Power steering: Three common shortcomings, two helpful tips

Power steering:  Three common shortcomings, two helpful tips

By Freddie Heaney.
Photography by Moore Good Ink:

 KRC Power Steering Pump -frontIn the early 1990’s, before power steering became prevalent in racing cars, Michael Schumacher, statistically the greatest driver the sport has ever seen, remarked, “You have to carefully judge the amount of steering angle required as you turn into a high-speed corner, as it is very difficult to correct if your assessment is wrong.”

MichaelSchumacherHis comment came as a repercussion of increased steering caster angles, functioning at 9-12 degrees that made the steering heavy. The problem was further exacerbated by increasingly high aerodynamic down forces.

Over twenty years later, power steering still has its abiding problems: slow response; unnecessary parasitic losses; and premature pulley failures are three of the most common.

Slow response

Cutaway showing Spool Valve

If the pressure relief valve (spool valve) encounters friction when it moves, it slows the response of the steering. To prevent the spool valve from sticking or cocking in its bore, KRC hone this oil passageway twice

If the pressure relief valve (spool valve) encounters friction when it moves, it slows the response of the steering. To prevent the pressure relief valve from sticking or cocking in its bore, KRC the power steering people, hone this oil passageway twice: once after initial machining and again after hard-anodizing. The final honed finish is specified at 4Ra (roughness average—a measure of the texture of the surface measured in micro inches).

“The roughness average,” says KRC’s head Ken Roper, “determines how quickly the pressure relief valve will react and the hard-anodizing (measuring 60Rc) contributes to its hard-wearing capabilities. But the integrity of its bore is equally important. It must be strictly round and straight.” KRC holds the pressure relief valve bore tolerance to 0.0002in over a 2in distance. If the steering wheel moves so, too, does the pressure relief valve.

Parasitic losses are usually associated with forfeiting energy to drag, friction, wear, and heat. And therein lies the trouble with most power steering pumps. KRC switched from bushings to bearings—using a ball bearing in the front of the pump and a needle bearing at the rear.

HTD (high torque drive) pulley systems are now pervading the upper echelons of most racing categories. However, the key to their effectiveness and their longevity lies in the shape of their pulley teeth. These should exhibit rounded profiles that promote free and easy belt release.

The teeth also need to be spaced precisely at 8mm center-to-center distance so the belt meshes well. Correctly machined teeth on an HTD pulley provide maximum contact area with the belt, contributing to belt and pulley longevity. Crucially, precision-machined HTD pulleys pillage the least amount of horsepower from the engine.

Shaft-Drive-PTO-On-DrySump-3R

The purpose of the PTO arrangement is to move weight toward the center of the race car, a popular pursuit in Dirt Late Model racing. The belt, powered by the crankshaft, drives a dry-sump pump with the power steering pump and the fuel pump in tandem. Add the weight of the alternator and, indisputably, the race car has better balance.

In appearance, anodizing closely resembles hard-anodizing, but the difference between the two is profound (as reflected in the price). In the absence of hard anodizing, power steering pulleys can fail prematurely. Further where there’s slippage, aluminum from the surface of the pulley will be transferred to the belt, precipitating rapid pulley wear.

Two tips

1) Should a power steering pump fail, ensure the lines are subsequently flushed clean. If not, the new replacement pump will be immediately sabotaged by shrapnel remaining in the system from the original failure.

2) Power steering hoses, in common with all high pressure hoses, are typically made from layers of rubber, steel braiding and cloth. If you use an abrasive cut-off wheel on power steering hoses, it will cause the rubber to melt. To complicate matters further, sand particles from the abrasive wheel together with metal particles from the braided steel will adhere to the melted rubber.

Later, when the system is assembled and operating at normal temperature, the globules of rubber with sand and metal particles glued to the inside of the hose will melt. Soon after, they’ll be delivered to the pump, which they’ll destroy, usually in the first or second race.

To avoid these imminent tragedies when using an abrasive cut-off wheel, always clean the power steering hoses with a rifle-bore brush.

KRC is displaying at the SEMA show November 5-8 (Booth #36222 near the New Products area) and at the PRI show in Indianapolis Dec 12-14 (Booth #3921)

Source

KRC Power Steering
2115 Barrett Pk. Dr.
Kennesaw GA 30144
(770) 422-5135
www.krcpower.com

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