KTH MMK JH TENTAMEN I HYDRAULIK OCH PNEUMATIK allmän kurs 2006-12-18 kl 09.00 13.00 Svaren skall vara läsligt skrivna och så uppställda att lösningen går att följa. När du börjar på en ny uppgift - tag ett nytt blad! Uppställda ekvationer skall motiveras. Kontrollera frågeställningen så du är säker på att har svarat på den ställda frågan. Är du osäker på hur du skall tolka en uppgift så fråga! Rätt löst uppgift ger 10 poäng. För godkänt i allmänna kursen krävs c:a 32 poäng samtidigt som det erfordras minst 10 poäng på de tre första uppgifterna och minst 10 poäng på de tre sista. Resultatet ser du på mina sidor senast den 12/1. Hjälpmedel: Räknedosa utan databank. 1 Combine following components and symbols and mention their names. a b c d e
f g h i j i ii iii iv v vi vii viii ix x Figure 1 HPak dec 06 Page 2
2 a) Explain the function of the valve in figure 1a. (2p) b) What is a plunger piston cylinder? (1p) c) How can you achieve a variable restriction at end position cushioning (ändlägesdämpning)? (2p) d) How is a screw pump constructed? Which advantages and disadvantages have these pumps? (3p) e) What is the duty of slipper pads (glidskor) in an axial piston pump? How do these work? (2p) 3 a) The lap extent (lappningsgraden) of a valve can vary. Describe how the valve caracteristics are influenced by the lap. (2p) b) Why are big valves pilot controlled? (1p) c) What quality of a hydraulic fluid do you measure by the viscosity index? (1p) d) Notice five things you have to pay attention to by the construction of a hydraulic tank. (2,5p) e) When you mount a clamp ring connection (klämringskoppling) and a cut ring connection (skärringskoppling) you do it in different ways. Which ways? (0,5p) f) Describe how you can use hydraulic accumulators in three different ways. (3p) 4 a) Deduce the formula η vp = 1 C v μ Ψ μω where Ψ = Δp 3 Δp bh Use the formula for the flow trough a clearance Q v = (5p) μ 12l b) Figure 4.1 at page 6 shows the characteristics for some pumps. Determine the volumetric efficiency of the pump PVV2-055 when the shaft speed is 50 r/min and the pressure is 0,5 MPa. (5p) HPak dec 06 Page 3
5 Figure 5.1 shows a hydraulic system to control the speed of a conveyor in a saw mill. The hydraulic motor will be loaded with a constant torque of 500 Nm. The flow control valve is adjusted so that the hydraulic motor speed is 20 r/min. The hydraulic motor is a slow moving radial piston motor with a displacement of 850 cm 3 /rev. It has a hydro mechanical efficiency of 97 % and a volumetric of 92 %. The pressure drop of the directional valve is shown in figure 5.2. The electrical motor is a four-polar induction motor with a speed of 1450 r/min and with a rated power of 22 kw. The pump, direct connected to the motor, is a vane pump with fixed displacement. The displacement is 33 cm 3 /rev and its hydro mechanical efficiency is 95 % and its volumetric is 92 %. The relief valve opens at 14,0 MPa. The pressure drop over the filter is assumed to be 0,1 MPa. a) Determine the total efficiency of the transmission. b) How much better will the efficiency of the transmission be if you by a more expensive piston pump with the volymetric efficiency of 96 % in stead of the vane pump? c) There are at least two possibilities to change the system so the efficiency wills increace and still keeping the function of the system. Indicate one Suggestion. M Last Figure 5.1 Pressure drop [MPa] 5 4 3 2 1 0 0 0,5 1 1,5 2 Q [l/s] Figure 5.2 Pressure drop per passage in the directional valve. HPak dec 06 Page 4
6 Choose cylinder and pumps to a two speed press. The diagram of connections is shown in figure 6.1. Following is demanded of the system: Stroke 120 mm Press distance 10 mm Total cycle time 4 s Press force (max) 300 kn Electrical motor speed 1450 r/min Neglect the losses. Figure 6.1 7 Draw a diagram of a pneumatic system performing following sequence: A+ B+ C+ C- B- A- Cylindrar Cylinder- Kolvstångs- A1 A2 Maxdiameter diameter tryck [mm] [mm] [cm 2 ] [cm 2 ] [MPa] 63 36 31,2 21,0 16 63 45 31,2 15,3 25 80 45 50,3 34,4 16 80 56 50,3 25,6 25 100 56 78,5 53,9 16 100 70 78,5 40,1 25 125 70 123 84,2 16 125 90 123 59,1 25 160 90 201 137 16 160 110 201 106 25 200 110 314 219 16 200 140 314 160 25 Kugghjulspumpar Deplacement Radian- Max- Maxdeplacement tryck varvtal [cm 3 /r] [cm 3 /rad] [MPa] [r/min] 1,2 0,19 21 3000 2,2 0,36 21 3000 3,2 0,51 21 3000 4,3 0,68 21 3000 4,7 0,75 25 2500 5,7 0,91 25 2500 8,3 1,32 22 2500 11,3 1,80 20 2500 16,6 2,64 18 2500 20,2 3,21 20 2800 25,6 4,07 20 2800 33,8 5,38 20 2500 40,2 6,40 18 2200 52,2 8,31 18 2000 HPak dec 06 Page 5
Figure 4.1 HPak dec 06 Page 6
7 Name:... Page... Draw a diagram of a pneumatic system performing following sequence: A+ B+ C+ C- B- A- HPak dec 06 Page 7