JPH0718463B2 - Leaf spring - Google Patents

Description

Description: [Industrial field of use] The present invention relates to a leaf spring composed of a parent plate and a single plate or a plurality of child plates.

[Conventional technology]

Generally, as a leaf spring, as shown in FIG. 1, a taper leaf spring is known in which a master plate 1 having a Berlin eye or a Berlin eye 2 and a plurality of slave plates 3 are stacked.

As a truck suspension, a leaf spring having a parent plate 8 having an upturned eye 9 is well known as shown in FIG. The spring constant, which is the load-deflection characteristic of the upturned leaf spring, has a characteristic as shown in FIG.

That is, FIG. 10 shows a characteristic diagram of the hysteresis generated due to the friction between the plates of the leaf spring when the leaf spring bends up and down. In this characteristic diagram, the load W increases when the deflection X is increased from the point a in the standard load state. When the deflection X is reduced after reaching the arbitrary point b, the load-deflection diagram draws another characteristic diagram such as b → c → d without increasing the characteristic diagram of a → b when increasing. . Furthermore,
If deflection X is reduced to point e and then increased again, e → f
→ Draw a characteristic diagram of b and form a loop. In this loop, b → c and e → f are generally referred to as a transition part. The inclination of this transition portion has a substantially equal shape even if it is obtained by another amplitude, that is, the deflection X value, and as shown in FIG. 10, for example, b ₁ → c ₁ , e ₁ → f ₁ and b ₂ → Draw c ₂ , e ₂ → f ₂ .

Further, for example, Japanese Utility Model Laid-Open No. 55-127141 discloses a laminated leaf spring in which a steel roll is provided between the spring plates of the laminated leaf spring.

Alternatively, JP-A-56-141433 discloses a leaf spring device in which the spring constant changes discontinuously at a predetermined load value.

[Problems to be Solved by the Invention]

By the way, in a leaf spring having the above characteristic diagram, the performance of the leaf spring is usually b → e, b ₁ → e ₁ , b ₂
→ diagonal spring constant tK determined from the slope of e _2, the width or friction of tK _1, tK ₂ (showing a substantially close to the dynamic spring constant) and shake a~d than the base point a load was determined by the amplitude It is almost determined by the characteristics.

Therefore, based on the load-deflection characteristics of the up-turned eye-shaped leaf spring as shown in FIG. 10, the diagonal spring constant, so-called dynamic spring constant, and the amplitude dependence of the friction are calculated. And, as shown by the alternate long and short dash line in FIG. That is, it can be seen that the diagonal spring constant is high in the range where the amplitude is small, and the diagonal spring constant decreases as the amplitude increases and approaches the static spring constant.

However, as a suspension of a vehicle, a spring that has a low spring constant at a small amplitude and provides a soft riding comfort, and has a high spring constant at a large amplitude, and that provides a highly stable and rigid feeling is desired. Therefore, the conventional leaf spring has a characteristic completely opposite to the ideal characteristic, which is a performance disadvantageous characteristic.

In this type of leaf spring, in order to obtain a soft ride comfort, in order to keep the diagonal spring constant at a small amplitude low, the number of springs constituting the leaf spring should be reduced, or
Alternatively, friction is reduced by inserting a low-friction material with a low coefficient of friction into the plate end, but if the laminated leaf spring is configured in this way, as shown by the dotted line in FIGS. 11 and 12. Become. That is, the friction at large amplitude is reduced and the diagonal spring constant is reduced, resulting in a suspension with no sense of rigidity and poor stability.

Also, with this method, the friction between the leaf springs of the leaf spring is only reduced, so the diagonal spring constant of the minimum amplitude (that is, the spring constant at the minimum amplitude that is approximately equal to the inclination of the transition portion) is also sufficiently reduced. It has a problem that it cannot be done.

An object of the present invention is to solve the above problems,
A laminated leaf spring composed of a parent plate having an eyeball and one or more child plates is formed so as to have ideal spring characteristics, and a contact point between the parent plate and the child plate, that is, a contact portion, is formed. By constructing the structure so that the amount of displacement within the deformation limit range of elastic deformation of the spring plate from the elastic deformation of the parent plate and the child plate to the beginning of slipping falls within a predetermined range, the small amplitude of the leaf spring The diagonal spring constant and friction are suppressed to ensure a soft ride comfort, and the diagonal spring constant and friction at a large amplitude are maintained at a sufficient size as in the past to achieve a highly stable and rigid feeling. It is to provide a leaf spring.

[Means for Solving the Problems]

The present invention is configured as follows to achieve the above object. That is, the present invention is composed of a parent plate and a child plate having eyeballs at both ends, the central portions of which are fixed to each other, and the eyeballs of the parent plate and the both ends of the child plate are in contact with each other so as to be relatively displaceable. In the leaf spring, the displacement amount at which the parent plate elastically deforms without contact between the eyeball of the parent plate and the child plate without causing relative slip under load is defined as the central portion of the parent plate. The converted displacement expressed by the following formula converted to the vertical displacement of the fulcrum of is 0.010m to 0.01
The present invention relates to a leaf spring having a structure set so as to exist within a range of 5 m. The following formula is as follows:

However, P; the contact force between the parent plate and the child plate when the load W acting on the spring plate at the maximum design load is applied to the entire spring plate,
μ: Friction coefficient between spring plates, L: Distance between U bolt of parent plate and contact point, H: Distance between parent plate and child plate at U bolt tightening part, R: Eyeball of parent plate Radius of the outer diameter of R, R '; distance between the center of the thickness of the master plate and the contact point, Kw; rigidity of the master plate.

[Action]

The leaf spring according to the present invention is configured as described above and operates as follows. That is, this leaf spring is
It consists of a parent board having eyeballs at both ends and a child board, and the contact area between the parent board and the child board adjacent to the parent board is elastically deformed without relatively sliding under load. Since the deformation amount has a structure in which the converted displacement amount converted into the vertical displacement amount of the fulcrum of the central portion of the parent plate is set within the range of 0.010 m to 0.015 m, the dynamic spring constant of the leaf spring is set. The characteristics can be set to the ideal type, and for the leaf spring, the diagonal spring constant and friction in the small amplitude region of the spring plate are suppressed, and the diagonal spring constant and friction at large amplitude with large span changes are Similarly, it can be configured to have a size large enough to obtain the characteristics governed by ordinary sliding friction between plates.

〔Example〕

An embodiment of a leaf spring according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a leaf spring as an embodiment of the present invention. This leaf spring is composed of a main leaf 1 which is the first leaf having Berlin-shaped eyeballs 2 at both ends and a plurality of leaf springs (in the figure, 2).
(The number of sub-boards 3) is overlapped over the entire length of the board and is fixed to each other by a center bolt 4 at the center of the board.

Further, the leaf spring itself is fixed by a pair of U bolts 10 arranged at a predetermined position with respect to the axle of the vehicle, that is, a position serving as a fulcrum for supporting the load at the central portion. This leaf spring is composed of a taper leaf spring in which a parent plate 1 and a daughter plate 3 are formed in a tapered shape. In addition,
In the figure, 5 indicates a clip.

In the leaf spring according to the present invention, for example, as shown in FIGS. 1 and 3, the contact point A between the parent plate 1 and the child plate 3 which is the second leaf is located below the center portion of the parent plate 1. Is located in. Further, the main plate 1 which constitutes this leaf spring has a structure in which its rigidity Kw and eyeball diameter R satisfy the following equation.

That is, this laminated leaf spring is composed of a parent plate having eyeballs at both ends and a child plate, and a contact point between the parent plate and the child plate adjacent to the parent plate causes relative slip under load. Deformation amount that elastically deforms the contact portion of the parent plate without, the converted displacement amount converted to the vertical displacement amount of the fulcrum of the central portion of the parent plate is set to exist within the range of 0.010m ~ 0.015m Is to have.

Specifically, the converted displacement amount satisfies the following equation.

However, all units are SI units.

P; Load W acting on the spring plate at the maximum design load
Is the contact force between the master plate 1 and the slave plate 3 when given to the whole spring plate. As shown in FIG. 1, in the case of a leaf spring composed of three spring plates, P≈W It is generally set to / 6.

μ: Friction coefficient between steel materials, that is, between spring plates, L: Distance between the contact point A with the child plate 3 on the parent plate 1 and the U bolt 10 that is the fulcrum of the central portion, H: U bolt 10 Distance between the parent plate 1 and the child plate 3 at the tightening portion (see FIG. 4), R: Radius of outer diameter of the eyeball 2 (see FIG. 3), R ′; Distance from contact point A (R = R 'when the master plate 1 is the Berlin eyeball 2, and R >>R'≈ when the master plate 8 is the upturned eye 9)
0), Kw; A value expressed by Kw = T / θ where θ is the rotation angle of the eyeball 2 when the torque T is applied to the eyeball portion due to the rigidity of the base plate 1.

Here, the rigidity Kw of the master plate 1 will be described. In the above-described embodiment, the master plate 1 and the slave plate 3 are configured by taper leaves, but if the master plate is configured by the same plate thickness over the entire length, the rigidity Kw Kw is represented by the following formula. This will be described with reference to FIG.

In the following equation, the second moment of area acting on the main plate 1 is I, the elastic modulus is E, and the radius of curvature of the curved connecting portion 7 between the eyeball 2 of the main plate 1 and the flat spring plate portion 6 is r.

First, the parent board 1 from the contact point A between the parent board 1 and the child board 3 to the point C of the straight end portion of the parent board 1 is made of a rigid body, and the end portion of the spring board portion 6 of the parent board 1 is Point C to point D where U bolt 10 is located
If the parent board 1 up to is composed of an elastic body, the angle change at the point C is μPRL / 2EI, and the eyeball part of the parent board 1 is μPRL.
/ 2 EI rotate.

Further, from the contact point A to the boundary point B between the eyeball 2 of the base plate 1 and the curved connecting portion 7, and from the point C to the point D are rigid bodies,
Further, if the points B to C are made of an elastic body,
The angle change at the point B with respect to the point C is Becomes

Further, if the points B to C are made of a rigid body and the points A to B are made of an elastic body, the angle change at the point A with respect to the point B is Becomes

Here, since the shape of the spring plate in a general leaf spring is L >> R >> r, the angle change of the eyeball portion of the master plate 1 is such that the rigidity is dominant from point C to point D, and Since the rigidity from A to point B and the rigidity from point B to point C can be ignored, it becomes μPRL / 2EI.

Therefore, The spring constant of the carrier plate 1, K _1, because it is ^{_{K 1 = 6EI / L 3,}} Kw = K 1 L 3 / 3L = K 1 L 2/3 becomes proportional to the windup rigidity of the parent plate 1 . Therefore, in the following description, for convenience, Kw is referred to as the windup rigidity of the master plate 1, that is, the rigidity of the master plate 1.

The leaf spring according to the embodiment of the present invention has the above-mentioned structure and operates as follows. The operation of this leaf spring will be described with reference to FIGS. 1, 3 and 7.

When the load applied when the vehicle is used in a constant loading state, that is, the load W at the time of maximum loading in design is applied to the leaf spring, the eyeball portion of the parent plate 1, that is, the parent plate 1 and the child plate 3 come into contact with each other. A force P is applied to the point A from the second and subsequent child plates 3. The friction force μP generated by this force P causes the torque μP
P'is applied to the master plate 1, that is, the wind-up torque is applied to the master plate 1, and the master plate 1 causes the wind-up.

That is, under the load of the leaf spring, the contact portion A between the parent plate 1 and the child plate 3 does not relatively slide, and the contact portion A of the parent plate 1 with the child plate 3 elastically deforms to rotate in a deformation range. Occurs. At this time, if the wind-up rigidity of the parent board 1 is Kw, the rotation angle of the eyeball portion of the parent board 1, that is, the contact portion A with the child board 3 is μP · R / Kw.

In this state, the design standard load W is increased by ΔW, and the spring displacement (corresponding to the vertical displacement amount), that is, the deflection X is increased by 15 mm (0.015 m).

In this case, since W >> ΔW, it is considered that the change in P is small. At this time, the relationship between the load W acting on the spring plate and the spring displacement X at the time of maximum design loading is from point E to point F (E → F), as shown in FIG.

Next, the load W is reduced. In this case, in the conventional leaf spring, the displacement between the springs immediately causes a slip between the spring plates, and a frictional force acts. Therefore, in FIG.
As shown by → c and e → f, the load changes rapidly,
When the leaf spring is constructed as in the embodiment of the present invention,
Before slippage occurs between the spring plates, the eyeball portion rotates due to the windup of the parent plate 1 which is the most leaf, and it starts to slide only after the torque accumulated by the rotation becomes larger than the frictional force. Therefore, as shown in FIG. 7, from point F to point G (F → G) changes gradually, and from point G begins to slip to point H, so that a smooth hysteresis curve is drawn as shown in the figure. Like

The rotation angle (μP · R '/ Kw) of the eyeball portion of the master plate 1 caused by the windup of the master plate 1 is determined by the amount of displacement of the arc of the contact portion A with the slave plate 3 of the master plate 1 corresponding to the rotation angle. That is, when converted into a displacement amount of elastically deforming the master plate 1, the following is obtained. In this case, taking into account the reverse windup that occurs in the main board 1 and doubling, Becomes

Further, referring to FIG. 6, the displacement amount X of elastically deforming the master plate 1 is determined by a fulcrum (U
The converted displacement amount converted into the vertical displacement amount in (corresponding to the portion of the bolt 10) is as follows.

Becomes

More specifically, as shown in FIG. 6, the displacement amount of the eyeball portion of the master plate 1, that is, the contact portion A of the master plate 1 with the slave plate 3 is X, and the spring plate is bent in accordance with the displacement amount X. Each angle, that is, the angle formed by the contact portion A between the parent board 1 and the child board 3 under no load is ψ ₁ , and the parent board 1 and the child board 3 are parent under load. An angle formed by a contact portion A between the board 1 and the child board 3 is ψ ₂ , and a contact area between the child board 3 of the parent board 1 and a rotation angle of the center portion of the parent board 1 caused by windup of the parent board 1. An angle corresponding to the displacement amount X (displacement amount of elastic deformation of the base plate 1) of the arc A, in other words, the base plate 1 and the child plate 3 exceed the elastic deformation range, and the main plate 1 and the child plate 3 are separated. first time slippage occurs between, when a corresponding angle to the displacement X between the master plate 1 and Coban 3 and [psi _3, a _{ψ 1 ≒ ψ 2 ≒ ψ 3} , yet [psi ₁ ≒ [psi ₂ ≈ ψ ₃ ≈ T Therefore, the converted displacement amount X · ψ ₃ obtained by converting the displacement amount X of the arc of the contact portion A of the master plate 1 with the slave plate 3 into the vertical displacement amount at the fulcrum is X · ψ ₃ = X · It becomes T / L.

Therefore, the displacement amount within the range of elastic deformation at the contact portion A of the parent plate 1 with the child plate 3, in other words, the displacement amount of the parent plate 1 at which the contact portion A of the parent plate 1 with the child plate 3 starts sliding for the first time. When the converted displacement amount of the above spring is set to 0.015 m, that is, 15 mm as in the embodiment according to the present invention, first, from the load W acting on the spring plate at the time of maximum design load on the spring plate, When the load is increased and the vertical displacement at the fulcrum (corresponding to the portion of the U bolt 10) that receives the load W at the central portion of the parent board 1 is deflected by 15 mm and then returned to the neutral point, that is, 15 mm, the parent Plate 1 begins to wind up and then reverse winds up. Then, when the spring plate is returned to 15 mm, the force accumulated by the reverse windup becomes equal to the friction force μP,
From this point, slippage occurs between the spring plates.

Therefore, the friction at the neutral point of the spring plate is equal to that of the conventional spring.

On the other hand, if the flexure of the spring plate is, for example, 10 mm, at the neutral point, slippage at the contact portion A of the parent plate 1 with the child plate 3 does not occur yet, so the friction at this time is greater than that of the conventional spring plate. small. From the results obtained by the above method, the diagonal spring constant and the amplitude dependence of friction are obtained as shown in FIGS. 8 and 9.

That is, for example, if the vehicle rolls while cornering or runs on a bad road, it is
When the above input occurs, the diagonal spring constant and friction equivalent to those of the conventional spring plate are provided for the input. On the other hand, when the vehicle is driving on a good road such as a highway, with a small input of 15 mm or less, the diagonal spring constant and friction are low, and a soft ride comfort can be obtained.

On the contrary, the converted displacement amount converted into the vertical displacement amount of the master board 1 is Then, even if the input to the spring plate is 15 mm or more, it will be softer than the conventional spring plate, and the unsprung vibration of the roll on cornering of the vehicle, bad road, etc. will increase,
Performance will decrease. For example, in FIG. Shows the displacement-load characteristics in the case of
mm) becomes longer, and 2F at an amplitude of ± 15 mm decreases (from 2F 'to 2F in the figure). If the 2F at 15 mm is reduced, the stability to rolls or the damping to spring resonance on bad roads deteriorates.

Further, in the case where the converted displacement amount of the spring at the contact point A of the master plate 1 with the slave plate 3 is 0.010 m, the load W acting on the spring plate at the time of maximum design load is added to the spring plate. With a deflection of 10 mm or more, it is equal to the conventional spring plate, and with an input of 10 mm or less, it is softer than the conventional spring plate.

Further, the converted displacement amount converted into the vertical displacement amount of the master board 1 is Then, even if an input of 10 mm or less is applied to the spring plate, the spring plate has the same hardness as that of the conventional spring plate, and it is impossible to secure a favorable ride comfort on a good road.

For example, in FIG. 14, Shows the displacement-load characteristics in the case of
m) becomes shorter, and the diagonal spring constant cannot be reduced when the small amplitude is 10 mm or less.

Therefore, the diagonal spring constant of ± 5 mm or more becomes equivalent to the conventional one, and in particular, the spring constant in the range where it is considered desirable to lower it to improve the riding comfort, ± 5 mm to ± 10 mm, becomes the same as the conventional one. Will end up.

The relationship between the above amplitude and 2F is shown in FIG. 15, and the relationship between the above amplitude and the diagonal spring constant is shown in FIG.

In FIG. 15, when the amplitude X is plotted on the horizontal axis and 2F is plotted on the vertical axis, it is preferable that the characteristic is in the range shown by the slanted lines until the amplitude X is ± 15 mm. An upturned eye type leaf spring may be used. However, the region where the amplitude X is ± 15 mm or more is a region that affects unsprungness on rolls and rough roads.

In FIG. 16, when the amplitude X is plotted on the horizontal axis and the diagonal spring constant is plotted on the vertical axis, it is preferable that the characteristic is in the range shown by the diagonal lines when the amplitude X is ± 10 mm or less. It is better to lower than the eye-shaped leaf spring.

However, 2F is the width of revival when the hysteresis loop of the spring is obtained, and is a factor that determines the damping performance of the spring unit. If the width of the above-mentioned revival is 2F, the damping property becomes poor. It may be possible to supplement with a shock absorber, but with a leaf spring it is much larger than the damping force of the shock absorber, and it is not possible to supplement with the damping force of the shock absorber alone. Therefore, when used with a large amplitude, the width of revival 2F should be large. On the contrary, the width of revival above 2F
When is large, the diagonal spring constant increases. Therefore, when used with a small amplitude, it is better to make the width of revival 2F as small as possible.

The diagonal spring constant is a characteristic that affects the vibration performance of the spring, and can be considered as a dynamic spring constant.
A high diagonal spring constant results in a hard spring, and a low diagonal spring constant results in a soft spring. In the case of a leaf spring, there is a large friction (equivalent to 2F), so
The diagonal spring constant at small amplitude increases, resulting in a hard and uncomfortable ride. Therefore, in order to reduce the diagonal spring constant at small amplitude, it is necessary to reduce 2F at small amplitude.

From the above, regarding the leaf spring according to the present invention, in the roll and the bad road when the vehicle is cornering,
To prevent flapping under the spring, when the amplitude X is ± 15 mm or more, it is preferable that the 2F be the same as that of the conventional leaf spring, and also improve the ride comfort of the vehicle on good roads and joint roads. In order to achieve this, when the amplitude X is ± 10 mm or less, it is preferable that the diagonal spring constant be lower than that of the conventional leaf spring. This is shown graphically in Figures 17 and 18
It becomes like the figure. Here, when the converted displacement amount of the spring obtained by converting the displacement angle X of the rotation angle of the eyeball portion at the contact portion between the parent plate and the child plate in contact with the parent plate is represented by S, the following equation is obtained.

In Fig. 17, the value of the converted displacement S of the spring and the amplitude are ± 15
The relationship of 2F when mm is shown. The horizontal axis plots the value of the spring displacement S and the vertical axis plots the value of 2F when the amplitude X is ± 15 mm. That is, in order to secure 2F with an amplitude X of ± 15 mm or more equivalent to a conventional leaf spring, the vertical displacement S of the spring is
Must be 0.015 mm or less.

In Fig. 18, the value of the converted displacement S of the spring and the amplitude are ± 10
The relation of the diagonal spring constant when mm is shown. The value of the spring equivalent displacement S is plotted on the horizontal axis, and the value of the diagonal spring constant when the amplitude X is ± 10 mm is plotted on the vertical axis. That is, in order to reduce the diagonal spring constant when the amplitude X is ± 10 mm or less, the spring displacement S must be 0.010 m or more.

Therefore, the main plate 1 constituting the leaf spring according to the present invention
It is preferable that the structure (1) is configured so that the converted displacement of the spring plate satisfies the following expression.

[Effects of the Invention] The leaf spring according to the present invention is configured as described above and has the following effects. That is, this leaf spring is composed of a parent plate and a child plate having eyeballs at both ends, the central portions of which are fixed to each other, and the eyeballs of the parent plate and both ends of the child plate are in contact with each other so as to be relatively displaceable. In the leaf spring, the displacement amount at which the contact point between the center plate of the master plate and the slave plate elastically deforms without causing relative slip under load is the fulcrum of the central part of the master plate. Since it has a structure in which the converted displacement converted to the vertical displacement exists within the range of 0.010 m to 0.015 m, it is possible to set the dynamic spring constant characteristic of the leaf spring to the ideal form. A layered leaf spring that suppresses friction with a small amplitude to obtain a soft ride comfort and has a large amplitude with a large amplitude as in the past, and provides a highly stable and rigid feeling it can.

That is, the friction is reduced in the small amplitude region of the spring plate, and in the large amplitude region in which the span change is large, it is possible to obtain a characteristic that is governed by normal inter-plate sliding friction.

Therefore, regarding the leaf spring according to the present invention, by applying the leaf spring to a vehicle, ride comfort characteristics of the vehicle, particularly, ideal friction characteristics in a small amplitude region can be obtained. It is not necessary to control the damping force as described above, and since it is possible to increase the friction more than before in the large amplitude region, the need for a stabilizer at the time of rolling can be reduced, which is a great effect. it can.

[Brief description of drawings]

1 is a schematic view showing an example of a leaf spring having a Berlin-shaped eyeball, FIG. 2 is an explanatory view showing an example of a leaf spring having an upturned eye, and FIG. 3 is a view showing a leaf spring according to the present invention. FIG. 4 is an explanatory view showing an operating state of the parent plate and the child plate, FIG. 4 is an explanatory view showing a part of the parent plate of the leaf spring according to the present invention, and FIG. 5 is one of the parent plates of the leaf spring according to the present invention. FIG. 6 is a diagram for explaining a vertical displacement amount during windup of a parent plate of the leaf spring according to the present invention, and FIG. 7 is a load-deflection characteristic of the leaf spring according to the present invention. FIG. 8 is a graph showing the relationship between the amplitude of the leaf spring according to the present invention and the diagonal spring constant, and FIG. 9 is a graph showing the relationship between the amplitude of the leaf spring according to the present invention and the friction. Is a graph showing the load-deflection characteristics of a conventional leaf spring. A graph showing the relationship between the amplitude and the diagonal spring constant of a conventional leaf spring, FIG. 12 is a graph showing the relationship between the amplitude and friction of a conventional leaf spring, and FIG. 13 is the load of the leaf spring according to the present invention. -A graph showing the bending characteristics, Fig. 14 is a graph showing the load-deflection characteristics of a conventional leaf spring, Fig. 15 is an explanatory diagram showing the relationship between the amplitude and 2F, and Fig. 16 is the relationship between the amplitude and the diagonal spring constant. Fig. 17 is an explanatory view showing the relationship between 2F when the value of the displacement of the spring and the amplitude are ± 15 mm, and Fig. 18 is the value of the displacement of the spring and the amplitude of ± 10 mm. It is explanatory drawing which shows the relationship of the diagonal spring constant at time. 1,8 …… Main plate, 2,9 …… Eyes, 3 …… Child plate, 4 …… Center bolt, 6 …… Flat spring plate part, 7 …… Curved connection part,
10 ... U bolt.

Claims (1)

[Claims] 1. A parent board and a child board having eyeballs at both ends,
In a leaf spring having central portions fixed to each other and both ends of the parent plate and both ends of the child plate contacting each other so that they can be displaced relative to each other, contact between the eyeballs of the parent plate and the child plate A displacement amount in which the base plate is elastically deformed without causing relative slippage under load, and a converted displacement amount represented by the following formula in which the vertical displacement amount of the fulcrum of the center part of the base plate is converted into A laminated leaf spring having a structure set so as to exist within the range of 0.010 m to 0.015 m. However, P; the contact force between the parent plate and the child plate when the load W acting on the spring plate at the maximum design load is applied to the entire spring plate,
μ: Friction coefficient between spring plates, L: Distance between U bolt of parent plate and contact point, H: Distance between parent plate and child plate at U bolt tightening part, R: Eyeball of parent plate Radius of the outer diameter of R, R '; distance between the center of the thickness of the master plate and the contact point, Kw; rigidity of the master plate.