FIELD OF THE INVENTION

The present invention relates to a stepper motor based linear actuator with no step loss and position feedback of rotor assembly. More particularly, the present invention relates to a can stack stepper motor based idle air control valve to adjust engine idle air that includes hall sensors to provide feedback to determine the position of rotor assembly and actuator.

BACKGROUND OF THE INVENTION

Stepper motor transforms electric pulse into angular displacement. When a pulse signal is received, the stepper motor rotates to a fixed angle performing rotary action according to the direction set for the stepper motor. The rotational velocity and acceleration of motor can be controlled by the pulse frequency to achieve the purpose of speed control. Further, the stepper motor is a brushless, synchronous electric motor that can drive a full rotation into an expansive number of steps.

Stepper motor is used widely due to its precision, high torque at startup and low speed, ruggedness, simplicity of construction, low maintenance, and so on. Some of the applications of stepper motor based Linear Actuator in automotive industry include intake valve drive used in idling control of two wheelers specially bikes, intake systems, thermal expansion valves, exhaust systems, suspension control and meter display drive etc. There is a type of stepper motor called “can stack stepper motor”. The can stack stepper motor is a form of permanent magnet stepper motor consisting of two stators and two coils stacked on the top of each other. The rotor consists of a permanent magnet and it has the same number of pole pairs that each stator has.

US7969048B2 discloses a linear actuator motor design including a rotor assembly that has an insert molded into a non-magnetic sleeve through a plurality of openings, which is kept from rotating within the non-magnetic sleeve by at least one opening arranged along the length of the non-magnetic sleeve which corresponds to at least one tab formed by the molded material of the insert and a stator assembly having a plurality of symmetrical and interchangeable magnetic pole plates. Each of the plurality of magnetic pole plates comprises a substantially planar plate portion with a central opening therein and a plurality of prongs extending from the central opening and substantially perpendicular to the plate portion. The prongs of the plurality of magnetic pole plates create an opening that is dimensioned to receive the rotor assembly therein. A non- conductive material is the molded over the plurality of magnetic pole plates. In the cited art, a can stack stepper motor as linear actuator is disclosed, however there is no provision to detect the position feedback of rotor and to detect actuator position.

W02015061900A1, discloses an electric linear actuator comprising of a linear array of poloidal electrical coils, a shaft, a power source, position sensors and a control processor that can be used in other industries where linear actuators or other haptic control feedback devices, are used involving industrial gate motors. The sensors used in this invention are position sensors for determining the relative axial position of shaft along central bore, however there is no provision to detect the position feedback of rotor and to detect actuator position to adjust engine idle air, therefor no feedback for step loss of stepper motor and hence the rotor assembly fails to reach a target position due to step loss.

DE102013104022A1, discloses an electric motor comprising, a stator, a rotor with a rotor core and a permanent magnet attached to the rotor core, an output shaft connected to the rotor core and a latching mechanism for a better holding torque and low vibration but there is no provision to detect the position feedback of rotor and to detect actuator position to adjust engine idle air, therefor no feedback for step loss of stepper motor and hence the rotor assembly fails to reach a target position due to step loss.

An idle air control valve with can stack stepper motor is basically an electrically controlled linear actuator located on the throttle body to adjust the engine idle air and is fitted such that it bypasses the throttle. In state of the art, in a can stepper motor based linear actuator there is no feedback of position of rotor assembly and it results in no feedback for step loss of stepper motor and hence the rotor assembly fails to reach a target position due to step loss. Further, in addition to that feedback of linear position of actuator fails to reach target position. Therefore, there is a need for a reliable technique to detect the position feedback of rotor to achieve desired position of the linear actuator.

OBJECT OF THE INVENTION

The main object of the present invention is to provide a stepper motor based linear actuator with position feedback of the rotor assembly.

Another object of the present invention is to provide a stepper motor based linear actuator to control linear position of stepper motor based linear actuator/plunger.

Yet another object of the present invention is to provide a stepper motor based linear actuator with no step loss.

Yet another object of the present invention is to detect the position of actuator using at least two hall sensors.

Yet another object of the present invention is to provide a mechanism to give position feedback to driver to control the degree of position change of rotor assembly in stepper motor.

Still another object of the present invention is to provide a steppe motor based linear actuator with optimized number of hall sensors to be used to detect position of linear actuator as well as provide position feedback of rotor assembly.

SUMMARY OF THE INVENTION

The present invention provides a stepper motor based linear actuator with no step loss to adjust engine idle air control and is fitted such that it bypasses the throttle, includes hall sensors to provide feedback to determine the position of rotor assembly and actuator.

In an embodiment, the present invention provides a stepper motor based linear actuator to adjust idle air control. Said stepper motor based linear actuator includes a housing, a plurality of stator cup, a plurality of claw plate, a first bobbin assembly, a second bobbin assembly, a bobbin slab, a PCB assembly, at least one bearing, a rotor assembly, a rotor insert, and a plunger/actuator. Said PCB assembly comprises of at least two hall sensors and said PCB assembly is hot crimped into said housing. Further, said hall sensors are soldered on the said PCB and are placed preferably at angle of 120° apart axially to the said bobbin assembly. The bearing is insert molded in the housing. Said hall sensors provide feedback to the driver i.e. an electronic control unit (ECU) to control degree of position change of rotor assembly in stepper motor. The position feedback obtained helps in controlling the linear position of stepper motor based linear actuator. Said stepper motor based linear actuator for adjustment of engine idle air is fitted in throttle body to bypass the air.

Therefore, in the present invention with help of an arrangement of hall sensors on a PCB, the position feedback of rotor assembly and linear position feedback of plunger/actuator is given to driver to prevent failing in reaching the linear target position due to step loss in motor.

BRIEF DESCRIPTION OF THE DRAWINGS

A complete understanding of the present invention may be obtained by reference to the following drawings:

Fig. 1 illustrates a sectional view of the stepper motor based linear actuator in accordance with the conventional design.

Fig. 2 illustrates a sectional view of the stepper motor based linear actuator in accordance with the present invention.

Fig. 3 illustrates an exploded view of the stepper motor based linear actuator in accordance with the present invention.

Fig. 4(a) illustrates a perspective view of the PCB sub-assembly in accordance with the present invention.

Fig. 4(b) illustrates a top perspective view of the housing of stepper motor based linear actuator in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION Many aspects of the invention can be better understood with references made to the drawings below. The components in the drawings are not necessarily drawn to scale. Instead, emphasis is placed upon clearly illustrating the components of the present invention. Moreover, like reference numerals designate corresponding parts through the several views in the drawings. Before explaining at least one embodiment of the invention, it is to be understood that the embodiments of the invention are not limited in their application to the details of construction and to the arrangement of the components set forth in the following description or illustrated in the drawings. The embodiments of the invention are capable of being practiced and carried out in various ways. In addition, the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.

The present invention provides a stepper motor based linear actuator to detect the position of rotor assembly using an arrangement of hall sensors on a PCB, and the position feedback of rotor assembly obtained by hall sensors is utilized to control the linear position feedback of plunger/actuator. Based on the position feedback from hall sensors, the driver adjusts the degree of position change such that the plunger/ actuator reaches the target position in case of any step loss.

In a most preferred embodiment, the present invention provides a stepper motor based linear actuator to adjust idle air control. Said stepper motor based linear actuator includes a housing, a plurality of stator cup, a plurality of claw plate, a first bobbin assembly, a second bobbin assembly, a bobbin slab, a PCB assembly, at least one bearing, a rotor assembly, a rotor insert and a plunger/ actuator. Said PCB assembly comprises of at least two hall sensors and said PCB assembly is hot crimped into said housing. Further, said hall sensors are soldered on said PCB and are placed preferably at angle of 120° apart axially to the said bobbin assembly. The bearing is insert molded in the housing. Said hall sensors take feedback of position of rotor assembly and provide this feedback to the driver i.e. an electronic control unit (ECU) to control degree of position change of rotor assembly in stepper motor. The position feedback obtained helps in controlling the linear position of stepper motor based linear actuator. Said stepper motor based linear actuator for adjustment of engine idle air is fitted in throttle body to bypass the air. Fig. 1 shows a sectional view of the stepper motor based linear actuator (20) as per the conventional design comprising of a housing (11), a first bobbin assembly (9a), a second bobbin assembly (9b), at least one bearing (3), a rotor assembly (1), a rotor insert (24), a plunger/actuator (2) and plurality of terminals (8). In the conventional design, there is no feedback for step loss of stepper motor and results in rotor assembly not reaching the rotary target position. Further, the plunger/actuator (2) fails to reach the linear target position due to step loss.

Fig. 2 shows a sectional view of the stepper motor based linear actuator (10) as per the present invention comprising of a housing (21), a first bobbin assembly (9a), a second bobbin assembly (9b), a PCB (6), at least one bearing (3), a rotor assembly (1), a rotor insert (24), a plunger/ actuator (2) and plurality of terminals (8). Said PCB (6) comprises an arrangement of hall sensors (4, 5) and said PCB (6) is hot crimped into said housing (21).

Said plunger/actuator (2) has threads on its outer peripheral surface and said rotor insert (24) has threads in its inner peripheral surface. When, can stack stepper motor is in On condition, said first bobbin assembly (9a) and second bobbin assembly (9b) gets energized and generates magnetic field which rotates the rotor assembly (1). Rotor insert (24) is insert-molded in rotor assembly (1). Both the plunger/actuator (2) and rotor insert (24) are engaged via threaded connection such that when rotor insert (24) rotates in rotary motion, the plunger/ actuator (2) moves in vertical linear motion axially to the rotor assembly (1). Said plurality of hall sensors take the position feedback of rotor assembly (1) and provide it to the driver i.e. ECU (not shown). The driver based on position feedback of rotor assembly controls the degree of position change of rotor assembly (1) to control the linear position of linear actuator/plunger (2). Accordingly, based on linear position of plunger/actuator (2), the engine idle air is maintained.

Here, the said plunger/actuator (2) is made of a material such as but not limited to steel, aluminum, brass, lead, ceramic, non-magnetic materials or like.

Fig. 3 illustrates exploded view of the stepper motor based linear actuator (10) as per the present invention. The first bobbin assembly (9a) includes a first bobbin (16a), a first coil (14a), a first stator cup (12a), a first claw plate (12b) and a first terminal (8a), and the second bobbin assembly (9b) includes a second bobbin (16b), a second coil (14b), a second stator cup (13a), a second claw plate (13b) and second terminal (8b) are connected axially with bobbin slab (25) and insert molded into the housing (21). A PCB assembly (6a) comprises a PCB (6) provided with plurality of hall sensors (4 and 5) and is placed in the bottom of the said housing (21). A rotor insert (24) is insert-molded in rotor assembly (1). A rotor assembly (1) is provided having threads in its inner periphery surface axially to the rotation of the said rotor assembly (1) and a plunger (2) is provided with threads in its outer periphery and is connected with the said rotor insert (24) with thread mechanism. A bearing (3) is insert-molded into the bottom of the said housing (21) and supports the rotational movement of the said rotor assembly (1). Wherein, the said first bobbin assembly (9a) and second bobbin assembly (9b) are stacked on the top of each other axially with bobbin slab (25) and insert molded into said housing (21).

Fig. 4(a) shows a perspective view of the PCB assembly (6a) as per the present invention comprising of a PCB (6) with at least two hall sensors (4, 5) soldered on the top surface of said PCB (6). Said PCB (6) is preferably of a shape including but not limited to circular, parabolic etc. Said hall sensor (4) and hall sensor (5) are soldered apart on the top surface of the PCB by an angle of 120° apart axially to the said PCB (6). Said hall sensors (4, 5) take feedback of position of rotor assembly (2) and provides such feedback to the ECU to control the degree of position change of rotor assembly. The number of halls sensors used is optimized as half of the number of steps commutation in one electric cycle. On the top surface of the PCB (6), there are plurality of grooves (22) which enable hot crimping into housing (21).

Fig. 4(b) shows a top perspective view of the stepper housing (21) comprising of PCB (6). The PCB (6) is attached to the bottom of the housing (21) in such a way that said PCB (6) and said rotor assembly (1) are axially aligned. Corresponding to the grooves on PCB (6), there are protrusions (23) in the housing (21) which upon hot crimp and make a strong bond with the housing (21) and hence does not move from its position.

Therefore, the present invention provides a technology that enables controlling the linear position of actuator and help it to reach target position without any step loss that increases efficiency of the linear actuator. The foregoing description of embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principals of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated.