Misplaced Pages

#760239

64-738: The Mazda Savanna is a rotary-powered automobile sold by the Japanese manufacturer Mazda between 1971 and 1978. Between 1978 and 1991, spanning two generations, Mazda sold the Savanna replacement as the Mazda Savanna RX-7 . Mazda exclusively used the Savanna nameplate in Japan. It was exported as the Mazda RX-3 in its first generation from 1971 to 1978, and as the Mazda RX-7 in its subsequent generations. For

128-576: A Wankel engine are thus mainly limited by tooth load on the synchronizing gears. Hardened steel gears are used for extended operation above 7,000 or 8,000   rpm. In practice, automotive Wankel engines are not operated at much higher output shaft speeds than reciprocating piston engines of similar output power. Wankel engines in auto racing are operated at speeds up to 10,000   rpm, but so are four-stroke reciprocating piston engines with relatively small displacement per cylinder. In aircraft, they are used conservatively, up to 6500 or 7500   rpm. In

192-405: A Wankel rotary engine, the chamber volume V k {\displaystyle V_{k}} is equivalent to the product of the rotor surface A k {\displaystyle A_{k}} and the rotor path s {\displaystyle s} . The rotor surface A k {\displaystyle A_{k}} is given by the rotor tips' path across

256-400: A Wankel rotary engine, the eccentric shaft must make three full rotations (1080°) per combustion chamber to complete all four phases of a four-stroke engine. Since a Wankel rotary engine has three combustion chambers, all four phases of a four-stroke engine are completed within one full rotation of the eccentric shaft (360°), and one power pulse is produced at each revolution of the shaft. This

320-399: A boundary layer from overheating working parts. The University of Florida proposed the use of heat pipes in an air-cooled Wankel to overcome this uneven heating of the block housing. Pre-heating of certain housing sections with exhaust gas improved performance and fuel economy, also reducing wear and emissions. The boundary layer shields and the oil film act as thermal insulation, leading to

384-406: A fresh air supply to the exhaust port. It also proved that a Reed-valve in the intake port or ducts improved the low rpm and partial load performance of Wankel engines, by preventing blow-back of exhaust gas into the intake port and ducts, and reducing the misfire-inducing high EGR, at the cost of a slight loss of power at top rpm. Elasticity is improved with a greater rotor eccentricity, analogous to

448-439: A glow-plug for the leading site spark plug improved low rpm, part load, specific fuel consumption by 7%, and emissions and idle. A later alternative solution to spark plug boss cooling was provided with a variable coolant velocity scheme for water-cooled rotaries, which has had widespread use, being patented by Curtiss-Wright, with the last-listed for better air-cooled engine spark plug boss cooling. These approaches did not require

512-431: A high incidence of sealing loss, both between the rotor and the housing and also between the various pieces making up the housing. Also, in earlier model Wankel engines, carbon particles could become trapped between the seal and the casing, jamming the engine and requiring a partial rebuild. It was common for very early Mazda engines to require rebuilding after 50,000 miles (80,000 km). Further sealing problems arose from

576-441: A high-conductivity copper insert, but did not preclude its use. Ford tested a Wankel engine with the plugs placed in the side plates, instead of the usual placement in the housing working surface ( CA 1036073   , 1978). Wankel engines are capable of high-speed operation, meaning they do not necessarily need to produce high torque to produce high power. The positioning of the intake port and intake port closing greatly affect

640-423: A longer stroke in a reciprocating engine. Wankel engines operate better with a low-pressure exhaust system. Higher exhaust back pressure reduces mean effective pressure, more severely in peripheral intake port engines. The Mazda RX-8 Renesis engine improved performance by doubling the exhaust port area relative to earlier designs, and there have been studies of the effect of intake and exhaust piping configuration on

704-412: A low temperature of the lubricating film (approximate maximum 200 °C or 390 °F on a water-cooled Wankel engine). This gives a more constant surface temperature. The temperature around the spark plug is about the same as in the combustion chamber of a reciprocating engine. With circumferential or axial flow cooling, the temperature difference remains tolerable. Problems arose during research in

SECTION 10

#1732859257761

768-406: A more steady idle, because it helps to prevent blow-back of burned gases into the intake ducts, which cause "misfirings" caused by alternating cycles where the mixture ignites and fails to ignite. Peripheral porting (PP) gives the best mean effective pressure throughout the rpm range, but PP was also linked to worse idle stability and part-load performance. Early work by Toyota led to the addition of

832-527: A result of the poor efficiency, a Wankel engine with peripheral exhaust porting has a larger amount of unburnt hydrocarbons (HC) released into the exhaust. The exhaust is, however, relatively low in nitrogen oxide (NOx) emissions, because the combustion is slow, and temperatures are lower than in other engines, and also because of the Wankel engine's good exhaust gas recirculation (EGR) behavior. Carbon monoxide (CO) emissions of Wankel and Otto engines are about

896-510: A rotary internal combustion engine with Felix Wankel, based upon Wankel's supercharger design for their motorcycle engines. Since Wankel was known as a "difficult colleague", the development work for the DKM was carried out at Wankel's private Lindau design bureau. According to John B. Hege, Wankel received help from his friend Ernst Höppner, who was a "brilliant engineer". The first working prototype, DKM 54 (see figure 2.), first ran on 1 February 1957, at

960-494: A single-rotor Wankel engine produces the same average power as a V h {\displaystyle V_{h}} single-cylinder two-stroke engine , with the same average torque, with the shaft running at the same speed, operating the Otto cycles at triple the frequency. Richard Franz Ansdale, Wolf-Dieter Bensinger and Felix Wankel based their analogy on the number of cumulative expansion strokes per shaft revolution. In

1024-403: A stationary center shaft, the DKM engine was impractical. Wolf-Dieter Bensinger explicitly mentions that proper engine cooling cannot be achieved in a DKM engine, and argues that this is the reason why the DKM design had to be abandoned. NSU development chief engineer Walter Froede solved this problem by using Hanns-Dieter Paschke's design and converting the DKM into what would later be known as

1088-456: A thermal reactor or catalyst converter may be used to reduce hydrocarbon and carbon monoxide from the exhaust. Mazda uses a dual ignition system with two spark plugs per chamber. This increases the power output and at the same time reduces HC emissions. At the same time, HC emissions can be lowered by reducing the pre-ignition of the T leading plug relative to the L trailing plug. This leads to internal afterburning and reduces HC emissions. On

1152-425: A thin dimensional galvanized chrome layer. This allowed Mazda to return to the 3mm and later even 2mm thick metal apex seals. Another early problem was the build-up of cracks in the stator surface near the plug hole, which was eliminated by installing the spark plugs in a separate metal insert/ copper sleeve in the housing instead of a plug being screwed directly into the block housing. Toyota found that substituting

1216-604: A trial basis 40-octane gasoline was produced by BV Aral, which was used in the Wankel DKM54 test engine with a compression ratio of 8:1; it ran without complaint. This upset the petrochemical industry in Europe, which had invested considerable sums of money in new plants for the production of higher quality gasoline. Direct injection stratified charge engines can be operated with fuels with particularly low octane numbers. Such as diesel fuel, which only has an octane number of ~25. As

1280-558: Is depicted in figure 7. Seals at the rotor's apices seal against the housing's periphery. The rotor moves in its rotating motion guided by gears and the eccentric output shaft, not being guided by the external chamber. The rotor does not make contact with the external engine housing. The force of expanded gas pressure on the rotor exerts pressure on the center of the eccentric part of the output shaft. All practical Wankel engines are four-cycle (i.e., four-stroke) engines. In theory, two-cycle engines are possible, but they are impractical because

1344-428: Is described in the thermodynamic disadvantages section , the early Wankel engines had poor fuel economy. This is caused by the Wankel engine's design of combustion chamber shape and huge surface area. The Wankel engine's design is, on the other hand, much less prone to engine knocking, which allows using low- octane fuels without reducing compression. NSU tested low octane gasoline at the suggestion of Felix Wankel. On

SECTION 20

#1732859257761

1408-440: Is different from a four-stroke piston engine, which needs to make two full rotations per combustion chamber to complete all four phases of a four-stroke engine. Thus, in a Wankel rotary engine, according to Bensinger, displacement ( V h {\displaystyle V_{h}} ) is: If power is to be derived from BMEP, the four-stroke engine formula applies: Eugen Wilhelm Huber, and Karl-Heinz Küttner counted all

1472-397: Is the number of chambers considered for each rotor and i {\displaystyle i} the number of rotors, then the total displacement is: If p m e {\displaystyle p_{me}} is the mean effective pressure , N {\displaystyle N} the shaft rotational speed and n c {\displaystyle n_{c}}

1536-594: The 1950s and 1960s. For a while, engineers were faced with what they called "chatter marks" and "devil's scratch" in the inner epitrochoid surface, resulting in chipping of the chrome coating of the trochoidal surfaces. They discovered that the cause was the apex seals reaching a resonating vibration, and the problem was solved by reducing the thickness and weight of the apex seals as well as using more suitable materials. Scratches disappeared after introducing more compatible materials for seals and housing coatings. Yamamoto experimentally lightened apex seals with holes. Now, weight

1600-541: The DKM engine were built; the design is described to have a displacement V h of 250 cm (equivalent to a working chamber volume V k of 125 cm ). The fourth unit built is said to have received several design changes, and eventually produced 29 PS (21 kW) at 17,000 rpm; it could reach speeds up to 22,000 rpm. One of the four engines built has been on static display at the Deutsches Museum Bonn (see figure. 2). Due to its complicated design with

1664-505: The KKM (see figure 5.). The KKM proved to be a much more practical engine, as it has easily accessible spark plugs, a simpler cooling design, and a conventional power take-off shaft. Wankel disliked Froede's KKM engine because of its inner rotor's eccentric motion, which was not a pure circular motion, as Wankel had intended. He remarked that his "race horse" was turned into a "plough horse". Wankel also complained that more stresses would be placed on

1728-460: The KKM type. Felix Wankel designed a rotary compressor in the 1920s, and received his first patent for a rotary type of engine in 1934. He realized that the triangular rotor of the rotary compressor could have intake and exhaust ports added producing an internal combustion engine. Eventually, in 1951, Wankel began working at German firm NSU Motorenwerke to design a rotary compressor as a supercharger for NSU's motorcycle engines. Wankel conceived

1792-483: The KKM ;502 was a powerful engine with decent potential, smooth operation, and low noise emissions at high engine speeds. It was a single-rotor PP engine with a displacement of 996 cm (61 in ), a rated power of 40 kW (54 hp) at 6,000   rpm and a BMEP of 1 MPa (145 lbf/in ). The Wankel engine has a spinning eccentric power take-off shaft, with a rotary piston riding on eccentrics on

1856-507: The KKM's apex seals due to the eccentric hula-hoop motion of the rotor. NSU could not afford to finance developing both the DKM and the KKM, and eventually decided to drop the DKM in favor of the KKM, because the latter seemed to be the more practical design. Wankel obtained the US patent 2,988,065 on the KKM engine on 13 June 1961. Throughout the design phase of the KKM, Froede's engineering team had to solve problems such as repeated bearing seizures,

1920-544: The NSU research and development department Versuchsabteilung TX . It produced 21 PS (15 kW). Soon after that, a second prototype of the DKM was built. It had a working chamber volume V k of 125 cm and also produced 21 kW (29 PS) at 17,000   rpm. It could even reach speeds of up to 25,000   rpm. However, these engine speeds distorted the outer rotor's shape, thus proving impractical. According to Mazda Motors engineers and historians, four units of

1984-443: The Wankel engine run much smoother. This is because the Wankel engine has a lower moment of inertia and less excess torque area due to its more uniform torque delivery. For example, a two-rotor Wankel engine runs more than twice as smoothly as a four-cylinder piston engine. The eccentric output shaft of a Wankel engine also does not have the stress-related contours of a reciprocating piston engine's crankshaft. The maximum revolutions of

Mazda Savanna - Misplaced Pages Continue

2048-609: The average torque, with the shaft running at 2/3 the speed, operating the Otto cycles at the same frequency: Applying a 2/3 gear set to the output shaft of the three-cylinder (or a 3/2 one to the Wankel), the two are analogous from the thermodynamic and mechanical output point of view, as pointed out by Huber. NSU licensed the Wankel engine design to companies worldwide, in various forms, with many companies implementing continual improvements. In his 1973 book Rotationskolben-Verbrennungsmotoren , German engineer Wolf-Dieter Bensinger describes

2112-422: The axially closer side housings in the cooler intake lobe areas was dealt with by using an axial rotor pilot radially inboard of the oils seals, plus improved inertia oil cooling of the rotor interior (C-W US 3261542   , C. Jones, 5/8/63, US 3176915   , M. Bentele, C. Jones. A.H. Raye. 7/2/62), and slightly "crowned" apex seals (different height in the center and in the extremes of seal). As

2176-407: The chambers, since each one operates its own thermodynamic cycle. So y = 3 {\displaystyle y=3} and n c = 3 {\displaystyle n_{c}=3} : With these values, a single-rotor Wankel engine produces the same average power as a V h {\displaystyle V_{h}} three-cylinder four-stroke engine, with 3/2 of

2240-438: The design and marketing of the second generation of Savanna. The subsequent two generations, released in 1978 and 1985 respectively, fitted the rotary engines to a unique coupe body that sold internationally as the Mazda RX-7 . The rotary engine had financial advantages to Japanese consumers in that the engine displacement remained below 1.5 litres, a significant determination when paying the Japanese annual road tax which kept

2304-426: The design of a triangular rotor in the compressor. With the assistance of Prof. Othmar Baier  [ de ] from Stuttgart University of Applied Sciences, the concept was defined mathematically. The supercharger he designed was used for one of NSU's 50 cm one-cylinder two-stroke engines. The engine produced a power output of 13.5 PS (10 kW) at 12,000   rpm. In 1954, NSU agreed to develop

2368-448: The early days, unique, dedicated production machines had to be built for different housing dimensional arrangements. However, patented designs such as U.S. patent 3,824,746 , G. J. Watt, 1974, for a "Wankel Engine Cylinder Generating Machine", U.S. patent 3,916,738 , "Apparatus for machining and/or treatment of trochoidal surfaces" and U.S. patent 3,964,367 , "Device for machining trochoidal inner walls", and others, solved

2432-416: The engine's torque production. Early closing of the intake port increases low-end torque, but reduces high-end torque (and thus power). In contrast, late closing of the intake port reduces low-end torque while increasing torque at high engine speeds, thus resulting in more power at higher engine speeds. A peripheral intake port gives the highest mean effective pressure ; however, side intake porting produces

2496-431: The engine. While this puts great demands on the materials used, the simplicity of the Wankel makes it easier to use alternative materials, such as exotic alloys and ceramics . A commonplace method is, for engine housings made of aluminum, to use a spurted molybdenum layer on the engine housing for the combustion chamber area, and a spurted steel layer elsewhere. Engine housings cast from iron can be induction-brazed to make

2560-421: The experience gained, from carbon alloys, to steel, ferritic stainless , Ferro-TiC, and other materials. The combination of housing plating and the apex and side seal materials was determined experimentally, to obtain the best duration of both seals and housing cover. For the shaft, steel alloys with little deformation on load are preferred, the use of Maraging steel has been proposed for this. Leaded petrol fuel

2624-463: The factor that controls the amount of unburnt hydrocarbons in the exhaust is the rotor surface temperature, with higher temperatures resulting in fewer hydrocarbons in the exhaust. Curtiss-Wright widened the rotor, keeping the rest of engine's architecture unchanged, thus reducing friction losses and increasing displacement and power output. The limiting factor for this widening was mechanical, especially shaft deflection at high rotative speeds. Quenching

Mazda Savanna - Misplaced Pages Continue

2688-404: The farthest, and a {\displaystyle a} as the shortest parallel transfer of the rotor and the inner housing and assuming that R 1 = R + a {\displaystyle R_{1}=R+a} and R 2 = R + a ′ {\displaystyle R_{2}=R+a'} . Then, Including the parallel transfers of the rotor and

2752-520: The following licensees, in chronological order, which is confirmed by John B. Hege: In 1961, the Soviet research organizations of NATI, NAMI, and VNIImotoprom began developing a Wankel engine. Eventually, in 1974, development was transferred to a special design bureau at the AvtoVAZ plant. John B. Hege argues that no license was issued to any Soviet car manufacturer. Felix Wankel managed to overcome most of

2816-449: The inner housing provides sufficient accuracy for determining chamber volume. Different approaches have been used over time to evaluate the total displacement of a Wankel engine in relation to a reciprocating engine: considering only one, two, or all three chambers. Part of this dispute was because of Europe vehicle taxation being dependent on engine displacement, as reported by Karl Ludvigsen . If y {\displaystyle y}

2880-532: The intake gas and the exhaust gas cannot be properly separated. The operating principle is similar to the Otto operating principle; the Diesel operating principle with its compression ignition cannot be used in a practical Wankel engine. Therefore, Wankel engines typically have a high-voltage spark ignition system. In a Wankel engine, one side of the triangular rotor completes the four-stage Otto cycle of intake, compression, expansion, and exhaust each revolution of

2944-414: The material suited for withstanding combustion heat stress. Among the alloys cited for Wankel housing use are A-132, Inconel 625, and 356 treated to T6 hardness. Several materials have been used for plating the housing working surface, Nikasil being one. Citroën, Daimler-Benz, Ford, A P Grazen, and others applied for patents in this field. For the apex seals, the choice of materials has evolved along with

3008-430: The number of shaft revolutions needed to complete a cycle ( N / n c {\displaystyle N/n_{c}} is the frequency of the thermodynamic cycle), then the total power output is: Kenichi Yamamoto and Walter G. Froede placed y = 1 {\displaystyle y=1} and n c = 1 {\displaystyle n_{c}=1} : With these values,

3072-468: The obligation affordable to most buyers, while having more power than the traditional inline engines. Wankel rotary engine In its basic gasoline fuelled form, the Wankel engine has lower thermal efficiency and higher exhaust emissions relative to the four-stroke reciprocating piston engine. The thermal inefficiency has restricted the engine to limited use since its introduction in the 1960s. However, many disadvantages have mainly been overcome over

3136-540: The oil flow inside the engine, and the engine cooling. The first fully functioning KKM engine, the KKM 125, weighing in at only 17 kg (37.5 lb) displaced 125 cm and produced 26 PS (19 kW) at 11,000   rpm. Its first run was on 1 July 1958. In 1963, NSU produced the first series-production Wankel engine for a car, the KKM 502 (see Figure 6.). It was used in the NSU Spider sports car, of which about 2,000 were made. Despite its "teething troubles",

3200-578: The original 1971 version of Savanna, Mazda fitted its 10A rotary engine to the Mazda Grand Familia to create a separately marketed product sold in coupé, sedan, and station wagon guises. The engine was upgraded to the larger 12A rotary in the GT model introduced in September 1972, and eventually this became the standard engine across the entire range. Coupé sales accounted for over half of total sales, influencing

3264-506: The other hand, the same ignition timing of L and T leads to a higher energy conversion. Hydrocarbons adhering to the combustion chamber wall are expelled into the exhaust at the peripheral outlet. Mazda used 3 spark plugs in their R26B engine per chamber. The third spark plug ignites the mixture in the trailing side before the squish is generated, causing the mixture to burn completely and, also speeding up flame propagation, which improves fuel consumption. According to Curtiss-Wright research,

SECTION 50

#1732859257761

3328-478: The performance of Wankel engines. Side intake ports (as used in Mazda's Renesis engine) were first proposed by Hanns-Dieter Paschke in the late 1950s. Paschke predicted that precisely calculated intake ports and intake manifolds could make a side port engine as powerful as a PP engine. As formerly described, the Wankel engine is affected by unequal thermal expansion due to the four cycles taking place in fixed places of

3392-463: The problem. Wankel engines have a problem not found in reciprocating piston four-stroke engines in that the block housing has intake, compression, combustion, and exhaust occurring at fixed locations around the housing. This causes a very uneven thermal load on the rotor housing. In contrast, four-stroke reciprocating engines perform these four strokes in one chamber, so that extremes of "freezing" intake and "flaming" exhaust are averaged and shielded by

3456-421: The problems that made prior attempts to perfect the rotary engines fail, by developing a configuration with vane seals having a tip radius equal to the amount of "oversize" of the rotor housing form, relative to the theoretical epitrochoid, to minimize radial apex seal motion plus introducing a cylindrical gas-loaded apex pin which abutted all sealing elements to seal around the three planes at each rotor apex. In

3520-429: The rotor (equivalent to three shaft revolutions, see Figure 8.). The shape of the rotor between the fixed apexes is to minimize the volume of the geometric combustion chamber and maximize the compression ratio , respectively. As the rotor has three sides, this gives three power pulses per revolution of the rotor. Wankel engines have a much lower degree of irregularity relative to a reciprocating piston engine, making

3584-410: The rotor housing and determined by the generating radius R {\displaystyle R} , the rotor width B {\displaystyle B} , and the parallel transfers of the rotor and the inner housing a {\displaystyle a} . Since the rotor has a trochoid ("triangular") shape, the sine of 60 degrees describes the interval at which the rotors get closest to

3648-443: The rotor housing. Therefore, The rotor path s {\displaystyle s} may be integrated via the eccentricity e {\displaystyle e} as follows: Therefore, For convenience, a {\displaystyle a} may be omitted because it is difficult to determine and small: A different approach to this is introducing a ′ {\displaystyle a'} as

3712-407: The same. The Wankel engine has a significantly higher (Δt K >100 K) exhaust gas temperature than an Otto engine, especially under low and medium load conditions. This is because of the higher combustion frequency and slower combustion. Exhaust gas temperatures can exceed 1300 K under high load at engine speeds of 6000 rpm . To improve the exhaust gas behavior of the Wankel engine,

3776-406: The shaft in a hula-hoop fashion. The Wankel is a 2:3 type of rotary engine, i.e., its housing's inner side resembles a two lobes oval-like epitrochoid (equivalent to a peritrochoid),. In contrast, its rotary piston has a three vertices trochoid shape (similar to a Reuleaux triangle ). Thus, the Wankel engine's rotor constantly forms three moving working chambers. The Wankel engine's basic geometry

3840-422: The succeeding decades as the production of road-going vehicles progressed. The advantages of compact design, smoothness, lower weight, and fewer parts over the reciprocating piston internal combustion engines make the Wankel engine suited for applications such as chainsaws , auxiliary power units (APUs), loitering munitions , aircraft , jet skis , snowmobiles , and range extenders in cars . The Wankel engine

3904-512: The uneven thermal distribution within the housings causing distortion and loss of sealing and compression. This thermal distortion also caused uneven wear between the apex seal and the rotor housing, evident on higher mileage engines. The problem was exacerbated when the engine was stressed before reaching operating temperature . However, Mazda Wankel engines solved these initial problems. Current engines have nearly 100 seal-related parts. The problem of clearance for hot rotor apexes passing between

SECTION 60

#1732859257761

3968-564: Was also used to power motorcycles and racing cars . The Wankel engine is a type of rotary piston engine and exists in two primary forms, the Drehkolbenmotor (DKM, "rotary piston engine"), designed by Felix Wankel (see Figure 2.) and the Kreiskolbenmotor (KKM, "circuitous piston engine"), designed by Hanns-Dieter Paschke (see Figure 3.), of which only the latter has left the prototype stage. Thus, all production Wankel engines are of

4032-452: Was identified as the main cause. Mazda then used aluminum-impregnated carbon apex seals in their early production engines. NSU used carbon antimony-impregnated apex seals against chrome. NSU developed ELNISIL coating to production maturity and returned to a metal sealing strip for the RO80. Mazda continued to use chrome, but provided the aluminum housing with a steel jacket, which was then coated with

4096-573: Was the predominant type available in the first years of the Wankel engine's development. Lead is a solid lubricant, and leaded petrol is designed to reduce the wearing of seals and housings. The first engines had the oil supply calculated with consideration of petrol's lubricating qualities. As leaded petrol was being phased out, Wankel engines needed an increased mix of oil in the petrol to provide lubrication to critical engine parts. An SAE paper by David Garside extensively described Norton's choices of materials and cooling fins. Early engine designs had

#760239