For the past 25 years, our engineers have worked with automotive, off-road and industrial customers to turn hydraulic control valve concepts into reality. More recently, we prototyped, developed flow testing and mass-produced a control valve for a braking system in a hybrid vehicle. The sleeve-spool matched sets had a target diametrical clearance of 2-5 microns, and cylindricity of 1.5 microns.
By teaming up our prototyping team with our advanced production capabilities, Camcraft developed an efficient, robust process to deliver the quality our client demanded for a safety-critical application.
Process development: safety critical braking system control valve
With hydraulic control valves of this type, many companies would manually match fit, prepare the sleeve, set up instrumentation to measure the bore, then grind the spool to a certain size and match it up per part. It’s effective, but very time consuming.
When you specialize in tight tolerance applications at extremely high volumes like we do at Camcraft, you have to come up with processes that go beyond the norm. So, we developed a process that leveraged our considerable knowledge of bore sizing to hold a 2 micron tolerance. Based on statistical lot data from the ground spool, the sleeve bore size would be determined for a perfect matched fit that meets, or—as is usually the case—exceeds customer requirements.
Mass-producing the valve
To ensure quality, we use our RONDCOM form tester to confirm the control valve meets our target cylindricity. In a recent test we conducted, cylindricity measured less than 1 micron. On our CNC grinding machines, the diamond-coated grinding wheels allow for superior precision. Multiple passes allow us to hold tolerances within 2 microns.
Flow testing the assembly
For fuel savings, hybrid vehicles often shut down their gasoline engines and rely solely on their electric drives for propulsion. The hydraulic braking system must maintain pressure regardless of engine or hydraulic pump state. This is accomplished through tighter system tolerances and control of leak paths. To ensure performance of the sleeve and spool assembly, a leak test was devised.
Hydraulic flow tests are generally an oily nuisance, and one goal of ours during this particular valve project was to come up with a “greener” way of flow testing. We worked with our customer to create a flow test correlation that used air instead of DOT 3 brake fluid.
This method of testing has decreased production time dramatically and provided robust quality assurance. By using air instead of oil, we provide a pre-packed assembly that’s clean and ready for customer integration immediately out of the package. Our customer does not need special fixtures to wash oils out, and they avoid the risk of spool and sleeve separation during the cleaning process.
Because we are able to prototype with maximum manufacturability in mind, hold tight tolerances during production and flow test efficiently, we are able to help our customer move through all phases of the product life cycle in a seamless and cost effective manner.
Do you have an upcoming project that could benefit from an innovative and practical approach to process design? Contact us today.