Hybrid electric vehicle control device

Abstract

To suppress start of an engine so that a torque amplification action of a torque converter can be appropriately obtained at the time of motor travelling.SOLUTION: At the time of BEV traveling (motor traveling), a target slip amount Nslipt with an input torque Ti equal to an output torque of a torque converter as a maximum value Timax is calculated on the basis of MG characteristics and TC characteristics, in response to input rotation speed Nia determined according to vehicle speed V, and an LU hydraulic pressure Plu is controlled so that a slip amount Nslip of an LU clutch becomes a target slip amount Nslipt. In other words, differential rotation of the torque converter is controlled so that a maximum input torque Timax can be obtained according to the vehicle speed V at that time, and accordingly a BEV travel region is widened, engine start, in other words, shift to HEV traveling is suppressed, and fuel consumption is improved.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a control device for a hybrid electric vehicle, and more particularly to a technique for appropriately utilizing a torque converter to suppress engine start-up during motor driving. [Background technology]

[0002] A control device for a hybrid electric vehicle is known that includes: (a) an engine and an electric motor as a power source for driving, and a torque converter having a direct-coupled clutch capable of controlling engagement torque and an automatic transmission arranged in series in that order from the power source side between the power source and the drive wheels; (b) a power source switching control unit that switches between engine driving, in which the engine is operated to drive the vehicle, and motor driving, in which the engine is stopped and the electric motor is operated to drive the vehicle; and (c) a direct-coupled clutch control unit that controls the amount of slip of the direct-coupled clutch, which is the differential rotation of the torque converter (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-207409 Summary of the Invention [Problem to be solved by the invention]

[0004] In such hybrid electric vehicles, for example, after starting on motor driving, there are cases where the required driving force increases and the vehicle switches to engine driving, and when the vehicle starts, the direct-coupled clutch is disengaged and torque amplification is achieved by the differential rotation of the torque converter. However, because the operating state of the torque converter changes over time depending on the torque of the electric motor, etc., the torque amplification effect is not properly achieved, and there is a possibility that engine start-up due to insufficient torque will result in insufficient fuel economy.

[0005] The present invention has been made against the background of the above circumstances, and its object is to appropriately obtain the torque amplification effect of the torque converter during motor driving, thereby suppressing engine start-up. [Means for solving the problem]

[0006] In order to achieve this object, the first invention relates to a hybrid electric vehicle (a) equipped with an engine and an electric motor as a power source for driving, and in which a torque converter having a direct coupling clutch capable of controlling engagement torque and an automatic transmission are arranged in series in that order from the power source side between the power source and drive wheels, (b) a power source switching control unit that switches between engine driving, in which the engine is operated, and motor driving, in which the engine is stopped and the electric motor is operated, and (c) a direct coupling clutch control unit that controls the slip amount of the direct coupling clutch, which is the differential rotation of the torque converter, by the engagement torque control, wherein (d) the direct coupling clutch control unit calculates a target slip amount at which the output torque of the torque converter is maximized in accordance with the output rotation speed of the torque converter during the motor driving, and performs the engagement torque control so that the slip amount becomes the target slip amount; and (e) The direct-coupled clutch control unit calculates the target slip amount according to a calculation method determined based on the electric motor characteristics, which are the relationship between the upper limit torque and rotational speed of the electric motor, and the torque converter characteristics, which are the relationship between the torque ratio and speed ratio of the torque converter.

[0007] A second invention is characterized in that, in the control device for a hybrid electric vehicle of the first invention, (a) the control device includes a characteristic storage unit in which the electric motor characteristics and the torque converter characteristics are stored in advance, and (b) the direct coupling clutch control unit calculates the target slip amount based on the electric motor characteristics and the torque converter characteristics.

[0008] A third aspect of the present invention is a control device for a hybrid electric vehicle according to the second aspect of the present invention, wherein (a) the electric motor is connected to a pump impeller of the torque converter, and the automatic transmission is connected to a turbine impeller of the torque converter; (b) when an upper limit torque of the electric motor is Tmup and a rotation speed is Nm, and an input torque of the automatic transmission is Ti and an input rotation speed is Ni, the output torque of the torque converter is the input torque Ti, the output rotation speed of the torque converter is the input rotation speed Ni, the electric motor characteristic is the relationship between the upper limit torque Tmup and the rotation speed Nm, the torque ratio t of the torque converter = Ti / Tm, the speed ratio e of the torque converter = Ni / Nm, and the torque converter characteristic is the relationship between the torque ratio t and the speed ratio e, while (c) the direct coupling clutch control unit calculates a torque ratio tb and an upper limit torque Tmupb at which the input torque Ti has a maximum value Timax, by the following equation (1), with the input rotation speed Ni fixed to a current value Nia: and the target slip amount is calculated based on at least one of the torque ratio tb and the upper limit torque Tmupb. Timax = tb × Tmupb (1)

[0009] A fourth aspect of the present invention is the control device for a hybrid electric vehicle according to the third aspect of the present invention, wherein the direct-coupled clutch control unit applies the torque ratio tb to the torque converter characteristics to obtain a target speed ratio eb, and calculates Nslipt as the target slip amount according to the following equation (2): Nslipt =(Nia / eb )-Nia ···(2)

[0010] A fifth aspect of the present invention is the control device for a hybrid electric vehicle of the third aspect of the present invention, wherein the direct-coupled clutch control unit applies the upper limit torque Tmupb to the electric motor characteristics to determine the rotational speed Nm when the input torque Ti becomes the maximum value Timax as a target rotational speed Nmb, and calculates Nslipt as the target slip amount according to the following equation (3): Nslipt = Nmb - Nia (3) [Effects of the Invention]

[0011] According to this control device for a hybrid electric vehicle, when running on the motor, a target slip amount at which the output torque of the torque converter is maximized is calculated according to the output rotation speed of the torque converter, which is determined according to the vehicle speed, using a calculation method determined based on the characteristics of the electric motor and the torque converter, and engagement torque control is performed so that the slip amount of the direct-coupled clutch becomes the target slip amount. In other words, since the differential rotation of the torque converter is controlled so that the maximum output torque is obtained according to the vehicle speed at that time, the motor running range is expanded, and engine start, i.e., transition to engine running, is suppressed, thereby improving fuel efficiency.

[0012] In the second aspect of the present invention, a characteristics memory unit is provided in which the electric motor characteristics and torque converter characteristics are stored in advance, and the direct coupling clutch control unit calculates the target slip amount based on these electric motor characteristics and torque converter characteristics, so that the target slip amount that maximizes the output torque of the torque converter can be appropriately calculated.

[0013] In the third invention, when an electric motor is connected to a pump wheel of a torque converter and an automatic transmission is connected to a turbine wheel of the torque converter, the torque ratio tb at which the input torque Ti reaches its maximum value Timax and the upper limit torque Tmupb are determined based on the relationship in equation (1), thereby making it possible to appropriately calculate the target slip amount at which the input torque Ti becomes maximum. The input torque Ti is the output torque of the torque converter, and the differential rotation of the torque converter is controlled so that the output torque is maximized, thereby appropriately achieving the effect of the present invention of suppressing engine start.

[0014] The fourth invention is a case where the torque ratio tb is applied to the torque converter characteristics to determine the target speed ratio eb, and the target slip amount Nslipt is calculated according to equation (2). The fifth invention is a case where the upper limit torque Tmupb is applied to the motor characteristics to determine the target rotation speed Nmb, and the target slip amount Nslipt is calculated according to equation (3). Either of these can appropriately implement the second invention. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram illustrating a hybrid electric vehicle equipped with an electronic control device as a control device according to an embodiment of the present invention; [Figure 2] 2 is a flowchart illustrating slip control during BEV driving, which is executed by an LU clutch control unit that the electronic control device of FIG. 1 functionally comprises. [Figure 3] 2 is a schematic diagram illustrating an example of an MG characteristic stored in advance in a characteristic storage unit of FIG. 1. FIG. [Figure 4] 2 is a schematic diagram illustrating an example of a TC characteristic stored in advance in a characteristic storage unit of FIG. 1. FIG. [Figure 5] 10 is a flowchart illustrating another example of slip control during BEV driving, which is executed by an LU clutch control unit that the electronic control device of FIG. 1 functionally comprises. DETAILED DESCRIPTION OF THE INVENTION

[0016] The engine and electric motor used as the power source are typically connected in series, but can also be connected in parallel. A motor-generator that also functions as a generator is suitable for the electric motor, but an electric motor without generator functionality can also be used. The automatic transmission connected between the power source and the drive wheels is typically a stepped transmission with multiple gears with different gear ratios, but a belt-type continuously variable transmission can also be used. The electric motor is connected to, for example, a pump wheel of a torque converter, but a speed-increasing or speed-decreasing transmission or a disconnecting clutch may be provided between them. The automatic transmission is connected to, for example, a turbine wheel of a torque converter, but a speed-increasing or speed-decreasing transmission may also be provided between them. The electric motor characteristics, which are the relationship between the electric motor's upper limit torque and rotational speed, can use the electric motor's maximum torque as the upper limit torque. However, when the electric motor is used to crank the engine to start the vehicle when switching to engine driving, it is desirable to use a torque value lower than the maximum torque by the amount of engine starting torque required for cranking.

[0017] The direct-coupled clutch control unit is configured to calculate the target slip amount based on the electric motor characteristics and torque converter characteristics stored in advance in a characteristics storage unit, for example, but it is also possible to set a map or a formula in advance that calculates the target slip amount that maximizes the output torque of the torque converter based on the electric motor characteristics and the torque converter characteristics, using the output rotation speed of the torque converter as a variable, and directly calculate the target slip amount from the current output rotation speed according to that map or formula. In this case, there is no need for a characteristics storage unit that stores the electric motor characteristics and the torque converter characteristics. [Example]

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that in the following embodiments, the drawings have been appropriately simplified or modified for the purpose of explanation, and the shapes, dimensional ratios, angles, etc. of the various parts are not necessarily drawn accurately.

[0019] FIG. 1 is a schematic diagram of the drive system of a hybrid electric vehicle 10 (hereinafter simply referred to as vehicle 10) equipped with an electronic control device 90 as a control device according to one embodiment of the present invention, and also shows key components of the control system and various control functions for the vehicle 10. The vehicle 10 is a parallel-type hybrid electric vehicle equipped with an engine 12 and an electric motor MG as power sources for driving. The vehicle 10 also includes a power transmission device 16 provided in a power transmission path between the engine 12 and drive wheels 14. The drive wheels 14 are the left and right rear wheels, and the vehicle 10 is a rear-wheel-drive (FR) vehicle with the engine 12 and electric motor MG mounted on the front of the vehicle. The engine 12 is an internal combustion engine such as a gasoline engine or a diesel engine, and the engine torque Te is controlled by the electronic control device 90 controlling an engine control device 50 including an electronic throttle valve, a fuel injection device, an ignition device, and the like. The electric motor MG is a motor-generator that functions both as an electric motor and as a generator, and is connected to a battery 54 via an inverter 52. The torque Tm and rotation speed Nm of the electric motor MG are controlled by controlling the inverter 52 by the electronic control device 90. In the following description, the torque Tm will also be expressed as MG torque Tm, and the rotation speed Nm will also be expressed as MG rotation speed Nm. The battery 54 is an electricity storage device that supplies and receives electric power to the electric motor MG.

[0020] The power transmission device 16 is housed in a case 18 attached to the vehicle body and includes a K0 clutch 20, a torque converter 22, and an automatic transmission 24 arranged in series from the engine 12 side, with an electric motor MG connected to the power transmission path between the K0 clutch 20 and the torque converter 22. The K0 clutch 20 is a clutch provided between the engine 12 and the electric motor MG and serves as an engine connecting / disconnecting device that connects / disconnects the electric motor MG and the engine 12. The torque converter 22 is a fluid-type power transmission device provided between the electric motor MG and the automatic transmission 24 and transmits power via hydraulic oil, which is a fluid, and is connected to the engine 12 via the K0 clutch 20. The automatic transmission 24 is connected to the torque converter 22 and is a transmission provided in series with the torque converter 22 between the engine 12 and the electric motor MG and the drive wheels 14. The power transmission device 16 includes a propeller shaft 28 connected to an output shaft 26, which is an output rotating member of the automatic transmission 24, a differential gear 30, a pair of drive shafts 32, etc. The power transmission device 16 also includes an engine connecting shaft 34 that connects the engine 12 and the K0 clutch 20, an MG connecting shaft 36 that connects the K0 clutch 20 and the torque converter 22, etc., and the rotor of the electric motor MG is connected to the MG connecting shaft 36.

[0021] The K0 clutch 20 is a hydraulic friction engagement device, and its engaged / disengaged state is switched by changing the K0 torque Tk0, which is the torque capacity of the K0 clutch 20, using the regulated K0 oil pressure Pk0 supplied from the hydraulic control circuit 56. The torque converter 22 includes a pump wheel 22a connected to the MG connecting shaft 36 and a turbine wheel 22b connected to an input shaft 38, which is an input rotating member of the automatic transmission 24. The pump wheel 22a is the input member of the torque converter 22, and the turbine wheel 22b is the output member of the torque converter 22. The torque converter 22 includes an LU clutch 40 connecting the pump wheel 22a and the turbine wheel 22b. The LU clutch 40 is a direct-coupled clutch, i.e., a lock-up clutch, that connects the input and output rotating members of the torque converter 22. The operating state of the LU clutch 40 is switched by changing the LU clutch torque Tlu, which is the torque capacity of the LU clutch 40, using the regulated LU oil pressure Plu supplied from the hydraulic control circuit 56. The operating states of the LU clutch 40 include a release state in which the LU clutch 40 is released, a slip state in which the LU clutch 40 is engaged with slippage, and an engaged state in which the LU clutch 40 is fully engaged. The LU clutch torque Tlu, which is controlled in accordance with the LU oil pressure Plu, corresponds to the engagement torque.

[0022] The automatic transmission 24 is a known planetary gear automatic transmission equipped with, for example, one or more planetary gear devices and multiple engagement devices CB. The engagement devices CB are hydraulic friction engagement devices (clutches and brakes), and their respective torque capacities, or CB torques Tcb, are changed by the CB hydraulic pressure Pcb regulated by the hydraulic control circuit 56, thereby switching between engagement and disengagement states. The automatic transmission 24 is a stepped transmission that can establish multiple gears with different gear ratios γ (= input rotation speed Ni / output rotation speed No) by engaging any of the engagement devices CB. The automatic transmission 24 selectively establishes multiple gears by switching between the established gears according to the driver's accelerator operation, vehicle speed V, and other driving conditions, using an electronic control device 90. Furthermore, when all of the engagement devices CB are disengaged, the automatic transmission enters neutral, cutting off power transmission. The input rotation speed Ni is the rotation speed of the input shaft 38, and is the input rotation speed of the automatic transmission 24. The input rotation speed Ni is equal to the turbine rotation speed Nt, which is the output rotation speed of the torque converter 22. The output rotation speed No is the rotation speed of the output shaft 26, and is the output rotation speed of the automatic transmission 24.

[0023] The vehicle 10 is equipped with a mechanical oil pump MOP 58, an electric oil pump EOP 60, a pump motor 62, and the like. The EOP 60 is driven by the pump motor 62 to discharge hydraulic oil OIL, and can discharge hydraulic oil OIL at any time, including when the vehicle 10 is stopped. The hydraulic oil OIL discharged by the MOP 58 and EOP 60 is supplied to a hydraulic control circuit 56. The hydraulic control circuit 56 outputs a K0 hydraulic pressure Pk0, an LU hydraulic pressure Plu, a CB hydraulic pressure Pcb, and the like, each adjusted based on the hydraulic oil OIL discharged by the MOP 58 and / or EOP 60. The hydraulic oil OIL is also supplied to the torque converter 22 for power transmission and is used for lubrication and cooling of various parts.

[0024] The vehicle 10 is equipped with an electronic control device 90 as a control device that executes various types of control. The electronic control device 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 types of control of the vehicle 10 by performing signal processing in accordance with programs stored in advance in the ROM while utilizing the temporary storage function of the RAM. The electronic control device 90 is configured to include multiple computers for engine control, MG control, hydraulic control, etc. as necessary.

[0025] The electronic control device 90 receives signals from various sensors provided in the vehicle 10, such as the engine rotational speed sensor 70, the turbine rotational speed sensor 72, the output rotational speed sensor 74, the MG rotational speed sensor 76, the accelerator pedal position sensor 78, the throttle valve position sensor 80, the battery sensor 84, the oil temperature sensor 86, and the selection range switch 88, which indicate the engine rotational speed Ne, which is the rotational speed of the engine 12; the turbine rotational speed Nt, which is the same as the input rotational speed Ni; the output rotational speed No, which corresponds to the vehicle speed V; the MG rotational speed Nm, which is the rotational speed of the electric motor MG; the accelerator pedal position θacc, which is the amount of operation of an accelerator operating member 79 such as an accelerator pedal and which indicates the output required by the driver; the throttle valve position θth, which is the opening of the electronic throttle valve; the battery temperature THbat, the battery charge / discharge current Ibat, and the battery voltage Vbat of the battery 54; the oil temperature THoil, which is the temperature of the hydraulic oil OIL in the hydraulic control circuit 56; The range selection device 64 is a lever or push button that can select, for example, a D range that allows forward travel, an R range that allows reverse travel, a P range for parking, an N range that cuts off power transmission, and the like.

[0026] The electronic control device 90 outputs an engine control signal Se for controlling the engine 12, an MG control signal Sm for controlling the electric motor MG, a CB hydraulic control signal Sbc for controlling the engagement device CB, a K0 hydraulic control signal Sk0 for controlling the K0 clutch 20, an LU hydraulic control signal Slu for controlling the LU clutch 40, an EOP control signal Seop for controlling the EOP 60, and the like to the engine control device 50, the inverter 52, the hydraulic control circuit 56, the pump motor 62, etc. The hydraulic control circuit 56 is provided with a plurality of solenoid valves for controlling hydraulic pressure and switching oil paths.

[0027] The electronic control device 90 functionally includes a power source control unit 92, a transmission control unit 94, and an LU clutch control unit 96. The power source control unit 92 has a function of cooperatively controlling the operation of the engine 12 and the electric motor MG. The power source control unit 92 calculates a drive demand for the vehicle 10 from the driver, for example, by applying the accelerator opening θacc and the vehicle speed V to a drive demand map. The drive demand may be, for example, a required drive torque Trdem at the drive wheels 14. The power source control unit 92 calculates, for example, a required TC input torque Ttcdem, which is the input torque of the torque converter 22 required to achieve the required drive torque Trdem, taking into account transmission loss, auxiliary load, the gear ratio γ of the automatic transmission 24, the torque ratio t of the torque converter 22, the state of charge value SOC of the battery 54, and the like, and outputs an engine control signal Se to control the engine 12 and an MG control signal Sm to control the electric motor MG so that the required TC input torque Ttcdem is obtained. The state of charge value SOC of the battery 54 is a value indicating the state of charge of the battery 54, that is, the remaining amount of stored electricity, and can be calculated based on, for example, the battery charge / discharge current Ibat and the battery voltage Vbat.

[0028] Furthermore, if the required TC input torque Ttcdem can be satisfied only with the output of the electric motor MG, the power source control unit 92 selects a BEV (Battery Electric Vehicle) driving mode, which is a motor driving mode in which the electric motor MG is driven only by power from the battery 54. In the BEV driving mode, the K0 clutch 20 is disengaged, the engine 12 is stopped, and BEV driving is performed, in which the vehicle is driven using only the electric motor MG as a power source. In this BEV driving mode, the MG torque Tm (=Ttcdem) is controlled to achieve the required TC input torque Ttcdem. On the other hand, if the required TC input torque Ttcdem cannot be satisfied without using at least the output of the engine 12, the power source control unit 92 selects an HEV (Hybrid Electric Vehicle) driving mode, which is an engine driving mode. In the HEV driving mode, the K0 clutch 20 is engaged, and engine driving, i.e., HEV driving, is performed, in which the vehicle is driven using at least the engine 12 as a power source. In the HEV driving mode, the engine torque Te is controlled to realize all or part of the required TC input torque Ttcdem, and the MG torque Tm is controlled to compensate for the torque that is insufficient when the engine torque Te is used to meet the required TC input torque Ttcdem. On the other hand, even if the required TC input torque Ttcdem can be met solely by the output of the electric motor MG, the power source control unit 92 establishes the HEV driving mode when warming up the engine 12 or the like is required. In this way, the power source control unit 92 switches between the HEV driving mode and the BEV driving mode by controlling the start / stop of the engine 12 and the engagement / disengagement of the K0 clutch 20 based on the required TC input torque Ttcdem, etc. That is, the power source control unit 92 functions as a power source switching control unit that switches between the HEV driving mode and the BEV driving mode.

[0029] When the D range is selected, the shift control unit 94 determines whether to shift the automatic transmission 24 using a predetermined shift map or the like with driving conditions such as the vehicle speed V and accelerator opening θacc as variables, and executes automatic shift control by outputting a CB hydraulic control signal Sbc to the hydraulic control circuit 56 as necessary to automatically shift between multiple forward gears of the automatic transmission 24. Furthermore, when the driver operates a manual shift operation member provided near the driver's seat and a shift instruction signal is supplied, the shift control unit 94 executes manual shift control to switch the forward gears of the automatic transmission 24 in accordance with the shift instruction.

[0030] The LU clutch control unit 96 controls switching of the operating state of the LU clutch 40, and controls the LU hydraulic pressure Plu of the LU clutch 40. This control of the LU hydraulic pressure Plu means control of the engagement torque of the LU clutch 40. The LU clutch control unit 96 switches the operating state of the LU clutch 40 between a released state, a slip state, and an engaged state according to a predetermined LU switching map or the like using operating conditions such as the vehicle speed V and the required drive torque Trdem as variables. The LU switching map is divided into three regions, for example, a release control region in which the LU clutch 40 is in a released state, a slip control region in which a predetermined slip state is achieved, and a lock-up control region in which the LU clutch 40 is in an engaged state. For example, the lock-up control region is set on the high vehicle speed side, and the release control region is set on the low vehicle speed side, and the slip control region is set in a region between the lock-up control region and the release control region where the required drive torque Trdem is small. Then, based on the actual vehicle speed V and the required drive torque Trdem, it is determined whether the control region is the release control region, the slip control region, or the lock-up control region, and the LU hydraulic control signal Slu is controlled and output to the hydraulic control circuit 56 so that the LU clutch 40 is in an operating state corresponding to the determined control region. In slip control, for example, the LU clutch 40 is in a predetermined slip state, that is, the LU hydraulic pressure Plu is controlled using feedback control or the like so that the slip amount Nslip, which is the differential rotation of the LU clutch 40, becomes a predetermined target slip amount Nslipt. The slip amount Nslip is the differential rotation (Nm - Ni) between the MG rotation speed Nm, which is the input rotation speed of the LU clutch 40, and the turbine rotation speed Nt (= input rotation speed Ni).

[0031] The LU clutch control unit 96 functions as a direct-coupled clutch control unit, and executes slip control during BEV driving in accordance with steps S1 to S4 of the flowchart in Fig. 2, separate from control based on the LU switching map. In step S1 of Fig. 2, it is determined whether or not a slip control execution condition is met, that is, the vehicle is driving in BEV mode and the vehicle speed is equal to or less than a predetermined determination vehicle speed Vs. If the slip control execution condition is not met, the process ends, but if the slip control execution condition is met, slip control from step S2 onwards is executed. The determination vehicle speed Vs is, for example, a vehicle speed V at which the vehicle can be switched to HEV driving mode, and when the vehicle starts moving and the vehicle speed V is equal to or less than the determination vehicle speed Vs, slip control from step S2 onwards is executed.

[0032] In step S2, the torque ratio tb and upper limit torque Tmupb at which the input torque Ti of the automatic transmission 24 becomes the maximum value Timax are calculated based on the current input rotation speed Ni (= Nia), MG rotation speed Nm (= Nma), MG characteristics, and TC characteristics, according to the relationship in the following equation (1). The MG characteristics are electric motor characteristics that are the relationship between the upper limit torque Tmup and the rotation speed Nm of the electric motor MG, and are determined, for example, as shown by the solid line in FIG. 3 and are stored in advance in the characteristics storage unit 98. The upper limit torque Tmup is the upper limit of the MG torque Tm that can be used during normal motor running, and is a torque value that is lower than the maximum torque by, for example, the engine starting torque Tme required for cranking when starting the engine 12. The MG characteristics have a tendency that when the MG rotation speed Nm exceeds a predetermined value, the upper limit torque Tmup decreases as the MG rotation speed Nm increases. The TC characteristic is a torque converter characteristic that is the relationship between the torque ratio t and the speed ratio e of the torque converter 22. For example, it is determined as shown by the solid line in FIG. 4 and is stored in advance in the characteristic storage unit 98. The torque ratio t is the ratio (Ti / Tm) between the input torque Ti of the automatic transmission 24, which is equal to the output torque of the torque converter 22, and the MG torque Tm, which is also equal to the input torque of the torque converter 22. Assuming that the MG torque Tm varies along the upper limit torque Tmup of the MG characteristic, it is expressed as t=Ti / Tmup. Furthermore, the speed ratio e is the ratio between the input rotation speed Ni of the automatic transmission 24, which is equal to the output rotation speed of the torque converter 22, and the MG rotation speed Nm, which is also equal to the input rotation speed of the torque converter 22, and is expressed as e=Ni / Nm. This TC characteristic has a tendency for the torque ratio t to decrease as the speed ratio e increases. Timax = tb × Tmupb (1)

[0033] Point A in Figures 3 and 4 is an example of the current values, where the MG rotational speed Nm = Nma, the upper limit torque Tmup = Tmupa, the speed ratio e = ea, and the torque ratio t = ta. Also, the current value of the input rotational speed Ni is Nia = ea × Nma, and the current value of the input torque Ti is Tia = ta × Tmupa.

[0034] Here, even if the torque ratio t or upper limit torque Tmup is changed, the input rotation speed Ni is maintained at its current value Nia in accordance with the vehicle speed V and the gear position of the automatic transmission 24. Therefore, if the MG rotation speed Nm and upper limit torque Tmup are changed in accordance with the MG characteristics while the input rotation speed Ni is fixed at its current value Nia, and the speed ratio e and torque ratio t of the TC characteristics are changed in accordance with the change in the MG rotation speed Nm, the input torque Ti (= t × Tmup) will change accordingly, and it is possible to determine the torque ratio tb and upper limit torque Tmupb at which the input torque Ti is maximized. Point B in Figures 3 and 4 is an example of the torque ratio tb and upper limit torque Tmupb at which the input torque Ti is maximized Timax.

[0035] In the next step S3, the target speed ratio eb is calculated from the torque ratio tb based on the TC characteristics. That is, as shown in FIG. 4, the speed ratio e at point B where the torque ratio t = tb is determined as the target speed ratio eb. In addition, in step S4, the target slip amount Nslipt is calculated according to the following equation (2) using the target speed ratio eb and the input rotational speed Nia. Since the speed ratio e = Ni / Nm in equation (2), (Nia / eb) represents the MG rotational speed Nm when the input torque Ti is maximized. Then, the LU hydraulic pressure Plu is controlled so that the slip amount Nslip of the LU clutch 40 becomes the target slip amount Nslipt. Nslipt =(Nia / eb )-Nia ···(2)

[0036] In this way, the LU clutch control unit 96 functionally provided in the electronic control device 90 of the vehicle 10 of this embodiment calculates the target slip amount Nslipt at which the input torque Ti, which is equal to the output torque of the torque converter 22, is maximized in BEV driving according to the input rotation speed Ni = Nia, which is determined in accordance with the vehicle speed V, using a calculation method determined based on the MG characteristics and TC characteristics, and controls the LU hydraulic pressure Plu so that the slip amount Nslip of the LU clutch 40 becomes the target slip amount Nslipt. In other words, the differential rotation of the torque converter 22 is controlled so that the maximum input torque Timax is obtained in accordance with the vehicle speed V at that time, thereby widening the BEV driving range and suppressing engine start, i.e., transition to HEV driving, and improving fuel economy.

[0037] Furthermore, this embodiment is provided with a characteristics storage unit 98 in which the MG characteristics and TC characteristics are stored in advance, and the LU clutch control unit 96 calculates the target slip amount Nslipt based on these MG characteristics and TC characteristics, so that it is possible to appropriately calculate the target slip amount Nslipt that maximizes the input torque Ti.

[0038] In this embodiment, when the electric motor MG is connected to the pump wheel 22a of the torque converter 22 and the automatic transmission 24 is connected to the turbine wheel 22b of the torque converter 22, the torque ratio tb and upper limit torque Tmupb at which the input torque Ti becomes the maximum value Timax are found based on the relationship in equation (1), the torque ratio tb is applied to the TC characteristic to find the target speed ratio eb, and the target slip amount Nslipt is calculated according to equation (2). This appropriately achieves the effect of controlling the differential rotation of the torque converter 22 so that the input torque Ti is maximized, thereby suppressing engine start-up.

[0039] In the above embodiment, the torque ratio tb is applied to the TC characteristic to determine the target speed ratio eb, and the target slip amount Nslipt is calculated according to the above equation (2). However, as shown in the flowchart of FIG. 5, the target slip amount Nslipt can also be calculated using the upper limit torque Tmupb at which the input torque Ti is maximized. Steps SS1 and SS2 in FIG. 5 are the same as steps S1 and S2 in the above embodiment. In step SS3, the upper limit torque Tmupb determined in step SS2 is applied to the MG characteristic to calculate the MG rotation speed Nm at which the input torque Ti reaches its maximum value Timax as the target rotation speed Nmb. That is, as shown in FIG. 3, the MG rotation speed Nm at point B where the upper limit torque Tmup = Tmupb is determined as the target rotation speed Nmb. In addition, in step SS4, the target slip amount Nslipt is calculated by subtracting the current value Nia of the input rotation speed Ni from the target rotation speed Nmb as shown in the following equation (3). Then, the LU oil pressure Plu is controlled so that the slip amount Nslip of the LU clutch 40 becomes the target slip amount Nslipt. In this case, too, the effect of suppressing engine start by controlling the differential rotation of the torque converter 22 so that the input torque Ti becomes maximum can be appropriately obtained. Nslipt = Nmb - Nia (3)

[0040] Although the embodiments of the present invention have been described in detail above with reference to the drawings, these are merely embodiments, and the present invention can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. [Explanation of symbols]

[0041] 10: Hybrid electric vehicle 12: Engine 14: Drive wheels 22: Torque converter 24: Automatic transmission 40: LU clutch (direct coupling clutch) 90: Electronic control unit (control unit) 92: Power source control unit (power source switching control unit) 96: LU clutch control unit (direct coupling clutch control unit) 98: Characteristics memory unit MG: Electric motor Tmup: Upper limit torque Nm: MG rotation speed (rotation speed of electric motor) Nmb: Target rotation speed t: Torque ratio e: Speed ​​ratio eb: Target speed ratio MG characteristics: Electric motor characteristics TC characteristics: Torque converter characteristics

Claims

1. A hybrid electric vehicle is provided with an engine and an electric motor as a power source for traveling, and a torque converter having a direct-coupled clutch capable of controlling engagement torque and an automatic transmission are disposed in series in that order from the power source between the power source and drive wheels, a power source switching control unit that switches between engine running, in which the vehicle runs by operating at least the engine, and motor running, in which the vehicle runs by operating the electric motor while stopping the engine; a direct coupling clutch control unit that controls a slip amount of the direct coupling clutch, which is a differential rotation of the torque converter, by the engagement torque control; A control device for a hybrid electric vehicle having the direct coupling clutch control unit calculates a target slip amount at which the output torque of the torque converter is maximized in accordance with the output rotation speed of the torque converter during the motor driving, and performs the engagement torque control so that the slip amount becomes the target slip amount, The direct coupling clutch control unit calculates the target slip amount according to a calculation method determined based on an electric motor characteristic, which is a relationship between an upper limit torque and a rotation speed of the electric motor, and a torque converter characteristic, which is a relationship between a torque ratio and a speed ratio of the torque converter. A control device for a hybrid electric vehicle.

2. the control device includes a characteristic storage unit in which the electric motor characteristic and the torque converter characteristic are stored in advance, The direct coupling clutch control unit calculates the target slip amount based on the electric motor characteristics and the torque converter characteristics.

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

3. the electric motor is connected to a pump wheel of the torque converter, and the automatic transmission is connected to a turbine wheel of the torque converter; If the upper limit torque of the electric motor is Tmup, the rotational speed is Nm, the input torque of the automatic transmission is Ti, and the input rotational speed is Ni, the output torque of the torque converter is the input torque Ti, the output rotational speed of the torque converter is the input rotational speed Ni, the electric motor characteristic is the relationship between the upper limit torque Tmup and the rotational speed Nm, the torque ratio t of the torque converter is Ti / Tmup, the speed ratio e of the torque converter is Ni / Nm, and the torque converter characteristic is the relationship between the torque ratio t and the speed ratio e, The direct coupling clutch control unit determines a torque ratio tb and an upper limit torque Tmupb at which the input torque Ti has a maximum value Timax based on the relationship of the following equations while fixing the input rotation speed Ni to Nia, which is the current value, and calculates the target slip amount based on at least one of the torque ratio tb and the upper limit torque Tmupb: Timax = tb × Tmupb 3. The control device for a hybrid electric vehicle according to claim 2.

4. The direct coupling clutch control section applies the torque ratio tb to the torque converter characteristics to obtain a target speed ratio eb, and calculates Nslipt as the target slip amount according to the following equation: Nslipt = (Nia / eb) - Nia 4. The control device for a hybrid electric vehicle according to claim 3.

5. The direct coupling clutch control unit applies the upper limit torque Tmupb to the electric motor characteristics, determines the rotation speed Nm when the input torque Ti reaches the maximum value Timax as a target rotation speed Nmb, and calculates Nslipt as the target slip amount according to the following equation: Nslipt = Nmb - Nia 4. The control device for a hybrid electric vehicle according to claim 3.

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