SIMPLIFIED HYDRAULIC BRAKING SYSTEM FOR AUTOMOBILES WITH ANTI-LOCK BRAKING FUNCTION

Abstract

Hydraulic braking system of a motor vehicle with anti-lock function, comprising a control master cylinder (2) delivering pressure to wheel brakes (6, 8, 12), a rotation speed sensor for each wheel, brake charging solenoid valves (20, 30, 40) allowing pressure to enter these brakes (6, 8, 12) and discharge solenoid valves (22, 32, 42) allowing it to exit, and comprising between the master cylinder (2) and the brake of each wheel (6, 8, 12) a charging solenoid valve (20, 30, 40), and in parallel a pumpless discharge circuit arranged in parallel, comprising successively from the wheel brake (6, 8, 12) a discharge solenoid valve (22, 32, 42), a pressure accumulator (24, 44), then a non-return valve (26, 46) leaving the passage to the master cylinder (2). Figure 1

Description

Title of the invention: SIMPLIFIED HYDRAULIC BRAKING SYSTEM FOR MOTOR VEHICLES WITH ANTI-LOCK BRAKING FUNCTION

[0001] The present invention relates to a simplified hydraulic braking system for a motor vehicle comprising an anti-lock function for the wheels, as well as a motor vehicle equipped with such a braking system and a method of operating this braking system.

[0002] A known type of hydraulic braking system comprising an anti-lock function, called "anti-blocking system" in English, "ABS" for short, presented in particular by document EP-A1-2396203, comprises a master cylinder controlled by a brake pedal, equipped with an electromechanical assistance which sends pressure to each brake by passing successively through two normally open supply solenoid valves.

[0003] If a wheel slows down too much, as detected by a rotational speed sensor, potentially causing the wheel to lock up, a relief pump located in parallel with the second supply solenoid valve draws a volume of fluid from the brake of that wheel via a relief solenoid valve, which opens to reduce the volume in the brake. This results in a decrease in brake pressure, limiting its braking force and allowing the wheel to recover the desired rotational speed.

[0004] By applying successive and rapid cycles in the brake of pressure increase and decrease, an average regulation of the braking power is obtained which avoids wheel lock-up, while maintaining the best possible braking according to the grip conditions.

[0005] This type of hydraulic braking system requires an electronic computer which receives impulses from each wheel sensor giving a signal at a frequency representing the rotation speed, and from various other sensors giving information such as temperature, or pressure in different places in the circuit, in order to deduce the commands to be delivered to the different controlled components.

[0006] In particular, the computer controls the discharge pump, the electromechanical assistance of the master cylinder, all solenoid valves, as well as check valves and additional pressure accumulators required for this circuit.

[0007] However, this type of hydraulic system comprises numerous components, particularly complex components such as the electromechanical assistance of the The master cylinder, two discharge pumps for two independent circuits, and the numerous solenoid valves and check valves to be controlled, require an electronic computer with large capacities to follow a large number of inputs and outputs, and to provide sufficiently fast reaction times to obtain the fine control of the brakes ensuring the safety of the vehicle.

[0008] Generally speaking, known anti-lock functions usually require one or more relief pumps to reduce the volume and pressure of fluid in each brake, which provides useful regulation accuracy for heavy vehicles, but results in high complexity, mass and size, and uses a computer with significant capabilities which add complexity and cost.

[0009] Moreover, to obtain the reliability of the whole, it is necessary to choose quality components and to develop fairly heavy computer programs, which poses problems of complexity of the whole and increases costs.

[0010] In practice, these hydraulic systems, designed for conventional motor vehicles, present significant mass and bulk with all their components, posing adaptation problems for smaller and lighter vehicles, particularly urban vehicles known as "cyclecars," which have low power and limited top speed. Furthermore, the cost of these hydraulic systems is too high relative to the production cost of this type of light vehicle.

[0011] The present invention is intended in particular to avoid these prior art problems, especially for light electric vehicles.

[0012] For this purpose, it proposes a hydraulic braking system for motor vehicles with anti-lock function, comprising a control master cylinder delivering pressure to wheel brakes, a rotation speed sensor for each wheel, brake charging solenoid valves allowing pressure to enter these brakes and discharge solenoid valves allowing it to exit, this system being remarkable in that between the master cylinder and the brake of each wheel, it includes a charging solenoid valve, and in parallel, a pumpless discharge circuit, comprising successively from the wheel brake a discharge solenoid valve, a pressure accumulator, then a non-return valve allowing passage to the master cylinder.

[0013] An advantage of this hydraulic system is that, without including a discharge pump, it directly achieves, by opening the discharge solenoid valve, the reduction of pressure in a brake which evacuates a volume of fluid towards the accumulator, while the non-return valve remains blocked because of the greater pressure coming from the master cylinder during braking.

[0014] Subsequently, the non-return valve opens automatically when the brake pedal is released with a pressure in the master cylinder that drops, which allows this valve to open, allowing the accumulator to be emptied in order to prepare for the next operation of the anti-lock function.

[0015] The braking system comprises a limited number of components to reduce pressure in a brake, which are simple and easy to control, without complex and expensive components such as the pump with its motor, comprising for each circuit, to one brake or to the two brakes of the same axle, only two solenoid valves, a pressure accumulator and a non-return valve.

[0016] Compared to prior art braking systems, reduced mass and size are obtained, and complex and expensive components are eliminated, resulting in reliability at a significantly reduced cost.

[0017] The hydraulic system, according to the invention, may further comprise one or more of the following characteristics, which may be combined with each other.

[0018] Advantageously, the hydraulic system includes the same charging solenoid valve and the same discharge circuit also supplying two wheel brakes of the same axle.

[0019] In this case, advantageously, the two equally supplied wheel brakes are brakes of a rear axle of the vehicle.

[0020] Advantageously, the hydraulic system includes for two wheel brakes of the same axle a discharge solenoid valve specific to each of these brakes, then an accumulator and a check valve which are common.

[0021] Advantageously, at rest the charging solenoid valves are normally open and the discharging solenoid valves are normally closed.

[0022] The invention also relates to a motor vehicle comprising a hydraulic braking circuit, remarkable in that this circuit is part of a hydraulic system comprising any one of the preceding characteristics.

[0023] The invention also relates to a method of operating a hydraulic system comprising any one of the preceding characteristics, remarkable in that in the event of detection of a slowdown of a wheel exceeding a speed difference threshold, it begins by closing the charging solenoid valve of this wheel while leaving the discharge solenoid valve open.

[0024] Advantageously, if the wheel's deceleration does not then decrease, it opens the discharge solenoid valve of that wheel.

[0025] Advantageously, if the wheel slowing then decreases, it closes the discharge solenoid valve of that wheel.

[0026] Advantageously, if the deceleration of the wheel then no longer exceeds the speed difference threshold, it opens the charging solenoid valve of that wheel.

[0027] The invention will be better understood and other features and advantages will become more apparent upon reading the following description, given by way of example, with reference to the accompanying drawings in which:

[0028] [Fig-1] presents a diagram of the circuit of a hydraulic braking system according to the invention;

[0029] [Fig.2] presents this circuit with first a limitation of the pressure rise of a front brake in case of risk of wheel lockup;

[0030] [Fig.3] presents this circuit with then a drop in the pressure of this front brake if the risk of his front wheel locking up persists;

[0031] [Fig.4] shows this circuit with a rise in front brake pressure if the risk Blockage decreases;

[0032] [Fig.5] presents this circuit at the end of the risk of blocking this wheel.

[0033] The [Fig.1] shows on a motor vehicle a brake master cylinder 2 controlled by a brake pedal, sending pressure on two independent circuits each linked to an axle, comprising a front brake circuit 4 which independently supplies a brake of a first front wheel 6 and a brake of a second front wheel 8, and a rear brake circuit 10 which equally controls in parallel the brakes 12 of the two rear wheels.

[0034] In particular, the vehicle may be a light urban vehicle of the cyclecar type, having limited dimensions, a reduced mass and low power giving a low maximum speed, which justifies a simplified hydraulic braking system with a reduced cost for disc or drum brakes.

[0035] The front brake circuit 4 includes, coming from the master cylinder 2, a first part comprising a first charging solenoid valve 20 which supplies the front first wheel brake 6, and in parallel a first discharge solenoid valve 22, then a front pressure accumulator 24, and finally a front check valve 26 which allows free passage in the direction of return towards the master cylinder and prohibits it in the other direction.

[0036] The front brake circuit 4 includes a second part comprising a second charging solenoid valve 30 which supplies the second front wheel brake 8, and in parallel a second discharge solenoid valve 32, then a return through the same front pressure accumulator 24 and then through the same front check valve 26.

[0037] The rear brake circuit 10 includes, coming from the master cylinder 2, a third charging solenoid valve 40 which supplies equally to the two brakes of the rear wheels 12, and in parallel a third discharge solenoid valve 42, then a rear pressure accumulator 44, and finally a rear check valve 46 which allows free passage in the direction of return to the master cylinder and prohibits it in the other direction.

[0038] The charging solenoid valves 20, 30, 40 are normally conducting and the discharging solenoid valves 22, 32, 42 are normally closed; a setpoint current that activates them reverses their position.

[0039] Each wheel has a rotational speed sensor that sends a signal to an electronic control unit (ECU) which checks the consistency between the different received speeds. These speeds may contain slight discrepancies due, for example, to differences in load on each wheel, in order to determine normal operation without risk of locking. If a wheel's speed is measured to be too low, for example, with a deviation greater than 10% from the average of the other wheels, or a zero speed, the ECU then detects a risk of that wheel locking.

[0040] During braking without risk of wheel lock-up, the master cylinder 2 sends a front control pressure to the front brake circuit 4 which is transmitted to each front wheel brake 6, 8, and a rear control pressure to the rear brake circuit 10 which is transmitted to the two rear wheels 12. With the relief solenoid valves 22, 32, 42 closed, the braking of all wheels fully reproduces the pressure requested by the driver on the brake pedal.

[0041] The [Fig.2] presents from the state shown [Fig. 1], in case of excessive slowdown Important of the first front wheel losing traction, indicating a risk of locking, the activation of the first charging solenoid valve 20 which closes the pressure inlet from the master cylinder 2. This closure in particular prevents a rise in pressure from the master cylinder 2 if the driver increases the force applied to the pedal.

[0042] Constant pressure on the front first wheel brake 6 is maintained as long as the driver keeps the brake pedal in the same position with the demand for the same braking intensity, or at the end of braking when the vehicle is stopped.

[0043] The [Fig.3] presents from the state shown [Fig.2], in case of rotational speed of the first front wheel which continues to decrease, the first charging solenoid valve 20 remaining closed, the activation of the first discharging solenoid valve 22 which opens it and releases a small amount of fluid from the first front wheel brake 6 in order to reduce its braking torque.

[0044] In parallel, the rotational speed of the first front wheel is always measured to check if it is rising again; if not, the activation of the first discharge solenoid valve 22 continues to further reduce the braking pressure until the wheel speed rises again.

[0045] Since the return pressure of the fluid removed from the front first wheel brake 6 is less than the front brake pressure delivered by the master cylinder 2, the front non-return valve 26 remains closed, and this fluid goes into the front pressure accumulator 24.

[0046] In the event of detection of excessive deceleration of a rear wheel, the third discharge solenoid valve 42 is activated in the same way, which reduces the braking torque of both rear wheels at the same time, presenting brakes 12 supplied in the same way.

[0047] The circuit presented, comprising a common control for the brakes of the two rear wheels 12, provides a reduction in the number of components and a simplification giving a common control of the rear wheels which may be sufficient on light vehicles.

[0048] Alternatively, a rear brake circuit 10 identical to the front brake circuit 4 can be made with individual control of the braking of each wheel, which will have a slightly higher cost.

[0049] Figure 4 shows, starting from the state shown in Figure 3, that if the rotational speed of the first front wheel begins to increase, indicating a braking level to be maintained, the first discharge solenoid valve 22 is deactivated, closing it, while the first charging solenoid valve 20 remains activated and closed. This establishes a constant pressure in the brake of the first front wheel 6 at a sufficiently low level suitable for the wheel's grip, thus maintaining vehicle braking with that wheel.

[0050] Figure 5 shows, starting from the state shown in Figure 4, that if the rotational speed of the first front wheel returns to match that of the other wheels, the first charging solenoid valve 20 is deactivated and opens. The braking pressure of the first circuit PI, supplied by the master cylinder 2, increases the pressure in the brake of the first front wheel 6.

[0051] If the rotational speed of the first front wheel remains normal, indicating a resumption of grip of this wheel, this state is maintained, whereas if this speed resumes a decrease too much, the cycle presented from [Fig.2] is restarted, then the following steps to reduce this pressure.

[0052] During the subsequent complete release of the brake pedal, which gives control pressures that fall, a pressure is then obtained in the accumulators 24, 44 higher than these control pressures, which allows the non-return valves 26, 46 to open, emptying the accumulators 24, 44, with a return to the reservoir of the master cylinder 2.

[0053] In the event of failure of the anti-lock function, for example with an electrical problem, all the solenoid valves return to their rest position and the vehicle's braking is maintained but without this function.

[0054] An anti-lock braking function is achieved in a very simple manner, with a reduced number of inexpensive and reliable components. Furthermore, unlike certain components of prior art braking systems, requiring special adaptations depending on the type of vehicle, with high development costs, the system according to the invention uses only standard components produced in large series, without special adaptation to the type of vehicle, which greatly reduces costs.

Claims

Demands

1. A hydraulic braking system for a motor vehicle with an anti-lock function, comprising a control master cylinder (2) delivering pressure to wheel brakes (6, 8, 12), a rotational speed sensor for each wheel, brake charging solenoid valves (20, 30, 40) allowing pressure to enter these brakes (6, 8, 12) and discharge solenoid valves (22, 32, 42) allowing it to exit, characterized in that between the master cylinder (2) and the brake of each wheel (6, 8, 12) it comprises a charging solenoid valve (20, 30, 40), and in parallel a pumpless discharge circuit arranged in parallel, comprising successively, starting from the wheel brake (6, 8, 12), a discharge solenoid valve (22, 32, 42), a pressure accumulator (24, 44), and then a check valve anti-return (26, 46) allowing passage to the master cylinder (2).

2. Hydraulic system according to claim 1, characterized in that it comprises the same charging solenoid valve (20, 30, 40) and the same discharge circuit to also supply two wheel brakes (12) of the same axle.

3. Hydraulic system according to claim 2, characterized in that the two equally supplied wheel brakes (12) are brakes of a rear axle of the vehicle.

4. Hydraulic system according to any one of the preceding claims, characterized in that it comprises for two wheel brakes of the same axle (6, 8) a relief solenoid valve (22, 32) specific to each of these brakes (6, 8), then an accumulator (24) and a check valve (26) which are common.

5. Hydraulic system according to any one of the preceding claims, characterized in that at rest the charging solenoid valves (20, 30, 40) are normally open and the discharging solenoid valves (22, 32, 42) are normally closed.

6. Motor vehicle comprising a hydraulic braking circuit, characterized in that this circuit is part of a hydraulic system according to any one of the preceding claims.

7. A method of operating a hydraulic system according to any one of claims 1 to 5, characterized in that, upon detection of a slowdown of a wheel exceeding a speed difference threshold, it begins by closing the charging solenoid valve (20, 30, 40) of this wheel by leaving the discharge solenoid valve (22, 32, 42) open.

8. A method of operation according to claim 7, characterized in that if the slowing of the wheel does not then decrease, it opens the discharge solenoid valve (22, 32, 42) of this wheel.

9. A method of operation according to claim 8, characterized in that if the slowing of the wheel then decreases, it closes the discharge solenoid valve (22, 32, 42) of this wheel.

10. A method of operation according to claim 9, characterized in that if the slowing of the wheel then no longer exceeds the speed difference threshold, it opens the charging solenoid valve (20, 30, 40) of this wheel.

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