Dashboard
That portion of an automobile body which forms the front of the forward seat space, and, in the accepted type of “motor-in-front” construction, the back of the bonnet space in which the motor is housed. It acts as a wind break, and as a support for various indicating and control devices. It is made either of wood or of metal.
Synonym: Dash.
Dashboard, Hooded
A rearward concave form of dashboard, usually made of pressed steel, the edges of which are curved backwardly so as to form surfaces which somewhat protect the front seat passengers by deflecting the moving air away from them. A common type upon runabouts, roadsters and speed cars.
Dashboard Adjustment
An arrangement which enables a carburetor to be adjusted from the driver’s seat, consisting of a handle mounted upon the dashboard so connected by a linkage with the needle valve or air intake control of the carburetor as to permit of its regulation by the driver while the car is in motion.
Dashpot
A device for automatically dampening or slowing down the movements of a part without preventing its free change of position. It consists of a piston fitting in a cylinder filled with a fluid, generally air, gasoline, oil, glycerine or mercury. Small orifices are provided for the gradual escape of the fluid from the cylinder. The dashpot piston is connected to the part the sudden motion of which is to be checked and the slow rate at which the fluid can enter or leave the cylinder prevents sudden movements. Used to prevent the fluttering of the air valves of carburetors under sudden fluctuations of engine suction.
Dead Centre
In a reciprocating steam or internal-combustion engine the two positions of the crank and the connecting rod in which they are in the same straight line. When so placed, pressure acting upon the piston cannot cause rotation of the crankshaft. Of these two positions, that in which the crank is upon the side of the crankshaft toward the piston is the inward dead centre and the other position is the outward dead centre.
Dead Storage
In garage practice, the housing of an automobile (usually at a special low rate), upon an understanding with the owner that it is not to be used, but is to remain idle.
Decarbonize (v.)
To remove carbon incrustations from the piston head, valves and combustion space of an internal-combustion motor.
Decarbonizer
A substance or device used to decarbonize a motor. Chemical or solvent decarbonizers are liquids or powders intended to be introduced into the combustion space and which are capable of disintegrating and loosening the deposits through a solvent action upon their binding materials. Mechanical decarbonizers are those devices which scrape or break off the deposits from the metal surfaces.
Synonym: Carbon remover.
Decelerate (v.)
To decrease in speed or velocity.
Deceleration
The rate of decrease in the speed or velocity of a moving body. Strictly speaking, the limiting ratio of the loss in velocity during an infinitely short period of time to the length of the period of time itself. In practice deceleration is generally measured in feet per second per second. The antonym of acceleration and used in connection with the effect of automobile brakes.
Synonym: Retardation, which is preferable.
Deflate (v.)
To reduce the pressure within a pneumatic tire by allowing the air within it to escape.
Deflector Plate
A specially formed, usually curved plate on the pistons of two stroke cycle engines, the function of which is to cause the fuel charge, as it enters the cylinder, to take such a path that it partially forces out the remaining exhaust gases, but does not escape wastefully through the exhaust passages.
Deflocculated Graphite
Graphite in such a very finely divided state that it will remain almost indefinitely in suspension in a liquid. It is added to oils and greases to increase their lubricating qualities and especially to gas engine cylinder oil for use in vehicle motors.
Demi Limousine
A form of limousine body in which, while the extreme rear portion is permanently enclosed and the roof is fixed, the sides are not entirely enclosed.
Demi Tonneau
A form of touring body with a small tonneau, usually seating two, which is occasionally made detachable. The front seat is usually placed well forward as in the roadster type.
Synonym: Baby tonneau; miniature tonneau; toy tonneau.
Denatured Alcohol
Ethyl or grain alcohol, which has been rendered undrinkable by the addition of wood alcohol, benzine or other substances, and which is sold at a much lower price than grain alcohol, on account of not being taxed. When added tc water it forms an excellent anti-freeze solution for use in the circulating systems of water cooled cars and in acetylene generators. Mixtures of denatured alcohol and water containing the following percentages of alcohol freeze at approximately the temperatures given below:
20% + 14 F.
30% -5 F.
40% 20 F.
50% -35 F.
Also used to a limited extent as a fuel for internal combustion motors, either alone or in combination with gasoline and benzol.
Depolarizer
A chemical substance with which the carbon or copper element of a primary battery cell is surrounded and which prevents the reduction of the cell’s activity, known as polarization, that results from the accumulation of hydrogen upon the element. Depolarizers are substances which readily give up oxygen which combines with the hydrogen while in a nascent state, forming water. Manganese dioxide is used in dry cells.
Diaphragm
A thin, somewhat flexible, usually circular plate or sheet of rubber, metal or other resilient material, held rigidly at its edges and so arranged that one side is subjected to a fluid pressure which bulges the central portion of the plate. Such deformation, the amount of which is somewhat proportional to the pressure acting, makes the diaphragm a detector of pressure variations and adapts it for use in pressure regulating devices. It is used to regulate the fire in steam vehicles, the diaphragm being under the influence of the steam pressure and acting upon the fuel valve; also in gasoline motor speed governors, the diaphragm being under the influence of the circulating water pressure, and controlling the throttle opening. A diaphragm, acted upon by a succession of intermittent pressures, is sometimes used as an impulse pump to pump gasoline or air in fuel feed systems.
Dielectric
An insulator or non-conductor (q. v.). Differential Brake See brake, differential. Differential Carrier The frame which carries the driven bevel gear, the differential gear and the bearings thereof in a floating type rear axle (see axle, full floating), and which is bolted to the inside of the axle housing in such a manner that it may be detached and removed there from through a hand-hole (q. v.) in the housing when the axle shafts have been withdrawn.
Differential Case
The housing that encloses and forms the main structural part of a differential gear. It is usually of cast iron or pressed steel, made in halves and provides two bearings in which the two master gears of the differential are supported. In it are fastened the studs upon which the differential pinions rotate and to it is also secured the driven gear or sprocket which receives the driving effort. It is often not a tight housing, but somewhat open to allow lubricant to enter from the axle housing. The term is often applied to the enlarged portion of the axle, housing which, in shaft driven cars, encloses the driving gears as well as the whole differential.
Differential Gear
A combination of gears included in the transmission system of an automobile, which permits driving effort to be equally transmitted to each of the two traction wheels, even when they are rotating at different speeds, as in rounding corners. It is mounted upon the driving axle in live axle cars and upon the divided countershaft in double chain driven cars, and forms the connection between the two axle shatts, or between the two sections of the countershaft respectively. It consists ‘of two master gears, one of which is secured to each of the adjacent ends of the divided shaft and between which, and in simultaneous mesh with both of which gears is a series of pinions carried upon studs fixed in a rotating frame or housing. To this frame or housing is fastened the driven gear or sprocket which receives the driving effort of the motor. So long as the traction wheels of the car are required to rotate at the same speed, driving effort is transmitted from the frame or housing, through the pinions equally to the two master gears and their shafts, and no rotation of the pinions takes place. When however, the traction wheels are required to rotate at differing speeds, the pinions rotate upon their studs and simultaneously revolve upon the master gears, permitting relative motion of rotation between the latter, and allowing each to turn at the speed required by its respective road wheel to which equal tractive efforts are transmitted.
Synonym: Differential; compensating gear; equalizing gear; jackin-the-box.
Differential, Bevel
A type of differential gear, the two master gears and the pinions of which are all of the bevel type, two, three or four of the latter generally were being used.
Differential, Spur
A type of differential gear in which spur gears and pinions are substituted for beve’s. To each of the adjacent ends of the divided axle or countershaft is secured a spur master gear and the frame or housing supports, two, three or four pairs of spur pinions. The two paralleling arranged spur pinions of each pair are in mesh with each other upon the inside half of their tooth faces, and one pinion of each such pair is in mesh upon the outside half of its tooth face with one of the master gears, while the other pinion of each pair is in mesh on the outside half of its tooth face with the other master gear. The action of the spur combination is, in effect, the same as that of the bevel arrangement.
Differential Lock
A device which, when in action, prevents the operation of the differential gear and which is installed upon some cars for the purpose of facilitating starting even though one driving wheel may lack adhesion on account of slippery road conditions, in which case it would slip and fail to drive and the other wheel would fail to rotate. The differential lock acts to so fasten together the master gears of the differ their shafts cannot rotate relatively and the traction wheels thus being rigidly fastened together turn at the same speed. It is usually put into action by means of a pedal.
Differential Master Gear
One of the main gears of a differential which is fastened to one of the abutting ends of a divided axle or countershaft and with which and the other master gear the pinions simultaneously mesh.
Differential Pinion
One of the small gears which acts to transmit the driving effort from the frame or housing of a differential to the master gears and their shafts and to divide the tractive effort equally between the two driving wheels.
Differential Spider
A part consisting of a hub and two, three or four symmetrically disposed radial arms which carry studs upon which the pinions of a differential gear rotate. It is rotatably mounted upon the ends of the two divided shafts or upon the inside portions of the hubs of the master gears. The outer ends of its arms are fast in the differential frame or housing.
Synonym: Pinion frame.
Dimmer
An arrangement for reducing the intensity of electric headlights, usually consisting of a rheostat (q. v.), more or less of the resistance of which can be introduced into the headlight circuit at the will of the operator. Direct Current See continuous current. Direct Drive The transmission of the driving effort of a vehicle motor from the crankshaft to the final drive mechanism without the use of a countershaft or system of gears under load. In a shaft driven car, when on the direct drive, transmission is effected by a connection of the crankshaft through the clutch, clutch shaft, the main shaft of the gearbox (in line with the clutch shaft), the drive shaft and its universal joints and the propeller shaft to the driving pinion at the rear axle, all these parts rotating at crankshaft speed. Reduced frictional losses and noise are advantages of the direct drive.
Direct Drive, Double
The transmission of the driving effort from a vehicle motor to the road wheels at two different speed ratios, without the use of a countershaft or system of speed gears under load. In a shaft driven car with the gearbox and rear axle constituting a single unit, a double direct drive is sometimes secured by mounting upon the differential housing two bevel gears of different diameters which are in constant mesh with two bevel pinions of correspondingly differing diameters which are loose upon the propeller shaft except when one or the other of them is made fast thereto by means of a double jaw clutch controlled by the gear shaft lever.
Discharge (n.)
In a storage cell, the flow of stored electricity therefrom into an external circuit. The opposite of charge.
In ignition practice, the passage of high tension electricity through a dielectric, usually an air gap in the form of a spark or arc; e. g., the disruptive discharge between the points of a spark plug.
Discharge (v.)
To produce such a flow or passage of electricity as above described.
Discharge,
Rate of The rate at which electricity flows from a storage cell through an external circuit, usually measured in amperes.
Discharge Terminals
The two conducting points between which a disruptive discharge of high tension electricity takes place. In a jump spark plug, the two discharge terminals are usually of platinum or an alloy thereof or of other not readily fusible or oxidizable metal.
Synonym: Sparking points.
Distance Rod
A rod the function of which is to maintain related parts at a fixed distance apart. The term is specifically applied to the two rods that maintain the fore and aft position of an axle, especially that of the driving axle, by resisting the reaction of the tractive effort which tends to shift the driving axle forward relatively to the rest of the car. The rods are usually of steel tubing, pressed steel or steel forged into an I-section.
Synonym: Strut rod.
Distributor
A device for directing high tension ignition current from a single secondary winding to the respective spark plugs of a multi-cylinder engine in the correct firing order. It consists of a stationary plate of insulating material, upon the surface of which are fastened symmetrically spaced, circularly disposed contact segments, in number equal to the cylinders to be served. A shaft, operated at one half motor speeds, passing through the shell carries an insulated contact brush, which, when in rotation, successively contacts or nearly contacts with the segments. One terminal of the secondary winding is electrically connected to the rotating brush and the other is grounded, and each segment is electrically connected to a spark plug. A distributor forms a part of nearly all synchronous jump spark magnetos and of all single-coil battery systems adapted to multicylinder motors.
Synonym: High tension distributor; secondary commutator.
Double Ignition
Ignition which can be obtained at will from either one of two complete and distinct ignition systems, which are in no way dependent one upon the other, and which can generally be used simultaneously, if desired. A double ignition outfit generally consists of a synchronous magneto, serving one set of spark plugs and some form of battery system serving another set of spark plugs, with a switching arrangement adapted to put into action, at will, either ignition source or both together.
Double Motor Equipment
In an electric vehicle, the provision of two electric motors each one of which drives its respective traction wheel only, being direct connected or geared thereto. No differential gear or live driving axle is thus required.
Double Spark Ignition
Ignition which is effected by two sparks produced simultaneously at two separate points in the combustion space of a gas motor, the object being to secure a more rapid combustion of the fuel charge. Two plugs, placed at a distance apart in the combustion space of each cylinder and served by two synchronized magnetos or a double magneto, are employed.
Synonym: Multipoint ignition, twin spark ignition.
Dowel Pin
A pin, usually of steel, fixed in a part which is to be positioned exactly upon a related part. Such pins exactly fit in corresponding, properly located holes, in the related part, and, when the pins are inserted in the holes, the two parts are always in exactly the same relationship.
Drag (v.)
The faulty action of a clutch which, even when in the released position, still communicates a slight turning effort from the driving to the driven member, and its shaft, occasioned by the failure of the engaging surfaces or the lubricant upon them completely to move out of contact.
In a brake, the failure of the band or shoe completely to move out of contact with the drum upon which it acts, even though the controlling mechanism is in the released position. Generally due to faulty adjustment or design.
Drag Link
In a steering gear, the rod which connects the steering device, mounted upon the vehicle frame, to one of the axle stubs and transmits the steering movements of the operator to the steering wheels. As the steering device has an up and down motion relatively to the axles the ends of the drag link have a universal movement at their fastenings, and ball joints are thus generally used Ht these points.
Drain Cock
A small cock, arranged to communicate with the steam chest of a steam engine cylinder which, when opened, permits the water of condensation to escape therefrom, thus preventing possible damage to the cylinder caused by the piston forcing water against the cylinder heads. Also, any cock which is used to drain a liquid from a space in which it is confined.
Draw-off Plug
A plug inserted in a hole at the lowest point of an enclosed space containing liquid, the removal of which permits the liquid to escape. Used in the bottoms of crank, gear and axle cases and carburetor bowls and in water and oil circulating systems, etc.
Drift Pin
A tapered steel pin used to line up two or more holes in parts which are to be put together, so that the bolt, pin or other part which is to be inserted in the holes may readily be passed through them.
Drive Shaft
In general, a shaft which transmits driving effort from one rotating part to another. In a shaft driven car, the shaft which transmits the driving effort from the transmission parts that are mounted upon the vehicle frame to the transmission parts at the driving axle. In a car with a rear axle mounted gear box, the front end of the drive shaft is connected, through its universal joint, to the driven member of the clutch and it* rear end is connected to the primary shaft of the gearset. In other shaft driven constructions, the front end of the drive shaft is universally connected to the final shaft of the gearset and its rear end to the pinion shaft in the rear axle, or it carries the driving pinion directly upon its rear end.
Drive Shaft, Double Jointed
A drive shaft with a universal joint at each end and usually including a slip joint.
Drive Shaft, Single Jointed
A drive shaft with a universal joint at its front end only, the shaft housing acting as a torque and distance rod, and the driving pinion being carried directly upon the rear end of the shaft, except in that type of construction in which the gearbox is integral with the rear axle housing.
Drive Shaft Housing
The tubular casing which encloses the drive shaft on a shaft driven car, supports the shaft bearings, excludes dust therefrom and retains lubricant. It also sometimes performs the functions of a torque rod and of a distance rod, preventing the axle casing from rotating unduly and from moving forward relatively to the rest of the car under the reaction of the tractive effort.
Driven Member
That one of two connected mechanical elements which receives its motion from the other, e. g., the member of a clutch which is not fast to the motor shaft; the gear which is mounted upon the differential housing in a shaft driven axle.
Driving Member
That one of two connected mechanical elements which transmits motion to the other, e. g., the member of a clutch which is secured to the motor shaft, the pinion upon the drive shaft of a shaft driven car.
Drop Forging
The process of producing parts from steel and other malleable metals when heated to a malleable condition, by forming the metal into the desired shape by repeated blows from dies carried in a powerful drop hammer. The term is used in contradistinction to “hand forging», and is also applied to the parts produced by the process.
Synonym: Die forging.
Dual System
A system of ignition employing two current sources, namely, a synchronous magneto and a battery. The makeand-break, the distributor, the transformer coil, the wiring and the plugs of the magneto, or a part at least of these elements are traversed in common by both battery and magneto current, the battery current utilizing the magneto parts, as the elements of a single coil and distributor battery system. This system facilitates starting of the motor by the use of battery current. A switch applies either battery or magneto current at will. Such a system may provide a timer for the battery current entirely distinct from the magneto make-andbreak and, in this case, only the magneto distributor and the spark plugs are common to both systems of ignition.
Dust Cap
A cap, screwed over the valve stem of a tire, seating upon the inside of the felloe. It prevents dust and water from entering the valve stem hole in the felloe and accumulating between the tire casing and rim.
A cap arranged over the exposed end of a bearing or over the exposed parts of a mechanism, to prevent the entrance of dust.
Dust Pan
The sod pan (q. v.).
Dynamo
A mechanical generator of electricity, the soft iron field magnets of which are charged by current generated by the machine itself. It consists of an electro-magnetic field between the poles of which is rotated, by external mechanical power, an armature (q. v.). The cutting of the magnetic field by the armature conductors generates in them an electromotive force (q. v.) and in the operation of the machine mechanical energy is transformed into electrical energy. A commutator (q. v.) and brushes (q. v.) are used to convert the current produced in the armature conductors into a continuous current (q. v.) in the external circuit. A relatively small portion of the output of the machine is utilized in magnetizing its fields. Used to charge the storage batteries of electric vehicles and also installed upon motor cars to charge storage batteries for lighting and ignition service.
Synonym: Dynamo electric machine.
Dynamo, Bipolar
A dynamo, the magnetic field of which produces a single north and a single south pole, arranged diametrically opposite with respect to the armature.
Dynamo, Compound Wound
A dynamo, the field magnets of which are magnetized by a combination of the methods used in the shunt wound dynamo (q. v.) and in the series wound dynamo (q. v.). It is used in some vehicle lighting systems.
Dynamo, Constant Current
A dynamo, so designed that the current it furnishes to the external circuit increases but sightly above normal with increased driving speed and reduced external resistance. Internal reactions caused by any slight increase of current produce a rapid drop in the external voltage and prevent further current increase. Used to charge the storage battery in some lighting and selfstarter systems.
Dynamo, Constant Voltage
A type of dynamo used in vehicle lighting, which delivers a nearly constant electrical pressure to the external circuit, independent of the speed of the vehicle motor which drives it. An automatic clutch, under the control of a device sensitive to speed fluctuations, may be interposed between the engine and the dynamo and the speed of the latter be maintained nearly constant by clutch slipping, or the field magnets may be automatically weakened and strengthened in proportion with increases or decreases of speed and the voltage produced thus regulated to a nearly constant, value.
Dynamo, Multipolar
A dynamo, the magnetic field of which comprises more than one pair of poles, produced by more than one electromagnet and symmetrically disposed around the armature. Each armature conductor cuts the magnetic field as many times per armature rotation as there are poles. The multipolar dynamo, especially the four pole type, is commonly used in vehicle lighting, as it is adapted for operation at a lower speed than is the bipolar type.
Dynamo, Series Wound
A dynamo, the field magnets of which are charged by coils of rather coarse wire and comparatively few turns, through which the entire current generated in the armature passes on its way to the external circuit.
Dynamo, Shunt Wound
A dynamo, the field magnets of which are charged by coils of rather fine wire and numerous turns wound about them. The coils are connected in series and one terminal of the series is connected to one brush and the other terminal to the other brush of the machine. A part of the current generated in the armature thus traverses the field coils and the remain tier supplies the external circuit. At a constant armature speed, this type of dynamo maintains a nearly constant electrical pressure, even though the current supplied the external circuit varies quite widely and it is therefore largely used in charging electric vehicle batteries and in vehicle lighting.
Dynamo Bracket
A support provided upon the base of a gas vehicle motor, for the convenient mounting of a dynamo in suitable driving relationship to some moving part of the engine.
Dynamometer
In general, an instrument or apparatus designed to measure the rate at which mechanical energy is being delivered by or to a power producing or power transmitting mechanism. In automobile practice, an instrument capable of measuring the rate at which mechanical energy is being delivered by a vehicle motor which is used by automobile manufacturers to determine whether such motors are in proper working condition. Also occasionally used to determine the rate at which mechanical energy is being delivered to the traction wheels of an automobile and for similar purposes. A dynamometer measures the torque or turning effort received by it in pounds-feet, and by multiplying its indication by the angular speed in radians per minute, and dividing the product by 33,000 the horse power is obtained. A dynamometer which dissipates the energy to be measured is an absorption dynamometer, and one which measures the turning effort transmitted to another machine is a transmission dynamometer. The fan dynamometer and the prony brake are examples of the former type, and the electric cradle dynamometer and the power scale are examples of the latter type.
Dynamometer Test
As applied to an automobile motor, a test made upon it by means of a dynamometer to determine its output at various speeds, before mounting it upon the vehicle which it is to drive.
Synonym: Brake test.
