The invention relates to a differential sensor which has been developed for the analog measurement of the stroke information of the movable shaft in the service chamber of air brake actuators by means of sensors and for the generation of digital signal, and to the operating method of this sensor.

Background of the I nvention

When the brake pedal or park brake is used for stopping a vehicle, the brake actuator shaft is pushed forward by way of the compressed air, and the vehicle is thus stopped. During this operation, the driver must be informed in order to control whether the shaft moves sufficiently and in case any inconvenience in the brake system is detected.

The air brake actuators used in heavy commercial vehicles are classified into two main types: spring brake actuators and service brake actuators.

The service brake chamber typically consists of a body, a service body, a diaphragm, a flange, a shaft, and a return spring

The most commonly employed application for the differential stroke measurement of the shaft of the service brake chamber in the air brake actuators within the state of the art is to perform differential stroke measurement by means of the magnets disposed on the shaft and the ha 11 -effect sensors located in the section of the service body in which the shaft moves. These measurements are incremental and the measurement are performed by counting the increments from the hall-effect sensors.

Again, in another embodiment in the state of the art, contacts are connected to the service body and it is controlled whether the movable flange is with total ( Full) stroke or not. In another embodiment, infrared sensors are used for reading the movement of the shaft. In the embodiments mentioned above;

• Since the environment in which the sensors are located is exposed, reading errors may be experienced as a result of contamination or deformation. (infra red yansitici malzeme diye eklemek gerekli olabilir.hangi metot belli degil)

• Because the movement of the shaft is gradual in drum brake systems, the distance between the reader sensor and the corresponding component may vary; therefore, the changes in the signal prevent a precise and accurate measurement.

• As the hall-effect measurements are sensitive against the changes in the magnetic field, a reliable measurement will not be possible.

Summary and Objects of the I nvention

In order to overcome the aforementioned technical problems, it has deemed necessary to make a different development in the embodiments of the prior art. In this regard, the differential stroke sensor according to the invention has been developed. The invention has two different embodiments.

In both of these embodiments, the sensor according to the invention is located inside a box which is resistant against liquid and powder contact, it remains unaffected by the environmental factors.

The first embodiment of the sensor according to the invention is the movable stroke sensor, in which 3 linear readers are provided such that a 120° angle will be formed therebetween. Thus, inaccurate reading resulting from the axis shifts in the shaft of the service brake actuator is eliminated.

In the second embodiment of the invention, i.e. the ring stroke sensor, the sensor is in the form of a single-piece ring. Hence, not only production and mounting efficiency increases, but also the service life may be very long. In this embodiment, the differential stroke reading is performed by means of the strain gauges located in appropriate positions inside the sensor.

In the systems in which the shafts using a spring for returning exist, the driving force is formed mechanically or by way of pressure, and the shaft is pushed back by means of the spring when the driving force is removed. In such systems, the shaft force changes with the changing driving force acting on the shaft, which, in turn, has an impact on the compression amount of the return spring compressed by the shaft. The force applied in proportion to the compression amount of the spring is measured by means of the sensors located under this spring, thereby making it possible to calculate the stroke section of the shaft.

There are two reading modes of sensors: incremental and absolute. The incremental sensors produce pulse in case of change. The interval between two pulses determines the resolution of the sensor. The microprocessor counts such pulses and performs measurement taking the zero point as the reference point.

In both embodiments of the invention, the sensors are capable of performing absolute (precise and accurate) reading.

In case of a power cut, the sensors in the state of the art may memorize their last point, and thus continue the reading process from the same point taken as reference; or alternatively they may go back to the zero point and continue the measurement process after resetting the reference point. The sensors capable of absolute reading used in the invention according to the present application, on the other hand, do not produce pulses but operate by generating a signal regarding their current position. Thus, in case of a power cut, they can continue operating without any need for resetting or determining a reference point.

While developing the differential sensor according to the invention, it has been aimed to:

· Read the differential stroke information of the shaft of the service brake actuator digitally in a reliable manner,

• Inform the user regarding the best maintenance time,

• Enable it to be mountable in the existing brake actuators,

• Monitor more than one air brake actuators with a single microprocessor,

· Allow remote connection, and

• Provide single-source and automated collection of the measurement information, and inform both the operators and the producers. Description of the Drawings

The drawings and related descriptions for a better understanding of the differential sensor having been developed according to the invention are given below.

Fig. 1 : Cross-sectional view of the second embodiment of the differential sensor according to the invention on the air brake actuator.

Fig. 2 : Cross-sectional view of the first embodiment of the differential sensor according to the invention on the air brake actuator.

Fig. 3 : .Exploded view of the first embodiment of the differential sensor according to the invention. Fig. 4 : Detailed view of the first embodiment of the differential sensor according to the invention when the shaft is in total stroke position.

Description of the Part References

The parts and components which are shown in the drawings illustrating the differential sensor developed with the present invention for a better understanding of the invention are enumerated individually and the reference numbers corresponding thereto are given below.

1 . non pressure housing

2. Return spring

3. Shaft

4. Conic section

5. Diaphragm

6. pressure housing

7. Flange

8. moving metal part cylinder

9. moving metal part body

1 0. Conductive brush of the moving metal part

1 1 . Return spring of the moving metal part 1 2. Sensor body

1 3. Sensor cap

1 4. moving metal part groove

1 5. Strip resistor body

1 6. Strip resistor

1 7. Return spring notch of the moving metal part body

1 8. Return spring housing of the moving metal part body

1 9. moving metal part

20. Movable differential sensor

21 . Ring differential sensor

Detailed Description of the I nvention

The differential sensor according to the invention which has been developed for mechanically measuring (analog measurement) the stroke information of the air brake actuators used in heavy commercial vehicles such as buses, trucks, semi-trailer trucks and converting such data into a digital value, as well as the operating method of this sensor has two different embodiments.

The movable differential sensor (20) according to the first embodiment of the invention comprises:

• A conic section (4) which is engaged in a shaft (3) of the flange (7) disposed on the diaphragm (5) which is located between an non pressure housing )(1) and a pressure housing (6), and

• A moving metal part (19) which is positioned in the closed area formed by the sensor body (12) and the sensor cap (13), said moving metal part

• comprising: o A moving metal part groove (14) in which the moving metal part body (9) moves in back and forth direction and which accommodates the return spring housing (18) of the moving metal part body to which the return spring (11) of the moving metal part body is engaged,

o A strip resistor body (15) which is stably positioned inside the moving metal part groove (14) and on which at least two strip resistors (16) are provided, o A body (9), said body (9) having thereon:

^■ A return spring notch (17) of the moving metal part body to which the return spring (11) of the moving metal part body is attached such that it will perform coiling and uncoiling movement,

^■ A conductive brush (10) of the moving metal part which, by performing sliding movement on the strip resistors (16), changes the resistance value, and

^■ A moving metal part cylinder (8) which enables the moving metal part (19) to be moved by the conic section (4), the contact distance of which varies upon the movement of the shaft (3).

The ring differential sensor (21) according to the second embodiment of the invention, on the other hand, comprises:

• More than one strain gauge disposed inside the sensor (21) body.

In both embodiments of the invention, the movable differential sensor (20) and the ring differential sensor (21) are located in the periphery of the shaft (3) by means of a body (12) in ring form.

In both embodiments of the invention, the movable differential sensor (20) and the ring differential sensor (21) perform absolute reading process. The difference of the absolute reading property from incremental reading property is as below. The incremental sensors operate by producing pulse when a change in resistance occurs. The interval between two pulses determines the resolution of the sensor. The microprocessor counts such pulses and performs measurement taking the zero point as the reference point. In case of a power cut, however, the sensors may memorize their last point, and thus continue the reading process from the same point taken as reference; or alternatively they may go back to the zero point and continue the measurement process after resetting the reference point. This cut and resetting process adversely affect the precision of the measurement and the accuracy of the obtained results. The sensors capable of absolute reading used in the invention according to the present application, on the other hand, do not produce pulses but operate by generating a signal regarding their current position. Thus, in case of a power cut, they can continue operating without any need for resetting or determining a reference point.

I n the first embodiment of the invention, since the movable differential sensor

(20) is in direct contact with the shaft (3) by way of the conic section (4), the measurement is performed by converting the perpendicular movement of the shaft (3) into horizontal movement. The conversion of the perpendicular movement of the shaft (3) into horizontal movement is conducted due to the fact that the conic section (4), which is located on the shaft (3) and the lower end diameter of which is larger than its upper end diameter, pushes the moving metal part (19) by way of the moving metal part cylinder (8) inside the sensor (20) during the upward movement of the shaft (3) in direction "a".

The upper end diameter of the conic section (4) is smaller than the lower end diameter thereof. When the shaft (3) is with zero stroke, the diameter value measured at the upper end is the same as the minimum defined diameter value. As the shaft (3) moves upwards, the diameter value measured with the reference point being taken at the upper end will be greater due to the geometry of the conic section (4). This diameter measurement method is performed with the logic of linear ruler.

The strip resistor body (15) is a non-conducting component and it is provided thereon with strip resistors (16). Such resistors are designed as two strips. Hence, the change distance used for measurement reading is doubled, and thus the precision is increased and the cables to be passed over the sensor are secured.

A resistance value is formed by providing a conductive bridge between two strip resistors (16) by means of the conductive brush (10) disposed on the moving metal part (19). As the conductive brush (10) changes place, the resistance distance will also change, leading to a variation in the resistance value. Because the diameter of the conic section (4) towards direction b will be smaller as the shaft (3) of the air brake actuator comes back in downward direction, the return spring (11) of the moving metal part is used in order for the moving metal part (19) to return.

In the first embodiment of the invention, 3 movable differential stroke sensors (20) that are located with 120° angle with respect to one another are used in the ring shaped body (12). Thus, differential reading process can be performed in a precise and accurate manner even in case of an axis shift at the shaft (3) end. In the first embodiment of the invention, the operating method of the movable differential sensor (20) comprises the process steps of:

• The movable differential sensor (20) contacting the moving metal part cylinder (8) therein and making the moving metal part (19) to move on the strip resistors (16), thanks to the conic section (4), which is disposed on the shaft (3), expanding to a larger diameter from a smaller diameter or narrowing down to a smaller diameter from a larger diameter during the movement of the shaft (3) in directions a and b,

• The conductive brush (10) of the moving metal part located at the lower portion of the moving metal part body (9) moving on the strip resistors (16), and thus creating a resistance difference on said resistors (16) during the movement of the moving metal part (19) on the strip resistors (16), and

• Conversion of the analog signal of the thus formed mechanical (analog) resistance difference into digital data, and showing such data on the indicator.

I n the second embodiment of the invention, the ring differential sensor (21) is not in contact with the shaft (3); the measurement process is performed by measuring the force applied by the return spring (2) on the sensor (21).

The strain gauges inside the ring differential sensor (21) are made of fine wire and located on the inclining surface of the sensor (21). Since the resistance values will change upon applying a force on the sensor (21), the measurement process can be readily performed by the strain gauges with a certain resistance value.

The strain gauges used inside the ring differential sensor (21) are located into said sensor (21) such that they will be able to perform differential measurement. Thus, the measurement values can be obtained without any error even in case of an axis shift in the shaft (3) of the air brake actuator. The sensor (21) measures the force of the return spring (2) in an absolute manner. Thanks to positioning the sensor (21) in a ring shaped geometry, not only the sensor (21) can be centered in the non pressure housing (1) but also it can allow centering of the return spring (2) over itself. Because the force applied by the return spring (2) on the sensor (21) will also change in case of a stroke change in the shaft (3) of the air brake actuator, such change is sensed by the sensor (21) and the analog signal is generated, which analog signal, in turn, being read by the microprocessor and converted into digital signal, and then being reflected on the indicator as the stroke information. In the second embodiment of the invention, the operating method of the ring differential sensor (21) comprises the process steps of:

• The return spring (2) connected to the diaphragm (5) becoming tight and loose, and thus creating a difference in the force acting on the ring sensor (21) during the movement of the shaft (3) in directions a and b,

• The force difference on the ring sensor (21) body creating a resistance difference in the strain gauges inside said sensor (21), and

• Conversion of the analog signal of the mechanical (analog) resistance difference formed on the strain gauges into digital data, and showing such data on the indicator.