Hydraulically propelled vehicle

Abstract

An earthworking machine having front and rear traction means and a hydraulic motor for each. The motors are connected in a closed loop parallel circuit with a pump, and one of them drives its traction means through a plural speed transmission. A first valve mechanism divides pump output fluid equally between the motors. An orifice device in the motor-pump circuit allows up to a predetermined small amount of fluid flowing to either motor to be diverted to the other motor. Second valve means in the hydraulic circuit maintains the first valve mechanism effective except at times when the transmission is in other than a low speed working position.

Description

This invention relates to earth working vehicles, and has more particular reference to hydrostatically propelled vibratory earth compacting machines.

One such compactor that has recently become available is made by RAYGO, INC. of Minneapolis, Minnesota, and is known in the trade as its Rascal 320-A. It features a pair of rear traction wheels driven through a two speed transmission by a first reversible hydraulic motor, and a compacting drum mounted on a yoke at the front of the machine for rotation on a generally transverse axis. The drum, which is of the same diameter as the wheels, is equipped with vibration producing mechanism and it is rotatably driven by a second reversible hydraulic motor. It thus constitutes the front part of the hydrostatic propulsion means on the machine.

One of the unusual features of the Rascal 320-A is that it is provided with a bulldozer blade at its front, ahead of the drum. This enables the machine to move a substantial amount of earth in levelling and scraping operations, for example, and at the same time effect compaction of the earth acted upon by the blade, by the drum behind it.

Inasmuch as the levelling blade is carried by the drum yoke, loading of the blade during use of the machine exerts force on the drum tending to lift it out of tractive engagement with the ground. This, of course, effects unloading of the drum, and as a result, seriously detracts from its effectiveness as a combination traction device and compacting tool.

This same phenomenon also prevents the drum and rear wheel traction devices from being driven by fluid motors connected in parallel with a single bidirectional pump, in a closed loop circuit. In that case, the lifting effect of the levelling blade on the drum would merely cause all of the pump output fluid to pass to the more lightly loaded drum motor, producing what is known as drum "spin out" and loss of vehicle propulsion.

Hence, it is one of the purposes of this invention to provide a hydrostatically driven earth working machine of the character described, wherein an equal ratio flow divider and combiner valve instrumentality is installed in one side of a closed loop parallel circuit for the two motors relied upon to drive the drum and rear wheels.

Inasmuch as it is also desirable to transmit driving torque to the rear wheels of the machine through a transmission having a low or "working" speed, and a higher speed for transit, it will be seen that a conventional flow divider can not afford a complete solution to the problem.

In fact, a further complication which tended to make the wheels drive the vehicle faster than the drum resulted from accumulations of sticky mud on the wheels. Such material buildup could, at times increase the effective wheel circumference to a dimension sufficiently greater than that of the drum as to cause the latter to act somewhat in the nature of a drag. It should be here mentioned that material is not allowed to build up on the drum, as scraper means continually removes mud and/or other accumulations therefrom during operation of the machine.

With these further problems in mind, it is another object of the invention to provide a hydrostatically driven compactor such as described, with valve instrumentalities that not only make it possible to drive the rear wheels through a plural speed transmission, but which also automatically overcome the undesirable effects of material buildup on the wheels that would otherwise interfere with the production of equal propelling rates by the drum and rear wheels of the machine.

More specifically, it is a purpose of this invention to connect the reversible drum and wheel motors of the machine in a closed loop parallel circuit with a bidirectional pump, and to incorporate an equal flow ratio dividing and combining valve in one side of said circuit, along with an orifice device that makes possible diversion of small portions of the fluid flowing in either branch of the closed loop circuit at one side thereof to the other branch of the circuit at said side thereof, to thus compensate for any change in the effective diameter of the wheels that may occur due to material build-up thereon.

It is also a more specific object of the invention to provide in the aforesaid closed loop parallel motor circuit, at one side thereof, a valve device which, in one position, renders the equal ratio flow divider and combiner valve mechanism effective, and which, in another position, acts to nullify the effect of said valve mechanism to thereby allow faster propulsion of the machine in a second speed position of the transmission.

Still another object of the invention resides in the provision of a valve device such as described in the preceding paragraph, which is of the electromagnetic type, and which can be actuated to its position cancelling the effect of the divider-combiner valve mechanism as a consequence of shifting of the transmission out of its working speed to a higher speed ratio.

With these observations and objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings, which exemplify the invention, it being understood that changes may be made in the specific apparatus disclosed herein without departing from the essentials of the invention set forth in the appended claims.

The accompanying drawings illustrate one complete example of an embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

FIG. 1 is a diagrammatic view showing the hydrostatically propelled traction means of a compacting machine embodying the principles of this invention; and

FIG. 2 is a diagram wherein graphic symbols illustrate the hydraulic circuitry for the hydrostatic propulsion means of this invention.

Referring now more particularly to the accompanying drawings, the numeral 5 generally designates a vibratory earth compacting machine of the type manufactured by RAYGO, INC. and known as its Rascal 320-A. The machine is characterized by front and rear traction means 6 and 7, respectively; reversible hydraulic motors 8 and 9 drivingly connected with the front and rear traction means, respectively; and a bidirectional piston type pump 10 to supply fluid under pressure to the motors. The pump is driven by an internal combustion engine 11, which may be of the Diesel variety, through a clutch 12 and a drive box 13.

The rear traction means 7 is here shown as comprising a pair of laterally spaced wheels 14 carried by an axle structure 15 and driven from the hydraulic motor 9 through a two speed transmission 16.

The front traction means 6 comprises a vibratory drum of the same diameter as the wheels, and which is rotatably carried by a yoke having arms indicated at 18, that embrace the opposite ends of the drum. These arms carry the bearings, not shown, in which the drum is rotatably journalled. Hydraulic motor driven vibration producing means is mounted inside the drum.

For purposes of illustration, the spacing between the wheels 14 has been exaggerated, as in the actual machine, they are spaced apart a distance less than the axial dimension of the drum 6. Also for purposes of illustration, the multiplicity of tamping feet which project from the exterior of the drum have been omitted.

One of the chief characteristics of the machine herein concerned, is that it is provided with a scraper or levelling blade 20 located ahead of the drum 6. The blade is supported from the yoke arms 18, as by links 21, and it is raised and lowered hydraulically by double acting cylinders, not shown, having one end pivotally mounted on the yoke arms and having piston rods connecting with brackets on the rear of the blade, as indicated at 22.

A lever 24 which is accessible to an operator of the machine, enables the transmission 16 to be shifted into low and high speed positions. The low speed position is the one selected for levelling and compacting operations of the machine, while the high speed position allows the machine to be more quickly driven from one work zone to another.

The presence of the plural speed transmission 16 causes one of the problems which are solved by this invention. The scraper blade 20 ahead of the vibrator drum causes another.

These problems can be best appreciated from a consideration of the FIG. 2 hydraulic diagram. This diagram illustrates by means of graphic symbols, that the drum and wheel drive motors 8 and 9, respectively, are connected in a closed loop parallel circuit with the bidirectional pump 10.

For this purpose, one of the ports 30 of the drum motor 8 is connected with one of the ports 31 of the wheel drive motor 9, as by means of a duct 32 having a branch 33 connected with one of the work ports 34 of the pump. Accordingly, the ducts 32 and 33 comprise one side of the closed loop parallel pump-motor circuit. The other side of the circuit comprises a duct 36 having its ends connected to the remaining ports 37 and 38 of the motors 8 and 9, respectively, and having a branch 39 connecting with the other work port 40 of the pump.

A characteristic of the closed loop parallel circuit thus far described, is that pressure fluid from either work port of the pump will flow to whichever hydraulic motor 8 or 9 is more lightly loaded, and will bypass the more heavily loaded motor. The propulsive effort will be dissipated, therefore, whenever the scraper or levelling blade 20 ahead of the compacting drum 6 exerts upward force on the drum sufficient to seriously reduce its tractive relationship to the ground over which the machine is travelling. At such times, all of the pump output fluid will flow to the hydraulic motor 8 for the then unloaded compacting drum 6, in bypass relation to the wheel drive motor 9. This produces what is known as drum "spin out;" and the machine stalls whenever such "spin out" occurs.

By to this invention, the danger of such "spin out" of the drum is eliminated through the provision of a valve instrumentality 42, connected in one side of the closed loop hydraulic circuit. The main component of the valve instrumentality 42 comprises an equal ration flow divider-combiner valve mechanism 43. It has a pair of motor ports 44 and 45 which are connected with the ports 37 and 38 of the drum and wheel motors 8 and 9, respectively, by the duct 36. It also has a pump port 47 which is connected with the work port 40 of the pump by the branch 39 of duct 36.

The flow divider valve mechanism 43 is of conventional construction and, for example, can be one such as manufactured by Fluid Controls, Inc. and characterized by a pair of pressure compensated plungers, not shown, to regulate flow of fluid in either direction between its pump port 47 and its motor ports 44, 45.

As is well known, the equal ratio flow divider-combiner valve mechanism 43 will function with reasonable accuracy to divide pressure fluid issuing from work port 40 of the pump, for example, into equal volumes for operation of the drum and wheel motors at the desired speeds. Moreover, it will perform this function regardless of whether or not the compactor drum is fully loaded. This is to say that even though the upward force exerted on the drum by the levelling blade may substantially reduce the loading thereof, the rear wheel motor 9 will still receive its share of pump output fluid, and there will be no possibility of drum "spin out" to interfere with propulsion of the machine.

The equal ratio flow dividercombiner valve operates in the same way when the motors 8 and 9 are being driven in the opposite direction by the pump. In that case, however, the flow of return fluid from the motors 8 and 9 to the work port 40 of the pump is controlled by the equal ratio combining action of the valve mechanism 43.

The valve instrumentality 42 also features a pressure compensated orifice device 50 which is shown as connected across the ports 37 and 38 of the two motors through the ends of the ducts 36 leading thereto. The orifice device 50 can be said to perform a speed control function in the sense that it acts to automatically compensate for the changing volumetric efficiency of the two motors 8 and 9 due to increase in the rolling radius of the wheels 14 by the build up of material thereon occurring whenever the machine is operated in sticky mud.

By way of example, if a substantially small quantity of mud should build up on the wheels 14, they would tend to drive the machine at a faster rate than the drum, due to the increase in wheel circumference.

A scraping device, not shown, prevents all but an insignificant amount of material build up on the drum. Hence, the orifice device is provided primarily because of build up on the rear wheels.

With the orifice device 50 in one side of the closed loop pump-motor circuit, however, a small amount of the pressure fluid will be allowed to pass between the ducts connecting the pump with the propel motors 8 and 9 at one side of the closed loop parallel circuit. As shown, the orifice device can be connected across the end portions of the duct 36 leading to the motor ports 37 and 38.

Depending upon changing fluid pressure conditions in the duct 36 as material builds up on the wheels, the orifice device 50 will be caused to open, for example, to allow up to a maximum of 3 gallons per minute of fluid to flow therethrough from one end of the duct 36 to the other thereof.

An equally important component in the circuit is a two position electromagnetic valve 53 which, in effect, removes the equal ratio flow divider valve 43 from the circuit any time the transmission 16 is shifted out of its low, or work speed position. Like the orifice device 50, the valve 53 is connected across the end portions of the duct 36 at a location between the propel motors (8 and 9) and the equal ratio flow divider 43.

In its position shown, the valve 53 establishes communication between the ports 37 and 38 of the propel motors, thus permitting supply fluid flowing to those motor ports from the pump, to pass to the motors in whatever proportions are necessary as determined by the ground as a differential. This, of course, allows the machine to travel in second or higher speed, and makes possible the use of a plural speed transmission through which driving torque is transmitted to the rear wheels from the wheel propel motor 9.

The solenoid valve 53 can be of the normally open type connecting motor ports 37 and 38 as shown, in which case it is actuated to its closed position upon energization of its solenoid 54. Solenoid 54 is in an energizing circuit which includes a switch 55. The switch can be closed to complete the energizing circuit for the solenoid 54 in consequence of actuation of the shift lever 24 to place the transmission in its low speed working position, as indicated in dotted lines in FIG. 2. Any suitable way of effecting such closure of switch 55 will suffice, as for example, a direct link connection 56 between the shift lever 24 and the movable contactor of the switch.

From the foregoing description, together with the accompanying drawings, it will by readily apparent to those skilled in the art that this invention provides an earth working machine in which improved hydrostatic propulsion means makes possible advantages which were herethereto unattainable.

Those skilled in the art will appreciate that the invention can be embodied in forms other than as herein disclosed for purposes of illustration.

The invention is defined by the following claims

Claims

I claim:

1. In an earth working machine having traction wheels at its rear and a compacting drum and leveling blade at its front, the compacting drum being power driven to coact with the traction wheels in effecting propulsion of the machine and being rotatably connected with a yoke that projects forwardly from the chassis of the machine, and the leveling blade being mounted on said yoke ahead of the compacting drum for maximum effectiveness, said machine being characterized by

an improved propulsion system which assures continued propulsion of the machine regardless of diminished traction between the drum and ground due to the inevitable upward force on the yoke resulting from loading of the leveling blade during use thereof,

and which improved propulsion system comprises:

A. a power driven bidirectional hydraulic pump;

B. a reversible hydraulic motor drivingly connected with the drum;

C. a second reversible hydraulic motor drivingly connected with the traction wheels;

D. a closed loop parallel hydraulic circuit including supply lines leading to the hydraulic motors connecting the pump with the hydraulic motors and through which pressure fluid is delivered to both of said motors; and

E. an equal ratio flow divider-combiner valve mechanism connected in one side of said closed loop hydraulic circuit to divide the pressure fluid issuing from the pump and flowing to the hydraulic motors into substantially equal volumes so that reduction in the load on the hydraulic motor driving the drum and resulting from loss of traction between the drum and ground as a consequence of increased loading of the leveling blade will not diminish traction at the rear wheels of the machine.

2. The invention defined by claim 1 further characterized by a pressure compensated orifice device connected in said hydraulic circuit in parallel with the equal ratio flow divider-combiner valve mechanism, said orifice device modifying the fixed ratio aspect of the flow divider-combiner valve mechanism by allowing a predetermined maximum amount of flow to pass between the supply lines leading to the two hydraulic motors to thereby compensate for change in the volumetric efficiency of the motors resulting from an increase in the rolling radius of the traction wheels by buildup of material thereon.

3. The invention defined by claim 1, wherein the hydraulic motor driving the rear traction wheels is drivingly connected therewith through a plural speed transmission having operator-controlled gear shifting means by which the transmission can be shifted from one to another of its speeds, and further characterized by a bypass passage connected in the hydraulic circuit in parallel with said equal ratio flow divider-combiner valve mechanism to communicate said supply lines leading to the hydraulic motors when said passage is open and thereby nulify the effect of the equal ratio flow divider-combiner valve mechanism on the functioning of the system but when closed having no affect thereon;

a valve in said bypass passage;

said valve being closed when the plural speed transmission is in its low speed mode; and

means operable in response to actuation of the operator-controlled gear shifting means in taking the transmission out of its low speed mode, to effect opening of said valve in the bypass passage.

4. In combination with an earth working machine having a compacting drum at its front, and wheels at its rear:

A. a yoke having arms embracing the opposite axial ends of the drum and in which the drum is journalled for rotation on a transverse axis;

B. a levelling blade carried by the yoke arms and located ahead of the drum;

C. means for transmitting rotation to the drum comprising a first reversible fluid motor having a pair of ports;

D. means for transmitting rotation to the wheels comprising a second reversible fluid motor having a pair of ports, and plural speed transmission means drivingly connecting the wheels with said second motor;

E. a bidirectional pump having a pair of work ports;

F. means connecting said motors in a closed loop parallel circuit with the pump, comprising a first duct connecting with one of each of the motor ports and having a branch connecting with one of the work ports of the pump, and a second duct connecting the other pump port with the other of said motor ports;

G. valve instrumentalities connecting with said first duct and comprising

1. an equal ratio flow divider valve having its inlet connected with one pump through said branch of said first duct, and having a pair of outlets connected with the ports of said one motor through said first duct,

2. an orifice device through which the ports of said one motor are connectible with one another,

3. and a valve mechanism movable from a first position communicating the ports of said one motor to a second position disrupting said last named communication;

H. and means to effect actuation of said valve mechanism to said second position thereof in consequence of actuation of the transmission means to a low speed position.