Misplaced Pages

#457542

93-498: It was never factory-equipped with the "long stick" shifter handle. The shifter interchanges, opening up swap possibilities. Owners have found that while the bearings' lifespan might be similar to that of the M40, the torque capacity is on the order of double. Gear ratios are effectively the same (though derived from a different tooth count) as the M40s and followed that transmission's change to

186-430: A rail ). For railroads, this is called curve resistance but for roads it has (at least once) been called rolling resistance due to cornering . Rolling friction generates sound (vibrational) energy, as mechanical energy is converted to this form of energy due to the friction. One of the most common examples of rolling friction is the movement of motor vehicle tires on a roadway , a process which generates sound as

279-399: A tractive force equal to 70% of the maximum traction, slip resistance becomes 10 times larger than the basic rolling resistance. In order to apply any traction to the wheels, some slippage of the wheel is required. For trains climbing up a grade, this slip is normally 1.5% to 2.5%. Slip (also known as creep ) is normally roughly directly proportional to tractive effort . An exception

372-450: A 20% increase in load decreases Crr by 3%. But, if the inflation pressure is not changed, then a 20% increase in load results in a 4% increase in Crr. Of course, this will increase the rolling resistance by 20% due to the increase in load plus 1.2 x 4% due to the increase in Crr resulting in a 24.8% increase in rolling resistance. When a vehicle ( motor vehicle or railroad train ) goes around

465-434: A 5% slip can translate into a 200% increase in rolling resistance. This is partly because the tractive force applied during this slip is many times greater than the rolling resistance force and thus much more power per unit velocity is being applied (recall power = force x velocity so that power per unit of velocity is just force). So just a small percentage increase in circumferential velocity due to slip can translate into

558-432: A Crr of 0.00013 (axle load of 21 tonnes). For empty freight cars with axle loads of 5.5 tonnes, Crr goes up to 0.00020 at 60 km/h but at a low speed of 20 km/h it increases to 0.00024 and at a high speed (for freight trains) of 120 km/h it is 0.00028. The Crr obtained above is added to the Crr of the other components to obtain the total Crr for the wheels. The rolling resistance of steel wheels on steel rail of

651-526: A Volvo version. The Volvo version kept the same package size as the J-type but with the updated 18 element freewheel and stronger splines through the planet carrier. The Gear Vendors U.S. version uses a larger 1.375 outer diameter output shaft for higher capacity and a longer rear case. Over a period of 40 years, Laycock Engineering manufactured over three and a half million overdrive Units, and over one million of these were fitted to Volvo motorcars. In 2008

744-420: A body (such as a ball , tire , or wheel ) rolls on a surface. It is mainly caused by non-elastic effects; that is, not all the energy needed for deformation (or movement) of the wheel, roadbed, etc., is recovered when the pressure is removed. Two forms of this are hysteresis losses (see below ), and permanent (plastic) deformation of the object or the surface (e.g. soil). Note that the slippage between

837-401: A by-product. The sound generated by automobile and truck tires as they roll (especially noticeable at highway speeds) is mostly due to the percussion of the tire treads, and compression (and subsequent decompression) of air temporarily captured within the treads. Several factors affect the magnitude of rolling resistance a tire generates: In a broad sense rolling resistance can be defined as

930-408: A car at any given set of conditions and speed is straightforward to calculate, based primarily on the total weight and the vehicle's speed. These produce two primary forces slowing the car: rolling resistance and air drag . The former varies roughly with the speed of the vehicle, while the latter varies with the square of the speed. Calculating these from first principles is generally difficult due to

1023-554: A car of 1000 kg on asphalt will need a force of around 100  newtons for rolling (1000 kg × 9.81 m/s × 0.01 = 98.1 N). According to Dupuit (1837), rolling resistance (of wheeled carriages with wooden wheels with iron tires) is approximately inversely proportional to the square root of wheel diameter. This rule has been experimentally verified for cast iron wheels (8″ - 24″ diameter) on steel rail and for 19th century carriage wheels. But there are other tests on carriage wheels that do not agree. Theory of

SECTION 10

#1732780577458

1116-490: A certain speed is reached (usually 70+ km/h [40-45 mph or more] depending on the load). When it is off, the automatic transmission shifting is limited to the lower gears. Overdrive should usually be selected when the average speed is above 70 km/h (40-45 mph). The automatic transmission automatically shifts from OD to direct drive when more load is present. When less load is present, it shifts back to OD. Under certain conditions, for example driving uphill, or towing

1209-484: A coefficient (ratio)or a multiple thereof. If using pounds or kilograms as force units, mass is equal to weight (in earth's gravity a kilogram a mass weighs a kilogram and exerts a kilogram of force) so one could claim that C r r {\displaystyle C_{rr}} is also the force per unit mass in such units. The SI system would use N/tonne (N/T, N/t), which is 1000 g C r r {\displaystyle 1000gC_{rr}} and

1302-404: A curve, rolling resistance usually increases. If the curve is not banked so as to exactly counter the centrifugal force with an equal and opposing centripetal force due to the banking, then there will be a net unbalanced sideways force on the vehicle. This will result in increased rolling resistance. Banking is also known as "superelevation" or "cant" (not to be confused with rail cant of

1395-409: A cylinder rolling on an elastic roadway also gives this same rule These contradict earlier (1785) tests by Coulomb of rolling wooden cylinders where Coulomb reported that rolling resistance was inversely proportional to the diameter of the wheel (known as "Coulomb's law"). This disputed (or wrongly applied) -"Coulomb's law" is still found in handbooks, however. For pneumatic tires on hard pavement, it

1488-436: A faster rate as the torque becomes higher. The rolling resistance coefficient, Crr, significantly decreases as the weight of the rail car per wheel increases. For example, an empty freight car had about twice the Crr as a loaded car (Crr=0.002 vs. Crr=0.001). This same "economy of scale" shows up in testing of mine rail cars. The theoretical Crr for a rigid wheel rolling on an elastic roadbed shows Crr inversely proportional to

1581-816: A few. Another British company, the former aircraft builder Fairey , built a successful all-mechanical unit for the Land Rover , which is still in production in America today. The first production vehicle to feature the Laycock system was the 1948 Standard Vanguard Saloon. The first unit to be created was the A-type overdrive, which was fitted to many sports cars during the 1950s, and into the late 1960s. Several famous marques used A-type overdrives, including Jaguar, Aston Martin, Ferrari, Austin-Healey, Jensen, Bristol, AC, Armstrong Siddeley and Triumph's TR sports car range, from

1674-409: A higher ratio first gear, which means more gears between the first and the last to keep the engine at its most efficient speed. This is part of the reason that modern automobiles tend to have larger numbers of gears in their transmissions. It is also why more than one overdrive gear is seldom seen in a vehicle except in special circumstances i.e. where high (numerical) differential gear is required to get

1767-417: A loss of traction power which may even exceed the power loss due to basic (ordinary) rolling resistance. For railroads, this effect may be even more pronounced due to the low rolling resistance of steel wheels. It is shown that for a passenger car, when the tractive force is about 40% of the maximum traction, the slip resistance is almost equal to the basic rolling resistance (hysteresis loss). But in case of

1860-473: A lower (numerically higher) first gear beginning with the 1973 model year. When equipped with the electrically operated overdrive , the gearbox was known as the M410 . This article about an automotive part or component is a stub . You can help Misplaced Pages by expanding it . This Sweden -related article is a stub . You can help Misplaced Pages by expanding it . Overdrive (mechanics) Overdrive

1953-421: A lower gear, with the engine turning at higher RPM. The power produced by an engine increases with the engine's RPM to a maximum, then falls away. The point of maximum power is somewhat lower than the absolute maximum engine speed to which it is limited, the " redline ". A car's speed is limited by the power required to drive it against air resistance, which increases with speed. At the maximum possible speed,

SECTION 20

#1732780577458

2046-883: A slow rigid wheel on a perfectly elastic surface, not adjusted for velocity, can be calculated by C r r = z / d {\displaystyle C_{rr}={\sqrt {z/d}}} where The empirical formula for C r r {\displaystyle C_{rr}} for cast iron mine car wheels on steel rails is: C r r = 0.0048 ( 18 / D ) 1 2 ( 100 / W ) 1 4 = 0.0643988 W D 2 4 {\displaystyle C_{rr}=0.0048(18/D)^{\frac {1}{2}}(100/W)^{\frac {1}{4}}={\frac {0.0643988}{\sqrt[{4}]{WD^{2}}}}} where As an alternative to using C r r {\displaystyle C_{rr}} one can use b {\displaystyle b} , which

2139-400: A tonne. This lighter weight per passenger, combined with the lower rolling resistance of steel wheels on steel rail means that an N700 Shinkansen is much more energy efficient than a typical automobile. In the case of freight, CSX ran an advertisement campaign in 2013 claiming that their freight trains move "a ton of freight 436 miles on a gallon of fuel", whereas some sources claim trucks move

2232-527: A trailer, the transmission may "hunt" between OD and the next highest gear, shifting back and forth. In this case, switching it off can help the transmission to "decide". It may also be advantageous to switch it off if engine braking is desired, for example when driving downhill. The vehicle's owner's manual will often contain information and suitable procedures regarding such situations, for each given vehicle. Virtually all vehicles (cars and trucks) have overdrive today whether manual transmission or automatic. In

2325-408: A train is far less than that of the rubber tires wheels of an automobile or truck. The weight of trains varies greatly; in some cases they may be much heavier per passenger or per net ton of freight than an automobile or truck, but in other cases they may be much lighter. As an example of a very heavy passenger train, in 1975, Amtrak passenger trains weighed a little over 7 tonnes per passenger, which

2418-513: A variety of models, including 1968–1980 MGBs , the MGC , the Ford Zephyr , early Reliant Scimitars , TVRs, and Gilberns . The J-type overdrive was introduced in the late 1960s, and was adapted to fit Volvo, Triumph, Vauxhall/Opel, American Motors and Chrysler motorcars, and Ford Transit vans. The P-type overdrive marked the last updates and was manufactured in a Gear Vendors U.S. version and

2511-407: A variety of real-world factors, so this is often measured directly in wind tunnels and similar systems. The power produced by an engine increases with the engine's RPM to a maximum, then falls away. This is known as the point of maximum power . Given a curve describing the overall drag on the vehicle, it is simple to find the speed at which the total drag forces are the same as the maximum power of

2604-438: Is hysteresis : A characteristic of a deformable material such that the energy of deformation is greater than the energy of recovery. The rubber compound in a tire exhibits hysteresis. As the tire rotates under the weight of the vehicle, it experiences repeated cycles of deformation and recovery, and it dissipates the hysteresis energy loss as heat. Hysteresis is the main cause of energy loss associated with rolling resistance and

2697-553: Is a different rolling resistance coefficient or coefficient of rolling friction with dimension of length. It is defined by the following formula: F = N b r {\displaystyle F={\frac {Nb}{r}}} where The above equation, where resistance is inversely proportional to radius r {\displaystyle r} seems to be based on the discredited "Coulomb's law" (Neither Coulomb's inverse square law nor Coulomb's law of friction) . See dependence on diameter . Equating this equation with

2790-417: Is achieved through the gearbox ratios, or by an unusually high final drive. Generally speaking, overdrive is the highest gear in the transmission. Overdrive allows the engine to operate at a lower RPM for a given road speed. This allows the vehicle to achieve better fuel efficiency, and often quieter operation on the highway. When it is switched on, an automatic transmission can shift into overdrive mode after

2883-413: Is assumed that all wheels are the same and bear identical weight. Thus:   C r r = 0.01 {\displaystyle \ C_{rr}=0.01} means that it would only take 0.01 pounds to tow a vehicle weighing one pound. For a 1000-pound vehicle, it would take 1000 times more tow force, i.e. 10 pounds. One could say that C r r {\displaystyle C_{rr}}

Volvo M400 & M410 transmission - Misplaced Pages Continue

2976-699: Is asymmetrical and is shifted to the right. The line of action of the (aggregate) vertical force no longer passes through the centers of the cylinders. This means that a moment occurs that tends to retard the rolling motion. Materials that have a large hysteresis effect, such as rubber, which bounce back slowly, exhibit more rolling resistance than materials with a small hysteresis effect that bounce back more quickly and more completely, such as steel or silica . Low rolling resistance tires typically incorporate silica in place of carbon black in their tread compounds to reduce low-frequency hysteresis without compromising traction. Note that railroads also have hysteresis in

3069-414: Is attributed to the viscoelastic characteristics of the rubber. This main principle is illustrated in the figure of the rolling cylinders. If two equal cylinders are pressed together then the contact surface is flat. In the absence of surface friction, contact stresses are normal (i.e. perpendicular) to the contact surface. Consider a particle that enters the contact area at the right side, travels through

3162-434: Is done in this article. They just sum up all the resistance forces (including aerodynamic drag) and call the sum basic train resistance (or the like). Since railroad rolling resistance in the broad sense may be a few times larger than just the pure rolling resistance reported values may be in serious conflict since they may be based on different definitions of "rolling resistance". The train's engines must, of course, provide

3255-529: Is force per unit mass, where g is the acceleration of gravity in SI units (meters per second square). The above shows resistance proportional to C r r {\displaystyle C_{rr}} but does not explicitly show any variation with speed, loads , torque , surface roughness, diameter , tire inflation/wear, etc., because C r r {\displaystyle C_{rr}} itself varies with those factors. It might seem from

3348-442: Is if the tractive effort is so high that the wheel is close to substantial slipping (more than just a few percent as discussed above), then slip rapidly increases with tractive effort and is no longer linear. With a little higher applied tractive effort the wheel spins out of control and the adhesion drops resulting in the wheel spinning even faster. This is the type of slipping that is observable by eye—the slip of say 2% for traction

3441-420: Is in lb(tow-force)/lb(vehicle weight). Since this lb/lb is force divided by force, C r r {\displaystyle C_{rr}} is dimensionless. Multiply it by 100 and you get the percent (%) of the weight of the vehicle required to maintain slow steady speed. C r r {\displaystyle C_{rr}} is often multiplied by 1000 to get the parts per thousand, which

3534-433: Is in part due to the fact that there is some slipping of the wheel, and for pneumatic tires, there is more flexing of the sidewalls due to the torque. Slip is defined such that a 2% slip means that the circumferential speed of the driving wheel exceeds the speed of the vehicle by 2%. A small percentage slip can result in a slip resistance which is much larger than the basic rolling resistance. For example, for pneumatic tires,

3627-428: Is largely dependent on the tractive force , coefficient of friction, normal load, etc. "Applied torque" may either be driving torque applied by a motor (often through a transmission ) or a braking torque applied by brakes (including regenerative braking ). Such torques results in energy dissipation (above that due to the basic rolling resistance of a freely rolling, i.e. except slip resistance). This additional loss

3720-501: Is much heavier than an average of a little over one ton per passenger for an automobile. This means that for an Amtrak passenger train in 1975, much of the energy savings of the lower rolling resistance was lost to its greater weight. An example of a very light high-speed passenger train is the N700 Series Shinkansen , which weighs 715 tonnes and carries 1323 passengers, resulting in a per-passenger weight of about half

3813-438: Is notable that slip does not occur in driven wheels, which are not subjected to driving torque, under different conditions except braking. Therefore, rolling resistance, namely hysteresis loss, is the main source of energy dissipation in driven wheels or axles, whereas in the drive wheels and axles slip resistance, namely loss due to wheel slip, plays the role as well as rolling resistance. Significance of rolling or slip resistance

Volvo M400 & M410 transmission - Misplaced Pages Continue

3906-409: Is noteworthy that V s / Ω {\displaystyle V_{s}/\Omega } is usually not equal to the radius of the rolling body as a result of wheel slip. The slip between wheel and ground inevitably occurs whenever a driving or braking torque is applied to the wheel. Consequently, the linear speed of the vehicle differs from the wheel's circumferential speed. It

3999-430: Is only observed by instruments. Such rapid slip may result in excessive wear or damage. Rolling resistance greatly increases with applied torque. At high torques, which apply a tangential force to the road of about half the weight of the vehicle, the rolling resistance may triple (a 200% increase). This is in part due to a slip of about 5%. The rolling resistance increase with applied torque is not linear, but increases at

4092-518: Is reported that the effect of diameter on rolling resistance is negligible (within a practical range of diameters). The driving torque T {\displaystyle T} to overcome rolling resistance R r {\displaystyle R_{r}} and maintain steady speed on level ground (with no air resistance) can be calculated by: T = V s Ω R r {\displaystyle T={\frac {V_{s}}{\Omega }}R_{r}} where It

4185-481: Is several times higher than the neglected resistances. The "rolling resistance coefficient" is defined by the following equation:   F = C r r N {\displaystyle \ F=C_{rr}N} where C r r {\displaystyle C_{rr}} is the force needed to push (or tow) a wheeled vehicle forward (at constant speed on a level surface, or zero grade, with zero air resistance) per unit force of weight. It

4278-406: Is the operation of an automobile cruising at sustained speed with reduced engine speed (rpm), leading to better fuel consumption, lower noise, and lower wear. The term is ambiguous. The most fundamental meaning is that of an overall gear ratio between engine and wheels, such that the car is over-geared , and cannot reach its potential top speed, i.e. the car could travel faster if it were in

4371-556: Is the same as kilograms (kg force) per metric ton (tonne = 1000 kg ), which is the same as pounds of resistance per 1000 pounds of load or Newtons/kilo-Newton, etc. For the US railroads, lb/ton has been traditionally used; this is just 2000 C r r {\displaystyle 2000C_{rr}} . Thus, they are all just measures of resistance per unit vehicle weight. While they are all "specific resistances", sometimes they are just called "resistance" although they are really

4464-484: Is used simply to keep the engine running at this speed. Every cycle of the engine leads to wear, so keeping the engine at higher RPM is also unfavorable for engine life. Additionally, the sound of an engine is strongly related to the RPM, so running at lower RPM is generally quieter. If one runs the same RPM transmission exercise outlined above for maximum speed, but instead sets the "maximum speed" to that of highway cruising,

4557-555: The English company Laycock Engineering (later GKN Laycock), at its Little London Road site in Sheffield . The system devised by de Normanville was adopted and manufactured by Laycock after his chance meeting with a Laycock Products Engineer. De Normanville overdrives were found in vehicles manufactured by Standard-Triumph , who were first, followed by Ford , BMC and British Leyland , Jaguar , Rootes Group and Volvo to name only

4650-440: The transmission unit. It can either couple the input driveshaft directly to the output shaft (or propeller shaft ) (1:1), or increase the output speed so that it turns faster than the input shaft (1:1 +  n ). Thus the output shaft may be "overdriven" relative to the input shaft. In newer transmissions, the overdrive speed(s) are typically as a result of combinations of planetary/epicyclic gearsets which are integrated in

4743-434: The "gearbox" or "transmission" mounted behind the engine, and the "final drive" mounted in the rear axle at the rear of the car. The reason for this separation of duties between the front and back of the car was to allow the drive shaft to run at lower torque, by using higher RPM. As power is the product of RPM and torque , running the shaft at higher RPM allowed more power to be transferred at lower torque. Doing so reduced

SECTION 50

#1732780577458

4836-692: The TR2 through to the end of the 1972 model year of the TR6. In 1959, the Laycock Engineering Company introduced the D-type overdrive, which was fitted to a variety of motor cars including Volvo 120 and 1800s , Sunbeam Alpines and Rapiers , Triumph Spitfires , and also 1962–1967 MGBs (those with 3-synchro transmissions). From 1967 the LH-type overdrive was introduced, and this featured in

4929-411: The U.S. company Gear Vendors, Inc. of El Cajon, California purchased all the overdrive assets of GKN to continue production of the U.S. version and all spares for J and P types worldwide. The system features an oil pressure operated device attached to the back of the standard gearbox operating on the gearbox output shaft. Through a system of oil pressure, solenoids and pistons, the overdrive would drop

5022-440: The above definition of C r r {\displaystyle C_{rr}} that the rolling resistance is directly proportional to vehicle weight but it is not . There are at least two popular models for calculating rolling resistance. The results of these tests can be hard for the general public to obtain as manufacturers prefer to publicize "comfort" and "performance". The coefficient of rolling resistance for

5115-437: The additional advantage that it could be offered as an easily installed option. With the use of front-wheel drive layouts, the gearbox and final drive are combined into a single transaxle. There is no longer a drive shaft between them and so the notion of "direct drive" is inapplicable. Although "overdrive" is still referred to, this is now mostly a marketing term to refer to any extra-high ratio for efficient cruising, whether it

5208-534: The automotive aftermarket you can also retrofit overdrive to existing early transmissions. Overdrive was widely used in European automobiles with manual transmission in the 60s and 70s to improve mileage and sport driving as a bolt-on option but it became increasingly more common for later transmissions to have this gear built in. If a vehicle is equipped with a bolt-on overdrive (e.g.: GKN or Gear Vendors) as opposed to having an overdrive built in one will typically have

5301-450: The axle), and tire size. The rotation speed problem comes into effect when the differential gearing is a high ratio and an overdrive is used to compensate. This may create unpleasant vibrations at high speeds and possible destruction of the driveshaft due to the centripetal forces or uneven balance. The driveshaft is usually a hollow metal tube that requires balancing to reduce vibration and contains no internal bracing. The higher speeds on

5394-472: The bearings, but a train car with steel wheels running on steel rails will roll farther than a bus of the same mass with rubber tires running on tarmac/asphalt . Factors that contribute to rolling resistance are the (amount of) deformation of the wheels, the deformation of the roadbed surface, and movement below the surface. Additional contributing factors include wheel diameter , load on wheel , surface adhesion, sliding, and relative micro-sliding between

5487-426: The benefit to fuel economy. Overdrive is included in both automatic and manual transmissions as an extra gear (or two in some cases). When using overdrive gearing, the car's engine speed drops, reducing wear and normally saving fuel. Since 1981 U.S. corporate average fuel economy (CAFE) legislation, virtually all domestic vehicles have included overdrive to save fuel. One should refer to the car's owner's manual for

5580-456: The contact patch and leaves at the left side. Initially its vertical deformation is increasing, which is resisted by the hysteresis effect. Therefore, an additional pressure is generated to avoid interpenetration of the two surfaces. Later its vertical deformation is decreasing. This is again resisted by the hysteresis effect. In this case this decreases the pressure that is needed to keep the two bodies separate. The resulting pressure distribution

5673-455: The days before automatic transmissions were common, especially in the 1950s, many rear-wheel drive American cars were available with an overdrive option. With substantial improvements developed in Muncie, Indiana , by William B. Barnes for production by its Warner Gear Division, BorgWarner provided the box that was factory-installed between the transmission and a foreshortened driveshaft. Since

SECTION 60

#1732780577458

5766-447: The desire for better fuel economy grew, especially after the 1973 oil crisis , the need for a "cruising gear" became more pressing. The obvious solution to this problem would be to add more gears to the transmission. Indeed, in modern vehicles this is common. However, due to historical particularities, this was not always practical. In the conventional rear-wheel drive layout , the transmission system normally contained two sections,

5859-399: The driveshaft and related parts can cause heat and wear problems if an overdrive and high differential gearing (or even very small tires) are combined, and create unnecessary friction. This is especially important because the differential gears are bathed in heavy oil and seldom provided with any cooling besides air blowing over the housing. The impetus is to minimize overdrive use and provide

5952-404: The driving wheel(s) becomes greater than the vehicle speed due to slippage. Since power is equal to force times velocity and the wheel velocity has increased, the power required has increased accordingly. The pure "rolling resistance" for a train is that which happens due to deformation and possible minor sliding at the wheel-road contact. For a rubber tire, an analogous energy loss happens over

6045-410: The energy dissipated by vibration and oscillation of both the roadbed and the vehicle, and sliding of the wheel on the roadbed surface (pavement or a rail). But there is an even broader sense that would include energy wasted by wheel slippage due to the torque applied from the engine . This includes the increased power required due to the increased velocity of the wheels where the tangential velocity of

6138-418: The energy to overcome this broad-sense rolling resistance. For tires, rolling resistance is defined as the energy consumed by a tire per unit distance covered. It is also called rolling friction or rolling drag. It is one of the forces that act to oppose the motion of a driver. The main reason for this is that when the tires are in motion and touch the surface, the surface changes shape and causes deformation of

6231-430: The engine is running at its point of maximum power, or power peak , and the car is traveling at the speed where air resistance equals that maximum power. There is therefore one specific gear ratio at which the car can achieve its maximum speed: the one that matches that engine speed with that travel speed. At travel speeds below this maximum, there is a range of gear ratios that can match engine power to air resistance, and

6324-414: The engine. This defines the maximum speed the vehicle is able to reach. The rotational speed of the wheels for that given forward speed is simple to calculate, being the tire circumference multiplied by the RPM. As the tire RPM at maximum speed is not the same as the engine RPM at that power, a transmission is used with a gear ratio to convert one to the other. At even slightly lower speeds than maximum,

6417-401: The entire tire, but it is still called "rolling resistance". In the broad sense, "rolling resistance" includes wheel bearing resistance, energy loss by shaking both the roadbed (and the earth underneath) and the vehicle itself, and by sliding of the wheel, road/rail contact. Railroad textbooks seem to cover all these resistance forces but do not call their sum "rolling resistance" (broad sense) as

6510-445: The final drive ratio, it made sense for all transmissions to use direct drive as the highest gear. As noted earlier, however, this would cause the engine to operate at too high an RPM for efficient cruising. Although adding the cruising gear to the main gearbox was possible, it was generally simpler to add a separate two-gear overdrive system to the existing gearbox. This not only meant that it could be tuned for different vehicles, but had

6603-739: The force per the rolling resistance coefficient , and solving for b {\displaystyle b} , gives b {\displaystyle b} = C r r r {\displaystyle C_{rr}r} . Therefore, if a source gives rolling resistance coefficient ( C r r {\displaystyle C_{rr}} ) as a dimensionless coefficient, it can be converted to b {\displaystyle b} , having units of length, by multiplying C r r {\displaystyle C_{rr}} by wheel radius r {\displaystyle r} . Table of rolling resistance coefficient examples: [3] For example, in earth gravity,

6696-406: The most fuel efficient is the one that results in the lowest engine speed. Therefore, a car needs one gearing to reach maximum speed but another to reach maximum fuel efficiency at a lower speed. With the early development of cars and the almost universal rear-wheel drive layout, the final drive (i.e. rear axle ) ratio for fast cars was chosen to give the ratio for maximum speed. The gearbox

6789-493: The need for the separate overdrive gearbox. With the popularity of front wheel drive cars, the separate gearbox and final drive have merged into a single transaxle . There is no longer a propeller shaft and so one meaning of "overdrive" can no longer be applied. However the fundamental meaning, that of an overall ratio higher than the ratio for maximum speed, still applies: higher gears, with greater ratios than 1:1, are described as "overdrive gears". The power needed to propel

6882-543: The option to use the overdrive in more gears than just the top gear. In this case gear changing is still possible in all gears, even with overdrive disconnected. Overdrive simply adds effective ranges to the gears, thus overdrive third and fourth become in effect "third-and-a-half" and a fifth gear. In practice this gives the driver more ratios which are closer together providing greater flexibility particularly in performance cars. An overdrive consists of an electrically or hydraulically operated epicyclic gear train bolted behind

6975-458: The output is a higher gear ratio that provides ideal fuel mileage. In an era when cars were not able to travel very fast, the maximum power point might be near enough to the desired speed that additional gears were not needed. But as more powerful cars appeared, especially during the 1960s, this disparity between the maximum power point and desired speed grew considerably. This meant that cars were often operating far from their most efficient point. As

7068-425: The overdrive function, if enabled, could be shifted by simply easing up on the accelerator without depressing the clutch pedal , the action was much like a semi-automatic. Also, an electrically operated solenoid would deactivate the unit via a switch under the accelerator pedal providing the equivalent of the kickdown of the automatic. A knob connected to a bowden cable , similar to some emergency brake applications,

7161-433: The proper speed to run at overdrive. All engines have a range of peak efficiency and it is possible for the use of overdrive to keep the engine out of this range for all or part of the time of its use if used at inappropriate speeds, thus cutting into any fuel savings from the lower engine speed. Overall drivetrain reduction comes down to three basic factors: transmission gearing (including overdrive), differential gearing (in

7254-399: The revs on whatever gears it was used on by 22% (.778). For instance, the overdrive system applied to a Triumph TR5 operates on 2nd, 3rd and top gear. When engaged, the overdrive would drop the revs from 3000 by 666 RPM, or from 3500 the drop would be 777 RPM to 2723 net. The advantages this reduced rpm had on fuel consumption was most often quite near 22% decrease during highway driving. In

7347-481: The roadbed structure. In the broad sense, specific "rolling resistance" (for vehicles) is the force per unit vehicle weight required to move the vehicle on level ground at a constant slow speed where aerodynamic drag (air resistance) is insignificant and also where there are no traction (motor) forces or brakes applied. In other words, the vehicle would be coasting if it were not for the force to maintain constant speed. This broad sense includes wheel bearing resistance,

7440-442: The so-called slip resistance involves friction , therefore the name "rolling friction" is to an extent a misnomer. Analogous with sliding friction , rolling resistance is often expressed as a coefficient times the normal force. This coefficient of rolling resistance is generally much smaller than the coefficient of sliding friction. Any coasting wheeled vehicle will gradually slow down due to rolling resistance including that of

7533-465: The square root of the load. If Crr is itself dependent on wheel load per an inverse square-root rule, then for an increase in load of 2% only a 1% increase in rolling resistance occurs. For pneumatic tires, the direction of change in Crr (rolling resistance coefficient) depends on whether or not tire inflation is increased with increasing load. It is reported that, if inflation pressure is increased with load according to an (undefined) "schedule", then

7626-430: The sum of components ): Wheel bearing torque losses can be measured as a rolling resistance at the wheel rim, Crr . Railroads normally use roller bearings which are either cylindrical (Russia) or tapered (United States). The specific rolling resistance in bearings varies with both wheel loading and speed. Wheel bearing rolling resistance is lowest with high axle loads and intermediate speeds of 60–80 km/h with

7719-464: The surfaces of contact. The losses due to hysteresis also depend strongly on the material properties of the wheel or tire and the surface. For example, a rubber tire will have higher rolling resistance on a paved road than a steel railroad wheel on a steel rail. Also, sand on the ground will give more rolling resistance than concrete . Sole rolling resistance factor is not dependent on speed. The primary cause of pneumatic tire rolling resistance

7812-410: The tire. For highway motor vehicles, there is some energy dissipated in shaking the roadway (and the earth beneath it), the shaking of the vehicle itself, and the sliding of the tires. But, other than the additional power required due to torque and wheel bearing friction, non-pure rolling resistance doesn't seem to have been investigated, possibly because the "pure" rolling resistance of a rubber tire

7905-421: The torque the driveshaft had to carry, and thus the strength and weight required. Although the designer was theoretically free to choose any ratio for the gearbox and final drive, there is one additional consideration which meant that the top gear of most gearboxes was 1:1 or "direct drive". This is chosen for efficiency, as it does not require any gears to transmit power and so reduces the power lost by them. This

7998-474: The total drag on the vehicle is considerably less, and the engine needs to deliver this greatly reduced amount of power. In this case the RPM of the engine has changed significantly while the RPM of the wheels has changed very little. Clearly this condition calls for a different gear ratio. If one is not supplied, the engine is forced to run at a higher RPM than optimal. As the engine requires more power to overcome internal friction at higher RPM, this means more fuel

8091-643: The transmission. For example, the ZF 8HP transmission has 8 forward gears, two of which are overdrive (< 1:1) gear ratios. In older vehicles, it is sometimes actuated by a knob or button, often incorporated into the gearshift knob, and does not require operation of the clutch . Newer vehicles have electronic overdrive in which the computer automatically adjusts to the conditions of power need and load. The vast majority of overdrives in European cars were invented and developed by Edgar de Normanville , and manufactured by

8184-404: The vehicle moving as in trucks or performance cars though double overdrive transmissions are common in other vehicles, often with a small number on the axle gear reduction, but usually only engage at speeds exceeding 100 kilometres per hour (62 mph). Rolling resistance Rolling resistance , sometimes called rolling friction or rolling drag , is the force resisting the motion when

8277-402: The wheel and the surface also results in energy dissipation. Although some researchers have included this term in rolling resistance, some suggest that this dissipation term should be treated separately from rolling resistance because it is due to the applied torque to the wheel and the resultant slip between the wheel and ground, which is called slip loss or slip resistance. In addition, only

8370-521: Was also provided to lock out the unit mechanically. Using overdrive with the main 3-speed transmission in 2nd gear was similar in ratio to 3rd gear, and with the main transmission in third, the overall ratio was fractional (i.e., "true overdrive"). This was important in reducing wear, tear, noise, and difficulty in control. Such add-on overdrive boxes were available from the 1930s to the 1970s for cars and light trucks. Today, most petrol and diesel cars and trucks come with an overdrive transmission because of

8463-526: Was designed so that, for efficiency, the fastest ratio would be a "direct-drive" or "straight-through" 1:1 ratio, avoiding frictional losses in the gears. Achieving an overdriven ratio for cruising thus required a gearbox ratio even higher than this, i.e. the gearbox output shaft rotating faster than the engine. The propeller shaft linking gearbox and rear axle is thus overdriven, and a transmission capable of doing this became termed an "overdrive" transmission. The device for achieving an overdrive transmission

8556-509: Was particularly important in the early days of cars, as their straight-cut gears were poorly finished, noisy and inefficient. The final drive then took this output and adjusted it in a fixed-ratio transmission arrangement that was much simpler to build. Final drive ratios of 4:1 were common, meaning that the wheels would turn at one fourth the rate they would if directly connected to the engine. In an era when different models of car with different wheel sizes could be accommodated by simply changing

8649-462: Was usually a small separate gearbox, attached to the rear of the main gearbox and controlled by its own shift lever. These were often optional on some models of the same car. As popular cars became faster relative to legal limits and fuel costs became more important, particularly after the 1973 oil crisis , the use of five-speed gearboxes became more common in mass-market cars. These had a direct (1:1) fourth gear with an overdrive fifth gear, replacing

#457542