A method of controlling piston motion and energy output in an opposed piston engine

Abstract

The application provides a kind of control method of piston motion and energy output of opposed-piston engine, comprising: obtaining the average phase difference of the crankshafts on both sides of the engine and the piston motion law of the pistons on both sides;According to the average phase difference and the target average phase difference, and based on the first crankshaft control strategy, determine the required torque cycle average value of the crankshafts on both sides, according to the piston motion law and the target piston motion law, and based on the second crankshaft control strategy, determine the required torque cycle pulsation value of the pistons on both sides;Superimposed processing is carried out on the determined torque cycle average value and torque cycle pulsation value to determine the required cycle torque of the crankshafts on both sides, and then interfere with the piston motion law.The application adopts the energy output mode of double motor, and controls the piston motion and energy output of the crankshafts on both sides of the engine respectively, to realize the purpose of improving overall efficiency and working stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of engines, and particularly relates to a control method for piston movement and energy output of an opposed-piston engine. BACKGROUND

[0002] The double-crankshaft opposed-piston engine has the feature that the two crankshafts output energy at the same time, and how to effectively control the phase relationship between the two crankshafts is the key to stable operation and performance improvement.

[0003] The prior art (such as CN109844283A - gear train for opposed-piston engine) usually adopts a transmission mechanism such as a gear train to associate the two crankshafts, which can keep the instantaneous rotational speeds of the two crankshafts consistent to ensure that the phase difference is unchanged, and is also helpful to integrate the output energy of the two crankshafts. However, mechanical loss caused by the transmission mechanism is difficult to avoid, which reduces the upper limit of the effective efficiency of the engine. The prior art ((CN105102763A - mechanism for changing crankshaft timing on a belt / chain driven double-crankshaft opposed-piston engine) also provides another way, that is, adjusting the crankshaft timing of the opposed-piston engine through belt / chain driving. However, this technology needs to adjust the position of the tensioner to change the timing, which is relatively complex, and it is difficult to adjust it in real time during work if there is an abnormality. Moreover, this technology still needs a complex transmission mechanism, causing mechanical loss.

[0004] Therefore, how to effectively control the average phase difference between the two crankshafts and the piston movement law of the two pistons of the double-crankshaft opposed-piston engine with double-motor power generation under the premise of ensuring stable operation of the engine, reduce the fluctuation of the output torque, and improve the overall efficiency are technical problems that need to be solved by those skilled in the art. SUMMARY

[0005] Therefore, how to effectively control the average phase difference between the two crankshafts and the piston movement law of the two pistons of the double-crankshaft opposed-piston engine with double-motor power generation under the premise of ensuring stable operation of the engine, reduce the fluctuation of the output torque, and improve the overall efficiency are technical problems that need to be solved by those skilled in the art.

[0006] To achieve the above-mentioned purpose, the technical scheme of the application is as follows:

[0007] In a first aspect, the application provides a control method for piston movement and energy output of an opposed-piston engine, comprising:

[0008] obtaining the average phase difference between the two crankshafts and the piston movement law of the two pistons of the engine;

[0009] According to the average phase difference and the target average phase difference, and based on a preset first crank control strategy, a required torque cycle average value of the two-side cranks is determined, and according to the piston motion law and the target piston motion law, and based on a preset second crank control strategy, a required torque cycle pulsation value of the two-side pistons is determined;

[0010] The torque cycle average value and the torque cycle pulsation value are superimposed to determine a required cycle torque of the two-side cranks, and then interfere with the piston motion law.

[0011] Further, the method further comprises:

[0012] The target average phase difference of the two-side cranks and the target piston motion law of the two-side pistons of the opposed-piston engine are obtained, and the energy output ratio of the two-side cranks is determined according to the target average phase difference.

[0013] The two-side cranks are respectively configured with corresponding flywheels according to the energy output ratio.

[0014] Further, the required moment of inertia of the flywheel is obtained based on an energy balance formula, and the flywheel is configured according to the moment of inertia, and the energy balance formula is:

[0015] ;

[0016] Wherein, ;

[0017] In the formula, represents the moment of inertia, represents the work done by the cycle, represents the average speed, represents the allowable speed fluctuation range, represents the maximum speed of the cycle, represents the minimum speed of the cycle.

[0018] Further, the piston motion law is calculated according to the current two-side crank angles and the structural parameters of the engine crank connecting rod mechanism, and through a piston displacement formula, the piston displacement formula is as follows:

[0019] ;

[0020] In the formula, represents the crank radius, represents the connecting rod length, represents the crank connecting rod ratio, represents the crank angle, represents the piston displacement.

[0021] Further, the first crank control strategy comprises:

[0022] According to the deviation result of the average phase difference from the target average phase difference and a set deviation threshold, in response to the deviation result being greater than or equal to the deviation threshold, the exhaust side performs speed closed-loop control, the intake side performs phase difference closed-loop control, and the circulating average torque of the motor to the crankshaft is adjusted through current intensity to adjust the average phase difference to the target average phase difference.

[0023] In response to reaching the target average phase difference, the two generators on the two sides respectively perform speed closed-loop control on the two crankshafts to determine the required torque circulating average value of the two crankshafts.

[0024] Further, the second crankshaft control strategy comprises:

[0025] According to the piston motion law and the corresponding measured original load torque, the original equivalent net torque is obtained through a dynamic equation;

[0026] Based on the target piston motion law, a target instantaneous speed is obtained, and a target instantaneous load torque is calculated according to the original equivalent net torque and the dynamic equation;

[0027] According to the target instantaneous load torque, the torque cycle pulsation value is obtained.

[0028] Further, the original equivalent net torque formula is as follows:

[0029] ;

[0030] In the formula, represents the original load torque, represents the derivative of the measured instantaneous speed with respect to the angle, represents the measured instantaneous speed, represents the original equivalent net torque.

[0031] Further, the target instantaneous load torque formula is as follows:

[0032] ;

[0033] In the formula, represents the derivative of the target instantaneous speed with respect to the angle, represents the target instantaneous speed, represents the target instantaneous load torque.

[0034] Further, the torque cycle pulsation value formula is as follows:

[0035] ;

[0036] In the formula, represents the target instantaneous load torque, represents the target instantaneous load torque average value, represents the torque cycle fluctuation value.

[0037] Further, the cycle torque formula is as follows:

[0038] ;

[0039] In the formula, represents the torque cycle average value, represents the torque cycle fluctuation value, represents the cycle torque.

[0040] Compared with the prior art, the method for controlling piston movement and energy output of an opposed-piston engine has the following beneficial effects:

[0041] The method described in the application achieves the purpose of improving overall efficiency and work stability by adopting the energy output mode of double motors and controlling the piston movement and energy output of the two crankshafts of the engine. BRIEF DESCRIPTION OF DRAWINGS

[0042] The accompanying drawings, which form a part of the present application, are intended to provide further understanding of the present application, and are used to explain the illustrative embodiments of the present application and their descriptions, and do not constitute improper limitations to the present application. In the drawings:

[0043] Figure 1 A flow chart of a method for controlling piston movement and energy output of an opposed-piston engine according to an embodiment of the present application;

[0044] Figure 2 A schematic diagram of a double-motor energy output and piston movement control mode according to an embodiment of the present application;

[0045] Figure 3 A schematic diagram of a target piston movement law of an opposed-piston engine according to an embodiment of the present application. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to specific embodiments and the accompanying drawings.

[0047] It should be noted that the technical terms or scientific terms used in the embodiments of the present application should be understood as the general meaning understood by those skilled in the art to which the embodiments of the present application belong, unless otherwise defined. The terms "first", "second" and the like used in the embodiments of the present application do not represent any order, number or importance, but are only used to distinguish different components. The terms "include" or "contain" and the like mean that the elements or objects before the terms cover the elements or objects listed after the terms and their equivalents, and do not exclude other elements or objects. The terms "connect" or "connected" and the like are not limited to physical or mechanical connection, but can include electrical connection, whether direct or indirect. The terms "upper", "lower", "left", "right" and the like are only used to represent relative positional relationship, and when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0048] The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0049] Please refer to Figure 1 As shown in the figure, the embodiments provide a method for controlling piston movement and energy output of an opposed-piston engine. The method adopts a double-motor energy output mode (schematic diagram of double-motor energy output and piston movement law control mode as shown in Figure 2 The method discards gear train, belt and chain transmission mechanisms, reduces engine mechanical loss; provides a flywheel for each of the two crankshafts, reduces torque and speed fluctuation, and improves power generation efficiency; respectively interferes with the speed of the two crankshafts, improves the constant volume degree of engine combustion, and further improves thermal efficiency; adopts a closed-loop control strategy switching mode to control the average speed and average phase difference of the two crankshafts, and ensure efficient and stable energy output, which specifically includes the following steps:

[0050] In step S101, the average phase difference of the two crankshafts and the piston movement law of the two pistons are obtained. Specifically, in the embodiments, a position sensor is installed at each of the two crankshafts or flywheels to obtain the average phase difference and the piston movement law. A magnetic induction type or Hall type position sensor is used, wherein the magnetic induction type generates an alternating voltage signal by sensing the signal tooth on the flywheel, and the signal frequency is proportional to the crankshaft speed; the Hall type uses a Hall element to detect the signal tooth and outputs a digital signal, which accurately reflects the crankshaft position. After obtaining the digital signal, the ECU can calculate the current two crankshaft angles according to the signal, and the instantaneous phase difference and the average phase difference can be obtained by subtracting the two crankshaft angles. The two pistons are controlled asynchronously in the embodiments to increase the potential for improving thermal efficiency, so the instantaneous phase difference is not a fixed value, and the average phase difference is the main concern here.

[0051] According to the current two crankshaft angles and the structural parameters of the engine crank connecting rod mechanism, the piston movement law is calculated by using the following formula:

[0052]

[0053] wherein, is the crank radius, is the connecting rod length, is the crank-connecting rod ratio (φ), ), is the crank angle, is the piston displacement.

[0054] In some embodiments, further comprising:

[0055] obtaining a target average phase difference of the two sides of the crankshaft of the opposed-piston engine and a target piston motion law of the two sides of the piston, determining the energy output ratio of the two sides of the crankshaft according to the target average phase difference;

[0056] configuring corresponding flywheels for the two sides of the crankshaft according to the energy output ratio.

[0057] Specifically, in the present embodiment, the phase difference of the opposed-piston engine has an influence on the compression ratio, the gas exchange process, the combustion process and the power output, and the target average phase difference is determined through tests and simulation calculations in the design stage, and the energy output ratio of the two sides of the crankshaft is determined according to the target average phase difference, and the specific method is:

[0058] assuming that the in-cylinder pressure of the engine is uniformly distributed, the pressure applied to the two sides of the piston is the same, and according to the phase of the two sides of the crankshaft, the indicator diagrams of the exhaust side and the intake side are drawn, and finally the energy output ratio is determined according to the area ratio of the indicator diagrams.

[0059] In the present embodiment, the phase of the intake side of the crankshaft is later than that of the exhaust side, the target average phase difference is 5°CA, and the energy output ratio of the exhaust side to the intake side is about 6:4 calculated by the indicator diagram.

[0060] For the target piston motion law, diesel engine performance calculation software and optimization algorithm can be used, taking the piston motion law as a variable, taking the maximum torque under the rated power of the generator as a constraint (the angular acceleration of the crankshaft is mainly determined by the in-cylinder pressure and the torque applied to the crankshaft by the generator, and it is necessary to ensure that the power of the generator is within the normal working range), and taking the improvement of the indicated power as the target for optimization to obtain the target piston motion law.

[0061] The method for determining the target piston motion law is relatively complex. In the initial prototype design process, the method for determining the target piston motion law can be simplified according to theoretical analysis: under the condition that the compression ratio is unchanged, the Otto cycle has higher thermal efficiency due to its higher constant volume degree. If the thermal efficiency is taken as the target, the actual cycle needs to be closer to the Otto cycle, which can be achieved by increasing the dwell time of the piston near the top dead center. Therefore, the rotational speed of the crankshaft is reduced when the piston is near the top dead center under the condition that the crankshaft angular acceleration requirement is met.

[0062] In this embodiment, the second method is adopted, that is, the target crankshaft rotational speed is determined by adjusting parameters based on the sine function. The rotational speed of the crankshaft is less than the average value when the piston is near the top dead center (-45°CA~45°CA), the constant volume degree of combustion is increased, and the thermal efficiency is improved. The rotational speed of the crankshaft is less than the average value when the piston is near the bottom dead center (135°CA~225°CA), the scavenging time is increased, and the proportion of waste residues is reduced. The rotational speed of the crankshaft is greater than the average value at other times (45°CA~135°CA and 225°CA~315°CA) to ensure that the average rotational speed is unchanged. The final target piston motion law is shown in FIG. 2. Figure 3

[0063] According to the energy output condition and based on the energy balance formula, the required rotational inertia of the flywheel is obtained, and the flywheel is configured according to the rotational inertia. The energy balance formula is:

[0064]

[0065] The rotational inertia of the flywheel is I, The work done by the cycle is W, The average rotational speed is n, The allowable rotational speed fluctuation range is Δn (0.01 in this embodiment), The definitions are as follows:

[0066]

[0067] The maximum rotational speed of the cycle is n max, The minimum rotational speed of the cycle is n min.

[0068] In step S102, the required torque cycle average value of the two side crankshafts is determined according to the average phase difference and the target average phase difference and based on the preset first crankshaft control strategy, and the required torque cycle pulsation value of the two side pistons is determined according to the piston motion law and the target piston motion law and based on the preset second crankshaft control strategy.

[0069] ​Specifically, in the present embodiment, during power generation, the motor applies a torque to the crankshaft opposite to the rotational speed, on the one hand, the average rotational speed of the engine needs to be controlled, on the other hand, the instantaneous rotational speed in the cycle also needs to be controlled, in order to quickly determine the required torque, the Reynolds decomposition concept in the reference fluid is used to decompose the torque, the torque cycle average value is determined through step S201, and the torque cycle pulsation value is determined through step S202.

[0070] Step S201, compare the average phase difference with the target average phase difference, and determine the required torque cycle average value .

[0071] Specifically, during normal operation, the rotational speed of the two crankshafts is controlled by the two generators respectively, the average phase difference is monitored, when the deviation of the average phase difference and the target average phase difference is greater than or equal to the deviation threshold, the rotational speed of the exhaust side is controlled by the rotational speed closed loop control, the rotational speed of the intake side is controlled by the phase difference closed loop control, the average torque of the crankshaft is adjusted by the current intensity, and the average phase difference is adjusted to the target average phase difference.

[0072] After reaching the target average phase difference, the rotational speed of the two crankshafts is controlled by the two generators respectively, the phase difference is continuously monitored, and then the required torque cycle average value of the two crankshafts is determined.

[0073] Step S202, compare the piston motion law of the two pistons with the target piston motion law respectively, and determine the required torque cycle pulsation value .

[0074] Specifically, the piston motion law in the present embodiment specifically refers to the curve of the change of the piston displacement with time. The monitored piston motion law and the target curve are compared, and the piston motion law is controlled in a closed loop with each cycle as a period, so that the piston motion law approaches the target curve. According to the difference between the monitored piston motion law and the target curve as shown in Figure 3 , combined with the engine design parameters such as moment of inertia, the required torque cycle pulsation value can be calculated according to the dynamics calculation method.

[0075] Further, first, the original equivalent net torque is calculated by using the piston motion law obtained in the above steps and the corresponding measured original load torque.

[0076] The dynamics equation of the engine crankshaft system is:

[0077]

[0078] In the formula, I is the total moment of inertia of the system, which is an engine design parameter; is the angular velocity; is the angular acceleration; The equivalent net torque (including all non-load torques such as indicated torque, friction torque, etc.) is equivalent to the load torque. The load torque is equivalent to the equivalent net torque.

[0079] For the convenience of calculation and understanding, the time derivative is converted into the crank angle derivative:

[0080]

[0081] The original equivalent net torque can be obtained by bringing the piston motion law and the corresponding measured original load torque into the dynamic equation:

[0082]

[0083] In the formula, The original equivalent net torque is equivalent to the load torque. The original load torque can be regarded as a constant value in each cycle when no active intervention is performed. The measured instantaneous speed is calculated by the measured piston motion law. The derivative of the measured instantaneous speed with respect to the angle is calculated.

[0084] Then, the target instantaneous load torque is calculated by using the target instantaneous speed calculated by the target piston motion law and the original equivalent net torque by using the dynamic equation:

[0085]

[0086] In the formula, The target instantaneous speed (the structure of the engine crankshaft and piston is a simple slider-crank structure, the target instantaneous speed is calculated by using common kinematics calculation software such as Creo and Ansys, and combining the engine structure according to the target piston motion law) is equivalent to the load torque. The target instantaneous load torque is equivalent to the equivalent net torque. The target equivalent net torque is equivalent to the load torque.

[0087] It should be noted that the original equivalent net torque mainly includes the indicated torque (non-load torque) , the friction torque (non-load torque) , etc. Among them, the indicated torque can be determined according to the in-cylinder pressure, system inertia force and structure parameters under normal circumstances. The in-cylinder pressure measurement cost is extremely high, especially for multi-cylinder engines. However, the in-cylinder pressure and system inertia force are strongly related to the engine operating conditions. Under the same operating conditions, the in-cylinder pressure and system inertia force are almost the same due to the same engine load and average speed. Therefore, the target indicated torque is approximately equal to the original indicated torque under the same operating conditions. Similarly, the friction torque is also mainly related to the engine operating conditions, and the target friction torque The original friction torque The original friction torque

[0088] Therefore, the target equivalent net torque in the embodiment The original friction torque The target instantaneous load torque is calculated, and the dependence on the in-cylinder pressure and other difficult-to-obtain parameters is avoided, and the target instantaneous load torque is finally calculated:

[0089]

[0090] Finally, the target instantaneous load torque obtained by the above method is used to calculate the required torque cycle fluctuation value:

[0091]

[0092] In the formula, The target instantaneous load torque is represented by Ttarget. The target instantaneous load torque average value is obtained by averaging the target instantaneous load torque, and is represented by Ttarget_avg. The torque cycle fluctuation value is represented by Tcycle.

[0093] Step S103, superimposing the determined torque cycle average value and the torque cycle fluctuation value to determine the required cycle torque of the two side crankshafts, and then interfering with the piston motion law.

[0094] Specifically, in the embodiment, the torque cycle average value applied to the two side crankshafts is determined according to the result of step S201, the torque cycle fluctuation value applied to the two side crankshafts is determined according to the result of step S202, the required cycle torque is determined by superimposition, and the generator current is back calculated.

[0095] .

[0096] The method described in the embodiment realizes the purpose of improving overall efficiency and work stability by adopting the energy output mode of the double motor and controlling the piston motion and energy output of the two side crankshafts of the engine respectively.

[0097] It should be noted that the above describes some embodiments of the present application. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims can be performed in an order different than that described in the above embodiments and still achieve the desired result. In addition, the processes depicted in the figures do not necessarily require the particular order shown or sequential order to achieve the desired results. In certain implementations, multitasking and parallel processing can be advantageous.

[0098] Embodiments of the present application are intended to embrace all such alterations, modifications, and variations that fall within the broad scope of the appended claims. Accordingly, any one or more features of a given embodiment are intended to be illustrative only and not limiting of the scope of the application.

Claims

1. A method of controlling piston motion and energy output of an opposed piston engine, characterized by, The method comprises the following steps: acquiring the average phase difference of the two crankshafts and the piston motion law of the two pistons; determining the required torque cycle average value of the two crankshafts according to the average phase difference and the target average phase difference and based on a preset first crankshaft control strategy, and determining the required torque cycle pulsation value of the two pistons according to the piston motion law and the target piston motion law and based on a preset second crankshaft control strategy; superimposing the determined torque cycle average value and the torque cycle pulsation value to determine the required cycle torque of the two crankshafts, and then interfering with the piston motion law; the first crankshaft control strategy comprises: comparing the deviation of the average phase difference from the target average phase difference with a set deviation threshold value, and in response to the deviation being greater than or equal to the deviation threshold value, performing speed closed-loop control on the exhaust side and phase difference closed-loop control on the intake side, adjusting the cycle average torque of the crankshafts by the current intensity of the motor, and adjusting the average phase difference to the target average phase difference; in response to reaching the target average phase difference, performing speed closed-loop control on the two crankshafts by the two generators respectively to determine the required torque cycle average value of the two crankshafts; the second crankshaft control strategy comprises: obtaining the original equivalent net torque through a dynamics equation according to the piston motion law and the corresponding measured original load torque; obtaining the target instantaneous speed according to the target piston motion law, and calculating the target instantaneous load torque according to the original equivalent net torque and the dynamics equation; obtaining the torque cycle pulsation value according to the target instantaneous load torque.

2. The method of claim 1, wherein, The method further comprises: acquiring the target average phase difference of the two crankshafts and the target piston motion law of the two pistons of the opposed-piston engine, and determining the energy output ratio of the two crankshafts according to the target average phase difference; configuring corresponding flywheels for the two crankshafts according to the energy output ratio.

3. The method of claim 2, wherein, obtaining the required moment of inertia of the flywheel based on an energy balance formula, and configuring the flywheel according to the moment of inertia, wherein the energy balance formula is: wherein, where I represents the moment of inertia, E represents the work done by the cycle, ω mean represents the average rotational speed, δ represents the allowable rotational speed fluctuation range, ω max represents the maximum rotational speed of the cycle, ω min represents the minimum rotational speed of the cycle.

4. The method of claim 1, wherein, obtaining the piston motion law by calculating through a piston displacement formula according to the current angles of the two crankshafts and the structural parameters of the engine crank connecting rod mechanism, wherein the piston displacement formula is as follows: wherein r represents the crank radius, l represents the connecting rod length, λ represents the crank connecting rod ratio, θ represents the crank angle, and x represents the piston displacement.

5. The method of claim 1, wherein, the original equivalent net torque formula is as follows: where T load_ori represents the original load torque, represents the derivative of the measured instantaneous rotational speed with respect to the rotational angle, ω meas (θ) represents the measured instantaneous rotational speed, T eff_ori represents the original equivalent net torque.

6. The method of claim 5, wherein, the target instantaneous load torque formula is as follows: In the formula, ω (θ) represents the derivative of the target instantaneous rotational speed with respect to the rotational angle, ω target ω (θ) represents the target instantaneous rotational speed, T load_target ω (θ) represents the target instantaneous load torque.

7. The method of claim 1, wherein, the torque cycle pulsation value formula is as follows: where T load_target (θ) represents the target instantaneous load torque, T' represents the torque ripple value.

8. The method of claim 1, wherein, the cycle torque formula is as follows: wherein denotes the torque cycle average value, T ′ denotes the torque cycle pulsation value, T denotes the cycle torque.

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