Low-friction bearing of the rotary axes in the automatic closure of a convertible top

• What was needed: iglidur ® plain bearing
• Requirements: Due to the only one-sided drive of the convertible top mechanism and the low spring force in the open position, a low-friction bearing of the rotary axes is necessary; the bearing should also allow a fixed axial clearance, but this should not be too large
• Industry: Automotive industry
• Success for the customer: With iglidur® plain bearings, the customer found a particularly cost-effective solution; the maximum axial clearance could be reduced from 1.5 mm to 0.5 mm by using the calibratable flanged bushing

The application case presented here for a plastic storage system relates to an automatic closure for a convertible top (soft top) for locking the front bow to the vehicle windscreen.
The soft top is moved over almost the entire swivelling range by means of a hydraulic system before the automatic closure, which is driven by an electric motor, closes the soft top completely. A side auxiliary lever and a four-bar linkage driven on one side at the front are used to do this. The four-bar linkage is opened by a roller in the base plate of the cowl after a slider has released the lock. The movement required for this is generated by the side lever and the soft top hydraulics. A coil spring supports this gear movement.
To ensure that the catch hook (coupling of the four-bar linkage) not only releases the roller of the base plate, but also actually reaches the constructive end position, a low-friction bearing of the pivot axles is essential due to the one-sided drive and the low spring force in the open position.
The bearing of the linkage lever is designed as a fixed bearing, the bearing of the delicate control lever as a floating bearing. However, due to the manufacturing tolerances in the cast parts, the axial clearance in the fixed bearing can be up to 1.5 mm to prevent jamming in the opposite tolerance position. However, the clearance causes the following problem: If the catch hook deviates too far from the desired position, it does not hit the immersion point in the cowl, which only allows a small amount of movement. The remaining movement range of the floating bearing on the control lever can be restricted in such a way that clamping on the control lever/catch hook or drive lever/catch hook pivot axes is possible.

The manufacturing company EDSCHA Cabrio-Dachsysteme GmbH had the following possible solutions to reduce the high reject rate:
A tool change on a cast part, gluing in the centre collar bushing during assembly in the drive lever or a calibratable version of the collar bushing in the centre. The drive lever is calibrated to a final dimension with a tolerance of ±0.1 mm when the collar bushes are fitted.  
While option 1 entailed high modification costs for the tool, for an additional tool for clamping and for milling over each drive lever, option 2 would have required an additional work step to coat the collar bushes with acrylate adhesive, which would also have been hazardous to health.
The decision was therefore made in favour of option 3, which offers significant advantages in terms of application:
While the tool for a new iglidur ® plain bearing could be provided cost-effectively by us, only a simple modification was required to the assembly tool for the flanged bushings, which also kept the costs manageable. In addition, a possible spring effect between the demoulding chamfer of the carrier part and the exposed flange of the bushing (wall thickness on the flange partially reduced to 0.5 mm) helps to reduce the maximum achievable clearance by a further 0.1 mm. 
The maximum axial clearance could be reduced from 1.5 mm to 0.5 mm by using the calibratable flange bushing.