小型汽车的传动系统采用VESPEL密封环
由于采用超级耐磨和高性能的VESPEL SP密封环，运动型MINI车的无级变速箱可以更加可靠地运行。该车型的CVT有德国ZF Getriebe GmbH 制造。
采用VESPEL密封环后，在不影响可靠性的情况下能够降低成本，节约空间和减轻重量。具有矩形截面的密封环可以在达55Bar的高压下提供动态的密封能力，转速达12,000RPM。一个密封环装在输入轴上，另外一个装在变速箱的输出轴上。这个CVT关键部件采用一对锥形盘来改变输出轴的速度和扭矩。
每个密封环的内径都有一个止转凸起来防止铝腔体和密封环的相对运动。密封环的缺口位置刚好在止转凸起的对面。在安装过程中，杜邦的专利缺口设计可以非常容易地把密封环装入轴上，由于VESPEL SP具有良好的弹性，密封环可以很容易地弹入密封槽内。这种弹性可以对密封环进行自动装配，而对于铸铁来说是不可能自动装配的。
在汽车预热阶段，密封环的缺口会轻微保持张开，这样膨胀的其他可以排出；当预热完成后，缺口闭合，实现的密封效果。采用VESPEL SP后，可以非常地计算缺口闭合的温度点，也可以把密封环设计成允许适当的泄露量，保持密封环和内壁之间形成的润滑膜，或者把润滑油进入到密封环后面的轴承里。
杜邦的VESPEL SP聚酰亚胺没有玻璃化转变温度，不会发生熔融。这个特性决定了它可以用于非常高的温度：长期使用温度290°C，短期可达480°C。对于所有的牌号来说，无论是有润滑还是无润滑，VESPEL具有很好的耐磨性能。
对于全球的自动变速箱用户来说，填充石墨的SP-21和SP-22是理想的密封环和密封垫片材料。杜邦利用DF成型方法生产出高精度的SP-21和SP-22部件。
杜邦公司是一家科学企业，提供以科学为基础的产品及服务。成立于1802年的杜邦公司致力于利用科学创造可持续的解决方案，让全球各地的人们生活得更美好、更安全和更健康。
如今，杜邦在全球拥有60,000多名员工，业务遍及70多个国家和地区，以广泛的创新产品和服务涉及农业与食品、楼宇与建筑、通讯和交通等众多领域。
文章来源：DuPont，以下是英文原版。
Mini Autos Stay on the Go With DuPont? Vespel? for Transmission Seals
The stepless automatic drive in the sporty MINI car can operate maintenance-free, thanks in part to the exceptional abrasion resistance and other high-performance capabilities of sealing rings made of DuPont? Vespel? SP polyimide. The drive, a continuously variable transmission (CVT) type, is made by ZF Getriebe GmbH of Germany.
The Vespel? sealing rings help save costs, space and weight without compromising reliability. The drive uses two such rings of rectangular cross-section to provide a dynamic high-pressure seal at differential pressures up to 800 psi (55 bar) and rotational speed differences up to 12,000 rpm. One ring is mounted on the driving shaft, the other on the driven shaft in the transmission’s variator. This key CVT component uses two opposed pairs of conical discs to vary the speed and torque of the driven shaft.
A locking tab on the inner diameter of each ring prevents relative movements between the CVT’s abrasion-sensitive aluminum housing and the rings. The ring’s circumference is split diametrically opposite to the tab (see photo). During transmission assembly, the split design (covered by a DuPont patent) allows the ring to slide easily over the shaft and into a groove designed to hold it; at the groove, the ring snaps firmly into place, thanks to the high elasticity of Vespel? SP. This elastic feature permits automated assembly of the rings, which would be impossible with cast-iron parts.
In the drive’s warm-up phase, the ring’s split remains slightly open, so that expanding air can escape; after warm-up, the gap closes, producing maximum sealing force. With Vespel? SP, the temperature at which the gap closes can be accurately set, and the ring can also be designed so as to allow some residual leakage, to maintain a permanent lubricating film between the ring and the mating surfaces, or to allow lubrication to reach a bearing behind the ring.
DuPont? Vespel? SP polyimides have no glass transition temperature, and they do not melt. This means that they can be used from very low to very high temperatures: up to about 290°C in continuous use and about 480°C for short periods. Very good wear resistance, both in lubricated and unlubricated environments, is common to all types.
For manufacturers of automatic drives worldwide, graphite-filled Vespel? SP-21 and SP-22 are the preferred types for seal rings and washers. DuPont fabricates these materials into high-precision finished parts with a direct-forming technique.
Thermoplastic Vespel? TP types offer even greater freedom to make multifunctional parts of complex shape. Their glass-transition temperatures of about 250°C are substantially higher than current requirements in CVT engineering. Depending on the application, DuPont offers types with high temperature and abrasion resistance combined with especially high strength or improved chemical resistance.
DuPont is a science company. Founded in 1802, DuPont puts science to work by creating sustainable solutions essential to a better, safer, healthier life for people everywhere. Operating in more than 70 countries, DuPont offers a wide range of innovative products and services for markets including agriculture, nutrition, electronics, communications, safety and protection, home and construction, transportation and apparel.