Vehicle control system

Abstract

To provide a vehicle control device capable of preventing unintended vehicle behavior even when air is taken in through an oil inlet.SOLUTION: A control device is for a vehicle which comprises: an oil pump which pumps up oil in an oil pan; a plurality of engaging mechanisms which adjusts pressure of the oil discharged through the oil pump to predetermined source pressure and can selectively engage according to engaging pressure adjusted from the source pressure; and an automatic transmission which sets a plurality of shift stages using the plurality of engaging mechanisms. If a predetermined condition is met for determining that the oil pump has a high possibility to take in air when pumping up the oil from the oil pan (Yes in Step S1 or Step S5), a controller makes an upper limit value of the engaging pressure to be supplied to a predetermined engaging mechanism that sets a predetermined shift stage lower than both the upper limit value when the predetermined condition is not met and the source pressure (Step S6).SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a device for controlling the hydraulic pressure for engaging or releasing a plurality of engagement mechanisms in a transmission capable of setting a plurality of shift stages by the plurality of engagement mechanisms.

Background Art

[0002] Patent Document 1 discloses a control device for an automatic transmission aimed at preventing air suction in which an oil pump sucks air at low oil temperatures and suppressing the occurrence of losses due to the rotation member stirring the oil at high speed stages. The device of Patent Document 1 has a first oil sump provided below a rotating member constituting a power transmission device for collecting oil circulating in the transmission, and a second oil sump having an oil hole that is separated from the rotating member and returns oil to the first oil sump while restricting the flow. In the device of Patent Document 1, oil is supplied to the second oil sump only when a high speed stage is set, and the setting of the high speed stage is prohibited when the oil temperature is low. That is, since the setting of the high speed stage is prohibited when the oil temperature is low in the device of Patent Document 1, oil is not supplied to the second oil sump, and the oil is stored only in the first oil sump. Therefore, Patent Document 1 describes that by not supplying oil to the second oil sump when the oil temperature is low, a sufficient amount of oil can be stored in the first oil sump, so that air suction of the oil pump can be suppressed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The device described in Patent Document 1 stores oil only in the first oil reservoir except during high-speed gears, thus suppressing not only air intake caused by a drop in the oil level at low oil temperatures, but also air intake caused by the acceleration of the vehicle in low-speed gears where acceleration is relatively high. However, air intake can occur due to a combination of factors, such as the vehicle traveling downhill or experiencing high acceleration. Furthermore, even if the amount of oil is increased, there is an upper limit, so it may inevitably occur even if the oil temperature is somewhat high. In other words, even if countermeasures such as those described in Patent Document 1 are taken, air intake may occur even when the oil temperature is close to the normal operating range due to a combination of the factors mentioned above. When air intake occurs, insufficient oil pressure may prevent the predetermined engagement mechanism from engaging, potentially causing the engine speed to increase, or the oil pressure, once lowered, to return to its original pressure, potentially leading to unintended engagement of the engagement mechanism. This could result in unintended vehicle behavior, such as a decrease in acceleration or shock.

[0005] This invention has been made in view of the above-mentioned technical problems, and aims to provide a vehicle control device that can suppress unintended behavior in the vehicle even if air is sucked in through the oil intake. [Means for solving the problem]

[0006] To achieve the above objective, the present invention provides a vehicle control device comprising: an internal combustion engine; drive wheels; an oil pump for drawing up oil accumulated in an oil pan; a plurality of engagement mechanisms that can selectively engage by adjusting the hydraulic pressure discharged by the oil pump to a predetermined source pressure and supplying an engagement pressure adjusted to the source pressure; and an automatic transmission connected between the internal combustion engine and the drive wheels, which can selectively set a plurality of gears by engaging or disengaging the plurality of engagement mechanisms, wherein the plurality of engagement mechanisms are supplied with a control device. oilThe system includes a pressure control controller, which determines whether predetermined conditions are met for determining whether there is a high probability of air being drawn in when the oil pump draws the oil from the oil pan, and if the predetermined conditions are met, , place A predetermined engagement mechanism for setting a fixed gear ratio A component that supplies torque to the predetermined engagement mechanism. The feature is that the upper limit of the combined pressure is set to a value smaller than that when the predetermined conditions are not met, and also smaller than the source pressure.

[0007] Furthermore, in the present invention, the plurality of engagement mechanisms are configured to continuously change the transmission torque capacity, and the upper limit of the engagement pressure is determined by multiplying the initial pressure supplied to the predetermined engagement mechanism by a predetermined coefficient, and the predetermined coefficient may be set to a value that can maintain the transmission torque capacity in the predetermined engagement mechanism when the engagement pressure supplied to the predetermined engagement mechanism is the initial pressure and when the engagement pressure is the upper limit.

[0008] Furthermore, in the present invention, the controller may be configured to calculate a value obtained by multiplying the lower limit of the engagement pressure that can maintain the transmission torque capacity when the engagement pressure supplied to the predetermined engagement mechanism is the source pressure by a predetermined safety factor, and to set the upper limit of the engagement pressure to be equal to or greater than the calculated value.

[0009] Furthermore, the present invention may further include a torque converter provided between the output shaft of the internal combustion engine and the input shaft of the automatic transmission, wherein the predetermined condition includes the condition that the output torque of the torque converter is equal to or greater than a predetermined threshold.

[0010] Furthermore, in the present invention, the predetermined conditions may be configured to include the setting that the gear with the largest gear ratio among the multiple gears in the forward gears is set as the target gear. [Effects of the Invention]

[0011] The vehicle control device of the present invention is equipped with an automatic transmission capable of setting multiple gears by generating hydraulic pressure by drawing up oil accumulated in the oil pan with an oil pump, regulating that hydraulic pressure to a predetermined source pressure, and engaging or disengaging multiple engagement mechanisms with the engagement pressure regulated from that source pressure. The vehicle control device determines whether predetermined conditions are met to determine whether there is a high probability of air being drawn in, so-called air intake, when drawing oil from the oil pan to set a predetermined gear. If the predetermined conditions are met, the upper limit of the engagement pressure supplied to engage the predetermined engagement mechanism for setting the predetermined gear is set to a value lower than when the predetermined conditions are not met, and also lower than the source pressure. In other words, the vehicle control device of the present invention is configured to lower the engagement pressure supplied to the predetermined engagement mechanism below the source pressure when there is a high probability of air intake. Therefore, even if air intake occurs and the supplied hydraulic pressure temporarily decreases, it is possible to prevent or suppress situations such as the valve provided to supply engagement pressure to the predetermined engagement mechanism failing to switch. Therefore, it is possible to prevent or suppress situations such as the engine speed increasing or the inability to set the target gear due to such circumstances.

[0012] Furthermore, the upper limit of the engagement pressure supplied to a predetermined engagement mechanism is determined by multiplying the initial pressure by a predetermined coefficient. This predetermined coefficient is set to a value that maintains the transmission torque capacity of the predetermined engagement mechanism, both when the engagement pressure supplied to the predetermined engagement mechanism is the initial pressure and when the engagement pressure is at the upper limit. Therefore, even if the engagement pressure supplied to the predetermined engagement mechanism decreases from the initial pressure to the upper limit hydraulic pressure, the transmission torque capacity of the predetermined engagement mechanism is maintained, allowing the vehicle to run with the desired gear appropriately set.

[0013] Furthermore, when setting the upper limit of the engagement pressure supplied to a predetermined engagement mechanism, the lower limit is set to a value obtained by multiplying the lower limit of the hydraulic pressure that can maintain the transmission torque capacity when the engagement pressure is the initial pressure by a predetermined safety factor. Therefore, even if the engagement pressure that can be supplied to the predetermined engagement mechanism is significantly reduced due to air intake, the upper limit is lowered accordingly, thereby preventing or suppressing situations where the transmission torque capacity in the predetermined engagement mechanism decreases and it becomes impossible to set the predetermined gear. Also, since air intake occurs for a relatively short time, even if a lower limit is set for the upper limit, the engagement pressure supplied to the predetermined engagement mechanism is reduced, so it is possible to suppress situations such as deterioration of vehicle behavior compared to when no upper limit is set.

[0014] Furthermore, the system is configured to set an upper limit for the engagement pressure supplied to a predetermined engagement mechanism when the output torque of the torque converter is above a predetermined threshold. In addition, if the gear with the largest gear ratio among the multiple gears is set as the target gear, the system is configured to set an upper limit for the engagement pressure supplied to the predetermined engagement mechanism described above. When the output torque of the torque converter is above a predetermined threshold or when the gear with the largest gear ratio among the forward gears is set as the target gear, the vehicle's acceleration increases or is likely to increase, and there is a high possibility of air intake. By setting an upper limit for the engagement pressure in such cases, it is possible to prevent or suppress engine over-revving due to air intake. [Brief explanation of the drawing]

[0015] [Figure 1] This is a skeleton diagram illustrating an example of a vehicle equipped with a control device for an automatic transmission according to an embodiment of the present invention. [Figure 2] This is a block diagram illustrating an example of a controller. [Figure 3]It is a flowchart for explaining an example of control executed by a control device for an automatic transmission in an embodiment of the present invention. [Figure 4] It is a time chart for explaining changes over time in the commanded pressure of the first clutch, the commanded pressure of the line pressure, the actual oil pressure of the first clutch, and the turbine torque when the control shown in FIG. 2 is executed. [Figure 5] It is an explanatory diagram for explaining the upper limit value of the engagement pressure in a predetermined engagement mechanism. [Figure 6] It is an explanatory diagram for explaining the lower limit value of the line pressure when setting the upper limit value of the engagement pressure in a predetermined engagement mechanism.

Mode for Carrying Out the Invention

[0016] Hereinafter, the present invention will be described based on the embodiments shown in the drawings. Note that the embodiments described below are merely examples when the present invention is embodied, and do not limit the present invention.

[0017] An example of a vehicle Ve in an embodiment of the present invention will be described with reference to FIG. 1. The vehicle Ve shown in FIG. 1 includes an engine (Eng) 1 corresponding to the “internal combustion engine” in the embodiment of this invention, and an automatic transmission 2 provided between the engine 1 and drive wheels (not shown) and capable of setting a plurality of gear ratios, which are input rotation speeds with respect to the output rotation speed, by engaging or disengaging each of a plurality of engagement mechanisms, and are arranged side by side on the rotation center axis of the engine 1.

[0018] The engine 1 can be configured in the same manner as a conventionally known gasoline engine, diesel engine, or the like. That is, it is configured to output drive torque by burning a mixture of supplied fuel and air, and also to output braking torque corresponding to friction torque, pumping loss, etc. by stopping the combustion of the mixture.

[0019] A torque converter 4 is connected to the output shaft 3 of the engine 1. This torque converter 4 is configured in the same manner as a conventional torque converter. That is, the torque converter 4 is composed of a pump impeller 5 connected to the engine 1, a turbine runner 6 arranged opposite to the pump impeller 5, and a stator 9 arranged between the pump impeller 5 and the turbine runner 6 and connected to the case 8 via a one-way clutch 7.

[0020] Further, the torque converter 4 is provided with a lock-up clutch 10 for transmitting the output of the engine 1 to the automatic transmission 2 without amplifying it by the torque converter. The lock-up clutch 10 is configured to be able to engage the output shaft 3 of the engine 1 and the turbine runner 6. This lock-up clutch 10 can be configured in the same manner as a conventional lock-up clutch. That is, the lock-up clutch 10 is configured to be able to appropriately change the rotational speed difference between the engine 1 and the turbine runner 6.

[0021] The input shaft 12 of the stepped automatic transmission 2 is connected to the output shaft 11 of the above-described turbine runner 6. The automatic transmission 2 shown in FIG. 1 is configured to be able to set transmission stages from the first forward gear stage to the eighth forward gear stage in addition to the reverse and neutral positions. Specifically, the automatic transmission 2 is composed of a double pinion type planetary gear mechanism 13, a Ravigneaux type planetary gear mechanism 14, four clutch mechanisms C1, C2, C3, C4 which are hydraulic friction engagement devices as the above-described plurality of engagement mechanisms, and two brake mechanisms B1, B2.

[0022] The double-pinion type planetary gear mechanism 13 is positioned on the rotational axis opposite the engine 1, with the torque converter 4 in between. It consists of a sun gear 15 fixed to the case 8, a ring gear 16 arranged concentrically with the sun gear 15, an inner pinion gear 17 that meshes with the sun gear 15, an outer pinion gear 18 that meshes with the inner pinion gear 17 and the ring gear 16, and a carrier 19 that holds the inner pinion gear 17 and the outer pinion gear 18 so that they can rotate and revolve. The input shaft 12 of the automatic transmission 2 is connected to the carrier 19. In other words, it is configured so that the torque of the engine 1 is transmitted to the carrier 19.

[0023] The Ravigno-type planetary gear mechanism 14 is positioned on the opposite side of the torque converter 4 from the double-pinion-type planetary gear mechanism 13, and consists of a relatively large-diameter first sun gear 20, a second sun gear 21 positioned next to the first sun gear 20 and smaller in diameter than the first sun gear 20, a ring gear 22 positioned concentrically with the first sun gear 20, a short pinion gear 23 that meshes with the second sun gear 21, a long pinion gear 24 that meshes with the short pinion gear 23, the first sun gear 20, and the ring gear 22, and a carrier 25 that holds the short pinion gear 23 and the long pinion gear 24 so that they can rotate and revolve. An output gear 26 that meshes with an output member such as a differential unit (not shown) is connected to the ring gear 22.

[0024] The first clutch mechanism C1 is configured to selectively connect the ring gear 16 and the second sun gear 21. The second clutch mechanism C2 is configured to selectively connect the input shaft 12 and the carrier 25. The third clutch mechanism C3 is configured to selectively connect the ring gear 16 and the first sun gear 20. The fourth clutch mechanism C4 is configured to selectively connect the carrier 19 and the first sun gear 20. The first brake mechanism B1 is configured to selectively fix the first sun gear 20. The second brake mechanism B2 is configured to selectively fix the carrier 25. The automatic transmission 2 is configured to set one of the above-described gear stages by selectively engaging these engagement mechanisms. In the following description, when describing any of the clutch mechanisms C1, C2, C3, C4 and brake mechanisms B1, B2, they may simply be referred to as engagement mechanisms.

[0025] Each of the forward gears, from the first to the eighth, is set by controlling the engagement and disengagement states of the engagement mechanism. The engagement and disengagement states of each gear and each clutch mechanism C1, C2, C3, C4 and each brake mechanism B1, B2 are shown in Table 1 below. In Table 1, the symbol "○" indicates the engaged state, and a blank space indicates the disengaged state. Note that the reverse gear and neutral are not shown in Table 1. [Table 1]

[0026] As shown in Table 1, each forward gear is set by the engagement of either the first clutch mechanism C1 or the second clutch mechanism C2 with either the third clutch mechanism C3, the fourth clutch mechanism C4, or the respective brake mechanisms B1 and B2.

[0027] Specifically, the first forward gear is set by engaging the first clutch mechanism C1 and the second brake mechanism B2. The second forward gear is set by engaging the first clutch mechanism C1 and the first brake mechanism B1. The third forward gear is set by engaging the first clutch mechanism C1 and the third clutch mechanism C3. The fourth forward gear is set by engaging the first clutch mechanism C1 and the fourth clutch mechanism C4. The fifth forward gear is set by engaging the first clutch mechanism C1 and the second clutch mechanism C2. The sixth forward gear is set by engaging the second clutch mechanism C2 and the fourth clutch mechanism C4. The seventh forward gear is set by engaging the second clutch mechanism C2 and the third clutch mechanism C3. The eighth forward gear is set by engaging the second clutch mechanism C2 and the first brake mechanism B1.

[0028] Therefore, when shifting gears between the first and fifth forward gears, the engagement of the commonly engaged first clutch mechanism C1 is maintained, and the transmission torque capacity of either the clutch mechanisms C3, C4 or the brake mechanisms B1, B2 is reduced while the transmission torque capacity of the other is gradually increased. Similarly, when shifting gears between the fifth and eighth forward gears, the engagement of the commonly engaged second clutch mechanism C2 is maintained, and the transmission torque capacity of either the clutch mechanisms C3, C4 or the brake mechanisms B1, B2 is reduced while the transmission torque capacity of the other is gradually increased. In other words, it is configured to shift gears using clutch-to-clutch control, similar to a conventional stepped automatic transmission 2.

[0029] Such gear shift control is similar to conventionally known gear shift control, where a gear shift map is prepared in advance, defining the range of each gear step according to the accelerator opening and vehicle speed. When the accelerator opening and vehicle speed change across the lines (gear shift lines) that define each range, a gear shift is executed. Therefore, the target gear step is determined by the required driving force such as the accelerator opening and the vehicle speed or the rotational speed of the corresponding rotating member, and each clutch mechanism C1, C2, C3, C4 and each brake mechanism B1, B2 are engaged and disengaged to set that target gear step. This gear shift control is not limited to changing gear steps one step at a time, but can also perform so-called skip gear shifts to gear steps two or more steps apart, and so-called multi-gear shifts, where the target gear step is set via intermediate gear steps during skip gear shifts.

[0030] Furthermore, each clutch mechanism C1, C2, C3, C4 and each brake mechanism B1, B2 are composed of a hydraulic engagement mechanism. In other words, each clutch mechanism C1, C2, C3, C4 and each brake mechanism B1, B2 are configured to change the torque capacity transmitted by switching between engagement and disengagement by controlling the hydraulic pressure.

[0031] The control of engaging and disengaging each of the clutch mechanisms C1, C2, C3, C4 and each of the brake mechanisms B1, B2 is performed by a conventionally known hydraulic control device 27. The hydraulic control device 27, although not shown in the figures, has a valve body with multiple oil passages, multiple regulator valves, multiple linear solenoid valves, etc., and regulates the hydraulic pressure from the oil pump to supply engagement pressure to each of the clutch mechanisms C1, C2, C3, C4 and each of the brake mechanisms B1, B2. An example of the hydraulic control device 27 is described below.

[0032] The hydraulic control device 27 uses a mechanical or electric oil pump to draw up oil from an oil pan located at the bottom of the automatic transmission 2, etc., via a strainer. The drawn-up oil is then regulated from the oil discharge pressure of the oil pump to the line pressure by a line pressure control valve such as a primary regulator valve. A linear solenoid valve is connected to the line pressure control valve, and this linear solenoid valve outputs a signal pressure based on the throttle opening of the engine 1, etc., using a constant hydraulic pressure, which is the modulator pressure, as the source pressure. The modulator pressure is output by the modulator valve when the line pressure exceeds a predetermined pressure, according to the biasing force of the spring.

[0033] The hydraulic control device 27 is equipped with a control valve to which the regulated line pressure, as described above, is supplied. When the line pressure is supplied to the control valve via the oil passage, the spool is actuated to one end in the axial direction against the elastic force of a spring installed inside. As the spool actsuated in this way, hydraulic pressure corresponding to the supplied line pressure is supplied to each solenoid valve provided in each of the clutch mechanisms C1, C2, C3, C4 and each of the brake mechanisms B1, B2. Conversely, when the supply of line pressure stops, the spool returns to its original position at the other end in the axial direction due to the elastic force of the spring. In this case, the supply of line pressure to each of the solenoid valves is cut off.

[0034] Furthermore, each of the clutch mechanisms C1, C2, C3, and C4, and each of the brake mechanisms B1 and B2, is equipped with a hydraulic actuator, and the hydraulic pressure regulated by each linear solenoid valve is supplied to each hydraulic actuator as the engagement pressure of the engagement mechanism. An orifice is provided in the oil passage that supplies hydraulic pressure to the linear solenoid valve of the first clutch mechanism C1. Since the first clutch mechanism C1 is engaged to form the first forward gear, when a so-called garage shift is performed, such as when parking, the orifice is configured to slow down the rate at which the hydraulic pressure drops from the solenoid valve corresponding to the first clutch mechanism C1, thereby suppressing a delay in the hydraulic response.

[0035] Figure 2 shows a block diagram illustrating the configuration of an electronic control unit (hereinafter simply referred to as ECU) 28 for controlling the engine 1, each clutch mechanism C1, C2, C3, C4, and each brake mechanism B1, B2. This ECU 28 corresponds to the "controller" in this embodiment of the invention and is mainly composed of a microcomputer. The ECU 28 receives data from various sensors mounted on the vehicle Ve and is configured to output command signals to the engine 1, each clutch mechanism C1, C2, C3, C4, each brake mechanism B1, B2, and hydraulic control unit 27 based on the input data and pre-stored maps and calculation formulas.

[0036] Figure 2 shows an example of data input to the ECU 28. Specifically, data such as vehicle speed, accelerator opening, rotational speed of the output shaft 3 of engine 1 (engine 1 rotational speed), output torque of engine 1, rotational speed of the output shaft 11 of torque converter 4 (i.e., input rotational speed of automatic transmission 2), output rotational speed which is the rotational speed of output gear 26, shift range selected by the shift lever, and the oil temperature that generates the engagement pressure for selectively engaging each clutch mechanism C1, C2, C3, C4 and each brake mechanism B1, B2 are input to the ECU 28. Based on the input data, the ECU controls the output of engine 1, the engagement or disengagement of each clutch mechanism C1, C2, C3, C4 and each brake mechanism B1, B2, and the amount of oil and hydraulic pressure supplied from the hydraulic control device 27 to the necessary parts.

[0037] In the control device of the automatic transmission 2 configured in this way, when setting the gear ratio in the automatic transmission 2 according to the driving conditions of the vehicle Ve, the target gear ratio is set by controlling the hydraulic pressure as described above. The hydraulic pressure required to perform such control is supplied to the necessary parts by drawing up oil that has dripped into the oil pan with an oil pump. Therefore, mainly when the oil temperature is lower than the oil temperature in the normal operating range, when the vehicle Ve is driving on an inclined road, or when the acceleration or deceleration of the vehicle Ve changes significantly, an imbalance may occur in the oil remaining in the oil pan. In such cases, the intake port of the oil pump may be exposed above the oil surface in the oil pan, and the oil pump may draw in air, a phenomenon known as air intake. When air intake occurs, the line pressure decreases, which may cause situations such as the control valve failing to switch, resulting in a temporary and rapid decrease in hydraulic pressure to a specific solenoid valve, making it impossible to engage the corresponding engagement mechanism.

[0038] To prevent such air intake, as mentioned above, it is conceivable to increase the amount of oil, change the position and orientation of the oil pump's intake port, or modify the shape of the oil pan. However, due to the structure of the vehicle Ve, such modifications are difficult, and even if the amount of oil is increased, air intake may still occur even when the oil temperature is close to the normal operating temperature, due to a combination of factors such as sudden acceleration on a steeply sloped road surface. Therefore, in this invention, when the line pressure drops, in order to suppress the shortage of oil to each clutch mechanism C1, C2, C3, C4 and each brake mechanism B1, B2 due to the drop in line pressure, the engagement pressure supplied to each clutch mechanism C1, C2, C3, C4 and each brake mechanism B1, B2 is set to be lower in advance when there is a high possibility of air intake. In other words, by keeping the required hydraulic pressure at the parts that supply hydraulic pressure lower than the line pressure, the invention is configured to suppress unintended behavior in the vehicle Ve even if air intake occurs.

[0039] Figure 3 shows a flowchart illustrating an example of such control. The flowchart shown in Figure 3 is executed by appropriate components in the ECU28. The flowchart shown in Figure 3 is a control that determines the upper limit of the hydraulic pressure described above when air intake may occur, based on the current state of the vehicle Ve and the target vehicle state, when the vehicle Ve starts moving.

[0040] In step S1, it is determined that the vehicle Ve is in a steady state. In other words, in step S1, it is determined whether or not a gear change is being performed on the vehicle Ve, and whether or not a gear change is being attempted. For example, even if the vehicle Ve is stopped, it is determined in step S1 that it is in a steady state. If it is determined that the vehicle Ve is not in a steady state, in step S1... negative If the result is negative, this flowchart will be terminated without executing any further controls.

[0041] Conversely, if it is determined that the vehicle Ve is in a steady state because it is not performing a gear change, the determination in step S1 is positive and the process proceeds to step S2. If the process proceeds to step S2, it is determined that the shift range is set to the drive range. In step S2, the shift range is determined based on the operating state of the manual valve that switches between shift ranges such as drive, reverse, and neutral in accordance with the position of the shift lever mounted on the vehicle Ve. If it is determined negative in step S2 because a shift range other than the drive range, such as reverse or neutral, has been selected as the shift range, this flowchart is terminated without executing any further control.

[0042] Conversely, if the drive range is selected as the shift range and a positive determination is made in step S2, the process proceeds to step S3, where the gear position is determined. In step S3, it is determined that the target gear position for the vehicle Ve is a predetermined gear position. The predetermined gear position is a gear position that results in a relatively large acceleration for the vehicle Ve, such as the first forward gear. Alternatively, the gear position may be set according to the engagement mechanism, such as the structure of the hydraulic control device 27, which is prone to situations where engagement becomes impossible when the line pressure drops.

[0043] For example, in the control valve described above, due to its structure, an oil pressure equivalent to the line pressure supplied to a predetermined linear solenoid valve may be supplied to a port other than the port to which the line pressure is supplied, and the oil passage from the primary regulator valve to the other port may be relatively long. In such cases, if the line pressure drops due to air intake, this drop in line pressure may not be immediately reflected in the other port, and the oil pressure supplied to the other port may temporarily exceed the line pressure. As a result, the spool is more likely to move unintentionally compared to other valves, and the control valve may fail to switch, or in other words, it may fail.

[0044] Thus, there may be engagement mechanisms that are structurally prone to failure. In such cases, the system may be configured to set the gear shift that engages with that engagement mechanism as a predetermined gear shift. If a negative result is determined in step S3 because no such predetermined gear shift is set as the target gear shift, this flowchart is terminated without executing the subsequent control steps.

[0045] Conversely, if a predetermined gear is set as the target gear, and the result is positive in step S3, the process proceeds to step S4, where the turbine torque determination is performed. In step S4, it is determined whether the turbine torque is above a predetermined threshold. The turbine torque is calculated, for example, by multiplying the output torque of engine 1 by the torque ratio of the torque converter. The predetermined threshold is set to a turbine torque that may cause air intake due to the acceleration of vehicle Ve, based on the amount of oil, the characteristics of the oil, the structure of the oil pan, etc. Alternatively, it is determined in advance based on the results of experiments or simulations. If the result is negative in step S4 because the turbine torque is below the predetermined threshold, this flowchart is terminated without performing any further control.

[0046] Conversely, if the turbine torque is above a predetermined threshold and a positive result is determined in step S4, the process proceeds to step S5, where it is determined that the oil temperature is within a predetermined range. The upper limit of the oil temperature within the predetermined range is set to an oil temperature at which air intake does not occur or is unlikely to occur, depending on the amount of oil, the characteristics of the oil, the structure of the oil pan, etc., as described above.

[0047] Furthermore, the lower limit of the oil temperature within a predetermined range may be set in consideration of other measures to prevent air intake. As mentioned above, structures and controls to prevent air intake when the oil temperature is extremely low may already be implemented. If such measures are in place, there is no need to perform the air intake control described later, so the lower limit of the oil temperature within the predetermined range is set to an oil temperature that falls outside the scope of those measures. Note that the upper and lower limits of the oil temperature within such predetermined ranges are determined in advance based on the results of experiments or simulations. If the oil temperature is outside the predetermined range and a negative result is determined in step S5, this flowchart is terminated without performing any further control.

[0048] Conversely, if the oil temperature is within a predetermined range and a positive result is determined in step S5, the process proceeds to step S6, where air intake prevention control is performed. In step S6, the engagement pressure required to engage each clutch mechanism C1, C2, C3, C4 and each brake mechanism B1, B2 in order to set the predetermined gear ratio described above is set to the upper limit, which is the maximum value of the available hydraulic pressure, i.e., a value smaller than the line pressure, which is the source pressure.

[0049] Normally, when engaging each engagement mechanism, the control system is configured to supply the line pressure, which is the maximum hydraulic pressure that can be supplied to each engagement mechanism. In other words, a hydraulic pressure greater than the hydraulic pressure required to secure the transmission torque capacity of each engagement mechanism is generated in each hydraulic actuator of each engagement mechanism. In step S6, the upper limit of the engagement pressure supplied to each engagement mechanism is configured to be a smaller value than the value when the conditions of steps S1 to S5 described above are not met, that is, a value smaller than the line pressure.

[0050] Specifically, in step S6, the line pressure, which is the maximum hydraulic pressure that can be applied to each engagement mechanism, is multiplied by a predetermined coefficient greater than 0 and less than 1. This predetermined coefficient is set to a value such that, even when each engagement mechanism is engaged by an engagement pressure based on the upper limit, a transmission torque capacity similar to that when line pressure is supplied to each engagement mechanism can be maintained. In step S6, the instruction hydraulic pressure to each engagement mechanism is controlled based on the upper limit of the engagement pressure of each engagement mechanism determined in this way.

[0051] The air intake prevention control in step S6 will be explained in detail based on the time chart shown in Figure 4. In Figure 4, the case where the first forward gear is set is explained, and the first clutch mechanism C1 is assumed to be a predetermined engagement mechanism corresponding to the predetermined linear solenoid valve described above. First, at time t0, the drive range is selected by the driver as the shift range, and the first forward gear is set as the target gear. In addition, the output torque of engine 1 increases according to the vehicle speed and accelerator opening, and the turbine torque increases accordingly.

[0052] When the first forward gear is set, the instruction hydraulic pressure to the first clutch mechanism C1 is set to its maximum value, and at time t1, the line pressure is increased in accordance with the turbine torque, i.e., the input torque to the first clutch mechanism C1. At time t1, the line pressure outputs hydraulic pressure that produces an engagement pressure in the first clutch mechanism C1 that does not cause slippage, in accordance with the turbine torque. Subsequently, at time t2, the hydraulic pressure actually supplied to the hydraulic actuator of the first clutch mechanism C1 is increased to a hydraulic pressure corresponding to the line pressure. Therefore, at time t2, the transmission torque capacity of the first clutch mechanism C1 increases, and consequently, the rate of increase in turbine torque decreases.

[0053] Subsequently, as the output torque of engine 1 increases, the turbine torque increases, and at time t3, when the turbine torque exceeds a predetermined threshold, control to increase the transmission torque capacity of the first clutch mechanism C1 is initiated, along with control to prevent air intake. Specifically, at time t3, as the turbine torque increases, the line pressure is increased in the first clutch mechanism C1 to raise the engagement pressure and prevent slippage, while the instruction hydraulic pressure to the first clutch mechanism C1 is reduced. In other words, when the turbine torque exceeds a predetermined threshold, the vehicle's acceleration increases, which may cause air intake. Therefore, by setting the line pressure higher than the actual hydraulic pressure of the first clutch mechanism C1, control is implemented to suppress control valve failure even if air intake occurs.

[0054] Specifically, the upper limit of the hydraulic pressure directed to the first clutch mechanism C1 is set to a value obtained by multiplying the line pressure by a predetermined coefficient, as described above. Furthermore, the lower limit of the line pressure when setting the hydraulic pressure directed to the first clutch mechanism C1 to such an upper limit is, for example, the value obtained by multiplying the minimum value at which slippage does not occur in the first clutch mechanism C1 when turbine torque is input by a predetermined safety factor. Such upper limits of engagement pressure and the lower limits of line pressure when setting those upper limits are determined in advance based on the results of experiments and simulations, and are shown in Figures 5 and 6, respectively.

[0055] Figure 5 shows the results of a trial to determine whether a so-called failure occurs in the control valve when air intake occurs due to the fulfillment of the conditions in steps S1 to S5. In Figure 5, the vertical axis represents the magnitude of the hydraulic pressure supplied to the hydraulic actuator of the first clutch mechanism C1, and the horizontal axis represents the line pressure (PL pressure). The dashed line in Figure 5 shows the case where the hydraulic pressure supplied to the first clutch mechanism C1 is the line pressure. As shown in Figure 5, when the hydraulic pressure supplied to the first clutch mechanism C1 is the line pressure, a failure occurs in the control valve regardless of the magnitude of the engagement pressure. Therefore, by gradually reducing the engagement pressure supplied to the first clutch mechanism C1, a failure no longer occurs in the control valve even if air intake occurs, beyond the position of the solid line shown in Figure 5. Accordingly, the relationship between the engagement pressure supplied to the first clutch mechanism C1 and the line pressure that satisfies that position of the solid line is defined as a predetermined coefficient. As shown in Figure 5, if the value multiplied by the line pressure is less than or equal to the predetermined coefficient, a failure will not occur in the control valve.

[0056] Figure 6 shows the relationship between the lower limit of the line pressure when setting the upper limit of the engagement pressure of the first clutch mechanism C1, as described above, and the hydraulic pressure required for the first clutch mechanism C1 to secure the transmission torque capacity. As shown in Figure 6, the bottom solid line of the four solid lines is the experimental value of the minimum hydraulic pressure required to achieve the transmission torque capacity of the first clutch mechanism C1. The second solid line from the bottom of the four solid lines in Figure 6 is the measured value of the minimum hydraulic pressure required to achieve the transmission torque capacity of the first clutch mechanism C1. The second solid line from the top of the four solid lines in Figure 6 is the value obtained by multiplying the measured value of the minimum hydraulic pressure required to achieve the transmission torque capacity of the first clutch mechanism C1 by a predetermined safety factor to ensure the transmission torque capacity is reliably secured. The top solid line of the four solid lines in Figure 6 is the value obtained by multiplying the measured value of the minimum hydraulic pressure required to secure the transmission torque capacity of the first clutch mechanism C1 by a predetermined safety factor and the reciprocal of a predetermined coefficient for setting the upper limit of the engagement pressure.

[0057] In other words, the uppermost solid line in Figure 6 represents the lower limit of the line pressure when setting the upper limit of the engagement pressure of the first clutch mechanism C1 described above. If the line pressure falls below this lower limit, the upper limit of the engagement pressure of the first clutch mechanism C1 will not be reduced any further. In other words, the lower limit when setting the upper limit of the engagement pressure of the first clutch mechanism C1 is set to be equal to or greater than the value shown by the second solid line from the top in Figure 6. That is, the upper limit of the engagement pressure is set to be equal to or greater than the value obtained by multiplying the lower limit of the engagement pressure that allows the first clutch mechanism C1 to maintain its transmission torque capacity by a predetermined safety factor. Therefore, even if the line pressure falls below the lower limit, the hydraulic pressure is controlled to maintain the engagement pressure necessary to secure the transmission torque capacity of the first clutch mechanism C1. Thus, by setting an upper limit of the engagement pressure, it is possible to prevent or suppress insufficient engagement pressure in the first clutch mechanism C1.

[0058] Subsequently, at time t4, the line pressure is increased to increase the hydraulic pressure supplied to the first clutch mechanism C1 in accordance with the increase in turbine torque. Then, at time t5, the turbine torque decreases due to factors such as the shifting of gears and reaching the target vehicle speed, and consequently, the instruction hydraulic pressure and line pressure of the first engagement mechanism decrease. Finally, at time t6, the air intake prevention control ends because the turbine torque has fallen below a predetermined threshold, so the restriction on the hydraulic pressure supplied to the first clutch mechanism C1 is removed, and the instruction hydraulic pressure of the first clutch mechanism C1 is set to its maximum value.

[0059] According to the control device for vehicle Ve in an embodiment of the present invention, when a predetermined gear ratio is set among the forward gears and certain conditions are met, such as the turbine torque being above a predetermined threshold, air intake countermeasure control is executed. In the air intake countermeasure control, the hydraulic pressure supplied to each engagement mechanism is reduced to a range in which slip does not occur, that is, a range in which the transmission torque capacity can be maintained. Therefore, even if air intake occurs in the oil pump and the line pressure drops, the reduction in hydraulic pressure supplied to the control valve and the like as described above is less likely to occur. Therefore, fluctuations in hydraulic pressure linked to the drop in line pressure in each engagement mechanism can be suppressed, and the occurrence of failures in the control valve can be suppressed. Consequently, it is possible to prevent or suppress unintended behavior in vehicle Ve, such as the inability to form the target gear ratio due to the inability of a predetermined engagement mechanism to engage, or the occurrence of shocks in vehicle Ve due to large fluctuations in the transmission torque capacity of the engagement mechanism. Furthermore, with such a configuration, the effects of air intake can be mitigated regardless of the oil temperature, so even if the oil temperature is close to the normal operating temperature, it is possible to suppress unintended behavior in vehicle Ve due to air intake.

[0060] Although embodiments of the present invention have been described above, the present invention is not limited to the examples described above, and may be modified as appropriate to achieve the objectives of the present invention. For example, in the control described above, the air intake prevention control is performed when the first forward gear is set, but depending on the structure of the hydraulic control device 27, it may be configured to be performed when the reverse gear is set. Even in that case, it may be configured to determine whether or not to perform the air intake prevention control based on the magnitude of the turbine torque, the oil temperature, etc. [Explanation of Symbols]

[0061] 1 Engine 2 Automatic transmission 4 Torque converter 5. Pump Impeller 6 Turbine Runners 7 One-way clutch 9 stata 27 Hydraulic control device 28 ECU B1, B2 Brake Mechanism C1, C2, C3, C4 Clutch Mechanism Vehicle

Claims

1. A vehicle control device comprising: an internal combustion engine; drive wheels; an oil pump for drawing up oil accumulated in an oil pan; a plurality of engagement mechanisms that can selectively engage by adjusting the hydraulic pressure discharged by the oil pump to a predetermined source pressure and supplying an engagement pressure adjusted to the source pressure; and an automatic transmission connected between the internal combustion engine and the drive wheels, which can selectively set a plurality of gears by engaging or disengaging the plurality of engagement mechanisms, The system includes a controller that controls the hydraulic pressure supplied to the plurality of engagement mechanisms, The aforementioned controller, When the oil pump draws up the oil from the oil pan, it is determined whether or not predetermined conditions are met to determine if there is a high probability of air being drawn in. When the predetermined conditions are met, the upper limit of the engagement pressure supplied to the predetermined engagement mechanism that sets the predetermined gear ratio and transmits torque to the predetermined engagement mechanism is set to be smaller than when the predetermined conditions are not met, and also to a value smaller than the original pressure. A vehicle control device characterized by the following features.

2. A vehicle control device according to claim 1, The aforementioned multiple engagement mechanisms are configured to allow for continuous changes in the transmission torque capacity. The upper limit of the engagement pressure is determined by multiplying the initial pressure supplied to the predetermined engagement mechanism by a predetermined coefficient. The predetermined coefficient is set to a value that can maintain the transmission torque capacity in the predetermined engagement mechanism, whether the engagement pressure supplied to the predetermined engagement mechanism is the initial pressure or the upper limit value. A vehicle control device characterized by the following features.

3. A vehicle control device according to claim 2, The aforementioned controller, A value is calculated by multiplying the lower limit of the engagement pressure that can maintain the transmission torque capacity when the engagement pressure supplied to the predetermined engagement mechanism is the original pressure by a predetermined safety factor. The upper limit of the engagement pressure is set to be equal to or greater than the calculated value. A vehicle control device characterized by the following features.

4. A vehicle control device according to any one of claims 1 to 3, The system further comprises a torque converter provided between the output shaft of the internal combustion engine and the input shaft of the automatic transmission, The predetermined conditions include the output torque of the torque converter being equal to or greater than a predetermined threshold. A vehicle control device characterized by the following features.

5. A vehicle control device according to any one of claims 1 to 3, The aforementioned predetermined conditions include the fact that the gear with the largest gear ratio among the multiple gears in the forward gears is set as the target gear. A vehicle control device characterized by the following features.

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