WO2009125063A1

WO2009125063A1 - Electrical system for a forklift

Info

Publication number: WO2009125063A1
Application number: PCT/FI2009/050262
Authority: WO
Inventors: Janne Polvilampi; Mika Sokka
Original assignee: Rocla Oyj
Priority date: 2008-04-09
Filing date: 2009-04-08
Publication date: 2009-10-15
Also published as: FI20085290A0

Abstract

The invention relates to an electrical system for a forklift, a method for manufacturing the electrical system for a forklift, and a forklift using the electrical system. The electrical system comprises a direct current source (4), a module (7), which is preferably an inverted rectifier, i.e. an inverter, and a technology platform (5), as well as additionally at least one module (6, 8, 10) for raising a voltage on the technology platform (5).

Description

Electrical system for a forklift

The invention relates to an electrical system for a forklift, a method for manufacturing the electrical system for a forklift, and a forklift operating on the electrical sys- tern. More specifically, the question is about an electrical system capable of converting a direct current supplied by a power source into an alternating current and at the same time raising the alternating current's voltage to a higher level.

In prior art forklifts, the employed power source is provided, among others, by 24V, 36V, 48V or 96V voltage batteries. When using a battery having some specific vol- tage, the entire electrical system has been built at the same time to match this specific voltage. Technology in forklifts, such as for example controllers and motors, is thus always specified according to the battery voltage. In practice, it has not been possible to refit a forklift with a new battery of another voltage but, instead, the voltage of a replacement battery must be equal to that of the old one.

In light of the above, the forklift manufacturers are forced to maintain technology platforms applicable to all commercially available, known battery voltages (for example 24V, 36V, 48V or 96V). This use of technology platforms based on several unequal battery voltages reduces further the production volumes of various electrical components as every voltage requires its specific components. The result of this is that several key components have long delivery times, which in turn leads to the necessity of being able to anticipate the order book development over a long term and to maintain an adequate component stock for maintenance work.

It is an object of the invention to eliminate the foregoing drawbacks and to provide a type of electrical system for a forklift, which enables the use of power sources of various voltages in a single forklift. In addition, by increasing at the same time the operating voltage on a technology platform to a higher level, other considerable extra benefits will be attained.

This is achieved according to the invention by disrupting the currently existing interconnection between a power source voltage and an applied technology, and by raising the electric voltage on the component side to a higher level.

An electrical system according to the invention, a method for manufacturing the electrical system, and a forklift operating on the electrical system are characterized by what is presented in the characterizing clauses of the independent claims. In addition, other preferred embodiments of the invention are presented in the sub- claims.

An advantage offered by the invention is the possibility of using power sources of unequal voltages in one and the same forklift without other component replace- ments. In the process of increasing the voltage of a direct current received from a power source, the system used for a voltage increase can be controlled in such a way that the obtained supply voltage will always be the same.

The above-described arrangement enables a development of consistent technology for all forklifts in production. No longer is it necessary to use different compo- nents with power sources of unequal supply voltages, thus harmonizing technology architecture and achieving major savings on the component/maintenance side.

Further benefit is achieved as the voltage is increased sufficiently (voltage being on the component side for example 230V or as high as 1000V), and it will also become possible to make use of components, which are in mass production even at the moment and have a high production volume, whereby the prices of such components will be but a fraction of those of the components currently used in forklifts. At the same time, the availability of components is improved, which enables faster maintenance work as necessary replacement components do not require a special order, which might involve quite a long delivery time. The same benefit is accom- pushed also in the production of new forklifts as the delivery times of especially so- called key components become shorter. A significant reduction in the range of various components contributes to reducing the component quantities held in the inventory by a forklift manufacturer, whereby the unfinished production capital tied up therewith can be minimized. In the past, the forklift manufacturer has also been forced to make preparations to produce components of various voltage levels, even though the prediction of sales regarding various forklift models can be extremely difficult. In the past, this has tied up a considerable amount of resources, which can now be released for other projects.

At the same time as the number of components needed in the production of for- klifts will be reduced considerably with all forklifts using components of the same voltage level (the same technology platform), the development of new products is plausible with less investment. This is a result of the considerably faster product development run-through cycle in the schedules of product development projects. The increase of voltage brings also other remarkable benefits, such as physical downsizing of components. Among other things, this enables the use of smaller electric motors and opens up new avenues in forklift engineering and design as the components are no longer in such a defining role. The size of motors is only about 1/3 of what it used to be, if the voltage is raised for example to 230V.

In addition, the increase of voltage reduces the amount of current needed for producing the same power (P=U*I). The decrease of current leads to a reduced loss of power and to an improved efficiency of the system. By virtue of the improved efficiency, the employed voltage source shall have an increased longevity. On the other hand, the higher voltage level enables a departure from technologies designed just for forklift applications (primarily motor & controller). Hence, it is possible to proceed to the use of generally known and considerably higher volume components, whereby the price of components comes down and the availability improves. At the same time, another advantage is gained in the form of physically smaller-size components, because the size of all employed components will become smaller.

The higher voltage level enables also the use of permanent magnet motors in for- klifts. As a result of this, the motors can be mounted directly on a drive pulley shaft without needing a separate gearshift, thus simplifying the forklift engineering. The use of permanent magnet motors enables also the design of totally new type of forklifts. Along with the use of other smaller components, the use of space can be optimized on a totally different level, hence opening up completely novel opportunities in forklift engineering.

The invention will now be described more closely with reference to the accompa- nying drawings, in which

fig. 1 shows, in a simplified sketch of principle, a forklift's electrical system according to the prior art,

fig. 2 shows, in a simplified sketch of principle, one embodiment for an electrical system according to the invention, fig. 3 shows, in a simplified sketch of principle, a second embodiment for an electrical system according to the invention, fig. 4 shows, in a simplified sketch of principle, a third embodiment for an electrical system according to the invention,

fig. 5 shows, in a simplified sketch of principle, a fourth embodiment for an electrical system according to the invention. Fig. 1 shows, in a simplified sketch of principle, a forklift electrical system according to the prior art, comprising a battery 1 , a DC/AC inverter 2, as well as a technology platform 3 adapted to the electrical system (battery voltage). In this, just like in subsequent figures, the technology platform is represented by a motor typically associated therewith. It should be appreciated, however, that this representa- tion refers to an entire technology platform and all of its components. The practical result of selecting a voltage for the battery 1 is that the voltage for, components, such as for example electric motors, used on the technology platform 3, will become fixed as well.

Fig. 2 shows, in a simplified sketch of principle, a solution according to the inven- tion for a forklift' s electrical system, in which electrical system a permanent interconnection between a voltage source 4 and a technology platform 5 has been disrupted. This has been done by placing between a voltage source 1 and the technology platform 5 a module 6 useful for raising the voltage, which increases the electrical system voltage to a desired level. This level can be for example 110V, 230V, 560V or as high as 1000V. The voltage increase is followed by using a module 7, which is preferably an inverted rectifier, i.e. an inverter/direct-current chopper, for converting direct current to alternating current and for conducting the current to the technology platform 5. The module 6, used for raising the voltage, is preferably of the type lending itself to be adjusted in compliance with the voltage of the employed power source 4, such that, by adjusting the module, each supply voltage can be processed into a desired output voltage which is always the same. Adjustment of the module 6 takes place simply from a forklift control unit (not shown in the figures) by regulating the direct-current chopper. Another embodiment is to have for example three direct-current choppers (three discrete modules 6), designed for unequal-voltage batteries, installed in parallel in the electrical system, in which case, by coupling a correct direct-current chopper with the electrical system, the reached end result will be the same as that obtained with an adjustable direct-current chopper.

Fig. 3 shows, in a simplified sketch of principle, a second alternative arrangement for executing the same functions (raising voltage and converting direct current to alternating current). What is performed first in this embodiment is a conversion of the current transmitted by a power source 4 from direct current to alternating current by means of a module 7 (inverted rectifier or inverter/direct-current chopper), and not until thereafter is the voltage increase performed by a module 8 to a de- sired level. The module 8 is preferably a transformer. From the module 8, the current is passed through a module 9 to an employed technology platform 3. The module 9 is preferably a frequency transformer, whereby alternating current is converted to direct current and back again to alternating current, thus enabling a change of the phase and/or frequency of the alternating current. This alternating current emerging from the module 9 is used, for example, for controlling a motor included in the technology platform 5. In a manner similar to the system of fig. 2, the module 8 can be adjusted in compliance with the voltage of a voltage source or the system can be arranged to include several modules for voltage sources of various voltages. Fig. 4 illustrates an embodiment, wherein the module 7 and the module 8 of fig. 3 are integrated into a single module 10. Thus, said module 10 is used for performing, in one and the same module, a conversion from direct current to alternating current and a voltage elevation. The employed module 10 is preferably a functionally appropriate frequency transformer, i.e. an inverter. Other than that, the system is similar to that of fig. 3. In a manner similar to the system of figs. 2 and 3, the module 10 can be adjusted in compliance with the voltage of a voltage source or the system can be arranged to include several modules for voltage sources of various voltages.

Fig. 5 illustrates yet another embodiment, wherein the solution of fig. 2 is further provided with a backup power source 11 , which enables operating the forklift even if the actual power source has gone flat. Such a solution, as shown in fig. 5, can also be used for example for momentarily storing the energy created in a forklift braking process. The storage of energy in such a solution and, respectively, the releasing of energy, are considerably more efficient than feeding it back to the ac- tual power source 4. The higher voltage level, which is used in the solutions according to the invention, enables also in this application the use of smaller components (capacitors).

Within a scope of protection as defined by the claims, there are still a wide variety of feasible embodiments, such as for example by including the backup power source 11 in the solution of fig. 3 and, respectively, in the same way as shown in fig. 4, an assembly consisting of the modules 7 and 8 (inverter and transformer) can be replaced by the integrated module 10.

In figs. 1-5, the technology platform has been represented by an electric motor M but, as obvious for a skilled artisan, the can be regarded as relating to any electric component in a forklift. Important components on forklift technology platforms include particularly various controllers and motors.

Described above are but a few preferred embodiments for a forklift electrical system of the invention, and it is obvious for a skilled artisan that various embodiments can be implemented without departing from the scope of protection defined by the subsequently presented claims.

Claims

1. An electrical system for a forklift, said electrical system comprising a direct current source (4), a module (7) for converting the voltage from direct current to alternating current, and a technology platform (5), characterized in that the electric- al system further comprises means for raising the voltage upstream of the technology platform (5).

2. An electrical system as set forth in claim 1 , characterized in that the means for raising the voltage comprise at least one module (6), which is a DC/DC voltage increasing module between the direct current source (4) and the module (7).

3. An electrical system as set forth in claim 2, characterized in that the module (6) is a regulating module or the system has in parallel two or more different modules (6), which are connectible one at a time to the electrical system for matching unequal voltages of voltage sources, thus enabling a conversion of unequal input voltages into an always constant operating voltage for the technology platform (5).

4. An electrical system as set forth in claim 1 , characterized in that the means for raising the voltage comprise, between the module (7) and the technology platform (5), a module (8) which is a transformer, and that the electrical system further includes a module (9), which is an AC/DC/AC inverter and located between the module (8) and the technology platform (5).

5. An electrical system as set forth in claim 4, characterized in that the module (8) is a regulating module or the system has in parallel two or more different modules (8), which are connectible one at a time to the electrical system for matching unequal voltages of voltage sources, thus enabling a conversion of unequal input voltages into an always constant operating voltage for the technology platform (5).

6. An electrical system as set forth in claim 1 , characterized in that the means for raising the voltage comprise, between the direct current source (4) and the technology platform (5), a module (10) which is an integrated DC/AC inverter and transformer, and that the electrical system further includes a module (9), which is an AC/DC/AC inverter and located between the module (10) and the technology platform (5).

7. An electrical system as set forth in claim 6, characterized in that the module (10) is a regulating module or the system has in parallel two or more different modules (10), which are connectible one at a time to the electrical system for matching unequal voltages of voltage sources, thus enabling a conversion of unequal input voltages into an always constant operating voltage for the technology platform (5).

8. An electrical system as set forth in any of claims 1-7, characterized in that the electrical system further includes a module (11), which is a backup power source/energy storage arrangement and comprises at least a capacitor.

9. A forklift, characterized in that the forklift includes an electrical system as set forth in any of claims 1-8.

10. A method for manufacturing a forklift electrical system, said method compris- ing the following steps of:

-providing a power source (4), which supplies a direct current -converting the direct current to an alternating current

-conducting the alternating current to a technology platform (5), characterized in that the method further comprises a step of

-raising the electrical system's voltage upstream of the technology platform (5).

11. A method as set forth in claim 10, characterized in that the electrical system's voltage is raised upstream of the DC/AC conversion.

12. A method as set forth in claim 10, characterized in that the electrical system's voltage is raised downstream of the DC/AC conversion.

13. A method as set forth in claim 10, characterized in that the technology platform (5) is supplied always with the same operating voltage, irrespective of a voltage of the voltage source (4), by using either a single adjustable module (6, 8, 10) for raising the voltage or several identical modules (6, 8, 10) connected in parallel.

14. A method as set forth in any of claims 10-13, characterized in that the elec- trical system is further fitted with a module (11), which is an arrangement for a backup power source/energy storage.