Vehicular velocity controlling apparatus and method to follow up a preceding vehicle running ahead of vehicle

[0002] a) Field of the Invention

[0003] The present invention relates to vehicular velocity controlling apparatus and method to follow up a preceding vehicle which is running ahead of the vehicle with an appropriate inter-vehicle distance maintained.

[0004] b) Description of the Related Art

[0005] A Japanese patent Application First Publication No. Heisei 10-272963 published on Oct. 13, 1998 exemplifies a previously proposed vehicular velocity controlling apparatus to follow up the preceding vehicle at a target inter-vehicle distance. This Japanese Patent Application First Publication corresponds to a U.S. Pat. No. 5,959,572 issued on Sep. 28, 1999.

[0006] A target relative velocity ΔV* is calculated on the basis of an inter-vehicle distance L and a relative velocity ΔV. The target relative velocity ΔV* is subtracted from the vehicular velocity Vt of the preceding vehicle to derive a target vehicular velocity V*. Atarget driving force is calculated on the basis of the target vehicular velocity V* to control the vehicular velocity by means of a vehicular velocity controlling section. It is noted that the target driving force includes a target braking force since a negative value of the target driving force means the target braking force.

[0007] In the previously proposed vehicular velocity controlling apparatus, a use of a simple control system can cause the inter-vehicle distance to be converged into a target value thereof. The previously proposed vehicular velocity controlling apparatus has adopted an architecture of a control system of placing a most importance on such a convergence response characteristic on the inter-vehicle distance at a vehicular braking is effected with a large braking pressure set for a vehicular brake system when the inter-vehicle distance to the preceding vehicle becomes so short as to converge the inter-vehicle distance quickly into the target inter-vehicle distance in order to cope with an abrupt interruption of another preceding vehicle from another traffic lane to a front preceding vehicle trap area of the vehicle at the same traffic lane.

[0008] Hence, a magnitude of a braking force developed at the vehicular brake system is set in accordance with the inter-vehicle distance to the preceding vehicle. Consequently, a relatively large braking force is acted upon the vehicle at an initial stage of the braking so that a mismatch to a vehicular driver's sense of vehicular driving would occur.

[0009] It is, therefore, an object of the present invention to provide vehicular velocity controlling apparatus and method which place a limitation on the braking force developed in the vehicular brake system when the shortened inter-vehicle distance is to be widened to match with the vehicular driver's sense of vehicular driving.

[0010] According to one aspect of the present invention, there is provided a vehicular velocity controlling apparatus for an automotive vehicle, comprising: an inter-vehicle distancedetector to detect an inter-vehicle distance from the vehicle the a preceding vehicle which is running ahead of the vehicle; an inter-vehicle distance calculating section that calculates a target vehicular velocity to make a detected value of the inter-vehicle distance substantially, equal to a target inter-vehicle distance; a vehicular velocity detector to detect a vehicular velocity of the vehicle; and avehicular velocity controlling section that adjustably controls the vehicular velocity of the vehicle to make a detected value of the vehicular velocity substantially equal to the target vehicular velocity, the vehicular velocity controlling section including a target braking pressure calculating section that calculates a target braking pressure for a vehicular brake system in accordance with a target deceleration variable calculated on the basis of the target vehicular velocity and the detected value of the vehicular velocity; and a target braking pressure limiter to place a limitation on a rate of increase in the target braking pressure when the target braking pressure is in excess of a predetermined braking pressure threshold value.

[0011] According to another aspect of the present invention, there is provided a vehicular velocity controlling method for an automotive vehicle, comprising: detecting an inter-vehicle distance from the vehicle to a preceding vehicle which is running ahead of the vehicle; calculating a target vehicular velocity to make a detected value of the inter-vehicle distance substantially equal to a target inter-vehicle distance; detecting a vehicular velocity of the vehicle; adjustably controlling the vehicular velocity of the vehicle to make a detected value of the vehicular velocity substantially equal to the target vehicular velocity; calculating a target braking pressure for a vehicular brake system in accordance with a target deceleration variable calculated on the basis of the target vehicular velocity and the detected value of the vehicular velocity; and placing a limitation on a rate of increase in the target braking pressure when the target braking pressure is in excess of a predetermined braking pressure threshold value.

[0012] This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.

[0013] FIG. 1A is a schematic circuit block diagram of a first preferred embodiment of a vehicular velocity controlling apparatus applicable to a rear road wheel drive vehicle.

[0014] FIG. 1B is a schematic internal circuit block diagram of a follow-up run controller shown in FIG. 1A.

[0015] FIG. 2 is a functional circuit block diagram of a specific example of a vehicular velocity controlling section shown in FIG. 1B.

[0016] FIG. 3 is a functional circuit block diagram of a specific example of a vehicular velocity controlling section.

[0017] FIG. 4 is an operational flowchart representing an example of a vehicular velocity control procedure executed in the case of the first preferred embodiment.

[0018] FIG. 5 is an explanatory view of a target braking pressure P_B* with respect to a target braking force F_OR.

[0019] FIGS. 6A, 6B, and 6C are integrally a timing chart for explaining an operation of the vehicular velocity controlling apparatus in the first embodiment on a vehicular velocity, a target braking pressure, and an actual braking pressure.

[0020] FIG. 7 is an operational flowchart for explaining another example of the vehicular velocity control procedure in a vehicular velocity controlling section of a second preferred embodiment of the vehicular velocity controlling apparatus.

[0021] FIG. 8 is a timing chart for explaining a variation in a braking pressure command value during an abrupt braking in the second embodiment.

[0022] FIG. 9 is an operational flowchart representing a still another example of the vehicular velocity control procedure in a third preferred embodiment of the vehicular velocity controlling apparatus according to the present invention.

[0023] Reference will hereinafter be made to the drawings in order to facilitate a better understanding of the present invention.

[0024] (First Embodiment)

[0025] FIG. 1A shows a schematic circuit block diagram of a vehicular velocity controlling apparatus in a first preferred embodiment according to the present invention.

[0026] In FIG. 1A, 1FL and 1FR denote front left and right road wheels as steered vehicles (or non-driven wheels) and 1RL and 1RR denote rear left and right road wheels as driven road wheels.

[0027] The rear left and right road wheels 1RL and 1RR are rotationally driven with the driving force of an engine (rotary driving source) 2 transmitted via a vehicular transmission 3, a propeller shaft 4, a final speed reduction gear unit 5, and a wheel axle 6.

[0028] A disc brake 7 is disposed around each of the front left and right road wheels 1FL and 1FR and the rear left and right road wheels 1RL and 1RR to develop a braking force to its corresponding road wheels. A brake controller 8 serves to control a braking liquid pressure developed for each of the disc brakes 7 (that is to say, the brake controller 8 actuates a braking actuator to make the actual braking liquid pressure substantially equal to a target braking liquid pressure) in accordance with a magnitude of a braking pressure command value PBD supplied from the follow-up run controller 20 in addition to the braking liquid pressure developed in accordance with a depression depth of a brake pedal (not shown).

[0029] The engine 2 is provided with an engine output controller 9 to control an output variable of the engine 2.

[0030] A method of controlling an engine output variable may include a method of adjusting an opening angle of an engine throttle valve 2 or a method of adjusting an opening angle of an idle control valve to control an idling revolution speed. However, in the first embodiment, the method of adjusting the opening angle of the throttle valve is adopted.

[0031] Furthermore, foran automatic transmission 3, an A/T (transmission) controller 10 is provided to control a gear position of the automatic transmission 3. When the A/T controller 10 receives an OD (an Over Drive) inhibit control signal TS representing a logical value of “1” from the follow-up run controller 20 to be described later, the A/T controller 10 inhibits a gear shift at a fourth-speed (OD) gear position of the automatic transmission 3 to make a down shift therefrom to a third-speed gear position (third gear). With the down shift from the fourth-speed gear position to the third-speed gear position, the OD inhibit signal TS is returned to a logical value of “0” so that an up shift operation occurs to make the up shift from the third-speed gear position to the fourth-speed (OD) gear position.

[0032] On the other hand, an inter-vehicle distance sensor 12 (constituted by a radar unit) is disposed on a front lower end portion of a vehicular body of the vehicle as an inter-vehicle distance detector which detects an inter-vehicle distance L to the preceding vehicle which is present at the same traffic lane and is trapped thereby. As the inter-vehicle distance sensor 12, a range measurement instrument to measure an inter-vehicle distance L can be applied utilizing a laser radar to measure the inter-vehicle distance L which sweeps, e.g., a laser beam in a front width-wise direction and receives a reflected laser beam from any object, e.g. , the preceding vehicle which is running ahead of the vehicle.

[0033] In addition, a vehicular velocity sensor 13 is disposed on an output axle of the automatic transmission 3 to detect a vehicular velocity V from a revolution speed of the output axle of the automatic transmission 3.

[0034] Each output signal of the inter-vehicle distance sensor 12 and the vehicular velocity sensor 13 is inputted to the follow-up run controller 20. The follow-up run controller 20 controls each required function to the brake controller 8, the engine output controller 9, and the A/T controller 10 on the basis of the actual inter-vehicle distance L detected by the inter-vehicle distance sensor 12 and the vehicular velocity V detected by the vehicular velocity sensor 13.

[0035] The follow-up run controller 20 includes, in terms of its hardware, a microcomputer having a CPU (Central Processing Unit) 20a,a ROM (Read Only Memory) 20b,a RAM (Random Access Memory) 20c,an Input Port 20d,an Output Port 20c,and a common bus, as shown in FIG. 1B.

[0036] FIG. 2 shows a functional block diagram of the vehicular velocity controlling apparatus in the first embodiment.

[0037] The follow-up run controller 20 functionally includes: a distance measuring signal processing section 21 to measure a time duration from a time point at which the inter-vehicle distance sensor 12 is operated to sweep the laser beam in the front width-wise direction to a time point at which the reflected laser beam from the preceding vehicle is received to calculate the inter-vehicle distance L of the vehicle to the preceding vehicle from the measured time duration; a vehicular velocity signal processing section 30 that measures a period of a pulse train signal outputted from a vehicular velocity sensor 13 to calculate the vehicular velocity Vs; an inter-vehicle distance controlling section 40 that calculates a target vehicular velocity V* to maintain the inter-vehicle distance L at a target inter-vehicle distance L* on the basis of the vehicular velocity Vs by the vehicular velocity signal processing section 30 and the inter-vehicle distance L from the distance measuring signal processing section 30; and a vehicular velocity controlling section 50 that controls functions of the brake controller 8, the engine output controller 9, and the transmission (A/T) controller 10 on the basis of the target vehicular velocity V* and the relative velocity ΔV, both of which being calculated by the inter-vehicle distance controlling section 40, to make the vehicular velocity Vs substantially equal to the target vehicular velocity V*.

[0038] The inter-vehicle distance controlling section 40 includes: a relative velocity calculating section 41 that calculates the relative velocity ΔV of the vehicle to the preceding vehicle on the basis of the inter-vehicle distance L inputted from the distance measuring signal processing section 21; a target inter-vehicle distance setting section 42 that calculates a target inter-vehicle distance L* between the preceding vehicle and the vehicle on the basis of the vehicular velocity Vs inputted from the vehicular velocity signal processing section 30; and an inter-vehicle distance command value calculating section 43 that calculates the target vehicular velocity V* to make the inter-vehicle distance L substantially equal to the target inter-vehicle distance L* on the basis of the relative velocity ΔV calculated by the relative velocity calculating section 41 and the target inter-vehicle distance L* calculated by the target inter-vehicle distance setting section 42.

[0039] The relative velocity calculating section 41 is constituted by a band pass filter (BPF) which processes the inputted inter-vehicle distance L in a, e.g., a band pass filter.

[0040] The band pass filter has its transfer function that can be expressed in the following equation (1).

[0041] Since a differential term of a Laplace transform operator s is included in a numerator of the equation (1), the relative velocity ΔV is substantially approximated from the differentiation of the inter-vehicle distance L.

[0042] F(s)=ω²s/(s²+2ζcωcs+ωc²)  (1).

[0043] In the above equation (1), ωc=2πfc and ζc denotes a damping factor.

[0044] As described above, since the band pass filter having the transfer function as given by the equation (1) is used as the relative velocity calculating section 41, the calculation of the relative velocity ΔV described above can avoid such an inconvenience case that is weak in a noise interference and that gives an ill influence on a vehicular dynamic (vehicular behavior) such as fluctuations occur in a vehicular body during the follow-up run control in a case where a simplified differential calculation is carried out from a variation rate of the inter-vehicle distance L so as to calculate the relative velocity ΔV. It is noted that a cut-off frequency fc in the equation (1) is determined according to a magnitude of a noise component included in the inter-vehicle distance L and an allowance value of an acceleration variation in a longitudinal direction of the vehicular body in a short period of time.

[0045] In addition, the calculation of the relative velocity ΔV may alternatively be carried out by a differential processing using a high pass filter to the inter-vehicle distance L in place of the band pass filter described above.

[0046] In addition, the target inter-vehicle distance setting section 42 calculates the target inter-vehicle distance L* in accordance with the following equation (2) from a vehicular velocity V* of the preceding vehicle (Vt=Vs+ΔV) calculated by an addition of the vehicular velocity Vs to the relative velocity ΔV and a time duration To (so-called, inter-vehicle time duration) during which the vehicle has reached to a position Lo (meters) behind the present position of the preceding vehicle.

[0047] That is to say, L*=Vt×To+Ls  (2).

[0048] Since a concept of the inter-vehicle time duration is introduced into the calculation of the target inter-vehicle distance L*, the target inter-vehicle distance L* is set in such a manner that as the vehicular velocity becomes faster, the inter-vehicle distance becomes large.

[0049] In the equation (2), Ls denotes an initial inter-vehicle distance when the vehicle stops.

[0050] Furthermore, the inter-vehicle distance calculating section 43 calculates the command value L_Tof the inter-vehicle distance on the basis of the actual inter-vehicle distance L, the target inter-vehicle distance L*, and the relative velocity ΔV to follow up the preceding vehicle maintaining the inter-vehicle distance L at its target value L*. Specifically, the target vehicular velocity V* is calculated in accordance with the following equation (3). More specifically, a filter processing for the inputted target inter-vehicle distance L* in a second order lag form is carried out in accordance with a reference model G_T(s) expressed in the equation of (3) using the damping factor ζ and the specific angular frequency ωn determined for the response characteristic in the inter-vehicle distance system to be the target vehicular velocity so that the inter-vehicle distance command value L_Tis calculated.

[0051] G_T(s)=ωn²/(s²+2ζωns+ωn)  (3)

[0052] Furthermore, the target vehicular velocity calculating section 44 calculates the target vehicular velocity V* using a feedback compensator on the basis of the inputted inter-vehicle distance command value L_T.

[0053] That is to say, the target relative velocity ΔV* is first calculated, as expressed in the equation (4), by subtracting a liner connection between a value of a multiplication of a distance control gain fd and a deviation (L*−L) between the target inter-vehicle distance L* and the actual inter-vehicle distance L and a value of the multiplication of a velocity control gain fv with the relative velocity ΔV from a vehicular velocity Vt of the preceding vehicle.

[0054] Namely, ΔV*=Vt−{fd(L*−L)+fvΔV}  (4).

[0055] The vehicular velocity controlling section 50 controls the opening angle θ of the throttle valve of the engine through the engine output controller 9, the gear position of the of the transmission 3 through the A/T controller 10, and outputs the command value P_BDto the brake controller 8 so that the vehicular velocity Vs is made substantially equal to the target vehicular velocity V*.

[0056] The vehicular velocity controlling section 50 includes: a vehicular velocity servo controlling section 51 which calculates a target acceleration α1 and a disturbance estimated value α2 to make the vehicular velocity Vs substantially equal to the inputted target vehicular velocity V* and to calculate a target braking force For by multiplying these deviations by a vehicular body mass M; a deceleration force margin calculating section 52 that calculates a deceleration force margin F_DMon the basis of the target braking force For and the target vehicular velocity V* calculated at the vehicular velocity servo section 51; andashiftposition determining section 53 that carries out a selection of an appropriate gear position to be shifted on the basis of the deceleration force margin F_DMcalculated by the deceleration force margin calculating section 52 and the relative velocity ΔV calculated by the relative velocity calculating section 41.

[0057] The vehicular velocity servo section 51 is designed by using a robust matching control method to make a serve system robust to an external disturbance such as a variation in a gradient of a road surface on which the vehicle is running. The servo system 51 can be described as shown in FIG. 3 if a transfer characteristic of a controlled object is supposed as a pulse transfer function P(z⁻¹). In FIG. 3, z denotes a delay operator and P(z⁻¹) represents a sampled value prior to one sampling period in a form multiplied by z⁻¹.

[0058] FIG. 3 illustrates a typical servo system including: a model matching compensator 51; a robust compensator 52 as an external disturbance compensator; a subtractor 53 to subtract the disturbance estimated value α2 outputted by the robust compensator 52 from an acceleration (the term of acceleration includes a deceleration since a minus acceleration means the deceleration) command value outputted by a model matching compensator 51 to calculate a target acceleration value α*; and a multiplier 54 that multiplies the target acceleration α* by the vehicular body mass M.

[0059] It is noted that the model matching compensator 51 is set so that a responsive characteristic of the controlled object when the target vehicular velocity V* is inputted and the actual vehicular velocity Vs is outputted is made substantially equal to the characteristic of the reference model H(z⁻¹) having a predetermined first order lag and a dead time.

[0060] Suppose that an element whose input is the target acceleration α* and whose output is the actual vehicular velocity Vs is an object to be controlled. A pulse transfer function P(z⁻¹) can be represented as a product between an integration element P1(z⁻¹) described in the following equation (5) and a dead time element P2(z⁻¹)=z⁻². It is noted that T denotes a sampling period.

[0061] P1(z⁻¹)=T·z⁻¹/(1−z⁻¹)  (5).

[0062] At this time, compensators C1(z⁻¹) and C2(z⁻¹) constituted by the robust compensator 52 are represented by the following equations (6) and (7).

[0063] In the equations (6) and (7), γ=exp(−T/Tb)

[0064] C1(z⁻¹)=(1−γ)·z⁻¹/(1−γ·z⁻¹)  (6)

[0065] C2(z⁻¹)=(1−γ)·(1−z⁻¹)/T·(1−γ·z⁻¹)  (7).

[0066] If the dead time of the controlled object is neglected and the reference model is a first order low pass filter having a time constant Ta, a feedback compensator C3 (C3(z⁻¹)) for the model matching compensator 51 gives a constant as expressed in the following equation (8).

[0067] C3(z⁻¹)=K={1−exp(−T/Ta)}/T  (8).

[0068] A deceleration force margin calculating section 52 includes: a filter (LPF) 52a;a maximum deceleration calculating section 52b;a multiplier 52b;and a subtractor 52d.

[0069] The filter 52afilters the target driving force F_ORthrough the LPF having, e.g., a cut-off frequency of 0. 5 Hz to output the deceleration force demand value F_Dto the subtractor 52d.

[0070] The maximum deceleration calculating section 52brefers to a characteristic memory table (in a two dimensional array form) representing a relationship of the deceleration a to the vehicular velocity V when the target vehicular velocity V* is inputted and when the gear position of the automatic transmission 3 is in the ifourth-speed (OD) gear position and the engine throttle valve is completely closed in response to the target vehicular velocity V* to calculate the maximum deceleration α_MAX. The multiplier 52ccalculates the maximum deceleration force F_DMAXin the fourth-speed (OD) gear position by multiplying the maximum deceleration α_MAXwith a division value (quotient) of the maximum deceleration α_MAXby a gross deceleration (speed reduction) ratio (fourth-speed gear ratio×final gear ratio).

[0071] The subtractor 52dsubtracts the maximum deceleration force F_DMAXfrom the deceleration force demand value F_D.

[0072] Furthermore, the shift position determining section 53 receives the relative velocity ΔV calculated by the relative velocity calculating section 41, previously set down shift threshold value TH_D, and up shift threshold value TH_U, and outputs the OD inhibit control signal TS having the logical value of “1” to inhibit the fourth-speed (OD) gear position when the gear position of the automatic transmission 3 is placed at the fourth-speed (OD) gear position, F_DM≦TH_D, and ΔV≦0, and outputs the OD inhibit control signal TS having the logical value of “0” to enable the fourth-speed (OD) gear position when F_DM≧TH_Uand ΔV>0 when the gear position of the automatic transmission 3 is placed at the third-speed gear position.

[0073] Therefore, the vehicular velocity controlling section 50 executes a timer interrupt routine called a vehicular velocity control procedure to a predetermined main routine for each predetermined (sampling) period of time (for example, 10 milliseconds) shown in FIG. 4.

[0074] As shown in FIG. 4, at a step S1, the CPU 20aof the follow-up run controller 20 reads the target vehicular velocity V* calculated by the inter-vehicle distance controlling section 40, reads a set vehicular velocity V_SETby the vehicular driver, selects one of the read target vehicular velocity V_SETwhich is smaller than the other to set the selected vehicular velocity value as a selected target vehicular velocity V*s; V*s=min [V*, V_SET].

[0075] Next, the routine goes to a step S2.

[0076] At the step S2, the CPU 20aof the follow-up run controller 20 viz., the vehicular velocity controlling section 51 reads the vehicular velocity controlling section reads the vehicular velocity Vs(n) and the actual inter-vehicle distance L(n).

[0077] At the step S3, the CPU 20aof the follow-up run controller 20 (viz., the vehicular velocity controlling section 51) performs the calculations shown in the equations (9) and (10) corresponding to the compensators C1(z⁻¹) and C2(z⁻¹) in the robust compensator 52 to calculate the compensator outputs y₁(n) and y₂(n) using equations (9) and (10), calculates the disturbance estimated value α₂(n) using an equation (11), calculates the compensator output α₁using an equation (12) corresponding to a model matching compensator 51 based on the selected target vehicular velocity V*s and vehicular velocity Vs, calculates the target acceleration α* using the equation (13) on the basis of the calculated compensator outputs y₁(n), y₂(n), and α1, stores and updates the value of α* into a present value memory area of the target acceleration as the present target acceleration α*(n−1) into a previous memory area of the target acceleration.

[0078] y₁(n)=γ·y₁(n−1)+(1−γ)·α*(n−1)  (9).

[0079] y₂(n)=γy₂(n−1)+(1−γ)/{T·Vs(n−1)}  (10).

[0080] α₂(n)=y₂(n)−y₁(n)  (11).

[0081] α₁(n)=K·(Vs*(n)−Vs(n))  (12).

[0082] α*=α₁(n)−α₂(n)  (13).

[0083] Next, the routine goes to a step S4.

[0084] At the step S4, the vehicular velocity controlling section 50 multiplies the target driving force F_ORwith the vehicular body mass M to calculate the value of F_OR(=M·α*(n)).

[0085] At a step S5, the vehicular velocity controlling section 50 calculates a target engine torque T_Efrom the calculated target driving force F_OR, refers to a non-linear characteristic data map previously stored for each engine revolution speed N_Ebased on a target engine torque T_Eto derive and output the opening angle θ of the throttle valve and outputs it to the engine output controller 9.

[0086] At the next step S6, the vehicular velocity calculating section 50 performs a calculation processing such that the maximum deceleration force α_ODat the fourth-speed (OD) gearpositionis calculated by referring to a maximum deceleration calculation map previously stored on the basis of the target vehicular velocity V*, calculates a maximum deceleration force F_BMAXby multiplying the vehicular body mass M/gross speed-reduction ratio with the maximum deceleration α_MAX, calculates a required deceleration force F_Dthrough the filtering for the target driving force F_OR, calculates a deceleration force margin F_DMby subtracting the maximum deceleration force F_BMAXfrom the required deceleration force F_D, outputs the OD inhibit control signal TS having the logical value of “0” to the A/T controller 10 when F_BM≧TH_U(up shift threshold value) and ΔV<0 to perform the up shift and down shift controls for the vehicular velocity of the automatic transmission 3.

[0087] At the next step S7, the vehicular velocity controlling section 50 refers to the target braking pressure calculation map (in the two-dimensional array form) shown in FIG. 5 on the basis of the target braking force F_ORto calculate the target braking pressure P(n)* into the present target braking pressure memory area, and stores and updates the previously stored target braking pressure P_B*(n−1) into the previously calculated target braking pressure memory area.

[0088] It is noted that a lateral axis of the target braking pressure calculation map shown in FIG. 5 denotes the target braking force F_OR, a longitudinal axis of the target braking pressure calculation map denotes the target braking pressure P_B*, and the target braking pressure P_B* maintains at zero while the target braking force F_ORis positive and is negative above a predetermined value of−Fs. If F_OR<−Fs, a liner increase in the target braking pressure P_B* is found in proportion to a negative increase of the target braking force F_OR.

[0089] Next, at a step S8, the vehicular velocity controlling section 50 determines if P_B*(n)≧P_B(n−1).

[0090] This means that the CPU 20aof the follow-up run controller 20 determines if the present braking pressure state is in the pressure increase state.

[0091] If P_B*(n)≧P_B*(n−1) (Yes) at the step S8, the vehicular velocity controlling section 50 determines that the braking pressure of the vehicular brake system falls in a pressure increase state and the routine goes to a step S9.

[0092] At the step S9, the vehicular velocity controlling section 50 determines if P_B*(n)>Ps, wherein Ps denotes a threshold value of the braking pressure.

[0093] If P_B*(n)>Ps (Yes) at the step S9, the routine goes to a step S12 and the braking pressure PB is set as follows: P_BD=P_BD+ΔP_BA, wherein ΔP_BAdenotes a predetermined value to determine a gradient of an increase in the braking pressure command value P_BDstored in a braking pressure command value memory area since the present target braking pressure P_B*(n) is so large as to give the vehicular driver to a mismatch feeling from the vehicular driver's sense of driving.

[0094] If P_B*(n)≦Ps (No) at the step S9, the vehicular velocity controlling section 51 determines that the present target braking pressure P_B*(n) is so small as to give the vehicular driver to the match to the vehicular driver's sense and the routine goes to a step S10 in which the present target braking pressure is stored and updated to the braking pressure command value P_BDto the braking pressure command value memory area and the routine goes to a step S11.

[0095] At the step S11, the vehicular velocity controlling section 51 outputs the braking pressure command value P_BDstored in the braking pressure command value P_BDstored in the braking pressure command value memory area to the braking controller 8, and the timer interrupt routine is ended, and the routine is returned to the predetermined main routine.

[0096] On the other hand, the routine goes from the step S12 to a step S13.

[0097] At the step S13, the vehicular velocity controlling section 51 determines if the braking pressure command value P_BDcalculated at the step S12 is equal to or larger than the present target braking pressure P_B*(n) calculated at the step S7 (P_BD≧P_B*(n)).

[0098] If P_BD≧P_B*(n) (Yes) at the step S13, the routine jumps to the step S11.

[0099] At the step S14, the present target braking pressure P_B*(n) is stored to update the braking pressure command value memory area as the braking pressure command value P_BD(P_BD=P_B*(n) After the step S14, the routine goes to the step S11 described above.

[0100] On the other hand, if the result of determination at the step S9 indicates that P_B*(n)<P_B*(n−1), the vehicular velocity controlling section 50 determines that the present braking pressure state is in the pressure decrease state and the routine goes to a step S15.

[0101] At the step S15, the braking pressure command value P_BDis stored into the braking pressure command value memory area to update the previously stored braking pressure command value by a subtraction a predetermined value ΔP_BDto determine a pressure decrease gradient previously set in the braking pressure command value P_BDfrom the stored braking pressure command value P_BDas follows: P_BD=P_BD−ΔP_BD.

[0102] Then, the routine goes to a step S16.

[0103] At the step S16, the vehicular velocity controlling section 50 determines if P_BD<P_B*(n). If P_BD<P_B*(n) (yes) at the step S16, the routine goes to a step S17 in which P_BD=P_B*(n), namely, the present target braking pressure P_B*(n) is stored into the braking pressure command value memory area as the braking pressure command value P_BDto update the braking pressure command value P_BDand the routine goes to the step S11.

[0104] If P_BD<P_B*(n) No at the step S16, the routine goes to the step S11.

[0105] In FIG. 4, the steps S1 through S17 correspond to target braking pressure calculating means, the steps S8 Ithrough S17 correspond to target braking pressure limiting means, the steps S8 through S14 correspond to target braking pressure increase limiting means; and the step S8 and the steps S15 through S17 correspond to target braking pressure decrease limiting means.

[0106] Next, an operation of the first embodiment described above will be described with chief reference to FIGS. 6A through 6C.

[0107] Suppose now that the vehicle is running straightly on a straight road surface with the preceding vehicle which is running at a cruise velocity (running at a constant velocity) on the same traffic lane of, for example, a city street as the vehicle trapped at a time point t0, as shown by FIG. 6A and the vehicular velocity Vs maintained at the target inter-vehicle distance L*.

[0108] In this state, since the actual inter-vehicle distance L detected by the inter-vehicle distance sensor 1 is made substantially equal to the target inter-vehicle distance L* and the preceding vehicle is cruising at the constant vehicular velocity, the inter-vehicle distance command value L_Tis substantially coincident with the actual inter-vehicle distance L. Consequently, the relative velocity ΔV calculated by the relative velocity calculating section 41 of the inter-vehicle distance controlling section 40.

[0109] The target braking pressure P_B*(n) calculated at the step S7 maintains approximately zero as shown in FIG. 6B. Then, the routine shown in FIG. 4 goes to the step S10 via the steps S8 and S9. Hence, the braking pressure command value P_BDis substantially made equal to the target braking pressure P_B*(n) which indicates approximately zero as shown by FIG. 6C. Hence, the disc brake 7 is held at an non-operation state in the braking controller 8.

[0110] At a time point t1 at which the vehicle is running at the constant vehicular velocity to follow up the preceding vehicleis, forexample, interrupted by the other vehicle from another traffic lane to the front detection zone of the vehicle so that the vehicle is in a relatively moderate deceleration state.

[0111] At this time, the inter-vehicle distance L detected by the inter-vehicle distance sensor 12 becomes moderately short as compared with the target inter-vehicle distance L*. Hence, the target vehicular velocity V* is moderately decreased which is calculated by the target vehicular velocity calculating section 44 of the inter-vehicle distance controlling section 40.

[0112] Hence, the target acceleration α*(n) calculated at the step S3 of FIG. 4 indicates negative. The target driving force F_ORcalculated at the step S4 indicates negative below the minus predetermined value−Fs.

[0113] In this state, the opening angle θ of the throttle valve is controlled under the full close state at the step S5.

[0114] Then, the OD inhibit control signal TS having the logical value of “1” is outputted at the step S6. The A/T controller 10 is operated to make the gear position of the transmission 3 down shift to the third-speed gear position. The target braking pressure P_B*(n) calculated at the step S7 becomes smaller than the braking pressure threshold value Ps and becomes a pressure decrease state. Hence, the routine goes from the step S8 to the step S9. However, since the target braking pressure P_B*(n) indicates the smaller value than the braking pressure threshold value Ps shown in FIG. 6A, the routine goes from the step S9 to the step S10 in which the calculated target braking pressure P_B*(n) is set directly as the braking pressure command value P_BD, as shown in FIGS. 6B and 6C. This braking pressure command value P_BDis outputted to the braking controller 8. The braking force through each disc brake 7 causes the moderate braking force to be developed so that the vehicular running state is transferred to the deceleration state. The deceleration control such as to make the actual inter-vehicle distance L to substantially equal to the target inter-vehicle distance L* so that the inter-vehicle distance L can be widened.

[0115] Thereafter, at a time point t2, the preceding vehicle is transferred from the deceleration state thereof to the cruise run state thereof, the vehicular velocity of the controlled vehicle becomes constant.

[0116] Thereafter, at a time point t3 shown in FIG. 6A, the other vehicle is interrupted from the other traffic lane into the front detection zone of the inter-vehicle distance sensor 12 so that the inter-vehicle distance L becomes abruptly short as compared with the target inter-vehicle distance L*. At this time, the target vehicular velocity V* calculated by the target vehicular velocity calculating section of the inter-vehicle distance controlling section 40 is abruptly reduced.

[0117] Hence, the target acceleration α*(n) calculated at the step S3 indicates negatively large representing the large deceleration. Accordingly, the target driving force F_ORindicates the negatively large. The opening angle θ calculated at the step S5 for the throttle valve is controlled in a full close condition. Then, the deceleration force margin F_BMcalculated at the step S6 indicates a negatively large so as to be lower than the down shift value TH_D. Hence, the OD inhibit control signal TS having the logical value of “1” is outputted to the A/T controller 10. Hence, the down shift from the fourth-speed gear position to the third-speed gear position occurs in the transmission 3 to increase the engine braking. Hence, the target braking pressure P_B(n)* calculated at the step S7 is abruptly increased as shown in FIG. 6B and is in excess of the braking pressure threshold value Ps.

[0118] Under the present condition, the routine goes from the step S8 to the step S9 via the step S12. Thus, thebraking pressure command value P_BDis increased by the predetermined value ΔP_BA. Hence, the braking force developed on each disc brake 7 is maintained at a constant value.

[0119] Thereafter, as the inter-vehicle distance L approaches gradually to the target inter-vehicle distance L* at a time point t5, the target driving force F_ORgradually approaches to zero. If the target braking pressure P_B*(n) accordingly starts to be decreased as shown in FIG. 6B, the routine goes from the step S8 to the step S15. Since the braking pressure command value P_BDis in the decrease state by the gradient of the predetermined value ΔP_BDas shown in FIG. 6C, the braking force of each disc brake 7 is gradually decreased.

[0120] At a time point of t6, the braking pressure command value P_BDis maintained at the target braking pressure P_B*. The braking force developed at each disc brake 7 is increased. When the deceleration force margin F_BMis above the up shift threshold value TH_D, the CD inhibit control signal having the logical value of “0” is outputted to the A/T controller 10 and the transmission 3 is shifted up to the fourth-speed (OD) gear position. Thereafter, the vehicular running condition is transferred to the cruise run state.

[0121] (Second Embodiment)

[0122] FIG. 7 shows an operational flowchart of the vehicular velocity control procedure executed in a second preferred embodiment according to the present invention.

[0123] In the second embodiment, an initial response characteristic is improved to an abrupt increase of the target braking pressure P_B*(n).

[0124] In the vehicular velocity control procedure performed by the vehicular velocity controlling section 50 in the case of FIG. 4 described in the first embodiment, steps S21, S22, and S23 are newly interposed in the case of the second embodiment as shown in FIG. 7 between the steps S9, S11, and S12.

[0125] In details, at the step S21, the vehicular velocity controlling section 50 determines if an initial state pass flag FB representing that the present time has passed an initial stage of the pressure increase state when set to “1”.

[0126] If FB=“1” (Yes) at the step S21, the vehicular velocity controlling section 50 determines that the present time of the vehicular brake system has passed the initial stage of the braking pressure increase and the routine goes to the step S22. At the step S22, the vehicular velocity controlling section 50 sets the braking pressure threshold value of Ps as the braking pressure command value P_BD. The set command value P_BDat the step S21 is outputted at the step S11 with the initial pressure increase pass flag of FB set to “1” at the step S23. It is noted that a step S24 is interposed between the steps S16 and S17 and the step S11 to reset the initial pressure increase pass flag of FB to “0”, as shown in FIG. 7.

[0127] The other same numbered steps in FIG. 7 as those shown in FIG. 4 have the same functions as described in the first embodiment. In addition, the other structures are the same as those described in the first embodiment. Hence, the detailed description thereof will herein be omitted.

[0128] In the second embodiment, in a case where the inter-vehicle distance L is reduced at a relatively moderate pace, the target acceleration α*(n) calculated at the step S3 of FIG. 7 indicates the relatively small value in the negative direction so that the target driving force F_OR(n) calculated at the step S4 is negatively below the minus predetermined value−Fs. The target braking pressure P_B*(n) calculated at the step S7 is negatively below the predetermined value of Ps. Hence, at this time, in the same manner as described in the first embodiment, the routine goes to the step S10 in which the target braking pressure P_B(n)* is directly set as the braking pressure command value.

[0129] Hence, the actual braking force at each disc brake 7 is controlled in accordance with the target braking pressure P*(n).

[0130] However, in a case where the inter-vehicle distance L is abruptly decreased such as the case where the preceding vehicle is interrupted at the short inter-vehicle distance from the other traffic lane, the target driving force F_OR(n) calculated at the steps S3 and S4 are abruptly increased in the negative direction at the vehicular velocity control procedure shown in FIG. 4 in the negative direction.

[0131] Hence, the target braking pressure P_B*(n) calculated at the step S7 becomes larger than the braking pressure threshold value Ps.

[0132] Hence, the routine goes from the step S8 to the step S21 via the step S9. Since the initial state pass flag FB is reset to “0” at the step S21, the routine goes to the step S22. The braking pressure threshold value Ps is set as the braking pressure command value P_BD. Then, the routine goes to the step S23 to set the initial state pass flag FB to “1”. Then, as shown by a time point of t11 in FIG. 8, the braking pressure command value P_BDwhich is equal to the braking pressure threshold value Ps is outputted to the braking controller 8. Hence, the braking pressure of each disc brake 7 is increased up to a value corresponding to the braking pressure threshold value Ps. Hence, since the relatively large braking force is developed at the initial stage of the increase in the braking pressure can be improved, and the deceleration control such that the inter-vehicle distance can immediately be widened with no continuation of the abrupt decrease state of the inter-vehicle distance L.

[0133] Then, after the present interrupt timer routine shown in FIG. 7 is executed for the predetermined time, the vehicular velocity control procedure in FIG. 7 is restarted. At this time, since the initial state pass flag FB is set to “1”, the routine shown in FIG. 8 goes from the step S21 to the step S12. In the same way as described in the first embodiment, the braking pressure command value P_BDis increased by the predetermined value ΔP_BDin the same manner as described in the first embodiment. Then, whenever the timer interrupt period is passed, the increase rate corresponding to the predetermined value ÄP_BAof the braking pressure command value P_BDis repeated as shown in FIG. 8.

[0134] Then, at a time point t12 at which the braking pressure command value P_BDhas reached to the target braking pressure P_B*(n), the braking pressure command value P_BDis thereafter maintained at the target braking pressure of P_B*(n).

[0135] Thereafter, when the actual inter-vehicle distance L has approached to the target inter-vehicle distance L* and the braking pressure P_B*(n) is started to be decreased at a time point t13, the routine goes from the step S8 to the step S15. In the same manner as the first embodiment, the braking pressure command value P_BDis decreased by the predetermined value ΔP_BD, the pressure decrease control is advanced, and the routine shown in FIG. 7 goes to the step S24 in which the initial state pass flag FB is reset to “0”.

[0136] Then, after the actual inter-vehicle distance L is approximately equal to the target braking distance L* and the target braking pressure P_B*(n) indicates zero, the braking pressure command value P_BDis below the target braking pressure P_B*(n) in the midway through the zeroed target braking pressure. In either of the cases, the target braking pressure P_B*(n) is set as the braking pressure command value P_BD.

[0137] (Third Embodiment)

[0138] That is to say, in the third embodiment shown in FIG. 9, steps S31 and S32 are newly interposed between the steps S9 and S21 shown in FIG. 8 of the second embodiment.

[0139] In details, the step S31 indicates that a subtraction result of the subtraction of the previous target braking pressure P_B*(n−1) from the present target braking pressure P_B*(n) is equal to or larger than a second threshold value Ps2 set larger than the threshold value of the braking pressure Ps described above. If {P_B*(n)−P_B*(n−1)}≧Ps2 (Yes) at the step S8, the vehicular velocity controlling section 50 determines that the present braking state is an abrupt pressure increase state that demands a higher initial response characteristic and the routine goes to the step S21. If (P_B*(n)−P_B*(n−1))<Ps2 (No) at the step S31, the routine goes to a step S32 since the vehicular velocity controlling section 50 determines that the present braking state is the abrupt pressure increase state that demands no higher response characteristic and the routine goes to the step S32. At the step S32, the initial stage pass flag FB is set to “1” and the routine goes to the step S21. The other steps than the steps S31 and S32 are the same as those described in FIG. 7. Hence, the detailed description thereof will herein be omitted.

[0140] In the case of the third embodiment, when the actual inter-vehicle distance L is abruptly shortened due to the interruption of the preceding vehicle from the other traffic lane to the same traffic lane as the vehicle, the present target braking pressure P_B*(n) calculated at the step S7 in the vehicular velocity control procedure shown in FIG. 9 is larger than the previous target braking pressure P_B*(n−1) by the braking pressure threshold value Ps but is smaller than the second braking pressure predetermined value Ps2, the routine of FIG. 9 is transferred from the step S31 to the step S32. Since the initial stage pass flag FB is set to “1”, the routine goes via the step S21 to the step S12. At this time, in the same manner as the first embodiment described above, the braking pressure command value P_BDprovides the relatively moderate braking state such as to be increased by the predetermined value ΔP_BAfor each timer interrupt period from the time at which the braking initial stage occurs so that the remarkably large braking force cannot be developed although the actual inter-vehicle distance L becomes narrow.

[0141] On the contrary, if the actual inter-vehicle distance L is abruptly reduced, the present target braking pressure P_B*(n) calculated at the step S7 in the vehicular velocity control procedure in FIG. 9 becomes larger than the previous target braking pressure P_B*(n−1) by the second predetermined value Ps2, the routine goes from the step S31 to the step S21. Since the initial state pass flag FB remains reset to “0”, the routine goes to the step S22 in which the braking pressure command value P_BDis increased by the predetermined value ΔP_BAfor each timer interrupt period of time after the braking pressure command value P_BDis abruptly increased up to the braking pressure command value Ps. The deceleration control that increases the response characteristic at the time of the narrowing of the actual inter-vehicle distance L can be moderated.

[0142] As described above, in the third embodiment, the braking characteristic can be modified in accordance with the magnitude of the target braking pressure P_B*(n) calculated during the initial stage of braking. Hence, the vehicular deceleration control can be carried out so as to match with the driver's sense of driving.

[0143] In each of the second and third embodiments, the braking pressure threshold value Ps is set as the braking pressure command value P_BDat the step S22. The target braking pressure command value P_B*(n) calculated, for example, at the step S7 may be multiplied with such a constant as ½. ⅓, or so on.

[0144] In addition, in each of the first, second, and third embodiment described above, the target braking pressure of P_B*(n) is calculated by reference to the target braking pressure P_B*(n) may be calculated using an equivalent equation representing the characteristic line of FIG. 5.

[0145] Furthermore, in each of the first, second, and third embodiment, the braking pressure command value P_BDis increased linearly by a constant gradient. At the initial stage of braking, the gradient is made larger at an earlier stage of braking, and, then, at a later stage of braking the gradient may be smaller. Furthermore, the braking pressure command value P_BDmay be increased in a quadratic curve.

[0146] In each of the first, second, and third embodiments, the vehicular velocity calculation processing on the follow-up run control is carried out by the follow-up run controller 20 in terms of the software. The vehicular velocity calculation processing may be constituted by the hardware of electronic circuitry such as a function generator, a comparator, a clock signal generator, up/down counter, an arithmetic/logic unit, and so forth.

[0147] The entire contents of a Japanese Patent Application No. Heisei 11-168265 (filed in Japan on Jun. 15, 1999) are herein incorporated by reference.

[0148] Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in the light of the above teachings. The scope of the invention is defined with reference to the following claims.