WO2004026747A1

WO2004026747A1 - Regenerative drive system for elevators

Info

Publication number: WO2004026747A1
Application number: PCT/AU2003/001238
Authority: WO
Inventors: Allan Rush
Original assignee: Permo-Drive Research And Development Pty Ltd
Priority date: 2002-09-20
Filing date: 2003-09-19
Publication date: 2004-04-01
Also published as: AU2002951537A0

Abstract

A drive mechanism (1) for an elevator system includes a primary motor (2) connected to a hoisting means load (4), further includes energy accumulation means (7) to store and release energy through controlled receipt and release of pressurised hydraulic fluid; a positive displacement hydraulic pump/motor assembly (8) in fluid communication with energy accumulation means (7), a low-pressure hydraulic reservoir (9) in fluid communication with the pump/motor assembly (8), a drive shaft (22), a control system (10) regulating pump/motor assembly (8) in response to predetermined operating parameters. The system progressively accumulates surplus energy during off-peak loads and augments power output from the primary motor (2) on demand accommodating transient peaks of the load (4). In neutral mode, the pump/motor assembly (8) exerts on substantial influence on the drive shaft (22).

Description

TITLE: REGENERATIVE DRIVE SYSTEM FOR ELEVATORS

FIELD OF INVENTION

The present invention relates generally to elevators, lifts, cage winders, hoists and the like.

The invention has been developed primarily for use in conjunction with electric hoisting motors of the type conventionally used in elevators and lifts. It will be appreciated, however, that the invention is not limited to this particular application, being also readily adaptable to other sources of motive power including internal combustion engines, turbines and hydraulic motors.

BACKGROUND OF THE INVENTION

The following discussion of the prior art of his intended solely to place the invention in an appropriate context and allow a proper appreciation of its technical significance. However, statements made in the specification about prior art information should not be construed as admissions that such information is widely known, or forms part of common general knowledge in the relevant field.

Elevator systems are known, and typically incorporate a diesel or electric hoisting motor connected to a winch drum by means of a drive shaft. A car or cage is suspended from the winch drum by a series of wire cables or ropes, which usually run over a corresponding series of pulleys and sheaves. The specific configurations of these basic components vary significantly between applications. However, the general principles of operation are well known by those skilled in the art, and so will not be described in great detail. A problem that has hitherto been inherent in known elevator systems, is that they are fundamentally energy inefficient. This is because each time the elevator car needs to be stopped, particularly on downward runs, enormous quantities of kinetic energy are converted into heat in the braking mechanism. This energy has hitherto been unrecoverable, and is consequently lost from the thermodynamic system altogether. Further energy is then consumed in accelerating the car from a standing start, particularly on upward runs when the hoisting motor is working against gravity. This cycle of the massive energy loss and subsequent replenishment continues almost incessantly, which is why elevator systems are inherently power hungry, and costly to run.

A further problem relates to the fact that in installations of this type the primary drive motor, whether electric, diesel or of any other type, is not subject to constant load. Rather, it is required to accommodate a wide spectrum of fluctuating loads, continuously varying between the minimum load condition which prevails where the elevator car is empty and stationary (or accelerating downwardly), and a maximum load condition which corresponds to the upward acceleration, from a standing start, of an elevator car loaded to maximum capacity. Added to the load imposed by the elevator car, is the massive torque typically required to be generated by the hoisting motor on start-up due to its own rotational inertia and that of the associated rotational components such as the drive shaft and winch drum. This start-up torque is often in fact higher than the maximum torque required to be generated by the motor under any other steady-state or transient operating condition. A fundamental problem with drive mechanisms of this type in elevators and analogous applications is that the hoisting motor must usually be specified at an output capacity corresponding the peak design loads in the most adverse operational circumstances, in order for those loads to be safely accommodated without risk of the motor burning out, stalling or otherwise failing at critical transient points in the operating cycle. However, because the average or mean load is typically well below these maximum transient peak loads, the motors specified in this way are usually underutilised for the vast majority of their duty cycles. The result is redundant capacity for most of the operational life of the motor, which is disadvantageous in several respects.

Most obviously, the initial capital cost of the motor is greater than that which would be dictated by most normal operating conditions. Furthermore, aside from the capital cost, larger capacity motors are typically heavier and larger in size, and these parameters in turn dictate larger, heavier and more costly mountings, bearings, supports, framing elements, transmissions and the like. Such motors are also more expensive to run. This is primarily because they are typically designed for maximum operating efficiency at or near the point of maximum power output. Consequently, when running at significantly less than maximum capacity, as is inevitably the case for most of the time, overall operating efficiency is compromised.

It is an object of the present invention to overcome or substantially ameliorate one or more of these deficiencies of the prior art, or at least to provide a useful alternative.

DISCLOSURE OF THE INVENTION

Accordingly, in a first aspect, the invention provides a drive mechanism for an elevator system, said drive mechanism including:- a primary motor; hoisting means connected to the primary motor and adapted to raise and lower an elevator car between a plurality of the preset levels; and a regenerative drive system, the regenerative drive system incorporating: energy accumulation means operable selectively to store and release energy through controlled receipt and release of pressurised hydraulic fluid; a positive displacement hydraulic pump/motor assembly in fluid communication with the energy accumulation means; a low-pressure hydraulic reservoir in fluid communication with the pump/motor assembly; a drive shaft adapted for connection to the primary motor; and a control system adapted selectively to regulate the pump/motor assembly in response to predetermined operating parameters, whereby: in an accumulation mode the pump/motor assembly operating as a pump draws surplus power from the drive shaft by diverting hydraulic fluid under pressure into the accumulation means; in an augmentation mode the pump/motor assembly operating as a motor supplies supplementary power to the drive shaft using pressurised hydraulic fluid from the accumulation means; and in a neutral mode the pump/motor assembly exerts no substantial influence on the drive shaft; the system being thereby adapted progressively to accumulate surplus energy during periods of off-peak load and to augment power output from the primary motor on demand to accommodate the transient peak values of the load.

The term "motor" as used throughout this specification is intended to be interpreted in the broadest sense, so as to cover any source of motive power including electric motors, diesel engines, petrol engines, steam engines, hydraulic motors, water turbines, gas turbines, wind turbines, and the like.

The term "elevator" is also intended to be broadly construed, encompassing any analogous configuration of elevator, lift, cage winder or hoisting apparatus. It should further be appreciated that because the same pump/motor assembly is used in one mode as a motor and in another mode as a pump, these terms may be used in conjunction, or interchangeably. In each case, unless the context clearly dictates otherwise, any reference to configuration of the unit as a pump should be understood to include configuration as a motor, and vice versa. Preferably, the hoisting means take the form of a rotary winch drum, adapted to support and regulate the level of the elevator car by means of at least one wire cable or rope.

Preferably, the maximum steady-state power output of the motor is less than the power required for anticipated transient peak values of the load on the winch drum, thereby enabling selection of a smaller capacity motor than would be required in a conventional elevator system of comparable load carrying capacity.

Preferably, the hydraulic pump/motor assembly includes :- a rotary cylinder block having a central axis and incorporating a generally circular array of cylinders disposed in parallel relationship around the axis; a corresponding plurality of axial pistons reciprocably disposed within the respective cylinders; a drive plate disposed at one end of the cylinder block to effect sequentially staggered reciprocation of the pistons in response to rotation of the cylinder block; a stationary valve plate disposed at an opposite end of the cylinder block, the valve plate having a valve face adapted for sliding rotational engagement with a complementary mating face formed on the cylinder block; the valve plate further including at least one inlet port adapted for fluid communication with the low-pressure reservoir and at least one outlet port adapted for fluid communication with the accumulation means; the ports being disposed such that in use, hydraulic fluid is progressively drawn into the cylinders in sequence through the inlet ports as the respective pistons are displaced away from the valve plate and subsequently expelled from the cylinders through the outlet ports as the pistons are progressively displaced toward the valve plate.

In this context, it should be understood that the inlet and outlet ports will alternate in function, according to the mode of operation of the unit.

Preferably, the drive shaft extends coaxially through a complementary bore formed in the cylinder block, to effect rotation of the cylinder block about the central axis. The pump/motor assembly preferably further includes a selectively releasable decoupling mechanism disposed effectively intermediate the drive shaft and the cylinder block. The decoupling mechanism is preferably adapted in an engaged mode to connect the drive shaft to the cylinder block and in a disengaged mode to allow the drive shaft to rotate substantially independently of the cylinder block. In the preferred embodiment, the decoupling means include a clutch mechanism, desirably in the form of a multi-plate clutch disposed coaxially around the drive shaft. The clutch desirably acts between the drive shaft and the cylinder block, so as to selectively transmit rotary drive. It should be appreciated, however, that in alternative embodiments, the drive shaft may be permanently connected to the cylinder block. It should also be appreciated that gears, clutches, or other coupling mechanisms may be interposed to transmit rotary drive between the output shaft of the primary motor and the drive shaft and/or between the drive shaft and the cylinder block of the pump/motor unit. Such transmissions may be mechanical, hydraulic, pneumatic or electromagnetic. They may also be permanently engaged or decouplable, manual or automatic, and may include constant or variable reduction ratios.

In a particularly preferred embodiment, the positive displacement pump/motor is a swash plate type unit. In this embodiment, the drive plate takes the form of a stationary swash plate, which is inclined with respect to the central rotational axis of the cylinder block. Preferably also, the ends of the pistons remote from the valve plate include followers adapted to slide over the swash plate as the cylinder block rotates. A hold-down plate is preferably disposed to capture the floating ends of the pistons and retain the followers in sliding contact with the swash plate. In alternative embodiment, however, springs or other suitable means may be used to retain the followers in contact with the swash plate.

Preferably, the angle of inclination of the swash plate is selectively adjustable, to provide variable flow rate characteristics. In particular, the swash plate is preferably adapted to be selectively inclined in a positive or a negative sense, thereby enabling the assembly alternately to operate as a motor or a pump. Most preferably, the variable swash plate can also be oriented in an intermediate or neutral position, effectively normal to the central axis, such that rotation of the cylinder block causes no movement of the pistons, hence induces no net flow into or out of the cylinders through the ports, and therefore causes no load on the system aside from a residual level of inherent frictional drag.

In other embodiments, it will be appreciated that the invention may also be applied to a bent axis type hydraulic pump. In that case, connecting rods for the pistons are pivotably attached to a thrust plate adapted to rotate with the cylinder block. The invention is also be adaptable to other configurations of motors and pumps. Preferably, the pump/motor assembly includes at least three external ports to permit ingress and egress of hydraulic fluid, with a first port communicating with an inlet of the hydraulic reservoir, a second port communicating with an outlet of the hydraulic reservoir, and a third port communicating with the accumulator. A heat exchanger is preferably disposed between the first port and the hydraulic fluid reservoir. In one embodiment of the invention, a plurality of positive displacement axial piston pumps is arranged axially along the drive shaft. These pumps may be connected hydraulically to operate in series, parallel, or a combination of both.

Preferably, the regenerative drive system includes a flow control circuit through which hydraulic fluid may be selectively directed, the control circuit being adapted to provide a controllable resistance, for example through a throttling valve, enabling the pump/motor unit selectively to exert a retarding force on the drive shaft when required, even if the accumulators are fully charged.

Preferably, the accumulation means include a gas/liquid accumulator comprising a double-ended cylinder and a piston adapted to float sealingly within the cylinder. One side of the cylinder preferably contains a compressible inert gas such as nitrogen, while the other side of the cylinder is preferably connected hydraulically to the pump/motor unit. The accumulator is preferably thereby adapted to store energy by pumping hydraulic fluid into one side of the cylinder, so as to compress the gas on the other side by displacement of the floating piston, and subsequently to release that energy by expulsion of hydraulic fluid as the compressed gas expands. The assembly preferably includes a plurality of such accumulators, which may be selectively connected in series, parallel or a combination of both, as required. In alternative embodiments, other forms of accumulator, such as bladder, bellows or diaphragm type accumulators, may be readily substituted. In one arrangement, the pump/motor unit is connected directly to an output shaft of the primary motor, such that the output shaft of the primary motor and the drive shaft of the pump/motor unit are coupled for conjoined rotation, optionally with an intermediate gearbox or transmission. In a particularly preferred form, however, these shafts are integrally formed, or effectively unitary in construction. Preferably,the control system is configured in response to predetermined system conditions so as selectively to: activate the accumulation mode in order to apply retardation torque to the winch drum; activate the augmentation mode in order to apply drive torque to the winch drum; and activate the neutral mode when no retardation or supplementary drive torque on the winch drum is required; the system being thereby adapted to accumulate surplus energy during periods of retardation or off-peak load and to augment power output from the primary motor on demand to accommodate the transient peak values of the load as the elevator car moves between the preset levels.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:- figure 1 is a diagrammatic perspective view showing the principal components of a regenerative drive system ("RDS") incorporated into the drive mechanism of an elevator, according to a first embodiment of the invention; figure 2 is an enlarged perspective view showing the primary electric motor, RDS and winch drum from the elevator arrangement of figure 1 ; figure 3 is an enlarged perspective view, similar to figure 2, showing a second embodiment of the invention wherein the primary motor is a diesel engine; figure 4 is an enlarged cross-sectional view showing the pump/motor unit from the RDS of figures 1 and 3; figure 5 is an enlarged cross-sectional view showing a hydraulic accumulator from the RDS of figures 1 to 3; and figures 6A to 6D show a sequence of schematics illustrating the hydraulic circuit connecting the pump/motor unit, low-pressure reservoir, high-pressure accumulators, and associated system controllers for the RDS in the various operational modes, according to the invention.

PREFERRED EMBODIMENT OF THE INVENTION

Referring to the drawings, the invention provides a drive mechanism 1 incorporating a regenerative drive system ("RDS"), adapted for use in an elevator system. The elevator system as illustrated in figure 1 includes a primary motor 2, a conventional friction brake mechanism 3, and a winch drum 4. In the embodiment of figures 1 and 2, the primary motor is electric, whereas in the embodiment of figure 3 the primary motor is diesel. In some installations, a gearbox (not shown) may be installed intermediate the primary motor and the winch drum. An elevator car or cage 5 is suspended from the winch drum within an elevator shaft by means of wire rope 6. Actuation of the primary motor effects transmission of rotational power through the RDS unit to the winch drum. The load on the winch drum will fluctuate significantly as the cage periodically accelerates, decelerates and stops, moving upwardly or downwardly between levels, with varying numbers of passengers on board. In broad overview, the RDS 1 includes energy accumulation means in the form of a series of accumulators 7, each operable selectively to store and release energy through controlled receipt and release of pressurised hydraulic fluid, as described in more detail below. The system further includes a positive displacement hydraulic pump/motor assembly 8 in fluid communication with the accumulators, a low-pressure hydraulic reservoir 9 in fluid communication with the pump/motor assembly, and a controller 10 to regulate the operation of the system in response to predetermined variable parameters. These primary system components, and the interactions between them, are described in more detail below.

Referring to figure 4, the pump/motor unit 8 includes a stationary housing 12 and a cylinder block 13 supported within the housing for rotation about a central axis 15. The block 13 incorporates a circular array of hydraulic cylinders 16 uniformly disposed in parallel relationship about the central rotational axis 15. A corresponding array of axial pistons 20 is reciprocably disposed within the respective cylinders.

A central drive shaft 22 extends through a complementary bore 23 formed in the cylinder block. The shaft is drivingly connected to the cylinder block 13 by coupling means including spline formations 24 to effect rotation of the block about the central axis, as described in more detail below.

A stationary drive plate in the form of swash plate 25 is disposed at one end of the cylinder block (the right-hand end when viewing the drawing). The swash plate is pivotably supported on a cradle within the housing, for adjustable movement within a predetermined range, about an axis substantially normal to the rotational axis of the cylinder block.

A hold-down plate 26 is disposed to locate the free ends of the pistons remote from the valve plate in the appropriate relative spatial relationship, while the end faces of the pistons are formed with followers 28 adapted to engage and slidably traverse the operative surface of the swash plate. In this way, rotation of the cylinder block effects sequentially staggered reciprocation of the pistons, with the amplitude of piston travel being determined by the selected angle of inclination of the swash plate.

A stationary valve plate 30 is disposed at the opposite end of the cylinder block (the left-hand end when viewing the drawings) and is rigidly connected to the housing. The valve plate includes a valve face 31 adapted for sliding rotational engagement with a complementary mating valve face 32 formed on the abutting end of the cylinder block.

The valve plate includes inlet and outlet ports adapted alternately for fluid communication with the low-pressure reservoir and the accumulators.

The valving is arranged such that hydraulic fluid is progressively drawn into the cylinders in sequence through the inlet ports as the pistons withdraw away from the valve plate and is subsequently expelled from the cylinders through the outlet ports as the respective pistons are progressively advanced toward the valve plate, under the influence of the swash plate.

The swash plate is pivotably supported within the housing such that the effective angle of inclination with respect to the rotational axis of the cylinder block is adjustable to provide selectively variable flow characteristics. In particular, the swash plate may be progressively and alternately inclined in both a positive and a negative sense, for example by means of hydraulic control cylinders (not shown). This enables the assembly alternately to operate as a motor or a pump, of variable but positive displacement. In this regard, it should be appreciated that the particular valve ports which function as inlets to the cylinders of the pump/motor unit, and those which function as outlets, will alternate according to the operational mode of the unit. Importantly, the swash plate can also be orientated in an intermediate or neutral position in a plane effectively normal to the central axis, such that rotation of the cylinder block produces no reciprocation of the pistons. In this mode, the pump/motor unit induces no net fluid flow into or out of the cylinders, and consequently transfers no significant hydraulic load to the shaft.

The essential elements of construction, and the basic principles of operation, are common to most positive displacement axial piston hydraulic pumps, and being well understood by those skilled in the art, need not be described in more detail. The hydraulic pump/motor assembly 8, as described above, forms part of the regenerative drive and energy management system 1. More particularly, in the configuration as illustrated, the output shaft from the primary diesel or electric motor extends coaxially through the pump/motor unit, to act as the primary drive shaft 22 for that unit, and thereby obviate the need for supplementary gearboxes, chain drives, belt drives, or other transmission mechanisms. This shaft will hereinafter be referred to as the drive shaft for the pump/motor unit and the RDS. If required, a plurality of positive displacement axial piston pumps of the type illustrated can also be arranged axially along the drive shaft and may be connected hydraulically to operate in series, parallel, or a combination of both. In alternative embodiments, it will also be appreciated that the pump/motor assembly of the RDS unit may alternatively be connected to a gearbox, the load (i.e. the winch drum in this particular example), or any other suitable part of the power train.

As shown diagrammatically in figure 1 , the system further includes energy accumulation means in the form of a set of hydraulically operable gas/liquid accumulators 5. As shown in more detail in figure 5, each accumulator comprises a double-ended cylinder 60 and a piston 61 adapted sealingly to float within the cylinder. One side 62 of each cylinder contains a compressible inert gas 63 such as nitrogen, while the other side 64 of the cylinder is in fluid communication with the pump/motor unit via hydraulic lines 65.

Each accumulator is thereby adapted to store energy by receiving pressurised hydraulic fluid into one end 64 of the cylinder so as to compress the gas 63 on the other side, and adapted subsequently to release that energy by expulsion of the hydraulic fluid as the compressed gas is allowed to expand.

This general method of energy accumulation is well understood by those skilled in the art, and is described in more detail in the present applicant's earlier application number

PCT/AU99/00740, the full contents of which are hereby incorporated by reference. Again, however, it should be emphasised that alternative forms of energy accumulator such as bladder, bellows or diaphragm type accumulators can readily be substituted and further, that any suitable number and combination of accumulators may be used.

In use, the system is selectively operable in any one of three primary modes. In a first energy accumulation or braking mode, the system operates to retard the drive shaft by pumping hydraulic fluid into the accumulators and thereby compressing the contained gas medium. Alternately, the system is operable in an energy augmentation or driving mode to supply supplementary power to the drive shaft using the pressurised hydraulic fluid from the accumulators. In the energy accumulation mode, it will be appreciated that the hydraulic unit operates as a pump powered by the drive shaft, whereas in the power augmentation mode, the unit operates as a supplementary motor powered by pressurised hydraulic fluid from the accumulators. Thus, in the accumulation mode, the RDS converts kinetic energy from the drive shaft into potential energy in the form of gas pressure in the accumulators and conversely, in the augmentation mode, the RDS converts the potential energy in the accumulators back into kinetic energy in the drive shaft. The system is also operable in a third neutral or "free wheeling" mode, whereby the drive shaft is substantially unaffected by the pump/motor unit.

The three primary operational modes are regulated according to the angle of inclination of the swash plate 25, which in turn is regulated by an hydraulic or pneumatic actuator (not shown) in response to control signals from the electronic RDS management or control system 10. The RDS control system is programmably responsive to a predetermined series of system parameters including static load, cage position relative to selected destination, preset maximum cage speed, motor power output, swash plate position, drive line torque, accumulator pressure and hydraulic pump/motor pressure. As a straightforward example, the system may be programmed to progressively initiate the energy accumulation or retardation mode, whenever the downward speed of the cage exceeds a preset level of, say, 5 metres per second. In that case, the system would automatically apply a progressive retardation force whenever the cage exceeds that speed, irrespective of whether any supplementary braking system is used. In this mode, retardation is commenced by ramping the swash plate angle of the pump/motor unit by an initial increment. If speed continues to increase, the swash plate angle is progressively increased until the vehicle is slowed to the selected speed. At that point, the controller will incrementally modulate the ramp angle of the swash plate to maintain the dynamic equilibrium, until the control parameters change.

When the various position switches and displacement transducers indicate that the cage is approaching the selected level, the controller initiates a preset deceleration mode, in response to which the swash plate is displaced to the maximum degree in the braking mode. This maximises the rate of energy accumulation, and at the same time minimises the extent of braking energy required by the conventional elevator braking system (whether based on frictional, hydraulic or electromagnetic retardation mechanisms). If the elevator restarts in a downward direction, the RDS unit need not be activated, on the basis that gravitational acceleration would suffice in most circumstances, although it will be appreciated that the RDS unit could be programmed to operate so as to enhance acceleration in this situation if desired. If the elevator restarts in an upward direction, however, the primary motor is required rapidly to accelerate the full mass of the cage, the passengers and the supporting cable against both the force of gravity and the inertia of the moving parts of the system, which represents the transient peak load on the primary motor. In this situation, the controller of the RDS is configured to activate the pump/motor unit in the power augmentation mode, usually with the swash plate initially displaced to the maximum degree, and progressively reducing in angular displacement as the cage approaches the preset maximum speed. In this mode, as previously indicated, the unit acts as a positive displacement hydraulic motor, motivated by the pressurised hydraulic fluid previously stored in the accumulators, to feed supplementary rotational power directly into the drive line, between the primary electric motor and the winch drum.

Once the cage reaches a constant speed with no further acceleration being required, the peak load condition subsides. At this point, the controller is configured to return the swash plate to the neutral position, wherein the pump/motor unit operates in the "free wheeling" mode. Optionally, however, the controller may be configured to continue to provide power augmentation while the cage moves upwardly at constant velocity, subject to the level of stored energy in the accumulators, the detected mass of the loaded cage, and other relevant system parameters. This mode may be particularly advantageous, for example, if the cage is heavily loaded at or near its maximum capacity such that power augmentation is desirable even under steady state conditions.

The system is also ideally provided with an emergency braking mode, actuable in response to a number of predetermined system parameters, indicative of potential brake failure. For example, accelerometers mounted to the cage indicating downward acceleration at a level beyond a predetermined threshold can readily be used to activate the emergency braking mode. A manual emergency override switch within the cage is also readily provided. In this mode, whether activated manually or automatically, the swash plate is fully displaced in the braking mode, whereby the pump/motor unit operates as a pump, diverting rotational energy from the primary drive line by pumping hydraulic fluid under pressure into the accumulators, and thereby slowing the elevator cage to a safe speed. Further regulation can be provided by the throttling valve in the hydraulic control circuit, which can be used to slow, and if necessary stop, rotation of the pump/motor unit, even if the accumulators are fully charged. Importantly, this mechanism can implemented so as to operate even in the event of a complete power failure, which would render both the primary electric motor and any electromagnetic braking mechanisms inoperative.

In addition to the provision of an emergency braking mode, the system can be used to allow the elevator to continue to operate effectively in an emergency operational mode, at least for a period, even in the event of a power blackout or brownout, using the energy already stored in the accumulators. This includes upward movement between floors, provided the power output of the hydraulic pump/motor unit is sufficient in itself to overcome the gravitational force acting on the cage, and provided the accumulators are sufficiently charged. This functionality can be critically important in environments such as underground mines, where the ability to wind up an elevator cage in the event of a complete power or other system failure, offers the potential to save lives.

Even in this emergency operational mode, some charging of the accumulators can take place while the elevator cage or car descends under gravity, and decelerates at each selected level during descending runs. It should also be noted that because in this particular application the weight of the RDS itself is not critical, a large number of accumulators can be provided to store significant quantities of energy, for use in augmenting, or even substituting for, the power of the primary motor for relatively prolonged periods.

Figures 6 A to 6D are a sequence of hydraulic schematics showing in detail one preferred configuration of hydraulic control circuitry for the system, operating in the different modes or states as outlined broadly above. In these schematics, the primary flow path of the hydraulic circuit in each state is highlighted, for ease of explanation. The principal components of the circuit are as follows:-

Piston Type Hydraulic Accumulators 5;

Pump/Motor Drive Unit 8;

Low-pressure Reservoir 9;

Bi-Directional Drive Logic Cartridge 70;

Dump/Thermal Relief Flow Control Logic Cartridge 72;

Oil- Air Cooler with Bypass 74;

Filter Assembly 76;

Anti-Cavitation Check Valve Cartridge 78; • Dump/Thermal Relief Solenoid 80;

Stand-by Relief Valve Logic Cartridge 82;

Stand-by Two-Way Solenoid Valve Cartridge 84;

Two-way Drive Solenoid Valve Cartridge 86;

Proportional Directional Control Valve 88; • Dummy Cartridge Valve 90;

Check Valve Cartridge 92;

Direct Acting Relief Cartridge (30 Bar Setting) 94;

Direct Acting Relief Cartridge (350 Bar Setting) 96;

Direct Acting Relief Cartridge (380 Bar Setting) 98; • Flow Controller 100;

Bladder Accumulator with Pre-Charge 102;

Check Valve with 2.5 Bar Cracking 104.

Ancillary components represented graphically using conventional symbols.

The circuit is selectively operable in the primary modes or states, as outlined below.

1. Natural State

With all control signals removed (i.e. all solenoids de-energized), the system is effectively disabled in a natural rest state, as represented in figure 6A. In this state, the system is not capable of holding accumulated pressure. However, the pump's natural position is biased to the retard side. This means that any forward pump rotation in this state will result in a small flow of oil from the reservoir, through the pump, and returning to the reservoir via the essentially unrestricted flow path (shown in bold in figure 6A) through the Drive Logic Cartridge 70 and Dump/Thermal relief Logic Cartridge 72, then via the cooler 74 and filter 76 without providing any significant retard torque or drag. Any reverse pump rotation in this state will result in the same small flow of oil around the Anti- Cavitation Check valve Cartridge 78. However reverse pump direction in this natural state for prolonged periods is ideally to be avoided (see Reverse State below).

2. Dump State

This state, as also illustrated in figure 6A, is identical to the natural state described above. However, if this state is entered from any of the dynamic states described below, it will result in the same disabled condition as outlined above, with the additional effect of dumping any oil stored in the accumulators at a controlled rate via the Dump/Thermal relief Logic Cartridge 72. The flow rate through this cartridge is adjustable and is set during commissioning.

3. Stand-by State

To achieve this state, which is illustrated in figure 6B, power is applied to the Dump/Thermal relief Solenoid 80. This changes the pilot condition of the Dump/Thermal relief Logic cartridge 72, which will now act as a 380 Bar relief valve, enabling the system to store oil in the accumulators. However, there is still minimal retard torque or drag in this state, as the pump is still only operating on a shallow swash plate angle and the oil flow is still circulating back to the reservoir via the Stand-By Logic Cartridge 82, the pilot condition of which causes it to act as a 30 Bar relief valve. The purpose of this is to provide some backpressure to the pump, as the system will operate in this state for relatively long periods of time.

4. Additional Cooling Additional cooling capacity can be achieved between retard and drive cycles if required. With the system in the Stand-by state (see figure 6B), increasing the swash plate angle will increase the flow of oil circulating around the system and returning to the reservoir via the cooler, without creating substantial additional drag.

5. Reversing State

When the rotational direction of the drive line is reversed, the system is ideally switched to the reversing state. This is exactly the same as Stand-by state. However, in order to achieve flow in the desired direction, the pump swash plate is moved to a shallow propulsion angle. 6. Retardation State

As best illustrated in figure 6C, when it becomes desirable to collect energy from the drive system, energization of the Stand-by Solenoid 84 will alter the pilot condition of the Stand-by Logic Cartridge 82 and cause it to act as a 350 Bar relief valve. The Dump/Thermal relief Solenoid 80 will also be energized to enable it to hold oil in the accumulators. In this state, any oil being pumped from the reservoir will flow via the Drive Logic Cartridge 70, which will act as a check valve and allow oil flowing in this direction to pass through to the accumulators. In this state, the retard torque available can be adjusted by varying the swash plate angle. Once the accumulators are full to a pressure of 350 Bar, the oil being pumped will flow through the Stand-by Logic Cartridge 82 at 350 Bar, and back to the reservoir via the cooler and filter. This flow path, which becomes operative only after the accumulators reach the threshold pressure of 350 Bar, is represented by the thickened dashed line in figure 6C. The swash plate angle required at any given time to provide a specified retard torque is a function, among other things, of the pump speed, accumulator pressure and hydro-mechanical efficiency. In the embodiment illustrated, the swash plate angle is limited so as not to exceed a system flow of 370 litres per minute. If a situation occurs where it is necessary to cancel the retarding effect quickly, then de-energizing the Stand-by Solenoid 84 will allow oil to flow through the Stand-by Logic Cartridge 82 at 30 Bar, thereby removing the load from the pump, and removing the retarding effect. At the same time, the pump swash plate angle should be commanded to the shallow Stand-by position.

7. Drive State

As best seen in figure 6D, when it becomes desirable to discharge energy back into the drive system, energization of all solenoids will create a state where the oil from the accumulators will be allowed to flow back to the pump. In particular, energization of the Drive Solenoid 86 will vent the pilot on the Drive Logic Cartridge 70, allowing the accumulators to open, and then hold the Logic Cartridge open as the oil from the accumulators flows through. With the swash plate in the propulsion or reverse direction, the pump will now act as a motor, supplying drive energy as the oil flows through it and back to the reservoir. The drive torque available can now be adjusted by varying the swash plate angle. The swash plate angle required at any given time to deliver a specified drive torque is again primarily a function of the speed, accumulator pressure and hydro- mechanical efficiency. During the drive cycle, the electronic control system is configured to monitor the accumulator or reservoir capacity, so that the swash plate can be moved back to neutral and the system returned to the Stand-by state, before the accumulators are completely discharged. If this fails to happen, the oil will begin to be pumped around the

Anti-Cavitation Check Cartridge 78.

8. Emergency Drive

If the existing drive system should become disabled, the regenerative energy management system can be utilized to provide emergency drive, provided there is oil in the accumulators. Forward drive can be achieved in the same way as described in relation to the above Drive state. Reverse emergency drive can also be achieved by switching to the Drive state, but commanding the swash plate to the Retard direction.

By providing an integral energy management system capable of storing surplus energy in off-peak periods and subsequently augmenting the power of the primary motor during transient periods of peak load, the primary motor can be scaled down and specified with a lower maximum capacity than would otherwise be the case in the same system. This significantly reduces the size, weight and capital cost of the primary motor, whether this motor is electric, diesel, petrol, or of any other type. Furthermore, dramatic reductions in power consumption can be achieved, firstly because the primary motor is able to operate within its optimal efficiency range for a greater proportion of the duty cycle, and secondly because energy that would otherwise be lost, for example as heat through conventional braking mechanisms, is able to be recovered and reused. Further, by providing supplementary braking in the energy accumulation mode, the regenerative management and drive system is able to significantly reduce wear in critical and costly components such as brakes, clutches, gearboxes and transmissions. At the same time, the invention provides a supplementary emergency braking system, operating entirely independently from the primary braking system, which confers an additional level of redundancy, and consequently greater safety. In all these respects, the invention represents both a practical and a commercially significant improvement over the prior art.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims

CLAΓMS

1. A drive mechanism for an elevator system, said drive mechanism including:- a primary motor; hoisting means operatively connected as a load to the primary motor and adapted to raise and lower an elevator car between a plurality of the preset levels; and a regenerative drive system, the regenerative drive system incorporating: energy accumulation means operable selectively to store and release energy through controlled receipt and release of pressurised hydraulic fluid; a positive displacement hydraulic pump/motor assembly in fluid communication with the energy accumulation means; a low-pressure hydraulic reservoir in fluid communication with the pump/motor assembly; a drive shaft adapted for connection to the primary motor; and a control system adapted selectively to regulate the pump/motor assembly in response to predetermined operating parameters, whereby: in an accumulation mode the pump/motor assembly operating as a pump draws surplus power from the drive shaft by diverting hydraulic fluid under pressure into the accumulation means; in an augmentation mode the pump/motor assembly operating as a motor supplies supplementary power to the drive shaft using pressurised hydraulic fluid from the accumulation means; and in a neutral mode the pump/motor assembly exerts no substantial influence on the drive shaft; the system being thereby adapted progressively to accumulate surplus energy during periods of off-peak load and to augment power output from the primary motor on demand to accommodate the transient peak values of the load.

2. A drive mechanism according to claim 1 , wherein the primary motor is of a type selected from a group comprising electric motors, diesel engines, petrol engines, steam engines, hydraulic motors, water turbines, gas turbines, and wind turbines.

3. A drive mechanism according to claim 1 or claim 2, wherein the hoisting means include a rotary winch drum, adapted to support and regulate the level of the elevator car by means of an interconnecting cable.

4. A drive mechanism according to any one of the preceding claims, wherein a maximum steady-state power output of the motor is less than the power required for anticipated transient peak values of the load, thereby enabling selection of a smaller capacity motor than would be required in a conventional elevator system of comparable load carrying capacity.

5. A drive mechanism according to any one of the preceding claims, wherein the hydraulic pump/motor assembly includes :- a rotary cylinder block having a central axis and incorporating a generally circular array of cylinders disposed around the axis; a corresponding plurality of pistons reciprocably disposed within the respective cylinders; a drive plate disposed at one end of the cylinder block to effect sequentially staggered reciprocation of the pistons in response to rotation of the cylinder block; a stationary valve plate disposed at an opposite end of the cylinder block, the valve plate having a valve face adapted for sliding rotational engagement with a complementary mating face formed on the cylinder block; the valve plate further including at least one inlet port adapted for fluid communication with the low-pressure reservoir and at least one outlet port adapted for fluid communication with the accumulation means; the ports being disposed such that in use, hydraulic fluid is progressively drawn into the cylinders in sequence through the inlet ports as the respective pistons are displaced away from the valve plate and subsequently expelled from the cylinders through the outlet ports as the pistons are progressively displaced toward the valve plate.

6. A drive mechanism according to claim 5, wherein the cylinders are disposed in generally parallel relationship around the axis.

7. A drive mechanism according to claim 5, wherein the cylinders are disposed in generally radial relationship around the axis.

8. A drive mechanism according to claim 5, wherein the drive shaft extends coaxially through a complementary bore formed in the cylinder block, to effect rotation of the cylinder block about the central axis.

9. A drive mechanism according to claim 8, wherein the pump/motor assembly further includes a selectively releasable decoupling mechanism disposed effectively intermediate the drive shaft and the cylinder block.

10. A drive mechanism according to claim 9, wherein the decoupling mechanism is adapted in an engaged mode to connect the drive shaft to the cylinder block and in a disengaged mode to allow the drive shaft to rotate substantially independently of the cylinder block.

11. A drive mechanism according to claim 10, wherein the decoupling means include a clutch mechanism disposed coaxially around the drive shaft, to selectively transmit rotary drive between the drive shaft and the cylinder block.

12. A drive mechanism according to claim 5, wherein the drive plate takes the form of a stationary swash plate, which is inclined with respect to the central rotational axis of the cylinder block.

13. A drive mechanism according to claim 12, wherein floating ends of the pistons remote from the valve plate include followers adapted to slide over the swash plate as the cylinder block rotates.

14. A drive mechanism according to claim 13, wherein a hold-down plate is disposed to capture the floating ends of the pistons and retain the followers in sliding contact with the swash plate.

15. A drive mechanism according to any one claims 12 to 14, wherein an angle of inclination of the swash plate is selectively adjustable, to provide variable flow rate characteristics.

16. A drive mechanism according to claim 15, wherein the swash plate is adapted to be selectively inclined in a positive or a negative sense, thereby enabling the assembly alternately to operate as a motor or a pump.

17. A drive mechanism according to claim 16, wherein the swash plate can also be oriented in an intermediate or neutral position, effectively normal to the central axis, such that rotation of the cylinder block causes no movement of the pistons, hence induces no net flow into or out of the cylinders through the ports, and therefore causes no substantial load on the system.

18. A drive mechanism according to claim 5, wherein the pump/motor assembly includes at least three external ports to permit ingress and egress of hydraulic fluid, with a first port communicating with an inlet of the hydraulic reservoir, a second port communicating with an outlet of the hydraulic reservoir, and a third port communicating with the accumulation means.

19. A drive mechanism according to claim 18, wherein a heat exchanger is disposed between the first port and the reservoir.

20. A drive mechanism according to any one of the preceding claims, wherein a plurality of the pumps is arranged axially along the drive shaft.

21. A drive mechanism according to any one of the preceding claims, wherein the regenerative drive system includes a flow control circuit through which hydraulic fluid may be selectively directed, the control circuit being adapted to provide a controllable resistance enabling the pump/motor unit selectively to exert a retarding force on the drive shaft when the accumulators are fully charged.

22. A drive mechanism according to any one of the preceding claims, wherein the accumulation means include a gas/liquid accumulator comprising a double-ended accumulation cylinder and a piston adapted to float sealingly within the cylinder.

23. A drive mechanism according to claim 20, wherein one side of the accumulation cylinder contains a compressible inert gas, and the other side of the cylinder is connected hydraulically to the pump/motor unit.

24. A drive mechanism according to claim 23, wherein the accumulator is adapted to store energy by pumping hydraulic fluid into one side of the cylinder, so as to compress the gas on the other side by displacement of the floating piston, and subsequently to release that energy by expulsion of hydraulic fluid as the compressed gas expands.

25. A drive mechanism according to any one of the preceding claims, wherein the pump/motor unit is connected directly to an output shaft of the primary motor, such that the output shaft of the primary motor and the drive shaft of the pump/motor unit are coupled for conjoined rotation.

26. A drive mechanism according to claim 25, wherein the output shaft of the primary motor and the drive shaft of the pump/motor unit are integrally formed.

27. A drive mechanism according to any one of the preceding claims, wherein: the control system is configured in response to predetermined system conditions so as selectively to: activate the accumulation mode in order to apply retardation torque to the winch drum; activate the augmentation mode in order to apply drive torque to the winch drum; and activate the neutral mode when no retardation or supplementary drive torque on the winch drum is required; the system being thereby adapted to accumulate surplus energy during periods of retardation or off-peak load and to augment power output from the primary motor on demand to accommodate the transient peak values of the load as the elevator car moves between the preset levels.