Patent Application
20060071542
The present invention relates generally to hydraulically held park brake systems, and more specifically, to a park pawl accumulator (PPA) for a service brake as part of a hydraulic brake system.
Typical hydraulic brake systems in applications such as ATV and snowmobile use a hydraulically held park brake. The service brake has a lever that the operator moves to apply pressure hydraulically to the brake caliper(s). The hydraulically held park brake operates by locking the service brake lever in the applied position. Typically this is accomplished by use of a pawl that is connected to the service brake lever that engages into the body of the master cylinder in such a way that the service brake lever remains in the position to which it was moved by the operator. The problem with this method is that when there is a change in temperature, the brake fluid expands or contracts (according to whether the temperature increases or decreases, respectively) thus changing the pressure in the brake system, and consequently, the brake torque exerted by the brake caliper. This is an issue, since there can be reduction in pressure such that there is insufficient brake torque to hold the vehicle in place (as on a grade). Conversely, when the pressure increases due to increase in temperature, the pressure in the brake system can increase so that damage to the brake components can occur.
It has been found that current products in the brake industry do not adequately address the problem of uncontrolled hydraulic brake pressure changes due to temperature changes. Moreover, current solutions do not provide any cost-effective solutions that are commercially viable for the industry.
A similar function to the park pawl can be accomplished by installing a separate hydraulic accumulator in the system which is typically done in (usually non-brake-related) hydraulic systems of much greater cost, space, complexity, and not in applications on ATVs or snowmobiles. The accumulator comprises a cylinder that has a spring pushing on a piston, with a seal on the piston that isolates the side of the piston where the spring resides from the hydraulic fluid on the “working” side of the piston. Obviously, this system is more expensive, and also introduces more failure modes, as there is another part inside of the hydraulic system.
Therefore, there is a need for a park pawl that has some capacity to absorb the additional pressures created from temperature increase of hydraulic brake fluid. Such a deflection capability would be necessary to handle the increase and decrease in brake pressure, and such a park pawl would be seen as beneficial to the brake industry.
Additional benefits would accrue from such a solution that could be implemented on a low-cost basis and without the need for additional separate hydraulic accumulators. Moreover, a need exists for a solution that minimizes the number of failure modes associated with the hydraulic system with a simple, low space solution.
The invention contemplates solutions to the above-identified problems and insufficiencies substantially in accordance with the foregoing summary.
A preferred exemplary embodiment of the invention is illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which:
A hand operated hydraulic brake assembly 10 used with a vehicle such as vehicle 5 is shown in more detail in
Still referring to
A park pawl 38 is pivotably secured to the hand brake lever 8. As used herein, the “park pawl” is any hinged or pivoted device that can fit into a notch or other engagement section so as to permit or impart motion of the engagement section in one direction and prevent motion of the section in the other direction as that device is used in the parking function. Park pawl 38 includes an end 40 that is engageable with the park pawl engagement section 33 of the handle bar attachment bracket 30 to lock the brake lever 8 in a locked position when the lever is in the applied position. The bracket park pawl engagement section includes a notched portion 39. More specifically, pin 42 is passable through hole 44 in park pawl ear section 45, with an identical hole in opposing ear section 47 to engage retainer ring 46. Finally spring clip 48 fits between ear sections 45 and 47 and permits the pin 42 to pass therethrough (passing through the holes in the ear section), hole 31 in lever 8, and engage the retainer 46. The spring clip provides necessary tensioning and bias against the movement of lever 8. Lever 8 includes should 49 which is in abutting contact with piston 22.
Advantageously, the pawl 38, spring clip 48 and pin 42 may be sold as part of a replacement or service kit, and in this respect, sold as an aftermarket package, which may also include lever 8.
Other features associated with the braking function and which may be used in conjunction with the present invention include brake light wiring 50 and connectors 52 for providing brake lights when the brake lever 8 is actuated.
For
Brake lever 8 is moved to applied position (
Referring to
The volume of hydraulic brake fluid, as noted previously, expands as brake fluid temperature increases and contracts as temperature decreases. As shown, and by way of example, during a brake fluid temperature increase, an expansion of fluid in brake line 18 causes piston 22 to move lever 8 in a direction indicated by arrow 66. Movement of the brake lever 8 creates a force about pin 34, which translates into an additional force upon pawl 38, and particularly, at end 64. Stated another way, the reciprocating master cylinder piston 22 urges the hand brake lever 8 to rotate from the applied position when park pawl compensation flexure occurs.
In response to this increased force, the inventive park pawl, while in the set position as shown, deflects. Significantly, this deflection capability permits the brake to maintain the proper brake line fluid pressure. It can be said that, during temperature increase, the park pawl compensation flexure is a park pawl expansive compensation flexure and that, when the hydraulic fluid incurs a temperature increase, the park pawl absorbs force created by movement of the lever from the applied position due to the expansion of the hydraulic fluid. In this way, the pawl stores the energy resulting from the force exerted upon it. Thus, the park pawl expansively deflects as a result of the lever movement.
Similarly, during a hydraulic brake fluid temperature decrease, the pawl 38 releases its stored energy and urges, via a reverse flexure, the lever 8 to the original set position (shown in dashed lines) when the brake is applied. In a preferred embodiment, there may be minimal functionality of the spring clip 48 during flexure. Rather, the preferred functionality of the spring clip 48 is to hold the park pawl 38 in and return the same to home position (i.e., released). Stated another way, the park pawl compensation flexure can be a park pawl contractive compensation flexure when the hydraulic fluid incurs a temperature decrease. In this way, the park pawl returns energy stored within the pawl that is created by a contraction of the hydraulic fluid. Here, the park pawl contractively deflects as a result of the lever movement. In short, the park pawl compensation flexure can be characterized as one of a park pawl expansive compensation flexure and a park pawl contractive compensation flexure. The expansive and contractive flexures result in opposing park pawl motion. The park pawl expansive compensation flexure and the park pawl contractive compensation flexure compensate for hydraulic fluid temperature changes so as to accommodate movement of the lever when the lever is in the applied position. The park pawl expansive compensation flexure and the park pawl contractive compensation flexure maintain brake pressure.
Section 68 generally of pawl 38 is shown as a generally contoured shape. However, it is contemplated that any shape having, for example, appropriate length, width, curvature and the like are within the scope of the present invention, provided that the section is capable of deflecting and resiliently deflecting back to an original position.
A handle bar master cylinder assembly is disclosed. The assembly has a resilient park pawl capable of flexure to compensate for hydraulic fluid temperature changes in the master cylinder assembly. The assembly supplies pressurized hydraulic fluid through a brake line to actuate a brake in a vehicle. The resilient park pawl can at least partially deflect. The park pawl flexes while engaged to a handle bar attachment bracket connected to the master cylinder at a bracket park pawl engagement section. The bracket park pawl engagement section includes a notched portion.
A method of compensating for a change in hydraulic fluid temperature in a handle bar master cylinder assembly for supplying pressurized hydraulic fluid through a brake line to actuate a brake in a vehicle is disclosed. The method includes providing a master cylinder having a master cylinder body that defines a hydraulic fluid reservoir. The reservoir contains the make-up hydraulic fluid. A reciprocating master cylinder piston is located within the hydraulic fluid reservoir. The piston pressurizes the hydraulic fluid to actuate the brake. A handle bar attachment bracket is connected to the master cylinder body and has a park pawl engagement section. A hand brake lever is rotatably secured to the handle bar attachment bracket and is in abutting contact with the reciprocating master cylinder piston. The lever is rotatable to an applied position for braking of the vehicle. A park pawl is pivotably secured to the hand brake lever. The park pawl includes an end that is engageable with the park pawl engagement section of the handle bar attachment bracket to maintain the brake lever in the applied position. When the pawl is in the set position, the park pawl is capable of a compensation flexure that occurs due to a change in the hydraulic fluid temperature. The flexing can further comprise expansively deflecting the park pawl as a result of the lever movement. The flexing can further comprise contractively deflecting the park pawl as a result of the lever movement. Significantly, the flexing capability ensures or maintains a substantially constant pressure within the master cylinder body despite a change in at least one of hydraulic fluid volume and temperature.
The inventive park pawl is an improvement over the previous park pawl designs. The park pawl has a deflection (i.e., spring-like) capability such that when the hydraulically held park brake is set by introducing the park pawl into engagement to hold the service brake in the “on” position, the force from the service brake lever (due to the hydraulic pressure created by the operator moving the lever to the desired position) deflects the park pawl slightly so that there is stored energy in the park pawl. When the temperature drops so that the brake fluid contracts, the stored energy from the park pawl allows fluid to replenish some of the volume of the contracted fluid and allows significantly more pressure to be retained in the brake system than with a park pawl that has no flexibility. This occurs since, in previous park pawl designs, as the fluid contracts, there is no spring in the park pawl to deliver energy back to the brake system. Furthermore, when the brake fluid expands as the temperature of the brake fluid increases, the inventive park pawl allows energy to be stored in the park pawl, limiting the rise of brake pressure, and therefore, reducing the chance of damage to the system from excessive pressure.
Despite any methods being outlined in a step-by-step sequence, the completion of acts or steps in a particular chronological order is not mandatory. Further, modification, rearrangement, combination, reordering, or the like, of the acts or steps is contemplated and considered within the scope of the description and claims.
Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.
