Unlocking control method for intermediate lock type variable valve timing system

Abstract

This invention discloses an unlocking control method for a center-lock variable valve timing system, comprising: S1: After obtaining an unlocking command and meeting the unlocking conditions, proceeding to S2; S2: Obtaining the current duty cycle, controlling the current duty cycle for time t1 in an open loop, and obtaining the current phase of the camshaft in real time. If the phase difference between the current phase and the initial phase is greater than or equal to a deviation threshold, unlocking is successful, and the current duty cycle is controlled in a closed loop to adjust the current phase to the target phase; otherwise, unlocking fails, proceeding to S3; S3: Adjusting the current duty cycle to the first duty cycle time t2; S4: Adjusting the current duty cycle for time t3 according to the oscillation-assisted unlocking rule, and obtaining the current phase in real time. If the phase difference is greater than or equal to the deviation threshold, unlocking is successful, and the current duty cycle is controlled in a closed loop to adjust the current phase to the target phase; otherwise, unlocking fails, and a fault code is reported. This method can shorten the unlocking time under normal conditions and reduce overshoot, thus reducing the phenomenon of failure to unlock.

Description

Technical Field

[0001] This invention belongs to the field of engine technology, and specifically relates to an unlocking control method for an intermediate lock-up variable valve timing system. Background Technology

[0002] To simultaneously meet fuel efficiency and performance requirements, modern engines widely employ Variable Valve Timing (VVT) technology. With increasingly stringent CO2 emission standards imposed by countries due to global warming, hybrid engines have become a trend in automotive internal combustion engine development. Naturally aspirated hybrid engines generally utilize the Atkinson cycle with a large intake cam wrap angle to reduce CO2 emissions. The Atkinson cycle requires significantly later intake valve closing, which is detrimental to engine cold starts. Therefore, intermediate lock-up VVT, with its wider adjustment range and ability to balance cold start emissions and idle stability, has begun to be used in hybrid engines from major OEMs.

[0003] Patent CN110410168B describes an intermediate lock-up VVT control system and method, which includes a 3-position 4-way Oil Control Valve (OCV) and an Oil Switching Valve (OSV). The lock-up pin oil circuit can be controlled independently, resulting in a high system cost and complexity. Its unlocking control strategy involves first opening the OCV valve in an open loop, then opening the OSV valve to unlock. If unlocking fails, the open-loop control is repeated. This control strategy does not demonstrate a significant improvement in cases where unlocking fails. Therefore, the unlocking method using the aforementioned intermediate lock-up VVT control system also has the possibility of failure to unlock.

[0004] Therefore, a mid-lock VVT system can be designed, which has a 4-position 5-way OCV valve and integrates the locking pin control oil circuit into the OCV valve. Compared with the aforementioned patent, this saves one OSV valve, effectively reducing component costs and control complexity. The basic structure and control oil circuit of the OCV valve are as follows: Figure 1 As shown, this intermediate lock-up VVT system receives a duty cycle signal from the electronic control unit via an electromagnet 300, generating an axial electromagnetic force to control the valve core 210 to move axially away from or towards the electromagnet 300 relative to the valve body 220. Different duty cycles result in different electromagnetic forces, different movement distances of the valve core 210, and different operating modes of the intermediate lock-up VVT system. The control oil circuits for these different operating modes are as follows: Figures 2a-2dAs shown, the movement distance of the valve core 210 varies, and the oil passages through the OCV valve 200 after entering through the oil inlet P also differ. This allows switching between the inlet and outlet oil paths leading to the advance oil chamber A, the lag oil chamber B, and the lock oil chamber L, thereby determining the rotation direction of the rotor 500 and the unlocking / locking state of the locking pin 700. Specifically, there are two oil chambers, advance oil chamber A and lag oil chamber B, on either side of the lock position. When the VVT ​​system unlocks, oil simultaneously flows from both inlets P into the advance oil chamber A and the lock oil chamber L. The oil pressure in the advance oil chamber A pushes the rotor 500 to rotate clockwise, while the oil in the lock oil chamber L pushes the locking pin 700 to lift and unlock.

[0005] Currently, the VVT ​​system is generally unlocked by controlling the duty cycle through open-loop control. However, the required duty cycle for unlocking varies under different conditions. When the oil pressure is high, the flow rate is large and fast, which can easily cause high back pressure on the locking pin 700 or the rotor 500 to rotate and the locking pin 700 to move to the side, resulting in excessive tangential force and unsuccessful unlocking.

[0006] To ensure successful unlocking, the duty cycle during open-loop unlocking can be increased and the open-loop control time extended. However, this would result in an excessively long unlocking time and potentially excessive overshoot, failing to meet the requirements of the intermediate lock-up VVT system during transient processes. Summary of the Invention

[0007] The purpose of this invention is to solve the risk of unlocking failure or excessive overshoot after unlocking in intermediate lock-up variable valve timing systems using a 4-position 5-way OCV valve. This invention provides an unlocking control method for intermediate lock-up variable valve timing systems, which can shorten the unlocking time under normal conditions, reduce the overshoot amplitude, and significantly reduce the phenomenon of unlocking failure, thereby reducing the engine failure rate.

[0008] To address the aforementioned technical problems, this invention discloses an unlocking control method for an intermediate lock-up variable valve timing system. The intermediate lock-up variable valve timing system includes a 4-position 5-way oil control valve, and the unlocking control method includes:

[0009] S1: Obtain the unlock command and the current phase of the camshaft, and determine whether the unlock conditions are met based on the current phase;

[0010] If the unlocking conditions are met, proceed to step S2.

[0011] S2: Obtain the current duty cycle, perform open-loop control on the current duty cycle, and maintain it for time t1; during time t1, obtain the current phase of the camshaft in real time, and determine whether the unlocking is successful based on the comparison between the current phase of the camshaft and the initial phase; if the phase difference between the current phase and the initial phase is greater than or equal to the deviation threshold, the unlocking is successful, the current duty cycle is controlled in a closed loop, and the current phase is adjusted to the target phase; if the phase difference between the current phase and the initial phase is less than the deviation threshold, the unlocking is unsuccessful, and proceed to step S3.

[0012] S3: Adjust the current duty cycle to the first duty cycle and maintain it for time t2.

[0013] S4: Adjust the current duty cycle according to the oscillation-assisted unlocking rule and maintain it for time t3. During time t3, acquire the current phase of the camshaft in real time and determine whether unlocking is successful based on the comparison between the current phase and the initial phase. If the phase difference between the current phase and the initial phase is greater than or equal to the deviation threshold, the unlocking is considered successful. Perform closed-loop control on the current duty cycle and adjust the current phase to the target phase. If the phase difference between the current phase and the initial phase is less than the deviation threshold, the unlocking is considered unsuccessful and a fault code is reported.

[0014] Adjusting the current duty cycle according to the oscillation-assisted unlocking rule includes:

[0015] S41: Adjust the current duty cycle to the second duty cycle and maintain it for time t4, then execute step S42; wherein, the second duty cycle is greater than the first duty cycle;

[0016] S42: Adjust the current duty cycle to the third duty cycle and maintain it for time t5, then continue to execute step S41; wherein the third duty cycle is less than the second duty cycle, and time t3 is greater than or equal to the sum of all times t4 and all times t5.

[0017] Using the above technical solution, after obtaining the unlock command and meeting the unlock conditions, the current duty cycle is acquired, and open-loop control is performed on the current duty cycle and maintained for time t1. During the open-loop control process (within time t1), the current phase of the camshaft is acquired in real time. The unlocking success is determined by comparing the current phase of the camshaft with the initial phase. If the phase difference between the current phase and the initial position is greater than or equal to the deviation threshold, the unlocking is considered successful, and closed-loop control is performed on the current duty cycle to adjust the current phase to the target phase. Compared with the conventional open-loop unlocking strategy, this shortens the unlocking time under normal conditions and reduces the overshoot amplitude, providing customers with a better driving experience and fuel economy, while reducing CO2 emissions.

[0018] Furthermore, during open-loop control, if the phase difference between the current phase and the initial position is less than the deviation threshold, unlocking is deemed unsuccessful. The current duty cycle is adjusted to the first duty cycle and maintained for time t2. Then, the current duty cycle is adjusted according to the oscillation-assisted unlocking rule and maintained for time t3. The oscillation-assisted unlocking rule includes first adjusting the current duty cycle to the second duty cycle (high duty cycle) and maintaining for time t4, where the second duty cycle is greater than the first duty cycle; then adjusting the current duty cycle to the third duty cycle (low duty cycle) and maintaining for time t5, where the third duty cycle is less than the second duty cycle. This cycle of adjusting the current duty cycle continues, with time t3 being greater than or equal to the sum of all times t4 and all times t5. This is equivalent to adjusting the current phase of the camshaft left and right to prevent unlocking failure caused by the locking pin getting stuck at the edge. During the adjustment of the current duty cycle according to the oscillation-assisted unlocking rule (within time t3), the current phase of the camshaft is acquired in real time. If the phase difference between the current phase and the initial position is greater than or equal to the deviation threshold, the unlocking is considered successful, and closed-loop control is applied to the current duty cycle, adjusting the current phase to the target phase. If the phase difference between the current phase and the initial position is less than the deviation threshold, the unlocking is considered unsuccessful, and a fault code is reported to remind the user to check. This significantly reduces the unlocking failure phenomenon of intermediate lock-up variable valve timing systems using 4-position 5-way OCV valves, reduces the engine failure rate, and saves customers a significant amount of after-sales inspection and maintenance costs.

[0019] According to another specific embodiment of the present invention, the unlocking control method of the intermediate lock-up variable valve timing system disclosed in the embodiment of the present invention, in step S1, determining whether the unlocking condition is met according to the current phase includes: if the current phase is in the initial phase, then it is determined that the unlocking condition is met; otherwise, it is determined that the unlocking condition is not met.

[0020] Using the above technical solution, the unlocking condition is determined to be met only when the current phase is in the initial phase, i.e., in the preset locking position. If the unlocking condition is not met, subsequent open-loop control unlocking can only be performed when the current phase is in the preset locking position.

[0021] According to another specific embodiment of the present invention, in the unlocking control method of the intermediate lock-up variable valve timing system disclosed in the embodiment of the present invention, the time t1 is 0.1s in step S1.

[0022] According to another specific embodiment of the present invention, in the unlocking control method of the intermediate lock-up variable valve timing system disclosed in the embodiment of the present invention, the deviation threshold is 3°CA in steps S2 and S4.

[0023] According to another specific embodiment of the present invention, in the unlocking control method of the intermediate lock-up variable valve timing system disclosed in the embodiment of the present invention, in step S3, the first duty cycle is 10% and the t2 time is 0.2s to 0.5s.

[0024] According to another specific embodiment of the present invention, in step S4 of the unlocking control method of the intermediate locking variable valve timing system as described in claim 1, the time t3 is 1 second.

[0025] According to another specific embodiment of the present invention, in the unlocking control method of the intermediate lock-up variable valve timing system disclosed in the embodiment of the present invention, the second duty cycle is 90% in step S41.

[0026] According to another specific embodiment of the present invention, in the unlocking control method of the intermediate lock-up variable valve timing system disclosed in the embodiment of the present invention, the time t4 in step S41 is 0.1s.

[0027] According to another specific embodiment of the present invention, in the unlocking control method of the intermediate lock-up variable valve timing system disclosed in the embodiment of the present invention, the third duty cycle is 35% in step S42.

[0028] According to another specific embodiment of the present invention, in the unlocking control method of the intermediate lock-up variable valve timing system disclosed in the embodiment of the present invention, the time t5 is 0.1s in step S42.

[0029] The beneficial effects of this invention are:

[0030] This invention provides an unlocking control method for a center-lock variable valve timing system. After receiving an unlocking command and meeting the unlocking conditions, the current duty cycle is acquired and maintained in an open-loop manner for a time t1. During this open-loop control (within t1), the current phase of the camshaft is acquired in real time. The unlocking success is determined by comparing the current phase with the initial phase. If the phase difference between the current and initial positions is greater than or equal to a deviation threshold, the unlocking is considered successful. Closed-loop control is then applied to the current duty cycle, and the current phase is adjusted to the target phase. Compared to an open-loop unlocking strategy, this method shortens the unlocking time under normal conditions and reduces overshoot, providing customers with a better driving experience and fuel economy, while reducing CO2 emissions.

[0031] Furthermore, during open-loop control, if the phase difference between the current phase and the initial installation position is less than the deviation threshold, unlocking is deemed unsuccessful. The current duty cycle is adjusted to the first duty cycle and maintained for time t2. Then, the current duty cycle is adjusted according to the oscillation-assisted unlocking rule and maintained for time t3. The oscillation-assisted unlocking rule includes first adjusting the current duty cycle to the second duty cycle and maintaining for time t4, then adjusting it to the third duty cycle and maintaining for time t5, and so on, cyclically adjusting the current duty cycle. The second duty cycle is greater than the first duty cycle and also greater than the third duty cycle, and time t3 is greater than or equal to the sum of all times t4 and all times t5. This is equivalent to adjusting the current phase of the camshaft left and right to prevent the locking pin from jamming and causing unlocking failure. During the adjustment of the current duty cycle according to the oscillation-assisted unlocking rule (within time t3), the current phase of the camshaft is acquired in real time. If the phase difference between the current phase and the initial installation position is greater than or equal to the deviation threshold, unlocking is deemed successful. Closed-loop control is then applied to the current duty cycle, and the current phase is adjusted to the target phase. If the phase difference between the current phase and the initial installation position is less than the deviation threshold, the unlocking is deemed unsuccessful, and a fault code is reported to remind the user to check. This significantly reduces the occurrence of unlocking failures in intermediate lock-up variable valve timing systems using 4-position 5-way OCV valves, lowering the engine failure rate and saving customers substantial after-sales inspection and repair costs. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the intermediate lock-up variable valve timing system and camshaft according to an embodiment of the present invention;

[0033] Figure 2a This is a schematic diagram of the control oil circuit and the position of the locking pin of the intermediate locking variable valve timing system in the lock-up mode according to an embodiment of the present invention;

[0034] Figure 2b This is a schematic diagram of the control oil circuit and the position of the locking pin in the advance adjustment mode of the intermediate lock-up variable valve timing system according to an embodiment of the present invention;

[0035] Figure 2c This is a schematic diagram of the control oil circuit and the position of the locking pin of the intermediate locking variable valve timing system in unlocking / phase holding mode according to an embodiment of the present invention;

[0036] Figure 2d This is a schematic diagram of the control oil circuit and the position of the locking pin in the lag mode of the intermediate lock-up variable valve timing system according to an embodiment of the present invention.

[0037] Figure 3 This is a flowchart illustrating the unlocking control method of the intermediate lock-up variable valve timing system according to an embodiment of the present invention.

[0038] Figure 4 This is a schematic diagram of the open-loop unlocking of the intermediate locking variable valve timing system according to an embodiment of the present invention;

[0039] Figure 5 This is a schematic diagram of the unlocking control method of the intermediate lock-up variable valve timing system according to an embodiment of the present invention.

[0040] Explanation of reference numerals in the attached figures:

[0041] 100: Camshaft; 200: OCV valve; 210: Valve core; 220: Valve body; 300: Electromagnet; 400: Wiring harness connector; 500: Rotor; 600: Sprocket; 700: Locking pin; 800: Locking pin groove; 900: Rear cover plate; A: Advance oil chamber; B: Lag oil chamber; P: Oil inlet; L: Locking oil chamber; T: Oil outlet. Detailed Implementation

[0042] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a deep understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0043] It should be noted that in this specification, similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0044] In the description of this embodiment, it should be noted that the terms "upper", "lower", "inner", "bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship that the product of the invention is usually placed in during use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0045] The terms “first”, “second”, etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0046] In the description of this embodiment, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set up," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this embodiment based on the specific circumstances.

[0047] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0048] This invention discloses an intermediate lock-up variable valve timing system, such as... Figure 1 As shown, the intermediate lock-up variable valve timing system includes a 4-position 5-way OCV valve 200, an electromagnet 300, a rotor 500, a sprocket 600, and a rear cover plate 900. The rotor 500 is fixed to the 4-position 5-way OCV valve 200, and both the 4-position 5-way OCV valve 200 and the rotor 500 are fixed to the camshaft 100. The sprocket 600 is fixedly connected to the rear cover plate 900, and the sprocket 600 has an oil chamber inside, where the rotor 500 is located. The sprocket 600 is connected to the engine crankshaft via a transmission device (chain). The power transmission method is as follows: once the engine crankshaft rotates, the rotational power is transmitted to the sprocket 600 through the transmission device. The oil pressure in the oil chamber causes the rotor 500 to rotate around its axis, which in turn rotates the camshaft 100. The cam on the camshaft 100 pushes the intake or exhaust valve downwards to open the valve.

[0049] The 4-position 5-way OCV valve 200 includes a valve body 220 and a valve core 210 that can move axially relative to the valve body 220. An electromagnet 300 is positioned opposite one end of the valve core 210. The electromagnet 300 is connected to an electronic control unit (ECU) via a wiring harness connector 400, receives a pulse width modulation (PWM) duty cycle signal from the ECU, generates an axial electromagnetic force, and thus controls the valve core 210 to move axially away from or towards the electromagnet 300 relative to the valve body 220. A larger duty cycle results in a stronger electromagnetic force and a greater movement distance of the valve core 210.

[0050] The control oil circuits of the intermediate lock-up variable valve timing system under different operating modes are as follows: Figures 2a-2d As shown. Figures 2a-2dAs shown, the OCV valve 200 has two oil inlets P, an oil outlet L, and multiple internal oil passages. The intermediate lock-up variable valve timing system also includes a locking pin 700, a locking pin groove 800, and multiple oil chambers. These oil chambers include an advance oil chamber A, a lag oil chamber B, and a lock-up oil chamber L. The locking pin groove 800 is located on the rear cover plate 900 near the rotor 500 and communicates with the lock-up oil chamber L. The rotor 500 has a locking pin hole; one end of the locking pin 700 passes through the locking pin hole, and the other end engages with the locking pin groove 800. With different duty cycles, the valve core 210 moves at different distances, and the internal oil passages of the OCV valve 200 after oil enters from the oil inlet P are also different. This allows the switching of the inlet and outlet oil passages to the advance oil chamber A, the lag oil chamber B, and the locking oil chamber L, thereby determining the rotation direction of the rotor 500 and the unlocking / locking state of the locking pin 700. When the locking pin 700 is located in the locking pin groove 800, the locking pin 700 is in the locked state.

[0051] like Figure 2a As shown, in the lock-up mode, the valve core 210 of the OCV valve 200 is in the initial position. At this time, the oil entering the OCV valve 200 from the oil inlet P does not flow to the advance oil chamber A, the lag oil chamber B, and the lock-up oil chamber L. The oil in the lock-up oil chamber L is discharged from the drain port T. The locking pin 700 is in the locked state. At this time, the rotor 500 cannot rotate relative to the sprocket 600. This mode is generally used when the engine is started.

[0052] like Figure 2b As shown, when the PWM duty cycle increases, the valve core 210 moves inward (to the right) and enters the advance adjustment mode. At this time, the oil entering the OCV valve 200 from the oil inlet P flows to the advance oil chamber A and the lock-up oil chamber L, while the oil in the lag oil chamber B is discharged from the drain port T. In this way, the locking pin 700 can remain in the raised state (moving upward), and the rotor 500 can rotate clockwise relative to the sprocket 600 around its axis, thereby causing the camshaft 100 to adjust in the advance direction.

[0053] like Figure 2c As shown, when the PWM duty cycle continues to increase, the valve core 210 continues to move inward (to the right) and enters the unlock / phase holding mode. At this time, the oil entering the OCV valve 200 from the oil inlet P only goes to the locking oil chamber L, pushing the locking pin 700 to rise or remain in the raised state. The rotor 500 cannot rotate relative to the sprocket 600, and the camshaft 100 phase is not adjusted.

[0054] like Figure 2dAs shown, when the PWM duty cycle continues to increase, the valve core 210 continues to move inward (to the right). At this time, the oil entering the OCV valve 200 from the oil inlet P flows to the hysteresis oil chamber B and the locking oil chamber L, while the oil in the advance oil chamber A is discharged from the drain port T. In this way, the locking pin 700 can remain in the raised state, and the rotor 500 can rotate counterclockwise relative to the sprocket 600 around its axis, thereby causing the camshaft 100 to adjust in the hysteresis direction.

[0055] In other words, by controlling the duty cycle of the electromagnet 300 provided by the electronic control unit, the working mode of the intermediate lock-up variable valve timing system can be controlled, that is, the moving position of the valve core 210 can be controlled, thereby controlling the phase of the camshaft 100.

[0056] Ideally, the unlocking of this intermediate lock-up variable valve timing system requires the duty cycle of the unlock / phase holding mode. However, during the transition from the lock-up mode to the unlock / phase holding mode, the valve core 210 of the OCV valve 200 is gradually pushed in, inevitably experiencing an advance adjustment mode. This means that there will be a brief period of time when the advance oil chamber A of the VVT ​​will be filled with oil. In the high-pressure mode of the engine, the more oil enters the advance oil chamber A, the more likely it is to cause the locking pin 700 to move to the side, that is, the right side of the locking pin 700 abuts against the locking pin groove 800. In this case, the oil pressure at the bottom of the locking pin 700 cannot overcome the frictional force generated by the shearing force of the locking pin 700, thus preventing unlocking. In addition, due to deviations in the consistency of parts manufacturing (differences in the electromagnetic force curve of the electromagnet 300, tolerance of the return spring force of the valve core 210, etc.), even with the same duty cycle, the actual position of the valve core 210 of the OCV valve 200 will have some deviation, resulting in the actual working mode being inconsistent with the expectation.

[0057] To address the risk of the locking pin 700 not unlocking due to being close to the edge under high oil pressure, and considering component deviations, a duty cycle slightly larger than the current duty cycle is generally set (reaching the hysteresis adjustment duty cycle range). This allows some oil to enter the hysteresis oil chamber B of the intermediate lock-up variable valve timing system during the initial unlocking process, pushing the rotor 500 to swing in the opposite direction, preventing the locking pin 700 from being close to the edge. This makes it easier for the locking pin 700 to lift and unlock.

[0058] However, the duty cycle provided by the electronic control unit is open-loop control with a fixed control time. To ensure sufficient time for unlocking, the open-loop time generally has a large margin. This means that towards the end of the open-loop time, after the locking pin 700 unlocks, there will be a certain time lag before oil chamber B continues to supply oil, pushing rotor 500 to adjust in the lag direction. This will cause the intermediate lock-up variable valve timing system to unlock successfully during the open-loop time, but with an overshoot in the lag direction. If the open-loop time is extended, it means that more oil enters the lag chamber B, resulting in a larger overshoot of the intermediate lock-up variable valve timing system.

[0059] To solve the above technical problems, such as Figure 3 As shown, this invention discloses an unlocking control method for an intermediate lock-up variable valve timing system, comprising:

[0060] S1: Obtain the unlock command and the current phase of the camshaft, and determine whether the unlock conditions are met based on the current phase; if the unlock conditions are met, proceed to step S2.

[0061] In one specific implementation, step S1, determining whether the unlocking condition is met based on the current phase, includes: if the current phase is in the initial phase, then the unlocking condition is met; otherwise, the unlocking condition is not met.

[0062] In this embodiment, when it is determined that the unlocking conditions are met, in addition to requiring the current phase to be in the initial phase, it is also required that the enabling conditions of the intermediate lock-up variable valve timing system are met. Generally speaking, if the current engine speed is greater than the idle speed and the current oil temperature is within the range of -10℃ to 130℃, then it is determined that the VVT ​​enabling conditions are met.

[0063] It should be noted that obtaining the current camshaft phase involves the electronic control unit (ECU) reading the phase sensor signal on the camshaft and calculating the current camshaft phase based on the phase sensor signal. The initial lock-up phase refers to the theoretically initial lock-up phase, i.e., the camshaft position when the engine is first started. When the engine is first started, the engine speed and oil temperature have not yet reached the enabling conditions for the intermediate lock-up variable valve timing system. At this time, the camshaft is fixed in the initial phase and cannot be adjusted. The camshaft phase at engine start needs to be determined and preset based on test results, taking into account combustion stability, emissions, and fuel consumption, and stored in the electronic control unit (ECU).

[0064] S2: Obtain the current duty cycle and perform open-loop control on it, maintaining it for time t1. During time t1, obtain the current phase of the camshaft in real time and determine whether unlocking was successful based on the comparison between the current phase and the initial phase. If the phase difference between the current phase and the initial phase is greater than or equal to the deviation threshold, unlocking is successful, and closed-loop control is performed on the current duty cycle, adjusting the current phase to the target phase. If the phase difference between the current phase and the initial phase is less than the deviation threshold, unlocking is unsuccessful, and proceed to step S3. In one specific embodiment, time t1 in step S1 is 0.1s. In another specific embodiment, the deviation threshold in step S1 is 3°CA.

[0065] It should be noted that the current duty cycle refers to the PWM duty cycle signal received by the electromagnet from the electronic control unit. Based on the current duty cycle, the electromagnet can generate axial electromagnetic force, thereby controlling the amount of axial inward pushing of the valve core. This allows switching between the inlet and outlet oil paths to the advance, lag, and lock-up oil chambers, thus determining the rotor's rotation direction and the unlocking / locking state of the locking pin, switching the operating mode of this intermediate lock-up variable valve timing system, and further controlling the current phase of the camshaft. In other words, adjusting the current duty cycle adjusts the current phase of the camshaft.

[0066] It should be further explained that, in this embodiment, as Figure 4 As shown, open-loop control of the current duty cycle refers to the electronic control unit assigning a fixed duty cycle (unlock duty cycle) to the electromagnet. The electromagnet operates according to this fixed duty cycle, pushing the valve spool to switch the operating mode of the intermediate lock-up variable valve timing system and adjust the current phase of the camshaft. This fixed duty cycle is preset based on the engine's oil temperature calibration. Each time unlocking is performed, the engine needs to look up the value from a table based on the real-time oil temperature.

[0067] Closed-loop control of the current duty cycle refers to PID closed-loop control, where the electronic control unit provides the electromagnet with a duty cycle that is adjusted in real time based on the difference between the preset target phase and the actual phase under the operating conditions. The electromagnet will then act according to this real-time adjusted duty cycle, pushing the valve core to adjust the current phase of the camshaft.

[0068] The target phase, which adjusts the current phase to the target phase, refers to the target position of the camshaft in the intermediate lock-up variable valve timing system under different operating conditions during engine operation. This target position is determined by a combination of factors such as fuel consumption, emissions, performance, combustion stability, responsiveness, smoothness, temperature, and altitude. It is usually determined through computer-aided engineering (CAE) calculations and experiments and preset in the ECU.

[0069] S3: As Figure 5 As shown, the current duty cycle is adjusted to the first duty cycle and maintained for time t2. In one specific embodiment, in step S3, the first duty cycle is 10%, and the time t2 ranges from 0.2s to 0.5s. The purpose of this is to keep the locking pin in the locked state, facilitating the entry into step S4.

[0070] It should be noted that in this embodiment, the time t2 can be any one of 0.2s, 0.3s, 0.4s, or 0.5s, or other times between 0.2s and 0.5s. This embodiment does not impose specific restrictions on this, and those skilled in the art can set it according to the actual situation.

[0071] S4: As Figure 5 As shown, the current duty cycle is adjusted according to the oscillation-assisted unlocking rule and maintained for time t3. During time t3, the current phase of the camshaft is acquired in real time, and the unlocking success is determined based on the comparison between the current phase and the initial phase. If the phase difference between the current phase and the initial phase is greater than or equal to the deviation threshold, the unlocking is considered successful, and closed-loop control is applied to the current duty cycle, adjusting the current phase to the target phase. If the phase difference between the current phase and the initial phase is less than the deviation threshold, the unlocking is considered unsuccessful, and a fault code is reported. In one specific embodiment, time t3 is 1 second. In another specific embodiment, the deviation threshold in step S4 is 3°CA.

[0072] Adjusting the current duty cycle according to the oscillation-assisted unlocking rule includes:

[0073] S41: Adjust the current duty cycle to the second duty cycle and maintain it for time t4, then execute step S42; wherein the second duty cycle is greater than the first duty cycle. In one specific embodiment, the second duty cycle is 90% and the time t4 is 0.1s.

[0074] S42: Adjust the current duty cycle to the third duty cycle and maintain it for time t5, then continue executing step S41; wherein the third duty cycle is less than the second duty cycle, and time t3 is greater than or equal to the sum of all times t4 and all times t5. In one specific embodiment, the third duty cycle is 35%, and time t5 is 0.1s.

[0075] It should be noted that in this embodiment, the second duty cycle is 90%, which is a high duty cycle, and the third duty cycle is 35%, which is a low duty cycle. The t3 time is 1 second, and the t4 and t5 times are both 0.1 seconds, meaning that the high and low duty cycles alternate no more than 5 times in the oscillation-assisted unlocking rule. Adjusting the current duty cycle according to the oscillation-assisted unlocking rule avoids the risk of the lock pin 700 being too close to the edge and failing to unlock.

[0076] In this embodiment, the longest running time of step S4 is the sum of time t3 and all judgment times for determining whether unlocking was successful based on the comparison between the current phase and the initial phase of the camshaft. If the longest running time of step S4 reaches time t6 and unlocking is still deemed unsuccessful, a fault code is reported. In one specific embodiment, time t6 ranges from 2s to 3s. Furthermore, if a fault code is reported in two consecutive driving cycles, the instrument panel will illuminate, requiring the customer to bring the vehicle in for inspection. A complete process of ignition, operation, and shutdown of the vehicle is called one driving cycle.

[0077] Using the above technical solution, after obtaining the unlock command and meeting the unlock conditions, the current duty cycle is acquired, and open-loop control is performed on the current duty cycle for a time t1. During the open-loop control process (within t1 time), the current phase of the camshaft is acquired in real time. The unlocking success is determined by comparing the current phase of the camshaft with the initial phase. If the phase difference between the current phase and the initial position is greater than or equal to the deviation threshold, the unlocking is considered successful, and closed-loop control is performed on the current duty cycle to adjust the current phase to the target phase. Compared with the open-loop unlocking strategy, this shortens the unlocking time under normal conditions and reduces the overshoot amplitude, providing customers with a better driving experience and fuel economy, while reducing CO2 emissions.

[0078] Furthermore, during the open-loop control process, if the phase difference between the current phase and the initial position is less than the deviation threshold, it is determined that the unlocking is unsuccessful. The current duty cycle is adjusted to the first duty cycle and maintained for time t2. Then, the current duty cycle is adjusted according to the oscillation-assisted unlocking rule and maintained for time t3. The oscillation-assisted unlocking rule includes adjusting the current duty cycle to the second duty cycle and maintaining for time t4, then adjusting the current duty cycle to the third duty cycle and maintaining for time t5, and so on, cyclically adjusting the current duty cycle. Among them, the second duty cycle is greater than the first duty cycle and greater than the third duty cycle, and the time t3 is greater than the sum of all the time t4 and all the time t5. This is equivalent to adjusting the current phase of the camshaft left and right (the rotor 500 swings due to the pressure difference between the advance oil chamber A and the lag oil chamber B), preventing the unlocking from being unsuccessful due to the locking pin getting stuck at the side. During the adjustment of the current duty cycle according to the oscillation-assisted unlocking rule (within time t3), the current phase of the camshaft is acquired in real time. If the phase difference between the current phase and the initial installation position is greater than or equal to the deviation threshold, the unlocking is considered successful, and closed-loop control is applied to the current duty cycle, adjusting the current phase to the target phase. If the phase difference between the current phase and the initial installation position is less than the deviation threshold, the unlocking is considered unsuccessful, and a fault code is reported to remind the user to check. This significantly reduces the unlocking failure phenomenon of intermediate lock-up variable valve timing systems using 3-position 4-way OCV valves, reduces the engine failure rate, and saves customers a significant amount of after-sales inspection and maintenance costs.

[0079] While the present invention has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the invention to these descriptions. Various changes in form and detail can be made by those skilled in the art, including several simple deductions or substitutions, without departing from the spirit and scope of the invention.

Claims

1. A method for unlocking a center-locking variable valve timing system, characterized in that, The intermediate lock-up variable valve timing system includes a 4-position 5-way oil control valve, and the unlocking control method includes: S1: Obtain the unlock command and the current phase of the camshaft, and determine whether the unlock conditions are met based on the current phase; If it is determined that the unlocking conditions are met, proceed to step S2; S2: Obtain the current duty cycle, perform open-loop control on the current duty cycle and maintain it for time t1; within the time t1, obtain the current phase of the camshaft in real time, and determine whether the unlocking is successful based on the comparison result between the current phase of the camshaft and the initial phase. If the phase difference between the current phase and the initial phase is greater than or equal to the deviation threshold, the unlocking is determined to be successful, the current duty cycle is controlled in a closed loop, and the current phase is adjusted to the target phase. If the phase difference between the current phase and the initial phase is less than the deviation threshold, it is determined that the unlocking is unsuccessful and proceeds to step S3; S3: Adjust the current duty cycle to the first duty cycle and maintain it for time t2; S4: Adjust the current duty cycle according to the oscillation-assisted unlocking rule and maintain it for time t3. During the time t3, obtain the current phase of the camshaft in real time, and determine whether the unlocking is successful based on the comparison result between the current phase of the camshaft and the initial phase. If the phase difference between the current phase and the initial phase is greater than or equal to the deviation threshold, then the unlocking is determined to be successful, the current duty cycle is controlled in a closed loop, and the current phase is adjusted to the target phase. If the phase difference between the current phase and the initial phase is less than the deviation threshold, the unlocking is deemed unsuccessful and a fault code is reported. Adjusting the current duty cycle according to the oscillation-assisted unlocking rule includes: S41: Adjust the current duty cycle to the second duty cycle and maintain it for time t4, then execute step S42; wherein, the second duty cycle is greater than the first duty cycle; S42: Adjust the current duty cycle to the third duty cycle and maintain it for time t5, then continue to execute step S41; wherein the third duty cycle is less than the second duty cycle; and the time t3 is greater than or equal to the sum of all the times t4 and all the times t5.

2. The unlocking control method for the intermediate lock-up variable valve timing system as described in claim 1, characterized in that, In step S1, determining whether the unlocking condition is met based on the current phase includes: if the current phase is in the initial phase, then the unlocking condition is met; otherwise, the unlocking condition is not met.

3. The unlocking control method for the intermediate lock-up variable valve timing system as described in claim 1, characterized in that, In step S1, the time t1 is 0.1s.

4. The unlocking control method for the intermediate lock-up variable valve timing system as described in claim 1, characterized in that, In steps S2 and S4, the deviation threshold is 3°CA.

5. The unlocking control method for the intermediate lock-up variable valve timing system as described in claim 1, characterized in that, In step S3, the first duty cycle is 10%, and the time t2 ranges from 0.2s to 0.5s.

6. The unlocking control method for the intermediate lock-up variable valve timing system as described in claim 1, characterized in that, In step S4, the time t3 is 1 second.

7. The unlocking control method for the intermediate lock-up variable valve timing system as described in claim 1, characterized in that, In step S41, the second duty cycle is 90%.

8. The unlocking control method for the intermediate lock-up variable valve timing system as described in claim 1, characterized in that, In step S41, the time t4 is 0.1s.

9. The unlocking control method for the intermediate lock-up variable valve timing system as described in claim 1, characterized in that, In step S42, the third duty cycle is 35%.

10. The unlocking control method for the intermediate lock-up variable valve timing system as described in any one of claims 1 to 9, characterized in that, In step S42, the time t5 is 0.1s.

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