Patent Publication Number: US-9429174-B1

Title: Enabling valve having separate float and lift down positions

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 61/793,845, which was filed on Mar. 15, 2013. 
    
    
     BACKGROUND 
     The present application is directed toward power machines. More particularly, the present application is directed toward hydraulic control valve arrangements that provide power signals to work elements such as lift arms. Power machines, for the purposes of this disclosure, include any type of machine that generates power for the purpose of accomplishing a particular task or a variety of tasks. One type of power machine is a work vehicle. Work vehicles are generally self-propelled vehicles that have a work device, such as a lift arm (although some work vehicles can have other work devices) that can be manipulated to perform a work function. Work vehicles include loaders, excavators, utility vehicles, tractors, and trenchers, to name a few examples. 
     Certain types of power machines with lift arms have hydraulic actuators (often hydraulic cylinders) that selectively provide power to move the lift arm in generally upward or downward directions in response to command signals generated by the operator. In many of these types of power machines, a proportional directional control valve allows hydraulic fluid to enter one end of a cylinder and exit the other end of the cylinder at a rate commanded by the operator. Control valves of this type are normally configured to prevent hydraulic fluid from being introduced into either end of the cylinder when an operator is not generating a command signal. 
     In some situations, the control valve is configured to allow hydraulic fluid to be evacuated from each end of the actuator, thereby allowing the lift arm to be controlled by gravity, with only engagement of an uneven terrain by an implement attached to the lift arm to allow the lift arm to be raised over a lowered position. Such a condition is known as a float condition, in that the lift arm is allowed to float up and down relative to the frame of the machine without any power, often in the form of pressurized hydraulic fluid, being provided to the actuator. 
     The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. 
     SUMMARY 
     In one embodiment, a power machine is disclosed. The power machine includes a frame, a work element operably coupled to the frame, a hydraulic actuator coupled to the work element and operable to move the work element relative to the frame, and power source capable of providing a hydraulic power signal as an output. A power conversion system controls the flow of the hydraulic power signal between the power source and the hydraulic actuator. The power conversion system has a control valve and an enabling valve. The control valve is capable of determining a direction of flow between the power conversion system and the actuator. The enabling valve is movable between a first enabling valve position in which flow between the control valve and the actuator is blocked, a second enabling valve position that allows substantially unrestricted flow between the control valve and the actuator, and a third enabling valve position that allows a restricted flow between the control valve and the actuator. 
     In another embodiment, a power conversion system for controlling the flow of a hydraulic power signal between a power source and a hydraulic actuator having first and second ports is disclosed. The power conversion system includes a control valve configured to selectively expose each of the first and second ports to one of the power source and a low pressure reservoir, and an enabling valve having a disabled position, a first enabled position, and a second enabled position, the enabling valve receiving an input from the control valve an providing an output configured to be provided to the hydraulic actuator. 
     This Summary and the Abstract are provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is side elevation view of power machine of the type in which a control valve assembly described herein can be advantageously employed. 
         FIG. 2  is a block diagram illustrating functional systems of a representative power machine on which embodiments of the present disclosure can be practiced. 
         FIG. 3  is a block diagram of a hydraulic circuit including a power conversion system according to one illustrative embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Before the concepts of the present application are disclosed and described in the form of the embodiments set forth below, it is to be understood that the concepts discussed herein are not limited in their application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The disclosed concepts are capable of being practiced in other embodiments. In addition, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
     The present application discloses a hydraulic control circuit for operating hydraulic functions for a power machine. More particularly, the present application discloses a hydraulic circuit for controlling the rate of change of evacuation of hydraulic fluid from an actuator under certain circumstances, as described below. 
       FIG. 1  is a side elevation view of a representative power machine  100  upon which the disclosed embodiments can be employed.  FIG. 2  is a block diagram illustrating certain function systems of the power machine  100 . The power machine  100  illustrated in  FIG. 1  is a skid-steer loader, but other types of power machines such as tracked loaders, steerable wheeled loaders, including all-wheel steer loaders, excavators, telehandlers, walk behind loaders, trenchers, and utility vehicles, to name but a few examples, may employ the disclosed embodiments. The power machine or loader  100  includes a supporting frame or main frame  102 , which supports a power source  104 , which in some embodiments is an internal combustion engine. A power conversion system  106  is operably coupled to the power source  104 . Power conversion system  106  illustratively receives power from the power source  104  and operator inputs to convert the received power to power signals in a form that is provided to and utilized by functional components of the power machine. 
     Some embodiments of power machines, such as loader  100  in  FIG. 1 , the power conversion system  106  includes hydraulic components such as one or more hydraulic pumps and various actuators and valve components that are illustratively employed to receive and selectively provide power signals in the form of pressurized hydraulic fluid to some or all of the actuators used to control work elements on the power machine. For example, a control valve assembly  204  (shown in  FIG. 2 ) can be used to selectively provide pressurized hydraulic fluid from a hydraulic pump  206  (shown in  FIG. 2 ) to actuators  208  (shown in  FIG. 2 ) such as hydraulic cylinders that are positioned on the power machine. In some embodiments, control valve assembly  204  also selectively provides pressurized hydraulic fluid to actuators  210  located on an implement  212  attached to the power machine. Other types of control systems are contemplated. For example, the power conversion system  106  can include electric generators or the like to generate electrical control signals to power electric actuators. For the sake of simplicity, the actuators discussed in the disclosed embodiments herein are referred to as hydraulic or electrohydraulic actuators, but other types of actuators can be employed to control some work elements. 
     Among the work elements that are capable of receiving power signals from the power conversion system  106  are tractive elements  108 , illustratively shown as wheels, which are configured to rotatably engage a support surface to cause the power machine to travel. Other examples of power machines can have tracks or other tractive elements instead of wheels. In an example embodiment, a pair of hydraulic motors (not shown in  FIG. 1 ), are provided to convert a hydraulic power signal into a rotational output. In power machines such as skid steer loaders, a single hydraulic motor can be operatively coupled to both of the wheels on one side of the power machine. Alternatively, a hydraulic motor can be provided for each tractive element in a machine. In a skid steer loader, steering is accomplished by providing unequal rotational outputs to the tractive element or elements on one side of the machine as opposed to the other side. In some power machines, steering is accomplished through other means, such as, for example, steerable axles. 
     The loader  100  also includes a work element in the form of a lift arm structure  114  that is capable of being raised and lowered with respect to the frame  102 . The lift arm structure  114  illustratively includes a lift arm  116  that is pivotally attached to the frame  102  at attachment point  118 . An actuator  120 , which in some embodiments is a hydraulic cylinder configured to receive pressurized fluid from power conversion system  106 , is pivotally attached to both the frame  102  and the lift arm  116  at attachment points  122  and  124 , respectively. Actuator  120  is sometimes referred to as a lift cylinder, and is a representative example of one type of actuator  208  shown in  FIG. 2 . Extension and retraction of the actuator  120  causes the lift arm  116  to pivot about attachment point  118  and thereby be raised and lowered along a generally vertical path indicated approximately by arrow  138 . The lift arm  116  is representative of the type of lift arm that may be attached to the power machine  100 . The lift arm structure  114  shown in  FIG. 1  includes a second lift arm and actuator disposed on an opposite side of the of the power machine  100 , although neither is shown in  FIG. 1 . Other lift arm structures, with different geometries, components, and arrangements can be coupled to the power machine  100  or other power machines upon which the embodiments discussed herein can be practiced without departing from the scope of the present discussion. 
     An implement carrier  130  is pivotally attached to the lift arm  116  at attachment point  132 . One or more actuators such as hydraulic cylinder  136  are pivotally attached to the implement carrier and the lift arm structure  114  to cause the implement carrier to rotate under power about an axis that extends through the attachment point  132  in an arc approximated by arrow  128  in response to operator input. In some embodiments, the one or more actuators pivotally attached to the implement carrier and the lift arm assembly are hydraulic cylinders capable of receiving pressurized hydraulic fluid from the power conversion system  106 . In these embodiments, the one or more hydraulic cylinders  136 , which are sometimes referred to as tilt cylinders, and are further representative examples of actuators  208  shown in  FIG. 2 . Although no implements are shown as being attached to the power machine  100  in  FIG. 1 , the implement carrier  130  is configured to accept and secure any one of a number of different implements (e.g., implement  212  shown in  FIG. 2 ) to the power machine  100  as may be desired to accomplish a particular work task. The types of implements that can be operably coupled to loader  100  or other similar power machines can range from simple implements such as buckets to complex implements. 
     A partial list of the types of implements that can be attached to the implement carrier  130  includes augers, planers, graders, combination buckets, wheel saws, and the like. These are only a few examples of the many different types of implements that can be attached to power machine  100 . The power machine  100  provides a source, accessible at connection point  134 , of power and control signals that can be coupled to an implement to control various functions on such an implement, in response to operator inputs. In one embodiment, connection point  134  includes hydraulic couplers that are connectable to the implement  212  for providing power signals in the form of pressurized fluid provided by the power conversion system  106  for use by an implement that is operably coupled to the power machine  100 . Alternatively or in addition, connection point  134  includes electrical connectors that can provide power signals and control signals to an implement to control and enable actuators of the type described above to control operation of functional components on an implement. Actuation devices  210  located on an implement are controllable using control valve assembly  204  of power system  106 . 
     Power machine  100  also illustratively includes a cab  140  that is supported by the frame  102  and defines, at least in part, an operator compartment  142 . Operator compartment  142  typically includes an operator seat (not shown in  FIG. 1 ) and operator input devices  202  (shown schematically in  FIG. 2 ) and display devices accessible and viewable from a sitting position in the seat. When an operator is seated properly within the operator compartment  142 , the operator can manipulate operator input devices  202  to control such functions as driving the power machine  100 , raising and lowering the lift arm structure  114 , rotating the implement carrier  130  about the lift arm structure  114  and make power and control signals available to implement  212  via the sources available at connection point  134 . 
     In some embodiments, an electronic controller  150  (shown in  FIGS. 1 and 2 ) is configured to receive input signals from at least some of the operator input devices  202  and provide control signals to the power conversion system  106  and to implements via connection point  134 . It should be appreciated that electronic controller  150  can be a single electronic control device with instructions stored in a memory device and a processor that reads and executes the instructions to receive input signals and provide output signals all contained within a single enclosure. Alternatively, the electronic controller  150  can be implemented as a plurality of electronic devices coupled on a network. The disclosed embodiments are not limited to any single implementation of an electronic control device or devices. The electronic device or devices such as electronic controller  150  are programmed and configured by the stored instructions to function and operate as described. 
     Referring now more particularly to  FIG. 2 , further features of power machine  100  are shown in block diagram form in accordance with exemplary embodiments. As shown, the one or more operator input devices  202  are operatively coupled to electronic controller  150  via a network  205  or other hard wired or wireless connection. The operator input devices  202  are manipulable by an operator to provide control signals to the electronic controller  150  via network  205  to communicate control intentions of the operator. The operator input devices  202  are to provide control signals for controlling some or all of the functions on the machine such as the speed and direction of travel, raising and lowering the lift arm structure  114 , rotating the implement carrier  130  relative to the lift arm structure, and providing power and control signals to an implement to name a few examples. Operator input devices  202  can take the form of joystick controllers, levers, foot pedals, switches, actuable devices on a hand grip, pressure sensitive electronic display panels, and the like. In various power machines, some, all, or none of the work elements can be controlled by a controller  150 . For example, a lift arm such as lift arm structure  114 , in various embodiments, is controlled via electronics such as electronics controller  150 . In other embodiments, work elements such as lift arms can be controlled via mechanical linkages (represented by arrow  209 ) from operator input devices  202  and control valve assembly  204 . 
     In response to control signals generated by operator input devices  202 , electronic controller  150  controls operation of control valve assembly  204  and actuators  208 . In addition, electronic controller  150  can control actuators  210  on implement  212  or alternatively provide signals to an implement controller  214  that can, in turn, directly control one or more actuators  210  or provide control signals back to the electronic controller  150  to signal that control valve assembly  204  be actuated to provide hydraulic fluid to one or more of the actuators  210 . Control of actuators  208  and  210  is, in at least some respects, performed using electrical signals on control lines or network  207  to control spool valves of control valve assembly  204  to selectively direct the flow of hydraulic fluid from pump  206  to those actuators. Flow of hydraulic fluid to actuators  210  on implement  212  is through hydraulic lines connected to the implement at connection point  134 . Disclosed embodiments are described with reference to control of a control valve assembly  204  for selectively providing pressurized hydraulic fluid to actuators  208  on power machine  100 , which can include lift cylinders  120  and tilt cylinders  136 , and actuators  210  on implement  212  attached to implement carrier  130 . 
       FIG. 3  illustrates a portion of a power conversion system  300  for providing control signals to one or more lift cylinders  302  and tilt cylinders  304  according to one illustrative embodiment. The power conversion system  300  includes a control valve  306  and an enabling valve  308 . The control valve  306  receives a power signal  301  from a source  310  in the form of pressurized hydraulic fluid. The source  310  can include one or more hydraulic pumps to provide the power signal  301 . The control valve  306  includes a lift valve  312  and a tilt valve  314 . The lift valve  312  is a four-position valve, operable between a neutral position  316 , lift up position  318 , lift down position  320  and float position  322 . The tilt valve  314  is a three-position valve including a neutral position  324 , a curl position  326  and a dump position  328 . The lift and tilt valve in this particular embodiment are variable spool valves, housed in a single housing. In other embodiments, the lift and tilt valves can be housed in separate housings or can be implemented using other types of valves besides spool valves. 
     The lift and tilt spool valves  312  and  314  are shown in  FIG. 3  in a default position. The lift and spool valves  312  and  314  are biased to these default positions by biasing elements (not shown) such as biasing springs. Forces are selectively applied to the lift and tilt spool valves  312  and  314  to cause the lift and spool valves to move from the neutral positions  316  and  324  to the other positions as desired. The selectively applied forces can applied using various different types of actuators. For the purposes of illustration, actuation devices  330 A and  330 B are shown on either side of the lift spool  312  indicating two actuators for shifting of lift spool in either direction. In one embodiment a pair of electrohydraulic cartridges can be employed to selectively port pressurized hydraulic fluid against one end or the other of the lift spool  312 . In alternate embodiments a single actuator, such as an electric drive mechanism or mechanical linkage from an operator input such as a hand or foot controlled device can engage the lift spool  312  to shift it from one position to another. Similarly, the tilt spool valve  314  can be controlled by a pair of actuators  332 A and  332 B or a single actuator similar to those discussed above with respect to the lift spool  312 . 
     Outputs  335  and  337  are provided from the lift spool valve  312  and the tilt spool  314 , respectively, to the enabling valve  308 . The enabling valve  308  has a lift enabling valve  334  and a tilt enabling valve  336 . The enabling valves receive an enabling signal  338  to shift them to an enabling position as discussed below. The lift enabling valve  334  has three positions, a blocking position  340 , a first enabling position  342 , and a second enabling position  344 . The tilt enabling valve  336  has two positions, a blocking position  346  and an enabling position  348 . As shown in this embodiment, the enabling valves are spool valves, but other types of valves can be used in alternative embodiments. 
     When the lift enabling valve  334  and the tilt enabling valve  336  are in their respective blocking positions, hydraulic fluid is incapable of passing from the control valve  306  to the actuators  302  and  304  and vice versa. The lift enabling valve  334  is biased to its blocking position  340  by biasing mechanism  350 . Similarly, tilt enabling valve  336  is biased to its blocking position  346  by biasing mechanism  352 . Because enabling valves are biased to a blocking position, an affirmative action is required to overcome the biasing mechanisms. The enabling valves thus prevent inadvertent or unwanted movement of the actuators  302  and  304 . 
     The enabling signal  338  is provided to act against the biasing mechanisms  350  and  352 . Enabling signal  338  can be an electrical signal, a hydraulic signal, or any other suitable signal capable of overcoming the biasing mechanisms. The enabling signal  338  is shown as a single signal provided to each of the lift enabling valve  334  and the tilt enabling valve  336 . Alternatively, separate signals can be provided to the two enabling valves. As discussed above, the lift enabling valve  334  has two enabling positions  342  and  344 . The second enabling position  344 , as shown in  FIG. 3 , has a restriction in it to reduce the rate at which pressurized fluid is allow to flow therethrough. Thus, in situations where it is desirable to reduce flow rate during an enabling condition, the second enabling position  344  should be selected over the first enabling position. For example, when an operator wishes to power the lift arm on a power machine up or down in normal operating conditions, the first enabling position  342  will allow for relatively quick cycle times (i.e. the time it takes to raise and lower the lift arm) unimpeded by a restriction in the enabling valve. If, however, an operator wishes to use the float function of the lift arm to allow the lift arm to float over the surface of the ground, a restriction in the enabling valve will slow down movement of the lift arm. In one embodiment, the enabling signal  338  is in communication with the actuators  330 A and  330 B so that an increased level provided to actuator  330 B to shift the lift spool into the float position is also provided to the enabling signal  338  to shift the lift enabling valve  334  into the second enabling position  344 . In other embodiments, the signal  338  provided to lift enabling valve  334  is provided independently from the actuator  330 B so that the lift enabling valve  334  can be controlled independently from the lift spool valve  316 . 
     The embodiments above provide important advantages. Having enabling valves in series with control valves provides the ability to require an affirmative action to overcome a biasing member and enable flow to an actuator. By providing an enabling valve with a plurality of different enabled positions, various flow rates can be provided for without requiring modifications and additional complexity in a control valve. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.