WO1992002730A1

WO1992002730A1 - Free-piston engine

Info

Publication number: WO1992002730A1
Application number: PCT/EP1991/001460
Authority: WO
Inventors: Gerhard Brandl
Original assignee: Gerhard Brandl
Priority date: 1990-08-02
Filing date: 1991-08-02
Publication date: 1992-02-20
Also published as: DE4024591A1

Abstract

A free-piston engine has one or more pistons (1) which are preferably rigidly connected to hydraulic pistons (2) and which move freely in cylinders along the longitudinal axis. The rear face of the piston (1) is used to convey the combustion air and the piston movement is induced and controlled by electronically actuated hydraulic valves (8).

Description

Free piston engine

The invention relates to a free-piston engine. Such motors are known for example from the following publications: DE 26 48 958 C2, DE-PS 12 60 860; DE 23 07 760 B2; DE 22 17 194 B2; DE-AS 14 80 101.

The invention aims to provide a free-piston engine that has a high efficiency with a simple structure. To achieve this object, the invention provides the measures mentioned in the claims.

The invention is described below with reference to the drawing. The drawing shows:

1 shows a longitudinal section through a first embodiment of a free-piston engine;

2 shows a section through a second exemplary embodiment of an exemplary embodiment of a free-piston engine; and

3 shows the section A-A in Fig. 2nd

The free-piston engine has one or more pistons 1, with which oil pistons 2 are rigidly connected, see FIG. 1, or two pistons 1 working against each other, see FIG. 2. The rear side of the pistons 1 is used to convey the combustion air via the inlet slot 4, overflow channel 5 and outlet slot 6 used.

The pistons 1 are set in a reciprocating movement by corresponding actuation of hydraulic valves 8. In the hydraulic valves 8, valve spools 9, which are excited by electrically operated pilot valves 10, execute an oscillating movement. The oscillation of the pistons 1 results from the oscillating movement of the valve slide 9. A microprocessor 12 switches the pilot valves 10 and thus ensures the starting and stabilization of the oscillation of the pistons 1.

Before starting, the pistons 1 are held at the bottom dead center by means of a spring 7. The pistons 1 are now accelerated towards the top dead center by pressure oil, which acts on the oil pistons 2. The time period of the pressure oil effect is chosen so that the pistons 1 reach that speed which is required to effect the desired compression of the combustion air.

To open the pressure oil connection 13, the pilot valves 10 are actuated electrically by the microprocessor 12. As a result, the valve spool 9 is accelerated with pressure oil. They swing out of the rest position and open the pressure oil connection 13. Then the valve slides 9 swing back due to the effect of pressure oil on the rear side. They are braked with a pressure oil effect on the front and remain at rest.

The opening time of the pressure oil connection 13 is determined by a corresponding choice of the control times of the pilot valves 10 and the choice of the reversal point of the valve spool 9. If the reversal point of the valve slide 9 is just behind the opening point of the pressure oil connection 13, the opening time is short. If the reversal point is further behind, the opening time is longer.

The ignition now takes place and the pistons 1 are accelerated by the combustion pressure in the direction of bottom dead center. The piston speed is measured with one or more sensors 11. Then the valve slide 9 open the pressure oil connection 13 and thereby brake the piston 1. The opening time and the opening time of the pressure oil connection 13 are calculated from the piston speed by the microprocessor 12 according to stored curve functions. By selecting from various curve functions, air pressure, oil pressure, temperature and other influences are taken into account.

The opening time is chosen so that the pistons 1 reverse their movement near the bottom dead center. The opening time is chosen so that the pistons 1, after the reversal of movement, reach the speed required for the next compression.

The opening time and duration of the pressure oil connection 13 are maintained by corresponding switching times of the pilot valves 10 switched by the microprocessor 12. The oscillating movement of the valve slide 9 is controlled according to the scheme described during the starting process.

By arranging several hydraulic valves 8 operating in parallel per piston 1, the switching speed of the control is increased.

With pistons 1 working in opposite directions, the movement is synchronized in that a piston is taken as the guide piston and the control times of the guided piston are corrected accordingly.

To switch off the engine, the pistons 1 are stopped at the bottom dead center by corresponding valve timing.

Since the energy from the combustion pressure is greater than the compression energy, oil is pumped during this process.

Although the above explanations give the expert a clear lesson on technical action, the following should also be emphasized. To accelerate the piston (s) in the direction of top dead center in order to initiate the starting process, the pilot valves 10 are actuated electrically by the microprocessor 12. One (upper) pilot valve 10 opens the pressure oil connection 13. The pressure oil acts on the top (front) of the valve spool (s) 9 and accelerates it. He (she) swings (swing) from the rest position and opens (open) the pressure oil connection 13. As a result, pressure oil acts on the piston (s) 1, accelerates it (them) towards top dead center and initiates the starting process.

Now the one (s) (upper) pilot valve (s) 10 close. The valve spool 9 now continues to move by swing.

At a pre-calculated time, the other (lower) pilot valve (s) 10 open (open) on the basis of a signal from the microprocessor 12. As a result, pressure oil now acts on the underside (rear) of the (the) Valve spool (s) 9 and slows down its movement. When this has come to a standstill, the other (lower) pilot valve 10 remains open.

The oil pressure acting on the underside (rear) of the valve spool (s) 9 now accelerates the valve spool (s) 9 in the opposite direction and begins to swing back. Then the lower (other) pilot valve 10 closes and the valve spool 9 continues to move with momentum.

After a certain time, the valve slide 9 has moved back so far that the pressure oil connection 13 is closed again. Now no more pressure oil acts on the piston 1 and it moves with momentum to top dead center, where it Combustion air compresses and where the ignition of the first work cycle takes place.

The time in which the pressure oil connection 13 was open was calculated so that the piston 1 has reached such a speed that the desired compression occurs at top dead center.

In order to maintain this opening time of the pressure oil connection 13, the valve slide 9 was braked at the right time by opening the lower (other) pilot valve (10) and then accelerated in the opposite direction.

The correct opening time of the lower (other) pilot valve 10 was calculated by the microprocessor 12 and the pilot valve 10 was actuated electrically by the microprocessor.

Now the valve slide 9 is braked by reopening the upper (one) pilot valve 10 and remains in the upper rest position. The valve spool 9 is held in the rest position by an oil pressure difference between the top (front side) and underside (rear).

Claims

Claims:

1. Free-piston engine in which one or more pistons (1), which are preferably rigidly connected to hydraulic pistons (2), are freely movable in cylinders along the longitudinal axis, characterized in that the rear side of the pistons (1) for conveying the combustion air is used and the piston movement of electronically controlled hydraulic valves (8) is started and controlled.

2. Free piston engine according to claim 1, characterized in that two pistons work against each other.

3. Free piston engine according to one or more of the preceding claims, characterized in that for each piston (1) several hydraulic valves (8) work in parallel, whereby the response time of the hydraulic control is reduced.

4. Free-piston engine according to one or more of the preceding claims, characterized in that the Kolbenge¬ speed is measured by one or more sensors (11) and then the start and duration of action of the high pressure oil on the hydraulic pistons (2) is dimensioned so that the Piston (1) in the vicinity of the lower hydraulic piston (2) is dimensioned such that the pistons (1) reverse their movement near the bottom dead center and are then accelerated so that the desired compression is produced.

5. Free piston engine according to one or more of the preceding claims, characterized in that the valve slide (9) accelerates the initiation of the control process from the rest position towards the opening of the high-pressure connection (13), then braked until the movement is reversed and accelerated in the opposite direction and then until it stops in the Rest position are braked again.

6. Free-piston engine according to claim 5, characterized in that the start and duration of the high-pressure oil on the hydraulic pistons (2) are determined by appropriate choice of the acceleration and deceleration times and thus the point of reversal of the valve slide (9).

7. Free-piston engine according to one or more of the preceding claims, characterized in that the electronic calculation of the valve timing takes place as a function of the piston speed according to stored curve functions, the corresponding one of several stored curve functions being selected according to oil pressure, air pressure, temperature and other influences.

8. Free-piston engine according to one or more of the preceding claims, characterized in that the synchronization of the two opposed pistons (1) is carried out electronically by correcting the control times, the control times of the guided piston being corrected in accordance with the actual movement of the guide piston.