BMW Cruise Control Actuator Technical Data

November 20, 2005

[draft]
Table of Contents Usage Cross Reference...3 Theory of Operation..5 Actuator Failure Modes...6 External Description..7 Internal Description..9 Throttle Cable Removal.. 10 Disassembly... 13 Actuator Removal... 21 Circuit Board Pictorial... 24 Circuit Board Schematic... 25
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Usage Cross Reference
This actuator was used on several BMW models from October 1985 through May 1999. The chart below may be used to cross reference the usage of the actuator. Part #: Chassis
E31 E31 E31 E31 E32 E32 E32 E32 E32 E32 E32 E32 E32 E32 E32 E32 E32 E32 E32 E34 E34 E34 E34 E34 E34 E34 E34 E34 E34 E34 E34 E34 E34 E34 E34

65711378315 Model

840i 840Ci 840i 840Ci 735i 735iL 740i 740iL 735i 730i 750iL 735iL 750i 730iL 750iLS 730i 740i 740iL 730iL 525i 535i M5 3.6 525i 525i 530i 530i 540i 535i 520i 525i 530i M5 3.6 525i 520i 518i
Coupe Coupe Coupe Coupe Sedan Sedan Sedan Sedan Sedan Sedan Sedan Sedan Sedan Sedan Sedan Sedan Sedan Sedan Sedan Sedan Sedan Sedan Sedan Touring Sedan Touring Sedan Sedan Sedan Sedan Sedan Sedan Sedan Sedan Sedan

Engine

M60 M62 M60 M62 M30 M30 M60 M60 M30 M30 M70 M30 M70 M30 M70 M60 M60 M60 M60 M20 M30 S38 M50 M50 M60 M60 M60 M30 M20 M20 M30 S38 M50 M50 M43
America America Europe Europe America America America America Europe Europe Europe Europe Europe Europe Europe Europe Europe Europe Europe America America America America America America America America Europe Europe Europe Europe Europe Europe Europe Europe

Manufactured from to

Sep-93 May-95 Dec-92 Dec-94 Aug-86 Jan-88 Jun-92 Jun-92 Oct-85 Jul-86 Nov-86 Jun-87 Jul-87 Dec-87 Sep-88 Mar-91 Sep-91 Oct-91 Jun-92 Jan-88 Jan-88 Sep-89 Jun-90 Oct-91 Nov-92 Nov-92 Nov-92 Mar-87 Jun-87 Jun-87 Jun-87 Apr-88 Jan-89 Mar-89 Mar-90 Nov-95 Jul-97 Feb-96 May-99 Jun-92 Jul-92 Apr-94 Mar-94 Jul-92 Mar-94 Mar-94 Jul-92 Mar-94 Mar-94 Mar-94 Mar-94 Mar-94 Mar-94 Mar-94 Aug-90 Feb-93 Mar-93 Dec-95 Jan-96 Dec-95 Nov-95 Dec-95 Apr-93 Sep-90 Aug-90 Jul-90 Apr-92 Dec-95 Dec-95 Dec-95

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E34 E34 E34 E34 E34 E34 E34 E34 E34 E34 E34 E34 E36 E36 E36 E36 E36 E36 E36 E36 E36 E36 E36 E36 E36 E36 E36 E36 E36 E36 E36 E36 E36 E36 E36 520i 525i 525ix 525ix M5 3.8 530i 540i M5 530i 540i 518i 518g 325i 325is 318i 318is 320i 325i 318i M3 325i 320i 325i 320i M3 325i 320i 316i 318i 316i 318is 316i 1.6 318i M3 318ti Touring Touring Sedan Touring Sedan Sedan Sedan Touring Touring Touring Touring Touring Sedan Coupe Sedan Coupe Sedan Convertible Convertible Coupe Sedan Sedan Coupe Coupe Coupe Convertible Convertible Sedan Sedan Coupe Sedan Compact Convertible Convertible Compact M50 M50 M50 M50 S38 M60 M60 S38 M60 M60 M43 M43 M50 M50 M42 M42 M50 M50 M42 S50 M50 M50 M50 M50 S50 M50 M50 M43 M43 M43 M42 M43 M43 S50 M42 Europe Europe Europe Europe Europe Europe Europe Europe Europe Europe Europe Europe America America America America America America America America Europe Europe Europe Europe Europe Europe Europe Europe Europe Europe Europe Europe Europe Europe Europe Nov-90 Dec-90 Apr-91 Jul-91 Jul-91 Mar-92 Mar-92 Mar-92 May-92 May-93 Nov-93 May-95 Oct-90 Nov-90 Nov-91 Nov-91 Sep-92 Nov-92 Oct-93 Nov-93 Nov-89 Jan-90 Oct-90 Feb-91 Mar-92 Aug-92 Nov-92 Feb-93 Feb-93 Mar-93 May-93 Jun-93 Nov-93 Nov-93 Mar-94 Jun-96 Jun-96 Dec-95 Mar-96 Jul-95 Dec-95 Dec-95 Jul-95 Jun-96 Jun-96 Jun-96 Jun-96 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94 Sep-94

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Theory of Operation
The throttle is simultaneously linked by cable to the cruise control actuator and by a second cable to the accelerator pedal. The core of the cruise control actuator is a small motorized drum which winds or unwinds a belt of rubberized fabric. This control belt is affixed to the cable connected to the throttle. Thus, by winding the belt the throttle cable can be retracted, or by unwinding it can be extended. When the cruise control is not in use, the motor drive is disengaged from the drum. This allows the drum to turn easily and the throttle cable to move freely in response to accelerator pedal action. A clockwork style spring supplies mild tension to keep the belt wrapped around the drum and also takes up slack from the throttle cable. A solenoid is used to engage the motor drive with the drum. When the solenoid is energized a small armature is moved which pushes a sprocket into contact with the integrated gear on the drum. At this point, if current is supplied to the drive motor, the drum will wind. If the polarity of the current is reversed, the drum will unwind. The control unit (brain) is located in the electronics bay. The control unit can thus command the actuator to engage or disengage, to reel in the throttle cable or extend it. This provides the necessary control capabilities. To maintain a set vehicle speed, the control unit needs to know the rotational position of the drum. A potentiometer (variable resistor) integrated into the drum supplies this information to the control unit. A resistance proportional to the position of the drum is constantly presented to the control unit. This feedback allows the control unit to determine how the actuator has responded to its commands. By using the current vehicle speed (supplied by another sensor) along with the feedback from the actuator, the control unit can adjust the actuator as necessary to maintain vehicle speed.

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Actuator Failure Modes
The cruise control actuator will seem to work only intermittently or partially when a tooth is broken in the gear driving the control belt drum. This is because the control unit will attempt to operate the actuator, but gets inconsistent feedback from the potentiometer when the drive encounters the broken tooth.
Figure 1 - Control belt drum with broken tooth
When the inconsistent feedback is received the control unit will eventually give up and disengage. A similar effect is noticed when the potentiometer resistance surface or wipers become pitted or burned. When the control belt breaks or the motor or solenoid burns out a complete failure of the actuator is observed.

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External Description
The cruise control actuator is enclosed in a two part plastic housing. The throttle control cable protrudes through a fixture on the top half. A round male electrical connector for the control cable is also located on the top half.
Figure 2 - Actuator top view
Figure 3 - Actuator side view

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Figure 4 - Actuator side view
Figure 5 - Actuator bottom view (mounting plate and cable removed)

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Internal Description
When the actuator is disassembled, the following components are revealed.
Figure 6 - Internal components
Figure 7 - Internal components (alt. view)

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Throttle Cable Removal
The throttle cable may be separated from the cruise control actuator. This may be accomplished while the cruise control actuator is in the automobile.
Figure 8 - Throttle cable release tab
Figure 9 - Depress tab and pull cable

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Figure 10 - Sliding out throttle cable
Figure 11 - Throttle cable separated from cruise control

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Figure 12 - Throttle cable disconnected

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Disassembly
The actuator may be disassembled in the following steps.
Figure 13 - Remove mounting plate nuts
Figure 14 - Remove shell perimeter screws

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Figure 15 - Using screwdriver to separate shell halves
Figure 16 - Shell halves separated showing internal components

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Figure 17 - Control belt drum gear and retraction spring removed

Figure 18 - Detail of control belt threading through clevis

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Figure 19 - Detail of control cable drum gear, flexible guide, and clevis
Figure 20 - Detail of control cable drum gear showing broken tooth

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Figure 21 - Detail of drive engagement sprocket
The drive engagement sprocket is disengaged when the solenoid is deenergized. When disengaged, the control belt drum will turn freely. This allows the control belt to pay in or out. The retraction spring (not shown) eliminates slack.
Figure 22 - View of circuit board with solenoid removed

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Figure 23 - Circuit board and solenoid
Figure 24 - Drive engagement sprocket and motor drive
When the circuit board and solenoid are removed, the drive engagement sprocket and motor drive with auxiliary gear are revealed.

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Figure 24 - Drive engagement sprocket and shaft
Figure 25 - Solenoid and drive engagement sprocket

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Figure 26 - Solenoid and drive engagement sprocket (partially reassembled)

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Actuator Removal
The cruise control actuator is easily removed from most E34 vehicles. For these vehicles, the actuator is located on the top of the engine compartment next to the power steering reservoir.
Figure 25 Typical E34 mounting (non-540i)
On E34 540is, the actuator is located below and in front of the brake pressure booster. This makes it difficult to remove the actuator.
Figure 26 - Cruise control mounting on E34 540i

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Actuator Removal A complex option is to remove the front fascia and headlight. A simpler method is to remove the mounting bracket bolt which holds the mounting bracket to the chassis.
Figure 27 - Overhead view of mounting bracket
Figure 28 - Elevation view of mounting bracket
The mounting bracket may then be temporarily bent. This allows space for the actuator mounting screws to be removed and for the

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Actuator Removal actuator to be slid out from under the brake pressure booster and alongside the radiator.
Figure 29 - Elevation view of temporarily deformed mounting bracket
Please note that the space will still be very tight. There will be a need for some maneuvering of the actuator before it will slide out.

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Circuit Board Pictorial
The Cruise Control Actuator has a simple printed circuit board with connections to a potentiometer, motor, solenoid, and eight pin connector. The motor has a measured resistance of 10 ohms and is designed for a 12vdc system. The solenoid has a measured resistance of 33 ohms and is used to engage the motor drive. The potentiometer has a measured resistance of 250 ohms and is used to sense the position of the control cable drum gear.

Figure 30 - Actuator circuit board (bottom)
Figure 31 - Actuator circuit board (top)

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Circuit Board Schematic
The cruise control actuator is electrically a simple circuit linked to an eight pin connector. The circuit and the connector are diagramed below.
Figure 32 Actuator Schematic
Actuator 8 pin connector Pin Description Drive motor (-) Drive motor (+)
2, 3 Engagement solenoid 5, 8 Position sense potentiometer Potentiometer center tap Not used
Table 1 Actuator 8 pin connector

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