Germany's Schaeffler exhibits new technology for reducing fuel consumption in powertrain systems

Schaeffler Group, a major German auto parts manufacturer, held a technical forum in Shanghai at the end of August 2010, unveiling new technologies such as the latest cam switching mechanism, low-cost continuously variable transmission (CVT) and differential gears with embedded motors.

The Schaeffler Group holds a technical forum every four years, and this is the first time it has been held in Asia. The group invited engineers from Asian automakers and parts manufacturers to attend the forum and promoted its latest technologies.

The main products of the Schaeffler Group include engine parts and transmission parts. The technology released this time is about how to use these products to improve fuel efficiency.

In terms of valve drive mechanism, the group announced a "three-stage switching system" that can change valve timing and lift by switching three cams. Although the principle is the same as Honda's variable valve timing and lift mechanism "VTEC" that switches two cams, the mechanism for switching cams is completely different. The two-stage switching mechanism has been put into practical use in the engines of Audi in Germany, and the product developed this time has changed the mechanism to a three-stage switching.

The basic principle of this cam switching mechanism is quite simple. There are three types of cams: low speed, medium speed, and high speed. The cam to be used is switched by shifting the position of the cam in the axial direction (Figure 1). The three types of cams are mounted on the camshaft via splines together with a slider with an S-shaped groove that rotates with the cam. An electric actuator is provided near the slider, and the actuator has a pin that pushes the cam in the axial direction.

Figure 1: Principle of the three-stage cam switching mechanism The cam moves along the axis by the engagement of the pin and the groove. The position of the moving cam is fixed by a mechanism using a spring and a ball (upper left).

In the upper right part of Figure 1, the rightmost cam (low-speed cam) is in contact with the cam follower. In this state, the actuator extends a pin and inserts it into the groove of the slider. Since the position of the pin is fixed, the slider will shift to the right along the shape of the S-shaped groove. In this way, the three sets of cams will also shift to the right, so that the medium-speed cam and the cam follower come into contact (middle right part of Figure 1).

The slider has an S-shaped groove, one per half circle, for a total of two. One is opened in a shape that makes the entire cam shift to the right, and the other is opened in a shape that makes the entire cam shift to the left. The cam to be used is switched by using these two grooves separately.

In addition, two actuators that extend the pin are also provided on each cylinder. When the actuator on the right side in Figure 1 extends the pin while the medium-speed cam is in contact with the cam follower, the slider will move further to the right, so that the cam follower comes into contact with the cam on the highest speed side. In this way, the cam to be used is switched by using two actuator pins and two grooves opened on the slider. The actuator is an electric type, so there is no need to process the camshaft for hydraulic piping, and the cam operation state can be switched independently for each cylinder.

The ball screw drives the rod to operate the clutch

In terms of transmission technology, the new technologies related to DCT (Double Clutch Transmission) and CVT stand out. Schaeffler Group has been supplying dry double clutch and electric hydraulic actuator components to Volkswagen's 7-speed DCT, which has been put into practical use.

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At this forum, Schaeffler Group announced that it supplied an electric clutch actuator to Getrag's 6-speed DCT in Germany (Figure 2). This DCT features an electric actuator for clutch switching and speed change mechanisms. The clutch is operated by driving the screw with a ball screw and pushing the rod with a roller mounted on the screw (Figure 3).

Figure 2: Getrag's 6-speed DCT "6DCT250" features an electrified clutch and transmission actuator. The clutch and actuator are supplied by Schaeffler.

Figure 3: Clutch actuator construction The ball screw moves the screw and the roller mounted on the screw pushes the actuator rod.

Schaeffler also announced the "High Value CVT" (Figure 4), which can reduce costs by about 20% compared to the original. The biggest feature is that it is based on a pulley manufactured by stamping. The existing pulley is manufactured by machining, but if it can be changed to stamping, the cost can be greatly reduced. The torque capacity is assumed to be 140N·m, the distance between the pulley axes is 155mm, and the weight is less than 55kg.

Figure 4: The CVT concept, which aims to reduce costs,
envisions manufacturing pulleys through stamping, which is expected to reduce costs by about 20%.

On the other hand, the "active eDifferential" (Figure 5) is developed to adapt to the electrification of the drive system, which embeds a drive motor and a motor for switching the torque distribution between the left and right wheels in the differential gear. By equipping a differential, ordinary front-wheel drive vehicles can be hybridized. In addition, the vehicle's handling performance can be improved by changing the left and right torque distribution. It is estimated that this differential is envisioned to be equipped on large SUVs (multi-purpose sports vehicles) and other models.

Figure 5: The "active eDifferential" with a built-in motor integrates the drive motor and the motor for changing the distribution of driving force between the left and right sides with the differential.