The invention relates generally to work vehicles. More particularly, it relates to auxiliary hydraulic valves and controllers for work vehicles. Even more particularly, it relates to automated methods and structures for calibrating the auxiliary valves for such vehicles.
This invention provides a way for automatically calibrating electronically controlled remote hydraulic valves. It is adaptable for use on all agricultural and construction vehicles equipped with electronically controlled remote hydraulic valves.
Remote hydraulic valves provide auxiliary hydraulic flows to implements that are coupled to vehicles for performing various tasks. Typically, such a vehicle will have several such valves, typically varying between two and eight. These valves are controlled in an operator station typically in the cab of the vehicle, most commonly by manipulating a lever or knob that provides a signal proportional to the movement of the lever or knob and indicates a desired flow rate to or from an auxiliary hydraulic valve. The hydraulic valves are typically connected to a manifold or manifolds, most commonly located at the rear of the vehicle, to which hydraulic actuators are mounted. These hydraulic actuators include such things as hydraulic motors and cylinders. By varying the position of the lever or knob, the operator can vary the flow rate to the manifold, and thence to the hydraulic actuators located on the implement.
Another common user input device located at the operator station is a flow rate control. The flow rate control is typically a small dial or knob that is set by the operator and indicates a maximum flow rate through the valve. Thus, by rotating the flow rate control, the operator can limit the operating range of the lever or knob from a flow rate of zero (0) to a positive maximum flow rate indicated by the flow rate control, and a negative maximum flow rate, also indicated by the flow rate control.
Vehicle operators usually expect the same flow rate curve from all the auxiliary hydraulic valves. Flow variations between valves may be severe, however, due to the tolerances of the valves, the actuators and the controls.
A typical problem that is commonly found with auxiliary hydraulic valves is that of hysteresis. From the operator""s perspective, hysteresis appears when the operator moves the lever or knob away from a zero flow rate position towards either a positive or negative flow rate and no flow passes through the valve.
The initial small movements of the lever or knob generate equivalent small electrical signals that are applied to the valve coil. These small initial signals are insufficient to overcome the valve""s static friction and therefore these initial small movements of the lever or knob will not cause the valve to open.
As the operator continues to move the lever or knob, indicating a higher flow rate, and generating a larger valve signal, the valve will still remain closed until the applied signal is sufficient to overcome the static friction, at which point a low flow rate begins to pass through the valve.
In some cases, the valve spool may indeed move when a signal is applied, but due to the location of the various lands and grooves, this movement may not be sufficient to open up a fluid flow path. The effect, from the operator""s perspective, is the same: movement of the lever or knob does not result in an equivalent flow rate.
In addition, a strong spring used in the valve may resist the movement of the spool and also result in no valve opening when small valve signals are applied.
During this movement of the lever or knob, the valve signal applied to the valve is indeed increasing. However, due to frictional effects in the valve, the resistance of the spring, or the location of the various lands and grooves, no hydraulic flow through the valve may occur. This region of no valve flow when the lever or knob is moved is often called a xe2x80x9cdead-band.xe2x80x9d
A way to cancel out this dead-band is needed in order to make the whole range of motion of the lever or knob provide an proportional flow rate.
The dead-band can be modeled as a constant valve signal offset that must be added to any signal sent by the controller. If the valve resists opening until a small positive valve signal is applied, this offset should be added to any signal transmitted by the lever or knob. In this manner, whenever the operator moves the proportional controlled lever or knob, even a small amount, some flow will begin to pass through the valve.
Determining this offset for a particular valve in a particular vehicle, generally requires actually applying a signal to the valve until the valve just opens or xe2x80x9ccracksxe2x80x9d. If one could observe the valve xe2x80x9ccrackingxe2x80x9d and identify the actual signal that was applied to the valve at the same time, the signal could be saved in the valve controller for later addition to the signal received from the proportional control lever or knob.
Identifying the valve xe2x80x9ccrackingxe2x80x9d point would normally require the attachment of a loop-back tool to each of the valves. When the valve cracks open, fluid will begin to flow through the valve, out through the quick-connect coupling, through the loop-back tool, back into the adjacent quick-connect coupling, back through the valve and then to a hydraulic reservoir or tank. This, however, would require that an additional tool be attached to the vehicle. During assembly of the vehicle, and when calibrating the vehicle in the field, it is awkward to use such a tool.
What is needed, therefore, is a method and apparatus for calibrating auxiliary hydraulic valves without the necessity of attaching a loop-back tool to the auxiliary hydraulic manifold. It is an object of this invention to provide such a method and apparatus.
It is also an object of this invention to provide a method and apparatus for sequentially and automatically calibrating each of the auxiliary hydraulic valves under computer control.
In accordance with the first embodiment of the invention, a method of computer calibrating at least one auxiliary hydraulic control valve is provided that includes the steps of selecting a first valve from a plurality of hydraulic control valves, applying a signal to that valve that is equivalent to a first degree of desired valve opening, measuring a first pressure in a restricted flow rate circuit, comparing the pressure with a predetermined pressure to identify a pressure change that indicates the cracking of the valve, incrementing the signal if the valve is not cracked and repeating the foregoing steps until the first valve cracks open, and finally saving a value indicative of the increment signal.