GB1566427A

GB1566427A - Hydraulic brake system for motor cycles

Info

Publication number: GB1566427A
Application number: GB5144276A
Authority: GB
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1975-12-27
Filing date: 1976-12-09
Publication date: 1980-04-30
Also published as: JPS5724272B2; DE2558825C2; DE2558825A1; IT1065583B; JPS5281482A

Description

(54) HYDRAULIC BRAKE SYSTEM FOR MOTOR CYCLES (71) We, ALFRED TEVES G.m.b.H., a joint stock Company organised under the Laws of Germany, of 7 Guerickestrasse, 6000 Frankfurt Am Main, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an hydraulic brake system for motor cycles having a hand master cylinder linked to a front-wheel brake and a pedal master cylinder linked to a rear-wheel brake.

In brake systems of this type, the hand master cylinder usually brakes only the front wheel by means of a manually-operated lever disposed on the handle-bar, while the pedal master cylinder brakes only the rear wheel by means of a pedal. During braking, the driver thus has to operate the lever and the pedal simultaneaously so that both wheels are braked. A particular problem with this arrangement is that, in order to achieve the best braking effect during panic" braking, the driver has to activate both hand and pedal master cylinders in such a manner that greatest possible use is made of the coefficient of friction at both wheels. The operator has to concentrate on both lever and pedal simultaneously.In addition, as a result of the relatively high centre of gravity in motor cycles, the braking capability of the two wheels is substantially changed because of the strong shift of axle load occurring during braking. To make this clear, assume that at the beginning of the braking process only the rear wheel is braked, with the driver applying such a measure of force to the pedal that the rear wheel is not overbraked. In this case, he cannot keep applying this pedal force constantly if the front-wheel brake is actuated subsequently. With the brake force at the front wheel increasing and in view of the attendant axle-load shift, the brake force at the rear wheel has to be reduced to avoid overbraking which would immediately cause the driver to be thrown off his cycle.On a surface where the tyres have a good grip a state may be reached in which the rear wheel must not be braked at all since the axle load of the rear wheel approaches zero.

In the journal "Motorrad", issue 13/75, page 94, a braking system is disclosed in which the brake-actuating arrangements are designed as hand and pedal cylinders, with the pedal cylinder activating the rear-wheel and the front-wheel brake with predetermined brake-force distribution, whilst the hand cylinder activates only the front-wheel brake. To achieve this, the front-wheel brake is a dual-circuit brake, that is, the system incorporates two brake discs each with one brake caliper, the one brake caliper being connected to the hand cylinder and the other to the pedal cylinder.

Thus, when the pedal cylinder is actuated, both the front and the rear wheel will be braked, with the brake force being distributed in a predetermined manner. However, this type of brake-force distribution can only cope with a defined load and defined road conditions. As soon as only one of these values changes, the hand cylinder has to be activated as well to achieve the best braking. The same problem as described above is present again, in that the driver has to bring two actuating forces into harmony.

An additional difficulty in this system is that the total braking force of the front wheel depends on both actuating forces. Consequently, if the actuating force at the pedal cylinder is reduced to avoid overbraking of the rear wheel, the braking force at the front wheel will likewise become less which has to be compensated for again by an increase in the actuating force applied to the hand cylinder. It will be obvious that this brake system makes still higher demands on the driver in respect of the balancing of the actuating forces he applies to the pedal and hand cylinders, which means asking too much from the average driver.

According to the present invention there is provided an hydraulic brake system for motor cycles having a hand master cylinder linked to a front-wheel brake and a pedal master cylinder linked to a rear-wheel brake through a pressure reducer unit, which unit controls the pressure applied to the rearwheel brake in dependence on the pressure generated by the hand master cylinder.

In such a brake system, with the pedal master cylinder being activated unchanged, the rear wheel thereby braked will not be overbraked because of the axle-load shift caused by the hand master cylinder actuation. The brake force at the rear wheel is reduced as soon as the hand master cylinder is activated, that is immediately before and during the axle-load shifts occurring. Thus, the reduction of the brake force at the rear wheel is not the late result of the removal of pressure from the rear wheel but the result of the cause of the axle-load shift.

The brake system is such that a reduction in the brake force of the rear-wheel brake is achieved without the existence of a direct link between the hand and pedal master cylinders.

In a preferred embodiment an additional direct connection between the front wheel brake and the pedal master cylinder is also provided. Thus, the hand master cylinder need produce only part of the high brake force necessary at the front wheel. This additional connection enables the system to be designed with greater responsiveness which permits better control of the brake force. The hand master cylinder need be activated only for harmonizing the brakeforce ratio between front and rear wheel in accordance with the friction ratios.

The reducer unit may comprise a sealingly slidable piston including at least three surfaces adapted to be subject to pressure, the first surface thereof being subject to the pedal-cylinder pressure, the second surface being subject to the pressure acting in the opposite direction from the rear-wheel brake, and the third surface being subject to the hand-cylinder pressure, likewise acting in opposition to the pressure on first surface. In this design, the influence of the brake pressure produced by the hand cylinder on the brake pressure produced by the pedal cylinder to be supplied to the rearwheel brake can be easily adjusted by suitably dimensioning the surfaces.The pressure-reducer unit has a valve member closing a passageway between an inlet chamber bounded by the first surface and an outlet chamber bounded by the second surface, and adapted to be pushed open when the piston has reached its end position in which the outlet chamber has its smallest volume; at the same time the valve member acts as a one-way valve inhibiting flow in the direction towards the outlet chamber is disposed in the connecting line between the inlet and outlet chamber, and the piston is urged towards the outlet chamber by a control force. This eliminates the need for designing the pressure-fluid circuit between pedal and hand cylinder with two permanently separated sections.

Because the piston is a stepped piston, the first surface thereof being of smaller area than its second surface, as soon as any braking commences, the rear-wheel brake receives less pressure from the pedal cylinder than the front-wheel brake, thereby roughly considering the axle-load shift thereby caused even if the pedal cylinder alone is activated The axle-load shift caused by the activation of the pedal cylinder is taken into account even better if the stepped piston is biassed in its end position in which the outlet chamber volume is smallest, by a said control force dependent on an axle load of the rear wheel.

An embodiment of the invention is described below with reference to the accompanying drawings, in which: Figure 1 is a schematic view of the structure of the brake system; Figure 2 is a sectional view of a reducer unit adapted for use in the brake system of Figure 1.

In Figure 1, are shown a hand master cylinder 1 and a pedal master cylinder 2 which are conventional master cylinders, with the hand cylinder 1 being activated by a manual control on a handle-bar of a motor cycle to generate a brake pressure by means of the manual force applied by the driver.

The pedal cylinder is activated by the driver's force on a pedal control to generate a brake pressure. Further, the brake system includes a dual-circuit front wheel brake 3, a reducer unit 4, and a rear-wheel brake 5.

The dual-circuit front-wheel brake 3 consists of a brake disc 6 with an associated brake caliper 7 and of a brake disc 8 with an associated brake caliper 9. The rear-wheel brake consists of a brake disc 10 with an associated brake caliper 11.

Master cylinder 1 connects with the brake caliper 7 of front-wheel brake 3 and the reducer unit 4 through a branched line 12.

Pedal cylinder 2 is in communication with reducer unit 4 via a line 13. From reducer unit 4, a line 13' leads to the brake caliper 9 of the front-wheel brake 3, and a line 14 connects with the brake caliper 11 of the rear-wheel brake 5.

The reducer unit 4 is shown in greater detail in Figure 2. It has a housing 15 accommodating sealingly and slidably a stepped piston 16. A first surface 17 of stepped piston 16 forms a bound of an inlet chamber 18, a second surface 19 forms a bound of an outlet chamber 20; and a third surface 21 forms a bound of a control chamber 22. A pressure in inlet chamber 18 acts on the first surface 17 to generate a force urging stepped piston 16 to diminish the volume of chamber 20, whereas the pressures in outlet chamber 20 and control chamber 22 act on the second surface 19 and the third surface 21, respectively, to generate a force on stepped piston 16 urging it to enlarge the volume of chamber 20. An arrow 23 indicates a further force acting on the stepped piston so as to aid the force on surface 17.This force may stem from a return spring in which case it would have no significant influence on the stepped piston, or it may be a preset or axle-load responsive control force. In the mode of operation described later, the control force is assumed to be a preset force.

Stepped piston 16 has also a passageway 24 connecting inlet chamber 18 with outlet chamber 20. In passageway 24 a springloaded valve closure member 25 is disposed which is kept in the open position by bearing upon the housing 15 when piston 16 has reduced chamber 20 to its smallest volume, and which closes passageway 24 as soon as piston 16 moves away from that position.

Inlet chamber 18 is in communication with lines 13 and 13'. Connected to outlet chamber 20 is line 14. Control chamber 22 communicates with line 12.

The mode of operation is the following: As long as no braking takes place, the stepped piston 16 of the reducer unit 4 is positioned as shown in Figure 2. Valve closure member 25 bears on housing 15, and passageway 24 between inlet chamber 18 and outlet chamber 20 is open.

If the pedal cylinder 2 is activated first, the pressure thereby generated is passed through line 13 into inlet chamber 18 thence, via line 13', to brake caliper 9 of the front-wheel brake 3 unchanged. From inlet chamber 18, the pressure is also transmitted through the open passageway 24 into outlet chamber 20 and to brake caliper 11 of the rear-wheel brake 5 via line 14. As a result of the difference in area between surface 17 and surface 19 at stepped piston 16, a force is generated which acts in opposition to the control force 23.When the pressure in inlet chamber 18 and outlet chamber 20 is such that the net resulting force overcomes said control force 23, stepped piston 16 will move so as to enlarge chamber 20, causing valve closure member 25 to close passageway 24, so that only a pressure which is reduced in accordance with the surface area ratio between surfaces 17 and 19 will be applied to brake caliper 11 of the rear-wheel brake 5.

If, for any reason whatsoever, for instance because the rear wheel is approaching a locked-wheel condition, the pressure generated by the pedal master cylinder cannot be increased further, the braking capability of the front wheel is not made use of fully in the majority of road conditions occurring.

In this case, the driver can operate the hand cylinder 1 to generate a braking pressure acting on brake caliper 7 of the front-wheel brake 3, thereby increasing the braking force at the front wheel. However, this braking pressure is also fed to control chamber 22 where acting on surface 21 it urges stepped piston 16 against the direction of force 23, thereby causing said piston to be displaced downwards until the pressures prevailing in inlet chamber 18, outlet chamber 20 and control chamber 22 are balanced again relative to the control force. This can only be achieved by reducing the pressure in outlet chamber 20 as long as the driver does not change the force applied to the pedal cylinder 2.Thus, as a result of the activation of hand cylinder 1 and the attendant additional application of brake caliper 7 of the front-wheel brake 3, the pressure supplied to brake caliper 11 of the rear-wheel brake 5 will be reduced simultaneously. Therefore, there is no need for an axle-load shift caused by the additional braking force at the front-wheel brake 3 to be compensated for by the driver reducing the force acting on the pedal cylinder 2 to avoid locking of the rear wheel.

WHAT WE CLAIM IS: 1. An hydraulic brake system for a motor cycle having a hand master cylinder linked to a front-wheel brake and a pedal master cylinder linked to a rear-wheel brake through a pressure reducer unit, which unit controls the pressure applied to the rearwheel brake in dependence on the pressure generated by the hand master cylinder.

2. A brake system as claimed in claim 1, wherein the pedal master cylinder is also linked to the front-wheel brake.

3. A brake system as claimed in claim 2 and wherein the reducer unit has a sealingly slidable piston including at least three surfaces adapted to be subjected to pressure, a first surface being subjected to pressure from the pedal master cylinder, a second surface being subjected to the brake pressure of the rear-wheel brake acting in the opposite direction to the pressure on the first surface, and a third surface being subjected to pressure from the hand master cylinder, likewise acting in the opposite direction to the pressure on the first surface.

4. A brake system as claimed in claim 3, in which the reducer unit has a valve closure member closing a passageway between an

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. accommodating sealingly and slidably a stepped piston 16. A first surface 17 of stepped piston 16 forms a bound of an inlet chamber 18, a second surface 19 forms a bound of an outlet chamber 20; and a third surface 21 forms a bound of a control chamber 22. A pressure in inlet chamber 18 acts on the first surface 17 to generate a force urging stepped piston 16 to diminish the volume of chamber 20, whereas the pressures in outlet chamber 20 and control chamber 22 act on the second surface 19 and the third surface 21, respectively, to generate a force on stepped piston 16 urging it to enlarge the volume of chamber 20. An arrow 23 indicates a further force acting on the stepped piston so as to aid the force on surface 17.This force may stem from a return spring in which case it would have no significant influence on the stepped piston, or it may be a preset or axle-load responsive control force. In the mode of operation described later, the control force is assumed to be a preset force. Stepped piston 16 has also a passageway 24 connecting inlet chamber 18 with outlet chamber 20. In passageway 24 a springloaded valve closure member 25 is disposed which is kept in the open position by bearing upon the housing 15 when piston 16 has reduced chamber 20 to its smallest volume, and which closes passageway 24 as soon as piston 16 moves away from that position. Inlet chamber 18 is in communication with lines 13 and 13'. Connected to outlet chamber 20 is line 14. Control chamber 22 communicates with line 12. The mode of operation is the following: As long as no braking takes place, the stepped piston 16 of the reducer unit 4 is positioned as shown in Figure 2. Valve closure member 25 bears on housing 15, and passageway 24 between inlet chamber 18 and outlet chamber 20 is open. If the pedal cylinder 2 is activated first, the pressure thereby generated is passed through line 13 into inlet chamber 18 thence, via line 13', to brake caliper 9 of the front-wheel brake 3 unchanged. From inlet chamber 18, the pressure is also transmitted through the open passageway 24 into outlet chamber 20 and to brake caliper 11 of the rear-wheel brake 5 via line 14. As a result of the difference in area between surface 17 and surface 19 at stepped piston 16, a force is generated which acts in opposition to the control force 23.When the pressure in inlet chamber 18 and outlet chamber 20 is such that the net resulting force overcomes said control force 23, stepped piston 16 will move so as to enlarge chamber 20, causing valve closure member 25 to close passageway 24, so that only a pressure which is reduced in accordance with the surface area ratio between surfaces 17 and 19 will be applied to brake caliper 11 of the rear-wheel brake 5. If, for any reason whatsoever, for instance because the rear wheel is approaching a locked-wheel condition, the pressure generated by the pedal master cylinder cannot be increased further, the braking capability of the front wheel is not made use of fully in the majority of road conditions occurring. In this case, the driver can operate the hand cylinder 1 to generate a braking pressure acting on brake caliper 7 of the front-wheel brake 3, thereby increasing the braking force at the front wheel. However, this braking pressure is also fed to control chamber 22 where acting on surface 21 it urges stepped piston 16 against the direction of force 23, thereby causing said piston to be displaced downwards until the pressures prevailing in inlet chamber 18, outlet chamber 20 and control chamber 22 are balanced again relative to the control force. This can only be achieved by reducing the pressure in outlet chamber 20 as long as the driver does not change the force applied to the pedal cylinder 2.Thus, as a result of the activation of hand cylinder 1 and the attendant additional application of brake caliper 7 of the front-wheel brake 3, the pressure supplied to brake caliper 11 of the rear-wheel brake 5 will be reduced simultaneously. Therefore, there is no need for an axle-load shift caused by the additional braking force at the front-wheel brake 3 to be compensated for by the driver reducing the force acting on the pedal cylinder 2 to avoid locking of the rear wheel. WHAT WE CLAIM IS:

1. An hydraulic brake system for a motor cycle having a hand master cylinder linked to a front-wheel brake and a pedal master cylinder linked to a rear-wheel brake through a pressure reducer unit, which unit controls the pressure applied to the rearwheel brake in dependence on the pressure generated by the hand master cylinder.

inlet chamber of which the first surface forms a bound and an outlet chamber of which the second surface forms a bouund, and adapted to be opened when the piston reaches the position in which the outlet chamber has its smallest volume.

5. A brake system as claimed in claim 4, in which the valve closure member also acts as a one way valve inhibiting flow from the passageway into the outlet chamber, and in which the piston is urged to diminish the volume of the outlet chamber by a control force.

6. A brake system as claimed in any one of claims 3, 4 or 5, in which the piston is a stepped piston, the first surface thereof being smaller in area than the second surface.

7. A brake system as claimed in claim 6 as appendant to claim 5, in which the stepped piston is urged to the position in which the outlet chamber volume is smallest by the control force.

8. A brake system as claimed in claim 7, wherein the control force depends on an axle load of the rear wheel.

9. A hydraulic brake system for motor cycles having a hand master cylinder linked to a front-wheel brake, and a pedal master cylinder linked to a rear-wheel brake, substantially as described with reference to the accompanying drawings.