Antiskid control device

Abstract: An antiskid control device (10) including a vehicle speed estimating device (12) for estimating a vehicle speed from a plurality of wheel speeds of driven and undriven wheels of a motor vehicle and the vehicle speed estimating device (12) includes a first comparator (32-34) for comparing the speeds of the wheels with each other, a storage (37) for temporarily storing the estimated vehicle speed or an ultimately selected one of the speeds of the wheels, a second comparator (36) for comparing the speed stored in the storage (37) with the speeds of the driven wheels and a storage updating device (AL) for causing, at the time when antiskid control has been started, the storage (37) to store the estimated vehicle speed obtained at the time or the ultimately selected one of the speeds of the wheels obtained at the time. During nonexecution of anti­ skid control, a highest speed among the speeds of the undriven wheels is selected such that the speed of the vehicle body is calculated from the highest speed, while during execution of antiskid control, another highest speed among the speeds of the undriven wheels in addition to the speeds of the driven wheels lower than the speed stored in the storage (37) is selected such that the speed of the vehicle body is calculated from the another highest speed.

Description: The present invention generally relates to anti-skid control and more particularly, to an antiskid control device which is provided with a means for properly estimating a speed of a vehicle body of a motor vehicle. An antiskid control device is arranged to control a slip ratio of wheels to a value falling within a range enabling most efficient achievement of a frictional force exerted between a road surface and tires. It is to be noted that the slip ratio of the wheels is expressed by [(vehicle speed)-(wheel speed)]/(vehicle speed)x100 (%) . Thus, the vehicle speed is an important factor in antiskid control. However, in most antiskid control devices in practical use at present, since a means for directly measuring the vehicle speed is not provided, the vehicle speed is estimated from the wheel speed. More concretely, the wheel speed is calculated by using a higher one of wheel speeds of undriven wheels. During normal running of the motor vehicle, the higher wheel speed of the undriven wheels free from wheel spin can be regarded as the vehicle speed as it is. It is to be noted that the term "wheel spin" in this specification represents a phenomenon in which tires are rotated at an extremely high speed through their skid relative to a road surface caused at the time when a driving force transmitted from an engine to the tires has exceeded a frictional limit between the tires and the road surface. However, during braking, especially, during execution of antiskid control, since each wheel randomly either approaches towards locking or recovers from locking, it is impossible to obtain an accurate vehicle speed from the wheel speed of a single wheel even if the wheel is an undriven wheel. Thus, in such a case, it is desirable that the highest one at each time is selected from wheel speeds of as many wheels as possible and is subjected to filtering, etc. so as to obtain the vehicle speed. To this end, such a method may be adopted in which the vehicle speed is estimated from the highest one of wheel speeds of undriven wheels during nonexecution of antiskid control and from the highest one of wheel speeds of all the wheels during execution of antiskid control. However, when the motor vehicle runs on a rather bumpy road surface, such a case occurs that change of the wheel speed due to the bumps is erroneously decided as locking of the wheels. Namely, if the motor vehicle runs on the bumpy road surface in a state where wheel spin of the driven wheels may take place, antiskid control may be started. At this time, if the estimated vehicle speed is calculated on the basis of the driven wheels subjected to wheel spin, the vehicle speed becomes extraordinarily high. Hence, it is decided that each wheel has a large slip ratio, so that a pressure reducing command is issued to a brake system and thus, braking is not effected even if the driver kicks the brake pedal fully. This is a quite dangerous state for the motor vehicle. In order to obviate such an undesirable phenomenon, the following countermeasure may be taken. Namely, a detection means for detecting manipulation of the brake pedal is provided. Even during execution of antiskid control, the estimated vehicle speed is calculated from the highest one of the wheel speeds of all the wheels including the driven wheels only at the time when a brake pedal signal indicates that the brake pedal is being kicked. In this countermeasure, the estimated vehicle speed is calculated from the highest one of wheel speeds of the undriven wheels when the brake pedal signal indicates that the brake pedal is not being manipulated, namely, when an accelerator pedal may be being manipulated with consequent wheel spin of the driven wheels. However, in this countermeasure, when the brake pedal detection means malfunctions or when in the case of a front-wheel drive type motor vehicle provided, at its rear wheels, with a parking brake, the parking brake is manipulated prior to manipulation of the brake pedal, attention is paid only to the undriven wheels. Hence, such problems arise that accuracy of the estimated vehicle speed during random approach of the wheels towards locking drops and that, in an extreme case, although the vehicle body is being actually displaced, the estimated vehicle speed assumes zero and thus, antiskid control is not performed. A known device for estimating vehicle speed under varying road conditions is shown in DE-A-2 706 132. The vehicle speed is calculated from a minimum of wheel speeds during unbraked motion and a maximum of wheel speeds during antiskid control. SUMMARY OF THE INVENTION Accordingly, an essential object of the present invention is to remedy the above described disadvantages inherent in conventional antiskid control devices, to provide an antiskid control device in which a vehicle speed is not calculated to an extraordinarily large value even if wheel spin occurs and the vehicle speed is not calculated to an excessively small value even when a detection means for detecting manipulation of a brake pedal malfunctions or, in the case of a front-wheel drive type motor vehicle provided, at its rear wheels, with a parking brake, the parking brake is manipulated during running or the motor vehicle such that a highly accurate estimated vehicle speed can be obtained at all times. According to the present invention, there is provided an antiskid control device comprising: a wheel speed detecting means for detecting speeds of driven and undriven wheels of a motor vehicle; a vehicle speed estimating means for calculating a speed of a vehicle body of said motor vehicle on the basis of wheel speed signals supplied from said wheel speed detecting means; an arithmetic and locking detecting means which performs arithmetic operation on the basis of signals supplied from said wheel speed detecting means and said vehicle speed estimating means; said arithmetic and locking detecting means, when having detected that the wheels are in a state towards locking, being arranged to issue a first command of decreasing a braking pressure of the wheels and, when having detected that the wheels are in a state towards recovery from locking, issue a second command of increasing the braking pressure; and a solenoid driving means for driving a solenoid of a pressure control valve of a hydraulic circuit in response to the first and second commands from said arithmetic and locking detecting means; wherein said vehicle speed estimating means comprises a first comparator means for comparing the speeds of the wheels with each other; and means for selecting, during nonexecution of antiskid control, a highest speed among the speeds of the undriven wheels to enable the speed of the vehicle body to be calculated on the basis of said highest speed, characterized by: a storage means for temporarily storing the speed of the vehicle body calculated by said vehicle speed estimating means or one of the speeds of the wheels selected ultimately by said first comparator means; a second comparator means for comparing the speed stored in said storage means with the speeds of the driven wheels; and a storage updating means for causing, at the time when antiskid control has been started, said storage means to store the speed of the vehicle body calculated at said time by said vehicle speed estimating means or said one of the speeds of the wheels selected ultimately at said time by said first comparator means; and wherein during non execution of anti-skid control, a highest speed among the speeds of undriven wheels is selected such that the speed of the vehicle body is calculated on the basis of said highest speed, while during execution of anti-skid control, another highest speed is obtained either by selecting the highest speed of the speeds of the undriven wheels and the speeds of the driven wheels which are lower than the speed stored in the storage means or by selecting the highest speed of the speeds of the undriven wheels and the highest speed of the driven wheel speeds, whereby this highest speed of the driven wheel speeds is considered only if it is lower than the speed stored in the storage means, the speed of the vehicle body being calculated on the basis of said another highest speed. In the antiskid control device of the present invention, even in the case where antiskid control is erroneously started during running of the motor vehicle on a bumpy road, etc., the estimated vehicle speed at that time is calculated from the wheel speed of the undriven wheels free from wheel spin and is stored in the storage means. Thus, even if wheel spin occurs subsequently, the wheel speed of the driven wheels rotating at a higher speed than that stored in the storage means is not used for calculating the estimated vehicle speed, so that the estimated vehicle speed does not become extraordinarily high. Furthermore, in the antiskid control device of the present invention, even if, in the case of a front-wheel drive type motor vehicle provided, at its rear wheels, with a parking brake, the wheel speeds of the undriven wheels becomes excessively low upon manipulation of the parking brake prior to manipulation of the brake pedal, the wheel speeds of the driven wheels also can be used for calculating the estimated vehicle speed, after start of antiskid control and thus, the estimated vehicle speed does not become excessively low. BRIEF DESCRIPTION OF THE DRAWINGS This object and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which: Fig. 1 is a diagram of an antiskid control device according to the present invention; and Fig. 2 is a block diagram of a vehicle speed estimating means employed in the antiskid control device of Fig. 1. DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, there is shown in Fig. 1, an antiskid control device according to the present invention, which includes an electronic control device 10. Upon reception of signals from wheel speed sensors S1, S2, S3 and S4, the electronic control device 10 performs various calculations and decisions so as to output a control signal of a hydraulic circuit. Hereinbelow, reference is given to only the wheel speed sensor S1 for the sake of brevity. The electronic control signal 10 includes a wheel speed detecting means 11, a vehicle speed estimating means 12, an arithmetic and locking detecting means 13, a solenoid driving circuit 14 and a motor driving circuit 15. An AC voltage signal from the wheel speed sensor S1 is converted into pulses and is supplied, as a wheel speed signal, to the vehicle speed estimating means 12 by the wheel speed detecting means 11 for counting and calculating the pulses. In the vehicle speed estimating means 12, a vehicle speed is estimated. When either a deceleration calculated by the arithmetic and locking detecting means 13 drops below a predetermined reference or a slip speed, i.e. a difference between the estimated vehicle speed and the estimated wheel speed exceeds a predetermined reference, the arithmetic and locking detecting means 13 detects creation of a locking trend of the wheels and issues a pressure reducing command to the solenoid driving circuit 14. Then, the solenoid driving circuit 14 energizes solenoids SOL1 and SOL2. As a result, a pressure control valve 21 is displaced in the leftward direction in Fig. 1 so as to cut off a hydraulic circuit from a master cylinder 23 to a wheel cylinder 24, while a pressure control valve 22 is displaced in the upward direction in Fig. 1 so as to communicate a circuit between the wheel cylinder 24 and a reservoir 25. A motor M is started by the motor driving circuit 15, so that brake fluid carried from the reservoir 25 by a pump P is returned to an accumulator 26 and the master cylinder 23 and thus, a hydraulic braking pressure drops. Subsequently, when the deceleration or the slip speed exceeds the corresponding reference value upon recovery of the wheels from locking, the arithmetic and locking detecting means 13 decides that the wheels have recovered from locking and outputs a pressure increasing command to the solenoid driving circuit 14. Thus, the solenoid driving circuit 14 de-energizes the solenoids SOL1 and SOL2 so as to reinstate the pressure control valves 21 and 22 to the states of Fig. 1. Therefore, the hydraulic circuit between the hydraulic pressure generation source and the wheel cylinder 24 is communicated, so that the hydraulic braking pressure is increased. Meanwhile, if, in the course of issuance of the pressure reducing command or the pressure increasing command, a pressure holding command is issued by interrupting issuance of the pressure reducing command or the pressure increasing command, it can be so arranged that the solenoid SOL1 is energized and the solenoid SOL2 is de-energized. As a result, the pressure control valve 21 is displaced in the leftward direction in Fig. 1 so as to cut off the hydraulic circuit from the master cylinder 23 to the wheel cylinder 24, while the pressure control valve 22 remains at the position of Fig. 1 and thus, the hydraulic braking pressure is maintained at a constant value since hydraulic pressure is contained in the wheel cylinder 24. In Fig. 1, reference numeral 27 denotes a by-pass valve. Furthermore, conditions and timing for issuing the pressure holding command in the course of issuance of the pressure reducing command can be selected variously as follows. For example, in one method, the pressure holding command is issued upon lapse of a predetermined time period from start of issuance of the pressure reducing command. In another method, the pressure holding command is issued when the wheel deceleration has exceeded a predetermined threshold value. Similarly, conditions and timing for issuing the pressure increasing command and the pressure holding command alternately can also be selected variously. Generally, the pressure holding command is issued at a fixed time interval by, for example, a pulse generator. Meanwhile, in order to decide that a locking trend of the wheels has been created or the wheels have recovered from locking, other factors can also be added to the above described deceleration and the slip speed. Hereinbelow, the vehicle speed estimating means 12 is described with reference to Fig. 2. As shown in Fig. 2, signals from the wheel speed sensors S1 and S2 of the driven wheels and signals from the speed sensors S3 and S4 of the undriven wheels are inputted to an interface circuit 30 so as to be converted into pulses. Then, the pulses are counted and calculated in a wheel speed calculating means 31 so as to be supplied, as binary wheel speed signals Vw, not only to the arithmetic and locking detecting means 13 but to the vehicle speed estimating means 12. Namely, the interface circuit 30 and the wheel speed calculating means 31 correspond to the wheel speed detecting means 11. The wheel speed signals Vw thus obtained are compared with each other by comparators 32 and 33, respectively. Namely, the wheel speeds of the driven wheels are compared with each other by the comparator 32 and a larger one of the wheel speeds of the driven wheels is selected. On the other hand, the wheels speed of the undriven wheels are compared with each other by the comparator 33 and a larger one of the wheel speeds of the undriven wheels is selected. The larger one of the wheel speeds of the undriven wheels is further applied to a comparator 34. On the other hand, the larger one of the wheel speeds of the driven wheels, which has been selected by the comparator 32, is applied to the comparator 34 through a switch 35. This switch 35 is opened and closed by a comparison and drive circuit 36. The comparison and drive circuit 36 compares a speed stored in a storage circuit 37 with the wheel speed selected by the comparator 32 and closes the switch 35 only when the wheel speed selected by the comparator 32 is smaller than the speed stored in the storage circuit 37. It should be noted that the storage circuit 37 is started for its actuation by a signal AL indicating that antiskid control is being performed so as to store the estimated vehicle speed Vv obtained at that time. Therefore, the speed stored in the storage circuit 37 is updated to a new estimated vehicle speed Vv during execution of antiskid control. Meanwhile, alternatively, as shown by the one-dot chain lines in Fig. 2, the speed stored in the storage circuit 37 may be updated to the wheel speed selected ultimately by the comparator 34. Meanwhile, the comparison and drive circuit 36 is likewise started for its actuation by the signal AL. During nonexecution of antiskid control, the signal AL is not produced, so that the circuits 36 and 37 are not actuated and the switch 35 is open. Hence, the larger one of the wheels speeds of the undriven wheels is applied from the comparator 33 to the comparator 34 and no signal is applied form the comparator 32 to the comparator 34. Therefore, the output of the comparator 33, namely, the larger one of the wheel speeds of the undriven wheels is selected and is applied to a calculation circuit 38 for calculating the estimated vehicle speed Vw. When antiskid control has been started, the signal AL is produced, so that the circuits 36 and 37 are actuated such that the estimated vehicle speed at that time is stored in the storage circuit 37. This speed stored in the storage circuit 37 and the wheel speed of the driven wheels selected by the comparator 32 are compared with each other by the circuit 36. If the latter is smaller than the former, the switch 35 is closed, so that the wheel speed of the driven wheels selected by the comparator 32 is inputted to the comparator 34 so as to be compared with the wheel speed of the undriven wheels selected by the comparator 33. Therefore, a maximum among the wheel speeds of the undriven wheels in addition to the wheel speeds of the driven wheels smaller than the speed stored in the storage circuit 37 is selected. Meanwhile, the circuits referred to above can be incorporated, as a program, into a microcomputer. As is clear from the foregoing description, in accordance with the present invention, the estimated vehicle speed is calculated without receiving the brake pedal manipulation signal. Thus, even if the detection means for detecting manipulation of the brake pedal malfunctions, accuracy of the estimated vehicle speed does not drop. Furthermore, in accordance with the present invention, even if wheel spin occurs when antiskid control has been erroneously started during running of the motor vehicle on a bumpy road, the wheel speeds of the driven wheels higher than the estimated vehicle speed are not used for calculating the estimated vehicle speed, so that the estimated vehicle speed does not become extraordinarily high. Moreover, in accordance with the present invention, even if the wheel speeds of the undriven wheels becomes excessively low by manipulating the parking brake prior to manipulation of the brake pedal, the wheel speeds of the driven wheels can be used for calculating the estimated vehicle speed, after start of antiskid control, so that the estimated vehicle speed does not become excessively low and thus, a highly accurate estimated vehicle speed can be obtained at all times.

Claims: An antiskid control device (10) comprising: a wheel speed detecting means (11) for detecting speeds of driven and undriven wheels of a motor vehicle; a vehicle speed estimating means (12) for calculating a speed of a vehicle body of said motor vehicle on the basis of wheel speed signals supplied from said wheel speed detecting means (11); an arithmetic and locking detecting means (13) which performs arithmetic operation on the basis of signals supplied from said wheel speed detecting means (11) and said vehicle speed estimating means (12); said arithmetic and locking detecting means (13), when having detected that the wheels are in a state towards locking, being arranged to issue a first command of decreasing a braking pressure of the wheels and, when having detected that the wheels are in a state towards recovery from locking, issue a second command of increasing the braking pressure; and a solenoid driving means (14) for driving a solenoid (SOL1,SOL2) of a pressure control valve (21,22) of a hydraulic circuit in response to the first and second commands from said arithmetic and locking detecting means (13); wherein said vehicle speed estimating means (12) comprises a first comparator means (32-34) for comparing the speeds of the wheels with each other; and means for selecting (32-35), during nonexecution of antiskid control, a highest speed among the speeds of the undriven wheels to enable the speed of the vehicle body to be calculated on the basis of said highest speed, characterized by: a storage means (37) for temporarily storing the speed of the vehicle body calculated by said vehicle speed estimating means (12) or one of the speeds of the wheels selected ultimately by said first comparator means (32-34); a second comparator means (32,36) for comparing the speed stored in said storage means (37) with the speeds of the driven wheels; and a storage updating means (AL) for causing, at the time when antiskid control has been started, said storage means (37) to store the speed of the vehicle body calculated at said time by said vehicle speed estimating means (12) or said one of the speeds of the wheels selected ultimately at said time by said first comparator means (32-34); and wherein during non execution of anti-skid control, a highest speed among the speeds of undriven wheels is selected such that the speed of the vehicle body is calculated on the basis of said highest speed, while during execution of anti-skid control, another highest speed is obtained either by selecting the highest speed of the speeds of the undriven wheels and the speeds of the driven wheels which are lower than the speed stored in the storage means (37) or by selecting the highest speed of the speeds of the undriven wheels and the highest speed of the driven wheel speeds, whereby this highest speed of the driven wheel speeds is considered only if it is lower than the speed stored in the storage means (37), the speed of the vehicle body being calculated on the basis of said another highest speed. An antiskid control device (10) as claimed in Claim 1, further comprising: a motor driving circuit (15) for driving a motor (M) for actuating a pump (P) for a brake of said motor vehicle. An antiskid control device (10) as claimed in Claim 1 or Claim 2, wherein said wheel speed detecting means (11) includes an interface circuit (30) and a vehicle speed calculating circuit (31) for calculating the speeds of the wheels.

Inventors: YOSHINO MASATO ITAMI WORKS OF, YOSHINO, MASATO ITAMI WORKS OF
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES LIMITED
Application year: 1988
Main classification: B60T8
IPC codes: B60T8, B60L7