From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Explanation of the central-point chassis lubrication system, detailing oil distribution, component design, and flow control.
| Identifier | ExFiles\Box 72\1\ scan0062 | |
| Date | 1st March 1925 guessed | |
| 6 CENTRAL-POINT CHASSIS LUBRICATION FIG. 11—DISTRIBUTION IN MECHANICAL FRONT-BRAKE AND STEERING CONNECTIONS Oil Is Fed from a Drip-Plug on the Side-Frame, at the Upper Right, through the Ball End of the Brake-Operating Shaft, Lubricating the Ball Joint and the Telescopic Joint between the Two Parts of the Shaft. Another Passage, Leads into and through the Universal Joint to the Camshaft Bearing within the Brake Drum. This Bearing Drains into a Collecting Pocket, Whence the Oil Is Distributed to the Ball Studs on the Steering-Rod and Tie-Rod Arms. An Oil Supply Having Been Brought to the Pin of Each Steering Knuckle, It Can Be Distributed to All Adjacent Bearings Without an Oil Line on the Front Axle handle with the usual ease, but in very cold weather the gun will require about 10 min. to discharge instead of the customary 1 min. HOW OIL IS CARRIED FROM FRAME TO AXLES Several methods to carry oil from the line on the frame to the axles with unquestioned reliability have been developed. One method is to use a length of hard seamless brass tubing that extends continuously from a junction on the frame to another on the rear axle by way of the spring, as in Fig. 5. A part of the tube is wound into a helix that is co-axial with the hinge-bolt of the vehicle spring, while the rest of the tube extends alongside of the main leaf, to which it is attached by a few clamps. These clamps fasten to the main leaf so securely that they cannot be dislodged and they hold the spring run of the tube in a protected position where it takes the same distributed flexure as the spring leaf. The helical portion is carried in a protective housing not shown in the photograph and accommodates itself readily to the hinging motion. The whole arrangement is such that the stresses anywhere in the tube never approach its elastic-limit. Those who have followed experiments on fatigue of metals may recall that no fatigue limit has been found for metals of this kind when thus stressed. We have tested such spring-runs for 1,000,000 cycles of alternate deflection through their full range, far beyond what they receive during the life of a car, without any resultant damage. Another type of “bridge,” carried in a protected position and concealed by the splash apron, is used at the forward end of the frame, where the large-diameter helix shown would be in an exposed position. The appearance of this “bridge,” with the splash apron removed, is shown in Fig. 6. A close-wound coil is screwed at its upper end over a threaded stud carried by the frame and the lower end is carried by a similar stud clamped to the top spring-leaf near its hinging point. DISTRIBUTION TO STEERING-MECHANISM BEARINGS AND SPRING-SHACKLES Given a reliable method of leading oil under pressure to the front axle, the distribution of oil on the axle is simple, as shown by Fig. 7, in which the steering-knuckle and its associated bearings are oiled without the use of oil pipes or swivels. The oil pipes are short, well protected and easily seen unless the wheel is removed, as when the photograph was taken. Oil may be carried from the ball stud on the wheel-knuckle back to the ball stud on the steering-gear lever through the drag-link, which can be arranged not only to have a small oil storage but to be a self-contained assembly capable of being mounted and dismounted as a unit regardless of the oiling system. Similarly, the ball stud in the steering-gear is removable without regard to the presence of oil ducts, and the steering lever is also removable, a diagonal hole conveying the oil to it without weakening the shaft. In fact, all ordinary assemblies and adjustments can be carried on as usual without regard to the oiling system. Furthermore, the mere assembling of the parts forms the proper oil ducts. If working parts of a car designed with fair regard to low unit-pressures are well lubricated, dirt, acting as an abrasive, becomes the principal cause of wear. A simple means of excluding dirt from a shackle is shown in Fig. 8, at the left. Whereas a conventional shackle has four open cracks in which dust can lodge, the parts here overlap and concealed felt rings are provided to prevent lateral travel of dirt. The bolts can be assembled in only one position in the hollow link and both bolts are alike; no rights or lefts or top and bottom have to be considered, so a general interchangeability is maintained throughout these constructions. A corresponding construction is used in the spring hinge. Feeding oil to the top bolt of a tension shackle with-out the use of flexible connections or extra parts possesses a point of interest. A shackle of this type, of conventional construction except for the lubrication, is shown at the right in Fig. 8. The long drilled hole in the link is filled with a pin a few thousandths of an inch smaller than the hole so that the entire annular space between the pin and the hole is constantly full of oil, held there by capillary attraction. The bolts are press-fitted in the links, so that a continuous oil-tight passage from the inlet in the lower bolt to the outlet of the upper bolt is provided. A groove around the lower bushing conveys oil to the top or loaded surface of the lower bolt, and it flows through a passage in the bolts and link to the upper bolt, and since this oil is transmitted across the loaded surfaces wear will not cause any appreciable leakage. The upper bolt has a groove at the top to permit free exit of oil and, inasmuch as the bolts are they are made of different sizes to prevent incorrect assembly. The oil pipe lies inside of the groove in the forging, where it cannot be damaged by a tow rope. OILING UNIVERSAL-JOINTS AND BRAKE LINKAGE One method of oiling both of the universal-joints is shown in Fig. 9. Whenever the front joint stops rotating in the position shown, a small quantity of oil runs by upper threaded part receiving a flared pipe-connection. CENTRAL-POINT CHASSIS LUBRICATION 3 Emission of oil is restricted by an accurate hole 1/16 in. in diameter and ½ in. long in which is placed a pin of nearly equal size but leaving a minute annular orifice that presents a high resistance to flow. Below this pin is a metal relief-valve faced with a soft material that is impervious to oil and is pressed against an annuar seat by a phosphor-bronze spring. A metal-to-metal valve that could be relied on to be tight when closed and yet open under light oil-pressure, would be a very expensive manufacture and even then would be likely to leak if the smallest particle of dirt lodged on the valve-seat. The soft facing overcomes these difficulties and, with the tight valves made possible by this construction, no oil leaks from the outlets, no oil drips on the garage floor, and the pipe line is always solidly full of oil from the central lubricator to each outlet. It is evident, however, that foreign particles must be prevented from lodging in a valve and that accumulation of dirt in a restriction would change its flow-resistance. To avoid this, a felt-strainer plug supported by a gauze cup is mounted in the inlet of the fitting. This strains out of the oil any small particles of dirt without offering any considerable resistance to slow flow, but it should not be called upon to filter large quantities of dirty oil, as there would be a likelihood of covering its surface with sufficient dirt to form an obstruction. To avoid this the entering oil is finely filtered in the central lubricator, leaving the strainers in the drip-plugs to intercept only the dirt that might come from the inside of new pipe or from threaded parts. The total quantity of dirt will not begin to clog them nor increase their flow-resistance measurably. A pressure of about 12 lb. per sq. in. is required to open a valve and, while the pressure lost in passing through the strainer varies with its use, it is of such a low order that it may be taken as averaging 3 lb. per sq. in. Thus, with a line pressure of 55 lb. per sq. in., 15 lb. is absorbed in the strainer and valve, leaving 40 lb. effective to force the oil through the restriction. FIG. 4—ASSEMBLY OF LUBRICATOR AND PUMP, IN SECTION Oil Introduced at the Top of the Lubricator Is Strained through a Fine-Mesh Gauze Bag, Filling the Tank Proper and Thence through a Dense Felt Diaphragm into the Spaces Below. Any Air Therein Escaping through Two Vent Tubes. The Pump Plunger Is Held in Its Normal Indicated Position by a Long Coil Compression-Spring. When the Spindle Is Pulled Out, About a Tablespoonful of Oil Is Drawn through the Valve at the Base of the Lubricator and through Two Small Holes into the Base of the Pump Cylinder. When the Spindle Is Released the Spring Forces the Piston Down Slowly and the Back-Pressure Closes the Valve and Forces the Oil Out through the Outlet Below the Pump End into the Chassis Oil Line. When the Piston Reaches the End of Its Stroke, It Seals Both the Inlet and Outlet FIG. 5—METHOD OF CONVEYING OIL FROM PIPING ON MAIN FRAME TO REAR-AXLE PARTS A Section of Hard Seamless Brass Tubing Is Connected to the Main Line on a Frame Wound into a Helix, at the Spring Hinge, and Continued along the Side of the Main Leaf of the Spring, to Which It Is Clamped. The Helix Absorbs the Bending Stresses Due to Flexure of the Spring without Fatigue of the Metal of the Tube. The Helical Portion Is Protected by a Housing That Was Removed for the Taking of the Photograph RATE OF OIL-FLOW With this pressure and using ordinary engine oil at room temperature, different rates of flow result from using pins of various diameters in the control outlet, as shown in Table 1 in which 1 cc. (0.061 cu. in.) is taken as equivalent to 20 drops of oil, although this relation is only approximate. TABLE 1—CONTROL-OUTLET SIZES AND RATE OF OIL-FLOW Rate of Oil-flow Hole Diameter, In. | Pin Diameter, In. | Cc. per Min. | Approximate Drops per Min. 0.063 | 0.061 | 0.15 | 3 0.063 | 0.060 | 0.25 | 5 0.063 | 0.059 | 0.40 | 8 0.063 | 0.058 | 0.63 | 12 0.063 | 0.057 | 1.00 | 20 0.063 | 0.056 | 1.50 | 30 Resistance to oil-flow in any chassis bearing, whether tight or loose, is obviously many times less than that of a drip-plug restriction and also, if a piping system is laid out with fair regard to even distribution, its resistance is so low compared with that of its drip-plugs that the pressure losses in it may be disregarded. Therefore the drip-plug is a means of controlling oil-flow that is substantially independent of the tightness of the bearing. In some cases oil may even be distributed to its destination by a loose fit, and in others oil may be fed to the center of a bearing and allowed to leak out at the ends. Thus the bearings will be replenished as fast as oil is consumed, even when the car is standing, and when the car is in motion, if the bearing is tight the lubrication is forced; whereas if the bearing is loose, oil is thrown about and the parts are copiously supplied. In any case, as long as the line is full of oil, leakage is absent. It may be thought that oil would be wasted by continuing to feed a bearing that is already full, but the small quantities of oil used are readily absorbed by the felt packing. With all parts in good order and the engine running, a film of oil is maintained over the entire bearing-surface, but if the felt should become saturated with oil the surplus runs off to the drip-pan and is not likely to fall on the tires. FIG. 6—TRANSFER OF OIL TO FRONT-AXLE PARTS BY A SPRING BRIDGE The Tubing Is Wound into a Long Coil That Is Screwed at Either End over Studs on the Frame and Top Leaf of the Spring. Thence the Tube Is Carried along the Top Leaf to a Point above the Axle, Then Down to the Rear of the Axle and Outward to the Steering-Knuckles at Either End | ||