US3614567A

US3614567A - Control of auxiliary movements on industrial trucks

Info

Publication number: US3614567A
Application number: US692849A
Authority: US
Inventors: Ivan Salisbury Payne; Cecil Goodacre
Original assignee: Lansing Bagnall Ltd
Current assignee: Linde Material Handling UK Ltd
Priority date: 1963-10-08
Filing date: 1967-12-22
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19
Also published as: DE1463393B2; AT249179B; NL6411730A; SE324512B; CH431381A; BE654142A; DE1463393A1; ES304788A1; SE324512C

Abstract

An industrial truck having several different auxiliary movements such as a carriage lift mechanism, a mast tilt mechanism and a reach mechanism has levers operative to select any one mechanism for operation alternatively. A pulse-controlled motor is provided for giving power to drive any one of the movements. The motor drives a variable speed hydraulic pump which is associated with respective valve mechanisms so that the pump provides hydraulic power to drive a mechanism when the respective valve mechanism is operated. The levers controlling the valve mechanisms are also operative to open or close various switches in a control arrangement for the motor such that when a respective one of the movements is selected the pulse-operated motor is driven at a pulse rate respective to the demands of the particular movement. Each movement has a power requirement demanding a different pulse rate and the required pulse rate is selected at the same time as the movement is selected by the appropriate operating lever.

Description

United States Patent [72] Inventors Ivan Salisbury Payne;

Cecil Goodacre, both of Basingstoke, England [21] Appl. No. 692,849 [22] Filed Dec. 22, 1967 [45] Patented Oct. 19, 1971 [7 3] Assignee Lansing Bagnall Limited Basingstoke, England [32] Priority Oct. 8, 1963 [3 3] Great Britain [31 13977 Continuation-impart of application Ser. No. 402,128, Oct. 7, 1964, now abandoned.

[54] CONTROL OF AUXILIARY MOVEMENTS 0N INDUSTRIAL TRUCKS 9 Claims, 5 Drawing Figs.

[52] U.S. Cl 318/305, 3 18/341 [51] Int. Cl 1102p 5/16 [50] Field of Search 318/341, 345, 17, 305; 307/293, 294

[5 6] References Cited UNITED STATES PATENTS 3,168,688 2/1965 Roggenkamp 318/109 Primary Examiner-Cris L. Rader Assistant Examiner-Thomas Langer Attorney-Martin Kirkpatrick ABSTRACT: An industrial truck having several different auxiliary movements such as a carriage lift mechanism, a mast tilt mechanism and a reach mechanism has levers operative to select any one mechanism for operation alternatively. A pulsecontrolled motor is provided for giving power to drive any one of the movements. The motor drives a variable speed hydraulic pump which is associated with respective valve mechanisms so that the pump provides hydraulic power to drive a mechanism when the respective valve mechanism is operated. The levers controlling the valve mechanisms are also operative to open or close various switches in a control arrangement for the motor such that when a respective one of the movements is selected the pulse-operated motor is driven at a pulse rate respective to the demands of the particular movement. Each movement has a power requirement demanding a different pulse rate and the required pulse rate is selected at the same time as the movement is selected by the appropriate operating lever.

PATENTEDum 19 19m 3, 14,553 7 V'ISHEET NF 4 VALVE LIFT 6M ECH-ANISM :V MECHANISM 2/ \63 P I 6/ L MUTUR 72 7/ 68 v v ai VALVE REACH MECHANISM MEIIHANISM 63 Z3 6.9 73 I' 62 v 66 i VALVE nu MECHANISM MECHANISM CONTROL OF AUXILIARY MOVEMENTS N INDUSTRIAL TRUCKS This application is a continuation-in-part of my prior copending application Ser. No. 402,128 filed on Oct. 7, 1964 and now abandoned.

The invention relates to an industrial truck of the kind having several, different, auxiliary movement mechanisms such as a carriage lift mechanism, a mast tilt mechanism and a reach mechanism. These mechanisms are operated at different times and can be selected by a suitable system of controlling levers. The mechanisms normally require different power inputs for operation. It has hitherto been usual to provide either separate motors for driving each of the mechanisms or to provide a single conventional direct current motor operative to drive the mechanisms selectably and to vary the speed of the motor in accordance with the power output required to effect the necessary movement. Both alternatives are uneconomical since the fonner requires more motors than is necessary and the second requires a continuous motor which is an excessive consumer of power, especially where speed-regulating circuits are employed and the motor is battery powered.

It is the main object of the present invention to enable the aforementioned mechanisms to operate in a manner which avoids waste of power while using a common power source.

It is known to control the speed and power of an electric power by providing pulse operation, that is to say, the motor is energized with intermittent power pulses at a rate determined by the required speed or power output. It is a further object of the present invention to employ such a motor to control the aforementioned movements in a relatively economical and simple manner.

The present .invention contemplates the employment of a pulseoperated motor and at a time when the required movement is selected to perform a simultaneous control operation which ensures that the motor is fed with pulses at a rate which is determined by the particular movement selected. Each movement has an appropriate power level associated with a respective pulse rate to the motor. With the present invention the appropriate pulse rate can be selected at the time when the particular movement is selected.

In a specific example of the invention each mechanism has its own control lever. Movement of a selected lever not only brings into operation the corresponding mechanism but also determines the speed at which the motor operates. Thus for a mechanism requiring high power the motor runs at a high pulse rate speed whereas a mechanism requiring only low power the motor runs at a low pulse rate. This avoids waste of power. If for each mechanism the motor were to run at the speed suited to the lift mechanism there could be considerable power waste when other mechanisms requiring less power were in use. The pressure, would be lost for example by highpressure hydraulic fluid in a hydraulic transmission system escaping through a bypass relief valve. Thus the present invention equates the power available to the power required for each mechanism. The speed at which each mechanism operates can be controlled by means of switches which when a particular mechanism is operated are operative to provide a particular value of resistance in circuit with a timing capacitor in the pulse generator whose output frequency is determined by the time constant of the resistance capacitance circuit. A different resistor or combination of resistors can be put in circuit with the capacitor for each movement. The frequency of the pulse generator will determine the pulse rate at the motor and accordingly the power output thereof.

Further objects and features of the present invention will be apparent from a consideration of the following detailed description, during which reference will be made to the accompanying drawings of an illustrative embodiment of the invention, in which:

FIG. I is a side elevation of a control panel of a lift truck;

FIG. 2 is a side elevation of the control panel of FIG. 1;

FIG. 3 is a side elevation of the opposite side of the panel of FIG. 1;

FIG.-4 is a diagram of the circuit of FIG. 1; and

associated with the panel FIG. 5 is a schematic drawing of a hydraulic transmission system for use with the apparatus of the preceding figures.

Referring to the figures and in particular FIG. 1, three control levers L1, L2 and L3 extend upwardly from three

hydraulic valve arrangements

64, 65 and 66 respectively (as shown in FIG. 5) which are mounted side by side on an industrial fork lift truck control panel 11. The levers are each pivotable on stub shafts about a common axis 12 in the upper portion of the valves. The levers L1, L2 and L3 respectively control the lift, reach and tilt operations of the cradle of the truck.

Referring now to FIG. 5, in this figure is shown the transmission means which couples the motor 21 for driving the auxiliary movement mechanisms through the

valve systems

64, 65 and 66 to provide when operated hydraulic motive power to the auxiliary movement mechanisms, i.e., the respective lift, reach and

tilt mechanisms

67, 68 and 69 shown diagrammatically in FIG. 5. It will of course be appreciated that the valve arrangements and the lift, reach and tilt mechanisms may be themselves conventional and their construction will be readily apparent to those skilled in the art.

The lift lever L1 is operatively connected to the valve arrangement 64 by a linkage 70 which may in accordance with usual practice be a purely mechanical linkage or may include microswitches or the like. Operation of the lift lever Ll renders the valve system 64 operative to feed the hydraulic output of a variable speed pump 61 to the lift mechanism 67. The lift mechanism 67 would usually be a hydraulic lift jack.

The lever L2 is operative to provide both forward and reverse reach operations and according to the movement of the lever L2 the valve mechanism 65 is operative through

mechanical linkage

71 or 72 respectively to provide hydraulic motive power from the pump 61 in the appropriate sense to the reach mechanism 68.

Likewise, the lever L3 is operative to provide for either direction of movement of the tilting mast motive hydraulic power in the appropriate sense to the tilt mechanism 69, the

linkage

73 or 74 being operated to control the corresponding valve arrangement 66 according to the direction of movement of the lever L3.

As will be apparent the variable speed pump 61 provides an output through conduits 62 'to the

valve arrangements

64, 65 and 66 and receives exhaust therefrom through the conduit 63. The variable speed pump 61 is driven by a motor 21 in a manner to be described.

Thus the movements of the control levers select the required movement in a manner which can be itself conventional.

Referring again to FIG. 1, there are mounted on the stub shafts for movement with each lever cams l3 formed by rocker arms with projecting adjustable screws 130. Each cam is mounted very close to an arm 15 so that a'slight movement of the levers L in either direction will cause the screws 13a to engage and depress the arms 15. The arms 15 associated with each lever L are pivoted about a common axis I6and are connected to further arms 17 which move with the first-mentioned arms 15 to operate microswitches M1, M2 and M3. The cams l3 operated by levers L1 and L3 are provided with extensions 14 which operate further microswitches as described later.

The arms 15 associated with both the tilt and the reach levers L2 and L3 are secured to a common shaft 116, and a further ann 17a connected to the shaft operates microswitch M2. The arm 13 associated with the lift lever L1 is connected to a sleeve 216 coaxial with the shaft 116. The arm 17b mounted on the sleeve 216 operates two microswitches M1, M3 the switch M3 being operated after the sleeve 216 has been rotated past the position in which the switch MI is operated, this operation being effected through an arm 117 on lever 17b engageable through an adjustable screw 118 with an arm 17c free on sleeve 216 and engageable with switch M3.

The cam extensions 14 are each mounted to move with the associated lever to operate a microswitch M4, M5 or M6 directly. The cam 14 associated with the tilt lever L3 is illustrated in FIG. 3 and has a U-shaped portion 18, the arms 19 of which will operate the microswitch M4 on movement of the tilt lever in corresponding directions. The cam 14 of the reach lever L2 is in two parts, one being an arm 19a operating microswitch M5 on movement of the reach lever in one direction and the other being a second arm 19b operating an adjacent microswitch M6 on movement of the reach lever in the other direction. There is no second cam 14 associated with the lever L1.

As shown in FIG. 4, the truck has a single traction motor 21 which drives the variable delivery pump 61 as shown in F IG. 5.

The motor 21 has an armature 22 and series field coils 23 and 24. The motor is pulse controlled by pulses obtained from a pulse control circuit denoted generally by the reference number 25. This circuit will be described in detail shortly.

Power for the motor is obtained from a 48 volt battery 26. The positive terminal of the battery is connected to one side of the armature through a contactor 27. Across the motor circuit is connected a conventional free wheeling diode 29.

The control circuit 25 comprises two

thyristors

31 and 32. The thyristor 31, when conductive permits current flow through the motor circuit. The thyristor 32, when rendered conductive, causes (in a manner to be described) the cutoff of the thyristor 31 and the cessation of current flow from the battery through the motor. The junction 33 of the second field coil 24 and the diode 29 is connected through a variable resistor 34 and a capacitor 35 to earth 36. The resistor 34 and capacitor 35 fonn a timing circuit determining the pulse rate at the motor; the value of resistor 34 is changed in accordance with the selection of the various auxiliary movements of the truck. The junction 37 of the variable resistance 34 and the capacitor 35 is connected through a pair of transistors 38 in cascade and through a diode 39 to a triggering electrode 41 of the thyristor 31. The variable resistance 34 comprises a number of parallel resistance arms R2 to R5 controlled by the microswitches M4 to M6 which are operated by the second cams 14 and by limit microswitches M7 an M8 operated at the ends of the reach operation. The microswitches are each arranged to operate respective switches 4 to 8, switches 4 to 6 being normally open and switches 7 and 8 normally closed. The point 33 is also connected through a diode 42 across a capacitor 43 and resistor 44 in parallel through a second diode 45 to a second pair of transistors 46 connected in cascade to the triggering electrode 47 of the thyristor 32. The first thyristor 31 is connected in parallel with an arm containing a capacitor 48 and the second thyristor 32 in series. A further voltage supply line 36a is fed with voltage through a resistor 81 from a positive voltage terminal through a resistor 81 from a positive voltage tenninal 84 when a switch 82 is closed. A fuse 83 may be included in series with the switch 82. The voltage between the lines 36 and 36a'is maintained at an appropriate regulated value by means of a capacitor 85 and a Zener or avalanche diode 86.

The two contactors 27 and 28 are controlled by relay coils energized through the microswitches M1, M2 and M3.

When the switch 82 is closed the supply line 36a is armed with voltage but the transistors 38 remain nonconducting since the tenninal 33 is not armed with voltage. When the first contactor 27 is closed and the contactor 28 is open power is fed to the motor 21. The reference voltage at the junction 33 rises and thus the capacitor 35 is charged up through the resistance 34, the potential at the point 37 rising exponentially at a rate determined by the time constant of the circuit containing the capacitance 35 and the variable resistance 34. Thus after a delay determined by that time constant the first transistor pair 38 conducts and applies a triggering signal to the first thyristor 31 which is rendered conductive and allows a pulse of current to pass through the armature 22 and the field coils 23 and 24. When the thyristor 31 conducts, the voltage at the point 33 drops to only a few volts positive and causes the capacitor 43 to discharge which switches on the second transistor pair 46. This applies a triggering signal to render the thyristor 32 conductive. When the thyristor 32 conducts the capacitor 48 connected in series with it discharges and switches off the thyristor 31'. The reference voltage at the junction 33 an the line 36a rises again and the pulse of current through the motor armature 22 an the field coils 23 and 24 ceases. After a delay again determined by the time constant of resistor 34 and capacitor 35 the voltage at the junction 37 rises sufficiently to effect the tum-on of transistors 38 and the pulse sequence repeats itself.

The delay period between the switching off of the current through the motor 21 and the time when the thyristor 31 again conducts can be controlled by varying the value of the variable resistance 34 by appropriate operation of the microswitches M4 to M8. It will be apparent that these switches are operative in accordance with the particular movement selected and as will be apparent hereinafter the delay period an hence the pulse rate is chosen in accordance with the selected movement.

The diode 29 connected in parallel with the motor circuit serves to prevent the occurrence of an excessive inductive voltage across the thyristor 31 at the moment when the thyristor switches off and to provide a means of carrying the inductive energy in the motor 21 while the first thyristor 31 is I switched off. In fact, the diode 29 provides a low resistance path in the motor loop during the periods when the thyristor 31 is switched off. The capacitor 48 in series with the thyristor 32 must normally have a capacitance such that its discharge current may be sufficient to exceed the forward motor coil current through the first thyristor 31 under heavy overload conditions. The actual value of the capacitor 48 can be reduced by the inclusion of a transformer 51 and a further diode 52, a resistor 53 and a transistor 54. When the first thyristor 31 starts to conduct the rise in current in the motor coils 23 and 24 induces a voltage in the secondary windings of the transformer 51, which voltage charges the capacitor 48 in series with the second thyristor through the further diode 52 to a voltage predetermined by the core size and turns ratio of the transformer 51, by the rate of rise of current and by the length of the current pulse. When the second thyristor 32 starts to conduct, the capacitor 48 is discharged to tumoff the thyristor 31 and thus terminate the pulse of currents through the motor 21. The collector of the transistor 54 is connected through terminals X to the base of the first transistor of the second transistor pair 46 so that the end of the further resistor 53 is earthed at the appropriate time to increase the rate of charge and discharge of the capacitor 48 in series with the second thyristor 32.

There follows a description of the way in which the appropriate pulse rate is selected when the particular movements, lift, tilt and reach are chosen for operation.

When the three levers L1, L2 and L3 are in their central neutral positions the contacts 1 to 8 associated respectively with the microswitches M1 to M8 are in the position shown in FIG. 4 and accordingly the motor 21 is switched off.

LIFT OPERATION One initial movement of the lift lever L1 the contact L1 is closed, energizing the coil 49 through diode 55. The first contactor 27 closes and power is supplied to the motor 21. The circuit 25 is also energizes so that the motor is energized by a succession of pulses whose rate is determined by the time constant of the resistor R2 and the capacitor 35. It will be recalled that this time constant controls the delay period between the switching off of the thyristor 31 and its next conduction period. The present arrangement includes facility for driving the motor at a high speed, not under pulse control during lift operation. This is effected by further movement of the lift lever to cause the closure of contact 3 which energizes the coil 49 of the second contactor 28. The second contactor 28 closes and energizes the main series winding 23 in the armature 22 of the motor directly and independent of the pulses. The motor is thus driven at a higher speed so that the lifting jack connected by the lift lever to the pump is supplied with hydraulic fluid at great pressure.

It will be recalled that operation of the tilt lever connects tilt mechanism to hydraulic circuit to provide hydraulic power for moving the tilt mechanism in either one of two selectable directions. The movement of the tilt lever L2 also moves the contact 2 to the position not shown in FIG. 4 so that the coil 49 of the first contactor 27 is energized. The contact 4 is also closed to place the resistance R3 in parallel with the resistor R2 in the timing circuit formed by the resistance 34 and the capacitor 35. The delay period is altered so that the pulse rate is appropriate for the tilting operation. The motor 21 is thus driven in the same way as for slow speed during lifting but at a different pulse rate.

REACH OPERATION As has been hereinbefore explained the movement of the reach lever is operative to connect the reaching mechanism to the hydraulic circuit so that the reaching mechanism can be driven in an appropriate direction as the pump 61 is driven by the motor 22. The pulse rate for the reach operation is different according to the direction of tilt. Depending on the direction of movement of the reach lever, contact 5 or contact 6 is closed to place either resistor R4 or resistor R5 in parallel with the resistor R2. The delay periods determine corresponding pulse rates for the motor 21 so that the motor runs at a speed appropriate for the reach operation in the selected direction.

As the limit of the reach operation is reached, the pulse rate must be slowed down and this is effected by the opening of either contact 7 or contact 8 according to the direction of reach. The opening of these contacts takes the respective resistor out of the timing circuit so that the pulse rate reverts to that determined by the time constant of the resistor R2 and the capacitor R5.

The circuit is interlocked to prevent closure of the second contactor 28 during tilt or reach operations in spite of movement of the lift lever so that under these conditions the motor is always supplied with pulses alone.

In place of the pump and hydraulic jacks, the motor 21 may, as will be apparent to those skilled in the art, driven the various operations of a lift truck through a direct linkage such as gearing chains, high efficiency screws and the like. The control levers L1 to L3 can then engage the linkage appropriate for the operation at the same time as operating the microswitches as described above. Spring brakes can be provided, the spring pressure being progressively removed by an electromagnet as power is supplied to the motor.

lclaim:

l. in an industrial truck, the combination comprising:

a plurality of auxiliary movement mechanisms,

a motor;

transmission means coupling said motor for driving the auxiliary movement mechanisms;

control means having a plurality of selectable conditions,

each of said conditions coupling the transmission means to a respective one of said movement mechanisms to effect operation thereof;

pulse control means for said motor, said pulse control means having a control circuit determining the pulse rate of the pulse control means;

said control circuit having a plurality of selectable conditions, in each of which the control circuit provides a respective pulse rate; and said control means being operative to select simultaneously a condition in the control circuit and a corresponding auxiliary movement for operation by said motor.

2. The structure as set forth in claim 1 wherein the pulse control means comprises a controlled rectifier means which when conductive provides energizing current for said motor, a pulse generator means operative to supply control pulses to the controlled rectifier means, the pulse generator having a timing circuit with a plurality of conditions, in each of which a different period between control pulses is provided, the timing circuit condition being selected by said control means.

3. An industrial truck having a plurality of auxiliary movement mechanisms, said mechanisms comprising a lift mechanism, a tilt mechanism, and a reach mechanism; first, second and third manually operable control elements for selecting operation of said mechanisms respectively, motor means operable to drive said mechanisms, means responsive to selective movement of said elements for coupling said mechanism for driving by said motor means, controllable supply means for supplying said motor means with pulses of current at a selectable rate, first-means coupled to said first element and said controllable supply means for determining a first pulse rate in response to selective movement of said first element, second means coupled to said second element and said controllable supply means for determining a second pulse rate in response to selective movement of said second element; and third means coupled to said third element and said controllable supply means for determining a third pulse rate in response to selective movement of said third element.

4. An industrial truck as set forth in claim 3 additionally comprising switch means and means responsive to additional movement of said first lever for operating said switch means, said switch means being operative to energize said motor means.

5. In an industrial truck, the combination comprising:

a plurality of auxiliary movement mechanisms each having respective power requirements;

a hydraulic circuit for actuating said mechanisms, said hydraulic circuit including a pump means for providing hydraulic pressure in the hydraulic circuit and selectively operable valve means for selective coupling of the hydraulic pressure to said auxiliary movement mechanisms;

an electric motor means coupled for driving said pump means;

pulse supply means for said electric motor means, said pulse supply means having a timing circuit having a plurality of selectable conditions each defining a respective one of a plurality of predetennined rates of supply of energizing pulses from said pulse supply means to said electric motor means, each of said predetermined rates of supply of energizing pulses corresponding to a respective one of said power requirements of said auxiliary movement mechanisms;

a plurality of manually operable elements each coupled to a respective one of said valve means for selective operation thereof in response to selective movement of said elements; and means responsive to selective movement of each element for simultaneously selecting the respective condition of said timing circuit, whereby the rate of supply of energizing pulses to said electrical motor means corresponds to the power requirement of the auxiliary movement mechanism selected for operation.

6. The combination as set forth in claim 5 in which said timing circuit includes a resistive network in circuit with a capacitor, the resistive network including a plurality of diflerent selectable resistive paths, and in which said means responsive to selective movement of each element comprises switch means disposed for actuation by the respective elements and circuit means coupling said switch means for selecting a respective resistive path.

7. The combination as set forth in claim 5 in which said auxiliary movement mechanisms comprise lifi, reach and tilt mechanisms.

8. The combination as set forth in claim 7 in which said manually operable elements comprise levers.

9. The combination as set forth in claim 6 in which said pulse supply means comprises a battery source, an electronic power switch coupled between the battery source and said electrical motor means, said electronic power switch having a control input, and pulse-generating means, including said tim ing circuit, coupled to said control input.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 61 4-567 Dated October 19, 1971 V Y a my Inventor) Iran oalisbury Payne, k/GCll Goodaere It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 67, after "description" add --of an illustrative embodiment of the invention--;

lines 58 and =59, delete --of an illustrative embodiment of the invention--; Column line 37, "an" should be --anri--;

line P8, delete "81 vfrom a positive voltage terminal thI'OIlg'fll a resistor"' Column line 7, "on" line "an" should be --and--; line 1, "energizes" :.should be --energ;ised--3 Column ",1, line IP, "driven" should be --drive--;. Column 1, line 95, claim t, after "means" add --eontinuously-.

should he --and--;

Signed and sealed this L .th day of July 1972.

(SEAL) Attest:

E WARD I LFLEICHEH, JR. ROBEhT GOTTSCHAIJK Attesting Officer Commissioner of Patents

Claims

1. In an industrial truck, the combination comprising: a plurality of auxiliary movement mechanisms, a motor; transmission means coupling said motor for driving the auxiliary movement mechanisms; control means having a plurality of selectable conditions, each of said conditions coupling the transmission means to a respective one of said movement mechanisms to effect operation thereof; pulse control means for said motor, said pulse control means having a control circuit determining the pulse rate of the pulse control means; said control circuit having a plurality of selectable conditions, in each of which the control circuit provides a respective pulse rate; and said control means being operative to select simultaneously a condition in the control circuit and a corresponding auxiliary movement for operation by said motor.

3. An industrial truck having a plurality of auxiliary movement mechanisms, said mechanisms comprising a lift mechanism, a tilt mechanism, and a reach mechanism; first, second and third manually operable control elements for selecting operation of said mechanisms respectively, motor means operable to drive said mechanisms, means responsive to selective movement of said elements for coupling said mechanism for driving by said motor means, controllable supply means for supplying said motor means with pulses of current at a selectable rate, first means coupled to said first element and said controllable supply means for determining a first pulse rate in response to selective movement of said first element, second means coupled to said second element and said controllable supply means for determining a second pulse rate in response to selective movement of said second element; and third means coupled to said third element and said controllable supply means for determining a third pulse rate in response to selective movement of said third element.

5. In an industrial truck, the combination comprising: a plurality of auxiliary movement mechanisms each having respective power requirements; a hydraulic circuit for actuating said mechanisms, said hydraulic circuit including a pump means for providing hydraulic pressure in the hydraulic circuit and selectively operable valve means for selective coupling of the hydraulic pressure to said auxiliary movement mechanisms; an electric motor means coupled for driving said pump means; pulse supply means for said electric motor means, said pulse supply means having a timing circuit having a plurality of selectable conditions each defining a respective one of a plurality of predetermined rates of supply of energizing pulses from said pulse supply means to said electric motor means, each of said predetermined rates of supply of energizing pulses corresponding to a respective one of said power requirements of said auxiliary movement mechanisms; a plurality of manually operable elements each coupled to a respective one of said valve means for selective operation thereof in response to selective movement of said elements; and means responsive to selective movement of each element for simultaneously selecting the respective condition of said timing circuit, whereby the rate of supply of energizing pulses to said electrical motor means corresponds to the power requirement of the auxiliary movement mechanism selected for operation.

6. The combination as set forth in claim 5 in which said timing circuit includes a resistive network in circuit with a capacitor, the resistive network including a plurality of different selectable resistive paths, and in which said means responsive to selective movement of each element comprises switch means disposed for actuation by the respective elements and circuit means coupling said switch means for selecting a respective resistive path.

7. The combination as set forth in claim 5 in which said auxiliary movement mechanisms comprise lift, reach and tilt mechanisms.

9. The combination as set forth in claim 6 in which said pulse supply means comprises a battery source, an electronic power switch coupled between the battery source and said electrical motor means, said electronic power switch having a control input, and pulse-generating means, including said timing circuit, coupled to said control input.