Carlisle Brake & Friction (CBF) recently showcased its latest technologies, including the quick fill master cylinder and the puller slave cylinder for the tractor market.
For over 30 years, Carlisle Brake & Friction (CBF) has been a supplier of brake systems and friction components to the agriculture and forestry industry. In 2005, CBF expanded its brake system capabilities with the acquisition of ArvinMeritors off-highway braking division (formerly known as Lucas Girling). Recently, CBF launched several new products for the Indian market targeting changing technological trends in the tractor industry. These products can replace the traditional linkages-based brake actuation with hydraulic-based actuation to give operators a passenger car brake pedal 'feel and improved driver comfort.
Quick-fill master cylinder
Operator comfort is the key advantage a quick-fill master cylinder technology provides when compared to the older master cylinder technology. The quick-fill is actuated when the pedal is applied and the plunger moves forward, displacing fluid from the larger chamber and brake master cylinder to the brakes. The fluid from the quick-fill chamber flows through the non-return valve and quickly fills the brake. The additional fluid volume from the quick-fill chamber is used to take up the running clearance at the drum-brake wheel cylinders. When an optimal pressure is achieved in the brake line, ie, when the running clearance is gone and the brake needs to be pressurised to torque, pressure will be built up in the brake master cylinder, but only after the non-return valve closes off. Any additional oil volume required compensating for brake stiffness or hose expansion due to pressurisation, for example, will be available from the plunger. However, the fluid that needs to be displaced from the quick-fill chamber for this to occur must go somewhere, in this case to the tank through the vent hole. One fine-tuned feature of this system is that it ensures that when the cylinder is first applied, the oil in the quick-fill chamber will flow through the non-return valve rather than out to reservoir. Some oil will inevitably get vented out, but this feature ensures most of the fluid is directed to the brake.
In emergencies, the operator may still stamp on the pedal, even though he does not want the high pedal force to be created by the quick-fill chamber diameter. In this case, the pressure-relief valve will crack open and relieve the back pressure created because the oil will not be able to get through the non-return valve quick enough. When the pedal is released, the cylinder recuperates from the quick-fill chamber through the non-return valve and the quick-fill chamber recuperates via the centre valve opening, letting oil flow readily from the reservoir.
CBFs cylinder has a self-bleed function that ensures that if air gets into the brake master cylinder and enters the annular section in front of the main master-cylinder seal, it will be ejected through the self-bleed hole each time the cylinder is stroked. This air will then be pushed out through the vent hole and into the reservoir, so the cylinder is self-bleeding, but will not bleed air from the brake system, if the air is not in the master cylinder.
Puller slave cylinder
This slave cylinder has been designed with the option for actuating a park brake. The service brake and park brake can be applied independently with the CBF design. To reduce the load required at the handbrake (to operate the park brake) the service brake can be applied and immediately after the handbrake can be operated at a much lower effort to provide the required park brake torque.
There will be a small partial vacuum created in the braking system when conducting this particular 'park brake procedure. This vacuum level will be dependent on various system characteristics including length/diameter of the hydraulic piping, slave cylinder diameter, master cylinder diameter and stroke, etc. However, CBF master cylinders are specifically designed to reduce the effects of partial vacuum by replacing fluid in the brake system through internal recuperation.