1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188 
Internal damping promises low-cost noise control
Page 91
If you've noticed an error in this article please click here to report it so we can fix it.
Review of noise problems included in first CAV press call. Turbocharging, combating corrosion in alternators and cold starting are also discussed.
MAKING GREATER USE of the energy dissipation properties of a standard type of cast-iron engine structure to reduce its noise level is the subject of continuing research of CAV Ltd. This was revealed at the company's first "press call" by Mr. M. F. Russell, head of the CAV noise section, in a paper on engine noise control by damping, one of a number of papers by CAV staff and issued to the Press.
In future, press calls will be quarterly so that technical journalists can be advised of the latest company studies in research, development and production techniques.
After referring to the CAV magnesiumalloy research engine and the two other types of research units having laminated aluminium and rubber side walls, Mr. Russell observed that these forms of construction were "not very attractive" to engine manufacturers because they were heavily committed to building cast-iron engines to utilize existing production plants. The research units provided a reduction in noise of about 10dB, which was equivalent to halving the loudness of the engine, measured in sones; further research was being undertaken to discover a means of achieving a comparable result with conventional means of construction by employing damping panels.
More bending resistance
This would have to be done by moving the panel resonances to a frequency outside the audio range, and could be assisted by employing smaller, thicker or contoured panels to provide greater resistance to bending. But such a measure was not sufficient to give an acceptable reduction in noise level and the possibility of reducing panel amplitudes at resonance by increasing effective panel damping was being explored.
Because damping sources had of necessity to be built into a framework designed to carry the gas loads of the engine, the main problem was to transfer the energy of the thin vibrating panels to the damping media without sacrificing the essential stiffness of the units.
Current research included tests of iron panels cast integrally with massive frames, and it had been shown that an increase in thickness improved damping and that progressively increasing the thickness towards the edges was effective. Sample methods included the use of appropriate ribbing.
Investigations continuing
Investigations were continuing to establish in greater detail means by which panel vibrations were excited and damped, so that the best use could be made of the material in the casting and of existing tooling. Damping by the panel method might add 50/100lb to the engine weight.
In a review of turbocharging, Mr. E. Kellett said the life expectancy of turbochargers was now at least equal to that of the power unit. He described tests of turbochargers in series applied to a Dorman 6LBT diesel having performance limits of 2,000 p.s.i. cylinder pressure, 750deg C exhaust temperature and 50 Hartridge smoke units. The output characteristics gave "a tendency towards constant horsepower" over the useful working range of the engine. In a paper on the cause and prevention of corrosion in alternators, Mr. K. F. Hutchun described recently developed methods of waterproofing. These included potting the connections to the diodes in resin, applying a thick porous layer of plastics insulating material to the heat sink, improving the impregnation of the stator (the machine was designed to facilitate run-off of water when it was standing) and applying a gasket cover and sealed ferrule to terminals to provide for attachment of a plastics cable conduit.
The measures described were particularly advantageous for engines mounted under floor or in any other exposed position. A machine could be fully enclosed but this necessitated derating by 50 per cent.
Cold starting
In a paper by Mr. B. E. Knight on "Prediction of diesel engine cold starting", Dr. A. E. W. Austen, director and chief engineer of the company, made the point that if there were no starting problems engine nakers would probably reduce the compression ratio of direct injection engines by 2/3 ratios and of indirect-injection-diesels by 6/7 ratios.