Brake pressure control device for vehicles

Abstract: A brake pressure control device introduces pump pressure which is produced by a pump (16) into piping which connects a master cylinder (4) and wheel brakes (11, 11′, 12, 12′). The increase, decrease and retention of the wheel brake pressure are effected by utilizing the pump pressure. Absorbers (19, 19′) which consume hydraulic fluid are installed in branches from piping which connects the master cylinder (4) and the wheel brakes (11, 11′, 12, 12′). 4-port 2-position control valves (5, 5′) are installed in the hydraulic passages which connect the master cylinder (4) and the absorbers (19, 19′) and at the inlet port for the pump pressure and at the outlet port to the absorbers (19, 19′). The 4-port 2-position control valves (5, 5′) selectively switch the hydraulic passages in such a manner that when the pump pressure is normal, they render conductive the hydraulic passage which connects the master cylinder (4) and absorbers (19, 19′) but when the pump pressure fails and thereby decreases, they render conductive the hydraulic passage which connects the master cylinder (4) and wheel brakes (11, 11′, 12, 12′).

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a brake pressure control device for vehicles and particularly to a brake pressure control device for vehicles, wherein a pump pressure is introduced into piping which connects a master cylinder and a wheel brake, said pump pressure being utilized for the increase, decrease or retention of the wheel brake pressure. Description of the Prior Art Heretofore, various brake power controls, such as vehicle brake power multiplication action, control power distribution, anti-lock control, traction control on driving wheels, stop retention, vehicle-to-vehicle distance control and obstacle avoidance as effected by automatic brakes, have been performed by controlling the brake working hydraulic pressure by individual devices or individual systems including electronic control devices. However, such brake power controls can be effected by a combination of three states, i.e., increase, decrease and retention of the brake working hydraulic pressure during both brake operation and non-operation. If the brake power controls described above are effected by individual devices or systems, some structural components will overlap each other, bringing about many problems including economic loss, decrease of reliability, decrease of space for mounting in vehicles and increase of vehicle weight. Therefore, coordination of brake power control devices is desired. The simplest means for effecting the increase, decrease and retention of the wheel brake pressure would be to provide a shut-off valve directly in piping which connects the master cylinder and the wheel brake and to introduce pump pressure between the shut-off valve and the wheel brake. And to improve cost/performance ratio, there is known a system wherein the shut-off valve is closed at all times rather than only in emergencies, such as anti-lock and traction control, so that also during normal brake operation the pump pressure adds to the wheel brake by an amount corresponding to the brake operation input to thereby enable brake multiplication action and brake power distribution to be effected. This system is proposed in West German Patent No. 3124755. In this system, if the pump pressure fails, the wheel brake should be pressurized directly by the master cylinder without closing said shut-off valve. This system, however, has a drawback that the pedal assumes a board stamp state (very stiff state) because of non-communication between the master cylinder and the wheel brake which takes place when the shut-off valve is closed. To prevent this, in said known example, as schematically shown in Fig. 4, and absorber which consumes hydraulic fluid is installed between the master cylinder and the shut-off valve to mitigate the board stamp feeling (very stiff feeling) on the pedal. However, if the pump pressure fails, it is necessary to pressurize the wheel brake as well as to feed hydraulic fluid to the absorber, resulting in an increase in the pedal stroke; thus, there is a drawback that the pedal feeling aggravates to a great degree. As to another method of avoiding the board stamp feeling, the same applicant as in this application has proposed in Japanese Patent Application No. 3758/1985 a system comprising spring means installed between the brake pedal and the master cylinder, the resilient force of said spring means being used to mitigate the board stamp feeling, the arrangement being such that when the pump pressure fails, said spring means is retracted to a position where it does not influence pedal effort, so as to maintain the pedal feeling unchanged. With this system, however, not only does the construction become complicated, but also it is necessary to lead the pump pressure to the position of the master cylinder, resulting in as increase in piping cost and a decrease in reliability. A hydraulic brake system is disclosed in DE-A-35 05 410. It is characterized by certain auxiliary valves which are inserted in the brake conduit connecting the brake pressure driving cylinder with the brakes and which are controlled to provide a slippage-adjusted break system. The patent publication DE-A-31 31 856 discloses a brake system including a driving cylinder with a simulator which provides the characteristic of the break system. This simulator is capable for switching up so that the full pedal length is given also in the case of an interruption of the driving pressure. The switching of the simulator is carried by an electro- magnetical valve. Accordingly, the invention is intended to solve the aforesaid problems inherent in the prior art by simple means and has for its object the provision of a brake pressure control device for vehicles according to the preamble of claim 1 which avoids the board stamp feeling on the brake pedal and makes it possible to obtain the same pedal stamp feeling also when the pump pressure fails. Fig. 1 shows the basic concept of the invention, the subject of which is characterized in claim 1. Referring to Fig. 1, the invention is a brake pressure control device for vehicles which introduce pump pressure into piping which connects a master cylinder and a wheel brake, said pump pressure being utilized to effect the increase, decrease and retention of the wheel brake pressure. And an absorber which consumes hydraulic fluid is installed in a branch from piping which connects the master cylinder and wheel brake. Further, switching means is provided which selectively switches the hydraulic passages in such a manner that when the pump pressure is normal, it renders conductive the hydraulic passage which connects the master cylinder and absorber but when the pump pressure fails and thereby decreases, it renders conductive the hydraulic passage which connects the master cylinder and wheel brake. The amount of hydraulic fluid to be consumed by the absorber can be determined as desired. Thus, it is possible to determine this amount of hydraulic fluid such that it approximates the wheel brake pressure. Further, when the pump pressure fails, the switching means shuts off the hydraulic passage which connects the master cylinder and absorber while rendering conductive the hydraulic passage which connects the master cylinder and wheel brake. Therefore, during normal brake operation and also during pump pressure failure, the same pedal feeling can be obtained. Further, any desired feeling setting for failure warning can be freely made. As described above, according to the invention, an absorber is installed in a branch from piping which connects the master cylinder and wheel brake, and switching means which selectively renders conductive the hydraulic passage which connects the master cylinder and absorber or the hydraulic passage which connects the master cylinder and wheel brake is installed. Therefore, it is possible to avoid the board stamp feeling on the brake pedal which has heretofore been a problem and to obtain substantially the same pedal feeling when the pump pressure is normal and also when the pump pressure fails. These objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing the basic concept of the invention; Fig. 2 is a hydraulic circuit diagram showing an embodiment of the invention applied to diagonal split piping; Fig. 3 is a hydraulic circuit diagram showing an embodiment of the invention applied to front-and-rear split piping; and Fig. 4 is a diagram showing the basic concept of an example of a conventional brake pressure control device. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 2 shows a hydraulic circuit showing an embodiment of the invention applied to diagonal split piping. In the figure, if a brake pedal 1 is stamped, the hydraulic fluid in a master cylinder 4 having a reserve tank 3 is pressurized through a push rod having a pedal effort sensor 2. The hydraulic pressure thus produced in the master cylinder 4 passes through 4-port 2-position control valves 5 and 5′ and branches at branch points 6 and 6′ to flow into front and rear brakes. The branch pressures pass through shut-off valves 7, 7′, 8 and 8′ constructed as 2-port 2-position control valves and pressure sensors 9, 9′, 10 and 10′ into wheel brakes 11, 11′, 12 and 12′. Further, it is arranged that the hydraulic brake fluid between the shut-off valves 7, 7′, 8, 8′ and the wheel brakes 11, 11′, 12, 12′ returns to the reserve tank 3 via discharge valves 13, 13′, 14 and 14′ constructed as 2-port 2-position control valves. On the other hand, pump pressure is introduced into the piping which connects the master cylinder 4 and wheel brakes 11, 11′, 12 and 12′. More particularly, the pressure produced by a pump 16 which is driven by an electric motor 15 and draws the hydraulic brake fluid from the reserve tank 3 and pressurizes it, is maintained in a fixed range by a pressure switch 17 and is stored in an accumulator 18. This pressure is also led to the 4-port 2-position control valves 5 and 5′. As shown, absorbers 19 and 19′ which consume hydraulic fluid are connected to the 4-port 2-position control valves 5 and 5′. The wheels have wheel speed sensors 20, 20′, 21 and 21′, respectively. Information from the wheel speed sensors 20, 20′, 21 and 21′, like information from the pedal effort sensor 2 and the pressure sensors 9, 9′, 10, 10′, is led to an electronic control device 22. The state shown in Fig. 2 is one which is assumed during non-brake operation. In this case, the 4-port 2-position control valves 5 and 5′, as shown, render conductive the hydraulic passage which connects the master cylinder 4 and wheel brakes 11, 11′, 12 and 12′ and shut off the hydraulic passage which connects the master cylinder 4 and absorbers 19 and 19′. In this state, if the brake pedal 1 is stamped, the start of brake operation is detected by the pedal effort force sensor 2 and the 4-port 2-position control valves 5 and 5′ are switched to the second position. In this case, the hydraulic passage which connects the master cylinder 4 and wheel brakes 11, 11′, 12 and 12′ is shut off, while the hydraulic passage which connects the master cylinder 4 and absorbers 19 and 19′ is rendered conductive. Therefore, the master cylinder 4 comes to pressurize the absorbers 19 and 19′ only. Further, the pump pressure is introduced into the hydraulic passage leading to the wheel brakes 11, 11′, 12 and 12′. This pump pressure is controlled by suitably switching the inlet valves 7, 7′, 8 and 8′ and the discharge valves 13, 13′, 14 and 14′ while comparing the brake operation input which is detected by the pedal effort sensor 2 with the brake pressure which is detected by the pressure sensors 9, 9′, 10 and 10′. In this way, addition of wheel brake including brake power multiplication action can be made. Further, by making use of the information from the wheel sensors 20, 20′, 21 and 21′, the so-called brake effectiveness control intended to maintain constant the relationship between vehicle deceleration and pedal effort, brake power distribution, anti-lock control, etc. can be effected to a great degree. Also during non-brake operation, the wheel brake 11, 11′, 12 and 12′ can be optionally pressurized, when necessary, by suitably switching the 4-port 2-position control valves 5, 5′, inlet valves 7, 7′, 8 and 8′ and discharge valves 13, 13′, 14 and 14′. Therefore, automatic brake operation for obstacle avoidance and vehicle-to-vehicle distance control, to say nothing of traction control on driving wheels and stop retention, can be made possible by the addition of other sensors. The pedal feeling during brake operation can be optionally determined by suitably selecting the amount of hydraulic fluid to be consumed by the absorbers 19 and 19′. Further, during failure of the power system, this state is detected by the pressure switch 17; thus, by retaining the 4-port 2-position control valves 5 and 5′ in the position shown in Fig. 2, it is possible to pressurize the wheel brakes 11, 11′, 12 and 12′ directly by the hydraulic pressure produced by the master cylinder 4. Fig. 3 is a hydraulic pressure circuit showing another embodiment of the invention applied to front-and-rear split piping. The brake operation input produced by the brake pedal 1 is detected by the pressure sensors 23 and 23′ as a pressure produced by the master cylinder 4. As shown, there are 3-port 2-position pressure-sensitive switching valves 24 and 24′ which use the pump pressure from the pump 16 as a control input. The pressure-responsive switching valves 24, 24′ operate in such a manner that when the pump pressure is less than a fixed value, the pressure-responsive switching valves 24 and 24′ allow the master cylinder 4 to directly pressurize the wheel brakes 11, 11′, 12 and 12′ and that when the pump pressure is normal, they allow the master cylinder 4 to pressurize the absorbers 19 and 19′ only. As shown, there are 3-port 3-position control valves 25 and 26 provided by combining the shut-off and discharge valves associated with the front wheels. There is an inlet valve 27 in the form of a 2-port 2-position control valve for introducing the pump pressure into the brake system associated with the front wheels. Only one pressure sensor 9′ for the rear wheels is provided at a point a little short of the branch point 6′ leading to the right and left wheel brakes. Thus, there is no need for providing a shut-off valve for each of the right and left wheels; only one 3-port 3-position control valve 25′ which is a combination of an inlet valve and a discharge valve is provided. Therefore, when the pump pressure is above a fixed value, the state shown in Fig. 3 is established. And the front wheel brakes 11 and 12 can be independently controlled by suitably switching the 3-port 2-position control valves 25, 26 and 25′ and the inlet valve 27, and under the same pressure the rear wheel brakes 11′ and 12′ can be controlled to respective desired pressures. Furthermore, since any desired pedal feeling can be obtained, various brake power controls are possible as in the embodiment shown in Fig. 2. When the pump pressure is less than the fixed value, the pressure-responsive switching valves 24 and 24′ are switched to render conductive the hydraulic passage which connects the master cylinder 4 and the wheel brakes 11, 12, 11′ and 12′. Therefore, it is possible to add to the wheel brakes by the hydraulic pressure from the master cylinder 4. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.

Claims: A brake pressure control system for vehicle brakes, comprising brake means (11, 11', 12, 12') for braking vehicle wheels, master cylinder means (4) driven by a pedal force for operating said brake means, first fluid conduit means for connection said master cylinder means to said brake means, pump means (15, 16, 18) for generating a pump pressure to operate said brake means, pump pressure detecting means (17) for detecting the pump pressure generated by said pump means, characterized by absorber means (19) for taking up fluid, first switchable valve means (5, 5', 24, 24') operatively inserted in said first fluid conduit means and having a first port connected with said master cylinder means, a second port connected with said brake means and a third port connected with said absorber means, wherein said first port is selectively communicated with one of said second and third ports by the operation of said switchable valve means, second fluid conduit means for connecting said pump means (15, 16, 18) to said first fluid conduit means positioned between said first switchable valve means (5, 5', 24, 24') and said brake means (11, 11', 12, 12'), second switchable valve means (5, 5', 25', 27) operatively inserted in said second fluid conduit means and having a first valve position to permit the pump pressure to enter said first fluid conduit means and a second valve position to prohibit the pump pressure from passing through said second switchable valve means, adjusting means (7, 7', 8, 8', 13, 13', 14, 14', 25, 25', 26) operatively inserted in said first fluid conduit means positioned between the entering portion of the pump pressure and said brake means for adjusting the amount of the pump pressure to be applied to said brake means, input force detecting means (2, 23) for continously detecting the amount of the force manually applied to said master cylinder means, speed detecting means (20, 20', 21, 21') for detecting the speed of a vehicle wheel, and electronic control means (22) for outputting driving signals so controlled in response to the detected signals by said input force detecting means, pump pressure detecting means and speed detecting means; wherein said pump pressure detecting means (17) detects the state in which the pump pressure is in the range over the predetermined value and said input force detecting means (2, 23) detects the pressure of the input force, said electric control means operates said first switchable valve means (5, 5', 24, 24') so as to communicate the first port with the third port and operates said second switchable valve means (5, 5', 25', 27) so as to be in the first valve position and operates said adjusting means (7, 7', 8, 8', 13, 13', 14, 14', 25, 25',26) so as to set the pressure to be applied to said brake means into a desired value in proportion to the amount of force manually applied to said master cylinder means, and wherein said pump pressure detecting means (17) detects the state in which the pump pressure is in the range over the predetermined value and said input force detecting means (2, 23) detects the state in which the input force is zero, said electronic control means (22) operates said first switchable valve means (5, 5',24, 24') so as to communicate the first port with the third port and operates said second switchable valve means (5, 5',25, 27) so as to be in the first valve position and operates said adjusting means (7, 7',8, 8', 13, 13', 14, 14',25, 25',26) so as to set the pressure to be applied to said brake means into a desired value in response to the detected signals by said speed detecting means (20, 20', 21, 21') and the other detecting means. A brake pressure control system of claim 1, wherein said first switchable valve means is a pressure-responsive switching valve (24, 24') adapted to operate in response to a variation in said pump pressure, and serves as said pump pressure detecting means as well. A brake pressure control system of claim 1, wherein said first and second switchable valve means are incorporated into a solenoid operated valve (5, 5') which has a first port connected with said master cylinder means (4), a second port connected with said brake means (11, 11', 12, 12'), a third port connected with said absorber means (19, 19') and a fourth port connected with said pump means (15, 16, 18) and is switchable by the electromagnetic force between a first valve position to communicate the first port with the second port and isolate the third and fourth ports and a second valve position to communicate the first port with the third port and communicate the second port with the fourth port.

Inventors: KOHNO TERUHISA C O ITAMI WORKS, KOHNO, TERUHISA C/O ITAMI WORKS OF SUM.ELEC.IND.
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1987
Main classification: B60T8
IPC codes: B60T8, B60T13, B60T11