Pump and driving motor assembly

BACKGROUND OF THE INVENTION

The invention relates to a pump and driving motor assembly, and in particular to an assembly of this kind wherein the return or compression stroke of the motor piston is effected by a pressure medium supplied from a pressure vessel to a resetting cylinder enclosing a re- 30 setting piston attached to the motor piston. The required pumping capacity of such an assembly may vary within wide limits, for instance in dependence on the load of a hydraulic motor driven by the medium which is compressed by the pump. 35

In the known free piston compressors, the working frequency is only variable within relatively narrow limits. Thus, if the pumping capacity must be variable within wide limits, it is necessary to vary, in addition to the frequency, the pumping capacity for each stroke. 40

The pumping capacity for each stroke may be regulated, for instance in fuel injection pumps, by recirculating a variable portion of the fuel displaced during each stroke to the supply vessel. However, in this case, the efficiency is considerably reduced by flow losses, and the 45 control equipment is rather complicated.

It is the main object of the invention to remove these disadvantages.

SUMMARY OF THE INVENTION

According to the invention, the working frequency is controlled by means of a regulating valve restricting the passage of the pressure medium during a first portion of the return stroke.

In this manner, the working frequency may be con- 55 trolled by simple means within very wide limits, and even between zero and a maximum value, so that the pumping capacity may always be adapted to the requirements without any change of the capacity for each stroke.

Further objects of the invention are to realise a maxi- θο mum efficiency with a simple construction of the assembly and to avoid undesirable phenomena, such as cavitation.

An important factor in the operation of the invention is the time expiring between the end of the forward stroke, and the end of the first portion of the return stroke, 05 during which the flow of the pressure medium is restricted. I have found that it is possible to control the speed of the resetting piston during the first portion of the return stroke from zero to a maximum value, and that the remaining portion of the return stroke is still sufficient ₇θ to impart to the resetting piston the kinetic energy required to compress the combustible mixture in the motor cyclinder to its final pressure during the last portion of the return stroke.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a first embodiment of the assembly according to the invention.

FIG. 2 shows a second, simplified embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, the driving motor comprises a motor cylinder 1, and a plunger-shaped motor piston 2, freely reciprocating within the cylinder 1. A scavenging piston 3, which is integral with the motor piston 2, is displaceable in a scavenging cylinder 4. The cylinder 4 is connected with a suction valve 4a for the scavenging air, and with a scavenging channel 5. The outlet of the motor cylinder is indicated at 6.

The piston 3 is connected with a plunger 7 operating as a pump piston within the pump cylinder 8. The medium to be displaced by the pump is sucked in from a tank 9 through a back pressure valve 10, and pumped into a pressure vessel or hydraulic storage vessel 11 through a back pressure valve 12. Hydraulic devices, such as a hydraulic motor (not shown) may be driven by the compressed medium in the vessel 12.

The plunger 7 is further connected with a plunger 12, operating as a resetting piston in the resetting cylinder 14, and serving to return the pistons 2 and 3 to their original positions after each expansion stroke.

The pressure medium for operating the plunger 13 is taken from a pressure vessel or hydraulic storage vessel 15, which comprises a membrane 16.

The control device for regulating the working frequency of the assembly is inserted in the connecting channel 17 between the pressure vessel 15 and the end of the resetting cylinder 14, and is formed as an adjustable valve 18, which might be indicated as a frequency control valve. In principle, a procedure would be possible wherein the valve 18 would be fully opened during the expansion stroke of the piston 2 in which the piston 13 presses the medium from the cylinder 14 into the pressure vessel 15, then partially closed during the first portion of the compression stroke in order to control the duration of said first portion, and fully opened during the remaining portion of the compression stroke in order to impart the required kinetic energy to the piston 2. However, in the preferred embodiment as shown, the operation has been considerably simplified by providing a separate connecting channel 19 between the pressure vessel and the resetting cylinder, terminating in a gate 20 in the wall of the resetting cylinder which is closed off by the plunger 13 during the first portion of the compression stroke. Thus, the frequency control valve 18 regulates the drive of the plunger 13 during the first portion of the compression stroke, before the gate 20 has been released. The distance covered by the resetting piston during this first portion of the compression stroke has been indicated at e in FIG. 1. After release of the gate 20, the remaining portion of the compression stroke is automatically performed, independentlv of the working frequency, with the full pressure of vessel 15. 1

In order to avoid the necessity of opening the regulating valve 18 during each expansion stroke in order that the medium may be returned to the vessel 15 without an excessive resistance, after the gate 20 has been closed by the plunger 13, an additional connecting channel 21 has been provided between the end of the resetting cylinder 14 and the pressure vessel 15; this channel contains a back pressure valve 21α.

3,606,591

Due to the fact that the number of strokes per time unit may be controlled in a simple maner, the amount of liquid displaced by the pump need never be larger than required, and the efficiency will be substantially constant through the entire capacity range.

FIG. 2 shows a simplified embodiment in which the cylinders 8 and 14 (as shown in FIG. 1) have been combined into a single auxiliary cylinder 24, enclosing a plunger 25 which serves both as a resetting piston and as a pump piston.

The connecting channels 17 and 19 and the regulating valve 18 are substantially the same as in FIG. 1. However, both channels are provided with a back pressure valve 26α, and 26, respectively, in order to prevent the medium from being returned to the vessel 22 during the expansion stroke. The connecting channel 21, which contains the back pressure valve 21α, is now connected with a pressure vessel 23, so that the medium is pressed into this vessel during the expansion stroke. The pressure medium in the vessel 23 is used to drive any desired hy- 20 draulic devices and is returned to the vessel 22 after use. The pressure in the vessel 23 will be usually higher, and never lower than the pressure in the vessel 22.

The assembly according to the invention may be started and stopped in a very simple manner. In the known mo- 25 tor compressors, the engine may be stopped by cutting the fuel supply or by interrupting the connection with the resetting vessel. In both cases, the engine will come to a stand-still in an arbitrary position. The piston must then be manually returned to its initial position, after which 30 the engine may be restarted by means of a separate starting device.

In the assembly according to the invention, the starting procedure is extremely simple, because the engine always stops in the same final position after closure of the reg- 35 ulating valve 18, and may be restarted from this position by re-opening the regulating valve.

The invention is not restricted to the embodiments described hereinbefore, which may be varied and modified in several ways within the scope of the invention. For ⁴⁰instance, the assembly may be constructed in such manner that the pressure medium is applied to the resetting piston with an adjustable delay after the end of the expansion stroke. It is also possible to arrange the regulating valve in a bypass-circuit connecting the spaces before ⁴⁵and behind the resetting piston; in this case, the main connecting channel 19 is always open, but the pressure medium is only effective after the counterpressure on the resetting piston has been relieved by means of the regulating valve. For this purpose the piston surface must be smaller on the backside than on the frontside of the piston.