AU478564B2 - Hydrostatic assist drive for vehicles - Google Patents

Description

S4, 3 9 4 74

Auxiliary traction wheels driveable intermittently road as may be required for traction under varied or adverse or field conditions have been bound to be desirable for

certain of such types of vehicles.

478,564 summary 74, 39474 Our invention relates to an auxiliary hydrostatic drive system for vehicles operable intermittently at the operator's option to provide auxiliary drive by means of drive pump and assist drive motor means to one or more idler wheels under marginal tractive conditions, and a control means for synchronizing the auxiliary wheel speed with the main drive wheel speed to avoid wheel scrub. The control means is vehicle speed responsive and operates independently of the drive pump means. It includes an adjustable flow divider operatively between the drive pump and motor means for con- trolling the volume flow to the motor means for synchronizing the above wheel speeds. The pump means of the auxiliary drive system may serve also hydraulically operated mechanism associated with the vehicle which is unrelated to the vehicle drive means. Other control means is provided for directing selectively the output of the pump means either to the auxiliary drive system or to the other hydraulic mechanism. Brief Description of the Drawing Figure 1 is a circuit diagram of our system embodied in a fork lift truck; Figure 2 is a control for a portion of the system shown in Figure 1; Figure 3 is a modification of a portion of the control shown in Figure 1; and Figure 4 is a diagrammatic view of a modified system. Description of the Preferred Embodiment An industrial lift truck is shown schematically in Figure 1 in which a pair of non-dirigible main drive wheels wheels are shown at numeral .10 and a pair of dirigible idler 4 478.564

74 394/74 at numeral 12, the latter also functioning as auxiliary

drive wheels operated intermittently as desired in

478.564

74,394/74 L zt~1 motors 14, traction drive by a pair of reversibte/4r- pump 16, the /Which are driven by a main fixed displacement system to be discharge of which is controlled by the control

described. Main drive wheels 10 are driven by the engine ijand a through a drive train which includes a transmissionl

differential drive 18 driving an axle lift The axle supports a conventional telescopic 22 having a lift truck upright represented by the numeral assembly 26 cylinder 24 and a load handling fork and carriage in a well-known supported from the mast for elevation thereon for forward manner. The mast 22 is pivoted from the axle of double-acting tilt and rearward tilting movement by a pair and to the mast. cylinders 30 connected to the truck body illustrated at Lift and tilt cylinder control valves are valves being operator numerals 32 and 34. respectively, the valve 32 being a~open controlled by manual levers 36 and 38, pressure fluid from center single-acting valve for conducting valve section pump 16 to lift cylinder 24 by way of load by way of a valve returning such fluid to a sump 42 under mast at any selected section 42. and holding the fork 26 and valve section elevation by manipulation to the open-center

44 as shown. Valve 34 operates similarly but is double-act- end to tilt the mast ing to pressurize cylinders 30 at either sections 46 and 22 forwardly or rearwardly by way of valve

48, respectively, and to hold any selected position by portion 50, all in manipulation-to the open-center valve through the open-center known manner. Pump 16 is connected of conduits 52 and 54 to sections of valves 32 and 34 by way 56 and 58 and to and the reservoir 42 by way-of conduits cylinders 24 and from the respective lift and tilt A' 478,5 64

74, 3 94.74 depending upon the actuation of the valves to direct the

pressure fluid, by way of conduits 60, 62, 64, 66 and 68,

return from conduits 62 and 66 to the reservoir being by way

of conduit 70, and return from the lift cylinder to the

reservoir being by way of conduits 60Lan&d-2- when valve 32 is

actuated to make operative section 42 thereof. A pressure

responsive relief valve 74 is responsive to the pressure in

conduit 54 to limit the pressure drop across control valves

32 and 34, and a pump pressure relief valve 76 is connected

between conduits 52 and 58. The hydraulic circuit and cont-

rols described thus far in respect of the lift and tilt

circuits is conventional. Other components utilized in the

hydraulic circuit, such as a counterbalance valve, a load

lowering control valve, and the like, have been omitted from

the circuit drawing in the interest of implicit!

Inserted in the above-described circuit between conduits 52 and 54 is an adjustable flow divider unit

having divider sections 92 and 94 therein adapted to be

supplied with pressure fluid from pump 16, divider section 92

supplying pressure fluid to the above-described tilt anr! lift

circuits, and divider section 94 being adapted to supply

pressure fluid to the auxiliary drive circuit, described

below, associated with hydrostatic motors 14. Other auxili- ary power components comprise a forward and reverse direction-

al control valve 96, a cooling loop valve 98, a pair of check

valves 100 and control means connected to the flow divider.

The flow divider is capable of directing the total

output of pump 16 either to the lift-tilt circuit or to the

reservoir, and substantially the total output thereof to the

auxiliary drive circuit. The flow divider and circuit as S47 8.5 6 4

74, 394/74 shown is positioned to direct the total flow to the reservoir

by way of divider section 92 and conduits 54, 56 and 58,

divider section 94 being substantially closed, and the

auxiliary power circuit being entirely closed at e4eeed

oazvz-e control valve 96. Such flow divider units capable of

varying the flow through one or the other sections from 0%

to 1000% are available commercially, one exemplary such unit

being manufactured by Fluid Controls, Inc. of Mentor, Ohio,

Model 2V21. The auxiliary power circuit is activated when an

actuator cylinder-piston unit 102 of the auxiliary power

control is energized to shift the flow-divider unit through

a push-pull cable 104 so that a controlled portion of the

output of pump 16 up to 100% thereof in the eibodiment

utilizing such a 2V21 flow divider, is directed to the power

assist circuit and not to the lift-tilt circuit. The auxili-

ary power circuit as shown is inactive with solenoid actuated

control valve 96 closed whereby the fluid in the circuit of

drive motors 14 is in the closed parallel loop of conduits

106 and 108 and circulates therein, particularly during

steering of the vehicle when differential wheel speeds are encountered at wheels 12. The fluid may circulate through

the motors in either direction, depending upon the direction

of vehicle movement and/or steering. A by-pass cooling

circuit is provided through conduits 111, 112 and 114, the

solenoid valve 98, and a pressure compensated flow control

valve 115 in series with valve 98. Valve 115 permits only a variat- predetermined fluid flow therethrough irrespective of

ions in inlet pressure to the valve. An exemplary valve of

the type contemplated is manufactured by Fluid Controls, 8 478,564

74, 394/74 Inc., supra, Model 2F74. The cooling circuit through condu- its 112 and 114 norz-ally functions when control valve 96 is

closed and the auxiliary power is not in use by exhausting a

relatively small volume of flow, as controlled by valve 115,

from the closed loop of motors 14 to the reservoir. Make-up fluid in the motor 14 loop is provided through one of the

check valves 100, depending upon the direction of vehicle

operation, as a result of a predetermined base pressure

maintained in conduits 56, 117 and 119 by a check valve 121

in conduit 58.

If valve 96 is actuated upwardly the output of pump 16 flows through section 94 of the flow divider, a conduit 118, a valve section 116 of valve 96, and conduits 111 and 106 through motors 14 to rotate wheels 12 in a for-

ward 1direction, returning to the reservoir by way of conduits

108, 110 and 114. A reversal of valve 96 to communicate a section 120 thereof with said conduits reverses the flow

through motors 14 to power assist the vehicle in reverse drive.

Flow divider 90 is controlled by a hydraulic servo system so that only that portion of the output of pump 16

flows through the power assist circuit as may be required to

effect a rotational speed of wheels 12 which is the same as

the speed of wheels 10, assuming that the wheels are of the

same diameter. If the wheels differ in diameter, a speed of wheels 12 is controlled to traverse the same circumferential

distance as wheels 10 in the same period of time. In other words, regardless of the diameter of one wheel or pair of

wheels in relation to the diameter of another pair of wheels,

the auxiliary powered wheels are operated at such wheel

9 478.564

74, 394./74 as between pairs speeds as to minirmize any scrubbing effect if the wheels were of wheels 10 and 12, which would result The term same or rotated at different effective speeds. equivalent, as used here- matching "effective speed", or its means is driven to in, shall mean that auxiliary wheel distance as traverse substantially the same circumferential of time irrespective of main wheel means in the same period as between said main variations in surface or road traction and auxiliary wheel means. 16 not required That portion of the output of pump speed is directed to operate wheels 12 at the controlled into the lift-tilt through section 92 of the flow divider the open-center valve circuit or to the reservoir through selection by the Operator. sections 44 and 50, depending upon which operate to position Hydraulic servo control components divider as required for the control of the proportional flow power assist conditions a given selected vehicle speed under 122, a pump pressure comprise a fixed displacement pump two-position valve 126, relief valve 124, a solenoid actuated 130. Pump 122 is connected an orifice 128 and a check valve discharge to solenoid valve to reservoir 42 and directs fluid 126 in the position 126 by way of a conduit 132, valve the pump discharge illustrated functioning to recirculate 134 and 136, pump 122 back to reservoir through conduits the transmission is being preferably operable only when the mechanical front wheel operating in first or low gear in embodiment pump 122 may drive version of Figure i. In such of the hydraulic servo be engine driven, which, in the use pressure output in actua- system illustrated, effects a pump speed. When tor 102 which is proportional to vehicle 478,564

74, 394/74 actuated, valve 126 directs pump output through a conduit 138

to the reservoir by way of conduits 140 and 136, restriction

128, and check valve 130, the intermediate pressure in

conduit 140 being directed through the branch conduit there-

of to actuator cylinder 102 which controls the division of

flow at divider 90 to the power assist and the lift-tilt

circuits. Persons skilled in the art will appreciate that

the matching of components 102,.122, 128 and 130 in the

hydraulic servo control circuit must be such as to produce a

pump flow and pressure which controls the position of the

piston in actuator 102 so that the flow divider setting

accurately controls the flow to motors 14 in proportion to

the speed of wheels 10, thereby matching effective speeds of

wheels 10 and 12. Inasmuch as the auxiliary drive system is

designed for intermittent use only as required, relatively

inexpensive components may be utilized, and in the embodiment

of Figure 1 equal effective wheel speeds is controlled by the

above described low gear transmission drive of pump 122 in

said servo system. The orifice 128 is sized such that

excess flow in the servo circuit returns to the reservoir

through check valve 130 upon the generation of a wheel speed

proportional pressure in cylinder 102.

Figure 2 illustrates control means for'operating

the solenoid valves in the power assist circuit which

includes a battery 150, an operator's master switch 152, a

second control switch 154 which may, for example, be operat-

ed in a mechanical drive system of wheels 10 by engaging a

gear shift selector lever in first and/or drive gear, and a

manual forward and reverse switch 156 for operating valve

96 by energizing solenoid 116a or 120a to operate valve 11 478.564

74,394/74 section 116 or 120. The closing of switch 156 in either valve 98, direction energizes the solenoid coil 98a to close coil 126a. and a switch 158 operates solenoid valve 126 by most Switch 158 is a normally closed switch so that under and 154 will conditions of operation closing of switches 152 auxiliary activate valves 96, 98 and 126, and thereby the 94 to drive wheels drive system through flow divider section are 12. Both the lift and tilt functions of the mast drive operative, but at slower speeds when the auxiliary fork 26, for system is in operation, the speed of lift of volume of fluid example, being inversely proportional to the

directed to flow divider section 94. connect- Switch 158 may, for example, be operatively demand for ed to the lift lever 36 so that upon operator's which automatically full lift speed switch 158 is opened motors by terminates fluid flow to the auxiliary drive

actuating valve 126 to its illustrated position causing 90 to the position cylinder 102 to actuate flow divider Switch 158 may shown at which full lift speed is available. actuated in the in addition to or alternatively also be the clutch, as when a mechanical front drive system shown by speed the clutch is lift truck operator demands a high lift to drive pump 16 depressed and the engine speed is increased would therefore open at a high rpm. Depression of the clutch remain closed for switch 158 while switches 152 and 154 clutch to again close auxiliary drive upon release of the

switch 158. system are In operation, the components of the 1 in respect of the normally positioned as shown in Figure circuits. Under normal lift, tilt and auxiliary drive 478.564

74, 394/74 operating conditions lift and/or tilt of the mast 22 and fork 26 is controlled by the operator as required for load hand-

ling operations by manipulation of control valves 32 and/or

34, flow being provided by pump 16 through flow divider section 92 while motors 14 free-wheel in the closed loop

above described. All other components of the auxiliary drive and control circuits are positioned as illustrated in Figures

1 and 2.

Under any adverse operating conditions which requires auxiliary power the switches 152 and 154 are closed as explained above to condition the auxiliary drive system

for operation, since it will be recalled that switch 158 is

normally closed under such.conditions. In this condition valve 126 is actuated to communicate conduit 132 with cylind-

er 102 through conduits 138 and 140 to actuate flow divider

to establish a division of flow as determined by the actuating pressure in cylinder 102. That pressure is inter- mediate the discharge pressure of fixed displacement servo

pump 122 and reservoir pressure as established by restrict-

ion 128 and check valve 130. Actuation of switch 156 by the operator in one direction or the other activates directional

control valve 96 for forward or reverse drive producing

traction flow through motors 14 which is recirculated through

the opposite section of valve 96 to the reservoir and pumps

16 and 122.

An alternate system of control is disclosed in Figure 3 wherein the speedometer output shaft 169 of the

transmission 17 drives through a magnetic coupling 170, a

potentiometer 172 connected thereto which is connected to a

battery by lines 171, and a servo motor 174 driven from the 13 47

74, 394/74 potentiometer and which is adapted to be connected directly to flow divider 90 by linkage means 176 thereby performing

the same function by electrical means as is performed by the hydraulic servo control shown in Figures 1 and 2.

It should be pointed out that a somewhat modified

electrical servo as shown in Figure 3 may be applied to drive pump 122 directly from a vehicle speed responsive device represented diagrammatically at numeral 177 in Figure 1. Such a device may be mounted on the rim of one of wheels and connected to a magnetic coupling, potentiometer and servo motor as in Figure 3, except that the servo motor should be of the rotary output type for coupling to drive pump 122. Such wheel rim speed responsive devices are manufactured by Endler Instrument Company of Jersey City, New Jersey. Figure 4 discloses in diagrammatic form the system of Figure i, except that it is not combined in a lift truck type vehicle. It utilizes a fluid volume division control, such as flow divider 90, the one section 92 of which is adapted to vent excess fluid not utilized during auxiliary

drive to a reservoir directly. The pump may be an engine driven fixed displacement pump, the same as pump 16 in Figure 1, and the vehicle speed responsive servo control may be as disclosed in Figure 1 or in Figure 3, or of any other suitable type. An engine is represented at 184.

478,5 64

74, 394-/74

It will be appreciated that a pair of engine driven

variable displacement pumps mounted on a common shaft may be

substituted for flow divider 90, particularly in an embodiment

which utilizes separate work means such as in the lift-tilt

circuit of Figure i, use of either the hydraulic servo control

of Figure 1 or the electric servo control of Figure 3 being operable to adjust the displacement of such pumps as required

to perform the function above-described in relation to the

operation of flow divider 90. Various other types of vehicles

may utilize our invention to advantage such as agricultural

vehicles which frequently encounter a variety of field

conditions in which auxiliary drive would be beneficial, as

in muddy and terraced fields, irrigated land with ditches,

and under other adverse field conditions. Likewise, road

building scraper machines, towing tractors, three-wheeled 478,564

74, 394/74 vehicles, chemical sprayers, and car spotters may intermitt-

ently use such auxiliary power regardless of the nature of

the main propulsion system to wheels 10, whether mechanical,

hydraulic or electric. In earth moving scraper machines, for

example, the benefit is apparent in the use of auxiliary

drive hydrostatic motors at the large idler wheels which

support the bucket, at which location no transverse drive

axle of any kind is possible.

Although a number of embodiments of our invention

have been described herein, this disclosure is merely for the

purpose of illustration and not as a limitation on the scope

of the invention. It is therefore to be understood that the

invention is not limited to any one or more of the specific embodiments shown, but may be used in various other ways, and

various modifications may be made to suit different require-

ments, and that other changes, substitutions, additions and

omissions may be made in the construction, arrangement and

manner of operation of the system without necessarily depart-

ing from the scope of the invention as defined in the

following claims.

16 478.5 64

74,394/74 The claims definiry cne invention are as follows:- 1. Propulsion means for a vehicle having front and rear drive wheel means comprising a main drive train for operating one of said wheel means, and an auxiliary drive train for operating the other of said wheel means, said auxiliary drive train including hydraulic motor means for operating said other wheel means, auxiliary drive pump means adapted to drive said hydraulic motor means, vehicle speed responsive means independent of said pump means and operat- ively connected to said auxiliary drive train to control the speed of said motor means such that said other wheel means is driven at an effective speed which is substantially equal to the driven effective speed of said one wheel means, and an operator control for selectively disengaging said auxiliary drive train, said independent vehicle speed responsive means including an adjustable fluid flow divider means operatively intermediate said pump and motor means for controlling the Nolume of fluid flowing to said hydraulic motor means to effect said driven effective speed of said other wheel means.

47 8.5 6 4

74, 39 4/74

S^c. Vehicle propulsion means as claimed in claim/'

wherein said pump means is a fixed displacement pump, and

said flow divider means is adjusted to separate that volume of fluid in excess of that required to maintain said effect-

ive speed and direct said excess volume of fluid out of the

hydraulic motor circuit. Vehicle propulsion means as claimed in claim/v

wherein said vehicle speed responsive means includes also

a hydraulic servo system controlling said flow divider means

comprising a vehicle speed responsive hydraulic pump and

actuator operatively connected to said flow divider means for

adjusting the latter means. B. A vehicle propulbion maas as claimed i

wherein said transmission is operativel e cted to adjust

said vehicle speed es ve means as a function of the

In a vehicle having front and rear drive wheel

means and work means supported from the vehicle, a main of drive train including a prime mover for operating one the said wheel means, an auxiliary drive train operating with other of said wheel means and adapted to be coordinated drive train the operation of said work means, said auxiliary said other including hydraulic motor means for operating

wheel means, auxiliary drive pump means adapted to drive, 8 47 8.5 64

74 394'74 said motor means, vehicle speed responsive means operatively connected to said auxiliary drive train to control the speed

of said motor means such that said other wheel means is driv-

en at an effective speed which is substantially equal to the

driven effective speed of said one wheel means, and an

operator control for selectively operating said hydraulic

motor means, said vehicle speed responsive means including

means operative in said auxiliary drive train and receiving

the discharge of said pump means for controlling the volume

of fluid flowing to said hydraulic motor means to effect

said driven effective speed of said other wheel means, the volume of pump discharge in excess of that required to thus

drive said other wheel means being available to operate said

work means.

TJ1c. A vehicle as claimed in claim/91wherein said

vehicle is a lift truck and said work means is elevatable load handling means mounted from the one end of said truck,

and a second operator control for directing said excess fluid

volume either to the work means to elevate the load handling

means or to the inlet side of said pump means.

47 A vehicle as claimed in claim/y wherein said

vehicle speed responsive means includes an adjustable fluid

flow divider means which is selectively operable to direct

fluid flow to said motor means in a volume to maintain said

effective speed or to direct the entire fluid discharge of

said pump means to elevate said load engaging means at the

operator's selection under which latter condition the said other wheel means is idler wheel means and the said one

wheel means .is operable in traction drive by said main drive

train. 19 478.5 64

74,394/74 7,1. A vehicle as claimed in claim11 wherein said servo vehicle speed responsive means includes hydraulic pump means control means including vehicle speed responsive

for adjusting said flow divider means. €-kYJ. A vehicle as claimed in claim ki wherein said servo vehicle speed responsive means includes electrical adjusting said control means responsive to vehicle speed for

flow divider means. 9 A vehicle as claimed in claim4T wherein said and said main drive one wheel means is a pair of front wheels drive axle train includes a transmission and transverse

driving said front wheels.

DATED this FOURTEENTH day of OCTOBER, 1974

CIARK EQUIPMENT COMPANY

Patent Attorneys for the Applicant SPRUSON FERGUSON

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