The invention resides in the field of mechanical engineering or precision engineering and can be applied for example in medical technology.

Fluid pumps have been known for a long time in the most varied of embodiments, having conveyor elements in the form of bladed wheels which convey a fluid in axial or radial direction, and also in the form of piston pumps with or without corresponding valve controls.

A particular field of application comprises the so-called pulsed pumps i.e. those which produce alternately pressures of specific different levels. In particular, it can be necessary to produce alternately high and low pressure. Such an application occurs for example in medical technology with blood circulation assistance since the mode of operation of the heart muscle can be assisted as a result of this function. The drive is also suitable for blood pumps which represent a so-called "complete heart replacement". The heart is thereby completely removed and replaced by such a blood pump. Basically, blood can hence be suctioned in by low pressure and conveyed by high pressure back into the vessels alternately by means of the pump. It is known to produce a function of this type of a blood pump by means of a housing through which blood flows, said housing being delimited by a moveable membrane and being equipped with controllable inflow and outflow valves. The membrane for its part can be connected to a pressure chamber in which high pressure and low pressure is produced alternately.

Such a device is known for example from DE OS 26 19 324. The emphasis of the description there resides however upon a pulse delimiter between a drive pump and the actual blood pump.

A pneumatic drive in the form of a rotational compressor is known from DE 203 07 003 Ul.

DD 264 380 finally discloses a computer control unit of a pump drive by means of a reverse stroke magnet, both the geometric characteristic line, by configuration of the magnets, and also the computer control unit contributing to the desired pressure profile.

Basically, a pulsed heart assistance system is also known from the company Berlin Heart, which has a heart pump with a blood chamber and an air chamber separated from the latter by a multiple membrane, which air chamber is in communication with an operating pump in the form of a piston pump. The blood chamber can be connected to the circulation system of a patient by means of an inlet and an outlet which are both valve-controlled. The alternating pressure levels on the air side of the membrane are produced by means of the operating pump which is connected to the housing of the blood pump via a hose. The problem is thereby produced in particular that the piston of the operating pump must be moved alternately in opposite directions in order to produce high and low pressure in a pressure chamber and that the mechanical loading of the piston drive for the high and low pressure production can be of different magnitudes.

Because of the high required serviceable lives and reliability, it is sensible to design the pump and the pump drive in an optimised way in order to avoid overloading and to ensure a long serviceable life.

The object hence underlying the present invention is to produce a drive device for a piston of a fluid pump which combines high reliability with as low loading of the pump as possible.

The object is achieved according to the invention by the features of patent claim 1.

The pump device according to the invention has a drive device and also a piston which can be actuated in two opposite directions and delimits a first fluid in an operating chamber, and also a motor element for actuating the piston and precisely one energy storage device which absorbs energy exclusively in a single direction of movement of the piston and has at least one energy store which is charged in the course of a piston movement in a first direction of movement and releases its energy during the piston movement in a second, opposite direction in order to assist the piston movement. This means that, when the piston moves in the second direction, no further energy storage device is charged.

The invention can be used advantageously if the piston or the motor element is loaded to a different degree in both directions of movement.

In this case, the energy store can be designed such that it is charged in the course of the piston movement in which a lower pump load occurs and release its energy in the course of the opposite piston movement in which a higher load must be applied, in the sense of assisting the piston movement. For example, the energy store can be charged during a suction movement, i.e. production of low pressure in an operating chamber. The energy store can be charged for example over the entire path of the piston movement or only over a part of the piston movement.

As a result, the piston drive or also the transmission of the actuation movement for both phases of the piston movement can be adapted such that the total loads for the drive are approximated to each other in the different phases. In the ideal case, the piston drive/ the motor element and the drive transmission are loaded almost to the same extent during production of high pressure and low pressure.

As a result, the peak load in the phase in which the piston would be loaded most highly without involvement of the energy store is in addition reduced. This leads, on the one hand, to less wear due to the more uniform loading and, on the other hand, possibly to a saving in energy if for example an electric motor is used as motor element and lower maximum torques are required of the latter than without assistance by the energy store.

The operating chamber can also be designed as bellows or as a rolled membrane, the bellows or the membrane being connected, on the one hand, to a plunger and the bottom of the bellows forming the piston.

The energy store can thereby be designed, on the one hand, such that it stores energy in any form and converts the latter during the piston movement into a force for assisting this movement. For this purpose, the energy can be stored for example in electrical or magnetic form.

The electrical energy can be fed back for example also directly to the motor element in order hence to reduce the necessary external electrical energy supply to the motor element. On the other hand, the energy store can also be constructed mechanically, the energy can be stored mechanically and supplied directly into the kinematic chain of the piston drive.

In this case, this means that the energy store releases its energy during the piston movement in the second direction in which the energy store releases its energy, by independent production of a force driving the piston movement.

This can be achieved particularly advantageously in that the energy store stores energy in mechanical form, in particular in a spring element. Storage in a mechanical element, in particular in a spring element, can be constructed mechanically in a particularly simple manner and operates also with particularly low energy losses since the energy between the charging and discharging of the energy store need not be converted into a different energy form.

A spring element is advantageously constructed and integrated in the drive device such that it engages directly and without diversion to the kinematic chain, in particular to the piston itself.

The spring element can advantageously have a helical spring, a conical spring or a plate spring.

Efficient energy storage is possible in a reliable form in the smallest space by means of such embodiments.

The motor element of the drive device can be configured particularly efficiently in that it has a linear drive. Hence no further energy conversion is required since also the piston can move linearly to and fro. The motor is advantageously connected to the piston by means of a drive rod which actuates the piston in both directions parallel to the longitudinal axis of the drive rod.

The motor element can, for this purpose, have a linearly moveable armature and an extended electrical or magnetic stator. Hence a magnetic or electrical direct drive is provided, which further minimises the losses during conversion of electrical energy into mechanical energy. Furthermore, such a motor is easy to control.

However, it can also be provided that the motor element has a rotational motor and a spindle. The spindle is thereby set in rotation about its longitudinal axis and actuates linearly a threaded nut guided on the latter. By changing the direction of rotation of the spindle, the linear movement of the threaded nut is cyclically reversed. The threaded nut must, in this case, be coupled to the piston in order to drive the linear movement thereof. Also other kinematic combinations are conceivable, such as e.g. a non-rota table spindle coupled to the piston and a rotationally actuated, stationary threaded nut or a non-rota table and stationary threaded nut in combination with a rotationally actuated and axially displaceable spindle connected to the piston, which can be actuated by a torsion-proof, displaceable motor.

In order to save space and to ensure a particularly simple construction, it can be provided according to the invention that the spindle penetrates the actuatable piston.

As energy store or part of the energy store, advantageously a helical spring or conical spring can be disposed in addition coaxially relative to the piston, on the first side of which it is supported and can be clamped between the latter and a fixed abutment, in particular can be compressed. This form of spring element can be integrated particularly easily in the piston guide and corresponding characteristic lines of helical springs or conical springs can be configured within wide ranges so that the corresponding spring elements can be adapted to the purpose of the invention. Also large piston paths can be assisted by means of such spring elements.

The spring elements can finally be subjected both to pressure and tension. Fatigue of conical springs or helical springs can be precluded over a long time.

When using such a spring which is supported directly on the piston and possibly is connected to the piston in a torsion-proof manner and to a stationary stop member, a further mechanical advantage results in addition: the spring can be used to torsion-proof the piston and prevent it being jointly rotated with the spindle. Because of the torsion resistance of the spring about the longitudinal axis thereof, this transmits a resistance to torsion even if it is not absolute. In reality, the spring permits however a certain minimal torsion of the piston, in particular at the reversal points of the movement. Because of the minimal rotational movement of the piston/ torsion vibration of the piston/ spring system, the piston can be prevented from becoming stuck in the axial direction during a momentary stoppage and becoming jammed due to friction. The rotation ensures that the piston remains constantly in the sliding friction range.

In order to guide the piston and to prevent jamming on the piston path, advantageously the piston can be connected to a guide pipe extending coaxially to the latter, said guide pipe being guided mechanically at least on a part of the piston path. The guide pipe can be produced for example in one piece with the piston or can be screwed or welded to the latter. Advantageously, the guide pipe seals the piston with a minimal increase in dead space. The guide pipe can protrude for example into a pressure chamber of the first fluid. The guide pipe can be positioned and configured such that it is guided on the threaded spindle penetrating it or in an external pipe surrounding the guide pipe externally.

The threaded spindle can then protrude for example into the guide pipe if the guide pipe is placed at the position at which the threaded spindle penetrates the piston. In this case, it is important that the guide pipe is connected to the piston in a gas-impermeable or fluid-impermeable manner.

Apart from a drive device of the initially mentioned type, the invention also relates to a pump device for a second fluid which has a first pressure chamber, a second pressure chamber and a moveable, fluid- impermeable intermediate element, the second pressure chamber being able to be subjected to pressure by the piston of an operating pump which can be actuated by means of the described drive device and is with or without intermediate connection of a hose element to the first fluid, and the first pressure chamber being designed to suction in and release a second fluid, in particular blood.

The fluid pump device which can be configured as a blood pump has a first pressure chamber in a rigid housing which is delimited by a moveable intermediate element, for example a membrane, which is moved in the course of pressure changes in a second pressure chamber and hence performs stroke movements. The first pressure chamber is connected for example to a blood circulation of a patient via two connections so that blood is suctioned in when the first pressure chamber is enlarged and blood is expelled when the first pressure chamber is reduced in size. By means of corresponding design of valves at the connections, for example as one-way valves, it is ensured that blood is suctioned in respectively only through one of the connections and is expelled through the respectively other connection. The movement of the intermediate element/ membrane is effected by pressure changes in the second chamber which is connected directly to an operating chamber delimited by the actuatable piston of an operating pump. Hence, by actuation of the piston of the operating pump, the pressure and the volume in the operating chamber delimited by it changes and hence the volume of the second pressure chamber in the blood pump, which results in a corresponding movement of the intermediate element/ membrane.

As fluid in the operating chamber and the second pressure chamber, a biocompatible gas, such as air or nitrogen, can advantageously be used, however basically also a liquid.

Finally, the invention relates to a method for operating a drive device for a piston which can be actuated in two opposite directions, as described above, and has an energy store in the form of a spring element, the operating range of the motor drive being adjusted, with respect to the drive path, according to the desired spring assistance, taking into account the maximum pressure to be produced and the required piston stroke.

The invention relates also to a method for operating a drive device for a piston which can be actuated in two opposite directions, as described above, and has an energy store in the form of a spring element, the sum of the provided energy stores absorbing energy only in a first direction of movement of the piston and releasing this during a movement in the opposite direction.

A spring element which assists the motor drive of the piston naturally has a force-path characteristic which leads to the fact that the spring assistance of the piston drive is of a different degree of strength respectively according to the point on the piston path. In the choice of the operating range of the motor drive on the piston path, this can be taken into account productively. If for example in particular when producing the high pressure, an intensive assistance of the piston drive by the spring is required as for example during operation of a blood pump with small children, then the operating point can be chosen such that the piston is moved alternately to and fro in the region of highest spring tension. If less assistance by the energy store is required, then the movement can be operated in the range of less spring tension, i.e. less charging of the energy store. In this way, the operation of the drive device can be optimised respectively according to the application case without changing anything about the basic principle.

If the absolute movement range of the piston with such an adjustment of the operating point is intended to remain unchanged, then the abutment of the spring can also optionally be displaced, when using a helical or conical spring, for example can be displaced in the axial direction of the piston movement. This can take place for example by means of an adjustment screw.

In the following, the invention is shown and subsequently described in a drawing with reference to an embodiment.

There are thereby shown

Fig. 1 schematically, the application of the invention as a blood pump in a human being,

Fig. 2 the cooperation of a piston pump which has the drive according to the invention, having a membrane pump which acts directly on the blood circulation,

Fig. 3 the piston pump/ operating pump actuated according to the invention, Fig. 4 the force course during actuation of the piston pump without a storage element in an application for actuation of a blood pump,

Fig. 5 the force course to be applied by the drive motor with assistance by an energy store, in this case a helical screw, in order to achieve a force course according to Fig. 4 acting on the piston,

Fig. 6 the force to be applied by the drive motor during operation in the highest pressure range,

Fig. 7 the force effect on the drive piston acting because of the drive according to Fig. 6 and increased by spring assistance and also

Fig. 8 the symmetry of the loading of the drive chain.

Fig. 1 shows schematically firstly the contour of a human being 1 with a membrane pump 2 which is likewise represented schematically, which membrane pump is connected via two cannulae to the blood circulation of the human being 1 and via a pressure line 3 to a fluid pump 4. Pump systems of this type are generally used in humans for assisting circulation and can be implanted or disposed ex corpore. The fluid pump 4 is normally disposed in a stationary manner or transportably outwith the body and requires an energy supply 5, for example by means of a battery.

In order to be able to construct the fluid pump and the battery to be as small as possible, however thereby reliably, as small a construction of the drive as possible is in particular sensible, and also a design which loads the drive as sensibly and uniformly as possible so that the latter need not be overdimensioned for peak loads. Included thereby in the drive are both a motor and the kinematic chain for transmitting drive forces to a piston. Fig. 2 shows the membrane pump 2 and the operating pump/ piston compressor 4 in somewhat more detail, however still schematically. The membrane pump has an inlet 6, characterised by the arrow 7, and also an outlet 8, characterised by the arrow 9, which are connected respectively to blood vessels or to the heart. By means of the membrane pump 2, blood is suctioned into a storage chamber/ first pressure chamber 10 via the inlet 6, which chamber is delimited, on the one hand, by a rigid housing 1 1 of the pump and, on the other hand, by a moveable membrane 12.

The housing 1 1 of the pump can consist for example of a transparent plastic material. The membrane can be configured either to be dimensionally elastic in the shape of bellows or materially elastic, for example made of rubber or a rubber-like material.

The inner walls of the storage chamber 10 can advantageously be coated with a material which prevents or delays coagulation of the blood. This material can also be at least partially incorporated in the housing walls or the membrane.

If the membrane 12 is moved in the direction of the arrow 13, then the storage chamber 10 is enlarged and blood is suctioned in through the inlet 6. For this purpose, the valve 14 opens so that blood can flow in.

The valve 15 which is configured like the valve 14 as a one-way valve closes at the same time so that no blood can be suctioned in through the outlet 8.

The drive of the membrane 12 is effected by pressure change in the drive chamber 16/ second pressure chamber of the membrane pump 2. A movement of the membrane 12 in the direction of the arrow 13 is effected by a pressure reduction in the drive chamber 16 so that a corresponding pressure reduction takes place also in the storage chamber 10/first pressure chamber. A movement of the membrane 12 in the direction of the arrow 17 takes place when the pressure in the drive chamber 16 is increased. This likewise leads to an increase in pressure in the storage chamber 10, which leads to the fact that the automatic return valve 14 closes and the return valve 15 opens towards the outlet 8. Hence, blood can be expelled in the direction of the arrow 9 towards a blood vessel through the outlet 8.

An alternating movement of the membrane 12 hence effects alternately pulsing suction of blood through the inlet 6 and subsequent cyclical expulsion of the blood through the outlet 8.

The drive of the membrane 13 takes place by cyclical pressure changes in the drive chamber/ second pressure chamber 16 by means of the operating pump/fluid pump 4, the operating chamber of which is connected to the membrane pump 2 via a pressure line 3 represented in broken lines.

In the operating pump 4, the pressure changes are effected by movement of a piston 18 in the directions of movement 19, 20. A movement of the piston 18 in the direction of the arrow 20 effects a pressure increase in the drive chamber 16, whilst a movement in the opposite direction 20a effects a reduction in pressure in the drive chamber 16.

Fig. 3 shows in more detail the fluid pump 4 which is configured as a piston compressor. For this purpose, an actuatable piston 18 is provided in a cylinder 19 and sealed displaceably relative to the latter. Within the cylinder 19, an operating chamber 20 is delimited by the piston, in which operating chamber the desired pressure is produced and is connected to the pressure line 3 via a connection 21. The piston 18 is actuated by means of a spindle drive via a threaded spindle 22 which runs in a threaded nut 23 connected to the piston 18. The threaded spindle 22 is connected in a rotationally actuatable manner via a coupling 25 by means of an electric motor 24. Guide bearings 26, 27 are provided for the spindle in a bearing block 28 within the cylinder 19.

The piston 18 is connected in a gas-impermeable manner to a hollow guide pipe 29 sealed at the end thereof. Into the hollow guide pipe 29 which is placed in a gas-impermeable manner on the piston 18 in the region of the threaded nut 23 or is connected in one piece to the latter, the threaded spindle 22 protrudes to different extents according to the adjustment of the piston 18. Hence the threaded spindle 22 can penetrate the piston 18 without a gas-impermeable leadthrough requiring to be formed there.

In addition, the guide pipe can run in a guide 30 and hence prevent jamming of the piston 18.

By rotating the spindle 22, an axial movement of the piston 18 is hence produced, which can be controlled in a pulsating manner by corresponding change in the direction of rotation of the spindle so that high pressure and low pressure can be adjusted alternately in the operating chamber 20.

The piston movement or the drive thereof can be assisted in an operating direction by a helical spring 31. If the helical spring 31 is configured as a pressure spring which is supported on the block 28 and on the piston 18, then the piston movement 18 is assisted during compression in the operating chamber 20. Correspondingly during an expansion in the operating chamber 20 and a movement of the piston 18 in the direction of the arrow 32 for compressing the spring 31 the spindle drive must perform additional work. Since however different requirements exist during application for the circulation assistance during compression and expansion, in particular the loading in the suction phase is less than in the compression phase, the spring can sensibly be used for making symmetrical the requirements on the drive and the mechanical loading of the drive.

This circumstance is explained in more detail with reference to Fig. 4. There, the stroke is plotted on the horizontal axis 33, whilst the force exerted by the piston on the operating chamber 20 is plotted on the vertical axis 34. The zero position of the greatest piston amplitude is designated with 35, in which the piston 18 begins its compression movement.

The positive stroke, in the upper right quadrant, can be equated with a piston movement in the direction of the arrow 42. The movement of the piston in the direction of the arrow 42 can be equated with production of a high pressure whilst applying a positively represented pressure force. The suction or low pressure phase is likewise represented to the right in the lower right quadrant. This corresponds to an increase in the operating chamber volume 20 during movement of the piston in the direction of the arrow 32 in Fig. 3.

During heart assistance of adult humans, typically a pressure of typically 100 mm/ Hg should be produced in the low pressure range, whereas a high pressure must be produced during the high pressure phase up to 300 mm/ Hg. This means that, in the low pressure range 36, for example a force of -37 N is exerted, the value of which is substantially less than the force of 1 12 N in the high pressure region 37 required during production of the high pressure.

In the illustration of the force-path diagram, some pneumatic aspects, such as for example the initial pressure build-up and reduction are not taken into account. A dynamic equilibrium state of the pressure respectively is a prerequisite. It emerges from the diagram of Fig. 4 obviously that the piston must be actuated at different strengths in the various directions of movement, which leads to an asymmetric loading of the motor element or of the force transmission elements. For this reason, the force necessary for the pneumatic pressure build-up and reduction can be superimposed by forces for charging and discharging a force store in order to design the forces acting on the drive and the drive transmission in both directions to be approx. the same size and hence to reduce peak forces.

This situation is illustrated graphically in the diagram of Fig. 5. The stroke applied by the motor drive on the piston is plotted there on the horizontal axis 33, whilst the force to be applied by the motor drive is represented on the vertical axis 34. Added to this force, as a function of the path, is the spring force (reducing to the right) during the compression movement. During the suction movement, the force to be applied to tension the spring must also be subtracted with respect to quantity from the lower force curve in order to obtain the force acting in total on the piston. The force- and path zero point is designated with 35. It results that the forces to be applied in quantity by the motor drive are situated in both phases of movement below the peak load which is achieved without spring assistance in the compression phase.

It becomes evident that the maximum force to be applied in quantity in both directions of movement is 91.8 N, with which this force of 1 12 N to be applied relative to that without a power store is significantly reduced in the indicated example.

Figure 8 shows in addition the maximum load M in quantity, which acts on the drive elements (with the exception of the spring element) in a selected operating range in hatched lines. The operating range can be selected by corresponding selection of an initial stroke of the piston. If the spring and the operating range are chosen to be suitable, then the same maximum loading in quantity is produced for the drive chain without a spring in the compression and in the suction phase.

Figure 6 shows the force course of the drive force applied by the motor in the case where as high a compression pressure as possible is intended to be produced. This is the case for example during operation of a heart assistance system with infants who require a higher pressure in the compression phase.

The drive force of the motor is then maximised in the compression phase and kept constant. In the suction phase, only the lower force required for producing the low pressure is applied.

The spring forces are added to these motor-driven powers so that the diagram of Figure 7 is produced as total force acting on the piston. If the pump is operated with the highest spring compression in the hatched region, then the spring assistance there has maximum effect during the compression and compression forces up to 166.9 N are achieved. The spring assistance reduces with the stroke to the right since the spring is unstressed.

In the production of the low pressure, the tensile force of the motor increases with the tensile movement in order to overcome the increasing spring counter-tension and in addition to maintain the desired low pressure.

Hence the system can be operated in a substantially higher pressure range without exceeding the highest limit of 1 12 N motor force thanks to the spring assistance.

Due to the reduced loading during normal operation of the motor drive, wear and tear to the actuating elements, such as the threaded spindle, the threaded nut, the coupling, the motor and the roller bearings, is hence reduced by the invention, or the achievable pressure can be increased during a given permissible maximum loading.