Abstract: An anti-skid brake control system is provided with two wheel acceleration deriving circuits. A first wheel acceleration deriving circuit provides a timing for deriving wheel acceleration data with a relatively longer interval, which longer interval is long enough to obtain a good number of wheel speed data for deriving first wheel acceleration with satisfactorily high precision level. On the other hand, a second wheel acceleration deriving circuit provides a timing for deriving wheel acceleration data with a relatively shorter interval, which shorter interval is short enough for deriving wheel acceleration data with satisfactorily high response characteristics. The wheel acceleration data derived by the first wheel acceleration data is utilized in deteceting timing for switching operational mode of the anti-skid brake control system from an APPLICATION mode or RELEASE mode in which braking pressure is decreased to a HOLD mode in which braking pressure is maintained at constant value.

Abstract: A fail-safe control system includes one or more circuits for detecting failures in sensors and an actuator of a driving force distribution control system of a 4WD vehicle, and a fail-safe means which, if a failure is detected, gradually disengage a transfer clutch until the 2WD state is reached, in such a gradual manner as to prevent spin or drift-out of the vehicle. The fail-safe means may decrease the magnitude of an electric control signal gradually, or may employ a fail-safe valve for gradually decreasing a fluid pressure supplied to the transfer clutch.

Abstract: A control system for a 4WD vehicle includes a transfer clutch capable of continuously varying a driving torque distribution ratio between front and rear axles, and a controller for producing a control signal to control the distribution ratio. In order to improve the stability of the vehicle during deceleration, the control system is provided with a sensor for sensing one or more of an engine speed, a throttle opening, a transmission gear ratio, a vehicle speed and other vehicle operating parameters affecting engine braking, and a controller section for controlling the distribution ratio in accordance with the amount of engine braking at a level which is higher enough than the level of 2WD to adequately distribute the engine braking force between the front and rear axles and which is lower enough than the 4WD level to allow the front and rear axles to rotate at different speeds.

Abstract: A control system for a 4WD vehicle includes a drive system for directly transmitting a torque to primary drive wheels such as rear wheels, and transmitting a torque to secondary drive wheels such as front wheels through a torque distributing transfer clutch, a group of sensors for determining a front and rear wheel speed difference, an engine condition such as a throttle opening, and a vehicle speed, and a control unit for controlling the engagement force of the transfer clutch. Normally, the control unit employs a first control mode based on the front and rear wheel speed difference. In rapid acceleration to start the vehicle, the control unit replaces the first mode by a second mode in which the clutch engagement force is increased in accordance with the engine condition such as the throttle opening independent of the wheel speed difference, and thereby prevents undesired spin of the primary drive wheels without delay.

Abstract: A method and a system derive a value representative of an actual vehicle speed in strict correspondence to actual vehicle speed. The value can be utilized to detect wheel slippage and allows precise traction control, anti-skid brake control and so forth. The method for deriving wheel slippage, according to the present invention, includes a step of deriving a projected vehicle speed, the rate of change of which varies with road surface friction. Wheel slippage is derived from on the projected vehicle speed and instantaneous wheel speed. In practice, the method includes a step for detecting the force exerted on a vehicular wheel, which force includes a resistance variable depending upon the road surface friction .mu.. Based on the detected force, the projected vehicle speed variation pattern is derived so as to derive an instantaneous projected vehicle speed.

Abstract: An anti-skid brake control system derives a projected vehicular speed representative data by summing a time dependent acceleration and deceleration value and a latched wheel speed data which is periodically updated. The time dependent acceleration and deceleration value is derived by integrating a vehicular acceleration/deceleration gradient indicative data. According to one particular feature of the invention, the integrated value is reset for minimizing error to be accumulated at a given timing. For detecting reset timing of the integrated value, the instantaneous wheel speed data is continuously compared with a predetermined zone which is set about the projected vehicular speed representative data. Namely, resetting of the integrated value is performed by detecting entry of the wheel speed data into the predetermined zone.

Abstract: A traction control system has a plurality of wheel speed sensor means for producing wheel speed indicative signals respectively representative of wheel speeds of associated vehicular wheels. Wheel slippage is detected by comparing wheel speed measured by the wheel speed sensor means and an approximated vehicle speed indicative value. The approximated vehicle speed indicative value is derived based on one of wheel speed selected depending upon a vehicle speed.

Abstract: A control system for a 4WD vehicle includes a drive system for directly transmitting a torque to primary drive wheels, and transmitting a torque to secondary drive wheels through a torque distributing clutch, at least one sensor for determining a front and rear wheel speed difference, at least one sensor for determining a lateral acceleration, and a control unit for controlling the engagement force of the clutch. When the primary wheel speed is lower than the secondary wheel speed, the control unit holds the clutch engagement force equal to zero to improve the steering response until the absolute value of the wheel speed difference reaches a predetermined level, and increase the clutch engagement force in accordance with the absolute value of the wheel speed difference to improve the vehicle stability after the absolute value of the wheel speed difference exceeds the predetermined level.

Abstract: An anti-skid brake control system is designed to periodically generate short commands ordering an APPLICATION mode operation to increase braking pressure while the system operates in a RELEASE mode. An anti-skid control signal is then monitored to make a judgement that failure occurs in the anti-skid brake control system when the control signal is not periodically switched from RELEASE mode to APPLICATION mode.

Abstract: An anti-skid brake control system for an automotive brake system performs anti-skid brake control for maintaining a rotation speed of a vehicular wheel in a optimal relationship with a projected vehicular speed. The projected vehicular speed is derived on the basis of the wheel rotation speed latched at predetermined timing in each skid cycle. Based on the latched wheel rotation speed, gradient value which represents variation rate of the projected vehicular speed, is derived. The gradient value is varied with a correction which is derived on the basis of a preselected correction factor, such as magnitude of braking force exerted on the vehicular wheel.

Abstract: A derivation of a vehicle speed representing value includes detection of wheel slip caused at least one of vehicular wheels. The process further includes a step for deriving vehicle speed representing value with respect to each vehicular wheel and a step for selecting one of the vehicle speed representing values derived with respect to each vehicular wheel when wheel slip at least one of the wheels is detected. Selection of one of the vehicle speed representing values is performed by omitting the vehicle speed representing value derived with respect to one of the wheels on which wheel slip is caused. The selected one of the vehicle speed representing value is used as a common vehicle speed indicative parameter for performing wheel slip control, such as anti-skid brake control, traction control and so forth.

Abstract: An anti-skid brake control system employs a technique for correcting a longitudinally based vehicular speed variation gradient by a road slop dependent correction value. The road slop dependent correction value is derived on the basis of an assumed road slop condition which is assumed on the basis of magnitude of increase of the braking pressure.

Abstract: An anti-skid brake control system detects wheel acceleration greater than a predetermined value. The predetermined value is set greater than an acceleration threshold which is used for switching operational mode from braking pressure decreasing mode (RELEASE mode) to decreased pressure hold mode (HOLD mode). When the wheel acceleration greater than the predetermined value is detected, the control system provide a delay time for projecting an estimated vehicle speed which is derived on the basis of wheel speed at which a predetermined wheel deceleration is obtained, which estimated vehicle speed is used for deriving a target wheel speed and defines a switching criteria for switching operational mode from braking pressure holding mode for holding brake pressure at decreased level to braking pressure application mode (APPLICATION mode) to increase the braking pressure.

Abstract: An anti-skid brake control system monitors wheel deceleration during a period from a timing at which vehicular braking operation is initiated to a timing at which anti-skid brake control becomes active. Because the magnitude of wheel deceleration during the period set forth above is approximately inversely proportional to a road friction, the difference of deceleration can be a road friction indicative data. A vehicle body deceleration gradient data for the first skid control cycle is approximated or projected on the basis of the road friction indicative data so as to derive a projected vehicle body speed indicative data and a target wheel speed indicative data for the first skid control cycle.

Abstract: An anti-skid brake control system detects wheel acceleration and deceleration. The operational mode, i.e. whether to increase or decrease fluid pressure in a wheel cylinder or to hold the fluid pressure in the wheel cylinder constant, is selected on the basis of brake control parameters including the wheel acceleration and deceleration. In an initial stage of each cycle of anti-skid control, the fluid pressure is held at a level at which wheel deceleration exceeds a predetermined deceleration threshold. The predetermined deceleration threshold is reduced to a predetermined modified value after wheel deceleration has dropped below the predetermined deceleration of the wheel and anti-skid brake control is thus started.

Abstract: A self-monitor system has a delay circuit active in response to the end of engine cranking to enforce a predetermined time delay which is long enough for battery voltage to recover to normal levels. The delay circuit outputs a command for execution of self-monitoring operations by the digital control system after the predetermined time delay. The self-monitor system in the digital control system is responsive to the command from the delay circuit to check the battery voltage and to apply dummy loads to system elements at levels sufficient to simulate actuation of the elements to be checked, such as sensors, actuators and/or indicators. By enforcing the time delay time, the influence of temporary drops in battery voltage due to overloading during engine cranking can be fully avoided.

Abstract: An anti-skid brake control system detects braking condition on at least two wheels for detecting synchronous braking condition in the wheels. Increasing of braking fluid pressure in one wheel cylinder associated with one of the wheels is delayed with respect to the brake fluid pressure increasing timing of the other wheel cylinder associated with the other wheel. By delaying increasing of the braking pressure, the braking fluid pressure in one of the wheel cylinder is maintained lower than that in the other. Therefore, when one of the wheel, for which higher braking pressure is applied through the associated wheel cylinder, the other wheel is maintained at non-locking state. Therefore, the wheel speed closely reflects the actual vehicle speed. This assures acurate brake control in the anti-skid brake control for the automotive vehicle utilizing the vehicle speed representing value derived based on the rotation speed of non-locking wheel.

Abstract: An anti-skid brake control system, detects braking condition on at least two wheels for detecting synchronous braking condition in the wheels. Increasing of braking fluid pressure in one wheel cylinder associated with one of the wheels is disabled with respect to the brake fluid pressure increasing timing of the other wheel cylinder associated with the other wheel until the wheel associated with the other wheel cylinder is placed at non-locking stage. By delaying increasing of the braking pressure, the braking fluid pressure in one of the wheel cylinder is maintained lower than that in the other. Therefore, when one of the wheel, for which higher braking pressure is applied through the associated wheel cylinder, the other wheel is maintained at non-locking state. Therefore, the wheel speed closely reflects the actual vehicle speed.

Abstract: A method for controlling an automotive anti-skid brake system allows control for braking pressure at each wheel independently of other wheels. The anti-skid brake control is initiated in response to a drop of wheel acceleration across a predetermined wheel deceleration threshold. In the anti-skid brake control operation, braking pressure for at least two wheels are released in synchronism with each other. On the other hand, increasing rate of the braking pressure at the synchroneously released wheels are varied to each other so that when one of the wheels causes wheel-locking, the other wheel is held in a non-locking condition, This assures that the derivation of the vehicle speed representing value will be based on the wheel speed of the other wheel which is not locking and to assure prevention of locking at any wheels.

Abstract: A traction control system includes means for detecting a vehicle driving condition and disabling traction control for reducing driving torque distributed to vehicular driven wheels for avoiding wheel slippage when a predetermined vehicle driving condition is detected. In the practical control, a vehicle speed is taken as a traction control enabling/disabling criterion for disabling control while the vehicle speed is lower than a given criterion.