Patent Description:
Liquid fuel rockets, as well as other similar systems, utilize valves and valve control to control the flow of fuel into a combustor, thereby controlling the thrust produced by the combustor. During operation of a valve the smallest period of time that the valve is maintained open is referred to as the minimum impulse bit (MIB) and the minimum impulse bit dictates the granularity of control that can be applied to fluid flow through the valve and thus, the granularity of the thrust controls of the liquid fuel rocket engine.

The minimum impulse bit time of any given valve can vary due to variations in the opening and closing responses of the valve. This variance depends on any number factors including the age of the valve, wear on the valve, environmental conditions in which the valve is operating, and the like. In order to compensate for the variation, and provide consistent predictable controls, discrete valve operations are typically run at slightly longer than the actual minimum impulse bit of the valve.

<CIT> discloses a method and device for monitoring an actuator device.

<CIT> discloses noncircular transient fluid fuel injector control channels in propellant injector combustion systems.

<CIT> discloses a valve controller for pressure stabilization.

According to an aspect of the present invention, a valve controller for a liquid fuel rocket engine includes at least one current sensor input, at least one voltage sensor input, a processor and a memory, the processor being connected to the at least one current sensor input and the at least one voltage sensor input, wherein the valve controller is configured to determine at least one actual minimum impulse bit of a valve based on a current profile and a voltage profile of a single valve operation, and wherein the valve controller is configured to adjust valve controls to account for the at least one actual minimum impulse bit.

In another preferred embodiment of the previously described valve controller, the actual minimum impulse bit is correlated with at least one external factor, and wherein the valve controller is configured to adjust the valve controls to account for the at least one actual minimum impulse bit and the at least one external factor.

In another preferred embodiment of any of the previously described valve controllers, the external factor is at least one of an engine pressure and a battery voltage.

In another preferred embodiment of any of the previously described valve controllers, the valve controller is configured to determine the at least one actual minimum impulse bit on an initial operation of the valve.

In another preferred embodiment of any of the previously described valve controllers, the valve controller is further configured to periodically determine an updated minimum impulse bit of the valve.

In another preferred embodiment of any of the previously described valve controllers, the valve controller is further configured to adjust valve controls based on a most recently determined updated minimum impulse bit of the valve.

In another preferred embodiment of any of the previously described valve controllers, the minimum impulse bit is based in part on an initial valve opening time, the initial valve opening time being determined to be a dip in a ramp up of the current profile.

In another preferred embodiment of any of the previously described valve controllers, the minimum impulse bit is based in part on a fully closed valve time, the fully closed valve time being determined to be a time between a voltage spike and a valve control current being driven to zero by the valve controller.

In another preferred embodiment of any of the previously described valve controllers, each of the at least one current sensor and the at least one voltage sensor are connected to, and configured to sense, a valve control signal line.

In another preferred embodiment of any of the previously described valve controllers, the valve control signal line is controllably connected to a liquid fuel rocket engine valve.

In another preferred embodiment of any of the previously described valve controllers, the liquid fuel rocket engine valve at least partially controls a flow of liquid fuel form a fuel repository to a combustor.

According to another aspect of the present invention a method for determining a minimum impulse bit of a valve includes monitoring a current profile and a voltage profile of a valve control signal, determining an initial valve open time to be a beginning of a dip in a current ramp up and determining a valve fully closed time to be a voltage spike of the valve control signal, and determining the minimum impulse bit of the valve to be a length of time from the initial valve open time to the valve fully closed time.

Another preferred embodiment of the above method includes correlating the minim impulse bit of the valve with at least one external environmental factor.

In another preferred embodiment of any of the above methods, the at least one external environmental factor includes at least one of an engine pressure and a battery voltage.

Another preferred embodiment of any of the above methods includes periodically reiterating the method and updating the determined minimum impulse bit of the valve at each iteration.

A liquid fuel rocket engine according to one preferred embodiment is provided in accordance with claim <NUM>.

<FIG> schematically illustrates an exemplary highly schematic liquid fuel rocket engine <NUM>. Systems and controls of the engine <NUM> unrelated to this disclosure are omitted and/or simplified for the purposes of explanation, and a practical liquid fuel rocket engine implementing the concepts described herein can include any number of additional configurations and systems as would be necessary to implement the practical example. The liquid fuel rocket engine <NUM> includes a liquid fuel repository <NUM>, an oxidizer repository <NUM> and a combustor <NUM>. The liquid fuel repository <NUM> is connected to the combustor <NUM> via a fuel line <NUM>, and a fluid valve <NUM> controls the flow of liquid fuel into the combustor <NUM>. Similarly, the oxidizer repository <NUM> is connected to the combustor <NUM> via a fluid line <NUM>, and the flow of oxidizer into the combustor <NUM> is controlled via a fluid valve <NUM>. Each of the valves <NUM>, <NUM> is controlled via a controller <NUM>.

Within the combustor <NUM>, the liquid fuel and the oxidizer are mixed and ignited, and the resultant combustion products are expelled through a nozzle <NUM> thereby generating thrust. The magnitude of the thrust generated is controlled by the amount of liquid fuel injected into the combustor <NUM>. Due to various conditions, such as wear and environmental conditions, as well as manufacturing variations from valve to valve, the minimum impulse bit of the valve <NUM> can include variations and fall within a tolerance window. In order to provide the most discrete control possible it is desirable to minimize the variations.

With continued reference to <FIG> schematically illustrates a valve configuration <NUM> including an electrically controlled valve <NUM> that allows a fluid <NUM> to pass through the valve <NUM> while the valve <NUM> is open and prevents the fluid <NUM> from passing through while the valve <NUM> is closed. The valve <NUM> is controlled via a current signal <NUM>. The current signal <NUM> originates from a current driver <NUM> portion of a controller <NUM>. A voltage sensor <NUM> and a current sensor <NUM> are configured to monitor the voltage and current (respectively) of the current signal <NUM> being input to the valve <NUM>. The sensor output of each sensor <NUM>, <NUM> is provided to a processor <NUM> within the controller <NUM>.

During operation of the valve <NUM>, the control signal <NUM> is commanded to a high current level to initially open the valve <NUM>, and then dropped to a lower "maintain" level to maintain the valve <NUM> in the open position for a sufficient time to allow fluid through the valve <NUM>. After the predefined duration, the current signal <NUM> is driven to zero, and the valve <NUM> is allowed to close. The total duration from initial opening to fully closed is the minimum impulse bit.

With continued reference to <FIG>, <FIG> illustrates a current (i) profile <NUM> and a voltage (v) profile <NUM> of a single exemplary minimum impulse bit with respect to time (t). The current profile <NUM> and the voltage profile <NUM> begin at t=<NUM> (point <NUM>), with the controller initiating a control open signal in the form of a steady current ramp up to point <NUM>. At point <NUM> of the current profile, the valve begins opening, and a current dip <NUM> occurs. The length of time between the controller beginning to output the open current and the valve beginning to open is referred to as an opening variable time <NUM>. The minimum impulse bit (MIB) is the time period from the time when the valve <NUM>, <NUM> is fully open (point <NUM>) to the time when the valve <NUM>, <NUM> is fully closed (point <NUM>).

Dashed line <NUM> represents the continued current ramp absent the valve opening. The current dip ceases at point <NUM>, which represents the "fully open" position of the valve. The current profile then continues ramping to the maximum current <NUM> of the open valve control signal, which is held for a predefined duration. After the predefined duration, the controller lowers the control current from the opening control level (at point <NUM>) to a maintain control level at point <NUM>. The maintain control current is held steady until the controller determines that the valve should close at point <NUM> (t=<NUM>). Once the close determination has been made, the controller drives the current to zero amps, causing the valve to close. The valve fully closes a point <NUM> (t=<NUM>).

As the valve does not fully close until some delay after control current has been driven all the way to zero, the controller monitors the voltage sensor signal as well as the current sensor signal. When the valve fully closes, at t=<NUM>, a voltage spike <NUM> occurs. The additional time <NUM> after the valve has been commanded closed and before the valve is fully closed impacts the minimum bit time, is a cause of variation within the minimum bit time, and is referred to as the close variable time <NUM>.

By monitoring the voltage and the current, the controller can determine the time from when the valve is controlled closed to the time when the valve is actually closed, and the minimum bit time of the valve is determined to be the duration that the controller drove the valve to be open plus the variable time <NUM>, <NUM>.

Existing systems utilize a preset controller on time, and the variable time results in variations of the minimum impulse bit. With continued reference to <FIG>, <FIG> schematically illustrates an exemplary method <NUM> to determine an exact minimum impulse bit length for a given valve <NUM>. Initially the valve <NUM> is assembled, installed and provided with a first open/close cycle in an "Initialize Valve" step <NUM>. During the open/close cycle the controller stores the current and voltage profiles <NUM>, <NUM> (as illustrated in <FIG>).

Once stored in a memory of the controller, the current profile <NUM> and the voltage profile <NUM> are analyzed to determine variable parameters in a "Determine Variable Parameters" step <NUM>. In one example, the variable parameters are the close variable time <NUM>, and the open variable time <NUM>. Once determined the variable times are stored in a controller memory, and the controller determines the minimum impulse bit time in a "Determine Minimum Impulse bit" step <NUM>.

The minimum impulse bit is the length of time from when the valve begins opening to when the valve becomes fully closed and is the time from the initial command on at point <NUM> to the command off at point <NUM>, plus the variable close time <NUM>, minus the variable on time <NUM>. Once determined, the minimum impulse bit is stored in a "Store MIB" step <NUM>, and the control sequence is adjusted to account for the actual minimum impulse bit of the specific valve.

In some examples, the minimum impulse bit generated via the above process is estimated to be accurate under all conditions for the specific valve, and can be utilized throughout operations of the liquid fuel rocket engine. In alternative examples, such as those where additional control capacity is available, the minimum impulse bit can be recalculated throughout operation of the liquid fuel engine with subsequent valve operations utilizing the most recently determined minimum impulse bit.

In yet another example, the minimum impulse bit can be determined under multiple conditions, such as engine pressure and battery voltage, and the like. In such an example, the determined minimum impulse bits are correlated in the controller with the environmental or other conditions that were present when the minimum impulse bit was determined. Subsequent operations of the valve <NUM> utilize the minimum impulse bit corresponding to the currently detected conditions of the valve, and can provide more accurate timing with less variation.

While described above with regards to a minimum impulse bit of a liquid fuel rocket engine, it is appreciated that the valve timing systems described herein can be applied to any fluid valve control system and are not limited to liquid fuel rocket engine applications.

Claim 1:
A valve controller (<NUM>) for a liquid fuel rocket engine (<NUM>) comprising:
at least one current sensor (<NUM>) input;
at least one voltage sensor (<NUM>) input;
a processor (<NUM>) and a memory, the processor (<NUM>) being connected to the at least one current sensor (<NUM>) input and the at least one voltage sensor (<NUM>) input, wherein the valve controller (<NUM>) is configured to determine at least one actual minimum impulse bit of a valve (<NUM>) based on a current profile (<NUM>) and a voltage profile (<NUM>) of a single valve operation, and wherein the valve controller (<NUM>) is configured to adjust valve controls to account for the at least one actual minimum impulse bit.