Method for matching characteristics of generator and engine in high-altitude environment

Abstract

The invention relates to the technical field of matching of a generator and a power device, and discloses a method for matching characteristics of a generator and an engine in a high-altitude environment. When the crank angle position of the engine is (0 degree, 180 degrees), the motor drags the engine to start, and if the engine cannot cross the first top dead center, the crank angle position is matched again; if yes, the engine enters the next cycle and is started to rotate; and in the last cycle before starting to reach the stable rotating speed, if the maximum rotating speed of the last cycle of the engine is larger than the rotating speed threshold value, starting matching succeeds, and if the maximum rotating speed is smaller than the rotating speed threshold value, the working point of the generator is matched again. And if the rotation angle position of the engine crankshaft is (0 degree, 180 degrees) and the engine driven by the starting generator cannot cross the first top dead center, reverse energy storage matching is carried out on the starting generator. According to the invention, the energy storage form is utilized to reduce the capacity requirement on the starting generator, the lowest boundary of starting matching is successfully expanded, and the application range of the starting generator under different environment conditions is expanded.

Description

Technical Field

[0001] The invention relates to the technical field of matching a generator with a power device, and in particular to a method for matching characteristics of a generator with an engine in a high-altitude environment. Background Art

[0002] The starting process is the most initial preparation stage before the engine enters the working state. The engine can only run stably when it overcomes the starting resistance torque and reaches a certain high speed during the starting process. Through the drag of the engine by the starter generator, the engine speed 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 powered off and disconnected from the engine. In the high-altitude, low-temperature and low-pressure environment, the starting characteristics of the starter generator and the engine resistance torque characteristics have changed differently compared to the ground. Therefore, the matching between the engine and the starter generator is particularly important in the complex and changeable high-altitude environment. The drag speed of the starter generator determines whether the engine can reach the minimum ignition temperature, and the engine resistance torque affects the drag speed and starting current of the starter generator under this load. The matched starter generator power determines the working point of the engine starting power in different high-altitude environments.

[0003] In the traditional matching process of the starter motor and the engine, the torque and speed of the starter motor are matched according to the average resistance torque and average speed when the engine is dragging, and the power of the matching starter motor is calculated from this. However, this method is reflected in the matching of the stable working condition of the starter generator. However, when 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 of the invention

[0004] In view of the above problems, the purpose of the present invention is to provide a method for matching the characteristics of a starter generator and an engine in a high-altitude environment. During the starter generator matching process, energy storage is used to reduce the capacity requirements of the starter generator, successfully expanding the minimum boundary of the starter matching and increasing the applicable scope of the starter generator in different environmental conditions. The technical solution is as follows:

[0005] A method for matching characteristics of a generator and an engine in a high altitude environment comprises the following steps:

[0006] Step 1: Analyze the transient process of the generator-driven engine starting

[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 time when the engine piston is at the bottom dead center, and the relationship between the starting torque of the generator and the engine friction resistance torque, compression resistance torque and inertia 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 the engine starting is determined;

[0008] Step 2: Matching strategy

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

[0010] If the engine crankshaft angle position is 0°<α<180°, and the engine cannot pass the first top dead center, the starter generator is reversed to store energy, and the engine piston is allowed to pass the first top dead center by reversing the starter generator to compress the engine gas and increase the acceleration distance of the inertia torque; after the starter generator reverses and stores 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 starting match is successful; if the maximum speed of the last cycle is less than the speed threshold, the starter generator operating point is re-matched; if it cannot pass the first top dead center after reversing energy storage, the reverse crankshaft angle position is re-matched; but if the starter generator maximum torque still cannot pass the first top dead center when starting at the reverse energy storage position that can be reached, it is considered that the starter generator exceeds the lowest starting boundary of the engine.

[0011] Furthermore, in step 1, the five parts of the start-up process of the first cycle are specifically:

[0012] In the first part, when the engine piston starts from the bottom dead center, the starting torque of the starter generator is greater than the static friction resistance torque of the engine; the starter generator drags the engine to start and accelerate, the drag speed increases, and the drag is a constant;

[0013] In the second part, the engine piston moves upward, and the generator output torque is greater than the sum of the engine's friction resistance torque, compression resistance torque and inertia resistance torque; the drag acceleration decreases, and the drag speed increases slowly;

[0014] In the third part, the output torque of the generator and the engine resistance torque reach the first equilibrium point in this cycle, and the output torque of the generator is equal to the sum of the compression resistance torque and the friction resistance torque of the engine; the output torque of the 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 piston reaches the top dead center in the first cycle of engine starting is:

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

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

[0018] In the fourth part, the engine piston moves to the top dead center, and the generator output torque and the 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;

[0019] In the fifth part, the engine piston passes the top dead center, the torque generated by the generator torque and the expansion of the gas in the cylinder is greater than the engine friction resistance torque and inertia resistance torque, and the engine accelerates to enter the next cycle;

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

[0021]

[0022] Where: T Zn The drag torque for the last cycle of engine starting; is the dynamic friction resistance torque at speed n; is the inertia moment of the last cycle speed n and the maximum speed of the previous cycle.

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

[0024] The expression for the starter generator starting torque matching the engine resistance torque 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 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 crankshaft angle, 0°<α<180°;

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

[0031]

[0032] Among them: F c is the friction between the piston and the cylinder liner; F z is the main bearing friction; r z is the radius of the inner ring of the bearing; r is the radius of the crank; l is the length of the connecting rod;

[0033] The inertia resistance moment includes the reciprocating inertia resistance moment T j and the rotational inertia resistance moment T r , then the integral expression of the inertial resistance moment is:

[0034]

[0035] Where: m j is the equivalent reciprocating mass of the piston and connecting rod; m r is the rotating equivalent mass of the crank and the connecting rod big end; is the first derivative of the crankshaft angle α, that is, the angular velocity of the crankshaft; is the second-order derivative of the crankshaft angle α, that is, the angular acceleration of the crankshaft angle;

[0036] The integral expression of the compression 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] When the integral of the difference between the starting torque of the starter generator and the engine resistance torque is greater than 0 at a crankshaft angle of 0° to 180°, the starter generator can drag the engine beyond the first cycle; if the integral of the difference is equal to 0 at a crankshaft angle of 0° to 180°, the engine piston just stops at the top dead center, and the ideal crankshaft angle α′ that just allows the piston to stop at the top dead center is calculated as above. When the crankshaft angle α is less than the ideal crankshaft angle α′, the piston can pass the top dead center; when the crankshaft angle α is greater than the ideal crankshaft angle α′, the piston cannot pass the top dead center.

[0040] Furthermore, the matching calculation for the last cycle of engine starting includes:

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

[0042]

[0043] Where: T emN is the electromagnetic torque of the generator in the last cycle; TGN is the moment of inertia during the last cycle of dragging;

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

[0045]

[0046] The speed expression of the piston passing the bottom dead center when the drag is stable is obtained from the rated power of the generator:

[0047]

[0048] Where: n max It is the maximum speed when the last cycle passes the top dead center; p e is the rated power of the generator;

[0049] The maximum engine speed is matched to:

[0050] n max ≥900r / min (11).

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

[0052] The expression of compressed energy storage for generator reversal is:

[0053]

[0054] Where: α″ is an angle symmetrically equal to the crankshaft angle α;

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

[0056]

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

[0058]

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

[0060]

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

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

[0063] 1) The present invention proposes a new matching method and compensation strategy for the starter generator and the engine high-altitude starting process. In the starter generator matching process, the energy storage form is used to reduce the capacity requirements of the starter generator, successfully expanding the minimum boundary of the starting matching and increasing the applicable scope of the starter generator in different environmental conditions;

[0064] 2) The present invention utilizes the compression energy storage and inertial energy storage of the piston engine to assist the starter generator to successfully pass the first top dead center, and is therefore applicable to various types of piston engines and has a certain degree of universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 Schematic diagram of the engine starting transient process.

[0066] Figure 2 This is the transient change diagram of the engine starting resistance torque.

[0067] Figure 3 This is a logic diagram for matching the starter generator with the engine starter.

[0068] Figure 4 This is a logic diagram for matching the generator with the engine for reverse energy storage starting.

[0069] Figure 5 This is the first cycle matching diagram of the generator and the engine.

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

[0071] Figure 7 (a)-(c) shows the instantaneous speed variation with time when the engine is started by the generator dragging the engine at crankshaft angles of 60°, 0° and -60°. DETAILED DESCRIPTION

[0072] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0073] The present invention analyzes the transient process of starting the engine with the starter generator, proposes a new method and strategy for matching the starting characteristics of the starter generator and the engine in a high-altitude environment, performs matching calculations, and proposes matching evaluation indicators.

[0074] 1. Analysis of startup transient process

[0075] The process of starting the engine with the starter generator is a dynamic process. Figure 1The diagram shows the first cycle of the starter-generator dragging the engine. The upper part of the diagram shows the change in speed when the starter-generator drags the engine to start, and the lower part shows the change in acceleration to which the engine is subjected.

[0076] exist Figure 1 In the figure, it is assumed that the engine piston is at the bottom dead center. The starting process in 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 resistance torque of the engine. The starter generator drags the engine to start and accelerate, and the drag speed increases. At this time, the engine compression resistance torque has little effect on the output torque of the starter generator relative to the friction resistance torque. Therefore, the acceleration can be regarded as a constant; when entering the second part, as the engine piston moves upward, the pressure in the cylinder gradually increases, and the compression resistance torque also gradually increases. The output torque of the starter generator at this time is greater than the friction resistance torque, compression resistance torque and inertia resistance torque of the engine at this time, but the drag acceleration is significantly reduced, and the drag speed growth slows down; in the third part, the output torque of the starter generator and the engine resistance torque reach the first equilibrium point in this cycle. At this time, the output torque of the starter generator is equal to the compression resistance of the engine The sum of the torque and the friction resistance torque, at this time the drag acceleration is 0, and the drag speed reaches the maximum speed in this cycle, after which the drag acceleration is a negative value, and the drag speed decreases accordingly, but the generator output torque and the engine inertia resistance torque 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 generator output torque and the engine resistance torque will reach the second equilibrium point in this cycle, at this time the drag acceleration is also 0, but the drag speed is the lowest speed in this cycle, at this time the generator torque is equal to the engine friction resistance torque; after crossing the top dead center, entering the fifth part, the drag engine acceleration is greater than 0 again, the generator torque and the torque generated by the expansion of the gas in the cylinder are greater than the engine friction resistance torque and the inertia resistance torque, and the engine accelerates to enter the next cycle.

[0077] Inside the engine, the engine starting resistance torque transient changes as follows Figure 2 As shown, the instantaneous resistance torque in the first cycle of engine starting is significantly greater than the resistance torque when the speed is stable after starting. In the first cycle, before the piston top dead center, the engine resistance torque is composed of friction resistance torque, compression resistance torque and inertia resistance torque that change alternately. Among them, the friction resistance torque changes from static friction resistance torque to dynamic friction resistance torque. The compression resistance torque increases sharply after the piston passes a certain crankshaft angle as it moves upward. The inertia resistance torque does positive or negative work as the output torque of the generator changes. Therefore, the expression of the resistance torque before the top dead center of the first cycle of engine starting is:

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

[0079] Where: T Z1 is the resistance torque before the top dead center of the first cycle of the engine; T M is the engine friction torque; T P is the engine compression resistance torque; T G is the engine inertia drag moment;

[0080] and Figure 2 The last cycle in does not refer to the last cycle of the engine in the entire starting process, but the last change value of the engine speed from 0 to the stable speed during the starting process when the starter generator drags the engine. It is also the first value of the stable speed. However, since the engine resistance torque fluctuates and the speed also fluctuates, the stable speed is the minimum speed and maximum speed of the piston no longer change when the engine is dragged every time it passes the top dead center and the bottom dead center. At this time, the engine speed is stable in a certain range. The stable speed taken at this time is the lower limit of the stable speed range, that is, the speed n when the piston runs to the top dead center, because the engine resistance torque when the piston reaches the top dead center in the last cycle determines the maximum speed that the starter generator can drag. Therefore, the expression of the engine resistance torque before the piston reaches the top dead center in the last cycle is:

[0081]

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

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

[0084] According to the resistance torque characteristics and the output characteristics of the starter generator when the engine is started, a new method for matching the characteristics of the starter generator and the engine in a high-altitude environment is proposed.

[0085] 2.1 Matching methods and strategies

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

[0087] If the engine cannot pass the first top dead center when the starting crankshaft angle position is matched at 0°<α<180°, the starter generator can be reversed to store energy, so that the engine piston can pass the first top dead center by reversing the starter generator to compress the engine gas and increase the acceleration distance of the inertia torque.

[0088] like Figure 4 The figure shows the logic diagram of the starter generator and the engine reverse energy storage starting matching. At this time, the crankshaft angle range of the motor dragging the engine to reverse to the previous top dead center is -180°<α<0°. After the starter generator reverses and stores energy, if it can pass the first top dead center and the maximum speed of the last cycle n≥900r / min, the starting matching is successful. If the maximum speed of the last cycle n<900r / min, the starter generator working point needs to be re-matched; if it cannot pass the first top dead center after reverse energy storage, the reverse crankshaft angle position is re-matched, but if the starter generator maximum torque still cannot pass the first top dead center when starting at the reverse energy storage position that can be reached, it is considered that the starter generator has exceeded the lowest starting boundary of the engine.

[0089] 2.2 The first cycle matching calculation

[0090] It is known from the analysis of the starting transient process that the engine resistance torque in the first cycle at the starting instant is significantly greater than the resistance torque in the subsequent cycles. Therefore, the maximum torque of the starter generator at starting is greater than any position point from 0° to 180° before the top dead center of the first cycle of the engine, such as Figure 5 As shown in 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; 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. Even if the maximum starting torque of the starter generator is less than the resistance torque at a certain point, the starter generator may reverse during starting, causing the starter generator to fail to successfully drag the engine to start successfully.

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

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

[0093] Where: T em is the starting torque of the generator.

[0094] However, during the starting process, since the engine friction resistance torque, compression resistance torque and inertia resistance torque are all changing, and the inertia resistance torque may do positive work or negative work in this process, the rate of change of the starter generator starting torque growth may be less than the rate of change of the compression resistance torque growth at a certain point. Therefore, the integral expression for the entire starting process before the top dead center of the first cycle is:

[0095]

[0096] Where: α is the crankshaft angle, 0°<α<180°

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

[0098]

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

[0100] Since the inertia resistance moment includes the reciprocating inertia resistance moment T j and the rotational inertia resistance moment T r , then the integral expression of the inertial resistance moment is:

[0101]

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

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

[0104]

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

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

[0107] As for the second cycle, since a compression energy storage is performed after the top dead center of the first cycle, the friction resistance torque entering the second cycle is smaller than the friction resistance torque of the first cycle. Therefore, the generator will also drag the engine successfully through the second cycle until the engine dragging speed stabilizes after the Nth cycle.

[0108] 2.3 The last cycle matching calculation

[0109] When the drag speed reaches the last cycle N before stabilization, this cycle determines the maximum speed that the generator can drag the engine to reach. Therefore, the integral expression of the torque difference before the top dead center of the last cycle and the bottom dead center of the previous cycle is:

[0110]

[0111] Where: T emN is the electromagnetic torque of the generator in the last cycle; is the dynamic friction resistance torque at speed n; T GN is the moment of inertia during the last drag cycle.

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

[0113]

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

[0115]

[0116] Where: n max It is the maximum speed when the last cycle passes the top dead center; p e Rated power of the generator.

[0117] When the engine ECU is designed, the injector starts to spray fuel when the engine speed reaches 900r / min. Once the fuel is sprayed, the mixture enters the cylinder and the spark plug ignites. Even if the cylinder does not ignite every cycle, as long as there is a point that starts to ignite, the entire starting process will have chemical energy combustion and work, and the speed will gradually increase. 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 maximum starting torque of the starter generator cannot drive the piston to pass the first top dead center at the engine crankshaft angle position 0°<α<180°, the starter generator can be reversed to store energy to increase the initial torque and acceleration distance of the inertia moment of the starter generator, so that the starter generator has a greater ability to pass the top dead center. Figure 6 The figure shows the schematic diagram of the generator reverse energy storage matching the engine crankshaft angle position. Figure 6 In the equation, if the generator can only drag the engine to the crankshaft angle α position in the position of 0° to 180°, then the generator can only reverse and drag the engine to the α″ position in the position of 0° to -180° when storing energy. The two positions are symmetrically equal to the 0° position. Therefore, the compression energy storage expression of the generator reversal is:

[0121]

[0122] Among them: α and α″ are symmetrical and equal in position.

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

[0124]

[0125] The integral expressions of friction resistance torque and inertia resistance torque are:

[0126]

[0127] Then the integral expression of the generator reverse energy storage is:

[0128]

[0129] If the generator can drag the engine piston past the first top dead center after reverse energy storage, and the maximum speed n of the last cycle max ≥900r / min, the reverse energy storage matching start is successful. If the maximum energy storage after the starter generator reverses still cannot cross the first top dead center, it can be determined that this starter generator is not compatible with the engine.

[0130] 3. Analysis of high altitude starting matching test results

[0131] When the engine is in a high-altitude, low-temperature and low-pressure environment, among the drag torque characteristics of the engine, the friction drag torque is mainly affected by temperature. The lower the temperature, the greater the friction drag torque. The compression drag torque is mainly affected by ambient pressure. The lower the ambient pressure, the lower the compression drag torque will be. Therefore, the starter generator is matched with the engine for high-altitude starting when the ambient temperature is -60℃, which is larger than that at normal temperature. The compression drag torque is also selected when it is the largest under normal pressure, that is, 95kPa atmospheric pressure. The starting conditions at different crankshaft angle positions of the engine are matched with the starter generator when the compression drag torque and the friction drag torque are the largest.

[0132] This embodiment uses a 72-tooth gear disc and a magnetoelectric sensor to collect the instantaneous speed of the start, uses a current clamp to collect the instantaneous current when the starter generator starts, and measures the starting conditions of the engine before the top dead center of the first cycle, at the bottom dead center, and after the top dead center of the previous cycle. Since, in the process of the starter generator dragging the engine to start matching, the starting conditions of the starter generator dragging the engine at different crankshaft torque positions are different, the number of cycles N used by the starter generator to drag the engine to start to the last cycle and the time taken when the speed reaches 1000r / min are used as the evaluation indicators of the start matching in the evaluation of the start matching between the starter generator and the engine, so as to evaluate the number of cycles used by the starter generator to drag the engine to start at different crankshaft angle positions. The fewer cycles it takes for the starter generator to drag the engine to reach the specified speed, the less starting capacity the starter generator can use to drag the engine to start, and the matching space between the starter generator and the engine is larger, and the applicable environment range is wider.

[0133] Figure 7 (a)-(c) are graphs showing the instantaneous speed variation with time when the engine is started by the generator at crankshaft angles of 60°, 0° and -60°. Figure 7 (a) shows the instantaneous speed variation with time at a crankshaft angle of 60°; Figure 7 (b) shows the instantaneous speed variation with time at a crankshaft angle of 0°; and Figure 7 (c) shows the instantaneous speed variation with time at a crankshaft angle of -60°.

[0134] As can be seen from the figure, when starting at different crankshaft angle positions, the instantaneous speed change of the drag is different. When the crankshaft angle position is 60°, since this position is close to the top dead center and the acceleration distance is short, at 0.026s after starting, the starting speed changes from acceleration to deceleration for the first time. At 0.0402s after passing the top dead center, the starting speed changes from deceleration to acceleration. At this point, the starter-generator drags the engine through the first cycle, and the speed range is 200r / min-400r / min. When the crankshaft angle is 0°, since the distance is farther than the 60° crankshaft angle position, the first and second speed changes occur at 0.0439s and 0.0518s, and the speed change range is 680r / min-800r / min. When the crankshaft angle is -60°, since it is farthest from the top dead center, the first and second speed changes occur at 0.0663s and 0.0772s, and the speed change range is 900r / min-1100r / min. Since the rate of change when the speed tends to be stable in the test is extremely small, it is difficult to distinguish the difference between the last cycle and the previous cycle. Therefore, in this test, the cycle time and time required for the engine to reach 1000r / min are selected. In Figure 7(a), the number of cycles experienced when the crankshaft angle is 60° and the speed reaches 1000r / min is 4, in Figure 7(b), the number of cycles experienced when the crankshaft angle is 0° and the speed reaches 1000r / min is 4, and in Figure 7(c), the number of cycles experienced when the crankshaft angle is -60° and the speed reaches 1000r / min is 3. It is obvious that the cycle time from starting at a crankshaft angle of -60° to a speed of 1000r / min is less than that from starting at a crankshaft angle of 60° and a crankshaft angle of 0°, but the number of cycles at a crankshaft angle of 60° and a crankshaft angle of 0° are both 4. Therefore, the time taken to reach a speed of 1000r / min is used to distinguish the starting conditions of these two positions. After comparing the data, the time required to start at a crankshaft angle of 60° and reach 1000r / min is 0.175s, and the time required to start at a crankshaft angle of 0° and reach 1000r / min is 0.16s, indicating that the time required for starting at a crankshaft angle of 60° is greater than that at a crankshaft angle of 0°, while the time required for a crankshaft angle of -60° is 0.152s, which is significantly less than the crankshaft angles of 0° and 60°.

[0135] The present invention analyzes the transient process of the starter generator dragging the engine to start, 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 calculations; finally, a starter generator and engine starting matching test is carried out, and a matching evaluation index is proposed. By analyzing the test results, the feasibility of the new starting matching method and strategy is verified, and the conclusions are as follows:

[0136] (1) When selecting the cycles that the engine goes through when the speed reaches 1000 r / min, the number of cycles experienced when starting at a crankshaft angle of 60° and a crankshaft angle of 0° to reach 1000 r / min is 4, and the number of cycles experienced when starting at a crankshaft angle of -60° to reach 1000 r / min is 3. Therefore, the number of cycles experienced when starting at a crankshaft angle of -60° to a speed of 1000 r / min is less than that when starting at a crankshaft angle of 60° and a crankshaft angle of 0°.

[0137] (2) When selecting the required time, the time required to start and reach 1000 r / min at a crankshaft angle of 60° is 0.175 s, and the time required to start and reach 1000 r / min at a crankshaft angle of 0° is 0.16 s. This means that the time required to start at a crankshaft angle of 60° is greater than that at a crankshaft angle of 0°, while the time required at a crankshaft angle of -60° is 0.152 s, which is significantly shorter than the crankshaft angles of 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: The following steps are involved: Step 1: Analyze the transient process of the generator-driven engine starting 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 time when the engine piston is at the bottom dead center, and the relationship between the starting torque of the generator and the engine friction resistance torque, compression resistance torque and inertia 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 the engine starting is determined; Step 2: Matching strategy The crankshaft angle position of the engine is initially at a crankshaft angle position of 0°<α<180°, and the starter generator drags the engine to start. If the engine cannot pass the first top dead center, the crankshaft angle position is re-matched; if the engine can pass the first top dead center, the engine enters the next cycle and starts to rotate; when the start reaches the last cycle, if the maximum speed of the engine in the last cycle is greater than the speed threshold, the start matching is successful, and if the maximum speed of the engine in the last cycle is less than the speed threshold, the starter generator working point is re-matched; If the engine crankshaft angle position is 0°<α<180°, but the engine cannot pass the first top dead center, the starter generator is reversed to store energy, so that the engine piston can pass the first top dead center by compressing the engine gas and increasing the acceleration distance of the inertia moment by reversing the starter generator; after the starter generator is reversed 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 starting match is successful; if the maximum speed of the last cycle is less than the speed threshold, the starter generator working point is re-matched; If the first top dead center cannot be crossed after reverse energy storage, the reverse crankshaft angle position is re-matched; but if the starter generator cannot cross the first top dead center when starting at the reverse energy storage position that can be reached, it is considered that the starter generator exceeds the minimum starting boundary of the engine.

2. The method for matching the characteristics of a generator and an engine in a high altitude environment according to claim 1, characterized in that: In step 1, the five parts of the startup process of the first cycle are: In the first part, when the engine piston starts from the bottom dead center, the starting torque of the starter generator is greater than the static friction resistance torque of the engine; the starter generator drags the engine to start and accelerate, the drag speed increases, and the drag 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 friction resistance torque, compression resistance torque and inertia resistance torque; the drag acceleration decreases, and the drag speed increases slowly; In the third part, the output torque of the generator and the engine resistance torque reach the first equilibrium point in this cycle, and the output torque of the generator is equal to the sum of the compression resistance torque and the friction resistance torque of the engine; the output torque of the 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; The expression of the engine resistance torque before the piston reaches the top dead center in the first cycle of engine starting is: T Z1 =T M +T P +T G (1) Where: T Z1 It is the resistance torque before the top dead center of the first cycle of engine starting; T M is the engine friction torque; T P is the engine compression resistance torque; T G is the engine inertia drag moment; In the fourth part, the engine piston moves to the top dead center, and the generator output torque and the 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 expansion of the gas in the cylinder is greater than the engine friction resistance torque and inertia resistance torque, and the engine accelerates to enter the next cycle; The expression of the engine resistance torque before the piston reaches the top dead center in the last cycle of engine starting is: Where: T Zn The drag torque for the last cycle of engine starting; is the dynamic friction resistance torque at speed n; is the inertia moment of the last cycle speed n and the maximum speed of the previous cycle.

3. The method for matching the characteristics of a generator and an engine in a high altitude environment according to claim 2, characterized in that: The matching calculations for the first cycle of engine starting include: The expression for the starter generator starting torque matching the engine resistance torque before the top dead center of the first cycle is: T em >T M +T G +T P (3) Where: T em is the starting torque of the generator; Integrate the entire starting process before the top dead center of the first cycle, and the integral expression is: Where: α is the crankshaft angle, 0°<α<180°; The integral expression of the engine friction torque is: Among them: F c is the friction between the piston and the cylinder liner; F z is the main bearing friction; r z is the radius of the inner ring of the bearing; r is the radius of the crank; l is the length of the connecting rod; The inertia resistance moment includes the reciprocating inertia resistance moment T j and the rotational inertia resistance moment T r , then the integral expression of the inertial resistance moment is: Where: m j is the equivalent reciprocating mass of the piston and connecting rod; m r is the rotating equivalent mass of the crank and the connecting rod big end; is the first derivative of the crankshaft angle α, that is, the angular velocity of the crankshaft; is the second-order derivative of the crankshaft angle α, that is, the angular acceleration of the crankshaft angle; The integral expression of the compression resistance torque is: Where: S is the equivalent area of ​​the engine piston; ΔP is the pressure difference between the cylinder and the crankcase; When the integral of the difference between the starting torque of the starter generator and the engine resistance torque is greater than 0 at a crankshaft angle of 0° to 180°, the starter generator can drag the engine beyond the first cycle; if the integral of the difference is equal to 0 at a crankshaft angle of 0° to 180°, the engine piston just stops at the top dead center, and the ideal crankshaft angle α′ that just allows the piston to stop at the top dead center is calculated as above. When the crankshaft angle α is less than the ideal crankshaft angle α′, the piston can pass the top dead center; when the crankshaft angle α is greater than the ideal crankshaft angle α′, the piston cannot pass the top dead center.

4. The method for matching the characteristics of a generator and an 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 of the torque difference between the last cycle top dead center and the previous cycle bottom dead center is: Where: T emN is the electromagnetic torque of the generator in the last cycle; T GN is the moment of inertia during the last cycle of dragging; At this time, the force is balanced when passing the top dead center of the last cycle, as shown in the following formula: The speed expression of the piston passing the bottom dead center when the drag is stable is obtained from the rated power of the generator: Where: n max It is the maximum speed when the last cycle passes the top dead center; p e is the rated power of the generator; The maximum engine speed is matched to: n max ≥900rmin (11)。 5. The method for matching the characteristics of a generator and an engine in a high altitude environment according to claim 4, characterized in that: The matching calculation of reverse energy storage includes: The expression of compressed energy storage for generator reversal is: Where: α″ is an angle symmetrically equal to the crankshaft angle α; The integral expression of the residual compression resistance torque in the first cycle after reverse energy storage is: The integral expressions of friction resistance torque and inertia resistance torque are: Then the integral expression of the generator reverse energy storage is: If the generator can drag the engine piston past the first top dead center after reverse energy storage, and the maximum speed n of the last cycle max ≥900rmin, the reverse energy storage matching start is successful; if the maximum energy storage after the starter generator reverses still cannot pass the first top dead center, it is determined that this starter generator is not matched with the engine.

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