2-Door Vehicle Without ABS

GENERAL DESCRIPTION
As shown in figure below, 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 above 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 overate it.

CONSTRUCTION
The LSPV components are grouped into three sections as follows.

"A": Sensor section:
The main parts in this section are a lever and a spring 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.





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 under 2 Operation of hydraulic pressure control section.





1) Operation of sensor section. One end of the sensor spring is installed to the rear suspension upper arm and the other end is to the LSPV lever.
The spring power P is applied to the plunger by way of the lever. The force on the plunger then is expressed as F = L p





2) Operation of hydraulic pressure control section
a) 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 in left figure.
The input hydraulic pressure passes between the bail and seat (valve) and without receiving any control, it is discharged through the outlet port.





b) As the input hydraulic pressure increases, the force applied to the plunger grows stronger than the sensor spring power and moves the plunger to the right in the figure and as a result, the valve closes the fluid passage. The hydraulic pressure then is represented by the bend point Pc in the graph.
As the incoming hydraulic pressure rises even higher, the plunger opens and closes between the ball and the seat (valve) so as to keep a good balance among the forces applied to itself. (i.e. forces from sensor spring, input hydraulic pressure and output hydraulic pressure). Thus the output hydraulic pressure is controlled according to the valve opening and therefore its characteristic is represented as a line with a certain gradient.





3) Operation when fail-safe is at work.

Should it occur that no hydraulic pressure is generated in the front wheel brake due to some fault in its system, the fail-safe piston, usually underthe hydraulic pressure of the front and rear wheel brakes, moves to the left as shown in the left figure by the hydraulic pressure from the rearwheel brake.
The piston, as it moves, opens the valve seal to allow the hydraulic pressure to pass through it. Then the hydraulic pressure is fed through the outlet port to the wheel cylinders of the rear wheel brake without being controlled.