MOBILE LOADERS

2!.03 iMPROVEMENTS IN OR RELATING TO MOBILE LOADERS i5 The present invention relates to loaders and particularly to the type of mobile loader which incorporates a variable height platform used for loading and unloading freight in, for example, the cargo holds of aircraft.

Mobile loaders are essential eqipment for the loading and unloading of cargo into and from the holds of aircraft:.

Such loaders often employ two platforms. One platform, usually referred to as a bridge provides an interface with the sill of the cargo door and remains in a substantially constant position with respect to the aircraft. The second platform cycles up and down either taking cargo from the bridge or delivering cargo to the bridge.

}Heretofore, the second platform has always been raised and lowered by means of hydraulic systems acting through approprìate mechanical linkage8 which ensure that the platform maintains a substantially horizcnta[ attitude.

The loaders are frequently moved by diesel engines with ail the attendant problem8 of noise, air pollution, fuel spillages, safety hazards and high maintenance cost etc.

In order to move away from diesel engines some designers have followed a conversion approach whereby substantially standard vehicle have been taken and converted te electric power by the installation of motors and batteries etc. Usually, however, the hydraulic platform actuating system has been retained with hydraulic pumps driven by electric motors. The major »rob]em with this approach is 1 ç 7109 27614-I that the resulting loaders have low performance and low energy efficiency, especially with respect to load lifting performance.

It has been calculated that for a typical service on a Boeing 747 aircraft where the hold is unloaded on arrival and then loaded for departure that over 55% of the energy required from a loader's power systems are required in the raising and lowering of the loading platform. Nearly 30% of the remaining demand is taken up in driving the loader to and from and around the aircraft.

It is, therefore, considered to be a pre-requisite that lifting efficiency is of paramount importance in mobile loaders.

Hydraulic systems are notably inefficient in terms of energy consumption, much energy being wasted in pumping fluids.

In the case of mobile !oaders in airports once energy has been expended in raising the loading platform it is all totally wasted during lowering of the platform. The platform is usually lowered by bleeding-off the hydraulic fluid through valves, usually into a reservoir for use again later in raising the platform. The energy efficiency of hydraulically operated systems is typically about 35%. A result of such low energy efficiency is that the overall performance of such loaders is relatively low. Their driving speed is low and endurance is relatively short.

By employing mechanical systems instead of hydraulics to raise the platform, the mobile loader of the present invention provides for recharging the batteries when the loading platform is being lowered by switching the drive motor into an electrical generator.

The present invention provides a loader vehicle i0 27614-I comprising a chassis having a variable height platform, the platform being connected to the chassis by means for maintaining the platform in a substantially level attitude irrespective of platform height, recirculating ball-screw jacks operably connected to the platform for varying the height of the platform with respect to the chassis, first electric motor drive means connected by mechanical transmìssion means to "Che ball-screw jacks for raising the platform, second electric motor drive means operably connected to vehicle drìve road wheels, battery means for powering said first and said second electric motor drive means, control means for controlling the operation and function of said first and said second electric motor drive means, at least said first electric motor drive means being convertible into generator means to provide retardation by regenerative braking of the platform when in the descending mode and to provide at least partial recharging of the battery means and switching means such that the control means is only operable on said first or said second electric motor drive means at any one time.

The lifting platform may be a relatively conventional design wherein the platform is maintained in a substantially level attitude by a known scissor arrangement. The re-circulating ballscrew jacks may be connected to the platform via the nut of the screw such that as the screw is rotated the nut and platform are caused "to be raised.

Preferably two re-circulating ball-screws may be used drlv n by a common electric motor vla a transmission.

1 67109 27614-1 During, for example, the unloading of an alrcraft cargo hold where a substantially empty platform is raised and a fully loaded platform is lowered it has been found that a nett overall gain in power may be realised at the batteries. It will be appreciated that the heavier the load being lowered the greater is the power generated during regenerative braking, thus giving more charging of the batteries.

It has been found that taken overall, that is, during loading and unloading of aircraft, the energy efficiency of the present invention is nearly 60%. This includes all of the losses associated with battery conversion, controls, motors and transmissions.

Preferably the vehicle chassis may also include thereon a second platform or bridge to provide a loading or unloading interface with the airoraft cargo hold. The bridge may be raised and lowered by any known method and since it remains at a substantially constant height during the aircraft loadin /unloædlng operation it may be found convenient to use hydraulic operation.

The chassis includes wheels and other traction means and drive and steering means for some of the wheels such that loader operation may be substantially autonomous. For the chassis drive means electric motor one type of motor which has been found particularly advantageous are hub mounted motors in the drive wheels. Steerable drive wheels may be employed and these have been found to give excellent manoeuverabJlity to the loader, Preferably the transmission means to the mechanical liftíng means aise includes a rail-sale brake which effectively locks the platform at the desired heíght. The brake is released by electrical signais to allow lowering of the platform. In the event of an electrical power failure the brake is automatically applied to prevent an uncontrolled descent of the platform.

According to a feature of the invention the mechanical lifting means are provided by re-circulating bail-screw jacks, Preferably two such jacks are employed to give rigidity to the platform when being either raised or lowered. It has been found that such devices allow very precise control of platform height in operation. During raising and loweríng of loads of up to 7000 kg height control at any position of better than 0.Smm may be reliably obtained.

Re-circulating ball-screw jacks are very efficiency in operation by virtue of having rolling element bearings. On release of the locking brake the platform begins to descend accelerating due to gravity, in the descending mode the electric motor used for raising the platform is switched by the control means into an electrical generator and the outrent generated is used to retard the platform and to at least partially recharge the batteries. Such a technique is known as regenerative braking and is a known technique used with electric powered vehicles to dissipate kinetic energy of a moving vehicìe. Even with moving vehicles the energy produced during regenerative braking is only 10% or so from the kinetic energy. In the present invention regenerative braking is used to convert the potential energy of the raised platform into useful energy part of which may be recouped to provide longer endurance and more economical operation.

[f hydraulic lifting means were to be employed it would not be practicable to turn a hydraulic pump into a motor for driving a generator/motor because of the low efficiency of the hydraulic transmission in this mode. The costs of installing such a system based on hydraulics would far outweigh any energy which may be generated for battery recharging.

In order that the invention may be more fully understood embodiments will new be described by way of example only with reference to the accompanying drawings of which:

Figures l(a), (b), (c) and (d) show a loader according to the invention in side and front elevations with bridge and platform raised and plan view and front elevation with brìdge and platform lowered respec relative Figure 2 shows a schematic view of a platform lifting mechanismand control system of a loader according to the invention; Figure 3 shows a schematíe view of an alternative control system of a leader according to the invention; Figures 4(a), (b) and (c) show schematic views of an elecoeical eircuil: for controlling the motor current during reining and lowering of the platform in a loader according to he invention; and i 7 17,675,.0,9 I5 Z0 Z5 Figures 5(a) and (b) show graphs of current flow in the motor armature and to the batteries during regenerative braking of the descending load in a loader according to the invention.

Referring now to the drawings and where the same features have common reference numerals.

Figures l(a) and l(b) show a loader lO having loading/unloading platform i1 and bridge 12 in the raised position. The platform 11 is supported and maintained in a level attitude with respect to a chassis 13 by a scissor jack arrangement 1{€. The bridge 1Z is similarly supported on a scissor jack arrangement 15 which is raised and lowered by hydraulic rams 16. The platform i1 is raised by means of re-circulating bail-screw jacks 17 and leaf chains 18, the chains being secured to the platform 11 at one end and to the chassis 13 at the other end. Attached to the bridge 12 is a cab 19 for an operator; within the cab 19 is a control panel (net shown). The chassis 13 is supported on four wheels, the rear pair 20 are free-wheeling and the front pair 21 incorporate steering king-pins (not shown) and hubmounted drive motors (not shown). Aise in the cab ì9 is a steering wheel 24 linked to the front wheels 21 by power-actuated hydraulic steering means 25 (not shown). At strategic points on the chassis 13 are retractable hydraulic jacks 26 to stabilise the loader 10 when in operation at an aircraft , (not shown). Mounted on the front of the chassis 13 is a housing 28 in which barrer'les (not shown)motoI'/ generator means (not shown) and associated transmission means (not shown) etc. are housed. These are described in detail in Figures 2, 3 nd/*.

l.Zt 7.1.0, The platform raising and lowering mechanism comprises the platform 11 linked to two re-circulating bail-screw jacks 17 as described with reference to Figure 1. The screws 17a are connected through gearbox transmission units 40 and shafts 41 to a series-wound D.C. motor/generator 42. Also on one of the shafts 41 is a brake Connected to the motor/generator 4Z is a motor/generator control unit /44 (described in greater detail in Figure 4) and an energy source whìch in this case is a 72 voit battery pack. Also connected to the control unit 44 is a function controller 46. In operation to lift a load /47 on the platform il the function controller selects motor drive and rotation of the output shaft of the motor 42 rotates the screws 17a of the re-circulating bail-screw jacks 17 via -he shafts 41 and transmission units 40. The nuts !7b of the ball-screw jacks are prevented from turning by being fixed in housings associated with the eha is i5 thus rotation of the screws 17a causes the nuts 17b to rise up the screws sg elevating the platform ii and load Z 7. When the platform 11 has reached a desired height the screws 17a are stopped and the brake 43 is automatically engaged and the load 47 removed from the platform. The function controller 46 now selects generator and the platform 11 is ready to be lowered. The platform is allowed to accelerate to a predetermined rate of descent (if there is a load on the platform the rate of acceleration will be greater). When the desired rate of descent is achieved Che generator 42 exerts a retarding force on the platform and prevent the rate of descent from increasing. This occurs regardless of the load 47 on the platform ll. The motor/generator 6,2 is driven by virtue of the 1; 6 î,103 screws 17a revolving by virtue of the load imposed through the nuts !7b. The revolving screws 17a drive the motor/generator 42 via the transmission units 40 and the shafts 41. As the platform 11 nears the desired lower level the retardation on the platform is increased by the motor/generator Z 2 and the platform is decelerated and brought to a gentle stop within 0.Smm of the desired position. The operation of the motor/generator control unit 44 is described below with respect to Figure b,.

Figure 3 shows a similar platform lifting mechanism and control i0 system therefor as that shown in Fìgure 2. In addition9 however, there is a further switching unit 50 to allow the motor/generator control unit 44 to control the operatìon of a further electric motor or motors 51 for driving the road wheels 2I of the loader. The motors 51 may be integral hub motor/gearbox units or may drive through separate tïansmìssion units 52.

It will be appreciated that a common control unit 44 may be employed sinoe the platform ll is never raised or lowered whilst the loader l0 is in motion and vioe versa.

The operation of the motor controuer 44 will now be described with reference to Figures 4(a), (b) and (c) and Figures 5(a) and (b).

When the platform 11 is being raised She current flow through the motor/generator 42 in the motor mode is generally as shown in Figure 4(a), The thyristor G0 may be switched on or off with varying relative periods of on to off to achieve controlled current flow through the armature G1 of the motor 42 and field coils G2« In this case the motor is driving the aerews 17a to effect liftìng of the io IZ671G9 "'i.

i0 platform 11. Aise in the electrical circuit is a regenerative braking diode 63, an inductance 64, a motor diode 65, a switch 66 and the battery pack 45. In the platform lifting mode the switch 66 is closed.

With the platform l! in the descending mode where the mass of the platform I1 and any load 47 thereon imposes a torque on the screw 17a via the nuts 17b and causes the motor armature 61 to accelerate in the reverse direction to the motor mode (see Figures 4(b) and (c)). To control the rate of descent of the platform 11 a counter-balancing torque is applied to the armature 61 by the technique of regenerative braking, in Figure 4(b) the switch 66 is opened thus breaking the cìrcuit continuity above the armature 61, there is, therefore, no current flow from the battery pack 45. As Che armature 61 coils cut through the magnetic field generated by the field coils 62 a voltage is generated. With the thyristor ON (Fig. 4(b)), current will flow through the regenerative braking diode 63, arma -ure 61, field coils 62 and inductance 64. Because of the nature of seríes wound D.C, motors, there is very Utile resistance to current flow and current will build up within this circuit loop exponentially (See Fig, 5(a) ). At; a pre-determined and set level of current, which may be varied to provide a greater or lesser degree of regenerative braking force, the thyristor 60 is made to switch off. With the thyristor 60 switched OFF as indicated in Fig. 4(c) the following set of circumstances pertain. Current had been flowing at a high rate within the field coils 6Z and inductance 64 prior to the thyristor witching off and thus there la electrical inertia within the circuit.

This electrical inertia takes the form of magnetic energy within the ,J.._ Iz IZ6'71...0 coils of the inductance 64 and the field coil 62. When the thyristor is switched off the energy díssipates through the motor diode into the battery pack 45. When the thyristor 60 switches off the voltage at the thyristor 60 may rise to many hundreds of volts which is easily sufficient to cause current flow back into the battery 45 to provide recharging thereof.

Figure 5(a) shows the current flow in the armature 61 whilst the thyristor 50 ís ON. The current is rising exponentially until the l:hyr]stor &O switches off when the euoeent flows into the battery As the current in the armature falls to a pre-determined and set level the thyristor again switches on to repeat the cycle. The graph at Figure 5(b) thus shows a typical current flow characteristic into the battery.

A smooth operation of the lìfting platform 11 is thus obtained by pulsing control of the thyristor 60. Where a heavy load is being lowered the rate at which the thyristor 60 switches on and off will be greater than for a lighter load.

By the use of regenerative braking of the descending platform very precise control may be obtained of the posìtion, acceleration and speed of the platform.

The figures given below in Table I show the calculated ideal energy consumptions to raise and lower a platform weighing 2500 kg with the indicated loads over a stroke of 1865mm compared to measured energy levels on an actual loader according to the invention.

Battery eonditiona were 72 volts and 75% charged.

J TABLE 1 LOAD (kg) IDEAL MEASURED EFFICIENCY Calculated (AHrs) Measured (AHrs) % Raise 7000 0.67 1.3"7 49 Raise 4000 0.46 0.95 b,8 Raise 2000 0.32 0.65 49 Raise 0 0.18 0.40 Lower 0 -0.18 -0.1Z 66 Lower 2000 -0.32 -0.20 62 Lower 4000 -0.46 -0.30 Lower 7000 -0.67 -0.42 62 It may be seen that in ail cases over 60% of the available potential energy of the raised platform is reoouped during lowering thereof.

Table Z below shows the overall energy oonsumed in a typical service on a Boeing 747 aircraft for the schedule indicated, Figures are oompared between a loader according to the invention, a typical hydraulic platform loader and idea] power consumption assuming 100% efficiency.

TABLE 2 FUNCTION IDEAL LOADER OF TYPICAL INVENTION HYDRAULIC ENERGY % ACTUAL % LOADER % Raise/Lower 8.35 Driving 4.01 Bridge 0.34 Conveying 0.80 Services 1.40 56 14.49 50 26.20 27 8.00 28 14.85 31 2 2.25 8 2.25 2.70 9 2.70 6 1.40 5 1.40 3 TOTAL lt 90 AHrs 28.84 AHrs 47.40 AHrs Duty per 747 aircraft service= 1 x 7 tonnes pallet load and unload 3 x 4 tonnes palier load and unload 8 x 2 tonnes container pair load and unload 400 meters driving 3 × bridge lifts 0.1 hour conveying 0.3 hour night lighting ;J& 09 Assumptions:

Platform deck 2500Kg8 Bridge deck 2000kgs Door height 2.8m Vehicle weight 13 tonnes Rolling resistance 200 N/Tonne IL is apparent from Table 2 that the increase in overall efficíency of the loader of the present invention is mainly due to the superior efficiency achíeved with the use of regenerative braking of the descending platform and the use of direct traction drive of the wheels by electric motors rather than using hydraulic transmission.

Although the present invention has been deseribed with reference fo aircraft loaders the same principles may equally well be applied to almost any lifting machine which uses electricity for power and has to control the descent of heavy loads. Machines such as fork-lift trucks operating in warehouses, for example, may employ the method and apparatus of the invention.

Other mechanical equivalents to scissor-jacks may also be used without departing from the scope of the invention.

Similarly, although the invention has been described employing two re-circula -íng ball-screw jacks located at the frontof the lífting platform, a single centrally placed unit may be equally suitable in some applications on smaller machine 'Z K iZ6 7.. OD THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

2761 -i i. A loader vehicle comprising a chassis having a variable height platform, the platform being connected to the chassis by means for maintaining the platform in a substantially level attitude ìrrespective of platform height, recirculating ball-screw jacks operably connected to the platform for varying the height of the platform with respect to the chassis, first electric motor drive means connected by mechanical transmission means to the ball-screw jacks for raising the platform, second electric motor drive means operably connected to vehicle drive road wheels, battery means for powering sa±d first and said second electric motor drive means, control means for controlling the operation and function of said first and said second electric motor drive means, at least said first electric motor drive means being convertible into generator means to provide retardation by regenerative braking of the platform when ±n the descending ,,ode and to provide at least partial recharging of the battery means and switching means such that the control means is only operable on said first or said second electric motor drive means at any one time.

2. A loader vehicle according to claim i wherein the motor/generator is a serles-wound DC device able to provide regenerative braking at low speeds of armature rotation.

FETHERSTONHAUGH & CO.

OTTAWA, CANADA PATENT AGENTS