外文翻译--汽车传动系统无级变速器CVT

附 录 A ABSTRACT High clamping force levels reduce the efficiency of the Continuously Variable Transmission (CVT). However, high clamping force levels are necessary to prevent slip between the belt and the pulleys. If a small amount of slip is allowed, the clamping force level can be reduced. To achieve this, slip in a CVT is investigated. From measurements on an experimental setup, Traction curve data and efficiency measurements are derived. A model describing slip in a CVT is verified using measurements with a belt with increased play. It is found that small amounts of slip can be controlled in a stable way on the setup. The traction curve was mostly dependent on the CVT ratio. Efficiency is found to be highest for 1 to 2% slip depending on the ratio. The model is in reasonable agreement with the measurements. 1. Introduction Applying a Continuously Variable Transmission (CVT) in an automotive driveline has several advantages. A CVT can operate at a wider range of transmission ratios, therefore the engine can be operated more efficiently than with a stepped transmission. Also, a CVT does not interrupt the torque transmission when shifting. This gives a more smooth ride than a stepped transmission does. A V-belt based Continuously Variable Transmission uses a belt or a chain to transmit torque from a driving side to a driven side by means of friction. The layout of the CVT and the V-belt are shown in figure 1. The variator consists of two pulleys which are wedge shaped. By changing the position of the pulleysheaves the ratio of the CVT can be adjusted. The V-belt consists of blocks which are held together by two rings that in turn exist of a set of bands. To achieve torque transmission sufficiently high clamping force levels are needed to prevent slip in the variator. Because the torque level is not exactly known at all times, since no torque sensor is used due to cost considerations, a safe clamping force level based on the maximum possible load is maintained at all times. This safety level is based upon assumed maximum shockload levels from the road, like bumps, and the engine torque. In order to maintain these safety levels higher clamping force levels are maintained then needed. Higher clamping force levels cause more losses in the CVT. These losses are caused by increases in power consumed by the hydraulic pump, by increases in the losses due to slip in the belt if a pushbelt is used, and by increases in deformation in the belt and in the pulleys. Furthermore wear is increased and fatigue life is reduced. In order to reduce these clamping force levels a method is needed to detect slip in the variator fast enough to prevent slip from reaching destructive levels. A method to detect and control slip is therefore needed. In this paper measurements are presented of the traction curve in a V-belt CVT. Figure 1. Layout of a CVT and a metal pushbelt 2. Traction curve The V-belt type CVT utilizes friction to transmit power from the primary pulley to the secondary pulley. The traction curve is the dimensionless relationship between transmitted torque and the slip. The maximum input torque that can be transmitted by the CVT is dependent on the applied clamping force. The traction coefficient is therefore chosen to be a dimensionless value. The traction coefficient is defined as: SSq RFT2 cos （ 1） In which qT represents the input torque, SR represents the secondary running radius of the belt on the pulley, SF represents the secondary clamping force and is the pulley wedge angle. Figure 2. CVT torque transmission scheme The second variable in the traction curve is the slip in the variator. Slip is defined as: 10 rPS （ 2） Where s is the angular speed of the secondary axle, p is the angular speed of the primary axle and 0r is the geometrical ratio, which is defined by: SPRRr 0 （ 3） PR is the running radius on the primary pulley. 2.1 Tangential slip Slip is defined in equation 2. When the CVT transmits power a certain amount of slip can be measured almost linear with the applied torque. This is called the microslip regime of the CVT, because traction is still increasing in this regime with increasing slip. The microslip is caused by gaps between the blocks on the idle part of the driving pulley as shown in figure 3. On the driving pulley an idle arc exists where no slip occurs. Also an active arc exists (see figure 2), where slip occurs relative to the total play in the belt and the active arc length. However, when the maximum torque capacity of the CVT is reached slip will increase dramatically. This situation, macroslip, is not stable during normal operation of the CVT, because the traction coefficient decreases with increased slipspeed. It is assumed that the total gap dt is evenly distributed along the idle arc of the driving pulley. The traction Figure 3. Gaps in the belt curve (figure 5) shows that torque transmission increases almost linearly with an increase in slip, until a certain maximum torque is reached. dt can be estimated by adding an initial gap do to the increase in belt length due to the internal stresses in the bands and a decrease in length of the blocks due to the compressive forces. dLt 0 （ 4） To calculate the slip caused by these gaps we can use the following equations: dRdtpstm （ 5） mmdv （ 6） In equation 5, a is the idle arc, d is the width of a belt element and dt is the total gap between the elements in the belt. To calculate the amount of slip the total gap dt has to be known. This effect has an influence on the traction coefficient in the macroslip regime. When macroslip occurs the traction will decrease with increasing slip. The Stribeck effect is modelled using equation 9. vcf 0 （ 7） 1210 vveaag （ 8） fgvv )sin( （ 9） Equation 7 gives a value for the friction caused by viscous friction component. Equation 8 gives a value for the coulomb friction component. a0,1, c0 and v1 are coefficients which can be chosen to match the measured values. With these equations we can derive slip and traction from measured data as shown in section 4. With Asayama 1995 we can obtain the tension and compression force distribution needed to calculate the lengthening of the belt. Also, we can calculate the idle arc from this model. From the idle arc, the length of the belt and the initial gap we can calculate an estimate for slip in the belt for a given load. 2.2 Radial slip Not only slip in tangential direction occurs, but also slip in radial direction. The first reason for radial slip is spiral running. When the belt runs along the arc of contact the radius at which it runs is not constant. This effect is caused by pulley deformation. One type of deformation is the bending of the axle between both pulley sheaves. The belt is not fully wrapped around the pulley, therefore the resulting normal force of the blocks on the pulley is not axial. This causes a bending moment in the axle. A second effect is the bending of the pulley itself. This effect is mostly dependent on the local normal force exerted on the pulley by the blocks. This effect is small when the belt is running on a small running radius, but on a large running radius this effect is significant. The second reason for slip in radial direction is due to shifting. When the CVT is shifted to a different transmission ratio, radial slip is forced. This is done by changing the clamping force ratio. The amount of radial slip that is forced depends on the shifting speed and the (primary) angular speed. 3. Experimental setup In the experiments the geometric cvt ratio is fixed and the clamping forces are constant, the traction coefficient then depends only on the slip in the system. The traction curve can be constructed from output torque and slip measurements. The test rig motors deliver a maximum torque of 298 Nm with a maximum speed of 525 rad/s. Both motors are equipped with a Heidenhain ERN1381 incremental rotary encoder with 2048 pulses/rev. The torque at both sides is measured using a HBM T20WN torque sensor. The maximum allowable torque is 200 Nm with speeds up to 1050 rad/s. A separate hydraulic unit is used to provide the required flow and pressure for the clamping forces. Figure 4 gives a schematic overview of the experimental setup. 4. Experimental results The geometric ratio of the CVT was fixed during the experiments using a so-called ratio ring and the limits of the primary pulley. This ratio ring limit the movement of the pulley. Primary and secondary pressure was held constant (clamping forces were held constant) during the experiments. Figure 4. Experimental setup 4.1 Traction coefficient The traction coefficient was measured at different ratios, at different primary speeds and at different pressures. In figure 6 and 7 can be seen that the traction coefficient depends little on primary speed or secondary clamping pressure, but mostly on the transmission ratio, as can be seen in figure 5. An increase in clamping force causes more slip (see figure 8). This is caused by an increase in tension in the bands and therefore in an increase in length of the belt. This causes the play to increase. Figure 5. Traction coefficient at 300rad/s, ratio low(0.4), Medium (1.1) and overdrive (2.26) 4.2 Efficiency The efficiency depends on pressure and on ratio. From figure 12 can be seen that an increase in pressure causes a decrease in efficiency. This effect is caused by the internal friction in the belt. Slip between the blocks and the bands also causes a strong dependency on ratio (see figure 9). Efficiency is clearly higher in medium than in overdrive or low. In medium no slip occurs between the blocks and the bands, but in overdrive or low the bands slip over the blocks. At high clamping levels this effect is greater, because the normal forces acting between the blocks and the bands increase linearly with an increase in clamping level. From figure 10 and 11 can be seen that input speed also has an influence on efficiency. Figure 6. Traction coefficient in overdrive, ws = 150,225,300 Figure 7. Traction coefficient in low, wp =150,225,300 Figure 8. Traction coefficient for resp. 5bar and 8bar secondary clamping pressure From figure 10 and 11 can be seen that input speed also has an influence on efficiency. 4.3 Play The microslip region is dependent on play in the belt. An experiment has been carried out with a belt with increased play. One block was taken out of the belt. The performance of the belt was measured with a total gap of 1.8mm. The cumulative gap in the belt was 0.3mm in the other experiments. A significant difference is measured in the LOW ratio of the CVT. In figure 4.3 the traction curve is shown for the low ratio of the CVT for the belt with increased play. Also the result of the numerical model is shown in figure 4.3. The results for overdrive show that in overdrive there is no significant change in the traction curve, see figure 4.3. However, the model is less consistent with the tractioncurve in overdrive than in low. Figure 9. Efficiency at 300rad/s, ratio low(0.4), Medium (1.1) and overdrive (2.26) Figure 10. Efficiency in overdrive, ws =150,225,300 Figure 11. Efficiency in low, PW = 150,225,300 Figure 12. Traction coefficient for resp. 5bar and 8bar secondary clamping pressure Figure 13. Effect of play in the belt, wp = 30rad/s, in low, with increased gap (1.8mm) Figure 14. Effect of play in the belt, wp = 30rad/s, in overdrive, with increased gap (1.8mm) 5. Conclusion The traction curve is mostly ratio dependent. This can be explained with the shown model as explained in section 4. Transmission efficiency is dependent on applied pressure, input speed and the CVT ratio. Gaps between the blocks of the belt cause at least part of the tangential slip of the belt. This was confirmed by the experiment with increased play in the belt. The consistency of the model is better in low than in overdrive. Future research will be directed at controlling slip in the CVT. This can enhance the efficiency of the CVT. 附 录 B 各级高夹紧力降低了无级变速器（ CVT）的效率。然而，各级高夹紧力之间的必要措施，防止金属带和滑轮滑。如果滑少量是允许的，夹紧力水平可以降低。要做到这一点，在无级变速器滑动进行了研究。从上一个实验装置测量，牵引效率测量数据和曲线推导。一个模型描述无级变速器滑动验证使用具有增加播放带测量。研究发现，少量的滑可在道路上设置稳定控制。牵引曲线主要是依赖于CVT的比率。效率是发现 1至 2的最高比例滑倒而定，该模型与测量合理的协议。 1. 简介 应用在汽车传动系统无级变速器（ CVT）有几个优点。无级变速器可以工作在更广泛的传动比，因此该引擎可以使用，其传输效率比阶梯。另外， CVT 的不中断换挡时的扭矩传递。这给出了一个比一个更平稳的传输并加强。阿 V 带无级变速器的使用金属带或链条传送通过摩擦意味着从驱动侧的扭矩到从动侧。该无级变速器和 V带的布局见图 1。该变速器由两个滑轮是楔形。通过改变位置的 CVT的比例可以调整。 V型带，其中包括分别由两个环一起，在乐队依次设置 存在的块。为了实现足够高的扭矩传递夹紧力水平是需要防止变速器滑。由于转矩是不完全知道在任何时候，因为没有采用扭矩传感器由于成本的考虑，一个安全级别夹紧力最大的可能是维持负载为基础在任何时候。这是基于安全等级最高的假定像颠簸道路上，和发动机扭矩水平。为了保持这些安全级别较高的夹紧力水平维持不变，然后需要。夹紧力水平造成的 CVT 更多的损失。这些损失是由由液压泵消耗功率提高造成的损失中带滑，如果在一个带使用的增加，并在带变形和滑轮增加。此外磨损增大，疲劳寿命降低。为了减少这些夹紧力的方法检测，需要足够快的变速器， 防止破坏性的水平失误达到的水平。一个方法来检测和控制，因此需要滑。本文介绍了测量中的 V带无级变速牵引曲线。 图 1 金属带式无级变速器布置 2. 牵引曲线 V型带式无级变速器采用了摩擦，从主滑轮传送到辅助电源滑轮。牵引曲线之间传递扭矩和滑量纲关系。最大输入扭矩，可以通过发送的 CVT 的夹紧力的应用而定。牵引系数因此选择是一个无量纲值。牵引系数的定义为： SSq RFT2 cos （ 1） 其中表示输入扭矩，代表着对金属带轮二次运行半径，代表了二次夹紧力，是滑轮楔角。 图 2 CVT的扭矩传输方案 牵引曲线中的第二个变量是在变速器滑移。 滑移的定义为： 10 rPS （ 2） s是次要轴角速度，p是主轴 角速度，0r是几何比例，将其定义为： SPRRr 0 （ 3） PR 正在运行的主滑轮半径。 2.1 切向滑移 滑移是指在公式 2。当无级变速器传递动力滑移一定量的可测与施加的扭矩几乎呈线性关系。这就是所谓的 CVT的 microslip政权，因为在此牵引仍随滑移区增加。该 microslip 是由块之间的间隙对传动滚筒闲置部分，如图 3 所示。在主动轮弧存在其中一个空闲无滑移发生。也是一个积极的弧存在（参见图 2），其中发生相对滑移，在带和总发挥积极的弧长。然而，当 CVT 的最大扭矩达到防滑能力将显着增加。这种情况， macroslip，是不是在本无级变速器的正常运行稳定，因为牵引系数降低与增加滑移率。据推测，总差距是均匀分布在主动轮的闲置弧线处。牵引曲线（图 5）显示，传递扭矩增大几乎呈线性增加，在滑动，直到达到一定的最大扭矩。t可以通过添加一个初始间隙做了带长度的增加，估 计由于内部应力的乐队，并在适当的块长度的压缩力下降。 dLt 0 （ 4） 图 3 空白带 计算的滑动造成这些差距的原因我们可以用以下的方程 : dRdtpstm （ 5） mmdv （ 6） 公式 5是一个空闲的弧线， D是一个带元素的宽度和t是在金属带之间的元素的总差距。要计算总的差距滑t的金额为已知。这种效应有一个关于在宏观滑移政权牵引系数的影响。当宏观滑移发生的牵引滑移的增加会降低。效果是模仿的摩擦模型使用公式 9。 vcf 0 （ 7） 1210 vveaag （ 8） fgvv )sin( （ 9） 公式 7给出了由粘性摩擦元件所造成的摩擦系数。公式 8给出了库伦摩擦组件的值。 0a 为 1， 0c 和 1 的是可以选择匹配的测量值系数。有了这些方程，我们可以从测量数据下滑牵引，在图 4所示，我们可以得到的张力和压缩力分布计算所需的金属带延长。另外，我们可以从这个模型计算出空闲的弧线。从闲置的弧线，金属带的长度和初始差距，我们可以计算出在金属带承保给定负载的估计。 2.2 径向滑动 不仅在切线方向发生滑动，而且滑径向方向。对于第一个原因是径向滑动螺 旋运行。当沿带的接触半径，在它运行的弧线运行的不是恒定的。这种效应是由滑轮变形。一类是变 形的两滑轮轴弯曲。金属带是不完全的滑轮包左右，因此导致正常的区块队在滑轮是不是轴向，这会导致轴弯矩。 第二个效应是金属带轮本身弯曲。这种影响主要是对当地正常的由