ELSEVIER JSAE Review 15 (1994) 15-19 O

Study of the simulation of piston skirt contact

Hiroshi Kageyama *, Sohichi Hara, Yasuhiro Kawabata Base Engine Components Group, Engineering Department, Engine Components Dicision, AISIN SEIKI Co., Ltd., 2-1, Asahi-machi,

Kariya, Aichi, 448 Japan

Received 25 August 1993)

Abstract

In order to reduce the number of engine tests, it ~s very important to simulate the piston-cylinder bore contact. In this paper, the method of piston skirt-cylinder bore contact pressures have been studied by using the data of piston skirt profiles, its stiffness, and its thermal expansions. Therefore, piston skirt-cylinder bore contact pressures finely correlate with the skirt conditions after running tests.

I. Introduction

During engine running, the pistons in an internal combustion engine are subject to lateral forces, caused by explosion forces and inertia forces, which cause the piston skirt to make contact with the cylinder bore. The resulting surface contact pressure of the cylinder bore acting on the piston skirt not only increases overall engine friction but also has far-reaching effects on overall engine durability factors such as oil con- sumption and piston seizure. For this reason, the pre- diction of piston skirt contact before actual engine testing is very important in reducing engine develop- ment manhours. In recent years, skirt contact pressure studies by using numerical analysis advances such as FEM have been carried out at the desktop stage, but in terms of precision and modelling manhours entailed, these methods cannot be described as satisfactory.

This paper introduces a method for predicting pis- ton skirt contact, using skirt stiffness values obtained by performing stiffness measurements on actual pis- tons, design profiles, and piston thermal expansions.

2. Measurement of piston skirt stiffness

The skirt stiffness measurement method is shown in Fig. 1 and the examined piston types are shown in Fig.

* Corresponding Author.

0389-4304/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0389-4304(93)E0008-3

2. Many reports concerning piston skirt stiffness [1-4] in the thrust-nonthrust direction have been made in the course of research into piston slap, but in the present study, in order to investigate the skirt contact pressure distribution, stiffness measurements were car- ried out at points including points aligned in the cir- cumferential direction. Examples of the stiffness distri- butions obtained are shown in Fig. 3. Generally, the effect of the direction on the stiffness values is greater than that of the the angle from the thrust-nonthrust direction for hole type pistons, while the effect of the latter is greater than the effect of the former for slot type pistons.

lh-Nth Lower Pin Upper Force

t!J tiJ u

Fig. 1. Measurement of piston skirt stiffness.

JSAE9430095

16 1t. Kag(3,ama ct al. / . ISAE Review 15 (1994) 1.5 19

IHole Typel

I F',

__ Pin ~ - . I - - l - - .- - - C e n t e r - - ~

- - Lover - - I

Oil Hole Oil Slo t

Fig. 2. Examined piston types.

~ l o t rypel

!

3. Skirt stiffness and profile

As a preliminary investigation in the course of this research, the relationship between the stiffness (G), the cylinder diameter (D), and the skirt profile (~), at an arbitrary height on the skirt, was examined, and is shown in Fig. 4. These results were obtained by calcu- lating the interference, due to thermal expansion, be- tween the skirt and the cylinder bore, with it being assumed that during actual engine running the temper- ature distribution in the skirt is uniform for all the conventional pistons. The results reveal that the profile is very affected by the stiffness values.

4. Skirt contact prediction theory

The analytical model is shown in Fig. 5. The theory uses the following assumptions:

(1) When the piston skirt makes contact with the bore, the piston interferes with the bore without rotat- ing;

(2) Imaginary points on the skirt are mutually inde- pendent and have no influence on each other.

(Ho le-Type) I (S l o t -Type )

k n g l e f r o . , Th -N th D i r e c t i o n

0 ° I 0 ° 2 0 0 3 0 0 4 0 " O * 1 0 " 2 0 ° 3 0 ° 4 0 *

Upper

Pin ~ Ceo er I

5 74.lH! Lover '~ ¢ .93 (R [N) ' I Fig. 3. Examples of piston skirt stiffness distribution (unit : MN /m).

F . . . . . .

| I o Hole type II ~ ,±u.u.~_ 0

v I

~ . ~ • o

20 °

0

i

I 0

Gaps from max. Piston Radii (8) Fig. 4. Relationships between skirt profiles (~), stiffness (G), and cylinder diameters (D).

From Fig. 5, the interference t5 0 between point A on the skirt and the cylinder bore is given by

2 sine0 (1) ~O = rp + Xp COS 0 - ~/r " 2 - Xp

where

Xp = ep COS /~ + H tan /3

/ B

Cylinder bor_e

Fig. 5. Analytical model.

H. Kageyama et al. /JSAE Review 15 (1994) 15-19 17

,,i i. i! i i i J_l; "'"

,,ILLJl i.: . . . . . • l l l i l • I l l

: : : - , - : i l l

• • • O l l l , •

No

Fig. 6. Imaginary force points on the piston skirt.

and x~ is an ellipse, with long d iameter rc/COS /3 and short d iameter r c.

The contact pressure Po at point A on the skirt, using stiffness value G o is given by

60 >f O, P o = ( O KGG°6°' 6 0 < 0 . (2)

Lower I p o r t i o n i ~ [ _ ~ ~ 0' 60" ~ . 150 I00 ~0 0 50 O0 150 ( , m)

Th-Oirection Th-Oirection Fig. 7. Pistonthermalexpansionsusedinthisanalysis.

F rom Eq. (2), lateral force F T acting on the piston skirt is given by

F T = fsPo cos OdS

= KGfsGo6 o cos 0 dS (3)

where S = skirt surface area.

S k i r t S t reak Abras ion R a t i o

a f t e r Engine Tests

e

4 "

i t ) a .

I'--"

( I n d i c a t i o n )

0 40 50 60 70 I 0 0 ( , ~

Thrust s ide

Rr Fr Non-Thrust Side

Fr Rr

~_i ~'\' "'"' "'~ )# ~ - - -Center

30" 20' 10" O' I0" 20" 30" 40'

Rr Fr Fr Rr 40" 30' 20" 10" 0 ° 10' 20' 30" 40,* 40" 30" 20" 10" 0 ° 10" 20" 30" 40'

upper

Contact Pressure

(Calculated,unit:MPa)

0 ° 10 ° 20 ° 30 ° 40 °

~ 3 ~ i Upper Pin

. . . . Center

Lover 7.6[HAX)

0 ° 10 ° 20 ° 30 ° 40 °

Upper

Pin Cente

Lower

Fig. 8. Contour maps of the streak abrasion ratio on piston skirt after engine tests and calculated piston-cylinder bore contact pressures.

18 tt. Kageyama et a l . / JSAE Rel'iew 15 (1994) 15-19

Table 1 Specifications

No. Piston Piston diameter type

Piston skirt temperature (°C)

Upper [rower

l 095 slot 140 120 2 Q86 hole 160 140 3 082.5 hole 160 140

From the lateral force acting on the piston given by Eq. (3) and actual engine test results, the correction coefficient K G was calculated.

The area of the skirt for which calculations were performed is shown in Fig. 6. The part of the piston skirt between the upper and the lower side was divided up into a grid of N o • N z sectors and an imaginary point of force action (e) was positioned in the center of each sector.

The thermal expansions of the sample pistons, ob- tained by thermal expansion measurement and actual engine testing, are shown in Fig. 7, and the specifica- tions of the sample pistons are shown in Table 1. Thermal expansion for the heights between the lower portion and the upper portion of the skirt were esti- mated by linear interpolation.

5. R e s u l t s o f a n a l y s i s a n d d e d u c t i o n s

5.1. Results o f piston skirt contact analysis

Analytical results and actual engine test contact (streak abrasion ratio on the piston skirt) results for the slot-type piston 1 and for the hole-type piston 3 of Table 1 are shown in Fig. 8. In Fig. 8, results obtained by actual engine testing are shown for the entire piston skirt, while the calculated results cover only one side of the skirt. The analysis was performed with the piston tilt angle taken as /3 = 0 °. On the thrust side, a good

(Designed) I (Deforzed)

Angle from Th-Nth Direction * 10" 20" 30" 40"

Upper

',enter

Lower \ 25 HI

0* 10" 20 ° 30 ° 40 °

• . 4 4 . 4 1 pin Center

° 171 LoNe, \ 251 INI

Fig. I0. Clearance distribution between piston skirt and cylinder bore at room temperature (unit: ~m).

correlation was obtained between the actual test re- sults and the analysis results for both pistons 1 and 3, and, in particular, the analysis confirmed a large con- tact pressure in the area above the gudgeon pin in piston 1 in the 10 ° direction, where the streak abrasion ratio after engine testing is large. However, the non- thrust side, and particularly the strong contact in the 10-20 ° region in piston 1 between the gudgeon pin center and the bottom of the skirt, was not successfully simulated. It is supposed that this is because the skirt of the piston 1 undergoes greater deformation during engine running than that of piston 3, and that this causes the piston attitude to deteriorate, altering the contact between the skirt and the bore.

Figure 9 shows the correlation between the streak abrasion ratios by actual engine test and predicted contact pressures, shown in Fig. 8, for the thrust side of the piston skirt. From Fig. 9 it can be seen that there is a sufficient correlation between the two, and that this prediction method is practicable. At predicted contact pressures of over 7 MPa in particular, streak abrasion is rapid and there is a danger of it leading to piston

[ ~ S L O T TYPE (~)

[ ~ H O L E TYPE (@) O .D

/ - i

5 Contact Pressure (NPa)

Fig. 9. Correlation between the streak abrasion ratio and calculated contact pressures on piston skirt.

(,~-0" ) l (,8=-0.15" )

Angle from Th-Nth Direction 0* 10* 20* 30* 40*

UPPer

~ i ~ ' - Pin Center

Lover 7.631HAX)

0* 10" 20" 30'

/6.351HAX)

40* ,I Upper

Pin Center

LoNer

Fig. 11. Calculated contact pressure distribution in deformed skirt profiles.

H. Kageyama et aL / JSAE Review 15 (1994) 15-19 19

cylinder bore seizure, and, therefore, improvements to either the profile or skirt stiffness appear to necessary.

5.2. Effects of change of the profile with time

During engine running, lateral forces acting on the piston cause the skirt profile to change. For the poor skirt and cylinder bore contact of piston 1 discussed in Section 5.1, Fig. 10 shows the clearance distribution between the piston skirt and the cylinder bore at the room temperature before and after engine testing, and Fig. 11 shows the results of the contact pressure pre- diction analysis. From this it can be seen that simula- tion especially of the strong contact in the 10-20 ° region between the gudgeon pin center and the bottom of the skirt on the nonthrust side can be further improved by taking into account the profile after en- gine running. However, in order to make the most use of this technique, it is necessary to estimate the post- endurance skirt deformation before the event.

5.3. Skirt contact improvement example

As an example, the application of the present tech- nique to piston 2 of Table 1 is shown in Fig. 12. The

4)

,,e,-

2

;o

z .

Streak Abrasion Rat io

(Thrust Slde,Nessured)

0 40 50 60 70 I 0 0 ( ~

Rr Fr 40" 30" 20" 10" O* 10' 20" 30" 40"

Upper

" --- lover

Rr Fr

40' 30" 20' 10" O" tO ° 20" 30" 40" ~ _ _ ~ _ _ ~ _ _ UPPer

__ Cente

Level

Contact Pressure

i (Cu lcu la ted , uni t :MPe)

( T i l t Angle:,8=O.05 ° )

0* 10" 20" 30" 40"

Upper

:entel

Lover

0* 10* 20" 30" 40"

Center

Lover \ 6.881HAX)

Fig. 12. Effect of skirt profiles on skirt streak abrasion ratio and contact pressures.

piston as before and as after profile improvement differs only in its profile distribution. It was confirmed that whereas in the unimproved piston the streak abra- sion ratio above the pin center in the thrust direction is large, and an area of high contact pressure is also predicted by the analysis results, in the improved pis- ton contact pressure is reduced and contact is uniform.

6. Results

Use of this prediction technique led to the following findings:

(1) A technique was developed for quantitatively predicting engine test piston skirt and cylinder bore contact using local skirt stiffness values and design profile and thermal expansion data for actual pistons.

(2) There is a close relationship between piston skirt stiffness and design profile. However, because piston skirt contact is greatly influenced by stiffness distribution, in order to improve skirt contact, it is necessary to somehow prevent sudden changes occur- ring in the stiffness distribution.

(3) When the predicted contact pressure exceeds a certain level, it is possible to predict that streak abra- sion in an engine test will suddenly increase.

(4) In order to predict strong skirt contact, it is necessary to take into account permanent piston defor- mation, and to improve piston skirt contact it is neces- sary to design a piston of which the lower portion of the skirt has high stiffness.

Finally, the researchers would like to thank the staff of Toyota Motor Corp. 4th Power Train Dept. 1st Function Design Room for their assistance with this research.

References

[1] Chucholowski et al., Computer Simulation of Piston Slap Motion (in German), MTZ No. 48, pp. 133-137 (1987).

[2l Watanabe et al., Numerical Analysis on Piston Slap Motion (in Japanese) Jidosha Gijutsukai (Automobile Technology Associa- tion Publication) No. 902-216, pp. 2.13-2.16 (1990).

[3] Fujimoto et al., Dynamic Deformation of Piston Skirt (in Japanese), Kikai Gakkai (Mechanical Engineering Society) RC88 Results Report No. 4.6 (1989).

[4] Furuhama et al., Piston Slap Simulation under Consideration of Piston Skirt Deformation (in Japanese), Kikai Gakkai (Mechani- cal Engineering Society) RC88 Results Report No. 4.2 (1989).