Mechanical load sensing valve

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The load sensing valve (L.S.V.) serves the purpose of automatically adapting the brake pressure and therefore the brake force according to the load of the vehicle. Automatic load-dependent brake force regulation is compulsory for semi trailer tractors with a permissible total weight of more than 7.5 t and semi-trailers with the sum of the permissible axle loads greater than 7.5 t when the vehicle was registered for the first time from 1st January 1963. EC regulations (RKEG 74/132 EWG) as well as the ECE stipulation No. 13 specify automatic brake force regulation for all motor vehicles and trailers with a total weight exceeding 3.5 t provided brake force regulation is necessary.

Installation

The load sensing valve regulator is attached with screws, nuts and washers to the attachment holes that are drilled into the assembly.

Attaching the control cable

The control cable’s spring is attached via an M12 Allen bolt to the bracket that is fitted to the axle. The bracket should be at least 8 mm thick. If the bracket is welded in place, authorisation must be sought from the manufacturer for this. The welded seams must always be in the neutral zone. Attach the control cable with a cable clamp in the “unladen” control lever position at the calculated interval (lever length) from the pivot of the control lever (torque for control screw: 6 Nm). In order to balance the settling of the vehicle springs, the supplied 5 mm thick disc should be fitted underneath the control spring of the control cable. If the vehicle spring has settled by approx. 5 mm, this disc is removed. Further adjustment can be made by moving the control cable in the clamp. In order to avoid damage or excessive wear on the linkage components, the following points must be noted when installing the cable link:

  • The control cable should be as long as possible
  • The control cable should be within the lever’s level of movement.
  • Ensure all parts can move easily
  • Attach the control cable as close as possible to perpendicular from the control lever on the bracket

The control cable is attached to the control lever or the load sensing valve regulator with a different linkage component for each version. When unloading the vehicle, the control springs pull the control lever downwards via the cable. If the vehicle is loaded, the control lever is lifted by a leg spring until the control cable is tensioned. Linking the cable and spring enables the spring deflection to be tapped from an axle even with twin-axle assemblies.

 

Function

lf the load of the vehicle is changed, then as a result, the deflection of the vehicle springs also changes.

While loading the vehicle, the vehicle body approaches the axles, when unloading the distance between the vehicle body and the axle becomes greater. The travel of the vehicle body can be used for controlling the load sensing valve.

The load sensing valve is mounted to the chassis of the vehicle, the control cable together with the spring is mounted an a bracket bolted or welded to the axle. The control cable is secured to the control lever of the load sensing valve by means of a clamp.

When unloading the vehicle, the tension spring pulls the control lever downwards over the cable.

When the vehicle is loaded, the control lever is raised by a spiral spring until the control cable is tensioned.

The shock absorber mounted on the control lever, together with the tension spring, takes up the dynamic impact caused by unevenness in the road.

The load sensing valve operates statically, i.e. changes in the spring path which occur during braking do not change the control ratio. The load sensing valve is slightly locked during braking.

Release Position, Half Load

The brake piston 1 moving in the upper part of the housing is connected to the valve sleeve 2 by means of the piston rod 5 on which the double valve cone 3 is mounted in a floating arrangement.

The valve sleeve 2 guides the balance spring and piston 4. The locating pin supported by a compression spring 7 on the housing is connected to the thrust piece by means of the balance lever 6 and the variable slide piece 8.

A change in movement downwards or upwards executed by the control lever results in the slide piece 8 being shifted and therefore changes the effective transmission ratio between the brake piston 1 and balance piston 4.

In the position “no-load”, the applied pressure P1 can be reduced in a control ratio of 6:1 with respect to the modulated pressure P2.

Each control ratio between “no-load” and “load” is continuously variable.

In the release position, the double valve cone 3 closes the inlet seat b; port 2 is connected to atmosphere via the open outlet seat a.

Brake Setting, Half Load

When the brake is actuated, compressed air flows through port 1 and presses the brake piston 1 upwards while the valve sleeve 2 is pressed against the double valve cone 3.

The outlet seat a is now closed, the inlet seat b opened. The compressed air now flows to port 2 and is applied to the balance piston 4. The force acting on the balance piston is transmitted via the thrust piece 5 and the balance levers 6 to the brake piston 1 thereby moving it downwards.

The inlet seat b is closed, the outlet seat a remains closed. A socalled partial braking setting is obtained.

Each change in pressure at port 1 results in a change in pressure at port 2 corresponding to the set control ratio. The brake piston 1 moves back into its initial position if air is allowed to escape at port 1. Air escapes via port 2 via the now open outlet seat a and the vent valve on the housing.

The load sensing valve has a proportional characteristic equipped with a pressure advance control of P = 0.3 ... 0.4 bar for overcoming in the response stages of subsequently connected brake devices.

In the event of the control cable breaking, the control lever is raised to the position “load” by the shock absorber or spiral spring. The pressure applied at port 1 is directed to port 2 uncontrolled.

Brake setting, loading

The transmission of the pistons and weighing lever must be arranged in such a way that, when in the “loading” position, the pressure introduced in Port 1 P1 is controlled without regulation – i.e. the regulating ratio P 1/P 2 = 1:1 – from Port 2.

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Technical data

  • Operating pressure: max 10 bar
  • Operating temperature: -40°C to +80°C
  • Ports 1, 2: M 16 X 1.5
  • Port 1 = Supply in
  • Port 2 = Delivery out
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