The Discussion of this exercise covers the following points:

Transcription

1 Exercise 3-2 Hydraulic Brakes EXERCISE OBJECTIVE When you have completed this exercise, you will be familiar with the hydraulic circuits of the yaw and the rotor brakes. You will control brakes by changing the state of some valves and evaluate brake pad thickness. Finally, you will bleed the brakes. DISCUSSION OUTLINE The Discussion of this exercise covers the following points: Yaw and rotor brake construction Brake bleeding Brake valve logic Yaw brake circuit. Rotor brake circuit. DISCUSSION Yaw and rotor brake construction Figure 3-57 shows the two brake calipers that house the pistons and brake pads. Figure Yaw (left) and rotor (right) brake calipers. The yaw brake caliper (Figure 3-58) is fixed and the brake pads are pressed against the rotating disk when oil pressure is applied to the moving pistons. Festo Didactic

2 Ex. 3-2 Hydraulic Brakes Discussion Caliper Oil pressure Piston Brake pad Disk Shaft Figure Yaw brake caliper being applied. The rotor brake caliper shown in Figure 3-59 and Figure 3-60 is of the floating type and features only one moving piston. The second brake pad is fixed and the caliper moves so that pressure is applied on both sides of the disk. When oil pressure is low (Figure 3-59), the brake is applied by the force of the internal spring. When oil pressure is high (as in Figure 3-60), the piston compresses the internal spring and the brake is released. 162 Festo Didactic

3 Ex. 3-2 Hydraulic Brakes Discussion Internal springs Low oil pressure Caliper Floating mechanism Brake pads Piston Shaft Disk Figure Rotor brake applied by the spring (low oil pressure). Internal springs High oil pressure Caliper Floating mechanism Brake pads Piston Shaft Disk Figure Rotor brake released by high oil pressure. Festo Didactic

4 Ex. 3-2 Hydraulic Brakes Discussion Brake bleeding The idea behind bleeding the brakes is to remove all of the air imprisoned in the hydraulic lines and calipers. Air is compressible and its presence results in sluggish braking action. Brake bleeding is accomplished after the installation of the hydraulic brake components or if air has entered the system following a caliper or hose removal. Since air has a lower density than oil, you need to use a bleeding port facing up. When the port is opened, oil pressure forces the air out, as shown in Figure a The yaw brake has two pistons and needs to be bled on each side. Bleed screw Air is forced out of the bleed screw Bleed screw Tube Figure Bleeding the brakes. Brake valve logic Let us analyze how oil pressure is applied to or removed from the brake calipers in the yaw and rotor braking systems. Yaw brake circuit Figure 3-62 depicts the two solenoid valves (SV2 and SV3) controlling the yaw brake. Pressure must be applied to actuate the brake. Therefore, SV2 and SV3 must be in their normal state as shown below. Pressure switch PSB1 is actuated if sufficient pressure is present. The brake is released when SV2 and SV3 are 164 Festo Didactic

5 Ex. 3-2 Hydraulic Brakes Discussion actuated or when there is no pressure in the system and SV2 is deactuated. The standby state is when the brake is isolated from the rest of the circuit and is not influenced by the accumulator pressure. Figure Yaw brake hydraulic circuit (brake applied). Table 3-2. Yaw brake control logic. Valve/Switch Brake 0% Brake 100% Standby SV2 On Off On SV3 On Off Off PSB1 Off On X Rotor brake circuit It is a little bit trickier to understand the circuit around the rotor brake since three solenoid valves and a relief valve are involved. Four cases are to be examined. The first is when SV4, SV5, and SV6 are in their normal state (Figure 3-63). This is when no pressure is applied to the caliper. In this case, the rotor brake is applied by means of the internal spring. Figure Rotor brake hydraulic circuit (brake applied). Festo Didactic

6 Outline Table 3-3. Rotor brake control logic. Valve/Sensor Brake 0% Brake 60% Brake 100% Standby SV4 On Off Off Off SV5 Off On Off Off SV6 On On Off On PSB2 On Off Off X When SV6 is actuated and then SV4 is actuated while SV5 remains in its normal state, pressure is applied against the brake internal spring. If sufficient pressure is present, the brake will disengage completely. The standby state is when the brake is isolated from the rest of the circuit and is not influenced by the accumulator pressure. Finally, once in standby state, if SV5 is actuated, pressure in excess of the pressure relief valve set value is evacuated. Therefore, the brake is only partially applied for soft braking. PROCEDURE OUTLINE The Procedure is divided into the following sections: Accessories needed Basic safety procedure Preparation questions Setting up the nacelle Starting the trainer Playing with valves Pressure at GB1 and GB2. Rotor brake valves. Yaw brake valves. Troubleshooting System shutdown Lockout/tagout Evaluating rotor brake pad thickness Bleeding the rotor brake End of the procedure PROCEDURE Accessories needed For this exercise, you will need the following accessories: Lockout device (hasp) One padlock and one tag per student 1/4 wrench (caliper bleed screw) Clear plastic tubing (to fit the caliper bleed screw) One measuring cup Rags (not included) Gloves (not included) 166 Festo Didactic

7 Basic safety procedure Before using the training system, complete the following checklist: You are wearing safety glasses, safety shoes, and gloves. You are not wearing anything that might get caught such as a tie, jewelry, or loose clothes. If your hair is long, tie it out of the way. The working area is clean and free of oil or water. Preparation questions For the following questions, you need to refer to the hydraulic schematics. 1. If you refer to the hydraulic circuit, what is going to happen if valve SV4 is actuated but valves SV5 and SV6 remain in their normal state? 2. Which valves control the yaw brake? 3. In which position (normal or actuated) must these valves be to release the yaw brake when there is high pressure at GP2? 4. Why does valve SV6 let hydraulic flow go through in normal position? Write your answer in terms of the rotor brake. Setting up the nacelle 5. Make sure the main switch is off and everything is secure inside and around the nacelle. 6. Open the safety panels. Festo Didactic

8 7. Depressurize the accumulator. a Do not forget to return MV1 to its original position. 8. Connect the pressure gauges to ports GB1 and GB2 on the manifold. 9. Close all safety panels. Starting the trainer 10. Notify all the people working around the nacelle that the system is about to be energized and ask your instructor for permission to power the nacelle training system. 11. Turn on the main power switch. Wait for the panel PC to boot and log into Windows. The HMI should start automatically. 12. Press the green (physical) start button under the main switch to start the system. 13. Press Start Trainer in the HMI MAIN screen. 14. Put the trainer in MANUAL mode. 168 Festo Didactic

9 Playing with valves Pressure at GB1 and GB2 15. Start the DEBUG Mode in the Service Hydraulic screen (Figure 3-64). Figure Hydraulic DEBUG mode. The DEBUG Mode in the SERVICE-HYDRAULIC screen disables the alarm caused by opening the safety panels. 16. What pressure is indicated at GB1 and GB2 at this point (no valve should be actuated)? Explain what this means in terms of the respective brake state and the PSP2 pressure value. 17. What is PSB2 pressure according to the HMI screen? Is this value similar to what you read on the GB2 pressure gauge? Festo Didactic

10 Rotor brake valves 18. On the HMI, actuate SV6, then actuate SV4. What is happening with the rotor brake and pressure at GB2 and PSB2? 19. Go to the back side of the nacelle and open the safety panels. Are you able to make the rotor disk turn with your hands? Yes No Are you able to move the rotor brake caliper horizontally with your hands? Yes No The term floating caliper should start to make sense now 20. Stop the hydraulic unit from the HMI. 21. Actuate MV1, wait approximately 10 seconds so that accumulator pressure drops entirely, and deactuate MV1. How is the pressure at GB2 compared to step 18? Why? 22. Use the hand pump to increase pressure at GP2. Check regularly if you are able to rotate the disk by hand. What pressure is needed to release the brake? 23. Go in standby mode (SV4 and SV5 are deactuated, SV6 is actuated). 24. Make the pressure in the accumulator drop by actuating MV1. Observe that the standby mode operates as planned and that the pressure at GB2 remains relatively constant. Deactuate MV Perform soft braking by actuating SV5. Observe that the pressure at GB2 drops to a pressure of bar ( psi), then keeps decreasing slowly. 170 Festo Didactic

11 Next, brake the rotor fully (SV5 deactuated, then SV6 deactuated). Observe that the pressure drops completely at GB Close the safety panels. 27. Start the hydraulic unit from the HMI and wait until it stops by itself. 28. Actuate SV4 (SV5 and SV6 are OFF). What is happening now with the pump, the pressure at GB2, and the rotor brake? 29. Is this what you had in mind at step 1? 30. Deactuate valve SV4. Yaw brake valves 31. Deactuate and reactuate the yaw brake by changing the state of the valves you have identified at steps 2 and 3. Do you hear a sound every time the brake changes state? a You can verify that the yaw brake is removed by manually rotating the nacelle tower where the numbers are printed. Yes No 32. Does the order in which the valves are actuated or deactuated make a difference? Explain why and describe the importance of the standby mode. Troubleshooting 33. Ask your instructor to add a fault to the hydraulic system while you are not watching. Festo Didactic

12 34. Actuate and deactuate the yaw and rotor brakes using buttons on the Service - Hydraulic screen in DEBUG mode. Do you observe something unusual? If so, describe what is happening and the potential cause of the problem. 35. Resolve the issue and tell your instructor what you did. 36. Turn off the DEBUG Mode. System shutdown 37. Exit the HMI by pressing X on the top-right corner of the screen. 38. Press the Windows Start button, select Shut Down, and press OK. Wait for the system to turn off. a You may have to reset alarms before exiting the software. 39. Use the main power switch to turn all system power off. Lockout/tagout For the operations to follow, the nacelle needs to be secured first. 40. Install the lockout hasp in the main switch. Next, install the student padlocks and tags in the hasp. 41. Try to turn on the main switch to verify that the system is electrically isolated. Press the start push-button to test whether the system can be energized. 42. Actuate MV1, wait approximately 10 seconds so that accumulator pressure drops entirely, and deactuate MV1. a At this point, the system can be considered secure. 172 Festo Didactic

13 Evaluating rotor brake pad thickness 43. Position yourself on the back side of the station and open the safety panels to access the rotor brake caliper (Figure 3-65). Figure Rotor brake caliper (top view). 44. Take a closer look at the brake pads. Do they look like they should be replaced? Bleeding the rotor brake As discussed in the DISCUSSION section, brakes need to be bled during installation and whenever air enters the hydraulic system. Here, we will practice the bleeding procedure by checking if air bubbles still come out of the rotor brake line. 45. Install one end of the clear plastic tubing on top of the rotor brake caliper bleed screw. Put the other end of the tubing inside the measuring cup (Figure 3-66). Figure Preparing to bleed the rotor brake. Festo Didactic

14 46. Unscrew the rotor brake caliper bleed screw slowly using the 1/4 wrench. Use the bleed screw on top because air sits on top of the oil. Do not unscrew the bleed screw too much or it will come out of the caliper and generate an oil spill. 47. Manually actuate SV6 (screw in completely) and SV4 (rotate one quarter turn) so that system pressure is sent to the rotor brake caliper. 48. Use the hand pump to increase pressure. Oil should start to flow out relatively quickly (Figure 3-67). Oil coming out of the tubing will accumulate in the measuring cup. Keep GB2 pressure below 0.3 bar (5 psi). a Bleeding pressure must be low to avoid a big spill if the bleed screw is accidentally unscrewed completely. This also ensures that the bleed screw o-ring does not extrude and become sheared off when tightened. Figure Oil flowing out of the rotor brake caliper. 49. Screw the bleed screw once you have established that no more air bubbles are coming out of the caliper. 50. Disconnect the tubing from the bleed screw. 51. Return valves SV6 and SV4 to their normal position. 52. Close the safety panels. End of the procedure 53. Clean the area and, more specifically, the accessories that were used for the bleeding of the rotor brake. 174 Festo Didactic

15 Ex. 3-2 Hydraulic Brakes Conclusion 54. Ask everyone to remove their individual padlock and tag. Next, remove the hasp from the main switch. 55. Test the rotor brake caliper under pressure to make sure there is no leak originating from the rotor bleed screw. b Use the hand pump to increase pressure slowly. CONCLUSION In this exercise, you became familiar with the rotor and yaw brake circuits. You controlled the brakes by changing the state of some valves and you evaluated their pad thickness. Finally, you bled the rotor brake caliper to make sure no air was present. REVIEW QUESTIONS 1. What parts can you find inside a brake caliper? 2. Why do you need to bleed the brakes? 3. What are the differences between the rotor and yaw brake calipers? 4. What is the purpose of the relief valve in the rotor brake circuit? 5. Why do you need to use a port facing up when bleeding brakes? Festo Didactic