Development of a semi-annular continuously variable transmission
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The development of the foreign bearing technology semi-annular continuously variable transmission NSK China Technology Center (NSK China Technology Center, Kunshan, Jiangsu 215335) speed, relying on the shear force of the elastic fluid lubricant film between the two rotating bodies to achieve power transmission. In response to the long life requirements of the traction drive WT, the WT special steel was developed and carbonitrided on the contact surface to achieve good results.
NSK began developing traction-driven semi-circular CVTs (continuously variable transmissions) in 1978 and successfully applied them to the Nissan Cedric and Gloria vehicles in November 1999. This article will summarize the development process of the past 21 years, introduce the technical characteristics of the traction-driven semi-circular CVT and its development prospects.
1 The history of the ring CVT was applied for a US patent on November 27, the patent number is 197472. In this patent, the oscillating wheel E is installed between the disc B and the disc D, and the disc B and the disc D are spherical. Changing the angle of the oscillating wheel changes the relative speed of the two discs. Due to its simple structure, it has been tried in industrial products. With the advent of automobiles, it has also been applied to automotive transmissions, and many samples were produced and sold in the 1920s. A car that used this device and called "friction drive" was once built. However, it has not been commercially successful. In 1937, dKraus and his son JKraus tested the traction drive CVT installed in an 85 hp Ford in the US state of TEXAS. The CVT transmission ratio of that test was from 265:1 to 06:1. According to the test results, they pointed out that CVT can achieve high acceleration, high fuel efficiency and cleaner vehicle emissions. In 1943, Wright's CVT. They conducted many comparative tests and actual vehicle tests. K.Krau pointed out that the reduction of power transmission 9 (October 2000), the original: Machida Shangcun Shangbaofu point, that is, the contact point of the spin, not only can increase the contact area, but also can improve transmission efficiency and durability and reduce the size. Professor M.Ishihara of the Institute of Industrial Technology of the University of Tokyo pointed out that CVT is more fuel efficient, so the development trend of the car gearbox is to adopt the semi-circular CVT. Learn from the oil crisis and adopt the advice of Professor M.Ishihara. NSK began in 1978. The basic structure 21 geometry with 2 annular CVTs can be divided into two categories according to the shape: annular CVT and semi-annular CVT. An example of a circular CVT is given. The geometric feature is that the line OO' connecting the contact points of the power roller with the power input disk and the power output disk must pass through the center of the power input disk and the power output disk. Therefore, the contact load generated between the power roller and the power input disk and the power output disk due to the transmission of power does not act on the support roller of the power roller. On the other hand, the tangent lines passing through the contact point 0, 0' are parallel to each other and do not intersect, and the spin at the contact point is severe.
A geometrical representation of the contact portion of the semi-annular CVT is given. The tangent through the contact point OO intersects at point E. When the intersection E is on the axis of rotation I, the spin of the contact point O0' is 0. The spin loss of the semi-annular CVT is less than the given annular CVT. This is due to the speed of the transmission. Within the range, the intersection E is close to the axis of rotation, and the semi-annular CVT can achieve no spin. According to the spin ws of point 0 as the power input disk, the dynamic diagram of the semi-annular CVT of the power roller is a schematic diagram of a semi-annular CVT, the torus of which is a concave spherical surface and the disk support bearing must bear on the disc. Axial load. In addition, since the middle straight line OO does not pass through the center of the spherical surface, the power roller bearing must withstand the axial load of the power roller and the axial component of the input and output discs.
The semi-annular CVT indicates the gear ratio of 2, the radius of rotation is the radius of rotation of the contact point of the Ri two-power roller, mR3 is the radius of rotation of the contact point of the output disc, m; R12 is the principal radius of curvature of the output/supplied disk, m; for the spherical diameter, m. 23 power transmission utilization illustrates the power transmission system. The input shaft power is transmitted sequentially to the loading cam, cam roller, input disc, power roller, output disc and output gear. From the Hertz contact theory, the point of contact between the input disk and the power roller, ie the midpoint O, is actually an ellipse. The long semi-axis a and the short semi-axis b are respectively the modulus of elasticity, nm2; E2 is the elastic modulus of the dynamic roller material, Nm2; V1 is the Poisson's ratio of the input disc material; V2 is the Poisson of the dynamic roller material Ratio; 11 is the main radius of curvature of the input disc (middle perpendicular to the paper surface, m); 12 is the main radius of curvature of the input disc (middle parallel to the paper surface m), R21 is the main radius of curvature of the power roller (middle Vertical to the paper, m); 22 the main radius of curvature of the power roller (medium parallel to the paper, m); m is the elliptic integral coefficient.
The average pressure at the contact point is the transmission torque and the traction force at point O.
The contact load Fc is a component of the axial load Fa of the loaded cam. The axial load Fa is proportional to the AA profile shown by the input shaft torque 24 force balance equation. The hydraulic load of the four cylinders is subjected to the reaction force of the traction force acting on the trunnion. When the power is transmitted between the disk and the power roller, the rotation axis of the power roller intersects with the rotation axis of the disk, and the force balance equation in the y-axis direction is the hydraulic load of the cylinder of the semi-annular CVT section number, Pa; Cylinder area, m2. Hydraulic load is provided by an external oil pump. The No. 4 cylinder and the No. 23 cylinder are connected by their respective oil lines, and the transmission control valve controls the oil pressure.
25 Transmission Control Device As described above, controlling the tilt angle of the power roller enables shifting of the semi-annular CVT. The direction of the central axis of the power roller in the y-axis direction is changed to generate a motion vector in the oblique direction of the contact region, thereby changing the tilt angle of the power roller. At this time, the lateral displacement of the contact area generates a tilt load. a shows the power transmission state when the load is balanced when the roller rotation axis and the disk rotation axis intersect. When the stepping motor controls the valve sleeve to move in the x-axis direction, the pressures Ph and Pl change, the trunnion moves in the J-axis direction (opposite direction) (b) and the contact point of the disk and the power roller also changes accordingly. Through this process, the tilting rotational load (c) is generated and the left and right trunnions are symmetrically tilted (the tilt amount is converted into the movement of the control valve groove in the x direction (in the same direction as the sleeve). The precessing cam moves the valve groove to adjust The displacement of the sleeve and the change of the pressure. When the force balance shown in the equation (16) is reached, the change in the amount of inclination is stopped (e). Therefore, the load required for the shift can be obtained by causing the control valve sleeve to move. The key feature of the servo mechanism is that the control load is completely unaffected by the magnitude of the transmitted load. A small stepper motor is used for the actual vehicle driving test.
26 loading cam can use the hydraulic system and mechanical system to generate contact load, a, b (c), dlle, semi-circular CVT shift control principle. The contact load generated by the hydraulic system depends on the amount of transmitted torque, and the control is precise and relatively simple. However, when the hydraulic system is installed in a car, the hydraulic cylinder must have a high pressure due to space constraints. Therefore, the cost of the oil pump and its energy loss become a major problem. In order to apply a semi-annular CVT to a car, a mechanical system has been developed which consists of a conical pressure regulating spring and a loading cam. The contact points O and , shown, are transmitted through the traction drive. Now, considering only the point O, the traction force generated by this point is (17) and (18). The contact load required to transmit the input shaft torque is to substitute the formula (2) into the above formula, within the range of the transmission ratio. The required contact load is to generate a contact load at the contact point, and a tapered pressure regulating spring and a loading cam can be used for both axial load generating mechanisms. Even if the input shaft torque is zero or very small, adjusting the conical spring pressure ensures that the contact point meets the minimum contact load required for the traction drive function. When the input shaft torque exceeds a certain value, that is, beyond the applicable range of the conical pressure regulating spring, the loading cam starts to work. The loading cam is connected by a spline and an input shaft. The loading cam is driven by the input shaft and produces an axial load as the cam roller rolls over the cam surface. This load forces the input disc into contact with the power roller, creating a contact load at the point of contact.
3 traction drive traction drive to achieve power transmission is achieved by the shear force of the elastic fluid lubricant film between the two rotating bodies, see. The fluid film thickness can be calculated based on the Hanrock-Dowson theory. When the contact surface pressure is Pmax=22GPa, the surface velocity is U=242m/s and the oil temperature is 120°C, the central oil film thickness hc is calculated to be about 0. The relationship between the contact load Fc and the tangential load Tc is shown in (13). formula.
Traction drive mechanism related to traction load, with the development of elastohydrodynamic lubrication theory, many theoretical discussions have been tried. In 1977, Johnson et al. proposed a reasonable explanation. They used the elastoplastic model of lubricating oil to illustrate the mechanism of traction load generation and classify the motion of the elasto-lubrication contact surface into three categories, namely sliding, side slip and spin. In subsequent studies, according to the Eyrhg theory, the traction fluid under high pressure was considered to be a nonlinear Maxwell rheological model. According to the test, the existence of the ultimate shear force was confirmed, and the fluid traction curve was obtained, so that the traction load driving mechanism was quickly grasped. Tana ka uses these theories to analyze the transmission efficiency of the traction load driven transmission.
4 Traction lubricating oil is specially driven traction oil driven by traction. It is a phenylcycloalkyne synthetic oil. Its maximum traction coefficient is 0 095 higher than cyclic hydrocarbon oil. In 1987, Hata and Aoyama of Japan Idemitsu Co., Ltd. used a double cylindrical roller tester to test the traction coefficients of various lubricating oils at 40~140 °C and predicted their application in traction drive vehicles. The test results show that the stool is sputum; the 沉 沉 km km 定 定 定 定 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - A lubricating oil which is less affected by temperature changes and has a high traction coefficient at a high temperature can be applied to automobiles. Later, Nlianeda and Achiha of NSK developed a double cylindrical roller tester that can test the traction coefficient of lubricating oil under simulated driving conditions. 0 gives a test result. The test results were obtained at different spin speeds. Since only one type of lubricating oil is currently used in the CVT, the lubricating oil not only has a high traction coefficient, but also has various characteristics as shown in 1. Developing traction lubricants for CVT is a huge technical challenge.
5 Durability 2 gives the fatigue analysis results of the disk fatigue tester. When the fatigue index is used to evaluate the fatigue condition, it is obvious that the fatigue condition of the traction drive CVT contact surface and the inside is very bad. Therefore, measures must be taken to prolong the rolling contact fatigue life of traction-driven CVT parts under heavy-duty operating conditions, and at the same time improve the ability to withstand surface and internal origin fatigue spalling.
3 shows the long life technology of NSK bearings. For internal origin fatigue spalling, SUJ2EP steel should be used. The development concept of this steel is to reduce the non-metallic inclusion content at the point of origin of fatigue spalling. Based on SUJ2EP steel, NSK has developed CVT special steel, in which the quantity, size and distribution of non-metallic inclusions are more strictly controlled. 4 shows the distribution of oxidized inclusions in ordinary purity carburized steel and high purity CVT carburized steel. As shown in the figure, the number and size of inclusions in the CVT carburized steel are small, and the curve distribution area is small. On the other hand, for surface-originated fatigue spalling, it is necessary to reduce the hazard of surface indentation caused by hard foreign matter. The lubricating oil of the differential gearbox contains many hard abrasive grains. Under the most severe working conditions, the rolling fatigue life is only 1/5 of the calculated life. The stress concentration around the shoulder is the main reason for the fatigue life reduction. This stress concentration can be reduced by using TF technology. 5 illustrates the stress set of foreign body indentation and shoulders | better surface reduction inclusions high purity coagulum I carbon nitrogen "stress concentration around the mad inclusions r origin 1 internal origin f fatigue 1 surface origin type fatigue measures - The degree of purity of the NSKEP steel CVT steel seal 'completely hardened steel carburized steel 4 steel. The stress concentration is characterized by the rA value, which is the ratio of the curvature r of the indented shoulder to the radius c of the indentation. It shows that the smaller the r/c value, the more serious the stress concentration. 6 shows the relationship between the r/c value and the retained austenite content. In essence, the TF technique increases the residual austenite content of the heat treatment, thereby increasing The r/c value.7 shows the test results of the rolling contact fatigue life. As the retained austenite content increases, the fatigue life is prolonged. In addition, the carbonitriding technique can increase the retained austenite content while To ensure hardness, further, the use of high-purity liquid nitrogen in the carbonitriding process can improve the durability performance under high temperature conditions and ensure long life under high temperature and high pressure conditions. 8 Endurance test of traction surface is given. Results. 1984~1987, frequent
8 ultra-pure steel (Editor: Wen Chaojie)