Method for matching generator and engine characteristics at high altitude

Abstract

The present application relates to the technical field of matching of starter-generator and power device, and discloses a method for matching characteristics of starter-generator and engine in high-altitude environment. The crankshaft angle position of the engine is in (0°, 180°), the engine is started by the motor, if the engine cannot cross the first top dead center, the crankshaft angle position is matched again, if the engine can cross the first top dead center, the engine enters the next cycle and is started to rotate, when the last cycle before the engine reaches the stable rotating speed, if the maximum rotating speed of the last cycle of the engine is greater than the rotating speed threshold, the starting matching is successful, if the maximum rotating speed is less than the rotating speed threshold, the working point of the starter-generator is matched again. If the crankshaft angle position of the engine is in (0°, 180°) and the starter-generator cannot cross the first top dead center, the starter-generator is matched by reverse rotation and energy storage. The present application reduces the capacity requirement of the starter-generator by using the form of energy storage, successfully expands the minimum boundary of the starting matching, and increases the application range of the starter-generator in different environmental conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of matching of starter-generator and power device, in particular to a method for matching characteristics of starter-generator and engine in high-altitude environment. BACKGROUND

[0002] The starting process is the initial preparation stage before the engine enters the working state. The engine can only run stably after overcoming the starting torque and reaching a certain high speed in the starting process. Through the drag of the starter-generator on the engine, the speed of the engine is accelerated from zero to the speed at which the engine ignites and the mixture burns, so that the engine can run stably, and the starter-generator is disconnected from the engine. In the high-altitude, low-temperature and low-pressure environment, the starting characteristics of the starter-generator and the torque characteristics of the engine change differently compared to the ground. Therefore, the matching between the engine and the starter-generator is particularly important in the complex and variable high-altitude environment. The drag speed of the starter-generator determines whether the engine can reach the minimum ignition temperature, and the torque of the engine affects the drag speed and starting current of the starter-generator under this load. The power of the matched starter-generator determines the working point of the engine starting power in different high-altitude environments.

[0003] In the traditional matching process of the starter-generator and the engine, the torque and speed of the starter-generator are matched according to the average torque and average speed of the engine during the drag. The power of the matched starter-generator is calculated accordingly. However, this method reflects the matching of the stable working condition of the starter-generator. However, in the case where the characteristics of the starter-generator and the engine change in the high-altitude, low-temperature and low-pressure environment, the traditional matching method will no longer be applicable. SUMMARY

[0004] To solve the above problems, the purpose of the present application is to provide a method for matching characteristics of starter-generator and engine in high-altitude environment. In the matching process of the starter-generator, the form of energy storage is used to reduce the demand for the capacity of the starter-generator, successfully expanding the minimum boundary of the starting matching and increasing the application range of the starter-generator in different environmental conditions. The technical solution is as follows:

[0005] A method for matching characteristics of starter-generator and engine in high-altitude environment, comprising the following steps:

[0006] Step 1: Analyzing the starter-generator drag engine starting transient process

[0007] According to the movement process of the engine piston, the starting process of the first cycle of the engine starting is divided into five parts from the bottom dead center of the engine piston, and the relationship between the starting torque of the starter-generator and the friction torque, compression torque and inertia torque of the engine in each part is analyzed; the engine torque before the piston of the first cycle and the last cycle of the engine starting reaches the top dead center is determined.

[0008] Step 2: Matching strategy

[0009] The engine crank angle position is initially at 0° < a < 180°, the starter generator drags the engine to start, if the engine cannot cross the first top dead center, the crank angle position is matched again; if the engine can cross the first top dead center, the engine enters the next cycle and starts to rotate; when the starting reaches the last cycle, if the maximum speed of the engine in the last cycle is greater than the speed threshold, the starting matching is successful, if the maximum speed of the engine in the last cycle is less than the speed threshold, the working point of the starter generator is matched again;

[0010] If the engine crank angle position is at 0° < a < 180°, and the engine cannot cross the first top dead center, the starter generator is reversed to store energy, the acceleration distance of the starter generator reverse rotation to the engine gas compression and increase the inertial torque makes the engine piston cross the first top dead center; after the starter generator reverse energy storage, if it can cross the first top dead center, and the maximum speed of the last cycle is greater than the speed threshold, the starting matching is successful; if the maximum speed of the last cycle is less than the speed threshold, the working point of the starter generator is matched again; if it cannot cross the first top dead center after reverse energy storage, the reverse crank angle position is matched again; but if the maximum torque of the starter generator cannot reach the starting position of the reverse energy storage, it is considered that the starter generator exceeds the minimum starting boundary of the engine.

[0011] Further, in step 1, the five parts of the starting process of the first cycle are specifically:

[0012] The first part, at the starting moment of the engine piston from the bottom dead center, the starting torque of the starter generator is greater than the static friction torque of the engine; the starter generator drags the engine to start and accelerate, the drag speed rises, and the drag is a constant;

[0013] The second part, the engine piston goes up, the output torque of the starter generator is greater than the sum of the friction torque, the compression resistance torque and the inertia resistance torque of the engine; the acceleration of the drag decreases, and the growth of the drag speed slows down;

[0014] The third part, the output torque of the starter generator and the resistance torque of the engine reach the first balance point in this cycle, the output torque of the starter generator is equal to the sum of the compression resistance torque and the friction resistance torque of the engine; the output torque of the starter generator and the inertia resistance torque of the engine drive the engine piston to continue to approach the top dead center, and the inertia resistance torque does positive work on the engine piston;

[0015] The expression of the engine resistance torque before the engine piston goes to the top dead center in the first cycle of starting is:

[0016] T Z1 =T M +TP +T G (1)

[0017] where: T Z1 is the resistance torque of the engine before the top dead center of the first cycle of engine starting; T M is the friction resistance torque of the engine; T P is the compression resistance torque of the engine; T G is the inertia resistance torque of the engine;

[0018] The fourth part, the engine piston moves to the top dead center, the output torque of the starter generator and the resistance torque of the engine will reach the second equilibrium point in this cycle; the drag acceleration is 0, and the torque of the starter generator is equal to the friction resistance torque of the engine;

[0019] The fifth part, the engine piston passes the top dead center, the torque of the starter generator and the force torque generated by the expansion of the cylinder gas are greater than the friction resistance torque and the inertia resistance torque of the engine, and the engine accelerates into the next cycle;

[0020] The expression of the resistance torque of the engine before the top dead center of the piston in the last cycle of engine starting is:

[0021]

[0022] where: T Zn is the resistance torque of the engine in the last cycle of engine starting; is the dynamic friction resistance torque at the speed n; is the inertia torque of the last cycle speed n and the maximum speed of the previous cycle.

[0023] Further, the matching calculation of the first cycle of engine starting includes:

[0024] The expression of the matching of the starting torque of the starter generator and the resistance torque of the engine before the top dead center of the first cycle is:

[0025] T em >T M +T G +T P (3)

[0026] where: T em is the starting torque of the starter generator;

[0027] Integrate the entire starting process before the top dead center of the first cycle, and the integral expression is:

[0028]

[0029] where: α is the crank angle, 0° < α < 180°;

[0030] The integral expression for the engine friction torque is:

[0031]

[0032] Wherein: F c F is the frictional force between the piston and the cylinder liner. z Main bearing friction force; r z r is the inner ring radius of the bearing; r is the crank radius; l is the connecting rod length;

[0033] Inertial drag torque includes reciprocating inertial drag torque T j and rotational inertial drag torque T r Then the integral expression for the inertial drag torque is:

[0034]

[0035] Where: m j m is the equivalent reciprocating mass of the piston connecting rod. r The equivalent mass of the crank and connecting rod big end rotation; This is the first derivative of the crankshaft rotation angle α, i.e., the crankshaft rotation angle angular velocity; This is the second derivative of the crankshaft rotation angle α, i.e., the crankshaft rotation angle angular acceleration;

[0036] The integral expression for the compressive resistance torque is:

[0037]

[0038] Where: S is the equivalent area of ​​the engine piston; ΔP is the pressure difference between the cylinder and the crankcase.

[0039] If the integral of the difference between the starter torque and the engine resistance torque is greater than 0 within a crankshaft angle of 0° to 180°, the starter torque can drive the engine through the first cycle. If the integral of the difference is equal to 0 within a crankshaft angle of 0° to 180°, the engine piston will just stop at top dead center. Calculate the ideal crankshaft angle α′ that will allow the piston to stop at top dead center. When the crankshaft angle α is less than the ideal crankshaft angle α′, the piston can pass top dead center. When the crankshaft angle α is greater than the ideal crankshaft angle α′, the piston cannot pass top dead center.

[0040] Furthermore, the matching calculations for the last cycle of engine starting include:

[0041] The integral expression for the torque difference between the top dead center of the last cycle and the bottom dead center of the previous cycle is:

[0042]

[0043] Wherein: T emN The electromagnetic torque of the generator during its last cycle; TGN is the inertia moment of the last cycle;

[0044] At this time, the force is balanced when the last cycle passes the top dead center, as shown in the following formula:

[0045]

[0046] Then, the expression of the rotational speed of the piston when passing the bottom dead center during the stable dragging of the starter generator rated power is:

[0047]

[0048] wherein n max is the maximum rotational speed when the last cycle passes the top dead center; p e is the starter generator rated power;

[0049] The maximum rotational speed of the engine is matched as:

[0050] n max ≥ 900 r / min (11).

[0051] Further, the matching calculation of the reverse energy storage includes:

[0052] The expression of the compression energy storage of the reverse starter generator is:

[0053]

[0054] wherein α" is an angle equal to the position of the crankshaft rotational angle α symmetrically;

[0055] The integral expression of the residual compression resistance moment of the first cycle after the reverse energy storage is:

[0056]

[0057] The integral expressions of the friction resistance moment and the inertia resistance moment are:

[0058]

[0059] Then, the entire integral expression of the reverse energy storage of the starter generator is:

[0060]

[0061] If the starter generator can drag the engine piston over the first top dead center after the reverse energy storage, and the maximum rotational speed n max ≥ 900 r / min, the reverse energy storage matching starting is successful; if the maximum energy storage of the reverse starter generator still cannot pass the first top dead center, it is determined that the starter generator and the engine are not matched.

[0062] The beneficial effects of the present application are:

[0063] 1) The present application proposes a new matching method and compensation strategy for the starting process of the starter-generator and engine. In the matching process of the starter-generator, the energy storage form is used to reduce the capacity demand of the starter-generator, successfully expanding the lowest boundary of the starting matching, and increasing the application range of the starter-generator in different environmental conditions.

[0064] 2) The present application uses the compression energy storage and inertial energy storage of the piston engine to assist in starting the starter-generator to successfully pass the first top dead center, so it is suitable for various types of piston engines and has a certain universality. BRIEF DESCRIPTION OF DRAWINGS

[0065] Figure 1 is a schematic diagram of the engine starting transient process.

[0066] Figure 2 is a transient variation diagram of the engine starting resistance torque.

[0067] Figure 3 is a schematic diagram of the starter-generator and engine starting matching logic.

[0068] Figure 4 is a schematic diagram of the starter-generator and engine reverse energy storage starting matching logic.

[0069] Figure 5 is a starter-generator and engine first cycle matching diagram.

[0070] Figure 6 is a schematic diagram of the starter-generator reverse energy storage matching.

[0071] Fig. 7(a)-(c) is a diagram of the instantaneous speed of the starter-generator dragging the engine starting engine at the crank angle of 60°, 0° and -60°. DETAILED DESCRIPTION

[0072] The present application will be further described in detail below in combination with the drawings and specific examples.

[0073] The present application analyzes the starter-generator dragging the engine starting transient process, proposes a new method and strategy for the starting characteristic matching of the starter-generator and engine in the high-altitude environment, and performs matching calculation. The matching evaluation index is also proposed.

[0074] 1. Starting transient process analysis

[0075] The starter-generator dragging the engine starting process is a dynamic process, such as Figure 1The figure shows the schematic diagram of the first cycle of the starter-generator dragging engine, the upper part of the figure is the change of the rotational speed of the starter-generator dragging engine at the start, and the lower part is the change of the acceleration of the engine.

[0076] In Figure 1 the first cycle, the engine piston is assumed to be at the bottom dead center, and the starting process of the first cycle can be divided into five parts. The first part is the starting moment, the starting torque of the starter-generator is greater than the static friction torque of the engine, the starter-generator drags the engine to start and accelerate, and the dragging rotational speed rises. At this time, the compression resistance torque of the engine has little effect on the output torque of the starter-generator, so the acceleration can be regarded as a constant. When entering the second part, with the upward movement of the engine piston, the in-cylinder pressure gradually increases, and the compression resistance torque also gradually increases. At this time, the output torque of the starter-generator is greater than the friction resistance torque, the compression resistance torque and the inertia resistance torque of the engine, but the dragging acceleration decreases obviously, and the dragging rotational speed grows slowly. In the third part, the output torque of the starter-generator and the resistance torque of the engine reach the first balance point in this cycle. At this time, the output torque of the starter-generator is equal to the sum of the compression resistance torque and the friction resistance torque of the engine, the dragging acceleration is 0, and the dragging rotational speed reaches the maximum rotational speed in this cycle. After that, the dragging acceleration is negative, and the dragging rotational speed decreases accordingly. However, the output torque of the starter-generator and the inertia resistance torque of the engine drive the engine piston to continue to approach the top dead center. At this time, the inertia resistance torque does positive work on the engine piston. In the fourth part, the engine piston moves to the top dead center. At this time, the output torque of the starter-generator and the resistance torque of the engine will reach the second balance point in this cycle. The dragging acceleration is also 0, but the dragging rotational speed is the lowest rotational speed in this cycle. At this time, the torque of the starter-generator is equal to the friction resistance torque of the engine. After passing the top dead center, the engine enters the fifth part, and the acceleration of the dragging engine is greater than 0 again. The torque of the starter-generator and the force generated by the expansion of the in-cylinder gas are greater than the friction resistance torque and the inertia resistance torque of the engine, and the engine accelerates into the next cycle.

[0077] Inside the engine, the transient change of the engine starting resistance torque is as shown in Figure 2 The instantaneous resistance torque of the engine during the first cycle of engine starting is obviously greater than the resistance torque when the rotational speed is stable after starting. Before the top dead center of the piston in the first cycle, the engine resistance torque is composed of the friction resistance torque, the compression resistance torque and the inertia resistance torque, among which the friction resistance torque changes from the static friction resistance torque to the dynamic friction resistance torque, the compression resistance torque increases sharply after passing a certain point of the crank angle with the upward movement of the piston, and the inertia resistance torque does positive work or negative work with the change of the output torque of the starter-generator. Therefore, the expression of the resistance torque of the engine before the top dead center in the first cycle of engine starting is:

[0078] T Z1 = T M + T P + TG (1)

[0079] Wherein: T Z1 T is the resistance torque before top dead center of the engine in the first cycle; M T is the engine frictional resistance torque; P T is the engine compression resistance torque; G This is the engine's inertial drag torque;

[0080] and Figure 2 The last cycle in this context does not refer to the final cycle of the entire engine starting process, but rather to the last change in engine speed as the starter generator pulls the engine from 0 to a stable speed, which is also the first value of the stable speed. However, since the engine resistance torque fluctuates, and so does the engine speed, the stable speed is the minimum and maximum speed at which the piston passes through top dead center and bottom dead center when the engine is being pulled. At this point, the engine speed stabilizes within a certain range, and the stable speed taken here is the lower limit of this range, which is the speed *n* when the piston reaches top dead center. This is because the engine resistance torque at top dead center in the last cycle determines the highest speed that the starter generator can pull the engine to. Therefore, the expression for the engine resistance torque before the piston reaches top dead center in the last cycle is:

[0081]

[0082] Wherein: T Zn The resistance torque for the last cycle of engine starting; The dynamic friction resistance torque is at rotational speed n; The torque of inertia is the sum of the rotational speed n of the last cycle and the maximum rotational speed of the previous cycle.

[0083] 2. Starter generator and engine starting matching strategy and calculation

[0084] A new method for matching the characteristics of the starter generator and the engine during engine start-up, considering the resistance torque characteristics and the output characteristics of the starter generator, is proposed for high-altitude environments.

[0085] 2.1 Matching Methods and Strategies

[0086] like Figure 3 As shown, the engine crankshaft angle position is initially at 0° < α < 180°. The starter generator drives the engine to start. If the engine cannot pass the first top dead center, the crankshaft angle position is rematched. If the engine can pass the first top dead center, the engine enters the next cycle and starts rotating. When the engine reaches the last cycle, if the maximum speed n of the last cycle is ≥ 900 r / min, the start-up matching is successful. If it is less than the maximum speed of the last cycle, the starter generator operating point is rematched.

[0087] If the matched starting crank angle position is 0° < a < 180°, the engine cannot cross the first top dead center, the motor generator can be reversed to store energy, and the motor generator is reversed to accelerate the distance of the gas compression and the inertial torque of the engine to make the engine piston cross the first top dead center.

[0088] As Figure 4 shown is a starting matching logic diagram of the motor generator and the engine reverse energy storage starting, at this time the motor drives the engine to reverse to the crank angle range of the previous top dead center -180° < a < 0°, after the motor generator is reversed to store energy, if the first cycle maximum speed n ≥ 900 r / min, the starting matching is successful, if the last cycle maximum speed n < 900 r / min, the motor generator operating point needs to be matched again, if the first top dead center cannot be crossed after the reverse energy storage, the reverse crank angle position needs to be matched again, but if the motor generator maximum torque cannot cross the first top dead center at the position of the reverse energy storage starting, it is considered that the motor generator exceeds the minimum starting boundary of the engine.

[0089] 2.2 First cycle matching calculation

[0090] In the starting transient process analysis, it is known that the engine resistance torque in the first cycle of the starting transient is obviously greater than the resistance torque in the subsequent cycles, and thus the maximum torque of the motor generator at the starting time is greater than the resistance torque of the engine at any position from 0° to 180° before the first cycle top dead center, as Figure 5 shown, from the figure, it can be seen that when the piston is at the bottom dead center, the engine resistance torque is the smallest, and the energy storage of the inertial resistance torque is the largest, and when the piston is at the previous moment, the engine resistance torque is the largest, and the energy storage of the inertial resistance torque is the smallest, and even if the motor generator starting maximum torque is less than the resistance torque at a certain point, the motor generator at the starting time may be reversed, causing the motor generator to fail to successfully drive the engine to start successfully.

[0091] Therefore, the expression of the motor generator starting torque and the engine resistance torque matching before the first cycle top dead center is:

[0092] T em > T M + T G + T P (3)

[0093] Wherein: T em is the motor generator starting torque.

[0094] But in the process of starting, the engine friction torque, compression resistance torque and inertia resistance torque are all changing, and the inertia resistance torque can do positive work or negative work, so the growth rate of the starter torque of the starter generator can be less than the growth rate of the compression resistance torque at some point. Therefore, the integral of the difference between the starter torque of the starter generator and the engine resistance torque is calculated for the whole starting process before the top dead center of the first cycle, and the integral expression is:

[0095]

[0096] Wherein: α is the crank angle, 0° < α < 180°

[0097] Since the engine friction torque is mainly concentrated in the friction between the piston and the cylinder sleeve and the friction of the main bearing, the integral expression of the engine friction torque is:

[0098]

[0099] Wherein: F c is the friction between the piston and the cylinder sleeve; F z is the friction of the main bearing; r z is the radius of the bearing inner ring; r is the crank radius; and l is the length of the connecting rod.

[0100] Since the inertia resistance torque includes the reciprocating inertia resistance torque T j and the rotating inertia resistance torque T r , the integral expression of the inertia resistance torque is:

[0101]

[0102] Wherein: m j is the equivalent reciprocating mass of the piston and connecting rod; and m r is the rotating equivalent mass of the crank and the big end of the connecting rod.

[0103] The integral expression of the compression resistance torque is:

[0104]

[0105] Wherein: S is the equivalent area of the engine piston; and ΔP is the pressure difference between the cylinder and the crankcase.

[0106] Therefore, when the integral of the difference between the starter torque of the starter generator and the engine resistance torque is greater than 0 at the crank angle of 0° to 180°, the starter generator can drag the engine over the first cycle; if the integral of the difference is equal to 0 at the crank angle of 0° to 180°, the engine piston just stops at the top dead center, and the ideal crank angle α' at which the piston just stops at the top dead center is calculated as above. When the crank angle α is less than the ideal crank angle α', the piston can pass the top dead center; when the crank angle α is greater than the ideal crank angle α', the piston cannot pass the top dead center.

[0107] And for the second cycle, since a compression energy storage is done after the top dead center of the first cycle, the friction torque of the second cycle is smaller than that of the first cycle, so the starter generator will also drag the engine to go through the second cycle successfully, until the engine drag speed tends to be stable after the Nth cycle.

[0108] 2.3 Last cycle matching calculation

[0109] When the drag speed reaches the last cycle N before the speed stabilizes, this cycle determines the maximum speed that the starter generator can drag the engine to reach, so the torque difference between the top dead center of the last cycle and the bottom dead center of the previous cycle is integrated as follows:

[0110]

[0111] Where: T emN is the electromagnetic torque of the starter generator at the last cycle; is the dynamic friction torque at speed n; T GN is the inertial torque when dragging the last cycle.

[0112] At this time, the force is balanced when passing through the top dead center of the last cycle, as shown below:

[0113]

[0114] Therefore, the expression of the speed of the piston passing through the bottom dead center when the drag is stable can be obtained from the rated power of the starter generator as follows:

[0115]

[0116] Where: n max is the maximum speed when passing through the top dead center of the last cycle; p e is the rated power of the starter generator.

[0117] And the engine ECU is designed to work when the engine drag speed reaches 900r / min, once the oil injector works, the mixture enters the cylinder, the spark plug ignites, even if not every cycle in the cylinder ignites, but as long as one point starts to ignite, the entire starting process has chemical energy combustion work, the speed will gradually rise. Therefore, the maximum speed matching is:

[0118] n max ≥ 900r / min (11)

[0119] 2.4 Reverse energy storage matching calculation

[0120] In the first cycle matching, if the starter-generator starting maximum torque at the engine crank angle position 0° < a < 180° cannot drive the piston over the first top dead center, the starter-generator can be reversed to store energy to increase the initial torque and the acceleration distance of the inertial torque of the starter-generator, so that the starter-generator has greater ability to overcome the top dead center. As shown in FIG. 3, the starter-generator reverse energy storage matching engine crank angle position diagram is shown in FIG. 3. Figure 6 As shown in FIG. 3, the starter-generator reverse energy storage matching engine crank angle position diagram is shown in FIG. 3. Figure 6 In the first cycle matching, if the starter-generator starting maximum torque at the engine crank angle position 0° < a < 180° cannot drive the piston over the first top dead center, the starter-generator can be reversed to store energy to increase the initial torque and the acceleration distance of the inertial torque of the starter-generator, so that the starter-generator has greater ability to overcome the top dead center. As shown in FIG. 3, the starter-generator reverse energy storage matching engine crank angle position diagram is shown in FIG. 3.

[0121]

[0122] Wherein: a and a" positions are symmetrically equal.

[0123] Therefore, the remaining compression resistance torque integral expression of the first cycle after reverse energy storage is:

[0124]

[0125] The integral expression of the friction resistance torque and the inertial resistance torque is:

[0126]

[0127] The entire integral expression of the starter-generator reverse energy storage is:

[0128]

[0129] If the starter-generator can drive the engine piston over the first top dead center after reverse energy storage, and the maximum speed n max ≥ 900 r / min, the reverse energy storage matching starting is successful. If the maximum energy storage of the starter-generator after reverse cannot overcome the first top dead center, it can be determined that the starter-generator and the engine are not matched.

[0130] 3. High-altitude starting matching test result analysis

[0131] In the drag torque characteristics of the engine in the high-altitude low-temperature low-pressure environment, the friction drag torque is mainly affected by temperature, the lower the temperature, the greater the friction drag torque, and the compression drag torque is mainly affected by the environmental pressure, the lower the environmental pressure, the compression drag torque will also decrease, therefore, when the starting generator is matched with the engine in high-altitude starting, the environmental temperature is selected as-60℃, which is relatively large compared with the normal temperature environment, and the compression drag torque is selected as the maximum under normal pressure, that is, 95kPa atmospheric pressure, so as to match the starting generator with the engine at different crankshaft angle positions when the starting condition is the maximum compression drag torque and the maximum friction drag torque.

[0132] In this embodiment, 72-toothed disc and magnetoelectric sensor are used to collect the instantaneous speed during starting, and current clamp is used to collect the instantaneous current during starting of the starting generator, so as to measure the starting condition of the engine before the top dead center, at the bottom dead center and after the top dead center of the previous cycle. During the process of matching the starting generator with the engine, the starting condition of the starting generator dragging the engine at different crankshaft torque positions is different, and in the evaluation index of the starting matching of the starting generator and the engine, the cycle number N used by the starting generator to drag the engine to start and the time used by the speed to reach 1000r / min are used as the evaluation index of the starting matching, so as to evaluate the cycle number used by the starting generator to drag the engine to start at different crankshaft angle positions, the fewer the cycle number used by the starting generator to drag the engine to reach the specified speed, the smaller the starting ability of the starting generator to drag the engine to start, the larger the matching space of the starting generator and the engine, and the wider the applicable environment range.

[0133] FIG. 7(a)-(c) is a diagram of the instantaneous speed of the engine changing with time when the starting generator drags the engine to start at the crankshaft angle of 60°, 0° and-60°. FIG. 7(a) is a diagram of the instantaneous speed changing with time at the crankshaft angle of 60°; FIG. 7(b) is a diagram of the instantaneous speed changing with time at the crankshaft angle of 0°; and FIG. 7(c) is a diagram of the instantaneous speed changing with time at the crankshaft angle of-60°.

[0134] It can be seen from the figure that the transient speed change of the drag is different when starting at different crank angle positions. When the crank angle position is 60°, the acceleration distance is short because the position is close to the top dead center, so the starting speed changes from acceleration to deceleration for the first time at 0.026s after starting, and changes from deceleration to acceleration at 0.0402s after passing the top dead center, thus the starter generator dragging the engine experiences the first cycle, and the speed interval is 200r / min-400r / min. When the crank angle position is 0°, the first speed change and the second speed change occur at 0.0439s and 0.0518s respectively because the position is far from the 60° crank angle position, and the speed change interval is 680r / min-800r / min. When the crank angle position is -60°, the first speed change and the second speed change occur at 0.0663s and 0.0772s respectively because the position is farthest from the top dead center, and the speed change interval is 900r / min-1100r / min. Because the change rate is very small when the speed tends to be stable in the test, it is difficult to distinguish the difference between the last cycle and the previous cycle, so the cycle time and the time required when the speed reaches 1000r / min are selected in the test. In figure 7(a), the cycle number experienced when starting at the crank angle position of 60° and reaching 1000r / min is 4, in figure 7(b), the cycle number experienced when starting at the crank angle position of 0° and reaching 1000r / min is 4, and in figure 7(c), the cycle number experienced when starting at the crank angle position of -60° and reaching 1000r / min is 3. It is obvious that the cycle time experienced when starting at the crank angle position of -60° and reaching 1000r / min is smaller than that at the crank angle positions of 60° and 0°, but the cycle numbers at the crank angle positions of 60° and 0° are both 4, so the time required to reach 1000r / min is used to distinguish the starting conditions at the two positions, and through comparison of the data, the time required to reach 1000r / min when starting at the crank angle position of 60° is 0.175s, and the time required to reach 1000r / min when starting at the crank angle position of 0° is 0.16s, which indicates that the time required when starting at the crank angle position of 60° is greater than that at the crank angle position of 0°, and the time required when starting at the crank angle position of -60° is 0.152s, which is obviously shorter than that at the crank angle positions of 0° and 60°.

[0135] The present application analyzes the starting transient process of the starter generator dragging the engine, proposes a new method and strategy for matching the starting characteristics of the starter generator and the engine in a high-altitude environment, and performs matching calculation; finally, a starter generator and engine starting matching test is performed, a matching evaluation index is proposed, and the feasibility of the new starting matching method and strategy is verified through analysis of the test results, and the conclusions are as follows:

[0136] (1) Select the cycle experienced by the engine when the speed reaches 1000r / min, the crank angle is 60° and the cycle number experienced when starting from the crank angle 0° to reach 1000r / min is 4, and the cycle number experienced when starting from the crank angle-60° to reach 1000r / min is 3, so the cycle number experienced when starting from the crank angle-60° to reach 1000r / min is less than that when starting from the crank angle 60° and the crank angle 0°.

[0137] (2) Select the required time, the time required for starting from the crank angle 60° to reach 1000r / min is 0.175s, the time required for starting from the crank angle 0° to reach 1000r / min is 0.16s, which indicates that the time required for starting from the crank angle 60° is greater than that from the crank angle 0°, and the time required for starting from the crank angle-60° is 0.152s, which is significantly shorter than that from the crank angle 0° and 60°.

Claims

1. A method for matching the characteristics of a generator and an engine in a high-altitude environment, characterized in that, Includes the following steps: Step 1: Analyze the transient process of starting the generator-driven engine. Based on the movement of the engine piston, starting from the bottom dead center, the starting process of the first cycle of engine starting is divided into five parts, and the relationship between the generator starting torque and the engine frictional resistance torque, compression resistance torque and inertial resistance torque in each part is analyzed accordingly; the engine resistance torque before the piston reaches the top dead center in the first and last cycles of engine starting is determined. Step 2: Matching Strategy The engine crankshaft angle position is initially at 0° < α < 180°. The starter generator drives the engine to start. If the engine cannot pass the first top dead center, the crankshaft angle position is rematched. If the engine can pass the first top dead center, the engine enters the next cycle and starts rotating. When the starting reaches the last cycle, if the maximum speed of the engine in the last cycle is greater than the speed threshold, the starting match is successful. If the maximum speed of the engine in the last cycle is less than the speed threshold, the starter generator operating point is rematched. If the engine crankshaft angle is between 0° and α, but the engine cannot pass the first top dead center, the starter generator is reversed to store energy. The acceleration distance caused by the starter generator's reverse rotation compressing the engine gas and increasing the inertial torque allows the engine piston to pass the first top dead center. After the starter generator reverses to store energy, if it can pass the first top dead center and the maximum speed of the last cycle is greater than the speed threshold, the starter matching is successful. If the maximum speed of the last cycle is less than the speed threshold, the starter generator operating point is rematched. If the crankshaft rotation angle cannot be exceeded after reversing the energy storage, the crankshaft rotation angle position is rematched. However, if the starter generator's maximum torque cannot exceed the first top dead center even when starting at the reachable reversing energy storage position, the starter generator is considered to have exceeded the engine's minimum starting boundary.

2. The method for matching the characteristics of a generator and engine in a high-altitude environment according to claim 1, characterized in that, In step 1, the five parts of the starting process of the first loop are as follows: In the first part, at the instant the engine piston starts from the bottom dead center, the starting torque of the starter generator is greater than the static friction torque of the engine; the starter generator drags the engine to start and accelerate, and the speed increases due to the dragging, which is a constant. In the second part, the engine piston moves upward, and the generator output torque is greater than the sum of the engine's frictional resistance torque, compression resistance torque, and inertial resistance torque; the drag acceleration decreases, and the increase in drag speed becomes slower. In the third part, the starter torque and engine resistance torque reach the first equilibrium point in this cycle. The starter torque is equal to the sum of the engine compression resistance torque and friction resistance torque. The starter torque and engine inertial resistance torque drive the engine piston to continue to approach the top dead center. The inertial resistance torque does positive work on the engine piston. The expression for the engine resistance torque before the piston reaches top dead center in the first cycle of engine startup is: T Z1 =T M +T P +T G (1) Wherein: T Z1 The resistance torque T is the torque required before the engine reaches top dead center during the first cycle of startup. M T is the engine frictional resistance torque; P T is the engine compression resistance torque; G This is the engine's inertial drag torque; In the fourth part, when the engine piston reaches top dead center, the generator output torque and engine resistance torque will reach the second equilibrium point in this cycle; the drag acceleration is 0, and the generator torque is equal to the engine friction resistance torque. In the fifth part, the engine piston passes the top dead center. The torque generated by the generator torque and the torque generated by the expansion of gas in the cylinder are greater than the engine friction torque and inertial resistance torque, and the engine accelerates into the next cycle. The expression for the engine resistance torque before the piston reaches top dead center in the last cycle of engine startup is: Wherein: T Zn The resistance torque for the last cycle of engine starting; The dynamic friction resistance torque is at rotational speed n; The torque of inertia is the sum of the rotational speed n of the last cycle and the maximum rotational speed of the previous cycle.

3. The method for matching the characteristics of a generator and engine in a high-altitude environment according to claim 2, characterized in that, The matching calculations for the first cycle of engine start-up include: The expression for matching the starter generator starting torque with the engine resistance torque before the top dead center of the first cycle is: T em >T M +T G +T P (3) Wherein: T em This refers to the starting torque of the generator; Integrating the entire starting process before the top dead center of the first loop, the integral expression is: Where: α is the crankshaft rotation angle, 0° < α < 180°; The integral expression for the engine friction torque is: Wherein: F c F is the frictional force between the piston and the cylinder liner. z Main bearing friction force; r z r is the inner ring radius of the bearing; r is the crank radius; l is the connecting rod length; Inertial drag torque includes reciprocating inertial drag torque T j and rotational inertial drag torque T r Then the integral expression for the inertial drag torque is: Where: m j m is the equivalent reciprocating mass of the piston connecting rod. r The equivalent mass of the crank and connecting rod big end rotation; This is the first derivative of the crankshaft rotation angle α, i.e., the crankshaft rotation angle angular velocity; This is the second derivative of the crankshaft rotation angle α, i.e., the crankshaft rotation angle angular acceleration; The integral expression for the compressive resistance torque is: Where: S is the equivalent area of ​​the engine piston; ΔP is the pressure difference between the cylinder and the crankcase. If the integral of the difference between the starter torque and the engine resistance torque is greater than 0 within a crankshaft angle of 0° to 180°, the starter torque can drive the engine through the first cycle. If the integral of the difference is equal to 0 within a crankshaft angle of 0° to 180°, the engine piston will just stop at top dead center. Calculate the ideal crankshaft angle α′ that will allow the piston to stop at top dead center. When the crankshaft angle α is less than the ideal crankshaft angle α′, the piston can pass top dead center. When the crankshaft angle α is greater than the ideal crankshaft angle α′, the piston cannot pass top dead center.

4. The method for matching the characteristics of a generator and engine in a high-altitude environment according to claim 3, characterized in that, The matching calculations for the last cycle of engine starting include: The integral expression for the torque difference between the top dead center of the last cycle and the bottom dead center of the previous cycle is: Wherein: T emN The electromagnetic torque of the generator during its last cycle; T GN This refers to the inertial torque during the final drag cycle. At this point, the forces are balanced when the cycle reaches its final stop, as shown in the following equation: The expression for the piston speed at bottom dead center when the drive is stable, derived from the generator's rated power, is as follows: Where: n max p is the maximum rotational speed when the last cycle passes the top dead center. e This is the rated power of the generator; The maximum engine speed is matched as follows: n max ≥900rmin (11)。 5. The method for matching the characteristics of a generator and engine in a high-altitude environment according to claim 4, characterized in that, Matching calculations for reverse energy storage include: The expression for compressed energy storage during generator reversal is: Where: α″ is the angle that is symmetrical and equal to the position of crankshaft rotation angle α; The integral expression for the residual compressive drag torque in the first cycle after reverse energy storage is: The integral expressions for frictional resistance torque and inertial resistance torque are: The integral expression for the generator reversing and storing energy is then: If the generator, after reversing and storing energy, can drive the engine piston past the first top dead center, and at the maximum speed n in the last cycle... max If the maximum energy storage after the starter generator reverses is ≥900 rpm, the starter generator and engine are successfully matched and started. If the maximum energy storage after the starter generator reverses is still unable to exceed the first top dead center, it is determined that this starter generator and engine are not matched.

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