A device to calculate a wheel speed of a vehicle Field of the invention

This disclosure relates to a device to calculate a wheel speed of a vehicle. More particularly, it relates to detecting wheel speed and vehicle speed of two wheeled vehicles.

Background of the invention:

Wheel bearing apparatus comprises a wheel speed detecting sensor within the wheel bearing. This reduces the size of the wheel bearing apparatus as well as eliminates troublesome in air gap adjustment between the wheel speed sensor and the magnetic encoder. The wheel speed sensor is usually mounted on a supporting rod of the wheel bearing apparatus. The speed of a wheel is often used to determine the speed of a vehicle. The systems employing sensors have used a magnetic ring frictionally coupled to the wheel, along with a Hall sensor to detect the magnetic field from the ring and determine the speed of the wheel. These sensor-based systems have various drawbacks including bulky size and difficulty in mounting in order to achieve the correct frictional coupling and to correctly position the sensor in the magnetic field. Since vehicles use CAN (controller area network) multiplexing, the wheel speed sensor information is often integrated with the vehicle speed sensor information to control various systems.

A Japanese patent document 2014065327discloses a device comprises a vehicle speed determination unit which determines moving vehicle speed based on output signal from a sensor detecting rotation angle of rotary body of a vehicle. A control unit controls a rear suspension unit based on the determined vehicle speed. The vehicle speed determination unit determines the vehicle speed value by using a correction coefficient of vehicle speed. Brief description of the accompanying drawings:

An embodiment of the disclosure is described with reference to the following accompanying drawings;

Figure 1 illustrates a block diagram of a device to calculate a wheel speed in a vehicle in accordance with an embodiment of this invention;

Figure 2 illustrates a graph of time pulse generated by a sensor upon detecting each tooth of a sprocket in accordance with an embodiment of this invention; and

Figure 3 illustrates a flowchart of working of a method for calculating a wheel speed in a vehicle in accordance with an embodiment of this invention.

Detailed description of the embodiments:

Figure 1 illustrates a device 10 to calculate a wheel speed in a vehicle in accordance with this disclosure. The device 10 comprises at least one sensor 12 placed in proximity to at least one sprocket (16, 13). The sensor 12 generates at least one pulse upon detecting each tooth 18(a) of the sprocket 16. The device 10 further comprises a control unit 14 adapted to receive at least one pulse that is generated. The control unit 14 calculates the wheel speed of the vehicle based on time taken for one rotation of at least one sprocket (16, 13).

Figure 2 illustrates a graph of a time pulse generated by a sensor 12 upon detecting each tooth 18(a) of a sprocket 16 in accordance with an embodiment of the invention.

Further construction of the device 10 to calculate a wheel speed in a vehicle is explained as follows. The sensor 12 disclosed in this invention according to one embodiment, is placed near a sprocket 16 present in a rear wheel of a vehicle, on a supporting element 15 connecting the rear wheel sprocket 16 and a front wheel sprocket 13 in the vehicle. For example, the sensor 12 can be mounted perpendicular to the sprocket 16 with a proper air gap. The sensor 12 generates a pulse upon detecting each tooth 18a of the sprocket (13, 16). The control unit 14 is connected to the sensor 12 to receive the pulse generated upon detecting each tooth of the sprocket 16. A display 20 present in a dash board of a vehicle, is connected to the control unit 14 to display the calculated wheel speed. The sensor 12 is chosen from a group of sensors like a position sensor, a proximity sensor, an inductive sensor, a magnetic sensor or the like. The sensor 12 detects one complete rotation of the sprocket 16 by taking the first tooth 18(a) of the sprocket which passes the sensor 12 when the vehicle is started (i.e., when a driving cycle is started), as a reference. The sensor 12 detects one rotation of the sprocket 16, when the same tooth 18 (a) of the sprocket 16 passes the sensor 12 during the vehicle driving cycle. This can be detected by counting the number of pulses generated by the sensor 12. When the number of teeth of the sprocket (13, 16) is known beforehand, the sensor 12 can determine the completion of one rotation of the sprocket (13, 16) by counting the number of pulses. The vehicle is chosen from a group of vehicles like a two-wheeler or the like.

In one embodiment of the invention, the sensor 12 placed in proximity to the sprocket 16 generates a pulse upon detecting each tooth 18 (a) of the sprocket 16. The generated pulse is a time pulse. The control unit 14 starts a timer 17 when the first tooth 18(a) of the sprocket 16 is detected by the sensor 12. The control unit 14 which is connected to the sensor 12, receives the generated pulses. The sensor 12 transmits a signal to the control unit 14 when the sprocket 16 completes one rotation (from a method explained in above para). The control unit 14 upon detecting one complete rotation of the sprocket 16, calculates the total time taken for the sprocket 16 to complete one rotation, i.e.,, the time difference between the ON time of the first pulse corresponding to the first tooth of the sprocket 13, 16 and the OFF time of the last pulse corresponding to the last tooth of the sprocket 13, 16 (). The control unit 14 calculates the wheel speed from detected time the method known to the person skilled in the art. The calculated wheel speed is displayed in the dashboard of the vehicle via the display 20. Further to the above process, the control unit 14 calculates the vehicle speed from the wheel speed and will be displayed same in the dashboard of the vehicle.

The above process is explained in the below example.

In this example, the control unit 14 starts the timer 17 upon detection of the first tooth 18(a) movement through the sensor 12 (i.e. the ON time of the first pulse). The sensor 12 detects one complete rotation of the sprocket 16 when the same tooth 18(a) is passed „

- 4 - through the sensor 12. Let the OFF time of the last pulse (upon detecting the last tooth of the sprocket) is 9ms. The control unit 14 converts the time from microseconds to minutes. (9ms= 0.009sec = 0.00015minutes). From the comparison method, the control unit 14 calculates the wheel speed as following:

If 0.00015minutes = 1 rotation, then for 1 minute = (1/0.00015) = 6666.67 rotations. The wheel speed of the vehicle will be 6666.67 RPM. The calculated wheel speed is displayed in the dash board of the vehicle.

In another embodiment of the invention, the sensor 12 detects each tooth 18(a) of the sprocket 12 and generates a pulse for corresponding tooth. The control unit 14 starts the timer 17 when the sensor 12 starts detecting the tooth 18(a) of the sprocket 16. The control unit 14 receives the generated chain of the pulses and ON and OFF times of the pulses from the timer 17. The control unit 14 calculates a time difference between the two consecutive pulses. I.e., either the ON times of the two consecutive pulses or the OFF times of the two consecutive pulses are considered to calculate the time difference.

In the one scenario, the control unit 14 calculates the time difference between two OFF times of the two consecutive pulses and continuously adds the time difference between OFF times of the every two consecutive pulses until the sprocket 16 completes one rotation. The total time difference is converted to minutes and with the comparison method, the control unit 14 calculates the wheel speed of the vehicle. In another scenario, if the time difference between all the two consecutive pulses during one complete rotation of the sprocket 16 is constant, the control unit 14 calculates the time difference between either two ON times of the two consecutive pulses or two OFF times of the two consecutive pulses. The control unit 14 calculates the wheel speed from the calculated time difference and the number of teeth 18 of the sprocket 16. The calculated wheel speed is displayed in the dashboard of the vehicle.

The above disclosed embodiment is explained with the example given below:

In this example, the time difference between OFF times of the two consecutive pulses varies as the speed of the vehicle changes. Let the sprocket 16 has 22 teeth and the sensor 12 detects the first tooth passing the sensor 12 as the reference tooth. The control unit 14 _r

- 5—

receives the chain of pulses generated upon detection of each tooth 18(a) of the sprocket 16. Let two consecutive pulses ON times are 28.8ms and 31.6ms and the OFF times are 29.6ms and 32.4ms as shown in the figure 2. The control unit 14 calculates the time difference between two OFF times of the consecutive pulses. The time difference is 2.8ms (32.4ms-29.6ms =2.8ms).

In another example, the time difference between any two consecutive pulses during one complete rotation of the sprocket 16 is constant, i.e., 2.8ms. In this case, then the control unit 14 calculates the wheel speed from the teeth 18 of the sprocket 16 and the calculated time difference.

Time taken for one rotation = No. of teeth of the sprocket * calculated time difference

= 22*2.8ms

=61.6ms

From the comparison method,

If 61.6ms or 0.00102minutes is taken for one rotation, then for one minute,

No. of rotations per minute = 1/0.00102 =980.39 RPM.

The control unit 14 transmits the calculated wheel speed (no of rotations per minute) as 980.39RPM to the display present in the dashboard of the vehicle.

In another scenario, if the time difference between the two consecutive pulses varies, and does not remain constant, then, the control unit 14 adds all the time differences calculated between every two consecutive pulses during the complete rotation of the sprocket. (I.e.., 2.8ms+7.6ms+...). Let the total time difference is 117.6ms. The control unit 14 coverts the time difference into minutes. (I.e. 117.6ms/60 =0.00196minutes).

From the comparison method, the control unit calculates the wheel speed as follows. If for 0.00196minutes, the sprocket is completing one rotation, then for one minute,

No of rotations of the sprocket in one minute =1/0.00196 =510.20 RPM.

The control unit 14 transmits the calculated wheel speed as 510.20RPM to the display present in the dashboard of the vehicle.

Figure 3 illustrates a method to calculate a wheel speed in a vehicle according to the disclosure. In step SI at least one pulse is generated upon detecting for each tooth 18(a) of at least one sprocket (16, 13). In step S2, at least one pulse which is generated is „

- 6 - received by a control unit (14). In step S3, the wheel speed of said vehicle is calculated based on a time taken for one rotation of at least one sprocket (16, 13). The time taken for one rotation of the sprocket (13, 16) can be calculated or measured by different ways as explained earlier. For example, a timer is switched on upon detecting a first pulse corresponding to a first tooth of the sprocket (13, 16). Since the control unit (14) knows the number of sprocket teeth beforehand, it measures the time till the last pulse corresponding to a last teeth of the sprocket (13. 16). Based on this time difference, the wheel speed is computed.

In another embodiment, when the vehicle has anti-lock braking system (ABS) and to maintain the accuracy of the wheel speed calculation, the control unit 14 adds an amplitude correction factor to the calculated wheel speed. The amplitude correction factor is a value which is stored in the control unit 14 during the calibration process.

The above device 10 and the method disclosed provides low cost solution for the vehicles especially two-wheelers where vehicle speed and wheel speed sensors to measure vehicle speed are not present. With the device 10 disclosed, a steel encoded ring which is used to measure the wheel speed can be eliminated. In addition to measuring the wheel speed and the vehicle speed, the user can get information about the wear of the sprocket (16, 13). The wear of at least one sprocket (16, 13) can be detected by the sensor 12 present in the vehicle. The control unit 14 detects the damages of sprocket teeth if there is a difference in the duty cycle with respect to a reference pulse.

It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this disclosure. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.