SECTION steering mechanism

Transcription

1 / MR17 SECTION GENERAL Description See Figure 1. The includes the steering wheel (1), the steering column, the miter box (3), the steering shafts (2 and 4), and the drag link (7). For more information on the steering wheel and the steering column, see section : steering column in this manual. The power adds a dual gear hydraulic pump (8), a reservoir with an integrated filtering element (9), a power steering gearbox (5). The function of the power steering is to decrease the effort required for the handling of the steering wheel, and to ensure a regular movement, required to avoid wheel comebacks. Pump 1 of the dual pump is used to activate the radiator fan. Pump 2 provides the pressure and the flow necessary for the correct operation of the power steering. Its continuous smooth motion can be attributed to the constant flow of 15.9 l/min, limited by the control valve, and to the variable pressure, provided by the pump. See section 09: hydraulic system for more details on the dual hydraulic pump. Operating Principles See Figure 1. When the steering wheel is turned, the rotational movement of the steering wheel (1) is transmitted to the intermediate steering shaft (2), which rotates the steering shaft (4) by means of the miter box (3). The steering shaft connects the miter box to the power steering gearbox (5). Inside the power steering gearbox, the steering shaft is connected to an input shaft, which in turn is connected to a worm shaft. The rotation of the worm shaft and the pressure of the hydraulic fluid move the piston rack. The turning command is then transmitted to the pitman arm (6) and then to the drag link (7). Finally, the drag link relays the movement to the front axle linkage parts, resulting in the movement of the wheels in the requested direction. For more information on the front axle linkage parts, see section 04: front axle and axle alignment in this manual Steering wheel 2. intermediate steering shaft 3. Miter Box 4. Steering shaft 5. power steering gearbox 6. Pitman arm 7. Drag link 8. dual hydraulic pump 9. hydraulic Reservoir 8 9 Figure 1 - Steering Mechanism

2 2011MR17 2 / The fluid supply of the steering system is provided by the dual hydraulic pump (8), mounted on the right-hand side of the engine and driven by an engine power takeoff. The hydraulic fluid flows from the hydraulic reservoir (9) to the pump. The fluid moved by the pump flows towards the power steering gearbox (5). A hose connects the steering gearbox to the hydraulic reservoir. For the location of the hydraulic hoses, see Figure 2, 3 or 4, depending on the vehicle model. Caution: O-rings are installed at the firewall adapter locations. These rings should be replaced whenever damaged. For more information on the cooling and hydraulic systems, see section 09: hydraulic system in this manual. Caution: When a component requires replacement, always choose a part carrying the same number or the equivalent. To ensure optimal performance of the, never use a replacement part of lower quality or different design. When the engine is running, there is a constant flow of oil passing through the. This constant flow provides an immediate response and absorbs road bumps, in order to eliminate steering wheel comebacks. The pressure is equal throughout the. The hydraulic fluid of the steering and cooling systems is filtered to prevent debris from getting into the pump, steering system mechanism or cooling system. This filtration occurs before the fluid enters the pump. SUPPLY HOSE Reservoir Pump RETURN HOSE ENGINE COMPARTMENT CONNECTORS RETURN HOSE FLEXIBLE HOSES Pump Reservoir SUPPLY HOSE FIREWALL ADAPTERS WITH O-RING Figure 2 - Rigid Hoses and Connector Locations on Nova LFS 40 ft Standard

3 / MR17 SUPPLY HOSE RESERVOIR PUMP RETURN HOSE ENGINE COMPARTMENT CONNECTORS RETURN HOSE FLEXIBLE HOSES SUPPLY HOSE FIREWALL ADAPTERS WITH O-RING PUMP RESERVOIR Figure 3 - Rigid Hoses and Connector Locations on Nova LFS 40 ft with T-Drive SUPPLY HOSE FLEXIBLE HOSES RESERVOIR PUMP RETURN HOSE ENGINE COMPARTMENT CONNECTORS FLEXIBLE HOSES RETURN HOSE SUPPLY HOSE FIREWALL ADAPTERS WITH O-RING PUMP RESERVOIR Figure 4 - Rigid Hoses and Connector Locations on Nova LFS articulated with T-Drive

4 2011MR17 4 / Housing 2. cover 3. Bolt 4. Seal 5. output Shaft 6. Cone bearing 7. gasket 8. cone bearing 9. grease fitting 10. input shaft 11. Seal 12. nylon shim 13. gear 14. oil filling plug Figure 5 - Sectional View of the Miter Box Miter BOX DESCRIPTION See Figure 5. The miter box is located in the front left corner of the underside of the bus. It allows the rotation transfer between the intermediate steering shaft and the steering shaft. The output shaft (5) is maintained in the cover (2) by a cone bearing (6). The lower end of the output shaft and the input shaft (10) are contained in the miter box housing (1) by cone bearings. LUBRICATION The gearing and bearing service life and efficiency are affected by the oxidation or contamination of the lubricating oil. Performance may be enhanced with periodic lubrication according to the following recommendations: After approximately 500 hours of initial operation, the housing should be completely drained. Fill the housing to the appropriate level with new oil. To drain and refill with fresh lubricant, the miter box must be removed from the vehicle. Follow the procedures for removal and installation indicated under the heading: replacement.

5 / MR17 Under normal operating conditions the gearing should be lubricated approximately every 2,500 hours. CAUTION: The fluid level in the miter box must be sufficient for smooth operation. The specified lubricant should be used. See section 19: fluids and lubricants for more information on the miter box lubrication. 1. Remove the nut, the clamping bolt and the washer from the coupling yoke connecting the intermediate steering shaft (2) to the miter box input shaft (3). Free the miter box input shaft from the intermediate steering shaft. 2. Remove the nut, the clamping bolt and the washer from the coupling yoke connecting the steering shaft (6) to the miter box output shaft (5). Free the miter box output shaft from the steering shaft. 3. Remove the bolts and washers retaining the miter box to the frame siderail. Lower the box with caution from underneath the bus. CAUTION: Lubricate frequently when the miter box is operating under high temperatures or unusually contaminated environment conditions. CAUTION: It is also important to lubricate the cone bearings of the miter box. The lubrication of this component can be carried out manually or automatically, depending on the selected greasing option. See section for more details on greasing systems and section 19: fluids and lubricants for recommended maintenance intervals and lubricants. The tie and end set should be inspected whenever the miter box is lubricated. If excessive play is found in the tie or end set, the housing should be checked. The tie and end set will generally require replacement when the operator notices more play while turning the steering wheel, or imprecise handling of the vehicle, or when uneven tire wear is noticed during servicing. INSTALLATION See Figure 6. See Figure 13 for torque values. 1. Align the miter box input shaft (3) with the intermediate steering shaft (2) and lift the miter box (4) into position. Install the miter box housing on the bracket located on the frame siderail by using the necessary bolts and washers. Tighten to the appropriate torque value. 2. Without tightening, install the washer, the clamping bolt and the nut on the coupling yoke that connects the steering shaft to the miter box output shaft (5). Insert a temporary 0.06 in (1.6 mm) spacer at the open end of the yoke and tighten until the spacer is tight or until the recommended torque value is reached. 3. Without tightening, install the washer, the clamping bolt and the nut on the coupling yoke that connects the intermediate steering shaft to the miter box output shaft (5). Insert a temporary 0.06 in (1.6 mm) spacer at the open end of the yoke and tighten until the spacer is tight or until the recommended torque value is reached. Maximum rolling torque should be 3 lb-in (0.34 N m). Replacement Removal See Figure 6. caution: Before removing the miter box, block the body of the bus. See section 18: hoisting and towing, for the proper hoisting procedures. 1. Steering column shaft 2. Intermediate steering shaft 3. Input shaft 4. miter box 5. output shaft 6. steering shaft Figure 6 - Miter Box Installation

6 2011MR17 6 / Upper poppet 2. Piston rack 3. Lower Poppet 4. Input shaft 5. Torsion bar 6. Rotary valve 7. Worm screw 8. Steel balls 9. sector shaft Figure 7 - Sectional View of the Power Steering Gearbox Power STEERING GEARBOX See Figure 7. For the power steering gearbox maintenance procedures, see the TRW maintenance manual. For the power steering gearbox adjustments, see section 04: axle alignment in this manual. The adjusting screw torque should be confirmed during periodic maintenance checks. See the TRW maintenance manual for torque values. Description When the steering wheel is turned, the steering shaft actuates the input shaft (4), to which it is connected. The input shaft is centered with the rotary valve (6), which actuates the worm screw (7). The worm screw moves along with the piston (2) on steel balls (8). The circular movement of the steering shaft creates a pressure increase at one end of the piston. This increased pressure moves the piston inside the power steering gearbox. The sector shaft (9) is engaged in the rack gear, which is machined on one side of the piston. The movements of the piston rack create a rotary effect in the sector gear and pitman arm. When the steering shaft rotation stops, the actuator valve returns to its neutral position. The release valve plunger or adjustable stops are used in the bearing cap and cylinder cover. When the plungers are correctly adjusted, they will discharge the hydraulic system if the wheels have a maximum steering angle in either direction. In the case of a sudden pressure drop during normal operation, the parts are engineered so that there will be a sufficient mechanical reserve to steer the vehicle to the shoulder.

7 / MR17 REPLACEMENT See Figure 1. See Figure 13 for torque values. b. Install the pitman arm on the shaft using the pinch bolt. Tighten the fastening device to the appropriate torque, indicated in Figure 13. For more information and important safety measures, see the TRW service manual, provided by Nova Bus. WARNING: Before working on the underside of the bus, make sure the body is blocked solidly to prevent it from dropping when the air pressure in the suspension is released. REMOVAL WARNING: To avoid injuries caused by the over 100 lb (45 kg) steering gearbox, have an appropriate wheeled stand ready to support the power steering gearbox after removal. USE CAUTION to avoid being trapped between the gearbox and the vehicle or stand while disconnecting the power steering gearbox from the shaft. 1. Disconnect the return and supply hoses from the power steering gearbox and drain the fluid into an appropriate container. Plug the open ends of the hoses to prevent debris from entering the system. 2. Remove the cotter pin and the slotted nut retaining the drag link (7) to the pitman arm (6). Free the drag link from the pitman arm. 3. Remove the nut, the clamping bolt and the washer from the coupling yoke linking the steering shaft (4) to the input shaft of the power steering gearbox (5). Free the steering shaft from the gearbox input shaft. 4. Remove the bolts and washers retaining the power steering gearbox to the structure welded mounting plate. 5. Place the power steering gearbox on the stand reserved for that purpose. See the TRW maintenance manual for additional information on the pitman arm installation. 2. Align the power steering gearbox (5) and the mounting holes in the welded plate. Install the hardened steel mounting bolts and washers. 3. Align the coupling yoke of the steering shaft (4) to the power input shaft of the power steering gearbox. Without tightening, install the washer, the clamping bolt and the nut on the coupling yoke. Insert a temporary 0.06 in (1.6 mm) spacer at the open end of the yoke. Tighten the screw until the spacer is tight or until the appropriate torque value is reached. 4. Insert the threaded end of the socket in the pitman arm orifice to connect the drag link (7) to the pitman arm (6). If the length of the drag link needs to be adjusted, loosen the clamping collar, adjust the length and retighten the collar to the appropriate torque value. Tighten the slotted nut to the appropriate torque value, advance to the next insertion slot, and install a new cotter pin. 5. Remove the protective plugs from the power steering mechanism supply and return hoses and connect the hoses to the gearbox. 6. Raise the vehicle and remove the shims located between the upper and lower air spring mounting plates. Remove the safety blocks used to shim the body of the vehicle. INSTALLATION 1. If the pitman arm (6) is not installed on the power steering gearbox (5), install it in the following manner: a. Align the timing mark on the sector shaft with the timing mark on the pitman arm. See Figure 8. There must be an angle of 90 between the sector shaft indicator and the horizontal axis of the power steering gearbox input shaft. Align the two lines Figure 8 - Alignment of Pitman Arm

8 2011MR17 8 / in (231.8 mm) MIN. COMPRESSED 11 in. (279.4 mm) MAX. STRETCHED Dust boot ARROWS SHOULD BE ALIGNED AS SHOWN Figure 9 - Intermediate Steering Shaft 7. Fill the power steering reservoir (9) up to the full mark on the gauge with fluid described under section 19: fluids and lubricants in this manual. Then, bleed the system according to the directions found in section 09: hydraulic system in this manual, under hydraulic system purge. 8. Follow the instructions regarding the alignment procedures, included in section 04: axle alignment in this manual. ADJUSTING THE HYDRAULIC PRESSURE See the TRW maintenance manual for hydraulic pressure adjustment methods. Maintenance Check the dust boot, the joints and the shaft for damage. Check the shaft for circular play. If wear or endplay is found in the shaft, replace the shaft. REPLACEMENT See Figure 9. REMOVAL 1. Remove the protective cover from the steering column. CAUTION: Before performing this adjustment, proceed to the stop and steering angle adjustments. See section 04: axle alignment in this manual for the procedures. INTERMEDIATE STEERING SHAFT See Figures 9 and 10. Description Steering wheel 2. bushing 3. Support 4. support 5. steering column shaft 6. Intermediate steering shaft 7. seal 8. screw 9. input shaft 10. miter box See Figure 9. The intermediate steering shaft (6) relays movement from the steering wheel (1) to the miter box (9). It is equipped with coupling yokes with needle bearings at each end. A splined slip joint allows for an easier adjustment during installation Figure 10 - Intermediate Steering Shaft Installation

9 / MR17 COUPLING YOKE in. (1232 mm) min. compressed in. (1393 mm) max. stretched COUPLING YOKE Tube inner face Dust boot TUBULAR STEERING SHAFT OUTPUT (power STEERING gearbox) ARROWS SHOULD BE ALIGNED AS SHOWN SLIP JOINT SLEEVE YOKE differential Spider INPUT (Miter Box) Figure 11 - Steering Shaft 2. Remove the clamping bolt, the nut and the washer from the coupling yoke connecting the intermediate steering shaft (6) to the input shaft (9) of the miter box (10). 3. Remove the clamping bolt, the nut and the washer from the coupling yoke connecting the intermediate steering shaft to the steering column shaft (5). 4. Loosen the seal (7) from the intermediate steering shaft. Using a soft hammer, lightly tap the intermediate steering shaft to free it from the steering column shaft. Remove the seal from the intermediate steering shaft. INSTALLATION 1 Align the mounting arrows on the intermediate steering shaft (6) and the slip joint sleeve. See Figure Install the seal (7) on the intermediate steering shaft. Install the intermediate steering shaft on the miter box input shaft (9) and on the steering column shaft (5). 3. Without tightening, install the washer, the nut and the clamping bolt on both coupling yokes of the intermediate steering shaft. Insert a temporary 0.06 in (1.6 mm) spacer at the open end of the yokes. Tighten until the spacer is tight or until the recommended torque value is reached. See Figure Install the steering column protective cover. Maintenance Check the dust boot (optional), the joints and the shaft for damage. Check the shaft for endplay. If wear or endplay is found in the shaft, replace the shaft. REPLACEMENT REMOVAL 1. Lower the dust boot under the working surface (optional). 2. Remove the clamping bolt, the nut and the washer from the coupling yoke connecting the steering shaft to the input shaft of the power steering gearbox. Free the steering shaft from the gearbox. 3. Remove the clamping bolt, the nut and the washer from the coupling yoke connecting the steering shaft to the miter box output shaft. 4. Using a soft hammer, lightly tap the steering shaft to remove it from the miter box output shaft. Remove the steering shaft. INSTALLATION See Figure 13 for torque values. STEERING SHAFT See Figure 11. Description A tubular steering shaft relays the movement between the miter box at the end of the steering column and the power steering gearbox. The steering shaft is equipped with U-joints with needle bearings at each end. A splined slip joint at the extremity of the shaft, where the power steering gearbox is connected, makes up for the variable length caused by the movements of the front end against the body of the vehicle. CAUTION: Apply a thin layer of grease on the spiders and on the inner surface of the tube. 1. Align the mounting arrows on the shaft and on the slip joint sleeve. See Figure Connect the steering shaft coupling yoke to the output shaft of the miter box.

10 2011MR17 10 / automatic greasing system (Optional) After a few collar tightenings, ensure there are at least 1.5 turns of thread visible. Figure 12 - Drag Link 3. Without tightening, install the washer, the clamping bolt and the nut on the coupling yoke. Insert a temporary 0.06 in (1.6 mm) spacer at the open end of the yoke. Tighten until the spacer is tight or until the recommended torque value is reached. 4. Connect the other steering shaft coupling yoke to the input shaft of the power steering gearbox. 5. Without tightening, install the washer, the clamping bolt and the nut on the coupling yoke. Insert a temporary 0.06 in (1.6 mm) spacer at the open end of the yoke. Tighten until the spacer is tight or until the recommended torque value is reached. 6. Install the dust boot (optional). Drag link See Figure 12. DESCRIPTION The drag link is designed to enable the link between the pitman arm and the steering arm. It is made of tubular steel and is threaded at one end to allow the insertion of a ball joint pivot. The other end can be adjusted with a clamping collar. Bent, twisted or misadjusted parts in the linkage between the steering gearbox and the front wheel-axle unit can badly affect the functioning of the steering system. Each time the steering linkage is either repaired, replaced or adjusted, check the steering alignment and the front wheel adjustment, as indicated in section 04: axle alignment. Inspect the clamping bolt and the clamping collar at regular intervals to verify if they are sufficiently tightened. See Figure 13 for torque value. Replacement Removal 1. Remove the steering drag link ends from the steering and pitman arms by removing the cotter pins and the slotted nuts. 2. Remove the balls from the steering and pitman arm. Proceed to step 3 and 4, only if the steering drag link ends need replacement or adjustment. 3. Loosen the clamping collar. 4. Free the pitman arm ends from the tube. 5. Verify the condition of all parts for signs of wear. Replace worn parts as necessary. MAINTENANCE A visual inspection is the most effective way to detect a problem. Perform a periodic examination to check the ball joint pivots, the automatic lubricating system and the grease fittings (optional). If so equipped, see section 19: fluids and lubricants in this manual, for more information regarding the automatic greasing system.

11 / MR17 INSTALLATION AND LENGTH ADJUSTMENT 1. Place the front wheels in a straight-ahead position. 2. Determine the steering movement center by turning the steering wheel from extreme right to extreme left and counting the number of revolutions. Turn in the opposite direction by exactly half the number of revolutions. 3. Check the pitman arm position. See section 04: axle alignment in this manual. 4. Screw the drag link ends in the tube without torquing. Make sure both ends are equally screwed into the tube. 5. Set the drag link into position on the vehicle and install the balls to the steering and pitman arm using slotted nuts. 6. Adjust the drag link by turning the tube until a length of in (68.09 cm) is reached between the center of the steering arm ball and the center of the pitman arm ball. 7. Position the collar so that the axis of the nut is at an angle of 45 relative to the tube opening. See Figure 13. Torque the clamping collar bolt until the torque value indicated in Figure 13 is reached. 8. Check the adjustment. The front wheels should be able to turn from extreme right to extreme left without the drag link ends blocking. Tighten the slotted nuts to the appropriate torque value. 9. Advance to the next insertion slot, and install new cotter pins. See Figure 13 for torque value. 10. Lubricate according to section 19: fluids and lubricants in this manual. TECHNICAL SPECIFICATIONS power STEERING gearbox Brand... TRW Model...TAS Type...Hydraulic miter box Brand... Curtis Series Type...Conical gear steering STEERING SHAFT Brand... TRW Length (compressed) in (1232 mm.) min. Length (extended) in (1383 mm.) min. INTERMEDIATE STEERING SHAFT Brand... TRW Length (compressed) in. (231.8 mm.) min. Length (extended)...11 in. (279.4 mm.) min. drag link Ends verification, maintenance, lubrication and replacement of the drag link ends are performed in the exact same way as for the tie rod ends. Only the torque values change. See Figure 13 for the torque values of the drag link. See section 04: front axle for the procedures relative to these ends. For additional information regarding the TRW linkage, see the TRW linkage service manual # TRW 1315.

12 2011MR17 12 / ±4 lb-ft) (47 ±6 N m) INTERMEDIATE STEERING SHAFT 35 ±4 lb-ft (47 ±6 N m) seal (UMBRELLA) miter BOX 28 ±2 LB-ft (38 ±3 N m) MOUNTING PLATE 35 ±4 lb-ft (47 ±6 N m) 393 ± 22 lb-ft (530 ± 30 n m) STEERING SHAFT (dust boot optional) 35 lb-ft ±4 (47 ±6 N m) POWER STEERING GEARBOX PITMAN ARM 295 ± 15 lb-ft (400 ± 20 n m) 133 ±15 lb-ft (180 ± 20 n m) (CLAMPING COLLAR) 85 ± 5 lb-ft (115 ± 7 n m) drag LINK collar 133 ± 15 lb-ft (180 ± 20 n m) tube openings NUT 85±5 LB-FT (115 ±7 N m) DETAIL A: DRAG LINK INSTALLATION Figure 13 - Torque Values

13 Backlash in steering. Erratic steering. Hard steering. Shimmy. Pull to one side. Wander; body sway. Tires squeal on turns / 13 TROUBLESHOOTING GUIDE PROBLEM PROBABLE CAUSE REMEDY a. Pitman arm loose. b. Worn or damaged parts in steering gear. a. Incorrect front wheel alignment. b. Incorrect steering gear adjustment. c. Loose steering linkage. d. Incorrect front wheel bearing adjustment. a. Incorrect tire pressure. b. Tires not of uniform size. c. Lack of lubrication. d. Incorrect steering adjustment. a. Incorrect tire pressure. b. Incorrect front wheel alignment. c. Incorrect steering gear adjustment. d. Tires not of uniform size. e. Loose steering linkage. f. Incorrect front wheel bearing adjustment. g. Weak front shock absorber h. Bent or worn spindle. i. Spring clip bolts loose. j. Steering knuckle ball seal worn. k. Bent wheel. a. Incorrect tire pressure. b. Incorrect front wheel alignment. c. Tires not of uniform size. d. Unequal brake adjustment. e. Incorrect front wheel bearing adjustment. f. Bent spindle arm. g. Sagging or broken suspension parts. a. Incorrect tire pressure. b. Tires not of uniform size c. Loose steering linkage. d. Incorrect steering gear adjustment. e. Loose steering gear mounting bolts. f. Incorrect front wheel alignment. g. Defective shock absorbers. a. Incorrect tire pressure. b. Incorrect front wheel alignment. c. Bent spindle arm. Table 1 - Troubleshooting Guide a. Tighten pitman arm nut. b. Verify steering gear and replace any worn parts. a. Adjust toe-in. b. Verify and adjust accordingly. c. Tighten all loose connections. d. Adjust wheel bearings. a. Inflate tires to proper pressure. b. Install tires of uniform size. c. Lubricate in accordance with recommendations. d. Verify and adjust steering components accordingly. a. Inflate tires to proper pressure. b. Check toe-in. c. Verify and adjust accordingly. d. Install tires of uniform size. e. Tighten steering linkage. f. Adjust wheel bearings. g. Replace front shock absorber. h. Replace spindle. i. Tighten loose bolts. j. Replace worn seal k. Replace wheel. a. Inflate tires to proper pressure. b. Adjust toe-in. c. Install tires of uniform size. d. Adjust service brakes. e. Adjust wheel bearing. f. Replace spindle arm. g. Replace suspension parts. a. Inflate tires to proper pressure. b. Install tires of uniform size. c. Tighten steering linkage. d. Verify and readjust steering gear. e. Tighten steering gear mounting bolts. f. Adjust toe-in. g. Replace shock absorbers. a. Inflate tires to proper pressure. b. Adjust toe-in. c. Replace spindle arm. 2011MR17

14 2011MR17 14 / BLANK PAGE