Vehicle speed control device for use in trolley-assisted dump trucks of single phase alternating current system

A vehicle speed control device for use in a trolley-assisted dump truck of a single phase alternating current system can control the driving torque in proportion to the amount of depression of an accelerator pedal in the same manner as in the case of running under an engine mode condition even when running under a trolley mode condition utilizing a commercial power source. The device comprises in combination an accelerator valve for controlling compressed air from a reservoir in proportion to the amount of depression of an accelerator pedal, an engine throttle control unit controlled by the compressed air passed through the accelerator valve, an acceleration pattern generator actuated by the compressed air to convert the air pressure into a voltage, a mode converted for sending out a voltage pattern to a main drive circuit of the truck in response to a voltage signal from the acceleration pattern generator, and an engine control solenoid operated valve for selectively controlling supply of the compressed air to the engine throttle control unit and to the acceleration pattern generator.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a vehicle speed control device for use in a 
trolley-assisted dump truck of a single phase alternating current system, 
and more particularly to the vehicle speed control device which can vary 
an output of an electric motor for driving the dump truck by varying a 
voltage applied to the motor in proportion to the degree of depression of 
an acceleration pedal. 
2. Description of the Prior Art 
In view of the availability of petroleum becoming tight increasingly in the 
recent years, there is a relevant tendency towards energy saving even in 
large mines. In particular, in the districts where sufficient power can be 
generated by hydraulic power and by thermal power obtained by burning 
coals, but are lacking in petroleum resources, there can be seen a strong 
demand for replacing petroleum driven mining machines by electrically 
driven mining machines in order to save petroleum products. 
Besides the tendency of petroleum saving, there can be seen a tendency of 
falling productivity due to the suspension of movements of vehicles so as 
to prevent a pit of the mine from oxygen deficient condition arising from 
the exhaust gas smog emitted from the engines of ore carrying vehicles and 
the amount of which increases as the pit becomes deeper. 
In order to eliminate such troubles in the late years, there has been 
proposed a double-wire trolley assisted dump truck system utilizing a 
cheap commercial power supply on the ascent courses extending from the 
bottom of the pits to the dumping areas. 
The trolley-assisted dump trucks can be driven either in a trolley mode 
utilizing a commercial power source or in an engine mode utilizing 
generators driven by internal combustion engines mounted on themselves, 
respectively. 
A commercial power source is utilized to run dump trucks in the trolley 
mode and the voltage applied across double trolley wires is maintained 
constant, and therefore the output of the drive motor can be kept 
constant. For this reason, it has so far been impossible for the operator 
to control the torque for driving dump trucks as desired. 
SUMMARY OF THE INVENTION 
The present invention has been contemplated in view of the above-mentioned 
circumstances, and has for its aspect to provide a vehicle speed control 
device for use in trolly-assisted dump trucks of single phase alternating 
current system which enables controls of the driving torque to be achieved 
in proportion to the amount of depression of the accelerator pedal in the 
same manner as in the case of the dump truck running in the engine mode 
even when it runs in the trolley mode. 
To achieve the above-mentioned aspect, in accordance with the present 
invention, there is provided a vehicle speed control device for use in a 
trolley-assisted dump truck of a single phase alternating current system, 
characterized in that it comprises in combination an accelerator valve 
adapted to variably control the pressure of compressed air from an air 
reservoir in proportion to the amount of depression of an accelerator 
pedal by the operator; an engine throttle control means adapted to receive 
the air pressure controlled by the accelerator valve to thereby control 
the engine throttle means; an acceleration pattern generator adapted to 
receive the air pressure controlled by said accelerator valve and convert 
the air pressure into a voltage; a mode convertor adapted to receive a 
voltage signal from the acceleration pattern generator and send out or 
transmit a voltage pattern to a mixed bridge rectifier installed in a main 
drive circuit and which comprises thyristors and diodes; and an engine 
control solenoid operated valve adapted to be actuated when a trolley mode 
change-over switch is turned on and occupy a trolley mode position wherein 
the compressed air controlled by said accelerator valve is directed or 
supplied into said acceleration pattern generator, said engine control 
valve being further adapted to be actuated by the resilient force of a 
spring associated therewith when the trolley mode change-over switch is 
turned off and occupy an engine mode position wherein the compressed air 
is directed or supplied into said engine throttle control means.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 1, there is depicted a dump truck practical application system of 
double trolley assisted type laid from a pit P.sub.1 or a loading area of 
a mine through a slope or ascent course P.sub.3 to a dumping area P.sub.3. 
As can be seen from FIG. 1, the trolley-assisted system is utilized only 
on the ascent course, and when dump trucks run on flat roads and descent 
courses with low fuel consumption, they utilize the power generated by the 
engines mounted on them. 
In FIG.2, there is shown a main circuit for running or driving 
trolley-assisted dumps of a single phase alternating current system. This 
main circuit comprises in combination a circuit for running the dump truck 
in an engine mode including drive motors M.sub.1 and M.sub.2 directly 
connected to drive wheels through a rectifier 12 electrically connected 
with an a.c. generator 11 directly connected to an engine 10 of the dump 
truck, and another circuit for running the dump truck in a trolley mode 
including a mixed bridge rectifier 14 comprised of thyristors 141 and 
diodes 142 which are connected through pantagraphs 111 with a commercial 
power supply. 
The vehicle drive system in the engine mode is arranged such that if and 
when the accelerator pedal is depressed, the number of revolution of the 
engine will increase thus completing a vehicle drive circuit at the same 
time. As a result, contacts EXR, ARP.sub.1 and P.sub.3 between the 
terminals LG0 and LG3 as shown in FIG. 2 are closed to render operative an 
excitor control unit and a chopper circuit thus allowing a required 
electric current to flow through the exciting windings of the exciter of 
the a.c. generator 11 thereby controlling the output of the latter. In 
consequence, the dump truck is driven and the drive force of the truck 
varies in proportion to the amount of depression of the accelerator pedal. 
Whilst, when applying braking forces on the wheels, controls of the 
generator 11 under a dynamic braking condition wherein the drive motors 
M.sub.1 and M.sub.2 are rotated by the driving forces transmitted from 
tires so as to act as generators are made such that when a brake pedal 102 
is depressed, contacts EXR, F.sub.22, BO.sub.1 and SR between terminals 
LGO and LG7 are closed to form a dynamic braking circuit, and the exciter 
unit 21 and the chopper circuit 22 are rendered operative thereby allowing 
a required electric current to flow through the exciting windings of the 
exciter and controlling the output of the a.c. generator 11. Consequently, 
the vehicle is subjected to braking effect or force which is controlled in 
proportion to the amount of depression of the brake pedal 102. 
This main drive circuit further comprises field windings F.sub.1 , F.sub.2 
of the motors M.sub.1 , M.sub.2 , brake resistors BR.sub.1 , BR.sub.2 , a 
blower motor BL, an exciter EX, solenoid contactors P.sub.1 and P.sub.2 
for propulsion, solenoid contactors BO.sub.1 , BO.sub.2 , B.sub.1 and 
B.sub.2 for braking, and field weakening contactors F.sub.11 , F.sub.12 , 
F.sub.21 and F.sub.22 . 
The trolley assisting device comprises pantagraphs 111 serving as current 
collectors, breakers PP.sub.1 and PP.sub.2 for trolley mode, breakers 
GP.sub.1 , GP.sub.2 and GP.sub.3 for engine mode, and A.C. filter 13, a 
mixed bridge rectifier 14 consisting of thyristors 141 and diodes 142, a 
reactor 15 for smoothing the signal phase alternating pulsating current, a 
battery 16 mounted on the dump truck, a battery switch 17, and a trolley 
mode change-over switch 18. The arrangement is made such that the 
propulsion solenoid contactors P.sub.1 , P.sub.2 are excited and closed by 
a pressure switch for accelerator not shown and the braking solenoid 
contactors BO.sub.1 , BO.sub.2 , B.sub.1 and B.sub.2 are excited and 
closed by a pressure switch for brake not shown, and further, both 
contactor groups such as, for example, a contactor group P.sub.1 , P.sub.2 
and another contact group BO.sub.1 , BO.sub.2 , B.sub.1 , B.sub.2 are 
electrically or mechanically interlocked so that both groups are not 
allowed to become operative at the same time. 
The arrangement is further made such that both the trolley assisting 
breakers PP.sub.1 and PP.sub.2 and the engine mode breakers GP.sub.1 , 
GP.sub.2 and GP.sub.3 are energized by the trolley mode change-over switch 
18, and the former and latter breakers are electrically or mechanically 
interlocked so that they may not be energized at the same time. 
FIG. 3 is an explanatory view of the schematic configuration of one 
embodiment of the vehicle speed control device according to the present 
invention. In this drawing, reference numeral 101 denotes an accelerator 
adapted to be controlled by an accelerator pedal 102, and 103 a brake 
valve adapted to be controlled by a brake pedal 104. Reference numerals 
105 and 106 denote pressure switches adapted to be turned on by the air 
pressure supplied from an air reservoir 107 when the above-mentioned 
valves 101 and 103 are actuated. Reference numeral 108 indicates a 
self-holding relay circuit for accelerator (for propulsion) and for brake 
(for braking). In this circuit, reference numeral 108a denotes a coil for 
resetting the above-mentioned relay 108 by an acceleration signal 
generated when the acceleration valve is operated, 108b a coil for 
resetting the relay 108 by an acceleration signal generated when the brake 
valve is operated, 108c a contact for accelerator connected with the 
solenoid contactor P for propulsion, and 108d a contact for brake 
connected with the breaking solenoid contactor B. Reference numeral 108e 
denotes an interlocking contact for illuminating a dynamic brake 
indication lamp when the vehicle is subjected to braking, 110 an engine 
throttle control means, 112 a mist separator, and 113 an engine control 
solenoid operated valve adapted to supply compressed air into the engine 
throttle control means when the vehicle runs in the engine mode and to 
supply compressed air into the acceleration pattern generator 114 when the 
vehicle runs in the trolley mode. Reference numeral 115 indicates a mode 
convertor. 
FIG. 4 shows the construction of an accelerator pattern generator 114. 
The acceleration pattern generator 114 contains therein a diaphragm 120, a 
spring 123 for setting the displacement of the diaphragm 120, a spring 
retainer 131 for the spring 123, and a cup 121 adapted to transmit the 
displacement of the diaphragm 120 to a crank 124. The crank 124 has a 
contact 126 connected to the leading end thereof and which is kept in 
sliding contact with a rheostat 127 so as to vary the value of resistance 
of the latter. Reference numeral 125 indicates a return spring for the 
crank 124. 
The rheostat 127 is coupled with a terminal 129 by means of a wire 128. 
Whilst, the contact 126 is electrically connected through the casing with 
a terminal 132. 
Thus, when the vehicle runs in the trolley mode, the engine control valve 
113 is changed over to the trolley mode position so that if the operator 
depresses the accelerator pedal 102 then the compressed air pressure may 
be supplied through the engine control valve 113 into the acceleration 
pattern generator 114. Where the air pressure is converted into a voltage, 
and a voltage pattern varying in proportion to the amount of depression of 
the accelerator pedal will be sent out. As a result, the gates of the 
thyristors 141 of the mixed bridge rectifier 14 are controlled so that the 
three phase alternating current (shown to the right of FIG. 5) which is 
the commercial power supply from the trolleys may be rectified and 
converted into a single phase direct current (shown to the right of the 
drawing), and also the phase angle .alpha. of the resultant direct current 
is controlled. 
Thus, a mean voltage Ed of the direct current and a mean electric current I 
thereof may be varied in proportion to the angle of the accelerator pedal 
depressed by the operator and supplied to the drive motors. Therefore, the 
driving force can be varied in the same manner as that in the control of 
the pattern of the a.c. generator 11 at the time of the above-mentioned 
engine mode, and therefore it is very convenient for the operation of the 
dump trucks. 
It is to be understood that the foregoing description is merely 
illustrative of a preferred embodiment of the present invention and that 
the invention is not to be limited thereto, but is to be determined by the 
scope of the appended claim.