4-Door Vehicle Without ABS

GENERAL DESCRIPTION
As shown in figure below, LSPV is included within the brake circuit which connects 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.
If the front hydraulic pressure fail to increase (failure in the front brake circuit), it is so designed that the fail-safe mechanism works and a hydraulic pressure higher than in normal condition is applied to rear wheel cylinders.





CONSTITUTION





OPERATION
LSPV is installed to the vehicle body, with the end of the lever at its top connected to the upper arm of the rear suspension by way of the sensor spring and the LSPV stay.
When some load is placed on the vehicle, the distance between the axle housing of the rear suspension and the vehicle body (chassis) (i.e. coil spring height) changes, whereby the sensor spring length also changes.
As the sensor spring length changes, the force affecting the plunger in LSPV by way of the lever changes so that the hydraulic characteristic suitable for the load weight becomes available.

When empty
As the sensor spring is pulled by comparatively weak force, the force applied to the plunger is also small and the hydraulic characteristic takes a low bend point as shown in the graph below.

When loaded
As the sensor spring is pulled by comparatively strong force, a larger force is applied to the plunger so that the hydraulic characteristic takes a higher bend point in the graph below.
The relationship between the force applied to the plunger and the bend point in the hydraulic characteristic Graph is described on the following page.





When LSPV not at work
Operation from the inoperative state till the input hydraulic pressure (fluid pressure from the master cylinder) reaches the bend point Pc in the graph as shown.
The input hydraulic pressure passes between the plunger and lip seal (valve) and without receiving any control, it is discharged through the outlet port.





When LSPV at work
As the input hydraulic pressure increases, the force applied to the plunger grows stronger than the sensor spring force and moves the plunger upward in the figure and as a result, the valve closes the fluid passage. Then the hydraulic pressure is represented by the bend point Pc in the graph.
As the incoming hydraulic pressure rises even higher, the hydraulic pressure "A" increases and pushes down the plunger, opening the fluid passage.
By repeating this operation (open/close), the valve controls the output hydraulic pressure (hydraulic pressure to the rear brake).
Therefore its characteristic is represented as a line with a certain gradient.





When fail-safe at work
When the hydraulic pressure is not applied to the front brake (secondary), the force to push up the plunger reduces by the amount corresponding to that of the front brake. This means that in order for the plunger to operate, a higher than normal hydraulic pressure is required for the rear brake (primary).
Thus, a hydraulic pressure exceeding the normal level is supplied to the rear brake (rear wheel cylinder).