The present invention concerns a method for the power supply for rack and pinion lifts according to the introduction to claim 1. The invention concerns also an arrangement for the power supply for rack and pinion lifts according to claim 10.

The power that is required to drive transport means, such as lifts, for persons or goods between floors in buildings varies, depending on a number of factors such as, for example, the instantaneous load on the lift, its speed, the direction of travel and in which part of the transport cycle the lift is currently operating. It is important that the power requirement be reduced as far as possible not only to reduce the installation and operating costs of the lift, but also to reduce the dimensions and space required for the power supply system of the lift. A rack and pinion lift comprises in general a load carrier such as a lift car that can be driven along a track by means of electric motors and cogged wheels, which track is normally in the form of a mast provided with a cogged rod. The electric motors that are selected are normally of three-phase type with a rated voltage of 380-500 V and a frequency of 50 or 60 Hz. The motors offer soft starting and stopping of the lift car at the selected landing by the use of frequency control. In a rack and pinion lift, not only the ele tric motor for driving the lift but also a control and monitoring unit for the control of the lift are supported by immediately by the lift car.

Rack and pinion lifts differ in a number of ways from conventional lifts such as cable- borne lifts and hydraulic lifts. One difference is, for example, that the lift car supports its own drive unit as it does also an associated control and monitoring unit for the control of the electric motor. The drive machinery is normally separated from the lift car in conventional lifts, for example arranged in a machine room and connected with the lift car in a manner that transfers motion through a cable or similar that runs from the machine room. Furthermore, rack and pinion lifts normally lack a counterweight and thus they lack the possibility of balancing the deadweight of the lift car, and this makes the start and acceleration phase critical, and requiring particularly high amounts of energy. Furthermore, as a consequence of the lift car supporting its own drive unit, the distance between a power supply unit at a ground level and the drive machinery of the lift car will vary, as the lift car moves upwards along the mast. This places particular demands on this type of lift. Rack and pinion lifts are thereby supplied by means of an electrical power line that leads from ground level up to the electric motor that is supported by the lift car. The electrical power line consists of electrical conductors surrounded by insulating material. The electrical power line is arranged, with the aid of a cable trolley or similar guided along the mast, to follow with an adapted length the lift car upwards and downwards along the mast, suspended under the lift car. It should be understood that, as the lift car carries its own drive unit, the electrical power line must be extended and shortened as the lift car moves along the mast. It can also be mentioned in addition to this that the length of the mast that is used in the currently used type of rack and pinion lift is formed from a number of sections that can be stacked and mounted on each other, in order to be able to vary the length of the mast. A consequence of this is, of course, that also the electrical power line is given a length that is adapted such that it can accompany the lift car along the complete height of the mast. It can finally be mentioned in this context that rack and pinion lifts are normally intended to be used for non-permanent use within the building industry, i.e. the lift is demounted when the building construction has been completed.

Lifts are, on the other hand, becoming evermore higher and it has proved to be the case that the weight of the electrical power line, for lift heights up to 500 m and higher, becomes so great that it influences the loading capacity of the lift. The extension of the electrical power line as the lift car moves along the mast creates also difficulties with housing the complete cable length, in particular, when the power cable is to supply powerful motors with the current they require. In the case in which lifts that are to move between floors in very high buildings, the length, stiffness and deadweight of the electrical power line constitute problems, whereby the relatively heavy-duty electrical power line that accompanies the lift car becomes difficult to control, heavy to carry and house.

It should be understood that the limited possibilities of the rack and pinion lifts to balance the potential energy of the lift car through its lack of a counterweight leads to a requirement for very powerful electric motors and associated electrical equipment such as electrical power lines with relatively large cross-sectional areas in order to be able to deliver the current required by the drive motors of the lift, in particular with respect to the instant of starting or the acceleration phase. When the lift car is driven to a certain level up the mast, its potential energy increases according to the equation: (E _pot =mgh; where m = mass, h = height and g = acceleration due to gravity). In the absence of a counterweight, the potential energy of a lift car that has been lifted to a certain height has increased considerably, whereby the lift has been supplied with considerable amounts of energy through the power supply system. It should be realised that the energy that has been supplied is collected at the lift car as potential energy, when the lift car is in its elevated position.

In addition to the said high elevations of the lift, it is, of course, also a problem that the lift motors drive the lift at full power only during certain periods, while the power supply system of the lift must be dimensioned based on the highest most critical power that is normally required only during short periods of the operation, in particular during the instant of starting and also during motion of the lift upwards along the mast. The greatest instantaneous force is, however, required at the instant of starting, i.e. during the initial part of the transport cycle when the lift car is accelerated. The power requirement falls considerably when the lift car has reached a constant speed. Changes in potential energy of the lift car of a conventional lift provided with a counterweight are balanced during motion by means of a counterweight. Rack and pinion lifts normally lack this possibility and the potential energy must be continuously overcome by the power supply system, which, of course, places considerable demands on this system. Enormous amounts of energy are generated when a rack and pinion lift car moves downwards along the mast during braking (retardation). The potential energy that is in this way released by the lift car is normally converted to heat energy in separate resistances (braking resistances) or it is fed back into the mains power network by a process known as "regenerative braking". It should be realised that a rack and pinion lift produces a considerably greater amount of energy during its motion downwards than conventional lifts provided with counterweights produce, due to the absence of a counterweight. Previous attempts to equip rack and pinion lifts with counterweights have been less than successful, mainly as a result of complicated designs and the extra work that the counterweight arrangement introduces during the tasks of mounting and demounting the lift.

Since the power supply system and the associated electrical plant must be dimensioned to cope with the highest output power that is required during short periods, while the appearance of the standard load places considerably lower requirements for the capacity of the power plant, overload protection, the conductor system and other equipment in the consumer circuit will not be used fully with respect to the capacity of the equipment. As a part of this, the investment costs for the power supply system will be significantly higher and more extensive than necessary and they will be inefficient from the point of view of costs.

While rack and pinion lifts are often used during the construction of buildings at locations that lack electrical power and the infrastructure of power stations, whereby alternative sources of energy are used as main power generator such as, for example, diesel-powered units, it should be understood that it would be desirable from a number of aspects to be able to reduce not only the size but also the cost of the external power- generating equipment and generator system that are required.

Figure 1 shows how a general mains power network 101 that is part of a main power generator 100 feeds a three-phase alternating current to a transformer 102 in order for it to be transformed down to a suitable level of voltage. An AC bus 105 and a three-phase electrical power line 106 supplies a three-phase electric motor 109 supported by a lift car 107 with electrical energy. As Figure 1a makes most clear, the lift car 107 is a rack and pinion car and it can be driven along a mast 110 through the interaction between a cogged wheel 111 driven by the electric motor 109 and a cogged rod 112 arranged on the mast. The selected speed during raising and lowering of the lift car 107 is controlled through appropriate frequency conversion of the electric motor 109, When the lift car 107 moves downwards along the mast 10 during braking, an inverted or inverse flow of AC alternating current is generated in the electric motor 109. The inverse flow of AC alternating current can, through what is known as "generative braking", be led back to the mains power network 101 (not shown in the drawings).

Figure 2 shows an example in which the main power generator 100 is part of a diesel-powered unit 113 intended to be used as a source of power. The diesel-powered unit 113 is mechanically coupled to an AC power generator 114. The power generator 114 supplies AC alternating current that supplies the electric motor 109 of the lift car 107 through an AC bus 105 and a three-phase electrical power line 106 (see Figure 1 ), The system from this point onwards is the same as that described in Figure 1. When the lift car 107 moves downwards along the mast, an inverted or inverse flow of AC alternating current is generated in the electric motor. The flow of inverse AC alternating current can be caused through generative braking to be dissipated as heat in a braking resistance, or it can be led back to the mains power network 101 (not shown in the drawings).

A first aim of the present invention is to achieve, based on the prior art technology, a method for the power supply of rack and pinion lifts that makes it possible to reduce the need for external power and in this way to reduce the cost of the power supply system of the lift as a whole. A second aim is to achieve a method for the power supply that solves the problems with the three-phase electrical power line that extends from the unit at ground level to the lift car. A third aim of the invention is to achieve an arrangement for the execution of the said method.

These aims of the invention are achieved through a method that demonstrates the distinctive features and characteristics that are specified in claim 1 , and an arrangement that demonstrates the distinctive features and characteristics that are specified in claim 10.

An embodiment of the invention will be described in more detail below with reference to the attached drawings, of which:

Figure 1 shows schematically a block diagram of a prior art power supply system, connected to the mains power network, for a rack and pinion lift that can be driven along a mast,

Figure 1a shows a view from the front and in greater detail of the power supply that is a component of a rack and pinion lift of the type shown in Figure 1 ,

Figure 2 shows schematically a block diagram of the power supply system according to Figure 1 but now in a design with a generator unit powered by a diesel engine, known as a "generator system",

Figure 3 shows schematically a block diagram of an arrangement according to the invention that has, for the power supply to a rack and pinion lift, an energy storage system that includes a supercondensor, and which system is connected to an AC alternating voltage supplied by the mains power network,

Figure 3a shows schematically and in more detail a block diagram of the supercondensor shown in Figure 3 and its associated electrical circuits,

Figure 3b shows schematically in a cross-sectional view a charging arrangement in an alternative design and that is part of the invention, including a current withdrawal trolley with current withdrawers, and with which arrangement a power receiver arranged at the lift car can be in continuous electrical connection with the principal power network,

Figure 4 shows schematically a block diagram of an arrangement for the power supply of a rack and pinion lift according to Figure 3, but in a design with an energy storage system that includes a flywheel,

Figure 5 shows schematically a block diagram of an arrangement according to Figure 3, but with an energy storage system that includes a battery pack,

Figure 5a shows schematically a block diagram in more detail of the battery pack and its associated electrical circuits shown in Figure 5,

Figure 6 shows schematically in the form of a graph the energy requirement of a prior art rack and pinion lift at various stages A-F of a transport cycle, and

Figure 7 shows schematically in the form of a graph corresponding to Figure 6 the energy requirement during the use of an arrangement for power supply according to the present invention.

With reference to Figures 3-5, a lift system with a rack and pinion lift for the transport of passengers or goods is shown. The lift comprises a load carrier in the form of a lift car 107 that can be driven by means of a drive unit, comprising an electric motor 109 and a transmission that has a rotatable shaft that interacts with a cogged wheel 111 , along a track in the form of a mast equipped with a cogged rod 112 (see Figure 1a). The said electric motor 109 is of three-phase type, having, for example, a rated voltage of 380-500 V and a frequency of 50 or 60 Hz. The present arrangement for power supply is shown in Figures 3-5 incorporated as a part of the two prior art designs that are shown in Figures 1 and 2, to which reference is also made.

An energy storage system is part of the present power supply arrangement generally denoted by reference number 10 and supported by the lift car 107, which energy storage system is designed to receive energy, store energy, and to supply the stored energy to the electric motor 109 of the lift car 107 through a first bus, a DC bus 11. The DC bus 11 has a positive side 13 and a negative side 14. A principal power network 100 that produces power supplies three-phase AC alternating voltage. The said principal power network 100 may be constituted by a mains power network, or by a generator system that comprises a diesel-powered unit with its associated power generator of the types shown in Figures 1 and 2. The energy storage system 10 that is supported by the lift car 107 is designed to store energy of the type that is produced during regenerative operation of the electric motor 109 of the lift car, i.e. the energy that is released when the lift car 107 is retarded during its movement downwards along the mast 110. Furthermore, the energy storage system 10 is designed for the storage of energy that has been collected directly from the principal power network 100, either when the lift car 107 is located at a ground level or when it is located at a predetermined location along the pathway of the lift car 107 along the mast 110. A second bus, an AC bus 20, extends from a ground level and it includes a three-phase electrical power line from the principal power network 100 and onwards vertically upwards along the mast 110. The three-phase electrical power line that functions as an AC bus is so attached and supported at the mast 110 that it can be considered as stationary relative to the lift car 107 that can be driven upwards and downwards along the mast. The expressions "AC bus", "DC bus" and "bus" are used below generally to denote a system of lines, current rails or similar current-transfer arrangements that bind several electrical units together.

The reference number 24 generally denotes a power transfer means that allows electrical energy to be transferred between the principal power network 100 and the energy storage system 10 that is supported by the lift car 107. It will be made clear below that the power transfer means 24 may be designed in a number of different ways. The power transfer means 24 is divided in the following into a number (n) charging stations 24:1 -24:n located at suitable distances from each other along the mast 110. A charging arrangement 25 is present in each charging station that is in electrical connection with the principal power network 100 through a branch cable 26 and the said AC bus 20. The charging arrangement 25 comprises a power deliverer 30 supported by the mast 110 and designed to interact with a power receiver 31 arranged at the lift car 107 in order to allow electrical energy to, by means of contacts 32 that are part of the charging arrangement 25, be transferred as is shown by the arrows 17 from the principal power network 100 to the energy storage system 10 when the lift car 107 is located in such a position along its track along the mast that the contacts 32 are in current-transferring contact with each other. In order to function as charger, the charging arrangement 25 comprises a direct current converter 35 supported by the lift car 107 to convert the AC alternating current of the principal power network to a DC direct current, which can be transferred to the energy store 10 as a charging current. As the drawings make clear, the interacting contacts 32 are supported by the mast 110 and by the lift car 107, respectively.

Figure 3b shows the power deliverer 30 and power receiver 31 of the power transfer means 24 in an alternative design, shown in a cross-section through the mast. The charging stations 24:1-24:n described above and the AC bus has been replaced in the design shown by a rail bar 50 with electrically conducting current rails that extend along the mast 110. Current supply takes place in this way by means of a current withdrawal trolley 51 with its associated current withdrawers that accompanies the lift car 107 and runs on insulating guides along the rail bar 50. The current withdrawal trolley 51 runs along and is supported by bearings through wheels 52 along a guide rail 53 in the form of a T-beam attached along the mast. There are here four current withdrawers, of which 55a, 55b, 55c constitute three-phase supply and 55d the earth connector. This design has the advantage that the power receiver 31 of the lift car 107 can be placed in electrical connection with the principal power network 100 through the contacts 32 at any freely chosen place along the track, i.e. charging can take place anywhere along the mast independently of the level at which the lift car is located. It is appropriate that connection and disconnection take place by means of a switch 55 of three- phase contact type, arranged at the location and in the manner that is suggested by the dash-dot line in Figure 4.

When the lift car 107 moves upwards along the mast 110 under the influence of the power supply and the AC alternating current electric motor 109 supported by the lift car 107, the electric motor is driven principally by energy that is stored in the energy storage system 10. Thus, the lift car increases its potential energy during the motion of the lift car 107 upwards along the mast through energy that is obtained from the energy storage system 10. In the case in which the energy stored in the energy storage system 10 is insufficient to drive the lift car 107 up to a predetermined level of the mast 110, further or supplementary energy can be retrieved from the principal power network 100. According to the invention, energy is retrieved from the principal power network 100 by the lift car 107 being temporarily stopped in association with any one of the charging stations 24:1-24:n arranged along the mast 110, whereby the energy store 10 is filled, with the contacts 32 being in a mutual current-transfer position. Alternatively, charging can take place at an arbitrary position along the mast 110 through the use of the technology described above that includes the supply of power by means of the current withdrawal trolley 51 and its associated current withdrawers 55a-55d. It should be understood that the time that is required to fill the energy storage system 10, i.e. the stop time or the charging time, may vary, depending of the energy storage technology chosen. This will, however, be described in more detail below.

During the motion of the lift car 107 downwards along the mast 110, what is known as "regenerative braking" of the electric motor 109 is used, whereby the energy generated during braking is collected and stored in the energy storage system 10 that is supported by the lift car. This means that the collected potential energy that is gradually released during the braking motion of the lift car 107 down the mast 110 is collected and led to the energy storage system 10. The collected energy can later be used for the driving of the electric motor 109 of the lift car during its movement upwards along the mast 110. In particular, the stored energy of the lift car 107 constitutes a significant addition during the acceleration phase of the lift car, which means that the requirement for external power supplied from the mains power network can be reduced in comparison with prior art technology, and thus also the capacity requirement placed on the external power supply system of the lift.

The power to and from the relevant units that are connected to the DC bus 11 are controlled and monitored by means of a control system 40, for example a programmable logic controller (PLC), or computer supported by the lift car 107. For monitoring and surveillance of the voltage levels of the energy store 10, what is known as a buck-boost circuit or a similar circuit for voltage monitoring can be used, arranged at a suitable location along the DC bus 11 (not shown in the drawings).

As has been stated above, the energy storage system 10 may be designed in a number of different ways whereby the time required for charging of the store is not the least of the factors that are influenced to a great degree by the selected energy storage technology, With reference to also Figures 3a and 5a, a number of energy storage systems of differing designs will be described in more detail below.

Figure 3 shows in a first embodiment of an arrangement according to the invention whereby an energy storage system 10 that includes an energy store 60 with a supercondensor 27 is used for the power supply to a rack and pinion lift car 107. The lift car 107 is braked regeneratively during its motion downwards along the mast 110 whereby the potential energy retrieved during the braking is led to the supercondensor 27 that is a component of the energy store 60 for storage. A DC/AC converter 12 is connected through the DC bus 11 to the AC electric motor 109 of the lift car for conversion of the DC direct current that is delivered by the supercondensor 27 into an AC alternating current adapted for driving the electric motor 109.

Figure 3 shows schematically in a block diagram how the supercondensor 27 that is a component of the energy store functions. To be precise, a diode 27a and a charging switch 27b are arranged in a first branch whereby the branch is connected in parallel across the positive side 13 and the negative side 14 of the DC bus 11. Further, a second branch is present with a switch 27c that, when closed, causes the supercondensor 27 to be discharged. The diode 27a allows current to pass only in a direction that leads to charging of the supercondensor 27, whereby discharge cannot take place through the said first branch, which contains the diode 27a. When the first branch is closed, the voltage of the supercondensor 27 increases such that it eventually exceeds the voltage across a condensor 27d that is part of the DC bus 11. Since the voltage across the supercondensor 27 is higher than the voltage across the condensor 27d of the DC bus 11 , the supercondensor can be connected for the delivery of stored energy in the form of current to the electric motor 109 of the lift car 107 through the converter 12, which takes place in practice through the second branch being closed by means of the switch 27c. Figure 4 shows a second embodiment of an arrangement according to the invention whereby an energy storage system 10 that includes an energy store 60 with a flywheel 23 is used for the power supply to a rack and pinion lift car 107. The lift car 107 is braked regeneratively during its motion downwards along the mast 110 whereby the potential energy retrieved during the braking is led to the flywheel 23 for storage. A DC/AC converter 12 is connected to the AC drive motor 109 of the lift car 107 through a DC bus 11 with a positive side 13 and a negative side 14. The energy storage system 10 comprises a DC/AC converter 21 , a three-phase AC induction motor 22 and the said flywheel 23. The induction motor 22 may be constituted by, for example, a traction motor, i.e. a three-phase synchronous motor with permanent magnets. When the lift car 107 moves downwards through the influence of the associated electric motor 109, energy is stored in the flywheel 23, and this takes place as a consequence of the electric motor 109 that is supported by the lift car 107 being reversed and functioning in this case as a generator. Thus the AC alternating current that is generated from the lift motor 109 is converted to DC direct current by the converter 20, which direct current is led after passage through the DC bus 11 to the energy storage system 10. The said energy storage system receives and stores the potential energy as kinetic energy in the flywheel 23 through this flywheel being accelerated by means of the motor 22. The kinetic energy in the flywheel can, when power is needed, be converted to electrical energy, which can be used by the drive motor 109 of the lift 107.

Figure 5 shows a third embodiment of an arrangement according to the invention whereby an energy storage system 10 that includes an energy store 60 with a battery pack 70 is used for the power supply to a rack and pinion lift car 107. The lift car 107 is braked regeneratively during its motion downwards along the mast 110 whereby the potential energy retrieved during the braking is led to the battery pack for storage. A DC/AC converter is connected to the AC drive motor 109 of the lift car 107 through a DC bus 11 with a positive side 13 and a negative side 14.

Figure 5a shows schematically in a block diagram how the energy store 60 with the battery pack 70 functions. To be more precise, the energy storage system 10 comprises in this case a battery pack that is controlled by means of a switch 71 , for the storage of energy and the supply of the said energy in the form of a DC direct current.

It should be realised that it may be suitable in certain cases of lift applications of the type described above to combine the alternative energy storage technologies described above. It would be conceivable, for example, to combine any one of the relatively large and permanent storage capacities of the supercondensor 27 or the battery pack 70 with the rapid and efficient energy management of the flywheel 23.

With reference to Figure 6, there is shown schematically in the form of a graph the energy requirement for a rack and pinion lift at various stages A-F of a transport cycle whereby block A corresponds to the electricity consumed during acceleration of the lift car 107 to a predetermined speed in a direction of motion upwards along the mast 5. Block B corresponds to the power consumption when the lift car 107 increases its potential energy through moving at a constant speed upwards along the mast. Block C corresponds to the energy consumption during retardation and stop of the lift car 107. Block D represents the inverse power or the return of potential energy for storage during acceleration downwards of the lift car 107. Block E represents inverse energy consumption during motion at constant speed downwards and block F represents the inverse energy during retardation and stop of the lift car 1, 2 during downwards motion.

Figure 7 shows graphically the power consumption that can be achieved according to the principles of the present invention whereby the power consumption is illustrated as constant with time in the hatched block and is obtained through stored potential energy from regenerative motor operation being recycled as power that is superimposed on the power that is consumed in Figure 6. The graph is intended to give an example of how residual power that is recycled and stored in the energy storage system 10 that has been obtained during braking of the lift car 107 during its motion downwards and that is stored as transferred potential energy in, for example, the energy storage system 10, can be returned at times during the transport cycle of the lift when the power that is required is at its greatest, for example, at the instant of starting when the lift car 107 is accelerated. It should be furthermore understood that the collected energy in the power supply system can be regarded as constant, as is stated by the general laws of thermodynamics, whereby the only energy that is consumed in a lift is the energy that is lost due to the appearance of mechanical and electrical losses.

As has been mentioned above, the present invention has the major advantage that the levels of potential energy of the lift car 107 can be balanced during the acceleration phase and motion upwards along the mast 110 by the potential energy that is recycled through regenerative operation and braking of the lift car during its motion downwards along the mast and stored in an energy storage system that is supported by the lift car being returned to the electric motor 109 of the lift car to be used as driving power. The said recirculation, i.e. the recycling of potential energy and the supply of recycled potential energy that has been stored in the energy store 60 to the electric motor 109 thus takes place in immediately in association with the lift car.

This distinctive feature of the invention is interesting since it means that the principal power network that produces power needs only to supply a limited part of the current that is required during the critical acceleration phase of the lift car (see also Figures 6-7). The invention is not limited to that which has been described above and shown in the drawings: it can be changed and modified in several different ways within the scope of the innovative concept defined by the attached patent claims.