Patent Application
20130056661
1. Field of the Invention
The invention relates to an actuation system for an electromagnetic valve, and more particularly to a radial permanent linear motor type actuation system for an electromagnetic valve.
2. Description of the Related Art
Currently known valve actuation systems for motors are mainly cam actuation systems, the opening and closing of the valve depends on the shape of the cam and thus the lift range and phase angle of the valve is difficult to adjust with the working conditions. For example, when a gasoline motor runs with a low load, the jaw opening of its air damper is very small so as to reduce the air input, and the damper loss is great. Subsequently, valve actuation machines with multiple cams emerge, which, however, can only allow minor adjustment. Therefore, electromagnetic valve actuation systems come into being, which can adjust the phase angle of valves and the air input by adjusting the phase angle of the inlet electromagnetic valve systems, thus the air damper can be removed and the damper loss can be eliminated. However, the electromagnet has two shortcomings: (1) large current is required for it to produce the same attraction force when the air gap is large; (2) power consumption is needed when the valve maintains an open state or closed state.
For conventional electromagnetic valve actuation systems with a single-spring structure, the single spring leaves the air valve in a normally closed state. High current is required when the valve tries to open through overcoming the spring force by the electromagnetic attraction force, thus the electromagnetic valve actuation demands a relatively high power, up to 5 KW or so, and is of no practical value.
In recent years, an actuation system for an electromagnetic valve with a dual-spring structure has been developed. Two compressed springs are fitted one against the other and connected with a valve rod or armature, and when they are in the rest position, the valve is half open. The valve, armature, and the springs form a vibration system and when the valve and the armature deviate from the rest position, the system will vibrate to realize the opening and closing of the valve. The actuation system for an electromagnetic valve with the dual-spring structure includes two electromagnets, the attraction force of which supplements the energy loss of the system and allows the valve to keep closed or picked-up, thus its power is significantly reduced, yet the two shortcomings above still exist. Besides, when the electromagnets are being picked up, the attraction force is high and problems of valve hitting valve seat or armature hitting electromagnet may be caused, so the supplemented energy is required to be appropriate and preferably closed-loop control shall be conducted on the current to control the seating speed; and in order to increase the efficiency, it is better to supplement energy when the armature is nearer to the electromagnet, yet the time for supplementing is short and energy supplementing is difficult to control, therefore, it is difficult to balance the two aspects. In addition, valve retaining also requires relatively high energy, and generally, the power of a single valve of this system can reach above 100 W, accordingly, a conventional 16-valve motor will demand power of up to 1-2 kW, which is still very high.
In view of the above-described problems, it is one objective of the invention to provide an actuation system for an electromagnetic valve.
To achieve the above objective, in accordance with one embodiment of the invention, there is provided an actuation system for an electromagnetic valve, comprising: an actuation housing; an upper electromagnet assembly and a lower electromagnet assembly, both being installed inside the actuation housing and the upper electromagnet assembly being arranged above the lower electromagnet assembly, the upper electromagnet assembly comprising a lower end surface which operates as an upper pickup surface, and the lower electromagnet assembly comprising an upper end surface which operates as a lower pickup surface; an armature, the armature being disposed between the upper pickup surface and the lower pickup surface and capable of moving up and down; a radial permanent magnet; a valve spring; and a valve rod. Each electromagnet assembly comprises an inner magnet core, a coil kit, and an outer magnet core, which are sleeved with each other from inside to outside. the coil kit comprises a coil winding and a magnetizer, and the coil winding and the magnetizer wind the inner magnet core by turns. The radial permanent magnet is disposed between the inner magnet core and the outer magnet core. The valve spring is disposed at an inner side of the inner magnet core. The valve rod passes through a center formed by the valve spring and is fixedly connected with the armature. The armature is interconnected with at least one radial permanent magnet to form an actuation compound rotor, or, the armature and the radial permanent magnet are independent with each other. The valve rod is capable of moving with the move of the armature up and down.
Advantages of the invention are summarized as follows:
The invention is described hereinbelow with reference to the accompanying drawings, in which:
To further illustrate the invention, experiments detailing an actuation system for an electromagnetic valve are described. It should be noted that the following examples are intended to describe and not limited to the invention.
As shown in
Each electromagnet assembly 2, 3 comprises an inner magnet core 5, a coil kit 6, and an outer magnet core 7, which are sleeved with each other from inside to outside. The coil kit 6 comprises a coil winding 6a and a magnetizer 6b, and the coil winding 6a and the magnetizer 6b wind the inner magnet core 5 by turns. The radial permanent magnet 8 is disposed between the inner magnet core 5 and the outer magnet core 7. The valve spring 9 is disposed at an inner side of the inner magnet core 5. The valve rod 10 passes through a center formed by the valve spring 9 and is fixedly connected with the armature 4. The armature 4 is interconnected with at least one radial permanent magnet 8 to form an actuation compound rotor, or, the armature 4 and the radial permanent magnet 8 are independent with each other; and the valve rod 10 is capable of moving with the move of the armature 4 up and down.
The actuation housing 1 can be fixed on a cylinder head of a motor or integrated with the cylinder head.
The magnetic circuit and working process of this invention is as follows:
By controlling the direction of the exciting current passing through the coil windings 6a of the upper and lower electromagnet assemblies 2 and 3 separately, the picking-up and releasing of the pickup surfaces 2a and 3a of the armature 4 can be controlled, and thus the up-and-down movement of the armature 4 can be controlled, i.e. the up-and-down movement of the valve rod 10 can be controlled, thereby achieving the opening and closing of the valve.
Radial magnetic flux 8a emitted by the radial permanent magnet 8 (the arrow direction as shown in
In embodiments of this invention, the structure of the radial permanent magnet 8 and the coil kit 6 can optimize the magnetic circuit of the permanent magnet linear motor, to form a parallel permanent magnetic circuit, realize permanent magnet pickup type retaining, reduce (or removing) valve retaining current significantly as well bring down the range of variation of the magnetic strength in the magnetic circuit, thus lowing the core loss.
The magnetic field of a mono-polar radial permanent magnet linear motor rotor will pass through the coil kit 6 in a radial way, and in order to ensure sufficient electromagnetic force and a lower resistance, the coil kit is required to have a relatively large thickness; here, a structure with the coil winding 6a and the magnetizer 6b winding by turns is adopted to reduce the working air gap of the magnetic circuit significantly.
Each valve spring 9 is installed in a valve spring seat 9a compressed. The valve spring valve 9a is disposed inside the inner magnet core 5, and the valve spring 9 each has its one end push against the spring valve 9a and the other end push against the armature 4. When the attraction force between the armature 4 and the pickup surface is greater than the spring force of the valve spring 9, the armature 4 will be picked up to the pickup surface; and when the former is lower than the latter, the armature 4 will be released.
A valve sleeve 10b is mounted on the upper part of the valve rod 10; the valve rod 10 can be disposed inside the valve sleeve 10b in a sliding way. The valve sleeve 10b is fixed on the cylinder head of the motor. The top of the valve sleeve 10b is provided with a valve seal 10c.
As shown in
The radial permanent magnet 8 can be disposed either between the inner magnet core 5 and the coil kit 6 or between the coil kit 6 and the outer magnet core 7. In the example, it is the former case, namely, space is left between the inner magnet core 5 and the coil kit 6 for the radial permanent magnet 8 to be disposed in and to move up and down. Between the outer wall of the inner magnet core 5 and the inner wall of the joint liner ring 12a is a first air gap 11 which is used to increase the magnetic resistance.
In an example, the structure with the coil winding 6a and the magnetizer 6b winding by turns may have the following two kinds of modes so as to facilitate efficient processing. One is as shown in
In a second winding structure, since the magnetizer 6b has no current in it and the electric potential is equal, the voltage between an adjacent conductor and the magnetizer can be as high as the voltage at both ends of the coil, thus the insulation thickness between the conductor and the magnetizer is required to be increased. In order to solve this problem, paralleling silicon strip and coil are adopted, make it possible for the electric potential of the silicon strip and the coil to change, and the voltage between the adjacent conductor and the silicon plate is reduced significantly. The method of short-connecting both ends of the silicon strip with those of the conductor can be adopted or the strip conductor can be superposed with the silicon strip without insulation, then coat the double-layer structure with insulation materials and finally wind for coils, making the electric potential of adjacent conductor and silicon plate equal and reducing the insulation thickness among coils. Since the magnetic field emitted from the permanent magnetic ring is radial, the macro-sectional area in the magnetic circuit reduces with the radius decrease; in order to balance the magnetic strength in the magnetic circuit and take full advantage of the magnetic conduction materials, the internal and external thickness of the magnetizer is designed to be inversely proportional to the internal and external perimeter (or diameter), thus the section is thick internally and thin externally, making the section area of the magnetic conduction part relatively stable; in order to make the internal and external thickness of the coil after superposing consistent, the strip conductor is thin internally and thick externally, thus balancing the thickness variation of the magnetizer.
As an example of this invention, as shown in
In an example, as shown in
In this embodiment, due to the limitation of volume, the inner and outer magnet cores 5 and 7 of the upper and lower electromagnet assemblies 2 and 3 restrict the increase of the magnetic flux, and the radial permanent magnetic ring 8 cannot be too high; in order to make the permanent magnet ring in the middle of the coil kit in most cases, the joint liner ring 12a is disposed between the radial permanent magnet 8 and the armature 4, this structure allows the magnetic flux to flow in two directions.
The radial permanent magnets 8 of both the upper and lower electromagnet assemblies 2 and 3 can be connected with the armature 4 to form the actuation compound rotor. Optionally, one of the radial permanent magnets 8 of the upper and lower electromagnet assemblies 2 and 3 can be connected to with the armature 4 to form the actuation compound rotor, with the other fixed between the inner magnet core 5 and the outer magnet 7 and does not move along with the actuation compound rotor.
In one of the embodiments, as shown in
In a second embodiment, as shown in
Furthermore, the combined-type compound rotor also comprises a locating ring 12f clamping the armature 4; one end of the joint liner ring 12a is connected to the armature 4 via the locating ring 12f and one end of the joint sleeve 12b close to the locating ring is disposed with a sleeve flange 12g; the joint sleeve 12b is disposed at the side of the joint liner ring 12a and integrates the joint liner ring 12a and the radial permanent magnet 8 into a whole, and the sleeve flange 12g is concentrically superposed on the locating ring 12f. Then, a screw is threaded through the sleeve flange 12g and the armature bracket joint hole 12i to fix them. Moreover, a locating step is disposed on the locating ring 12f, one side of the locating step is matched up with the armature locating step 4a and the armature bracket locating step 12h and the other side cooperates well with the joint liner ring 12a to realize a positioning function. In this embodiment, the locating ring 12f can strengthen the armature 4 comprising the fan-shaped magnetic sheet and realize a positioning function. The radial permanent magnet 8 is a ring-shaped magnet with its interior and exterior each as one pole, and covers the joint sleeve 12b. The sleeve flange 12g presses on the locating ring 12f and is installed on the armature 4 and fixed with screws. In order to reduce the magnetic resistance of the magnetic circuit and increase the magnetic field, the joint sleeve 12b is made of magnetic conduction materials. Besides, the locating ring 12f can adopt high-resistance non-magnetic conduction materials and high mechanical strength materials, mainly to strengthen the armature 4. Generally, the sleeve flange 12g and the joint liner ring 12a adopts high-resistance non-magnetic conduction materials and the joint sleeve 12b adopts high-resistance and highly magnetic conduction materials.
In a second embodiment of the compound rotor above, the combined-type compound rotor can be changed to one with only one linear motor rotor, i.e. the joint sleeve 12b, joint liner ring 12a, radial permanent magnet assembly 8, armature 4, locating ring 12f, and sleeve flange 12g are superposed concentrically in proper sequence and fixed together with a screw through the armature bracket joint hole 12i to constitute a combined-type compound rotor with a single radial magnet; at the same time, another set of joint sleeve 12b, joint liner ring 12a, radial permanent magnet assembly 8 and armature 4 are directly fixed between the inner magnet core 5 and the outer magnet core 7.
In a third embodiment, as shown in
As shown in
Specifically, the inner magnet core 5 comprises a magnetic group 5b and a cylindrical inner magnetic core frame 5c (refer to
Refer to
In this example, when the armature 4 of the actuation compound rotor is combined with the upper and lower pickup surfaces 2a and 3a, the radial permanent magnet 8 will produce absorption force. In the magnetic circuit constituting the linear motor, magnetic flux split flows to two ends. Permanent magnet can produce absorption force, but in case that it is incapable of producing enough absorption force, this example chooses to increase the magnetic resistance on the original linear motor, which can substantially increase the magnetic flux passing through the armature 4 during the pickup of the armature 4 to ensure sufficient absorption force for the pickup of the armature 4 and the pickup surfaces 2a, 3a, and to retain the valve closed or open. Here, there are two methods to increase the magnetic resistance:
A first method to increase the magnetic resistance is to expand the air gap. There is a first air gap 11 in the open end of the magnet core. When the joint liner ring is a magnetizer, e.g. the first air gap 11 exists between the outer wall of the inner magnet core 5 and the inner wall of the joint liner ring 12a, and the inner wall of the outer magnet core and the outer wall of the joint liner ring 12a (refer to
A second method to increase the magnetic resistance is to change the magnetic conductivity. In
A manufacturing method of the magnetic conductivity changeable iron core can be: changing the proportion of insulation materials to form the gradient of magnetic conductivity decrease from the open end to the closed end of iron core, or single-direction suppressing by setting the suppressing punch on the opening part to result in the reduction of density of magnet core from the open end to the closed end owing to the friction, thus causing a higher magnetic conductivity in the open end.
Furthermore, the structure of the permanent magnetic linear motor formed in the mode of execution can generate electromotive force to reduce the actuation current when the armature 4 is farther from the pickup surface. The method to increase air gap or change magnetic conductivity can be used to enhance the magnetic resistance around the connection member 5a and the magnetic circuit of the coil cover 6d, thus the magnetic resistance of the magnetic circuit of linear motor is not too high when the armature 4 gets released to ensure the working magnetic strength of the linear motor, meanwhile the magnetic resistance between the armature 4 and the pickup surface during the pickup of the armature 4 is greatly reduced and the magnetic flux through the armature 4 and pickup surface is substantially increased, thus generating sufficient absorption force.
The specific magnetic circuit and working process is: the radial magnetic flux 8a emitted by the radial permanent magnet 8 flows to the two ends via the outer magnet core 7 and then flows into the inner magnet core 5 via the magnetic circuit of the two ends, and returns to the radial permanent magnet 8. Thus, two parallel magnetic circuits are formed. For the electromagnet assembly, when the armature 4 moves away from the upper pickup surface 2a, the magnetic resistance between the armature 4 and the upper pickup surface 2a is very high, and the magnetic flux of the radial permanent magnet 8 flowing through the armature is little. On both ends of the inner and outer magnet cores 5 and 7, most of the magnetic flux 8a flows through the connection member 5a and the magnetic conduction coil cover 6d; when the armature 4 is being picked up to the upper pickup surface 2a, the magnetic resistance between the armature 4 and the upper pickup surface 2a is very low. Since the air gap 11 and 13 in the magnetic circuit can increase the magnetic resistance, the magnetic flux flowing through the connection member 5a and the magnetic coil cover 6d is reduced and that flowing through the armature 4 and the upper pickup surface 2a is increased to make the armature 4 retained in its pickup status. When release is needed, reverse exciting current goes through the coil winding 6a, thus the magnetic flux of the armature 4 is reduced and the absorption force is also decreased, eventually the armature 4 gets released. The abovementioned parallel magnetic circuit retaining mechanism can cancel the retaining current, decrease the demagnetizing effect of permanent magnet and the magnetic strength variation of the magnetic circuit, and reduce the energy consumption.
In addition, when adopting the structure of the inner magnet core 5 shown in
In
In the actuation system shown in
In the actuation system shown in
In the actuation system shown in
In the actuation system shown in
As shown in
Specifically, the gap adjusting mechanism 14 comprises a gap adjusting hydraulic cylinder, and the gap adjusting hydraulic cylinder has a gap adjusting cylinder body 14a and a gap adjusting piston 14b that can slide up and down and is connected to the gap adjusting cylinder body 14a. The gap adjusting cylinder body 14a is fixedly connected to the actuation housing 1. One end of gap adjusting piston 14b presses on the surface of upper electromagnet assembly 2. Besides, clearance fit is used between the gap adjusting piston 14b and the gap adjusting cylinder body 14a to allow the leakage of internal liquid due to external pressure.
Furthermore, a one-way valve is installed on the inlet of gap adjusting cylinder body 14a and connected with motor lubricant. When the valve is closed, namely the armature 4 and the upper pickup surface 2a are in a pickup status, the armature 4 will produce relatively large downward pull towards the upper electromagnet assembly 2. The absorption force of the armature 4 is adjusted to make the pull higher than the pressure of the valve spring 9, thus reducing the pressure of the gap adjusting cylinder body 14a, then the one-way valve is open and external lubricant fills the gap adjusting cylinder body 14a. When the armature 4 is in other states, the downward pull of the armature 4 towards the upper electromagnet assembly 2 is very low, the gap adjusting piston 14b makes the one-way valve closed under the pressure of the spring, and lubricant slowly leaks through the gap between gap adjusting cylinder body 14a and the gap adjusting piston 14b. The process does not need human control.
As an example, as shown in
Specifically, the stoke adjusting mechanism 15 comprises a stoke adjusting hydraulic cylinder. The stoke adjusting hydraulic cylinder comprises a stoke adjusting cylinder body 15a and a stoke adjusting piston 15b. The stoke adjusting piston 15b can slide up and down and is connected to the stoke adjusting cylinder body 15a. The stoke adjusting cylinder body 15a is fixedly connected on the actuation housing 1. One end of the stoke adjusting piston 15b is against the lower surface of the lower electromagnet assembly 3. The lower pickup surface 3a of the lower electromagnet assembly 3 can float up and down under the push of the stoke adjusting piston 15b. As the position of the pickup surface 3a is adjusted, the mobile distance of the armature 4 is changed, i.e. the stroke of the valve rod 10 which is fixedly connected with the armature 4 is adjusted.
Furthermore, an inlet with a one-way valve and an outlet with a priority valve are disposed in the stoke adjusting cylinder body 15a. The inlet and outlet of the stoke adjusting hydraulic cylinder of the same kind valves of all different cylinders are connected in parallel respectively and then connected to the oil line by an electronically controllable valve. As the compression amount of the valve spring 9 changes periodically in the process of the valve rod 10 driving the movement of the armature 4, the pressure in stoke adjusting cylinder body 15a also changes periodically, either higher than external oil line pressure or lower than external pressure. At the same time, the working phase of the valve of each cylinder is different. Therefore, the inlet and outlet valve of the stoke adjusting cylinder body 15a of different cylinders can be opened according to phases. By controlling the on and off time, the inlet and outlet amount of each stoke adjusting cylinder body 15a can be controlled and the valve stroke can be controlled through detecting displacement and speed sensor.
As shown in
This execution mode can get position parameter with low cost, i.e. get the voltage and the change rate of the voltage on inductor 17a or get the distance between the armature 4 and the pickup surface of the electromagnet assembly according to the principle that the inductance of electromagnet assembly will increase with the decrease of the distance of the armature 4.
The top of the valve rod 10 is disposed with a speed sensor 16, which can be a radial permanent magnet ring rotor speed sensor, a radial permanent magnet columnar rotor speed sensor or an axial permanent magnet columnar rotor speed sensor.
Specifically, the radial permanent magnet ring rotor speed sensor is as shown in
Here, the top of the inner magnet core of sensor 16g is fixedly connected to the sensor shell 16a through an end cover 16h. Furthermore, the end cover 16h is fixed with the flange plate on the sensor shell 16a through a mounting hole 16i by screw 16j. The non-magnetic conduction ring 16d can be high-resistance non-magnetic conduction ring and the sensor shell 16a can be made of magnetic conduction materials.
The radial magnet 16c moves up and down with the valve rod 10 through the actuation rod 16b and produces voltage in direct proportion to movement speed in the sensor coil 16f. The screw can adopt non-magnetic conduction materials so as to lower the magnetic conduction section of this part and stabilize the magnetic field.
Specifically, the radial permanent magnet columnar rotor speed sensor is as shown in
The sensor coil 16q, sensor coil former 16o, and sensor shell 16k can be compressed to a whole by using iron cores separately.
The columnar rotor comprising the actuation rod 16m and the radial magnet 16n moves up and down with the valve rod 10 and produces voltage in the sensor coil 16q in direct proportion to movement speed.
Specifically, the axial permanent magnet columnar rotor speed sensor is as shown in
The sensor coil 16x, sensor coil former 16y, and sensor shell 16r can be compressed to a whole by using iron cores separately.
The working process of the actuation system of this embodiment is as following:
Step 1: initialize the valve and inspect the state of each sensor of the system. For inductive position and speed measurement circuit, judge the pickup state of valve actuation armature 4 though the method of measuring electromagnet coil inductance. If the valve is in the middle position, make it in a closed position through the method of supplementing energy for many times, and calibrate the temperature drift of the speed sensor (zero calibration and permanent magnet temperature influence calibration); then inspect the absolute corner of bent axle and define the working sequence and working phase of each cylinder;
Step 2: start the motor, inspect the corner of bent axle in time and confirm the opening moment of each cylinder according to the working sequence and working phase of each cylinder;
Step 3: open the valve. When the valve needs to be opened (advance corner needs to be considered), supply a reverse excitation current to the coil winding 6a of the upper electromagnet assembly 2 to make the magnetic field direction produced in the coil opposite to that of the permanent magnet and overcome the attraction force of the latter. When the attraction force of the permanent magnet is smaller than the spring force, compound rotor will open the valve driven by the valve spring 9.
Step 4: central control of valve movement. Continue to supply current through the coil on coil winding 6a of the upper electromagnet assembly 2 and produce downward actuation force with the armature 4 repulsion of the electromagnet and the electric power of the linear motor rotor to supplement system energy. The speed sensor measures the speed and calculates the displacement according to the current size, then increase or decrease the current according to the relationship of set speed and displacement. Meanwhile, when the energy supplemented is higher, the coil winding 6a of the lower electromagnet assembly 3 can also produce downward actuation force through current, especially in the opening process of valve, where due to the existence of high pressure gas which may impulse the valve upwardly, the simultaneous function of two coils can help to reduce current. In the process of movement, the distance between the armature and upper pickup surface becomes farther and farther while the distance to the lower pickup surface is nearer and nearer. The upper electromagnet assembly 2 is transformed from mainly working in an electromagnet state to mainly working in a linear motor state and the lower electromagnet assembly 3 is transformed from mainly working in a linear motor state to mainly working in an electromagnet state.
Step 5: pickup speed control of valve movement. When the armature 4 is near to the pickup surface 3a of the lower electromagnet assembly 3, reduce the current of the lower electromagnet assembly 3 in advance first to avoid relative large attraction force produced between the coil winding 6a of the lower electromagnet assembly 3 and the armature 4. If necessary, supply reverse current to the upper electromagnet assembly 2, but not limited to the upper electromagnet assembly 2. When the performance of the magnet core used is good enough, reverse current can also be supplied to the electromagnet assembly 3. When the armature 4 moves to the pickup position, speed of the whole system will be lowered to a properly low speed, the current in the upper and lower electromagnet assemblies 2, 3 shall be lowered to zero fast, the pickup surface of the lower electromagnet assembly 3 and the pickup surface of compound rotor will produce enough attraction force to make the attraction force in the pickup surface of compound rotor sufficient to overcome the spring force of the valve spring and make the valve kept in its open position. At this time, make dynamic calibration to the speed sensor. Valve closing process is similar to method above. When the motor stops, pick the valve up to its closed position, which is helpful for the next time of start.
The actuation system for the electromagnetic valve of this execution mode is a dual-valve electromagnetic actuation system.
Specifically, as shown in
While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201010162840.X | May 2010 | CN | national |
| 201010526680.2 | Nov 2010 | CN | national |
This application is a continuation-in-part of International Patent Application No. PCT/CN2011/000786 with an international filing date of May 5, 2011, designating the United States, now pending, and further claims priority benefits to Chinese Patent Application No. 201010162840.X filed May 5, 2010, and to Chinese Patent Application No. 201010526680.2 filed Nov. 1, 2010. The contents of all of the aforementioned applications, including any intervening amendments thereto, are incorporated herein by reference. Inquiries from the public to applicants or assignees concerning this document or the related applications should be directed to: Matthias Scholl P.C., Attn.: Dr. Matthias Scholl Esq., 14781 Memorial Drive, Suite 1319, Houston, Tex. 77079.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2011/000786 | May 2011 | US |
| Child | 13668364 | US |
