GB2332414A

GB2332414A - Control system for tailgate lifts

Info

Publication number: GB2332414A
Application number: GB9726743A
Authority: GB
Inventors: John Alexander Gourley
Original assignee: Ross and Bonnyman Engineering Ltd
Current assignee: Ross and Bonnyman Engineering Ltd
Priority date: 1997-12-19
Filing date: 1997-12-19
Publication date: 1999-06-23
Anticipated expiration: 2017-12-19
Also published as: GB2332414A9; GB2332414B; GB9726743D0

Abstract

A tailgate lift of the type having the platform folded/unfolded by a cam follower (4) is provided with a control system for restricting the folding/unfolding speed. The system preferably comprises proximity sensors F1, F2 and flow restrictor valves A, G operable, preferably on a timer E, to restrict the flow to or from a cylinder R operating the tailgate. The system may also comprise a safety valve B, a pressure relief valve and normal up/down switch 12. During normal raising valves A, B and G are closed, during normal lowering valve A is closed and valves B and G open. During folding/unfolding, valve A is open for eg. 10 to 20 seconds.

Description

P07995GB LOAD LIFTING AND LOWERING APPARATUS The present invention relates

to a load lifting and lowering apparatus and in particular, but not exclusively, to vehicle 5 tail lifts of the folding and unfolding type.

A commonly known type of vehicle tail lift comprises two spaced apart tail lift columns along each of which travels a runner mounted on a load carrier or platform. The platform is arranged with drive means, usually hydraulic drive means, to drive the platform between upper and lower horizontal positions to facilitate loading or unloading of a vehicle and a second folded or stowed position with the platform in a generally vertical position against a vehicle. The mechanism used to facilitate the folding and unfolding of the tail lift platform is carried out by means of a cam mechanism. This type of folding or unfolding of a tail lift platform is used commonly in platforms that are too large or heavy to be folded by manual effort and will known to those skilled in the art as "cam closure".

Conventionally with "cam closure" tail lifts, the folding and unfolding of the platform in order to deploy it for use as a load lifter and to stow it away after use, is commonly carried out at the same speed at which the tail lift rises and descends on the vehicle tail lift column.

"Cam closure" tail lifts are generally well known and are described hereinbelow with reference to Figures 1A to C. As shown in Fig. 1A, a tail lift platform 1 is shown rising in P07995GB -2the direction of arrow 'G' under hydraulic power. A cam follower arm assembly 2 (which may, or may not, be equipped with a roller) is placed in position A (shown by arrow H from position 'T shown in broken line) to bring about folding of the platform. As the roller of the cam follower arm assembly 2 comes into contact with a cam 6 on the tail lift column 8 the continuing upward movement of the platform in the direction of arrow 'A' causes the platform to start to rotate in the direction of arrow 'B' about its mounting pivot points 10 (as shown in Fig. 1B). The upward movement of the platform ceases when either the platform engages in a retaining catch or the lift operator switches off the electro-hydraulic power pack supplying hydraulic power to the tail lift hydraulic cylinder or ram. In a stowed position the cam follower arm has passed around the cam so that the platform is in a folded vertical condition as shown in Fig. 1C. Unfolding of the platform occurs in the reverse order to the foregoing when the tail lift operator causes the platform to lower and the cam follower passes around the cam in the downwards direction.

A disadvantage of this commonly used method and apparatus is that the speed of ascent and descent of the tail lift platform gives rise to excessively fast folding rotational speeds of the platform about its pivots. European Union regulations for vehicle tail lifts have set a maximum rotational speed of 10 degrees per second for tail lift mechanisms that are power operated. Accordingly such commonly known methods and apparatus of cam closure will not meet such regulations except by use of very slow normal ascent and descent speeds of the WM5GB -3platform in use as a load lifter which would be unacceptable to the majority of tail lift users due to the greatly increased time that would be required to load and to unload a vehicle. This problem is particularly exacerbated on vehicles with two floors or decks. on these vehicles higher speeds of ascent and descent of the tail lift platform are advantageous due to the greater height of the upper deck from the ground. Also the lower deck is normally closer to the ground than with single deck vehicles, necessitating a short cam which unfortunately results in increased rotational speed of the platform when folding and unfolding.

Other mechanisms are known which allow tail lifts to fold and unfold and which meet various national and other regulations but such systems are costly and complex to install and to operate.

It is an object of the present invention to avoid or minimise one or more of the foregoing disadvantages and to provide a cam closure tail lift platform which meets national and other requirements.

In a first respect the present invention provides a control system for use on a cam closure vehicle tail lift of the type comprising a tail lift, a tail lift platform, a cam means and a cam follower means, said cam follower means being formed and arranged to be disposable between a first position in engagement with said cam means for folding of said tail lift platform and a second position for facilitating the raising and lowering of said tail lift platform, which control system POW5GB -4comprises power supply means for powering a drive means formed and arranged for raising and lowering and folding of said tail lift platform of a said vehicle tail lift; sensor means arranged with said cam means of said tail lift, said sensing means being formed and arranged with said cam means for detecting the presence of said cam follower in a first closed or folded position of said tail lift platform and a second open or unfolded position of said tail lift platform; drive means power supply means reduction means formed and arranged for reducing the amount of power to said drive means when said sensor means detects the presence of a said cam follower portion of said tail lift platform proximal said cam means of said tail lift whereby the tail lift platform of a cam closure type tail lift in use of the control system may be folded and unfolded between said first and second positions at a reduced rate and said tail lift platform substantially raised and/or lowered at a normal rate.

Preferably said control systems provided with manually operable switching means formed and arranged for raising and lowering or folding of said vehicle tail lift in use of the control system. Conveniently this may be effected by a simple switch means of the type generally found on known types of &&cam closure" vehicle tail lifts.

Preferably said power supply means is of the generally known electrohydraulic power pack type supplying hydraulic power to a hydraulic cylinder or ram. Such power supply means will be generally known to those skilled in the art.

P07995GB -5 Said sensor means for detecting the presence of a cam follower on the cam may be in the form of proximity sensors or microswitches. Preferably said sensor means are of the inductive proximity detector type. Desirably said sensor means are built into the cam means so that they cannot be damaged or otherwise interfered with in their normal mode of operation. By building the sensors into the cam means it will be appreciated that no sensor, wiring or additional hydraulic piping or the like or any other equipment is required on, or in, the platform. This avoids the difficulties involved in passing electrical or hydraulic connections between the vehicle and the tail lift platform which must rise, fall and fold in order to fulfil its functions as a vehicle tail lift.

is Any suitable form of drive means power supply reduction means may be utilised though preferably there is used a valve formed and arranged for use with a hydraulic fluid powered by said electro-hydraulic power supply means. Most desirably this is of a hydraulic fluid flow control valve having a solenoid connected to a timer relay formed and arranged to actuate said solenoid on said flow control valve so as to restrict, to a greater or lesser extent, the flow of fluid through said control valve and to divert a portion of the hydraulic fluid supplied by said power supply means to said hydraulic ram to the electro- hydraulic power pack reservoir. Preferably said timer relay is formed and arranged to activate the flow control valve for a set period in the range from 5 seconds to 60 seconds, preferably 10 seconds to 30 seconds, desirably 15 seconds which is sufficient in most circumstances for the tail P07WSGB lift platform to be folded.

In another respect the present invention provides a vehicle tail lift including a control system according to the present invention.

In yet another respect the present invention provides a vehicle having a tail lift including a control system according to the present invention.

Further preferred features and advantages to the present invention will appear from the following detailed description given by way of an example of a preferred embodiment illustrated with reference to the accompanying drawings in which:Fig.1 A - C show side views of a vehicle tail lift according to one aspect of the present invention; Fig.2 is a circuit diagram of a control system according to a first aspect of the invention; and Fig.3 is a simplified circuit diagram of the control system shown in Fig. 2.

A cam closure tail lift platform, generally indicated by reference number 1, and tail lift is shown in Fig.l. As shown in Fig. 1A, a tail lift platform 1 is shown rising in the direction of arrow 'G' under hydraulic power. A cam follower arm assembly 2 is placed in position W (shown by arrow H from position 'B' shown in broken line) to bring about folding of the platform. As the roller of the cam follower arm assembly PO7WY,-B -72 comes into contact with a cam 6 on the tail lift column 8 the continuing upward movement of the platform in the direction of arrow ^A' causes the platform to start to rotate in the direction of arrow 'B' about its mounting pivot points 10 (as shown in Fig. 1B). The upward movement of the platform ceases when either the platform engages in a retaining catch or the lift operator switches off the electro-hydraulic power pack supplying hydraulic power to the tail lift hydraulic cylinder or ram. In a stowed position the cam follower arm has passed around the cam so that the platform is in a folded vertical condition as shown in Fig. 1C. Unfolding of the platform occurs in the reverse order to the foregoing when the tail lift operator causes the platform to lower and the cam follower passes around the cam in the downwards direction.

Turning now to the circuit diagram shown in Fig.2, the primary components are a solenoid valve incorporating a flow control valve A connected to and across an hydraulic electric power pack C comprising a pump P and an electric motor M, which is connected via a safety solenoid "lock" valve B to the hydraulic ram R of the vehicle tail lift platform 1. A timer relay E of the "on pulse" constant supply type is connected between the hydraulic electric power pack C and two inductive proximity detectors E,, F2 mounted within the cam D and cam follower assembly. the timer relay E so that a user may actuate the control system so as to raise or lower and/or fold the tail lift platform 1.

A user operable hand control 12 is connected across POM5GB -8The mode of operation of the tail lift control system is described below.

In order to be able to raise the tail lift platform with it in a horizontal loading and unloading orientation an operator manually switches a hand control 12 to the "up" position as shown in Figs. 2 & 3, valve A is un-energised and therefore in a closed position so that the full flow of hydraulic fluid from the hydraulic electric power pack C drives the ram R through safety solenoid valve B so that the tail lift platform 1 may be raised at a normal speed. In order that the tail lift platform may be lowered at the normal speed the operator switches the hand control 12 into the down position so as to energise valves A and G into an open condition so that full flow of hydraulic fluid from the ram flows back to the tank portion T of the hydraulic electric power pack C.

To enable the platform to be folded from the horizontal position into a folded generally vertical position as shown in Fig.1C and for this movement to be at a reduced speed not exceeding 10' per minute the system operates as follows.

The cam follower arm is placed into position A as shown in Fig. 1 and the platform is raised as described as above.

cam follower roller touches the cam and the lower proximity sensor F2 on the cam D detects the presence of the cam follower arm roller 4. This detection serves to activate the timer relay which energises i.e. opens valve A such that a portion of the flow of hydraulic fluid from the hydraulic electric P07995GB -9power pack C flows back into the tank T and the other portion drives the ram R. The reduced flow of hydraulic fluid to the ram means that the speed of the ram movement is reduced and thereby the speed of angular rotation of the platform from a horizontal position to a vertical folded position is reduced.

The timer relay E then switches off after a pre-set period of approximately 15 seconds so that valve A- closes and the full flow and pressure of hydraulic fluid is restored. By this time the cam follower arm roller 4 has passed by the upper proximity sensor F1 and so the system remains at a normal operating speed.

In order that the platform 1 may be unfolded at a reduced speed the platform is lowered in the conventional manner until the upper proximity detector F1 detects the presence of the cam follower arm roller 4, thereby causing the timer relay to de-energise valve A which reduces the flow of hydraulic fluid from the ram back to the tank and therefore reduces the speed at which the ram moves and thereby the angular speed of rotation of the tail lift platform. When the timer relay switches off after a pre-set period of approximately 15 seconds valve A opens i.e. it is energised so that full flow and pressure of hydraulic fluid is restored and so that the vehicle tail lift may operate at its normal operating speed.

The simplified diagram shown in Fig.3 is now described. As shown in the enlarged diagram of valve A the valve functions in a first energised state such that hydraulic fluid is P0799Y3B -10prevented from passing in the direction from 'B' to W though flow may pass from W to 'B' without restriction. In the coil energised position of the valve fluid flow may pass from 'B' to W but is controlled to a pre-determined flow rate. Flow may pass from W to 'B' without restriction though in practice this is not usually required. This is a well-known type of valve, described only to make the following clearer. The flow rates of the valves A and G are selected to give the speeds of ram movement required. It will be appreciated that the flow rates and thus the ram speeds will vary from one application to another but by way of an example the following flow rates and speeds would be suitable for use with a typical lift platform. For a certain commonly used type of lift rated at 1.5 tons capacity valve A may have a flow rate of 6 L per min and valve B a flow rate of 4 L per min. There are several variables which will determine the flow rates amongst which are working hydraulic pressure of tail lift with platform unloaded diameter of hydraulic cylinder, geometry of cam and cam follower.

As shown in Fig.3 when valve A is closed i.e. un-energised full flow of hydraulic fluid is available to the ram with valve G in an un-energised or closed position. This is the usual condition for the standard component used in tail lift 25 platform raising and lowering equipment.

In order to close/fold the tail lift platform the procedure is as noted above with reference to Fig.2.

P07995GB In order that the tail lift platform may descend at its normal operating speed valve A is energised i.e. opened so that full flow back to the tank is provided as is valve G which is the usual condition for the standard component used with platform 5 equipment.

To unfold the tail lift platform from a vertical to horizontal position the procedure noted above with reference to Fig.2 is undertaken.

Various modifications may be made to the above described embodiment without departing from the scope of the present invention. Accordingly instead of using a timer relay there could be employed manual control means formed and arranged such that when the tail lift platform requires to be folded or unfolded an operator can activate valve A to be in an open or closed position according to whether the tail lift platform is opening or closing. The embodiment described is suitable for retro-fitting to existing "cam- closure" tail lifts thereby allowing such lifts to meet new regulations.

P08721GB 12

Claims

CLAIMS 1. A control system for use on a cam closure vehicle tail lift of

the type comprising a tail lift, a tail lift platform, a cam means and a cam follower means, said cam follower means being formed and arranged to be disposable between a first position in engagement with said cam means for folding of said tail lift platform and a second position for facilitating the raising and lowering of said tail lift platform, which control system comprises power supply means for powering a drive means formed and arranged for raising and lowering and folding of said tail lift platform of a said vehicle tail lift; sensor means arranged with said cam means of said tail lift, said sensor means being formed and arranged with said cam means for detecting the presence of said cam follower in a first closed or folded position of said tail lift platform and a second open or unfolded position of said tail lift platform; drive means power supply means reduction means formed and arranged for reducing the amount of power to said drive means when said sensor means detects the presence of a said cam follower portion of said tail lift platform proximal said cam means of said tail lift whereby the tail lift platform of a cam closure type tail lift in use of the control system may be folded and unfolded between said first and second positions at a reduced rate and said tail lift platform substantially raised and/or P08721GB 13 lowered at a normal rate.
2. A control system as claimed in claim 1 provided with manually operable switching means formed and arranged for raising and lowering or folding of said vehicle tail lift in use of the control system.
3. A control system as claimed in claim 1 or claim 2 where in said power supply means is in the form of an electro-hydraulic power pack supplying hydraulic power to an hydraulic cylinder or ram.
4. A control system as claimed in any one of claims 1 to 3 wherein said sensor means for detecting the presence of a cam follower on the cam is in the form of a proximity sensor or microswitch.
5. A control system as claimed any one of claims 1 to 4 where in said sensor means is of the inductive proximity detector type.
6. A control system as claimed in any one of claims 1 to 5 wherein said sensor means are built into the cam means.
7. A control system as claimed in any one of claims 3 to 6 wherein said drive means power supply means reduction means is in the form of a valve formed and arranged for use with a hydraulic fluid powered by said electro-hydraulic power supply means.
8. A control system as claimed in claim 7 wherein said P08721GB 14 hydraulic fluid flow control valve has a solenoid connected to a timer relay formed and arranged to actuaate said solenoid an said flow control valve so as to restrict flow of fluid through said flow control valve and to divert a portion of the hydraulic fluid supplied by said power supply means to said hydraulic ram to a reservior of said electro-hydraulic power pack reservoir.
9. A control system as claimed in claim 8 wherein said timer relay is formed and arranged to activate the flow control valve for a set period in the range of from
10 to 30 seconds. 10. A vehicle tail lift including a control system according to claim 1.
11. A vehicle having a tail lift including a control system according into claim 1.
12. A control system substantially as described herein before and with reference to Figs.1 to 3 of the accompanying drawings.
13. A vehicle tail lift substantially as described hereinbefore with reference to Figs. 1 to 3 of the accompanying drawings.