Service Manual. Servotwin Type 8298

Transcription

1 Service Manual Servotwin Type S en V02 Version Robert Bosch Automotive Steering GmbH Schwaebisch Gmuend Germany Telephone global.service@bosch.com

2 Safety Instructions en Safety Instructions These instructions are to be referred to when carrying out necessary service work and repair on the Automotive Steering unit. Read these instructions first before starting the service work. Authorized, specialized staff must make sure that the product works perfectly again after the service work has been completed. Automotive Steering units may only be repaired in workshops with - staff trained by Robert Bosch Automotive Steering GmbH - specified equipment and special tools corresponding to the work to be performed - original Bosch spare parts This manual should only be used by technicians whose practical and theoretical training in our Global Service Training Centre is supplemented by this reference book and by service information. As a basic principle, only work listed in the instructions may be carried out on the steering gear. Additional changes or adaptations are not permitted and could cause a safety-critical deficiency. However, if in exceptional circumstances, other work should be necessary, then separate information which is only applicable for this case will be provided (e.g. service information). All work on Automotive Steering units must be carried out with great care and conscientiousness. This applies in particular to units and transmission parts from vehicles which have been involved in accidents. Before removing the hydraulic unit, any operating fluid (e.g. lubricant) must be drained without residue and must be routed through company-internal disposal. All metal parts which can no longer be used must be recycled in metal recycling. Other parts (e.g. seals) must be disposed of properly according to the respective applicable regulations. The manufacturer will not be held liable for damage and associated consequences caused by improper and/or unqualified repair. The numbers indicated in round brackets refer to the picture numbers used in the figures. The numbers indicated in square brackets refer to the used tools. Important notes These instructions are not subject to the change management service. Pay attention to further written service information. Protection notice Passing on or reproducing this document, utilizing, and communicating its content is prohibited, unless expressly permitted. Contraventions obligate compensation in damages. All rights reserved in the event of patent and utility model registration. Servotwin is a registered trademark of Robert Bosch Automotive Steering GmbH. List of changes Index Date of issue Author Chapter Comment 01 06/2014 n.a. - Initial version 02 05/2016 NJ OTG All Layout changed II 8298 S en V02

3 en Content Content 1 Symbols Used Safety Instructions Design and Function Design Overall system System depiction RB-Servocom Electric servo unit Function Electric servo unit RB-Servocom Steering to the right (piston with right-handed thread) Steering to the left (piston with right-handed thread) Torque flow Service Work Notes Maintenance Conducting test drive Checking external leak tightness/damage Checking oil level Reading out/erasing error memory Inspection Inspection intervals Test drive Visual inspection Oil filter change Steering system play (ST component) Ease of movement of steering system (ST component) Snap-in locks (ST component) Steering wheel (ST component) Reading out/erasing error memory Checking steering limiter Oil change and venting Oil change Filling oil Venting Elimination of External Leakages Valve core: pressure relief valve Screw plug(s) Removal and Reinstallation Removal Reinstallation Mount the pushrods or tie rods S en V02 III

4 Content en Check oil level Select vehicle model Teach-in the straight-ahead position Set the steering limiter Special Tools Troubleshooting Troubleshooting on steering system Checking steering spindle bearing play in the steering column Checking circumferential backlash or sluggishness Checking leak tightness Checking driving straight-ahead position of steering and vehicle Checking the hydraulic function of the Pump and the Servotwin Install tool [1] (Servotest 600) Checking maximum pressure of the pump Checking the flow rate of the Pump Checking the Servotwin maximum pressure and leakage oil Checking valve return mechanism Checking steering play Troubleshooting path Legend and Detailed Picture Maintenance Report Servotwin Inspection Report Servotwin IV 8298 S en V02

5 en Symbols Used 1 1 Symbols Used Pictograms used in this document: ATTENTION ATTENTION indicates a hazardous situation which, if not avoided, can lead to personal injury or endanger life. NOTICE NOTICE is used to address practices not related to physical injury. 2 Safety Instructions ATTENTION Important safety instructions for the driver and workshop staff With an intact steering system, the driver must apply low actuating forces (e.g. 30 N corresponds to approx. 3 kg) to the steering wheel. If the assistance fails (e.g. through a lack of oil), the actuating force required for steering increases significantly (to, e.g. 450 N corresponds to approx. 45 kg). As this occurs rarely and unexpectedly, the driver may be misled to believe that the steering system is blocked. This is not the case; it is merely sluggishness that has set in. Even in case of hydraulic or electric assistance failure, a mechanical connection from the steering wheel to the wheel always exists. This ensures the ability to steer with increased actuating force. In order to avoid damage to the Servotwin and the steering column, the actuating force on the steering wheel when steering while stationary without hydraulic assistance may not exceed - given a steering wheel diameter of 500 mm N (approx. 45 kg) S en V02 5 of 40

6 3 Design and Function en 3 Design and Function 3.1 Design Overall system RB-Servocom Elektric servo unit Fig. 1: Overall system The Servotwin augments the RB-Servocom hydraulic steering gear by one electric servo unit. In addition to the steering wheel actuating torque, the servo unit can increase the torque acting upon the steering gear. The electric servo unit enables, depending on the application, following additional features: Comfort functions - Speed-dependent actuating forces - Active return - Direct steering gear ratio - Additional torque Safety functions - Emergency steering function Reduction of operating costs - Reduction of fuel consumption - Software end stop Assistance functions - Lane assist - Crosswind compensation 6 of S en V02

7 en Design and Function System depiction In Fig. 2 the overall system is depicted. For the realization of all functions, two different circuits (red - electrical/blue - hydraulic) are required. RB-Servocom Fig. 2: System depiction RB-Servocom The housing of RB-Servocom comprises steering valve, working cylinder, as well as a complete mechanical steering gear. The oil flow and pressure required for the RB-Servocom are supplied by an engine-driven pump (I). For this, the oil is extracted from the oil reservoir (H) and led, via the pump (I) and the RB-Servocom, back to the oil reservoir (H) (Fig. 3). The housing (A) and the piston (B) have the function of a cylinder. The piston (B) converts the slewing motion of the steering spindle (C) and the worm gear (D) into an axial movement and transfers this to the steering sector shaft (F). The piston (B) and worm gear (D) are connected in a positive lock via a ball chain. When the worm gear (D) rotates, the balls at the one end of the chain are taken up by a recirculating tube and again added to the other end. This process creates an infinite ball chain. Through the gearing on the piston (B) and steering sector shaft (F), the displacement of the piston causes the steering sector shaft to execute a slewing motion S en V02 7 of 40

8 3 Design and Function en Straight-ahead driving Fig. 3: Straight-ahead driving Number Description Number Description A Housing B Piston C Valve slide/steering spindle D Control bushing/worm gear E Torsion bar F Steering sector shaft G Pressure relief valve H Oil reservoir I Pump The steering valve consists of the valve slide with needle bearings (C) in the worm gear (D) and the worm gear (D). Both possess six control slots (Fig. 3). A torsion bar (E), which is pinned to the valve slide (C) and the worm gear (D), holds the steering valve in the middle position, as long as no force is applied on the steering wheel. A pressure relief valve (G) that limits the maximum pressure in the steering system can be integrated into the housing (A). 8 of S en V02

9 en Design and Function Electric servo unit The main components of the electric servo unit are the electric motor (J), helical gear drive (K), control unit (L), torsion bar (M) and a torque/steering angle sensor (N) (Fig. 4). Fig. 4: Electric servo unit Number Description Number Description J Electric motor K Helical gear drive L Control unit M Torsion bar N Torque/steering angle sensor (not visible) 8298 S en V02 9 of 40

10 3 Design and Function en 3.2 Function Electric servo unit The torque/steering angle sensor captures the steering-wheel torque and transmits this value to the control unit (Fig. 4). From this parameter and the vehicle speed, the control unit calculates the required supporting torque of the electric motor. The helical gear drive transfers this onto the valve slide (C) (Fig. 3). In this way, additional supporting torque is provided supplemental to the steering-wheel torque, therefore permitting realization of the additional features listed in Chapter The mechanical connection from the steering wheel to the steering linkage is maintained, despite the possible failure of the electronics. Hydraulic assistance continues to be available. In case of failure of the hydraulics, the supporting torque of the electric motor ensures safe steering until the vehicle is stationary. In case of failure of the vehicle power supply, an onboard safety device guarantees power supply to the electric servo unit and thus ensures its mechanical assistance RB-Servocom With the transfer of torque from the valve slide (C) to the worm gear (D), the torsion bar (E) is deformed in the elastic region such that a rotation occurs between the valve slide (C) and the control bushing (D) (Fig. 3). In this way the control slots of the valve slides (C) are displaced from the middle position vis-à-vis the control slots of the control bushing (D). If the steering wheel is let go, the torsion bar (E) ensures that the steering valve is rotated back to the middle position. As long as the steering valve is in the middle position, the oil can flow to both cylinder chambers and then via the valve slide (C) to the oil reservoir (H). 10 of S en V02

11 en Design and Function Steering to the right (piston with right-handed thread) When turning the steering wheel to the right, the piston is shifted to the right (Fig. 5). Fig. 5: Steering to the right Depending on the required steering force, pressure is built up in the left cylinder chamber of the Servotwin and the working cylinder. The oil from the right cylinder chambers is displaced. It flows via the valve slide to the oil reservoir. Moreover, the additional features of the electric servo unit listed in Chapter may be active S en V02 11 of 40

12 3 Design and Function en Steering to the left (piston with right-handed thread) Fig. 6: Steering to the left When turning the steering wheel to the left, the piston is shifted to the left (Fig. 6). Depending on the required steering force, pressure is built up in the right cylinder chamber of the Servotwin and the working cylinder. The oil from the left cylinder chambers is displaced. It flows via the valve slide to the oil reservoir. Moreover, the additional features of the electric servo unit listed in Chapter may be active. 12 of S en V02

13 en Design and Function Torque flow The torque/steering angle sensor captures the actuating torque of the driver (Fig. 7). From this value and other parameters, the control unit calculates the required supporting torque of the electric motor. The helical gear drive transfers this supporting torque onto the RB-Servocom. In this way, additional supporting torque is provided supplemental to the steering-wheel torque. Both of these torques are transferred via linkage to the steered front wheels. RB-Servocom Fig. 7: Torque flow 8298 S en V02 13 of 40

14 4 Service Work en 4 Service Work 4.1 Notes For vehicles with space for more than 8 passengers or with more than 7.5 t permissible total weight, statutory provisions of various countries stipulate the execution of a safety test (ST). ATTENTION For vehicles not subject to the ST obligation, additionally perform the work listed in Service Work Chapter Building on a test drive and a subsequent visual check of the entire steering system (steering column, angle transmission, Servotwin, pushrods, pump, and hydraulic lines), we recommend performing the following work: Within the context of maintenance, the function of the steering system is tested by conducting a test drive/visual check. Safety-critical features are tested during an inspection. 4.2 Maintenance Maintenance intervals We recommend performing the following work within the context of maintenance work (see instructions of the vehicle manufacturer) Conducting test drive During the test drive, pay particularly close attention to the following features: Return mechanism Sluggishness/hook Increased friction Play Checking external leak tightness/damage NOTICE When cleaning with a high-pressure cleaner, do not point water spray directly onto the sealing parts and electrical plug connectors of the steering system. The penetration of water and contamination could lead to malfunctions. Check Servotwin, working cylinder, pump, power lines, and screw connections for leakage and damage Checking oil level Oil grade: refer to the List of Lubricants TE-ML 09 Before extracting the oil dipstick, thoroughly clean the oil reservoir and the area directly near it so that the hydraulic oil is not contaminated. ATTENTION An oil level that is too low can lead to malfunctions, which may result in failure of the steering system hydraulic assistance. 14 of S en V02

15 en Service Work 4 Oil level check when engine is not running The oil must be filled up to the upper marking of the oil dipstick. Oil level check when engine is running When the engine is running, the oil must be filled to between the lower and the upper marking. When the engine is switched off, the oil level is permitted to rise by 1 2 cm (depending on the size of the steering system). If the oil level rises more than 2 cm, bleed the steering system again. Start engine Reading out/erasing error memory Read out the error memory via the OBD connector with ZF-TESTMAN or another suitable diagnostic tester. If current errors have been entered, search for their cause and eliminate them (see diagnostic manual). Erase error memory. Check whether the malfunction indicator light is off or the display error message is cancelled. 4.3 Inspection ATTENTION The inspection intervals depend on the type of application of the vehicle. Therefore, a distinction is made between the different types of application, which may, however, encompass similar characteristics. To enhance road safety, we recommend inspection of the steering system at the following inspection intervals. Minor adaptations of these inspection intervals to the vehicle-specific intervals are permitted. NOTICE The following is a list of work that must be performed within the context of the safety test (ST). This work is designated with (ST component). Therefore, these test steps marked as such may be omitted with ST-compulsory vehicles within the context of normal inspections. In addition, the applicable regulations concerning safety tests (ST) of the respective country of registration must be observed Inspection intervals Type of application 1st inspection Further inspections Long-distance vehicles Coaches with high mileage Buses Construction site vehicles Vehicles for short-distance use Vehicles with heavy load duty cycles km after each additional km km every km Test drive During the test drive, pay particularly close attention to the following features: Return mechanism Sluggishness/hook Increased friction Play 8298 S en V02 15 of 40

16 4 Service Work en Visual inspection Check all steering system screws (steering column thread, angle transmission, Servotwin, pushrods, and working cylinder) and their anchorage. Check sheet metal and split pin securings. Check whether the steering-gear arm still sits firmly on the steering sector shaft by alternating steering to the left and the right and by putting weight on the steering wheel. Check the steering column thread, angle transmission, Servotwin, axle stops, pushrods and tie rods, and lines for damage, fissures, and corrosion. With the engine running, inspect the external leak tightness of the entire steering system Oil filter change ATTENTION Before removing the oil reservoir cover, thoroughly clean the oil reservoir and the area directly near it so that the hydraulic oil is not contaminated. Pull the filter insert from the oil reservoir. Do not allow any dripping into the oil reservoir. Clean the oil reservoir if it is very dirty. Fit in new filter insert. ATTENTION The following is a list of all the work that must be performed on the steering system within the context of the safety test (ST). This list represents the currently valid status and is not subject to the change management service Steering system play (ST component) Start engine Set steering system to straight-ahead position. Slowly rotate steering wheel and simultaneously observe at the front wheel how far one has to turn the steering wheel before the front wheel moves. - permissible total distance (steering wheel ø 500 mm): maximum 55 mm - for models with angle transmissions: maximum 60 mm Ease of movement of steering system (ST component) If the steering system has a hydraulic/electrical defect, this is noticeable when greater actuating force is applied. Start engine. While stationary, quickly turn steering system twice from stop to stop (steering speed 180 /s). In doing so, no sluggishness should occur Snap-in locks (ST component) Defective transmission parts (angle transmission, steering column, universal joints...) may cause sluggishness (snap-in locks) from time to time. Relieve front axle (observe instructions provided by vehicle manufacturer). While the engine is off, turn steering system from stop to stop and pay attention to the snap-in locks. 16 of S en V02

17 en Service Work Steering wheel (ST component) Check steering wheel anchorage. Check the steering wheel for damage Reading out/erasing error memory Read out the error memory via the OBD connector with ZF-TESTMAN or another suitable diagnostic tester. If current errors have been entered, search for their cause and eliminate them (see diagnostic manual). Erase error memory. Check whether the malfunction indicator light or the display error message are off Checking steering limiter ATTENTION The steering limiter must engage at the steering stop or before the steering stop is reached. Turn the steering wheel as far as possible to the left. In case the vehicle manufacturer stipulates a distance dimension regarding the steering locks check these. Turn the steering wheel as far as possible to the right. In case the vehicle manufacturer stipulates a distance dimension regarding the steering locks check these. 4.4 Oil change and venting Oil change Draining oil NOTICE An oil change is necessary only when steering system units have been repaired or replaced. Do not refill drained oil. Mixing oils is not permitted. Draining steering system Raise steering axle(s) (see instructions of the vehicle manufacturer). Unscrew the pressure and return line on the Servotwin. Afterwards, turn off the engine for a short period, maximum 10 seconds, until the oil has been siphoned out of the pump and the reservoir. Collect the oil as it comes out. Re-fasten disassembled components S en V02 17 of 40

18 4 Service Work en Draining Servotwin Fig. 8: Oil change and venting Unscrew the screw plugs (55) from the cylinder head or housing (Fig. 8). For models with working cylinders Unscrew cylinder connections. Quick draining is achieved by, of the components listed above, opening the component arranged at the furthest bottom of the installation position. Manually turn the Servotwin from stop to stop only until oil no longer runs out. Re-fasten unscrewed components using the following tightening torque: Screw plug (55): Nm (M 18 x 1.5) For models with working cylinders also re-fasten cylinder connections. NOTICE Even when opening all above-mentioned components, a quantity of oil will remain in the Servotwin. Depending on the degree of contamination of the oil, a complete draining of the Servotwin may be necessary. For this, remove the Servotwin and request a service partner to dismantle it Filling oil ATTENTION When filling the steering system with hydraulic oil, there is a risk that the steering oil circuit will be contaminated. To prevent malfunctions caused by foreign objects in the equipment, ensure utmost cleanliness during initial or subsequent filling. Oil grade: refer to the List of Lubricants TE-ML 09 Fill the oil up to the upper edge of the reservoir. Start the engine and let it run at idling speed, in order to fill the steering system with oil. During this process, the oil level in the reservoir sinks rapidly. Therefore constantly refill the oil reservoir in order to prevent the intake of air. 18 of S en V02

19 en Service Work Venting NOTICE Automatic ventilation valves only work in the pressure flow area. Therefore avoid a build-up of pressure. When the steering system has been filled so that the oil level no longer sinks from the upper marking of the oil dipstick, run the engine at low speed for 2 3 minutes. Turn the steering wheel from stop to stop several times. Observe the oil level while turning. Top up oil if necessary. If venting correctly, the oil level in the oil reservoir should not rise more than 1 to 2 cm when the engine is switched off. Switch engine off. Lower steering axle and driven axle S en V02 19 of 40

20 5 Elimination of External Leakages en 5 Elimination of External Leakages Fig. 9: Elimination of External Leakages 5.1 Valve core: pressure relief valve Unscrew valve core (22) from the housing (Fig. 9). Eliminate O-ring residue. Re-fasten valve core (22) with new greased O-ring (23). Tightening torque: Nm 5.2 Screw plug(s) Unscrew screw plug(s) (55) and re-fasten with new sealing ring (54). Tightening torque: 50+5 Nm (M18x1.5) 20 of S en V02

21 en Removal and Reinstallation 6 6 Removal and Reinstallation NOTICE As the sensors and electronics in the Servotwin are sensitive to impact, please avoid blows or impacts to the Servotwin during removal and reinstallation. During removal and reinstallation, do not lift the Servotwin by the steering spindle/steering column connection. 6.1 Removal Thoroughly clean the Servotwin and the area directly near it, in particular the line connections. Drain the oil as described in Chapter 4. Note the position of the pressure/return lines. Disconnect pressure/return lines and electrical plug connectors. Close the pressure/return lines (risk of contamination). Disconnect the pushrods from the steering-gear arm and remove them. For vehicles with adjustable steering column also Move the driver workplace into the highest position in order to relieve the ball joint shaft as much as possible. Relieve the ball joint shaft with a suitable tool, e.g. a ratchet strap in such a way that there is no longer any shear force towards the Servotwin. When using a ratchet strap, weave the strap through the fork gaps if possible (see arrows on Fig. 10). Pull the strap tight to prevent damage to the sealing parts or protective cover of the Servotwin from displacement of the universal joints during disconnection of the clamping screws. Fig. 10: Fork gaps 8298 S en V02 21 of 40

22 6 Removal and Reinstallation en Disconnect universal joint or flexible coupling between the Servotwin and steering column or separately installed angle transmission. Unscrew retaining screws and remove the Servotwin (possibly with bearing block). NOTICE Note the position of the fit bolt, if used. Check the marking coverings of the steering sector shaft and steering-gear arm. NOTICE If the markings are offset from each other, ask the vehicle manufacturer prior to assembly of the steeringgear arm whether deviating installation instructions exist. Unscrew securing nut (50) and pull off steering-gear arm with tools [5]. ATTENTION It is not permitted to warm-up the steering-gear arm, drive a spline between the housing and steeringgear arm, or remove the steering-gear arm with hammer blows. This could result in changes in the material or damage to the Servotwin. 6.2 Reinstallation ATTENTION To guarantee the safe function of the steering system, ensure utmost cleanliness during reinstallation of all units belonging to the equipment. NOTICE To prevent malfunctions caused by foreign objects in the steering oil circuit, do not remove the sealing plugs on the power connections of the Servotwin, oil pump, etc. until connecting the connections. If possible, remove protective sleeves only after they have been installed. Connection lines and screw connections must be thoroughly cleaned and deburred. Set steering wheel to straight-ahead position. Clean contact surfaces of the bearing block and Servotwin. For vehicles with adjustable driver workplace also Pull the ball joint shaft together with a suitable tool, e.g. a ratchet strap in such a way that there is enough free space for the Servotwin to be reinstalled (Fig. 10). 22 of S en V02

23 en Removal and Reinstallation 6 Set the steering system in middle position by halving the entire steering wheel turn. Then continue turning until the markers (see Fig. 11) on the steering spindle/protective cover and housing are aligned. Fig. 11: Steering system in middle position Set the Servotwin into the bearing block and screw into place. NOTICE Note the position of the fit bolt. For tightening torque see the technical cover sheet of the spare parts list. In case no information is provided there, the following values apply. Depending on the vehicle type, prior assembly of the steering-gear arm may be necessary due to lack of space. Tightening torque: Thread Bolt grade Tightening torque M 20 x ± 10 % Nm ATTENTION Observe vehicle manufacturer specifications. Reinstall universal joint or flexible coupling between steering column and Servotwin. NOTICE Clamping slot in the universal joint must point toward the cap or steering spindle marking. Observe deviating instructions provided by the vehicle manufacturer. For vehicles with adjustable driver workplace also Attach universal joint without damaging the seal of the Servotwin. Tighten clamping screw (see instructions of the vehicle manufacturer). Carefully release and remove tools, e.g. ratchet strap see Fig S en V02 23 of 40

24 6 Removal and Reinstallation en Set the turned wheels of the vehicle into straight-ahead position. This is achieved when the turned wheels are set parallel to the second set of wheels (place a measuring ledge next to the front and rear wheels). Attach the steering-gear arm onto the gearing so that the markings on the steering-gear arm and the steering sector shaft are aligned (see Fig. 11). Screw on and tighten securing nut (50). NOTICE For tightening torque see the technical cover sheet of the spare parts list or information provided by the vehicle manufacturer Mount the pushrods or tie rods Mount and tighten the pushrods or tie rods. Perform wheel alignment. Turn the steering system to the left up to the stop. Dismount the pushrods or tie rods. Check the steering wheel to see if it can be turned farther to the left. If it cannot be turned farther to the left, reset the steering or axle stop. ATTENTION Ensure that the steering angle limiter occurs on the steering or axle stop and not through the Servotwin. Remount the pushrods or tie rods (see instructions of the vehicle manufacturer). Repeat the test to the right and if necessary reset the steering or axle stop. Mount the pushrods or tie rods (see instructions of the vehicle manufacturer). Connect pressure/return lines and electrical plug connectors as noted during removal. NOTICE The electrical plug connectors must be snapped into place with an audible click. Fill the steering system with oil and bleed it (see Chapter 4) Check oil level Before extracting the oil dipstick, thoroughly clean the oil reservoir and the area directly near it so that the hydraulic oil is not contaminated. ATTENTION An oil level that is too low can lead to malfunctions, which may result in failure of the hydraulic steering assistance Select vehicle model Using ZF-TESTMAN or a diagnostic tool recommended by the vehicle manufacturer, select the vehicle model (left hand drive, right hand drive/8x4/8x8). 24 of S en V02

25 en Removal and Reinstallation Teach-in the straight-ahead position Set Servotwin in the straight-ahead position. Using ZF-TESTMAN or a diagnostic tool recommended by the vehicle manufacturer, teach-in the straight-ahead position Set the steering limiter Using ZF-TESTMAN or a diagnostic tool recommended by the vehicle manufacturer set the steering limiter on both sides S en V02 25 of 40

26 7 Special Tools en 7 Special Tools NOTICE The following tools are universal tools. For particular applications, it may be necessary to use special tools as recommended by the vehicle manufacturer. Tool number and name Figure Order number Tool [1] Servotest Tool [2] Scale with pointer Tool [3] Thrust piece Tool [4] Expanding device (2 units are needed) 1 unit Tool [5] Extracting device of S en V02

27 en Troubleshooting 8 8 Troubleshooting NOTICE The requirement for troubleshooting as follows is that no errors have been entered into the error memory and that no electronic/electric errors exist in the steering system. 8.1 Troubleshooting on steering system Checking steering spindle bearing play in the steering column Move the steering wheel sideways back and forth (jiggle) to see if there is play. In case of play, replace or repair the steering column/bearing Checking circumferential backlash or sluggishness Checking circumferential backlash or sluggishness in universal joint, in telescopic shaft, and angle transmission. If play (audible clatter while turning back and forth) or sluggishness is determined, replace damaged parts Checking leak tightness Start engine. Check leak tightness of all screw connections, power lines, and sealing parts of the entire steering system (angle transmission, Servotwin, pump, and working cylinders). Check all hoses, protective covers, bellows, and power lines for possible chafe marks and brittle fractures. Switch engine off. ATTENTION For hose assemblies with damage, only reinstall authorized spare parts S en V02 27 of 40

28 8 Troubleshooting en Checking driving straight-ahead position of steering and vehicle Vehicles with independent suspension Place wheels of the steering axle on the rotary table. Vehicles with beam axle Raise steering axle (see instructions of the vehicle manufacturer). Determine total steering wheel rotations and halve. Rotate the Servotwin by the halved value into the middle position. Then continue turning until the markers (see Fig. 12) are aligned. Fig. 12: Checking driving straight-ahead position of steering Now rotate turned wheels to straight-ahead position. Undertake a correction by unscrewing or tightening the ball joints on the tie rod/pushrod. ATTENTION If the steering wheel setting is incorrect or a correction has to be made in the length of the steering linkage, the reason for this may be a previous accident-like event. For this purpose, inspect the serrated gear on the steering sector shaft for distortion (lift steering-gear arm to do this), the steering spindle for warped fitting, and all other transmission parts for deformation or fissures. In addition, perform a play inspection, see Chapter 4.3. Do not re-bend deformed parts, but instead replace them. 28 of S en V02

29 en Troubleshooting Checking the hydraulic function of the Pump and the Servotwin Install tool [1] (Servotest 600) In order to perform the pressure and leakage oil tests described in the following, a distinction between 2 types (variant 1 and 2) of steering systems is required. Variant 1 Steering systems in which the pressure relief valve is arranged in the Pump or in the pressure line between the Pump and tool [1] (Servotest 600) (Fig. 13). This means that pressure limitation takes place prior to installation of the tool [1].With this steering system, the type plate of the Pump or the pressure relief valve specifies the maximum pressure, e.g. 130 bar. Fig. 13: Variant 1 Number Description Number Description 1 Pump 2 Oil reservoirs 3 Pressure line 4 Suction line 5 Return line 6 Servotest Pressure relief valve 8298 S en V02 29 of 40

30 8 Troubleshooting en Variant 2 Steering systems in which the pressure relief valve is installed in the Servotwin or in the pressure line between the tool [1] (Servotest 600) and Servotwin (Fig. 14). With this steering system, the type plate of the Servotwin or the pressure relief valve specifies the maximum pressure, e.g. 130 bar. Fig. 14: Variant 2 Number Description Number Description 1 Pump 2 Oil reservoirs 3 Pressure line 4 Suction line 5 Return line 6 Servotest 7 Pressure relief valve Install tool [1] (Servotest 600) according to variant or so that the display can be seen from the driver s seat. Check oil level and bleed the steering system - see Chapter 4. Test conditions: oil temperature 50 C 30 of S en V02

31 en Troubleshooting Checking maximum pressure of the pump Read the maximum permissible pressure value on the type plate of the Servotwin/the pump or the separately arranged pressure relief valve. Start the engine. Set the pressure limitation of tool [1] (Servotest 600) so that the steering system is not damaged during subsequent tests. For steering systems with pressure limitation in front of the the tool [1]: variant 1 Let the engine run at idling speed. Close the shut-off valve of the tool [1] (Servotest 600) and read the maximum pressure value. Target value: maximum pressure (type plate) +10 % ATTENTION Allow maximum pressure for a short time only, at the most 10 seconds, as the internal parts of the pump get overly heated, which can lead to premature wear. Re-open shut-off valve. If the target value is not achieved, replace or repair the pump. For steering systems with pressure limitation behind the tool [1]: variant 2 ATTENTION Allow maximum pressure for a short time only, at the most 10 seconds, as the internal parts of the pump get overly heated, which can lead to premature wear. Let the engine run at idling speed. Observe the pressure gage of tool [1] and slowly close the shut-off valve until the specified maximum pressure has been reached. Do not close the shut-off valve any further (allow maximum pressure for a short time only, at the most 10 seconds, as the internal parts of the pump get overly heated). Rotate shut-off valve to its original position. If the maximum pressure is not achieved during the measurement, replace or repair the pump Checking the flow rate of the Pump NOTICE Target values for flow rate, test pressure, and test speed, see table. Designations and operation of tool [1] (Servotest 600), see separate operating instructions for Servotest 600. Checking the regulated flow rate Increase engine speed until the supply rate of the Pump remains constant despite additional speed increases, approx rpm. The Pump is now in the breakaway range. Target value: see Pump technical cover sheet Checking the minimum flow rate While the engine is running at idling speed, close the shut-off valve so far that the test pressure specified for the pump type is created. Target value: see Pump technical cover sheet Read the flow rate value. Pay attention to the engine speed to pump speed ratio S en V02 31 of 40

32 8 Troubleshooting en Checking the Servotwin maximum pressure and leakage oil For steering systems with pressure limitation in front of the tool [1]: Variant Hold the tool [3] or thrust pieces with a thickness of approx. 15mm (Fig. 15) between the steering stops so that the steering angle is limited to ½ or ¾ of a steering wheel turn before reaching the axle or steering stop. The limitation of the steering angle must occur at the tool [3] or at the thrust pieces, but not at the Servotwin via the piston. Fig. 15: Tool [3] ATTENTION A tool [3] under pressure may be pushed out - avoid direct visual contact with the tool. Risk of accident caused by clamping. Depending on the axle model, use a special tool as specified by the vehicle manufacturer. While the engine is running at idling speed, turn the steering wheel up to the stop and then turn the steering wheel further for approx. 5 seconds with a force of N. Read the maximum pressure and leakage oil values. Repeat the test in the opposite steering wheel direction. maximum permissible leakage oil value: 2.5 l/min Causes for maximum pressure that is too low/leakage oil that is too high: - Defective pressure relief valve. - Defective seals in the Servotwin. - Necessary steering angle is not achieved because the steering limitation is active. Using ZF-TESTMAN or a diagnostic tool recommended by the vehicle manufacturer, increase the possible steering angle. After another test, re-enter the original values. For steering systems with pressure limitation behind the tool [1] variant Close shut-off valve completely and throttle valve so far that pressure of 30 bar less than the maximum pressure is created. Re-open shut-off valve. Perform test as described above. 32 of S en V02

33 en Troubleshooting Checking valve return mechanism NOTICE Pay attention to the movement of the steering column (floor mats, paneling). Close the steering valve by turning the steering wheel and thus building up maximum pressure. Then turn the steering wheel back so that flow pressure exists. Subsequently, set the pressure to a pressure flow of +10 bar. Let go of the steering wheel and observe pressure values. The pressure must drop to the flow pressure (maximum 0.5 bar higher) within 1 second. Example: Flow pressure: 4.0 bar maximum permissible value: 4.5 bar Checking steering play Requirement for the following test Transmission parts between the steering wheel and the wheel must be free of clearance. Models with leaf spring Lock the left front wheel (for right-hand vehicles, the right front wheel) in the straight-ahead position by installing tool [4] between the wheel rim (rear and front) and front spring (Fig. 16). Fig. 16: Tool [4] ATTENTION Do not allow any pressures larger than those listed below to impact tools and wheel rim as this may cause damage to the wheel rim. Models with independent suspension Lock the left front wheel (for right-hand vehicles, the right front wheel) according to instructions from the vehicle manufacturer S en V02 33 of 40

34 8 Troubleshooting en Place tool [2] on the steering wheel and affix pointer to the dashboard or the windshield (Fig. 17). Fig. 17: Placing of Tool [2] Increase engine speed to approx rpm. Read pressure flow value on tool [1] (Servotest 600/pressure gage). Turn steering wheel to the left until 1 bar over the pressure flow is displayed. While doing so, read the scale value on tool [2]. Turn steering wheel to the right until 1 bar over the pressure flow is displayed. Read the scale value on tool [2]. Calculate the total distance covered. - Target value: maximum 55 mm (steering wheel Ø 500 mm) - for models with angle transmissions: maximum 60 mm If the maximum value is exceeded, check the play of the steering column, if necessary repair or maintain the Servotwin. Remove tool [1] (Servotest 600)/pressure gage. Check oil level and bleed the steering system (see Chapter 4). 34 of S en V02

35 en Troubleshooting Troubleshooting path Error Cause Remedy Noise Sluggishness on both sides Air in oil Oil level too low Pump is defective Electric servo unit is defective Oil level too low Steering system is taking in air (suction area) Universal joints/steering column sluggish Bleed the steering system (refer to Chapter 4) Replenish oil Repair (contact Service Partner) Replace (contact Service Partner) Replace (refer to Repair Manual) Eliminate leakage Replenish oil (refer to Chapter 4) Eliminate leakage Replenish oil (refer to Chapter 4) Bleed the steering system (refer to Repair Manual) Check Replace (see instructions of the vehicle manufacturer) Oil filter is soiled Replace (refer to Chapter 4) Servotwin is defective Pump is defective Repair (contact Service Partner) Exchange (contact Service Partner) Repair (contact Service Partner) Replace (contact Service Partner) Wrong oil used Perform oil change (refer to Chapter 4) Fill the steering system with the correct oil (refer to Chapter 4) Sluggishness on one side Sluggishness during quick steering Oil temperature too high Electric servo unit is defective Steering limitation is set incorrectly Servotwin is defective Electric servo unit is defective Steering system is taking in air (suction area) Pump is defective or wrong model Electric servo unit is defective Supplement oil-cooling measures (refer to Chapter 4) Read out the error memory Eliminate errors (refer to Troubleshooting Guide) Set (refer to Chapter 4) Repair (contact Service Partner) Replace (contact Service Partner) Read out the error memory Eliminate errors (refer to Troubleshooting Guide) Eliminate leakage Replenish oil Bleed the steering system (refer to Chapter 4) Replace pump (contact Service Partner) Read out the error memory Eliminate errors (refer to Troubleshooting Guide) 8298 S en V02 35 of 40

36 8 Troubleshooting en Error Cause Remedy Sluggish/inhibited return Precise straight-ahead driving is not possible Axle/axle location parts sluggishness Servotwin/steering column installation warped Steering column is heavy/hard to move Flow pressure too high Servotwin is defective Electric servo unit is defective Oil level too low Axle/axle location parts/steering column not free of clearance Repair (see instructions of the vehicle manufacturer) Eliminate distortion (see instructions of the vehicle manufacturer) Eliminate sluggishness (see instructions of the vehicle manufacturer) Wrong cable cross-section Line is kinked/narrowed Cover wrongly installed or wrong cover is installed (see instructions of the vehicle manufacturer) Repair (contact Service Partner) Replace (contact Service Partner) Read out the error memory Eliminate errors (refer to Troubleshooting Guide) Eliminate leakage Replenish oil (refer to Chapter 4) Bleed the steering system (refer to Chapter 4) Check (see instructions of the vehicle manufacturer) Exchange (see instructions of the vehicle manufacturer) Servotwin has clearance Check (refer to Chapter 4) Exchange (contact Service Partner) Electric servo unit is defective Read out the error memory Eliminate errors (refer to Troubleshooting Guide) 36 of S en V02

37 en Legend and Detailed Picture 9 9 Legend and Detailed Picture Fig. 18: Detailed Picture Number Description Number Description 22 Valve core 23 O-ring 54 Sealing ring 55 Screw plug 8298 S en V02 37 of 40

38 10 Maintenance Report Servotwin en 10 Maintenance Report Servotwin Customer: steering gear model: Vehicle manufacturer: Pump manufacturer: Vehicle type (model): Pump model: Mileage (km): Emergency steering pump: Maintenance Work Conducted test drive? O.K. Not O.K. External leak tightness/damage checked or inspected? Checked oil level? Error memory read out/erased? Original for duplication Remarks: Inspected by (name): Date: 38 of S en V02

39 en Inspection Report Servotwin Inspection Report Servotwin Customer: Vehicle manufacturer: Vehicle type (model): Servotwin model: Pump manufacturer: Pump model: Mileage (km): Inspection intervals see Chapter 4 Inspection work Conducted test drive? Performed visual inspection? O.K. Not O.K. Original for duplication Changed oil filter? Checked steering play? Target value: maximal 55 mm Measured value: mm for models with angle transmissions: maximum 60 mm O.K. Not O.K. Performed ST tests? Error memory read out/erased? Checked steering limitation? Inspected by (name): Date: 8298 S en V02 39 of 40

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