Page 551 - Cam Design Handbook

THB16 9/19/03 8:04 PM Page 539

AUTOMOTIVE CAMSHAFT DYNAMICS 539

Harmonic analysis with the lowest jerk curve values requires fine-tuning on the
dynamometer to adjust the valve lash intake and exhaust system. This is to maximize the
engine horsepower. To quote Crane (2000), “Do what the engine wants.”
Figure 16.7 shows the effect of increasing valve train lash on the harmonic resonance
factors. Figure 16.7a shows a street rocker arm/pushrod hydraulic roller-cam profile with
a valve spring having a natural frequency of 24,000cpm. It is acceptable to 5333rpm,
where it reaches 0.16, which exceeds the allowable coefficient limit of 0.12. Figure 16.7b
shows the harmonic analysis of the same street rocker arm/pushrod hydraulic roller-cam
profile but having lash of 0.012 inch at the follower. It looks good to 5333rpm, where it

0.25
.329 5 N = 4
Direct limit
Harmonic resonance factors ZN 2 0.15 12 10 9 8 7
6
0.20

Pushrod limit
0.10

0.05

0 13 11
3 4 5 6 7 8 9 10 11 12 13 14000
Synchronous Engine RPM
(a) Zero lash.

0.25
.248
.367 5 N = 4
Direct limit
9
Harmonic resonance factors ZN 2 0.15 12 11 10 8
6
7
0.20
Pushrod limit
0.10

0.05

0 13
3 4 5 6 7 8 9 10 11 12 13 14000
Synchronous Engine RPM
(b) Lash = 0.012 inches.
FIGURE 16.7. Harmonic resonance street performance rocker arm/pushrod hydraulic roller-cam profile
(spring natural frequency of 24,000cpm).