Brake Proportioning/Combination Valve: Description and Operation

LSPV (Load Sensing Proportioning Valve) Assembly (If Equipped) Construction





As shown in the figure, LSPV is included within the brake circuit which connects the master cylinder and the rear wheel brake. It controls the hydraulic pressure applied to the rear wheel brake according to the loaded state of the vehicle (or weight of the load), whereby preventing the rear wheels from getting locked prematurely. Also, it releases the described control over the hydraulic pressure applied to the rear wheel brake, should any failure occur in the hydraulic circuit of the front wheel brake so that the hydraulic pressure produced in the master cylinder is applied to the rear wheel brake directly to operate it.

Constitution





The LSPV components are grouped into three sections ("A", "B", "C" as shown in the figure) as follows.

"A": Sensor section
The main parts in this section are a lever and a spring which senses variation in the vehicle height as affected by the loaded condition and converts it into the load.

"B": Hydraulic pressure control section
Included in this section are a stepped plunger and valve mechanism to execute proportional control.

"C": Fail-safe section
The main parts in this section are a chamber which draws in the hydraulic pressure from the front wheel brake system and a fail-safe piston which releases the valve mechanism in the control section connected to the rear wheel brake, should any failure occur in the front wheel brake system.