cycle speed. Figure 6 presents two graphs comparing dynamic cycle test results for grooved and 

 nongrooved poppet seats, both with the biasing spring. 



There did not appear to be any significant difference between the behaviors of the 

 grooved and nongrooved poppets. As in the static tests, the expected differences between the 

 grooved and nongrooved poppets was not substantiated. 



One series of model runs focused on changing the area values in the poppet actuator 

 elements to cause the poppet to open more quickly. In the model, the desired effect was 

 achieved by increasing the opening area from 0.0182 square inches to 0.0382 square inches and 

 decreasing the closing area from 0.1329 square inches to 0.1129 square inches. The 

 improvement was small and suggests that enlarging the poppet area is not detrimental to impact 

 mechanism performance. Later, drill hardware tests showed equal results when using the 

 nongrooved poppet suggesting that the grooved feature is not required. 



Minimized Drill Body Motion 



Movement of the drill body was identified early in the evaluation process as a key 

 influence on impact mechanism performance. The impact mechanism optimization process, 

 therefore, used drill body displacement as a measure of cycle performance. During cycling of 

 the impact mechanism, hydraulic pressure driving the plunger and piston downward also lifts the 

 drill body up. The concern is the movement of the plunger sleeve in the drill body and the 

 relative position of the sleeve with respect to the plunger during the cycle. There is a point 

 where the drill/sleeve has moved far enough up from nominal such that the kicker port is 

 actuated before piston impact against the anvil. The result is a missed or weak impact caused 

 by the premature actuation of the kicker port to close off drive chamber supply. 



Hardware testing was performed using a test stand that held the drill upright and allowed 

 the drill unrestricted vertical displacement. A force transducer was used to measure impact 

 force. This transducer was calibrated by dropping a 10-pound weight from 1 foot to obtain a 

 measurement for 10 foot-pounds of potential energy. A Temposonic position transducer 

 measured the vertical displacement of the drill body. One accelero meter was attached to the drill 

 body and a second to the impact plate at the base of the test stand. The accelerometers did not 

 provide useful data, since they were somewhat noisy. The measurements using the force 

 transducer and Temposonic transducer provided repeatable data. 



The drill was modeled at the operating condition of 1,500 psi supply pressure with a 50- 

 pound force applied as the weight of the drill. This model showed a drill body displacement of 

 over 0.4 inches. Hardware testing confirmed a smaller 0.12-inch drill body displacement and 

 showed a qualitative improvement in drill cycle rate with the application of downward force to 

 the drill. This confirmed the relation between drill body movement and impact mechanism 

 performance. 



Two methods were applied to minimize drill body motion. The approach was to first 

 optimize operating pressure for the existing drill weight of 50 pounds. Reduced operating 

 pressure resulted in less energy to the tool to cause drill body movement. This is evident in the 

 model results shown in Figure 7 obtained with an additional 150-pound downward force applied. 

 Best drill performance was selected at 1 ,000-psi system pressure. 



Then, additional downward force representing increased drill weight was added until 

 consistent energy transfer was achieved. Adding 100 pounds downward force in the model was 

 insufficient for reducing drill body displacement while 150 pounds downward force reduced drill 

 body displacement by a factor of two. Adding 200 pounds or 400 pounds downward force 



