ELECTRO-HYDRAULIC SYSTEM

An example of an electro hydraulic system is the Dunlop Maxivue which

comprises 2 wiper head arms and blades and two electrically driven twin cylinder hydraulic pump units. The wipers are independently controlled by two switches labelled

PORT (or STBD)

WIPER: FAST – OFF - SLOW Hydraulic Pump Assembly

The complete assembly comprises a fully suppressed electric motor complete with gears driving a twin cylinder pump unit.

JAR 66 CATEGORY B1 MODULE 11.12

ICE AND RAIN PROTECTION

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Electro-Hydraulic Wiper Pump Figure 28

The light alloy pump body carries two horizontally opposed cylinders and pistons and is bored internally to accommodate an eccentric driving shaft mounted within a ball bearing housed in the body. A roller bearing fitted to the eccentrically machined portion of the shaft and retained in position by a washer and circlip, makes contact with the reciprocating pistons which are correctly spaced by a cradle. A locknut and tab washer retain the ball bearing in position on the driving shaft. A base plate, sealed against leakage by an ‘0’ ring is clamped to the base of the pump body by countersunk headed screws.

Each cylinder has an integral pipe connection and is secured to the body by washers and locknuts fitted to the body studs that also serve to locate a cover plate. A sealing ring is housed between the cover plate and the cylinder head and a gasket is sandwiched between the cylinder shoulder and pump body. The top face of the pump body houses a sealing ring and the four screwed studs and locknuts provide means of attachment to the motor unit. The reservoir filler cap is prevented from loss by a chain anchored to a lug that is fastened to the filler cap by a rivet. The free end of the chain is attached to a motor mounting

JAR 66 CATEGORY B1 MODULE 11.12

ICE AND RAIN PROTECTION

engineering

uk

A peg screwed into the pump body is fitted with a leaf spring that ensures that the filler cap remains correctly seated within the reservoir mouth.

The light alloy pump body carries two horizontally opposed cylinders and pistons and is bored internally to accommodate an eccentric driving shaft mounted within a ball bearing housed in the body. A roller bearing fitted to the eccentrically machined portion of the shaft and retained in position by a washer and circlip, makes contact with the reciprocating pistons which are correctly spaced by a cradle. A locknut and tab washer retain the ball bearing in position on the driving shaft. A base plate, sealed against leakage by an ‘0’ ring is clamped to the base of the pump body by countersunk headed screws.

Each cylinder has an integral pipe connection and is secured to the body by washers and locknuts fitted to the body studs that also serve to locate a cover plate. A sealing ring is housed between the cover plate and the cylinder head and a gasket is sandwiched between the cylinder shoulder and pump body. The top face of the pump body houses a sealing ring and the four screwed studs and locknuts provide means of attachment to the motor unit. The reservoir filler cap is prevented from loss by a chain anchored to a lug that is fastened to the filler cap by a rivet. The free end of the chain is attached to a motor mounting stud.

A peg screwed into the pump body is fitted with a leaf spring that ensures that the filler cap remains correctly seated within the reservoir mouth.

Wiper Head

Each wiper head comprises a light alloy body which accommodates a pair of piston and cylinder assemblies, racks and a bearing mounted pinion shaft. A cover plate is secured to the front face of the body by tubular bolts and counter- bolts in the rear face of the body are fitted with pressed in tubular distance pieces. These bolts and distance pieces provide accommodation for the wiper head mounting bolts.The body houses a pair of racks which are alternately actuated by individual pistons, a pinion shaft engaging the racks, ball bearings and oil seals. Each rack slides in a cylinder that is held in position by a piston cylinder screwed into the body. The piston cylinders have radially disposed ports and the outer ends of the cylinders are internally threaded to carry the connection unions. Rubber sealing rings within annular grooves prevent fluid leakage past the cylinders and unions. A double locking plate engaging the hexagons of the piston cylinders prevents their disturbance during the fitting and removal of the feed pipe union nuts.

Each piston assembly comprises a body, a ball and a plug and acts as a non- return valve permitting the flow of fluid in one direction only. The two ball

bearings housed within the body locate the pinion shaft, the bearing adjacent to the cover plate being retained by an internal circlip. Two oil seals of special construction locate around the pinion shaft and prevent external leakage from the wiper head body.

JAR 66 CATEGORY B1 MODULE 11.12

ICE AND RAIN PROTECTION

engineering

uk

Windscreen Wiper Head Figure 29

Operation

The windscreen wiper head is operated by a twin cylinder hydraulic pump, the outlet ports of which are connected to the unions on the wiper head. Thus basically, on the power stroke of one of the pump cylinders, a column of fluid is thrust along the pipeline, forcing the corresponding wiper head piston to

reproduce the movement of the pump piston. This movement thrusts the

operating rack along a cylinder to rotate the wiper head pinion shaft. The rotation of the pinion shaft carries the opposing rack and piston backwards, following the receding column of fluid in the other pipeline. Reversal of the movement of the pump pistons produces the reverse movement of the wiper head pinion.

JAR 66 CATEGORY B1 MODULE 11.12

ICE AND RAIN PROTECTION

engineering

uk

To render the system self-priming and self-bleeding, one of the supply pump cylinders is made with a slightly larger capacity than the wiper head cylinders. Each receiving piston is fitted with a ball valve, and the ports that are provided in the walls of the wiper head cylinders are uncovered at the end of the operating stroke.

During the operating stroke the ball valve in the operating piston seals under fluid pressure ensuring positive action. When the operating piston reached the end of its stroke, the surplus fluid available from the pump is injected into the pinion housing causing circulation through the opposing cylinder, and back to the body of the pump via the ball valve in the opposing piston.

NOTE:

The pipeline from the large capacity cylinder of the pump unit is marked with a plus sign (+) on the connection at the pump unit. This pipeline must be

connected to the wiper head to drive the blade downwards.

Wiper Blade Actuating Arm Figure 30

The actuating arm assembly comprises an attachment piece, a leaf spring an actuating arm and a blade shoe. The attachment piece is bored and slotted for attachment to the operating spindle. The actuating arm, located to the

attachment piece by a pivot pin, may be adjusted to produce the necessary blade pressure on the screen by means of the leaf spring.

The spring tension should be adjusted to produce a blade pressure as quoted in the maintenance manual.

NOTE:

JAR 66 CATEGORY B1 MODULE 11.12

ICE AND RAIN PROTECTION

engineering

uk