JSAE Review 19 (1998) 129—135

Improvement in the noise and vibration performance for the new 1996model V6 engine

Shinichi Murakami, Toshimitsu Shinohara, Hirokazu Nagai, Misako KamedaEngineering Research Department 10, Tochigi R&D Center, Honda R&D Co., Ltd., 4630 Shimotakanezawa, Haga-machi, Haga-gun, Tochigi 321-3393 Japan

Received 7 July 1997

Abstract

To achieve suitable quietness and smoothness for high-quality luxury vehicles, the new V6 engine was substantially improved fromits predecessor. Idling vibration was improved by reducing first-order inertia force and stabilizing combustion. Idling quietness wasimproved by reducing piston slap noise. Acceleration quietness was improved by reducing engine mount point vibration andradiation noise. Engine starting noise was improved by reducing the starter motor gear noise. ( 1998 Society of AutomotiveEngineers of Japan, Inc. and Elsevier Science B.V. All rights reserved.

1. Introduction

The fundamental layout of the new V6 engine wasdecided as a 90° bankangle and a front longitudinalmount, to maintain a compact and lightweight size andthe most suitable weight distribution, which were thecharacteristics of its predecessor. Moreover, already hav-ing an established reputation, the displacement was ex-panded to 3.5 L to improve drive feel. This gives easierhandling torque characteristics which are realized in themost commonly used rpm range. The specification of thisengine compared with the previous engine are shown inTable 1.

The development concept of this engine was the“Good feeling in the most commonly used rpm range”,and noise and vibration were the important factors whichmost influenced the concept. The following four factorswere chosen as indices for the “Good feeling” in terms ofnoise and vibration. This was created as a developmentgoal. The overall level of noise and vibration should besmall. The time series fluctuation in the noise and vibra-tion should be small, and should not have a protrusiveelement for the noise and vibration frequency composi-tion. Any change in the noise and vibration caused bychange in the engine rpm should be linear.

Idling engine vibration, idling engine noise, acceler-ation engine noise and vibration and engine starting

noise were emphasized as development issues in order toimprove the new engine.

2. Idling engine vibration

The engine is the major source of vibration felt withinthe vehicle cabin, such as from the seat, floor and steeringwheel. Because of the 90° V6 cylinder layout, the 1storder couple of inertia forces generating reciprocatingmass cannot be eliminated in the case of the previousengine. In order to increase engine horsepower in thehigh rpm range, combustion during idling has to besacrificed and vibration caused by irregular combustionis experienced in some cases.

2.1. Reduced first-order vibration

The first-order couple balancer was newly adoptedwith the new engine to eliminate the first-order vibration.So that the first-order couple balancer is most effective,the inertia mass dispersion was reduced by 80% in thereciprocating mass, and by 75% in the rotating mass. Thefirst-order reduces the effect of vibration from the enginemounting points due to the introduction of the balancershaft, the reduction of dispersion in pistons and connect-ing rod mass, etc., as shown in Fig. 1. The first-order

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Table 1Engine specification

New Previous

Engine type C35A C32ACylinder layout 90° V6 90° V6Bore]stroke (mm) 90]91 90]84Displacement (cm2) 3473 3206Compressiion ratio 9.6 : 1 10.0 : 1Max. power (kW/rpm) 158/5200 158/5500Max. torque (N m/rpm) 312/2800 299/4500Max. engine speed (rpm) 5900 6300

Fig. 1. Applied technology and reduction of first-order vibration.

Fig. 2. Arrangement of balancer shaft.

vibration of the engine mounting points was reduced bymore than 10 dB as a result.

The layout of the balancer shaft is shown in Fig. 2.The precision improvements of the piston mass were

attained by a high precession casting method. The fea-tures of this manufacturing method are the improved die

Fig. 3. New manufacturing method for connecting rod (blockingforging).

precision which prevents displacement, and the castingdie alloy, which was strengthened to prevent prematurewear. The mass precision improvement of connectingrods was attained by the blocking forging shown inFig. 3. This is a new method of processing [1] whichensures the accuracy in the amount of materials to beprocessed by managing their mass before forging begins.Four directional sliding forms were added so that theblocking forging method, which was formerly used forprocessing simple forms like gears, could be applied.

2.2. Vibration reduction which occurs during imperfectcombustion

Combustion stability in idling is largely influenced bythe valve overlap area. Generally, engine horsepower athigh rpm is increased by the enlarged valve overlap area.In contrast, in the low rpm range combustion tends tobecome unstable, especially during idling, due to theworsening of combustion.

The new engine has a 300 cc displacement increase, thevalve overlap area was reduced by half and valve timingwas optimized. This new engine realized a low rpmtorque improvement and idling combustion stabilitywhile maintaining maximum power.

In Fig. 4 the new engine overlap area and valve timingare compared with the previous engine, and the valve liftcharacteristics are shown.

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Fig. 4. Valve lift characteristics and reduction of valve overlap area.

Combustion conditions were compared with the pre-vious engine in Fig. 5. A calorific value difference incombustion causes a difference in the rotational speedfluctuation. The horizontal axis in Fig. 5 is the rpmwhich rose by a single explosion, and the vertical axis isfrequency. combustion became more stable in the newengine with the prevented occurrence of extremely weakcombustion. Fig. 6 shows the effect of reducing the com-bustion variation. The fluctuation in the engine speedand vibration became substantially more stable.

3. Idling and low rpm engine noise

Because both the rpm and load are low when idlingand at extremely low rpm, the overall engine noise is low,and a subtle noise is noticeable.

The piston slap and timing belt noise were reduced inthe new engine to improve quietness.

As with the previous engine, when piston clearancewas close to its maximum tolerance, piston slap noisebecame loud after 20 000 km. To improve this, the stiff-ness of the ceiling and skirt part of the piston was im-proved. In Fig. 7, the transfer function between the sleeveand the cylinder block outer wall are compared, and thereduction of inertance in 2—3 kHz is about 10 db. Thevibration reduction of the cylinder block outer wall isshown in Fig. 8.

Fig. 5. Combustion stability at idling.

Fig. 6. Reduction of idling vibration by stable combustion.

S. Murakami et al. / JSAE Review 19 (1998) 129—135 131

Fig. 7. Reduction of inertance by increasing stiffness of cylinder blockouter wall.

Fig. 8. Vibration reduction at cylinder block outer wall.

4. Acceleration engine noise

Engine noise heard in the vehicle cabin during acceler-ation is a combination of engine vibration noise trans-mitted by the engine mounts, drive shafts, pipes etc., andthe engine noise penetrating the vehicle body. For theformer, the usual noise levels reached a maximum of1 kHz. Over 1 kHz is common for the latter.

4.1. Transmitted vibration

The vibration origin characteristics between200—800 Hz are important to reduce crank rumbling

noise, called growling noise, whose characteristics aresound pressure fluctuation and roughness. These arecaused by the crankshaft knocking the bearing cap due tocombustion pressure. Vibration of the engine mount in-stallation points is influenced by resonance from suchparts as the crankshaft, cylinder block and engine mountbracket.

In terms of crankshaft stiffness, the 90° bankangle V6engine is more advantageous than the 60°V6. Because thephase difference between 2 pins is only 30° with the90°V6 engine, it is easy to secure crank stiffness in com-parison with the 60°V6, whose phase difference is 60°.The crankshaft structure of the new engine follows itspredecessor, and the new engine’s crank pulley weightwas reduced by 25%, resulting in a reduction in the crankbending vibration. Furthermore, the vibration transfercharacteristics from the crank journal to the enginemounts were improved substantially by improving stiff-ness of the crank journal area, engine mount bracketinstallation area of the cylinder block, engine mountbracket, torque converter case and oil pan. The enginemounting points could be reduced by as much as 2—4 db.The area with increased stiffness of the cylinder block isshown in Fig. 9 and the improvement of the vibrationtransfer characteristics is shown in Fig. 10. The reductionof the engine mounting points vibration is shown inFig. 11.

4.2. Engine radiation noise

Improvement of the cylinder block stiffness, improve-ment of the piston stiffness and full-floating of the pistonpin largely contributes to the reduction of engine radi-ation noise. Furthermore, by installation of the enginecover using a dual sheet catalyzer cover, and by eliminat-ing the exhaust pipe cover which amplifies the vibrationand increases noise, engine radiation noise was reduced

Fig. 9. Increasing stiffness of the cylinder block.

132 S. Murakami et al. / JSAE Review 19 (1998) 129—135

Fig. 10. Inertance reduction by increasing stiffness of cylinder block.

Fig. 11. Vibration reduction at engine mount.

by about 1—4 dB from no-load to full-load. Moreover, thenoise characteristics that were obtained showed that thenoise changes smoothly and linearly according to thechange in the engine speed. Radiation noise of the newengine at maximum and no load compared with theprevious engine are shown in Fig. 12.

5. Engine starting noise

The starter motor used in large displacement engineshas an internal gear which reduces the motor’s rpm, thustransferring torque. The planetary gear type which wasadopted in the internal reduction mechanism was thesame as the previous engine. The planetary gear type hasa decreased noise level during engagement.

With the new engine model, the contact ratio of theinside gear is further improved by increasing the tooth

Fig. 12. Reduction of engine radiation noise.

length, optimizing the tooth surface profile of the startermotor pinion gear which engages with the ring gear onthe engine side. The noise level in the cranking wasreduced by about 4 dB. The structure of the internal gearof the starter motor and the improvement points areshown in Fig. 13. The improvement effect of the crankingnoise is shown in Fig. 14.

6. Noise and vibration reduction summary

The part of the engine whose specifications werechanged for the improvement of noise and vibration, andthe contents of improvement, are shown in Table 2. Posi-tions 1—11 that were mentioned in Table 2 are shown inFig. 15.

7. Complete vehicle noise and vibration improvementeffects

Improvement effects from the engine mounts andbody, together with engine improvements have substan-tially reduced the noise and vibration level, comparedwith the previous model.

Seat vibration was reduced by about 14 dB whileidling, compared with the previous model. Fig. 16 illus-trates the improvement effects for seat vibration.

S. Murakami et al. / JSAE Review 19 (1998) 129—135 133

Table 2Changed parts and improvements in noise and vibration

Benefit

Part Improvement Idling vibration Idling noise Acceleration noise Starter noise

1 Balancer New #

2 Connecting rod Mass variation reduction #

3 Piston Full floating piston pin, stiffnessincrease, Mass variation reductionthrough high precision casting

# #

4 Cylinder block Improved stiffness # #

5 Oil pan C #

6 Engine mounting bracket C #

7 Cam shaft Valve overlap optimization #

8 Crank pulley Weight reduction #

9 Timing belt Material change, narrow width #

10 Engine cover New # #

11 Starter motor Improved gear tooth profile #

12 Catalyzer cover Damping increase by dual sheet(unequal thickness)

#

13 Exhaust pipe cover No cover # #

14 Torque converter casing stiffness increase #

15 Transmission clutch piston Mass unbalance reduction #

Fig. 13. Structure and improvement of starter motor gear.

Cabin noise decreased about 5 dB during idling incomparison with the previous model. Fig. 17 illustratesthe improvement effect for cabin noise.

Cabin noise from low to high frequency, during accel-eration, was reduced in comparison with the previousvehicle. Sound pressure by engine rpm and frequency areillustrated in Fig. 18. Overall, sound pressure is reducedby approx. 7 dB in the 250—500 Hz range and by 1.5 dBin the 500 Hz—1 kHz range.

Fig. 14. Reduction of starter gear noise.

Cabin noise at starting the engine was reduced byabout 4 dB from the previous model.

8. Summary

The noise, vibration, harshness performance of the new1996 model V6 engine were substantially improved, asdescribed above 2—7. Suitable quietness and smoothnessfor high-quality luxury vehicles was attained, and the“Good feeling in the most commonly used rpm range”development concept was realized.

134 S. Murakami et al. / JSAE Review 19 (1998) 129—135

Fig. 15. Improvement of parts of engine.

Fig. 16. Vibration reduction of sheet while idling.

Fig. 17. Noise reduction at cabin centre while idling.

Fig. 18. Acceleration noise reduction at cabin centre.

References

[1] Soga, R. and Kihara, T., The case study of the closed forgingsystem (in Japanese with English summary), Proceedings of JSAE,No.9633414, pp. 201—203 (1996).

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