Patent Publication Number: US-H1953-H

Title: Apparatus and method for preparing a hydraulic work machine for towing

Description:
TECHNICAL FIELD 
     This invention relates generally to an apparatus and method for preparing a hydraulic work machine for towing and, more particularly, to an apparatus and method for raising a work implement and releasing a parking brake under dead engine conditions. 
     BACKGROUND ART 
     Hydraulic work machines, in particular mobile machines such as wheel loaders, tractors, scrapers, graders, and the like, are used extensively to perform work functions such as altering terrain, moving material, constructing roads, lots, runways, and repairing the same. Generally these hydraulic work machines have a power source, i.e., an engine, to move about, and this same power source is also used to power the hydraulic systems on the machine. 
     Occasionally, an engine will malfunction on a machine, thus disabling the machine from moving about, and also disabling the hydraulic systems. It is common for such a machine to use a spring applied, hydraulic pressure released brake system; that is, the brakes are always engaged by spring action until controlled hydraulic pressure to the brakes overcomes the spring force and releases the brakes. In a dead engine situation, the brakes will be engaged. If the machine is required to be towed, some means is needed to release the brakes for towing. 
     Several patents exist which disclose methods for releasing brakes for towing under dead engine conditions. For example, in U.S. Pat. No. 4,195,716, Wirt discloses a brake release mechanism for vehicle towing which uses a manual hydraulic pump means to manually pump fluid into the brake system and thus disengage the brakes for towing. Although the system disclosed by Wirt accomplishes the purpose of releasing the brakes, some significant effort is required by a human to perform this procedure. What is needed is a means to release the brakes for towing while minimizing the human effort required. 
     In addition to the need to release the brakes for towing under dead engine conditions, it often occurs that a work implement is in contact with the ground when the engine fails. In this situation, the implement would need to be raised above the ground to prepare the machine for towing. The hydraulic pressure required to raise an implement, particularly a heavy implement or an implement with a heavy load, would be tremendous. For example, a compactor/hammer mounted on a wheel loader may weigh in excess of 14,000 kg. Historically, an implement is raised for towing by either manually pumping hydraulic fluid into lift cylinders or by connecting a pump from a service vehicle to the disabled work machine and then pumping hydraulic fluid into the lift cylinders. In either case, it is desired to enable lifting of an implement for towing by some convenient means located within easy access to an operator, and without requiring the manual connection of some other system. 
     The present invention is directed to overcoming one or more of the problems as set forth above. 
     DISCLOSURE OF THE INVENTION 
     In one aspect of the present invention an apparatus for preparing a hydraulic work machine for towing in response to a dead engine condition is disclosed. The apparatus includes a source of hydraulic fluid, a standby pump system hydraulically connected to the source, a plurality of pilot controls adapted for electrical activation by the standby pump system, and a hydraulic brake system. The apparatus also includes a supply valve connected to the pilot controls, and at least one lift cylinder connected to the supply valve and adapted to lift an implement on the work machine. The hydraulic brake system and the lift cylinder are enabled for hydraulic control in response to activation of the standby pump system. 
     In another aspect of the present invention an apparatus for lifting an implement on a hydraulic work machine in response to a dead engine condition is disclosed. The apparatus includes a source of hydraulic fluid, a standby pump system hydraulically connected to the source, and a plurality of pilot controls adapted for electrical activation by the standby pump system. The apparatus also includes a supply valve connected to the pilot controls, and at least one lift cylinder connected to the supply valve and adapted to lift an implement on the work machine. The lift cylinder is enabled for hydraulic control in response to activation of the standby pump system. 
     In yet another aspect of the present invention an apparatus for releasing a set of hydraulically actuated brakes on a hydraulic work machine in response to a dead engine condition is disclosed. The apparatus includes a source of hydraulic fluid, a standby pump system hydraulically connected to the source, and a hydraulic brake system. The apparatus also includes a sequence valve adapted to controllably deliver hydraulic fluid to the hydraulic brake system. The hydraulic brake system is enabled for hydraulic control in response to activation of the standby pump system. 
     In yet another aspect of the present invention a method for preparing a hydraulic work machine for towing in response to a dead engine condition is disclosed. The method includes the steps of depressing a switch to activate a standby pump system, activating a motor in response to depressing the switch, activating a hydraulic pump in response to activating the motor, lifting an implement as a function of the switch being depressed and in response to engaging a hydraulic implement lift control lever, and releasing a set of brakes as a function of the switch being depressed and in response to engaging a brake release lever. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic illustration of an apparatus as embodied for use in one aspect of the present invention; 
     FIG. 2 is a diagrammatic illustration of a control panel as embodied for use in one aspect of the present invention; and 
     FIG. 3 is a flow diagram illustrating a method of the present invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Referring to the drawings, and with particular reference to FIG. 1, an apparatus  100  for preparing a hydraulic work machine for towing in response to a dead engine condition is shown. Preferably, the hydraulic work machine is a mobile machine, such as a wheel loader, tractor, scraper, grader, dozer, and the like. The work machine, in the preferred embodiment, has a work implement, such as a bucket, blade, scraper, compactor, or other such implement designed to perform a work function. 
     In the preferred embodiment, the work machine has a power source, i.e., an engine, to provide power for the machine to move about, and to provide power for hydraulic systems used for various purposes, such as controlling the work implement or operating a set of brakes on the machine. 
     Occasionally, the engine will malfunction, and the machine will not be able to move on its own power. In addition, a malfunction of the engine will disable the hydraulic systems. In this situation, it may be required to tow the machine away from the work site. 
     The machine must be prepared for towing by hydraulically lifting the implement off the ground, and hydraulically disengaging the brakes. 
     In FIG. 1, solid lines with arrows depict hydraulic circuits, and solid lines with arrows and diagonal slashes indicate electrical circuits. 
     A hydraulic tank  102  located on the work machine provides a source of hydraulic fluid for the various hydraulic systems. Preferably, the hydraulic tank  102  provides fluid during normal operation and also during dead engine operation for use with the present invention. 
     A standby pump system  104 , located on the work machine and hydraulically connected to the source of hydraulic fluid, provides pressurized hydraulic fluid to the hydraulic systems on the work machine in the event of a dead engine condition by means described below. 
     The standby pump system  104 , in the preferred embodiment, includes a hydraulic pump  106 , a motor  108  electrically connected to the pump  106 , at least one battery  109  electrically connected to the motor  108 , and a manual switch  110  electrically connected to the motor  108 . The switch  110  is adapted to controllably activate the standby pump system  104 . During activation of the switch  110 , the battery  109  provides electrical power to the motor  108 , which in turn drives the pump  106 . The pump  106  then provides pressurized hydraulic fluid to select hydraulic systems located on the work machine. 
     In one embodiment, the battery  109  may be a single battery capable of supplying electrical power to the motor  108  for a desired period of time. However, a plurality of batteries  109  may be required and used to supply adequate electrical power. 
     In the preferred embodiment, the switch  110  is a spring loaded mechanism, activated only during the time it is held in an on position. For example, the switch  110  may be a push button type of switch that is engaged only when it is pushed, and is disengaged when it is released. An advantage of this type of switch is that the standby pump system  104  is only activated during time periods in which an operator intentionally holds the switch  110  in the on position. A configuration of this sort will prevent the standby pump system  104  from being engaged longer than desired. 
     In the preferred embodiment, the hydraulic systems on the work machine include a plurality of pilot controls  116  that are, preferably, electrohydraulic. The electrohydraulic pilot controls  116  are, in the present invention, adapted for electrical activation by the standby pump system  104  during those periods of time in which the switch  110  is engaged. 
     The work machine includes a hydraulic brake system  120 . Typical hydraulic brake systems on work machines of the type used with reference to the present invention are spring loaded and hydraulically disengaged. That is, springs maintain the brakes in an engaged mode until the activation of hydraulic pressure overcomes the force of the springs and releases the brakes. In a dead engine situation, there is normally no hydraulic pressure available to release the brakes. This is normally desired to prevent the machine from moving should an engine failure occur, or to keep the machine from moving when the engine is shut off. However, if the machine is required to be towed, it is then desired to release the brakes by an alternate means, such as is discussed in the present invention. 
     In one embodiment of the present invention, the hydraulic brake system  120  referred to is a parking brake system. However, the present invention could be applied equally to the main hydraulic brake system on a machine. 
     A sequence valve  112  is hydraulically connected to the standby pump system  104  and is adapted to controllably deliver hydraulic fluid to the hydraulic brake system  120 . In FIG. 1, the sequence valve  112  is designed to activate in response to the hydraulic pressure at a point P being at least a predetermined minimum value. This allows the standby pump system  104  to create hydraulic pressure adequate to lift a work implement before diverting hydraulic fluid to the hydraulic brake system  120 . 
     Alternatively, the present invention may be designed to operate without a sequence valve. This embodiment would reduce the costs of the system with some sacrifice in the quality of operations of the invention. 
     A supply valve  118  hydraulically connected to the pilot controls  116  provides hydraulic fluid to at least one lift cylinder  122 . The supply valve  118  also provides for the release of hydraulic fluid from the lift cylinder  122 . For example, the supply valve  118  may supply hydraulic fluid to a head end  126  of the lift cylinder  122  and release fluid from a rod end  124  of the lift cylinder  122  to enable the lift cylinder  122  to lift an implement. 
     In the preferred embodiment, fluid is supplied to the head end  126  of the lift cylinder  122  by the standby pump system  104  through a check valve  114 . The pilot controls  116 , which operate the supply valve  118 , are enabled hydraulically by pressure from the lift cylinder  122  via a resolver valve  128 . The resolver valve  128  provides hydraulic pressure from either the head end  126  or the rod end  124 , whichever is greater. As the pilot controls  116  operate the supply valve  118 , hydraulic fluid is released from the rod end  124  of the lift cylinder  122 , thus enabling fluid to enter the head end  126 , which enables the lift cylinder  122  to lift the work implement. 
     It is assumed in the above discussion that fluid supplied to the head end  126  of the lift cylinder  122  causes the work implement to raise. 
     However, the present invention would function equally well if the lift cylinder  122  is configured to raise an implement by delivering hydraulic fluid to the rod end  124  instead. In addition, the present invention could be configured to supply hydraulic fluid to other hydraulic devices, for example a pitch cylinder, to enable operations of other hydraulic features on the machine. 
     It is common for a hydraulic work machine to have more than one lift cylinder to raise and lower an implement. For example, a typical wheel loader may have two lift cylinders, a right lift cylinder and a left lift cylinder. It is understood that, while discussion of the present invention may refer to a lift cylinder in the singular sense, application of the present invention would also include any number of lift cylinders on a hydraulic work machine. 
     The check valve  114  is preferably located on the hydraulic output of the standby pump system  104  to prevent hydraulic fluid from returning to the standby pump system  104 . 
     In the preferred embodiment, portions of the apparatus  100  shown in FIG. 1 may be part of the hydraulic systems on the work machine under normal operating conditions. For example, the electrohydraulic pilot controls  116 , the supply valve  118 , the hydraulic brake system  120 , and the lift cylinder  122  may all be part of the normal hydraulic systems on the machine. However, the above components are also adapted for use with the standby pump system  104  when needed. 
     Referring to FIG. 2, a diagrammatic illustration of a control panel  200  for use with one aspect of the present invention is shown. Preferably, the control panel  200  is located within easy access to an operator, e.g., within reach of an operator in the cab of the work machine. The control panel  200  includes the manual switch  110  for activation of the standby pump system  104  and the pilot controls  116 . 
     The control panel  200  also includes at least one hydraulic control lever  202 . Preferably, a hydraulic control lever  202  on the control panel  200  is an implement lift control lever. However, other hydraulic control levers could additionally be included. For example, FIG. 2 is shown having three hydraulic control levers  202   a,b,c.  Examples of additional control levers may include an implement tilt control lever, a brake release override lever, steering control levers, and any number of other hydraulic control levers as may be used on a hydraulic work machine. Additionally, the control panel  200  may include other controls and indicators used in operation of the work machine without deviating from the spirit of the present invention. Alternatively, the switch  110  and the hydraulic control levers  202  may not be located on a control panel, but may be incorporated in other locations on the work machine, e.g., on a dashboard, armrest, and the like. 
     Referring now to FIG. 3, a method for preparing a hydraulic work machine for towing in response to a dead engine condition is shown. 
     In a first control block  302 , the switch  110  is pressed to activate the standby pump system  104  and to provide power from the battery  109  to the electrohydraulic pilot controls  116 , as shown in a fourth control block  308 . 
     In a second control block  304  the motor  108  is activated in response to pressing the switch  110 , which in turn activates the pump  106  in a third control block  306 . 
     Control then proceeds to a fifth control block  310 , in which the implement is lifted as a function of the switch  110  being depressed and in response to engaging the hydraulic implement lift control lever  202 . Preferably, the implement lift operation only takes place while both the switch  110  is depressed and the implement lift control lever  202  is activated. 
     In one aspect of the invention, the lift cylinder  122  performs a lifting operation on the implement when the hydraulic system delivers hydraulic fluid to the head end  126  of the lift cylinder  122  and releases hydraulic fluid from the rod end  124  of the lift cylinder  122 . 
     In a sixth control block  312 , the brakes are released as a function of the switch  110  being depressed and in response to engaging the brake release lever. Preferably, the brakes are released by delivering hydraulic fluid to the hydraulic brake system  120 . 
     INDUSTRIAL APPLICABILITY 
     As an example of use of the present invention, a hydraulic work machine, e.g., a wheel loader, may become disabled at a work site due to a dead engine condition. It may be desired to tow the disabled machine away from the site to perform repairs at a more convenient location, and to remove the machine from the site so that another machine may continue operations. 
     However, the conditions of the brakes being applied and the work implement being lowered to the ground may impede towing. In addition, the work machine may have been operating in an environment too harsh or hostile for a human operator to exit the machine. For example, other machines may be working at the site and it is desirable for the operator to remain on his disabled machine. 
     The present invention is designed for an operator of a hydraulic work machine that is disabled due to a dead engine condition to be able to prepare the machine for towing, i.e., lift the implement and release the brakes, without leaving the cab of the machine. 
     Other aspects, objects, and features of the present invention can be obtained from a study of the drawings, the disclosure, and the appended claims.