Vehicle control system

Abstract

The present invention provides a vehicle control device that can reduce the discomfort experienced by the driver when resolving or suppressing the occurrence of a lost drive state. [Solution] When there is a possibility of a lost drive condition occurring, the direct-drive clutch, which is in the disengaged state when the vehicle is stopped, is controlled to switch to the engaged state when starting, thereby suppressing a decrease in the power transmission capacity of the fluid-type transmission system. As a result, the occurrence of a lost drive condition is eliminated or suppressed when starting. In addition, when there is a possibility of a lost drive condition occurring, the upper limit of the engine's rotational speed is set to an upper limit value lower than the maximum rotational speed that defines the usable range of the engine. As a result, the engine's rotational speed is suppressed during the transition to the engaged state of the direct-drive clutch when the occurrence of a lost drive condition is eliminated or suppressed.

Description

Technical Field

[0001] The present invention relates to a control device for a vehicle equipped with a fluid transmission device with a direct clutch.

Background Art

[0002] A control device for a vehicle including an engine, a fluid transmission device provided in a power transmission path between the engine and drive wheels, and a direct clutch that connects an input member and an output member of the fluid transmission device is well known. For example, the control device for a vehicle described in Patent Document 1 is such a device. Patent Document 1 discloses that during a stop, when a transmission mechanism provided at a rear stage of the fluid transmission device is in a state where power transmission is possible and the engine rotation speed is equal to or higher than a reference rotation speed, it is determined as a lost drive state. Further, Patent Document 1 discloses that when it is determined as a lost drive state, at the time of starting the vehicle, the direct clutch is controlled from a released state to an engaged state so as to suppress a decrease in power transmission ability. The lost drive state is a state in which, in the fluid transmission device, air is mixed into the oil used for fluid transmission, resulting in a decrease in the power transmission ability from the engine to the transmission mechanism, that is, the power transmission ability from the input member to the output member.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, even if the direct-drive clutch in a fluid-type transmission system is controlled to suppress a decrease in power transmission capacity, there is a possibility that the driving torque may be insufficient during the transient period when the decrease in power transmission capacity is suppressed, that is, during the transient period when the direct-drive clutch is switched to the engaged state. In this case, if the engine speed increases due to the driver's increased accelerator operation, it may cause discomfort to the driver.

[0005] The present invention was made against the above circumstances, and its objective is to provide a vehicle control device that can reduce the discomfort experienced by the driver when eliminating or suppressing the occurrence of a lost drive state. [Means for solving the problem]

[0006] The gist of the first invention is a control device for a vehicle comprising: (a) an engine; a fluid-type transmission device provided in a power transmission path between the engine and the drive wheels; and a direct-drive clutch connecting an input member and an output member of the fluid-type transmission device, the control device comprising: (b) a state determination unit that determines whether or not there is a possibility of a lost drive state occurring in the fluid-type transmission device, in which the power transmission capacity from the input member to the output member is reduced; (c) a reduction suppression control unit that, when it is determined that there is a possibility of the lost drive state occurring, controls the direct-drive clutch, which is in an unlocked state when the vehicle is stopped, to be engaged when the vehicle starts moving, thereby suppressing the reduction in the power transmission capacity; and (d) a limit value setting unit that, when it is determined that there is a possibility of the lost drive state occurring, sets the upper limit of the rotational speed of the engine to an upper limit value lower than the maximum rotational speed that defines the usable range of the engine. [Effects of the Invention]

[0007] According to the first invention, if there is a possibility of a lost drive condition occurring, the direct-drive clutch, which is in the disengaged state when the vehicle is stopped, is controlled to switch to the engaged state when starting, thereby suppressing a decrease in the power transmission capacity of the fluid-type transmission system. As a result, the occurrence of a lost drive condition is eliminated or suppressed when starting. Furthermore, if there is a possibility of a lost drive condition occurring, the upper limit of the engine's rotational speed is set to an upper limit value lower than the maximum rotational speed that defines the usable range of the engine. As a result, the engine's rotational speed is suppressed during the transient of switching the direct-drive clutch to the engaged state when the occurrence of a lost drive condition is eliminated or suppressed. Therefore, the discomfort felt by the driver when eliminating or suppressing the occurrence of a lost drive condition can be reduced. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram illustrates the schematic configuration of a vehicle to which the present invention is applied, as well as the main parts of the control functions and control systems for various control functions in the vehicle. [Figure 2] This figure shows an example of setting a predetermined time for determining the duration of a vehicle's stationary state. [Figure 3] This figure shows an example of setting an upper limit guard value for engine rotation speed when a lost drive condition may occur. [Figure 4] This flowchart explains the key aspects of the control operation of an electronic control unit, specifically the control operations designed to reduce discomfort to the driver when resolving or suppressing the occurrence of a lost drive state. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Examples]

[0010] Figure 1 is a diagram illustrating the schematic configuration of a vehicle 10 to which the present invention is applied, as well as illustrating the main parts of the control functions and control systems for various controls in the vehicle 10. In Figure 1, the vehicle 10 comprises an engine 12, drive wheels 14, and a power transmission device 16 provided in the power transmission path between the engine 12 and the drive wheels 14.

[0011] Engine 12 is a known internal combustion engine. The engine torque Te of engine 12 is controlled by an electronic control device 50, which is provided in the vehicle 10 and includes an electronic throttle valve, fuel injection device, ignition device, etc., and is controlled by an electronic control device 80, which will be described later.

[0012] The power transmission device 16 includes a torque converter 20 connected to the engine 12, an automatic transmission 22 connected to the torque converter 20, etc., housed in a case 18 which is a non-rotating member attached to the vehicle body. The power transmission device 16 also includes a propeller shaft 26 connected to the transmission output shaft 24, a differential gear 28 connected to the propeller shaft 26, a pair of drive shafts 30 connected to the differential gear 28, etc. The transmission output shaft 24 is the output rotating member of the automatic transmission 22. The power transmission device 16 also includes an engine connecting shaft 32 that connects the engine 12 and the torque converter 20.

[0013] The torque converter 20 comprises a pump impeller 20p connected to the engine connecting shaft 32 and a turbine impeller 20t connected to the transmission input shaft 34. The transmission input shaft 34 is the input rotating member of the automatic transmission 22. The pump impeller 20p is the input member of the torque converter 20, and the turbine impeller 20t is the output member of the torque converter 20. The torque converter 20 is a fluid-type transmission device of the present invention, installed in the power transmission path between the engine 12 and the drive wheels 14. The torque converter 20 transmits power from the engine 12 to the transmission input shaft 34 via fluid from the engine connecting shaft 32.

[0014] The torque converter 20 is equipped with a lock-up clutch 36 that connects the engine connecting shaft 32 and the transmission input shaft 34. The lock-up clutch 36 is a direct-drive clutch of the present invention that connects the pump impeller 20p and the turbine impeller 20t. The lock-up clutch 36 is, for example, a known hydraulic friction engagement device. The lock-up clutch 36's control state is switched by changing the lock-up torque Tlu, which is the torque capacity of the lock-up clutch 36, using the lock-up hydraulic pressure PRlu. The lock-up hydraulic pressure PRlu is the hydraulic pressure of the regulated oil FLD supplied to the lock-up clutch 36 from the hydraulic control circuit 52 provided in the vehicle 10. Oil FLD is a hydraulic fluid used for the operation of the automatic transmission 22, fluid transmission in the torque converter 20, and the switching operation of the lock-up clutch 36, etc.

[0015] The lock-up clutch 36 can be in three states: a released state (also known as a fully released state), a slipped state where the lock-up clutch 36 is engaged with slippage, and an engaged state (also known as a fully engaged state). When the lock-up clutch 36 is in the released state, the torque converter 20 is in a torque converter state where torque amplification is achieved. When the lock-up clutch 36 is in the engaged state, the torque converter 20 is in a lock-up state (also known as a fully locked-up state) where the pump impeller 20p and the turbine impeller 20t are rotated together.

[0016] The automatic transmission 22 is located in the power transmission path between the torque converter 20 and the drive wheels 14. The automatic transmission 22 is a known planetary gear type automatic transmission, for example, equipped with an engagement device CB. The engagement device CB includes a plurality of known hydraulic friction engagement devices, such as clutches and brakes. Each engagement device CB is switched between engaged, slipped, and released states by changing the engagement torque Tcb, which is the torque capacity of the engagement device CB, by an engagement hydraulic pressure PRcb. The engagement hydraulic pressure PRcb is the hydraulic pressure of the regulated oil FLD supplied to the engagement device CB from the hydraulic control circuit 52.

[0017] The automatic transmission 22 forms one of several gear stages with different gear ratios γ (=Ni / No) by engaging any of the engagement devices CB. "Ni" is the rotational speed of the transmission input shaft 34, which is the input rotational speed of the automatic transmission 22, i.e., the transmission input rotational speed Ni. "No" is the rotational speed of the transmission output shaft 24, which is the output rotational speed of the automatic transmission 22, i.e., the transmission output rotational speed No. The automatic transmission 22 switches the gear stage formed by switching the control state of the engagement device CB according to the driver's accelerator operation, vehicle speed V, etc., by the electronic control device 80, which will be described later.

[0018] Vehicle 10 is further equipped with a mechanical oil pump 38 connected to a pump impeller 20p, and an oil pan 40 located at the bottom of the case 18. The oil pump 38 is rotationally driven by the engine 12, drawing up the oil FLD that has returned to the oil pan 40 through a strainer (not shown) and supplying it to the hydraulic control circuit 52. The hydraulic control circuit 52 supplies lock-up hydraulic pressure PRlu and various engagement hydraulic pressures PRcb, etc., which are regulated based on the oil FLD from the oil pump 38. A portion of the oil FLD supplied to the hydraulic control circuit 52 is supplied to multiple lubrication points in the power transmission device 16, for example. The oil FLD discharged from the hydraulic control circuit 52 and the oil FLD supplied to the lubrication points are returned to the oil pan 40 by gravity or other means. The oil pan 40 is an oil reservoir in which oil FLD is drawn up and recirculated.

[0019] Vehicle 10 further includes a power switch 54. The power switch 54 is, for example, a self - reset push - button switch. The power switch 54 is a power switch that is operated by the driver so that the power control state in the vehicle 10 can be switched. The power control state includes, for example, a power - on state, a partial - power - on state, and a power - off state. The power - on state is an ignition - on (IG - ON) state that enables the engine 12 to be driven. The partial - power - on state is an accessory - on (ACC - ON) state that disables the engine 12 from being driven but enables some functions not related to the driving of the engine 12 to operate. The power - off state is an ignition - off (IG - OFF) state that makes the vehicle unable to run and also makes some functions not related to vehicle running inoperable. For example, when the power switch 54 is pressed in the power - off state, it is switched to the ignition - on state, and the engine 12 that has been stopped is started.

[0020] Vehicle 10 further includes an electronic control unit 80 as a controller related to the control of the engine 12 and the like. The electronic control unit 80 is configured to include a so - called microcomputer including, for example, a CPU, a RAM, a ROM, an input / output interface, and the like. The CPU executes various controls of the vehicle 10 by performing signal processing according to a program stored in the ROM in advance while using the temporary storage function of the RAM. The electronic control unit 80 is configured to include each computer for engine control, hydraulic control, etc. as necessary. The electronic control unit 80 functions as the control device of the present invention.

[0021] Various signals and the like based on detection values from various sensors and the like provided in the vehicle 10 are respectively supplied to the electronic control device 80. The various sensors and the like are, for example, the power switch 54, engine speed sensor 60, input speed sensor 62, output speed sensor 64, accelerator opening sensor 66, brake sensor 68, oil level sensor 70, operation position sensor 72, and the like. The various signals and the like are, for example, the power switch signal SWpwr, engine speed Ne, transmission input speed Ni, transmission output speed No, accelerator opening θacc, brake operation amount θbra, oil level LVfld, operation position POSop, and the like.

[0022] The power switch signal SWpwr is a signal indicating that the pressing operation of the power switch 54 has been performed. The engine speed Ne is the rotational speed of the engine 12. The transmission input speed Ni has the same value as the turbine rotational speed Nt which is the rotational speed of the turbine impeller 20t. The transmission output speed No is a rotational speed corresponding to the vehicle speed V. The accelerator opening θacc is the driver's accelerator operation amount representing the magnitude of the driver's acceleration operation. The brake operation amount θbra is a signal indicating that the brake pedal for operating the wheel brake is being operated by the driver and is also a signal representing the magnitude of the stepping operation of the brake pedal. The oil level LVfld is a signal representing the height of the liquid level of the oil FLD in the oil pan 40.

[0023] The vehicle 10 further includes a shift device 56 in which any one of a plurality of operation positions POSop is selected by the driver. The shift device 56 is a switching device for switching the shift position (the shift range Rsh is also synonymous) of the automatic transmission 22. The operation position POSop is a signal representing the selected state of the power transmission state in the automatic transmission 22 and includes, for example, the P, R, N, D operation positions and the like. The shift range Rsh represents the power transmission state of the automatic transmission 22 and includes, for example, the P, R, N, D positions (the P, R, N, D ranges are also synonymous) and the like.

[0024] The P (Parking) operating position represents the selection of the P range of the automatic transmission 22, where the automatic transmission 22 is in neutral and the transmission output shaft 24 is mechanically fixed so as not to rotate. The neutral state of the automatic transmission 22 is a state in which no power transmission is possible as no gears are engaged. The R (Reverse) operating position represents the selection of the R range of the automatic transmission 22, which enables reverse driving. The R range of the automatic transmission 22 is the reverse driving position (reverse driving range is synonymous) of the automatic transmission 22. The N (Neutral) operating position represents the selection of the N range of the automatic transmission 22, where the automatic transmission 22 is in neutral. The D (Forward) operating position represents the selection of the D range of the automatic transmission 22, which enables forward driving by executing automatic gear shifting control of the automatic transmission 22. The D range of the automatic transmission 22 is the forward driving position (synonymous with forward driving range) of the automatic transmission 22. The R and D ranges of the automatic transmission 22 are driving positions (synonymous with driving range) that enable power transmission in the automatic transmission 22. The P and N ranges of the automatic transmission 22 are non-driving positions (synonymous with non-driving range) that disable power transmission in the automatic transmission 22.

[0025] The electronic control unit 80 outputs various command signals to each device installed in the vehicle 10. These devices include, for example, the engine control unit 50, the hydraulic control circuit 52, and the information notification device 58. The various command signals include, for example, the engine control command signal Se, the engagement hydraulic control command signal Scrb, the lock-up hydraulic control command signal Slu, and the information notification control command signal Sinf.

[0026] The information notification device 58 is a device that notifies the driver of various information. The information notification device 58 is, for example, a display device such as a monitor, display, or alarm lamp, and / or a sound output device such as a speaker or buzzer. The information notification device 58 notifies the driver of, for example, selectable menus, notices, guidance, the status of malfunctions related to driving, and the status of deterioration of driving-related functions.

[0027] The engine control command signal Se is a command signal for controlling the engine 12. The engagement hydraulic control command signal Sb is a command signal for controlling the engagement device CB and is the instruction hydraulic pressure for the engagement hydraulic pressure PRcb. The lock-up hydraulic control command signal Slu is a command signal for controlling the lock-up clutch 36 and is the instruction hydraulic pressure for the lock-up hydraulic pressure PRlu. The information notification control command signal Sinf is a command signal for controlling the notification of various information to the driver and is the notification content from the information notification device 58.

[0028] The electronic control unit 80 includes an engine control unit 82, a hydraulic control unit 84, a state determination unit 86, and a decrease suppression control unit 88 in order to realize various controls in the vehicle 10.

[0029] The engine control unit 82 calculates the amount of drive requested by the driver to the vehicle 10 by applying, for example, the accelerator opening θacc and the vehicle speed V to the drive request amount map. The drive request amount map is a predetermined relationship for determining the amount of drive requested, which is, for example, determined and stored in advance experimentally or by design. The amount of drive requested is, for example, the requested drive torque Twdem, which is the requested value of the drive torque Tw at the drive wheels 14. The engine control unit 82 outputs an engine control command signal Se to control the engine 12 so that an engine torque Te that realizes the requested drive torque Twdem is obtained.

[0030] The engine control unit 82 outputs an engine control command signal Se to control the engine 12 so that the engine rotational speed Ne does not exceed the maximum rotational speed Nemax. For example, if the engine rotational speed Ne is near the maximum rotational speed Nemax, the engine control unit 82 performs fuel cut control to stop the fuel supply to the engine 12. The maximum rotational speed Nemax is, for example, the upper limit of the engine rotational speed Ne defined by the predetermined rating of the engine 12, which prevents the performance of the engine 12 from deteriorating. In other words, the maximum rotational speed Nemax is the upper limit of the engine rotational speed Ne that defines the usable range of the engine 12. The maximum rotational speed Nemax is, for example, a predetermined upper limit rotational speed Nelim or an allowable maximum rotational speed Nepmt. The predetermined upper limit rotational speed Nelim is, for example, an engine rotational speed Ne predetermined as a high rotational speed that should not be exceeded in terms of the durability of the engine 12. The allowable maximum rotational speed Nepmt is, for example, an engine rotational speed Ne predetermined to be lower by a margin α than the predetermined upper limit rotational speed Nelim. The margin α is a predetermined allowance, for example, to ensure that the engine rotational speed Ne does not exceed a predetermined upper limit rotational speed Nelim.

[0031] The hydraulic control unit 84 makes a shifting decision for the automatic transmission 22 using, for example, a predetermined shifting map, and outputs an engagement hydraulic control command signal Sbc to supply the engagement torque Tcb that executes the shifting of the automatic transmission 22 according to the result of the shifting decision. The shifting map is a predetermined relationship having a shifting line for determining the shifting of the automatic transmission 22 on a two-dimensional coordinate system with, for example, vehicle speed V and accelerator opening θacc as variables.

[0032] The hydraulic control unit 84 determines the control region using, for example, a predetermined lock-up region diagram, and outputs a lock-up hydraulic control command signal Slu to supply lock-up hydraulic pressure PRlu that realizes the control state corresponding to the determined control region. The lock-up region diagram is a predetermined relationship on a two-dimensional coordinate system with, for example, vehicle speed V and required drive torque Twdem as variables, having a release region corresponding to the release state, a slip region corresponding to the slip state, and a lock-up region corresponding to the engagement state.

[0033] When the oil pump 38 draws oil FLD from the oil pan 40, if the oil level LVfld is low, air bubbles are more likely to form in the oil FLD. The oil FLD with air bubbles circulates within the hydraulic control circuit 52 and flows into, for example, the torque converter 20. When air bubbles are present in the oil FLD, the fluid transmission function of the torque converter 20 is reduced or disabled. Due to the formation of air bubbles in the oil FLD, a lost drive condition may occur in the torque converter 20, where the power transmission capacity from the engine 12 to the automatic transmission 22, that is, the power transmission capacity from the pump impeller 20p to the turbine impeller 20t, is reduced. When a lost drive condition occurs, the vehicle 10 may not move quickly when the accelerator is pressed to start. As a countermeasure against the lost drive condition caused by the formation of air bubbles in the oil FLD, that is, as a substitute for the power transmission capacity of the torque converter 20, it is conceivable to control the system to switch the lock-up clutch 36 from the disengaged state to the engaged state when the vehicle 10 starts moving.

[0034] The state determination unit 86 determines whether or not a lost drive state is likely to occur. For example, the state determination unit 86 determines whether or not the oil level LVfld in the oil pan 40 is below a predetermined level LVfldf. The predetermined level LVfldf is a predetermined threshold for determining, for example, that the oil level LVfld is such that bubbles are likely to form in the oil FLD. The state determination unit 86 also determines whether or not the shift range Rsh of the automatic transmission 22 is in the driving range. In the driving range, the engagement hydraulic pressure PRcb is required to engage the engagement device CB, so the flow rate of oil FLD drawn up from the oil pan 40 is higher compared to the non-driving range, making it easier for bubbles to form in the oil FLD. The state determination unit 86 also determines whether or not the stopped state has continued for a predetermined time Tzero or longer, that is, whether or not the vehicle speed V has been zero for a predetermined time Tzero. The predetermined time Tzero is a predetermined threshold for determining, for example, that the duration of a stopped state in the driving range is such that many bubbles form in the oil FLD.

[0035] The state determination unit 86 determines that there is a possibility of a lost drive condition occurring if it determines that the oil level LVfld is less than or equal to a predetermined level LVfldf, the shift range Rsh is in the driving range, and the stationary state has continued for a predetermined time of Tzero or longer. The state determination unit 86 determines that there is no possibility of a lost drive condition occurring if it determines that the oil level LVfld is greater than the predetermined level LVfldf, or the shift range Rsh is in the non-driving range, or the stationary state has continued for a predetermined time of less than Tzero.

[0036] Figure 2 shows an example of setting a predetermined time Tzero to determine the duration of a stationary state. In Figure 2, the lower the oil level LVfld, the more air bubbles are generated in the oil FLD even if the stationary state in the driving range is short, so the predetermined time Tzero is set to be shorter. The predetermined time Tzero is predetermined to be shorter the lower the oil level LVfld is.

[0037] When the engine 12, which had been stopped, is started by operating the power switch 54, bubbles are likely to form in the oil FLD. The state determination unit 86 determines whether the power control state is in the ignition on (IG-ON) state. If the state determination unit 86 determines that the power control state is in the ignition on state, it determines whether there is a possibility of a lost drive state occurring.

[0038] If the state determination unit 86 determines that a lost drive state may occur, the deceleration suppression control unit 88 outputs a command Ss to the hydraulic control unit 84 to control the vehicle 10 to switch the lock-up clutch 36, which is in the released state when the vehicle is stopped, to the engaged state when the vehicle 10 starts moving. By outputting the command Ss to the hydraulic control unit 84, the deceleration suppression control unit 88 performs lost drive elimination control, which suppresses the decrease in the power transmission capacity of the torque converter 20. Lost drive elimination control is a control that enables the vehicle 10 to start even if a lost drive state occurs to the extent that the fluid transmission function of the torque converter 20 does not work at all. In other words, lost drive elimination control is a control that eliminates or suppresses the occurrence of a lost drive state.

[0039] Incidentally, even if lost drive elimination control is performed when starting up and a lost drive condition occurs, the drive torque Tw may be insufficient during the transient when the lock-up clutch 36 is switched to the engaged state. In this case, if the engine speed Ne increases due to the driver's increased accelerator operation, it may cause discomfort to the driver. When the lock-up clutch 36 is engaged, the engine speed Ne (=Ni=γ×No) is determined by the transmission output rotational speed No and the gear ratio γ. Therefore, it is desirable to suppress the increase in engine speed Ne during the transient when the lock-up clutch 36 is switched to the engaged state.

[0040] Therefore, the electronic control unit 80 further includes a limit value setting unit 90. When the state determination unit 86 determines that there is a possibility of a lost drive state occurring, the limit value setting unit 90 performs an upper limit guard by setting the upper limit value of the engine rotation speed Ne to the upper limit guard value Negrd. The upper limit guard value Negrd is the upper limit value of the present invention, which is lower than the maximum rotation speed Nemax. When the state determination unit 86 determines that there is a possibility of a lost drive state occurring, the engine control unit 82 outputs an engine control command signal Se to control the engine 12 so that the engine rotation speed Ne does not exceed the upper limit guard value Negrd.

[0041] The upper limit guard value Negrd is a predetermined value that is, for example, higher by a margin β than the synchronous rotational speed Nisyc (=γ×No) of the transmission input rotational speed Ni, which is determined by the transmission output rotational speed No and the gear ratio γ. The margin β is, for example, a predetermined amount of acceleration that makes it difficult to perceive the engine speed Ne revving up. Alternatively, the upper limit guard value Negrd is, for example, a predetermined constant value that makes it difficult to perceive the engine speed Ne revving up. Furthermore, the upper limit guard value Negrd is set to a value that prevents engine 12 from stalling during the transient when the lock-up clutch 36 is switched to the engaged state in the lost drive elimination control. This reduces the discomfort felt by the driver and also provides a measure to prevent engine 12 from stalling.

[0042] Figure 3 shows an example of setting the upper limit guard value Negrd for engine speed Ne when a lost drive condition may occur. In Figure 3, the smaller the accelerator opening θacc, the more likely the driver is to feel something is wrong even if the engine speed Ne does not rev up slowly, so the upper limit guard value Negrd is set low. When upper limit guarding is not performed, the upper limit of engine speed Ne is set to the maximum rotational speed Nemax. The limit value setting unit 90 sets the upper limit guard value Negrd to a lower value as the accelerator opening θacc decreases, for example, as shown in Figure 3.

[0043] If the driver understands the decrease in acceleration responsiveness when a lost drive condition occurs, or the decrease in acceleration responsiveness due to the upper limit guard of engine rotation speed Ne during the transient of the lost drive elimination control, they are less likely to feel any discomfort. In other words, if the driver is informed that a lost drive condition may occur, they are less likely to feel any discomfort.

[0044] Therefore, the electronic control unit 80 is further equipped with a notification unit 92. When the status determination unit 86 determines that there is a possibility of a lost drive state occurring, the notification unit 92 outputs an information notification control command signal Sinf to notify that there is a possibility of a lost drive state occurring. For example, the notification unit 92 displays on the information notification device 58 that there is a possibility of a lost drive state occurring. Alternatively, the notification unit 92 outputs an audio message from the information notification device 58 indicating that there is a possibility of a lost drive state occurring.

[0045] Figure 4 is a flowchart illustrating the main parts of the control operation of the electronic control unit 80, and is a flowchart illustrating the control operation to reduce discomfort to the driver when resolving or suppressing the occurrence of a lost drive state, and is, for example, executed repeatedly.

[0046] In Figure 4, first, in step S10, which corresponds to the function of the state determination unit 86 (the steps are omitted hereafter), it is determined whether the power control state is ignition on (IG-ON). If the determination in S10 is affirmative, then in S20, which corresponds to the function of the state determination unit 86, it is determined whether the oil level LVfld is below a predetermined level LVfldf. If the determination in S20 is affirmative, then in S30, which corresponds to the function of the state determination unit 86, it is determined whether the shift range Rsh is in the driving range. If the determination in S30 is affirmative, then in S40, which corresponds to the function of the state determination unit 86, it is determined whether the vehicle speed V has been zero for a predetermined time Tzero. If the determination in S40 is affirmative, then in S50, which corresponds to the functions of the limit value setting unit 90, the notification unit 92, and the decrease suppression control unit 88, an upper limit guard for the engine rotation speed Ne is performed. In addition, the driver is notified that there is a possibility of a lost drive condition occurring. Furthermore, lost drive elimination control is performed when starting. Following S50, this routine is terminated. If any of the judgments in S10, S20, S30, and S40 above are rejected, this routine is terminated.

[0047] As described above, according to this embodiment, if there is a possibility of a lost drive condition occurring, lost drive elimination control is performed when starting. As a result, the occurrence of a lost drive condition is eliminated or suppressed when starting. In addition, if there is a possibility of a lost drive condition occurring, an upper limit guard is placed on the engine rotation speed Ne. As a result, during the transient switching to the engaged state of the lock-up clutch 36 when the occurrence of a lost drive condition is eliminated or suppressed, the increase in engine rotation speed Ne is suppressed. Therefore, the discomfort given to the driver when eliminating or suppressing the occurrence of a lost drive condition can be reduced.

[0048] Furthermore, according to this embodiment, the upper limit guard value Negrd in the upper limit guard for engine rotation speed Ne is set to a lower value as the accelerator opening θacc decreases. As a result, the upper limit guard value Negrd is set according to the driver's accelerator operation, which can appropriately reduce any discomfort felt by the driver.

[0049] Furthermore, according to this embodiment, if there is a possibility of a lost drive condition occurring, the driver is notified that a lost drive condition may occur. This reduces the discomfort felt by the driver, even if a decrease in acceleration responsiveness occurs due to the upper limit guard of the engine rotation speed Ne, or if a decrease in acceleration responsiveness occurs when a lost drive condition occurs. In other words, the driver becomes aware of the situation, thus reducing the anxiety felt by the driver.

[0050] Furthermore, according to this embodiment, a lost drive condition is determined to be possible if the oil level LVfld is below a predetermined level LVfldf, the shift range Rsh is in the driving range, and the vehicle remains stationary for a predetermined time of Tzero or longer. As a result, the possibility of a lost drive condition occurring can be determined with high accuracy, thereby appropriately reducing any discomfort or anxiety the driver may experience.

[0051] Furthermore, according to this embodiment, the predetermined time Tzero is set to be shorter the lower the oil level LVfld is. This allows for the loss drive elimination control, which is a countermeasure against the lost drive condition, to be performed appropriately while minimizing the execution of the loss drive elimination control.

[0052] Although embodiments of the present invention have been described in detail above with reference to the drawings, the present invention is also applicable to other embodiments.

[0053] For example, in the above-described embodiment, step S10 in Figure 4 may be omitted. Also, the notification in S50 in Figure 4 that a lost drive state may occur may not be performed. Even in this case, a certain effect of the present invention can be obtained, which is to reduce the discomfort felt by the driver when resolving or suppressing the occurrence of a lost drive state.

[0054] Furthermore, although a planetary gear type stepped transmission was exemplified as the automatic transmission 22 in the above-described embodiment, the present invention is not limited to this embodiment. For example, the automatic transmission 22 may be a synchronous meshing type parallel two-axis automatic transmission including a known DCT (Dual Clutch Transmission), or a known continuously variable transmission such as a belt type with a forward / reverse switching device provided in the front or rear stage. In addition, other fluid-type transmission devices such as a fluid coupling that does not have a torque amplification effect may be used instead of the torque converter 20. In short, the present invention can be applied to any vehicle equipped with an engine, a fluid-type transmission device, and a direct-drive clutch.

[0055] It should be noted that the above-described embodiment is merely one example, and the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. [Explanation of symbols]

[0056] 10: Vehicle 12: Engine 14: Drive wheels 20: Torque converter (fluid-type transmission) 20p: Pump impeller (input component) 20t: Turbine impeller (output component) 22: Automatic transmission 36: Lock-up clutch (direct drive clutch) 40: Oil pan 80: Electronic control unit (control unit) 86: State determination unit 88: Decrease suppression control unit 90: Limit value setting unit 92: Notification unit FLD: Oil

Claims

1. A control device for a vehicle comprising an engine, a fluid-type transmission device provided in a power transmission path between the engine and the drive wheels, and a direct-drive clutch connecting the input member and output member of the fluid-type transmission device, A state determination unit that determines whether or not a lost drive state may occur in the fluid transmission device, in which the power transmission capacity from the input member to the output member decreases, If it is determined that the aforementioned lost drive condition may occur, the reduction suppression control unit controls the vehicle to switch the direct-drive clutch, which is in the disengaged state when the vehicle is stopped, to the engaged state when the vehicle starts moving, thereby suppressing a decrease in the power transmission capacity. If it is determined that the aforementioned lost drive condition may occur, the limit value setting unit sets the upper limit of the engine's rotational speed to an upper limit value lower than the maximum rotational speed that defines the usable range of the engine. A vehicle control device characterized by including [a specific feature].

2. The vehicle control device according to claim 1, characterized in that the limit value setting unit sets the upper limit value to a lower value as the accelerator operation amount decreases.

3. The vehicle control device according to claim 1, further comprising a notification unit that notifies that there is a possibility of the aforementioned lost drive state occurring when it is determined that such a state may occur.

4. The vehicle further comprises an automatic transmission provided in the power transmission path between the fluid-type transmission device and the drive wheels, and an oil pan from which oil used for the operation of the automatic transmission device and fluid transmission in the fluid-type transmission device is drawn up and the oil is circulated. The vehicle control device according to any one of claims 1 to 3, characterized in that the state determination unit determines that the lost drive state may occur when the oil level in the oil pan is below a predetermined level, the shift position of the automatic transmission is a driving position that enables power transmission by the automatic transmission, and the stationary state continues for a predetermined time or longer.

5. The vehicle control device according to claim 4, characterized in that the predetermined time is set to be shorter the lower the oil level is.

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