乘用车机械式变速器设计【两轴式机械式变速器】【4档】
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附录:THE FILE TRANSMISSION GEAR SELECTION OF THE BASIC PARAMETERS1, Reasonable choice of module:Modulus is an important gear basic parameters, the greater the modulus, the greater the tooth thickness, the bending strength of gear is also greater, and its greater carrying capacity. Instead modulus smaller tooth thickness will be thinner, the bending strength of gear will be smaller. The low profile of the gear, due to the low rotational speed, torque, and gear of the relatively large bending stress, so need to choose a larger module in order to ensure its strength. And high-speed file gear, due to the high-speed, torque small gear bending stress is relatively small, so to ensure that the bending strength of gear under the premise of the general selection of the smaller module, so that gear teeth can be increased in order to obtain larger degree of overlap, so as to achieve the purpose of reducing noise.In a modern gearbox design, the file selection module gear is different. For example, a transmission gear of a file to the five-gear gear module are: 3.5; 3; 2.75; 2.5; 2; to change over the past modulus or modulus of the same can not be the situation of Latin America.2, a reasonable selection of pressure angle:When a gear module and set the number of teeth, the gear diameter is determined, and the gear tooth involute base circle depends on the size, the size of the base circle and under pressure angle. For the same pitch circle of gear, if its pitch circle a different pressure angle, base circle is different. When the greater the pressure angle, the base circle diameter of the smaller, more curved involute, tooth root of the tooth will thicken, increase the tooth surface radius of curvature, which can increase the tooth bending strength and contact strength. When reducing the pressure angle, the base will become larger diameter, involute tooth profile will change some of the straight, thinning of the tooth root, tooth smaller radius of curvature, making the tooth bending strength and contact intensity will decrease, but decrease with the pressure angle, to increase the contact ratio gears, reducing the stiffness of the tooth, and can reduce the entry and exit load at the time of engagement, all of which are beneficial to reduce noise. There-fore, low profile gear, often larger pressure angle in order to meet the strength requirements; and regular use of high-speed file smaller gear pressure angle in order to meet the requirements of its lower noise.For example: a gear module 3, the number of teeth of 30, when the pressure angle of 17.5 degrees for the circular tooth thickness of the base to 5.341; when the pressure angle of 25 degrees, the tooth thickness of the base circle to 6.716; its base circle to increase the tooth thickness 25%, so increase the pressure angle to increase their flexural strength.3, A reasonable selection of Helix Angle:Compared with the straight gear, helical gear drive with a smooth, coincidence degree, the impact is small and the advantages of small noise. As a result of the present with synchronous transmission, and transmission will no longer be a direct mobile gear meshing with another gear, but with all the gears are meshing, so thatll bring convenience to the use of helical gear, so to bring the gearbox synchronizer Most of the use of helical gear.Helical gear as a result of the characteristics of the entire tooth width decision not to enter the mesh at the same time all but one end of first gear into the mesh, with the drive gear along the tooth width direction mesh gradually until all the teeth have wide access to mesh, so the actual meshing helical gear spur the region than the large. When the tooth when a certain width, the contact ratio of helical gear with helix angle increases. Carrying capacity is also stronger, have better stability. In theory, the better helix angle, but the helix angle increases, the axial force will also increase, so that reduces the transmission efficiency.In the modern design of the gearbox, in order to ensure smooth gear drive, low noise and less impact, all . Files forgear should choose a larger helix angle, generally about 30 high-speed gear as a result of the higher speed, for a smooth, low impact, low noise, so the use of small modulus, large helical angle; and low-profile gear module using the larger, smaller helix angle.4, The perspective of a reasonable modification is selected:With good conditions for the lubrication of the hardened gear is generally believed that the main danger is in the cycle under alternating stress, the fatigue crack Dedendum gradual expansion of the tooth root fracture caused by the failure. Failure in the gear transmission is a part of this. In order to avoid a broken tooth, should be to maximize the tooth root bending strength, and the use is changed, and can achieve this objective. Under normal circumstances, the greater the coefficient, the smaller values tooth, tooth bending stress on the smaller, the higher the bending strength of teeth.In the hardened gear, the tooth surface pitting failure is one of the reasons off. Increased engagement angle, can reduce the inter-tooth contact stress and maximum slip rates, can greatly increase the ability of anti-pitting. And increased engagement angle, it must have a gear shift is introduced, thereby enhancing contact strength of tooth surface can improve the flexural strength of tooth roots, so as to enhance the effect of the carrying capacity of gears. However, for helical gear drive, variable coefficient is too large, and will total tooth length of the contact line, but to reduce its carrying capacity. At the same time, the greater the coefficient, as a result of tooth to tip increases, the thickness of the tip will be smaller, which will affect the strength of the top teeth.Therefore, in the design of a modern gearbox, the majority of all reasonable use of gear shift is the angle in order to maximize its advantages. Mainly in the following design criteria:low profile for the gear pair, the driving gear of the coefficient should be larger than the passive gear shift coefficient, and pair of high-speed profile, the driving gear of the coefficient should be less than passive coefficient gear.gear with the modification coefficient increased gradually stalls xiajiang. This is because low-grade zones as a result of low rotational speed, torque, and gear for high intensity, so the need to use more of the modification coefficient da.The total of the gear profile shift coefficient is positive (of the anglel shift as amended), and increased with the stalls and gradually decreased. The smaller the total coefficient, a pair of pair of tooth root of the thickness of the total will be thin, tooth root becomes weak, the lower the bending strength, but decreased as a result of the stiffness of the tooth, easy to absorb shock and vibration, so can reduce the noise. And tooth contact ratio will increase, which bear a single tooth at the time of maximum load Dedendum recent focus distance, the reduced bending moment, which is equivalent to increase the strength of the tooth root, which as a result of thinning and weakened tooth root strength offset factor. Therefore, the greater the overall coefficient, the higher the strength of the tooth root, but the noise may increase. Thus high-speed gear to choose a smaller file of the total coefficient, and low-profile gear must be chosen larger coefficient5, to improve tip high coefficient:Top gear in the transmission of high quality factor, the impact of focusing on adaptation, in the main impact of helical gear contact ratio face. Coincidence degree by the end of the formula, we can see that when the number of teeth and meshing certain angle, the tooth tip is affected by tooth pressure angle coefficient of the top high impact factor the greater the high-tip, round tip the greater the pressure angle, contact ratio is The greater and ore stable drive. However, the high coefficient the greater the tip, the thickness of the top teth will become thin, thus affecting the strength tip. At the same time, at least not from the tooth root formula, the high coefficient the greater the tip, at least not the root will increase the number of gear, otherwise, they would have a root cutting. As a result, guarantees of non-root tip-cut and sufficient strength, increased tooth top high coefficient of coincidence degree for the increase is significant.Top gear in the transmission of high quality factor, the impact of focusing on adaptation, in the main impact of helical gear contact ratio face. Coincidence degree by the end of the formula, we can see that when the number of teeth and meshing certain angle, the tooth tip is affected by tooth pressure angle coefficient of the top high impact factor the greater the high-tip, round tip the greater the pressure angle, contact ratio is The greater and more stable drive. However, the high coefficient the greater the tip, the thickness of the top teeth will become thin, thus affecting the strength tip. At the same time, at least not from the tooth root formula, the high coefficient the greater the tip, at least not the root will increase the number of gear, otherwise, they would have a root cutting. As a result, guarantees of non-root tip-cut and sufficient strength, increased tooth top high coeff-icient of coincidence degree for the increase is significant.The above is from the module, pressure angle, helix angle, coefficient and a high coefficient of this addendum to an independent analysis of the five aspects of gear design trends. In fact between the various para-meters are inter-related, involved with each other, the choice of transmission parameters, it is necessary to take into account their strengths and weaknesses, but also consider the relationship between them, so in order to maximize their strengths and avoid weaknesses to improve transmission performance.变速箱各档齿轮基本参数的选择1、合理选用模数模数是齿轮的一个重要基本参数,模数越大,齿厚也就越大,齿轮的弯曲强度也越大,它的承载能力也就越大。反之模数越小,齿厚就会变薄,齿轮的弯曲强度也就越小。对于低速档的齿轮,由于转速低、扭矩大,齿轮的弯曲应力比较大,所以需选用较大的模数,以保证其强度要求。而高速档齿轮,由于转速高、扭矩小,齿轮的弯曲应力比较小,所以在保证齿轮弯曲强度的前提下,一般选用较小的模数,这样就可以增加齿轮的齿数,以得到较大的重合度,从而达到降低噪声的目的。在现代变速箱设计中,各档齿轮模数的选择是不同的。例如,某变速箱一档齿轮到五档齿轮的模数分别是:3.5;3;2.75;2.5;2;从而改变了过去模数相同或模数拉不开的状况。2、合理选用压力角当一个齿轮的模数和齿数确定了,齿轮的分度圆直径也就确定了,而齿轮的渐开线齿形取决于基圆的大小,基圆大小又受到压力角的影响。对于同一分度圆的齿轮而言,若其分度圆压力角不同,基圆也就不同。当压力角越大时,基圆直径就越小,渐开线就越弯曲,轮齿的齿根就会变厚,齿面曲率半径增大,从而可以提高轮齿的弯曲强度和接触强度。当减小压力角时,基圆直径就会变大,齿形渐开线就会变的平直一些,齿根变薄,齿面的曲率半径变小,从而使得轮齿的弯曲强度和接触强度均会下降,但是随着压力角的减小,可增加齿轮的重合度,减小轮齿的刚度,并且可以减小进入和退出啮合时的动载荷,所有这些都有利于降低噪声。因此,对于低速档齿轮,常采用较大的压力角,以满足其强度要求;而高速档齿轮常采用较小的压力角,以满足其降低噪声的要求。例如:某一齿轮模数为3,齿数为30,当压力角为17.5度时基圆齿厚为5.341;当压力角为25度时,基圆齿厚为6.716;其基圆齿厚增加了25%左右,所以增大压力角可以增加其弯曲强度。3、合理选用螺旋角与直齿轮相比,斜齿轮具有传动平稳,重合度大,冲击小和噪声小等优点。现在的变速箱由于带同步器,换档时不再直接移动一个齿轮与另一个齿轮啮合,而是所有的齿轮都相啮合,这样就给使用斜齿轮带来方便,因此带同步器的变速箱大多都使用斜齿轮。由于斜齿轮的特点,决定了整个齿宽不是同时全部进入啮合的,而是先由轮齿的一端进入啮合,随着轮齿的传动,沿齿宽方向逐渐进入啮合,直到全部齿宽都进入啮合,所以斜齿轮的实际啮合区域比直齿轮的大。当齿宽一定时,斜齿轮的重合度随螺旋角增加而增加。承载能力也就越强,平稳性也就越好。从理论上讲,螺旋角越大越好,但螺旋角增大,会使轴向分力也增大,从而使得传递效率降低了。在现代变速箱的设计中,为了保证齿轮传动的平稳性、低噪声和少冲击,所有齿轮都要选择较大的螺旋角,一般都在30左右。对于高速档齿轮由于转速较高,要求平稳,少冲击,低噪声,因此采用小模数,大螺旋角;而低速档齿轮则用较大模数,较小螺旋角。4、合理选用正角度变位对于具有良好润滑条件的硬齿面齿轮传动,一般认为其主要危险是在循环交变应力作用下,齿根的疲劳裂纹逐渐扩张造成齿根断裂而失效。变速箱中齿轮失效正是属于这一种。为了避免轮齿折断,应尽量提高齿根弯曲强度,而运用正变位,则可达到这个目的。一般情况下,变位系数越大,齿形系数值就越小,轮齿上弯曲应力越小,轮齿弯曲强度就越高。 在硬齿面的齿轮传动中,齿面点蚀剥落也是失效原因之一。增大啮合角,可降低齿面间的接触应力和最大滑动率,能大大提高抗点蚀能力。而增大啮合角,则必须对一副齿轮都实行正变位,这样既可提高齿面的接触强度,又可提高齿根的弯曲强度,从而达到提高齿轮的承载能力效果。但是,对于斜齿轮传动,变位系数过大,又会使轮齿总的接触线长度缩短,反而降低其承载能力。同时,变位系数越大,由于齿顶圆要随之增大,其齿顶厚度将会变小,这会影响齿顶的强度。 因此在现代变速箱的设计中,大多数齿轮均合理采用正角度变位,以最大限度发挥其优点。主要有以下几个设计准则:l 对于低速档齿轮副来说,主动齿轮的变位系数应大于被动齿轮的变位系数,而对高速档齿轮副,其主动齿轮的变位系数应小于被动齿轮的变位系数。l 主动齿轮的变位系数随档位的升高而逐渐下降。这是因为低档区由于转速低、扭矩大,齿轮强度要求高,因此需采用较da的变位系数。l 各档齿轮的总变位系数都是正的(属于角变位修正),而且随着档位的升高而逐渐减小。总变位系数越小,一对齿轮副的齿根总的厚度就越薄,齿根就越弱,其抗弯强度就越 低,但是由于轮齿的刚度减小,易于吸收冲击振动,故可降低噪声。而且齿形重合度会增加,这使得单齿承受最大载荷时的着力点距齿根近,使得弯曲力矩减小,相当于提高了齿根强度,这对由于齿根减薄而消弱强度的因素有所抵消。所以总变位系数越大,则齿根强度越高,但噪声则有可能增大。因此高速档齿轮要选择较小的总变位系数,而低速档齿轮则必须选用较大的总变位系数。5、提高齿顶高系数齿顶高系数在传动质量指标中,影响着重合度,在斜齿轮中主要影响端面重合度。由端面重合度的公式可知,当齿数和啮合角一定时,齿顶圆压力角是受齿顶高系数影响的,齿顶高系数越大,齿顶圆压力角也越大,重合度也就越大,传动也就越平稳。但是,齿顶高系数越大,齿顶厚度就会越薄,从而影响齿顶强度。同时,从最少不根切齿数公式来看,齿顶高系数越大,最少不根切齿数就会增加,否则的话,就会产生根切。因此,在保证不根切和齿顶强度足够的情况下,增大齿顶高系数,对于增加重合度是有意义的。因此在现代变速箱的设计中,各档齿轮的齿顶高系数都选择较大的值,一般都大于1.0,称为细高齿,这对降低噪声,增加传动平稳性都有明显的效果。对于低速档齿轮,为了保证其具有足够的齿根弯曲强度,一般选用较小的齿顶高系数;而高速档齿轮,为了保证其传动的平稳性和低噪声,一般选用较大的齿顶高系数。以上是从模数、压力角、螺旋角、变位系数和齿顶高系数这五个方面去独立分析齿轮设计趋势。实际上各个参数之间是互相影响、互相牵连的,在选择变速箱的参数时,既要考虑它们的优缺点,又要考虑它们之间的相互关系,从而以最大限度发挥其长处,避免短处,改善变速箱的使用性能。
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