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Why would a gearset be designed like this? (two-piece/grooved gear)

Why would a gearset be designed like this? (two-piece/grooved gear)

Why would a gearset be designed like this? (two-piece/grooved gear)

(OP)
I came across the pictured set of gears at work and it caught my eye - the gears are for a set of dual overhead cams. I can't tell for sure without taking it apart whether the gear itself it actually two pieces or just a single gear that was grooved, however upon close inspection it looks like it is actually two separate pieces. It struck me as very strange and I can't figure out why this might be designed in this manner. I know that driving a camshaft is probably a relatively low load application, especially for such a relatively large gearset, however I would think that at the very least there would be a significant reduction in strength due to the groove/two piece. The only thing I can really think of is that somehow this might be used to mitigate some NVH issue due to tooth mesh - has anyone ever come across something like this?





RE: Why would a gearset be designed like this? (two-piece/grooved gear)

It may be an anti-backlash system.

RE: Why would a gearset be designed like this? (two-piece/grooved gear)

It is indeed an anti-backlash system to reduce noise. The narrow part of the gear will be spring-loaded in the reverse-torque direction.

Toyota 2RZ-FE or 3RZ-FE by any chance?

RE: Why would a gearset be designed like this? (two-piece/grooved gear)

It's called a scissor gear. They're used on engines with cam/accessory gear drives to reduce dynamic tooth loads due to torsional oscillations. In the case of your Toyota cam gear, the torsional oscillations are produced by the varying forces acting on the cam lobes. There is a moment in one direction as each leading cam flank pushes a valve open, and a moment in the opposite direction as the valve spring pushes against the trailing cam flank during closing. Conventional gears (not scissor gears) require some amount of backlash at the mesh to prevent interference. When there is backlash, reversing torsional oscillations will cause high dynamic contact loads on the gear tooth flanks at the mesh. These high dynamic tooth contact forces also produce noise. While a scissor gear can reduce dynamic tooth loading and noise, it also involves some mechanical losses.

You'll see them used on other engines like Cummins diesels and Honda motorcycle engines

Here's a video that shows the Toyota scissor gear internal parts.

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