A method for dual-lift camshaft valve timing for extended range engine

Abstract

A valve train method for a dual-lift camshaft in a range-extending engine belongs to the field of automotive engine technology. The invention includes the following steps: Cam profile design: designing the cam profile of the camshaft, wherein the cam buffer section adopts a constant acceleration-constant velocity profile, and the cam working section adopts a high-power polynomial cam profile design method to design the first cam profile and the second cam profile respectively; Cam profile correction: using a cam profile dynamic correction method, obtaining the final first target cam profile and the second target cam profile used for machining the camshaft; Operating condition selection and valve drive: selecting the engine's operating point, and driving the valves to open and close according to the corresponding valve motion law through a rocker arm valve train mechanism to achieve valve train operation. This invention can solve the technical problems of existing fixed-lift camshafts in range-extending engines, which cannot simultaneously meet the requirements of economic operating conditions and rated operating conditions, as well as poor NVH performance and high mechanical losses.

Description

Technical Field

[0001] This invention belongs to the field of automotive engine technology, and specifically relates to a valve train method for a dual-lift camshaft in a range extender engine. Background Technology

[0002] With improvements in engine thermal efficiency and electric motor efficiency, as well as the promotion of new energy technologies, new energy vehicles have received increasing attention and popularity. Compared to fully electric vehicles, new energy vehicles generally employ range extenders and hybrid power to increase driving range and eliminate range anxiety. With the gradual emergence of high-efficiency range extender technology, range extender systems are developing towards greater efficiency and quieter operation.

[0003] In traditional technology, range-extending engines typically use camshafts with fixed valve lift. This fixed valve timing and lift cannot simultaneously meet the performance requirements of the engine under two different operating conditions: the economic power range and the rated power range. At the economic power point, a fixed valve lift may result in significant pumping losses, negatively impacting fuel economy; conversely, at the rated power point, a fixed valve lift may fail to meet the intake demands under heavy loads, limiting power output. Furthermore, when the engine operates under fixed conditions for extended periods in range-extending mode, traditional camshafts are prone to significant noise, vibration, and harshness (NVH) issues, as well as mechanical wear, leading to decreased ride comfort and energy waste. Summary of the Invention

[0004] This invention addresses the aforementioned problems and overcomes the shortcomings of existing technologies by providing a valve train method for a dual-lift camshaft in a range-extending engine. This invention solves the technical problems of existing fixed-lift camshafts in range-extending engines, which cannot simultaneously meet the requirements of economic and rated operating conditions, as well as poor NVH performance and high mechanical losses.

[0005] To achieve the above objectives, the present invention adopts the following technical solution.

[0006] This invention provides a method for valve timing with a dual-lift camshaft in a range-extending engine, characterized by comprising the following steps:

[0007] S1. Cam profile design: Design the cam profile of the camshaft. The cam buffer section adopts the constant acceleration-constant speed profile form, and the cam working section adopts the high-power polynomial cam profile design method. Design the first cam profile that conforms to the valve motion law of the economic operating point of the range extender engine and the second cam profile that conforms to the valve motion law of the rated operating point.

[0008] S2. Cam profile correction: The cam profile dynamic correction method is used to correct the first cam profile and the second cam profile to obtain the first target cam profile and the second target cam profile used for machining the camshaft.

[0009] S3. Operating Condition Selection and Valve Drive: The vehicle control unit (VCU) selects the engine's operating condition point by integrating the battery state of charge (SOC), vehicle speed, and pedal opening signals. Once the operating condition point is confirmed, the engine electronic control unit (ECU) sends a command to the tappet control mechanism to drive the tappet to move, so that the tappet selectively contacts the target cam on the camshaft corresponding to the operating condition point. Then, the rocker arm valve train drives the valve to open and close according to the corresponding valve movement law to achieve valve distribution. The target cam is a cam with the first target cam profile or a cam with the second target cam profile.

[0010] Furthermore, the characteristic feature is that the constant acceleration-constant velocity profile selected for the cam buffer section in step S1 includes:

[0011] The constant acceleration segment is expressed as: h t =cφ c 2 ,

[0012] In the formula, c is the coefficient of the quadratic term, and φ c 2 The cam rotation angle is defined as 0 ≤ φ. c ≤Φ 01 Φ 01 The angle of containment is constant acceleration;

[0013] The constant velocity segment is expressed as: h t =v0(φ c -Φ 01 )+h 01 ,

[0014] In the formula, v0 is the geometric velocity in mm / °, and h 01 φ is the tappet displacement at the end of the constant acceleration phase and the beginning of the constant velocity phase. c The range is Φ 01 ≤φ c ≤Φ0, Φ 01 This is the buffer zone's wrap angle.

[0015] Furthermore, the high-order polynomial cam profile design method used in step S1 for the cam working section is expressed as follows:

[0016]

[0017] Where: C0, C2, C p,··· are the coefficients of each term in the equation, θ is the working half-wrap angle of the cam, p, q, r, s are the power exponents sorted by power of lift, x is the camshaft rotation angle, and its range is 0≤x≤θ; y is the corresponding tappet lift.

[0018] Furthermore, the cam profile dynamic correction method in step S2 is performed using the following formula:

[0019]

[0020] This modified formula is used to establish the relationship between equivalent tappet lift, physical acceleration, and geometric acceleration, where the parameters are: L0 is the valve clearance, F0 / C0 is the static deformation of the mechanism caused by the spring preload, and C... s y / C0 represents the static deformation of the mechanism caused by the valve spring force. The dynamic deformation caused by inertial force, equivalent tappet lift x t * =ix t x t Let i be the actual displacement of the tappet, and i be the rocker arm ratio. The physical acceleration is mm / s. is the geometric acceleration in mm / °, and n is the harmonic order.

[0021] Furthermore, in step S3, the vehicle control unit (VCU) selects the engine's operating condition point by integrating the battery state of charge (SOC), vehicle speed, and pedal opening signals. Specifically, when the operating condition point is confirmed as the economic operating condition point, the target cam is a cam with the first target cam profile; when the operating condition point is confirmed as the rated operating condition point, the target cam is a cam with the second target cam profile.

[0022] Furthermore, in step S3, the engine electronic control unit (ECU) sends a command to the tappet control mechanism to drive the tappet to move. Specifically, the tappet control mechanism moves the tappet axially according to the command of the ECU, so that the working surface of the tappet contacts and engages with the working surface of the target cam.

[0023] Furthermore, the constant acceleration-constant velocity profile in step S1 is used to ensure that the acceleration is zero when the valve opens or sits, so as to reduce the impact.

[0024] Furthermore, the cam-type linear dynamic correction method in step S2 is used to make the valve train operate more smoothly under both operating conditions, in order to optimize noise, vibration and acoustic roughness (NVH) and reduce mechanical losses.

[0025] Furthermore, the high-order polynomial cam profile design method in step S1 is used to make the cam profile have a continuous acceleration curve, a small negative acceleration, and a positive inertial force, so as to prevent fly-off and reduce impact.

[0026] The beneficial effects of the present invention.

[0027] This invention, by designing two independent cam profiles and coordinating with a controllable tappet movement mechanism, enables the engine to utilize optimal valve lift patterns under both economic and rated operating conditions. This resolves the contradiction of traditional fixed-lift camshafts being unable to meet the demands of different operating conditions, achieving efficiency optimization across the entire operating range. The cam buffer section employs a constant acceleration-constant velocity profile, ensuring smoothness during valve opening and seating, and reducing impact and noise. The cam working section utilizes a high-power polynomial cam profile design method, resulting in a continuous acceleration curve with lower peak values, reducing vibration and the risk of valve train failure. Furthermore, a cam profile dynamic correction method is used to further optimize the profile dynamics, significantly improving the stability of the valve train across the entire operating speed range, reducing NVH issues and mechanical losses, and meeting the development requirements of high efficiency and quiet operation for range extender systems. Attached Figure Description

[0028] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0029] Figure 1 This is a schematic flowchart of the gas mixing method of the present invention. Detailed Implementation

[0030] Referring to the accompanying drawings, this embodiment provides a valve train method for a dual-lift camshaft in a range-extending engine. The method specifically includes the following steps:

[0031] S1, Cam profile design

[0032] First, for the two typical operating conditions of the range extender engine—the economic operating point and the rated operating point—two different cam profiles are designed, namely the first cam profile and the second cam profile.

[0033] In the design of the cam profile, the cam buffer section adopts a constant acceleration-constant velocity profile. Its specific expression consists of two parts:

[0034] The constant acceleration segment is expressed as: h t =cφ c 2 .

[0035] In the formula, c is the coefficient of the quadratic term, and φ c 2 The cam rotation angle is defined as 0 ≤ φ.c ≤Φ 01 Φ 01 The angle of containment is the constant acceleration.

[0036] The constant velocity segment is expressed as: h t =v0(φ c -Φ 01 )+h 01 .

[0037] In the formula, v0 is the geometric velocity in mm / °, and h 01 φ is the tappet displacement at the end of the constant acceleration phase and the beginning of the constant velocity phase. c The range is Φ 01 ≤φ c ≤Φ0, Φ 01 This is the buffer zone's wrap angle.

[0038] This valve profile design ensures that the valve's acceleration is zero at the moment of opening and closing, thereby effectively reducing the impact caused by inertial forces.

[0039] The working section of the cam adopts a high-order polynomial cam profile design method, the expression of which is shown in the following formula:

[0040] .

[0041] Where: C0, C2, C p ,··· are the coefficients of each term in the equation, θ is the working half-wrap angle of the cam, p, q, r, s are the power exponents sorted by power of lift, x is the camshaft rotation angle, and its range is 0≤x≤θ; y is the corresponding tappet lift.

[0042] By adjusting various coefficients and power exponents, the first and second cam profiles can be designed to conform to the valve motion laws at the economic and rated operating points of the range extender engine. The profiles obtained by this design method have the characteristics of continuous acceleration curves, small negative acceleration, and small positive inertial forces, which helps to prevent mechanism fly-off and reduce impact during operation.

[0043] S2, Cam Profile Correction

[0044] After completing the initial geometric profile design, to further improve the dynamic performance of the valve train, this invention employs a cam profile dynamic correction method to modify the first and second cam profiles, resulting in the final first and second target cam profiles used for machining the camshaft. The correction method is performed using the following formula:

[0045] .

[0046] This modified formula is used to establish the relationship between equivalent tappet lift, physical acceleration, and geometric acceleration, where the parameters are: L0 is the valve clearance, F0 / C0 is the static deformation of the mechanism caused by the spring preload, and C... s y / C0 represents the static deformation of the mechanism caused by the valve spring force. The dynamic deformation caused by inertial force, equivalent tappet lift x t * =ix t x t Let i be the actual displacement of the tappet, and i be the rocker arm ratio. The physical acceleration is mm / s. is the geometric acceleration in mm / °, and n is the harmonic order.

[0047] This modification takes into account practical factors such as the elastic deformation and clearance of the valve train, so that the final cam profile can make the movement of the valve train smoother in actual operation, significantly optimize NVH performance and reduce mechanical wear.

[0048] S3, Operating Condition Selection and Valve Actuation

[0049] The valve train adopts a rocker arm type valve train and is combined with a double-lift camshaft, which integrates two different profile cams, corresponding to the economic operating condition and the rated operating condition respectively.

[0050] During engine operation, the vehicle control unit (VCU) continuously monitors and integrates various signals such as battery state of charge (SOC), vehicle speed, and pedal opening to determine and select the most suitable engine operating condition.

[0051] Once the operating point is confirmed, such as when the engine needs to generate electricity at the economy point, the engine electronic control unit (ECU) receives the command from the VCU and then sends a control signal to the tappet control mechanism. The tappet control mechanism operates according to the ECU's command, driving the tappet to move axially, so that the tappet's contact surface moves from its current position to a position where it contacts the target cam (economy cam) with the first target cam profile. As the camshaft rotates, this target cam drives the valves through the tappet and rocker arm valve train, causing them to open and close according to the predetermined economy valve movement pattern, achieving efficient and economical valve timing.

[0052] Conversely, when the VCU determines that the engine needs to output rated power, the ECU controls the tappet control mechanism to move the tappet to contact the target cam (rated operating condition cam) with the second target cam profile, thereby driving the valve to work according to the valve movement law of rated operating condition to meet the intake demand of high load.

[0053] The above methods enable the range extender engine to switch valve lift and valve timing on demand under different operating conditions, balancing economy and power. At the same time, through optimized cam profile design and correction, the engine's NVH performance and reliability are significantly improved.

[0054] It is understood that the above specific description of the present invention is only for illustrating the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention to achieve the same technical effect; as long as the use needs are met, they are all within the protection scope of the present invention.

Claims

1. A valve train method for a dual-lift camshaft in a range-extending engine, characterized in that, Includes the following steps: S1. Cam profile design: Design the cam profile of the camshaft. The cam buffer section adopts the constant acceleration-constant speed profile form, and the cam working section adopts the high-power polynomial cam profile design method. Design the first cam profile that conforms to the valve motion law of the economic operating point of the range extender engine and the second cam profile that conforms to the valve motion law of the rated operating point. S2. Cam profile correction: The cam profile dynamic correction method is used to correct the first cam profile and the second cam profile to obtain the first target cam profile and the second target cam profile used for machining the camshaft. S3. Operating Condition Selection and Valve Drive: The vehicle control unit (VCU) selects the engine's operating condition point by integrating the battery state of charge (SOC), vehicle speed, and pedal opening signals. Once the operating condition point is confirmed, the engine electronic control unit (ECU) sends a command to the tappet control mechanism to drive the tappet to move, so that the tappet selectively contacts the target cam on the camshaft corresponding to the operating condition point. Then, the rocker arm valve train drives the valve to open and close according to the corresponding valve movement law to achieve valve distribution. The target cam is a cam with the first target cam profile or a cam with the second target cam profile.

2. The valve train method for a dual-lift camshaft in a range-extending engine according to claim 1, characterized in that, The constant acceleration-constant velocity profile used in the cam buffer section in step S1 includes: The constant acceleration segment is expressed as: h t =cφ c 2 , In the formula, c is the coefficient of the quadratic term, φc2 is the cam rotation angle, and its range is 0≤φc≤Φ01, where Φ01 is the constant acceleration wrap angle; The constant velocity segment is expressed as: h t =v0(φ c -Φ 01 )+h 01 , In the formula, v0 is the geometric velocity in mm / °, and h 01 φ is the tappet displacement at the end of the constant acceleration phase and the beginning of the constant velocity phase. c The range is Φ 01 ≤φ c ≤Φ0, Φ 01 This is the buffer zone's wrap angle.

3. The valve train method for a dual-lift camshaft in a range-extending engine according to claim 1, characterized in that, The high-order polynomial cam profile design method used in step S1 for the cam working section is expressed as follows: In the formula: C0, C2, C p ,··· are the coefficients of each term in the equation, θ is the working half-wrap angle of the cam, p, q, r, s are the power exponents ordered by their powers of 1, x is the camshaft rotation angle, with a range of 0 ≤ x ≤ θ; y is the corresponding tappet lift.

4. The valve train method for a dual-lift camshaft in a range-extending engine according to claim 1, characterized in that, The cam profile dynamic correction method in step S2 is performed using the following formula: ， This modified formula is used to establish the relationship between equivalent tappet lift, physical acceleration, and geometric acceleration, where the parameters are: L0 is the valve clearance, F0 / C0 is the static deformation of the mechanism caused by the spring preload, and C... s y / C0 represents the static deformation of the mechanism caused by the valve spring force. The dynamic deformation caused by inertial force, equivalent tappet lift x t * =ix t x t Let i be the actual displacement of the tappet, and i be the rocker arm ratio. The physical acceleration is mm / s. is the geometric acceleration in mm / °, and n is the harmonic order.

5. The valve train method for a dual-lift camshaft in a range-extending engine according to claim 1, characterized in that, In step S3, the vehicle control unit (VCU) selects the engine's operating condition point by integrating the battery state of charge (SOC), vehicle speed, and pedal opening signals. Specifically, when the operating condition point is confirmed as the economic operating condition point, the target cam is a cam with the first target cam profile; when the operating condition point is confirmed as the rated operating condition point, the target cam is a cam with the second target cam profile.

6. The valve train method for a dual-lift camshaft in a range-extending engine according to claim 1, characterized in that, In step S3, the engine electronic control unit (ECU) sends a command to the tappet control mechanism to drive the tappet to move. Specifically, the tappet control mechanism moves the tappet axially according to the command of the ECU, so that the working surface of the tappet contacts and engages with the working surface of the target cam.

7. The valve train method for a dual-lift camshaft in a range-extending engine according to claim 1, characterized in that, The constant acceleration-constant velocity profile in step S1 is used to ensure that the acceleration is zero when the valve opens or sits, so as to reduce the impact.

8. The valve train method for a dual-lift camshaft in a range-extending engine according to claim 1, characterized in that, The cam-type linear dynamic correction method in step S2 is used to make the valve train operate more smoothly under both operating conditions, in order to optimize noise, vibration and acoustic roughness (NVH) and reduce mechanical losses.

9. A method for valve timing with a dual-lift camshaft in a range-extending engine according to claim 1, characterized in that, The high-order polynomial cam profile design method in step S1 is used to make the cam profile have a continuous acceleration curve, a small negative acceleration, and a positive inertial force to prevent fly-off and reduce impact.

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