Patent Description:
Dump trucks are used for transport of material from one place to another. One such use may include transport of mined material from an extraction site to a processing site. A dump truck generally includes a load carrying container such as a dump body that holds the material. The dump truck may discharge the material by extending hoist cylinders to tilt the load carrying container and allowing the material to slide out of the load carrying container under the influence of gravitational forces.

In certain environments, the nature of the transported material may resist sliding out of the load carrying container until the container is raised to an extreme position. For example, large mining dump trucks operating in the oil sands region of Alberta, Canada, will dump high grade oil sand ore into open hoppers for processing. During the body raise event, the sticky ore payload can adhere together and adhere to the surface of the dump body and stay within the dump body for greater than <NUM>% of the maximum dump body angle of the dump body. When the payload eventually releases from the dump body as a cohesive "loaf" at between <NUM>% and <NUM>% of the full dump body angle, the combined dump body weight and the payload center of gravity of the loaf can cause an over-center effect on the hoist cylinders. The over-center effect can shift the hoist cylinder load from a compressive push load with high head end pressures and low rod end pressures to a tensile pull load with high rod end pressures and low head end pressures. The hoist hydraulic system absorbs the over-center loading energy by increasing the rod end pressure to resist the over-center effect. One method currently used to increase the rod end pressure is through the use of a counterbalance valve that closes when a head end signal pressure reduces to near zero and allows the rod end pressure to increase, much like a relief valve. However, with cold oil or other external issues, the head end signal pressure acting on the counterbalance valve may not reduce to zero and may instead oscillate, thereby causing the counterbalance valve to become unstable and not provide enough rod end pressure to absorb the loafing load. With that, the operator may feel a potentially violent jarring effect after the loafing event.

An example of a hydraulic circuit for controlling hoist or lift cylinders is provided in <CIT> discloses an articulated dump truck provided with an electro-hydraulic bin control system including a proportional control valve for the bin lift cylinders and including a solenoid-operated regenerative valve assembly mounted adjacent the lift cylinders and being actuated, during lifting the bin for dumping a load of material from the bin, to cause a regenerative flow to occur when the force required by the bin lift cylinders to continue lifting the bin falls to a predetermined force. The force required for tilting the bin is continuously calculated by an electronic control unit taking into account a sensed bin load, a sensed bin tip amount and a sensed side-to-side inclination of the bin. A hydraulic circuit for lifting a boom is known from patent document <CIT>.

In one aspect of the present invention, a hoist valve assembly for a cylinder of a work machine having a head end and a rod end according to claim <NUM> is provided.

In another aspect of the present invention, a work machine according to claim <NUM> is provided.

In a further aspect of the present invention, a method for shutting off counterbalancing during extension of a hydraulic cylinder of a work machine according to claim <NUM> is provided.

Additional aspects of the present invention are defined in the dependent claims.

<FIG> illustrates one example of a work machine <NUM> that may incorporate hoist system counterbalance valve shutoff in accordance with the present invention.

The work machine <NUM> may be autonomous, that is remote controlled or having programmed movement, may be semi-autonomous (having partially remote controlled or programmed functions), or may be manually operated. The work machine <NUM> generally includes a main frame <NUM>, a dump body <NUM> pivotally mounted to the main frame <NUM> by a dump body shaft <NUM> for rotation about a dump body axis defined by the dump body shaft <NUM>, and a cab <NUM> mounted on the front of the main frame <NUM> above an engine enclosure <NUM>. The work machine <NUM> is supported on the ground by front tires <NUM> (one shown) each mounted on one of two front wheel assemblies <NUM>, and rear tires <NUM> (one shown) each mounted on one of two rear drive wheel assemblies <NUM>. One or more engines (not shown) may be housed within the engine enclosure <NUM> to supply power to the drive wheel assemblies <NUM> via a mechanical or electric drive train, and to provide power for electrical systems, hydraulic systems and other systems of the work machine <NUM>.

As discussed, the dump body <NUM> may rotate about the dump body shaft <NUM>. The dump body <NUM> may rotate between a normal downward position as shown in <FIG> and a hoisted position (not shown) to dump a load of material that has been deposited in the dump body <NUM> by another work machine (not shown). The dump body <NUM> may be moved between the downward position and the hoisted position by one or more hoist cylinders <NUM> (one shown) each having a rod end <NUM> pivotally connected to the main frame <NUM> and a head end <NUM> pivotally connected to the dump body <NUM>. In other implementations, the rod end <NUM> may be pivotally connected to the dump body <NUM> and the head end <NUM> may be pivotally connected to the main frame <NUM>. The hoist cylinders <NUM> are retracted when the dump body <NUM> is in the downward position, and are extended by providing pressurized hydraulic fluid to the head ends <NUM> to extend piston rods (not shown) from the rod ends <NUM> and rotate the dump body <NUM> about the dump body shaft <NUM> toward the hoisted position.

<FIG> illustrates a hoist valve assembly <NUM> that is configured and operates to control the extension and retraction of the hoist cylinders <NUM> to raise and lower, respectively, the dump body <NUM>. The hoist valve assembly <NUM> may include a housing enclosing the various valve stems, springs, passages and other control components for controlling the flow of hydraulic fluid to and from the hoist cylinders <NUM>. The hoist valve assembly <NUM> may include one or more high pressure (H. ) fluid supply ports <NUM> fluidly connected to an H. fluid source <NUM> by H. fluid supply lines <NUM>. fluid supply passages <NUM> may extend from the H. fluid supply ports <NUM> to a main control valve <NUM> and terminate at a first H. supply port <NUM> and a second H. supply port <NUM>. fluid supply passages <NUM> may also be fluidly connected to a dump valve <NUM> by a dump fluid passage <NUM>. The main control valve <NUM> may be an <NUM>-way, <NUM>-position spool valve that is solenoid actuated via a lower position control valve <NUM> and a raise position control valve <NUM>. The main control valve <NUM> further includes a valve drain port <NUM> fluidly connected by a drain passage <NUM> to a drain port <NUM> that in turn is fluidly connected to a low pressure (L. ) tank or reservoir <NUM> by a drain line <NUM>. A rod end fluid port <NUM> of the main control valve <NUM> may be connected to rod end ports <NUM> of the hoist valve assembly <NUM> by a rod end fluid passage <NUM>, and rod end fluid lines <NUM> may fluidly connect the rod end ports <NUM> to the rod ends <NUM> of hoist cylinders <NUM>. Similarly, a head end fluid port <NUM> may be connected to head end ports <NUM> by a head end fluid passage <NUM>, and head end fluid lines <NUM> may fluidly connect the head end ports <NUM> to the head ends <NUM> of hoist cylinders <NUM>.

A brake cooling fluid port <NUM> of the main control valve <NUM> may be connected to brake cooling ports <NUM> by a brake cooling fluid passage <NUM> to provide fluid to a brake cooling system (not shown) via brake cooling fluid lines <NUM>. A rod end pressure relief port <NUM> may be fluidly connected to the brake cooling fluid passage <NUM> by a restricted passage <NUM> to provide drainage from the rod ends <NUM> when the main control valve <NUM> is in a neutral position N as shown in <FIG>. A metered pilot pressure port <NUM> may be placed in fluid communication with a selector spool <NUM> that is associated with pilot relief valves <NUM>, <NUM> by a selector pilot pressure passage <NUM>, and with a counterbalance valve <NUM> via a solenoid-operated counterbalance shutoff valve <NUM> by a counterbalance pilot pressure passage <NUM>. The counterbalance valve <NUM> may provide a return flow path for hydraulic fluid from the rod ends <NUM> to the rod end fluid port <NUM>, and is controlled by head end and rod end pressure pilot signals to perform counterbalancing when raising the dump body <NUM> as discussed further below. A rod end restricted drain passage <NUM> may allow some flow of hydraulic fluid around the counterbalance valve <NUM>.

While the hoist valve assembly <NUM> as illustrated and described herein provides hydraulic fluid to the brake cooling system under certain conditions where the hydraulic fluid would otherwise be drained from the hoist valve assembly <NUM>, those skilled in the art will understand that the hydraulic fluid could be drained to any appropriate low pressure reservoir. For example, in other implementations, the hydraulic fluid may be drained to the tank <NUM>. In further alternatives, the hydraulic fluid may be drained to a low pressure reservoir of another hydraulic system of the work machine <NUM>. Such implementations and corresponding modifications to the elements and passages of the hoist valve assembly <NUM> to route hydraulic fluids will be apparent to those skilled in the art and are contemplated by the inventors.

<FIG> illustrates an exemplary arrangement of electrical and control components of the work machine <NUM> that are capable of implementing hoist cylinder operation and counterbalance valve shutoff in the hoist valve assembly <NUM> in accordance with the present invention.

A controller <NUM> may be capable of processing information received from monitoring and control devices using software stored at the controller <NUM>, and outputting command and control signals to devices of the work machine <NUM>. The controller <NUM> may include a processor <NUM> for executing a specified program, which controls and monitors various functions associated with the work machine <NUM>. The processor <NUM> may be operatively connected to a memory <NUM> that may have a read only memory (ROM) <NUM> for storing programs, and a random access memory (RAM) <NUM> serving as a working memory area for use in executing a program stored in the ROM <NUM>. Although the processor <NUM> is shown, it is also possible and contemplated to use other electronic components such as a microcontroller, an application specific integrated circuit (ASIC) chip, or any other integrated circuit device.

While the discussion provided herein relates to the functionality of the hoist valve assembly <NUM> including counterbalance valve shutoff, the controller <NUM> may be configured to control other aspects of operation of other systems of the work machine <NUM>, including other hydraulic cylinders, propulsion, steering, braking, and the like. Moreover, the controller <NUM> may refer collectively to multiple control and processing devices across which the functionality of the work machine <NUM> may be distributed. Portions of the functionality of the work machine <NUM> may be performed at a controller of a remote computing device (not shown) that is operatively connected to the controller <NUM> by a communication link, such as in an autonomous vehicle with functions control at a central command station. The controllers may be operatively connected to exchange information as necessary to control the operation of the work machine <NUM>. Other variations in consolidating and distributing the processing of the controller <NUM> as described herein are contemplated as having use in work machines <NUM> implementing hoist valve operation and counterbalance valve shutoff in accordance with the present invention.

The controller <NUM> may be operatively coupled to various input devices providing control signals to the controller <NUM> for the operation of hoist valve assembly <NUM> to extend and retract the hoist cylinders <NUM> and correspondingly raise and lower the dump body <NUM>. A control lever sensor <NUM> may detect displacements of manual levers, joysticks or other inputs devices (not shown) manipulated by an operator to cause the hoist cylinders <NUM>, respectively, to operate to raise and lower the dump body <NUM>. The control lever sensor <NUM> may respond to the displacements by transmitting control lever sensor signals to the controller <NUM> having values corresponding to the displacement of the input device. In autonomous operation implementations, signals similar to the control lever sensor signals may be generated by an autonomous operation controller, generated by autonomous control software of the controller <NUM>, or transmitted from a remote operations control center, for example. The controller <NUM> may respond to the control lever sensor signals by transmitting valve control signals to the solenoids or other actuation devices of the valves <NUM>, <NUM>, <NUM> to operate the hoist valve assembly <NUM> to extend or retract the hoist cylinders <NUM> as commanded.

As discussed previously, the characteristics of a material such as oil sand ore being handled by the work machine <NUM> may cause unstable operating conditions when the dump body <NUM> is raised to dump the material. Consequently, it may be advantageous provide an indication to the controller <NUM> as to whether the material may affect the operation of the hoist valve assembly <NUM>. The cab <NUM> may have a material switch (not shown) with an accompanying material switch position sensor <NUM> that may detect displacements of the material switch by the operator. The material switch position sensor <NUM> may respond to the displacements by transmitting material switch position sensor signals to the controller <NUM> having values corresponding to the position of the material switch. In alternate embodiments, the work machine <NUM> may be provided with material sensors that can detect characteristics of the material in the dump body <NUM> to indicate whether instability will be an issue. The controller <NUM> may respond to the machine switch position signals by storing the current position of the material switch as an indication of whether the material being handled may cause unstable operating conditions.

As discussed below, some configurations of counterbalance valve shutoff strategy may be dependent on the position of the dump body <NUM>, the ambient temperature of the work environment, the oil temperature at relevant locations in the hoist valve assembly <NUM> and the hoist cylinders <NUM>, or a combination thereof. Consequently, a dump body position sensor <NUM> may be operatively connected to the controller <NUM> and operative to sense a parameter indicative of a dump body angle relative to the normal lowered position of the dump body <NUM> as shown in <FIG>, and to direct dump body position sensor signals representative of the sensed dump body angle to the controller <NUM>. An ambient temperature sensor <NUM> may be mounted on an exterior surface of the main frame, dump body <NUM>, cab <NUM> or other appropriate location to sense the ambient temperature of the work environment in which the work machine <NUM> is operating, and to transmit ambient temperature sensor signals representative of the sensed ambient temperature to the controller <NUM>. An oil temperature sensor <NUM> may be installed at an appropriate location to sense the temperature of the oil functioning as hydraulic fluid to operate the hoist cylinders <NUM>. In one implementation, the oil temperature sensor <NUM> may be installed at the rod end <NUM> of one of the hoist cylinders <NUM> to sense the temperature of the fluid that may flow from the rod end <NUM> to the counterbalance valve <NUM>. In other implementations, the oil temperature sensor <NUM> may be installed at an appropriate location within the hoist valve assembly <NUM>. Further alternative positions are contemplated. In any appropriate position, the oil temperature sensor <NUM> is operatively connected to the controller <NUM> to direct oil temperature sensor signals representative of the sensed oil temperature to the controller <NUM>.

Returning to <FIG>, the controller <NUM> may transmit position control valve control signals to actuate the solenoids of the position control valves <NUM>, <NUM> to move the spool of the main control valve <NUM> to various positions to extend and retract the hoist cylinders <NUM> and raise and lower the dump body <NUM>. The lower position control valve <NUM> receives pilot supply fluid from a lower pilot supply port <NUM> via a lower pilot supply passage <NUM>, and the raise position control valve <NUM> receives pilot supply fluid from a raise pilot supply port <NUM> via a raise pilot supply passage <NUM>. The pilot supply ports <NUM>, <NUM> are in fluid communication with a pilot fluid source (not shown) via a pilot fluid supply line <NUM>. The position control valves <NUM>, <NUM> have similar configurations with a normal open position wherein the pilot fluid passes through the position control valves <NUM>, <NUM> to main valve pilot passages <NUM>, <NUM> to act on corresponding ends of the spool of the main control valve <NUM>. When both position control valves <NUM>, <NUM> are in the open position, the main control valve <NUM> is in the neutral position N as shown in <FIG>. In the neutral position N, the first H. supply port <NUM> and the head end fluid port <NUM> are blocked to maintain fluid within the head ends <NUM> of the hoist cylinders <NUM> and hold the dump body <NUM> in an essentially static position. The rod end fluid port <NUM> is placed in fluid communication with the brake cooling fluid passage <NUM> via the restricted passage <NUM> to allow some drainage of fluid from the rod ends <NUM>. The second H. supply port <NUM> is also fluidly connected to the brake cooling fluid passage <NUM>, and the selector pilot pressure passage <NUM> is fluidly connected to the drain passage <NUM> to reduce the pilot pressure on the selector spool <NUM>.

To move the main control valve <NUM> to one of three available dump body lower positions L1, L2, L3 in response to control lever sensor signals from the control lever sensor <NUM>, the controller <NUM> transmits proportional control signals to cause the solenoid of the lower position control valve <NUM> to move toward a second position wherein the main valve pilot passage <NUM> is fluidly connected to the drain passage <NUM>. The reduced fluid pressure in the main valve pilot passage <NUM> allows fluid pressure of the main valve pilot passage <NUM> to force the spool of the main control valve <NUM> to the corresponding dump body lower position L1, L2, L3. In the same way, in response to control lever sensor signals from the control lever sensor <NUM> to raise the dump body <NUM>, the controller <NUM> transmits control signals to cause the solenoid of the raise position control valve <NUM> to move toward its second position to fluidly connect the main valve pilot passage <NUM> to the drain passage <NUM> and reduce the fluid pressure in the main valve pilot passage <NUM> to allow the fluid pressure of the main valve pilot passage <NUM> to force the spool of the main control valve <NUM> to a dump body raise position R.

The dump body lower positions L1, L2, L3 control the rate at which the hoist cylinders <NUM> retract and the dump body <NUM> is lowered. The first dump body lower position L1 may be a power down position with a maximum rate of descent of the dump body <NUM>. In this position, the rod end fluid passage <NUM> is placed in fluid communication with the fluid supply passages <NUM> to deliver pressurized fluid to the rod ends <NUM> of the hoist cylinders <NUM>, and the head end fluid passage <NUM> is placed in fluid communication with the drain passage <NUM> to drain fluid from the head ends <NUM> of the hoist cylinders <NUM> to the tank <NUM>. The selector pilot pressure passage <NUM> is also fluidly connected to the drain passage <NUM> so that the selector spool <NUM> is spring biased to a position to distribute metered fluid from the dump fluid passage <NUM> to both pilot relief valves <NUM>, <NUM>. At the same time, the head end pressure pilot signal to the counterbalance valve <NUM> via the counterbalance pilot pressure passage <NUM> is reduced. The second H. supply port <NUM>, the brake cooling fluid port <NUM> and the rod end pressure relief port <NUM> are blocked to prevent fluid flow to the brake cooling fluid passage <NUM>. The second dump body lower position L2 may be a float position where the dump body <NUM> is lowered at a slower rate. The rod end and the head end connections are similar to the position L1, but the brake cooling fluid passage <NUM> is fluidly connected to the fluid supply passages <NUM> to divert a portion of the hydraulic fluid away from the rod ends <NUM> and to the brake cooling system, thereby slowing the retraction of the hoist cylinders <NUM>. The third dump body lower position L3 may be a snub position where a greater portion of the hydraulic fluid is diverted away from the rod ends <NUM> to further reduce the rate of descent of the dump body <NUM> and manage the impact as the dump body <NUM> reaches the fully lowered position of <FIG>.

The main control valve <NUM> in the illustrated embodiment has the single dump body raise position R, but additional raise positions are contemplated if necessary for greater control of the extension of the hoist cylinders <NUM> to raise the dump body <NUM> in a particular implementation of the hoist valve assembly <NUM>. In the dump body raise position R as illustrated, the head end fluid passage <NUM> is placed in fluid communication with the fluid supply passages <NUM> to deliver pressurized fluid to the head ends <NUM> and extend the hoist cylinders <NUM>, and the rod end fluid passage <NUM> is placed in fluid communication with the brake cooling fluid passage <NUM> to drain fluid from the rod ends <NUM> of the hoist cylinders <NUM> to the brake cooling system. The second H. supply port <NUM>, the valve drain port <NUM> and the restricted passage <NUM> are blocked. The first H. supply port <NUM> is fluidly connected to the metered pilot pressure port <NUM> to provide pilot signals corresponding to the head end pressure in the head end fluid passage <NUM> to the selector spool <NUM> via the selector pilot pressure passage <NUM> and to the counterbalance valve <NUM> via the counterbalance pilot pressure passage <NUM>. The pilot signal to the selector spool <NUM> shifts the selector spool <NUM> to a raise position wherein the dump fluid passage <NUM> is fluidly connected only to the raise pilot relief valve <NUM>.

The head end pressure pilot signal from the counterbalance pilot pressure passage <NUM> acts on the counterbalance valve <NUM> in the same direction as a rod end pressure pilot signal when the counterbalance shutoff valve <NUM> is in the open position shown in <FIG>. A counterbalance valve outlet pressure pilot signal and a biasing member such as a spring may act in the opposite direction as the head end and rod end pressure pilot signals. With this configuration, pressure spikes in either the head ends <NUM> or the rod ends <NUM> of the hoist cylinders <NUM> while raising the dump body <NUM> will cause the counterbalance valve <NUM> to open and drain fluid from the rod ends <NUM> to the brake cooling system. Under certain operating conditions such as those discussed further below, it may be desired to remove the head end pressure pilot signal from the counterbalance valve <NUM> and allow the counterbalance valve <NUM> to function as a rod end pressure relief valve that is only influenced by the rod end pressure pilot signal from the rod ends <NUM>. During these conditions, the controller <NUM> may transmit solenoid valve control signals to the counterbalance shutoff valve <NUM> to cause the counterbalance shutoff valve <NUM> to move to a shutoff position where the counterbalance pilot pressure passage <NUM> is blocked and the portion of the pilot pressure passage <NUM> between the counterbalance valve <NUM> and the counterbalance shutoff valve <NUM> is fluidly connected to the drain passage <NUM> via a shutoff drain passage <NUM> to drain the head end pressure pilot fluid to the tank <NUM>. With the counterbalance shutoff valve <NUM> in the shutoff position, the counterbalance valve <NUM> will only open during raising of the dump body <NUM> in the event of pressure supplied from the rod ends <NUM>.

<FIG> provides a graphic illustration of various parameters during the operation of the hoist valve assembly <NUM> to dump a load from the dump body <NUM> with the counterbalance shutoff valve <NUM> in its normal open position to communicate the head end pressure pilot signal to the counterbalance valve <NUM>. In this example, the work machine <NUM> is dumping a sticky payload of a material such as oil sand ore at an ambient temperature in which the pressurized fluid flows freely through the hoist cylinders <NUM> and the hoist valve assembly <NUM>. The X-axis represents time during which the dump body <NUM> is raised, dumps the load, and is lowered back to its normal position by the hoist cylinders <NUM>. A dump body angle curve <NUM> illustrates the dump body angle that would be indicated by the dump body position sensor <NUM> during the load dump cycle, a head end pressure curve <NUM> and a rod end pressure curve <NUM> illustrate the pressures in the head ends <NUM> and the rod ends <NUM>, respectively, of the hoist cylinders <NUM>, and a vertical acceleration curve <NUM> and a longitudinal acceleration curve <NUM> indicating acceleration of the main frame <NUM> in the respective directions.

When the main control valve <NUM> moves to the raise position R and pressurized fluid flows to the head ends <NUM> of the hoist cylinders <NUM>, the hoist cylinders <NUM> extend and increase the dump body angle. During the initial stage, the head end pressure is greater than the rod end pressure as the hydraulic fluid fills the head ends <NUM> to raise the dump body <NUM> and the counterbalance valve <NUM> opens to drain fluid from the rod ends <NUM> to the brake cooling system. Some pressure oscillation occurs as the dump body angle approaches an over-center load angle <NUM>, but the counterbalance valve <NUM> controls the rod end pressure to minimize the vertical and longitudinal accelerations of the main frame <NUM>. In one implementation, the over-center load angle <NUM> occurs at approximately <NUM>% of the maximum dump body raise angle of the dump body <NUM>, and may be within a range from <NUM>° to <NUM>°. When the dump body <NUM> reaches the over-center load angle <NUM>, the center of mass of the combined dump body <NUM> and load of material passes the dump body shaft <NUM> and switches the direction of the moment about the dump body shaft <NUM>. The load on the hoist cylinders <NUM> switches from a compressive load to a tensile load that must be resisted by the rod ends <NUM>. The rod end pressure increases while the head end pressure decreases such that the counterbalance valve <NUM> moves toward a throttled position to restrict the fluid flow out of the rod ends <NUM> and prevent rapid rotation of the dump body <NUM> about the dump body shaft <NUM>. Eventually, the load of material slides off the surface of the dump body <NUM> at a load detachment angle <NUM>. The load on the hoist cylinders <NUM> switches back to a compressive load that increases the head end pressure and decreases the rod end pressure.

The described operation of the hoist valve assembly <NUM>, and in particular the counterbalance valve <NUM>, can be adversely affected in cold temperatures that make the hydraulic fluid resistant to flow. <FIG> illustrates graphs similar to <FIG> where the work machine <NUM> is operating at an ambient temperature of approximately -<NUM>. Due to the flow resistance, there is a lag in pressure changes in the head ends <NUM> being communicated to the counterbalance valve <NUM> in the head end pressure pilot signal, and a corresponding lag in the response of the counterbalance valve <NUM>. As a consequence, the pressure oscillations and main frame accelerations prior to the over-center load angle <NUM> are greater as the counterbalance valve <NUM> is slow in responding. Further pressure oscillations of greater magnitude occur after the dump body <NUM> passes the over-center load angle <NUM> and create accelerations of the main frame <NUM> that potentially cause jarring effects for the work machine <NUM> and the operator.

In the hoist valve assembly <NUM> in accordance with the present invention, the counterbalance shutoff valve <NUM> is controlled during low temperatures or other unstable operating conditions to remove the head end pressure pilot signal from the counterbalance valve <NUM> so that only the rod end pressure pilot signal acts on the counterbalance valve <NUM> to regulate the fluid pressure in the rod ends <NUM>. As discussed above, the solenoid of the counterbalance shutoff valve <NUM> is actuated to move the counterbalance shutoff valve <NUM> to a shutoff position where the counterbalance pilot pressure passage <NUM> is blocked and the portion of the pilot pressure passage <NUM> between the counterbalance valve <NUM> and the counterbalance shutoff valve <NUM> is fluidly connected to the drain passage <NUM> to drain the pilot fluid to the tank <NUM>. At low rod end pressures, the counterbalance shutoff valve <NUM> will remain closed and a small amount of hydraulic fluid can flow through the rod end restricted drain passage <NUM> to the brake cooling system. At higher rod end pressures, the rod end pressure pilot signal opens the counterbalance valve <NUM> to drain hydraulic fluid from the rod ends <NUM> to the brake cooling system through the counterbalance valve <NUM>. After the unstable operating conditions are no longer present (e.g., ambient temperature rises above a threshold instability temperature), the solenoid of the counterbalance shutoff valve <NUM> can be deactivated to return the counterbalance shutoff valve <NUM> to its normal position so that the head end pressure pilot signal can act on the counterbalance valve <NUM> in conjunction with the rod end pressure pilot signal.

<FIG> illustrates an exemplary counterbalance valve shutoff routine <NUM> that may be executed by the controller <NUM> to identify unstable operating conditions and actuate the counterbalance shutoff valve <NUM> in response. The counterbalance valve shutoff routine <NUM> may begin at a block <NUM> where the controller <NUM> detects control lever sensor signals from the control lever sensor <NUM> or other source indicating displacement of the input device by the operator of the work machine <NUM>. After detection of the control lever sensor signals, control may pass to a block <NUM> where the controller <NUM> determines from the control lever sensor signals whether the work machine <NUM> is commanded to raise the dump body <NUM>. If the control lever sensor signals are not signals to raise the dump body <NUM>, control may pass to a block <NUM> where the controller <NUM> may control the solenoid of the counterbalance shutoff valve <NUM> to deactivate and allow the counterbalance shutoff valve <NUM> to move to its normal position or to maintain the counterbalance shutoff valve <NUM> in the normal position if it is already set in the normal position. After ensuring the counterbalance shutoff valve <NUM> is in the correct position, control may pass back to the block <NUM> to monitor for subsequent control lever sensor signals.

If the control lever sensor signals are signals to raise the dump body <NUM> at the block <NUM>, control may pass to a block <NUM> where the controller <NUM> may determine whether the work machine <NUM> is operating in unstable operating conditions. As discussed above, unstable operating conditions can include operating the work machine <NUM> at an ambient temperature or an oil temperature that is below a threshold instability temperature and fluid flow is affected, raising the dump body <NUM> beyond the over-center load angle <NUM>, or combinations of temperature, dump body angle and other operating parameters. If the controller <NUM> determines that the work machine <NUM> is not operating in unstable conditions at the block <NUM>, control may pass to the block <NUM> to ensure the counterbalance shutoff valve <NUM> is in the normal position and then to the block <NUM> to monitor for subsequent control lever sensor signals. If the controller <NUM> determines that the work machine <NUM> is operating in unstable conditions at the block <NUM>, control may pass to a block <NUM> where the controller <NUM> may actuate the solenoid of the counterbalance shutoff valve <NUM> to move the counterbalance shutoff valve <NUM> to the shutoff position and disconnect the head end pressure pilot signal from the counterbalance valve <NUM> and drain the pilot passage to the tank <NUM>. After moving the counterbalance shutoff valve <NUM> to the shutoff position, control may pass back to the block <NUM> to monitor for subsequent control lever sensor signals.

<FIG> illustrate several alternative strategies for the controller <NUM> to determine when the work machine <NUM> is subjected to unstable operating conditions that may necessitate counterbalance shutoff in accordance with the present invention.

<FIG> illustrates an implementation where the work machine <NUM> may be dumping sticky material such as oil sand ore where the nature of the material may cause jarring of the work machine <NUM> regardless of the current ambient temperature or oil temperature. In this embodiment, the processing at the block <NUM> may begin at a block <NUM> where the controller <NUM> detects dump body position sensor signals from the dump body position sensor <NUM>. After detecting the signals, control may pass to a block <NUM> where the controller <NUM> determines whether a current dump body angle indicated by the signals is greater than a threshold instability angle that may be less than but close to the over-center load angle <NUM>. The threshold instability angle may be used as a shutoff reference if it is desirable to execute counterbalance shutoff prior to reaching the over-center load angle <NUM>. If the dump body angle is less than the threshold instability angle, the work machine <NUM> has not yet reached an unstable operating condition, and control may pass back to the block <NUM> for execution as described above. If the dump body angle is greater than the threshold instability angle, the work machine <NUM> has reached the unstable operating condition, and control may pass to the block <NUM> to actuate the counterbalance shutoff valve <NUM> to the shutoff position.

<FIG> illustrates an implementation where the work machine <NUM> may operate in cold environments where instability can occur at low temperatures regardless of the nature of the work material loaded in the dump body <NUM>. The processing at the block <NUM> may begin at a block <NUM> where the controller <NUM> detects temperature sensor signals from a relevant temperature sensor such as the ambient temperature sensor <NUM> or the oil temperature sensor <NUM>. The sensed temperature for a given implementation may be the temperature that most closely accurately correlates to the unstable operating conditions for the work machine <NUM>. After detecting the temperature sensor signals, control may pass to a block <NUM> where the controller <NUM> determines whether a current sensed temperature indicated by the signals is greater than a threshold instability temperature. If the sensed temperature is greater than the threshold instability temperature, the flow of hydraulic fluid will not be adversely affected, and control may pass back to the block <NUM>. If the sensed temperature is less than the threshold instability temperature, the work machine <NUM> is operating in unstable operating conditions, and control may pass to the block <NUM> to actuate the counterbalance shutoff valve <NUM> to the shutoff position.

<FIG> provides an implementation that may be a combination of the implementations of <FIG> where unstable operating conditions occur when the work machine <NUM> is operating at low temperatures and the dump body <NUM> is being raised and is approaching or past the over-center load angle <NUM>. In this embodiment, the controller <NUM> may initially execute blocks <NUM>, <NUM> to determine whether the current sensed temperature is less than the threshold instability temperature, and control passes back to the block <NUM> if the sensed temperature is greater. If the sensed temperature is less than the threshold instability temperature, then control may pass to the blocks <NUM>, <NUM> to determine whether the dump body angle is greater than the threshold instability angle. Control will pass back to the block <NUM> if the dump body angle is less than the threshold instability angle, and will pass back to the block <NUM> if the dump body angle is greater than the threshold instability angle.

<FIG> illustrates an implementation where unstable operating conditions may occur when the work machine <NUM> is handling materials such as oil sand ores that can create a loaf that adheres to the surface of the dump body <NUM> beyond the over-center load angle <NUM>, or can cause the shift from the compressive push load to the tensile pull load to occur before the dump body <NUM> reaches the over-center load angle <NUM>. In this embodiment, the controller <NUM> detects the material switch position sensor signals from the material switch position sensor <NUM> at a block <NUM>. Block <NUM> may be executed in real time, or the controller <NUM> may retrieve from memory <NUM> values of the material switch position sensor signals that were received from the material switch position sensor <NUM> the last time the material switch position sensor <NUM> detected a change in the position of the material switch. Control then passes to a block <NUM> where the controller <NUM> determines whether the material or material characteristics corresponding to the material switch position correspond to a potentially unstable material. If the material indicated by the material switch position is not an unstable material, control may pass back to the block <NUM>. If the controller <NUM> determines that the material switch position indicates an unstable material, then control may pass to the blocks <NUM>, <NUM> to determine whether the dump body angle is greater than the threshold instability angle. Control will pass back to the block <NUM> if the dump body angle is less than the threshold instability angle, and will pass back to the block <NUM> if the dump body angle is greater than the threshold instability angle. In some implementations where the character of the material in evaluate, the ambient temperature or oil temperature may also be considered in determining when to actuate the counterbalance shutoff valve <NUM>.

The hoist valve assembly <NUM> and the counterbalance valve shutoff routine <NUM> of the work machine <NUM> in accordance with the present invention provide an effective solution to instability that occurs with a counterbalance valve in certain operating conditions. The counterbalance shutoff valve <NUM> constitutes a single control element actuated by the controller <NUM> to disengage counterbalancing in the hoist valve assembly <NUM>, which stands in contrast to systems such as the regenerative hydraulic circuit of the Ramler et al. patent that implements many controlled elements in addition to a main control valve that must be controlled by a controller to control operation of the circuit. At the same time, the counterbalance valve shutoff routine <NUM> can be configured as necessary for a particular implementation in a work machine <NUM> to determine when the work machine <NUM> is operating in unstable operating conditions. In most implementations, the controller <NUM> may make use of sensor information that is already available based on the operation and control of other systems of the work machine <NUM>. In this way, potentially adverse jarring of the work machine <NUM> can be reduced, thereby reducing maintenance on the work machine <NUM> and extending its useful life.

The hoist valve assembly <NUM> is illustrated and described herein as being implemented to control operation of the hoist cylinders <NUM>. However, those skilled in the art will understand that the hoist valve assembly <NUM> and the counterbalance valve shutoff routine <NUM> may be implemented to control the operation of any hydraulic cylinder in a work machine where counterbalancing during extension or retraction of the hydraulic cylinder provides benefits and counterbalance shutoff is desired during unstable operating conditions. Such implementations could include boom cylinders, stick cylinders and/or implement cylinders in excavators, lift cylinders in loaders and bulldozers, and the like. Such implementations are contemplated by the inventors.

Claim 1:
A hoist valve assembly (<NUM>) for a cylinder (<NUM>) for a work machine (<NUM>), the cylinder (<NUM>) having a head end (<NUM>) and a rod end (<NUM>), the hoist valve assembly (<NUM>) configured to be fluidly connected to a pressurized fluid source, a low pressure reservoir, the head end and the rod end of the cylinder and comprising:
a main control valve (<NUM>) having a raise position in which the head end (<NUM>) of the cylinder (<NUM>) can be put in fluid communication with a pressurized fluid source (<NUM>) and can be put in fluid communication with a counterbalance pilot pressure passage (<NUM>) configured to transmit a head end pressure pilot signal from the head end (<NUM>), and in which the rod end (<NUM>) of the cylinder (<NUM>) can be put in fluid communication with a low pressure reservoir (<NUM>);
a counterbalance valve (<NUM>) positioned in a fluid flow path between the rod end (<NUM>) of the cylinder (<NUM>) and the main control valve (<NUM>), wherein the counterbalance valve (<NUM>) is biased to a closed position configured to prevent fluid flow from the rod end (<NUM>) to the low pressure reservoir (<NUM>) and has an open position in which the rod end (<NUM>) of the cylinder (<NUM>) can be put in fluid communication with the low pressure reservoir (<NUM>), and wherein a rod end pressure pilot signal from the rod end (<NUM>) and the head end pressure pilot signal from the counterbalance pilot pressure passage (<NUM>) apply a force to the counterbalance valve (<NUM>) in a direction of the open position; and
a counterbalance shutoff valve (<NUM>) positioned along the counterbalance pilot pressure passage (<NUM>) between the main control valve (<NUM>) and the counterbalance valve (<NUM>), wherein the counterbalance shutoff valve (<NUM>) has a normal position where the head end pressure pilot signal applies the force to the counterbalance valve (<NUM>) in the direction of the open position and a shutoff position where the head end pressure pilot signal is blocked from the counterbalance valve (<NUM>).