WO2008044879A1

WO2008044879A1 - Drive wheel system capable of measuring torque

Info

Publication number: WO2008044879A1
Application number: PCT/KR2007/004955
Authority: WO
Inventors: Jong Soon Im; Jin Yong Kim; Han Soo Yun
Original assignee: Il Jin Global Co., Ltd.
Priority date: 2006-10-10
Filing date: 2007-10-10
Publication date: 2008-04-17
Also published as: KR20080032450A; KR100842392B1

Abstract

There is provided a drive wheel system capable of measuring torque applied to a wheel by an engine while transmitting the power output of the engine to the wheel. The drive wheel system includes: a hub bearing unit; a first sensor portion for measuring a rotational speed of the wheel; a second sensor portion; a Birfield joint connected to the hub bearing unit; a drive axle for connecting the Birfield joint and a tripod joint; and the tripod joint connected to one end of the drive axle. An outer peripheral surface of an outer ring of the tripod joint includes circular arc portions and concave portions as many as the circular arc portions. The second sensor portion is disposed radially apart from the circular arc portion. The torque is measured from a phase difference between waveforms detected from the first and the second sensor portions.

Description

DRIVE WHEEL SYSTEM CAPABLE OF MEASURING TORQUE

TECHNICAL FIELD

The present invention generally relates to a drive wheel system capable of measuring torque, and more particularly to a drive wheel system capable of measuring torque, wherein minute torque can be measured, wherein torque actually acting on a wheel can be measured without amplifying minute torque, and wherein torque can be precisely measured without any error even in case of a large deformation angle caused by the torque.

BACKGROUND ART

In recent years, automotive vehicles are configured to control a high-tech control system such as an Anti-lock Brake system (ABS), a Traction Control system (TCU), an Electric Stability Program (ESP) or a Limited Slip Differential (LSD). This is accomplished by mounting an encoder-integrated seal to a bearing mounted to a suspension device of an automotive vehicle, detecting rotation of the bearing from variation of magnetic field produced by the encoder to measure rotational speed of the wheel, and measuring a torque outputted from the engine.

A drive wheel system, which is used herein, is described in a simple manner. In conventional automotive vehicles, the power output of an engine is transmitted to a transmission. Further, the power output of the transmission is transmitted to both wheels via a differential gear. The power output is transmitted from the differential gear to the wheel via a tripod joint, a drive axle and a Birfield joint. Between the Birfield joint and the wheel is provided a hub bearing unit for rotatably supporting the wheel. The tripod joint, the drive axle, the Birfield joint and the hub bearing unit are referred to as a drive wheel system.

Fig. 1 is a schematic sectional view showing a prior art drive wheel system. Fig. 2 is an enlarged sectional view of A of Fig. 1. As shown in Fig. 1 , a prior art drive wheel system 1 comprises the following: a hub bearing unit 10; a Birfield joint engaged to an inner periphery of the hub bearing unit 10 by splines 11a and 41a and being secured thereto by a nut 23; a drive axle 50 connecting the Birfield joint 40 and a tripod joint 60; and the tripod joint 60 transmitting rotational force to the Birfield joint 40 via the drive axle 50. A stem 61 of the tripod joint 60 is spline-engaged to a differential gear of a transmission (not shown). The power output is transmitted to the stem from the differential gear.

The hub bearing unit 10 includes: a hub 11 formed with one or more races; an outer ring 13 formed with a plurality of races and having a flange 14 with a threaded hole 14a for securing a knuckle (not shown) thereto; a plurality of rows of rolling elements 15 disposed between the hub 11 and the outer ring 13; and a cage 17 for maintaining intervals of the rolling elements. The hub 11 has a flange with a hub bolt 20, to which a wheel (not shown) is mounted together with a brake pad (not shown).

In Fig. 1, a reference numeral 18 denotes a rotational speed sensing portion. A reference numeral 18a denotes an encoder-integrated seal. A reference numeral 18b denotes a sensor for sensing variation of magnetic force from the encoder- integrated seal. The rotational speed is outputted from the variation of magnetic force measured by the rotation speed sensing portion 18 and is used as control data for use with an ABS or the like. A reference numeral 19 denotes an inner ring formed with a race and being inserted to an outer periphery of the hub 11.

The Birfield joint 40 and the tripod joint 60 serve to transmit a rotation force at constant velocity without varying a rotational speed within a certain angular range. The Birfield joint 40 includes: a stem portion 41 inserted to the inner periphery of the hub 11 and being secured thereto by the nut 23; a cup-shaped outer ring portion 43 integrally formed together with the stem portion 41 and supporting one side of the hub 11 at its one side; an inner ring portion 47 inserted into an inside of the outer ring portion 43; a plurality of balls 45 disposed between the inner ring portion 47 and the outer ring portion 43; and a retainer 49 maintaining intervals of the balls 45. The drive axle 50 is inserted into an inside of the inner ring portion 47 and is fixed thereto. At an outer periphery of the outer ring portion 43 and an outer periphery of the drive axle 50, there is provided a boot 42 for preventing a lubricant from leaking and preventing foreign substances from entering.

The other end of the drive axle 50 is inserted into a spider 64 of the tripod joint 60 and is fixed thereto. The tripod joint 60 includes: the spider 64 for fixing the drive axle 50; a roller 67 rotatably coupled to a trion 65 of the spider 64; and a joint outer ring 63, into which the spider 64 is inserted, and in which the roller 67 is seated. A stem 61 is formed protrusively on one side of the joint outer ring 63. A boot 62 is provided as fixed to the outer periphery of the drive axle 50 and an outer periphery of the joint outer ring 63.

In order to measure torque in such a prior art, as shown in Figs. 1 and 2, a niagnetostrictive ring 21b is provided around the outer periphery of the hub 11. Further, a magnetic sensor 21a, which measures magnetic variation occurring when the magnetostrictive ring 21b deforms, is provided outside the magnetostrictive ring 21b. If torsion occurs in the hub 11 by torque transmitted via the tripod joint 50, the drive axle 50 and the Birfield joint 40, then torsion also occurs in the magnetostrictive ring 21 b together with the torsion of the hub 11. The torque acting on the hub 11 is measured by calculating back the torsion of the hub 11 from the magnetic variation caused by the torsion of the magnetostrictive ring 21b.

As another approach for measuring torque, the torque is measured by means of an engine map using a torque chart, which is a characteristic curve of an engine, and which is plotted as a function of revolution numbers and a throttle valve.

However, when measuring torque using the magnetostrictive ring 21b, since an amount of the torsion of the hub 11 is small and measured signals are weak, a separate amplification circuitry is necessary. Further, there is a problem with such an approach in that minute torque variation cannot be precisely measured, and that disturbance is prone to occur in the signals. Also, the magnetic sensor 21 is difficult to be calibrated since it is located in the hub bearing unit 10 and the maintenance costs are high. Furthermore, there is also a problem with the approach for measuring a torque using an engine map in that time lag occurs and errors occur due to an external environmental factor such as temperature or moisture. Additionally, torque actually acting on a wheel cannot be precisely measured since torque is measured at an engine. Moreover, a real-time and precise wheel control cannot be performed since torque cannot be measured in real time at a drive wheel system.

DISCLOSURE TECHNICAL PROBLEM The present invention is directed to solving the foregoing problems of the prior art torque measurement. It is an object of the present invention to provide a drive wheel system capable of measuring torque, wherein minute torque can be measured and torque acting on a wheel can be measured in real time to thereby allowing a real-time and precise wheel control, wherein installation cost is low, and wherein torque can be measured precisely without any error even in the case of a large deformation angle caused by the torque irrespective of the magnitude of waveforms.

TECHNICAL SOLUTION In order to achieve the above objects, the present invention provides a drive wheel system capable of measuring torque, comprising: a hub bearing unit; a first sensor portion for measuring a rotational speed of the wheel; a second sensor portion; a Birfield joint connected to the hub bearing unit; a drive axle for connecting the Birfield joint and a tripod joint; and the tripod joint connected to one end of the drive axle; wherein an outer peripheral surface of an outer ring of the tripod joint includes a plurality of circular arc portions and concave portions as many as the circular arc portions, the concave portion being formed between the circular arc portions; wherein the second sensor portion is disposed apart from the circular arc portion by a predetermined gap in a radial direction of the circular arc portion, and wherein the torque is measured from a phase difference between waveforms detected from the first sensor portion and the second sensor portion.

The circular arc portions of the outer peripheral surface of the outer ring of the tripod joint may be provided with a plurality of protrusions at regular intervals. The second sensor portion may be disposed apart from the protrusion by a predetermined gap in the radial direction of the circular arc portion. The present invention also provides a drive wheel system capable of measuring a torque, comprising: a hub bearing unit; a first sensor portion for measuring a rotational speed of the wheel; a second sensor portion; a Birfield joint connected to the hub bearing unit; a drive axle for connecting the Birfield joint and a tripod joint; and the tripod joint configured as one end of the drive axle and being protected by a boot; wherein the boot is fixed at one side thereof to an outer ring of the tripod joint by a fixation member, wherein the fixation member includes an axially extended portion with a plurality of through-holes at circumferentially regular intervals, and wherein the second sensor portion is disposed radially apart from the axially extended portion by a predetermined gap. The present invention further provides a drive wheel system capable of measuring torque, comprising: a hub bearing unit; a first sensor portion for measuring a rotational speed of the wheel; a second sensor portion; a Birfield joint connected to the hub bearing unit; a drive axle for connecting the Birfield joint and a tripod joint; and the tripod joint connected to one end of the drive axle; wherein a tone wheel having a plurality of protrusions is mounted on the tripod joint, and wherein the second sensor portion is disposed radially apart from the protrusion by a predetermined gap.

The first sensor portion may be comprised of a seal provided in the hub bearing unit and a sensor portion disposed apart from the seal by a predetermined gap for sensing signals from the seal. The seal may include a supporting body formed with circumferentially equally spaced recesses or through-grooves or have a magnet portion with one or more N-poles and S-poles alternately circumferentially arranged. The first sensor portion may be comprised of a tone wheel mounted on an outer periphery of an outer ring of the Birfield joint and having a plurality of protrusions circumferentially. It may be also comprised of a sensor portion disposed radially apart from the protrusion by a predetermined gap for sensing signals from the tone wheel.

The circular arc portions, the protrusions formed at the circular arc portion, the protrusions of the tone wheel mounted on the outer ring or the through-holes formed at the fixation member may be configured so that one or more irregular pulses are detected. The recesses, the through-grooves or the magnet portion provided in the supporting body of the seal provided in the hub bearing unit or the protrusions of the tone wheel provided in the Birfield joint may be configured so that one or more irregular pulses are detected.

The drive wheel system of the present invention may further comprise: a detecting portion connected to the first sensor portion and the second sensor portion for detecting waveforms from the first sensor portion and the second sensor portion; and a computing portion connected to the detecting portion for computing the waveforms detected from the detecting portion and transferring computation results to a control portion. The computing portion may compute a rotational speed from the waveforms detected from the first sensor portion or the second sensor portion, extract a time difference by comparing the waveforms detected from the first sensor portion and the second sensor portion, and compute the torque from the time difference.

Further, the drive wheel system of the present invention may further comprise: a detecting portion connected to the first sensor portion and the second sensor portion for detecting waveforms from the first sensor portion and the second sensor portion; and a computing portion connected to the detecting portion for computing the waveforms detected from the detecting portion and transferring computation results to a control portion. The computing portion may extract a time difference from an initial phase difference and a phase difference between the irregular pulse detected from the first sensor portion and the irregular pulse detected from the second sensor portion. It may then compute the torque from the time difference.

ADVANTAGEOUS EFFECTS

According to the drive wheel system capable of measuring torque of the present invention, a minute torque can be precisely measured without any amplification. Since the torque acting on the wheel is measured, the torque actually acting on the wheel can be measured. Since the wheel speed and the torque acting on the wheel are precisely measured, a traction control can be performed precisely in real time at each wheel. Further, installation space or installation cost is hardly increased. Also, the torque can be precisely outputted without any error even in the case of a large deformation angle caused by the torque irrespective of the magnitude of waveforms.

DESCRIPTION OF DRAWINGS

Fig. 1 is a schematic sectional view showing a prior art drive wheel system. Fig. 2 is an enlarged view of A of Fig. 1.

Fig. 3 is a schematic sectional view showing a drive wheel system capable of measuring torque according to a preferred embodiment of the present invention. Fig. 4 is a sectional view showing an alternative of a first sensor portion in the drive wheel system of Fig. 3.

Fig. 5 is a sectional view taken along the line A-A of Fig. 3. Fig. 6 shows an alternative of Fig. 5.

Fig. 7 is a sectional view showing an alternative of a second sensor portion in the drive wheel system of the present invention.

Fig. 8 is a sectional view showing yet another alternative of the second sensor portion in the drive wheel system of the present invention.

Fig. 9 shows a constitution of a vehicle with the drive wheel system capable of measuring torque according to the present invention. Figs. 10 and 11 show examples of the waveforms detected by the drive wheel system capable of measuring torque according to the present invention.

Figs. 12 and 13 show alternatives of a tone wheel of the drive wheel system capable of measuring torque according to another preferred embodiment of the present invention, respectively. Fig. 14 shows waveforms detected using the tone wheels shown in Figs. 12 and 13.

Fig. 15 is a graph showing a relationship between torques and torsional angles, which are measured by the drive wheel system capable of measuring torque according to the present invention. BEST MODE

A drive wheel system capable of measuring torque of the present invention will now be described in detail with reference to the accompanying drawings. Regarding descriptions of a drive wheel system capable of measuring torque of the present invention, elements equivalent to those of a prior art drive wheel system are named using the same terminology as that of a prior art. Thus, repetitive detailed descriptions relating thereto are omitted herein.

Fig. 3 is a schematic sectional view showing a drive wheel system 100 capable of measuring torque according to a preferred embodiment of the present invention. Fig. 4 is a sectional view showing a Birfield joint shown in Fig. 3. Fig. 5 is a sectional view taken along the line A-A of Fig. 3. Fig. 6 is a sectional view showing an alternative of Fig. 5. Fig. 7 is a sectional view showing another alternative of the drive wheel system 100 of the present invention. Fig. 8 is a sectional view showing yet another alternative of the drive wheel system 100 of the present invention. Fig. 9 shows a constitution of a vehicle with the drive wheel system of the present invention. Figs. 10 and 11 show examples of the waveforms detected by the drive wheel system capable of measuring torque of the present invention. Fig. 15 is a graph showing a relationship between torques and torsional angles, which are measured during operation of the drive wheel system 100 capable of measuring torque of the present invention.

As shown in Fig. 3, the drive wheel system 100 capable of measuring torque, which is constructed in accordance with the preferred embodiment of the present invention, comprises the following: a hub bearing unit 110; a Birfield joint 140 inserted into an inner periphery of the hub bearing unit 110 and connected thereto; a drive axle 150 connecting the Birfield joint 140 and a tripod joint 160; and the tripod joint 160 connected to one side of the drive axle 150.

In the hub bearing unit 110, a reference numeral 111 denotes a hub. A reference numeral 112 denotes a flange radially extending from the hub. A reference numeral 113 denotes an outer ring. A reference numeral 114 denotes a flange extending from the outer ring 113. A reference numeral 115 denotes rolling elements disposed between the hub 111 and the outer ring 113. A reference numeral 117 denotes a retainer maintaining regular intervals of the rolling elements 115. A reference numeral 119 denotes an inner ring seated on an outer peripheral surface of the hub 111. A reference numeral 123 denotes a nut locking the Birfield joint 140 to the hub bearing unit 110. Reference numerals Ilia and 141a denote a spline formed on the inner periphery of the hub 111 and splines formed on an outer periphery of a stem portion 141 of the Birfield joint 140, respectively. Two separate inner rings may be seated on the outer peripheral surface of the hub 111, as shown with dashed lines in Fig. 3. In Fig. 3, a reference numeral 112a denotes a hub bolt for securing a wheel (not shown) and a brake pad (not shown) to the flange 112. Further, a reference numeral 114a denotes a knuckle hole for securing a knuckle (not shown) to the flange 114.

In the Birfield joint 140, a reference numeral 141 denotes the stem portion inserted into the inner periphery of the hub 111. A reference numeral 143 denotes a cup-shaped outer ring portion integrally formed together with the stem portion 141. A reference numeral 147 denotes an inner ring portion inserted into the outer ring portion 143. A reference numeral 145 denotes balls disposed between the outer ring portion 143 and the inner ring portion 147. A reference numeral 149 denotes a retainer maintaining regular intervals of the balls 145. A reference numeral 142 denotes a boot preventing a lubricant filled in the Birfield joint 140 from leaking while preventing foreign substances from entering it.

The drive wheel system 100 capable of measuring torque according to the present invention comprises a first sensor portion 120 for measuring a rotation speed of a wheel (not shown) and a second sensor portion 130 for measuring a rotation speed of the tripod joint 160. The first sensor portion 120, as shown in Fig. 3, includes: a seal 122 provided at the hub bearing unit 110; and a first sensor 121 positioned apart from the seal 122 by a predetermined gap to sense the rotation of the seal 122.

The seal 122 serves not only to prevent the lubricant filled in the hub bearing unit 110 from leaking, but also to prevent foreign substances from entering from the outside into the hub bearing unit 110. The seal may include: a supporting body (not shown) made from a metallic material; and seal lips (not shown) attached to said supporting body for sealing. The seal 122 is rotated together with the inner ring 119 or the outer ring 113 of the hub bearing unit 110. In such a case, in order to allow the first sensor 121 to sense such a rotation, said supporting body may be formed circumferentially at predetermined intervals with holes or recessed grooves. Alternatively, said supporting body may include one or more magnet portions (not shown), which include alternately arranged N-pole and S-pole in a circumferential direction.

As shown in Fig. 4, it is possible that the first sensor portion 120 may include: a tone wheel 124 mounted the outer ring portion 143 of the Birfield joint 140 and having a plurality of protrusions 126; and the first sensor 121 positioned apart from the protrusion 126 by a predetermined gap.

The tripod joint 160 includes: a stem 161; an outer ring integrally formed together with the stem 161; a spider 164 inserted inside the outer ring 163; and rollers 167 rotatably coupled to a trion 165 of the spider 164. The tripod joint further includes a boot 162 having the same functions as the boot 142 of the Birfield joint 140.

As for forming the outer ring 163 of the tripod joint 160, as shown in Fig. 5, the outer peripheral surface of the outer ring 163 is formed with a plurality of circular arc portions 163 a, the centers of which coincide with a rotation center of the stem 161, and concave portions 163b as many as the circular arc portions 163 a between the circular arc portions 163 a. A second sensor 131 is positioned apart from the circular arc portion 163 a by a predetermined gap in a radial direction of the circular arc 163a, thereby constituting the second sensor portion 130. As such, the outer ring 163 of the tripod joint 160 becomes a detected component and waveforms can be detected.

Further, as shown in Fig. 6, it is possible that the second sensor portion 130 can be constituted by providing one or more protrusions 163c on the circular arc portions 163a and positioning the second sensor 131 radially apart from the protrusion 163c by a predetermined gap. Since the outer peripheral surface of the outer ring 163 of the tripod joint 160 becomes the detected component and the second sensor 131 is positioned to constitute the second sensor portion 130, the second sensor portion 130 can be simply equipped at low costs without any additional mount space.

Fig. 7 is an enlarged sectional view showing the tripod joint 160. The boot 162 of the tripod joint 160 is rigidly fixed to the outer ring 163 by means of a fixation member 169. As shown in Fig. 7, the fixation member 169 includes an axially extended portion 169a. The extended portion 169a is formed circumferentially with a plurality of through holes 169c. The second sensor 131 is positioned radially apart from the through-hole 169c by a predetermined gap. As such, the second sensor portion 130 can be constituted. In Fig. 7, a reference numeral 169b denotes a longitudinally extended portion, which longitudinally extends from said extended portion 169a and serves to prevent the extended portion 169a from longitudinally deforming.

On the other hand, as shown in Fig. 8, the second sensor portion 130 may be constituted by mounting a tone wheel 134 having a plurality of protrusions 136 circumferentially to the outer periphery of the outer ring 163 of the tripod joint 160, and by positioning the second sensor 131 apart from said protrusion 136 by a predetermined gap. In such a case, as to forming the circular arc portions 163 a provided at the outer ring 163 of the tripod joint 160, it is unnecessary that the centers of the circular arc portions 163 a coincide with the rotation center of the stem 161.

In order to prevent the tone wheel 134 from being relatively rotated with respect to the outer ring 163 of the tripod joint 160 during rotation of the tripod joint 160, it is preferable that an inner periphery of the tone wheel 134 is provided with two or more protrusions 138. In the drive wheel system 100 capable of measuring torque according to the preferred embodiment of the present invention, the first sensor 120 of the first sensor portion 120 and the second sensor 131 of the second sensor portion 130 are connected to a detecting portion 171, as shown in Fig. 9. Further, waveforms shown in Figs. 10 and 11 are detected therefrom, as shown in Figs. 10 and 11. The detecting portion 171 is connected to a computing portion 173. The computing portion 173 is connected to an ECU 175 of a vehicle. The computing portion computes the waveforms detected from the detecting portion 171 and transfers computation results to the ECU 175. The ECU 175 transfers control signals to a control device 180 based on the computation results transferred from the computing portion 173. The control device 180 may be configured in various manners according to performances of vehicles.

In Figs. 10 and 11, the waveform indicated by 131 shows a waveform detected from the second sensor 131 of the second sensor portion 130. The waveform indicated by 121 shows a waveform detected from the first sensor 121 of the first sensor portion 120. Assuming that a phase difference does not occur between said two waveforms in an initial state where torque is not produced in the drive wheel joint 100, when a power is transmitted from the tripod joint 160 and torsion occurs in any structure (e.g., the drive axle 150) between the first sensor portion 120 and the second sensor portion 130, time difference Δt can be detected from the first waveforms and the second waveforms shown in Figs. 10 and 11. A torsional angle can be calculated using an equation ΔΘ=2πNΔt/60 from said detected time difference Δt. In the above-mentioned equation, Δθ is a torsional angle (rad), N is a revolution number (rpm) and Δt is a time difference (sec), as described above. Further, torque can be calculated using a equation T=ΔΘGJ/L from the torsional angle Δθ. In the above-mentioned equation, G is a shear modulus of elasticity (N/m²), J is a polar moment of inertia (m⁴), and L is a distance (m) between the first sensor portion 120 and the second sensor portion 130.

As such, the drive wheel system 100 according to the preferred embodiment of the present invention is capable of measuring torque in a simple manner. Further, it is capable of precisely measuring a very small torque without any amplification since the distance between the first sensor portion 120 and the second sensor portion 130 is large. Referring to the third waveforms shown in Figs. 10 and 11, however, in case the time difference Δt is larger than a period of the waveforms detected from the second sensor portion 130 after action of a larger torque, the magnitude of the time variation can be detected as Δt', which is smaller by the period of the waveforms than Δt, and a smaller torque than the actually acting torque can be thus computed. In other words, in case a torque variation rate is faster than time intervals relating to torque detection, the torque can be miscomputed due to recognition of Δt' instead of Δt.

In the above-described embodiment, assuming that the numbers of the protrusions 126 of the tone wheel 124 provided at the first sensor portion 120 is 48 similar to that of a generally widely used tone wheel, the number of pulses, which is indicated by 121 in Figs. 11 and 12, will be 48. Further, assuming that periods between each pulse are equal, the period, which each pulse has, will become 15°, if represented as a rotational angle. Thus, in case a torsional angle produced by the acting torque is larger than 15°, the torque can be miscalculated due to recognition of Δt' instead of Δt.

Fig. 15 is a graph showing torques and torsional angles measured during operation of the drive wheel system 100 according to the present invention. In Fig. 15, the vertical axis shows torques acting on the drive wheel system 100 and the horizontal axis shows torsional angles produced by the torques. As shown in Fig. 15, the torsional angles may be produced at more than 15° within a general torque range of a vehicle.

In order to cope with such a case where a time difference is larger than the period of the waveforms detected from the first sensor portion 120 due to action of the above-described torque, the circular arc portions 163a, the protrusions 163c provided at the circular arc portions 163a, the protrusions 136 of the tone wheel 134 mounted on the outer ring 163 or the through-hole 169c of the fixation member 169 is configured such that one or more irregular pulses are included in the waveforms detected from the second sensor portion 131. Similarly, the recessed portions, through-holes or magnetic portions provided at the supporting body of the seal 122 of the hub bearing unit 110, or the protrusions configured so that one or more irregular pulses are included in the waveforms detected from the first sensor portion 121.

Figs. 12 and 13 show elements used to detect irregular waveforms from the first sensor portion 120 and the second sensor portion 130, respectively. Fig. 14 shows waveforms detected using the tone wheel shown in Figs. 12 and 13.

In the drive wheel system 100 according to another preferred embodiment of the present invention, the tone wheels 124 provided at the first sensor portion 120 include a plurality of the protrusions 126 and the tone wheels 134 provided at the second sensor portion 130 include a plurality of the protrusions 136. As shown in Fig. 12, the tone wheel 124 includes a protrusion 126a, which is narrower (or wider) than the protrusion 126 between the protrusions 126. Similarly, as shown in Fig. 13, the tone wheel 134 includes a protrusion 136a, which is narrower (or wider) than the protrusion 136 between the protrusions 136. When such tone wheels 124 and 134 are rotated, the waveforms shown in Fig.

14 are detected. In said waveforms, an irregular waveform IP is detected by the protrusion 126a that is narrower (or wider) than other protrusions 126. Similarly, an irregular waveform IR is detected by the protrusion 136a that is narrower (or wider) than other protrusions 136. When the waveform (indicated by 130 in Fig. 14) of the second sensor portion 130 and the waveform (indicated by I in Fig. 14) of the first sensor portion 120 are referred to as a reference waveform in a state where no torque acts, a phase difference between the irregular pulses IR and IP in said two waveforms is referred to as an initial phase difference T. If a torque is applied and time delay takes place similar to the third waveform (indicated by II), then the phase difference between the irregular pulses IR and IP in the waveform 130 and the waveform II decreases to Tl . Thus, the time difference Δt can be obtained from the difference between said initial phase difference T and Tl . Also, in case the torque is increased and the time difference Δt then becomes larger than the period of the waveform detected from the first sensor portion 120 as shown in a waveform III, a phase difference T2 between the irregular pulses IR and IP in the waveform 130 and the waveform III can be easily obtained. Accordingly, the time difference Δt can be precisely obtained based on the difference between the initial phase difference T and other phase differences irrespective of the time intervals relating to torque detection. By making said initial phase difference T sufficiently larger than the torsional angle produced by the torque, the torque can be always precisely detected even in the case

12 where the torsional angle produced by the torque becomes larger than the period of the pulse IP.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

INDUSTRIAL APPLICABILITY The drive wheel system of the present invention is capable of measuring torque applied to a wheel by an engine, while transmitting the power output of the engine to the wheel.

Claims

1. A drive wheel system for measuring a torque applied to a wheel by an engine while transmitting a power output of the engine to the wheel, comprising: a hub bearing unit; a first sensor portion for measuring a rotational speed of the wheel; a second sensor portion; a Birfield joint connected to the hub bearing unit; a drive axle for connecting the Birfield joint and a tripod joint; and the tripod joint connected to one end of the drive axle; wherein an outer peripheral surface of an outer ring of the tripod joint includes a plurality of circular arc portions and concave portions as many as the circular arc portions, the concave portion being formed between the circular arc portions, wherein the second sensor portion is disposed apart from the circular arc portion by a predetermined gap in a radial direction of the circular arc portion, and wherein the torque is measured from a phase difference between waveforms detected from the first sensor portion and the second sensor portion.

2. The drive wheel system of Claim 1, wherein the circular arc portions of the outer peripheral surface of the outer ring of the tripod joint are provided with a plurality of protrusions at regular intervals, and wherein the second sensor portion is disposed apart from the protrusion by a predetermined gap in the radial direction of the circular arc portion.

3. A drive wheel system for measuring a torque applied to a wheel by an engine while transmitting a power output of the engine to the wheel, comprising: a hub bearing unit; a first sensor portion for measuring a rotational speed of the wheel; a second sensor portion; a Birfield joint connected to the hub bearing unit; a drive axle for connecting the Birfield joint and a tripod joint; and the tripod joint configured as one end of the drive axle and being protected by a boot; wherein the boot is fixed at one side thereof to an outer ring of the tripod joint by a fixation member, wherein the fixation member includes an axially extended portion formed with a plurality of through-holes at circumferentially regular intervals, and wherein the second sensor portion is disposed radially apart from the axially extended portion by a predetermined gap.

4. A drive wheel system for measuring a torque applied to a wheel by an engine while transmitting a power output of the engine to the wheel, comprising: a hub bearing unit; a first sensor portion for measuring a rotational speed of the wheel; a second sensor portion; a Birfield joint connected to the hub bearing unit; a drive axle for connecting the Birfield joint and a tripod joint; and the tripod joint connected to one end of the drive axle; wherein a tone wheel having a plurality of protrusions is mounted on the tripod j oint, and wherein the second sensor portion is disposed radially apart from the protrusion by a predetermined gap.

5. The drive wheel system of Claim 1, wherein the first sensor portion comprises a seal provided in the hub bearing unit and a sensor portion disposed apart from the seal by a predetermined gap for sensing signals from the seal, the seal including a supporting body formed with circumferentially equally spaced recesses or through-grooves or having a magnet portion with one or more N-poles and S-poles alternately circumferentially arranged, or the first sensor portion is comprised of a tone wheel mounted on an outer periphery of an outer ring of the Birfield joint and having a plurality of protrusions circumferentially and a sensor portion disposed radially apart from the protrusion by a predetermined gap for sensing signals from the tone wheel.

6. The drive wheel system of any one of Claims 1 to 5, wherein the circular arc portions, the protrusions formed at the circular arc portion, the protrusions of the tone wheel mounted on the outer ring or the through-holes formed at the fixation member are configured such that one or more irregular pulses are detected, and wherein the recesses, the through-grooves or the magnet portion provided in the supporting body of the seal provided in the hub bearing unit or the protrusions of the tone wheel provided in the Birfield joint are configured such that one or more irregular pulses are detected.

7. The drive wheel system of any one of Claims 1 to 5, wherein the drive wheel system further comprises: a detecting portion connected to the first sensor portion and the second sensor portion for detecting waveforms from the first sensor portion and the second sensor portion; and a computing portion connected to the detecting portion for computing the waveforms detected from the detecting portion and transferring computation results to a control portion, wherein the computing portion computes a rotational speed from the waveforms detected from the first sensor portion or the second sensor portion, extracts a time difference by comparing the waveforms detected from the first sensor portion and the second sensor portion and computes the torque from the time difference.

8. The drive wheel system of Claim 6, wherein the drive wheel system further comprises: a detecting portion connected to the first sensor portion and the second sensor portion for detecting waveforms from the first sensor portion and the second sensor portion; and a computing portion connected to the detecting portion for computing the waveforms detected from the detecting portion and transferring computation results to a control portion, wherein the computing portion extracts a time difference from an initial phase difference and a phase difference between the irregular pulse detected from the first sensor portion and the irregular pulse detected from the second sensor portion and computes the torque from the time difference.