Valve timing systems for liquid fuel rockets

Abstract

According to one example, a liquid fuel rocket engine includes: a burner; a liquid fuel tank connected to the burner via a fuel line and a first valve; an oxidizer tank connected to the burner via an oxidizer line and a second valve; a valve controller configured to output a valve control current to the first valve, the valve controller storing instructions for determining at least one actual minimum pulse element of the valve based on a current curve and a voltage curve of a single operation of the first valve, and the valve controller is configured to adjust the valve control to take into account the at least one actual minimum pulse element.

Description

Technical Field

[0001] The present disclosure relates generally to valve control, and more particularly to valve timing and control for shortening the minimum impulse bit duration in liquid fuel rockets. Background Art

[0002] Liquid fuel rockets and other similar systems utilize valves and valve controls to control the flow of fuel into a burner, thereby controlling the thrust produced by the burner. During operation of a valve, the minimum period of time that the valve is maintained open is called the minimum impulse bit (MIB), and the minimum impulse bit dictates the granularity of control that can be applied to the flow of fluid through the valve, and therefore the granularity of thrust control of a liquid fuel rocket engine.

[0003] The minimum pulse element time for any given valve may vary due to variations in the opening and closing responses of the valve. This variation depends on any number of factors, including the age of the valve, wear on the valve, the environmental conditions in which the valve operates, etc. In order to compensate for this variation and provide consistent, predictable control, discrete valve operations are typically run slightly longer than the actual minimum pulse element of the valve. Summary of the invention

[0004] In one example, a valve controller 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 pulse element of the valve based on a current curve and a voltage curve of a single valve operation, and wherein the valve controller is configured to adjust the valve control to take into account the at least one actual minimum pulse element.

[0005] In another example of the previously described valve controller, the actual minimum pulse element is associated with at least one external factor, and wherein the valve controller is configured to adjust valve control to account for the at least one actual minimum pulse element and the at least one external factor.

[0006] In another example of any of the previously described valve controllers, the external factor is at least one of an engine pressure and a battery voltage.

[0007] In another example of any of the previously described valve controllers, the valve controller is configured to determine at least one actual minimum pulse element based on an initial operation of the valve.

[0008] In another example of any of the previously described valve controllers, the valve controller is further configured to periodically determine an updated minimum pulse element of the valve.

[0009] In another example of any of the previously described valve controllers, the valve controller is further configured to adjust valve control based on a most recently determined updated minimum pulse element of the valve.

[0010] In another example of any of the previously described valve controllers, the minimum pulse element is based in part on an initial valve opening time determined as a dip in a ramp up of the current curve.

[0011] In another example of any of the previously described valve controllers, the minimum pulse element is based in part on a fully closed valve time determined as a time between a voltage peak and a valve control current driven to zero by the valve controller.

[0012] In another example of any of the previously described valve controllers, the minimum pulse element is based in part on an initial valve opening time, which is determined as a drop in the ramp-up of the current curve.

[0013] In another example of any of the previously described valve controllers, each of the at least one current sensor and the at least one voltage sensor is connected to the valve control signal line and is configured to sense the valve control signal line.

[0014] In another example of any of the previously described valve controllers, the valve control signal line is controllably connected to a liquid fuel rocket engine valve.

[0015] In another example of any of the previously described valve controllers, a liquid fuel rocket engine valve at least partially controls the flow of liquid fuel from a fuel reservoir to a combustor.

[0016] An exemplary method for determining a minimum pulse element of a valve includes: monitoring a current curve and a voltage curve of a valve control signal; determining an initial valve opening time as the starting point of a decline in a current ramp, and determining a valve full closing time as a voltage peak of the valve control signal; and determining the minimum pulse element of the valve as the length of time from the initial valve opening time to the valve full closing time.

[0017] Another example of the above method includes correlating a minimum pulse element of the valve with at least one external environmental factor.

[0018] In another example of any of the methods above, the at least one external environmental factor includes at least one of engine pressure and battery voltage.

[0019] Another example of any of the above methods includes periodically re-iterating the method and updating the determined minimum pulse element for the valve at each iteration.

[0020] According to one example, a liquid fuel rocket engine includes: a burner; a liquid fuel tank connected to the burner via a fuel line and a first valve; an oxidizer tank connected to the burner via an oxidizer line and a second valve; a valve controller configured to output a valve control current to the first valve, the valve controller storing instructions for determining at least one actual minimum pulse element of the valve based on a current curve and a voltage curve of a single operation of the first valve, and the valve controller is configured to adjust the valve control to take into account the at least one actual minimum pulse element.

[0021] Another example of the liquid fuel rocket engine described above includes at least one current sensor configured to sense a current curve of the valve control current and at least one voltage sensor configured to sense a voltage curve of the valve control current.

[0022] These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 An exemplary liquid fuel rocket engine is shown highly schematically.

[0024] Figure 2 Schematically showing the Figure 1 An exemplary valve control system utilized in a liquid fuel rocket engine.

[0025] Figure 3 Schematically showing the Figure 2 Valve timing diagram for a valve control system.

[0026] Figure 4 A process for operating a valve is schematically shown, using empirical timing data to determine the minimum pulse element for a particular valve. DETAILED DESCRIPTION

[0027] Figure 1An exemplary highly schematic liquid fuel rocket engine 10 is schematically shown. Systems and controls of the engine 10 that are not relevant to the present disclosure are omitted and / or simplified for purposes of explanation, and an actual liquid fuel rocket engine implementing the concepts described herein can include any number of additional configurations and systems as would be necessary to implement an actual example. The liquid fuel rocket engine 10 includes a liquid fuel reservoir 20, an oxidizer reservoir 30, and a burner 40. The liquid fuel reservoir 20 is connected to the burner 40 via a fuel line 22, and a fluid valve 24 controls the flow of liquid fuel into the burner 40. Similarly, the oxidizer reservoir 30 is connected to the burner 40 via a fluid line 32, and the flow of oxidizer into the burner 40 is controlled via a fluid valve 34. Each of the valves 24, 34 is controlled via a controller 50.

[0028] Within the combustor 40, liquid fuel and oxidant are mixed and ignited, and the resulting combustion products are discharged through the nozzle 42, thereby generating thrust. The amount of thrust generated is controlled by the amount of liquid fuel injected into the combustor 40. Due to a variety of conditions (such as wear and environmental conditions and valve-to-valve manufacturing variations), the minimum pulse element of the valve 24 can include variations and fall within a tolerance window. In order to provide the most discrete control possible, it is desirable to minimize the variation.

[0029] In the continued reference Figure 1 At the same time, Figure 2 A valve configuration 100 is schematically shown that includes an electrically controlled valve 110 that allows a fluid 120 to pass through the valve 110 when the valve 110 is open, and prevents the fluid 120 from passing through the valve 110 when the valve 110 is closed. The valve 110 is controlled via a current signal 130. The current signal 130 originates from a current driver 142 portion of a controller 140. A voltage sensor 132 and a current sensor 134 are configured to monitor the voltage and current (respectively) of the current signal 130 as inputs to the valve 110. The sensor output of each sensor 132, 134 is provided to a processor 144 within the controller 140.

[0030] During operation of valve 110, control signal 130 is commanded to a high current level to initially open valve 110, and then reduced to a lower "maintaining" level to maintain valve 110 in an open position for a sufficient time to allow fluid to pass through valve 110. After a predefined duration, current signal 130 is driven to zero and valve 110 is allowed to close. The total duration from initial opening to full closure is the minimum pulse element.

[0031] In the continued reference Figure 1 and Figure 2 At the same time, Figure 3A current (i) curve 210 and a voltage (v) curve 220 of a single exemplary minimum impulse unit are shown with respect to time (t). The current curve 210 and the voltage curve 220 begin at t=0 (point 201), where the controller initiates a control opening signal in the form of a steady current ramp up to point 202. At point 202 of the current curve, the valve begins to open, and a current drop 203 occurs. The length of time between when the controller begins to output the opening current and when the valve begins to open is referred to as the open variable time 213. The minimum impulse unit (MIB) is the time period from the time when the valve 24, 34 is fully open (point 205) to the time when the valve 24, 34 is fully closed (point 209).

[0032] Dashed line 204 represents the continuous current ramp without the valve opening. The current drop ends at point 205, which represents the "fully open" position of the valve. The current curve then continues to ramp up to a maximum current 206 of the open valve control signal, which is maintained for a predefined duration. After the predefined duration, the controller reduces the control current from the open control level (at point 206) to the maintenance control level at point 207. The maintenance control current is held steady until the controller determines that the valve should be closed at point 208 (t=1). Once the closing decision has been made, the controller drives the current to zero amperes, causing the valve to close. The valve is fully closed at point 209 (t=2).

[0033] Since the valve does not fully close until some delay after the 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 is fully closed, at t=2, a voltage peak 221 occurs. The additional time 211 after the valve has been commanded closed and before the valve is fully closed affects the minimum meta time, is responsible for variations in the minimum meta time, and is referred to as the closing variable time 211.

[0034] By monitoring the voltage and current, the controller can determine the time from when the valve is controlled to close to when the valve is actually closed, and the minimum meta time of the valve is determined as the duration of the controller driving the valve open plus the variable time 211, 213.

[0035] Existing systems utilize preset controller on-times, and variable times result in variations in the minimum pulse element. Figure 1-3 At the same time, Figure 4 An exemplary method 300 for determining an accurate minimum pulse cell length for a given valve 110 is schematically shown. Initially, in an "initialize valve" step 310, the valve 110 is assembled, installed, and provided with a first opening / closing cycle. During the opening / closing cycle, the controller stores the current curve 210 and the voltage curve 220 (e.g., Figure 3as shown in ).

[0036] Once stored in the controller's memory, the current curve 210 and the voltage curve 220 are analyzed to determine the variable parameters in a "determine variable parameters" step 320. In one example, the variable parameters are the closing variable time 211 and the opening variable time 213. Once determined, the variable times are stored in the controller memory and the controller determines the minimum pulse element time in a "determine minimum pulse element" step 330.

[0037] The minimum pulse element is the length of time from when the valve begins to open to when the valve is fully closed, and is the time from the initial commanded opening at point 201 to the commanded closing at point 208 plus the variable closing time 211 minus the variable opening time 213. Once determined, the minimum pulse element is stored in a "Store MIB" step 340, and the control sequence is adjusted to account for the actual minimum pulse element for the particular valve.

[0038] In some examples, for a particular valve, the minimum pulse element generated via the above process is estimated to be accurate under all conditions, and can be utilized throughout the operation of the liquid fuel rocket engine. In alternative examples (such as those where additional control capabilities are available), the minimum pulse element can be recalculated throughout the operation of the liquid fuel engine, wherein subsequent valve operations utilize the most recently determined minimum pulse element.

[0039] In yet another example, the minimum pulse element can be determined under a variety of conditions, such as engine pressure and battery voltage. In such an example, the determined minimum pulse element is associated in the controller with the environmental conditions or other conditions that existed when the minimum pulse element was determined. Subsequent operation of the valve 110 utilizes the minimum pulse element corresponding to the current detected condition of the valve, which can provide more accurate timing with less variation.

[0040] Although described above with respect to a minimum pulse element for a liquid fuel rocket engine, it will be appreciated that the valve timing system described herein can be applied to any fluid valve control system and is not limited to liquid fuel rocket engine applications.

[0041] It is further understood that any of the concepts described above can be used alone or in combination with any or all of the other concepts described above. Although embodiments of the present invention have been disclosed, those of ordinary skill in the art will recognize that certain modifications will fall within the scope of the present invention. For this reason, the attached claims should be studied to determine the true scope and content of the present invention.

Claims

1. A valve controller, comprising: at least one current sensor input; at least one voltage sensor input; a processor and a memory, the processor 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 pulse element of the valve based on a current curve and a voltage curve of a single valve operation, and wherein the valve controller is configured to adjust valve control to account for the at least one actual minimum pulse element; The minimum pulse element is the minimum time period during which the valve is maintained open.

2. The valve controller according to claim 1, characterized in that: The actual minimum pulse element is associated with at least one external factor, and wherein the valve controller is configured to adjust the valve control to account for the at least one actual minimum pulse element and the at least one external factor.

3. The valve controller according to claim 2, characterized in that: The external factor is at least one of an engine pressure and a battery voltage.

4. The valve controller according to claim 1, characterized in that: The valve controller is configured to determine the at least one actual minimum pulse element based on an initial operation of the valve.

5. The valve controller according to claim 1, characterized in that: The valve controller is further configured to periodically determine an updated minimum pulse element for the valve.

6. The valve controller according to claim 5, characterized in that: The valve controller is further configured to adjust valve control based on the most recently determined updated minimum pulse element of the valve.

7. The valve controller according to claim 1, characterized in that: The minimum pulse element is based in part on an initial valve opening time determined as a dip in the ramp-up of the current curve.

8. The valve controller according to claim 1, characterized in that: The minimum pulse element is based in part on a fully closed valve time, which is determined as the time between a voltage peak and a valve control current being driven to zero by the valve controller.

9. The valve controller according to claim 8, characterized in that: The minimum pulse element is based in part on an initial valve opening time determined as a dip in the ramp-up of the current curve.

10. The valve controller according to claim 1, characterized in that: Each of the at least one current sensor and the at least one voltage sensor is connected to a valve control signal line and is configured to sense the valve control signal line.

11. The valve controller according to claim 10, characterized in that: The valve control signal line is controllably connected to a liquid fuel rocket engine valve.

12. The valve controller according to claim 11, characterized in that The liquid fuel rocket engine valve at least partially controls the flow of liquid fuel from a fuel reservoir to a combustor.

13. A method for determining a minimum pulse element of a valve, comprising: Monitor the current curve and voltage curve of the valve control signal; determining an initial valve opening time as the start of a drop in the current ramp-up, and determining a valve full closing time as a voltage peak of a control signal for said valve; as well as The minimum pulse element of the valve is determined as the length of time from the initial valve opening time to the valve fully closing time.

14. The method according to claim 13, characterized in that The method further includes correlating a minimum pulse element of the valve to at least one external environmental factor.

15. The method according to claim 14, characterized in that The at least one external environmental factor includes at least one of engine pressure and battery voltage.

16. The method according to claim 13, characterized in that The method further includes periodically re-iterating the method and updating the determined minimum pulse element of the valve at each iteration.

17. A liquid fuel rocket engine comprising: Burner; a liquid fuel reservoir connected to the burner via a fuel line and a first valve; an oxidant reservoir connected to the burner via an oxidant line and a second valve; as well as A valve controller configured to output a valve control current to the first valve, the valve controller storing instructions for determining at least one actual minimum pulse element of the valve based on a current curve and a voltage curve of a single operation of the first valve, and the valve controller configured to adjust the valve control to take into account the at least one actual minimum pulse element.

18. The liquid fuel rocket engine according to claim 17, characterized in that: The liquid fuel rocket engine further includes at least one current sensor configured to sense a current curve of the valve control current and at least one voltage sensor configured to sense a voltage curve of the valve control current.

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