The present invention relates to a load sensor used in an electric braking device.
A conventional load sensor disclosed in Japanese Patent Laid-Open Publication No. 09-254778 will be described below.
The fold point P is not found in the load characteristic diagram of the hydraulic brake in
A load sensor includes a load-input unit, an hourglass-shaped coil spring having an end coupled to the load-input unit, a load-applying unit provided at other end of the hourglass-shaped coil spring, and a load detector for receiving the load from the load-applying unit and detecting the load.
The load sensor does not give a user an uncomfortable pedal feeling, similarly to a hydraulic brake.
At least one end of a load-input unit 2 projects out of a case 1. Another end of the load-input unit 2 is connected to one end of an hourglass-shaped coil spring 6, and the other end of the hourglass-shaped coil spring 6 is provided with a load-applying unit 7. A load detector 8 is disposed on an inner surface of the case 1, and faces the load-applying unit 7. One end of the load-input unit 2 is fixed to a brake arm 22. The brake arm 22 has one end fixed to a car body 23 and has other end provided with a pedal 21.
The load detector 8 will be described hereinafter. The load detector 8 includes a straining body 12 to be strained by a load applied thereto, an insulating layer 13 on the straining body 12, and a strain-resistance element 14 as a strain detector on the insulating layer 13 for detecting an amount of the strain in the straining body 12. The straining body 12 is made of elastic material, such as metal, that can be strained by a load applied thereto. The straining body 12 preferably has a shape strained easily by the applied load, and, for example, has a recess A, as shown in
The insulating layer 13 is made of glass ceramics, such as glass enamel, ceramic, mixture of glass and ceramic, or oxide of aluminum. The insulating layer 13 is mounted to the strain resistance element 14 without an adhesive or the like, thus having a high reliability of a contact with the element. As shown in
The load detector 8 faces the load-applying unit 7, and a surface of the load-applying unit 7 facing the load detector 8 has a projection 102. The projection 102 efficiently applies a load from the pedal 21 to the load detector 8. The projection 102 may have a semi-spherical surface to reduce variation of a point to apply the load to the load detector 8 even when the load-applying unit 7 tilts, hence increasing detection accuracy to the load of the load detector 8.
The recess A or a through-hole formed in the load detector 8 corresponding to the projection 102 reduces a variation of the action point of the load to the load detector 8, hence increasing the detection accuracy of the load. The opening of the recess A or the through-hole is preferably smaller than the projection area of the projection 102.
An operation of the load sensor will be described.
When a driver starts to step on the pedal 21, the load-input unit 2 moves together with the brake arm 22. Then, the load-applying unit 7 transmits the load to the load detector 8 via the hourglass-shaped coil spring 6, and the load produces a change of a strain resistance, and the change is converted to an electric signal. The load is balanced with a reaction of the hourglass-shaped coil spring 6, and hence, the load characteristic depends on the coil spring 6. The coil spring 6 has a nonlinear spring characteristic. In the nonlinear spring characteristic, the reaction of the coil spring 6 is small when an amount of a deformation of the spring is small, and rapidly increases when the amount of the deformation exceeds a predetermined value.
The load characteristic shown in
The diameter of the hourglass-shaped coil spring gradually decreases toward its center. Therefore, windings at both ends of the spring having a larger diameter are firstly displaced when the spring receives a load, and the coil spring has a smooth load curve. According to an increase of the load applied to the spring, an inner winding of the spring is then displaced, and a gradient of the load curve becomes sharp. Thus, in the hourglass-shaped coil spring, the load characteristic has no fold point found therein and has a smooth curve.
The hourglass-shaped coil spring has a structure including two conical springs connected to each other at their ends having smaller diameters. This coil spring has a sharper load characteristic curve on receiving a load than a single conical spring, and hence has a load characteristic similar to that of the hydraulic brake.
Additionally, the load sensor of Embodiment 1 has a single spring, hence allowing the sensor to have a cumulative error smaller than that of a sensor including plural springs and to produce a small variation of a pedal feeling.
The stopper 3 disposed on the load input unit 2 may be provided in the case 1, as shown in
Elements other than discussed above in the load sensor of Embodiment 2 are the same as those of Embodiment 1, and are not described.
Elements other than discussed above in the load sensor of Embodiment 3 are the same as those of Embodiment 2, and are not described.
A structure of the stroke sensor will be described hereinafter.
A first magnet 9 is fixed to a load-input unit 2, and a first magnetic pole vector 9a of the first magnet 9 is substantially parallel with a movable direction of the load-input unit 2. A second magnet 10 facing the first magnet 9 is fixed in a case 1 such that the position of the magnets is fixed with respect to a load detector 8 relatively. A second magnetic pole vector 10a of the second magnet 10 is substantially orthogonal to the first magnetic pole vector 9a. A first semiconductor magnetic resistance element 11a and a second semiconductor magnetic resistance element 11b are disposed on the second magnet 10. The resistance elements 11a and 11b have magnetism sensing directions substantially orthogonal to both the first magnetic pole vector 9a and the second magnetic pole vector 10a. The semiconductor magnetic resistance element 11a faces one end of a surface of the second magnet 10 facing the first magnet 9. The semiconductor magnetic resistance element 11b faces other end of the surface of the magnet 10 opposite to the one end with respect to the load-input unit 2.
An operation of the stroke sensor will be described hereinafter.
When a load is applied to move the load-input unit 2, the position of the first magnet 9 mounted to the load-input unit 2 changes. At this moment, the strength of a magnetic field applied to the semiconductor magnetic resistance elements 11a and 11b on the second magnet 10 facing the first magnet 9 varies. A change of the strength of the magnetic field changes resistances of the first semiconductor magnetic resistance element 11a and the second semiconductor magnetic resistance element 11b to generate an electric signal. This provides an output depending on the stroke of the pedal. The load sensor of Embodiment 4 has the load characteristic shown in
Therefore, the load sensor of Embodiment 6 detects a load directly with the load detector 8 and indirectly with the stroke sensor, hence having a fail-safe function.
This stroke sensor can detect an amount of the stroke in a non-contact manner, hence providing the load sensor with an improved reliability.
Elements other than discussed above in the load sensor of Embodiment 4 are the same as those of Embodiment 2, and are not described.
One of the stroke sensor and a combination of a stopper 3 and impact buffers 5 may be installed, or Both of them may be installed.
The stroke sensor may be disposed inside the case 1, as shown in
The stroke sensor is installed in load sensors of Embodiments 2 and 4, but may be installed in load sensors of the other embodiments of the present invention.
The load detectors 8 of Embodiments 1 to 4 have an advantage of the hourglass-shaped coil spring not only in the structure discussed above but also in another structure.
A load sensor of the present invention has a load characteristic having no fold point and reduces an uncomfortable pedal feeling similarly to a hydraulic brake.
Number | Date | Country | Kind |
---|---|---|---|
2002-161198 | Jun 2002 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/JP03/06916 | 6/2/2003 | WO | 00 | 2/24/2004 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO03/102526 | 12/11/2003 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
4319650 | Brendel | Mar 1982 | A |
4818036 | Reinecke | Apr 1989 | A |
4922722 | Kazumoto et al. | May 1990 | A |
5090249 | Bielewicz | Feb 1992 | A |
6460835 | Hamano et al. | Oct 2002 | B1 |
6588542 | Nakajima et al. | Jul 2003 | B1 |
6880639 | Rhodes et al. | Apr 2005 | B1 |
20020056622 | Yamanashi et al. | May 2002 | A1 |
20050269871 | Saito | Dec 2005 | A1 |
Number | Date | Country |
---|---|---|
0 602 606 | Jun 1994 | EP |
59-29553 | Feb 1984 | JP |
9-254778 | Sep 1997 | JP |
2603578 | Jan 2000 | JP |
2001-281074 | Oct 2001 | JP |
Number | Date | Country | |
---|---|---|---|
20040238235 A1 | Dec 2004 | US |