Hybrid vehicle charging control device

Abstract

To provide a charging control device of a hybrid vehicle that can restore a battery which 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 first determination value SOC1, an engine rotation speed-increase control part 94 increases a target lower-limit rotation speed Nt1 of rotation speed control of an engine 12 or an electric motor MG up to a target lower-limit rotation speed Ntl1 so that an operation point of the engine 12 is 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 negative torque of the 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 which 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, Patent Document 1 discloses a charge control device for a hybrid vehicle. In Patent Document 1, when generating electricity by rotating the electric motor using the engine's idle speed, the idle speed of the engine and the (negative) torque consumption of the electric motor are changed according to the charge level of the battery, and when the charge level of the battery is low, the idle speed of the engine is increased and the torque consumption of the electric motor is reduced, thereby reducing the load on the high-voltage 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] During battery charging, the output of the electric motor is maintained by balancing the positive torque of the engine and the negative torque of the electric motor (motor generator). However, when the engine is idling at low speeds, such as when the vehicle is stopped or creeping, high engine intake air temperature, engine knocking, or engine misfire can cause the actual engine torque to be insufficient relative to the required engine torque, i.e., a mismatch in 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 in the battery. Furthermore, if the engine torque significantly decreases due to the mismatch in 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, resulting in a decrease in rotational speed. This insufficient torque can be obtained from the low-speed engine, further resulting in an insufficient charge in the battery. The hybrid vehicle control device described in Patent Document 1 does not at all take into consideration the above-mentioned problem when the actual engine torque is insufficient relative 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 even 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 speed can be increased to obtain accurate control of the engine torque, 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 present 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 When the remaining charge of the battery drops below a predetermined value, the engine speed is adjusted so that the engine operating point is within a preset engine torque stable region. The minimum target speed, which is the lowest target value for control Increase lower target limit a rotation speed increase control section; and (c) the lower target limit The rotation speed increase control unit controls the engine so that the actual charge amount by the electric motor becomes the predetermined target charge amount while the operating point of the engine is set within the engine torque stable region. engine a charging control unit that controls the torque of the (d) the engine torque stability region is a region excluding an engine torque unstable region in which the engine torque accuracy is insufficient and unstable due to high engine intake air temperature, engine knocking, engine misfire, or resonance of a power transmission member, within a two-dimensional coordinate system of the engine speed and the engine torque; (e) the charging control unit executes rotation speed feedback control of the electric motor when the hybrid vehicle is stopped so that the actual rotation speed becomes the predetermined target lower limit rotation speed; and (f) the target lower limit rotation speed is a value on the boundary line between the engine torque unstable region in which the engine torque accuracy is insufficient and unstable due to two-dimensional coordinate system of the engine speed and the engine torque, and the engine torque stability region in which the engine torque is stable and has high torque accuracy. The reason is that. [Effects of the Invention]

[0008] According to the present invention, The hybrid vehicle stops and the engine speed drops to a predetermined value or less, and When the battery charge level drops below a certain level, lower target limit The rotation speed increase control unit increases the target lower limit rotation speed of the engine so that the engine operating point is within a preset engine torque stable region. Then, with the engine operating point within the engine torque stable region, the charge control unit controls the actual charge amount by the electric motor to match the preset target charge amount. engine This allows the battery to recover from a low 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. In addition, when the hybrid vehicle is stopped, the charging control unit performs rotation speed feedback control so that the actual engine rotation speed becomes the predetermined target lower limit rotation speed, thereby maintaining the rotation speed of the electric motor stably, and making it possible to easily recover the battery from a state in which the battery is insufficiently charged. Furthermore, the target lower limit rotation speed is a value on the border between an unstable engine torque region where the engine torque accuracy is insufficient and the engine torque is unstable, and an stable engine torque region where the engine torque is stable and accurate, in a two-dimensional coordinate system of the engine rotation speed and the engine torque. This eliminates the region where the engine torque is unstable and controls the motor rotation speed so that the actual battery charge amount becomes the predetermined target charge amount in a region where the engine torque control accuracy is likely to be achieved, thereby making it easy to recover from an insufficient battery charge state. [Brief explanation of the drawings]

[0012] [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 the engine torque accuracy is unstable and an area where the engine torque accuracy is stable in a two-dimensional coordinate system of the engine rotation speed and the engine torque. FIG. [Figure 3] 2 is a flowchart illustrating the main control functions of the electronic control device of FIG. 1. [Figure 4] 2 is a time chart illustrating the main control operations of the electronic control device of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Example]

[0014] Fig. 1 is a diagram illustrating the schematic configuration of a hybrid vehicle 10 to which the present invention is applied, and also illustrates the main parts of the control functions and control system for various controls in the hybrid vehicle (hereinafter referred to as 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.

[0015] 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).

[0016] 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.

[0017] 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.

[0018] The power transmission path 16 also 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.

[0019] 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 driver's accelerator operation, vehicle speed V, etc. The MG rotation speed Nmg 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] The electronic control unit 90 includes an engine control unit 92 a, an electric motor control unit 92 b, an electric motor control unit 92 c, an electric motor control unit 92 d, an electric motor control unit 92 e, an electric motor control unit 92 f, an electric motor control unit 92 g, an electric motor control unit 92 h, an electric motor control unit 92 i, an electric motor control unit 92 j, an electric motor control unit 92 i ... lower target limit The system is provided with a power generation control unit 98 for when the charge is insufficient, which includes a rotation speed increase control unit 94 and a charge control unit 96 .

[0024] 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.

[0025] 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 from the lower limit value by warming up the engine 12, etc.

[0026] 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.

[0027] 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.

[0028] 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 decrease in engine torque Te resulting from idling 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 decrease in engine torque Te resulting from a decrease in accuracy of the optimal ignition timing MBT resulting from knocking of the engine 12; a region of decrease in engine torque Te resulting from misfire in the engine 12; and a region of decrease in engine torque Te resulting from rotation fluctuations due to 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.

[0029] 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, as shown by the arrow in Figure 2, increases the rotation speed Ne of the engine 12 to bring the operating point of the engine 12 into an engine torque stability region TS where the torque of the engine 12 is stable, while maintaining the target charge amount of the battery 54.

[0030] Power generation control unit 98 when charging is insufficient lower target limitWhen the state of charge (SOC) of the battery 54 falls below 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 rotation speed increase control unit 94 temporarily increases the target lower limit rotation speed of the target value for the rotation speed control of the engine 12 or the electric motor MG driven by the engine 12 by a predetermined value from the previously used target lower limit rotation speed Ntl to set it as the target lower limit rotation speed Ntl1, so that the operating point of the engine 12 is located at a predetermined position within the engine torque unstable region TU to the engine torque stable region TS in FIG. 2. The predetermined value is a value that sufficiently raises the operating point of the engine 12 above line L. The target lower limit rotation speed is the lowest value of the target value for the rotation speed control of the engine 12 or the electric motor MG driven by the engine 12, which may vary for warm-up purposes, etc.

[0031] Also, lower target limit When the operating point of the engine 12 is within the stable engine torque region TS and the remaining charge SOC of the battery 54 becomes greater than a second determination value SOC2 that is set greater than the first determination value SOC1, the rotation speed increase control unit 94 ends the temporary increase in the target lower limit rotation speed and returns the target lower limit rotation speed from Ntl1 to Ntl.

[0032] The charge control unit 96 of the power generation control unit 98 during insufficient charge is lower target limit With the rotation speed increase control unit 94 setting the operating point of the engine 12 within the engine torque stable region TS, the throttle opening θ of the engine 12 is adjusted so that the actual charge amount (per unit time) of the battery 54 by the electric motor MG becomes the predetermined target charge amount (per unit time), that is, so that a charging current by the electric motor MG is obtained that makes the actual charge amount of the battery 54 the predetermined target charge amount. adjustment The torque of the engine 12 is controlled while maintaining the rotation speed of the engine 12 so that the operating point of the engine 12 is within the stable engine torque region TS. The charge amount (kW) is calculated from the charge current and charge voltage of the battery 54.

[0033] Furthermore, when the vehicle 10 is stopped, the charge control unit 96 executes rotation speed feedback control so that the actual rotation speed Ne of the engine 12, with the operating point of the engine 12 being within the engine torque stable region TS, becomes the preset target lower limit rotation speed Ntls. This allows the rotation speed Ne of the engine 12 to be stably maintained, making it possible to easily recover the battery 54 from a state in which the amount of charge is insufficient.

[0034] FIG. 3 is a flowchart illustrating the main control operations of the electronic control unit 90 for power generation control when the charge is insufficient, and FIG. 4 is a time chart illustrating the main control operations of the electronic control unit 90 for power generation control when the charge is insufficient. Steps S1 (hereinafter, "step" will be omitted), S2, S5, and S6 in FIG. 3 are as follows: lower target limit S1 and S2 correspond to the control functions of the rotation speed increase control unit 94, and S3 and S4 correspond to the control functions of the charge control unit 96.

[0035] In S1 of Fig. 3, it is determined whether the state of charge SOC of the battery 54 has decreased to a predetermined first determination value SOC1 or less. If the determination in S1 is negative, and if the determination in S5 is also negative, the flow in Fig. 3 is repeated. This state is shown in the section from time t0 to time t1 of Fig. 4. In this section, the state of charge SOC of the battery 54 continuously decreases.

[0036] If the determination in S1 is positive, in S2, the target lower limit rotation speed of the target value for the rotation speed control of the engine 12 or the electric motor MG driven by the engine 12 is temporarily increased by a predetermined value from the target lower limit rotation speed Nt that has been used until then to a target lower limit rotation speed Ntl1. This state is shown at time t1 in Figure 4.

[0037] Next, in S3, it is determined whether the vehicle 10 is stopped. If the determination in S3 is negative, S4 is skipped. However, if the determination in S3 is positive, in S4, rotation speed feedback control is executed to cause the rotation speed of the engine 12 or the electric motor MG driven by the engine 12 to follow the target lower limit rotation speed Ntl1. Since the vehicle 10 is stopped, idle rotation speed control of the engine 12 is executed, with the target lower limit rotation speed Ntl1 as a target value. This state is shown after time t1 in FIG. 4, and at time t2, the actual rotation speeds of the engine 12 and the electric motor MG are made to match the target lower limit rotation speed Ntl1. From time t1 to time t2, the actual rotation speeds of the engine 12 and the electric motor MG increase toward the target lower limit rotation speed Ntl1, and during this period, the actual charge amount of the battery 54 is increased toward the target charge amount.

[0038] While the above steps are repeatedly executed, if the determination in S1 becomes negative, then in S5 it is determined whether the remaining charge SOC of the battery 54 has become greater than a preset second determination value SOC2. In this case, if the determination in S1 is negative, S6 is skipped, but if the determination in S5 becomes positive, then in S6 the temporary increase in the target lower limit rotation speed is ended. That is, the target lower limit rotation speed is decreased from the target lower limit rotation speed Ntl1 to the target lower limit rotation speed Nt.

[0039] 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 the predetermined first determination value SOC1, the engine speed increase control unit 94 increases the target lower limit rotation speed Ntl of the rotation speed control of the engine 12 or the electric motor MG to the target lower limit rotation speed Ntl1 so that the operating point of the engine 12 falls within the predetermined 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 negative torque of the electric motor MG so that the actual charge amount of the electric motor MG becomes the predetermined target charge amount. This allows the battery 54 to recover from an insufficient charge state.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] Furthermore, in the above-described embodiment, the target lower limit rotation speed is increased in a stepwise manner as shown at time t1 in FIG. 4, but it may also be increased smoothly.

[0046] 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]

[0047] 10: Hybrid vehicle 12: Engine 14: Drive wheels 16: Power transmission path 90: Electronic control unit (control unit) 94: lower target limit Rotation speed increase control unit 96: Charging control unit 98: Power generation control unit when charging is insufficient MG: Electric motor

Claims

[Claim 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, a target lower limit rotation speed increase control unit that increases a target lower limit rotation speed, which is the lowest target value of a rotation speed control of the engine, when the hybrid vehicle stops and the rotation speed of the engine drops to a predetermined value or less and the remaining charge of the battery drops to a predetermined value or less, so that an operating point of the engine is within a predetermined engine torque stable region; a charge control unit that controls the torque of the engine so that an actual charge amount by the electric motor becomes a predetermined target charge amount while the target lower limit rotation speed increase control unit sets 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 speed and the engine torque, excluding an unstable engine torque region in which the engine torque becomes unstable due to insufficient torque accuracy being obtained due to high engine intake air temperature, engine knocking, engine misfire, or resonance of a power transmission member, the charging control unit executes a rotation speed feedback control of the electric motor so that an actual rotation speed becomes the predetermined target lower limit rotation speed when the hybrid vehicle is stopped, The target lower limit rotation speed is a value on the borderline between the unstable engine torque region, in which the engine torque accuracy is insufficient and the engine torque becomes unstable, and the stable engine torque region, in which 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.

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