point of the engine 12 to be sufficiently below line L. In addition, the energy management priority process is a process that increases the rotation speed of the engine 12 and increases the power generation current of the electric motor MG when the torque of the engine 12 is insufficient for charging the battery 54 so that the actual charge amount of the battery 54 follows the target charge amount.

[0033] If the engine 12 rotation speed continues to decrease even after prohibiting the above-mentioned energy management priority processing and reducing the torque of the engine 12 to reduce the actual charge amount of the battery 54, the engine torque reduction control unit 94 stops charging the battery 54 and further reduces the torque of the engine 12 as shown by arrow A2 in Figure 2 so as to make the negative torque of the electric motor MG zero, thereby putting the engine 12 into an autonomous operating state where the output torque is zero, i.e., an idle rotation state.

[0034] When the engine torque reduction control unit 94 determines that the operating point of the engine 12 is within the stable engine torque region TS, and the vehicle 10 is stopped, the engine 12 speed is reduced to a low speed of 950 rpm or less, or the state of charge (SOC) of the battery 54 is not greater than a predetermined value, for example, a first determination value SOC1 for determining whether the SOC has dropped below the normal operating range to the extent that torque is considered to be insufficient, the charging control unit 96 permits energy management priority processing and increases the engine 12 speed and torque, thereby increasing the actual charge amount of the battery 54. This also increases the state of charge (SOC) of the battery 54. Arrow A3 in FIG. 3 indicates the direction in which the operating point of the engine 12 moves due to such increases in engine 12 speed and torque.

[0035] In addition, when the operating point of the engine 12 is within the engine torque stable region TS, the charging control unit 96 executes rotation speed feedback control so that the actual rotation speed Ne of the engine 12 or the actual rotation speed Nmg of the electric motor MG becomes a preset target lower limit rotation speed Nit.

[0036] When the engine torque reduction control unit 94 prohibits energy management priority processing and the rotation speed of the engine 12 continues to decrease, if the engine 12 is placed in an autonomous driving state where the output torque is zero, i.e., an idle rotation state, the idle rotation learning control unit 100 executes learning control in which the engine torque that maintains the idle rotation at that time is set as the target torque during idle control of the engine 12 in subsequent ISC control in which the rotation speed of the engine 12 is set to a preset target value. This eliminates the torque discrepancy of the engine 12 during idling and the decrease in rotation speed of the engine 12.

[0037] Fig. 4 is a flowchart illustrating the main control operations of the power generation control during insufficient charging by the electronic control unit 90, and Fig. 5 is a time chart illustrating the main control operations of the power generation control during insufficient charging by the electronic control unit 90. Steps S1 (hereinafter, the term "step" will be omitted), S2, S4, and S5 in Fig. 4 correspond to the control functions of the engine torque reduction control unit 94, and steps S3 and S6 correspond to the control functions of the charging control unit 96.

[0038] In S1 of Fig. 3, the vehicle 10 stops, the rotation speed of the engine 12 decreases, and it is determined whether the state of charge SOC of the battery 54 has decreased to a predetermined value or less, for example, a preset first determination value SOC1 or less. If the determination in S1 is negative, in S5, energy management priority processing is permitted and the charge amount of the battery 54 is increased. For example, the section from time t0 to time t1 in Fig. 5 shows this state. In this section, rotation speed feedback control is executed to set the actual rotation speed Ne of the engine 12 or the actual rotation speed Nmg of the electric motor MG to a preset target lower limit rotation speed NeTs.

[0039] If the determination in S1 is negative, the vehicle 10 is traveling, the engine 12 rotation speed is maintained relatively high, and the state of charge (SOC) of the battery 54 is greater than a predetermined value, such as a preset first determination value SOC1. Therefore, energy management priority processing is permitted to improve fuel efficiency by setting the engine 12 at a low rotation speed and high torque operating point, and the amount of power generated by the electric motor MG is relatively increased. However, if the determination in S1 is positive, the energy management priority processing to improve fuel efficiency by setting the engine 12 at a low rotation speed and high torque operating point is prohibited in S2, and the required torque of the electric motor MG is reduced, thereby relatively reducing the amount of power generated (charge amount) by the electric motor MG. This state is shown at time t2 in FIG. 5. As a result, the engine 12 rotation speed is maintained at the target rotation speed.

[0040] In the next step S3, when the vehicle 10 is stopped, the rotation speed of the engine 12 is reduced, and the remaining charge SOC of the battery 54 is reduced to a predetermined value or less, for example, a predetermined first judgment value SOC1 or less, the energy management priority processing is prohibited and the amount of power generated by the electric motor MG is relatively reduced, and it is determined whether the reduction in the rotation speed of the engine 12 continues.

[0041] If the determination in S3 is negative, in S6, charging of the battery 54 by the electric motor MG is permitted. Also, rotation speed feedback control is executed to set the actual rotation speed Ne of the engine 12 or the actual rotation speed Nmg of the electric motor MG to a preset target lower limit rotation speed NeTs.

[0042] However, if the determination in S3 is positive, charging of the battery 54 by the electric motor MG is stopped in S4, and the engine 12 operates autonomously. This state is shown at time t3 in Figure 4. When the engine 12 operates autonomously, learning control is executed in which the torque of the engine 12 that maintains the idle speed is set as the target engine torque for subsequent ISC control.

[0043] As described above, according to the electronic control device 90 of this embodiment, when the state of charge SOC of the battery 54 falls below a predetermined value, the engine torque reduction control unit 94 reduces the torque of the engine 12 so that the operating point of the engine 12 falls within a preset engine torque stable region TS. Then, with the operating point of the engine 12 within the engine torque stable region TS, the charge control unit 96 controls the torque of the electric motor MG so that the actual charge amount of the electric motor MG reaches a preset target charge amount. This allows the battery 54 to recover from an insufficient charge amount state.

[0044] Furthermore, according to the electronic control device 90 of this embodiment, the stable engine torque region TS is a region within a two-dimensional coordinate system of the engine 12 rotation speed and the torque of the engine 12, excluding the unstable engine torque region TU in which the torque of the engine 12 becomes unstable because of insufficient torque accuracy of the engine 12 due to high intake air temperature of the engine 12, knocking of the engine 12, misfire of the engine 12, resonance of the pulsation absorbing damper 21 of the power transmission system, etc. In this way, the unstable engine torque region TU in which the torque of the engine 12 is unstable is excluded, and the torque of the electric motor MG is controlled so that the actual charge amount of the electric motor MG becomes the predetermined target charge amount in the stable engine torque region TS in which the torque control accuracy of the engine 12 is easily achieved, so that the battery 54 can easily recover from an insufficient charge amount.

[0045] Furthermore, according to the electronic control device 90 of this embodiment, if the rotation speed of the engine 12 continues to decrease even after reducing the torque of the engine 12, the engine torque reduction control unit 94 stops charging the battery 54 and causes the engine 12 to operate autonomously. This puts the engine 12 into an unloaded idling state. This allows the rotation of the engine 12 to continue stably.

[0046] Furthermore, the electronic control device 90 of this embodiment includes an idle speed learning control section that, when the engine torque reduction control section 94 causes the engine 12 to operate autonomously, learns the torque of the engine 12 during the autonomous operation of the engine 12 as the target torque of the engine 12 for subsequent target idle speed control. This eliminates any discrepancy in the torque of the engine 12 during idle speed control.

[0047] Furthermore, according to the electronic control device 90 of this embodiment, the charge control unit 96 executes rotation speed feedback control so that the actual rotation speed of the electric motor MG becomes a target value based on a preset target lower limit rotation speed while the vehicle 10 is stopped. This allows the rotation speeds of the engine 12 and the electric motor MG to be maintained stably, making it possible to easily recover the battery 54 from a state in which the amount of charge is insufficient.

[0048] Furthermore, according to the electronic control device 90 of this embodiment, the value is on or along the boundary line (line L) between an unstable engine torque region TU, where sufficient engine torque accuracy is not obtained and the torque of the engine 12 becomes unstable, and an stable engine torque region TS, where the torque of the engine 12 is stable, within a two-dimensional coordinate system of the rotation speed of the engine 12 and the torque of the engine 12. As a result, the region where the torque of the engine 12 is unstable is excluded, and the rotation speed of the electric motor MG is controlled so that the actual charge amount of the battery 54 becomes the predetermined target charge amount in a region where the torque control accuracy of the engine 12 is likely to be achieved, so that the battery 54 can easily recover from an insufficient charge amount.

[0049] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the present invention can also be applied to other embodiments.

[0050] For example, in the above-described embodiment, the torque converter 22 is provided in the power transmission path 15 of the vehicle 10, but instead of the torque converter 22, a starting clutch may be provided.

[0051] Furthermore, in the above-described embodiment, the engine torque request and the MG torque request are changed at a predetermined gradient as shown in FIG. 5, but they may also be changed in a stepwise manner.

[0052] It should be noted that the above is merely one embodiment, and the present invention can be embodied in various forms with various modifications and improvements based on the knowledge of those skilled in the art. [Explanation of symbols]

[0053] 10: Hybrid vehicle 12: Engine 14: Drive wheels 16: Power transmission path 90: Electronic control unit (control unit) 94: Engine torque reduction control unit 96: Charging control unit 98: Power generation control unit when charging is insufficient MG: Electric motor

Claims

1. A control device for a hybrid vehicle comprising: an engine; an electric motor connected to a power transmission path between the engine and drive wheels so as to be capable of transmitting power; and a battery charged with electric power generated by the electric motor driven by the engine, the control device controlling the torque of the electric motor so as to balance the positive torque of the engine and the negative torque of the electric motor, while maintaining the rotational speed of the electric motor, an engine torque reduction control unit that reduces the torque of the engine so that an operating point of the engine is within a predetermined engine torque stable region when the hybrid vehicle stops and the engine speed drops below a predetermined value and the remaining charge of the battery drops below a predetermined value; a charge control unit that controls the torque of the electric motor so that an actual charge amount by the electric motor becomes a predetermined target charge amount while the engine torque reduction control unit places the operating point of the engine within the engine torque stable region, the stable engine torque region is a region within a two-dimensional coordinate system of the engine rotation speed and the engine torque, excluding a region in which the engine torque accuracy is insufficient and the engine torque becomes unstable, the charging control unit executes a rotation speed feedback control of the electric motor so that an actual rotation speed becomes a preset target lower limit rotation speed when the hybrid vehicle is stopped; The target lower limit rotation speed is a value on the borderline between an unstable engine torque region where the engine torque accuracy is insufficient and the engine torque becomes unstable, and an stable engine torque region where the engine torque is stable and the torque accuracy is high, within a two-dimensional coordinate system of the engine rotation speed and the engine torque. A control device for a hybrid vehicle.

2. The engine torque reduction control unit stops charging of the battery and causes the engine to operate autonomously if the engine speed continues to decrease even after reducing the torque of the engine.

2. The control device for a hybrid vehicle according to claim 1.

3. and an idle rotation learning control unit that, when the engine is autonomously operated by the engine torque reduction control unit, learns the torque of the engine at this time as a target torque of the engine during idle rotation control.

4. The control device for a hybrid vehicle according to claim 3.

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