Method for protecting a friction element of a clutch for an automatic transmission

Abstract

Method for protecting a friction element of a clutch for an automatic transmission, characterized in that the method comprises: Calculating an equivalent rotational speed X of a friction element using a trigonometric function equation based on a virtual right-angled triangle by a control unit (130); entering a friction element protection mode by the control unit (130) when a rotational speed of an engine exceeds a predetermined limit value when traveling in a constant speed stage above a predetermined shift stage of an automatic transmission; Determining whether the calculated equivalent rotational speed X of the friction element exceeds a predetermined critical value by the control unit (130) when the control unit (130) enters the friction element protection mode; and Reducing the speed of the engine by applying a target engine torque limit by the control unit (130) when the equivalent speed X of the friction element exceeds the predetermined critical value in a state in which the control unit (130) enters the friction element protection mode, wherein the virtual right-angled triangle is obtained by using a rotational speed Z of an output shaft, a rotational speed Y of a turbine and an equivalent rotational speed X of the friction element of the automatic transmission as the height and by using a number of teeth α corresponding to the turbine, a number of teeth β corresponding to the output shaft and a virtual extension line γ as the base line.

Description

General state of the art

[0001] Various embodiments of the present disclosure relate to an automatic transmission for a vehicle, and more particularly, to a method for protecting a friction element of a clutch for the automatic transmission, which can prevent damage to the friction element by calculating a rotational speed of the friction element and reducing the rotational speed of an engine when the rotational speed of the friction element exceeds the firing timing of the friction element, in an automatic transmission that does not have a rotational speed sensor for measuring the rotational speed of the friction element. 2. State of the art

[0002] A four-speed or four-ratio automatic transmission generally consists of a planetary gear train, friction elements for controlling each element of the planetary gear train to perform the four gears, such as an underdrive clutch, an overdrive clutch, a reverse clutch, a second brake, and a low reverse brake, a final retarder for final retarding the transmission output achieved by the selective operation of the friction elements, and a differential device for transmitting the output of the final retarder to a drive shaft.

[0003] Compared to the design of the four-speed automatic transmission, a five-speed or five-stage automatic transmission typically also has a separate planetary gear set, a direct clutch to control each element of the planetary gear set to perform the five gears, a one-way clutch, and a reduction brake.

[0004] However, one problem with automatic transmissions is that the friction element burns out when the engine speed increases too much when driving in a constant speed range above a certain gear ratio in which one of the clutches, such as an overdrive clutch, is engaged.

[0005] The damage of the friction element can be prevented by calculating the rotational speed of the friction element, that is, a critical rotational speed of the friction element, using a rotational speed sensor and detecting a firing timing to reduce the rotational speed of an engine at the detected firing timing of the friction element.

[0006] However, in a transmission that does not have a speed sensor to measure the speed of the friction element, it is not possible to protect against or prevent damage to the friction element because the firing point of the friction element cannot be detected.

[0007] Therefore, in a transmission that does not have a speed sensor for measuring the speed of the friction element, a method is required that prevents the damage of the friction element by estimating or calculating the speed of the friction element and reducing the speed of an engine when the speed of the friction element, that is, a critical speed of the friction element, exceeds the firing timing.

[0008] The prior art of the present disclosure is disclosed in Korean Patent Application Laid-Open No. KR 10 2005 0 046 188 A, published on May 18, 2005, entitled “5-speed automatic transmission.”

[0009] Additionally, DE 10 2007 000 667 A1 discloses a control device for a vehicle drive system, comprising an electric differential portion and a mechanical power transmission portion arranged in series in a power transmission path between an internal combustion engine and a drive wheel of a vehicle. The control device is configured to limit an output of the internal combustion engine according to a difference between an actual rotational speed of the mechanical power transmission portion and a theoretical rotational speed estimated from a currently established rotational speed ratio of the mechanical power transmission portion.

[0010] DE 10 2008 048 442 B4 discloses an automatic transmission, comprising: a shifting device configured to perform a shifting operation from a current gear position to a target gear position by selectively engaging and disengaging a plurality of friction elements. A current heat load calculation device is provided for calculating a current heat load state of the friction element. A shift control device is configured to, if the heat load state predicted by the heat load prediction unit upon completion of the shifting operation is within a predetermined range, either perform the shifting operation or prevent the shifting operation. The shift control device is configured to perform a forced upshift in predetermined cases. Short summary

[0011] According to one embodiment, a method for protecting a friction element of a clutch for an automatic transmission is provided. The method may include: calculating, by a control unit, an equivalent rotational speed X of a friction element using a trigonometric function equation based on a virtual right-angled triangle; entering, by the control unit, a friction element protection mode when a rotational speed of an engine exceeds a predetermined limit value during constant-speed driving above a predetermined shift speed of an automatic transmission; determining, by the control unit, whether the calculated equivalent rotational speed X of the friction element exceeds a predetermined critical value when the control unit enters the friction element protection mode;and reducing the speed of the engine by applying a target engine torque limit by the control unit when the equivalent speed X of the friction element exceeds the predetermined critical value in a state where the control unit enters the friction element protection mode, wherein the virtual right-angled triangle is obtained by using a speed Z of an output shaft, a speed Y of a turbine, and an equivalent speed X of the friction element of the automatic transmission as a height, and by using a number of teeth α corresponding to the turbine, a number of teeth β corresponding to the output shaft, and a virtual extension line γ as a baseline.;

[0012] The method may further comprise: enabling the friction element protection mode to disapply the desired engine torque limit by the control unit when the automatic transmission is shifted below a predetermined gear or the engine speed is below the predetermined critical value.

[0013] The specified switching level may be the fourth level.

[0014] The virtual right-angled triangle is obtained by: drawing a virtual straight line (a first height) corresponding to the equivalent rotational speed of the friction element X so as to coincide with the height in the Y-axis direction, based on a right angle of the right-angled triangle; drawing a virtual straight line so as to coincide with the baseline in the X-axis direction, the virtual straight line corresponding to a sum of a number of teeth α corresponding to the turbine, a number of teeth β corresponding to the output shaft, and the virtual extension line γ; drawing a virtual straight line (a second height) corresponding to a rotational speed Y of the turbine at an end point of the number of teeth α corresponding to the turbine in the Y-axis direction; drawing a virtual straight line (a third height) corresponding to the rotational speed Z of the output shaft at an end point of the number of teeth β corresponding to the output shaft in the Y-axis direction;Connecting endpoints of the first, second, and third altitudes to draw a virtual straight line corresponding to a hypotenuse of the virtual triangle; and extending the hypotenuse of the virtual triangle to a point that coincides with the x-axis so that it corresponds to the baseline.;

[0015] A distance from the end point of the number of teeth β corresponding to the output shaft to a vertex where the virtual extension line of the hypotenuse meets the base line can become a length of the virtual extension line γ.

[0016] The length of the virtual extension line γ can be calculated by the control unit using Equation 1 below. Z:Y=γ:γ+β→γ=Z×β(Y−Z)

[0017] The equivalent speed X of the friction element can be calculated by the control unit using equations 2 and 3 below. Y:X=γ+β:γ+β+α X=Y(α+β+Z×βY−Z)Z×βY−Z+β Brief description of the drawings

[0018] Various embodiments of an inventive idea emerge with reference to the attached drawings and the accompanying detailed description, wherein: Fig. 1 is an explanatory view schematically illustrating a configuration of a clutch friction element protecting apparatus for an automatic transmission related to an embodiment of the present disclosure; Fig. 2 is a flowchart for explaining a method for protecting a friction element of a clutch for an automatic transmission according to an embodiment of the present disclosure; and Fig. 3 is an exemplary view for explaining a method for calculating the rotational speed of a friction element in Fig. 2 is. Detailed description

[0019] Embodiments of a method for protecting a friction element of a clutch for an automatic transmission according to the present disclosure will be described in detail below with reference to the accompanying drawings.

[0020] It should be noted that the drawings are not to scale and may be disproportionate in line thickness or component dimensions solely for the sake of clarity and illustration. Furthermore, the terms used herein are defined with the functions of the invention in mind and may vary according to the customs and intent of users or adopters. Therefore, the definitions of terms should be consistent with the overall disclosures presented herein.

[0021] Fig. 1 is an exemplary view schematically illustrating a configuration of a clutch friction element protecting device for an automatic transmission relating to an embodiment of the present disclosure.

[0022] As in Fig. 1, the device for protecting a friction element of a clutch for an automatic transmission according to one embodiment may include: a clutch actuator 110 responsible for clutch control; a shift device 120 for controlling a shift fork of the transmission to perform an actual shift; a control unit 130, for example, a transmission control unit, for controlling the shift device 120 according to a vehicle speed, a throttle opening, or the like; and an engine control unit 140 for controlling a function, for example, a rotational speed of an engine, according to information output from the control unit 130.

[0023] The control unit 130, for example, the transmission control unit, estimates or calculates a rotational speed of the friction element in a transmission that does not have a rotational speed sensor for measuring the rotational speed of the transmission's friction element. If the estimated or calculated rotational speed of the friction element, i.e., a critical rotational speed of the friction element, exceeds a predetermined firing point, the control unit 130 reduces the engine speed via the engine control unit 140. Thus, damage to the friction element can be prevented.

[0024] Hereinafter, a method for protecting the friction element by calculating the rotational speed of the friction element will be described with reference to Fig. 2 and Fig. 3 described in detail.

[0025] Fig. 2 is a flowchart for explaining a method for protecting a friction element of a clutch for an automatic transmission according to an embodiment of the present disclosure, and Fig. 3 is an explanatory view for explaining a method for calculating a rotational speed of the friction element in Fig. 2.

[0026] According to Fig. 2, the control unit 130 generates a virtual right-angled triangle using a rotational speed Z of an output shaft, a rotational speed (≒ an engine speed) Y of a turbine, and an equivalent rotational speed X of the friction element as a height, and using a number of teeth α corresponding to the turbine, a number of teeth β corresponding to the output shaft, and a virtual extension line γ as a baseline (S101).

[0027] More precisely, according to Fig.3, a virtual straight line (a first height) corresponding to the equivalent rotational speed X of the friction element is drawn so as to coincide with a height in the Y-axis direction, and a virtual straight line is drawn which corresponds to a sum of the number of teeth α corresponding to the turbine, the number of teeth β corresponding to the output shaft and the virtual extension line γ so as to coincide with the base line in the X-axis direction, on the basis of a right angle of the right-angled triangle.

[0028] Next, a virtual straight line (second height) corresponding to the turbine speed Y is drawn at an endpoint of the number of teeth a corresponding to the turbine in the Y-axis direction, and a virtual straight line (third height) corresponding to the output shaft speed Z is drawn at an endpoint of the number of teeth β corresponding to the output shaft in the Y-axis direction. Then, the endpoints of the first, second, and third heights are connected, and a virtual straight line corresponding to the hypotenuse of the virtual right-angled triangle is drawn. The hypotenuse of the virtual right-angled triangle is extended to a point that coincides with the X-axis so that it corresponds to the baseline, thereby creating the virtual right-angled triangle.

[0029] A distance from an end point of the number of teeth β corresponding to the output shaft to a vertex where an extended line of the hypotenuse and the base line meet then becomes a length of the virtual extension line γ.

[0030] Thus, the baseline and the height are determined, and consequently the virtual right-angled triangle can be created.

[0031] Accordingly, the control unit 130 calculates the equivalent rotational speed X of the friction element using the trigonometric function equation based on the generated virtual right-angled triangle (S102).

[0032] The length of the virtual extension line γ can be calculated using the following equation 1). Furthermore, when the length of the virtual extension line γ is calculated, the total length of the base line of the virtual right-angled triangle can be obtained, and thus the equivalent rotational speed X of the friction element, which corresponds to the height of the virtual right-angled triangle, can be calculated using the following equations 2 and 3. Z:Y=γ:γ+β→γ=Z×β(Y−Z) Y:X=γ+β:γ+β+α X=Y(α+β+Z×βY−Z)Z×βY−Z+β

[0033] Thereafter, the control unit 130 determines whether the rotational speed of the engine exceeds a predetermined limit value when traveling in a constant speed stage above a predetermined gear stage, for example, the fourth stage of the automatic transmission (S103).

[0034] According to a result of the determination in step S103, when the rotational speed of the engine exceeds the predetermined limit value when traveling in a constant speed stage above a predetermined shift stage, for example, the fourth stage, the control unit 130 inputs a friction element protection mode (S104).

[0035] However, according to the result of the determination in step S103, if the automatic transmission is shifted below the predetermined gear stage, for example, the fourth stage, or the engine speed is below the predetermined limit value, the control unit 130 checks the current gear stage and the engine speed again (S107).

[0036] As described above, when the control unit 130 enters the friction element protection mode, the control unit 130 determines whether the calculated equivalent rotational speed X of the friction element exceeds the predetermined critical value (S105).

[0037] In a state where the control unit 130 enters the friction element protection mode, when the equivalent rotational speed X of the friction element exceeds the predetermined critical value, the control unit 130 reduces the rotational speed of the engine by applying a target engine torque limit via the engine control unit 140 (S106).

[0038] Meanwhile, if the automatic transmission is shifted below the predetermined stage, for example, the fourth stage, or the engine speed is below the predetermined critical value, the control unit 130 releases the friction element protection mode and does not apply the target engine torque limit (S108).

[0039] If the automatic transmission is not shifted below the predetermined gear, for example, the fourth gear, or the engine speed remains in a state exceeding the predetermined limit, the control unit 130 checks the current gear stage and the engine speed again (S103).

[0040] As described above, according to an embodiment of the present disclosure, in an automatic transmission that does not have a speed sensor for measuring the speed of the friction element, the damage of the friction element can be prevented by calculating the speed of the friction element and reducing the speed of the engine when the speed exceeds the firing timing of the friction element.

[0041] The embodiments of the inventive concept have been disclosed above for illustrative purposes. Those skilled in the art will recognize that various modifications, additions, and substitutions are possible without departing from the scope and spirit of the inventive concept disclosed in the appended claims.

Claims

[1] Method for protecting a friction element of a clutch for an automatic transmission, characterized by that the procedure includes: Calculating an equivalent rotational speed X of a friction element using a trigonometric function equation based on a virtual right-angled triangle by a control unit (130); entering a friction element protection mode by the control unit (130) when a rotational speed of an engine exceeds a predetermined limit value when traveling in a constant speed stage above a predetermined shift stage of an automatic transmission; Determining whether the calculated equivalent rotational speed X of the friction element exceeds a predetermined critical value by the control unit (130) when the control unit (130) enters the friction element protection mode; and Reducing the speed of the engine by applying a target engine torque limit by the control unit (130) when the equivalent speed X of the friction element exceeds the predetermined critical value in a state in which the control unit (130) enters the friction element protection mode, wherein the virtual right-angled triangle is obtained by using a rotational speed Z of an output shaft, a rotational speed Y of a turbine and an equivalent rotational speed X of the friction element of the automatic transmission as the height and by using a number of teeth α corresponding to the turbine, a number of teeth β corresponding to the output shaft and a virtual extension line γ as the base line. [2] The method of claim 1, further comprising: Enabling the friction element protection mode to disapply the target engine torque limit by the control unit (130) when the automatic transmission is shifted below a predetermined stage or the engine speed is below the predetermined critical value. [3] The method of claim 1, wherein the predetermined switching stage is the fourth stage. [4] The method according to claim 1, wherein the virtual right-angled triangle is obtained by: Drawing a virtual straight line (a first height) corresponding to the equivalent rotational speed of the friction element X so as to coincide with the height in the Y-axis direction based on a right angle of the right-angled triangle; Drawing a virtual straight line so that it coincides with the base line in the X-axis direction, the virtual straight line corresponding to a sum of a number of teeth α corresponding to the turbine, a number of teeth β corresponding to the output shaft and the virtual extension line γ; Drawing a virtual straight line (a second height) corresponding to a rotational speed Y of the turbine at an end point of the number of teeth α corresponding to the turbine in the Y-axis direction; Drawing a virtual straight line (a third height) corresponding to the rotational speed Z of the output shaft at an end point of the number of teeth β corresponding to the output shaft in the Y-axis direction; Connecting endpoints of the first, second, and third altitudes to draw a virtual straight line corresponding to a hypotenuse of the virtual triangle; and Extend the hypotenuse of the virtual triangle to a point that coincides with the x-axis so that it corresponds to the baseline. [5] The method according to claim 4, wherein a distance from the end point of the number of teeth β corresponding to the output shaft to a vertex at which the virtual extension line of the hypotenuse meets the base line becomes a length of the virtual extension line γ. [6] The method of claim 4, wherein the length of the virtual extension line γ is calculated by the control unit (130) using the following equation 1. Z:Y=γ:γ+β→γ=Z×β(Y−Z) [7] The method of claim 4, wherein the equivalent rotational speed X of the friction element is calculated by the control unit (130) using the following equations 2 and 3. Y:X=γ+β:γ+β+α X=Y(α+β+Z×βY−Z)Z×βY−Z+β

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