GB2373302A

GB2373302A - Engine/motor braking being maintained by a throttle pedal interlock

Info

Publication number: GB2373302A
Application number: GB0106593A
Authority: GB
Inventors: Murray Turner
Original assignee: BOSS Manufacturing Ltd; BOSS UK HOLDING Co Ltd
Current assignee: BOSS Manufacturing Ltd; BOSS UK HOLDING Co Ltd
Priority date: 2001-03-16
Filing date: 2001-03-16
Publication date: 2002-09-18
Anticipated expiration: 2021-03-16
Also published as: GB0106593D0; GB2373302B; DE10210680A1

Abstract

A vehicle, eg a forklift truck, has a transmission with forward, reverse and neutral selected by a gear-shift 59 acting on electrical switches 68, 69, 70 which form part of an electrical drive control circuit 57. A throttle pedal 86 operates an on/off switch 60, an interlock relay 41 and an interlock switch 42 so that when the pedal 86 is depressed and forward or reverse is selected the interlock relay 41 energises and the interlock switch 42 is made. Thus once the pedal 86 is depressed the interlock relay 41 is set and will hold itself giving power to drive solenoids 22, 21, which activate a hydraulic circuit, until neutral is selected. This means that even if the pedal 86 is released the solenoids 22, 21 will be energized, thereby maintaining the transmission in forward or reverse such that a motor 58 will provide a braking action to the forklift truck when, for example, on a steep hill.

Description

THROTTLE INTERLOCK The present invention is concerned with a method and apparatus for controlling the drive movement of a forklift vehicle.

Forklift vehicles are used extensively in manufacturing environments where goods need to be transported from one location to another. Broadly speaking, a forklift has two primary drive control systems. Firstly, the drive system of the vehicle itself which typically consists of three gears, i. e. forward, reverse and neutral which are self-explanatory terms describing the selected movement of the forklift by the driver along the horizontal plane (i. e. road surface). Secondly, the drive system associated with the actual control of the lifting device, which typically might consist of movement in the vertical plane (i. e. up or down). The present invention is concerned with the first drive control system.

As with most other vehicles, a forklift has a throttle or throttle pedal whereby the driver is able to control the speed of the vehicle. By pressing down on the throttle, more power is supplied from the drive motor and the speed of the vehicle is increased. When the driver lifts his foot slightly, the pedal is released and less drive power is supplied to the vehicle causing it to slow (assuming natural resistances).

There is a need to increase safety by providing the possibility for maintaining engine braking of the forklift when the throttle pedal is released until neutral is engaged.

According to one aspect of the present invention there is provided a vehicle with a motive power supply for supplying power through an electrically actuable transmission system for engaging forward, reverse and neutral transmission modes to drive wheels, said vehicle comprising; user actuable forward, reverse and neutral switches; a user actuable speed controller for controlling the speed of the vehicle, the speed selector being biased to an idle position; a speed selector switch actuable by movement of the speed selector from its idle position; and a drive control circuit arranged to control the transmission system, the drive control circuit having a first mode of operation in which it causes the transmission system to take its neutral transmission mode, and a second mode of operation entered when the speed selector switch is actuated, in which it permits the forward mode to be selected in response to actuation of the forward switch and the reverse mode to be selected in response to actuation of the reverse switch; and comprising a latching arrangement for latching the drive control circuit in the second mode of operation, the latching arrangement being actuable by actuation of the speed selector switch and de-actuable by actuation of the neutral switch.

Figure 1 shows the main elements of a simplistic drive system for a forklift truck; Figure 2 shows a known drive control diagram for the drive system; Figure 3 shows the configuration of the present invention used in the drive control system; Figure 4 shows a diagram of the throttle pedal ; Figure 5 shows an example of the control panel circuitry for a forklift ; Figure 6 shows an example of a generic diagram that combines the control system of the present invention with the actual drive system; and Figure 7 shows an example of a hydraulic system of a forklift.

Figure 1 provides a general overview of a drive system for a forklift vehicle. The forklift has an axle 54 that connects the two drive wheels 52. The axle is driven by a drive shaft 51 which is coupled through a gearbox 55 to the rotor 56 of an internal combustion engine 58. Broadly speaking, the speed of a forklift vehicle is controlled by the throttle 86 in determining the amount of drive power supplied by the engine 58 to the drive wheels 52 and is offset by the resistance to movement of the vehicle itself. More generally, the magnitude of power supplied from the motor 58 is controlled by varying the amount by which the throttle is depressed.

The resistance to movement of the forklift may take many forms, the most obvious being the gradient of the surface over which the forklift is moving. Thus, a forklift moving up a hill will require more power from the engine to drive the forklift at the same speed as when the forklift is moving on a flat surface. More generally, a forklift moving down a steep gradient might gather momentum and in fact increase speed without any engine power being applied at all, i. e. even if the driver has released the throttle pedal 86.

Purely from a safety point of view, the dangers associated with a runaway forklift truck carrying a heavy load are self-evident. This may occur in a number of circumstances such as the driver falling out of the forklift or being rendered unconscious for some reason. Therefore, the present invention proposes an apparatus for allowing the natural braking action of the engine to be maintained when the throttle is released.

Figure 2 provides a typical control circuit for the drive system of a forklift vehicle as known in the art. The circuit is shown with the power off and NEUTRAL selected. The various modes of operation of the forklift are now described with power on (i. e. 12V).

With NEUTRAL selected the neutral switches 70 are closed resulting in a potential difference of 12V across the neutral relay 72. Neutral relay 72 becomes energised causing switch 74 to changeover leaving the potential at node A floating. More generally, the path to ground for solenoids 22 and 21 is broken.

Therefore, in effect when NEUTRAL is selected the drive solenoids (i. e.

FORWARD and REVERSE) cannot be energised.

When FORWARD is selected, the forward switch 66 is made and the neutral switches 70 open. By opening the neutral switches 70, the neutral relay is deenergised and switch 74 connects the potential at node A to ground. Therefore, whenever the driver depresses the throttle the forward solenoid 22 is energised.

Similarly, when REVERSE is selected, the reverse switch 68 is made and the neutral switches 70 open causing the potential at node A to be connected to ground. When the driver depresses the throttle the reverse solenoid 21 is energised.

Figure 3 is a diagram showing the control circuit of the present invention. The interlock relay 41 and the associated interlock switch 42 are used with the throttle switch 60 such that whenever the throttle 86 is depressed and the forklift is not in NEUTRAL then the interlock relay energises and the interlock switch 42 is made. The circuit configuration is such that once the throttle is depressed the interlock relay 41 is set and will then hold itself giving power to the direction solenoids 22, 21 until NEUTRAL is selected. This means that even if the driver of the forklift releases the throttle, the drive solenoids will be energised such that the motor 58 will provide a braking action for the runaway forklift.

Referring to Figure 1, it should be understood that when NEUTRAL is selected the drive shaft 56 of the motor 58 provides no resistance to movement and the rotor may be viewed as being disconnected from the motor resulting in a form "free-wheeling". So if a forklift is moving down a steep gradient, the motor provides no resistance to the motion of the forklift down the hill resulting in the vehicle picking up speed. On the other hand, if FORWARD is selected, the connection of the rotor 56 to the motor 58 provides an inherent resistance to movement. Therefore, so long as the throttle remains in the fully released position (i. e. no power supplied), the motor provides an inherent braking action to the movement of the forklift down the gradient. Similarly, if REVERSE is selected, the motor provides an inherent resistance to movement of the drive wheels.

Therefore, if the driver of the vehicle selects either the FORWARD or REVERSE drive directions but applies no drive power, the vehicle will idle. In the system of figure 2, if the throttle pedal was not depressed no drive power was supplied to the motor and since the switch 60 was broken neither forward nor reverse could be selected and in effect the motor was disconnected from the drive wheels where because of the lack of resistance to the wheels a creep speed at idle could develop that would be considered higher than may be considered permissible. In contrast, the system of figure 3 allows the driver to invoke the natural braking afforded by the motor when the throttle pedal is depressed and then released.

Thus, although a small amount of drive power will be supplied, this is quickly counter-acted by the natural braking action afforded by the motor resulting in a lower creep speed during idle.

It should be appreciated that the purpose of the throttle switch 60 in the control diagram shown in figure 3 is quite different from that used in the actual speed control of the vehicle itself. Figure 4 shows a basic example of a throttle pedal being spring-connected to the floor 88 of the forklift vehicle. When the driver applies downward pressure, a spring device 84 contracts and a strain gauge 80 measures this downward force. A modulation valve is then able to control the amount of fuel supplied to the engine depending on the amount that the throttle pedal 84 has been depressed. Therefore, the more downward pressure exerted the more drive power is applied to the wheels of the vehicle. The throttle switch 60 is connected just below the equilibrium position (i. e. the resting position when the throttle pedal is released) and merely provides a logical ON/OFF input to the control circuit. Therefore, a distinction must be made between the manner in which the throttle pedal affects the drive control system (i. e. throttle switch 60) and the actual magnitude of power supplied to the drive wheels themselves, i. e. where the magnitude of power supplied to the wheels has an effect on the speed of the vehicle.

Figure 5 is an example of the control panel circuitry of a forklift. The control panel is shown to contain a number of warning indicators visible to the driver of the forklift, for example the fuel lamp gauge 27. Annex 1 contains a list of the reference numerals referred to in the electrical diagrams of the forklift as shown in figures 5 and 6.

Figure 6 shows the drive system comprising the alternator 3. Also shown is the drive control system 100 containing the interlocking relay 41 and associated switch 42 of the present Invention. The drive co ol system comprises forward 22 and reverse solenoids 21 respectively. These solenoids 22,21 are powered by the drive control system and are used as electrically actuate the forward and reverse electrical gear valves shown in the hydraulic diagram of Figure 7.

Figure 7 shows the hydraulic diagram as providing two principle purposes i) providing lubricating oil for the motor 58 and ii) using the hydraulics to place the motor into forward and/or reverse gear. The electrical drive solenoids, i. e. the forward solenoid 22 and the reverse solenoid 21 provide electrical actuating means for moving the forward and reverse electrical gear valves 117,119 respectively.

In more detail, when the driver of the forklift selects the vehicle to move FORWARD then switch 68 is made resulting in the forward solenoid 22 of the electrical drive control system being energised. The forward solenoid 22 in turn actuates the forward gear electrical valve 117 of the hydraulic system causing the electrical gear valve 118 to be pushed to the right resulting in a high pressure hydraulic connection which hydraulically selects the motor's forward gear 130.

Referring back to Figure 1, it can be seen that the driver is able to select the mode of transmission required using a standard gear-shift 59. The driver selects FORWARD, REVERSE or NEUTRAL using the gear-shift which makes the corresponding electrical switch 68,69 or 70. These switches form part of the electrical drive control circuit 57. When FORWARD or REVERSE are selected the respective electrical solenoids, 22, and 21 are energised, which in turn actuate the hydraulic valves resulting in hydraulic actuation signals being sent to the gearbox 55. If NEUTRAL is selected, the rotor 56 of the motor 58 is disconnected from the drive shaft 51. If FORWARD is selected the motor is connected to the drive shaft and rotates in a particular direction, whereas for REVERSE the drive shaft rotates in the alternate direction. Thus, it is evident that the motor will apply an inherent braking force to the drive shaft when either the FORWARD or REVERSE gears are selected. Therefore so long as the throttle pedal is not depressed for a sustained period, the supplied motor power will not be sufficient to overcome the natural retarding force provided by the connection of the motor to the drive wheels.

The present invention in the form of the interlock relay 41 and interlock switch 42 allow the power initially supplied by depressing throttle switch 60 to be maintained during the forklift's FORWARD and REVERSE modes of operation irrespective of whether the throttle pedal 86 is subsequently released or not. The power supply to the drive control circuit only being broken once the driver selects NEUTRAL.

It should be appreciated that the present invention can be used in different types of forklift and indeed may be used across the range of trucks used by the applicant. Furthermore, the type of motor used per se has no effect on the present invention, i. e. the motor that drives the forklift can be for example an internal combustion engine being diesel or petrol-powered or an electric motor. It should also be appreciated that Figure 4 is merely an example of a throttle pedal, where the actual amount of power supplied to the wheels may be controlled in a numerous well-known ways including fuel injection and carburettor control systems.

Annex 1 t Fuse Box 2 Switch-Ignition 3 Alternator 4a Preheat Relay, only A-Diesel Version

4b Glow Plug Controller, only B-Diesel Version 5 Glow Plugs so Fuel Valve Solenoid 6b Start-Fuei Valve Solenoid, only B-Version 7 Clock (Panel) 8 L2 = Preheat on Indicator Lamp (Panel) 9 L7 = Charge Warning Lamp (poney 10 Hour Counter (Panel) 11 L8 = Engine Oil Pressure Warning Lamp, (P anel) 12 L4 = Park Brake Lamp (Panel)

13 Engine Oil Pressure Switch 14 Hondbrake Switch 15 Starter 16 Battery Isolation Switch 17 Starter Battery 18 Horn Push 19 Horn 20 Direction Switch 21 Reverse Solenoid 22 Forward Solenoid 23 Storter Relay 24 Neutral Start Relay 25 Fuel Sender and Level Switch 26 LI = Fuel Reserve Lamp (Panel) 27 Fuel Level Gauge (Option) 28 L3 = Neutral Indicator Lamp (monel) 29 Water Temperature Gauge (Panel)

30 L9 =-H !ign Coolant Temperature Lamp (pones) 31 L13 = Transmission Oil Warning Lamp (Panel) 32 L18 = Brake Fluid level Lamp (poney) 33 Water Temperature Sender 34 Water Temperature Switch 35 Transmission Oil Warning Switch 36 Broke Fluid Switch 37 Two Speed Solenoid 38 HEATED SEAT PAD 39 HEATED SEAT SWITCH

Claims

CLAIMS : 1. A vehicle with a motive power supply for supplying power through an electrically actuable transmission system for engaging forward, reverse and neutral transmission modes to drive wheels, said vehicle comprising; user actuable forward, reverse and neutral switches; a user actuable speed controller for controlling the speed of the vehicle, the speed selector being biased to an idle position; a speed selector switch actuable by movement of the speed selector from its idle position; and a drive control circuit arranged to control the transmission system, the drive control circuit having a first mode of operation in which it causes the transmission system to take its neutral transmission mode, and a second mode of operation entered when the speed selector switch is actuated, in which it permits the forward mode to be selected in response to actuation of the forward switch and the reverse mode to be selected in response to actuation of the reverse switch; and comprising a latching arrangement for latching the drive control circuit in the second mode of operation, the latching arrangement being actuable by actuation of the speed selector switch and de-actuable by actuation of the neutral switch.
2. A vehicle according to claim 1, wherein the latching arrangement comprises an interlock relay and an interlock switch such that once said speed selector switch is actuated the interlock switch becomes energised and the interlock switch is retained.
3. A vehicle according to claim 1, wherein in said second mode of operation the motor is connected to the drive wheels such as provide a natural resistance to movement of said vehicle whereas for said first mode of operation the motor is disconnected from the drive wheels of said vehicle such that no resistance to the movement of the vehicle is provided.
4. A vehicle according to any preceding claim, wherein said vehicle is a forklift.
5. A vehicle according to any preceding claim, wherein the motive power supply is a diesel-powered internal combustion engine.
6. A vehicle with a motive power supply for supplying power through an electrically actuable transmission system for engaging forward, reverse and neutral transmission modes to drive wheels substantially as herein described with reference to the accompanying drawings.