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
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212 
REFINING PASSENGER VEHICLE CHASSIS.
Page 144
Page 145
Page 146
If you've noticed an error in this article please click here to report it so we can fix it.
Gradually the Equipment of the Passenger Chassis is Becoming More Complete. In this Article Some of the Most Outstanding Developments are Reviewed.
AN extraordinarily complacent character would have to be possessed by anyone who, suddenly confronted with a modern passenger chassis and a chassis of 1919 vintage side by side," did not pronounce the difference as
astounding. Engines, gearboxes, transmission systems, axles and brakes, have been improved out of all recog
ition, but this is not all, for maintenance work has been reduced considerably, and the performance of "the vehicle e has been enhanced most markedly, due to the inclusion of accessories which, although not absolutely necessary to make the various components function, nevertheless provide a degree of refinement impossible of attainment without them.
In the "good old days" maintenance work was quite different from what it is now. To quote only one or two odd examples of the difficulties which the passenger-vehicle owner of a decade ago had to face : It was, for instance, quite the usual thing to clean out the engine sump, grind valves and decarbonize, at what is considered nowadays too frequent intervals, whilst considerable wear on cylinder barrels and pistons was almost expected after the vehicle had completed one or, at most, two seasons' running. Again flooding the carburetter was an absolute sine qua non if the engine was to be persuaded to start from cold without prostrating most of the garage staff in the attempt. Properly to lubricate a chassis in those days was quite half a day's job for one man, whilst brakes, if they were to be at all effective, required refacing at frequent intervals— often a laborious business—and adjusting practically after every ran; anti so one could go on ad lib.
The position nowadays, how
ever, is entirely altered. Maintenance work is always grumbled at, but is now required at very infrequent intervals, whilst the fitting of effective electric starters, which, in conjunction with improved carburetters, air stranglers, hot-spots in the manifolding, etc., has enabled an almost instantaneous start to be effected without any manual effort whatever. Indeed, most vehicles run for extraordinarily long distances without the driver even having to lift the bonnet to inspect any component—much less effect an adjustment.
How has all this come to pass? Who is to be thanked for it, and what does the future hold in store as a possibility for further development? The answers to these questions cannot be summed up briefly, as the ramifications of the general improvement are so wide and practically every section of the industry may be considered as having helped, in some measure, towards a common goal.
Let us begin our investigation of the value of accessories in chassis layout by a consideration of the engine. Such items as oil filters, air cleaners, petrol filters, calorimeters, gauges, etc., not to mention the electrical equipment, all play their part in making the unit more foolproof and easy to look after.
In the lubrication system, for example, great care is taken nowadays to ensure that the oil is kept scrupulously clean. In. quite a number of engines there are at least three filters actually built into the crankcase itself, whilst an additional "oil cleaner" is usually coupled to the system.
The lubricant, as it is pOured into the engine, passes through a preliminary gauze located in the filler spout and then, before it is circulated, it has to pass through a further gauze surrounding the pump body. Again, before the oil reaches the bearings it is forced through a pressure filter consisting of a very fine water-resisting gauze which, of course, excludes from the bearings any very fine particles of foreign matter suspended in the fluid.
Now, both of these filters are in the majority of engines very easily get-atable, the former usually taking the form of a circular gauze attached to a flange which, by undoing a ring of.bolts, can be removed from the sump for cleaning purposes. The 'latter, however, is. more often than not located on the upper half of the crankcase and is cap-able of being removed from the top—an operation taking the matter of a few moments only.
Features such as these, whilst forming part of the basic design of the vehicle, all help towards the continued useful life of the working parts, as it is known that by maintaining -the lubrication system in an absolutely clean state, wear is reduced to a minimum.
A lubrication accessory which is becoming more and more popular is the oil
cleaner. This component calls for a portion of the circulated oil to be bypassed through a chamber in which the lubrication has to pass through a flannel pad and, judging by the amount of dirt—sludge would be a better term— that is regularly obtained from the inlet side of these filters, the bearings are saved from an enormous amount of abrasioa.
The modern tendency appears particularly to aim at cleanliness. Thus, in a good many instances, the orifice of the crankcase air release is connected to the air intake of the carburetter, so that the ordinary atmosphere (which may be dusty or laden with moisture) is not drawn into the crankcase to defile the oil in the sump. Further, the air entering the carburetter through the normal intake is often filtered, an action which excludes all dust and so helps to preserve the life of the working parts of the pistons, cylinders, valve gear, etc. There are several air cleaners now on the market, but all work on approximately the same lines. In one, the air is drawn through a large sheet of fabric resembling flannel in texture (which is spread over a framework, corrugated on its outside diameter in order to make the device more compact) and is attached to the air intake of the carburetter. This is a comparatively cheap, but nevertheless an effective, means for keeping the interior of the engine clean, at the same time avoiding any restriction of the flow of air into the cylinders. Petrol systems, too, have been vastly Improved of late. Most tanks are now fitted with gauges of tome sort or other, which can be read either from the driver's seat or from the exterior of the tank itself and show at a glance the exert quantity of fuel contained within the tank. In addition practically all supply fines nowadays contain a dirt trap, and the ' earburetter is nearly always fitted with a water-resisting filter, thus the old trouble of choked jets, etc., is seldom experienced.
The vagaries of the English climate result in an extraordinary variation of temperature from day to day, a fact which makes it difficult for the bus and coach owner properly to equip his vehicles to suit the weather conditions for a few days together. Temperature is, of coarse, a very important item in the running of an internal-combustion engine, and if a whole fleet of vehicles be operating at varying but inefficient heats, the operating cost is bound to
be increased. To counteract this the accessory manufacturer has stepped in again, and by the expenditure of just a few pounds a saving can be effected of many times the value of the accessories.
A thermostat included in the cooling system can be made to work automatically, either to operate radiator shutters or to operate a valve in the circulating system which allows a ProPostion only of the radiator cooling water to be circulated through the water jacket. Everyone is familiar with the principle on which the thermostat works and, simple though it is, it is proportionally effective.
Take the case of a bus which makes repeated journeys of, say, six miles with a wait of 20 minutes or so at each end of the journey ; without some form of thermostat or system of radiator shutters the engine would take very nearly the whole of the six miles to warm .up thoroughly and so reach its best working temperature. With a thermostat, however, the water surrounding the cylinders only has to be warmed, and as its volume is only a small proportion of the total volume of water carried, the length of time occupied in warming up is very small indeed. There are, of course, radiator shutters which can be operated by hand. To obtain the best results with this form of heat retainer it is necessary to equip the radiator with a calorimeter, otherwise the driver is liable to allow the engine to become too warm, causing boiling, loss of water, and possibly damage to some part of the engine.
The modern braking system is, of course, a vastly improved arrangement over the somewhat haphazard methods employed less than a decade ago. Practically every chassis of note has four-wheel brakes, each individual brake being of sensible proportions, of efficient design, and capable of working smoothly and silently. Recently, however, a further, development has taken place—the addition of a servo motor to the system.
There are, of course, several systems
at present in vogue in which certain, or all, of the brakes are self-energizing, i.e., the application of one shoe by the pedal or the lever causes another shoe, or pair of shoes, to be applied with greatly increased force. On the other hand, however, a large number of chassis is equipped with a definite servo motor which usually operates a valve, causing power to be applied either in the form of suction, or pressure, to a
piston to which all the brake rods are connected.
Taking a census of the vehicles exhibited at the recent Olympia Show, the vacuum servo appears to be most popular. The depression below atmospheric pressure which takes place in the induction pipe of an engine when the throttle is closed is used as a means for causing a pull on a Piston of large diameter. This pull can, of course, become a very big force, especially when the engine is turning over at high speed. Supposing there is only a 3-lb. drop in pressure in the induction pipe—with a cylinder of 8 ins, diameter over 150 lb. pull would be given to the brake rod, practically no effort being exerted by the driver. A proportionate decrease in induction-pipe pressure would, of course, cause a corresponding increase in the brake-rod pull. With a servo motor of this type it is possible for the driver to apply the brake pedal, with the equivalent pressure required in a highgrade private car, but the stopping power of the brakes is quite as effective in the commercial vehicle as in the car.
Again, 'adjustment is much easier to effect nowadays than in the past, care having been taken in most chassis to bring the points requiring attention into convenient positions; such items as lubrication for the compensating gear, etc., and the general disposition of the controls, all show that they have received the designers' attention, with the result that they are easy to loot after and maintain in proper adjustment.
No passenger chassis nowadays is complete without a proper and fully equipped facia board for the driver. A speedometer, mileage recorder, clock, etc., are nearly always included in She grouped set of instruments, adding materially to the convenience of driving. The latest development in instrument equipment is the inclusion of a petrol-tank depth gauge which, through the medium of an inverted-tumbler-type siphon, operates a gauge which can be mounted on the facia board, conseT quently the driver is always aware of the exact amount of fuel in the tank or tanks.
Such a review as this might be concluded by making reference to the desirability or necessity of some of the fitmhts that have been described. Whilst we make no excuse for unnecessary complication, a complete—even elaborate—equipment is of definite
1-EST COCK CLEAN Oil BACK TO CRANKCASE
DIRTY Olt ENTERS
UNDER PRESSURE
utility, in that certain operations, either in maintenance or driving, are simplified, and the work of the garage staff is reduced.
It must be remembered that these accessories and devices are designed not merely as extra and possibly superfluous impedimenta, each has a definite function to fulfil and there is no doubt that vehicles equipped with them will run more satisfactorily and possess et longer wearing life. Their value is considered by some makers to be so great that certain of them are now, in many instances, provided as standard equipment.
It is somewhat unfortunate that such additions as these are apt to detract from the clean and simple appearance of the chassis and, as exemplified at the Olympia Show, may cause an otherwise simple layout to appear complicated to those who do not delve below the surface.