1、- AR 7781 AEROSPACE IN FORM AT10 N REP0 RT SOGIETV OF AUTOMOTIVE ENGINEERS. Inc. 485 LEXINGTON AVENUE NEW YORK 17, N.Y. GUIDE: FOR DE-G EmGIME STARTER IUU U-15-59 DEVE TORQUE REQW ROVISO 9-1-62 1. 2. 3. HTRPOSE : The purpose of this report is to provide a general guide to the factors utilized and th
2、e methods employed in determining turbine starter torque and engine pad strength requirements. SCOPE: A general discussion is presented herein, to outline the starter functions which are necessary for a successful engine start. calculations are included to illustrate an accepted method of determinin
3、g the engine starting time from known data. Further consideration is then given to the relationship between starter torque output and engine pa strength and a generalized formula is presen-bed for calculating the theoret- ical transient torque peaks for a simplified starter-engine system. Sample cal
4、culations for actual tests are included, and the results of these calcu- lations are compared with measured values. In addition, sample DIscussm : 3.1 Starter Functions: Figure 1 pictorially illustrates the torque versus speed characteristics of a typical starter on an assumed jet engine. provide su
5、fficient torque to accelerate a jet engine, incluirig its aecesso- ries, up to its firing speed and to continue supplying torque assist until the engine is developing sufficient torque to rapidly accelerate itself to idling speed. the drag torque imposed by friction, windage, and pumping losses of t
6、he engine and its accessories, with engine ignition occurring at point b, Path b-c-d occurs after engine ignition, with net drag torque stillsresent from b to c an with net engine output torque being supplied from c to 4. The starter should range which is dependent upon the engines characteristics.
7、designated as point d on the engine torque curve and, although stabilized engine idle occurs at zero net torque output, the point of idking is repre- sented as shownto depict a condition where the aircraft power lever has been set for a higher speed range. purposes of providing a standard for starti
8、ng time calculations which is not affected b;y the various types of fuel control scheduling utilized to approach the stabilized idle condition. In general, the starte? must Path a-b on the engine torque curve of Figure 1 represen-bs designed to cutout (point f) within a finite speed Idle speed is Th
9、is assumption is made purely for the Referring again to Figure 1, it can be seen that curve e-g represents the net torque for the engine-starter system, i.e., the algebraic summation of the engine an starter torques. The shaded area under this curve then be- comes a measure of the net energy availab
10、le for engine acceleration up to cutout speed. Application of this available energy to the c8.JcutatPon of engine starting time is covered in the following section. JS DOCUMEIST SUPEWWES AEID WJIS AIR 62, WHICH WAS ISSUED u-15-59 l_l_-_ - ll_l_ SAE AIR8781 b2 IB 8357340 0008504 W -2- 3.2 Calculation
11、 of Starting Time to Engine Idle: Since one of the important considerations used in selecting a starter for an aircraft engine combination is the time lapse between start initiation and attainment of engine idle, it appears desirable to dis- cuss a method of determining this time lapse. tion for the
12、 acceleration time formula: Following is the deriva- From dynamics we have: do T = JLm U = 1, - dt Where: T = Net -torque in lb ft I along curve e-g of bigura 1. average net torque aong curve e-g for the speed increment AN %v bt - aaceleration tirils increment for epee8 increment AN Using equation (
13、2) along the entire length of curve e-g an su!nmng the resultant time increments will then give the time to englne Idle, the accuracy of thls method increasing with the number of increments %taken. SAE AIR*78L b2 8357340 0008505 T -3- 3.2.1 Samp le C but since this factor varie8 with different engin
14、e-starter combinations, a more accurate determination should be established. Accordingly, the foliowing section presents a theomtical derivation of an equation re- lating steady state and impact torque, engine and starter inertia and torsianal stiffness, and system backlash. 3.3.1 !theoretical Consi
15、demtions: The torque driving sysliem of an engine-starter combination can gener- ally be simplifisd as 13hown on Figure 3. For this system: Is = starter equivalent mass moment of inertia I, = engine equivalent mass moment of inertia kts = starter torsional spring constant k, = angine torsional spriq
16、 constant Two ulsu: position of startar clutch half e2 = angw position of engine ciutch haif 8, = a,nguLar position of I, 8, = el = 8% = 8, = O at the time of engagement 4a - i i - -.c.sc . I SAE AIR$7 = - T since - where Cl = O da T IS 1, where C, x O T2 also a = 1;/2 - t + cS IS thus = JF Substitu
17、ting (2) in (l), the relative velocity at time of engagement is: da dt T I, JFG JF (3) After engagement : where T, = torque tranEimltted by clutch Simlsrly 2 = - + 8, TC ke d2, T, = Te - dt2 Since (I! - Tc) = I, - d2 e, and dt2 11 -+na 5s 11. -I- Let o2 = where o = the system natural frequency ks %
18、-7- d2 2 T tit2 S Then - (es - e,) +a) (e8 - ee) = (7) Solution for (7) is: es - e, = 1 sin ut + c2 cos ut + 2 T Q) Is Solving for the constants: When t = O then 8, - Be = O and from (3) d (0, - e,) = - :+i- T e, - e, = o + c2 + -2 = o a If3 m . Equation (8) is a nurximum when first derivative = O = tian,.I.: I. .i I . -.I._ -. i 1- . , . +.“- , i p- p . .I . ! $.I;. e : I I. . - . . I , .i i ! I! !.-;y !. ! I. -, II -_-_. *- . -.- L ,.-.- -i.-
