DIRECTIONAL CONTROL SYSTEM

Abstract: A circuit for controlling the drive direction of an electrically-driven vehicle, the circuit having a plurality of spring return input switches (20) each actuation of which changes, via a flip-flop circuit (21) and an amplifier (22), the energisation of a relay (13) direction contactor coils being connected in alternative circuits through the contacts of the relay (13).

Description: "DIRECTIONAL CONTROL SYSTEM" This invention relates to a directional control circuit for an electrically-driven vehicle such as a fork lift-truck. PRIOR ART Directional control of a fork lift truck is usually achieved by one of two basic systems, namely by providing a) a three position hand operated switch providing visual indication of the directio of travel selected and a neutral position; or b) two accelerator pedals for forward and reverse directions respectively. Neither method is entirely satisfactory as both have inherent disadvantages for the truck operator. The first method, (a) above, as it involves use of the operator's hand, renders it impossible to reverse the direction of drive, i.e. to use electric braking, and simultaneously operate any of the truck hydraulic functions whilst retaining adequate control of steering of the truck. The second method, (b) above, does not suffer from that particular disadvantage, but with an unfamiliar or inexperienced operator incorrect operation can result, with dangerous consequences. Moreover, this method so _OMPI differs from normal automotive practice as to be considered hazardous by many authoritive bodies. It is an object of the present invention to provide a simple and effective directional control circuit that does not suffer from the aforementioned disadvantages. The present invention is a circuit for controlling the drive direction of an electrically-driven vehicle, the circuit comprising forward and reverse contactor coils controlling the drive direction, and characterised by a relay having a coil and contacts to which the contactor coils are connected in alternative circuits for energisation and an input switch controlling energisation of the relay co DRAWINGS An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a block diagram of part of a first embodiment of a drive control system of a fork-lift truck; Fig. 2 is a view in elevation of an hydraulic function operating lever; Fig. 3 is an enlarged section of part of Fig. 2; and Fig. 4 is a block diagram of part of a second -embodiment of a drive control according to the present invention. SPECIFIC EMBODIMENT Referring now to Fig. 1 , a circuit according to the present invention for controlling the drive direction of a fork-lift truck consists essentially of contactor coils 10 and 11, energisation of which determines the direction of drive, a relay 13 controlling energisation of the coils 10 and 11, a power supply.circuit 16 for the coil 14 of the rel 13 and control switches 20 for supplying control signals to the circuit 16. It will, of course, be understood immediate that the circuit illustrated in Fig. 1 is not the complete drive control circuit for the truck and that in particular there are not shown in Fig. 1 the drive motor, its field circuits in which are located the contacts associated with the contactor coils 10 and 11 and the controller by means of which the output power of the main drive motor is regulated. All these are, however, well known in principle and the details of them are not relevant to the present invention. The power supply 16 is connected to the terminals B+ and B- of the main battery of the fork-lift truck and comprises a D-type flip-flop 21 whose output is connected to an amplifier 22 which in turn controls the energisation of the relay coil 14. In the embodiment illustrated DC-DC converters 23 and 24 are provided between the battery terminals and the flip-flop 21 and amplifier 22 respectively to ensure appropriate supply voltages for the flip-flop and amplifier. The switches 20, as will be described in more detail later, are spring return switches connected in parallel to the signal input of the flip-flop so that actuation of any one of the switches 20 causes the flip- flop 21 to change its output. The output of the flip-flop 21 is either zero or a voltage which, after amplification by amplifier 22, is sufficient to operate the relay 13 and thus actuation of any one of the switches 20 changes the energis¬ ation of the relay coil 14 from the energised state to the de-energised state or vice versa, depending only on the state of energisation of the coil when the switch 20 is actuated. The contacts of the relay 13 comprise two pairs of normally open contacts, two pairs of normally closed contacts, and two movable contacts 27 and 28 which bridge respective pairs of the normally closed contacts when the relay coil is, as illustrated, not energised and respective pairs of the normally open contacts when the relay coil 14 is energised. The contact 27 bridges the normally closed pair of contacts as illustrated in a circuit comprising, in series, the controller (not illustrated), a conductor 30, the contact 27, the contactor coil 11 (the reverse contactor coil), a footswitch 31 in the accelerator pedal of the truck, first contacts of a neutral switch 32, a conductor 33 and the controller. When the relay 13 is energised the contact 27 bridges a normally open pair of contacts to substitute the contactor coil 10, the forward contactor coil, for the reverse contactor coil 11 in the above circuit. Similarly, the movable contact 28 co-operates with normally closed or normally open contacts to connect reverse or forward indicator lamps 35 and 36 respectively in a circuit across the main battery terminals and including a dropping resistor 37 and second contacts of the neutral switch 32. It can now be seen that when the relay 13 is not energised, assuming the neutral switch 32 to be closed the reverse indicator lamp 35 is energised and the reverse contactor coil 11 is energised if the footswitch 31 is closed, i.e. the circuit is set up for reverse movement of the truck. Similarly when the relay 13 is energised, the circuit is set up for forward movement of the truck. Thus, in operation, when the truck operator wishes to change the direction of drive he need only actuate any one of the switches 20 long enough to toggle the flip-flop 21. When he wishes to revert to his origina direction of drive, again all that is needed is a brief actuation of any one of the switches. Fork-lift trucks are generally provided with a number of function control levers, typically as illustrate at 40 in Fig. 2. Each lever 40 is associated with an hydraulic valve block 39 and in this embodiment a switch 20 is built into the top end of the control lever, as seen in more detail in Fig. 3. The body 41 of the switch 20 is secured in position at the top of the lever 40 while the push-button spring biased switch actuator 42 is located in a recess 43 in the knob 44 at the end of the lever to prevent inadvertant operation of the switch. A flexible membrane 45, in this embodiment of rubber, seals the recess 43 against the ingress of dust and moisture. The switch is connected to the rest of the control circuit of Fig. 1 by cables 50 extending from the switch down the lever 40. It can be seen that with the arrangement described the truck operator can change the drive direction of his vehicle using the same hand that is already involved in controlling one of the vehicle's hydraulic functions, leaving his other hand in full control of steering. Modifications may be made to the embodiment described. In particular the circuit between the switches 20 and the relay coil 14 in a number of ways, it being necessary only that the switches 20 control the energisation of the coil. In the embodiment illustrated in Fig. 4, for example, in which the same reference numerals as in Fig. 1 have been used to denote corresponding circuit elements, the flip-flop 21 and amplifier 22 of Fig. 1 have been replaced by a latching relay having its coil 60 connected between the fixed contacts of the switches 20 and the battery terminal B- and its normally open contact 61 in series with the coil 13 of the relay 14. The switch 62 is the conventional key- switch provided in fork-lift trucks. - Assuming that the switches 62 and 32 are closed, the operation of the embodiment of Fig. 4 is the same as that of Fig. 1. Each closure of a switch 21 will change the condition of the contacts 61 of the latching relay and hence the energisation of the relay 14 to determine which of the contactor coils 10 and 11 is at any time energisable via the ootswitch 31. It should also be noted that electrical braking can be achieved by actuating any of the switches 20 to change the drive direction while the vehicle is moving. Also when either the keyswitch 62 or the neutral switch 32 are opened, as for example when the driver leaves the vehicle, and subsequently closed, the control circuit is automaticall put in condition for forward movement of the vehicle.

Claims: CLAIMS 1. A circuit for controlling the drive direction of an electrically-driven vehicle, the circuit comprising forward and reverse contactor coils controlling the drive direction, and characterised by a relay (13) having a coil (14) and contacts to which the contactor coils (10, 11) are connected in alternative circuits for energisation, and an input switch (20) controlling energisation of the relay coil. . 2. A circuit as claimed in claim 1, characterised in that the input switch (20) is connected to the signal input of a flip-flop circuit (21) having two output levels of which one is insufficient to energise the relay coil (14). 3. A circuit as claimed in claim 1, characterised by a latching relay having a coil connected for energisation through the input switch and contacts controlling energisation of the coil (14). 4. A circuit as claimed in any preceding claim, characterised by a pair of direction indicator lamps (35, 36) alternatively responsive to energisation of the relay to indicate respective directions of drive selected. 5. A circuit as claimed in any of claims 1 to 3, characterised by a plurality of input switches (20) functionally connected in parallel to control energisation of the relay coil. 6. A circuit as claimed in claim 1, characterised in that the or each input switch (20) is a spring return switch. 7. A circuit as claimed in claim 6, characterised in that the vehicle has at least one hydraulic function operating lever and characterised in that the or each said lever (40) has an input switch (20) mounted at the end thereof. 8. A circuit as claimed in claim 7, characterised in that the input switch (20) is recessed in the end of its associated lever (40).

Inventors: MOORE J, RICE D
Applicants: EATON LTD, MOORE J, RICE D
Application year: 1979
Main classification: B60L11
IPC codes: B60L15, B62D1, H02P7