Working Principles of Adjustable Brake Proportioning Valve

For automotive distributors and wholesalers, understanding the core components that ensure vehicle safety is not just a technical necessity—it’s a competitive business advantage. This article provides a comprehensive, expert-level explanation of how this adjustable brake proportioning valve operates, why it’s indispensable for modern vehicles.

I. Terms and Definitions

1. Load-Sensing Proportioning Valve

A hydraulic-mechanical control element used to ensure the load ratio between the front and rear wheels during driving and to prevent the rear wheels from locking during emergency braking.

2. Reduction Coefficient (also called Proportional Coefficient or Distribution Ratio)

On the proportional valve characteristic curve, above the inflection point hydraulic pressure range, the ratio of the increase in output hydraulic pressure to the increase in input hydraulic pressure.

3. Hydraulic Inflection Point

On the proportional valve characteristic curve, the transition point where the slope of the characteristic curve begins to decrease.

4. Safety Feature

When the input pressure of the front brake circuit is zero, that is, when the front brake circuit fails, the output hydraulic pressure of the proportional valve equals the input hydraulic pressure, providing sufficient pressure to the rear brake circuit to achieve the required braking deceleration.

5. Input Hydraulic Pressure

During braking, the hydraulic pressure output by the master brake cylinder enters the proportional valve.

6. Output Hydraulic Pressure

During braking, the hydraulic pressure, after passing through the proportional valve, enters the brake slave cylinder or brake caliper.

7. No-Load

The load of a vehicle when only the driver is present and no other load is present.

8. Fully loaded

The load at the vehicle’s maximum laden mass.

II. Introduction to Hydraulic Brake Proportional Valve

The automotive hydraulic brake proportional valve serves as a control element in the service braking system, connected between the master brake cylinder and the rear wheel cylinders.

This paper uses an adjustable proportional valve to explain its operating principle and assembly precautions. This proportional valve combines two functions: a proportional valve and a pressure alarm. The functions of each valve are as follows:

① Proportional valve: Proportionally distributes braking force between the front and rear wheels to prevent rear wheel locking during service braking, resulting in slippage and tailspin, and ensures directional stability. The proportional valve in this paper is adjustable, meaning that the spring resistance is varied by adjusting the height of the handle, thereby achieving different hydraulic breakpoints within a certain range.

② Pressure Alarm Valve: In simple models, the power supply is connected to the pressure alarm switch through a fuse. When the brakes are applied, the brake lights illuminate to alert vehicles behind. The red display enhances the penetrating power of the light, making it easier for vehicles behind to detect the braking of the vehicle ahead, even in low visibility conditions. This alerts vehicles behind to take action and prevent rear-end collisions.

III. Structure and Working Principle of the Adjustable Proportional Valve

1) Structure of the Adjustable Proportional Valve

The Adjustable Proportional Valve primarily consists of the valve body, proportional valve piston, proportional valve plug, valve, proportional valve spring, adjusting sleeve, adjusting bolt, adjusting handle, and pressure alarm switch assembly. Its structure is shown in Figure 1:

2) Working Principle of the Adjustable Combination Valve Proportional Valve Proportional Valve Connections

The inputs of the proportional valve chamber and the pressure alarm chamber are connected to the two oil outlets of the brake master cylinder via pipes, respectively. The output of the proportional valve chamber is connected to the rear wheel cylinder via pipes. The pressure alarm chamber is connected to the front wheel brake calipers or wheel cylinders via pipes. The pressure alarm switch in the pressure alarm chamber is also connected to the rear brake lights.

When not in operation, the proportional valve piston is at its lower limit due to the action of the proportional valve spring, and the valve port is open (see the enlarged view in Figure 3). Hydraulic pressure flows through the oil inlet, the annular channel inside the valve, and the valve port to the output chamber. When not in braking mode, the system’s hydraulic pressure is connected to the brake master cylinder reservoir and to the atmosphere. At this point, there is no hydraulic pressure in the system. The pressure alarm chamber is connected to another circuit of the brake master cylinder. Similarly, when there is no hydraulic pressure in the system, the spring seat is at its lower limit due to the action of the alarm switch spring, the two connecting pins are disconnected, and the brake lights are off. (See Figure 2)

3) Operating Principle of the Pressure Alarm Valve in the Adjustable Combination Valve. Alarm Switch Connection

In simple models, the power supply is connected to the pressure alarm switch through a fuse. When the brakes are applied, the brake lights illuminate to alert vehicles behind. The red display enhances the penetrating power of the light, allowing vehicles behind to easily detect the braking of the vehicle ahead, even in low visibility conditions, and alerting them to take action to prevent rear-end collisions.

When not braking, the system’s hydraulic pressure is connected to the brake master cylinder via a pipeline and vented to the atmosphere. The system’s hydraulic pressure P₁ is zero. The alarm spring forces the alarm piston to its lower limit position, disconnecting the two connecting pins and turning the brake lights off (see Figure 6).

Summary

This paper primarily explains the operating principle of the proportional valve, enabling us to better analyze product failure modes and implement preventive measures promptly. It also enables quality control personnel and workshop staff to effectively control the process.