Method and system of estimating vehicle velocity

Abstract: Velocities (V WF ,V WR ) of drive wheels and follower wheels of a vehicle are determined, and then the velocity (V ref ) of the vehicle is estimated based on the fastest wheel velocity (V WM ). When the estimated vehicle velocity (V ref ) is faster than the velocities of the follower wheels (V WF ) and lower than the fastest wheel velocity (V WM ), the estimated vehicle velocity (V ref ) determined immediately before the above estimating process is set as the estimated vehicle velocity. Also described are methods and apparatus for controlling braking pressure based on wheel slip, wheel acceleration/deceleration and brake pressure membership functions, which may be varied depending on tyre and vehicle stability characteristics, and in which data amounts and space for setting data about the slip ratio and wheel acceleration/deceleration are set so as to increase as their absolute values increase from zero. A method and apparatus of limiting the rate of increase of brake pressure during, for example, breakthrough by repeatedly opening and closing a cut-valve for set periods of time is also described.

Description: The present invention relates to a method of and an apparatus for estimating a vehicle velocity, which are suitable for use in a vehicle having drive wheels and follower wheels. In a vehicle such as a motorcar, a motorcycle or the like, a so-called brake control system is used in which a speed or velocity of each wheel placed under braking is compared with a vehicle speed and controlling of brakes is effected based on the result of comparison. In the brake control system, a slip ratio is determined from the wheel velocity and the vehicle velocity. When the slip ratio reaches a target slip ratio or above, the slip ratio is reduced by decreasing brake hydraulic pressure, thereby producing the optimum braking force. Further, a driving force control apparatus is known which controls a driving force of an engine by adjusting the ignition timing of the engine upon a vehicle rapid start or depending on a variation in a friction coefficient of a road surface, for example. Even in the case of the driving force control apparatus, the wheel velocity and the vehicle velocity are used as data. Now, the wheel velocity, i.e. the rotational speed of each wheel, can be directly detected by a sensor. It is however difficult to directly detect the vehicle velocity by a sensor. It is also next to impossible to detect the velocity of a vehicle such as a motorcycle whose weight and size are greatly restricted to accommodate the sensor therein. Accordingly, a method is normally used which estimates the vehicle velocity from the wheel velocity. EP-A-0374924, EP-A-322911, EP-A-435227 and DE-A-3924448, all mention methods in which the estimated vehicle speed is based upon the highest of the measured wheel velocities, and attempt to provide various improvements thereon. The present case also relates to a method and apparatus for improving such an estimate. There is often a situation in which an estimated vehicle velocity is set to be larger or smaller than an actual vehicle velocity under the conditions in which each wheel slips against the road surface. In this case, the brake control system or the driving force control apparatus tend to effect unsuitable control. It is a principal object of the present invention to provide a method of and an apparatus for estimating a vehicle speed, which are suitable for use in a vehicle, wherein a desired vehicle speed required to control brakes and brake driving forces or the like can be estimated easily and with high accuracy. Viewed from one aspect the present invention provides a method of estimating vehicle speed which is suitable for use in a vehicle, the method comprising: a first step of determining the speed of at least one drive and one follower wheel of the vehicle; a second step of selecting the fastest one of the speeds determined in the first step; and a third step of estimating the speed of the vehicle based on the fastest wheel speed selected in the second step; a cycle of the first through third steps being executed repeatedly at given time intervals; the method being characterised by the step of: comparing the follower wheel speed determined in a present cycle with the vehicle speed estimated in the previously executed cycle, the estimated vehicle speed of the present cycle being set to the estimated vehicle speed of the previous cycle when the estimated vehicle speed of the previous cycle is greater than the follower wheel speed of the present cycle. Viewed from a second aspect, the present invention provides an apparatus for estimating a vehicle speed, which is suitable for use in a vehicle, said apparatus comprising: first wheel speed detecting means for detecting speeds of drive wheels; second wheel speed detecting means for detecting speeds of follower wheels; wheel speed selecting means (4) for selecting the fastest one (V WM ) of the respective wheel speeds detected by the first and second wheel speed detecting means; and vehicle speed estimating means for estimating the speed of the vehicle based on the fastest wheel speed selected by the wheel speed selecting means (4); characterised in that the apparatus further includes: vehicle speed storing means (6) for storing therein the vehicle speed estimated by the vehicle speed estimating means; and comparing means for comparing the vehicle speed stored in the vehicle speed storing means with the follower wheel speeds detected by the second wheel speed detecting means; the vehicle speed estimating means being activated to supply a vehicle speed which was stored in the vehicle speed storing means in an estimation cycle immediately preceding a present estimation cycle as the estimated vehicle speed of the present estimation cycle when it is determined based on the result of comparison by the comparing means that the stored vehicle speed from the previous cycle is greater than the speeds of the follower wheels detected in the present cycle. The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example. FIG. 1 is a block diagram showing the structure of a vehicle speed estimating apparatus according to the present invention, which is suitable for use in a vehicle; FIG. 2 is a view for describing the relationship between a wheel speed selected by a wheel speed selecting circuit of the apparatus shown in FIG. 1 and an estimated vehicle speed determined from a basic computing process of an estimated vehicle speed computing circuit; FIG. 3 is a view for describing the relationship between the speed of a follow-up wheel, the speed of a drive wheel, a selected wheel speed and a vehicle speed estimated and corrected based on these speeds, all of which are determined by the apparatus shown in FIG. 1; FIG. 4 is a view for describing the relationship between the speed of the follow-up wheel, the speed of the drive wheel, the selected wheel speed and the vehicle speed estimated and corrected based on these speeds, all of which are determined by the apparatus A method of and an apparatus for estimating a vehicle speed or velocity, according to the present invention, which are suitable for use in a vehicle, will hereinafter be described in detail with reference to the accompanying drawings in which preferred embodiments are shown by way of illustrative example. FIG. 1 is a block diagram showing a vehicle speed estimating apparatus according to the present embodiment. The vehicle speed estimating apparatus comprises a follower wheel rotational speed sensor 1 for detecting the rotational speed or velocity of each follower wheel (e.g. a front wheel of a motorcycle, i.e. a 2-wheeled automotive vehicle), a drive wheel rotational speed sensor 2 for detecting the rotational speed or velocity of each drive wheel (e.g. a rear wheel of the motorcycle), wheel speed computing circuits 3A, 3B for computing wheel speeds or velocities based on signals outputted from the follower wheel rotational speed sensor 1 and the drive wheel rotational speed sensor 2 respectively, a wheel speed selecting circuit (wheel speed selecting means) 4 for selecting the fastest wheel velocity from the wheel velocities which have been computed by the wheel speed computing circuits 3A, 3B, an estimated vehicle speed computing circuit (vehicle speed estimating means) 5 for computing an estimated vehicle speed or velocity based on the wheel velocity which has been selected by the wheel speed selecting circuit 4, an estimated vehicle speed storing circuit (vehicle speed storing means) 6 for storing the computed estimated vehicle speed therein as data, and a comparator (comparing means) 7 for comparing the estimated vehicle speed stored in the estimated vehicle speed storing circuit 6 with each follower wheel velocity computed by the wheel speed computing circuit 3A. In this case, the output of the comparator 7 is used to control the estimated vehicle speed computing circuit 5. Incidentally, the follower wheel rotational speed sensor 1 and the wheel speed computing circuit 3A serve as a first wheel speed detecting means, whereas the drive wheel rotational speed sensor 2 and the wheel speed computing circuit 3B serve as a second wheel speed detecting means. The vehicle speed estimating apparatus according to the present embodiment is basically constructed as described above. A description will now be made of a method of estimating the speed or velocity of a motor-cycle, for example, which is carried out by the vehicle speed estimating apparatus. First of all, during a period in which the motorcycle is running, the follower wheel rotational speed sensor 1 and the drive wheel rotational speed sensor 2 respectively detect the rotational speeds of the front and rear wheels as pulses outputted from a rotary encoder or the like, for example, and output same, to the corresponding wheel speed computing circuits 3A, 3B. The wheel speed computing circuits 3A, 3B compute a follower wheel speed or velocity V WF and a drive wheel speed or velocity V WR in response to the pulses inputted from the follower wheel rotational speed sensor 1 and the drive wheel rotational speed sensor 2 respectively, and output the velocities thus computed to the wheel speed selecting circuit 4 as data. Incidentally, the wheel velocities V WF, V WR can be obtained by counting the number of pulses outputted from the follower wheel rotational speed sensor 1 and the drive wheel rotational speed sensor 2 and converting same into the peripheral speeds of the wheels. The wheel speed selecting circuit 4 then selects the fastest wheel velocity from the wheel velocities V WF , V WR and outputs it to the estimated vehicle speed computing circuit 5 as a wheel velocity V WM . That is, this selection is made because the fastest wheel velocity approaches an actual vehicle speed provided that a slip ratio of each wheel against a road surface is less than or equal to 0. The estimated vehicle speed computing circuit 5 basically computes an estimated vehicle speed or velocity V ref for each given computing period or cycle (3 ms, for example) in the following manner. Assuming that the motorcycle is not decelerated at - 9.8 m/s 2 (-1G) or below and not accelerated at + 29.4 m/s 2 (+3G) or more, the estimated vehicle speed computing circuit 5 sets a lower limit deceleration G DEC and an upper limit acceleration G ACC as follows: G DEC = - 9.8 m/s 2 G ACC = + 29.4 m/s 2 When a wheel acceleration dV WM(n) /dt falls within a range of from above G DEC to below G ACC , an estimated vehicle velocity V ref(n) is determined as follows: V ref(n) = V WM(n) where (n) represents a value obtained upon execution of an nth computation. When the wheel acceleration dV WM(n) /dt is reduced at the low limit deceleration of G DEC or below, the estimated vehicle velocity V ref(n) is determined as follows: V ref(n) = V ref(n-1) - ΔG DEC where V ref(n-1) represents an estimated vehicle velocity in the previous computing cycle and ΔG DEC represents a lower limit deceleration corresponding to the given computing cycle. This equation (4) represents that the estimated vehicle velocity V ref is set to the lower limit deceleration G DEC when the wheel velocity V WM(n) is reduced at the low limit deceleration of G DEC or below. Similarly, when the wheel acceleration dV WM(n) /dt is increased at the upper limit acceleration of G ACC or above, the estimated vehicle velocity V ref(n) is determined as follows: V ref(n) = V ref(n-1) + ΔG ACC where ΔG ACC represents an upper limit acceleration corresponding to the given computing cycle. This equation (5) shows that the estimated vehicle velocity V ref is set to the upper limit acceleration G ACC when the wheel velocity V WM(n) is increased at the upper limit acceleration of G ACC or above. FIG. 2 shows the estimated vehicle velocity V ref determined based on the above equations (3), (4) and (5) when the wheel velocity V WM indicated by the dashed line is given by the wheel speed selecting circuit 4. In the present embodiment, the estimated vehicle velocity V ref determined in the above-described manner is further corrected by comparing with the follower wheel velocity V WF . This process will be described below with reference to FIG. 3. FIG. 3 shows a case in which the acceleration is made by increasing a driving force of a motorcycle's engine. The velocity V WR of the rear wheel, which serves as the drive wheel, abruptly increases with respect to the velocity V WF of the front wheel which serves as the follower wheel because the rear wheel is brought to an idle running state upon its initial acceleration. At this time, the wheel speed selecting circuit 4 selects the fastest wheel velocity from V WR , V WF and outputs the velocity V WR of the drive wheel to the estimated vehicle speed computing circuit 5 as the wheel velocity V WM . When, on the other hand, the estimated vehicle speed computing circuit 5 computes the estimated vehicle velocity V ref based on the wheel velocity V WM as it is, the estimated vehicle velocity V ref different from an actual vehicle velocity is obtained. Thus, in the present embodiment, the estimated vehicle velocity V ref(n-1) obtained by the previous computation is temporarily stored in the estimated vehicle speed storing circuit 6 as data. Then, the estimated vehicle velocity V ref(n-1) is compared with a follower wheel velocity V WF(n) for the present computation in the comparator 7 to thereby correct the estimated vehicle velocity V ref(n) . That is, the comparator 7 compares the follower wheel velocity V WF(n) and the estimated vehicle velocity V ref(n-1) . If the following condition is satisfied, then a signal for inhibiting the estimate vehicle velocity V ref from being brought up to date is outputted to the estimated vehicle speed computing circuit 5. V ref(n-1) >V WF(n) and V ref(n-1) <V WM(n) Accordingly, the estimated vehicle speed computing circuit 5 outputs an estimated vehicle velocity V ref(n) identical to the previous estimated vehicle velocity V ref(n-1) . The estimated vehicle velocity V ref thus computed is shown in FIG. 3. When the drive wheel velocity V WR is greater than the follower wheel velocity V WF , the estimated vehicle velocity V ref is changed so as to follow the follower wheel velocity V WF without following the fastest wheel velocity. This is because the follower wheel can provide less slip on a road surface, thereby making it possible to obtain the estimated vehicle velocity V ref close to the actual vehicle velocity. As a result, the estimated vehicle velocity V ref can be computed with higher accuracy. FIG. 4 is a view illustrating the relationship between the follower wheel velocity V WF , the drive wheel velocity V WR and the estimated vehicle velocity V ref computed in accordance with the present embodiment at the time that the brake control system is in operation. The brake control system determines a slip ratio from the estimated vehicle velocity V ref and the wheel velocity V WF or V WR and adjusts a braking force so as to avoid an increase in the slip ratio, thereby effecting decelerating control. Thus, each of the wheel velocities V WF , V WR is of a substantially vibration type as illustrated in FIG. 4. Further, the wheel velocity V WM , which has been selected by the wheel speed selecting circuit 4, is represented as indicated by the dashed line in FIG. 4. On the other hand, the computed estimated vehicle velocity V ref is represented as indicated by the solid line in FIG. 4 seeing it in broad perspective on the analogy of FIG. 3. Incidentally, the estimated vehicle velocity V ref is updated again upon its deceleration. It is therefore possible to obtain the estimated vehicle velocity V ref similar to that shown in FIG. 3. Thus, the estimated vehicle velocity V ref closest to the actual vehicle velocity can be obtained. It is therefore possible to stably and reliably effect the brake control, for example. The driving force can also be accurately controlled in addition to the appropriate brake control. Further, since the control referred to above can be realized with an extremely simple arrangement, the capacity of a program can be reduced and a high-speed computation can be effected. It is thus possible to execute computations at a shorter computing cycle or period and to achieve an improvement in accuracy. According to a vehicle velocity estimating method and a vehicle velocity estimating apparatus of the present invention, as has been described above, a high-accuracy estimated vehicle velocity corresponding to an actual vehicle velocity can be obtained, thereby making it possible to control brakes and driving forces, for example, with high accuracy using the estimated vehicle velocity thus obtained. Further, the control itself is easy and hence the entire structure is also simple. As a result, a high-speed computation can be effected by using a simple program. Accordingly, the number of computations can be increased, thereby making it possible to achieve a further improvement in accuracy. Having now fully described the invention, it will be apparent to those skilled in the art that many changes and modifications can be made without departing from the scope of the invention as set forth in the claims.

Claims: A method of estimating vehicle speed (V ref ), which is suitable for use in a vehicle, said method comprising: a first step of determining the speed (V WR ,V WF ) of at least one drive and one follower wheel of said vehicle; a second step of selecting the fastest one (V WM ) of the speeds (V WR ,V WF ) determined in said first step; and a third step of estimating the speed (V ref ) of the vehicle based on the fastest wheel speed (V WM ) selected in the second step; a cycle of the first through third steps being executed repeatedly at given time intervals; the method being characterised by the step of: comparing the follower wheel speed (V WF(n) ) determined in a present cycle with the vehicle speed (V ref(n-1) ) estimated in the previously executed cycle, the estimated vehicle speed (V ref(n) ) of the present cycle being set to the estimated vehicle speed (V ref(n-1) ) of the previous cycle when the estimated vehicle speed (V ref(n-1) ) of the previous cycle is greater than the follower wheel speed (V WF(n) ) of the present cycle. The method of claim 1, wherein the vehicle speed (V ref(n-1) ) estimated in the previous cycle is also compared with the fastest wheel speed (V WM(n) ) of the present cycle, and wherein the estimated vehicle speed (V ref(n) ) of the present cycle is set to the estimated vehicle speed (V ref(n-1) ) of the previous cycle when the estimated vehicle speed (V ref(n-1) ) of the previous cycle is greater than the follower wheel speed (V WF(n) ) of the present cycle and lower than the fastest wheel speed (V WM(n) ) of the present cycle. An apparatus for estimating a vehicle speed, which is suitable for use in a vehicle, said apparatus comprising: first wheel speed detecting means (3B) for detecting speeds (V WR ) of drive wheels, second wheel speed detecting means (3A) for detecting speeds (V WF ) of follower wheels; wheel speed selecting means (4) for selecting the fastest one (V WM ) of said respective wheel speeds (V WR ,V WF ) detected by said first and second wheel speed detecting means (3A, 3B); and vehicle speed estimating means (5) for estimating the speed (V ref ) of said vehicle based on said fastest wheel speed (V WM ) selected by said wheel speed selecting means (4); characterised in that said apparatus further includes: vehicle speed storing means (6) for storing therein said vehicle speed estimated by said vehicle speed estimating means (5); and comparing means (7) for comparing said vehicle speed (V ref ) stored in said vehicle speed storing means (6) with said follower wheel speeds (V WF ) detected by said second wheel speed detecting means (3A); said vehicle speed estimating means (5) being activated to supply a vehicle speed (V ref(n-1) ) which was stored in the vehicle speed storing means (6) in an estimation cycle immediately preceding a present estimation cycle as the estimated vehicle speed (V ref ) of the present estimation cycle when it is determined based on the result of comparison by said comparing means (7) that said stored vehicle speed from the previous cycle is greater than the speeds of said follower wheels detected in the present cycle. The apparatus of claim 3, including second comparing means for comparing the vehicle speed stored in the previous cycle in said vehicle speed storing means (6) with the fastest wheel speed (V WM ) of the present cycle selected by said wheel speed selection means (4), and wherein said vehicle speed estimating means (5) is activated to supply the vehicle speed stored in the vehicle speed storing means (6) from the previous cycle as the estimated vehicle speed (V ref ) of the present cycle when it is determined based on the result of comparison by said first comparing means (7) and said second comparing means that said stored vehicle speed (V ref(n-1) ) is both greater than the speeds of said follower wheels in the present cycle and lower than the fastest wheel speed (V WM ) selected in the present cycle by said wheel speed selection means (4).

Inventors: HAYASHI TATSUO, KUMAGAI CHIAKI, MATSUTO TAKUSHI, OTA ATSUO, SAKURAI TAKESHI, SUZUKI OSAMU, TANAKA KEISHIN, HAYASHI, TATSUO, KUMAGAI, CHIAKI, MATSUTO, TAKUSHI, OTA, ATSUO, SAKURAI, TAKESHI, SUZUKI, OSAMU, TANAKA, KEISHIN, Hayashi, Tatsuo, c/o Kabushiki Kaisha, Kumagai, Chiaki, c/o Kabushiki Kaisha, Matsuto, Takushi, c/o Kabushiki Kaisha, Ota, Atsuo, c/o Kabushiki Kaisha, Sakurai, Takeshi, c/o Kabushiki Kaisha, Suzuki, Osamu, c/o Kabushiki Kaisha, Tanaka, Keishin, c/o Kabushiki Kaisha
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: B60T8
IPC codes: B60T8