WO2002011969A1

WO2002011969A1 - Injection unit for a plastic injection molding machine

Info

Publication number: WO2002011969A1
Application number: PCT/EP2001/008443
Authority: WO
Inventors: Jörg Dantlgraber
Original assignee: Bosch Rexroth Ag
Priority date: 2000-08-08
Filing date: 2001-07-21
Publication date: 2002-02-14
Also published as: DE10135443A1

Abstract

The invention relates to an injection unit for a plastic injection molding machine, comprising an endless screw which can be driven via a drive mechanism in a rotating manner for plastification of the material to be injected, and an electric motor that includes an element that is stationarily mounted on the frame and an output element that can be displaced linearly with respect thereto and via which the endless screw is axially displaced for injection of the plastic into a mold. In known injection units the output element of the electric motor is disposed in the power train between the drive element and the endless screw, and the power that can be output by the electric motor via the output element is limited. The aim of the invention is therefore to improve the known injection units in such a manner that only a relatively small electric motor is required for injecting the plastic material with the desired injection pressure into the mold and for producing the desired dwell pressure. To this end, the drive element is disposed in the power train between the electric motor and the endless screw and introduces into the drive element upstream of the electric motor, when viewed from the endless screw, a torque for rotating the endless screw, and a power transmission device is mounted between the output element of the electric motor and the drive element.

Description

description

Injection unit for a plastic injection molding machine

The invention relates to an injection unit for a plastic injection molding machine, which has the features from the preamble of claim 1.

Such an injection unit is known from US-A 4,895,505. Here two electric motors are used to bring about the different movements of the screw. The first electric motor is an electric rotary motor which is coupled via a sliding joint having a spline shaft and this can drive the screw in rotation ^• for plasticizing plastic. There is a second electric motor that can move the screw straight for injecting plastic into a mold. This second electric motor is an electric linear motor with a linearly movable output part, which lies in the power flow between the spline shaft and the worm and is aligned with the electric rotary motor.

An injection unit with the features from the preamble of claim 1 is also known from DE 43 44 335 C2. There, two electric motors of the same size, which are designed as hollow shaft motors, are arranged one behind the other in alignment with the axis of the screw. The worm is firmly connected to a movement spindle which is guided in a spindle nut. The screw joint between the movement spindle and the spindle nut contains balls as rolling elements. The spindle nut forms the hollow shaft of the second electric motor, which, seen from the worm, is located in front of the first electric motor. The movement spindle can be regarded as a linearly movable output part of the second electric motor. The hollow shaft of the first electric motor engages with a wedge pin located in the axis of the movement spindle in a wedge recess of the movement spindle, so that the wedge pin and movement spindle del are rotatably connected to each other, but the movement spindle can be moved axially relative to the wedge pin.

When plasticizing, the first electric motor drives the screw at a certain speed via the movement spindle and the wedge pin. The second electric motor rotates the spindle nut at a speed that differs from the speed of the rear electric motor by a small amount. For example, the front electric motor can turn slightly slower than the rear electric motor. The speed difference determines the speed at which the screw moves back. The speed difference is controlled so that a certain dynamic pressure builds up and is maintained in the screw space into which the plasticized plastic material is conveyed. To inject the plastic material into the mold, the screw must be moved forward. For this purpose, the front electric motor continues to turn the spindle nut, while the rear electric motor is energized in such a way that it prevents the moving spindle from rotating via the wedge pin.

In the known injection units, an electric motor is used not only for the rotary drive of the screw during the plasticizing of plastic, but also for the linear movement of the screw during the injection of plastic into a mold. Be this latter electric motor now an electric linear motor or an electric rotary motor, the force that can be directly exerted directly via the linearly movable output part of this second electric motor is only limited. When using a rotary motor, the rotary movement of a rotor is normally converted into the straight-line movement of the output part by means of a screw drive that can only be loaded to a limited extent, primarily via a ball screw drive. The force that can be exerted by an electric linear motor is in any case small in relation to the size.

The invention is therefore based on the objective of further developing an injection unit which has the features from the preamble of patent claim 1 in such a way that a relatively small electric motor is sufficient to carry the plastic material with it inject the desired injection pressure into the mold and also be able to reach the desired pressure level when repressing.

The desired goal is achieved in that in an injection unit with the features from the preamble of claim 1 according to the characterizing part of this claim, the drive part in the power flow between the electric motor and the screw, so that a torque for rotating the screw, from the screw viewed from, is introduced into the drive part before the electric motor, and that a device for power transmission is arranged between the output part of the second electric motor and the drive part. In an injection unit according to the invention, a device for power transmission is assigned to the electric motor, so that a relatively small force exerted by the output part is sufficient to move the screw axially with a high resistance. The transmission of a rotary movement to the screw is not impaired by the device for force transmission. Because according to the invention, the drive part is between the electric motor and the screw. The torque required to turn the screw is thus, viewed from the screw, introduced into the drive part in front of the electric motor and in front of the device for power transmission.

Advantageous refinements of an injection unit according to the invention can be found in the subclaims.

In the preferred embodiment according to claim 2, two electric motors are also used in an injection unit according to the invention in order to drive the screw in a rotating manner or to move it axially.

In an injection unit according to the invention, too, it is favorable to design the second electric motor as an electric linear motor, which is simple and compact in construction. However, electric linear motors are still relatively expensive and, under certain circumstances, are still too weak if the size is still acceptable. Then according to claim 4, the electric motor for the method the screw can also be an electric rotary motor with a rotating part, the rotational movement of which is converted into a straight-line movement of the output part via a screw drive. A movement of a part in a certain direction, z. B. the locomotion of a spindle driven in rotation with a fixed spindle nut, also referred to as rectilinear, if this locomotion is superimposed on a rotation of the part about its own axis.

The electric motor for moving the screw is advantageously arranged laterally next to the screw and drive part, so that the injection unit can be relatively short and compact. With regard to the coupling of parts lying in the power flow from the electric motor to the screw, it appears particularly favorable if, according to claim 7, the output part of the electric motor and the drive part are each moved axially in opposite directions, the device for force transmission effecting the reversal of direction.

A rotating movement of parts of the device for power transmission can be impossible or undesirable. Therefore, a rotary joint is provided between the drive part and the device for force transmission, which is designed as an axial roller bearing according to claim 8, so that high axial forces can be transmitted.

According to claim 9, the device for power transmission comprises a pivotable lever about an axis of rotation, the introduction of force between the output part of the electric motor and the lever occurs at a substantially greater distance from the axis of rotation than the introduction of force between the lever and the drive element. You then have an injection unit that has no components with a hydraulic fluid. However, a rigid lever limits the flexibility in machine design. There is greater freedom of design and the mechanical structure becomes easier if, according to claim 12, the device for power transmission is a hydraulic device. Each textbook on physics or specifically on hydraulics describes how hydraulically a large force can be generated with a small force. A hydraulic device for power transmission has an input piston and an output piston, each of which closes off a pressure chamber filled with a pressure fluid and which differ from one another in the size of their effective areas delimiting the respective pressure chamber. The two pressure chambers are fluidly connected to one another. The input piston has the smaller effective area and the output piston has the larger effective area. A small force on the input piston therefore generates a large force on the output piston. The input piston, which is moved for the injection of plastic and for the corresponding movement of the screw in the sense of reducing the pressure space adjoining it, is mechanically coupled to the output part of the second electric motor and the output piston is mechanically coupled to the drive part. A hydraulic power converter is a self-contained system without a hydraulic pump and pressure medium reservoir.

A hydraulic power converter of the type described has the following advantages in particular:

It has a very good efficiency.

It is low-noise compared to hydraulic power transmission with a hydraulic pump because there are no reversing processes. The wear is low, since there are only low relative speeds compared to a hydraulic pump.

Operation with water as the hydraulic fluid is easily possible because no hydraulic pump is used which requires a fluid with good lubricating properties. Due to the higher elasticity of a hydraulic fluid compared to a metal, high-frequency vibrations (shocks) are dampened and the service life of the mechanics (rack, screw drive, etc.) is extended. A modular structure is possible because different desired speeds of an output piston can be obtained by using different numbers of identical input pistons.

According to claim 13, the output piston and the input piston are each designed as differential pistons and, on the side remote from the first pressure chamber, each delimit a second pressure chamber with an annular, second active surface, the two second pressure chambers being fluidly connected to one another. Then the electric motor can also brake and retract the worm. If the size ratio between the second effective areas is the same as the size ratio between the first effective areas of the input piston and the output piston, the total volume of the two second pressure spaces remains constant and no measures for volume compensation are necessary.

For an exact dosage of the plastic mass pressed into the mold, it is advantageous that a speed profile is followed as precisely as possible during the injection process with the screw. For this, it is favorable if the drive system has a certain rigidity even when using a hydraulic device for power transmission. This can be achieved in the manner specified in claim 15. According to this patent claim, the output piston is designed as a differential piston which, on the side remote from the first pressure chamber, defines a second pressure chamber with an annular, second active surface, which is fluidly connected to a third pressure chamber. There is also a further electric motor, from which a piston immersed in the third pressure chamber can be moved and from which a counterpressure acting at the outlet piston against the pressure in the first pressure chambers can thus be built up in the third and second pressure chambers.

The claims 17 to 19 contain advantageous developments with regard to the arrangement of the first electric motor and the transmission of the torque generated by it to the drive part for the screw. If the first Electric motor according to claim 18 has a rotating hollow shaft through which the drive part extends and with which the drive part is primarily coupled via a spline, so the first electric motor can be arranged in alignment with the axis of the worm. A gearbox is not necessary. The worm is then driven by the first electric motor in a space-saving and quiet manner. However, a special electric motor is required, which is expensive. It could be more cost-effective to arrange an electric motor available at a lower price to the side of the drive part and to drive the drive part via a transmission.

In order to ensure a constant quality of the injection molded parts, the various movement processes on the injection unit of a plastic injection molding machine usually take place according to predetermined speed profiles. Electric motors controlled mainly by frequency converters are therefore used as electrical drive sources. Frequency converters are still relatively expensive today. Therefore, it is provided according to claim 20 that the electric motor for moving the screw is an electric rotary motor and the screw for injecting plastic into the mold can move axially via a first switchable coupling and can rotate for plasticizing plastic via a second switchable coupling. Only one electric motor and only one frequency converter are then required, so that the injection unit is inexpensive.

According to claim 21, a belt transmission with a flat belt is preferably used for rotatingly driving the worm. Such a gearbox is low in price because pulleys for a flat belt can be easily manufactured. Such a belt transmission is also very quiet.

A dynamic pressure desired when plasticizing, when the electric motor drives the screw with the first and the second clutch disengaged, advantageously according to claim 23, by a defined actuation of a brake or by a defined control of an electrical accumulation pressure motor set, the brake or the dynamic pressure motor opposing a backward movement of the screw to build up the dynamic pressure necessary resistance.

It should be pointed out here that the use of a belt drive with a flat belt can be advantageous regardless of the design of the injection unit for rotating the screw and other elements of a plastic injection molding machine to be driven. However, such a gearbox appears particularly favorable for the worm drive, since plasticizing does not depend on the exact adherence to a certain speed of the worm, which is therefore not disadvantageous for belt drives with flat belts that have their own slip between belts and pulleys. The back pressure to be maintained in front of the screw can be maintained by the second electric motor, the brake or the back pressure motor regardless of the speed of the screw.

In a configuration according to claim 24, a screw drive is provided with two mutually engaging drive elements, one of which can be driven in rotation by the first electric motor. One of the two screw elements is arranged between the device for power transmission and the worm. Thus, on the one hand, an axial force can be exerted on the screw via the screw drive from the first electric motor and, on the other hand, via the force converter from the second electric motor, the thread and any engagement bodies of the screw drive that may be present not being loaded by the force exerted via the force converter. The additional screw drive is particularly advantageous if the force intensifier is a hydraulic force intensifier. With the additional screw drive, it is possible to follow the actual value profile of force and / or speed very precisely the setpoint profile according to which the screw is to be moved, since the mechanical power transmission is stiffer than that via the hydraulic force converter. Several exemplary embodiments of an injection unit according to the invention are shown schematically in the drawings. The invention will now be explained in more detail with reference to the figures of these drawings.

Show it

1 shows the first exemplary embodiment, in which a first electric motor is coupled directly to the drive part via a thrust joint, and a second electric motor designed as a linear motor acts on the drive part via a hydraulic device for power transmission, the pistons of which are designed as plungers.

Figure 2 shows the second embodiment, in which, in contrast to the first embodiment, the pistons of the hydraulic device for power transmission are designed as differential pistons, Figure 3 shows the third embodiment, which differs from that according to Figure 2 in that only the output piston of the device for

Power transmission is designed as a differential piston and can be pressurized against the direction of movement during injection via a piston movable by a third electric motor. 4 shows the fourth exemplary embodiment, in which a first electric motor drives the drive element located to the side of it via a gear transmission and a second electric motor designed as a rotary motor has a spindle as an output part, FIG. 5 shows the fifth exemplary embodiment, which differs from that according to FIG. 4, that the first electric motor drives the drive part via a belt transmission, and

6 shows the sixth embodiment, which differs from that according to FIG. 4 in that a single electric motor designed as a rotary motor both drives the screw in a rotating manner and moves axially, FIG. 7 shows the seventh embodiment, which differs from that according to FIG. 6 in that the electric motor does not move the screw axially via a screw drive, but via a rack and pinion drive, 8 shows the eighth exemplary embodiment, in which the device for power transmission is a lever,

9 shows the ninth and last exemplary embodiment, in which the worm is rotatable by a first electric motor and jointly displaceable by the first electric motor via a screw drive and axially displaceable by a second electric motor via a further screw drive and a hydraulic force booster arranged downstream thereof

Figure 10 shows schematically a complete sequence of movements of the further screw drive during the working cycle.

According to FIGS. 1 to 3, a screw 10 is rotatable and axially movable in a plasticizing and injection cylinder 11. At one end of the cylinder 11 there is a nozzle 12, via which plasticized plastic, which is located in front of the end of the screw 10 facing the nozzle, is pressed into a mold by moving the screw 10 in the direction of the nozzle. The screw is turned for plasticizing. The plasticizing process begins in a position of the screw close to the nozzle. By rotating the screw, plastic is conveyed into the space between the nozzle and the screw, the screw moving away from the nozzle while maintaining a desired dynamic pressure.

The worm 10 is a component of a component 9, which is usually multi-part and can be rotated and moved axially in its entirety, to which a rod 13 adjoining the worm and which emerges from the cylinder 11 belongs. The rod 13 is followed as a drive part for the rotary movement of the screw by a spline shaft 14, which is provided with axially running keyways 15 and is connected via a rod 16 to a washer 17 located at the end of the component.

The spline shaft 14 can be driven in rotation by a first electric motor 20. This is designed as a hollow shaft motor with a hollow shaft 21 which has splines 22 on the inside which engage in the splines 15 of the spline shaft 14. The splines 15 in the spline shaft 14 and the splines 22 in the hollow shaft 21 between the elec- Tromotor 20 and the component 9 with worm 10 a thrust joint is formed, which allows a linear movement in the direction of the axis 23 of the component 9 between the spline shaft 14 and the hollow shaft 21. A housing 24 of the electric motor 20, which receives a stator with windings 25, is arranged fixed to the frame. The hollow shaft 21, which carries the rotor 26, is rotatably mounted in the housing 24 via two roller bearings 27, which can absorb both radial and axial forces. The electric motor 20 has the sole function of rotating the screw 10 for plasticizing plastic.

A second electric motor 30 is used to control the axial movement of the screw 10 along the axis 23. This second electric motor 30 is an electric linear motor with a stator 31 and with a linearly movable secondary part 32. Electric linear motors as well as electric rotary motors are generally known, so that the structure of the motor 30 need not be discussed in more detail here. The electric motor 30 is arranged on the frame of a plastic injection molding machine in such a way that its axis 33 is at a distance from the axis 23 of the component 9 and the electric motor 20 and that its stator 31 is viewed in the direction of the axes 23 and 33, approximately at the level of the Electric motor 20 is located.

If it is not intended to be excessively large, the electric linear motor 30 can only exert a limited force with which the necessary injection pressure could not be generated if the secondary part 32 were to act directly on the component 9.

In the power chain between the secondary part 32 of the electric motor 20 and the component 9, a device 40 for power transmission is therefore inserted according to the invention, which is designed as a hydraulic power converter in the exemplary embodiments under consideration according to FIGS. 1 to 3. In the schematic illustration according to the figures mentioned, this consists of a one-piece housing 41 with two circular-cylindrical pressure spaces 42 and 43, which are fluidly connected to one another at one end via a channel 44. The pressure chamber 42 has a smaller cross section and is longer than the pressure chamber 43 and is aligned with the axis 33 of the electric motor 30. The pressure chamber 43, on the other hand, is aligned with the axis 23 of the component 9. In the pressure chamber 42 an input piston is axially movable, which in the embodiments according to FIGS. 1 and 3 as a plunger 45, which is directly on the secondary part 32 of the electric motor 30 is fastened, and in the embodiment according to FIG. 2 is designed as a differential piston 46, which is fastened to the secondary part 32 via a piston rod 47. An output piston is axially movable in the pressure chamber 43, which is designed as a plunger 48 in the embodiment according to FIG. 1 and as a differential piston 49 with a piston rod 50 in the embodiments according to FIGS. 2 and 3.

Outside the pressure chamber 43, the plunger 48 (FIG. 1) or the piston rod 50 carries a bearing flange 51 which, in the embodiment according to FIG. 1, faces the disk 17 of the component 9 on one side, while in the embodiments according to FIGS. 2 and 3 it holds the disk 17 embraces. Between the flange 51 and the disk 17 there are balls 52 as rolling elements. Together with the disk 17 and the flange 51, these form an axial roller bearing 53 between the component 9 and the output piston 48 or 49. Due to this axial roller bearing 53, the component 9 and the output pistons 48 and 49 can be rotated slightly against each other. In addition, axial forces can be transmitted between the component 9 and the output piston. In this case, an axial force can only be transmitted in one direction from the output piston in the embodiment according to FIG. In contrast, in the embodiments according to FIGS. 2 and 3 it can be transmitted in two opposite directions.

An input piston 45 or 46 has an active surface 55 which axially delimits the pressure chamber 42 and which corresponds to the cross section of the pressure chamber 42. The effective area 56 of the output piston 48 or 49 delimiting the pressure space 43 is equal to the cross section of the pressure space 43 and thus larger than the effective area 55 of an input piston.

On the side facing away from the pressure chamber 42, the differential piston 46 delimits an annular second pressure chamber 57. The differential piston also delimits 49 on the side facing away from the pressure chamber 43 an annular second pressure chamber 58. In the embodiment according to FIG. 2, the two second pressure chambers 57 and 58 are fluidly connected to one another via a channel 59. The diameters of the two piston rods 47 and 50 are matched to one another in such a way that during the movements of the pistons 46 and 49, during which the piston 46 covers a larger axial distance than the piston 49, the volume change of the pressure chamber 57 is equal is equal to the change in volume of the pressure chamber 58.

In the embodiment according to FIG. 3, the annular second pressure chamber 58 is at

Output piston 49 is fluidly connected via a channel 64 to a third pressure chamber 65, which is also formed in the housing 41 and into which a plunger 66 is immersed. This is attached to the secondary part 67 of a second electric linear motor 70 which, like the linear motor 30, is arranged on the side of the electric motor 20 and whose axis 68 runs parallel to the axes 23 and 33. The linear motor 70 is weaker than the linear motor 30. The effective area of the plunger 66 facing the third pressure chamber 65 is smaller than the annular effective area of the piston 49 facing the second pressure chamber 58, so that between the secondary part 67 of the electric motor 70 and the piston 49 also one Power transmission takes place.

In operation, the screw 10 is driven by the first electric motor 20 via the spline shaft 14 for plasticizing plastic. Plastic material is thereby conveyed into the space between the nozzle 12 and the end of the screw. The screw and with it the entire component 9 and the output piston 48 or 49 of the hydraulic pressure booster 40 are loaded backwards in the direction of arrow A by the dynamic pressure building up in the room. A certain height or a certain height profile is desired for the dynamic pressure. For this purpose, the second electric motor 30 is acted upon by such a current that an electrical force acting in the direction of arrow A is exerted on the secondary part 32 and thus on the input pistons 45 and 46 of the hydraulic force converter 40. In the pressure rooms 42 and 43 thus a pressure given by the electrical force and the active surface 55 of the input piston, which in turn generates a larger force determining the dynamic pressure on the active surface 56 of the output piston. By detecting the pressures in the pressure spaces 42, 43 and 58, 65 and controlling the electric motors 30 and 70 accordingly, a desired dynamic pressure can be maintained very precisely. When plasticizing, the screw and the output piston 48 or 49 are moved in the direction of arrow A and the input piston 45 or 46 against the direction of arrow A.

If enough plastic is plasticized, the electric motor 20 is stopped. The current flowing through the electric motor 30 is increased to such an extent that the secondary part 32 and the pistons 45 and 46 move to the right in the direction of the arrow A. The piston displaces pressure fluid from the pressure chamber 42 via the channel 44 into the pressure chamber 43. As a result, the output piston 48 or 49 of the force booster 40 and with it the component 9 together with the screw 10 are moved to the left against the direction of the arrow A. For this movement, a certain force must be applied by the pistons 48 and 49, respectively. The force to be applied by the second electric motor 30 is smaller by a factor which is equal to the ratio of the size of the active surface 56 to the size of the active surface 55. The distance traveled by the input piston 45 or 46 is greater than the path of the output piston 48 or 49 by a factor equal to the reciprocal ratio. A desired injection pressure can be precisely maintained by measuring the pressure in the pressure chambers of the hydraulic power converter.

In the embodiment according to FIG. 2, it is possible due to the design of the input piston 46 and output piston 49 as a differential piston, to brake the screw 10 with the aid of the second electric motor 30 and to retract it in the direction of the arrow A.

In the embodiment according to FIG. 3, with the aid of the third electric motor 70, a counterpressure can be generated in the pressure chamber 58 during the injection process, which counter pressure acts in the pressure chamber 43 from the second electric motor 30 Pressure acts on the piston 49. Of course, this means that the pressure for moving the screw must be higher in the pressure chamber 43 than otherwise without a back pressure, given otherwise the same conditions. The advantage of a clamping of the piston 49 achieved by the back pressure is that the drive system has a greater rigidity and the speed of the screw can be better controlled. In addition to braking the screw, the third electric motor 70 of the third exemplary embodiment can also be used to move it back against the direction of arrow A.

In the embodiment according to FIG. 4, the screw located within a plasticizing cylinder 11 is in turn part of a rotatably drivable and axially displaceable component 9 which, as in the embodiments according to FIGS. 1 to 3, comprises a rod 13 and a spline shaft 14 with splines 15. To the side of the spline shaft, an electric standard motor 71 with speed control is arranged as the first electric motor, which carries on its shaft a pinion 72 which meshes with a gear wheel 73 with a larger diameter on the spline shaft 14. This engages with splines 22 in the splines 15 of the spline 14. Thus, the spline shaft 14 is on the one hand non-rotatably coupled to the gear 73, but on the other hand can be axially displaced against the axially stationary gear. The worm can thus be driven to rotate independently of its axial position by the electric motor 71.

The second electric motor of the exemplary embodiment according to FIG. 4 is now an electric rotary motor 75 with a rotating hollow shaft 76, which is internally provided with a trapezoidal thread over a certain length. The position of the electric motor 75 to the side of the component 9 and the orientation of the motor axis 33 are the same as the electric motor 30 from FIGS. 1 to 3. A spindle 77 projects into the hollow shaft 76 as the output part of the electric motor 75, which is secured against rotation and with an external thread engages in the internal thread of the hollow shaft 76. When the hollow shaft 76 rotates, the spindle 77 moves along the axis 33. In the exemplary embodiment according to FIG. 4, a hydraulic force intensifier 40 is inserted between the spindle 77 and the spline shaft 14, which has an input piston designed as a differential piston 46 and fastened to the spindle 77 via a piston rod 47 and an output piston designed as a differential piston 49. In contrast to the embodiments according to FIGS. 2 and 3, the piston rod 50 of the differential piston 49 is now fastened to the spline shaft 14. When the electric motor 71 drives the spline, the piston 49 also rotates. The pressure chamber 42 is located on one side of the piston 46 and the pressure chamber 57 on the other side. The piston 49 borders the pressure chamber 43, which is fluidly connected to the pressure chamber 42, and the pressure chamber 58, which is connected to the pressure chamber 57 is fluidly connected. In this respect, the force intensifier according to FIG. 4 is the same as that according to FIG. 2. However, in FIG. 4 it is indicated schematically that the pistons 46 and 49 and the adjacent pressure chambers are also located in two separate cylindrical housings 41a and 41b and that the corresponding ones Pressure spaces can be connected to one another by channels 44 and 59 designed as pipes or flexible lines.

The embodiment according to FIG. 5 represents a variant of the embodiment according to FIG. 4 with regard to the rotary drive of the spline shaft 14. Namely, the two gear wheels 72 and 73 according to FIG. 4 are by two pulleys 78 and 79 and by a flat belt 80 wound around the pulleys replaced. The small pulley 78 sits on the shaft of the electric motor 71, the large pulley 79 on the spline shaft 14, so that the rotation of the electric motor 71 and the torque are reduced by the transmission according to FIG. 5 as well as by the gear transmission 72, 73 according to FIG elevated. However, a belt transmission is quieter and less expensive than a gear transmission. Any slip that may occur between the flat belt and the pulleys is no longer harmful to the plasticizing process or can be compensated for by regulating the speed of the electric motor. The functioning of the embodiment according to FIG. 4 and the variant according to FIG. 5 is the same as that according to FIG. 2, so that a reference to the corresponding part of the description is sufficient here.

In the two embodiments according to FIGS. 6 and 7, as in the embodiment according to FIG. 4, the screw located within a plasticizing cylinder 11 is in turn part of a rotatably drivable and axially displaceable component 9, which comprises a rod 13 and a spline shaft 14 with splines 15. On the spline shaft 14 sits the gear 73 which engages with splines 22 in the splines 15 of the spline shaft 14. Thus, the spline 14 is on the one hand non-rotatably coupled to the gear 73, but on the other hand can be axially displaced against the axially stationary gear 73. As with the embodiment according to FIG. 4, the worm can thus be driven to rotate independently of its axial position via the gear 73.

In contrast to the exemplary embodiment according to FIG. 4, the worm can be driven in rotation by the gear 73 not by a separate electric motor, but by the electric motor, from which it can also be moved axially. As in the embodiment according to FIG. 4, this electric motor is an electric rotary motor 75. The position of the electric motor 75 to the side of the component 9 and the orientation of the motor axis 33 are the same as in the embodiment according to FIG. 4.

In the exemplary embodiment according to FIG. 6, the electric motor 75 has a rotating hollow shaft 76 which, however, is smooth on the inside and is only hollow so that the threaded spindle 77, which now forms a screw drive together with an additional spindle nut 91, can be immersed in a constructional length. The spindle 77 is in turn secured against twisting. The spindle nut 91, however, can be driven as an output element of a clutch 92 via this and the hollow shaft 76 of the electric motor 75 rotating. The input element of the clutch 92 forms a clutch disc 93 which is axially displaceable but non-rotatably on the hollow shaft 76 near the end of the hollow shaft at which the threaded spindle protrudes. The spindle nut 91 is on one Side of the clutch plate 93 in front of the end of the hollow shaft and engages there in the threaded spindle 77. The screw can be moved axially via the threaded spindle 77.

On the other side of the clutch disc 93, a gear 94 is axially fixed but rotatably mounted on the hollow shaft 76, which gear is the output element of a second clutch 95, which has the same disk 93 as the input element 93 as the clutch 92 or a second disk 93. The gear 94 is located exactly at the level of the gear 73, viewed in the direction of the axes 23 and 33. The two gear wheels 73 and 94 are coupled to one another via a toothed belt 96. The diameter of the gear 94 is larger than that of the gear 73, so that when the gear 94 is driven, the speed of this gear is translated into a higher speed of the gear 73.

In the exemplary embodiment according to FIG. 7, the electric motor 75 has a full motor shaft 97, by means of which the two different movements of the worm can be brought about, as with the hollow shaft 76 via switching clutches 92 and 95. The input element of the two clutches 92 and 95 is in turn a clutch disc 93, which is axially displaceable but non-rotatably close to one end of the motor shaft 97. The output element of the clutch 95 is in turn a gear 94 which is coupled to the gear 73 via the toothed belt 96. The output element of the clutch 92 is now a further gear 98, which is rotatably mounted on a bearing journal of the motor shaft 97 and engages in a toothed rack 99 running perpendicular to the motor shaft 97, via which the worm can be moved axially. The rack and pinion drive consisting of the gear 98 and the rack 99 of the embodiment according to FIG. 7 and the screw drive consisting of the spindle nut 91 and the threaded spindle 77 of the embodiment according to FIG. 6 correspond.

Between the threaded spindle 77 or the toothed rack 99 and the spline shaft 14 there is also a hydraulic one in the exemplary embodiments according to FIGS. 6 and 7 4, which has an input piston designed as a differential piston 46 and attached to the spindle 77 via a piston rod 47 and an output piston designed as a differential piston 49. The pressure chamber 42 is located on one side of the piston 46 and the pressure chamber 57 on the other side. The piston 49 borders the pressure chamber 43, which is fluidly connected to the pressure chamber 42, and the pressure chamber 58, which is connected to the pressure chamber 57 is fluidly connected. A comparison of the two exemplary embodiments according to FIGS. 6 and 7 shows that the hydrostatic power transmission with the power booster 40 brings with it a high degree of flexibility in the arrangement of individual components, since the two components 41a and 41b of the power booster can in principle be arranged in any manner relative to one another.

In order to plasticize plastic granules, the clutch 95 is actuated in the exemplary embodiments according to FIGS. 6 and 7 and the electric motor 75 is driven to rotate in one direction. The gear 94 is driven via the clutch disc 93 and the worm is rotated via the toothed belt 96 and the gear 73. This feeds plastic material in front of the end of the screw. There is a dynamic pressure which leads to a backward movement of the screw and with it of the piston 49 in the sense of a reduction in the pressure space 43. Hydraulic fluid is displaced from the pressure chamber 43 via the line 44 into the pressure chamber 42 and the piston 46 including the threaded spindle 77 or rack 99 is thereby displaced. This happens when the clutch 92 is open. Without further measures, the dynamic pressure would be undefined. In order to be able to regulate a desired dynamic pressure, in the two exemplary embodiments according to FIGS. 6 and 7 the output element of the clutch 92, that is to say the spindle nut 91 or the gear 98, can be braked in a defined manner by a brake 100, so that the output element 91 or 98 can only be turned against resistance. This resistance can be varied by braking to different extents in order to obtain the desired dynamic pressure. The dynamic pressure can be detected, for example, by measuring the pressure prevailing in the pressure spaces 43 and 42. Instead of a brake 100, a (small) electric dynamic pressure motor can also be used, from which a torque is exerted on the spindle nut 91 or on the gear 98.

To inject plastic into the mold, clutch 95 is open and clutch 92 is actuated. The electric motor 75 is driven to rotate in one direction such that the threaded spindle moves the piston rod 47 into the cylinder housing 41a. The piston 46 displaces pressure fluid from the pressure chamber 42 via the line 44 into the pressure chamber 43. As a result, the output piston 49 of the force booster 40 and with it the component 9 together with the screw 10, in the view according to FIGS. 6 and 7 moved to the left. For this movement a certain force must be applied by the piston 49. The force to be applied by the electric motor 75 is smaller by a factor which is equal to the ratio of the size of the active surfaces of the two pistons 49 and 46. The path covered by the input piston 45 or 46 is greater than the path of the output piston 49 by a factor equal to the reciprocal ratio. Pressure detection in one of the pressure chambers 42 and 43 of the hydraulic force booster can precisely maintain a desired injection pressure.

As a variant of the two exemplary embodiments according to FIGS. 6 and 7, a drive device is conceivable in which the clutch 92 is replaced by a continuously adjustable clutch, two input elements then being present for the two clutches. A dynamic pressure could then be set during the plasticizing by a corresponding actuation of the clutch 92. For this purpose, the electric motor 75 then rotates for plasticizing in a direction opposite to the direction of rotation of the spindle nut 91 or the gear 98 when the threaded spindle 77 or the rack 99 is retracted.

In the exemplary embodiment according to FIG. 8, a component 9 with worm 10, rod 13 and spline shaft 14 can be driven in rotation by an electric motor 20 having a hollow shaft 21, as in the embodiments according to FIGS. 1 to 3. The second electric motor is in turn an electric linear motor 30 with a secondary part 32 that can be moved along an axis 33.

The device for power transmission is now a two-armed lever 85 with a. long lever arm 86 and with a short lever arm 87. The axis of rotation 88 of the lever 85 is perpendicular to the plane spanned by the two axes 23 and 33. Their distance from the axis 33 is about 3.5 times greater than their distance from the axis 23. The component 9 is supported with the spline shaft 14 via an intermediate piece 89, which is both in the plane spanned by the two axes 23 and 33 opposite the Spline 14 and pivotable relative to the lever 85, from the short lever arm 87. The secondary part 32 of the electric motor 30 is supported on the long lever arm 86 via an identical pivotable intermediate piece 89. The intermediate piece 89 between the spline shaft 14 and the lever 85 is mounted so that the spline shaft can rotate without the intermediate piece 89 also rotating.

In a central position of the worm 10 between the two end points of its axial displacement, the two intermediate pieces 89 lie in the axes 23 and 33. Their points of attack on the lever 85, which are diametrically opposite with respect to the axis of rotation 88, are on a perpendicular to the axis 23 and 33 running line.

To plasticize plastic material, the electric motor 20 rotates the screw 10, which moves back in the direction of the arrow A and the lever 85 is pivoted clockwise in the view according to FIG. The position of the force transmission points between the intermediate pieces 89 and the lever 85 changes with respect to the axes 23 and 33. This change is compensated for by the pivotability of the intermediate pieces 89. The secondary part 32 of the electric motor 30 migrates backwards in the direction of the arrow A. The dynamic pressure desired during the plasticizing is obtained by a corresponding energization of the electric motor 30. For injecting plastic material into a mold, the electric motor 30 is supplied with more current, so that the secondary part 32 moves in the direction of arrow A to the right and, via the lever 85, the screw 10 is moved to the left against the arrow A. Because of the leverage of approximately 3.5, the force acting on the worm is 3.5 times greater than the force exerted by the electric motor 30.

According to FIG. 9, a plastic injection molding machine, not shown in its entirety, has an injection unit 110 with a housing 111, on which the plasticizing cylinder 11 is arranged. On the housing 111, an injection mechanism is rotatably and axially displaceably mounted, which comprises the screw 10, which is located essentially within the plasticizing cylinder 11. A conical end of the plasticizing cylinder 11 facing an injection mold (not shown) is designed as an injection nozzle 112. Outside the plasticizing cylinder 11, the spline shaft 14 adjoins the worm 10 after a one-way clutch 113 and is provided with axially extending wedges and grooves. This is followed by a threaded spindle 114, which has a ball screw thread and on the free end of which a disk 115 is attached. This is part of a ball bearing 116. The threaded spindle is a drive element of a screw drive and is in engagement with a spindle nut 117, which is the second drive element, via balls. The spindle nut 117 is supported axially against the direction of movement of the screw 10 during injection via an axial bearing 118 on the housing 111. It is freely rotatable on the threaded spindle and can be blocked against rotation relative to the housing 111 by a brake 119

The spline shaft 14 is surrounded by the gear 73, which is rotatably mounted axially stationary on the machine frame 146 and engages with the splines and grooves of the spline shaft 14 with splines and grooves on its inner diameter. The gear 73 is coupled via a toothed belt to the pinion 72 seated on the motor shaft of an electric motor 71. The screw 10 and the spline shaft 14 of the injection mechanism can thus be driven in rotation by the electric motor 71, which is mounted on the housing 111 or on the machine frame 146. This The drive serves to plasticize plastic granulate and to convey the plasticized mass into the space inside the plasticizing cylinder 11 between the end of the screw 10 and the nozzle 112. For plasticizing, the electric motor 71 rotates the spline shaft 14 in such a direction that the Rotation is transferred to the worm 10 via the freewheel 113.

The electric motor 71 not only serves to rotate the screw 10, but is also used to axially move the screw together with the second electric motor 75 to inject plastic into the mold. For this purpose, the screw drive with the threaded spindle 114 and with the spindle nut 117 is provided. The electric motor 71 rotates in one direction for plasticizing and in the opposite direction for injection. So that the screw does not rotate when injecting, the freewheel 113 is inserted between the latter and the spline shaft 14.

The cylinder 128 of a piston-cylinder unit 130 and the cylinder 129 of a piston-cylinder unit 131 are fastened to the housing 111 of the injection unit 110. The piston-cylinder unit 130 is aligned with its axis with the axis of the worm 10, the spline 14 and the threaded spindle 114 and has a differential piston 132 with a piston rod 133, which has a disk 134 at its free end with a disk 115 of the threaded spindle 114 axially projecting collar. The disks 115 and 134 are parts of the roller bearing 116, which ensures the rotatability of the threaded spindle 114 relative to the piston rod 133 and which can transmit axial forces between the piston rod 130 and the threaded spindle 114 in both directions. The differential piston 132 divides the interior of the cylinder 128 into an annular cylinder space 135 on the piston rod side and into a circular cylindrical cylinder space 136 away from the piston rod.

The piston-cylinder unit 131 has a synchronous piston 137, which is provided on both sides with piston rods 138 of the same thickness, and thus the inside of the cylinder 129 in two annular cylinder spaces 139 and 140 that have the same cross section divides. The two piston rods 138 are fastened to the machine frame 146 in a manner not shown. The piston 137 thus remains at rest with respect to the machine frame 146.

The drive source for the linear movement of the injection unit for applying the nozzle 112 to the mold and for moving the nozzle away from the mold, as well as together with the electric motor 71 for the axial movement of the injection mechanism, is a second rotating electric motor 75, which is not closer below the injection unit 110 in FIG is attached to the machine frame 146 in such a way that its axis runs parallel to the axis of the injection mechanism and thus parallel to the direction of the linear movements of the injection unit and the injection mechanism. On the motor shaft 147, a pinion 148 is secured against rotation, which is coupled via a toothed belt 149 to an externally toothed spindle nut 150 which is axially fixed on the machine frame 146. The spindle nut 150 is provided with a ball screw thread on the inside. A threaded spindle 151 passes through it and is provided with an external thread designed as a ball screw thread. Balls 152 engage in the internal thread of the spindle nut 150 and in the external thread of the threaded spindle 151, so that these two parts are connected to one another via a screw joint. The threaded spindle 151 is guided in a straight line in a manner not shown in detail, so it cannot rotate, so that when the spindle nut 150 rotates, it moves straight in one direction or in the opposite direction depending on the direction of rotation. The electric motor 75 can rotate in two directions. At each end, the threaded spindle 151 carries a disk 153 or 154, which represents the input element of an electromagnetically actuated clutch 155 or 156.

A piston-cylinder unit 160 or 180 is arranged in front of each input clutch plate 153, 154 in alignment with the threaded spindle 151. In a cylinder housing 161, the piston-cylinder unit 160 has a differential piston 162 with a piston rod 163, which projects out of the cylinder housing 161 in the direction of the threaded spindle 151. At its outer end, the piston rod 163 carries a disc 164, which represents the output element of the clutch 155 and accommodates an electrical coil 165 and, together with the disk 153 on the threaded spindle 151, forms the electromagnetically actuated clutch 155. The differential piston 162 divides the interior of the cylinder housing 161 into an annular cylinder space 166 on the piston rod side and into a circular cylindrical cylinder space 167 away from the piston rod. The cylinder space 166 is permanently fluidly connected to the cylinder space 135 of the piston-cylinder unit 130 via a hydraulic line 168. A hydraulic line 169 leads from the cylinder space 167 to the cylinder space 136 of the piston-cylinder unit 130. In this line 169 there is an electromagnetically actuatable 2/2-way seat valve 175, the rest position of which is the blocking position, in which it free the cylinder space 136 from leakage to the cylinder chamber 167, and which can be brought into a through position by the electromagnet 186. The effective area 170 of the hydraulic piston 162 adjoining the cylinder space 167 is substantially smaller than the effective area 171 of the hydraulic piston 132 adjoining the cylinder space 136. The cross sections of the piston rods 133 and 163 are matched to one another in such a way that the ratio of the opposing effective areas of the hydraulic pistons 162 and 132 is equal to the ratio of the effective areas 171 and 170 to one another. The cross sections of the piston rods 163 and 133 then have the same relationship between the cross sections of the cylinder spaces 167 and 136. As in the exemplary embodiments according to FIGS. 1 to 7, the force is translated between the two piston-cylinder units 160 and 130. In the case of a force transmission between the two piston-cylinder units 130 and 160, a high injection pressure can be applied without the screw drive 150, 151 and the toothed belt 149 being stressed too much. A small electric motor 75 can also be used.

The piston-cylinder unit 180 in front of the other end face of the threaded spindle 151 has a synchronous piston 182 located in a cylinder housing 181, which has a piston rod 183 on both sides. The two piston rods have the same cross-section and emerge from the cylinder housing 181 on opposite end faces. The piston rod 183 directed towards the threaded spindle 151 carries at its end a disc 184 which has a coil in it 185 receives and forms the second clutch 156 as the output element together with the clutch disc 154 on the threaded spindle 151. The synchronous piston 182 divides the interior of the cylinder housing 181 into two cylinder spaces 186 and 187 which have a cross section. The cylinder chamber 186 is permanently fluidly connected to the cylinder chamber 140 of the piston-cylinder unit 131 via a hydraulic line 188. A line 189 leads from the cylinder space 187 of the piston-cylinder unit 180 to the cylinder space 139 of the piston-cylinder unit 131. In this line 189 there is a 2/2-way seat valve 195, which assumes its open position at rest and through which Electromagnets 196 can be brought into a blocking position in which the cylinder space 139 is blocked off from the cylinder space 187.

According to FIG. 9, the cross sections of the cylinder spaces 186 and 187 of the piston-cylinder unit 180 are larger than the cross sections of the cylinder spaces 139 and 140 of the piston-cylinder unit 131. This means that a reduction in force and a translation of the displacement between the two piston Has cylinder units. A relatively small path of the hydraulic piston 182 and thus of the threaded spindle 151 is therefore sufficient to bring the injection nozzle into contact with the mold from its rest position and back again. .

FIG. 9 shows the injection unit 110 in a state in which the injection nozzle 112 is at a distance from the injection mold. After plasticizing an appropriate amount of plastic material, the screw 10 and the entire injection mechanism and the hydraulic piston 132 with the piston rod 133 are in a retracted position. The corresponding positions of the threaded spindle 151 and the input clutch plates 153, 154 and the output clutch plates 164 and 184 of the two clutches 155 and 156 are shown schematically in the partial figure 10a. These correspond to the positions from FIG. 9.

To inject plastic into the mold, the nozzle 112 must first be moved to the mold. For this purpose, the electric motor 75 is turned into a device controlled that the threaded spindle 151 moves in the view according to Figures 9 and 10 to the left to the clutch disc 164 of the clutch 155. The clutch 156 is actuated so that the two clutch plates 154 and 184 of the clutch 156 adhere to each other, so that the hydraulic piston 182 of the piston-cylinder unit 180 follows the threaded spindle 151. Pressure medium is displaced from the cylinder space 187 via the line 189 and the open shut-off valve 195 into the cylinder space 139 of the piston-cylinder unit 131. As a result, the entire injection unit 110 moves to the left. After the path of the threaded spindle 151 required to place the nozzle 112 on the mold, as shown in FIG. 10b, the clutch disc 153 has reached the clutch disc 164 of the other clutch 155. Now the shut-off valve 195 is first brought into its locked position and then the clutch 156 is deactivated. No pressure medium can flow out of the cylinder space 139 of the piston-cylinder unit 131, so that the injection unit with the injection nozzle 112 remains on the mold. The electric motor 75 continues to rotate in the same direction, so that the threaded spindle 151 moves further to the left and subsequently moves the piston rod 163 and the hydraulic piston 162 to the left via the clutch disks 153 and 164. As a result, pressure medium is displaced from the cylinder space 167 of the piston-cylinder unit 160 via the line 169 and the opened directional valve 175 into the cylinder space 136 of the piston-cylinder unit 130. The hydraulic piston 132 displaces the injection mechanism 113. to the left so that plastic material is injected into the mold. The positions of the threaded spindle 151 and the various clutch disks at the end of the injection process are shown in sub-figure 10c. While the threaded spindle 151 pushes the clutch disk 164 in front of it via the clutch disk 153, the clutch 155 can also be activated. Then it is also possible to brake the component of the plastic injection molding machine to be moved from the drive source.

At the end of the injection movement, the valve 175 is brought into its blocking position so that the injection mechanism 113 remains in its foremost position. The electric motor 75 is driven in the reverse direction and thereby moving the threaded spindle 151 to the right. The clutch 155 is ineffective. If the threaded spindle 151 has traveled the distance covered for injection in the opposite direction, it hits the clutch disc 184 of the clutch 156 with the clutch disc 154. Shortly before. the check valve 195 is brought back into its open position. The hydraulic piston 182 can now be shifted to the right, pressure medium being displaced from the cylinder space 186 into the cylinder space 140 and from the cylinder space 139 into the cylinder space 187. The injection unit 110 is moved away from the injection mold. The end position of the threaded spindle 151 and the different clutch disks is shown in the partial figure 10d. Then the check valve 195 is brought back into its locked position so that the injection unit 110 is blocked in its position. The clutch 156 is released. The electric motor 75 is actuated again in the former direction of rotation, so that the threaded spindle 151 approaches the clutch disc 164 of the clutch 155 to the left, as shown in the partial figure 10e.

In addition to the electric motor 75, the electric motor 71 is also controlled to inject plastic. Namely, the electric motor 71 rotates in a direction that the freewheel 113 does not transmit the rotation of the spline shaft 14 to the worm 10. The brake 119 blocks the spindle nut 117 against rotation, so that the threaded spindle moves to the left at a speed determined by the speed of the electric motor 71. In this case, only a part of the force required for displacement is to be applied via the screw drive 114, 117. The greater part of the force is exerted by the hydraulic cylinder 130, so that the threaded drive is not excessively loaded. On the other hand, because of the greater rigidity of the mechanical power transmission from the electric motor 71 via the screw drive 114, 117 to the screw, the desired speed of the screw and the injection pressure can be kept very precisely by changing the speed or torque of the electric motor 71.

To plasticize plastic, the electric motor 71 is controlled so that it rotates the spline shaft in a direction in which the freewheel 113 rotates on the Worm 10 transmits. The injection mechanism together with the screw 10 is rotated in such a direction that plastic material is conveyed in front of the screw. A certain pressure builds up there, which wants to move the injection mechanism together with the hydraulic piston 132 backwards in the sense of a reduction in the size of the cylinder space 136 of the piston-cylinder unit 130. With the shut-off valve 175 in the through position, the speed controlled by the electric motor 75 at which the threaded spindle 151 moves to the right and thus displacing pressure medium from the cylinder space 136 of the piston-cylinder unit 130 via the valve 175 and the line can now be achieved 169 in the cylinder space 167 of the piston-cylinder unit 160, a specific dynamic pressure can be set or a specific dynamic pressure profile can be traversed. A specific state of the threaded spindle 151 and the clutch disks of the couplings 155 and 156 during the plasticizing process is shown in the partial figure 10f. At the end of the plasticizing process, the clutch disc 164 has again reached the position shown in the partial figure 10a. The spindle nut 117 can rotate freely during the plasticizing with axial support via the axial bearing 118 and does not hinder the movement of the threaded spindle 114 and thus of the injection mechanism to the rear.

Claims

claims

1. Injection unit for a plastic injection molding machine with a screw (10) which can be driven in rotation for plasticizing plastic via a drive part (14), and with an electric motor (30, 75) which has a part (31) fixed to the frame and a straight line Movable output part (32, 77), via which the screw (10) can be moved axially for injecting plastic into a mold, characterized in that the drive part (14) in the power flow between the electric motor (30, 75) and the screw ( 10), so that a torque for rotating the screw (10), viewed from the screw (10), is introduced into the drive part (14) in front of the electric motor (30, 75), and that between the output part (32, 77) of the electric motor (30, 75) and the drive part (14) a device (40) for power transmission is arranged.

2. Injection unit according to claim 1, characterized in that the drive part (14) of a first electric motor (20, 71) can be driven in rotation and the screw (14 by the second electric motor (30, 75) is axially movable and that one of the first electric motor (20, 71) generated torque from which

Auger (10) viewed from before the second electric motor (30, 75) is introduced into the drive part (14).

3. Injection unit according to claim 1 or 2, characterized in that the second electric motor (30) is an electric linear motor.

4. Injection unit according to claim 1 or 2, characterized in that the electric motor (75) for moving the screw (14) is an electric rotary motor and that the rotary movement of a rotating part (76) of the electric rotary motor (75) via a screw drive can be converted into a linear movement of the output part (77).

5. Injection unit according to claim 1 or 2, characterized in that the electric motor (75) for moving the screw (14) is an electric rotary motor and that the rotary movement of a rotating part (76) of the electric rotary motor (75) via a rack and pinion drive in a rectilinear movement of the output part (77) can be implemented.

6. Injection unit according to a preceding claim, characterized in that the axis (33) of the electric motor (30, 75) for moving the screw (14) from the axis (23) of the screw (10) and the drive part (14) a distance and that the electric motor (30, 75) is arranged laterally next to the screw (10) and drive part (14).

7. Injection unit according to claim 6, characterized in that the output part (32, 77) of the electric motor (30, 75) and the drive part (14) are each moved axially in opposite directions and an axial movement of the output part (32, 77) by the device (40) for power transmission is converted into the opposite axial movement of the drive part (14).

8. Injection unit according to one of the preceding claims, characterized in that an axial roller bearing (53) is arranged between the drive part (14) and an output part (48) of the device (40) for power transmission.

9. Injection unit according to one of the preceding claims, characterized in that the device (40) for power transmission comprises a lever (85) which can be pivoted about an axis of rotation (88) and that the force transmission between the output part (32) of the electric motor (30) and the lever (85) at a substantially greater distance from the axis of rotation (88) than the introduction of force between the lever (85) and the drive element (14).

10. Injection unit according to claim 9, characterized in that the

Lever (85) is a two-armed lever on which the points of force application are approximately diametrically opposed.

11. Injection unit according to claim 9 or 10, characterized in that between the lever (85) and the drive part (14) and between the lever (85) and the output part (32) of the electric motor (30) each have a tiltable intermediate part ( 89) is arranged.

12. Injection unit according to one of claims 1 to 8, characterized in that the device (40) for power transmission is a hydraulic device which has two movable pistons, namely an input piston (45, 46) and an output piston (48, 49) , each of which closes a pressure chamber (42, 43) filled with a pressure fluid and which differ from one another in the size of their effective surfaces (55, 56) delimiting the respective pressure chamber (42, 43), that the two pressure chambers (42, 43) are fluidly connected to one another and that the input piston (45, 46), which has the smaller active surface (55), moves to inject plastic and to move the screw (10) accordingly in order to reduce the pressure space (42) adjacent to it is coupled to the output part (32, 77) of the electric motor (30, 75) and the output piston (48, 49) having the larger active surface (56) to the drive part (14).

13. Injection unit according to claim 12, characterized in that the input piston (46) and the output piston (49) are each designed as differential pistons and on the side remote from the first pressure chamber (42, 43) with an annular, second active surface each have a second pressure chamber (57, 58) limit and that the two second pressure chambers (57, 58) are fluidly connected to one another.

14. Injection unit according to claim 13, characterized in that the size ratio between the second active surfaces is the same as the size ratio between the first active surfaces (55, 56) of the input piston (46) and the output piston (49).

15. Injection unit according to claim 13, characterized in that the output piston (49) is designed as a differential piston which delimits a second pressure chamber (58) on the side remote from the first pressure chamber (43) with an annular, second active surface, that this second pressure chamber (58) is fluidly connected to a third pressure chamber (65), that there is a further electric motor (70) and that a piston (66) immersing in the third pressure chamber (65) can be moved by the latter.

17. Injection unit according to one of the preceding claims, characterized in that the drive part (14) via a thrust joint with an axially stationary part (21) of the first electric motor (20) or with a rotationally drivable and axially stationary part (73, 79) is coupled.

18. Injection unit according to claim 17, characterized in that the first electric motor (20) has a rotating hollow shaft (21) through which the

Drive part (14) extends and with which the drive part (14) is coupled via a spline (15, 22).

19. Injection unit according to one of the preceding claims, characterized in that the first electric motor (71) is arranged on the side of the drive part (14) and that the drive part (14) from the first electric motor (71) via a transmission 872, 73; 78, 79, 80) can be driven in rotation.

20. Injection unit according to one of the preceding claims, characterized in that the electric motor (75) for moving the screw (14) is an electric rotary motor and that the screw (14) can be moved axially by this electric motor (75) via a first switchable clutch and can be driven in rotation via a second switchable clutch.

21. Injection unit according to claim 19 or 20, characterized in that the worm (14) can be driven in rotation via a belt transmission.

22. Injection unit according to claim 20 or 21, characterized in that the first and the second clutch have a common input element which can be driven by the electric motor (75).

23. Injection unit according to one of claims 20 to 22, characterized in that when the first clutch is released, a dynamic pressure in the plasticized plastic material is set by a defined actuation of a brake or by a defined control of an electric dynamic pressure motor.

24. Drive device according to one of the preceding claims, characterized in that a screw drive (101, 102) with two mutually engaging drive elements (101, 102) is provided, of which the one drive element (101) can be driven in rotation by the first electric motor (24) and of which a drive element (101) is arranged between the device (40) for power transmission and the worm (14).