In this article, we’ll be discussing a Spring Rate Adjuster by Ohlins, US publication 20210148431. The publication date is May 20th, 2021 and the filing date is Jan 12th, 2021. This has not been granted yet.
This is the second document relating to the new Ohlins shock. The first one can be read here. We know Ohlins is developing this new shock with a more robust and easier-to-service outer seal system. Now, we’re going to introduce an external spring rate adjuster. I’m going to skip the fluff on this one and just dive right into the meat.
I will admit that the last article has incorrect assumptions. The dials/knobs are not exactly what I had assumed, and this article will clear that up.
Intro
Ohlins has a line about how you’d typically change the spring rate on an air spring:
When it comes to adjustments of prior art gas spring shock absorbers, the pressure in one or more air chambers can normally be adjusted by adding or removing gas therefrom and if the spring rate needs to be changed, volume spacers can be rearranged, removed and/or replaced in order to obtain the wanted setup.
We’ve all changed air pressures and added volume spacers to adjust the characteristics of an air spring. It can be annoying or tedious at times, especially when you have to take the whole damn thing apart to get to the volume spacers. It appears as though Ohlins has a solution.
There’s a line explaining exactly what they’re doing. In short, they’re using a damping chamber to affect an air chamber with an expanding bladder.
The disclosure is based on the realization that a characteristic of the air spring in a hydropneumatic shock absorber can be changed from the outside by affecting indirectly the gas spring through the chamber containing the damping media.
Why
Ohlins wants to provide the ability to adjust air volume without having to get inside the shock itself:
…the spring rate of the gas spring can be adjusted by reducing or increasing the volume available inside the shock absorber to the gas spring…
You’ll also be able to change the ride height of the shock:
…it is also possible to change a ride height of a shock absorber at a given pressure…
and you can adjust the balance between the compression and rebound chambers:
…it will also be possible to change the balance between the compression spring chamber and the rebound spring chamber due to the fact that the volume of the compression spring chamber is adjustable whereas the rebound spring chamber remain the same.
Lastly, this is for Ohlins, but they’ll be simplify manufacturing and services:
The present disclosure may also simplify manufacturing and service of the shock absorber since it makes it possible to compensate for an inaccurate amount of oil in the shock absorber. If too little or too much oil is used in the damping chamber, the piston is simply moved to compensate for this.
What
First things first, FIG. 1 shows a cross-section of this new shock. The valve 5 is at the bottom and the adjuster 15 is the volume adjustment knob. I had assumed the knob was rebound, but this document has cleared that up. We’re also going to focus on flexible membrane 9 (expanding bladder).
In the last article, Ohlins had claimed this shock will be smaller but didn’t explain that claim in the last document. They do in this one saying because the piston is inside the piston rod, the entire package can be smaller:
Another advantage with the present disclosure resides in the fact that the piston 12 is arranged inside piston rod 12. This solution does not add to the overall length of the shock absorber and it does not require any adaptations of the attachments 3 and 4 in comparison with a regular shock absorber.
They also say the arrangement of this knob is for added convenience:
Further, the arrangement of adjustment knob 15 connected to the piston 12 through a worm drive 14 also allows for adjustments from the outside in a convenient manner. Especially considering the fact that shock absorbers on e.g. bicycles are arranged in intricate linkages with sometimes very limited space and since the placement of attachment 3 is a common solution, the example of the present disclosure with knob 15 arranged with a 90 degree offset to the longitudinal direction of the piston rod 2 is convenient.
FIG. 2 shows the system in action. It’s pretty simple, the rider can turn the knob 15 to move the piston 12 into the flexible membrane, and the flexible membrane expands into the compression spring chamber 10. As a result, the expansion reduces the volume of the compression spring chamber. In other words, the volume of the compression spring chamber gets smaller, and the volume of the rebound damping chamber gets stays the same.
It’s important to note the compression spring chamber is the air you’ll pump into the shock and the rebound damping chamber is oil bath. Oil is incompressible, air is compressible. So, the incompressible fluid chamber takes volume away from the compressible air chamber.
That’s it, there’s nothing more to it than that. Turn knob -> reduce air volume chamber using flexible damper membrane.
Lastly, I’m a huge fan of what’s going on here. Simpler service, longer service intervals, cool adjustments. Sign me up. We got one more (so far) to go over. I’ll publish soon.