Sma single channel air valve for sphygmomanometer

Abstract

This invention discloses a single-channel SMA valve for a blood pressure monitor, comprising a valve seat, valve plate, valve core, control wheel assembly, SMA wire assembly, and flexible reset assembly. The valve core is slidably mounted inside the valve seat, and the valve orifice communicates with the air passages on both sides. After being heated, the SMA wire assembly recovers its memory deformation and pulls the valve core laterally, forming a gradually changing eccentric flow channel between the valve orifice and the air passages to achieve slow-release pressure control of the blood pressure monitor. The control wheel assembly integrates a heated wheel, cam, and shaft structure, enabling multiple control modes such as electrothermal drive, servo drive, and manual adjustment. The flexible reset assembly is used for buffering and guiding the valve core and for automatic reset. This structure can reduce pressure fluctuations and noise problems caused by the instantaneous opening and closing of traditional solenoid valves, improving the pressure relief stability, pulse wave acquisition accuracy, and overall reliability of the blood pressure monitor.

Description

Technical Field

[0001] This invention relates to the field of medical device pneumatic control technology, specifically to an SMA single-channel pneumatic valve for a blood pressure monitor. Background Technology

[0002] The sphygmomanometer valve is a core pneumatic control component used to control the flow, maintenance, and release of air pressure inside the cuff. It is widely used in electronic sphygmomanometers, ambulatory blood pressure monitoring devices, and portable medical testing equipment. As home medical devices increasingly focus on low noise, miniaturization, and high precision, traditional solenoid valve structures, due to their significant electromagnetic noise, noticeable instantaneous pressure fluctuations, and high power consumption, are gradually becoming insufficient to meet the demands of high-precision blood pressure monitoring. Therefore, SMA (shape memory alloy) valves, driven by shape memory alloy materials, have begun to be applied in the field of sphygmomanometer pneumatic control. This type of structure typically utilizes the shape memory deformation characteristic of SMA filaments after heating to traction and drive the valve core, thereby achieving pneumatic flow and slow-release pressure control.

[0003] Most existing SMA sphygmomanometer valves use a single heating-driven control method. This involves continuously heating the SMA wire via a fixed heating structure, causing the wire to contract and pull the valve core. While this structure provides basic pneumatic control, the overall control method is relatively simple, making it difficult to achieve flexible adjustment under conditions of partial control abnormalities, unstable local heating, or different pressure relief conditions. Furthermore, some existing SMA drive structures typically use only one side of the SMA wire or a single-point traction method. During valve core movement, issues such as force misalignment, local tilting, or movement jitter can easily occur. This is especially problematic under slow-release pressure relief conditions with small strokes, leading to unstable valve core slippage. This instability affects the consistency of the airflow channel cross-sectional area change, causing fluctuations in the sphygmomanometer's pressure curve and impacting the accuracy of pulse wave acquisition.

[0004] In addition, some existing SMA valves use ordinary springs or rigid rebound structures during the reset process. After long-term cyclic use, these are prone to reset impact, structural fatigue, and local jamming. At the same time, the rigid reset structure is also prone to instantaneous pressure disturbances during the rapid return of the valve core, which is not conducive to the stable control of the internal air circuit of the sphygmomanometer. Summary of the Invention

[0005] This invention aims to solve the problems of single control mode, insufficient valve core traction stability, and poor reset buffer effect in the existing SMA blood pressure monitor valve. It provides an SMA single-channel valve for blood pressure monitors, which drives the valve core to slide laterally through the thermal deformation of the SMA wire assembly, and forms a multi-mode drive and flexible reset structure with the control wheel assembly and flexible reset component, making the blood pressure monitor depressurization process more stable, thereby improving the blood pressure measurement accuracy and overall stability of use.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a single-channel SMA valve for a blood pressure monitor, comprising a valve seat, a flexible reset assembly, an SMA wire assembly, and valve plates arranged on both sides of the valve seat. Both valve plates have coaxially arranged air passages fixedly mounted on their surfaces. A valve core is slidably mounted inside the valve seat, and a control wheel assembly is rotatably mounted inside the valve seat. The SMA wire assembly is symmetrically arranged on both sides of the control wheel assembly, and both ends of the SMA wire assembly are respectively fixed to the inside of the valve seat and one end of the valve core. The valve core surface has valve holes for communicating with the surfaces of the air passages on both sides. The flexible reset assembly includes a float and a first and a second connecting piece arranged on the surface of the float. One end of the first connecting piece is fixedly connected to the inside of the valve seat, and one end of the second connecting piece is fixedly connected to the surface of the valve core. The guide head and the valve holes are arranged parallel to each other and symmetrically on both sides of the valve core.

[0007] In a preferred embodiment, the control wheel assembly is further configured as follows: the control wheel assembly includes a rotating shaft, a heating wheel, and cams fixed to both sides of the heating wheel. The rotating shaft is fixed to the axis of the heating wheel and one end penetrates the surface of the valve plate. The cams are elliptical and abut against the surfaces of the SMA wire assemblies on both sides. An electric heating wire is provided inside the heating wheel, and an electrode ring for electrically connecting to the end of the electric heating wire is provided on the outer periphery of the heating wheel. By integrating an electric heating structure inside the heating wheel, the control wheel assembly synchronously generates a local heat source output during rotation adjustment, rapidly and stably heating the SMA wire assemblies, thereby improving the SMA drive response speed and structural integration.

[0008] In a preferred embodiment, the valve core is further configured such that it is slidably mounted inside the valve seat, and one end of the valve core is provided with a guide head. The two sides of the valve core are in sealing sliding contact with the opposing surfaces of the valve plates on both sides. By forming a sealing sliding structure between the valve core and the valve plates, the valve core can maintain a stable seal in the air passage during lateral movement, reducing air leakage during pressure relief.

[0009] In a preferred embodiment, the configuration is further as follows: there are four of each of the first and second linkage plates, arranged symmetrically in pairs on both sides of the valve core. Under normal conditions, the valve orifice is connected to the air passages on both sides. The multiple linkage plates form a flexible and elastic support structure, which keeps the valve core stable during movement and achieves an automatic reset effect after the SMA wire assembly cools down.

[0010] In a preferred embodiment, the SMA wire assembly is further configured such that: in its normal state, it is straight, with a fixed block at each end fixed to the inner side of the valve seat and a connecting block fixed to one end of the valve core, respectively. After heating, the SMA wire assembly returns to its memory state and becomes curved, which is used to pull the valve core laterally, causing the valve hole and the air passage opening to be misaligned. Through the SMA wire assembly's recovery of its memory deformation by heating, a synchronous traction drive is formed on the valve core, creating a gradually changing eccentric flow channel between the valve hole and the air passage opening, thereby realizing the slow-release pressure relief control of the blood pressure monitor.

[0011] In a preferred embodiment, the valve seat is further configured such that: a groove for controlling the rotation of the wheel assembly is provided on the inner side of the valve seat, and an electrical contact for corresponding electrical connection with the electrode ring is provided on the inner side of the groove for power input to the heating wire inside the heating wheel. The electrical contact and the electrode ring form a rotating conductive structure, enabling the heating wheel to continue supplying power for heating while rotating, thus improving control stability.

[0012] In a preferred embodiment, the shaft is further configured such that one end extends through the valve plate surface and is detachably fitted with a knob. The cam abuts against the surface of the SMA wire assembly via both sides of the short shaft, and after the cam deflects 90 degrees, it abuts against the surface of the SMA wire assembly via both ends of the long shaft, thereby bending the SMA wire assembly. By changing the pretension state of the SMA wire assembly through cam deflection, the SMA wire assembly can form different deformations and drive sensitivities, improving the overall adjustment capability.

[0013] In a preferred embodiment, the shaft is further configured such that a drive servo motor is detachably mounted at its end for controlling the automatic rotation of the control wheel assembly. By driving the control wheel assembly to deflect via the drive servo motor, this structure can achieve multiple control modes besides electrothermal drive, including servo motor drive and manual adjustment, thereby improving overall applicability and control flexibility.

[0014] The beneficial effects achieved by this invention are as follows: 1. In this invention, by integrating multiple drive adjustment methods such as electric heating control, servo motor control, and manual control into the control wheel assembly, the SMA single-channel air valve can not only perform thermal drive control of the SMA wire assembly through electric heating, but also achieve auxiliary control through automatic adjustment by servo motor or manual knob operation. This adapts to the control needs of different types of blood pressure monitors, improves the overall control flexibility and the applicability of the equipment, and at the same time, in the event of some electronic control malfunctions, emergency adjustment can still be performed manually, improving the reliability of the device.

[0015] 2. In this invention, multiple SMA wire groups are used for symmetrical linkage control, so that the valve core can form synchronous traction force on both sides during the driving process, reducing the problems of unbalanced load, tilting or jamming caused by unilateral driving, making the overall sliding process of the valve core more stable. At the same time, the combined action of multiple SMA wire groups can disperse the driving load of a single SMA wire, reduce fatigue wear, and improve the action stability and cycle service life of the SMA drive structure.

[0016] 3. In this invention, by setting a flexible reset component and using the first linkage plate, the second linkage plate, and the float to form a flexible elastic reset structure, the valve core can form a flexible buffer and stable guide during movement. After the SMA wire assembly cools down, it automatically drives the valve core to return to the initial conduction state, reducing the impact, shaking, and jamming phenomena caused by the traditional rigid reset structure. At the same time, it improves the valve core sliding stability and the air circuit sealing stability, which is beneficial for the blood pressure monitor to maintain a stable pressure change curve during the slow release process. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of one embodiment of the present invention; Figure 2 This is an exploded structural diagram of an embodiment of the present invention; Figure 3 This is a schematic diagram of the internal structure of a valve seat according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the valve seat, flexible reset assembly, and valve core structure according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the control wheel assembly, SMA wire assembly, and valve core structure according to an embodiment of the present invention; Figure 6 This is a schematic diagram of an SMA filament assembly structure according to an embodiment of the present invention.

[0018] Figure label: 100. Valve seat; 110. Valve plate; 120. Air passage port; 130. Knob; 140. Valve core; 141. Guide head; 142. Valve hole; 150. Control wheel assembly; 151. Rotating shaft; 152. Heating wheel; 153. Cam; 154. Electrode ring; 200. Flexible reset assembly; 210. Float block; 211. First linkage piece; 212. Second linkage piece; 300, SMA wire assembly; 301, stationary block; 302, linkage block. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0020] It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the invention.

[0021] The following describes, with reference to the accompanying drawings, some embodiments of the present invention, providing an SMA single-channel air valve for a blood pressure monitor.

[0022] Combination Figures 1-6 As shown, the present invention provides a single-channel SMA air valve for a blood pressure monitor, comprising a valve seat 100, a flexible reset assembly 200, an SMA wire assembly 300, and valve plates 110 arranged on both sides of the valve seat 100. Both valve plates 110 have coaxially arranged air passage openings 120 fixedly mounted on their surfaces. A valve core 140 is slidably mounted inside the valve seat 100, and a control wheel assembly 150 is rotatably mounted inside the valve seat 100. The SMA wire assembly 300 is symmetrically arranged on both sides of the control wheel assembly 150, and both ends of the SMA wire assembly 300 are respectively fixed to… The valve seat 100 has an inner side and one end of the valve core 140. The surface of the valve core 140 is provided with a valve hole 142 for communicating with the surface of the air passage 120 on both sides. The flexible reset assembly 200 includes a float 210 and a first connecting piece 211 and a second connecting piece 212 arranged on the surface of the float 210. One end of the first connecting piece 211 is fixedly connected to the inner side of the valve seat 100, and one end of the second connecting piece 212 is fixedly connected to the surface of the valve core 140. The guide head 141 and the valve hole 142 are arranged in parallel to each other and symmetrically arranged on both sides of the valve core 140.

[0023] In this embodiment, the control wheel assembly 150 includes a rotating shaft 151, a heating wheel 152, and cams 153 fixed on both sides of the heating wheel 152. The rotating shaft 151 is fixed to the axis of the heating wheel 152 and one end passes through the surface of the valve plate 110. The cams 153 are elliptical and abut against the surfaces of the SMA wire assemblies 300 on both sides. The heating wheel 152 is provided with an electric heating wire on its inner side, and an electrode ring 154 is provided on the outer periphery of the heating wheel 152 for electrically connecting with the end of the electric heating wire. The electrode ring 154 is connected to the electric contact on the inner side of the valve seat 100, so that the heating wheel 152 can continue to generate conductive heating in the rotating state, thereby performing thermal drive control on the SMA wire assembly 300 in the adjacent area.

[0024] refer to Figure 3 and Figure 4As shown, in this embodiment, the valve core 140 is slidably mounted inside the valve seat 100, and one end of the valve core 140 is provided with a guide head 141. The two sides of the valve core 140 are in sealing sliding contact with the opposing surfaces of the valve plates 110 on both sides. A flexible sealing layer is provided between the valve core 140 and the valve plates 110. The flexible sealing layer is arranged around the valve hole 142, so that the valve core 140 can maintain a stable sealing state during lateral sliding, reducing gas leakage during depressurization. The end of the guide head 141 facing the air passage 120 has a smooth guiding structure, which can reduce the airflow switching resistance during the movement of the valve core 140, making the airflow guidance process more stable.

[0025] In this embodiment, there are four first linkage plates 211 and four second linkage plates 212, arranged symmetrically in pairs on both sides of the valve core 140. Under normal conditions, the valve orifice 142 is connected to the air passages 120 on both sides of the valve core 140. Both the first linkage plate 211 and the second linkage plate 212 can be made of metal spring sheets or flexible engineering plastic sheets, forming a flexible reset capability through their own elastic deformation. The float 210 is located between the first linkage plate 211 and the second linkage plate 212, serving to form a flexible buffer support during the sliding process of the valve core 140, reducing the instantaneous impact and vibration during the movement of the valve core 140.

[0026] refer to Figure 5 and Figure 6 As shown, in this embodiment, the SMA wire assembly 300 is normally in a straight state, with a fixed block 301 fixed to the inside of the valve seat 100 and a connecting block 302 fixed to one end of the valve core 140 at each end. After the SMA wire assembly 300 is heated, it returns to its memory state and becomes curved, which is used to pull the valve core 140 to move laterally, so that the valve hole 142 is misaligned with the axis of the air passage 120. In this embodiment, the SMA wire assembly 300 adopts a symmetrical arrangement structure on both sides, which can form synchronous traction force during the driving process, reduce the offset or jamming problem caused by unilateral traction, and make the overall sliding of the valve core 140 more stable.

[0027] In this embodiment, the valve seat 100 has a groove on its inner side for controlling the rotation of the wheel assembly 150, and an electrical contact on its inner side for corresponding electrical connection with the electrode ring 154, for power input to the heating wire inside the wheel 152. One end of the rotating shaft 151 passes through the surface of the valve plate 110 and is detachably mounted with a knob 130. By manually rotating the knob 130, the wheel assembly 150 can be driven to deflect as a whole. During the deflection process, the cam 153 gradually switches from a short shaft contact state to a long shaft contact state, thereby forming an external support abutment on the SMA wire assemblies 300 on both sides, so that the SMA wire assemblies 300 are in a pre-bent state to adjust the initial tension and driving sensitivity of the SMA wire assemblies 300.

[0028] In another embodiment, a drive servo motor can be detachably installed at the end of the rotating shaft 151. The drive servo motor drives the control wheel assembly 150 to rotate automatically, thereby realizing the automatic adjustment of the control wheel assembly 150. In this structure, not only can the SMA wire assembly 300 be thermally driven by heating the electric heating wire inside the rotating wheel 152, but the cam 153 can also be driven by the drive servo motor to mechanically deform the SMA wire assembly 300, thus forming multiple control modes such as electric heating, servo motor driving, and manual adjustment, improving the overall control flexibility.

[0029] Working principle and usage process of this invention: The two air passages 120 are connected to the air pump output pipe and cuff air passage inside the blood pressure monitor, respectively, and are connected to the electric heating wire inside the heating wheel 152 and the drive servo motor through an external control circuit. In the initial state, the SMA wire assembly 300 is in a flat state at room temperature. At this time, the two SMA wire assemblies 300 do not generate lateral traction force on the valve core 140. Under the elastic support of the flexible reset assembly 200 formed by the first linkage plate 211 and the second linkage plate 212, the valve core 140 is kept in the middle conduction position, so that the valve hole 142 is connected to the axis of the two air passages 120, thereby forming a complete airflow passage, which facilitates the air pump to inflate the blood pressure monitor cuff or maintain the air pressure conduction state.

[0030] When the blood pressure monitor needs to release pressure slowly, the control circuit controls the heating wire inside the heating wheel 152 to be energized and heated, and forms continuous conductivity through the electrode ring 154 and the electrical contacts inside the groove. After heating, the heating wheel 152 conducts heat to the adjacent area, causing the temperature of the SMA wire groups 300 on both sides to gradually rise. After reaching the memory phase transition temperature, the SMA wire groups 300 begin to recover the preset bending memory shape, gradually bending and shrinking from the original straight state to the arc state. During this process, the SMA wire groups 300 on both sides simultaneously form a lateral traction force on one end of the valve core 140, causing the valve core 140 to slide laterally along the inside of the valve seat 100.

[0031] During the lateral movement of the valve core 140, the first connecting plate 211 and the second connecting plate 212 simultaneously undergo elastic deformation. The float 210 forms a flexible buffer support between the two sets of connecting plates, thereby reducing the instantaneous impact and vibration during the movement of the valve core 140 and making the overall sliding of the valve core 140 more stable. At the same time, the flexible sealing layer on the surface of the valve core 140 remains in contact with the surface of the valve plate 110 to ensure that the air passage remains in a stable and sealed state during the lateral movement, preventing leaked airflow from interfering with the pressure detection of the blood pressure monitor.

[0032] As the valve core 140 continues to move laterally, the valve orifice 142 gradually forms an eccentric misalignment with the air passage openings 120 on both sides, and the cross-sectional area of ​​the original airflow passage gradually decreases, causing the air pressure inside the cuff to gradually and slowly release. Since the valve orifice 142 and the air passage opening 120 are not disconnected instantaneously, but form a continuously changing flow cross section during the lateral movement, the pressure fluctuations and airflow pulse phenomena caused by the instantaneous opening and closing of the traditional solenoid valve can be avoided, so that the blood pressure monitor forms a more stable blood pressure reduction curve during the measurement process, improving the stability of pulse wave acquisition and the accuracy of blood pressure measurement.

[0033] After the pressure relief ends or heating stops, the electric heating wire inside the heating wheel 152 is de-energized, and the SMA wire group 300 gradually cools down and returns to its original straight state. Its lateral traction force on the valve core 140 gradually decreases. At this time, the first linkage plate 211 and the second linkage plate 212 rely on their own elastic recovery ability to drive the valve core 140 to reset in the opposite direction, so that the valve hole 142 is reconnected with the air passage port 120, thereby restoring the normal conduction state of the air passage and realizing the automatic reset cycle control of the entire SMA single-channel air valve.

[0034] In addition to the drive method of using the electric heating wire inside the heating wheel 152 to generate heat, the entire wheel assembly 150 can be rotated by driving the servo motor, causing the cam 153 to deflect and push the SMA wire assembly 300 to deform and bend, thereby pulling the valve core 140 to slide, thus realizing the function control of the blood pressure monitor.

[0035] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0036] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. An SMA single pass air valve for a sphygmomanometer, characterized by, include: Valve seat (100), flexible reset assembly (200), SMA wire assembly (300); Valve plates (110) are arranged on both sides of the valve seat (100). A coaxial air passage (120) is fixedly installed on the surface of each of the two valve plates (110). A valve core (140) is slidably installed on the inner side of the valve seat (100). A control wheel assembly (150) is rotatably installed on the inner side of the valve seat (100). The SMA wire assembly (300) is symmetrically arranged on both sides of the control wheel assembly (150). The two ends of the SMA wire assembly (300) are fixed to the inner side of the valve seat (100) and one end of the valve core (140), respectively. The surface of the valve core (140) is provided with valve holes (142) for communicating with the surfaces of the air passages (120) on both sides. One end of the flexible reset assembly (200) is fixedly connected to the inside of the valve seat (100), and the other end is fixedly connected to the surface of the valve core (140).

2. The SMA single pass air valve for sphygmomanometer according to claim 1, wherein The flexible reset assembly (200) includes a float (210) and a first connecting piece (211) and a second connecting piece (212) arranged on the surface of the float (210). One end of the first connecting piece (211) is fixedly connected to the inner side of the valve seat (100), and one end of the second connecting piece (212) is fixedly connected to the surface of the valve core (140).

3. A SMA single pass air valve for a sphygmomanometer according to claim 2, wherein There are four of the first linkage plate (211) and the second linkage plate (212), and they are arranged in parallel and symmetrically on both sides of the valve core (140). Under normal conditions, the valve hole (142) is connected to the air passages (120) on both sides. Both the first linkage piece (211) and the second linkage piece (212) are metal spring pieces or flexible engineering plastic sheet structures, used for the reset movement of the valve core (140).

4. The SMA single pass air valve for sphygmomanometer according to claim 1, wherein A flexible sealing layer is provided between the valve core (140) and the valve plate (110). The flexible sealing layer is arranged around the valve hole (142) to improve the air passage sealing during the transverse movement of the valve core (140) and reduce gas leakage under pressure.

5. The SMA single pass air valve for sphygmomanometer according to claim 1, wherein The valve core (140) is slidably installed inside the valve seat (100), and one end of the valve core (140) is provided with a guide head (141). The guide head (141) and the valve hole (142) are arranged in parallel to each other and symmetrically arranged on both sides of the valve core (140). The two sides of the valve core (140) are in sealed sliding contact with the opposite surfaces of the valve plates (110) on both sides.

6. The SMA single pass air valve for sphygmomanometer according to claim 1, wherein The SMA wire assembly (300) is in a straight state under normal conditions. At both ends, there is a fixed block (301) fixed to the inside of the valve seat (100) and a connecting block (302) fixed to one end of the valve core (140). After the SMA wire assembly (300) is heated, it returns to its memory state and becomes curved, which is used to pull the valve core (140) to move laterally, so that the valve hole (142) is misaligned with the axis of the air passage (120).

7. The SMA single-channel air valve for a blood pressure monitor according to claim 1, characterized in that, The control wheel assembly (150) includes a rotating shaft (151), a heating wheel (152), and cams (153) fixed on both sides of the heating wheel (152). The rotating shaft (151) is fixed to the axis of the heating wheel (152) and one end passes through the surface of the valve plate (110). The cam (153) is elliptical and abuts against the surfaces of the SMA wire assemblies (300) on both sides. The heating wheel (152) is provided with an electric heating wire on the inner side and an electrode ring (154) for electrically connecting to the end of the electric heating wire is provided on the outer periphery of the heating wheel (152).

8. The SMA single-channel air valve for a blood pressure monitor according to claim 7, characterized in that, The valve seat (100) has a groove on the inner side for controlling the rotation of the wheel assembly (150). The groove has an electrical contact on the inner side for corresponding electrical connection with the electrode ring (154) and for power input for heating the heating wire inside the wheel (152).

9. A single-channel SMA valve for a blood pressure monitor according to claim 7, characterized in that, One end of the rotating shaft (151) passes through the surface of the valve plate (110) and is detachably mounted with a knob (130). The cam (153) is used to abut against the surface of the SMA wire assembly (300) through both sides of the short shaft. After the cam (153) deflects ninety degrees, it abuts against the surface of the SMA wire assembly (300) through both ends of the long shaft, and is used to bend the SMA wire assembly (300) by abutment.

10. A single-channel SMA valve for a blood pressure monitor according to claim 7, characterized in that, The end of the shaft (151) is detachably equipped with a drive servo motor for controlling the automatic rotation of the control wheel assembly (150).

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