Vehicle control device

Abstract

To provide a vehicle control device suppressing vibrations of a vehicle.SOLUTION: A vehicle control device has an engine, a transmission that can selectively establish a plurality of gear stages with different transmission ratios, and a torque converter with a lock-up clutch that transmits the torque of the engine to the transmission. The vehicle control device includes: a condition determining portion that determines whether or not a condition is satisfied, the condition including the matters that the lock-up clutch is in an engagement state, a predetermined gear stage is established in the transmission, and an operation point decided according to engine speed and a load belongs to a predetermined area; a resonance determining portion whether or not the engine and the transmission resonate, when the condition determining portion made affirmative determination, and a control portion that controls the lock-up clutch to be in a slip state, when the resonance determining portion made affirmative determination.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a vehicle control device. [Background technology]

[0002] There is known a vehicle that includes an engine, a transmission that can selectively establish multiple gears with different gear ratios, and a torque converter with a lock-up clutch that transmits engine torque to the transmission (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6579053 Summary of the Invention [Problem to be solved by the invention]

[0004] In such vehicles, torque fluctuations in the engine may cause resonance between the engine and the transmission, which may cause the vehicle to vibrate under certain conditions.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a vehicle control device that suppresses vibrations of the vehicle. [Means for solving the problem]

[0006] The object is to provide a control device for a vehicle having an engine, a transmission capable of selectively establishing a plurality of gear stages with different gear ratios, and a torque converter with a lock-up clutch that transmits torque of the engine to the transmission, the control device comprising: a condition determination unit that determines whether or not conditions are established, including that the lock-up clutch is in an engaged state, that a predetermined gear stage is established in the transmission, and that an operating point determined according to the engine speed and load belongs to a predetermined region; a resonance determination unit that determines whether or not the engine and the transmission have resonated, if the condition determination unit makes a positive determination; and a control unit that controls the lock-up clutch to a slip state, if the resonance determination unit makes a positive determination. The control unit maintains the lock-up clutch in a slip state for a longer period of time as the gear stage established in the transmission among the predetermined gear stages becomes lower. This can be achieved by the vehicle's control device.

[0008] The object is to provide a control device for a vehicle having an engine, a transmission capable of selectively establishing a plurality of gear stages with different gear ratios, and a torque converter with a lock-up clutch that transmits torque of the engine to the transmission, the control device comprising: a condition determination unit that determines whether or not conditions are established, including that the lock-up clutch is in an engaged state, that a predetermined gear stage is established in the transmission, and that an operating point determined according to the engine speed and load belongs to a predetermined region; a resonance determination unit that determines whether or not the engine and the transmission have resonated, if the condition determination unit makes a positive determination; and a control unit that controls the lock-up clutch to a slip state, if the resonance determination unit makes a positive determination, the condition determination unit determines whether or not the predetermined region is reached, On the low load side of the engine By extension, this can also be achieved by the vehicle's control device.

[0009] The transmission may be capable of selectively establishing three or more gear stages with different reduction ratios, and the condition determination unit may exclude a lowest gear stage and a highest gear stage from the predetermined gear stages.

[0010] The condition determination unit may limit the predetermined region to a high load region equal to or greater than half of the maximum load of the engine.

[0011] The condition determining unit may include, as one of the conditions, that an accelerator opening degree is greater than a predetermined opening degree.

[0012] The condition determination unit may include, as one of the conditions, that the vehicle speed is equal to or less than a predetermined speed.

[0013] The resonance determination unit may determine whether or not resonance has occurred in the transmission based on the rotation speed of a crankshaft of the engine and the rotation speed of an output shaft of the transmission. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a vehicle control device that suppresses vibrations of the vehicle. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram of a vehicle. [Figure 2] FIG. 2 is a timing chart showing an example of vibration suppression control. [Figure 3] FIG. 3 is a flowchart showing an example of vibration suppression control executed by the ECU. [Figure 4] FIG. 4 is a map showing the region of engine operating points where resonance occurs. [Figure 5] FIG. 5 is a graph showing the required slip time according to the gear position. DETAILED DESCRIPTION OF THE INVENTION

[0016] [Vehicle outline] 1 is a schematic diagram of a vehicle 1. The vehicle 1 includes an engine 10, a torque converter 20, a lock-up clutch (hereinafter referred to as an LU clutch) 30, a transmission 40, a differential device 50, drive wheels 60, a hydraulic control circuit 70, and an ECU (Electronic Control Unit) 80.

[0017] The engine 10 is a driving force source for traveling, and is typically a multi-cylinder gasoline engine, but is not limited to this and may be, for example, a diesel engine. A crankshaft 11, which is the output shaft of the engine 10, is connected to a torque converter 20.

[0018] The torque converter 20 includes a pump impeller 21 on the input shaft side, a turbine runner 22 on the output shaft side, a stator 23 that exhibits a torque amplification function, and a one-way clutch 24, and transmits power between the pump impeller 21 and the turbine runner 22 via a fluid. The torque converter 20 is provided with an LU clutch 30. The LU clutch 30 is a single-plate or multi-plate hydraulic friction clutch that connects the input side and output side of the torque converter 20 directly or in a slip state, but is not limited to this and may be an electromagnetic friction clutch.

[0019] The transmission 40 is a stepped automatic transmission and includes a plurality of hydraulic friction engagement elements and a planetary gear device. In the transmission 40, a plurality of gear stages can be selectively established by selectively engaging the plurality of friction engagement elements. As shown in FIG. 1 , an input shaft 41 of the transmission 40 is connected to the turbine shaft 26 of the torque converter 20. An output shaft 42 of the transmission 40 is connected to drive wheels 60 via a differential device 50 and the like.

[0020] The engagement and disengagement of multiple friction engagement elements are controlled depending on whether the shift range of the transmission 40 is a parking range, a reverse drive range, a neutral range, or a forward drive range. In the forward drive range, the engagement and disengagement of multiple friction engagement elements are controlled so that one of eight forward gears is selectively established depending on the accelerator pedal position, vehicle speed, etc. Of the eight forward gears, the lowest gear with the largest gear ratio is the first gear, and the highest gear with the smallest gear ratio is the eighth gear. The multiple friction engagement elements are specifically multiple clutches and multiple brakes. The transmission 40 is not limited to an automatic transmission and may be, for example, a manual transmission. While the gears that can be established by the transmission 40 are eight forward gears, this is not limiting, and any gear with different gear ratios may be established.

[0021] The hydraulic control circuit 70 is a known hydraulic control circuit that uses a mechanical oil pump driven by the engine 10 as a hydraulic pressure supply source, and supplies hydraulic pressure to the torque converter 20, the LU clutch 30, and the transmission 40 to control their respective operations. Furthermore, hydraulic pressure command values ​​output from the ECU 80 are input to the hydraulic control circuit 70, and the hydraulic pressures supplied to the torque converter 20, the LU clutch 30, and the transmission 40 are controlled based on the hydraulic pressure command values. Furthermore, the LU clutch 30 is switched between a released state, a slip state, and an engaged state depending on the hydraulic pressure supplied.

[0022] The ECU 80 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and a backup RAM. The ROM stores various control programs and maps referenced when executing the various control programs. The CPU executes calculations based on the various control programs and maps stored in the ROM. The RAM temporarily stores the results of calculations performed by the CPU and data input from the sensors, and the backup RAM is a non-volatile memory that stores data to be saved when the ignition is turned off, for example. The CPU, ROM, RAM, and backup RAM functionally implement a condition determination unit, a resonance determination unit, and a control unit, which will be described in detail later.

[0023] Various sensors and switches, such as an air flow meter 90, an engine rotation speed sensor 91, a turbine rotation speed sensor 92, an output shaft rotation speed sensor 93, an accelerator opening sensor 94, a vehicle speed sensor 95, a gear position sensor 96, and an ignition switch 97, are connected to the ECU 80, and signals from these sensors and switches are input to the ECU 80. The ECU 80 controls the operating state of the engine 10 and the gear position of the transmission 40 based on the detection results of the various sensors, etc.

[0024] The air flow meter 90 detects the amount of intake air of the engine 10. The engine speed sensor 91 detects the rotation speed of the crankshaft 11 (referred to as engine speed). The turbine speed sensor 92 detects the rotation speed of the turbine shaft 26 of the torque converter 20 (referred to as turbine speed). The output shaft rotation speed sensor 93 detects the rotation speed of the output shaft 42 of the transmission 40 (referred to as output shaft speed). The accelerator opening sensor 94 detects the accelerator opening operated by the accelerator pedal. The vehicle speed sensor 95 detects the traveling speed of the vehicle 1. The gear stage sensor 96 detects the gear stage established in the transmission 40. The ignition switch 97 detects whether the ignition is on or off.

[0025] When the LU clutch 30 is engaged, the crankshaft 11 of the engine 10 and the input shaft 41 of the transmission 40 are connected. In this state, if the frequency of torque fluctuations of the engine 10 matches the primary torsional natural frequency of the transmission 40, the engine 10 and the transmission 40 resonate with each other. Under certain conditions, such resonance may cause the vehicle 1 to vibrate. The ECU 80 executes vibration suppression control to suppress such vibrations of the vehicle 1.

[0026] [Vibration suppression control] Next, the vibration suppression control executed by the ECU 80 will be described. FIG. 2 is a timing chart showing an example of vibration suppression control. FIG. 2 shows the changes in the rotation speed difference [rpm], a resonance occurrence flag indicating the occurrence of resonance, a clutch request flag indicating the request state for the LU clutch 30, the engine rotation speed [rpm], the turbine rotation speed [rpm], and the vehicle G. The turbine rotation speed is indicated by a dotted line, and the others are indicated by solid lines. Note that, as will be described in detail later, the rotation speed difference is the difference between the engine rotation speed and the output shaft rotation speed converted to an equivalent of the engine rotation speed. Vehicle G indicates the acceleration of the vehicle 1 in the longitudinal direction. FIG. 2 shows the case where the vehicle 1 is accelerating with the LU clutch 30 in an engaged state and the engine rotation speed and the turbine rotation speed are the same.

[0027] At time t0, resonance occurs, increasing the amplitude of vehicle G. At time t1, when the rotation speed difference exceeds a threshold, the resonance occurrence flag is temporarily turned on and the clutch request flag is switched from the engaged state to the slip state. At time t2, a predetermined time lag after time t1, the LU clutch 30 is actually switched to the slip state, and the engine rotation speed increases relative to the turbine rotation speed. In other words, the torque transmission rate from the crankshaft 11 of the engine 10 to the turbine shaft 26 of the torque converter 20 decreases. This suppresses resonance between the engine 10 and the transmission 40, and vehicle G decreases. At time t3, when a slip request time (described later) has elapsed since time t1, the clutch request flag is switched from the slip state to the engaged state, and at time t4 the LU clutch 30 is actually engaged.

[0028] 3 is a flowchart showing an example of vibration suppression control executed by the ECU 80. This control is executed repeatedly at a predetermined cycle while the ignition is on. The ECU 80 determines whether or not a vibration generation condition that causes the vehicle 1 to vibrate due to resonance is met (step S1). The processing of step S1 is an example of processing executed by a condition determination unit.

[0029] The vibration generation conditions include the following conditions (A) to (E). (A) The LU clutch 30 is in an engaged state. (B) The transmission 40 is in a predetermined gear position. (C) The operating point determined according to the engine speed and engine load belongs to a predetermined region. (D) The accelerator opening is greater than the specified opening. (E) The vehicle speed is below a specified speed.

[0030] The reason why condition (A) is included in the vibration occurrence conditions is that when the LU clutch 30 is in an engaged state, torque fluctuations of the engine 10 are more likely to be transmitted to the transmission 40 than when the LU clutch 30 is in a slipping state or a disengaged state. Therefore, if resonance occurs, the vibration level increases, which may cause large vibrations in the vehicle 1. The ECU 80 references the clutch request flag to determine whether condition (A) is met.

[0031] The reason why condition (B) is included in the vibration occurrence conditions is that the impact of vibration on the vehicle 1 due to resonance is small in gears other than the predetermined gear. In this embodiment, the predetermined gear is a medium gear, i.e., fourth and fifth gears. This is because, in the low gears of first to third gears, the gears are shifted sequentially in a short time while the vehicle 1 is accelerating, and even if resonance occurs, the gear is shifted immediately, so the impact on the vehicle 1 is small. Also, in the high gears of sixth to eighth gears, the reduction ratio is small, so the difference between the engine rotation speed and the output shaft rotation speed is small, and the impact on the output shaft 42 due to torque fluctuations of the engine 10 is small. Furthermore, in the high gears of sixth to eighth gears, the vehicle speed is high, so the impact on the vehicle 1 is greater from vibration from the road surface than from resonance.

[0032] The ECU 80 determines whether or not condition (B) is satisfied based on the detection value of the gear sensor 96. Note that the predetermined gears in condition (B) are not limited to fourth and fifth gears, as long as the predetermined gears exclude at least first gear with the largest reduction ratio and eighth gear with the largest reduction ratio.

[0033] Condition (C) is included in the vibration occurrence conditions because the range of operating points of the engine 10 where resonance occurs is limited. Furthermore, the range of the operating point region of the engine 10 where resonance occurs varies depending on the gear. FIG. 4 is a map showing the operating point region of the engine 10 where resonance occurs. The horizontal axis represents engine speed [rpm], and the vertical axis represents engine load [N·m]. FIG. 4 also shows the power line PL, which indicates the maximum load on the engine 10. As shown in FIG. 4, when the gear is in fourth gear (4th), resonance occurs in the high load region surrounded by line L4 and the power line PL shown in FIG. 4. Similarly, when the gear is in fifth gear (5th), resonance occurs in the high load region surrounded by line L5 and the power line PL shown in FIG. 4. Here, the region where resonance occurs in fourth gear is expanded toward the low load side compared to the region where resonance occurs in fifth gear. This is because the fourth gear has a larger reduction ratio than the fifth gear, so the torque fluctuation of the engine 10 has a larger effect on the output shaft 42, and the vibration level of the resonance is also larger. As shown in Figure 4, when the engine 10 is rotating at high speed, the maximum load of the engine 10 is limited to a lower load side than the range where resonance occurs.

[0034] The ECU 80 determines whether or not the condition (C) is satisfied based on the engine load calculated based on the intake air amount detected by the air flow meter 90 and the detected value of the engine speed sensor 91. The predetermined region for the condition (C) is not limited to the region shown in Fig. 4, and may be any high load region where the engine load is half or more of the maximum load.

[0035] The predetermined opening degree in condition (D) is 0. That is, condition (D) requires that the accelerator opening degree is greater than 0 and the accelerator pedal is depressed. For example, if the accelerator opening degree becomes 0 while the vehicle 1 is traveling with the LU clutch 30 engaged, a fuel cut is executed and so-called deceleration flex control is executed, which controls the LU clutch 30 to a slip state. Because the engine load is decreasing due to the fuel cut and the execution of deceleration flex control causes the engine speed to fall below the turbine speed, even if resonance occurs, the impact on the vehicle 1 is small. Note that the ECU 80 determines whether or not condition (D) is satisfied based on the detection value of the accelerator opening degree sensor 94.

[0036] The predetermined vehicle speed in condition (E) is, for example, a high speed. That is, condition (E) requires that the vehicle speed is medium or low. As described above, when the vehicle speed is high, vibrations from the road surface have a greater effect on the vehicle 1 than resonance. The ECU 80 determines whether condition (E) is satisfied based on the detection value of the vehicle speed sensor 95.

[0037] If the result of step S1 is No, that is, if at least one of the conditions (A) to (E) is not satisfied, the control is terminated. If the result of step S1 is Yes, that is, if all of the conditions (A) to (E) are satisfied, the ECU 80 determines whether resonance has occurred (step S2). Specifically, the above determination is made as follows. The ECU 80 converts the output shaft rotation speed into an equivalent engine rotation speed by multiplying the output shaft rotation speed by the reduction ratio of the current gear of the transmission 40. Next, the ECU 80 calculates a rotation speed difference, which is the difference between the output shaft rotation speed converted into the equivalent engine rotation speed and the actual engine rotation speed, and determines whether the absolute value of this rotation speed difference is equal to or greater than a threshold. If the rotation speed difference is equal to or greater than the threshold, the determination of step S2 is Yes. If the rotation speed difference is less than the threshold, the determination of step S2 is No. The processing of step S2 is an example of processing executed by the resonance determination unit. If the result of step S2 is No, the control is terminated.

[0038] If the answer is Yes in step S2, the ECU 80 turns on the resonance occurrence flag and switches the clutch request flag from the engaged state to the slip state, thereby controlling the LU clutch 30 to the slip state (step S3). This reduces the torque transmission rate from the engine 10 to the transmission 40, thereby suppressing resonance. Therefore, vibration of the vehicle 1 is also suppressed. In this way, the LU clutch 30 is controlled to the slip state only when resonance occurs, assuming that the vibration occurrence conditions are met. Therefore, even when the effect on vibration of the vehicle 1 is small, it is possible to avoid switching the state of the LU clutch 30 and causing discomfort to the driver. The processing of step S3 is an example of processing executed by the control unit.

[0039] Next, the ECU 80 determines whether a predetermined slip request time has elapsed since the clutch request flag was switched to the slip state (step S4). The slip request time is set to a time sufficient for vibrations due to resonance occurring when the LU clutch 30 is engaged to attenuate while the LU clutch 30 is in a slip state. FIG. 5 is a graph showing the slip request time [s] according to the gear position. As shown in FIG. 5, the slip request time is longer for the fourth gear than for the fifth gear, so the fourth gear is maintained in a slip state longer than the fifth gear. This is because, as described above, the vibrations due to resonance occur more strongly in the fourth gear than in the fifth gear. If the determination in step S4 is No, the LU clutch 30 is maintained in a slip state.

[0040] If the answer is Yes in step S4, the ECU 80 switches the clutch request flag from the slip state to the engaged state, and returns the LU clutch 30 from the slip state to the engaged state (step S5). Here, when the ECU 80 is controlled to the slip state, the torque transmission rate from the engine 10 to the transmission 40 decreases and fuel economy deteriorates, but because the LU clutch 30 is controlled to the slip state only for the predetermined slip request time as described above, the effect on fuel economy can be minimized.

[0041] The vibration generation conditions described above do not necessarily include conditions (D) and (E). For example, with regard to condition (D), in a vehicle in which deceleration flex control is not immediately executed even when the accelerator pedal position is set to 0, or in a situation in which deceleration flex control is limited, the vehicle may vibrate due to resonance regardless of the accelerator pedal position. Furthermore, with regard to condition (E), if the vehicle body is lightweight, for example, and resonance occurs during high-speed driving, the vehicle may vibrate significantly due to resonance in addition to vibration from the road surface.

[0042] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0043] 1 vehicle 10 Engine 11. Crankshaft 20 Torque converter 30 Lock-up clutch 40 Transmission 42 Output shaft 80 ECU (vehicle control unit, condition determination unit, resonance determination unit, control unit)

Claims

1. A control device for a vehicle having an engine, a transmission capable of selectively establishing a plurality of gear stages with different gear ratios, and a torque converter with a lock-up clutch that transmits torque of the engine to the transmission, a condition determination unit that determines whether or not conditions are met, including that the lock-up clutch is in an engaged state, that a predetermined gear stage is established in the transmission, and that an operating point determined according to the engine speed and load is within a predetermined region; a resonance determination unit that determines whether or not the engine and the transmission are resonating when a positive determination is made by the condition determination unit; a control unit that controls the lock-up clutch to a slip state when a positive determination is made by the resonance determination unit, The control unit maintains the lock-up clutch in a slip state for a longer period of time as the gear stage established in the transmission is lower among the predetermined gear stages.

2. A control device for a vehicle having an engine, a transmission capable of selectively establishing a plurality of gear stages with different gear ratios, and a torque converter with a lock-up clutch that transmits torque of the engine to the transmission, a condition determination unit that determines whether or not conditions are met, including that the lock-up clutch is in an engaged state, that a predetermined gear stage is established in the transmission, and that an operating point determined according to the engine speed and load is within a predetermined region; a resonance determination unit that determines whether or not the engine and the transmission are resonating when a positive determination is made by the condition determination unit; a control unit that controls the lock-up clutch to a slip state when a positive determination is made by the resonance determination unit, The condition determination unit expands the predetermined range to a low load side where the load on the engine is low as the gear stage established in the transmission among the predetermined gear stages becomes lower.

3. the transmission is capable of selectively establishing three or more gear stages with different reduction ratios, The vehicle control device according to claim 1 or 2, wherein the condition determination unit excludes a lowest gear and a highest gear from the predetermined gears.

4. 4. The vehicle control device according to claim 1, wherein the condition determining unit limits the predetermined region to a high load region equal to or greater than half of a maximum load of the engine.

5. 5. The vehicle control device according to claim 1, wherein the condition determining unit includes, as one of the conditions, that an accelerator opening is greater than a predetermined opening.

6. 6. The vehicle control device according to claim 1, wherein the condition determining unit includes a condition that the vehicle speed is equal to or less than a predetermined speed as one of the conditions.

7. 7. The vehicle control device according to claim 1, wherein the resonance determination unit determines whether resonance has occurred in the transmission based on the rotation speed of the crankshaft of the engine and the rotation speed of the output shaft of the transmission.

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