VEHICLE CONTROL UNIT AND METHOD FOR CONTROLLING A VEHICLE

Abstract

A vehicle control device that controls a vehicle (10) having an engine (12) and an automatic transmission (14), the vehicle control device comprising an electronic control unit (30) configured to: estimates the power that can be generated by the engine (12) based on a state of the engine (12) and a state of the automatic transmission (14) in a non-drive range; calculates a load on the automatic transmission (14) in a drive range based on a state of the automatic transmission (14) in the drive range; determines whether a difference between the power and the load is equal to or less than a predetermined threshold by which an engine stall can be identified; and inhibits a gearshift request from the non-drive range to the drive range if the difference is equal to or less than the predetermined limit, whereby the state of the engine (12) is a temperature of a coolant used to cool the engine (12); the state of the automatic transmission (14) in the non-drive range is a temperature of a hydraulic oil of the automatic transmission (14) in a disengaged state; and the state of the automatic transmission (14) in the drive range is a temperature of the hydraulic oil of the automatic transmission (14) in an engaged state.

Description

BACKGROUND OF THE INVENTIONTechnical FieldThe present disclosure relates to a vehicle control apparatus and a method for controlling a vehicle.Prior ArtThere is known a vehicle control apparatus configured to control a vehicle including an engine and an automatic transmission. In particular, various technologies related to automatic transmissions are known (see JP 2019-39 488 A, JP H07-96 779 A and JP 2000-220 500 A). For example, the following technology is proposed. When a driver performs an operation to request switching from a parking range to a driving range but the engine load is equal to or greater than a predetermined value, switching to an arbitrary driving range is prohibited (see JP 2004-60 803 A). In the following description, the parking range is referred to as "P range" and the drive range is referred to as "D range". DE 103 04 130 A1 discloses a method for preventing stalling of an engine arranged in a drive train of a vehicle in combination with an automatic clutch. DE 41 05 106 A1 discloses a control device for controlling an engine and an automatic transmission of a vehicle. DE 35 46 634 C2 discloses a control device for an automatic transmission of a vehicle. JP 2002-349 695 A discloses a vehicle equipped with an engine, a starter for starting the engine, and a transmission provided with limiting means for preventing the change of the shift position of the transmission when the engine is started by the drive of the starter. DE 698 14 303 T2 discloses a device for controlling the idle speed of an engine.SUMMARY OF THE INVENTIONThe engine may stall when a gear shift lever is operated from a non-drive range such as the P range to a drive range such as the D range in a predetermined environment such as a low air temperature. For example, when the air temperature is low, the viscosity of the lubricating oil flowing through the engine increases, and a load depending on the increased viscosity of the lubricating oil acts on the performance of the engine.When the air temperature is low, the viscosity of the hydraulic oil flowing through the automatic transmission also increases. Thus, when the gear shift lever is operated from the non-driving range to the driving range, a load caused together with the operation of the gear shift lever, for example, a load depending on the viscosity of the hydraulic oil in the non-driving range is added. The resulting load acts on the performance of the motor.That is, the two loads on the engine and the automatic transmission act on the engine output. If the power of the engine does not exceed the sum of the two loads, the engine will stall.The present invention aims to suppress engine stalling when a shift from a non-driving range to a driving range is performed at least in a low temperature environment.A first aspect of the invention relates to a vehicle control apparatus that controls a vehicle including an engine and an automatic transmission, the vehicle control apparatus including an electronic control unit configured to estimate power that can be generated by the engine based on a state of the engine and a state of the automatic transmission in a non-driving range, calculate a load on the automatic transmission in a driving range based on a state of the automatic transmission in the driving range, determine whether a difference between the power and the load is equal to or less than a predetermined threshold by which an engine stall is identifiable, and prohibit a gear shift request from the non-driving range to the driving range when the difference is equal to or less than the predetermined threshold, wherein the state of the engine is a temperature of a coolant used to cool the engine; the state of the automatic transmission in the non-driving range is a temperature of a hydraulic oil of the automatic transmission in a clutch-off state; and the state of the automatic transmission in the driving range is a temperature of the hydraulic oil of the automatic transmission in a clutch-on stateIn the above aspect, the electronic control unit may be configured to correct the performance based on an atmospheric pressure.In the above aspect, the electronic control unit may be configured to estimate the power also on the basis of a load caused by an accessory of the engine.In the above aspect, the electronic control unit may be configured to, when the difference is equal to or less than the predetermined threshold, estimate, based on a change in the state of the engine, a time required for the difference to exceed the predetermined threshold and cause a display to display a graphical object that changes at least one of a shape, a pattern, and a color of the graphical object depending on the elapse of the estimated time.In the above aspect, the electronic control unit may be configured to, when the difference is equal to or less than the predetermined threshold, cause a speaker to output a sound indicating that a switching operation from the non-driving range to the driving range is prohibited.In the above aspect, the electronic control unit may be configured to stop the gear shift request when the difference is equal to or less than the predetermined threshold.A second aspect of the invention relates to a method for controlling a vehicle having an engine and an automatic transmission, the method comprising the steps of: estimating power producible by the engine based on a state of the engine and a state of the automatic transmission in a non-driving range; calculating a load on the automatic transmission in a driving range based on a state of the automatic transmission in the driving range; determining whether a difference between the power and the load is equal to or less than a predetermined threshold by which an engine stall is identifiable; and prohibiting a gear shift request from the non-driving range to a driving range when the difference is equal to or less than the predetermined threshold, wherein the state of the engine is a temperature of coolant for cooling the engine; the state of the automatic transmission in the non-driving range is a temperature of hydraulic oil of the automatic transmission in a clutched state; and the state of the automatic transmission in the driving range is a temperature of hydraulic oil of the automatic transmission in a clutched state.According to the present invention, it is possible to suppress the engine stall in the shift from the non-driving range to the driving range at least in the low temperature environment.Brief Description of the FiguresFeatures, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: FIG. 1 is a block diagram showing the overall configurations of a drive system and a control system of a vehicle; FIG. 2A shows an example of an engine torque map; FIG. 2B shows an example of an atmospheric pressure map; FIG. 3A shows a load torque map for an automatic transmission in a P range; FIG. 3B shows a load torque map for an automatic transmission in a D range; FIG. 4 is a flowchart showing an example of processes executed by an electronic control unit (ECU); FIG. 5A shows an example of a dashboard; FIG. 5B is a diagram showing an example of display change of a display; FIG. 5C is a diagram showing an example of display change of a display; and FIG. 5D is a diagram showing an example of display change of a display.DETAILED DESCRIPTION OF THE EMBODIMENTSHereinafter, an embodiment of the present invention will be described with reference to the drawings.As illustrated in FIG. 1, a vehicle 10 includes an engine 12, an automatic transmission 14, a reduction gear 16, and right and left drive wheels 18. the engine 12 is a drive source of the vehicle 10. the engine 12 is an internal combustion engine such as a gasoline engine or a diesel engine. The engine 12 may be a hybrid engine with an electric motor. The vehicle 10 also includes an accessory 13 provided in communication with the engine 12. Examples of the accessory 13 include a starter, a self-starter, an alternator, a water pump, and a compressor of an air conditioner.The engine 12 includes an oil passage and a water cooling jacket. Through the oil passage, lubricating oil used for lubricating the engine 12 flows. Water to be used for cooling the motor 12 (i.e., a coolant) flows through the water cooling jacket. In this embodiment, the temperature of at least one of the lubricating oil and water may be used as the condition for the engine 12. An estimated temperature of the engine 12 may be used as a state of the engine 12. The estimated temperature may be estimated based on the temperature of at least one of the lubricating oil and water. Instead of the water, a refrigerant containing an antifreeze may be used.An engine control device 20 controls the engine 12. The injector supplies fuel. The spark plug ignites an air-fuel mixture containing the fuel and fresh air. The electronic throttle is opened or closed in response to an operation of an accelerator pedal to adjust the intake amount of the fresh air. The fuel may be gasoline or light oil. When the motor 12 includes an electric motor, the motor controller 20 includes an inverter. In this case, the electric motor is supplied with electric power from an energy storage device such as a battery or a fuel cell using hydrogen and the like.The automatic transmission 14 includes a torque converter and a clutch mechanism. The torque converter increases or decreases an engine torque using hydraulic oil (specifically, an automatic transmission oil (AGO)). The clutch mechanism is engaged or disengaged depending on the hydraulic pressure of the hydraulic oil. The automatic transmission 14 also includes a stepped transmission of the planetary gear type. The hydraulic oil also lubricates various components (gears and the like) of the automatic transmission 14. In this embodiment, a temperature of the hydraulic oil in the engaged state may be used as a state of the automatic transmission 14 in a driving range, and a temperature of the hydraulic oil in the disengaged state may be used as a state of the automatic transmission 14 in a non-driving range. The drive range is a range in which the automatic transmission 14 transmits the driving force from the drive source of the vehicle 10 to the reduction gear 16 and the right and left drive wheels 18. The non-driving range is a range in which the automatic transmission 14 does not transmit driving force from the driving source of the vehicle 10 to the reduction gear 16 or the right and left driving wheels 18. An estimated temperature of the automatic transmission 14 may be used as a state of the automatic transmission 14 in the driving range or the non-driving range. The estimated temperature may be estimated based on the temperature of the hydraulic oil. In place of the step-variable transmission, a belt mechanical continuously variable transmission or an electric continuously variable transmission having a differential mechanism may be used. By engaging the clutch mechanism, a forward running state and a reverse running state can be achieved. In the forward driving state, the vehicle can travel forward. In the reverse running state, the vehicle can run backward. By disengaging the clutch mechanism, a parked state and a neutral state can be achieved. In the parked state and in the neutral state, the transmission of power from the engine 12 to the automatic transmission 14 is interrupted.The parked state and the neutral state are different from each other in the following points. In the parked state, an output shaft of the automatic transmission 14 is mechanically fixed by a parking mechanism. In the neutral state, the output shaft of the automatic transmission 14 is not mechanically fixed by the parking mechanism. Examples of the parking mechanism are a parking lock gear (or a parking gear) and a parking pawl. By mechanically fixing the output shaft of the automatic transmission 14 by the parking mechanism, the vehicle 10 can be kept in the parked state.The vehicle 10 includes an electronic control unit (ECU) 30. the ECU 30 is a vehicle control device configured to execute various types of control including the power control for the engine 12 using the engine control device 20 and the gear shift control for the automatic transmission 14. The microcomputer includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), and an input / output interface (specifically, an input / output circuit). The ECU 30 implements various functions described later and performs various types of signal processing described later based on programs stored in the ROM (pre) and using a temporary storage function of the RAM. The programs may be based on a flowchart described later.A lever position sensor 48 configured to detect a lever operation position Psh of a gear shift lever 46 provides a signal that conveys the lever operation position Psh to the ECU 30. An atmospheric pressure sensor 31 supplies a signal that transmits the atmospheric pressure Ta to the ECU 30. A coolant temperature sensor 32 provides a signal that communicates a coolant temperature Tw to the ECU 30. An engine oil temperature sensor 33 provides a signal that transmits an oil temperature To of the lubricating oil of the engine 12 to the ECU 30. An oil temperature sensor 34 of the automatic transmission (AT) supplies a signal that transmits an oil temperature Tq of the hydraulic oil of the automatic transmission 14 to the ECU 30. An engine output rotational speed sensor 35 supplies a signal indicative of the number of output revolutions Ne of the engine 12 to the ECU 30. The number of output revolutions may be considered an output speed. An AT input rotational speed sensor 36 supplies a signal that transmits the number of input revolutions Nf of the automatic transmission 14 to the ECU 30. The number of input revolutions may be considered an input speed.The coolant temperature sensor 32, the engine oil temperature sensor 33, and the engine output rotational speed sensor 35 are provided on the engine 12. The AT oil temperature sensor 34 and the AT input rotational speed sensor 36 are provided on the automatic transmission 14. The air pressure sensor 31 may be provided on the engine 12, the automatic transmission 14, or any location in the vehicle 10 other than the engine 12 and the automatic transmission 14. In place of the atmospheric pressure sensor 31, an intake pressure sensor configured to provide a signal indicative of a fresh air pressure may be used, and the atmospheric pressure Ta may be estimated based on the signal.For example, the gear shift lever 46 is provided in the vicinity of a driver's seat. The gear shift lever 46 can be manually operated to any operating position that is at least one of a D position, an R position, a P position, and an N position. By shifting to the D position, a D range for forward travel can be selected. In the D range, the automatic transmission 14 is in the forward running state. By shifting to the R position, a reverse program (i.e., an R range) for reverse travel can be selected. In the R range, the automatic transmission 14 is in the reverse running state. In this embodiment, the D range and the R range may be used as driving ranges. By switching to the N position, an N range can be selected. In the N range, the automatic transmission 14 is in the neutral state. By switching to the P position, a P range can be selected. In the P range, the automatic transmission 14 is in the parked state. In this embodiment, the N region and the P region may be used as non-driving regions.A display 50 is connected to the ECU 30. The display 50 is disposed on an instrument panel 52 near the driver's seat. Examples of the display 50 are a vacuum fluorescent display (VFD) and a liquid crystal display. When a first indication signal is received from the ECU 30, the display 50 displays a vehicle speed, a remaining fuel amount, the number of revolutions (or the rotational speed) of the engine 12, and the like. Although details will be described later, when there is a possibility that the engine may stall from the non-driving range to the driving range in response to an operation of the gear shift lever 46, a graphic object depending on a waiting time for avoiding the engine stall is displayed in the display 50 based on a second display signal received from the ECU 30. Specifically, the display 50 shows a graphic object that changes its shape depending on the elapse of the waiting time.A speaker 60 is connected to the ECU. For example, the speaker 60 is mounted near a driver door of the vehicle 10, a ceiling of a vehicle cabin, or the driver's seat. When a first output signal corresponding to an instruction to output an alarm sound is received from the ECU 30, the speaker outputs an alarm sound (for example, a beep) based on the received output signal. Examples of the alarm sound include a sound that indicates to a driver that a seat belt is not worn or a door is not fully closed. Although details will be described later, when there is a possibility that the engine may stall from the non-driving range to the driving range in response to an operation of the gear shift lever 46, a rejection sound based on a second output signal received from the ECU 30 is output from the speaker 60. The reject sound informs the driver that the ECU 30 prohibits a gear shift request from a non-driving range to a driving range. The reject sound may correspond to or be different from the alarm sound. In order to securely notify the driver that the ECU 30 rejects the gear shift request, the reject sound is preferably different from the alarm sound.The ECU 30 controls the output of the engine 12 via the engine controller 20 depending on an accelerator operation amount (an accelerator position) or the like. The ECU 30 shifts the gears of the automatic transmission 14 based on a predefined shift map (not shown). The ECU 30 functionally includes a processor 70, a memory 80, an input device 91, and an output device 92. The memory 80 may be implemented by either or both of RAM and ROM memories. The input device 91 and the output device 92 may be implemented by the input / output interface.The processor 70 includes, as components, a first calculator / calculator 71, a second calculator / calculator 72, and an estimator 73. the processor 70 includes, as components, a third calculator / calculator 74, a determiner / determiner 75, and a limiter 76. the memory 80 includes, as components, a first map memory 81, a second map memory 82, and a third map memory 83.The first map memory 81 stores an engine torque map. As shown in FIG. 2A, in the engine torque map, combinations of the coolant temperature of the engine 12, the oil temperature of the lubricating oil of the engine 12, and the output rotational speed of the engine 12 are associated with the engine torques. For example, a combination of a coolant temperature "Tw_ 1 (° C.)", an oil temperature "To_ 1 (° C.)", and the output rotational speed "Ne_ 1 (U / min)" is associated with an engine torque "Te_ 111 (Nm)". That is, when the coolant temperature, the oil temperature of the lubricating oil, and the output rotational speed are determined, the engine torque may be determined in association with the combination of the coolant temperature, the oil temperature, and the output rotational speed. For example, if a coolant temperature "-30 (° C.)", an oil temperature "-30 (° C.)", and the output speed "1000 (U / min)" can be determined, the engine torque may be determined in conjunction with the combination of the determined values.The engine torque shown in FIG. 2A is a difference between an output torque of the engine 12 and a load torque of the engine, which is dependent on the viscosity of the lubricating oil. That is, the motor torque is a torque that can be generated by the motor. The oil temperature of the lubricating oil correlates with the viscosity. Thus, when the oil temperature of the lubricating oil can be determined, the load torque of the engine 12 can be determined depending on the viscosity of the lubricating oil. Engine torque may be measured using a torque sensor attached to an uninstalled engine, i.e., engine 12, prior to installation in vehicle 10. When combinations of the coolant temperature, the oil temperature, and the output rotational speed of the unincorporated engine are measured and the engine torques associated with the combinations are measured, it is possible to prepare an engine torque map in which the combinations of the coolant temperature, the oil temperature, and the output rotational speed are associated with the engine torques. The engine torque map may be prepared in advance by using the unincorporated engine or may be prepared during the running of the engine 12 by providing the torque sensor to the engine 12. Some engine torques may be measured and the other engine torques may be estimated based on the measured engine torques and a predetermined calculation rule.The first map memory 81 stores an atmospheric pressure map. As shown in FIG. 2B, in the atmospheric pressure map, ranges of the atmospheric pressure are associated with atmospheric pressure coefficients. For example, an atmospheric pressure "1000 to 900 (hPa)" is associated with an atmospheric pressure coefficient of "1.00". The relationship between the atmospheric pressure and the atmospheric pressure coefficient is an example not limited to this relationship shown in the example.As the atmospheric pressure decreases, the output of the engine tends to decrease. Therefore, an atmospheric pressure coefficient that decreases as the atmospheric pressure decreases is used. Thus, even in upland at a height of 3000 m, for example, an air pressure specific to the upland can be taken into account. Although details will be described later, the engine output X of the engine 12 may be calculated by multiplying at least the engine torque and the output rotational speed. The engine output X of the engine 12 may be calculated by multiplying the engine torque by the output rotational speed and the atmospheric pressure coefficient. Thereby, the accuracy of the engine output X of the engine 12 can be improved.The second map memory 82 stores a load torque map for the automatic transmission 14 in the P range (hereinafter referred to as "P range load torque map"). As illustrated in FIG. 3A, in the P-range load torque map, combinations of the oil temperature of the hydraulic oil of the automatic transmission 14 in the P-range and the input rotational speed of the automatic transmission 14 in the P-range are associated with load torques. For example, a combination of an oil temperature "Tq_ 1 (° C.)" and the input rotational speed "Nf_ 1 (U / min)" is associated with a load torque "Tlp_ 11 (Nm)". That is, when the oil temperature of the hydraulic oil and the input rotational speed of the automatic transmission 14 can be determined, the load torque in the P range can be determined in association with the combination of the oil temperature and the input rotational speed.The load torque illustrated in FIG. 3A is a torque of the automatic transmission 14 in the P range depending on the viscosity of the hydraulic oil. The oil temperature of the hydraulic oil correlates with the viscosity. Thus, when the oil temperature of the hydraulic oil can be determined, the load torque of the automatic transmission 14 in the P range can be determined depending on the viscosity of the hydraulic oil. The second map memory 82 may store a load torque map for the automatic transmission 14 in the N range, similar to the load torque map of the P range. Although details will be described later, a P range load Y 1 for the automatic transmission 14 in the P range may be calculated by multiplying the load torque and the input speed in the P range by each other.The third map memory 83 stores a load torque map for the automatic transmission 14 in the D range (hereinafter referred to as "D range load torque map"). As illustrated in FIG. 3B, in the load torque map of the D range, combinations of the oil temperature of the hydraulic oil of the automatic transmission 14 and the input rotational speed of the automatic transmission 14 are associated with the load torques. For example, a combination of an oil temperature "Tq_ 1 (° C.)" and the input rotational speed "Nf_ 1 (U / min)" is associated with a load torque "Tlp_ 11 (Nm)". That is, when the oil temperature of the hydraulic oil and the input rotational speed of the automatic transmission 14 can be determined, the load torque in the D range can be determined in association with the combination of the oil temperature and the input rotational speed.The load torque shown in FIG. 3B is a torque of the automatic transmission 14 in the D range along with an operation for the gear shift lever. For example, when the D range is selected and the power of the engine 12 is transmitted to the automatic transmission 14, a large force is required to rotate the gears at low oil temperature and high viscosity of the hydraulic oil. Therefore, the load torque increases. Thus, the oil temperature of the hydraulic oil correlates with the viscosity, and the load torque of the automatic transmission 14 in the D range can be determined along with an operation of the shift lever. The third map memory 83 may store a load torque map for the automatic transmission 14 in the R range, similar to the load torque map of the D range. Although details will be described later, a D range load Y 2 for the automatic transmission 14 in the D range may be calculated by multiplying the load torque and the input speed in the D range by each other.The load torque may be measured using a torque sensor attached to an uninstalled automatic transmission, i.e., the automatic transmission 14, prior to installation in the vehicle 10. When combinations of the oil temperature and the input rotational speed of the uninstalled automatic transmission are measured and the load torques associated with the combinations are measured, it is possible to prepare a load torque map of the P range in which the combinations of the oil temperature and the input rotational speed are associated with the load torques. The load torque map of the D range is the same as the load torque map of the P range. The P range load torque map and the D range load torque map may be established in advance by using the uninstalled automatic transmission. Some load torques may be measured and the other load torques may be estimated based on the measured load torques and a predetermined calculation rule.The components of the processor 70 execute various processes by accessing the components of the memory 80. For example, the first calculator 71 calculates the engine output X of the engine 12 based on the output rotational speed of the engine 12, the coolant temperature of the water flowing through the engine 12, the oil temperature of the lubricating oil flowing through the engine 12, and the engine torque map. As described above, the engine torque map defines the output speed, the coolant temperature, the oil temperature, and the torque of the engine 12 in conjunction with a combination of these values. The first calculator 71 may also calculate the engine output X of the engine 12 based on the atmospheric pressure coefficient. The other components of the processor 70 will be described in detail in the functional description of the ECU 30.Next, the operation of the ECU 30 will be described with reference to FIGS. 4 and 5A to 5D.The processes illustrated in a flowchart of FIG. 4 are executed immediately after the engine 12 is started. The ECU 30 may periodically repeatedly execute the series of processes illustrated in the flowchart of FIG. 4 (for example, every few seconds or every few milliseconds). The following description exemplarily refers to the P range and the D range, and the N range may be used instead of the P range or the R range may be used instead of the D range.As illustrated in FIG. 4, the first calculator 71 first calculates the output X of the motor 12 (step S 1). More specifically, the first calculator 71 detects a signal indicating the atmospheric pressure Ta supplied from the atmospheric pressure sensor 31 via the input device 91 in response to the start of the engine 12. Similarly, the first calculator 71 acquires a signal indicating the coolant temperature Tw supplied from the coolant temperature sensor 32. The first calculator 71 detects a signal indicating the oil temperature To of the lubricating oil of the engine 12 supplied from the engine oil temperature sensor 33. The first calculator 71 detects a signal indicative of the output rotational speed Ne of the engine 12 supplied from the engine output rotational speed sensor 35. The order of detection of the signals is not particularly limited.When the four signals are detected, the first calculator 71 detects an engine torque by accessing the engine torque map (see FIG. 2A ) stored in the first map memory 81. Specifically, the first calculator 71 acquires, from the engine torque map, an engine torque associated with three signals, namely, the signal indicating the coolant temperature Tw, the signal indicating the oil temperature To, and the signal indicating the output rotational speed Ne. Similarly, the first calculator 71 obtains an atmospheric pressure coefficient by accessing the atmospheric pressure map (see FIG. 2B ) stored in the first map memory 81. Specifically, the first calculator 71 acquires, from the atmospheric pressure map, an atmospheric pressure coefficient associated with the signal indicating the atmospheric pressure Ta. When the engine torque and the atmospheric pressure coefficient are detected, the first calculator 71 calculates the engine output X of the engine 12 by multiplying the engine torque, the output rotational speed Ne, and the atmospheric pressure coefficient together.When the process of step S 1 is completed, the second calculator 72 calculates the P range load Y 1 of the automatic transmission 14 (step S 2). More specifically, the second calculator acquires a signal indicating the oil temperature Tq of the hydraulic oil of the automatic transmission 14 supplied from the AT oil temperature sensor 34 via the input device 91. Similarly, the second calculator 72 acquires a signal indicating the input rotational speed Nf of the automatic transmission 14 supplied from the AT input rotational speed sensor 36. The order of detection of the signals is not particularly limited.When the two signals are detected, the second calculator 72 detects a load torque of the P range by accessing the load torque map of the P range (see FIG. 3A ) stored in the second map memory 82. Specifically, the second calculator 72 acquires, from the P-range load torque map, a P-range load torque associated with the two signals, namely, the signal indicating the oil temperature Tq and the signal indicating the input rotational speed Nf. When the P-range load torque is detected, the second calculator 72 calculates the P-range load Y 1 of the automatic transmission 14 by multiplying the P-range load torque and the input rotational speed Nf by each other.When the process of step S 2 is completed, the estimator 73 estimates the generative power α of the motor 12 (step S 3). More specifically, the estimator 73 estimates the generative power α of the engine 12 based on a difference between the engine power X of the engine 12 and the P range load Y 1 of the automatic transmission 14. By this process, the power that can be generated from the P range to the D range by the engine 12 immediately after the operation of the gear shift lever 46 is estimated.When the process of step S 3 is completed, the third calculator 74 calculates the D range load Y 2 of the automatic transmission 14 (step S 4). More specifically, the third calculator 74 acquires a signal indicating the oil temperature Tq of the hydraulic oil of the automatic transmission 14 supplied from the AT oil temperature sensor 34 via the input device 91. Similarly, the third calculator 74 acquires a signal indicating the input rotational speed Nf of the automatic transmission 14 supplied from the AT input rotational speed sensor 36. The order of detection of the signals is not particularly limited.When the two signals are detected, the third calculator 74 detects a load torque of the D range by accessing the load torque map of the D range (see FIG. 3B ) stored in the third map memory 83. Specifically, the third calculator 74 acquires, from the D-range load torque map, a D-range load torque associated with the two signals, namely, the signal indicating the oil temperature Tq and the signal indicating the input rotational speed Nf. When the D range load torque is detected, the third calculator 74 calculates the D range load Y 2 of the automatic transmission 14 by multiplying the D range load torque by the input rotational speed Nf.When the process of step S 4 is completed, the determiner 75 then calculates a difference between the producible power α of the motor 12 and the D range load Y 2 (step S 5) and determines whether the difference is equal to or less than a predetermined threshold (step S 6). A threshold at which engine stall is detectable may be used as a predetermined threshold. When the difference is larger than the predetermined threshold (step S 6: NO), the limiter 76 ends the processes by skipping subsequent processes. That is, when the difference is larger than the predetermined threshold, the determiner 75 determines that the likelihood of engine stall is low, and does not execute the subsequent processes.When the difference is equal to or less than the predetermined threshold (step S 6: YES), the limiter 76 determines whether a shift is detected (step S 7). More specifically, the limiter 76 determines whether a garage shift operation to operate the gear shift lever 46 from the P range to the D range is detected. When the shift operation is not detected (step S 7: NO), the limiter 76 ends the processes by skipping subsequent processes. That is, when the probability of engine stall is high but the shift operation is not detected, the limiter 76 does not execute the subsequent processes. When the garage shift operation is executed, the garage shift control is executed. In garage shift control, the clutch mechanism is smoothly / smoothly engaged by supplying the clutch mechanism with a garage shift hydraulic pressure controlled to be lower than the hydraulic pressure of a modulator for engaging the clutch mechanism.When the shift operation is detected (step (S 7: YES), the limiter 76 prohibits the gear shift request (step S 8). The limiter 76 may interrupt the gear shift request. That is, when the lever position sensor 48 provides a signal indicative of the lever actuation position Psh for the D position, the limiter 76 may reject the signal or deactivate the signal upon receipt of the signal. Thus, the ECU 30 maintains the P range of the automatic transmission 14 by prohibiting the selection of the D range. Even when the driver operates / depresses the accelerator pedal, the clutch mechanism is disengaged and the transmission of the power of the engine 12 to the automatic transmission 14 is interrupted. Accordingly, engine stalling is avoided.When the process of step S 8 is completed, the limiter 76 calculates a power change amount Xc (step S 9). The power change amount Xc is an amount of change in the engine power X indicating a change in the state of the engine 12. For example, the restrictor 76 periodically measures the temperature of at least one of water and lubricating oil, and calculates the power change amount Xc based on a gradient of the measured temperature (specifically, a temperature rise). The limiter 76 may estimate a heat generation amount of the engine 12 based on, for example, the output rotational speed Ne of the engine 12, and calculate the power change amount Xc based on the estimated heat generation amount. The limiter 76 may periodically measure the coolant temperature, the oil temperature of the lubricating oil, and the output rotational speed Ne, determine the engine torque based on the engine torque map, and calculate, as the power change amount Xc, a difference in the engine power X calculated periodically based on the determined engine torque. As the oil temperature of the lubricating oil increases, the viscosity of the lubricating oil decreases and the load torque of the engine 12 decreases. Thus, the engine output X increases and the likelihood of engine stalling decreases.When the process of step S 9 is completed, the limiter 76 calculates a waiting time T 1 (step S 10). More specifically, the limiter 76 calculates, based on the power change amount Xc, a time required for the producible power α to exceed the D range load Y 2 as a waiting time T 1 for the driver. When the power change amount Xc can be calculated, the time required for the generative power α to exceed the D range load Y 2 can be estimated, and the estimated time can be calculated as the waiting time T 1 for the driver.When the process of step S 10 is completed, the limiter 76 causes the display 50 to display a graphic object 51 depending on the waiting time T 1 (step S 11). More specifically, the limiter 76 generates a second display signal for the graphic object 51 that changes at least its shape, pattern, and / or color depending on the elapse of the waiting time T 1, and outputs the generated second display signal to the display 50 via the output device 92. As shown in FIG. 5A, the display 50 is disposed on the instrument panel 52. The display 50 may be disposed between, for example, a tachometer 52 aand a tachometer 52 bon the instrument panel 52. The arrangement position of the display 50 is not particularly limited.The display 50 includes a timer portion 50a. As illustrated in FIGS. 5B and 5C, the graphic object 51 that changes its shape depending on the elapse of the waiting time T 1 is illustrated in the timer area 50 a. In this embodiment, the length of the rectangular graphic object 51 decreases depending on the elapse of the waiting time T 1. The graphic object 51 may have a circular shape. At least the pattern and / or color of the graphical object may change as its shape changes. Alternatively, at least the pattern and / or color of the graphical object may be changed without changing its shape. When the driver views the graphic object 51, he can recognize how much of the waiting time T 1 has elapsed.The display 50 further includes a message area 50b. A notification for the driver is displayed in the notification area 50 b. For example, as illustrated in FIG. 5D, when the waiting time T 1 reaches zero and the graphic object 51 disappears from the timer area 50 a, a predetermined message is displayed in the message area 50 b. The predetermined message may inform the driver that a shift is permitted or the possibility of engine stalling is excluded. Thus, the driver brings the shift lever 46 back to the P position from the D position and moves the shift lever 46 back to the D position. The driver can return the gear shift lever 46 from the D position to the P position when the reject sound described later is outputted.When the process of step 11 is completed, the limiter 76 causes the speaker 60 to output the reject sound (step S 12). More specifically, the limiter 76 generates a second output signal for outputting the reject sound, and outputs the second output signal to the speaker 60 via the output device. By receiving the second output signal, the speaker 60 outputs the reject sound. Through the reject noise, the driver can determine that the gear shift request from the P range to the D range is prohibited. The driver may understand that the reason why the vehicle 10 is not driving forward despite the depression of the accelerator pedal is not due to problems in the vehicle 10. When the process of step S 12 is completed, the limiter 76 ends the process. The order of the process of step S 12 and the process of step S 11 may be changed.According to the present embodiment, the ECU 30 controls the vehicle 10 including the engine 12 and the automatic transmission 14. the ECU 30 includes the estimator 73, the third calculator 74, the determiner 75, and the limiter 76. the estimator 73 estimates the generative power α of the engine 12 based on the state of the engine 12 and the state of the automatic transmission 14 in the non-driving range.The third calculator 74 calculates the D range load Y 2 on the automatic transmission 14 in the D range based on the state of the automatic transmission 14 in the drive range. The determiner 75 determines whether the difference between the generative power α and the D-range load Y 2 is equal to or less than the predetermined threshold value by which the engine stall is recognizable. When the difference is equal to or less than the predetermined threshold, the limiter 76 prohibits the gear shift request from the P range to the D range. In this way, it is possible to suppress the engine stall when the switching from the P range to the D range is performed at least in a low temperature environment. In particular, engine stall can be suppressed even in a high-altitude mountain where the performance of the engine decreases and the likelihood of engine stall increases due to a decrease in atmospheric pressure.In the above-described embodiment, the load torque depending on the viscosity of the lubricating oil is described as an example of the load torque 12 acting on the output torque of the engine. The load acting on the output of the engine 12 is not limited to the load depending on the viscosity of the lubricating oil. For example, a load torque caused by an accessory 13 provided in association with the engine 12 may be used. Examples of the accessory 13 include a starter, a self-starter, an alternator, a water pump, and a compressor of an air conditioner. When the generative power α is estimated using the load torque of the accessory 13 depending on the output rotational speed of the engine 12 together with the load depending on the viscosity of the lubricating oil, the accuracy of the generative power α can be increased and the engine stall can be accurately suppressed.Although the preferred embodiment of the present invention is described above in detail, the present invention is not limited to the specific embodiment, and various modifications and changes may be made within the scope of the gist of the present invention described in the claims. for example, an intake pressure sensor may be used, and the atmospheric pressure may be estimated based on an intake pressure. As for the input rotational speed, the output rotational speed may be used. In the above-described embodiment, various maps are used. In place of the maps, predefined calculation expressions may be used to calculate the engine output X, the P-range load Y 1, and the D-range load Y 2.

Claims

A vehicle control apparatus that controls a vehicle (10) including an engine (12) and an automatic transmission (14), the vehicle control apparatus comprising an electronic control unit (30) configured to: estimate power producible by the engine (12) based on a state of the engine (12) and a state of the automatic transmission (14) in a non-driving range; calculate a load on the automatic transmission (14) in a driving range based on a state of the automatic transmission (14) in the driving range; determine whether a difference between the power and the load is equal to or less than a predetermined threshold by which an engine stall is identifiable; and prohibits a gear shift request from the non-driving range to the driving range when the difference is equal to or less than the predetermined threshold, wherein the state of the engine (12) is a temperature of a coolant used for cooling the engine (12); the state of the automatic transmission (14) in the non-driving range is a temperature of a hydraulic oil of the automatic transmission (14) in a disengaged state; and the state of the automatic transmission (14) in the driving range is a temperature of the hydraulic oil of the automatic transmission (14) in a engaged state.The vehicle control apparatus according to claim 1, wherein the electronic control unit (30) is configured to correct the performance based on an atmospheric pressure.The vehicle control apparatus according to claim 1 or 2, wherein the electronic control unit (30) is configured to estimate the power also based on a load caused by an accessory (13) of the engine (12).The vehicle control apparatus according to any one of claims 1 to 3, wherein the electronic control unit (30) is configured to, when the difference is equal to or less than the predetermined threshold value: estimate, based on a change in the state of the engine (12), a time required for the difference to exceed the predetermined threshold value; and cause a display (50) to display a graphical object that changes at least one of a shape, a pattern, and a color of the graphical object depending on the elapse of the estimated time.The vehicle control apparatus according to any one of claims 1 to 4, wherein the electronic control unit (30) is configured to, when the difference is equal to or less than the predetermined threshold, cause a speaker to output a sound indicating that a shift from the non-driving range to the driving range is prohibited.The vehicle control apparatus according to any one of claims 1 to 5, wherein the electronic control unit (30) is configured to stop the gear shift request when the difference is equal to or less than the predetermined threshold.A method of controlling a vehicle (10) having an engine (12) and an automatic transmission (14), the method comprising the steps of: estimating power producible by the engine (12) based on a state of the engine (12) and a state of the automatic transmission (14) in a non-driving range; calculating a load on the automatic transmission (14) in a driving range based on a state of the automatic transmission (14) in the driving range; determining whether a difference between the power and the load is equal to or less than a predetermined threshold by which an engine stall is identifiable; inhibiting a gear shift request from the non-driving range to the driving range when the difference is equal to or less than the predetermined threshold, wherein the state of the engine (12) is a temperature of a coolant used for cooling the engine (12); the state of the automatic transmission (14) in the non-driving range is a temperature of a hydraulic oil of the automatic transmission (14) in a disengaged state; and the state of the automatic transmission (14) in the driving range is a temperature of the hydraulic oil of the automatic transmission (14) in a engaged state.

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