Lifting device with movable lifting columns

A lifting device having separately displaced lifting column with a carriage controllably driven in a longitudinal direction. Connecting lines connect the control of the column. The connecting lines function as part of a digital data bus in order to exchange digital control signals with each lifting column having a separate operation device connected to the connecting lines to provide simultaneous actuation of the control of all lifting columns.

FIELD OF THE INVENTION
 The invention relates to a vehicle lift which comprises at least two
 separately displaceable lifting columns.
 BACKGROUND OF THE INVENTION
 Such a vehicle lift is known from AT-A-325,811 and is used particularly for
 lifting heavy vehicles, such as cars, trucks and buses.
 The signals required to cause all lifting columns to operate as a unit are
 transmitted along separate connecting lines. These signals comprise
 activating signals for switching on and off the drive means of each
 lifting column and also monitoring signals for comparing the lifting
 height of each lifting column. The lifting columns are thus mutually
 coupled by the connecting lines to form one lifting device which functions
 in substantially the same manner as a customary vehicle lift.
 SUMMARY OF THE INVENTION
 The invention has for its object to further develop the known vehicle lift
 in order to give it more application options.
 The lifting columns are hereby no longer considered as composite parts of a
 whole device but as separate devices which co-act in random numbers. With
 the invention is achieved that a wide diversity of control and monitoring
 signals can be exchanged between the separate lifting columns mutually and
 with the operating means, whereby the options for use of the lifting
 device according to the invention are greatly increased.
 It is remarked here, that European patent application 0,747,535 relates to
 a lifting device with at least two lifting columns, where the connecting
 lines are a data base for exchange of control signals. However, this
 publication relates to transport of a building, where the lifting columns
 are necessarily displaceable, when a load is resting thereupon. Also,
 simultaneous actuation of the lifting columns is not an issue, but keeping
 the loads on each lifting column below a predetermined maximum is.
 Further, the structural requirements on a system for lifting and
 transporting a building, and the forces, which need to be generated in
 doing so, are considerably greater or higher than those in the case of a
 vehicle lift according to the present invention.
 Communicating the safety signals via the data bus ensures that a random
 number of co-acting lifting columns can co-act reliably and, in
 particular, with great safety.
 The CAN data bus and components therefor are well standardized, so that the
 control and operating means can be constructed and embodied in reliable
 manner. Because this data bus only requires two wires, the connecting
 lines remain well manageable and little vulnerable.
 The proper operation of all lifting columns can be ascertained from the
 operating means whereby control signals for setting the safety means into
 operation can be transmitted in one direction in the closed circuit, which
 results in a high reliability.
 User can select the lifting column which is most suitable for him for the
 operation of the whole device.
 The energy supply for each, or at least a number of the lifting columns can
 take place via the at least one lifting column. It is possible for
 instance to dimension the supply voltage lines such that a total of four
 lifting columns are supplied via the one lifting column. The at least one
 lifting column can herein be provided with overload protection means which
 ensure switching off of the power supply in the case of overload of
 several or all coupled lifting columns.
 According to another suitable embodiment the relative position of each
 lifting column is easily identifiable by the operating means.
 The lifting columns which are disposed on either side of the same vehicle
 axle as pairs. It hereby becomes possible, when a vehicle is supported by
 more than four lifting columns, for instance to build in or remove an axle
 by independently operating the two lifting columns forming part of one
 pair.
 Separate operation of the lifting columns mutually associated to form a
 pair can be performed in simple manner from the operating means.
 After adjustment of one of the pairs, the other co-acting pairs can be
 identified simply by the operating means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 The lifting device 1 according to the invention shown in FIG. 1 comprises
 four separately displaceable lifting columns 2 which co-act to lift a bus
 4. For the co-action the lifting columns 2 are mutually coupled by means
 of connecting lines 3 which form part of a digital data bus of the CAN
 type.
 As shown in FIG. 2, each lifting column 2 comprises a column 6 in which a
 carriage 7 is guided slidably in longitudinal direction. On the bottom end
 of column 6 is arranged a support foot 8 with which the column can be
 deployed stably on a ground surface.
 Carriage 7 bears on its lower end a lifting member 9 which is provided with
 two protrusions 16 which can engage around a vehicle wheel. Carriage 7 can
 be displaced in column 6 by means of drive means in the form of a
 hydraulic cylinder 10. This hydraulic cylinder 10 is fed with hydraulic
 oil under pressure from a hydraulic unit 11, which is per se known and not
 shown in detail. Such a hydraulic unit 11 comprises a hydraulic pump
 driven by an electric motor, which can draw hydraulic oil out of a
 reservoir and press it under pressure into cylinder 10 in order to move
 the carriage 7 upward.
 Control of hydraulic unit 11 takes place with per se known control means
 which are accommodated in a box 14 on lifting column 2.
 In order to enable displacement of lifting column 2 and positioning with
 protrusions 16 on either side of a vehicle wheel, the lifting column 2 is
 provided with wheels 12. These wheels 12 form together with push-bar 13 a
 mechanism which is per se known for pallet trucks. By moving push-bar 13
 up and downward in pumping manner the wheels 12 can be moved downward
 relative to support foot 8 whereby lifting column 2 becomes displaceable
 on wheels 12. By operating a hydraulic valve the wheels 12 are retracted,
 whereby support foot 8 comes to lie on the ground.
 In the mobile situation the lifting column 2 can be manoeuvred using
 push-bar 13.
 Control means 14 comprise per se known switching means for switching on and
 off hydraulic unit 11. This switch-on/off command is given by activating
 the operating means 18. Control means 14 for each lifting column 2 and the
 operating means 18 are embodied such that they can exchange signals via
 the connecting lines 3.
 As shown in FIG. 1, each of the lifting columns is provided with a length
 of line 3 which carries on its end a connector which is connected to a
 connector terminal 15 of an adjacent lifting column 2. Control means 14
 and operating means 18 are thus connected in a series as shown in FIG. 3
 for a lifting device comprising six lifting columns.
 In the shown embodiment two conductors in connecting lines 3 form parts in
 each case of a digital CAN data bus. Connecting lines 3 can further
 comprise conductors for the supply current of the hydraulic units.
 Because the control means and operating means are mutually coupled by means
 of the CAN data bus, a variety of signals can be sent to and from each
 lifting column. For a good co-action with the CAN data bus the control
 means are based on a microprocessor, so that the different options can be
 entered by programming.
 A suitable possibility, which can be applied particularly when more than
 four lifting columns are used, is to cause determined lifting columns to
 be raised and lowered independently. The two lifting columns deployed on
 either side of an axle of a vehicle can for instance be jointly moved
 upward and downward, while others retain the adjusted height, for the
 purpose of changing a vehicle axle.
 For this purpose a serial number is assigned to each of the lifting columns
 for addressing the control signals. In FIG. 3 these serial numbers are
 designated schematically with I-VI. Assigning of these serial numbers can
 take place simply after arranging connecting lines 3. operating means 18
 can perform a program-controlled query over the data bus in order to
 establish how many lifting columns are connected to the data bus and
 subsequently assign the serial number to each of these lifting columns.
 The software can be embodied such that the lifting columns associated in
 each case with one axle are then mutually associated to form independently
 operable pairs. In the diagram of FIG. 3 the lifting columns designated II
 and V can for instance be operated in suitable manner as a separate pair
 in order to move an axle supported by these lifting columns separately
 upward and downward.
 FIG. 3 shows that each column bears operating means 18, so that the whole
 lifting device can be operated at each column. It is also possible to
 embody the operating means 18 as a separate unit which can exchange
 signals with control means 14 via a cable connection. The cable connection
 can for instance be made as required with a random column.
 As shown in FIG. 3, the connecting lines 3 are connected in a closed
 circuit, wherein one lifting column in each case is connected to a
 subsequent one. Control and safety signals can hereby be fed back via the
 closed circuit to the operational operating means 18, whereby monitoring
 of the proper operation of all connected columns becomes possible and the
 data flow can for instance take place in one direction, which results in a
 simple and therefore reliable embodiment.
 Mutually associating determined lifting columns to form an independently
 operable pair can also take place in a less well developed embodiment of
 the invention in that an operator enters data concerning the co-acting
 columns into the control means. Each lifting column can thus be provided
 with an independently actuable adjusting member which, after actuation,
 places the device in a learning mode. If within a determined time after
 actuation of the adjusting member on one column a corresponding adjusting
 member on another column is actuated, the control device will mutually
 associate these two columns to form an independently operable pair.
 The invention is not limited to the embodiments shown in the figures and
 described above. Through use of the digital data bus in combination with
 suitable programming of the control and operating means a lifting device
 can be given the functionality desired for a particular application.