GB2051986A

GB2051986A - Automatically applied brakes

Info

Publication number: GB2051986A
Application number: GB8016862A
Authority: GB
Original assignee: Coventry Climax Ltd
Current assignee: Coventry Climax Ltd
Priority date: 1979-06-02
Filing date: 1980-05-22
Publication date: 1981-01-21

Abstract

As a safety feature, the driver's seat of an industrial truck has a switch 2 which senses when the seat is empty and which then applies a brake to the traction motor 3. The switch 2 operates a solenoid 12 which in turn operates a hydraulic valve (not shown) to depressurise a piston and cylinder 11 which normally holds the brake off against a tension spring 10. If the driver gets off his seat, the spring 10 pulls the brake on. For normal operation with the driver on his seat, the solenoid moves the valve 12 to a position where the piston and cylinder can be pressurised. The power steering pump may be used to generate the pressure. A separate parking brake may be provided although the traction motor brake may be used as a parking brake. <IMAGE>

Description

SPECIFICATION Industrial truck This invention relates to industrial trucks.

It has previously been proposed to provide a brake for the traction motor of an industrial truck which is spring-biased to the on position and which is releasable by means of the movement of a vertical rod which is depressed when the driver sits in his seat. The seat is hinged at the rear to allow it to move the rod.

The invention provides an industrial truck which includes an electric switch associated with the driver's seat for sensing the presence of a person in the seat, and the arrangement is such that a brake for the traction motor cannot be released when the switch is in the position corresponding to the seat being empty.

As compared with the previously proposed arrangement, the arrangement according to the invention has the advantage that the seat no longer nesds to be mounted in such a way as to permit movement of a rod and can thus be mounted more securely.

Advantageously, the traction brake is biased by resilient means into the on position and hydraulic means (for example, a piston-and-cylinder) is provided for releasing the brake. Preferably, a solenoid operated by the electric switch is provided for actuating the hydraulic means. The solenoid may operate a valve which in one position allows the hydraulic means to be pressurised while in another vents the hydraulic means. The valve may, in the position that allows the hydraulic means to be pressurised, block the flow through the valve by means of a non-return valve associated with the valve, The hydraulic means and the valve may be fed via a second nonreturn va!ve, the non-return valves being so arranged that pressure is retained in the hydraulic means once pressurised when the solenoidoperated valve is in the appropriate position.The pressure may be provided by a power steering pump.

Advantageously, there is provided an additional electric switch associated with a parking brake control, which switch is in series with the driver sensing switch. In this way, the traction motor brake is utilised as the parking bra) < e and a separate parking brake need not be provided.

Alternatively, an additional electric switch may be associated with a control for a separate parking brake, which switch is in series with the traction motor and arranged so that the traction motor is not supplied with current when the parking brake control is on.

Advantageously, a further electric switch is provided in series with the traction motor, which switch is arranged to be opened when the traction brake has been applied.

The driver's seat electric switch may be inductive, but is preferably one or more microswitchcs set into the seat.

Industrial trucks constructed in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure I shows in schematic form the electric circuit of the first truck; Figure 2 shows in schematic form the hydraulic circuit oF the truck; Figure 3 shows a brake actuator for the traction motor of the truck and Figure 4 shows in schematic form an electric circuit of a second truck.

Like reference numerals are given to like parts throughout each of the figures.

Referring to Figure 1 , the industrial truck has a driver's seat 1 in which are embedded two microswitches 2 (only one of which is shown) in parallel, one on either side of the seat. The truck has an electrically-operated traction motor 3 whose speed is controlled by an accelerator pedal 4. The truck also has a key switch 5, a power steering pump 6 and motor 7 and a handbrake lever 8, which operates a mechanical parking brake.

The truck also has a service brake (not shown) operated by a brake pedal (not shown).

The traction motor 3 is provided with a brake actuator (shown in Figure 3 and described in detail hercinafter) which includes a brake lever 9 which is biased by tension spring 10 into a position to apply the brake. The brake acts on the transmission adjacent the output shaft of the traction motor 3. A piston-and-cylinder 11 can be pressurised by means of the operation of a solenoid 12 connected in series with the seat switch 2 in order to release the brake.

Referring to Figure 2, the power steering pump 6 is used to pressurise the piston-and-cylinder 11.

The pump 6 is connected via line 13 and sequence valve 14 to the power steering unit (not shown! and via line 1 5 ancl non-return valve 1 6 first to the piston-and-cylinder and second to a valve 1 7 operated by the solenoid 12.

Referring to Figure 3, the brake actuator comprises a drum brake 1 8 acting on the transmission leading from the traction motor.

When piston-and-cylinder 11 1 is pressurised, brake lever 9 is pivoted clockwise about the fixed pivot 9a at its right-hand end, against the action at the tension spring 10. The parts are then in the position shown in Figure 3. A line 9b depending from the right-hand and of the lever 9 and rigidly connected to the brake lever 9 pivots with the lever 9 and moves puli-link 19 to the left (as seen in Figure 3!, causing expander wedge 20 to release the brake shoes so that they become free of the brake drum. When the fluid in the cylinder is allowed to escape, spring 10 causes the brakes to be re--applied. The spring load can be released by unscrewing item 9c manually, thus allowing for truck movement on assembly or traction brake adjustment.

The operation of the truck is as follows. The driver sits in his seat and, in so doing, normally open microswitch 2 is ciosed. Key switch 5 is operated to close normally open switch 5. The solenoid 2 as a result causes the valve 17 to move to the left (as seen in Figure 2) to allow the cylinder 11 to be pressurised. Since the steering pump 6 is used to supply the hydraulic fluid, the driver briefly touches his foot on the accelerator to operate the pump 6. Hydraulic fluid passes along line 1 5 to valve 1 7 where the path is now blocked by a non-return valve 1 7a. Pressure rapidly builds up in the cylinder 11 and the brake actuator is operated to release the brake.It is to be noted that because of opposed non-return valves 16, 1 7a, the pressure is trapped in line 1 5 so that the cylinder remains pressurised even when the pump stops. Now that the cylinder 11 is pressurised, pressure can build up to pass through valve 14 along line 13 to the power steering unit. Powerassisted steering is now possible.

Referring now to Figure 1, the fully rotated brake lever 9 closes a normally-open microswitch 21 which is in series with a normally-open microswitch 22 and with the traction motor 3.

Operation of handbrake lever 8 to release the parking brake closes normally open microswitch 22 and thus connects the traction motor in circuit.

The truck can then be driven by using the speed control 4.

If for any reason the drive leaves his seat, switch 2 opens and valve 1 7 is returned by a spring 23 to the position shown in Figure 2 where the line 1 5 is vented, that is, passageway 1 7b connects the line 15 back to the sump. The line 1 5 and hence the cylinder 11 are immediately depressurised and spring 10 re-applies the brake.

Brake lever 9 rotates anti-clockwise causing switch 21 to open and thus switch off the traction motor supply.

Consequently the brake is applied immediately the driver leaves his seat.

The truck described is an electric truck, but the invention is applicable to an internal combustion engine driven truck. The truck may be a counterbalance fork lift truck, or a side-loader, or a reach truck.

As compared with previous methods for applying seat-operated brakes, the method of the invention has the advantage that the switches do not interfere with the mounting of the seat, which can therefore be designed with safety and comfort only in mind.

Referring to Figure 4, the second truck differs from the first only in the form of handbrake.

Instead of the handbrake lever 8 directly or indirectly operating on a separate parking brake, no separate parking brake is provided, and the handbrake lever 9 instead operates the transmission brake. This is achieved by means of a switch 24 in series with the seat-operated switch 2.

When the parking brake lever 8 is applied, the switch 24 is opened, and the transmission brake is applied in the same way as when the switch 2 is opened in the first truck. Also, the supply to the traction motor 3 is also interrupted as before.

When the parking brake lever 8 is released, normally open switch 24 is closed and, provided normally open switch 2 is also closed, the brake can be released and the truck started as described hereinbefore for the first truck.

Claims

1. An industrial truck which includes an electric switch associated with the driver's seat for sensing the presence of a person in the seat, and the arrangement is such that a brake for the traction motor cannot be released when the switch is in the position corresponding to the seat being empty.

2. An industrial truck as claimed in claim 1, wherein the traction motor brake is biased by resilient means into the on position and hydraulic means is provided for reieasing the brake.

3. An industrial truck as claimed in claim 2, wherein the hydraulic means is a piston-andcylinder.

4. An industrial truck as claimed in claim 2 or claim 3, wherein a solenoid operated by the electric switch is provided for actuating the hydraulic means.

5. An industrial truck as claimed in claim 4, wherein the solenoid operates a valve which in one position allows the hydraulic means to be pressurised while in another position vents the hydraulic means.

6. An industrial truck as claimed in claim 5, wherein the valve, in the position that allows the hydraulic means to be pressurised, blocks flow through the valve by means of a non-return valve associated with the valve.

7. An industrial truck as claimed in claim 6, wherein the hydraulic means and valve are ted via a second non-return valve, the non-return valves being so arranged that pressure is retained in the hydraulic means when pressurised when the solenoid-operated valve is in the appropriate position.

8. An industrial truck as claimed in any one of claims 2 to 7, wherein the pressure is provided by the power steering pump.

9. An industrial truck as claimed in any one of claims 1 to 8, wherein a further electric switch is provided in series with the traction motor, which switch is arranged to be opened when the traction brake has been applied.

1 0. An industrial truck as claimed in any one of claims 1 to 9, wherein there is provided an additional electric switch associated with a control for a separate parking brake, which switch is in series with the traction motor and arranged so that the traction motor is not supplied with current when the parking brake control is on.

11. An industrial truck as claimed in any one of claims 1 to 9, wherein there is provided an additional electric switch associated with a parking brake control, which switch is in series with the driver sensing switch.

1 2. An industrial truck substantially as hereinbefore described with reference to, and as shown in, Figures 1 to 3, or Figure 4, of the accompanying drawings.