Piston rod position detector, autotensioner and belt tension adjuster

A piston rod position detecting mechanism is proposed which can detect continuously or in a multiple-point manner that the piston rod position has changed due to increase or decrease in the protruding amount of the piston rod due to aging. The protruding amount from a cylinder end wall is detected by a position detecting mechanism comprising a detecting coil housed in a bobbin provided at the cylinder end, a flange portion formed on the piston rod, and a coil spring. Also, an autotensioner and an electromagnetic valve with such a position detector are proposed. Further, a belt tension adjusting device is provided with a detector for detecting the position of a tension pulley which is pivotable with increase or decrease in the belt tension.

BACKGROUND OF THE INVENTION

This invention relates to a piston rod position detector for detecting the position of a piston rod connected to a piston slidably mounted in a cylinder so as to protrude from the cylinder. It also relates to an autotensioner and a belt transmission device carrying such a piston rod position detector and to a belt tension adjusting device with a tension pulley position detector.

A cylinder unit is used to convert hydraulic force to mechanical force and transmit the mechanical force to a device through a piston rod. It is also used to measure a moving distance.

A cylinder unit of the former type is shown inFIG. 12and is generally called an “autotensioner” in the art and is used to apply tension to the timing belt in a belt transmission device.

FIG. 12shows such a belt transmission device used to drive automotive engine camshafts. It comprises a pulley P1mounted on an engine crankshaft1, pulleys P2mounted on camshafts2, a pulley P3mounted on an oil pump drive shaft3, and a timing belt4trained around these pulleys. The camshafts2and the drive shaft3are driven as the crankshaft1rotates. The belt transmission device further includes a belt tension adjustor comprising a tension pulley9rotatably mounted on a pulley arm6which is pivotable about a shaft5, and an autotensioner7having a pushrod8protruding from a cylinder and biased by a spring, not shown, to press the tension pulley9against the belt4to absorb any change in belt tension, thereby keeping the belt tension constant.

The tension in the belt changes as it stretches gradually with time or due to changes in the distance between pulleys due to thermal expansion during operation of the engine. The autotensioner absorbs any such change in the belt tension by advancing and retracting the pushrod. For example, when the belt stretches and slackens, the pushrod8advances to absorb slack of the belt.

Such autotensioners are disclosed e.g. in Japanese patent No. 1891868 and Japanese patent publication 7-117130.

If the belt transmission system has no such autotensioner, it is usually necessary to exchange the timing belt each time the vehicle has traveled 100 thousand kilometers. The autotensioner suppresses flapping of the belt and thus prolongs its life, so that the belt guarantee period can be extended until the vehicle travel distance far exceeds 100 thousand kilometers.

But since the pushrod stroke is limited, if the pushrod has advanced beyond its stroke limit, the autotensioner loses its ability to keep constant the belt tension. The belt thus tends to get slack and begins to flap. This may cause flapping or “jump of pulley teeth”. Also, flapping of the belt shortens the life of the belt. Also, the timing belt stretches, so that the pushrod protrudes too much and the timing belts fails to function properly. One may therefore think of providing a means for detecting the fact that the pushrod has advanced to the stroke limit or to a position near the stroke limit. A specific such means would be a detector including a sensor (coil) and a nonmagnetic ring fitted on the push rod. When the edge of the nonmagnetic ring reaches the center of the sensor, magnetic permeability changes. The detector thus detects a specific position of the pushrod.

But with this arrangement, only one specific position of the pushrod is detectable. Thus, it is desired to detect the position continuously or a plurality of different positions of the pushrod.

As with an autotensioner, in spite of the fact that it is known that as the travel distance of a vehicle increases, a timing belt stretches unnoticed and the position of the pushrod of the autotensioner changes, the change in the amount of protrusion of the pushrod is not actually detected. During the process of increase in the amount of protrusion of the pushrod, if alarms such as “caution” at half the elongation at expected breakage, “warning” at 80% elongation, and “broken” at the breakage point are given according to the elongation of the belt, measures regarding an exchange period of the belt can be taken. But no such measures are taken now. Also, there are various kinds of devices for which it is desirable to take similar measures like autotensioners.

An object of the invention is to provide a piston rod position detector capable of detecting the position of a piston rod continuously or at a plurality of different positions and to provide an autotensioner provided with such a detector.

FIG. 33shows a belt transmission device with a belt tension adjustor which is another type of autotensioner.

A timing belt4is trained between a pulley P1of a crankshaft1, pulleys P2of camshafts2, and a pulley P3of a drive shaft3for an oil pump. The autotensioner shown is one disclosed in Japanese patent publication 8-338488 and is a compact type autotensioner in which a hydraulic damper is housed in the periphery of a tension pulley9for compactness.

For the autotensioner, the tension pulley9is provided so as to be pressed against the timing belt4so as to be pivotable about a shaft5, and keeps the tension of the timing belt constant by the tension adjusting force of a spring and the hydraulic damper. The tension pulley9pivots counterclockwise to relax tension when the tension is excessive, and pivots clockwise when the tension is decreasing to adjust tension. As the use period extends, the entire length of the timing belt tends to stretch due to secular change. Thus, as the operating period and use period extend, the tension pulley9of the autotensioner pivots clockwise.

The pivoting angle of the tension pulley in the autotensioner is limited, so that as operation exceeding the pivot limit point continues, it becomes impossible to keep the tension of the timing belt constant. The tension of the timing belt decreases, so that due to flapping of the timing belt, the belt tends to deteriorate. This will ultimately cause breakage of the belt.

But no detecting mechanism is provided for detecting the pivoting angle of the tension pulley to detect whether or not it is operated beyond the pivot limit point. Thus, it is impossible to know if the tension of the timing belt is kept properly, and to properly judge the period for exchanging the timing belt, and thus to know beforehand even if there is an abnormality in the autotensioner.

Another object of this invention is to provide a belt tension adjusting device provided with a means for detecting the position of the tension pulley and indicating the exchange period of the timing belt or abnormality of the autotensioner.

SUMMARY OF THE INVENTION

According to this invention, there is provided a piston rod position detecting mechanism for detecting the position of a piston rod connected to a piston slidably mounted in a cylinder having both ends thereof closed, the mechanism comprising a detecting coil provided at one end of the cylinder from which the piston rod protrudes out of the cylinder, and a flange provided on the piston rod opposite to the detecting coil to detect the position of the piston rod by a detection signal based on a change in inductance of the detecting coil which changes with the change in the position of the flange and thus the piston rod.

According to this invention, there is also provided an autotensioner comprising a cylinder having both ends closed, a piston slidably mounted in the cylinder, a piston rod connected to the piston to protrude from one end of the cylinder, a pressure chamber and a reservoir chamber defined in the cylinder by the piston, the pressure chamber and the reservoir chamber being filled with hydraulic oil, and a rod spring for biasing the piston rod so as to protrude out of the cylinder, characterized in that the position detecting mechanism described above is provided at an end at which the piston rod protrudes from the cylinder.

According to this invention, there is also provided an electromagnetic valve comprising a cylinder having both ends closed, a piston slidably mounted in the cylinder, a pair of electromagnetic coils provided at both sides of the piston, a piston rod coupled to at least one side of the piston so that the piston rod has one end thereof protruding out of the cylinder, the piston being driven by the magnetic force of the electromagnetic coils to protrude one end of the piston rod out of the cylinder, characterized in that the position detecting mechanism described above is provided.

According to this invention, there is also provided a belt transmission device comprising a pulley mounted on a crankshaft, a pulley mounted on a shaft to be driven, a belt trained around the pulleys to drive the shaft, an autotensioner including an engaging member, a cylinder, a pushrod mounted in the cylinder, a tension adjusting spring and a damper mechanism for damping the vibration of the belt through the engaging member, and a detecting unit for detecting the axial position of the pushrod.

According to this invention, there is also provided a belt tension adjusting device comprising an inner member supported so as to be pivotable about a fixing bolt passing through an eccentric hole formed in the inner member, a tension pulley rotatably mounted on the inner member, a tension adjusting spring and a hydraulic damper for pivoting the inner member and thus the tension pulley to adjust tension of a belt, and a magnetic sensor for detecting the position of the tension pulley.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a first embodiment, in which the cylinder unit10includes a cylinder11having end walls11a,11b.A piston12is slidably received in the cylinder11to define chambers A and B in the cylinder. A piston rod13is secured to the piston12and has one end thereof protruding from the cylinder through the end wall11b.At the protruding end, the piston rod13carries a flange14of a magnetic material. A coil spring15is mounted around the piston rod13between the flange14and the end wall11b.

The flange14serves as a presser ring for the coil spring. Like an autotensioner, the cylinder unit10of this embodiment is a kind of hydraulic damper. Thus, the piston is formed with small holes (not shown) or minute gap for communication between chambers A and B.

Although the flange14is press fit on the piston rod13, it may be formed integrally with it. If the flange14is a separate member from the rod13, it may be formed of a nonmagnetic and conductive material such as aluminum or copper.

Mounted on the outer side of the end wall11bis a bobbin16around the coil spring15. A sensor coil17for detecting the position of the piston rod13is housed in the bobbin16. A predetermined source voltage is supplied to the coil17from a detecting circuit19to form a magnetic circuit. Thus, when the flange14moves relative to the coil17and the spring15is compressed or expanded, the inductance of the magnetic circuit and thus the voltage or current of the coil changes. The detector circuit19thus detects the position of the flange and thus the piston rod based on the voltage or current of the coil received, which corresponds to the inductance of the magnetic circuit. The coil17, flange14and coil spring15thus form a piston rod position detector unit.

If the cylinder unit works as a kind of hydraulic damper, a load is usually applied on the protruding end of the piston rod13and thus the spring15is compressed to such a position where the load balances with the elasticity of the spring. When the load decreases for some reason, the coil spring15expands and the piston rod13advances (moves rightwardly in the figure). As the coil spring expands, gaps between coils increase.

To the sensor coil17, as described above, a predetermined source voltage is supplied. By the magnetic circuit formed by the sensor coil17, magnetic coupling indicated by an inductance value takes place among the detection coil, spring15and flange14. When the piston rod13advances, the flange14moves away from the coil17and the gaps between the coils of the spring15increase. The inductance thus decreases. Conversely, when the load increases and the piston rod retracts, the flange14approaches the sensor coil17and the coil gaps of the coil spring15decrease. The inductance thus increases.

FIG. 3shows the relationship between the inductance and the length of the coil spring15between the flange14and the end wall11bwhen the flange was formed of a magnetic material and the coil spring had a wire diameter of 0.55 mm and an outer diameter of 10 mm. The inductance is a combined value of those to the spring15and the flange14.

As seen from the graph, the inductance changes with the length of the coil spring. This changes the resistance of the electric circuit formed by the sensor coil17and thus the current or voltage supplied to the coil17. The detecting circuit19detects this change, thereby detecting the change in the position of the piston rod continuously or at a plurality of points.

FIG. 4shows the relationship between the inductance and the coil spring length when the flange14was formed of a nonmagnetic, conductive material, e.g. aluminum or copper. In this case, as the coil spring is compressed and the flange14approaches the coil17, the inductance decreases as shown. This is the reverse of the embodiment in which the flange14is formed of a magnetic material. This is because an eddy current produced in the flange14disturbs the flow of magnetic flux of the magnetic circuit formed by the coil17. In this modified embodiment, however, the inductance changes more than in the first embodiment. That is, the detector circuit of this embodiment is higher in sensitiveness of the detecting circuit.

The second embodiment, not shown, has no coil spring15. If this cylinder unit10is used as a damper, instead of the coil spring15, a coil spring may be mounted in the chamber A to pull or push the piston12. If the cylinder unit10is used as an ordinary cylinder for transforming a hydraulic power to a pressing force through the piston rod13, hydraulic fluid is supplied into the chambers A and B through external pipes. The flange14is formed of a nonmagnetic, conductive material such as aluminum or copper.

The piston rod position detector unit of this embodiment comprises the coil17and the flange14and operates in the same way as the detector of the first embodiment. Although the sensitiveness of the detector is slightly lower in the second embodiment because of omission of a coil spring, this will pose practically no problem.

FIG. 2shows a third embodiment in which the flange14is omitted and one end of the coil spring15is engaged in a hole18formed in the piston rod13.

The piston rod position detector unit of this embodiment operates in the same way as the detector of the first embodiment. Although the sensitiveness of the detector is slightly lower in this embodiment because of omission of a flange, this will pose practically no problem.

FIG. 5shows a fourth embodiment, which is an autotensioner having a position detector unit of any of the first to third embodiments. Although the autotensioner itself is conventional, its structure and operation will be briefly described below.

The autotensioner20includes a cylinder21having a closed bottom21aand an open top and a sleeve21′ fixedly received in the cylinder21at its bottom, and a piston22slidably received in the sleeve21′ and partitioning the interior of the cylinder into a lower pressure chamber, A and an upper reservoir chamber B. The latter has its top end closed by an oil seal21bretained in position by snap rings24received in grooves formed in the inner wall of the cylinder21.

A pushrod (or piston rod)23has its bottom end received in a hole formed in the top face of the piston22and slidably extends through the oil seal21b.Its top end protrudes from the cylinder21. The piston22is biased upwardly by a spring25mounted in the pressure chamber A so as to be movable together with the pushrod23. The chambers A and B communicate with each other through a passage27formed in the piston22. A ball26retained by a retainer on the other end of the piston22forms a check valve.

The pushrod23carries a guide flange22′ slidable along the inner wall of the cylinder21. A pressure adjusting spring25′ is mounted around the pushrod23between the guide flange22′ and the top end of the sleeve21′ to bias the pushrod upwardly. The flange22′ is formed with a hole28through which hydraulic fluid in the reservoir B flows. Without the hole28, the flange22′ and thus the pushrod cannot move. Hydraulic oil L is filled so that an air layer C is present between the top of the hydraulic oil and the oil seal21b(i.e., as illustrated inFIG. 5, the autotensioner20utilizes both a gas C and a liquid L). A separator29is provided to prevent air above the hydraulic oil from invading into the pressure chamber B.

Between the upper and lower snap rings24, the coil17and the bobbin16of the detector unit of any of the first to third embodiments are provided. The bobbin16has a bottom wall having its radially inner periphery in slide contact with the pushrod23. A coil spring15is mounted around the pushrod and supported between the bottom wall of the bobbin16and the flange14fixed to the pushrod near its top end. But instead, the spring15may be supported between the flange14and the lower snap ring24by reducing the inner diameter of the lower snap ring24and increasing the inner diameter of the lower wall of the bobbin.

The autotensioner20, as mounted in the belt transmission system ofFIG. 12, operates as follows. When the tension in the timing belt4increases, the pushrod23and the piston22are pushed down, so that the pressure in the pressure chamber A rises. The passage27is thus closed instantly by the ball26of the check valve.

A narrow gap is formed in the inner surface of the sleeve21′ or the radially outer surface of the piston22. Thus, when the pressure in the pressure chamber A rises, hydraulic fluid in the pressure chamber gradually leaks through the narrow gap into the reservoir chamber B. The volume of the pressure chamber thus decreases and the pushrod23descends slowly until the downward pressure on the pushrod balances with the force of the spring25′. In other words the pushing force applied to the pushrod is damped by the damping action of the autotensioner.

When the belt4slackens, the pushrod is pushed up by the spring25′ and the piston22is pushed up by the spring25. Thus, the pressure in the pressure chamber A instantly drops below the pressure in the reservoir chamber B. The check valve thus instantly opens the passage27, allowing hydraulic fluid in the chamber B to flow smoothly into the chamber A as the pushrod rises. The pushrod can thus rise quickly to absorb the slack of the belt and keep belt tension constant.

The timing belt tends to gradually stretch due to aging. The pushrod23absorbs the stretch of the belt by protruding beyond its initial stroke. With a prolonged use of the belt, the pushrod advances more and more.

Although the stroke of the pushrod23of the autotensioner20is determined taking these factors into consideration, due to increased travel distance of the car between routine maintenances of the belt4or due to sudden abnormal elongation of the belt, the pushrod23may protrude to its stroke limit. The stroke limit of the pushrod23is at a point where the guide flange22′ abuts the oil seal21bbecause once the flange abuts the oil seal, the spring25′ cannot push the pushrod23outwardly any further.

The detector of the autotensioner20can detect the position of the pushrod continuously or at a plurality of points until the stroke limit is reached because of the provision of the coil17, the coil spring15, and the flange14.

In the embodiment, since the position detecting mechanism has both of the flange14and the coil spring15, if a magnetic material is used as the material of the flange14, detection by the inductance properties (as shown inFIG. 3) in the first embodiment is possible by the detecting circuit19. As a modified embodiment, if aluminum or copper material is used for the flange14, detection based on the inductance as shown inFIG. 4can be made.

In the position detecting mechanism of the second embodiment, the coil spring15is omitted, and as the material of the flange14, aluminum or copper is used. As described above, although detection sensitivity is inferior to the inductance properties shown inFIG. 4, it can be used as a means for detecting the movement of the pushrod23of the autotensioner20. Also, with the position detecting mechanism of the third embodiment, since position detection can be made based on change of inductance due to expansion and shrinkage of the coil spring15while omitting the flange14, this detecting mechanism can also be applied.

By applying any of the position detecting mechanisms of the first to third embodiments as described above to detect the position of the pushrod23in a multiple-point manner or as a continuously changing position, as the stroke of the pushrod23changes gradually with a long-term use due to such factors as change of the timing belt with age, the detection signal from the detecting circuit19also changes according to the amount of change from the initial setting value of the moving stroke.

Thus, in the circuit for comparing with a plurality of reference values corresponding to the respective stages of the change of the moving stroke based on the output signal, it is possible to output warning signals such as “caution”, “dangerous”, “limit”, or stop signals based on comparison of the above signals. Thus, measures can be taken by performing the maintenance earlier.

FIG. 6shows a fifth embodiment, in which the position detector of any of the first to third embodiments is used in an electromagnetic valve. The detector shown includes the flange14and the detection coil17but not the coil spring. The valve shown comprises an open-topped, bottom-closed cylinder11and a piston12of a magnetic material slidably received in the cylinder. Piston rods13are connected to both sides of the piston12. But instead, a single piston may extend through the piston. The free ends of the piston rods13protrude from both ends of the cylinder.

In the cylinder, two electromagnetic coils30,31are mounted so as to surround the respective piston rods on both sides of the piston12in members30a,31aof a magnetic material. By activating the coil30or31, the piston12is attracted toward the activated one of the coils. Outside the coil30, the detection coil17housed in the bobbin16is mounted in the cylinder11. The flange14, which is of a conductive material, is mounted on the top end of the upper piston rod13.

As in the previous embodiments, the detector circuit19receives the signal from the coil17and detects the position of the flange. The lower piston rod13is slidably guided by a bearing bushing32mounted in the bottom end wall of the cylinder11and carries at its bottom protruding end a valve body13V adapted to be moved into and out of contact with an unillustrated valve seat of an electromagnetic valve to close and open the valve.

The electromagnetic valve is used as a valve for feeding fluid such as fuel gas into e.g. an internal combustion engine. Since it is possible to arbitrarily set the amount of opening of the valve, it is possible to set optimum burning conditions according to the driving state. If the amount of opening of the valve changes due to a secular change, such a change is detected by the position detecting mechanism in the same manner as in the other embodiments.

For opening and closing of the valve, when one of the electromagnetic coils30,31is activated, the electromagnet containing the activated electromagnetic coil attracts the piston12to move the piston rod13in an upward or a downward direction to open or close the electromagnetic valve body. The opening of the valve is adjusted by adjusting the current intensity supplied to the electromagnetic coils30,31. In this embodiment, too, detection of the moving amount by the detection coil is made in a similar manner to other embodiments. It is a matter of course that the change is detected continuously or in a multiple-point manner.

In this embodiment, the flange14is made of a conductive material. But if it is made of a magnetic material, a coil spring should be used. A nonmagnetic flange14and a coil spring may be combined as already described. Also, as in the third embodiment, only the coil spring15is used with the flange14omitted.

FIG. 7shows a sectional view of a sixth embodiment. This embodiment is provided with a detecting mechanism in a cylinder unit10″ having a flange14on the piston rod13as in the first embodiment ofFIG. 1. This position detecting mechanism comprises a coil spring15provided between an end wall11band the flange14, and an exciting coil17aand a detecting coil17provided opposite to each other with the coil spring15sandwiched between them. This position detecting mechanism is shown inFIG. 8in perspective. The flange14serves as a presser ring in this embodiment, too.

As shown inFIG. 8, the exciting coil17aand the detecting coil17are provided opposite to each other so that the direction of magnetic lines passing both coils will be normal to the axial direction of the piston rod13. In the illustrated example, the exciting coil17ais provided separately from the detecting coil17. When the magnetic flux (or lines) produced by causing a high-frequency signal to flow from a signal generator17x,e.g. a signal current of 1–50 KHz passes through the piston rod13and the coil spring15wound around its outer periphery and reaches the detecting coil17, a small current induced by electromagnetic induction by the magnetic flux is detected by the detecting coil17, and the signal of the small current is amplified and detected by the detecting circuit19.

In this position detecting mechanism, when the piston rod13protrudes and the position changes, the coil spring15expands and the gaps between coils increase, so that the inductance of the detecting coil17decreases when it is transmitted from the exciting coil17ato the detecting coil17. In other words, with the expansion and shrinkage of the coil spring15, the sectional area of the magnetic material of the coil spring changes, thus changing the inductance of the detecting coil17. Thus, the current or voltage signal at the detecting coil17changes, so that by detecting the change by detecting circuit19, it is possible to detect the change in position of the piston rod13.

FIG. 9shows the change in the output voltage measured by the position detecting mechanism. The coil spring15used in this measurement had a 0.6 mm wire diameter and a coil winding diameter of 10 mm. The abscissa indicates the displacement of the rod and the obscissa indicates the output voltage. For the position change of the piston rod13, the change in the output voltage is large. Thus, it is apparent that a good sensitivity was obtained.

In this embodiment, the exciting coil17aand the detecting coil17are formed separately. But both coils may be formed integrally. In such a case, as with the detecting coil of the first embodiment, an exciting current is fed to the detecting coil itself. The magnetic flux produced by the current is influenced by the expansion and shrinkage of the spring coil15, so that the inductance changes. Thus, since its detecting signal is detected by the detecting circuit19, the position change can be measured.

FIG. 10shows a sectional view of a seventh embodiment. In this embodiment, the position detecting mechanism of the sixth embodiment ofFIGS. 7 and 8is combined with the autotensioner ofFIG. 5. Since the structure of the autotensioner has already been described, a detailed description of this embodiment is omitted.

FIG. 11shows an electric circuit for temperature compensation. In this modification, the coil17serves both as an exciting coil and a detecting coil. For temperature compensation, another coil of the same type as the detecting coil17is provided parallel to a signal generator17xas a temperature compensating coil17′. The detecting signal by the temperature compensating coil17′ is set (by adjusting the resistor r′) so that the influence by the temperature change will be small. By using this as a reference, it is sent through a rectifier17pand a filter17f.As the measuring line, the signal sent through a rectifier17pand a filter17fis compensated by a differential amplifier (operational amplifier)17opby an offset amount due to temperature change by the temperature-compensating-line signal for accurate position detection.

FIG. 14is a schematic view of a belt transmission device in which the position detecting device and the autotensioner of the present invention are mounted. Since the belt transmission device is the same as that shown inFIG. 12, like numerals are affixed to like members and the description is omitted. In this embodiment, at an open end of a cylinder of the autotensioner20from which a pushrod supported in the cylinder so as to advance and retract protrudes, a detecting coil17is provided and a flange portion is provided on the pushrod. These form a detecting means for detecting a change in the axial position of the pushrod continuously or in a multiple-point manner. For its details, description has already been made. Also, the autotensioner itself has already been described.

FIG. 13shows a belt transmission device that is different in type from that ofFIG. 12. The autotensioner and its position detecting means applied to the belt transmission device of the first type are equally applicable to the belt transmission device of this type, too. The one shown in the figure shows a serpentine type belt transmission device. In this device, a belt4comprising a single V-belt is trained between a pulley P1mounted to a crankshaft1, a pulley P11mounted to a rotary shaft S1of an alternator, a pulley P12mounted to a rotary shaft S2of a fan of a radiator, a pulley P13mounted to a rotary shaft S3of an air compressor, and a pulley P14mounted to a rotary shaft S4of a motor for power steering, so that by the rotation of the crankshaft1, these various engine accessories including the alternator are adapted to be driven simultaneously.

A tension pulley9for adjusting the tension of the belt4is rotatably supported at one end of a pulley arm6. On the other hand, the pulley arm6is supported so as to be pivotable about a support shaft5mounted to an engine block. To the other end of the pulley arm6, a gas/liquid two-phase autotensioner20is connected. Although the autotensioner shown is of a type in which the spring is mounted outside, it will be needless to say that it may be of an inside-mount type.

A belt tension adjustor of a first embodiment is shown inFIGS. 15–18. It includes an eccentric ring53having an eccentric hole54. A fixing bolt56extends through the eccentric hole54and tightened to an engine block57to pivotably support the eccentric ring53through a slide bearing55. A tension pulley51is rotatably mounted around the eccentric ring53through a rolling bearing52. A hydraulic damper58is mounted in the gap defined between the eccentric ring53and the engine block57. As shown inFIG. 16, the damper58is arranged completely within the outer periphery of the tension pulley51.

The damper58includes, as shown inFIG. 16, an integral block64comprising a damper cylinder59formed with a cylindrical bore60and a protrusion62at one side. The cylindrical bore60is partitioned into a pressure chamber66and a main reservoir65by a plunger61slidably received in the bore60. In the protrusion62, a sub-reservoir63and a fixing bolt56are provided. The plunger61has a passage67through which the main reservoir65and the pressure chamber66communicate with each other. A check valve68provided at the lefthand end of the passage67opens and closes the passage. The plunger61is biased rightwardly by a coil spring69mounted in the pressure chamber66in a compressed state.

A rod92has one end thereof received in a recess formed in the righthand end of the plunger61and is loosely supported by a wear ring93so as to be axially movable. The other end of the rod92extends through an oil seal95closing the bore60and protrudes from the damper cylinder59. A sub-reservoir63is formed in the protrusion62. It extends perpendicular to the bore60and communicates with the main reservoir65through a passage71. Its open end is closed by a rubber cap72. The tension adjustor is mounted with the sub-reservoir63located over the main reservoir65. In this state, hydraulic oil fills the main reservoir65and the pressure chamber66and a lower part of the sub-reservoir63with its upper portion filled with air.

The hydraulic damper58is fixed to the engine block57by the bolt56extending therethrough (FIG. 18) with its rod92abutting a pin77on the eccentric ring53(FIG. 16). Since two reservoirs are provided perpendicular to each other, it is possible to arrange the hydraulic damper58within the circumference of the pulley51as shown and keep small the gap W1between the tension pulley51and the engine block57(FIG. 15).

In its side facing the engine block, the eccentric ring53for supporting the tension pulley51is formed with a recess78ain which is loosely received a pin76(FIG. 17), which extends through the protrusion62of the damper58. A cylindrical slide sleeve101of synthetic resin having a closed bottom is received in the recess78a.A tension adjusting spring81is received in the sleeve101in a compressed state with one end thereof supported on the bottom of the sleeve101and the other end on the pin76through a slide cap102slidably received in the sleeve101. As shown inFIG. 17, the spring81biases the eccentric ring53to pivot it counterclockwise (in the figures) about the bolt56, thereby pressing the pulley51against the belt A. Instead of the double-coil spring81shown inFIG. 17, a single-coil spring may be used.

In order to set the tension adjustor of this embodiment in an operable state such as shown inFIG. 16or17, the tension adjustor is mounted on the engine block57, the eccentric ring53is pivoted clockwise with a hexagonal wrench engaged in a hexagonal hole83formed in the eccentric ring53while compressing the spring81and pushing in the plunger61, the belt A is engaged on the tension pulley51, and the wrench is disengaged to allow the eccentric ring to pivot counterclockwise to press the pulley51against the belt.

FIG. 18will be helpful for understanding the relation between the tension pulley51and the hydraulic damper58.

The belt tension adjustor of this embodiment is provided with a detector for detecting the position or displacement of the pulley51. As shown inFIG. 17, the detector includes a detection rod122inserted in the spring81and having a flange at the bottom of the sleeve101. Thus, together with the cap102, the rod122is axially movable in and relative to the sleeve101toward and away from the bottom of the sleeve101as the spring81is compressed or expands. A cylindrical, axially magnetized magnet121is bonded or otherwise fixed to the other end of the rod122.

The tension adjusting spring81has one end abutting the flange of the rod122and the other end on the bottom of the sleeve101. A magnetic sensor123is embedded in the bottom of the slide sleeve101. The sensor123may be a Hall sensor. It produces a signal indicative of the distance between the sensor and the magnet121and thus the position of the pulley51.

The operation of the belt tension adjustor of the first embodiment will be described. When the tension in the belt A increases in the state ofFIG. 16, the pin77urges the protruding end of the rod92and the plunger61. This increases the pressure in the pressure chamber66. Hydraulic oil in the pressure chamber66thus leaks through a small gap formed between the plunger61and the inner wall of the bore60into the main reservoir65to dampen the movement of the plunger, and part of the oil flows through the passage71into the sub-reservoir63. The tension pulley51and the eccentric ring53are thus allowed to slowly pivot clockwise about the bolt56while pushing in the rod92and the plunger61until the belt tension balances with the force of the tension adjusting spring81.

On the other hand, when the tension in the belt A decreases, the tension adjustor spring81quickly pivots the pulley51and the eccentric ring53counterclockwise. The pin77thus moves rightwardly inFIG. 16. This causes the pressure in the pressure chamber66to drop below the pressure in the reservoir65, so that the check valve68opens the passage67. Thus, the plunger61and the rod92are quickly moved rightwardly by the spring69, following the movement of the pin77, because hydraulic oil in the main reservoir65and hydraulic oil in the sub-reservoir63smoothly flow into the pressure chamber66through the passage67and into the main reservoir65through the passage71, respectively.

The detecting unit includes a detecting circuit40, which, based on the signal from the sensor123, detects the distance between the sensor123and the magnet121and thus the position of the pulley51. As will be apparent fromFIGS. 16,17and19, the detector unit is arranged such that when the tension in the belt increases and the pulley51pivots clockwise (moves leftwardly), the magnet121moves closer to the sensor123, and thus the magnetic flux passing the sensor increases. Conversely, as the tension in the belt decreases and the pulley pivots counterclockwise to the limit (as shown by solid line inFIG. 19), the magnetic flux picked up by the sensor will become minimum. Thus, by detecting the intensity of magnetic flux passing through the sensor123, it is possible to detect the distance between the sensor123and the magnet121and thus the position of the pulley51. If the sensor123is a Hall sensor having an analog-output, the position of the rod92can be detected continuously as a function of the distance between the sensor and the magnet.

As the output of the analog Hall sensor, if the magnetic flux of the magnet acting thereon is zero, half the source voltage is outputted. The output voltage increases or decreases in the piercing direction of the magnetic flux as the magnet approaches or moves away. Since the direction of the magnetic flux piercing through the analog Hall sensor is the same while the source voltage is constant, the change in the output remains half the change in the source voltage.

Thus, the detector unit can detect the position of the pulley51continuously or at multiple points.FIG. 20shows how the geometric center53P of the pulley51moves between two limit points53P and53PL along an arc from the state shown inFIG. 17to the state shown inFIG. 19.

The relationship between the sensor-to-magnet distance and the position of the geometric center53P of the pulley51is determined by geometric shapes and arrangements of various parts of the tension adjustor including the fixing bolt56, eccentric ring53and pulley51. Thus, by “teaching” the detecting circuit40this relationship beforehand, the detecting circuit40can detect the position of the pulley51by detecting the moving distance of the rod92or122.

FIGS. 21 and 22show a second embodiment of the belt tension adjustor, which differs only in the structure of the position detector unit from the first embodiment.

As shown inFIG. 21, the detector unit includes a semicylindrical rod122aon which are mounted axially magnetized and axially spaced cylindrical magnets121aand121bwhich are mounted so that the polarity differs. The direction of magnetic flux is perpendicular to the axis of the tension adjusting spring81. The rod122ais inserted in the spring81and immovably secured to the slide cap102by having its flange at one end thereof sandwiched between the bottom of the slide cap102and the spring81. The detector unit further includes a semicylindrical sensor holder124inserted in the spring81opposite the rod122aand having a magnetic sensor123embedded therein. The sensor holder124has a flanged end secured to the bottom of the sleeve101. A lead wire connected to the sensor123extends outwardly through the flange of the holder124. The parts are all housed in the recess78bformed in the eccentric ring53(FIG. 22B).

The belt tension adjustor of this embodiment operates mechanically in exactly the same way as the adjustor of the first embodiment. Only the operation of the detector unit will be described.FIG. 22Ashows a state when the tension pulley51is in its initial position, in which one magnet121ais close to the sensor123and thus the magnetic flux passing through the sensor is maximum. As the tension in the belt A decreases, the eccentric ring pivots counterclockwise and the distance between the magnet121aand the sensor123increases, while the distance between the other magnet121band the sensor123decreases. Thus, beyond one point, the latter distance becomes shorter than the former distance. This causes reversal of magnetic flux.FIG. 22Bshows the state when the rod92has protruded to the maximum, where the reversed magnetic flux becomes maximum. If an analog output Hall sensor is used as the magnetic sensor123, its output will change continuously within the range of the source voltage, so that compared with the arrangement of the first embodiment, the output change rate will be about two-fold. Thus the detecting sensitivity increases extremely.

FIGS. 23A and 23Bshow a modification of the second embodiment, in which the two magnets121aand121bare arranged in a slightly different manner from the second embodiment. That is, they are arranged such that the directions of the magnetic flux of the magnets121a,121bcoincide with the axis of the spring81and that their polarity is such that the flux passing through the sensor123has directions opposite to each other. The detector unit of this modification operates in exactly the same way as the second embodiment.

FIG. 24shows a third embodiment of the belt tension adjustor. The belt tension adjustor of this embodiment operates in exactly the same way as that of the first embodiment. Only the detector unit is described. In this embodiment, a magnet121is buried in a lever125(FIG. 25) pressed on the pin76. Since the lever125is fixed to the stationary pin76, the magnet121does not pivot when the eccentric ring53pivots. Since the recess78formed in the eccentric ring is deeper than the recess78aof the first embodiment, the lever125does not touch the inner wall of the recess78when the eccentric ring53pivots. A magnetic sensor123is embedded in a protrusion of the slide member101bsimultaneously when the protrusion is formed by molding.

As the tension pulley51pivots from the initial position ofFIG. 24(where the magnet-to-sensor distance is maximum) toward the limit position ofFIG. 26, where the tension pulley51has pivoted to its limit, the sensor123gradually approaches the stationary magnet121and thus the magnetic flux passing through the sensor gradually increases. Thus, by detecting the magnetic flux, it is possible to linearly detect the position of the eccentric ring.

FIGS. 27A and 27Bshow a fourth embodiment of the belt tension adjustor. The belt tension adjustor of this embodiment operates in exactly the same way as the adjustor of the first embodiment. Only the detector unit is described. In this embodiment, a magnet121is fitted in a cutout formed in a half ring126pressed onto the pin77pressed in the eccentric ring53. A magnetic sensor123is embedded in a sensor holder127mounted on the body of the hydraulic damper58at such a position that the distance between the sensor123and the magnet121will be minimum when the tension pulley51has pivoted to its limit. In this embodiment, the sensor holder127is inserted in a tapered groove128formed in the damper body and retained in position by a pin129, but may be mounted to the damper body in any other way.

As the tension pulley51pivots from the initial position ofFIG. 27Atoward the limit position ofFIG. 28, where the rod92has protruded to its limit, the magnet121gradually approaches the stationary sensor123and thus the magnetic flux passing through the sensor increases. Thus, by detecting the magnetic flux, it is possible to detect the position of the tension pulley linearly or at multiple points.

FIGS. 29A and 29Bshow a fifth embodiment of the belt tension adjustor. The belt tension adjustor of this embodiment operates in exactly the same way as that of the first embodiment. In this embodiment, two magnets121aand121bmagnetized in the axial direction of the eccentric ring53are embedded in the eccentric ring, circumferentially spaced from each other, so that they have different polarities at the surfaces. A magnetic sensor123is embedded in a sensor holder127afitted in a circular hole formed in the body of the hydraulic damper58. If the eccentric ring53is formed of a magnetic material, the magnets121a,121bmay be enclosed in a non-magnetic material, to increase the density of flux passing through the sensor123.

FIG. 29Ashows a state when the tension pulley51is in its initial position, in which the magnet121ais close to the sensor and thus the magnetic flux passing through the sensor is maximum. As the tension in the belt A decreases, the eccentric ring53pivots counterclockwise and the distance between the magnet121aand the sensor123increases, while the distance between the magnet121band the sensor123decreases. Thus, at one point, the latter distance becomes shorter than the former. This causes reversal of direction of the magnetic flux.FIG. 29Bshows the state when the rod92has protruded to the maximum, where the reversed magnetic flux is maximum. Thus, if an analog-output Hall sensor is used as the sensor, its output will change continuously within the source voltage. Substantially the same output can be obtained as in the second embodiment. One of the magnets121a,121bmay be omitted.

FIG. 31shows a modification of the fifth embodiment, in which a substantially circumferentially tapered magnet121cis used. With this arrangement, when the eccentric ring pivots in either direction, the distance between the sensor and the magnet121cchanges gradually. Thus, by detecting the magnetic flux, which changes as a function of the sensor-to-magnet distance, it is possible to linearly detect the position of the pulley. Or instead, only the limit position of the pulley may be detected by using a contact-output Hall sensor.

The magnetic force of a magnet weakens as the temperature rises. A Hall sensor used as a magnetic sensor has a temperature-dependent output offset. Thus, for accurate detection of the position of the pulley, the detector of any of the embodiments may be provided with a temperature-compensation means as shown inFIG. 32. Without such means some error can result with temperature change. This means comprises a temperature sensor131and a processor130including A/D converters for converting signals from the Hall sensor123and the temperature sensor131into digital signals, and a CPU programmed to correct the position detection signal from the magnetic sensor based on the temperature signal from the temperature sensor131. The latter sensor may be embedded in a molded resin member. Instead of the temperature sensor131, any existing temperature gauge used in various parts of the vehicle such as a temperature gauge for the radiator may be used. Such a correction means may be incorporated in a control unit for the vehicle.

As described in detail so far, in the piston rod detection mechanism of the present invention, for a piston rod of a cylinder unit, the detecting coil and the flange or the coil spring are provided to detect the position of the piston rod continuously or in a multiple-point manner by the detection signal based on change in the inductance coupling. Thus, it is possible to detect change in the amount of protrusion of the piston rod due to secular change of the cylinder unit or a device cooperating therewith. Also it is possible to know beforehand the timing for taking measures against deterioration of the cylinder unit or a similar device due to secular change with the detecting mechanism having a simple structure. Also, for the autotensioner and electromagnetic valve using this detecting mechanism, too, a similar effect is obtained. By combining a detecting coil with an exciting coil, the detecting sensitivity further improves.

As has been described above, with the belt tension adjusting device of this invention, a tension pulley is rotatably supported by an inner member, a tension adjusting spring and a hydraulic damper are provided to adjust tension, and the position of the tension pulley is detected by a magnetic sensor. Thus, by detecting the movement of the tension pulley to the limit position from the detection signal of the magnetic sensor, it is possible to know the timing for exchange of the timing belt and to indicate the exchange period or abnormality of the timing belt by sending this detection signal to a control unit (computer) and indicating it on a display.