Variable Valve Timing Actuator: Description and Operation
Engine timing, valves
1 Bolt, M6 X 18
2 Solenoid with 2-pole plug
3 Washer-head bolt, M5 X 12
4 Armature with roll pin
6 Nut, M20 X 1.5, wrench size 30 mm
7 Front left cover
12 Cover
13 Camshaft sprocket
14 Adjustment piston
14a Spiral cone spring
15 Washer-head bolt, M7 X 12
16 Flanged hub
17 Compression spring
18 Control piston
19 Retaining ring, 18 X 1
20 Sealing cap for oil passage, A18
21 Dowel pin in camshaft
22 Intake camshaft
Camshaft timing adjusters
With the engine running both camshaft timing adjusters hydraulically/mechanically rotate the intake camshafts relative to the driving camshaft sprocket by 20° of crankshaft angle in the advanced position and back to the retarded position. The adjustment is controlled electromagnetically through the engine control unit.
The adjustment time of about 1 second is dependent on the engine oil pressure at the camshaft adjusters and the temperature or viscosity of the oil.
The camshaft position indicator on the camshaft sprocket (13) sends the camshaft rpm signal from the camshaft position sensor as an input parameter for the ignition control unit. The angle of rotation for the camshaft advancement is limited by circumferential stops between the camshaft sprocket (13) and the flanged hub (15).
A spiral cone spring (14a) prevents gear play from causing noise during cranking.
Function
Engine off (retarded)
The compression spring (17) forces the control piston (18) against the retaining ring (19). Oil pressure in the camshaft adjuster is released.
From 0 to between 1000 and 2000 rpm (retarded)
The torque of the internal helical-geared camshaft sprocket (13), working in the direction of engine rotation, forces the external helical geared adjustment piston (14) against the cover (12).
In this way the adjustment piston (14), which also has internal helical gears, holds the external helical geared flanged hub (16), which is bolted directly to the camshaft (22), in the retarded position. The compression spring (17) pushes the control piston (18) against the retaining ring (19). The engine oil runs through 2 angled holes in the camshaft flange and in the flanged hub (16) into working chamber A. This engine oil pressure also serves to hold the adjustment piston (14) in the retarded position.
Retarded
A Working chamber
Y49 Solenoid, adjustable camshaft timing
12 Cover with ring insert
13 Camshaft sprocket
14 Adjustment piston
14A Spiral cone spring
16 Flanged hub
17 Compression spring
18 Control piston
19 Retaining ring 18 x 1
22 Camshaft
23 Oil return hole
From 1000 to 2000 rpm up to 4700 rpm (advanced)
The control piston (18) is pulled forward by the adjustable camshaft timing solenoid (Y49) against the compression spring (17) up to the stop in the flanged hub (16).
The control piston (18) closes the oil supply passage to working chamber A and simultaneously opens the oil supply passage to working chamber B through two holes in the flanged hub (16) and in the adjustment piston (14). Oil pressure moves the adjustment piston (14) against the stop in the flanged hub (16).
Because of the axial movement of the adjustment piston (14), the camshaft (22), bolted to the flanged hub (16), turns to the advanced position. The camshaft advance results from the effect of the helical teeth in the camshaft sprocket (13), the adjustment piston (14), and flanged hub (16).
At the same time, pushed by the adjustment piston, the engine oil in working chamber A flows out through the flanged hub (16) and the 2 holes (23) drilled through the camshaft flange.
Advanced
A Working chamber A
B Working chamber B
Y49 Solenoid, adjustable camshaft timing
13 camshaft sprocket
14 Adjustment piston
14A Spiral cone spring
16 Flanged hub
17 compression spring
18 Control piston
22 Camshaft
23 Oil return hole
Above 4700 rpm (retarded)
The adjustable camshaft timing solenoid (Y49) has no voltage applied and releases the control piston. The control piston (18) is driven by the compression spring (17) against the retaining ring (19). The oil supply passage to working chamber "B" is closed off, and the passage to working chamber "A" is opened through the 2 holes in the flanged hub (16). The control piston (18) is moved against the cover (12) by the engine oil pressure.
This axial movement of the adjustment piston (14) turns the camshaft (22), bolted to the flanged hub (16), to the "retarded" position. The camshaft retard results from the effect of the helical teeth in the camshaft sprocket (13), the adjustment piston (14), and flanged hub (16). At the same time engine oil in working chamber "B", pushed by the adjustment piston, runs out through the 2 holes in each of the adjustment piston (14), the flanged hub (16) and the control piston (18) and the two holes (23) in the camshaft flange (22).
Assembly note
The individual parts of the camshaft timing adjuster can be assembled together only in one specific, predetermined sequence.
The solenoid is sealed to the cover with a sealant.
Testing
See Diagnostic Manual, Engine.
4 Armature
6 Nut
12 Cover with ring insert
13 Camshaft sprocket
14 Adjustment piston
16 Flanged hub
18 Control piston
22 Intake camshaft
Idler sprocket
The idler sprocket (1) with its bushing is mounted on a hardened journal (2) and is guided axially by the timing chain.
The hollow-bored journal with 2 oil passages to the bushing surface is mounted in the cylinder head and fastened with a left-hand-thread screw (3).
Timing chain, guide and tensioning rails
One double roller timing chain drives the four camshafts. For improved wear resistance, the rollers are calibrated.
Both the upper left and right guide rails are also designed as suction ducts for crankcase ventilation.
Timing chain tensioner
The hydraulic timing chain tensioner with compression spring tensions the timing chain via the tensioning rail. The chain tensioner cannot be disassembled.
1 Housing
2 Spring retainer
3 Thrust bolt
4 Push rod
5 Compression spring
6 Sealing cap
7 Return flow check valve
8 Oil supply bore
9 Sealing ring, 10 x 14
10 Screw plug, M10 x 1 mm
Hydraulic valve lifters
The hydraulic valve lifters are carbon nitrated and manganese phosphate treated on the running surfaces of the camshafts. The integral oil return check valve (6) prevents the valve lifters from draining when the engine is shut off.
The valve lifters must be stored with the running surface downward. They cannot be disassembled.
The manufacturer's identifying mark is stamped on the sealing cover.
1 Hydraulic valve lifter
2 Thrust piece
3 Compression spring
4 Oil supply groove (circumferential)
5 Oil supply hole
6 Oil return flow check valve
7 Piston with check valve
8 Retaining ring
9 Oil accumulator
10 Oil supply space
11 Working chamber
a Diameter 35 mm
b Height 26.5 mm
c Minimum valve lift: 2.3 mm
Camshafts
The hollow chilled cast iron camshafts are supported by 5 bearings each in the cylinder head and guided axially at the second bearing.
The positioning hole in the camshaft flange of all 4 camshafts is located for a crankshaft position of 45° before compression TDC of cylinder no. 1, with the camshaft adjuster in the retarded position.
Positioning is attained with 4 locator pins (1) 119 589 00 15 00 (1 set) using the hole in the no. 1 camshaft bearing cap.
Valve timing
Removal and installation of camshafts
(only when camshaft lobes are not depressing any valve lifters). For this purpose position crankshaft at 45° before compression TDC of no.1 cylinder (front right) and with the timing chain removed turn camshaft with open end wrench 119 589 00 01 00 accordingly.
Valves
The valves were made smaller and reduced in weight.
The exhaust valves have hardened seats and are sodium filled.
The Viton valve shaft seals are metal banded.
Valve springs
Opposite-wound double springs with rotating valve spring retainer.