Wiper motor


  • General
  • Wiper Motor Parts
  • Connecting wiper motor
  • Wiper motor plus switched
  • From the theory to the manufacturer's scheme
  • Two-speed wiper motor
  • LIN bus controlled wiper motor

The rear wiper motor is mounted in the tailgate of the car. There is a hole in the window or in the tailgate sheet metal through which the wiper motor shaft protrudes. The wiper arm is mounted on this shaft with the wiper blade. The shaft cannot of course make full rotations, because then not only the rear window, but also the rest of the tailgate or rear bumper is wiped clean by the wiper blade. That is why there is a mechanism in the motor that ensures that the shaft can make a movement of a maximum of 180 degrees.

The rear wiper motor always has one speed. The wiper switch allows it to be turned on and off and usually has an interval on it; after switching on, the motor will be activated every few seconds.
The wiper always returns to its initial position after it has been turned off. If not, the wiper arm would stop halfway down the window when the switch is turned to the “off” position. Instead of the motor's power supply being lost, it remains on until zero is reached.

Wiper Motor Parts:
To allow the wiper arm to move back to its initial position, it contains an internal contact plate with sliding contacts. The following illustrations explain how the wiper motor works.

The rear plate of the wiper motor has been disassembled. The red arrow indicates where the round cam of the mechanism in the back plate moves back and forth. The mechanism ensures that the rotating movement of the yellow plastic gear is converted into a reciprocating movement of the output shaft. The output shaft is upright in the picture. The wiper arm is mounted on this shaft.

The image on the right shows the cutaway wiper motor with the worm gear and plastic gear. Here the mechanism is disassembled.

The following text relates to the image below. The yellow plastic gear is now reversed. Here the notches and recesses of the conductive contact disc are clearly visible. Red, blue and green indicate the position at which the sliding contacts touch the contact disc.

To make it clear at which positions the sliding contacts make contact with the conductive contact plate, these are indicated by the colors red, blue and green. Below is what the sliding contacts are for:
Red: This always shows 12 volts when the ignition is switched on.
Blue: This sliding contact is responsible for the zero position.
Green: This is the mass. This connects the motor in the zero position.

The three sliding contacts “drag” over the gold-coloured contact plate when the engine is running. A notch and a recess are provided in the contact plate. The sliding contacts therefore never touch all three of the contact discs at the same time. The middle one (indicated in blue) is responsible for the movement to the zero position. The contact plate is conductive; if the motor is not yet in home position, the inner (red) and center (blue) sliding contacts are connected. The voltage is transferred from the red to the blue contact via the contact plate. This allows the motor to continue running until the red sliding contact reaches the notch. At that moment, it can no longer transmit voltage to the blue one. The control of the motor is thereby stopped.
At the same time, the outer sliding contact makes contact with the blue sliding contact via the recess (indicated in green) via the contact plate. The green sliding contact is connected to the ground of the vehicle. This sliding contact acts as a kind of brake. This stops the wiper motor. The mass is passed through green to blue. The motor is short-circuited to ground on both sides and thus remains in the zero position.

Connecting the wiper motor:
To connect the wiring of the wiper motor, the operation of, among other things, the contact plate and the sliding contacts must first be studied. Only when one understands at which points there will be voltages, can you proceed to measuring and connecting the wiring.
The wiring harness in the tailgate for the rear wiper motor often consists of three or four wires. A constant voltage, switched voltage and a ground must be measured on these wires. The remaining wire on which nothing is measured often shows a supply voltage (with a ground-switched motor) or a plus (with a positive-switched motor) when the motor is in the rest position. A measurement will therefore only be possible on this wire when all wires are connected and the wiper motor is in the starting position. In all other cases nothing is measured.

There are plus-switched and mass-switched wiper motors. This means that the switch is located on the plus or ground side of the electric motor. This is very important to know before measuring. Each step is described in detail in the chapters below. Pay close attention to the differences between the plus and mass switched variants!

Wiper motor plus gear:
On the basis of the diagrams, it is also possible to see how this should be linked to, for example, the infamous part of the practical exam. Below is a diagram with a legend of the plus-switched rear wiper motor. The wiper motor is stopped and the switch “0” is closed.

The electric motor (7) only receives the direct battery voltage at a constant speed. In that case switch 1 is closed and switch 0 is open. The electric motor (7) drives the worm gear (6), which in turn makes the gear (4) rotate. The gray conductive contact disc is attached to the plastic gear and will therefore also start to rotate. When the wiper switch is placed in the off position, the contact disc (5) and the wiper contacts A, B and C (2) ensure that the motor comes to a stop in the correct position. This is clarified below.

Wiper motor switched on:
In this situation, the wiper motor is switched on. The power supply is supplied via the red plus wire. The switch 1 is closed, providing the motor with a constant supply voltage. The other side of the motor is grounded, so the motor will run at a constant speed. The worm gear is driven by the wiper motor and will therefore start to rotate. In this case, this has no influence on the voltage supply of the motor.

Switch in position off, wiper still moves:
In the illustration below, the wiper switch is set to the “off” position. This means that switch 1 is open and switch 0 (of the zero position) is closed. At this moment a current flows through sliding contact A, via the gray contact plate to sliding contact B. The current then flows from sliding contact B, via switch 0 to the wiper motor. Since the gear is driven by the wiper motor via the worm gear, the contact plate will also rotate. The motor will continue to run until the contact plate notches return to the top.

Switch in off position; windshield wiper stops:
The gear continues to rotate until the contact plate notches are at the top. This interrupts the contact between sliding contacts A and B. Wiper contact A is isolated by the (yellow) plastic gear, so that no current can flow to sliding contact B. No current will flow to the wiper motor. When the contact plate is turned far enough, sliding contact C also makes contact with the small conductive part of the contact plate. At this point, the sliding contacts B and C are connected to each other. Because C is always connected to ground, B now also makes contact with ground via the contact plate. The wiper motor is currently connected to ground on both sides, so that it comes to a stop immediately. This actually works as a kind of brake. In this way, the wiper motor always stops in the same place.

In this animation the different positions of the switch and the contact plate are clearly visible. Here is a brief summary of the explanation given above.

  1. switched off: the switch is in the zero position and the electric motor is short-circuited to the positive and ground.
  2. switched on, constant speed: the switch is in position 1 and the contact plate makes two revolutions clockwise. In this position the contact plate is not used.
  3. Switch position 0, turns to zero position: the contact disc provides the power supply to the motor until the notches have reached the sliding contacts.
  4. AB (plus interrupted), BC make contact. This has a braking effect on the motor, which stops almost immediately.

When, for example, cabling has to be connected during a practical exam, it is necessary to look for the correct switch positions. With the diagram of the wiper motor it can be read which pin in the plug is responsible for the power supply, ground or the zero position. By measuring which wire is 12 Volt in the wiring harness of the car, it can already be connected. With the aid of a resistance measurement, it can be determined which connection is the ground. The Ohmmeter will indicate a resistance value of less than 1 Ohm at this connection. Of course, the mind board must be kept at a good ground point on the body. By then moving the switch in several positions, you can find out which wire belongs to which position of the switch. Then, using the diagram, it can be determined which wires should be connected to each other.

From the theory to the manufacturer's scheme:
The theory of the rear wiper motor was covered in the previous section. The diagrams clearly show how the contact plate in the cutaway wiper motor provides voltage to the motor to return to its initial position. This section explains how this scheme can be translated into a manufacturer's scheme.

Below electrical diagram is based on the rear wiper motor of a Hyundai Getz. The wire colors (blue, brown, white and black) correspond to the colors of the car.

Numbers 1 to 4 in the diagram to the right and below show the pins of the plug connecting the wiper motor to the vehicle's wiring harness. The numbers and wire colors in both schemes match. The schedule below was retrieved from HGS-data.com. The rear wiper motor has the component code herein: M51.

In both diagrams it can be seen that the blue wire (pin 1 in the plug) is the constant positive wire from the fuse. The brown wire (pin 2) is responsible for turning back to the zero position. In the diagram below, the contact plate is shown as a mechanical switch. The switched positive wire from the switch is connected to the white wire (pin 3). The black wire is the ground wire (pin 4) and is connected to a ground point on the body (G55).

In the rest position, the electric motor is short-circuited to ground; the white and brown wires connect to each other through the contact disc.

Two-speed wiper motor:
So far, only the single-speed wiper motor has been talked about. This is suitable for the rear window. The windshield wiper motor can often run at two different speeds, namely the normal speed associated with both the intermittent (first position of the switch) and continuous wipe (second position) and high speed (the third position). There is therefore a speed difference between the second and third position of the wiper switch at which the electric motor rotates. This is achieved by using multiple carbon brushes. In the one-speed wiper motor there are two carbon brushes, in the two-speed wiper motor there are three. The image to the right shows the symbols of a one-speed and two-speed wiper motor.

At the higher speed, fewer armature windings are engaged. The counter tension generated by turning the armature is now smaller. Because less counter voltage is generated, the armature, so ultimately the entire electric motor, makes a higher speed.

The scheme of the two-speed wiper motor is very similar to the scheme already discussed above. The wiper motor is switched positive again here.
There are now three positions of the switch to be seen.
– Position 1: low speed, continuous rotation.
– Position 2: high speed, continuous rotation.
– Position 0: switch off, return to starting position (zero position).

In the diagram on the right, the first position is switched on. This is the low speed.

Mode 2 is switched on here. Now the motor gets the plus through another carbon brush. There is now a lower counter voltage in the electric motor, so that the speed is higher than at the connection of the other carbon brush.

In this scheme, position 0 is selected. The motor is switched off, but first returns to the starting position. The contact plate connects the sliding contacts A and B with each other, so that the wiper motor still has a supply voltage. When the contact plate is rotated 180 degrees further, the contact between the sliding contacts A and B is interrupted, so that the supply voltage is lost. 

The operation with the contact plate and the sliding contacts is the same as with the 1 speed wiper motor.

In this situation the contact plate has twisted again, so that the sliding contacts B and C now make contact with each other. The engine is now grounded on both sides. In this position, the wiper motor remains in place until it is switched on again.

LIN bus controlled wiper motor:
The systems mentioned earlier make use of voltages that come from the windshield wiper switch. Control via LIN bus is increasingly used in modern cars. The control unit controls the wiper motor. Multiple inputs, from both the switch (S) and the rain/light sensor (RLS) provide a signal to the ECU to turn the wiper motor (RWM) on, have it wipe at a different speed, or turn it off.

The diagram shows the components that control the wiper motor.
The switch (S) is connected to the ECU with the three green wires. The position of the switch is transmitted via these wires.
The switch therefore has no direct connection to the RWM, as was the case with the conventional control. The RLS gets its power from the ECU (12 volts), gets its ground through a ground point and passes its signal through the LIN bus wire to the other connected components. The RWM is controlled by means of a signal on the LIN bus. The control unit in the RWM (recognizable by the transistor sign) takes care of the actual control of the electric motor.

In the conventional wiper motor, the position of the conductive contact plate caused the movement to the zero position. With a LIN bus controlled wiper motor, this contact plate is replaced by a position disc and Hall sensors. The position of the position disc depends on the position of the plastic gear wheel, and therefore on the position of the windscreen wiper arm. The position disk is divided into a number of north and south poles (the N of North and the S of South). Because each north and south pole on the position disc has a different size, the control unit in the RWM can determine the exact position of the gear wheel by means of the Hall sensors. When the RLS or the switch ends controlling the wiper motor, the control unit in the RWM controls the electric motor until the position disc has reached the “zero position”.

Advantages of this control are:

  • PWM control makes it possible to run different speeds.
  • The direction of rotation of the electric motor can be reversed; turning clockwise moves the wiper arms up and turning counterclockwise moves the wiper arms down. This allows for a smaller installation space for the wiper mechanism.
  • The zero position can vary; sometimes by moving the wiper blades a little bit up, the rubber of the wiper blade tilts the other way. The wiper blade now does not always occupy the same position on the windscreen. This has a positive influence on the life of the wiper blade.

The LIN bus signal can be measured with an oscilloscope. The scope image shown is of the communication between the ECU (the master) and the rain/light sensor and the wiper motor (the slaves).

On the page LIN bus describes the structure of a LIN bus message. Also, the communication of the wiper system is described in detail and it is explained how faults in the LIN bus signal can be recognized.

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