What is a PTO shaft?
The purpose of a driveshaft is to transmit torque. In cars, it is installed between the gearbox and the axle gearbox. For rear-wheel-drive models, one shaft is mounted, in all-you can repair-drive models – two. The same design is used in the steering system to connect external units to special equipment – tractors, excavators.
In the catalogs of manufacturers, you can see what Cardan driveshafts are, the features of their design, and the principle of operation. But for almost all models, the general principle of layout is preserved. This makes them universal, partially interchangeable.
A Cardan shaft consists of one or more sections of a hollow tube with the following components:
- Flange fork. They connect the shaft to the gearbox and the gearbox.
- Cross tube. Necessary to mate the 2 tubes of the shaft when changing the angle (standard up to 20°) relative to each other.
- Sliding spline connection (sliding fork). Compensates for changes in distance between gearbox and axle gearbox, which occurs during driving.
- Suspension bearing. Mounts the structure to the car body. The number is equal to the number of Cardan sections.
- Oil seals and oil seal cage. Used for sealing the nodes.
The design of the driveline depends on the operating conditions and load. In cars, the shaft has fewer parts, which increases reliability.
For special equipment models are developed for extreme conditions – a large mechanical load, minimizing the impact of pollution.
What is Cardan gear for in a truck?
In a car, the Cardan is needed to transmit torque from the gearbox or transfer case to the axle gears. The difficulty lies in the fact that the axes of rotation of the box and the axle are in different planes. Therefore, the cardan is not mounted clearly in the horizontal plane but at a slight angle.
When a gear is engaged and the throttle is depressed, torque is transferred to the sliding fork. The motion is transmitted to the cruciate joint and then goes to the rear axle gearbox.
The goal of the designers is to minimize torque losses. Since the cardan works constantly when driving and it is necessary to ensure the reliability of its functioning, the following methods of compensation have been created:
- Composite construction of several tubes. Provides a reliable connection between the gearbox and the axle, which are located in different planes.
- The minimal backlash of the crosses and forks is necessary for soft torque transmission, which affects the smooth running.
- Compensation of rear axle mobility with a sliding fork.
Ideally, the speed of the transmission shaft should coincide with the movement of the rear axle drive pinion. In practice, however, this depends on the actual condition of the driveline. It is necessary to monitor the wear of the joints and bushings, support bearings.
Types of PTO shafts
The type of cardan gear depends on the purpose. The layout is developed at the design stage. The choice of why you need a PTO shaft of a particular design is determined by the technical characteristics of the vehicle. In some cases, the installation of a multi-shaft mechanism with several joints is necessary.
Asynchronous
The asynchronous scheme is used in many cars with rear or all-wheel drive. The peculiarity is that unequal angular velocities are formed in the process of movement. This is due to the connection of two forks with a right-angle cross. The secondary shaft lags behind and overtakes the main shaft twice.
Additional universal joints of unequal speeds are installed to compensate. They are mounted on the shaft ends. This scheme is allowed to change the angle between the tubes up to 20 °. The disadvantage – because of the complication, frequent maintenance, repairs are needed.
Synchronous
The solution to the problem of asynchronous models were CV joints – constant velocity joints. They have different designs. On Pegout and Renault cars, “Tripod” is mounted. It transmits torque through three spherical rollers. They slide in the slots of the forks of the driven shaft.
The peculiarity of synchronous propshafts is the ability to operate at angles of deviation up to 70°. There is a decrease in vibration, increased life without repair. Disadvantages – there is a probability of damaging the dust covers off-road.
Flexible and rigid half prop shaft transmission
This is one of the varieties of driveshafts designed to compensate for angular turns, a slight change in distance between the gearbox and the rear axle during driving. The elastic link is made of rubber fabric material or rubber. Compensation for angle changes is made by compressing or stretching this element.
A rigid universal joint is rarely installed in cars. The reason is the low degree of reliability, increased noise during operation. The design is used to compensate for installation defects.
How to check the condition of the driveshaft
The first signs of malfunctions in the Cardan shaft are noise and increased vibration. Secondary “symptoms” are oil leakage at the junction of the shaft with the gearbox. During gear shifting, there is a knock. For checking, you need a trestle or an inspection pit. You need free access to all elements, good illumination.
What parts you need to check:
- Fasteners. Check the presence of a lockwasher and the degree of its tightness on the nut of the intermediate support and connection flanges. Possible defects – the appearance of play and vibration.
- Condition of the elastic coupling. Possible violation of integrity, mechanical damage. They affect the degree of compensation of PTO shaft elements displacement. Check – slow rotation of the cardan in a clockwise direction and back. There should be no play.
- Gaps appear between the sliding yoke and the shaft. The cause is wear and tear on the parts. Turn the shaft with the coupling to check. If there is play or play in the shaft, the yoke must be replaced.
- Joints. It is convenient to check with a slotted screwdriver. It is inserted into the eyes of the forks. A sign of malfunction – when moving, there is a backlash.
- Suspension bearing. If during the rocking of the shaft, run out of the bearing is observed, this indicates its replacement.
It is recommended to balance the driveshaft on the stand. For this purpose, special balancing plates are installed on the shaft. After the work, their condition is checked. An alternative way – turning.
Important: you can try to do cardan balancing at home. But this does not guarantee the complete elimination of defects.
What a breakdown leads to
The most dangerous situation occurs when a shaft breaks due to wear. More often than not, this leads to a serious car accident, especially if the cardan is not isolated from the outside environment. The function check must be carried out whilst driving, with all components of the machine fully functional.
Dismantling and installing the Cardan shaft
Only specialists can determine the exact time when you need to replace the Cardan shaft. Significant mechanical damage, defective joints, deformations are obvious signs of malfunction. To dismantle the cardan, you need to put the car on an overpass or over the observation pit.
Order of cardan removal:
- Unscrew the bolts connecting the flanges of the axle and gimbal.
- The shaft will be lowered down. It is necessary to prepare for it in advance.
- Remove the rubber clutch fasteners.
- Slide the card out of the gearbox.
- Dismantle the outboard bearing bracket.
After this, you can repair, service the cardan. Before installing the new one, it is necessary to check the operability of all components. Reassembly is performed in the reverse order.
