Abstract:
In an adjusting method for remedying the coil pitch tolerance and fatigue deformation of an adjustable helical spring, an adjusting mechanism is mounted at one end of the casing for the adjustable helical spring for changing the precompression or the pretension of the helical spring to thereby remedy the coil pitch tolerance and fatigue deformation thereof, and rotating a rotatable element mounted in the casing and connected to one end of the helical spring, so that the helical spring is adjusted to a preset number of effective turns, and then the precompression or the pretension of the helical spring is adjusted. The adjusting method not only solves the problem of coil pitch tolerance and fatigue deformation existed in the adjustable helical spring, but also reduces noises produced by the adjustable helical spring in use.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an adjusting method and adjusting mechanism for remedying the coil pitch tolerance and fatigue deformation of an adjustable helical spring, and more specifically to an adjusting method for remedying the coil pitch tolerance and fatigue deformation of an adjustable helical spring used in a shock absorber.  
         [0003]     2. Description of the Related Art  
         [0004]     A conventional spring has an elastic coefficient determined at the time of production, and is therefore not always useable for different types of machines. As a result, different helical springs must be designed for different machines or different purposes, and it is uneconomical to do so.  
         [0005]     To overcome the above shortcomings, the same inventor of the present invention has invented a casing for adjustable helical spring, which was published under Taiwanese Patent Publication No. 436588 on May 28, 2001. The casing for adjustable helical spring disclosed in Taiwanese Patent Publication No. 436588 comprises a male and a female case, and a rotatable element to enable adjustment of the helical spring to different elastic coefficients to meet the requirement of different machines. The helical spring has an end fixedly connected to a seat at a bottom center of the female case, and another opposite end located in the male case. The rotatable element is provided on an external or an internal surface with a plurality of stoppers to contact with coils of the helical spring. When the rotatable element is turned, the number of effective coils of the helical spring subjected to compressive force or tension force is changed to thereby adjust the elastic coefficient of the helical spring corresponding to actual need. With the casing for adjustable helical spring disclosed in Taiwanese Patent Publication No. 436588, the helical spring is more practical for use, and the problems existed in the conventional helical springs could be effectively solved.  
         [0006]     While the casing for the adjustable helical spring disclosed in Taiwanese Patent Publication No. 436588 is able to solve the problem existed in the conventional helical springs, it fails to overcome another common problem in the helical springs, that is, the fatigue and deformation of the helical spring caused by using the helical spring over a prolonged time or overusing the helical spring. So, it is desirable to develop a method and mechanism to effectively solve the above problem to reduce the rate of replacement of the adjustable helical spring.  
       SUMMARY OF THE INVENTION  
       [0007]     A primary object of the present invention is to provide an adjusting method for remedying the coil pitch tolerance and fatigue deformation of an adjustable helical spring. In implementing the adjusting method, an adjusting mechanism is mounted at one end of the casing of the adjustable helical spring to effectively turn the rotatable element in the casing, so as to solve the problems caused by the coil pitch tolerance and fatigue deformation of the adjustable helical spring, obtain a preset number of effective turns of the helical spring, and reduce noises produced by the adjustable helical spring in use.  
         [0008]     Another object of the present invention is to provide an adjusting method for remedying the coil pitch tolerance and fatigue deformation of an adjustable helical spring that could be employed on all kinds of casing for the adjustable helical spring, including adjustable compression and tension helical springs.  
         [0009]     A further object of the present invention is provide an adjusting method for remedying the coil pitch tolerance and fatigue deformation of an adjustable helical spring, so as to prolong the service span of the adjustable helical spring and to reduce the rate of failure of machines using helical springs.  
         [0010]     To achieve the above and other objects, the adjusting method of the present invention includes the steps of mounting an adjusting mechanism to one end of the casing of the adjustable helical spring and connecting the helical spring to the adjusting mechanism; changing the precompression or pretension of the helical spring to thereby remedy the coil pitch tolerance and fatigue deformation thereof, so that the helical spring is recovered to a coil pitch the same as that of the rotatable element; leaving a small clearance between the stoppers of the rotatable element and the spring coils, against which the stoppers press; rotating the rotatable element, which is mounted in the casing and connected to one end of the helical spring, so that the helical spring is adjusted to a preset number of effective turns; and then adjusting the precompression or pretension of the helical spring.  
         [0011]     During the process of fabricating the helical spring, each coil pitch inevitably has an allowable tolerance. When the adjustable helical spring has been used for a long time, it is subjected to deformation due to elastic fatigue thereof, and accordingly changed coil pitch that has an increased range of tolerance. However, the pitch of the rotatable element remains unchanged. In other words, when the rotatable element is rotated by one turn, a distance of the axial displacement thereof is the same. To ensure that the rotatable element may be effectively rotated without being adversely affected by the coil pitch tolerance or the fatigue deformation, the adjusting mechanism is therefore mounted at one end of the casing of the adjustable helical spring and set to an initial state. In the initial state, a small clearance is left at the location at where the stoppers of the rotatable element is pressed against the spring coils, so that the spring coils are separated from the rotatable element, enabling a maximum adjusting range for the precompression or the pretension of the helical spring, and a maximum adjusting range for the number of effective turns of the helical spring.  
         [0012]     The steps for adjusting the number of effective turns of the adjustable helical spring are as follows:  
         [0013]     Step 1: changing the precompression or pretension of said helical spring using said adjusting mechanism, so that said helical spring is recovered to a coil pitch the same as that of said rotatable element (i.e., a preset coil pitch), and said stoppers on said rotatable element and said spring coils are separated from one another at where the stoppers of the rotatable element press against the spring coils with a small clearance left between them;  
         [0014]     Step 2: turning the rotatable element to obtain the number of effective turns preset for the helical spring; and return to Step 1 in case the stoppers of the rotatable element are in contact with the spring coils to prevent the rotatable element from rotating effectively; and  
         [0015]     Step 3: using the adjusting mechanism to increase the precompression or pretension of the adjustable helical spring, causing the stoppers of the rotatable element to closely press against the spring coils of the helical spring. 
     
    
     BRIEF DESCRIPTIONS OF THE DRAWINGS  
       [0016]      FIG. 1  is an exploded perspective view of an adjusting mechanism for remedying the coil pitch tolerance and fatigue deformation of an adjustable helical spring according to a first embodiment of the present invention, wherein the adjusting mechanism is mounted at an end of a male case of a casing for an adjustable helical spring and works with an externally grooved rotation member;  
         [0017]      FIG. 2  is an assembled view of  FIG. 1 ;  
         [0018]      FIG. 3  is an assembled sectional view of  FIG. 1 ;  
         [0019]      FIG. 4  is an assembled sectional view of an adjusting mechanism for remedying the coil pitch tolerance and fatigue deformation of an adjustable helical spring according to a second embodiment of the present invention, wherein the adjusting mechanism is mounted at an end of a male case of a casing for an adjustable helical spring and works with an internally grooved rotation member;  
         [0020]      FIG. 5  shows the manner of using the adjusting mechanism of  FIG. 1  to adjust an adjustable compression helical spring mounted in a male case having an outer diameter smaller than an inner diameter of a female case of the casing for the adjustable helical spring;  
         [0021]      FIG. 6  shows the manner of using the adjusting mechanism of  FIG. 1  to adjust an adjustable tension helical spring mounted in a male case having an outer diameter smaller than an inner diameter of a female case of the casing for the adjustable helical spring;  
         [0022]      FIG. 7  shows the manner of using the adjusting mechanism of  FIG. 4  to adjust an adjustable compression helical spring mounted in a male case having an outer diameter smaller than an inner diameter of a female case of the casing for the adjustable helical spring; and  
         [0023]      FIG. 8  shows the manner of using the adjusting mechanism of  FIG. 4  to adjust an adjustable tension helical spring mounted in a male case having an outer diameter smaller than an inner diameter of a female case of the casing for the adjustable helical spring. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]      FIGS. 1, 2  and  3  are exploded and assembled perspective views, and assembled sectional view of an adjusting mechanism  70  for remedying the coil pitch tolerance and fatigue deformation of an adjustable helical spring according to a first embodiment of the present invention. As shown, the adjusting mechanism  70  according to the first embodiment of the present invention includes a fixing case  701 , a preset barrel  702 , a turning knob  703 , a drive cylinder  704 , a rotator knob  705 , a drive shaft  706 , and a spacer  707 , and is mounted at an end of a male case of a casing for an adjustable helical spring  40  to work with an externally grooved rotatable element  30  having a plurality of stoppers  301  provided around an outer surface thereof.  
         [0025]     The fixing case  701  is a hollow case having a central hole formed at a bottom end. The bottom central hole has an inner diameter smaller than that of a front end of the fixing case  701  opposite to the bottom end. The fixing case  701  is provided at a predetermined position near the bottom central hole with first external threads to mesh with internal threads provided in an open end of the male case of the adjustable helical spring  40 , so as to fixedly connect the whole adjusting mechanism  70  to the casing of said adjustable helical spring  40 . The fixing case  701  is provided with an axial slot  708  of a predetermined length. The axial slot  708  has a bottom end close to the bottom end of the fixing case  701 , and a front end opposite to the bottom end. The fixing case  701  is also provided around the bottom end with second external threads to mesh with internal threads on the spacer  707 .  
         [0026]     The preset barrel  702  is a hollow member with internal threads provided in a first end thereof to mesh with external threads provided on the drive cylinder  704 , and in an opposite second end to mesh with external threads on the rotatable element  30 . The helical spring  40  is connected at an end to an outer peripheral surface of the second end of the preset barrel  702 , so as to fixedly connect the helical spring  40  to the adjusting mechanism  70 .  
         [0027]     The retaining key  709  is mounted at a predetermined position on the outer peripheral surface of the preset barrel  702  and guided by the slot  708  on the fixing case  701  to axially move the preset barrel  702 .  
         [0028]     The drive cylinder  704  is also a hollow member with a first end extended through the bottom central hole of the fixing case  701  to tightly engage with the turning knob  703 , and an opposite second end provided with external threads to mesh with the internal threads in the first end of the preset barrel  702 .  
         [0029]     The turning knob  703  is manually operable for adjusting precompression or pretension of the helical spring  40 , and is located at an outer side of the bottom central hole of the fixing case  701  to tightly engage with the drive cylinder  704 . The turning knob  703  is smoothly turnable relative to the fixing case  701  to rotate the drive cylinder  704 . The drive cylinder  704  rotated by the turning knob  703  and the retaining key  709  mounted on the preset barrel  702  and guided by the slot  708  on the fixing case  701  together cause the preset barrel  702  to move axially.  
         [0030]     The spacer  707  is an internally threaded hollow member screwed to the second external threads of the fixing case  701 .  
         [0031]     The drive shaft  706  has a first end extended through the bottom central hole of the fixing case  701  and a central hole on the spacer  707  to tightly engage with the rotator knob  705 , and an opposite second end having axially extended drive keys spaced on an outer surface thereof to slidably fit in an axial keyway provided on the rotatable element  30 .  
         [0032]     The rotator knob  705  is manually turnable for adjusting the number of effective turns of the helical spring  40 , and is located at an outer side of the spacer  707  to tightly engage with the first end of the drive shaft  706 . The rotator knob  705  is smoothly turnable relative to the spacer  707  to rotate the drive shaft  706  and, accordingly, the rotatable element  30 , which is connected to the drive shaft  706  via engagement of the axial keyway on the rotatable element  30  with the axial drive keys on the drive shaft  706 . And, the rotatable element  30  is brought to turn and axially move at the same time due to the retaining key  709  on the preset barrel  702  and the engagement of the external threads on the rotatable element  30  with the internal threads in the second end of the preset barrel  702 .  
         [0033]      FIG. 4  is an assembled sectional view of an adjusting mechanism  80  for remedying the coil pitch tolerance and fatigue deformation of an adjustable helical spring  40  according to a second embodiment of the present invention, wherein the adjusting mechanism  80  is mounted at an end of a male case  10  of the casing for the adjustable helical spring  40  to work with an internally grooved rotation member  30 . The internally grooved rotatable element  30  has a plurality of stoppers  301  formed on an inner wall surface thereof. The adjusting mechanism  80  includes a preset turning knob  801 , an outer extractable tube  802 , an inner extractable tube  803 , a bearing  804 , and a seal cap  805 .  
         [0034]     The outer extractable tube  802  is a hollow member having an externally threaded first end sealed by the seal cap  805 , and an opposite second end having the bearing  804  fixedly mounted therein. The distance between the bearing  804  and the seal cap  805  defines a range within which the inner extractable tube  803  may be axially moved, or a travel of the adjustable helical spring  40 , either a compression or a tension helical spring.  
         [0035]     The inner extractable tube  803  has a first end fixedly connected to a bottom of a female case  20  of the casing for the adjustable helical spring  40 , and an opposite second end slidably extended through the bearing  804  on the outer extractable tube  802 , such that the inner extractable tube  803  is axially movable in the outer extractable tube  802 .  
         [0036]     A spring seat  101  is located in the bottom of male case  10  to fix the helical spring  40  in place.  
         [0037]     The preset turning knob  801  has an internally threaded central opening meshing with external threads provided on the first end of the outer extractable tube  802 . An end of the preset turning knob  801  is tightly pressed against but smoothly turnable relative to the male case  10 . Whereby when the preset turning knob  801  is rotated, the male case  10  is brought to axially move without turning, When the preset turning knob  801  is rotated, both the male case  10  and the rotatable element  30  are axially moved to change the precompression or the pretension of the helical spring  40 .  
         [0038]      FIG. 5  shows the manner of using the adjusting mechanism  70  of  FIG. 1  to work with an externally grooved rotatable element  30  to adjust an adjustable compression helical spring  40  mounted in a male case  10  having an outer diameter smaller than an inner diameter of a female case  20  of the casing for the adjustable helical spring. As shown, a compression stroke of the adjustable compression helical spring  40  is determined by the length of a locating seat  201 . When a maximum compression stroke is reached, the male case  10  and the female case  20  will contact with each other at the same end. After the adjustable compression helical spring is assembled, the helical spring  40  is subjected to an initial precompression. This is the initial precompression applied to the male case  10  and the locating seat  201 . A coil pitch formed under the initial precompression is an initial coil pitch. A distance difference between the initial coil pitch and a coil pitch not subjected to the initial precompression defines a specific range of the fatigue deformation of the helical spring  40 . When the helical spring  40  is subjected to a fatigue deformation within an operating cycle thereof, and it is desired to recover the helical spring  40  to the initial coil pitch, a precompression less than the initial precompression is required. To effectively adjust the number of effective turns of the helical spring  40 , the stoppers  301  on the rotatable element  30  and the pitch of the stoppers must be equal to or slightly smaller than the initial coil pitch. In other words, an axial displacement produced by rotating the rotatable element  30  one turn must be equal to or slightly smaller than the initial coil pitch.  
         [0039]     The initial state of the adjusting mechanism  70  working with the externally grooved rotatable element  30  is as follows:  
         [0040]     1. The retaining key  709  on the preset barrel  702  is located at the bottom end of the slot  708 , so that a maximum axial displacement of the preset barrel  702  in the direction of compressing the helical spring  40  may be obtained.  
         [0041]     2. The stoppers  301  on the rotatable element  30  is in slight contact with the preset barrel  702 , so that a maximum axial displacement of the rotatable element  30  in the direction of compressing the helical spring  40  may be obtained.  
         [0042]     3. The stoppers  301  on the rotatable element  30  and the spring coils  401  of the helical spring  40  are separated from one another at where the stoppers  301  are pressed against the spring coils  401 , and a small clearance is existed between the stoppers  301  and the spring coils  401 .  
         [0043]     The adjustable compression helical spring  40  in the initial state has the smallest elastic coefficient but the largest number of effective turns.  
         [0044]     When it is desired to increase the precompression, simply turn the turning knob  703  to drive the drive cylinder  704  and the preset barrel  702 , so that the preset barrel  702  moves axially in the direction of compressing the helical spring  40 . In the meantime, the rotatable element  30  moves axially and brings the stoppers  301  to closely press against the spring coils  401 , so that the precompression applied to the effective turns of the helical spring  40  is increased.  
         [0045]     The number of effective turns of the helical spring  40  may be decreased to increase the elastic coefficient thereof through the following adjusting steps:.  
         [0046]     Step 1: Decrease the precompression to recover the coil pitch to the pitch of the rotatable element  30 . This can be done by turning the turning knob  703  to drive the drive cylinder  704  and the preset barrel  702 , so that the preset barrel  702  moves axially in a direction reverse to the direction of compressing the helical spring  40 , and the rotatable element  30  moves axially at the same time to separate the stoppers  301  from the spring coils  401  with a small clearance existed between them.  
         [0047]     Step 2: Decrease the number of effective turns of the helical spring  40 . This can be done by turning the rotator knob  705  to drive the drive shaft  706  and the rotatable element  30 , so that the rotatable element  30  rotates and moves axially in the direction of compressing the helical spring  40  until a preset number of turns is reached. In case the stoppers  301  on the rotatable element  30  are in contact with the spring coils  401  to prevent the rotatable element  30  from effectively rotating, go back to the step 1.  
         [0048]     Step 3: Increase the precompression. This can be done in the manner as described earlier.  
         [0049]     The number of effective turns of the helical spring  40  may be increased to decrease the elastic coefficient thereof through the following adjusting steps:  
         [0050]     Step 1: Decrease the precompression to recover the coil pitch to the pitch of the rotatable element  30 . This can be done in the manner as described earlier.  
         [0051]     Step 2: Increase the number of effective turns of the helical spring  40 . This can be done by turning the rotator knob  705  to drive the drive shaft  706  and the rotatable element  30 , so that the rotatable element  30  rotates and moves axially in a direction reverse to the direction of compressing the helical spring  40  until a preset number of turns is reached. In case the stoppers  301  on the rotatable element  30  are in contact with the spring coils  401  to prevent the rotatable element  30  from effectively rotating, go back to the step 1.  
         [0052]     Step 3: Increase the precompression. This can be done in the manner as described earlier.  
         [0053]     When the male case has an inner diameter larger than the outer diameter of the female case, the adjusting mechanism  70  working with the externally grooved rotatable element  30  may still be operated in the above-describe manner to adjust the adjustable compression helical spring.  
         [0054]      FIG. 6  shows the manner of using the adjusting mechanism  70  of  FIG. 1  to work with an externally grooved rotatable element  30  to adjust an adjustable tension helical spring  40  mounted in a male case  10  having an outer diameter smaller than an inner diameter of a female case  20  of the casing for the adjustable helical spring. As shown, a tension stroke of the adjustable tension helical spring  40  is determined by the length of a locating seat  201 . When a maximum tension stroke is reached, the male case  10  will contact at the second end with the locating seat  201 . After the adjustable tension helical spring is assembled, the helical spring  40  is subjected to an initial pretension. This is the initial pretension applied to the male case  10  and the female case  20 . A coil pitch formed under the initial pretension is an initial coil pitch. A distance difference between the initial coil pitch and a coil pitch not subjected to the initial pretension defines a specific range of the fatigue deformation of the helical spring  40 . When the helical spring  40  is subjected to a fatigue deformation within an operating cycle thereof, and it is desired to recover the helical spring  40  to the initial coil pitch, a pretension less than the initial pretension is required. To effectively adjust the number of effective turns of the helical spring  40 , the stoppers  301  on the rotatable element  30  and the pitch of the stoppers must be equal to or slightly larger than the initial coil pitch. In other words, an axial displacement produced by rotating the rotatable element  30  one turn must be equal to or slightly larger than the initial coil pitch.  
         [0055]     The initial state of the adjusting mechanism  70  working with the externally grooved rotatable element  30  is as follows:  
         [0056]     1. The retaining key  709  on the preset barrel  702  is located at the front end of the slot  708 , so that a maximum axial displacement of the preset barrel  702  in a direction of tensioning the helical spring  40  may be obtained.  
         [0057]     2. The stoppers  301  on the rotatable element  30  is in slight contact with the preset barrel  702 , so that a maximum axial displacement of the rotatable element  30  in a direction reverse to the direction of tensioning the helical spring  40  may be obtained.  
         [0058]     3. The stoppers  301  on the rotatable element  30  and the spring coils  401  of the helical spring  40  are separated from one another at where the stoppers  301  are pressed against the spring coils  401 , and a small clearance is existed between the stoppers  301  and the spring coils  401 .  
         [0059]     The adjustable tension helical spring  40  in the initial state has the smallest elastic coefficient but the largest number of effective turns.  
         [0060]     When it is desired to increase the pretension, simply turn the turning knob  703  to drive the drive cylinder  704  and the preset barrel  702 , so that the preset barrel  702  moves axially in the direction of tensioning the helical spring  40 . In the meantime, the rotatable element  30  moves axially and brings the stoppers  301  to closely press against the spring coils  401 , so that the pretension applied to the effective turns of the helical spring  40  is increased.  
         [0061]     The number of effective turns of the helical spring  40  may be decreased to increase the elastic coefficient thereof through the following adjusting steps:.  
         [0062]     Step 1: Decrease the pretension to recover the coil pitch to the pitch of the rotatable element  30 . This can be done by turning the turning knob  703  to drive the drive cylinder  704  and the preset barrel  702 , so that the preset barrel  702  moves axially in a direction reverse to the direction of tensioning the helical spring  40 , and the rotatable element  30  moves axially at the same time to separate the stoppers  301  from the spring coils  401  with a small clearance existed between them.  
         [0063]     Step 2: Decrease the number of effective turns of the helical spring  40 . This can be done by turning the rotator knob  705  to drive the drive shaft  706  and the rotatable element  30 , so that the rotatable element  30  rotates and moves axially in a direction reverse to the direction of tensioning the helical spring  40  until a preset number of turns is reached. In case the stoppers  301  on the rotatable element  30  are in contact with the spring coils  401  to prevent the rotatable element  30  from effectively rotating, go back to the step 1.  
         [0064]     Step 3: Increase the pretension. This can be done in the manner as described earlier.  
         [0065]     The number of effective turns of the helical spring  40  may be increased to decrease the elastic coefficient thereof through the following adjusting steps:  
         [0066]     Step 1: Decrease the pretension to recover the coil pitch to the pitch of the rotatable element  30 . This can be done in the manner as described earlier.  
         [0067]     Step 2: Increase the number of effective turns of the helical spring  40 . This can be done by turning the rotator knob  705  to drive the drive shaft  706  and the rotatable element  30 , so that the rotatable element  30  rotates and moves axially in the direction of tensioning the helical spring  40  until a preset number of turns is reached. In case the stoppers  301  on the rotatable element  30  are in contact with the spring coils  401  to prevent the rotatable element  30  from effectively rotating, go back to the step 1.  
         [0068]     Step 3: Increase the pretension. This can be done in the manner as described earlier.  
         [0069]     When the male case has an inner diameter larger than the outer diameter of the female case, the adjusting mechanism  70  working with the externally grooved rotatable element  30  may still be operated in the above-describe manner to adjust the adjustable tension helical spring.  
         [0070]      FIG. 7  shows the manner of using the adjusting mechanism  80  of  FIG. 4  to work with an internally grooved rotatable element  30  to adjust an adjustable compression helical spring  40  mounted in a male case  10  having an outer diameter smaller than an inner diameter of a female case  20  of the casing for the adjustable helical spring. As shown, a compression stroke of the adjustable compression helical spring  40  is determined by a range of axial displacement of the inner extractable tube  803  in the outer extractable tube  802 . When a maximum compression stroke is reached, the second end of the inner extractable tube  803  contacts with the seal cap  805  at the first end of the outer extractable tube  802 .  
         [0071]     After the adjustable compression helical spring is assembled, the helical spring  40  is subjected to an initial precompression. This is the initial precompression applied to a location between the second end of the inner extractable tube  803  and the bearing  804  at the second end of the outer extractable tube  802 . A coil pitch formed under the initial precompression is an initial coil pitch. A distance difference between the initial coil pitch and a coil pitch not subjected to the initial precompression defines a specific range of the fatigue deformation of the helical spring  40 . When the helical spring  40  is subjected to a fatigue deformation within an operating cycle thereof, and it is desired to recover the helical spring  40  to the initial coil pitch, a precompression less than the initial precompression is required. To effectively adjust the number of effective turns of the helical spring  40 , the stoppers  301  in the rotatable element  30  and the pitch of the stoppers must be equal to or slightly smaller than the initial coil pitch. In other words, an axial displacement produced by rotating the rotatable element  30  one turn must be equal to or slightly smaller than the initial coil pitch.  
         [0072]     The initial state of the adjusting mechanism  80  working with the internally grooved rotatable element  30  is as follows:  
         [0073]     1. The preset turning knob  801  is screwed to the first end of the outer extractable tube  802  closed by the seal cap  805 , so that a maximum axial displacement of the preset turning knob  801  in the direction of compressing the helical spring  40  may be obtained.  
         [0074]     2. The stoppers  301  in the rotatable element  30  is in slight contact with one end of the male case  10 , so that a maximum axial displacement of the rotatable element  30  in the direction of compressing the helical spring  40  may be obtained.  
         [0075]     3. The stoppers  301  in the rotatable element  30  and the spring coils  401  of the helical spring  40  are separated from one another at where the stoppers  301  are pressed against the spring coils  401 , and a small clearance is existed between the stoppers  301  and the spring coils  401 .  
         [0076]     The adjustable compression helical spring  40  in the initial state has the smallest elastic coefficient but the largest number of effective turns.  
         [0077]     When it is desired to increase the precompression, simply turn the preset turning knob  801  to drive the male case  10  and the rotatable element  30  to move axially in the direction of compressing the helical spring  40 , causing the stoppers  301  in the rotatable element  30  to closely press against the spring coils  401 , so that the precompression applied to the effective turns of the helical spring  40  is increased.  
         [0078]     The number of effective turns of the helical spring  40  may be decreased to increase the elastic coefficient thereof through the following adjusting steps:  
         [0079]     Step 1: Decrease the precompression to recover the coil pitch to the pitch of the rotatable element  30 . This can be done by turning the preset turning knob  801  to drive the male case  10  and the rotatable element  30  to move axially in a direction reverse to the direction of compressing the helical spring  40 , causing the stoppers  301  in the rotatable element  30  to separate from the spring coils  401  with a small clearance existed between them.  
         [0080]     Step 2: Decrease the number of effective turns of the helical spring  40 . This can be done by turning the rotatable element  30 , so that the rotatable element  30  rotates and moves axially in the direction of compressing the helical spring  40  until a preset number of turns is reached. In case the stoppers  301  in the rotatable element  30  are in contact with the spring coils  401  to prevent the rotatable element  30  from effectively rotating, go back to the step 1.  
         [0081]     Step 3: Increase the precompression. This can be done in the manner as described earlier.  
         [0082]     The number of effective turns of the helical spring  40  may be increased to decrease the elastic coefficient thereof through the following adjusting steps:  
         [0083]     Step 1: Decrease the precompression to recover the coil pitch to the pitch of the rotatable element  30 . This can be done in the manner as described earlier.  
         [0084]     Step 2: Increase the number of effective turns of the helical spring  40 . This can be done by turning the rotatable element  30 , so that the rotatable element  30  rotates and moves axially in a direction reverse to the direction of compressing the helical spring  40  until a preset number of turns is reached. In case the stoppers  301  on the rotatable element  30  are in contact with the spring coils  401  to prevent the rotatable element  30  from effectively rotating, go back to the step 1.  
         [0085]     Step 3: Increase the precompression. This can be done in the manner as described earlier.  
         [0086]     When the male case  10  has an inner diameter larger than the outer diameter of the female case  20 , the adjusting mechanism  80  working with the internally grooved rotatable element  30  may still be operated in the above-describe manner to adjust the adjustable compression helical spring.  
         [0087]      FIG. 8  shows the manner of using the adjusting mechanism  80  of  FIG. 4  to work with an internally grooved rotatable element  30  to adjust an adjustable tension helical spring  40  mounted in a male case  10  having an outer diameter smaller than an inner diameter of a female case  20  of the casing for the adjustable helical spring. As shown, a tension stroke of the adjustable tension helical spring  40  is determined by a range of axial displacement of the inner extractable tube  803  in the outer extractable tube  802 . When a maximum tension stroke is reached, the second end of the inner extractable tube  803  contacts with the bearing  804  at the second end of the outer extractable tube  802 . After the adjustable tension helical spring is assembled, the helical spring  40  is subjected to an initial pretension. This is the initial pretension applied to a location between the second end of the inner extractable tube  803  and the seal cap  805  at the first end of the outer extractable tube  802 . A coil pitch formed under the initial pretension is an initial coil pitch. A distance difference between the initial coil pitch and a coil pitch not subjected to the initial pretension defines a specific range of the fatigue deformation of the helical spring  40 . When the helical spring  40  is subjected to a fatigue deformation within an operating cycle thereof, and it is desired to recover the helical spring  40  to the initial coil pitch, a pretension less than the initial pretension is required. To effectively adjust the number of effective turns of the helical spring  40 , the stoppers  301  in the rotatable element  30  and the pitch of the stoppers must be equal to or slightly larger than the initial coil pitch. In other words, an axial displacement produced by rotating the rotatable element  30  one turn must be equal to or slightly larger than the initial coil pitch.  
         [0088]     The initial state of the adjusting mechanism  80  working with the internally grooved rotatable element  30  is as follows:  
         [0089]     The preset turning knob  801  is screwed to the first end of the outer extractable tube  802  closed by the seal cap  805 , so that a maximum axial displacement of the preset turning knob  801  in the direction of tensioning the helical spring  40  may be obtained.  
         [0090]     The stoppers  301  in the rotatable element  30  is in slight contact with one end of the male case  10 , so that a maximum axial displacement of the rotatable element  30  in a direction reverse to the direction of tensioning the helical spring  40  may be obtained.  
         [0091]     The stoppers  301  in the rotatable element  30  and the spring coils  401  of the helical spring  40  are separated from one another at where the stoppers  301  are pressed against the spring coils  401 , and a small clearance is existed between the stoppers  301  and the spring coils  401 .  
         [0092]     The adjustable tension helical spring  40  in the initial state has the smallest elastic coefficient but the largest number of effective turns.  
         [0093]     When it is desired to increase the pretension, simply turn the preset turning knob  801  to drive the male case  10  and the rotatable element  30  to move axially in the direction of tensioning the helical spring  40 , causing the stoppers  301  in the rotatable element  30  to closely press against the spring coils  401 , so that the pretension applied to the effective turns of the helical spring  40  is increased.  
         [0094]     The number of effective turns of the helical spring  40  may be decreased to increase the elastic coefficient thereof through the following adjusting steps:  
         [0095]     Step 1: Decrease the pretension to recover the coil pitch to the pitch of the rotatable element  30 . This can be done by turning the preset turning knob  801  to drive the male case  10  and the rotatable element  30  to move axially in a direction reverse to the direction of tensioning the helical spring  40 , causing the stoppers  301  in the rotatable element  30  to separate from the spring coils  401  with a small clearance existed between them.  
         [0096]     Step 2: Decrease the number of effective turns of the helical spring  40 . This can be done by turning the rotatable element  30 , so that the rotatable element  30  rotates and moves axially in a direction reverse to the direction of tensioning the helical spring  40  until a preset number of turns is reached. In case the stoppers  301  in the rotatable element  30  are in contact with the spring coils  401  to prevent the rotatable element  30  from effectively rotating, go back to the step 1.  
         [0097]     Step 3: Increase the pretension. This can be done in the manner as described earlier.  
         [0098]     The number of effective turns of the helical spring  40  may be increased to decrease the elastic coefficient thereof through the following adjusting steps:  
         [0099]     Step 1: Decrease the pretension to recover the coil pitch to the pitch of the rotatable element  30 . This can be done in the manner as described earlier.  
         [0100]     Step 2: Increase the number of effective turns of the helical spring  40 . This can be done by turning the rotatable element  30 , so that the rotatable element  30  rotates and moves axially in the direction of tensioning the helical spring  40  until a preset number of turns is reached. In case the stoppers  301  on the rotatable element  30  are in contact with the spring coils  401  to prevent the rotatable element  30  from effectively rotating, go back to the step 1.  
         [0101]     Step 3: Increase the pretension. This can be done in the manner as described earlier.  
         [0102]     When the male case  10  has an inner diameter larger than the outer diameter of the female case  20 , the adjusting mechanism  80  working with the internally grooved rotatable element  30  may still be operated in the above-describe manner to adjust the adjustable tension helical spring.