How RENCOL® Tolerance Ring Slip Clutches Work

Slip Clutches provide mechanical overload protection and control the torque in order to protect mechatronic systems. A tolerance ring designed to slip at a certain torque is one example of a slip clutch.

How does a slip clutch work? 

A RENCOL® Tolerance Ring Slip Clutch controls the torque between two mating components. For example, in a typical servo motor the tolerance ring is assembled between the drive gear and the output shaft. When the output drives against an obstruction or receives a shock load, the tolerance ring will slip between the gear and the shaft. This single tolerance ring does the same work as a Friction Type torque limiter. Where the two friction plates (or clutch plates) provide a slippage at a certain torque range. Compared to a Friction Type, the tolerance ring provides the same function in a much smaller design envelope.

The RENCOL® Tolerance Ring uses spring force and friction as its operating principle. This tolerance ring is “automatically resetting,” which means that nothing needs to be done after a torque slip condition; the robot or machine using a RENCOL® Tolerance Ring can continue with its operation without any delays or pauses. The RENCOL® Tolerance Ring installs coaxially into a drive assembly instead of being installed in series with an assembly. And it has wave features that compress to provide a radial force which acts as the spring force to provide friction between components.

Why a Slip Clutch?

Some systems require protection from damage caused by end user misuse or occasional situations like an input shock or an unexpected block. Such systems can be found in electric motors for robotics or automotive systems including: rack and pinion, belt drive, steering column anti-theft, powered tailgate hinges, and braking assist systems.

The RENCOL® Tolerance Ring fixes driven components together and transfers torque unless a threshold is exceeded. At this point the RENCOL® Tolerance Ring allows the components to slip relative to each other. This will limit the torque that the components have to withstand and protect those components from damage that might otherwise occur. RENCOL® Tolerance Rings allow designers to take advantage of opportunities to use lighter and less bulky components in their systems, relying on the protection from overload afforded by the RENCOL® Tolerance Ring.

Torque Overload Protection

The RENCOL® Tolerance Ring solution is custom designed to the optimal torque level rather than having to choose. Tolerance ring designs for 0.2 Nm to 300 Nm torque range and beyond are possible, depending on physical dimensions and the strength of the system for which the tolerance ring is designed.

Figure 1: These are theoretical guidance values for typical tolerance ring configurations. Applications outside of these limits are possible.

Benefits using RENCOL® Tolerance Ring Slip Clutch

•    Reduced system inertia
•    Increased system acceleration and responsiveness
•    Stable and consistent torque over multiple slip cycles of operation
•    Reduced system complexity compared to other alternatives
•    Smaller installation envelope - - space savings
•    When activated, provides a quality of movement that avoids noise or vibration
•    Allows for increased tolerance compensation of mating components

Consistent Torque for Life

In some applications, maintaining consistent torque level over a large number of slip-cycles is required. RENCOL® Tolerance Rings can be designed to reduce torque-drop over multiple slip-cycles that is often seen on other torque overload protection devices. Using RENCOL® Tolerance Rings in this way gives consistent performance for the life of the system. The tolerance ring offers a smooth feel, defining the perception of quality for human operated systems.

Figure 2: This illustration shows typical torque performance of a 50 mm diameter tolerance ring slipping on a steel shaft over 5000 slip cycles.

Tolerance Ring waves of a Slip Clutch 

In some instances, e.g. when being used as a torque limiter it is useful to deliberately design for the plastic zone so that large variations in component size will have minimal effect on the torque at which slip occurs. The ring is designed such that the crests of the waves embed slightly into the mating component and the base of the waves acts as a bearing surface and slips against the mating surface. Rings can be designed to slip either on the shaft or the bore, depending on materials, surface finish and hardness issues etc.

Rings coated with a proprietary dry lubricant have been developed to provide further enhanced performance and to eliminate the need for a greasing station on assembly lines.

Savings in Torque Slip Applications 

Torque slip devices -- or slip clutches -- can be complicated systems with many components. A RENCOL® Tolerance Ring solution uses one component in-line with the mating components to reduce weight, space and overall cost.

Torque slip devices come in many forms such as: magnetic clutch, friction slip devices, and ball detent devices. Compared to a RENCOL® Tolerance Ring, all of these devices require more space to reach similar levels of torque.

The space saving for tolerance rings is enabled because tolerance rings work as an inline fixing between the driving and driven components. This means there is no need for an extra slip-clutch unit which takes up more space and weight.

How We Make a Big Difference

A tolerance ring isn’t just a stand-alone component; it is an integral part of a larger system that means a detailed, knowledge-based approach is needed for tolerance ring design. That is why a RENCOL® Tolerance Ring is designed in collaboration with our customers, engineer to engineer. This process is made more powerful by using our FEA capabilities along with in-house testing to analyze the system, with mating components included and under key conditions. This means that we and our customers can have confidence in the solutions we provide.