Impact mechanism of electric wrench

Abstract

The utility model discloses an impact mechanism of an electric wrench, which comprises a cam shaft, the front end of the cam shaft is rotatably sleeved with a hammer head, the rear end of the cam shaft is convexly provided with a circle of shaft shoulder, and a spiral pressure spring is compressed between the shaft shoulder and the hammer head; the side face of the outer circumference of the cam shaft is concavely provided with two raceway grooves in central symmetry. The raceway grooves are in a V shape, and openings of the raceway grooves face the rear end of the cam shaft. The inner hole wall of the hammer head is provided with two stress grooves matched with the roller path grooves in a one-to-one mode, the stress sides of the stress grooves are also in a V shape, openings of the stress grooves face the front end of the cam shaft, and steel balls used for transmitting force are arranged between the stress grooves and the matched roller path grooves. The line shape of the stress side of the roller path groove of the cam shaft or / and the stress side of the hammerhead stress groove expanded on the designed expansion circle comprises a polynomial curve. According to the structure, the center line of the roller path is designed to be a polynomial curve or a combination of the polynomial curve and a straight line, and continuity of a second derivative is achieved, so that more stable steel ball movement is achieved, vibration is reduced, and the stability and durability of a tool are improved.

Description

Technical Field

[0001] The utility model belongs to the technical field of handheld electric tools, and in particular relates to an impact mechanism of an electric wrench. Background Art

[0002] Electric wrenches are widely used in industrial production, machinery manufacturing, home maintenance and other fields. They are tools driven by electric motors and are characterized by ease of use, labor saving, and high efficiency. When impact torque is required, the impact mechanism can also provide and output impact torque. Figure 1 The impact mechanism in the electric wrench mainly consists of a camshaft 1, a hammer 2, a spring and an output shaft 6. The motor in the electric wrench provides power, which is connected to the camshaft through a planetary reducer that reduces speed and increases torque, driving the camshaft to rotate. The front end of the camshaft 1 is the output shaft 6 (not integrated), and the outer circumference of the camshaft is sleeved with a hammer 2 for striking the aforementioned output shaft 6 to provide impact force. This structural form is used in existing products, and there are also domestic and foreign patent technologies disclosed, such as US11938594B2. The design of the camshaft driving the hammer to strike the output shaft is very clever. Two rolling grooves 11 are designed and manufactured on the outer circumferential side of the camshaft 1, which are symmetrical with the center of its axis. See Figure 1-4 The rolling groove 11 itself also extends into a symmetrical V-shape, and the cross section is an arc shape; steel balls 3 with matching diameters are rolled in the two rolling grooves, serving as the force transmission member from the camshaft 1 to the hammer head 2. The hammer head 2 is sleeved on the outside of the camshaft 1, and its inner hole wall is also designed and manufactured with two force-bearing grooves 21 that match the rolling groove 11 one to one. One side wall of the force-bearing groove is V-shaped and matches the rolling groove. Figure 5-7 , the opening faces forward, and the direction of the opening is opposite to the V-shaped direction of the rolling groove, which is the force-bearing side 211. The aforementioned spring acts forward on the hammer head, and the lower half of the aforementioned steel ball 3 falls in the rolling groove 11, and the upper half higher than the rolling groove acts on the force-bearing side 211 of the force-bearing groove 21. The wall of the force-bearing side 211 transitions to the bottom wall of the force groove 21 in an arc shape (matching the diameter of the steel ball), and the other side of the force groove 21 axially penetrates the hammer head 2 for assembly.

[0003] The camshaft raceway groove is generally machined by a ball-end milling cutter on a four-axis machining center. Whether from a design or machining perspective, it is necessary to define the raceway groove in order to clarify the shape and machining dimensions of the raceway groove, which is convenient for design analysis or manufacturing. The raceway groove is defined in design by assuming that the raceway groove extends along a center line that winds around a cylindrical surface and is a spatial curve. Figure 8, the cylindrical surface is expanded and flattened along the circumferential direction to obtain the plane curve diagram of the center line (also called the expansion diagram). The cylindrical surface is called the "expanded circle". The total length of the X axis on the plane curve diagram corresponds to the circumference of the "expanded circle", and the Y axis corresponds to the axial size of the camshaft. The plane curve formed by the expansion of the center line on the plane curve diagram is defined, and the raceway groove is also defined. Figure 9 Of course, to facilitate machining, the necessary "expanded circle" diameter and the arc radius of the raceway groove section are also required. The arc radius of the raceway groove section determines the diameter of the ball-end milling cutter used for machining, and the circumference of the expanded circle is obtained through the "expanded circle" diameter. The circumference is one circle of the circle, corresponding to 360°. The corresponding points on the curve on the circumference (X value) can be converted into the angle that the four-axis machining center turntable needs to rotate. During machining, the axis of the milling cutter is perpendicular to the axis of the camshaft and is coplanar. After the milling cutter reaches the designed depth, the milling cutter moves in the axial direction of the camshaft in conjunction with the turntable to drive the camshaft part to rotate circumferentially, and the raceway groove can be machined on the outer circumferential side of the camshaft.

[0004] The plane curve formed by the expansion of the center line of the raceway groove on the currently defined plane curve diagram can be further referred to. Figure 9 , are two symmetrical oblique lines, the two oblique lines are V-shaped, and the intersection is transitioned through the arc defined by the R (radius) value to form an intermediate arc. The two oblique lines are tangent to the two ends of the intermediate arc, and the free ends of the two oblique lines are tangent to the arc defined by the R (radius) value to form the end arc. The end arc extends to the tangent point parallel to the Y axis (the most convex point in the X direction of the center of the circle) at most, and will not bend inward. The arc satisfies the formula: (X-XC1) 2 +(Y-YC1) 2 =R1 2 In the formula, (XC1, YC1) is the coordinate of the center of the arc, and R1 is the radius of the arc, which is determined by combining the position and shape of the curve. In this way, the form of the end arc segment, the straight line segment, the middle arc segment, the straight line segment, and then the end arc segment is a tangent transition, which seems to be a smooth transition. However, further research on the first-order derivative and second-order derivative of the curve, that is, the velocity curve and the acceleration curve, can be found in Figure 10 Its second-order derivative produces a convex change and discontinuity at the intersection of the arc and the oblique line, indicating that its motion physical characteristics are discontinuous at this point. When the steel ball moves to this point, there will be a convex change in force and acceleration, which affects the service life of the steel ball, causing large vibrations and related components may fail earlier, shortening the service life of the entire machine or increasing the frequency of maintenance and repairs, and causing users to easily fatigue when using it. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present utility model is to provide an impact mechanism for an electric wrench, which solves the technical problem that the rolling grooves of the cam shaft to the steel ball and the hammer head driving the force transmission in the current electric wrench cause the force and acceleration of the steel ball to change convexly during its movement, thereby achieving the effect of reducing vibration during use, improving service life and user experience.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] An impact mechanism of an electric wrench includes a camshaft, a hammer head is rotatably provided on the outer circumferential side surface of the front end of the camshaft, a circle of shaft shoulders are raised on the outer circumferential side surface of the rear end of the camshaft, and a spiral compression spring is compressed between the shaft shoulder and the hammer head; two centrally symmetrical rolling grooves are recessed on the outer circumferential side surface of the camshaft, and the rolling grooves are V-shaped and open toward the rear end of the camshaft; two force-bearing grooves that match the rolling grooves one-to-one are formed on the inner hole wall of the hammer head, and the force-bearing sides of the force-bearing grooves are also V-shaped and open toward the front end of the camshaft, and a steel ball for transmitting force is provided between the force-bearing groove and the matching rolling groove; the linear shape of the center line of the camshaft rolling groove and / or the force-bearing side of the hammer head force groove unfolded on the designed unfolding circle includes a polynomial curve.

[0008] To further optimize the above technical solution, the raceway centerline of the raceway groove is unfolded on the designed unfolding circle and includes two inclined straight lines, the intersection of the two straight lines is connected by a tangent transition through an intermediate curve, the free ends of the two straight lines are tangently connected to the terminal curves, the intermediate curve, the two straight lines and the two terminal curves are symmetrically arranged and constitute the raceway centerline of the raceway groove; the intermediate curve and / or the terminal curve is a polynomial curve.

[0009] Furthermore, the center line of the force-bearing side is developed on a designed development circle, which has a polynomial curve adapted to the center line of the raceway.

[0010] Furthermore, the polynomial curve adopts a polynomial function curve of cubic, quartic, quintic or higher order.

[0011] Furthermore, the polynomial curve on the centerline of the raceway adopts a fifth-order polynomial function curve, which conforms to the formula: Y=C0+C1×X+C2×X 2 +C3×X 3 +C4×X 4 +C5×X 5 , where Y represents the axial dimension of the camshaft, X represents the circumferential dimension of the camshaft, and C0, C1, C2, C3, C4, and C5 are variable coefficients.

[0012] Furthermore, a flange is provided on the outer circumferential side of the hammer head, and an outer ring portion is provided on the outer edge of the flange toward the shaft shoulder. An annular cavity is formed between the outer ring portion and the outer circumferential side of the hammer head. The front end of the spiral compression spring slides into the annular cavity, and a plane bearing is provided on the bottom wall of the annular cavity. The front end of the spiral compression spring abuts against one surface of the plane bearing.

[0013] Furthermore, the plane bearing is a plane thrust bearing with needle rollers.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The impact mechanism of the electric wrench of the present invention replaces the traditional arc form by designing the center line of the raceway of the camshaft and the hammer head into a polynomial curve or a combination of a polynomial curve and a straight line, thereby achieving the continuity of the second-order derivative. The adjustability of the polynomial curve is utilized to design a smoother motion path, reducing the sudden changes in force and acceleration during motion, thereby achieving smoother steel ball motion. The utility model solves the problem of sudden changes in force and acceleration of the steel ball at the intersection of the arc and the straight line in the traditional design, realizes the optimization of the impact mechanism of the electric wrench, reduces vibration, improves the stability and durability of the tool, and enhances the user experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the impact mechanism of the electric wrench of the embodiment;

[0017] Figure 2 for Figure 1 Separate schematic diagram of the middle camshaft;

[0018] Figure 3 for Figure 2 A top view of

[0019] Figure 4 for Figure 2 A perspective view of the middle camshaft;

[0020] Figure 5 for Figure 1 Right side view of the hammer head;

[0021] Figure 6 for Figure 5 Middle AA section view;

[0022] Figure 7 for Figure 5 Stereoscopic view of the hammer head;

[0023] Figure 8 Schematic diagram of the space and plane curves corresponding to the existing rolling groove mentioned in the background technology;

[0024] Figure 9 For a separate indication Figure 8 A plane curve diagram of the center line of the raceway groove unfolded to a plane;

[0025] Figure 10 for Figure 9 Schematic diagram of the mid-plane curve and its first-order derivative and second-order derivative curves;

[0026] Figure 11 A planar curve diagram showing the center line of the newly designed raceway groove of the embodiment unfolded onto a plane;

[0027] Figure 12 for Figure 11 Schematic diagram of the new design plane curve and its first-order derivative and second-order derivative curves;

[0028] Figure 13 A processing dimension data diagram of a newly designed raceway groove in an embodiment;

[0029] Among them, the camshaft 1, the rolling groove 11, the shaft shoulder 12, the hammer head 2, the force groove 21, the force side 211, the steel ball 3, the spiral compression spring 4, the flange 22, the outer ring part 23, the ring cavity 24, the plane bearing 5, and the output shaft 6. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention.

[0031] See Figure 1-Figure 7 An impact mechanism of an electric wrench includes a camshaft 1, a hammer head 2 being rotatably sleeved on the outer circumferential side surface of the front end of the camshaft 1, a raised shaft shoulder 12 being provided on the outer circumferential side surface of the rear end of the camshaft 1, a helical compression spring 4 being compressed between the shaft shoulder 12 and the hammer head 2, and the helical compression spring 4 also being sleeved on the camshaft 1; two centrosymmetrical rolling grooves 11 are recessed on the outer circumferential side surface of the camshaft 1, and the rolling grooves 11 are V-shaped and open toward the rear end of the camshaft 1; The cross-section of the rolling groove 11 is arc-shaped; two force-bearing grooves 21 that match the rolling groove 11 one-to-one are opened on the inner hole wall of the hammer head 2, and the force-bearing side 211 of the force-bearing groove 21 is also V-shaped that matches the rolling groove 11 and opens toward the front end of the camshaft 1. A steel ball 3 for transmitting force is provided between the force groove 21 and the matching rolling groove 11 as a medium for relative motion. The wall of the force-bearing side 211 transitions to the bottom wall of the force groove 21 in an arc shape (matching the diameter of the steel ball 3).

[0032] See Figure 11After the rolling groove 11 is unfolded on the designed unfolding circle, the rolling center line of the rolling groove 11 includes two inclined straight lines, and the intersection of the two straight lines is connected by a tangent transition through an intermediate curve. The free ends of the two straight lines are tangently connected to the terminal curves respectively. The intermediate curve, the two straight lines and the two terminal curves are symmetrically arranged and constitute the rolling center line of the rolling groove 11; the intermediate curve and the terminal curve are polynomial curves.

[0033] The polynomial curve is a cubic, quartic or quintic polynomial function curve.

[0034] Taking the polynomial curve as an example, the polynomial curve is a fifth-order polynomial function curve, which conforms to the formula:

[0035] Y=C0+C1×X+C2×X 2 +C3×X 3 +C4×X 4 +C5×X 5 ,

[0036] Among them, Y represents the axial size of the camshaft, and X represents the circumferential size of the camshaft, that is, the circumference of the designed expansion circle. For further research, the first-order derivative and second-order derivative of the curve, that is, the velocity curve and acceleration curve, can be found in Figure 12 , its second-order derivative is continuous at the intersection of the curve and the line.

[0037] Specifically, its first-order derivative equation is: Y′=C1+2×C2×X+3×C3×X 2 +4×C4×X 3 +5×C5×X 4 ;

[0038] Second-order derivative equation: Y″=2×C2+2×3×C3×X+3×4×C4×X 2 +4×5×C5×X 3 ;

[0039] C0, C1, C2, C3, C4, and C5 are variable coefficients, which are determined by the design curve shape, position (machine tool coordinates during processing), and the tangent point with the straight line.

[0040] by Figure 11 Taking the middle curve as an example, C0=0, because the curve passes through the origin (0,0), X=0, Y=C0, so C0=0;

[0041] C1=0, because when X=0, the first-order derivative of Y, Y′=C1, and C1=0 makes the middle curve tangent to the horizontal line, so that the left and right parts of the middle curve are tangent at X=0;

[0042] C2, C3, and C4 satisfy the following three conditions:

[0043] The curve passes through point P1 (L0, H0), so:

[0044] C2×L0 2 +C3×L0 3 +C4×L0 4 +C5×L0 5 =H0; (1)

[0045] The curve is tangent to the line at point P1, that is, its first-order derivative is equal to the first-order derivative of the line, so:

[0046] 2×C2×L0+3×C3×L0 2 +4×C4×L0 3 +5×C5×L0 4 =k; (2)

[0047] k is the slope of the line;

[0048] In order to make the second derivative of the curve continuous with the straight line at point P1, the second derivative of the curve at point P1 is 0, so:

[0049] 2×C2+2×3×C3×L0+3×4×C4×L0 2 +4×5×C5×L0 3 =0;(3)

[0050] C5 is an input item used to additionally control the shape of the polynomial curve. In the curve example shown in the figure, C5=0.0012.

[0051] C2, C3, and C4 satisfy equations (1), (2), and (3) and can be solved using a general iterative solution method. The terminal curve can be obtained using the same method. The centerline of the force-bearing side 211 of the force-bearing groove 21 is unfolded on the designed unfolding circle, which has a polynomial curve adapted to the centerline of the camshaft raceway. From a linear perspective, they are exactly the same, only with different orientations, and can also be obtained using the same method.

[0052] The impact mechanism of the electric wrench of the embodiment realizes the continuity of the second-order derivative by designing the center line of the raceway as a combination of a polynomial curve and a straight line, replacing the traditional arc form, and utilizing the adjustability of the polynomial curve to design a smoother motion path, reducing the sudden changes in force and acceleration during motion, thereby achieving smoother movement of the steel ball 3; solves the problem of sudden changes in force and acceleration of the steel ball 3 at the intersection of the arc and the straight line in the traditional design, realizes the optimization of the impact mechanism of the electric wrench, reduces vibration, improves the stability and durability of the tool, and enhances the user experience.

[0053] Please see again Figure 13, Processing example: the raceway groove to be processed is unfolded on a circle with a diameter of 20.785. The unfolded circle is slightly larger than the diameter of the outer circumference of the solid. The X-axis is the circumference of 65.29. The corresponding points on the figure are, such as the tangent points (4.239, 1.126) and (8.586, 3.932). Between the two points, it means that the distance the ball end mill moves along the axial direction of the camshaft is 3.932-1.126=2.806, and (8.586-4.239) / 65.29×360°=23.97°, which means that the camshaft rotates 23.97° circumferentially during this process. According to the formula, the polynomial curve can be drawn on the 3D solid design software (such as NX, etc.), which can generate corresponding continuous point information. According to the above method, the axial movement size of the milling cutter and the circumferential rotation angle of the turntable can be continuously generated to complete the processing of the raceway groove 11. The hammer head stress groove 21 (stress side) is processed perpendicular to Figure 5 The direction of the paper is processed with a milling cutter. First, plane milling is used to mill out the ordinary arc-shaped force groove part above the force side. The force side is drawn with a curve on the three-dimensional solid design software, and corresponding continuous point information is generated. The machining center is XYZ three-axis linkage and the ball head milling cutter is used to mill it out.

[0054] In addition, a flange 22 is provided on the outer circumferential side of the hammer head 2. An outer ring portion 23 is provided on the outer edge of the flange 22 toward the shaft shoulder 12. An annular cavity 24 is formed between the outer ring portion 23 and the outer circumferential side of the hammer head 2. The front end of the helical compression spring 4 slides into the annular cavity 24. A flat bearing 5 is provided on the bottom wall of the annular cavity 24. The front end of the helical compression spring 4 abuts against one surface of the flat bearing 5. Because the helical compression spring 4 rotates essentially synchronously with the camshaft 1 during use, and the hammer head 2 rotates relative to the camshaft 1, the addition of the flat bearing 5 ensures that the helical compression spring 4 continuously provides forward force to the hammer head 2 while allowing for flexible rotation relative to the hammer head 2, thereby avoiding affecting the life of the spring. Specifically, the flat bearing 5 is a flat thrust bearing with a needle roller, which can reduce the axial space occupied and make the overall structure more compact.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Ordinary technicians in this field should understand that those modifications or equivalent replacements of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution of the present invention should be included in the scope of the claims of the present invention.

Claims

1. An impact mechanism of an electric wrench, comprising a camshaft, a hammer head rotatably sleeved on the outer circumferential side surface of the front end of the camshaft, a raised shaft shoulder on the outer circumferential side surface of the rear end of the camshaft, a helical compression spring compressed between the shaft shoulder and the hammer head; two centrosymmetrical rolling grooves recessed on the outer circumferential side surface of the camshaft, the rolling grooves being V-shaped and opening toward the rear end of the camshaft; two force-bearing grooves cooperating one-to-one with the rolling grooves are formed on the inner hole wall of the hammer head, the force-bearing side of the force-bearing grooves also being V-shaped and opening toward the front end of the camshaft, a steel ball for transmitting force being provided between the force-bearing groove and the cooperating rolling groove; and characterized in that: The linear shape of the force side of the camshaft raceway groove and / or the hammer head force groove developed on the designed development circle includes a polynomial curve.

2. The impact mechanism of an electric wrench according to claim 1, characterized in that: The raceway centerline of the raceway groove is unfolded on the designed unfolding circle and includes two inclined straight lines. The intersection of the two straight lines is connected by a tangent transition through an intermediate curve. The free ends of the two straight lines are tangently connected to the terminal curves. The intermediate curve, the two straight lines and the two terminal curves are symmetrically arranged and constitute the raceway centerline of the raceway groove; the intermediate curve and / or the terminal curve are polynomial curves.

3. The impact mechanism of an electric wrench according to claim 2, characterized in that: The center line of the force-bearing side is developed on a designed development circle, which has a polynomial curve adapted to the center line of the raceway.

4. The impact mechanism of an electric wrench according to any one of claims 1 to 3, characterized in that: The polynomial curve adopts a polynomial function curve of cubic, quartic, quintic or higher order.

5. The impact mechanism of an electric wrench according to claim 2, characterized in that: The polynomial curve on the centerline of the raceway adopts a fifth-order polynomial function curve, which conforms to the formula: Y=C0+C1×X+C2×X 2 +C3×X 3 +C4×X 4 +C5×X 5 , where Y represents the axial dimension of the camshaft, X represents the circumferential dimension of the camshaft, and C0, C1, C2, C3, C4, and C5 are variable coefficients.

6. The impact mechanism of an electric wrench according to claim 1, characterized in that: A flange is raised on the outer circumferential side of the hammer head, and an outer ring portion is raised on the outer edge of the flange toward the shaft shoulder. An annular cavity is formed between the outer ring portion and the outer circumferential side of the hammer head. The front end of the spiral compression spring slides and falls into the annular cavity. A plane bearing is provided on the bottom wall of the annular cavity, and the front end of the spiral compression spring abuts against one surface of the plane bearing.

7. The impact mechanism of an electric wrench according to claim 6, characterized in that: The plane bearing is a plane thrust bearing with needle rollers.

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