US3280397A

US3280397A - Industrial truck

Info

Publication number: US3280397A
Application number: US354647A
Authority: US
Inventors: Bruns William Henry
Original assignee: Otis Elevator Co
Current assignee: Otis Elevator Co
Priority date: 1964-03-25
Filing date: 1964-03-25
Publication date: 1966-10-18
Anticipated expiration: 1983-10-18

Description

Oct. 18, 1966 w. H. BRUNS 3,280,397

INDUSTRIAL TRUCK Filed March 25, 1964 4 Sheets-Sheet l CHARGER 24 D AND SPEED AND PUMP 4| REVERSING 1 REVERSI MOTOR SWiTCH g; SWITCH e l l l 25 42 k ACCESSORY 52 i l 57 32 @lZ'----- GP' 43 58 i l 26 e5 LIQUID 59 W/L LL41? HEMQYEEUMS l N V E N TO R BY Vim ATTORNEY Oct. 18, 1966 w. H. BRUNS INDUSTRIAL TRUCK 4 Sheets-Sheet 5 Filed March 25, 1964 W/LL lflN/JENKYBAUNS IN VE NTOR BY mi M ATTORNEY Oct. 18,1966

Filed March 25, 1964 W. H. BRUNS INDUSTRIAL TRUCK 4 Sheets-Sheet 4 VOLTAG E VVVV l l w W GASOLINE ENGINE mum ymeyszu/vs INVE NTOR BYWZW ATTORNEY United States Patent 3,280,397 INDUSTRIAL TRUCK William Henry Bruns, Lincolndale, N.Y., assignor to Otis Elevator Company, New York, N.Y., a corporation of New Jersey Filed Mar. 25, 1964, Ser. No. 354,647 12 Claims. (Cl. 318 -139) This invention relates generally to fork lift trucks and particularly to a novel system for controlling the speed of both the truck itself and the hoist associated therewith.

Small self-propelled industrial trucks are widely used for handling material in warehouses. The usual truck includes a motor for propelling the truck and a power operated hoist, often with a pair of forks as the platform, for raising and carrying the load. Power plants of various kinds, such as gasoline, electric, and combinations thereof have been used. One of the most common arrangements comprises a pair of series motors, one for propelling the truck and one for operating the hoist, both supplied with electricity from a battery mounted on the truck. In this arrangement, the propulsion motor is geared to the Wheels and the running speed is controlled by varying the amount of resistance connected in series with the motor. A friction brake is used to decelerate the truck for stopping and to control the speed on down grades. Typically the hoisting motor drives a pump which forces fluid into a cylinder to raise the load. The load is lowered by a valve which controls the rate at which fluid in the cylinder is released to a reservoir.

The above and other similar arrangements have certain disadvantages. For example, with any particular setting of the speed controller, the resulting speed varies widely with different torque requirements due to the inherent operating characteristics of a series motor. For the propulsion motor, torque requirements depend upon the weight of the load and the grade encountered. For the hoisting motor, torque requirements depend upon the load on the forks. In order to obtain any given speed the operator must adjust the controller in accordance with different load conditions.

Another disadvantage is that the above-described arrangement wastes power. Whenever either motor is running at less than full speed, power is dissipated in the series resistors. Whenever there is a negative load, as when the truck is decelerating or going down hill or when the load on the fork is being lowered, the kinetic and/or potential energy is dissipated either in the friction brake or in the hydraulic lowering valve.

A fork lift truck in normal operation is starting or stopping, and raising or lowering a load practically continuously. A large proportion of the energy drawn from the battery does no useful work but is wasted. As a result, the battery must either have a very large capacity or be recharged frequently. Truck mounted battery chargers have been unattractive because of the size and cost of a charger of sufficient capacity to replenish the large amount of power withdrawn.

It is a general object of the present invention to provide an improved industrial truck.

Another object is to improve the running speed control of an industrial truck.

A more specific object is to provide an industrial truck with a running speed control system by which an operator can select a desired speed, which speed is substantially independent of either the grade, whether up or down, or the load being carried.

Another object is to provide a fork lift truck with improved control of the hoisting and lowering speed.

Anotherobject is to provide a system for controlling the hoist of a lift truck by which an operator can select a desired hoisting or lowering speed which is substan- I 3,280,397 Patented Oct. 18, 1966 tially independent of the weight of the load on the hoist.

Another object is to provide a battery powered electric truck in which the power drawn from the battery is used efliciently.

Another object is to provide a battery powered truck which requires but a small battery.

Another object is to provide an improved charging system for the battery of an electric truck.

Briefly stated, the invention comprises two fixed excited electric motors, one for propelling the truck and the other for operating the hoist, both supplied with power from a multi-celled battery mounted on the truck. The battery is tapped to make available several different voltages. The running speed of each motor is determined by its own switch controller which selects the desired portion of the total battery voltage and applies it to the armature. Each position of the controller corresponds to a preselected motor speed which, because of the inherent operating characteristics of a motor with fixed field excitation, varies very little with the torque requirements. When the load tends to drive one of the motors, as when going down grade, decelerating, or lowering the load on the hoist, the motor acts as a generator and charges the battery.

The invention also contemplates a charging system which may operate either continuously or intermittently. In either case, each group of cells between taps is charged from a source of alternating current the peak value of which is regulated to be substantially equal to the fully charged potential of the cells and which is applied to the cells through a rectifier. Thus, although the cells may discharge at different rates, the charging rate is automatically accommodated to the condition of the cells and overcharging is prevented.

For a clearer understanding of the invention reference may be made to the following detailed description and the accompanying drawing, in which:

FIGURE 1 is a simplified pictorial view of a lift truck;

FIGURE 2 is a schematic diagram illustrating the principles of the invention;

FIGURE 3 is a schematic diagram illustrating the principles of the speed control switch;

FIGURES 4 to 7, inclusive are fragmentary diagrams similar to FIGURE 3 showing the switch in various operating positions;

FIGURE 8 is a schematic diagram of the electrical circuits associated with the propulsion machine;

FIGURE 9 is a schematic diagram of one of the relays;

FIGURE 10 is a fragmentary schematic digaram of the electrical circuits associated with the hoisting machine;

FIGURE ll is a schematic diagram of a preferred form of a battery charger;

FIGURES 12 and 13 are schematic diagrams of a modification of the battery charging circuit; and

FIGURE 14 is a schematic diagram of another modification of the battery charging circuit.

Overall description Referring first to FIGURE 1, there is shown a lift truck 15 incorporating the invention. The truck 15 includes rear steerable wheels 16, front drive wheels 17, uprights 18, and a platform such as the forks 19 on which a load may be placed for lifting or transporting. The elements comprising the invention, although not visible in FIG. 1, are all mounted on the truck 15 and will be described in connected with the remaining figures of the drawing.

Referring now to FIGURE 2 there is shown a simplified schematic diagram of the principal elements of the invention all of which may be mounted on the lift truck 15. There is shown a battery 21 for supplying the necessary power which comprises a number of cells connected in series and having taps connected at various intermediate points to provide a source of variable voltage. A dynamo electric machine 22 includes an armature 23 and a field winding 24 which is separately, or fixed, excited by being connected to an intermediate tap of the battery 21. The machine 22 is mechanically connected through a gear box 25 to a mechanical differential 26 which, in turn, is connected to the drive wheels 17. A mechanical brake is shown schematically as comprising a brake drum 31 fastened to the shaft between the gear box 25 and the differential 26 and a brake shoe 32 applied by a foot pedal 33. A switch 34 actuated by the pedal 33 is closed when the brake is released and is open when the brake is applied. The machine 22 operates as a lIIlOtOI to drive the wheels 17 unless the load overhauls the machine in which case it acts as a generator.

A speed and reversing switch 35, to be more fully described, enables an operator to select various voltages from the taps of the battery 21 to be applied to the armature 23 to control the speed of the truck. The speed versus torque characteristics of a D.C. machine with fixed excitation has a small slope which means that the speed is dependent almost entirely on the voltage applied to the armature and depends very little on the torque requirements. In comparison with a series motor, a fixed field motor may be regarded as operating at a substantially constant speed for any given armature voltage, regardless of the torque requirements, whether positive or negative.

Hoisting is controlled by a similar dynamo electric machine 37 comprising an armature 38 and a field winding 39 the latter also being connected to an appropriate intermediate tap of the battery 21. The machine 37 is mechanically connected to a positive displacement pump 41, more properly described as a pump-motor or as a pump-motor device because it is capable of being driven in either direction by the machine 37 to act as a pump and is also capable of acting as a motor to drive the machine 37 in either direction. One side of the device 41 is hydraulically connected through a valve 42 to an accumulator 43 which may, for example, be a closed vessel with an air-liquid interface. The other side of the device 41 is hydraulically connected to a cylinder 44 which operates a piston rod 45. The piston rod 45 is mechanically connected to a sprocket 46 over which passes a chain 37 one end of which is fixed and the other end of which is connected to the platform 19 on which a load 49 may be placed in order to be raised or lowered. A speed and reversing switch 51 interconnects the armature 48 and the various taps of the battery 21 to control the speed. This switch may be similar to the switch 35 except that it also includes an auxiliary contact which is open when the switch is in the Zero speed position but which is closed at all other times. This switch, when closed, energizes a solenoid 52 which opens the valve 42. When the solenoid is deenergized the valve is spring-biased to its closed position. It is to be understood that the electrical, mechanical and hydraulic connections shown in FIGURE 2 are schematic only and are simplified versions of those which would actually be used on a commercial truck.

A battery charging system 55 is connected to each tap of the battery 21 so that each group of cells may be charged separately while non are overcharged. The charger preferably includes a truck mounted gasoline engine and generator and may also include provision for plugging into an electrical outlet. A suitable charger will be more fully described subsequently.

The truck is moved by releasing the brake and actuating the switch 35 to connect the lowest voltage tap of the battery 21 to the armature 23. The machine 22 operates as a motor and quickly accelerates the truck to the speed corresponding to this tap. To go faster, a higher voltage tap is selected and the truck quickly accelerates to the new speed. If the truck encounters an up grade, the speed tends to fall slightly, reducing the counter electromotive force of the machine 22 thus increasing the armature current and thereby preventing any substantial decrease in speed. If the truck encounters a down grade, the speed tends to increase, whereupon the machine 22 acts as a generator, providing regenerative braking and recharging of the battery. To reduce speed, the operator selects a lower voltage tap. When the battery voltage is first reduced, the counter electromotive force is much larger than the battery voltage and a large charging current is supplied to the battery. Thus, regenerative braking quickly decelerates the truck to the speed corresponding to the newly selected tap. It is apparent that each voltage tap selected corresponds to a predetermined speed which speed remains substantially constant regardless of whether the truck is going up grade or down grade. The truck may be stopped by actuating the switch 35 to the zero voltage tap which substantially short circuits the armature 23 quickly halting the truck. The truck may be held stationary by depressing the brake pedal 33.

The hoist is operated by actuating the switch 51 to the first hoisting speed position. The valve 42 is opened, the machine 37 is energized and the pump-motor device 41 is operated. If a very heavy load is being lifted, the machine 37 acts as a motor, the device 41 operates as a pump and pumps liquid from the accumulator 43, which now constitutes a source of fluid, to the cylinder 44. The connecting rod 45 raises the sprocket 46, the platform 19 and the load 49. To stop the hoist, the switch 51 is returned to the zero speed position at which the armature 38 is substantially short circuited and the valve 42 is closed. The load may be lowered by actuating the switch 51 to, for example, its first lowering speed position. The valve 42 again opens. If the load is very heavy it drives the rod 45 downward, fluid drives the device 41 as a motor, and the machine 37 is driven as a generator thereby charging the battery and providing regenerative braking. At the same time fluid is pumped into the accumulator 43, thereby further compressing the trapped air and storing energy.

If a lighter load is to be raised the switch 51 may again be actuated to its first hoisting speed position. The pressure in the accumulator 43 may be sufficient to drive the device 41 as a motor thereby raising the load 49, driving the machine 37 as a generator and charging the battery. In this case energy previously stored in the accumulator is expended both to raise the load and to charge the battery. To lower a light load the switch 51 is actuated to one of its lowering speed positions. The machine 37 acts as a motor driving the device 41 as a pump to transfer fluid from the cylinder 44 to the accumulator 43. In this case energy is transferred from the battery to the accumulater.

It is apparent that during a number of hoisting and lowering cycles, energy is automatically transferred among the battery, the accumulator and the load. No energy is uselessly dissipated in resistors, valves or mechanical brakes, or wasted by allowing fluid to return to a reservoir. The net energy expended is only that required to do useful work and to supply the inherent losses in the system.

In addition to the propulsion and hoisting systems, lift trucks are often provided with a number of power operated auxiliary devices such as devices to shift the position of the forks and devices to clamp a load. Such devices are herein termed accessories. One accessory is shown schematically in FIGURE 2 by the rectangle 56, mechanically connected to a piston rod 57 actuated by a hydraulic cylinder 58. The cylinder 58 is connected through a valve 59 to a hydraulic line 61 which, in turn, is connected to the accumulator 43. The valve 59 may be a conventional three way valve. In its first position all ports are closed. In its second position liquid from the line 61 is admitted to the cylinder 58. In its third position liquid is allowed to escape from the cylinder 58 through the line 62 to a sump or reservoir 63.

The accumulator 43 is maintained charged and the reservoir 63 prevented from overflowing by an auxiliary pumping system. A pump 64 driven by an electric motor 65 draws liquid from the reservoir 63 and pumps it through a check valve 66 to the line 61 and thence to the accumulator 43. A float 67 is mechanically connected to close a switch 68 when the liquid in the reservoir 63 reaches a predetermined level. Closure of the switch 68 completes a circuit from a source of power such as a battery 69 to the motor 65 which drives the pump 64 thereby reducing the liquid level in the reservoir 63 and charging the accumulator 43.

By the above arrangement there is always enough energy stored in the accumulator to operate the various accessories without energizing the hoisting motor 37. The energy consumption of the accessories is small and it has been deemed unnecessary to attempt to recover any of the energy expended in their operation.

Speed changing switch The batteries ordinarily used in industrial trucks consist of many cells connected in series and accordingly there is available a wide range of voltages. It would appear at first glance that it would be possible to eliminate the starting resistors simply by applying various voltages to the armature by means of taps connected to various numbers of cells of the battery. Upon analysis, however, it is found that this approach is not as simple as it would at first appear. The difliculty is two fold. First, it is necessary, to avoid short circuiting any cells of the battery during tap changing because the resulting currents would be so large as to damage the battery and the associated electrical circuits. Therefore, a simple make before break switch cannot be used. Second, the armature constitutes a large inductance which may be carrying a substantial current. If this circuit were broken, the high voltage induced by the sudden change in current could cause severe damage to the equipment. Additionally, if the armature circuit were broken, the motor would in effect be disconnected from the truck and speed control would be lost. If the truck were going up hill, the speed would fall suddenly while if the truck were going down hill, the speed would rise suddenly. Therefore, a simple break before make switch cannot be used. According-1y, it is an object of the invention to provide a switch arrangement for applying the various voltages of a multicelled battery to a DC. motor without either short circuiting any battery cells or opening the armature circuit during voltage changes.

Referring now to FIGURE 3, there is shown the multicelled battery 21 with opposite ends connected to

terminals

71 and 72. A plurality of taps 73-79 inclusive are provided, the tap 73 being connected to the terminal 71, the tap 79 being connected to the terminal 72 and the remaining taps connected to various intermediate points on the battery. The difference in potential between adjacent taps may be equal or unequal depending upon the requirements of the particular application. The terminal 71 is connected to a common or ground conductor 81.

The electric motor 22 is shown mechanically connected to a load 83 such as the driving wheels of an industrial truck. The field winding 24 has one terminal connected to the common conductor 81 and the other terminal connected to one of the battery taps such as the tap '75.

A principal contact 84 makes sliding contact with the taps 7379 and is connected to one terminal of the armature 23 the other terminal of which is connected to the common conductor 81. Two

auxiliary contacts

85 and 86 are positioned on either side of the principal contact 84 and are mechanically connected thereto as indicated schematically by the dashed line 87. All three contacts are movable as a unit, up or down as viewed in FIGURE 3, as indicated by the

arrows

88 and 89. One of the auxiliary contacts leads the position of the contact 84 while the other lags. As the contacts are moved upward, as viewed in FIGURE 3, the contact 86 leads and the contact S5 lags. As the contacts are moved downward, the contact leads while the contact 86 lags.

The contact 86 is connected to the cathode of a diode 91 the anode of which is connected to the contact 84. The contact 85 is connected to the anode of a diode 92 the cathode of which is connected to the contact 84. Each of the

diodes

91 and 92 may be any suitable kind of unidirectional conducting device, or rectifier, such as an electron tube, or a germanium or silicon rectifier, or other solid state device. The term diode is intended to comprehend any such device.

The relative widths and spacings of the taps 73-79 and the contacts 84-86 are selected so that as the contacts are moved (1) each contact disengages a tap before engaging the next succeeding tap, and (2) two adjacent contacts can engage the same tap simultaneously. A simple arrangement is illustrated wherein the spacing between taps is equal to the width of each tap, each contact is approximately one-half the width of a tap and the spacing between the center lines of adjacent contacts is approximately equal to the width of a tap. Obviously there are other arrangements of taps and contacts which can be used to accomplish the same result.

FIGURE 3 illustrates the position of the parts when the motor is running at an intermediate speed. Current flows to the armature 23 through the tap 76 and the contact 84. The

contacts

85 and 86 do not engage any tap at this time. If it is desired to increase the speed the contacts are moved'upward. The first change in connections is illustrated in FIGURE 4 wherein

contacts

84 and 85 are both engaging the tap 76 and contact 86 is engaging the tap 77. Most of the armature current flows through the contact 84 although a small amount may flow through the contact 85 and the diode 92. Although the contact 86 is engaging the tap 77, the diode 91 prevents current from flowing from the tap 77 to the tap 76. FIG- URE 5 illustrates the next change in connections. The contact 84 is not in engagement with any tap but armature current flows from the tap 76 through the contact 85 and the diode 92. As before, the diode 91 prevents current from flowing from the tap 77 to the tap 76. FIGURE 6 illustrates the next change in connections. The contact 85 engages the tap 76 while

contacts

84 and 86 bot-h are engaging the tap 77. Armature current now flows from the tap 77 through the contact 84. The diode 92 now prevents the flow of current from the tap 77 to the tap 76. FIGURE 7 illustrates the connections when the next speed has finally been selected. The

contacts

85 and 86 are disengaged while the contact 84 engages the tap 77. The motor is now operating at a higher speed. It is to 'be noted that throughout the tap changing operation the armature circuit was never broken and adjacent taps were never short circuited.

When it is desired to decelerate the motor, the sequence of events is reversed. Assume first that the machine 22 is acting as a motor, as it would if the truck were going up hill, and that the switch is in the position shown in FIGURE 7. The counter electromotive force of the motor is less than the voltage of the tap 77 by an amount equal to the IR drop in the armature and is greater than the voltage of the tap 76. The current that flows from the tap 77 through the contact 84 to the motor is the amount required to keep the truck running at a constant speed. When the switch is moved to the position shown by FIG- URE 6, there is no change. Current continues to flow from the tap 77 through the contact 84 to the motor. But when the position of FIGURE 5 is reached, conditions change. Current cannot flow from the tap 77 to the motor because of the diode 91. The counter electromotive force is not large enough to cause a current to fl ow through the diode 91 to the tap 77. The voltage of the tap 76 is less than the counter electromotive force so that current does not immediately flow from left to right through the contact 85 and the diode 92 and current cannot flow from right to left through the diode 92. Current is thus reduced. This change in current causes a voltage to be induced in the armature due to its inductance which voltage is in a direction tending to perpetuate the flow of current. This induced voltage is in opposition to the counter electrornotive force and is added to the battery voltage. Since the sum of the voltage drops in the closed circuit from the tap 76, through the diode 92, the motor armature, and the battery must be equal to zero, and since the counter electrornotive force remains momentarily at its former value which is the voltage of tap 77 less the IR drop in the armature, the induced volt-age rises only until it is equal to the difference in potential between the taps 77 and 7 6, whereupon current flows from the tap 76 through the contact 85 and the diode 92 to the motor. In other words, the induced voltage can never exceed the voltage between adjacent taps, and a smooth transition occurs. When the switch reaches the position shown in FIGURE 4, current can flow between the tap 76 and the contact 84 in either direction, depending upon the magnitude of the counter electromotive force which depends upon the speed of the machine 22.

Assume now that the switch is in the position shown in FIGURE 7 and that the machine 22 is acting as a generator as it would, for example, if the truck were going down grade. Current then flows through the contact 84 and the tap 77 to the battery. As the switch is moved to the position of FIGURE 6, current flows as before. In the position of FIGURE 5, current flows through the diode 91 and the contact 86 to the tap 77. In the position of FIGURE 4, current flows through the contact 84 and the tap 76 to the battery.

It is thus apparent that the system above described enables the armature of a dynamo electric machine to be connected successively to various taps of a multi-celled battery. No battery cells are ever short circuited. Large induced voltages and destructive arcing are eliminated because the armature circuit is-never opened.

Propulsion motor circuit Referring now to FIGURE 8, there are shown further details of the electrical connections of the battery 21, the dynamo electric machine 22, and the speed control and reversing switch 35. The latter comprises a speed control switch shown in the upper part of the figure and designated generally by the reference character 101, and a reversing switch shown in the lower left and designated generally by the reference character 102. Both are shown schematically 'as drum controller switches. The switch 101 comprises a plurality of contact fingers 103-112, inclusive and a plurality of contact segments 115-119, inclusive. The

segments

115, 116 and 117 correspond to the

segments

84, 85 and 86, respectively of FIGURES 3-7, and each comprises a plurality of segments electrically connected as shown. The segment 115 is connected directly to the segment 118 while the

segments

116 and 117 are connected to the segment 118 through the

diodes

92 and 91, respectively. The reversing switch 102 comprises a plurality of contact fingers such as the finger 121 and a plurality of contact segments 122-128, inclusive.

Also shown in FIGURE 8 are the operating windings F1 and F2 of two relays, connected in series with the armature 23, and provided with contacts F1-1 and F2-1, respectively. A diode 131 is connected across the field winding 24 to provide a discharge path when the energizing circuit is broken. A relay F3 is provided with two operating windings F3A and F3B and with two contacts F3-1 and F3-2. The relay F3 preferably comprises two separate solenoids, as shown schematically in FIGURE 9, mechanically connected together and arranged so that either winding when energized will operate the relay and the contacts F3-1 and F3-2.

The remainder of the circuit of FIGURE 8 can best be described by considering the operation. To move the truck forward, the reversing switch 102 is moved to its FWD position. The contact segment 122 partially completes a circuit for energizing the field Winding 24.

This circuit may be traced from that tap of the battery 21 which is connected to the contact finger 105, through a conductor 132, the anode-cathode circuit of a diode 133, the segment 122 and the brake switch 34. When the latter switch is closed, the circuit is completed through the field winding 24 to the ground conductor 81 and then to the battery terminal 71. At the same time, the armature 23 is substantially short circuited, the circuit including the low resistance windings F1, F2 and F313. The circuit may be traced from the upper armature brush through the windings F2 and F1, the segment 123, a conductor 134, the finger 110, the segment 118, the segment 115, the contact finger 103, the terminal 71, the ground conductor 81, the winding F3B, and the segment 124 to the lower brush of the armature 23. Next, the switch 101 is moved to its first position. The segment 119 completes a circuit from that tap of the battery which is connected to the finger 105, through the fingers 111 and 112, a conductor 135, the normally closed contacts F3-2, the winding F3A, and the ground conductor 81 to the battery terminal 71. The contacts F3-1 close, bridging the switch 34 and the contact fingers associated with the segment 122 so that the field winding 24 remains energized even if one of these circuits is opened. As soon as the relay F3 operates, the normally closed contact F3-2 opens, inserting a resistor 136 in series with the winding F3A (to reduce the current and consequent heating because less current is required to hold the relay than to operate it).

The sequence of engagement of the

segments

115, 116 and 117 during the transition from the zero position to the first speed position is identical to that previously described for

contacts

84, and 86 in connection with FIGURES 3-7, inclusive and need not be repeated. When the first speed position is reached, the armature is energized by a circuit which can be traced from the first tap of the battery 21, the contact finger 104, segment 115, segment 118, contact finger 110, conductor 134, segment 123, windings F1 and F2, the armature 23, segment 124, winding F3A and the conductor 81 to the battery terminal 71. The truck moves forward. Higher speeds are obtained by moving the switch 101 to higher speed positions which increase the voltage applied to the armature 23.

The curve of torque as a function of armature current for a DC. motor with constant field excitation is approximately linear for a considerable range of armature currents. But as the armature current is increased further and further, the curve tends to flatten out. In this region a very large increase in armature current is required in order to obtain a small increase in torque. The excitation of the field winding 24 from the contact finger is selected so that for normal loads, operation occurs in the approximately linear portion of the curve. However, to obtain the high torque required for unusually heavy loads, it is preferred to increase the field excitation. Such an increase has the effect of increasing the slope of the curve and extending the approximately linear portion to higher torques.

An increase in field excitation is obtained by means of the previously mentioned relays F1 and F2. If a heavier than normal load is encountered, the speed tends to decrease, thereby increasing the armature current. At a predetermined current, the relay F1 operates, closing its contacts F1-1 thereby increasing the available torque by increasing the field excitation. A circuit may now be traced from that battery tap connected to finger 106, a conductor 137, the anode-cathode circuit of a diode 138, and the contacts F1-1 to the field winding 24. The diode 133 prevents short circuiting of adjacent battery taps. If the torque now available is not sufiicient, the armature current increases further until a second predetermined value is reached at which time the relay F2 operates closing its contacts F2-1 thereby further increasing the field excitation through a conductor 139 to that tap connected to the finger 107. The diode 138 now also acts, along with the diode 133, to prevent short circuiting of adjacent cells. As the load decreases, the current through Windings F2 and F1 decreases sufficiently to release the contact F2-1 and then the contact F1-1, restoring normal field excitation.

An increase in field excitation is, of course, accompanied by a decrease in speed. It is preferred, under unusually heavy load conditions, to sacrifice substantially constant speed for each setting of the speed controller in the interest of limiting the armature current to reasonable values and minimizing the drain on the battery. In the high torque region of operation the total power drawn from the battery for both the armature and field is substantially less when the field excitation is increased as above described.

To decrease the speed of the truck, the switch 101 is actuated to a lower speed position. The counter electromotive force then exceeds the applied voltage and the machine 22 acts as a generator thereby charging the battery and quickly decelerating the truck. To stop the truck, the switch 101 is actuated to its zero speed position. The contact segment 119 disengages the contact finger 111 thereby deenergizing the relay winding F3A. However, the contact F3-1 does not open because the winding P38 is in the armature circuit, as previously pointed out, and the regenerative braking current therethrough holds the contact F3-1 closed, thereby maintaining the field excitation. The truck is stopped quickly and may be held by applying the mechanical brake.

Hoisting motor circuit The electrical circuit for the hoisting machine 37 may be identical to that of the propulsion machine 22 except for the circuit controlling the valve 42 which requires additional contacts on the speed control switch. Referring to FIGURE 10, there is shown a fragmentary view of a speed control switch, denoted generally by the reference character 151. The parts which are identical to those of FIGURE 8 are denoted by primed reference characters corresponding to like unprimed reference characters in FIGURE 8. There are shown in FIGURE the contact finger 112' connected to the conductor 135 and a fragment of the contact segment 119'. Also shown are two additional contact fingers 152 and 153 which cooperate with a contact segment 154. The finger 152 is connected to the conductor 132 (which, it will be recalled, is connected to an intermediate tap of the battery). The finger 153 is connected by a conductor 155 to one terminal of the solenoid 52, the other terminal of which is connected to the common or ground conductor 81. When the switch 151 is in the off position, the solenoid is not energized and the valve 42 is held in its closed position by an internal spring (not shown). When the switch 151 is actuated to any position other than the off position, the contact segment 154 engages contact finger 152 thereby energizing the solenoid 52 and opening the valve 42.

The battery charger Referring now to FIGURE 11, there is shown schematically a preferred form of the battery charger 55. A single phase alternating current generator or alternator 161 has its output connected through a double pole double throw switch 162 to the primary winding 163 of a transformer 164. The transformer 164 has secondary windings equal in number to the number of sections of the battery 21. In one embodiment the battery has six sections, 21a to 21], inclusive and the transformer 164 has six secondary windings 165 to 170, inclusive. The winding 165 has one end connected to the anode of a diode 173 the cathode of which is connected to the terminal 72. The other end of the winding 165 is connected to the junction of

battery sections

21a and 21b. The winding 166 is similarly connected, one end being connected to the anode of a diode 174 the cathode of which 10 is connected to the junction of the

battery sections

21a and 21b while the other end is connected to the junction of the battery sections 21b and 210. The

windings

167, 168, 169 and 170 are similarly connected to

battery sections

21c, 21d, 21c and 21 through the

diodes

175, 176, 177 and 178, respectively. The diodes are poled, that is, the cathodes and anodes are connected, so as to prevent the flow of current from any battery section through the corresponding winding while allowing current to flow from the winding to the corresponding section in such a direction as to charge the battery. For example, with the battery polarity as shown in FIGURE 11, the terminal 72 is positive and is connected to the cathode of the diode 173 while the anode is connected to the winding 165.

The turns ratios of the transformer 164 are selected in conjunction with the voltage of the alternator 161 to make the peak voltage (as contrasted with the R.M.S. voltage) of each winding equal to the terminal voltage of the corresponding battery section when fully charged plus the voltage drop across the diode. For example, if the battery section 21a has a terminal voltage when fully charged of 12.0 volts and the diode 173 has a drop of 0.5 volt, the number of turns of the winding 165 would be selected to make the peak voltage 12.5 volts. If all the battery sections have the same number of cells, the windings 165 178 may be identical. If the various sections have different numbers of cells and, therefore, different terminal voltages, the number of turns of the various windings are selected accordingly. The various secondary windings constitute, in effect, separate sources of alternating current.

When a storage battery is fully charged, it has a definite terminal voltage. As power is withdrawn, the battery dis charges and its terminal voltage falls. With the present arrangement the charging current is greatest when the battery section is most fully discharged and decreases as the battery becomes charged, falling to substantially zero when the battery becomes fully charged. Although the various sections may be discharged at different rates, the charging current is automatically adjusted in accordance with the condition of each section and no section is ever overcharged.

The alternator 161 is driven by a truck mounted engine 181 such as an internal combustion engine or a gasoline turbine. The output voltage of the alternator 161 depends upon its speed and to keep the voltage constant, the speed of the engine 181 is controlled by a suitable circuit such as the circuit 182. The engine 181 is provided with a throttle, shown as comprising a shaft 183 to which an arm 184 is fastened. A tension spring 185 is connected between the arm 184 and the frame of the engine 181 to bias the throttle towards its open position.

The circuit 182 includes a voltage divider comprising a diode 186, a resistor 187, a zener diode 188 and a resistor 189 serially connected in that order across the

output conductors

191 and 192 of the alternator 161. A transformer 193 has a primary winding 194 connected across the resistor 189 and a secondary winding 195 connected to a servo amplifier 196. The latter controls the energization of a torque motor 197 which is mechanically connected, as shown schematically by the dashed line 198, to the throttle shaft 183 and tends to close the throttle in opposition to the spring 185.

The zener diode 188 is selected to have a breakdown voltage substantially equal to the desired output voltage of the alternator 161. If the voltage is less than the desired voltage, no current flows through the voltage divider and no input signal is applied to the amplifier 196. The servo amplifier 196 is designed to apply a small current to the torque motor 197 in the absence of an input signal but this current is not sufiicient to overcome the urging of the spring 185 and accordingly the throttle is opened, increasing the speed of the engine 181 and increasing the output voltage. When the out-put voltage rises to the desired value, the zener diode 188 breaks down and a current flows through the diode 186, the resistor 187, the zener diode 188 and the resistor 189. This current is a pulsating direct current, due to the rectifying action of the diode 186. The alternating component of the voltage drop across the resistor 189 is coupled by the transformer 193 to the servo amplifier 196 which increases the current applied to the motor 197 thereby moving the throttle toward its closed position, decreasing the speed of the engine 181 and decreasing the output voltage. The servo amplifier 196 has a very high gain and is provided with the usual anti-hunt circuits so that the system is soon stabilized with the speed of the engine 181 and the output voltage of the alternator 161 substantially constant.

It would be possible to dispense with the transformer 164 by providing the alternator 161 with a suitable number of separate windings. A three phase or six phase alternator could be used or the various windings could have any other phase relationship since phase is not important in the present invention. If such an alternator were used, the various windings would be connected in place of the secondary windings 165-170. However, at present it is preferred to use the system illustrated in order to provide a convenient arrangement for charging the battery from the commercial power lines. The system is designed so that the output voltage of the alternator 161 is substantially equal to the line voltage. To charge the battery from the line, the switch 162 is moved to the upper position, as viewed in FIGURE 11, thereby disconnecting the primary winding from the alternator 161 and connecting it to the

conductors

201 and 202. These conductors are connected to the output of an AC. voltage regulator 203, the input of which may be connected by the

conductors

204 and 205 and the plug 206 to any convenient source. The charging operation is the same as previously described except that the engine 181 and the alternator 161 are not used. If the voltage regulation of the source is good enough, the voltage regulator 203 may be omitted.

FIGURES 12 and 13 illustrate a modification of the charger previously described wherein only one-half the number of secondary windings are required. FIGURE 12 shows a transformer 164' having a primary winding 163' which may be connected as previously described in connection with FIGURE 11. The transformer 164 is provided with a secondary winding 221 having

terminals

222 and 223, another secondary winding 224 having terminals 225 and 226, and a third secondary winding 227 having

terminals

228 and 229. As shown in FIGURE 13, the terminal 222 is connected to the junction of the battery section-

s

21a and 21b. The terminal 223 is connected to the anode of a diode 231 the cathode of which is connected to the terminal 72. The terminal 223 is also connected to the cathode of a diode 232 the anode of which is connected to the junction of the battery sections 21b and 210. The secondary winding 224 is similarly connected to

diodes

233 and 234 and to the battery sections 210 and 21d, as shown. Likewise the winding 227 is connected to the

diodes

235 and 236 and to the battery sections 21s and 21 During the half cycle when the terminal 223 is positive, the battery section 2112 is charged through the diode 231. During the next half cycle, the terminal 222 is positive and the battery section 21b is charged through the diode 232. Similarly the battery sections 21c and 21d are charged during alternate half cycles by the current flowing through the winding 224 and likewise the battery sections 21c and 21 are charged during alternate half cycles by the current flowing in the winding 227. By this arrangement, six battery sections may be charged using but three secondary windings, provided that the pairs of sections, such as the

sections

21a and 21b, charged by the same winding have the same voltage.

FIGURE 14 shows a further modification. The winding 221 is provided with an intermediate tap 241 which is connected to the anode of the diode 231. The cathode of the diode 234 is connected to a tap 242 on the Winding 224 instead of to the terminal 226. The winding 227 is connected as before. By this arrangement the winding 221 can charge the

sections

21a and 21b when the section 21b has a higher voltage (more cells) than the section 21a. Similarly, the winding 224 charges the sections 210 and 21d when the section 21c has a higher voltage than the section 21d.

The use of a truck mounted charger as above described makes it possible to use the truck in remote areas where there are no power lines from which to charge the battery. Unlike a straight gasoline truck, the truck of the present invention can be operated for limited periods in areas where exhaust fumes cannot be tolerated, simply by turning otf the engine. The previously described regenerative braking. feature reduces the net drain on the battery so that a small engine is sufiicient for charging. Additionally, the battery may be charged from the house current whenever such .a source is available.

Summary It is apparent that the present invention provides improved running speed control of both the propulsion and hoisting functions. Indeed, running speed is selected, rather than controlled, because each controller position corresponds to a definite speed which is substantially constant regardless of the load imposed. Such speed selection is made possible by the use of fixed excited motors, instead of series motors, and by selecting the armature voltage from the wide range available from a multi-celled battery. At the same time, power is conserved by the automatic regenerative braking and battery charging feature. This in turn reduces the size of the battery required. Since less net power is consumed per hour of operation, it is feasible to use a small, truck mounted, gasoline driven battery charger. Equal charging of all cells is obtained by the use of multiple sources of alternating current and rectifiers, with the peak voltage controlled to be substantially equal to the voltage of the cells when fully charged.

It is to be understood that the description has omitted many conventional details in order to avoid obscurring the invention. For example, it may be desirable to restrict the operation of the speed control switch by dash pots or other time delay devices. Similarly, compensating motor windings have not been illustrated although their use is desirable, as is the use of conventional protective devices such as circuit breakers.

It is also to be noted that the invention contemplates a substantially constant field flux and that such a flux may be obtained with a permanent magnet field structure.

Although a preferred embodiment has been described in considerable detail for illustrative purposes, many modifications will occur to those skilled in the art. It is therefore desired that the protection afforded by Letters Patent be limited only by the true scope of the appended claims.

What is claimed is:

1. An industrial truck, comprising,

drive wheels,

a hoisting mechanism,

a storage battery comprising a plurality of cells connected in series,

a first direct current dynamo electric machine having an armature operating in a substantially constant magnetic field and operatively connected to said wheels,

first switch means for selectively connecting various numbers of said cells to said armature of said first machine,

said first switch means including a first principal movable contact and first and second auxiliary contacts leading and lagging, respectively, the position of said first principal contact and each connected through a diode to said first principal contact,

a second direct current dynamo electric machine having an armature operating in a substantially constant magnetic field and operatively connected to said hoisting mechanism, and 4 second switch means for selectively connecting various numbers of said cells to said armature of said second machine,

a said second switch means including a second principal movable contact and third and fourth auxiliary contacts leading and lagging, respectively, the position of said second principal contact and each connected through a diode to said second principal contact.

2. An industrial truck, comprising,

drive wheels,

a hoisting mechanism,

a storage battery comprising a plurality of cells connected in series,

first and second terminals connected to those cells which have maximum potential difference therebetween,

first and second taps connected to said first and second terminals respectively,

a plurality of additional taps connected to intermediate cells of said battery, the cells between taps constituting sections, 1

first switch means for selectively connecting various ones of said taps to said armature of said first machine,

a second direct current dynamo electric machine having an armature operating in a substantially constant magnetic field and operatively connected to said hoisting mechanism,

second switch means for selectively connecting various ones of said taps to said armature of said second machine,

an engine,

an alternating current generator driven by said engine,

and

means for charging said battery sections separately with power obtained from said generator,

3. A tap changing system for adjusting the potential applied to a load from a multi-potential direct current source, comprising,

first and second terminals connected to those points of said source which exhibit maximum potential difference,

a plurality of additional taps connected to intermediate points on said source,

a principal movable contact cooperating with said taps for adjusting the potential applied to said load,

first and second auxiliary contacts movable simultaneously with said principal contact, one leading and one lagging the position of said principal contact, and

first and second diodes interconnecting said first and second auxiliary contacts respectively with said principal contact,

said diodes being poled to prevent passage of current between taps.

4, A tap changing system for adjusting the potential applied to a load from a multi-potential direct current source, comprising,

a common conductor interconnecting said first terminal of said source and one terminal of said load,

a plurality of additional taps connected to points on 15 plied to a load from a multi-potential direct current source, comprising,

first and second terminals connected to those points of said source having maximum potential difierence therebetween,

a plurality of additional taps connected to points on said source bearing potentials intermediate those of said first and second terminals,

a principal contact connected to the other terminal of said load and selectively connectable to any of said taps,

first and second auxiliary contacts movable with said principal contact,

one of said auxiliary contacts making a connection with any tap prior to connection thereto by said principal contact,

the other of said auxiliary contacts making a connection with any tap subsequent to connection thereto by said principal contact,

each contact breaking its connection with any tap before making a connection to the next succeeding tap,

said principal contact retaining its connection with any one tap until one of said auxiliary contacts has made its connection with the next succeeding tap, and

first and second diodes connected between said first and second auxiliary contacts respectively and said principal contact,

said diodes being poled to prevent short circuiting of any portion of said source as said contacts are actuated.

6. A motor control system, comprising,

a multi-celled battery,

first and second terminals connected to those points on said battery which exhibit maximum potential difference therebetween,

a plurality of additional taps connected to various cells of said battery bearing potentials intermediate those of said first and second terminals,

a principal contact,

first and second auxiliary contacts positioned oneither side of said principal contact,

all of said contacts being mechanically connected together for simultaneous movement relative to and engagement with said taps,

the width and spacing of said taps and contacts being selected so that each contact breaks contact with a tap before making contact with the next adjacent tap and so that two contacts can engage the same tap simultaneously,

an electric motor,

a connection between said principal contact and said motor, and

first and second diodes connected between said first and second auxiliary contacts respectively and said motor,

said diodes being poled to prevent passage of current between adjacent taps.

7. A motor control system, comprising,

a multi-celled battery,

first and second terminals connected to opposite ends of said battery,

a plurality of additional taps connected to various cells between said ends of said battery,

a common conductor connected to one terminal of said battery,

a principal contact,

first and second auxiliary contacts positioned on either side of said principal contact,

said contacts being fixedly spaced with respect to each other and relatively movable unitarily with respect to said taps for adjustable engagement therewith,

the width and spacing of said taps and contacts being selected so that each contact breaks contact with one tap before making contact with the next adjacent tap and so that two contacts can engage the same tap simultaneously,

an electric motor having one terminal connected to said common conductor,

a connection between said principal contact and a second terminal of said motor, and

first and second diodes connected between said first and second auxiliary contacts respectively and said second terminal of said motor,

said diodes being poled to prevent passage of current between adjacent taps.

8. A motor control system, comprising,

a storage battery including a plurality of cells connected in series,

first and second terminals connected to opposite ends of said battery,

a common conductor connected to said first terminal of said battery,

a plurality of additional taps connected to various cells of said battery between said first and second terminals,

a dynamo electric machine including an armature and a field structure,

means for supplying a substantially constant magnetic flux to said field structure,

a connection between one terminal of said armature and said common conductor,

a selectively actuatable switch mechanism interconnecting the other terminal of said armature and said taps,

said switch mechanism including a principal contact connected to said other terminal of said armature and selectively connectable to any of said taps,

said switch mechanism also including first and second auxiliary contacts movable with said principal contact,

the other of said auxiliary contacts making a connec tion with any tap subsequent to connection thereto by said principal contact,

said principal cont-act retaining its connection with any one tapuntil one of said auxiliary contacts has made its connection with the next succeeding tap, and

said diodes being pole-d to prevent short circuiting of said battery cells as said switch mechanism is actuated.

9. A speed control system for an industrial truck including drive wheels, comprising,

a direct current dynamo electric machine including an armature and a field structure mounted on said truck,

means for mechanically connecting said machine to said drive wheels for rotation therewith,

a multi-celled battery mounted on said truck,

a plurality of additional taps electrically connected to various cells of said battery bear-ing potentials intermediate those of said first and second terminals,

means for supplying a substantially constant magnetic flux to said field structure, and

multi-position switch means cooperating with said taps for selecting the voltage to be applied to said armature, whereby each position of said switch means corresponds to a preselected speed of said truck regardless of whether said truck encounters an up grade or a down grade.

10. A speed control system for an industrial truck including drive wheels, comprising,

a direct current dynamo electric machine including an armature and a field winding mounted on said truck,

a multi-celled battery mounted on said truck,

first and second terminals connected to opposite ends of said battery,

a plurality of additional taps electrically connected to various cells of said battery so as to bear potentials intermediate the potentials of said first and second taps,

multi-position switch means cooperating with said taps for selecting the voltage to be applied to said armature,

means normally energizing said field winding with a predetermined voltage, and

means responsive to an increase in armature current above a predetermined magnitude for increasing the voltage applied to said field Winding.

11. A speed control system for an industrial truck including drive wheels, comprising,

a multi-celled battery mounted on said truck,

first and second terminals connected to opposite ends of said battery,

a plurality of additional taps connected to various cells of said battery at various potentials intermediate the potentials of said first and second terminals,

selectively actuatable switch means interconnecting said armature with said taps and having an off position in which no voltage is applied to said armature and having a plurality of other positions in which various volt-ages from said battery are applied to said armature,

an auxiliary contact operated by said switch means,

means for normally energizing said field winding through said auxiliary contact when said switch means is in any position other than its off position, and

means responsive to the flow of armature current for energizing said field winding regardless of the condition of said auxiliary contact.

12. A speed control system for an industrial truck including drive Wheels, comprising,

means for mechani-cally connecting s-aid machine to said drive wheels for rotation therewith,

a multi-celled battery m-ounted on said truck,

a common conductor connected to one terminal of said battery,

a plurality of taps, one connected to said common conductor and the remainder connected to various cells of said battery,

a relay including first and second operating solenoids energization of either of which actuates said relay,

said relay including a normally open contact,

said first solenoid being connected between said common conductor and one terminal of said armature,

multi-position switch means cooperating with said taps for connecting a selected tap to another terminal of said armature,

whereby when said switch means selects that tap connected to said common conductor a closed circuit comprising said armature and said first solenoid is completed and whereby when said switch means selects another tap a voltage is applied to said armature,

said field winding having one terminal connected to said common conductor and the other terminal connected through said normally open contact to one of said taps,

an auxiliary switch operated by said switch means to its open position when said switch means selects that tap connected t-o said common conductor and to its closed position when any other tap is selected, and

circuit means connecting one terminal of said second solenoid to said common conductor and the other terminal through said auxiliary switch to one of said t aps,

whereby when said switch means applies a voltage to said alrrnrature said second solenoid is energized thereby energizing said field winding and whereby when said switch means selects that tap connected to said common conductor, any counter eleotromotive force generated by said armature energizes said first winding thereby maintaining the energ-ization of said field winding.

References Cited by the Examiner UNITED STATES PATENTS 2,813,984 11/1957 Dolecki et al 290-17 X 2,864,047 12/ 1958- Greene 318-338 2,964,691 12/1960 Dinger 318-338 3,018,849 1/ 1962: Kush 187-9 3,021,469 2/ 19-62 Ganiere 320-15 3,064,7 6 1 11/ 1962 Ramsey 187-9 3,134,063 5/1964 Hastings 318-139 3,153,186 10/1964 Medlar 320-15 3,168,688 2/1965- Roggenkamp 318-17 3,179,198 4/1965 Hastings 318-139 3,182,742 5/1965 Dow 31 8-139 X 3,188,543 6/1965 Colvill et a1. 318-139 FOREIGN PATENTS 1,197,508 7/ 1959 France.

oRrs L. RADER, Primary Examiner.

ANDRES H. NIELSEN, Examiner.

G. SIMMONS, Assistant Examiner.

Claims

1. AN INDUSTRIAL TRUCK, COMPRISING, DRIVE WHEELS, A HOISTING MECHANISM, A STORAGE BATTERY COMPRISING A PLURALITY OF CELLS CONNECTED IN SERIES, A FIRST DIRECT CURRENT DYNAMO ELECTRIC MACHINE HAVING AN ARMATURE OPERATING IN A SUBSTANTIALLY CONSTANT MAGNETIC FIELD AND OPERATIVELY CONNECTED TO SAID WHEELS, FIRST SWITCH MEANS FOR SELECTIVELY CONNECTING VARIOUS NUMBERS OF SAID CELLS TO SAID ARMATURE OF SAID FIRST MACHINE, SAID FIRST SWITCH MEANS INCLUDING A FIRST PRINCIPAL MOVABLE CONTACT AND FIRST AND SECOND AUXILIARY CONTACTS LEADING AND LAGGING, RESPECTIVELY, THE POSITION OF SAID FIRST PRINCIPAL CONTACT AND EACH CONNECTED THROUGH A DIODE TO SAID FIRST PRINCIPAL CONTACT,