GB2336413A

GB2336413A - Vehicle brake control based upon pedal stoke and master cylinder pressure

Info

Publication number: GB2336413A
Application number: GB9905429A
Authority: GB
Inventors: Yutaka Onuma; Tatsuo Sugitani
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 1998-04-16
Filing date: 1999-03-09
Publication date: 1999-10-20
Also published as: GB9905429D0; DE19917311A1; JPH11301434A

Abstract

A brake control device for a vehicle brake system comprises means for sensing the depression stroke Sp of a brake pedal, means for sensing master cylinder pressure Pm, and means for determining pressure of brake fluid to be supplied to selected wheel cylinder(s), wherein the pressure is determined by laying first and second weights (1-α, α) on the brake pedal depression stroke (or on a target deceleration Gst corresponding to the depression stroke of the brake pedal) and the master cylinder brake fluid pressure (or on a target deceleration Gpt corresponding to the master cylinder pressure), respectively, the first weight decreasing and the second weight increasing with increasing determined brake fluid pressure.

Description

BRAKE CONTROL DEVICE OF VEHICLE BASED UPON WEIGHTED COMBINATION OF PEDAL

STROKE AND MASTER CYLINDER PRESSURE 2336413

Background of the Invention

Field of the In ven tion

The present invention relates to a brake system of a vehicle, and more particularly, to a brake control device for a vehicle brake system which operates with motor powered pump in response to a depression of the brake pedal by a driver.

Description of the Prior Art

An art of powered brake system of vehicles such as automobiles is already known, in which the wheel cylinders of a vehicle are selectively supplied with a brake fluid pressurized by a motor powered pump under a control of control means which calculate and determine the pressure of the brake fluid to be supplied to each selected one or ones of the wheel cylinders based upon a depression of the brake pedal by a driver so that a more powerful and more ingeniously controlled braking is applied to the wheels than the braking simply dependent upon a compression of the brake fluid in the master cylinder effected by a depression of the brake pedal by a driver.

An example of such a powered brake system is shown in, for example, Japanese Patent Laid-open Publication 9-30394 based upon German Patent Application 19526659.5, according to which a target deceleration of a vehicle is calculated based upon a pressure of the master cylinder and its change rate, whereby the braking force is controlled to attain a deceleration of the vehicle conforming to the target deceleration. It will be expected that such a control of the braking force based upon the master cylinder pressure and its change rate provides a better braking performance than the conventional hydraulic brake system dependent only upon the master cylinder pressure generated by a depression of the brake pedal.

- 4 selected one or ones of the wheel cylinders under a control of the control means so as to be increased along with increase of the depression stroke of the brake pedal as well as increase of the brake fluid pressure by the master cylinder by laying first and second weights on the increase of the depression stroke of the brake pedal and the increase of the brake fluid pressure by the master cylinder, respectively, the first weight being decreased while the second weight being increased relative to one another along with increase of the brake fluid pressure determined by the brake fluid pressure determination means.

By the pressure of the brake fluid supplied to the wheel cylinders being determined according to a weighted combination of a first parameter corresponding to the brake pedal depression stroke and a second parameter corresponding to the master cylinder pressure so that the weight is shifted from the first parameter to the second parameter along with increase of the braking force, the initial insensibleness of the brake control based upon the detection of the master cylinder pressure against the brake pedal depression force corresponding to the driver's intention for a deceleration of the vehicle is compensated for by the high sensibleness of the brake pedal depression stroke against the brake pedal depression force so that such a compensation is gradually cancelled according to increase of the braking force out of the initial insensible region, so as to ensure a desirable linearity in the relationship between the braking force applied to the wheels and the reaction force perceived by the driver against the depression of the brake pedal.

In the brake control device of the above-mentioned basic construction, the brake fluid pressure determination means may determine the brake fluid pressure supplied to the selected one or ones of the wheel cylinders to be a sum of a first product of a first quantity which increases along with increase of the depression stroke of the brake pedal and a first weighting factor and a second product of a second quantity which increases along with increase of although the precision swiftly substantially lowers when the pedal depression increases.

Summary of the Invention

In consideration of such particular characteristics as described above of the relationship between the master cylinder pressure and the depression force of the brake pedal and the relationship between the depression stroke and the depression force of the brake pedal, it is a primary object of the present invention to improve a brake control device for a powered brake system of a vehicle which estimates a braking force to be applied to the wheels of the vehicle based upon the operation of the brake pedal by a driver, so as to obviate an inefficiency due to the initial insensibleness of the master cylinder pressure to the brake depression force, while effectively utilizing the high sensitivity of the brake pedal depression stroke in estimating the driver's intention for a substantial deceleration of the vehicle in the initial stage thereof.

According to the present invention, the above-mentioned primary object is accomplished by a brake control device of a vehicle having wheels and a brake system for the wheels including wheel cylinders for applying a braking force to each corresponding one of the wheels according to a supply of a pressurized brake fluid thereto, a brake pedal adapted to be depressed by a driver, a master cylinder adapted to compress the brake fluid according to a depression of the brake pedal by the driver, motor powered pump for pressurizing the brake fluid, and control means including on-off valves for controlling supply of the brake fluid pressurized by the master cylinder and the brake fluid pressurized by the pump to the wheel cylinders, the device comprising:

means for detecting a stroke of the depression of the brake pedal, means for detecting a pressure of the brake fluid compressed by the master cylinder, and means for determining a pressure of the brake fluid supplied to a - 6 weighting factor to be deceleratedly increased along with increase of the brake fluid pressure determined by the fluid pressure determination means when the brake fluid pressure determined by the brake fluid pressure determination means is higher than the predetermined medium value Brief Description of the Drawings

In the accompanying drawing, Fig. 1A is a diagram showing an example of the hydraulic circuit of a brake system of a vehicle in which the brake control device according to the present invention is incorporated-, Fig. 1B is a diagram showing a basic construction of the brake control device according to the present invention; Fig. 2 is a flowchart showing an embodiment of the brake control device according to the present invention in the form of its control operation; Fig. 3 is a graph showing an example of the performance of target deceleration Gst vs. brake pedal depression stroke Sp, i.e. a value of deceleration of the vehicle to be attained by the brake pedal being depressed to generate a corresponding value of the depression stroke; Fig. 4 is a graph showing an example of the performance of target deceleration Gpt vs. master cylinder pressure Pm, i.e. a value of deceleration of the vehicle to be attained by the brake pedal being depressed to generate a corresponding value of the master cylinder pressure; Fig. 5 is a graph showing an example of the performance of weighting factor a vs. final target deceleration Gt, i.e. a factor for weighting the target deceleration Gpt dependent of the master cylinder pressure in determining the braking force to he applied to the wheels according to a weighted combination of the target decelerations Gpt and Gst; Fig. 6 is a graph showing a general performance of the master cylinder pressure vs. the brake pedal depression force; and Fig. 7 is a graph showing a general performance of the brake pedal depression stroke vs. the brake pedal depression force.

the brake fluid pressure by the master cylinder and a second weighting factor, the first and second weighting factors being varied according to the brake fluid pressure determined by the brake fluid pressure determination means such that the first weighting factor is decreased while the second weighting factor is increased complementarily to the decrease of the first weighting factor along with increase of the brake fluid pressure determined by the brake fluid pressure determination means.

In this case, the brake fluid pressure determination means may determine the first quantity to be acceleratedly increased along with increase of the depression stroke of the brake pedal so that the steep inclination of the performance curve of the pedal depression stroke vs. pedal depression force in the initial braking region is desirably compensated for.

On the other hand, the brake fluid pressure determination means mav determine the second quantity to be increased at a substantially constant rate along with increase of the brake fluid pressure by the master cylinder so that the control is approached to such a hneaity.

Further, the brake fluid pressure determination means may determine the first weighting factor to be acceleratedly decreased while the second weighting factor to be acceleratedly increased along with increase of the brake fluid pressure determined by the brake fluid pressure determination means when the brake fluid pressure determined by the brake fluid pressure determination means is lower than a predetermined medium value thereof, so that the brake control based upon the brake pedal depression stroke is swiftly transferred to the brake control based upon the master cylinder pressure when the braking force increases out of the initial region.

The swift transfer of the brake control based upon the brake pedal depression to the brake control based upon the master cylinder may be compensated for by the fluid pressure determination means determining the first weighting factor to be deceleratedly decreased while the second 1 F) - 8 cylinders 20FR, 20FL, 20RR and 20RL through on-off valves 40FR, 40FL, 40RR and 40RL, respectively. An accumulator 31 may be connected to the outlet passage 29. The on-off valves 40FR, 40FL, 40RR and 40RL are each of a normally closed type which maintains each of the supply passages 36FR, 36FL, 36RR and 36RL in an interrupted condition when no electric current is supplied thereto, and is selectively opened by a supply of an actuating electric current thereto.

The wheel cylinders 20FR, 20FL, 20RR and 20RL are exhaustible through exhaust passages 38FR, 38FL, 38RR and 38RL including on-off valves 42FR, 42FL, 42RR and 42RL, respectively, toward an exhaust passage 30 leading to the reservoir 26. The on-off valves 42FR, 42FL, 42RR and 42RL are each also of a normally closed type which maintains each of the exhaust passages 38FRY 38FL, 38RR and 38RL in an interrupted condition when no electric current is supplied thereto, and is selectively opened by a supply of an actuating electric current.

The pressures of the brake fluid in the wheel cylinders 20FR, 20FL, 20RR and 20RL are detected by pressure sensors 44FR, 44FL, 44RR and 44RL, respectively. The pressure of the brake fluid compressed by the master cylinder 14 is detected by a pressure sensor 48. The pressure of the brake fluid in the outlet passage 29 is detected by a pressure sensor 50.

The changeover of each of the on-off valves 22FR and 22FL, the on-off valves 40FR-40RL and the on-off valves 42FR-42RL is controlled by control means 52 diagrammatically shown in Fig. IB, or in more detail, by a microcomputer 54 thereof through a drive circuit 56 thereof. The microcomputer may be of a common type including a central processor unit (CPU), a read only memory (ROM), a random access memory (RAND, input and output port means and bi-lateral bus means interconnecting these elements, all not shown in detail in the figure. The microcomputer 54 is supplied with signals of pressures Pi Q = fr fl, rr and rl) of the brake fluid in the corresponding wheel cylinders from the wheel cylinder pressure sensors Descliption of the Preferred Embodiment In the following, the present invention will be described in more detail with respect to a preferred embodiment thereof by referring to the accompanying drawings.

Referring to Fig. 1A, the hydraulic circuit totally designated by 10 of a brake system of a vehicle not shown in the figure and having pairs of front and rear wheels also not shown in the figure comprise wheel cylinders 20FR, 20FL, 20RR and 20RL for applying braking forces to fi.ont right, front left, rear right and rear left ones of the wheels, respectively. The hydraulic circuit comprises a master cylinder 14 adapted to compress a brake fluid supplied from a reservoir 26 according to a depression of a brake pedal 12 by a driver, so as to deliver a pressurized brake fluid through passages 16 and 18 toward the wheel cylinders 20FL and 20FR, respectively. On-off valves 22FL and 22FR are provided in the passages 16 and 18, respectively, so as normally not to obstruct communication of the passages 16 and 18, while selectively interrupting the communication of the passages 16 and 18, respectively. Indeed, the on-off valves 22FL and 22FR are solenoid actuated valves which are maintained in a through open condition such as shown in the figure when no electric current is supplied thereto, while they are changed over to a position interrupting the communication of the passages 16 and 18, respectively, when they are supplied with an electric current when an ignition switch (not shown) is turned on, desirably on an additional condition that the voltage of a battery (not shown) of the vehicle is not lower than a normal threshold level.

34 is a pump adapted to be selectively driven by an electric motor 32 powered by the afore-mentioned battery via control means described in detail hereinunder, so as to pump up the brake fluid supplied from the reservoir 26 through a suction passage 28 for providing a pressurized source of the brake fluid in an outlet passage 29 branching to passages 36FR, 36FL, 36RR and 36RL for supplying the pressurized brake fluid to the wheel inclination of the performance curve of Fig. 7 the initial braking region appropriately compensated for by inversely curving the shape of the performance curve of Fig. 3.

In step 30, by looking up a map such as shown in Fig. 4 stored in the ROM, a value of the target deceleration Gpt is read out against a current value of the master cylinder pressure Pm, thereby estimating the driver's intention for a deceleration of the vehicle form the view point of the master cylinder pressure which is substantially proportional to the pedal depression force by the driver except the insensible initial region of the compression of the brake fluid as shown in Fig. 6.

In step 40, by looking up a map such as shown in Fig. 5 stored in the ROM, a value of the weighting factor a for weighting the target deceleration Gpt based upon the master cylinder pressure Pm against the target deceleration Gst based upon the brake pedal depression stroke Sp is 1.5 estimated against total target deceleration Gt which is a weighted sum of the target decelerations Gpt and Gst by the weighting factor a according to the following equation:

Gt = (1 - a)Gst + a Gpt In the brake control carried out according to the repetitive calculations of the steps 10-710 of Fig. 2, the reading out of the weighting factor a by the map of Fig. 5 is executed based upon the value of Gt obtained by each previous cycle of the calculations through the flowchart of Fig. 2.

As will be appreciated from the rightward upward sloping shape of the curve of Fig. 5, the weighting of the parameters in the estimation of the deceleration of the vehicle to be targeted at is gradually shifted from on the brake pedal depression stroke to on the master cylinder pressure along with increase of the target deceleration, i.e. as a higher braking force is applied to 44FL-44R11, a signal of depression stroke Sp of the brake pedal 12 by a driver from a brake pedal stroke sensor 46, a signal of master cylinder pressure Pm of the brake fluid compressed by the master cylinder 14 from the master cylinder pressure sensor 48, and the pressure of the brake fluid in the pump outlet passage 29 from the powered source pressure sensor 50, and carries out certain control calculations based upon the values of the parameters input by the signals from the sensors 44FL-44RR, 46, 48 and 50 for determining the pressure of the brake fluid to be established in each of the wheel cylinders 20FR-20RL at each moment of the operation of the vehicle as described in detail hereinunder, and controls the on-off valves 22FR and 22FL, 40FR-40RL and 42FR-42RL together with an on-off operation of the electric motor 32 via the chive circuit 56.

Fig. 2 shows an embodiment of such control calculations in the form of a flowchart. As well known in the art, control operations such as shown by the flowchart of Fig. 2 are started upon a turning on of the ignition switch and are carried out repetitively during the operation of the vehicle at a cycle time such as tens of microsecond so as to be able to follow quick changes of the operating conditions of the vehicle.

When the control operations are started, in step 10, signals from the sensors shown in Fig. 1B are read in.

In step 20, by looking up a map such as shown in Fig. 3 stored in the ROM of the microcomputer 54, a value of the target deceleration Gst is read out against a current value of the depression stroke Sp of the brake pedal by the driver, thereby estimatinga driver's intention for a deceleration of the vehicle from the view point of the stroke of depression of the brake pedal by the driver. As will be appreciated from the shape of the performance curve shown in Fig. 3, the estimation of the driver's intention for a deceleration of the vehicle against the depression stroke of the brake pedal is designed to reflect thereon the general relationship between the pedal depression stroke and the pedal depression force shown in Fig. 7. In other words, the steep

Claims

Claims

1. A brake control device of a vehicle having wheels and a brake system for the wheels including wheel cylinders for applying a braking force to each corresponding one of the wheels according to a supply of a pressurized brake fluid thereto, a brake pedal adapted to be depressed by a driver, a master cylinder adapted to compress the brake fluid according to a depression of the brake pedal by the driver, motor powered pump for pressurizing the brake fluid, and control means including on-off valves for controlling supply of the brake fluid pressurized by the master cylinder and the brake fluid pressurized by the pump to the wheel cylinders, the device comprising:

means for detecting a stroke of the depression of the brake pedal, means for detecting a pressure of the brake fluid compressed by the master cylinder, and means for determining a pressure of the brake fluid supplied to a selected one or ones of the wheel cylinders under a control of the control means so as to be increased along with increase of the depression stroke of the brake pedal as well as increase of the brake fluid pressure by the master cylinder by laying first and second weights on the increase of the depression stroke of the brake pedal and the increase of the brake fluid pressure by the master cylinder, respectively, the first weight being decreased while the second weight being increased relative to one another along with increase of the brake fluid pressure determined by the brake fluid pressure determination means.

2. A brake control device according to claim 1, wherein the brake fluid pressure determination means determine the brake fluid pressure supplied to the selected one or ones of the wheel cylinders to be a sum of a first product of a first quantity which increases along with increase of the the wheels. Further, as will be appreciated in more detail from the shape of the curve of Fig. 5, the weighting factor a for the target deceleration Gpt based upon the master cylinder pressure may desirably be so determined that it is acceleratedly increased (in other words, 1- a is acceleratedly increased) along with increase of the total target deceleration Gt, i.e. the braking force to be targeted, when the total target deceleration Gt increases from zero to a certain medium value, so that the brake control based upon the brake pedal depression stroke is swiftly transferred to the brake control based upon the master cylinder pressure when the intensity of braking force increases out of the initial insensitive region in the performance of the master cylinder pressure against the brake pedal depression force as shown in Fig. 6, so as to ensure as soon as possible the linearity between the braking force applied to the wheels and the reaction force which the driver feels at his or her foot by the depression of the brake pedal, with a decelerated increase of the factor a along with further increase of the total target deceleration Gt following thereto for a corresponding compensation of the accelerated increase in the preceding region of increase.

In step 60, target wheel cylinder pressures Pwti ( 1 == fr, fl, rr and rl) are calculated based upon the total target deceleration Gt, possibly with incorporation of other control calculations for vehicle stability control known in various ideas in the art of the computer control of automobiles.

In step 70, the microcomputer 54 outputs the control signals based upon the calculations in step 60 to the drive circuit 56 so that the motor 32, the on-oll valves 22FR and 22FL, 40FR-40RL and 42FR-42RL are correspondingly operated to generate a corresponding braking force at each of the wheels.

Although the invention has been described in detail with respect to a preferred embodiment thereof, it will be apparent for those skilled in the art that various modifications are possible within the scope of the present invention.

deceleratedIv decreased while the second weighting factor to be deceleratedly increased along with increase of the brake fluid pressure determined by the brake fluid pressure determination means when the brake fluid pressure determined by the brake fluid pressure determination means is higher than the predetermined medium value.

7. A brake control device substantially as hereinbefore described with reference to the accompanying drawings.

depression stroke of the brake pedal and a first weighting factor and a second product of a second quantity which increases along with increase of the brake fluid pressure by the master cylinder and a second weighting factor, the first and second weighting factors being varied according to the brake fluid pressure determined by the brake fluid pressure determination means such that the first weighting factor is decreased while the second weighting factor is increased complemental-fly to the decrease of the first weighting factor along with increase of the brake fluid pressure determined by the brake fluid pressure determination means.

3. A brake control device according to claim 2, wherein the brake fluid pressure determination means determine the first quantity to be acceleratedly increased along with increase of the depression stroke of the brake pedal.

4. A brake control device according to claim 2, wherein the brake fluid pressure determination means determine the second quantity to be increased at a substantially constant rate along with increase of the brake fluid pressure by the master cylinder.

5. A brake control device according to claim 2, wherein the brake fluid pressure determination means determine the first weighting factor to be acceleratedly decreased while the second weighting factor to be acceleratedly increased along with increase of the brake fluid pressure determined by the brake fluid pressure determination means when the brake fluid pressure determined by the brake fluid pressure determination means is lower than a predetermined medium value thereof.

G. A brake control device according to claim 5, wherein the brake fluid pressure determination means determine the first weighting factor to be 3. A brake control device according to Claim 2, wherein the brake fluid pressure determination means determine the first quantity to acceleratedly increase aloner with increase of the WI depression stroke of the brake pedal.

4. A brake control device according to Claim 2, wherein the brake fluid pressure Z 1 determination means deter-mine the second quantity to increase at a substantially constant rate alone. with increase of the brake fluid pressure by the master cylinder.

5. A brake control device according to Claim 2, wherein the brake fluid pressure determination means determine the first weighting factor to acceleratedIv decrease while the second W wel(yhtinú factor to acceleratedIv increase alona with increase of the vehicle deceleration expected W - 1 W by the brake fluid pressure determined by the brake fluid pressure determination means when the expected vehicle deceleration is lower than a predetermined medium value thereof.

6. A brake control device according to Claim 5, wherein the brake fluid pressure determination means determine the first weighting factor to deceleratedly decrease while the second weighting factor to deceleratedly increase along with increase of the expected vehicle deceleration when the expected vehicle deceleration is higher than the predetermined medium value.

7. A brake control device substantially as hereinbefore descriffiedwith reference to the accompan ing drawings.

Y1 = - Amendments to the claims have been filed as follows 1. A brake control device for a vehicle having wheels and a brake system for the wheels including wheel cylinders for applying a braking force to each corresponding one of the wheels according to a supply of a pressurized brake fluid thereto, a brake pedal adapted to be depressed by a driver, a master cylinder adapted to compress the brake fluid according to a depression of the brake pedal by the driver, motor powered pump for pressurizing the brake fluid, and control means including on-off valves for controlling supply of the brake fluid pressurized by the master cylinder and the brake fluid pressurized by the pump to the wheel cylinders, the device comphising: means for detecting a stroke of the depression of the brake pedal, means for detecting. a pressure of the brake fluid compressed by the master cylinder, and means for determining a pressure of the brake fluid for supply to a selected one or ones of the wheel cylinders under a control of the control means to increase along with increase of the depression stroke of the brake pedal as well as increase of the brake fluid pressure by the master cylinderbyla ing first and second weights on the participation of the depression stroke of the brake Y1 E> pedal in the pressure increase and the participation of the brake fluid pressure by the master cylinder in the pressure increase, respectively, the first weight being decreased while the second weight being 1 increased relative to one another along with increase of the brake fluid pressure determined by the brake fluid pressure determination means.

? A brake control device according to Claim 1, wherein the brake fluid pressure determination means determine the brake fluid pressure supplied to the selected one or ones of the wheel cylinders to correspond to a sum of a first product of a first quantity which increases along with increase of the depression stroke of the brake pedal and a first weighting factor and a second c:- product of a second quantity which increases along with increase of the brake fluid pressure by the master cylinder and a second weighting factor, the first and second weighting factors being varied i n according to a deceleration of the vehicle expected by the brake fluid pressure determined by, the brake fluid pressure determination means such that the first weighting factor decreases while the second weighting factor increases complementarilyto the decrease of the first weighting factor along with increase of the vehicle deceleration expected by the brake fluid pressure determined by the brake fluid pressure determination means.