JP4082975B2 - Creep force control method for starting clutch - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a creep force control method for a starting clutch that can be used in combination with an engine and a transmission and that can freely change the engagement force.
[0002]
[Prior art]
[Patent Document 1]
In general, in the case of an automatic transmission equipped with a torque converter, an extremely smooth start is possible, but in the idling state of the traveling range, a so-called creep is transmitted in which the rotational force is transmitted to the output shaft due to the drag torque. Cause a phenomenon. There is no problem because the creep force is small during normal idling, but there is a problem that the creep force becomes large when idling up and the vehicle moves forward without depressing the accelerator pedal.
[0003]
In order to solve such a problem of the torque converter, a clutch using a clutch capable of freely changing the engagement force such as a hydraulic clutch or a dry clutch as a starting clutch has been proposed. When generating a creep force in a vehicle using such a starting clutch, it is desirable to generate the creep force as quickly as possible when shifting from the N range to the D range. For example, in the case of the clutch characteristic shown in FIG. 1A, the optimum creep force Ttg can be obtained by quickly engaging the clutch up to the stroke Xa. However, the relationship between the clutch transmission torque and the stroke changes like B or C depending on the temperature or the like. For example, when the characteristics change as in C, if the clutch is quickly engaged up to Xa, Tac transmission torque is generated, which causes problems such as engine stop and excessive shock. In order to avoid this, conventionally, the clutch is engaged very slowly while performing feedback control before the stroke Xa, which seems to be optimal, and there is a drawback that it takes a long time to generate the creep force.
[0004]
[Problems to be solved by the invention]
In Patent Document 1, the clutch is pressed at a high speed, and the position where the input rotational speed to the transmission reaches a predetermined rotational speed is set as an approximate contact point, and then the position is slightly returned to the clutch disengagement side, and the clutch is restarted from that position. A control method for determining a contact point by pressing at a low speed is disclosed.
However, when the above contact point is applied to the starting point of creep control, the following problem occurs. In other words, since there is always an operation delay in the actuator that controls the engagement force of the clutch, if the engine speed at which creep control is started is set to a value close to the creep target engine speed, when the clutch is pressed at a high speed, the actuator There is a risk of engine stoppage due to operation delay. Therefore, the engine speed at which creep control is started must be made considerably higher than the creep target engine speed. However, if the engine speed at which creep control is started is set too high, the target creep force will be generated. There is a problem that it takes time.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to provide a starting clutch creep force control method capable of quickly shifting a clutch to a creep state and solving problems such as engine stoppage.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the invention described in claim 1 is a creeping force control method for a starting clutch that can be used in combination with an engine and a transmission and that can freely change the engaging force, in a running range and in an idling state. And a step of instantaneously shifting the starting clutch from the disengaged state to the initial clutch point when in the running range and idling state, and an open loop at a constant first engagement speed from the initial clutch point A step of engaging by control, a step of calculating an expected engine speed after a predetermined time from the current engine speed and a rate of change of the engine speed while being engaged at a first engagement speed; When the predicted engine speed is less than the set value, the step of returning the start clutch by a predetermined amount and the disconnection of the start clutch by a predetermined amount After returning to direction, starting clutch comprising the steps of: number of engines rotate at slower than the first engagement speed second engagement speed feedback control the engaging force of the starting clutch to approach the creep target engine speed, the The creep force control method is provided.
[0007]
When switching from the N range to the D range in the idling state, the starting clutch is first engaged from the disengaged state at the first engagement speed. This engagement speed is preferably faster than the engagement speed by the conventional feedback control. When the clutch is engaged at the first engagement speed, the engine speed starts to decrease, that is, the transmission torque starts to increase. Therefore, the engine speed after a predetermined time is predicted from the current engine speed and the change rate (decrease rate) of the engine speed. The predetermined time is determined on the basis of a time lag due to an actuator operation delay or the like. Then, when the expected engine speed is compared with the set value and the expected engine speed is equal to or less than the set value, if the clutch is engaged at the first engagement speed as it is, the transmission torque becomes too high and the engine stops. The starting clutch is returned to the disengagement direction by a predetermined amount. The predetermined amount is an amount that causes a gradual change after the rapid decrease in the engine speed is stopped, and may be updated by learning control or the like. At this point, the clutch has reached a position near the creep state. Thereafter, the engagement force of the starting clutch is controlled at a second engagement speed slower than the first engagement speed so that the engine speed approaches the creep target engine speed. Therefore, a constant creep force can always be generated even when there are various variations in the clutch and changes with time.
[0008]
As described above, in the present invention, a predetermined creep region is quickly engaged, and after entering the creep region, the engine speed is slowly engaged so as to approach the creep target engine speed. The time required until is greatly reduced.
In addition, when the clutch is engaged at the first engagement speed, if the operation delay of the actuator or the transmission torque-stroke characteristic of the clutch changes depending on the temperature or the like, the engine speed decreases rapidly, causing problems such as engine stop. May occur. However, in the present invention, such a rapid decrease in the engine speed is predicted in advance by comparing the predicted engine speed with the set value, so that the engine stop can be reliably prevented.
[0009]
When the clutch is engaged at the first engagement speed as described above, the timing for returning the starting clutch by the predetermined amount in the disengagement direction is determined by comparing the expected engine speed and the set value. The set value is preferably a value close to the creep target engine speed as in claim 2.
Thus, since the engine speed which shifts to creep control is close to the target engine speed at the time of creep, a preset creep state can be reached in a short time.
The set value may be the creep target engine speed itself, or may be a value slightly higher or lower than the creep target engine speed. The creep state can be reached in a shorter time if the set value is set to a value lower than the creep target engine speed.
[0010]
The creep force control method of the present invention can be applied not only to switching from N to D, but also to a method in which the starting clutch is disengaged when the brake is turned on.
In the present invention, the starting clutch may be provided between the engine and the transmission, or may be provided inside the transmission. In the former case, the input speed of the starting clutch is equal to the engine speed, and in the latter case, the input speed of the starting clutch is equal to the quotient of the engine speed and the reduction ratio inside the transmission. In either case, the input rotational speed of the starting clutch can be obtained from the engine rotational speed.
The transmission used in the present invention may be an automatic transmission (AT) having a plurality of friction engagement elements, a continuously variable transmission (CVT), or a manual transmission that is automatically shifted by an actuator. An automatic MT may be used.
As the start clutch, any clutch such as a dry clutch, a wet clutch, and an electromagnetic powder clutch that can freely adjust the engagement force (transmission torque) can be used. As a method for controlling the engagement force of such a starting clutch, the stroke amount may be adjusted in the case of a dry clutch, and the hydraulic pressure may be controlled in the case of a wet clutch. In the case of an electromagnetic powder clutch, the input current may be controlled.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 2 shows an example of a drive mechanism of a vehicle provided with a start clutch according to the present invention.
The output shaft of the engine 1 is connected to the automatic transmission 3 via the starting clutch 2, and the output shaft of the automatic transmission 3 is connected to the drive wheels 5 via the differential device 4. The engine 1 is subjected to ignition control and fuel injection control by an engine controller (EG controller) 10. For this purpose, signals are input from a throttle opening sensor 11, idle-up detection means 12, engine speed sensor 13, and the like. .
[0012]
The starting clutch 2 is equipped with an actuator 20 for freely adjusting its engaging force, and this actuator 20 is controlled by a transmission controller (TM controller) 30 described later. In this embodiment, a dry single-plate clutch is used as the starting clutch 2, and the actuator 20 adjusts the clutch engagement force by changing the stroke amount of the clutch plate.
[0013]
As is well known, the automatic transmission 3 includes a plurality of friction engagement elements (clutch and brake). By selectively engaging the friction engagement elements, a plurality of shift stages are obtained. Its internal structure is well known and will be omitted. The gear stage of the automatic transmission 3 is automatically selected by the TM controller 30 according to the running state. Therefore, the TM controller 30 includes a vehicle speed sensor 31 that detects the vehicle speed, a brake sensor 32 that detects the depression of the foot brake, a shift position sensor 33 that detects a shift range such as P, R, N, and D, and an input rotation speed sensor. A signal is input from 34, etc., the gear position is determined by these input signals and a preset shift program, and the signal is output to an electromagnetic valve that controls the hydraulic pressure of the friction engagement element. The TM controller 30 is also connected to the EG controller 10 and shares the input signals with each other.
[0014]
FIG. 3 shows changes over time in the clutch stroke, the engine speed, and the rate of change of the engine speed when the creep force control method according to the present invention is switched from the N range to the D range.
When the transmission 3 is switched from the N range to the D range at time t1, the clutch plate of the starting clutch 2 instantaneously moves to the initial clutch point C1. At time t2, engagement is started from the clutch point C1 at the first engagement speed. This first engagement speed is set to a speed earlier than the conventional engagement speed. When the clutch is engaged at the first engagement speed, the engine speed starts to decrease. When the engine speed starts to decrease, the transmission torque is increasing. Therefore, the engine speed Ne + Te · dNe / dt after a predetermined time Te is predicted from the current engine speed Ne and the change rate dNe / dt of the engine speed. The predetermined time Te is set to about 100 ms, for example. The predicted engine speed (Ne + Te · dNe / dt) is compared with the creep target engine speed Netg. When the predicted engine speed becomes lower than the creep target engine speed Netg (t3), the starting clutch 2 is set to a predetermined amount ΔS. Only return in the direction of disconnection. This is because it is determined that if the clutch is engaged at the first engagement speed as it is, the engine is stopped. When the starting clutch 2 is a dry clutch, the return amount (stroke amount) ΔS is set to about 1 mm, but may be updated to an optimal value by learning control or the like.
[0015]
As shown in FIG. 1, the transmission torque-stroke characteristic of the start clutch 2 changes depending on the temperature or the like. Therefore, the rate of decrease dNe / in the engine speed Ne when the start clutch 2 is engaged at the first engagement speed. dt is also not constant. Further, since there is a delay in operation of the actuator 20, even if the actuator 20 is operated when the engine speed Ne is reduced to the creep target engine speed Netg, problems such as engine stoppage or occurrence of shock may not be avoided. In the present invention, in view of such a point, the engine speed Ne + Te · dNe / dt after a predetermined time Te is predicted from the current engine speed Ne and the change rate dNe / dt of the engine speed. Even if there is a temperature change or a delay in the operation of the actuator 20, a stable prediction can always be made, and the problem of engine stop can be solved reliably.
The predetermined time Te may be a constant value, but may be varied according to the decrease rate dNe / dt of the engine speed Ne. That is, it may be shortened when the decrease rate dNe / dt is large, and may be lengthened when the decrease rate dNe / dt is small.
[0016]
By returning the stroke of the start clutch 2 by the predetermined amount ΔS at time t3, the rapid decrease in the engine speed is settled, and thereafter, the engagement of the start clutch 2 so that the engine speed Ne approaches the creep target engine speed Netg. The resultant force is feedback controlled. Since the starting clutch 2 has already reached the position near the creep at the time t3, the time required until the creep force is generated can be shortened. Further, by performing feedback control, various variations and changes with time of the clutch 3 can be eliminated, and a constant creep force can always be generated.
[0017]
Next, a specific example of the creep force control method for the starting clutch 2 will be described with reference to FIG.
When the control is started, it is determined whether or not the shift position of the transmission is a travel range (D, R, L, etc.) or a non-travel range (P or N) (step S1). In the non-traveling range, the starting clutch 2 is disengaged (step S2). In the traveling range, it is determined whether or not the vehicle is in an idling state (step S3). If the vehicle is in a non-idling state, it is determined that the vehicle is already in the traveling state, and clutch engagement control is performed (step S4).
[0018]
If it is in the running range and idling state, it is determined whether or not creep control is being performed (step S5). If creep control is being performed, the start clutch is set so that the engine speed becomes the creep target engine speed Netg. 2 is feedback-controlled (step S6). If creep control is not being performed, the starting clutch 2 is engaged at the first engagement speed (step S7). Then, the engine speed (Ne + Te · dNe / dt) after a predetermined time Te is predicted from the current engine speed Ne and the engine speed change rate dNe / dt (step S8), and the predicted value and the creep target are calculated. The engine speed Netg is compared (step S9). If Ne + Te · dNe / dt ≧ Netg, it is determined that the engine speed has not yet decreased sufficiently, in other words, the clutch transmission torque has not increased sufficiently, and steps S7 to S9 are repeated. When Ne + Te · dNe / dt <Netg in step S9, the clutch is returned by a predetermined amount ΔS (step S10), and the rapid decrease in engine speed is suppressed. Then, feedback control is executed so that the engine speed Ne approaches the creep target engine speed Netg (step S6).
[0019]
In the creep force control method of FIG. 4, when the predicted value of the engine speed after a predetermined time is less than the predetermined value, the clutch is returned by a predetermined amount, and the control shifts to the feedback control. As shown, it may be added that the clutch stroke is equal to or less than a predetermined value Sc (a region that is likely to be engaged), or a condition that the engine speed Ne is lower than the reference value Nes. The reference value may be, for example, a value higher by a predetermined value (for example, 80 rpm) than the creep target engine speed Netg, or a constant value (for example, 50 rpm) from the maximum engine speed Nemax in the N range immediately before switching to the D range. It may be a lower value. By adding such a start condition, it is possible to prevent erroneous determination of the transition to the creep state.
In the above embodiment, the clutch is engaged at the first engagement speed by the open control until the creep region is entered, and after entering the creep region, the clutch is engaged by the second engagement speed by the feedback control. However, as a method of changing the engagement speed, feedback control may be performed from the beginning, and the feedback gain may be changed before and after the creep region. For example, the gain may be increased before the creep region and decreased after the region.
[0020]
【The invention's effect】
As is apparent from the above description, according to the present invention, the clutch is quickly engaged at the first engagement speed until the creep region is entered, and is slower than the first engagement speed after entering the creep region. Since the engine speed is controlled to approach the creep target engine speed at the second engagement speed, the time required until the occurrence of creep can be greatly shortened.
Further, when the clutch is engaged at the first engagement speed, if the transmission torque-stroke characteristic of the clutch changes depending on the temperature or the like, the engine speed is rapidly reduced, and the actuator is operated to prevent this. However, there is a possibility that problems such as engine stop may occur due to the delay in operation of the actuator. In the present invention, such a rapid decrease in the engine speed is predicted in advance based on the engine speed and the rate of change thereof. Therefore, it is possible to reliably prevent the engine from being stopped even if there is a delay in the operation of the actuator or a change in characteristics.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between transmission torque and clutch stroke of a conventional starting clutch.
FIG. 2 is a drive mechanism diagram of an example of a vehicle equipped with a starting clutch according to the present invention.
FIG. 3 is a time change diagram of a clutch stroke, an engine speed, and an engine speed change rate when the creep control according to the present invention is performed.
FIG. 4 is a flowchart of an example of creep control of a starting clutch according to the present invention.
[Explanation of symbols]
1 Engine 2 Start clutch 3 Transmission 20 Actuator

Claims (2)

A starting clutch creep force control method that can be used in combination with an engine and a transmission and that can freely change the engagement force,
A step of determining that the vehicle is in a running range and in an idling state;
A step of instantaneously shifting the starting clutch from the disengaged state to the initial clutch point when in the running range and idling state ;
Engaging with an open loop control at a constant first engagement speed from an initial clutch point ;
Calculating an expected engine speed after a predetermined time from the current engine speed and the rate of change of the engine speed while engaging at a first engagement speed;
A step of returning the starting clutch to the disengagement direction by a predetermined amount when the predicted engine speed is equal to or less than a set value;
After the start clutch is returned in the disengagement direction by a predetermined amount, the engagement force of the start clutch is feedback- controlled so that the engine speed approaches the creep target engine speed at a second engagement speed that is slower than the first engagement speed. A starting clutch creep force control method. 2. The starting clutch creep force control method according to claim 1, wherein the set value is a value close to the creep target engine speed.

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