Abstract: The variable of the hydraulic pump is realized by changing the working volume of the pump chamber. Taking CY-type piston pump as an example, the angle γ between the normal of the swash plate and the rotary axis of the cylinder is changed, that is, Working volume, when the maximum γ angle, the maximum working volume of the plunger chamber, to achieve full displacement oil supply, when the γ angle is 0, the working volume of the plunger chamber is 0, then the hydraulic pump does not supply oil. If the γ angle is negative, then the hydraulic pump reverse fuel. There are many ways to change the gamma angle, each with its own control features. This article details two ways to control the gamma angle. 1 sequence valve and valve control plunger cylinder on the control of the reset spring (structure diagram shown in Figure 1) Figure 1 The first control structure Schematic diagram of work: Figure 2 for the cylinder axis of rotation, 3 for the Hydraulic pump swashplate. The swash plate manipulating arm 4 and the variable plunger 8 stay in the original position under the action of the return spring 5. At this time, the swash plate inclination γ is the largest, and the hydraulic pump is supplied with the full displacement. When the system pressure is slightly higher than the set pressure of the sequence valve 1, the sequence valve 1 is opened, and at the same time, the directional control valve 7 is changed over, the system pressure oil enters the plunger cylinder 6, the variable plunger 8 overcomes the force of the return spring 5, Change the inclination angle of the swash plate, hydraulic pump to achieve variable oil supply. If the system pressure increases again, the pressure in the variable displacement piston cylinder 6 will increase again to make the γ angle close to 0 (some leakages, the γ angle can not be 0), the hydraulic pump will maintain a certain pressure but will not supply oil to the system, that is Unloading of the hydraulic pump under pressure (since N = p × Q, N → 0 when Q → 0). After the system pressure is reduced, the variable plunger 8 resumes its original state immediately. In the figure, the directional control valve 7 is mainly designed for increasing the response speed of the variable plunger 8 when the system uses a large amount of oil. This control is constant pressure variable control, its characteristics shown in Figure 2. Figure 2 constant pressure variable control characteristic map In the figure, AB is the full displacement oil supply section, BC is the variable section, C is the unloading point under the pressure condition, also called standby pressure. Variable pressure range (pB-pC) is very small, suitable for multiple actuators can work at the same time, the pressure within 90% of the use of pressure required full-fuel supply system. 2 system direct effect of pressure oil cylinder piston multi-stage spring control (structure diagram shown in Figure 3) Figure 3 the second control structure diagram in Figure 3 for the cylinder axis of rotation, 4 for the hydraulic pump swash plate . Structural principle and the first way is roughly the same, mainly to remove the sequence valve and the valve, the system pressure directly into the variable piston cylinder 1. In addition, the spring is changed to a multi-stage spring set 5. If the multi-stage spring set 5 is an ordinary cylindrical spring, the deformation of the conventional cylindrical spring is inversely proportional to the system pressure, that is, the swash plate inclination γ (displacement of the hydraulic pump) linearly inversely proportional to the system pressure. In order to make the displacement and pressure of the hydraulic pump approximate to the function of Q = 1 / p × N, the ordinary cylindrical bomb is changed into two or more springs and connected in series, the stiffness of each spring should have a certain gap, and a Level than the level of a spring of the smallest stiffness. In addition to the last level, all levels of spring design a limit block. Figure 10,8,6, respectively, one, two, three springs, 9,7 for one, two spring limit block. When the system pressure is applied to the variable plunger 11, the three springs are deformed at the same time. However, the deformation of the first-stage spring 10 is the smallest due to its minimum rigidity. At this time, the tilt angle γ of the swash plate and the system pressure exhibit a linear change similar to that of the first- , The slope is steeper. When the system pressure is higher, the primary spring 10 is pressed to the limit height of the limit block 9, the primary spring 10 is no longer deformed, and the secondary and tertiary springs continue to be compressed. Likewise, the secondary spring 8 has a stiffness less than that of the tertiary spring 6 so that the swash plate inclination γ and the system pressure are similar to those of the secondary spring 8. System pressure increases again, you can get basically follow the three-stage spring 6 displacement pressure characteristics, see Figure 4A-B, BC, CD. Figure 4 Displacement pressure characteristics If the spring stiffness at all levels and the stopper limit height properly designed, A, B, C, D together can be a very similar to Q, p reciprocal curves of each other. This curve is called the constant power curve, also called the pressure compensation curve, that is, when the displacement is reduced (increased), it is compensated by the increase (decrease) pressure. Like the constant pressure variable, the hydraulic pump can be under pressure Unloading, suitable for baler hydraulic system, the hydraulic power can be more reasonable use, reducing the installed capacity of the prime mover.
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