"It will be noticed that the first position for curves, 1-8, 1-4 and 3-8, are low, which would bring the intersection of the curve with the speed axis at a point before zero. As to whether this is correct or not, cannot be determined without further testing. "With the muffler cutout data obtained curves have been plotted and a curve showing in a very general way the increase of back pressure with increase of speed due to opening the throttle on the level." MUFFLER DEPRESSES POWER DELIVERY By conducting a series of experiments on various types of mufflers in connection with a Thomas motor, it developed that power is materially reduced if the muffler offers much back pressure, and Fig. 5 is a curve of results of one of these experiments made by using a somewhat inefficient muffler for the purpose. Fig. 2 was given to prove that Thomas results are better than A.L.A.M. ratings, whereas Fig. 5 presents contrary evidence in that the power delivered by the particular motor used in this test fell well below the A.L.A.M. rating when the back pressure due to the muffler used was increased, whereas the Reed ejector muffler regularly used in Thomas work offered no such resistance to the flow of the exhaust. Table III, which is given in this article, shows some of the series of readings taken in the road test, from which the curve Fig. 4 was plotted. This series of data will help materially in the process of following up the test, especially if the reader is not skilled in such reading diagrams as Fig. 4. PISTON DEFORMATION UNDER LOAD CONDITIONS Considering perfection of design of automobile motors the end is not as yet, and this is to be looked upon as a hopeful sign rather than with a despairing eye. In order, however, to advance the work, facilities, inclination, and time in which to accomplish the tedious tasks must be available. As an indication of the underlying situation, refer to Fig. 6, which shows, theoretically, and in an accentuated manner, how pistons do deform in service, and, as to the extent of this deformation, it is enough to examine Table IV, connected with the report of the test, in conjunction with the report of J. M. L. Howe, of the E. R. Thomas staff, as follows: HOWE REPORT OF PISTON DEFORMATION The idea in this test was to determine under various loads the distortion of the piston from a true cylindrical form. A straight ground piston of .003 clearance was used and measurements taken as follows, both at an angle and parallel to the piston pin of the four bridges, and space between clearance and fourth bridge. The lower portion of the piston was measured in two places, i.e., near the top and near the web. Wristpin clearance groove is 1-2 inch. A wristpin and straight connecting rod were used. Then the crankshaft bushing on the rod (a short piece of shafting) was slipped and box tightened up. The piston and rod were next put under a 30-ton hydraulic press, the piston being up and a piece of blotting paper being interposed between the piston head and the plunger. The shafting was supported by two V blocks. Care was taken that the axis of the combined piston and rod coincided with that of the plunger. This is a fine illustration of the futility of theorizing in a garret and building on paper; it takes facilities, experience and persistence if the product is to be thoroughly good in every way. Fig. 7-Chart contrived for convenience in testing motors, showing horsepower at various speeds and brake loads 50 55 60 65 70 75 80 85 90 6 Indicated Horse Power 45 40 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600 Mean Effective Pressure, Pounds per Sq. Inch Fig. 8-Chart contrived to show mean effective pressure under different loads as measured in indicated horsepower The claim is frequently made that a piston is lighter than all others; it is ribbed, or it is without ribs, and that the fit is within some fraction of a thousandth of an inch. If the ribs are not properly placed, or if the walls are not suitably designed, there is every likelihood that warping will be far in excess of any allowed fit allowance and the piston will stick in the cylinder every time it reaches the top of the stroke, in which event the result will be disastrous, and it is in this way that many of the failures of the past can be readily traced. There are divers points of this character to be settled in connection with proper designing, and it is a serious question if the work can be prop erly done in the absence of tools devised for the purpose and in the hands of men of proven competence. A weight of two tons was applied and piston measured up while under pressure. This gives the maximum explosion load approximately as from the manograph cards on the "L" motor. The maximum explosive force was from 375-400 pounds to square inch of piston area. Fig. 9-Curve of thermal efficiency with a motor running at maximum load in horsepower and a speed of 1,000 revolutions per minute force of piston. =400 x 3.625 x .7854. = 4,140 pounds. = approximately 2 tons. The results are shown on the data sheet. It will be noticed that the cylindrical form of the piston is changed to an ellipse with the major axis parallel to the piston pin, or, in other words, the axis of the piston pin and the major axis of the ellipse lie in the same plane for above pin. The greatest deformation of decreased diameter occurs at portion between fourth bridge and wristpin clearance. The positive deformation lessens from here to top of piston. In space below clearance the deformation is slightly negative and the axis of the deformation has swung to one side slightly, but at portion near web the axis again assumes parallelism. Next, a load of 5 tons was applied and measurements taken. These measurements show the characteristic distribution as previously given, but are increased about directly proportional to the load, i.e.. 2 to 5. The pressure was next carried up until the connecting rod collapsed, as shown. The pressure was approximately 7 tons, which gives a factor of safety of 3 1-2. The rod failed at what is known as the "square"-ended column failure," which means that the two ends were fixed in contrast to a pin-ended column. The connecting rod, if it had failed in a plane at right angles to the piston pin, would have failed in a "pin-ended column." It is a peculiar fact that the square-ended column is four times as strong as a pin-ended one. The failure in actual practice, if these excessive pressures were used, might lie in a plane at right angles to the present failure, due to the whipping or inertia forces which are added to the piston load. The permanent deformation of the piston is given. It will be noticed that the major axis now runs at right angles to the pin. On taking the wrist pin out it was found to be bowed upwards approximately .02 inch. The wrist pin is made of 3-4-inch x 3-16-inch wall steel tubing, 37-16 inches long, hardened and ground down to .7192 inch. For a theoretical consideration on strength of wrist pin, the custom is to treat it as a beam held at both ends and loaded at the middle instead of by a uniform load. The reason for the deformation is shown by the following sketch. As the piston pin bends, the walls of the piston, being very light, are forced outwards, and the walls below the pin inwards. As tests have been made on the heating of the "L" cylinder and piston, and these tests have shown that there is no appreciable deformation, the cause of scoring is due to weakness of the wrist pin. Proper webbing in plane at right angles and perpendicular to pin across head and following down to bosses would greatly decrease deformation. WITHIN THE PIERCE-ARROW LABORATORY While there is a certain similarity between the laboratories in the several automobile plants, it remains that severally specialized methods prevail in them to a vast extent. As to these methods much depends upon the progress previously made and there is something to be attached to the objects sought. Characteristic of the line of investigation conducted in the Pierce laboratory, or in connection therewith, is the system of motor investigations pursued for the express purpose of ascertaining the exact facts 24 Pounds of Gasoline per D.H.P. in relation to fuel economy, power of range and flexibility. Referring to Fig. 7, which is a curve plotted to show horsepower on the Prony brake, it will be observed that by a series of diagonal lines, each one of which represents some one speed of the motor, they, in conjunction with ordinates reading "net brake load in pounds" and "abscissa," afford a means for determining the horsepower of the motor at any one of the respective speeds when the net brake load in pounds is known. Referring again to the figure and to a net load of 90 pounds, the point of intersection of the speed diagonal representing 1,100 revolutions per minute is at the abscissa line representing 60 horsepower. In other words, if the motor during test shows a pull of 90 pounds on the brake arm when the speed of the crankshaft is 1,100 revolutions per minute, the motor will be delivering 60 actual horsepower. By proceeding as above for any other pull in pounds at any other speed the actual horsepower delivered may be determined quickly and without calculation, the chart being sufficiently extended to cover the whole range of performance for any motor. When a manograph is used for the purpose of investigating the condition of the motor, the manograph readings, suitably interpreted, may be resolved into indicated horsepower. However, this information is of small value in the absence of more or less exact knowledge of the pumping losses in a motor. Figure 8 was contrived for convenience in testing Peerless motors. This chart will give, at a glance, the mean effective pressure in pounds per square inch, provided the indicated horsepower is known and by considering the speed of the motor at which the power may have been developed. The diagonal lines represent crankshaft speeds and the abscissa are given in terms of horsepower so that the mean effective pressure will be found as ordinates in the chart. Taking 40 horsepower for illustration, and following out to the point of intersection of the diagonal line representing 1,250 revolutions per minute, it will be found that the ordinate has a value of 440 which is given as mean effective pressure in pounds per square inch. High Thermal Efficiency Ascertained-Perhaps Fig. 9 will show a condition which is beyond the belief of the old time engineer, who may not have followed closely investigations which were conducted by automobile engineers within the last ten years. As the chart shows, the curve of thermal efficiency, under conditions of maximum power for the particular motor, is maximum at 20 per cent. with the gasoline consumption at about .326 pound per 1,000 revolutions of the crankshaft. This thermal efficiency was unheard of in any other type of power-delivering machine and was not approached in internal combustion motors until refinements were made in automobile types-unless it be remembered that the Diesel type of internal combustion motor has delivered some noteworthy results. Since the motor in this test was run at maximum power, it follows that the thermal efficiency varied with the gasoline consumption, bringing out very clearly the information which should be of the most use to the average autoist, i.e., that there is only one right mixture, and that fuel economy is maximum when the motor is delivering its best power. This curve gives a wide range of fuel consumption, showing that the thermal efficiency fell to the low level of 14 1-2 per cent. when the fuel consumption was .532 pound per 1,000 revolutions; the thermal efficiency fell away as the amount of fuel used decreased below .325 pound per 1,000 revolutions and a decrease in thermal efficiency when the fuel is in excess or if the mixture is weak. Relation of Gasoline Used to Fuel Economy-In still another test conducted on the same Pierce motor the data when tabulated and then plotted on a curve as shown in Fig. 10, brought out some interesting points involving the relation of the total fuel used to the gasoline per horsepower. The curved line in this chart reads "pounds of gasoline per delivered horsepower" and the amount of gasoline used decreased as the power of the motor increased, so that, considering a constant speed of 1,250 revolutions per minute, the least amount of fuel per horsepower was found when the power increased beyond 35 horsepower. The straight line in the curve shows that the gasoline consumption increased as the power of the motor increased. This is as it should be, but the point is made here in effect that the position of the diagonal line in the curve is very materially influenced by the decreasing rate of fuel consumption with increasing power. Influence of Carburetor Needle Valve-Before departing from this phase of the subject, it will be the purpose here to reflect something more which can be construed as having a practical value to the average autoist. A needle valve when placed in the nozzle of a carburetor is there for the purpose of regulating the flow of gasoline. Through its agency the mixture can be made rich or lean at will. It frequently transpires that autoists find themselves in deep water after making a needle valve adjustment. They probably fail to appreciate just what it means to Fig. 14-Presents a set of records from the Woods tire-testing machine, giving information as to contact area under different conditions alter the relation of gasoline to air. Furthermore, it has been found that mere discussion falls short of the necessary explanation. Fig. 1 shows variations in thermal efficiency, in view of variations in power, considering different positions of the needle in the nozzle of the carburetor. The several needle valve adjustments are referred to in degrees. To be explicit, the needle was turned 360, 540, or to other positions as stated in degrees, and a curve of performance is given for each of the needle positions. The best performance noted in Fig. 1I is for the opening given as 350 degrees. The thermal efficiency resulting from the test was maximum at 30 horsepower of the motor. With the 360 degree position of the needle the performance was that which would indicate a condition of easy stalling of a motor in the hands of the average autoist; the motor with this adjustment would deliver a little more power at the lower range due to an enriched mixture, but the thermal efficiency falls away rapidly with increasing power and drops to substantially two-thirds of its best value, between 25 and 30 horsepower. It has been shown that the power changes with the thermal efficiency and that the thermal efficiency as shown in Fig. 11, with the 360-degree needle valve adjustment would be, in all probability, attended by a change in power. Referring to Fig. 12, a means is at once afforded for checking the relations of thermal efficiency to power for different adjustments of the needle valve. The information thus far afforded in connection with Pierce work is sufficient to indicate, in part, the extent to which matters of this sort are pursued in the well-equipped establishments devoted to the manufacture of automobiles. TIRE PROBLEMS INTELLIGENTLY COPED WITH Experimental investigations in wide extent have been carried on in several establishments. In view of this, it is a little difficult to sort out a few of them which can be included in a limited talk on the subject. Consequently it will be the idea here to "touch and go," as it were, for the purpose of presenting a widely diversified situation. Fig. 13, for illustration, presents a tire-testing machine, devised by F. J. Newman, Chief Engineer of the Woods Electric Vehicle Company, Chicago, used by the Fig. 15 Curve showing the tire loss in watts under differing load conditions company for the purpose of determining tire losses and life. In this machine the tire to be tested T1 is mounted upon its wheel Wr and presses against a wooden wheel W2. The wheel Ti is mounted on a shaft and a pulley, PI, being mounted on the same shaft, is driven by a belt BI which takes its power from the pulley P2, the same having connection with an electric motor which is the source of power. On the same shaft with the wheel W2 a brake drum B2 is placed and brake shoes B3 and B4 are arranged to fit over and be clamped against the drum B2, so that the Arm Ar measures the force of the twisting moment which will be exerted through the brake drum B2, which force is interpreted in pounds on the platform of the scales S1. Since the wheel W1, on which the tire Tr is placed, is provided with an adjustment in order to vary the distance between the tire and the drum W2, it is possible to increase or decrease at will the force which will be exerted between the tire Tr and the drum W2. Since the tire Tr is driven by the belt B1, over the pulley P1, the drum W2 must be rotated by traction against the tire TI. The amount of the traction will therefore be registered on the scales S1, through the brake arm AI and varied by altering the clamping of the brake shoes B3 and B4 against By painting the surface of the wheel W2 and pressing the tire Fig. 16-Curve interpreting data as procured in connection with tests made on tires at the Woods plant TI against the painted periphery of the wheel, it is possible to measure the area of contact of the tire being tested, since a piece of paper slipped in between will receive paint over the surfaces of contact and make a permanent record-which record will be characteristic of any particular tire under a given condition of inflation and for a given pressure. Since it is not the purpose at this time to reach conclusions in relation to tests of this character, it will be sufficient for the present purpose to reproduce tire contact records as shown in Fig. 14, A, B, C, D and E, they representing tires as follows: (A) Represents an endless solid tire showing 6.8 square inches area of contact. (B) Represents an endless solid tire, showing 7.1 square inches area of contact. (C) Represents an endless solid tire, showing 8 square inches area of contact. (D) Represents an endless solid tire, showing 8.5 square inches area of contact. (E) Represents an endless solid tire, showing 5.65 square inches area of contact. It will be seen that the performance, when reference is had to tires from the point of view of life and energy consumed, will not be the same when all of the tires do not flatten the same amount under a given load and other equal conditions of the tire on the periphery of the brake drum B2. |