WO1994016452A1

WO1994016452A1 - Apparatus for accelerating the action of a periodically operating hydraulic reversing valve

Info

Publication number: WO1994016452A1
Application number: PCT/FI1994/000016
Authority: WO
Inventors: Reijo Mononen
Original assignee: Sampower Oy
Priority date: 1993-01-14
Filing date: 1994-01-13
Publication date: 1994-07-21
Also published as: AU5835094A; FI930146A; FI94567B; FI930146A0; FI94567C

Abstract

The invention relates to an apparatus for accelerating the action of a periodically operating hydraulic reversing valve (1), the reciprocating action of the reversing valve being achieved by means of a solenoid coil (2), the current passing therethrough being repeatedly switched on and off at a certain frequency by means of a semiconductor switch (3) connected in series with the solenoid coil. Parallel to the solenoid coil (2) is connected a safety diode (4) having a barrier voltage, said barrier voltage being so high that the self-induction current of the solenoid coil passes through the safety diode (4) in such a manner that a voltage spike produced by said switch-off across the semiconductor switch (3) remains by a safe margin below the maximum resisting ability (UCEmax) of the semiconductor switch (3). This arrangement is capable of performing e.g. the hydraulic actuation of a free-piston engine at a starting frequency which is even higher than the operating frequency.

Description

Apparatus for accelerating the action of a periodically operating hydraulic reversing valve.

The present invention relates to an apparatus for accelerating the action of a periodically operating hydraulic reversing valve, the reciprocating action of the reversing valve being achieved by means of a solenoid coil, the current passing therethrough being repeatedly switched on and off at a certain frequency by means of a semiconductor switch connected in series with the solenoid coil.

It is prior known to connect parallel to a solenoid coil a diode for facilitating passage of the self-induction current of the solenoid coil in order not to produce in the switch-off operation a voltage spike which destroys the semiconductor switch used for control. However, this passage of self-induction current decelerates substantial¬ ly the action of a reversing valve, since a reversing valve is not capable of reversing its position until the current has become sufficiently lower, whereby the force of a solenoid pulling the valve in one direction exceeds the remaining force of the first solenoid. When it is desired to control the reciprocating action of a valve at a high speed, the forces of solenoids are acting in directions opposite to each other whereby the reversal of the position of the valves becomes unreliable and/or the reversing frequency of the position of the valve remains low.

An object of the invention is to provide an apparatus for substantially accelerating the action of a reversing valve in view of making the valve operable in a hydraulic actuating circuit included in a free-piston engine. This object is achieved on the basis of the characterizing features set forth in the annexed claim 1.

When parallel to a solenoid coil or a semiconductor switch is connected a safety diode with a barrier voltage, a so- called transzorb safety diode, producing a barrier voltage which is near the limit of the voltage resisting ability of the semiconductor switch (yet distinctly lower), the following benefits are achieved:

- eliminating the unnecessarily long-lasting passage of self-induction current in the inductance of a solenoid coil caused by a normal diode and substantially decelerating the action

- preventing effectively a breakdown in a valve- controlling semiconductor switch, since the safety diode is conductive that part of the time when the voltage spike exceeds the UCEmax-resisting ability of the semiconductor switch, such as a transistor

- a commercially available compact component can be used for the short-time handling of extremely high pulse outputs (e.g. 1 ms/1.5 kW) .

One exemplary embodiment of the invention will now be described with reference made to the accompanying draing, in which

fig. 1 shows a hydraulic actuating circuit for a free- piston engine, including a reversing valve accelerated by means of an apparatus of the invention;

fig. 2 shows an apparatus of the invention for accelerating the action of a reversing valve (an alternative configuration is shown with dash lines) , and fig. 3 shows the UCE-voltage of a switching transistor as a function of a control pulse.

Fig. 1 illustrates a hydraulic actuating circuit for a free-piston engine, described in detail in the Applicant's Patent publication US-5, 123,245. The position of a reversing valve 1 is reversed by delivering a current pulse alternately to solenoid coils 2. This is effected by bringing a semiconductor switch, such as a transistor 3, by means of a control circuit 13 periodically to a conductive and non-conductive state. The control circuit 13 produces at a desired frequency the control pulses required for this purpose. In the embodiment shown in fig. 1 , a periodic control is used for delivering hydraulic pressure from a pressure accumulator 5 alternately into cylinder chambers 16 and 17 for setting a piston 15 in reciprocating motion at a frequency equalling the position-reversing frequency of valve 1.

To the opposite ends of a piston rod 18 are connected the pistons of a free-piston engine, which should be provided with a sufficient striking frequency at the time of starting the engine.

When a piston-cylinder unit 12 is operated by using the reciprocating control action of reversing valve 1 , one-way pressure valves 8 and 9 are brought to a shut-off position by means of a valve 6, located between pressure valves 8, 9 and a load 14.

In order to control the action a reversing valve 11 at a sufficiently high speed for reliably starting an engine, parallel to the solenoid coils 2 or switch 3 of the valve is connected a safety diode 4 having a barrier voltage. When switch 3 switches off the current in solenoid 2, the passage of the self-induction current of solenoid 2 only continues for a very short moment, determined in accordance with the barrier voltage value of safety diode 4. The discharge of energy charged in a magnetic field carried out by means of the self-induction current preferably commences with a voltage, which is below the UCE-resisting ability of switching transistor 3 by a suitable margin. If the transistor 3 has a UCE-resisting ability of e.g. 80 V, the switch-on of the current through safety diode 4 may occur at 68 V.

When safety diode 4 is connected parallel to solenoid coil 2, the self-induction current of solenoid coil 2 travels through safety diode 4 only when a voltage spike produced by the switch-off on the collector of switch 3 exceeds the operating voltage by the barrier voltage of a safety diode. When safety diode 4 is in parallel with switch 3, the voltage spike is cut off by the barrier voltage of said safety diode. In both cases, the voltage spike remains by a safe margin below the maximum resisting ability UCEmax of switch 3 and yet the magnetic field energy charged in coil 2 will be discharged as quickly as possible.

Safety diodes 4 are commercially available components, which are capable of withstanding extremely high pulse outputs for short periods. Above a certain barrier voltage value, said safety diode 4 can be conductive in both directions.

The reciprocating action of a reversing valve acxcelerated according to the invention can take e.g. 30 ms. Thus, for example, a free-piston engine can be actuated at a starting frequency which is even higher than the normal operating frequency. Hence, the idling of an engine is unnecessary since the starting is always reliable and involves no delay.

Claims

1. An apparatus for accelerating the action of a periodically operating hydraulic reversing valve (1), the reciprocating action of the reversing valve being achieved by means of a solenoid coil (2), the current passing therethrough being repeatedly switched on and off at a certain frequency by means of a semiconductor switch (3) connected in series with the solenoid coil, c h a r a c - t e r i z e d in that, in view of increasing the frequency of periodic action performed by the valve (1), parallel to the solenoid coil (2) or the semiconductor switch (3) is conventionally connected a safety diode (4) having a barrier voltage, said barrier voltage being so high that the self-induction current of the solenoid coil passes through the safety diode (4) in such a manner that a voltage spike produced by said switch-off between the main current electrodes of the semiconductor switch (3) remains by a safe margin below the maximum resisting ability (UCEmax) of the semiconductor switch (3), and that said reversing valve (1) is included in a hydraulic actuating circuit for a free-piston engine between a pressure accumulator (5) and a hydraulic piston-cylinder unit (12).

2. An apparatus as set forth in claim 1 , c h a r a c - t e r i z e d in that, during the reciprocating control action of the reversing valve (1), one-way pressure valves (8, 9) fitted between said piston-cylinder unit (12) and a load (14) are brought to a shut-off position by means of a valve (6), located between said pressure valves (8, 9) and the load (14) .