Type: HPV375+375
Outline
• The pump unit is composed of 2 variable-capac-ity swash plate-type piston pumps, VC valves, EPC valves and self pressure reducing valves.
CE1 : Front EPC output pressure pick-up port CE2 : Rear EPC output pressure pick-up port CH1 : Front servo actuator pick-up port CH2 : Rear servo actuator pick-up port
CP1 : Front pump discharge pressure pick-up port CP2 : Rear pump discharge pressure pick-up port CP3 : Fan pump discharge pressure pick-up port CPR: Pilot basic pressure pick-up port
CS1 : Front control pressure pick-up port CS2 : Rear control pressure pick-up port P1 : Front discharge port
P2 : Rear discharge port P3 : Fan pump discharge port P4 : Gear pump discharge port
PF : Self pressure reducing valve basic pressure port
PR2 : Pilot basic pressure output port (preceding the inline filter attached to the machine) PR3 : Pilot basic pressure input port (succeeding to the inline filter attached to the machine) PR5 : Pilot basic pressure pick-up port
PR8 : Pilot basic pressure output port (to fan EPC) PR9 : Pilot basic pressure output port (to pilot valve) S1 : Main pump suction port
S3 : Fan pump suction port S4 : Gear pump suction port T1 : Drain port
T2 : Drain plug T3 : Drain plug T4 : Drain plug T5 : Drain plug T6 : Air bleeder T7 : Drain plug T8 : Drain plug T9 : Drain plug T10 : Drain plug T11 : Drain plug T16 : Drain port T17 : Drain plug T18 : Air bleeder 1. Front pump 2. Rear pump 3. VC valve 4. EPC valve
5. Self pressure reducing valve 6. Filter
7. Cooling fan pump 8. PTO lubrication pump
1. Front shaft 2. Cradle 3. Front case 4. Rocker cam 5. Shoe 6. Piston
7. Cylinder block 8. Servo piston
9. Valve plate 10. End cap 11. Rear case 12. Rear shaft 13. Bevel gear 14. lmpeller pump 15. lmpeller shaft 16. lmpeller pinion CS3 : Fan pump control pressure pick-up port
PF1 : Self pressure reducing valve basic pressure output port (from pilot to self pressure reducing valve) PF2 : Self pressure reducing valve basic pressure input port
PR9 : Fan EPC basic pressure input port
PR11: Pilot basic pressure input port (pilot valve back pressure)
Function
• The engine speed and torque are transmitted to the shaft of this pump. Then, this pump converts the speed and torque into oil pressure and dis-charges pressurized oil according to the load.
• It is possible to change the delivery by changing the swash plate angle.
Structure
• Cylinder block (7) is supported to shaft (1) by spline (17).
• Shaft (1) is supported by front and rear bearings (18).
• The end of piston (6) has a spherical hollow and is combined with shoe (5).
• Piston (6) and shoe (5) form a spherical bearing.
• Shoe (5) slides along an elliptic orbit while being kept pressed against plane (A) of rocker cam (4).
• Rocker cam (4) brings high pressure oil at
cylin-• Piston (6) carries out relative movement in the axial direction inside each cylinder chamber of cylinder block (7).
• Cylinder block (7) seals the pressurized oil to valve plate (9) and carries out relative rotation.
• This surface is designed so that the oil pressure balance is maintained at a suitable level.
• The pressurized oil inside each cylinder chamber of cylinder block (7) is sucked in and discharged through valve plate (9).
• Impeller pump (14) and impeller pinion (16) are united by impeller shaft (15) and connected to shaft (1) through bevel gear (13).
• They rotate along with the shaft. Thus, they help supplying the sucked pressurized oil to cylinder block (7) and also help sucking it there by use of centrifugal force.
Operation of pump
• Cylinder block (7) rotates together with shaft (1), and shoe (5) slides on flat surface (A).
• When this happens, rocker cam (4) moves along cylindrical surface (B), so angle (a) between center line (X) of rocker cam (4) and the axial di-rection of cylinder block (7) changes.
• Angle (a) is called the swash plate angle.
• With center line (X) of rocker cam (4) at swash plate angle (a) in relation to the axial direction of cylinder block (7), flat surface (A) acts as a cam in relation to shoe (5).
• In this way, piston (6) slides on the inside of cyl-inder block (7), so a difference between volumes (E) and (F) is created inside cylinder block (7).
• A single piston (6) sucks and discharges the oil by the amount (F) – (E).
• As cylinder block (7) rotates and the volume of chamber (E) becomes smaller, the pressurized oil is discharged.
• On the other hand, the volume of chamber (F) grows larger and, in this process, the oil is suctioned.
• As center line (X) of rocker cam (4) matches the axial direction of cylinder block (7) (swash plate angle = 0), the difference between volumes (E) and (F) inside cylinder block (7) becomes 0.
• Suction and discharge of pressurized oil is not carried out in this state. Namely pumping action is not performed. (Actually, however, the swash plate angle is not set to 0)
Control of delivery
• If the swash plate angle (a) becomes larger, the difference between volumes (E) and (F) be-comes larger and pump delivery (Q) increases.
• Swash plate angle (a) is changed with servo pis-ton (8).
• Servo piston (8) moves in a reciprocal movement according to the signal pressure from the pump controller.
• This linear motion is transmitted to rocker cam (4) through rod (19).
• Rocker cam (4) slides on the cylindrical surface of cradle (2).
• With servo piston (8), the area receiving the pressure is different on the left and the right. The pump discharge pressure (self pressure) (PH) is constantly led to the pressure chamber of the small diameter piston end.
• The pressure chamber of the large diameter pis-ton end is supplied with the VC valve output
• The relationship in the size of pressure (PH) at the small diameter piston end and pressure (PS) at the large diameter piston end, and the ratio be-tween the area receiving the pressure of the small diameter piston and the large diameter pis-ton controls the movement of servo pispis-ton (8).