Reciprocating compressor

Abstract

In a reciprocating compressor with delivery rate control the actuation device (3) for the valve unloader (2) of the suction valve (1) to be held open comprises as drive an electric motor (5), whose driven element (6) in conjunction with the non-rotating lifting element (10) of the valve unloader (2) and the rolling elements (8) arranged in between forma ball screw drive. This results in a small-dimensioned, precisely to be regulated actuation device (3) with high actuating forces and with high motion dynamic.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The invention relates to a reciprocating compressor with capacity control control, comprising a valve unloader arranged at at least one automatically acting suction valve of the compressor, said valve unloader holding open at least one sealing element of the suction valve over a portion of the compressor's cycle by means of an electrically operated actuation device, as well as a method for controlling the capacity of such a reciprocating compressor.[0003]2. The Prior Art[0004]To control the capacity of reciprocating compressors, preferably running at a constant rotational speed, one frequently resorts to the so-called reverse flow control, in which at least one suction valve per cylinder is kept open over a certain area of the compression stroke. The drag forces exerted by the the gas pushed back through the held-open suction valve close the sealing element of the respective suction valve after overcoming a certain port...

AI Technical Summary

Benefits of technology

[0009]Particularly advantageous in this connection is a further embodiment of the invention, according to which the driven element of the electric motor in conjunction with the non-rotating lifting element and the rolling elements arranged in between form a ball screw drive. Such drives are known and in use in the most diverse contexts as nearly friction-free linear drives, and make it possible to exert relatively extensive control on the actuating force and dynamic by converting a number of revolutions of the electric motor—limited only by length and incline—into the resulting linear motion.

[0010]Another preferred embodiment of the invention comprises a simpler design, but a smaller diversity of possible variations, according to which the driven element of the electric motor in conjunction with the non-rotating lifting element and the rolling elements arranged in between form an inclined ramp drive permitting only a limited angular rotation. This allows only for a portion of the electric motor's revolution to be used to generate the linear motion, however with significantly lower design cost and also with the possibility of using cylinders, truncated cones or tons instead of balls as rolling elements, which may make sense with higher actuating forces.

[0011]In a further preferred embodiment of the invention the electric motor is developed as a brushless direct current motor comprising surface-mounted bandaged permanent magnets, which allows for a high dynamic with small construction. It is particularly preferred in this context to develop the electric motor with a hollow-shaft rotor, with the nut of the ball screw drive integrated, which minimizes the inertia of the rotor or of the rotary drive overall.

[0014]To accelerate and / or brake the actuation device's movement additional spring elements may be provided, allowing for the relief of stress on the electric motor drive with appropriate adjusting.

[0015]In a further preferred embodiment of the invention switching elements for dynamic braking and for temporary storage and reuse of the electric energy recovered therefrom may be provided in the electric drive of the electric motor. The energy may preferably be stored temporarily in capacitors, during the process of which the generated and stored current may be used either for the next actuation process at the same valve or at a different suction valve of the compressor. This way, the energy consumption to actuate the valve unloader is significantly reduced and, simultaneously, less lost heat is generated also within the system, thereby reducing the thermal stress and avoiding cooling problems in the actuation device.

[0016]A further preferred embodiment of the invention, according to which the current unloading force is adjusted to the progress of the reverse flow force, also serves to reduce unnecessary heating of the actuation device. While the suction valve is kept open, the level of the reverse flow force depends on the current piston speed, which for example is derived from a crankshaft angle sensor. The motor current for generating the necessary hold-open force may then be adjusted accordingly.

Problems solved by technology

The greater this counteracting force is, the later the respective suction valve in the compression stroke closes, resulting in the reduction of the capacity.

Furthermore, reciprocating compressors with an electrically operated reverse flow control of the initially mentioned type have also been known for a very long time.

Due to the—in part—very high reverse flow forces acting upon the sealing element of the suction valve large solenoids with a correspondingly large power consumption are required.

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