A smooth DCT coast-down shift control method

Abstract

A smooth DCT coasting downshift control method, comprising the following steps: step 1), judging whether the vehicle enters the coasting downshift working condition; step 2), in the vehicle coasting downshift working condition, monitoring whether the engine recovery oil supply flag bit is set in real time, if the engine recovery oil supply flag bit is set, entering step 3), otherwise, entering step 4); step 3), adjusting the engine speed by controlling the clutch and the engine; step 4), adjusting the engine speed by controlling the clutch; step 5), synchronizing the engine speed with the clutch speed, and completing the downshift.

Description

Technical Field

[0001] This invention relates to the field of automotive automatic transmission technology, and particularly to a smooth DCT coasting downshift control method. Background Technology

[0002] DCT is short for Dual Clutch Transmission. Because it operates using two clutches, it's generally called a dual-clutch transmission. The clutch is located between the engine and the transmission, acting as a "switch" for power transmission between them. It's a transmission mechanism that can both transmit and disconnect power. One clutch in a DCT corresponds to odd-numbered gears, and the other to even-numbered gears. When the vehicle shifts gears, the other clutch and the corresponding next gear are already in a ready state. As soon as the clutch for the current gear disengages, the clutch for the next gear immediately engages. Therefore, DCT shifts faster than conventional automatic transmissions or even manual transmissions. DCT coasting downshifts refer to downshifting that occurs when the vehicle decelerates due to driving resistance or braking resistance without throttle input. During a DCT coasting downshift, the clutch for the current gear disengages, and the transmission disengages from the engine. The engine speed gradually decreases, resulting in a significant speed difference between the engine and transmission speeds. When the clutch for the next gear (the target gear) immediately engages, it can easily cause a shift shock and abnormal noise, thus reducing the driving experience. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies by providing a smooth DCT coasting downshift control method, thereby solving the problem of shift jerking and abnormal noises that easily occur during DCT coasting downshifts, which in turn reduces the driving experience of the vehicle.

[0004] The objective of this invention is achieved as follows:

[0005] A smooth DCT coasting downshift control method includes the following steps:

[0006] Step 1), determine whether the vehicle has entered coasting downshifting mode;

[0007] Step 2): During the vehicle's coasting downshifting condition, monitor in real time whether the engine's fuel supply recovery indicator is set. If the engine's fuel supply recovery indicator is set before the clutch torque switching is completed, proceed to step 3); otherwise, proceed to step 4.

[0008] Step 3), adjust the engine speed by controlling the clutch and the engine;

[0009] Step 4): Adjust the engine speed by controlling the clutch;

[0010] Step 5) The engine speed and clutch speed are synchronized to complete the downshift.

[0011] Preferably, the fuel supply recovery flag in step 2) is set when the engine real-time speed drops to the engine speed threshold.

[0012] Preferably, the method for adjusting the engine speed by controlling the clutch and the engine in step 3) is as follows:

[0013] 3-1) If the clutch corresponding to the current gear is disengaged and the clutch corresponding to the target gear is partially engaged, the engine angular acceleration is adjusted using the clutch corresponding to the target gear until the real-time engine angular acceleration reaches the engine target angular acceleration.

[0014] 3-2), the engine target torque correction value is obtained based on the engine angular acceleration, and the engine target torque is corrected.

[0015] Preferably, the method for obtaining the engine target torque correction value based on the engine angular acceleration in step 3-2) is as follows: if the real-time value of the clutch engagement torque corresponding to the target gear reaches the maximum value of the clutch engagement torque, and there is a difference between the engine target angular acceleration and the engine real-time angular acceleration, an engine torque increase request is triggered. According to the engine target torque correction reference table, the engine target torque correction value is obtained, and the engine target torque is corrected.

[0016] The beneficial effects of the smooth DCT coasting downshift control method of the present invention are as follows: By real-time monitoring of whether the engine's fuel supply recovery indicator is set, the method fully utilizes the characteristic that the engine torque increases and the engine speed increases when the fuel supply recovery indicator is set, thereby minimizing the clutch engagement torque value and avoiding shifting jerks and abnormal noises. The smooth DCT coasting downshift control method of the present invention achieves open-loop control by controlling the clutch and closed-loop control by controlling the engine; thus, it realizes a DCT coasting downshift control method with open-loop as the primary approach and closed-loop as the secondary approach, making engine speed control more precise. By limiting the upper limit of the clutch engagement torque value and adjusting the engine torque to ensure that the engine speed is the same as the clutch speed of the target gear, shifting jerks and abnormal noises are further avoided. Attached Figure Description

[0017] Figure 1 This is a logic diagram of a smooth DCT coasting downshift control method. Detailed Implementation

[0018] refer to Figure 1 A smooth DCT coasting downshift control method includes the following steps:

[0019] In step S1, the TCU determines whether the vehicle has entered a coasting downshifting mode based on the shifting pattern. If the vehicle has entered a coasting downshifting mode, proceed to step 2); otherwise, repeat step 1. The shifting pattern is a calibrated quantity and is pre-existing in the TCU.

[0020] Step S2: During the vehicle coasting downshifting condition, the TCU monitors in real time whether the engine's fuel supply recovery flag is set. If the engine's fuel supply recovery flag is set before the clutch torque switching is completed, proceed to step 3; otherwise, proceed to step 4.

[0021] Preferably, the fuel supply recovery flag is set when the engine speed drops to a calibrated threshold value.

[0022] Step S3: Adjust the engine speed by controlling the clutch and the engine.

[0023] S3-1, if the clutch corresponding to the current gear is disengaged and the clutch corresponding to the target gear is partially engaged, the engine angular acceleration is adjusted using the clutch corresponding to the target gear until the real-time engine angular acceleration reaches the target engine angular acceleration.

[0024] The target engine speed for each gear during the entire shift cycle is set on the TCU. The target engine speed is calculated from the current vehicle speed based on the target gear ratio, i.e., target engine speed rad / min = [(real-time vehicle speed m / s × 60) / 2πr] × target gear ratio. Differentiating the target engine speed yields the engine speed rise slope, i.e., the target engine angular acceleration. The target clutch engagement torque for each gear is then calculated using the following formula:

[0025] Engine target angular acceleration × engine moment of inertia - engine real-time torque = clutch engagement torque target value.

[0026] Therefore, when the engine's fuel supply indicator is set to the correct position, the engine's real-time torque increases, the engine's real-time speed increases, and the target clutch engagement torque value decreases, making it easier to reach the target clutch engagement torque value. In other words, when the clutch corresponding to the target gear is partially engaged, the driven disc of the clutch in that gear adjusts the angular acceleration of the driving disc, which in turn adjusts the real-time angular acceleration of the engine connected to the driving disc until the engine's real-time angular acceleration reaches the target angular acceleration.

[0027] The target clutch engagement torque value can be adjusted during actual debugging. To ensure smoothness, the upper limit of the target clutch engagement torque value should be limited, and the maximum target clutch engagement torque value should be obtained from actual vehicle testing.

[0028] S3-2, based on the engine angular acceleration, obtains the engine target torque correction value and corrects the engine target torque.

[0029] If the real-time clutch engagement torque value corresponding to the target gear reaches the maximum target clutch engagement torque, and there is a difference between the engine target angular acceleration and the engine real-time angular acceleration, an engine torque increase request is triggered. According to the engine target torque correction lookup table, the engine target torque correction value is obtained, and the engine target torque is corrected until the engine real-time angular acceleration reaches the engine target angular acceleration.

[0030] The data in the engine target torque correction reference table were all obtained from calibration tests, as shown in Table 1:

[0031] Table 1

[0032]

[0033] Step S4: Adjust the engine speed by controlling the clutch.

[0034] If the clutch corresponding to the current gear is disengaged, the clutch corresponding to the target gear is partially engaged, and the engine angular acceleration is adjusted using the clutch corresponding to the target gear until the real-time engine angular acceleration reaches the target engine angular acceleration.

[0035] In step S5, the engine speed is synchronized with the target gear clutch speed, and the coasting downshift is completed.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A smooth DCT coasting downshift control method, characterized in that: Includes the following steps: Step 1): The TCU determines whether the vehicle has entered the coasting downshifting mode based on the shifting pattern. If the vehicle has entered the coasting downshifting mode, proceed to step 2); otherwise, repeat step 1). The shifting pattern is a calibrated quantity and is pre-existing in the TCU. Step 2): During the vehicle's coasting downshifting condition, monitor in real time whether the engine's fuel supply recovery indicator is set. If the engine's fuel supply recovery indicator is set before the clutch torque switching is completed, proceed to step 3); otherwise, proceed to step 4. In step 2), the fuel supply recovery flag is set when the engine speed drops to the engine speed threshold. Step 3), by controlling the clutch and engine, adjust the engine speed in the following manner; 3-1) If the clutch corresponding to the current gear is disengaged and the clutch corresponding to the target gear is partially engaged, the engine angular acceleration is adjusted using the clutch corresponding to the target gear until the real-time engine angular acceleration reaches the target engine angular acceleration. The engine target angular acceleration is obtained by the TCU after calculating the engine target speed based on the current vehicle speed and the target gear ratio, and then differentiating the engine target speed. The engine target speed is calculated as follows: Engine target speed rad / min = [(real-time vehicle speed m / s × 60) / 2πr] × target gear ratio, where r is the wheel rolling radius. The target value of clutch engagement torque is calculated based on the engine target angular acceleration. The calculation formula is: target value of clutch engagement torque = engine target angular acceleration × engine moment of inertia - engine real-time torque; The target value of clutch engagement torque is subject to an upper limit constraint, which is the maximum target value of clutch engagement torque obtained from actual vehicle test calibration. 3-2) Obtain the engine target torque correction value based on the engine angular acceleration, and correct the engine target torque in the following manner: If the real-time clutch engagement torque value corresponding to the target gear reaches the maximum target clutch engagement torque, and there is a difference between the engine target angular acceleration and the engine real-time angular acceleration, an engine torque increase request is triggered. According to the engine target torque correction lookup table, the engine target torque correction value is obtained, and the engine target torque is corrected until the engine real-time angular acceleration reaches the engine target angular acceleration. The data in the engine target torque correction table were all obtained from actual vehicle calibration tests; Step 4): If the clutch corresponding to the current gear is disengaged, the clutch corresponding to the target gear is partially engaged. Use the clutch corresponding to the target gear to adjust the engine angular acceleration until the real-time engine angular acceleration reaches the engine target angular acceleration, thus completing the engine speed adjustment. Step 5) The engine speed and clutch speed are synchronized to complete the downshift.

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