Master cylinder device

A master cylinder device includes a reservoir tank, a master cylinder, a piston, and a pair of cup seals. The master cylinder includes a cylinder body having a cylinder chamber and a master port. The piston is inserted into the cylinder chamber, and has a relief port that communicates with the master port. The cup seals are provided on an inner circumference of the cylinder chamber, being positioned in front and rear of the master port, and seals a space between the inner circumference of the cylinder chamber and an outer circumference of the piston. The relief port is closed by the front cup seal, as the piston moves forward, to generate brake fluid pressure in a brake fluid in a hydraulic chamber. The relief port is tilted from a front side to a rear side, from the outer circumference toward an inner circumference of the piston.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Japanese Patent Application No. 2019-193211 filed on Oct. 24, 2019, the entire contents of which are hereby incorporated by reference.

BACKGROUND

The technology relates to a master cylinder device having a relief port that is provided in a piston and communicates with a reservoir tank.

As a plunger master cylinder, Japanese Unexamined Patent Application Publication (JP-A) No. 2005-273714 discloses a master cylinder in which a cup seal is fixed to a cylinder and a relief port is provided in a piston. When a driver depresses a brake pedal, the piston slides, causing the relief port to pass by the cup seal. Thus, a pressure chamber is cut off from a path communicating with a reservoir, and brake fluid pressure is generated, causing a brake fluid to be sent under pressure to wheel cylinders.

JP-A No. 2017-197052 discloses an automatic brake device interposed between a master cylinder and wheel cylinders. In response to an instruction from a device such as a side slip prevention device or an automatic emergency brake device, the automatic brake device drives an electric pump to supply brake fluid pressure to the wheel cylinders, thereby activating a brake regardless of a brake operation performed by a driver. Examples of the side slip prevention device include vehicle dynamics control (VDC) and electronic stability control (ESC).

SUMMARY

An aspect of the technology provides a master cylinder device including a reservoir tank, a master cylinder, a piston, and a pair of cup seals. The master cylinder includes a cylinder body. The cylinder body has a cylinder chamber and a master port that is open to an inner circumference of the cylinder chamber and communicates with the reservoir tank. The piston is configured to be inserted into the cylinder chamber to move back and forth in a front-rear direction, and has a relief port that communicates with the master port. The pair of cup seals is provided on the inner circumference of the cylinder chamber, with the cup seals being positioned in front and rear of the master port in an axial direction of the cylinder chamber, and is configured to seal a space between the inner circumference of the cylinder chamber and an outer circumference of the piston. The relief port is configured to be closed by the cup seal provided on a front side in a movement direction of the piston, as the piston moves forward in the cylinder chamber, to generate brake fluid pressure in a brake fluid that is stored in a hydraulic chamber defined by the cylinder chamber and the piston. The relief port is tilted from the front side to a rear side in the movement direction of the piston, from the outer circumference toward an inner circumference of the piston.

DETAILED DESCRIPTION

As illustrated inFIG. 1, a master cylinder device1may include a master cylinder2and a reservoir tank3that is coupled to the master cylinder2. The master cylinder2may generate brake pressure. In one example, the reservoir tank3may be fixedly installed on an upper surface of the master cylinder2. The reservoir tank3may store a brake fluid.

The master cylinder2may be a plunger tandem master cylinder including a cylinder body2a. A cylinder chamber4of the cylinder body2amay have an opening at one end. A secondary piston5and a primary piston6may be inserted into the cylinder chamber4via the opening. A secondary support shaft7extendable in its axial direction may be interposed between the secondary piston5and a front end of the cylinder chamber4. A secondary return spring8may be interposed between retainers provided at both ends of the secondary support shaft7.

A primary support shaft9extendable in its axial direction may be interposed between the primary piston6and the secondary piston5. A primary return spring10may be interposed between retainers provided at both ends of the primary support shaft9. Although not illustrated, a push rod may be inserted into the primary piston6from a rear end, protruding from the cylinder body2a, of the primary piston6. The push rod may be coupled, via a servo mechanism, to a brake pedal to be depressed by a driver.

In a state in which the pistons5and6are inserted into the cylinder chamber4, the secondary piston5and a front wall4aof the cylinder chamber4may be separated from each other by a predetermined distance, under urging force of the secondary return spring8. The secondary piston5and the primary piston6may be separated from each other by a predetermined distance, under urging force of the primary return spring10.

On the secondary piston5side of an inner circumference of the cylinder chamber4, a pair of first and second secondary cup grooves4band4cmay be provided with a predetermined interval therebetween. On the primary piston6side of the inner circumference of the cylinder chamber4, a pair of first and second primary cup grooves4dand4emay be provided with a predetermined interval therebetween.

A secondary pressure (S.P) cup11may be installed in the first secondary cup groove4b, and a pressure (Pr) cup12may be installed in the second secondary cup groove4c. The cups11and12may each have a cup-shaped cross-section and include an inner circumference (inner side surface), an outer circumference (outer side surface), and a cup bottom joining the inner circumference and the outer circumference. The cup bottom may configure the back of the cup, and may also be referred to as a rear part for the secondary pressure cup11. The cups11and12may be provided in a state in which the respective cup bottoms are opposite to each other. A primary pressure (P.P) cup13may be installed in the first primary cup groove4d, and a primary supply (P.S) cup14may be installed in the second primary cup groove4e. The cups13and14may each have a cup-shaped cross-section. Each of the cups13and14may be provided in a state in which its opening faces forward and its cup bottom is positioned in the rear. The cup bottom may also be referred to as a rear part for the primary pressure cup13. In one embodiment, the cups11to14may serve as a “cup seal”.

The cylinder body2amay have a secondary master port4fand a primary master port4g. The secondary master port4fmay be provided in the cylinder chamber4between the S.P cup11and the Pr cup12. The primary master port4gmay be provided in the cylinder chamber4between the P.P cup13and the P.S cup14. In one embodiment, the master ports4fand4gmay serve as a “master port”. The master ports4fand4gmay communicate with the reservoir tank3. In some embodiments, a “port” may also be referred to as a “through hole”.

A space between an outer circumference of the secondary piston5and the inner circumference of the cylinder chamber4may be sealed by the cups11and12. A space between an outer circumference of the primary piston6and the inner circumference of the cylinder chamber4may be sealed by the cups13and14.FIG. 1illustrates the master cylinder2in a brake released state in which the brake pedal is undepressed.

In this state, a secondary relief port5aprovided in the secondary piston5may be open toward the rear part of the S.P cup11, as illustrated inFIG. 2. A primary relief port6aprovided in the primary piston6may be open toward the rear part of the P.P cup13, as illustrated inFIG. 3.FIG. 2illustrates a portion indicated by “II” inFIG. 1, andFIG. 3illustrates a portion indicated by “III” inFIG. 1.

In the cylinder chamber4, a space between the secondary piston5and the front wall4amay be sealed by the S.P cup11to configure a secondary hydraulic chamber21. Moreover, a space between the secondary piston5and the primary piston6may be sealed by the cups12and13to configure a primary hydraulic chamber22, as illustrated inFIG. 3. Consequently, in the state in which the brake pedal is undepressed as illustrated inFIG. 1, the hydraulic chamber21may communicate with the reservoir tank3via the relief port5aand the master port4f, and the hydraulic chamber22may communicate with the reservoir tank3via the relief port6aand the master port4g.

A secondary inlet and outlet port21amay be provided on the inner circumference of the cylinder chamber4on the secondary hydraulic chamber21side. A primary inlet and outlet port22amay be provided on the inner circumference of the cylinder chamber4on the primary hydraulic chamber22side. The inlet and outlet ports21aand22amay communicate with a brake fluid pressure circuit of a known automatic brake device. In some embodiments, the inlet and outlet ports21aand22amay communicate with a brake fluid pressure circuit of an automatic brake device disclosed in JP-A No. 2017-197052. The brake fluid pressure circuit may communicate with the wheel cylinder of a brake caliper provided for each wheel.

A positional relationship of the secondary relief port5awith respect to the S.P cup11in the axial direction may be the same as a positional relationship of the primary relief port6awith respect to the P.P cup13in the axial direction. Consequently, when the driver depresses the brake pedal, the pistons5and6may slide, causing the relief ports5aand6ato be closed at the same time by the S.P cup11and the P.P cup13, respectively. This raises brake fluid pressure in the secondary hydraulic chamber21and the primary hydraulic chamber22, causing the brake fluid to be discharged from the inlet and outlet ports21aand22a. When the driver releases force applied to the brake pedal, the pistons5and6may be returned to their initial positions under the urging force of the return springs8and10, respectively, causing the relief ports5aand6ato be opened at the same time.

As illustrated inFIG. 2, the relief port5amay be tilted from a front side toward a rear side (base end side) in a movement direction of the piston5, from the outer circumference toward an inner circumference of the piston5. As illustrated inFIG. 3, the relief port6amay be tilted from a front side toward a rear side (base end side) in a movement direction of the piston6, from the outer circumference toward an inner circumference of the piston6. Each of the relief ports5aand6amay be tilted at a predetermined angle θ with respect to an axial direction of the cylinder chamber4. In the example embodiment, the axial direction of the cylinder chamber4may be parallel to axial directions of the cylinder body2aand the pistons5and6. The predetermined (tilt) angle θ may be an angle, other than a right angle, provided from the front side toward the rear side in the movement direction of each of the pistons5and6, from the outer circumference toward the inner circumference of each of the pistons5and6. The predetermined angle θ may be set as appropriate for each type of a vehicle to be equipped with the master cylinder device1and the automatic brake device.

Furthermore, a part11aof the inner circumference at the back (i.e., the rear part) of the cup11may be exposed to the relief port5ain an open state. A part13aof the inner circumference at the back (i.e., the rear part) of the cup13may be exposed to the relief port6ain an open state. Hereinafter, these parts11aand13amay be referred to as exposed parts11aand13afor convenience.

Now, description will be given on operation of the master cylinder device1based on such a configuration. Assume a case where the vehicle equipped with the master cylinder device1and the automatic brake device is traveling. When the automatic brake device is activated and the electric pump supplies the brake fluid to the wheel cylinder of the brake caliper provided for each wheel, the wheel cylinder may operate the brake caliper to generate brake force for each wheel, thereby decelerating the vehicle.

When the automatic brake device supplies the brake fluid to the wheel cylinder, negative pressure may be generated upstream, e.g., on the reservoir tank3side. The brake fluid stored in the reservoir tank3may thus be sucked toward the primary master port4gand the secondary master port4fprovided in the cylinder body2aof the master cylinder2.

The brake fluid sucked toward the primary master port4gmay flow into the cylinder chamber4on the outer circumference of the primary piston6, which is sealed by the P.P cup13and the P.S cup14. The brake fluid sucked toward the secondary master port4fmay flow into the cylinder chamber4on the outer circumference of the secondary piston5, which is sealed by the S.P cup11and the Pr cup12.

The brake fluid that has flowed into the cylinder chamber4on the outer circumference of the primary piston6may pass through the primary relief port6aprovided in the primary piston6, to be sucked into the primary hydraulic chamber22. The brake fluid may thereafter flow to the brake fluid pressure circuit of the automatic brake device via the primary inlet and outlet port22a. The brake fluid that has flowed into the cylinder chamber4on the outer circumference of the secondary piston5may pass through the secondary relief port5aprovided in the secondary piston5, to be sucked into the secondary hydraulic chamber21. The brake fluid may thereafter flow to the brake fluid pressure circuit of the automatic brake device via the secondary inlet and outlet port21a.

Assume a case where, as illustrated inFIG. 5, a relief port104provided in a piston103is not tilted, being perpendicular to an axial direction of a cylinder chamber. In this case, when the brake fluid flows through the relief port104, the brake fluid generates negative pressure in the relief port104. This causes an exposed part102aon an inner circumference of a cup seal102to be pulled to bulge toward the relief port104. The cup seal102is attached to a cylinder101.

Suction caused by the automatic brake device being activated by an instruction from the side slip prevention device does not cause the exposed part102aof the cup seal102to greatly bulge toward the relief port104. However, when causing the own vehicle to suddenly stop, as with automatic emergency braking, the automatic brake device supplies the brake fluid under raised pressure to the wheel cylinder. This increases a flow velocity of the brake fluid stored in a reservoir tank, and accordingly increases the negative pressure in the relief port104.

As a result, the exposed part102aof the cup seal102greatly bulges toward the relief port104. In that case, when the driver strongly depresses the brake pedal to cause the piston103to slide forward, passage of the piston103is likely to cause shearing of the exposed part102aof the cup seal102that has entered the relief port104, as illustrated inFIG. 6. This results in a decrease in durability of the cup seal102.

A measure against the above concern may be to increase hardness of the cup seal102. However, this makes it difficult to guarantee long-term airtightness, and shortens a maintenance cycle. Another measure may be to restrict raised-pressure output of the brake fluid by the automatic brake device to suppress an amount of bulging, toward the relief port104, of the exposed part102aof the cup seal102. However, this results in a decrease in brake performance upon activation of the automatic brake device based on automatic emergency braking. Another measure may be to restrict pressure of a brake booster upon activation of the automatic brake device to restrict a brake operation to be performed by the driver. However, this changes a feel of depressing the brake pedal, causing the driver to feel anxiety.

In contrast, in the example embodiment, the primary relief port6aprovided in the primary piston6may be tilted at the predetermined angle θ with respect to a front-rear direction, from the outer circumference toward the inner circumference, as illustrated inFIG. 3. Similarly, the secondary relief port5aprovided in the secondary piston5may also be tilted in the same direction at the same angle θ as that of the primary relief port6a, as illustrated inFIG. 2.

Consequently, as indicated by an arrow inFIG. 4, the brake fluid that passes through the relief port5amay partially be sucked from the cylinder chamber4side to collide with a wall of the relief port5aon the S.P cup11side, and thereafter flow out to the master port4f. Moreover, the brake fluid that passes through the relief port6amay partially be sucked from the cylinder chamber4side to collide with a wall of the relief port6aon the P.P cup13side, and thereafter flow out to the master port4g.

When the brake fluid collides with the wall of the relief port5a, the brake fluid may partially splash up to the S.P cup11. This generates a fluid accumulation A between the exposed part11aof the S.P cup11and the brake fluid colliding with the wall. When the brake fluid collides with the wall of the relief port6a, the brake fluid may partially splash up to the P.P cup13. This generates the fluid accumulation A between the exposed part13aof the P.P cup13and the brake fluid colliding with the wall. This causes the generated fluid accumulation A to suppress generation of negative pressure near each of the exposed parts11aand13aof the S.P cup11and the P.P cup13.

Consequently, for example, in a case where the automatic brake device applies sudden braking at high brake fluid pressure in response to an instruction from an automatic emergency brake device, high negative pressure is not generated near the exposed parts11aand13aeven if the brake fluid passes through the relief ports5aand6aat a high flow velocity. This makes it is possible to suppress bulging of the exposed part11atoward the relief port5aand bulging of the exposed part13atoward the relief port6a.

Therefore, when the automatic brake device is activated, even if the driver strongly depresses the brake pedal to cause the secondary piston5and the primary piston6of the master cylinder2to slide, passage of the secondary piston5and the primary piston6of the master cylinder2does not cause the exposed parts11aand13ato shear. This makes it possible to keep durability of the S.P cup11and the P.P cup13.

In the example embodiment as described above, the relief port provided in the piston is tilted from the front side to the rear side in the movement direction of the piston, from the outer circumference toward the inner circumference of the piston. Thus, when the brake fluid stored in the reservoir tank is sucked into the hydraulic chamber via the relief port, the brake fluid may collide with an inner wall of the relief port to generate, as the piston moves, the fluid accumulation near the cup seal provided on the front side in the movement direction. This makes it less likely for the inner circumference of the cup seal to bulge toward the relief port under negative pressure, making it possible to suppress shearing of the inner circumference of the cup seal due to the back-and-forth movement of the piston. This helps to suppress a decrease in durability of the cup seal, shortening of the maintenance cycle, and a decrease in the brake performance, and prevent the feel of depressing the brake pedal from changing, making it possible to suppress the feeling of anxiety of the driver.

In one example, the secondary relief port5aprovided in the secondary piston5and the primary relief port6aprovided in the primary piston6may be tilted from the front side toward the rear side in the movement direction, from the outer circumference toward the inner circumference. In other words, the secondary relief port5aand the primary relief port6amay be tilted in a direction of departing from the S.P cup11and the P.P cup13, respectively, from the outer circumference toward the inner circumference. Thus, when the automatic brake device, for example, is activated and the brake fluid stored in the reservoir tank3passes through the secondary relief port5aand the primary relief port6ato be sucked into the hydraulic chamber21and the hydraulic chamber22, respectively, it is possible to cause the brake fluid to collide with the walls of the relief ports5aand6a.

As a result, it is possible to generate the fluid accumulation A near each of the exposed parts11aand13aof the S.P cup11and the P.P cup13, which makes it possible to suppress generation of negative pressure in these parts, and suppress bulging of the exposed part11atoward the relief port5aand bulging of the exposed part13atoward the relief port6a. Consequently, even if the pistons5and6move forward, the movement does not cause the exposed parts11aand13ato shear, which makes it possible to improve the durability of the cups11and13.

Improving the durability of the cups11and13makes it possible to lengthen the maintenance cycle, which helps to reduce economic burdens on the driver. The improvement in the durability also makes it unnecessary to restrict the raised-pressure output of the brake fluid by the automatic brake device, which prevents a decrease in the brake performance. Furthermore, the improvement in the durability makes it unnecessary to restrict pressure of the brake booster upon activation of the automatic brake device. This prevents the feel of depressing the brake pedal from changing, preventing the driver from feeling anxiety.

The technology is not limited to the example embodiment described above. For example, a structure in which the relief ports5aand6aare tilted at the predetermined (tilt) angle θ may also be applied to a normal brake system not equipped with an automatic brake device and in which the master cylinder device1directly communicates with a wheel cylinder of a brake caliper.

Although some embodiments of the technology have been described in the foregoing by way of example with reference to the accompanying drawings, the technology is by no means limited to the embodiments described above. It should be appreciated that modifications and alterations may be made by persons skilled in the art without departing from the scope as defined by the appended claims. The technology is intended to include such modifications and alterations in so far as they fall within the scope of the appended claims or the equivalents thereof.