Patent Application
20080140292
This application claims priority to Japanese Patent Application No. 2006-330140, filed on Dec. 7, 2006. The entire disclosure of Japanese Patent Application No. 2006-330140 is hereby incorporated herein by reference.
1. Field of the Invention
The present invention generally relates to the technological field of detecting acceleration devices and detecting acceleration methods. More specifically, the present invention relates to correcting an error in a detected acceleration of a vehicle.
2. Background Information
In conventional acceleration detection devices, a zero point correction of an acceleration sensor is carried out by averaging detected acceleration values each time that the vehicle stops, and adding or subtracting this average value (drift from the zero point of the acceleration sensor) to or from the current detected acceleration value (see for example, Japanese Laid-Open Patent Application No. 7-159438). Thus, the zero point correction aids in eliminating the effect of a sloping road on the acceleration sensor.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for correcting the drift error or the like of a vehicle acceleration sensor. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
However, it has been discovered that since the conventional technology mentioned above employs detected acceleration values taken when the vehicle is stopped, a problem may arises in that it will not be possible to detect correctly drift in instances where there are frequent stops on sloping roads, such as where the parking space of the home is on an incline, for example. Thus, the precision of zero point correction may be poor.
Therefore, in view of the foregoing problem, one object of the present invention to improve the accuracy for detecting acceleration.
In order to achieve the above object of the present invention, an acceleration detection device for detecting detected acceleration of a vehicle is provided that basically comprises a calculation unit and a correcting unit. The calculation unit calculates an averaged acceleration sensor output value every time the vehicle travels a prescribed distance based on detected acceleration sensor output values. The correcting unit corrects a current acceleration sensor output value based on the averaged acceleration sensor output value. Thus, the acceleration detection device aids in correcting for errors by an acceleration sensor due to the effects of sloping roads and traffic conditions
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.
Referring now to the attached drawings which form a part of this original disclosure:
Selected embodiments of the present invention will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments of the present invention are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
Referring initially to
The vehicle is provided with various on-board sensors such as an accelerator position sensor 6, a brake switch 7, a vehicle speed sensor 8, an acceleration sensor (G sensor) 9, a shift sensor 10, and the like.
The accelerator position sensor 6 outputs an accelerator position signal to the engine controller 4. The brake switch 7 outputs a brake switch signal to the engine controller 4 for indicating whether the brake (not shown) pedal has been depressed to apply a braking force to the wheels. The vehicle speed sensor 8 detects the driving speed of the vehicle (vehicle speed) on the basis of the rotational speed of the wheels as determined from wheel speed sensors provided to the wheels, and outputs a vehicle speed signal to the engine controller 4. The G sensor 9 detects acceleration acting on the vehicle, and outputs an acceleration signal to the engine controller 4. The shift sensor 10 detects the shift position of the automatic transmission 2, and outputs a shift position signal to the automatic transmission controller 5.
The vehicle is considered to be in the neutral state for neutral control by the neutral control device (e.g., the engine controller 4 and the automatic transmission controller 5) shown in
Specifically, the neutral control device will perform neutral control provided that the shift position signal from the shift sensor 10 indicates a forward drive position, that the accelerator position signal of the accelerator position sensor 6 is zero, that the brake switch signal from the brake switch 7 is ON (indicating the brake pedal is depressed), that the vehicle speed signal from the vehicle sensor 8 is a prescribed value (≈0), and that the acceleration signal from the G sensor 9 indicates an acceleration that corresponds to a sloping road of prescribed angle or less. At the point in time that any of the above-described conditions for execution of neutral control is no longer met, such as the brake switch going OFF, the neutral control device will cancel neutral control.
The distance counter 12 is a counter that counts the travel distance of the vehicle and outputs a sampling flag (=1) to the drift calculating unit 13 every time the vehicle travels a prescribed distance (threshold value A). The counter is reset every time the count value reaches the threshold value A, and the sampling flag is set to zero.
When the sampling flag is 1, the drift calculating unit 13 calculates the amount of drift of a G sensor 9 from a zero point on the basis of the G sensor output value and the previous value of the drift amount, and the drift amount is output to the zero point correction unit 14.
The zero point correction unit 14 is a comparator for outputting a difference value of the two input values, and the zero point correction unit subtracts the drift amount from the G sensor output value and outputs a corrected G sensor output value.
In step S1, it is determined whether or not the vehicle is traveling on the basis of a vehicle speed signal from the vehicle speed sensor 8. If the vehicle is traveling, then the process proceeds to step S2. If the vehicle is not traveling, then step S1 is repeated.
In step S2, it is determined by the distance counter 12 whether or not the counter value has reached the threshold value A. If the threshold value A has been reached, then the process proceeds to step S3. If the threshold value has not been reached, then step S2 is repeated.
In step S3, the G sensor output value is stored in the drift calculating unit 13, and the process proceeds to step S4.
In step S4, the drift amount is calculated by the drift calculating unit 13 on the basis of the G sensor output value stored in step S3 and the previous value of the drift amount, and then the process proceeds to step S5.
In step S5, the drift amount is subtracted from the G sensor output value by the zero point correcting unit 14. Then, the corrected G sensor output value is output by the zero point correcting unit 14, and the process returns.
In the drift calculating unit 13, the drift amount is calculated as the weighted sum of the G sensor output value and the previous value of the drift amount. Specifically, the drift amount y is calculated from the following Equation (1):
y=(1−a)×y(−1)+a×u
The weighting coefficient “a” is greater than 0 and is much less than () 1. The weighting coefficient “a” is a constant that is set to a lower value as the threshold value A is decreases. As will be apparent to those skilled in the art from this disclosure, this weighted method is a type of “averaging” of the G sensor (acceleration) sensor output values so as to minimize the effect of any one particular detected value. Thus, the terms “average”, “averaged”, and “averaging” are not used in a limiting manner herein.
Next, the zero point correction operation based on the G sensor output value during travel will be described.
In the acceleration sensor correction device disclosed in Japanese Laid-Open Patent Application No. 7-159438, the G sensor output value of a stopped vehicle is sampled and the drift amount is calculated. Therefore, it will not be possible to calculate a correct drift amount in instances where, for example, there are frequent stops on sloping roads, such as where the parking space of a home is on an incline, and the precision of zero point correction may therefore be poor.
On the other hand, in the acceleration detection device 11 of the illustrated embodiment, the previous G sensor output values generated while the vehicle is traveling are averaged, whereby the amount of drift from the zero point of the G sensor 9 is calculated and zero point correction is carried out using the drift amount. Therefore, it is possible to calculate a drift amount that is not affected by the slope when the vehicle is stopped, and the precision of the zero point correction can be improved.
As shown in
In the illustrated embodiment, distance sampling rather than time sampling is used as the sampling method for the G sensor output values.
For example, when a house is at the foot of a hill, a work place is at the top of a hill, and the vehicle is only being used to commute, the vehicle always travels slowly in congested traffic during the outbound trip (
In these conditions, when a method is used in which the G sensor output values are sampled at regular time intervals, the drift amount calculated thereby is a value that is biased toward the incline of the outbound trip, as shown in
By contrast, the acceleration detection device 11 of the illustrated embodiment uses distance sampling in which the drift amount is calculated once every time a prescribed distance has been traveled. Specifically, the travel distance is the same for the outbound trip and the inbound trip, regardless of the traffic conditions. Therefore, the average value of the acceleration/deceleration rate when climbing and descending equals out to be zero, and the drift amount can be accurately calculated.
In the drift calculating unit 13 in the illustrated embodiment, the drift amount is calculated as the weighted sum of the G sensor output value and the previous value of the drift amount. Therefore, the drift amount can be calculated by storing only the previous drift amounts. Specifically, since it is not necessary to save previous G sensor output values, it is possible both to reduce the storage capacity of memory or the like and to improve the computing speed.
In the illustrated embodiment, the drift amount is calculated with reference to Equation (1) in the drift calculating unit 13. It is assumed that the weighting coefficient “a” of the G sensor output value u is much less than 1, and the weighting coefficient of the G sensor output value u is set so as to be considerably less than the weighting coefficient (1−a) of the previous value y(−1) of the drift amount.
When the weighting coefficient “a” is increased, the drift amount varies greatly according to the currently detected G sensor output value, as shown in
Consequently, in the illustrated embodiment, the weighting coefficient “a” is set to a value that is considerably less than 1, and the effect of a single G sensor output value on the drift amount is minimized, whereby the drift amount is gradually corrected according to the travel distance, and the effect of the sensor noise or the like can be kept low.
In the illustrated embodiment, the weighting coefficient “a” is set to a smaller value as the threshold value A decreases, i.e., as the sampling distance decreases. For example, when the sampling distance is reduced to half without any change to the weighting coefficient “a”, the magnitude of the effect of the G sensor output value on the drift amount increases twofold as the correction rate is doubled. Therefore, it is impossible to gradually correct the drift amount according to the travel distance.
Consequently, in the illustrated embodiment, the weighting coefficient “a” is set to a smaller value as the sampling value A decreases, whereby the magnitude of the effect of the G sensor output value on the drift amount is kept at a constant value, and the drift amount can be gradually corrected, regardless of the sampling distance.
Next, the effects will be discussed.
The acceleration detection device of the illustrated embodiment affords effects such as the following, by way of example.
(1) The acceleration detection device 11 has a drift calculating unit 13 for averaging the previous G sensor output values generated every time a vehicle travels a prescribed distance, and calculates the amount of drift from a zero point of the G sensor output value; and a zero point correcting unit 14 for correcting the G sensor output value for the zero point on the basis of the drift amount. It is thereby possible to eliminate the effect of sloping roads and traffic conditions, and it is possible to achieve more accurate zero point correction.
(2) The drift calculating unit 13 calculates the drift amount as a weighted sum of the G sensor output value and the previous value of the drift amount. Therefore, it is not necessary to save the previous G sensor output values, and it is possible both to reduce the storage capacity of memory or the like and to improve the computing speed.
(3) The drift calculating unit 13 sets the weighting coefficient “a” of the G sensor output value to a value that is considerably less than the weighting coefficient (1−a) of the previous value of the drift amount. It is therefore possible to gradually correct the drift amount according to the travel distance, and the effect of sensor noise and the like can be kept low.
(4) The drift calculating unit 13 calculates the drift amount y on the basis of Equation (1), where u is the G sensor output value, a is the weighting coefficient, and y(−1) is the previous value of the drift amount. It is therefore possible to gradually correct the drift amount according to the travel distance, and the effect of sensor noise or the like can be kept low.
(5) The drift calculating unit 13 sets the weighting coefficient “a” to a lower value as the prescribed distance decreases. Therefore, the magnitude of the effect of the G sensor output value on the drift amount is kept at a constant value, and the drift amount can be gradually corrected, regardless of the sampling distance.
(6) The invention provides a method of correcting the drift error of a G sensor for correcting the error that a G sensor output value from the G sensor 9 mounted in a vehicle has in relation to the zero point, wherein the method comprises averaging previous G sensor output values generated every time the vehicle travels a prescribed distance, calculating the amount of drift from the zero point of the G sensor output value, and corrects the G sensor output value for the zero point on the basis of the drift amount. It is thereby possible to eliminate the effects of sloping roads and traffic conditions, and to achieve more accurate zero point correction.
For example, whereas the illustrated embodiment was described with reference to a case in which the acceleration detection device of the invention was used as roadway gradient detecting unit in a neutral control device, the acceleration detection device of the invention can also be appropriately employed in other vehicle control devices as a device for the zero point correction of acceleration sensors mounted on vehicles. The example was also described with reference to a case in which the current acceleration sensor output value was corrected for the zero point, but the present invention is not limited to this example and can also envision performing a correction by adding or subtracting the drift amount to or from an acceleration sensor output value. Furthermore, in the example, the drift amount was calculated as a weighted sum of the current acceleration sensor output value and the previous drift amount, and the acceleration sensor output values were averaged. However, it is also possible to use a method for averaging the acceleration sensor output values in which a numerical value, obtained by adding an acceleration output signal generated every time a prescribed distance has been traveled, is divided by a sampling number, and the acceleration sensor output value is averaged.
In understanding the scope of the present invention, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. Also, the terms “part,” “section,” “portion,” “member” or “element” when used in the singular can have the dual meaning of a single part or a plurality of parts. As will be apparent to those skilled in the art from this disclosure, the terms “average”, “averaged”, “averaging”, and the like is not limited to adding a sampling of detected values and dividing the total value by the sampling number. Rather, the terms “average”, “averaged”, “averaging”, and the like include other calculation in which the detected values are weighted so as to minimize the effect of any one particular detected value.
While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. For example, the size, shape, location or orientation of the various components can be changed as needed and/or desired. Components that are shown directly connected or contacting each other can have intermediate structures disposed between them. The functions of one element can be performed by two, and vice versa. The structures and functions of one embodiment can be adopted in another embodiment. It is not necessary for all advantages to be present in a particular embodiment at the same time. Every feature which is unique from the prior art, alone or in combination with other features, also should be considered a separate description of further inventions by the applicant, including the structural and/or functional concepts embodied by such feature(s). Thus, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-330140 | Dec 2006 | JP | national |
